OJorneU Uniuerstty Slibrarg Stljara. Nrm fork ALEXANDER GRAY MEMORIAL LIBRARY ELECTRICAL ENGINEERING THE GIFT OF The McGraw-Hill Book Co., Inc. 1921 Cornell University Library TK3251.M13 Surface insulation of pipes as a means o 3 1924 004 038 992 m Cornell University Library The original of tiiis book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/cletails/cu31924004038992 DEPARTMENT OF COMMERCE Technologic Papers OP THE Bureau of Standards S. W. STRATTON. Director No. 15 surface insulation of pipes as a means OF preventing electrolysis BY BURTON McCOLLUM, Associate Physicist and O. S. PETERS, Assistant Physicist Bureau of Standards [JANUARY 5, 1914] WASHINGTON GOVERNMENT PRENTING OFFICE 1914 SURFACE INSULATION OF PIPES AS A MEANS OF PREVENTING DAMAGE BY ELECTROLYSIS By Burton McCollum and O. S. Peters CONTENTS Page I. Introduction 3 II. Work of previous investigators 4 III. Materials available for insulation purposes 5 IV. Tests of paint 7 1. General outline of tests 7 u. Preparation of specimens 8 3. Form of specimens g 4. Period required for drying of paints 10 5. Preliminary test 10 6. Resistance measurements 11 7. Final test of paint coatings 12 8. Discussion of results of paint tests 16 V. Tests of pipe wrappings and dips 18 X. General features of the test 18 ^. Preparation of specimens 18 3. Final test of pipe wrappings 19 4. Discussion of results 20 VI. Tests of wrapped pipes buried in earth 24 i. General description of specimens 24 2. Description of test 25 3. Discussion of results 26 VII. Cause of the failure of the coatings 27 VIII. Conclusions 28 Appendix 30 Experience and opinions of pipe-owning companies with regard to the prevention of electrolysis and soil corrosion by means of insulating coatings. I. INTRODUCTION One of the methods first resorted to as a possible means of pre- venting damage to buried water pipes and gas pipes by electrol- ysis and soil corrosion, and one which is still in use to a con- siderable extent, consists in covering the surface of the pipes with a coating intended to insulate them from the surrounding earth. In numerous instances in practice, pipes have been protected 3 4 Technologic Papers of the Bureau of Standards against soil corrosion by such coatings, which appeared to remain in good condition for a number of years; but it is still doubtful whether there is any instance on record wheire damage by elec- trolysis has been effectually prevented in this way if the voltage conditions were at all severe. On the contrary, there have been cases where efforts to prevent electrolysis of pipes by this means have undoubtedly done actual harm. The causes of this are brought out later in this paper; in general, it may be said to be due to peculiarities of the coatings used, which cause them to fail in spots and thus allow greatly aggravated cases of local damage to occur, in place of the more distributed trouble which would take place if the pipes were not coated, assuming the voltage conditions to be the same in both cases. At the present time there are a great many paints and water- proofing materials on the market which might appear to be suitable for insulating coatings on underground pipes, and which are, in fact, often recommended by their makers as being well adapted for the purpose. Since these coatings are commercially available, and are used occasionally as insulating coatings with the view of reducing damage from electrolysis, the Btireau of Standards has undertaken, in connection with a general inves- tigation of the subject of electrolysis, to test a large number of these coatings with the special view to determining their value as preventives of electrolytic damage. II. WORK OF PREVIOUS INVESTIGATORS A considerable amoimt of work along this line has been done by previous investigators, the most extensive of which was reported by R. B. Harper before the Illinois Gas Association in March, 1909. In this investigation more than 38 different com- pounds, including paints, dips, and wrappings, were tested. The conclusions given in the report state that no insulating coating was foimd that would resist the attacks of electrolysis for any considerable length of time. Against the results of these tests, however, there has been directed the criticism that the voltage used on the coatings (no volts) was abnormally high. Since the voltages to which a pipe coating would be subjected under most Surface Insulation of Pipes 5 practical conditions would not exceed a few volts, tests made on no volts would not appear to furnish altogether reliable data as to the value of the coating as a protection against electrolysis. In addition to the work just mentioned, that of various other investigators also points to the fact that at least a large proportion of the paints sold for the purpose of preserving metals from corro- sion are not impervious to water. From the standpoint of soil corrosion the access of water to the protected iron may not be a serious matter, provided the paint is an inhibitor of corrosion, or at least does not form a galvanic couple with the iron; but if there is a difference of potential of several volts between the pipes and soil the results may be very serious, as shown by the experimental data presented later in this paper. III. MATERIALS AVAILABLE FOR INSULATION PURPOSES The materials which are practicable commercially for insulating coverings for underground pipes may be divided into six general classes : (o) Paints, or compounds which are to be applied at ordinary temperatures, depending on oxidation or other chemical action, drying, etc., for their setting properties. (b) Dips or compoiuids intended to be melted at a high tempera- ture and the iron immersed and left until bath and iron are at the same temperature, when the iron is removed and allowed to cool, the compound hardening with decreasing temperature. These dips include asphalts, coal-tar pitches, and their allied products. (c) Wrappings, which consist of alternate layers of compound and fabric. The compounds used include the classes mentioned under both (a) and (b) while the fabric may be either felt, cloth, or paper. The latter may be treated or untreated, according to the ideas of the manufacturer or the person making the test. There are a great many subdivisions of these three classes, but since it is the object of this work to determine the value of the various mate- rials as preventives of electrolysis when applied according to the specifications of the manufacturer, it does not seem to be necessary to go into them here. A short description of each material in the record of the results of the tests appears to be sufficient. 6 Technologic Papers of the Bureau of Standards (d) Fiber conduit, in which pipe can be laid quite conveniently. This conduit can be used with or without pitch filling and can be made up with screw joints. In point of cost of materials and labor of putting in place it compares quite favorably with the best wrappings. (e) Enamels, or those coatings of glass of peculiar toughness with which iron can be covered and which are quite impervious to moistture. They will stand a considerable amount of rough usage, but crush imder a pipe wrench, and will crack when the metal underneath them is bent. The durability of these enamel coat- ings is well shown in the cases of enameled iron washbowls, bath- tubs, and cooking utensils. (/) Cement mortar and concrete coatings have been used to a considerable extent as protective coatings for pipes, and in this paragraph it may be well to set forth briefly the results of certain tests on these coatings which have been made at the Bureau of Standards. It has been shown in these tests that cement and concrete are insulating only when perfectly dry. The addition of a slight amount of moisture reduces the resistance to such a low value that the protective power, through insulation, of a mortar coating when damp would be of no moment whatever. Cement mortar absorbs water quite readily and the mortar coating of a pipe laid in damp ground would therefore be a conductor of elec- tricity at all times, and thus no reliance could be placed upon protection through insulation in this way. The following table gives the resistivities of various samples of mortar and concrete which had been soaked in water at room temperature and under atmospheric pressure until no further increase in weight was noted : Resistivity of Concrete ^ Proportions of concrete. Resistivity. ^Proportions ol concrete. Resistivity. 3500 2300 2100 6300 1 iZ^ :4 concrete 8000 8200 1:4:7 concrete 9900 1 The resistivity of concrete will, of course, vary greatly with the aggregate, method of makinfi, etc., and the above values are indicative only of the order of magnitudes of resistivities that may be expected. Surface Insulation of Pipes 7 It may also be well to state here that in the course of the work on electrolysis in concrete, which is described in Technologic Paper No. i8 of the Bureau of Standards, no waterproofing com- pound or paint was found which would permanently render con- crete a nonconductor of electricity when subjected to the action of moisture. When concrete is new and contains a large amount of calcium hydroxide there is a considerable passivating action which allows current to leave a pipe coated with cement mortar with compara- tively little corrosion of the iron, but with age the calcium hydrox- ide is carbonated and the passivating action is destroyed, with the result that the pipe corrodes quite rapidly. Tests carried out at the Bureau of Standards on cement-coated pipes with lead joints showed that in less than two years cracking of the mortar coating and pitting of the pipe occurred to a marked degree, even with low voltages applied. The conclusion to be drawn from these results is that a cement or mortar coating is of no practical value as a preventive of electrolysis of underground pipes. Tests have been carried out on various paints, dips, and wrap- pings, and these tests are described below. The tests on fiber conduits and enamels have not progressed far enough at present to give conclusions as to their values as preventives of electrolysis, but they will be reported on later. IV. TESTS OF PAINTS 1. GENERAL OUTLINE OF TESTS In the process of formulating a series of tests to accomplish the object outlined at the end of Section I, the following facts were considered as having an important bearing: (a) That the effectiveness of an insulating coating as a preven- tive of electrolysis depends primarily upon its continuity. (b) That in practice electrolytic corrosion takes place in the presence of soil water or other water containing various chemicals in more or less dilute solution. (c) That air and the above-mentioned water alternate to a greater or less degree in coming in contact with the coating. 28868°— 14 2 8 Technologic Papers of the Bureau of Standards (d) That the potential differences encountered are usually low. (e) That an insulating coating which is unable to withstand the combined action of water, air, and a low electric stress can not reasonably be expected to make a better showing when the water in contact with it contains an active chemical in solution. With these in mind a series of tests was outlined which was cal- culated to determine the effectiveness of each insulating coating under voltage conditions approximating those which measurements had shown to be cotomon in practice. The severity of these conditions was modified to suit the different classes of coatings, the idea being that a coating suited to mild conditions should be tested under such conditions, while for the more rugged coatings the conditions should be made more severe. The object of such a series of tests was to avoid all undue acceleration and to give to each coating every advantage to which it seemed entitled. The test itself consisted in causing water and air to alternate in coming in contact with a continuous coating of each substance while a low potential difference was applied across the coating from the water to the metal sturface upon which the coating had been placed. In the case of each coating the metal was made positive in some speci- mens and negative in others, while as a check on the effect of the electric stress on the paints certain specimens were subjected to the alternate action of water and air with no difference of potential applied. 2. PREPARATION OF SPECIMENS In preparing specimens for the tests the first difficulty encoun- tered was that of obtaining a continuous coating of a paint. The only way by which this could be overcome was by applying a suffi- cient number of coats to completely eliminate all pinholes and flaws. Four coats, when carefully put on, were usually found sufficient to give the best results of whicJi a paint is capable. The procedure in preparing painted specimens which was formulated diiring the early progress of the work and adhered to quite closely thereafter was as follows: It was found to be preferable that the paint be applied to a smooth, flat, or nearly flat, surface having no projections or rough spots, and care was taken'^to see that the surface was free from grease, scale, or rust, especially grease. In brushing on quick-drying paints the brush was not passed over the Surface Insulation of Pipes g surface after the paint had gained its initial set, which usually took but two or three minutes. It was found essential that the paint be thinned until it would spread well, and the coating was never applied so thickly that it would run in ridges and dry or leave blisters. The thinning agents used were those recommended by the manufactiurers of the paints and included turpentine, benzine, and gasoline. Each coat was thoroughly dried before the appli- cation of the next. In cleaning brushes, while passing from one paint to another, great care was taken that no gasoline, alcohol, or other cleaning agent was retained by the brushes, as some paints are extremely sensitive to them. 3. FORM OF SPECIMENS To obtain a smooth, nearly flat surface, and, at the same time, other distinct advantages, specimens were made of a form shown SHEET IRON -60LDER Fig. 1. — Sheet-iron cone used m paint tests in Fig. I . These consisted of sheet-iron cones of about 7 inches diameter of base and i^ inches altitude. The interior of the apex of each cone was filled with solder and the overlapping joint soldered to a smooth surface, in order to do away with the sharp comers which would be hard to paint or otherwise coat. The interior surface of the cone was coated. When the coating was completed a portion of the surface a little more than covering the area of the solder at the apex was strongly reinforced against dampness and electrical stress, in order to do away with the effect of any chance roughness of surface which might be present. This reinforcing was done with a coat of warm paraffin. Trial was made of several substitutes for paraffin, one of which consisted of paint and muslin, but they were all found to be quite xinsatisfac- tory. It may be said, without exception, that no painted cone to Technologic Papers of the Bureau of Standards failed in or around the edge of the paraffined portion of the surface during the progress of the tests. The cone presents marked advantages for the purpose of testing insulating coatings of the character of those under consideration. The surface of the cone being smooth, and nearly flat, it is easy to coat uniformly. There are no ends or comers where defects may appear. After they are coated they may be laid down any- where to dry or set, and no ordinary handling is likely to damage the coat. The cone also forms the containing vessel for the liquid used in the tests. 4. PERIOD REQUIRED FOR DRYING OF PAINTS When the tests were first begun a total of lo days drying for the whole nimiber of coats was thought to be a sufficient prepara- tion for testing a paint, but later results showed that two months was hardly time enough for the greater number of the paints to attain their full power as waterproofers. Many paints depend upon the action of oxygen from the air for their setting properties, and as this action is comparatively slow it is not complete when the paints are dry enough for handling. S. PRELIMINARY TEST The first test to which the painted specimens were subjected after the paint had dried was the test for pinholes and flaws. This test consisted at first m filling the cone to about one-half inch from the rim with mercury and applying a 6o-cycle alter- nating difference of potential of 80 volts (effective) with the mercury and the sheet iron of the cone as contact pieces. Eighty volts was settled upon as a test voltage which would not inrnie- diately break down even a thin coating of a paint if dry and flawless and still would give an unmi|||;akable indication if the coating were not perfectly continuous. This test was later modi- fied by using a 10 per cent NaCl solution in the place of mercury. The salt solution was not only more convenient to handle, but it seemed to search out flaws in the coating more readily than mer- cury. An alternating current milliammeter of 831 ohms resist- ance and 0.050 ampere full-scale deflection was put in series with the cone, and a kick of the needle when the circuit was closed indicated a defect in the coating. The potential was applied for Surface Insulation of Pipes ii 30 seconds, and if no deflection of the needle occurred, the coating was considered perfect. Specimens which did not pass this test were rejected and others made and tested until a set of five per- fect specimens was obtained of each paint. The effect of the length of the drying period was the most evident in the results of this test. Out of a number of tests at the end of 10 days drying and of others at two months the percentage of defective coatings for the shorter period was four or five times as great as for the longer period. 6. RESISTANCE MEASUREMENTS This test (as well as those following) was carried out on the specimens surviving the first test, and consisted in measuring the electrical resistance of the paint coatings in ohms per square centi- meter. This was done by filling each cone with salt water, as in the first test, placing it in parallel with a resistance of 25 000 ohms and measuring the resistance of the parallel circuit with a Wheatstone bridge, using direct current. , The resistances of the coatings were very high, and this procedure was necessary in order to bring the resistances to be measured within the limits of the capacity of the bridge. A very sensitive galvanometer was used, and if placing the cone in or out of parallel with the known resistance made a change of 0.5 ohm, it could easily be detected. After calculating the resistance of the whole area of the coating by the method of parallel circuits the area of the cone multiplied by the- value obtained gave the resistance of the coating in ohms per square centimeter. A great many of the paint coatings were of such high resistance that balancing the bridge on the 25 coo- ohm resistance and then putting the cone in parallel with it caused no deflection of the galvanometer. Calculations and trial showed that if a paint coating had a resistance of more than 2X10" ohms per square centimeter this would be the case and in the table of results the resistance of such paints is designated as greater than this value. Those paints having a resistance lower than the above value showed an action resembling polarization, in that the resistance increased very rapidly while the cone was in the bridge circuit. The method is not highly accurate, but gives the order of magnitude of the resistances of the paint coat- ings, which is about all that is required. 12 Technologic Papers of the Bureau of Standards 7. FINAL TEST OF PAINT COATINGS In the final test each painted cone was filled to one-half inch from the rim with water from the city water mains (or other electrolyte, as the case required) and placed in a rack made and wired especially for the purpose of the test. The one-half inch strip of dry paint around the rim was left in order to prevent leakage of current over the edge as much as possible. Two cones of each set of five mentioned above were connected up electrically with the sheet iron of the cone anode and the negative terminal in the fbrm of a couple of turns of bare copper wire brought into the tap water. Another cone was connected with the sheet-iron cathode and the positive terminal brought into the tap water. (See Fig. 2.) The two remaining cones were not subjected to METAL ANODE METAL CATHODE Fig. 2. — Connections of specimens to electrical circuit electrical stress but the electrical connections were made avail- able for current readings, when the potential was applied long enough for the reading to be taken. A direct-current difference of potential of 4 volts was impressed upon the circuit con- tinuously, a storage battery being used for the purpose. This potential difference was assumed to represent the mean rather than an extreme of those foimd in practice under conditions favorable to electrolysis where a paint might be expected to act with success as a preventive. Durii^| a period of about two weeks, under normal atmospheric conditions, almost complete evaporation of water from the cones would occiur. They would then be refilled and two days later current readings would be taken. In this way any error which might be caused by leakage of current over the damp edges of the cones immediately after refilling was eliminated; the ctirrent reading included the flow through all of the painted surface upon which the water and air had acted, and the conditions of the test as outlined above Surface Insulation of Pipes 13 were fulfilled with a minimum of labor and expenditure of time. The first appearance of current flow is indicated by the number of hours to f ailxire in Table i , and is to be taken as meaning the end of the insulating power of the paint. After the first appear- ance of current flow the life of a paint coating with continuously applied potential is very short. Specimens were left in circuit imtil failture was complete and the ciurent became 1.5 milliamperes or more. TABLE 1 Tests of Metal- Preservative Paints as Insulating Coatings Name ot paint 1 CO i3 s Resis., ohms peicm.2 Electrolyte i 1 1 1 Polarity o{ cone Hours to failure 1^ 1 1 i 1 1 & •d 1 Antakwa, heavy Antakwa, metal pro- tection. R. I. W., numbei not known. Caibonkote, interior Mindura, brine-ie- Mlndura, ordinary finish. Nev-a-Rnst 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 2.0x10" 2.0x10" >2.0xl0" >2.0xl0" >2.0X10" 2.0 1 10" 1.6xl0» >2.0xl0" >2.0xlO" >2.0j:10" 2.0x10" >2.0X10" >2.0xl0" >2.0xlO" >2. X 10 " 3.0xl0i» 3.6X10" >2.0ll0" >2.0X10" >2.0xl0" 7.0x10' 3.2xl0» >2.0xl0" >2.0xlO" >2.0xl0" 10.8X10« 3.2xl0» >2.0xl0" >2.0X10" >2.0X10" 1.7xl0> 7.7x108 1.6xl0» 1.6X109 2. 1 1 10 9 2.0x10" 5.5x10" >2.0xl0" >2.0xl0" >2.0xl0" 2%NaiCO.... Water 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 P03... P03... Neg . 312 384 ? 7 do do do 2%Na!C03... 2000 'iioo' 1400 8 Neat.. 8 Neut.. 8 ?, Pos... POB... Neg 192 ? ? do do do 2000 'iioo" 1400 8 Neut. . 8 Neut. . R 3 Pos... Pos... Neg 312 5000 ?, ? do do do J%HjSO, Water 600 "eoo' 1350 A Neut. . 8 Neut. . 8 4 Pos... Pos... Neg ., 528 2 2 do do do 3%NaCl Water n ■f 8 Neut.. 8 Neut.. 8 5 Pos... Pos... 840 120 ?. 2 do do do 2% NajCOa. . . Water 760 "576' 570 8 Neut n Neut. . 8 A Pos... Pos... Neg... 5 7 ? f do do do 2000 '2806' 2800 8 Neut. . 8 Neut 8 7 2%Na.CO,... Water Pos... Pos. . . Neg... 5 240 ? Carbonall,'No. 10... ? do do do }%H2SO, Water 120 ■336' 902 8 Neut.. 8 Neut. . 8 8 Pos... Pos... 5 552 ? ? do do do 3144 'iioo' 1100 8 Neut.. 8 Neut.. 8 ' No sign of current after lo ooo hours. H Technologic Papers of the Bureau of Standards TABLE 1— Continued Tests of Metal-Preservative Pamts as Insulating Coatings — Continued Name of paint I S o Resis., olims percm.2 Electrolyte 1 1 Polarity of cone Hours to failure « i 1 i ^ t Caibonkote, No. 100 Sareo 1 2 3 4 5 1 2 3 4 5 1 1 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 S 3.0x109 1.6x109 1.1x10" 1.1x10" 5.5x1010 2.0x10" 3.4x10' 9.2x100 1.2x10 = 1. X 10 6 4.5x108 3. 6 X 10 6.2x109 5.4x109 5.6x10 9 1.0x109 6.6x109 >2.0xl0" l.lxlO" 1.1x10" 1.2 X 10 9 >2.0xl0Jl 1.1x10 9 3.5x10' 9.2 X 10 8 1.0 X 10 10 2.2 X 10 9 1.8 X 10 s 6.8 X 10 9 2.0 X 10 ' 1.0x10 2.2 X 10 9 >2.0xl0n 4.2 X 10 ' 1.8 X 10 ' 1.5 X 10 9 1.6 X 10 9 1.6x10 9 3.7 X 10 10 3.7x1010 5.0x1010 5.6 X 10 9 3.9 X 10 9 >2.0xl0" >2.0xl0ll 5.0x10" 2.5X1010 2.5x1010 8.5x1010 I.OXIO' 4.6x109 8.4xl0» >2.0X10" 2.5x10' 4.3X10' 2%Na2COs... Water 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Pos..- Pos... Heg .. 72 1368 2 8 do do do 6000 '2806' 2800 8 Neut 8 Neut.- 8 10 Pos... Pos-.- Neg - 312 2 AeOnlte, preserva- tive paint. Crysolite, No. 10 Neponset, Water- dyke paint. No. 107, H.F.Scott. . Insulite 8 do do do do do do do do do do do do do do 1752 "336' 336 S Neut 8 Neut.- R 11 Pos..- POS--. Neg . 5 2 ?, 2952 "336" 1208 8 Neut 8 Neut.- 8 u Pos... Pos-.- Neg 240 2 2 860 iioo' 600 8 Neut 8 Neut.- 8 l^l Pos... Pos... Neg 2800 2 do 2 do do do do do do do do do 10000 1752' 2376 8 Neut-- 8 Neut. 8 14 Pos... Pos... Neg 5 6500 2 8 912 "912" 3200 8 Neut- - 8 Neut s IS Pos... Pos... 10000 48 Bar-OZ .--..do do do do do do do do *•■-•■■ do do do do do do 2 2700 "336" 336 Neut 8 Neut- . 16 Pos..- POB... Neg 3300 816 8 R.I.W.,No.5 Gllddens, acid proof and graphite acid proot H;drex, preservative paint. 8 206 "760' 1400 8 Neut- - Neut.. 8 17 Pos... Pos... Neg--. 1320 480 8 3900 'im 1400 Neut. . 8 Neut.. 18 Pos... Pos... Neg. . . 4500 5300 8 do do do do do do do 8 2800 '2880' 2800 8 Neut.. Neut. . 8 19 Pos... Pos... Neg 2600 816 8 8 2600 "912" 912 8 do do Neut.. 8 Neut.. 8 Surface Insulation of Pipes TABLE 1— Continued Tests of Metal-Preservative Paints as Insulating Coatings— Continued 15 Name of paint 1 1 Resis,,ohms per cm.2 Electrolyte j f 1 Polarity of cone Hours to failure bfl 1 1 s t. 1 n I iin R. I. W., No. 49, over Tockollth. 1 2 3 4 5 1 2 3 4 5 <1 2 3 4 5 <1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 S 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 3 3 3 3 3 4 7. 2 X 10 » 7.2x10' 5.6x10" >2.0X10" >2.0X10" >2.0xlO" >2.0xl0" 3. 1 X 10 » >2.0xl0" 4.2xl0« 4.0xl0« Water do do do do do do do do do do do 4 4 4 4 4 4 4 Pos... Pos... Neg -. 192 192 8 R 100 ieoo" 2000 R Neut . 8 Neut 8 21 Pos... Pos... Neg 100 1586 R Insulator, Carman.. Damp-proofer, Car- man. CrysoUte, No. 8 Dixon's graphite S. P. C, flexible iron paint. P4B,No.2 P & B, black, air- National, double K. natural graphite pahit. 8 2800 'iMo' 900 8 Neut. . 8 Neut.. 8 >?.?. do do do 823 1.2x108 do do do do dn 24 >2.0xl0" 7.0x108 I.OXIO" l.OxlO" 1.0x10" 9.0x10' 3.3x108 1.6x10" 1.6x10" 1.8X10 8 1.2x108 2.3X10' 1.8x10 8 1.0x10 a 2. 2 X 10 8 9.8x10' 2. X 10 8 2. X 10 ' 2.9X10 8 1.0xlO< 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Pos... Pos... Neg. . . 150 1032 8 8 120 1632' 1032 R Neut Neut 8 ?S Pos... Pos... Neg 48 2800 r ■> 120 ■"126' 120 a Neut. - 8 Neut. . R 26 Pos... Pos... Neg. . . 96 R R 10000 "672' 672 R Neut. - 8 Neut 8 27 Pos... Pos... Neg... 6500 912 R 8 288 "912' 912 8 Neut.. 8 Neut. . 8 >m Pos... Pos... Neg 96 96 8 do do.. R 96 'esoo' 6500 8 do do Neut.. 8 Neut 8 29 4.0x10 8 3.4x108 3.4X108 3.4x108 3.4x108 do do do do do Pos... Pos... Neg... 10000 10000 R R 912 ' '912' 912 R Neut.. R Neut. . 8 ' Four holes eatea through cone in 48 hours. Ten specimens in all were required to obtain one which would withstand the first test. All were carefully treated and dried 8 weeks. * Nos. 2 to s failed on 80 volts. " Five holes eaten through cone in 48 hours. Ten specimens in all were required to obtain one which would withstand the first test. All were carefully treated and dried 8 weeks. ^ Resistance very low« about 1,000 ohms. 28868°— 14-^3 1 6 Technologic Papers of the Bureau of Standards TABLE 1— Continued Tests of Metal-Preservative Paints as Insulating Coatings — Continued Name of paint a u 1 Resla., ohms per cm.2 Electrolyte ii 1 ■s a 1 Polarity of cone Hours to failure ^ i I 1 §? a 3 « s •0 HI in Des Moines, elater- ite, No. 40. Des Moines* elater- ite. No. 10. I.D. P., steel paint.. 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 2.7xl0« 2.2x108 1.8x10 8 6. X 10 ' 4.0x108 9.7x105 2.1X10' 4.0xl0« 1.8x10' 9.7x10" 4.0X10" 6.5x10' 6.0x10' 5. 7 X 10 ' 1.0 X 10" Water do do do :. do do do do do do do do do do do 4 4 4 4 4 4 4 4 4 Pos... Pos... Neg 10000 10000 8 8 120 '2446' 2000 8 Neat.. 8 Neut. . 8 31 Pos.... Pos... Neg . 120 3300 8 8 120 "'96' 96 8 Neut 8 Neut.. 8 32 Pos... Pos... 120 120 8 8 120 "'96' 96 3112 8 Neut . 8 Neut fl Av.= 1647 —2900 8. DISCUSSION OF RESULTS OF PAINT TESTS Table i gives the condensed data of the tests, indicating the number of coats given each specimen, the resistance in ohms per square centimeter before the test was started, the electrolyte used (which in most cases was water from the city mains) , the voltage of the time test, the polarity of the iron of the cone, the hours elapsing before the first appearance of current flow in positive, negative, and neutral specimens, and the weeks of drying in each case. The general appearance of the data under the three columns headed "Hours to failure" which, of course, is the most important, shows that none of these paints is to be depended upon as a preventive of electrolysis ill the presence of moisture even though the voltage between pipes and earth be only 4 volts. Here and there individual specimens appear which seem to have withstood the action of the water for a considerable period of time, and in No. 4 only one of the four specimens has failed after a little more than a year. It may be said of No. 4, therefore, that it gives far greater promise of good results in practice than any Surface Insulation of Pipes 17 of the others, although the fact that one of these coatings has aheady failed indicates that the useful life of the coatings is not to be depended on for any great length of time. The averages of the hours to failure seem to indicate that positive specimens lose their insulating power first, with negative specimens second, and those not subjected to a difference of potential third. That this should be the order does not seem unlikely, but the differ- ences between the averages are too small to be conclusive in this respect. On the contrary, an examination of the data specimen by specimen shows quite clearly that the low electrical stress applied had no apparent effect at all toward reducing the insu- lating power of the paint. The time of failure evidently depends on the characteristics of the individual specimens and the action of the water. The manner in which failiure of the coatings occurred was distinctive of the direction of current flow. The anode speci- mens would show rust spots at the places where failure first took place. These rust spots would grow to craters in some cases if the paint coating was brittle and easily broken, or bubbles would form if the coating was elastic. The removal of this crater or bubble would reveal a pit filled with iron rust, the pit sometimes extending through the sheet iron. The cathode specimens failed in an entirely different way. No rusting of the iron occurred under the paint coating but gas was liberated which lifted the paint film until a blister was formed which would sometimes break and leave a large area of the iron exposed. These forms of failture are illustrated in Fig. 3, the specimen on the right being an anode specimen, while the one on the left is a cathode specimen. The specimens having no potential applied showed no deterioration of the coatings which was visible to the eye, except in one or two cases where the paint blistered somewhat as it did when the specimens were made cathode. No. 6 showed this type of failure in the greatest degree. i8 Technologic Papers of the Bureau of Standards V. TESTS OF PIPE WRAPPINGS AND DIPS 1. GENERAL FEATURES OF THE TEST The tests of pipe wrappings were conducted in much the same manner as the tests on the paints. Sheet-iron cones were used, and the interiors of the cones were Uned with the material to be tested. The preliminary test to determine whether the coatings, were continuous or not was omitted, and also the meastu-ement of the electrical resistances of the coatings. These omissions were made after experimenting with a number of specimens and find- ing that the electrical resistances were invariably greater than 2 X lo" ohms per square centimeter, while the test for pinholes and flaws showed no defective specimens. This is not extraordi- nary, in view of the thickness of the coatings (three thirty-seconds- to one-fourth of an inch). The two measiurements above men- tioned were therefore omitted, on the assiunption that all speci- mens of this character would probably respond to these two tests in a similar manner. The specimens with no potential applied were also omitted, because there seemed to be no reason to believe that the low electrical stress used in testing these wrappings (15 volts) wotdd act on them in a different manner from that shown- in the results of the paint tests, where it is seen that the electrical stress had very little apparent effect in hastening the initial break- down of the coatings. Four specimens constituted a set. A number of sets were made up with each material, however, the object of the several sets being to test different thicknesses of the coating. Several of the compounds were intended for both wrappings and dips, and a number of cones were dipped in order to determine whether it is practicable to coat a pipe effectively in ^s way. 2. PREPARATION OF SPECIMENS The materials tested included asphalts, pitches, and a few paints which were especially recommended for pipe-wrapping purposes. These were used in various combinations with felts, cloths, and papers. In preparing the various materials for lining the cones a circular piece of the fabric used was first cut out and slit from center to circumference, after which the edges of the slit. Surface Insulation of Pipes 19 •were lapped until the circular piece of fabric assumed a conical shape corresponding to the shape of the cone in which it was to fit. If the compound to be tested was an asphalt or a pitch, the interior of the cone was then swabbed with the hot compotmd and the conical piece of fabric pressed into it. This was immediately followed by another swabbing with the compound and another layer of fabric, and so on until the desired number of layers had been placed. The last layer of fabric was always thoroughly swabbed with the compound and formed as nearly a perfect union with it as could be expected. In preparing specimens in which paints were used, the interior of the cone was first painted and allowed to dry thoroughly. This was followed by another light coat of paint and a layer of fabric (muslin) , into which a coat of paint had been well brushed. When this had dried the performance was repeated tmtil the desired num- ber of layers had been placed. This process was rather tedious, because paints in general do not dry readily when applied in this way. In preparing dipped specimens the cones were immersed in the melted compound and manipulated imtil all air bubbles beneath the coating and been eliminated. The specimens were then re- moved and allowed to cool, after which they were dipped again rather quickly, in order to give a thicker coat. The first coat was very thin, because the iron and bath were at the same tempera- ture and there was a great tendency for the compound to run off when the specimen was removed. The tliicknesses of the coatings when finished were from one thirty-second to one-sixteenth of an inch. In melting the compounds enough heat was applied to render the material quite liquid, but overheating and burning was care- fully avoided. 3. FINAL TEST OF PIPE WRAPPINGS In this test the cones were filled with water from the city mains and placed in a rack in a manner similar to that described in con- nection with the paint tests. Two of the four specimens in each set were connected up electrically with the sheet iron of the cone positive and the other two with the iron negative. In the case of the cones lined with compoimd and fabric a voltage of 1 5 volts 20 Technologic Papers of the Bureau of Standards was impressed continuously. The dipped specimens had 4 volts impressed upon them. The higher voltage was used in the case of the wrappings because such coatings would be expected to with- stand rather severe electrolysis conditions, and in fact their use would as a rule be justified only where electrolysis conditions were unusually bad. The water was allowed to evaporate from the cones after which they were refilled. This was followed on occasions by the taking of current readings. The current readings were taken as often as seemed necessary. At first the readings were taken on alternate days, but this period of time was gradually extended to two months, because of later developments which showed that the life of the wrappings was such as to make more frequent readings unnecessary. The first appearance of current flow was taken as an indication that the insulating power of the coatings had ended. Specimens were usually left in circuit until there was abundant evidence of failure, or at least ^ntil the current became 2 or 3 milliamperes. 4. DISCUSSION OF RESULTS Table 2 gives the condensed data of the tests, showing the num- ber of layers or dippings in each case, the polarity of the iron, and the hours to the first appearance of current flow. From this data it is seen that 82 per cent of the total number of specimens under test have failed to date. Sets Nos. 25, 26, and 33, seem to remain intact, but they were of the last ones put in circuit, so their behavior is not yet definitely determined. Set No. 27, however, which is of the same material as 25 and 26, shows two individual specimens to have failed. These are of one layer of compound and burlap and it seems reasonable to say that they forecast the futiu^e behavior of the others of the same material. There is no indication at present as to the ultinfete effect on set No. 33. The results taken as a whole do not indicate that the life, as an insulator, of a coating of this character can be expected to be more than two or three years even when put in place on the pipes and buried in perfect condition, and in most cases failure may be expected within a few months. The attempt to dip specimens is seen to have yielded very poor results, and it is questionable whether coating pipes in this way is any better than painting them, so far as protection against electrolysis is concerned. Surface Insttlation of Pipes 21 TABLE 2 Tests of Pipe Wrappings, Dips, Etc., as Insulating Coatings [Water served as electrolyte in all cases. Voltage^ij except in i-i and 4-1 where V=4, and also 306 to 325.] Coating Material Layers or dipphigs Speci- men Polarity of cone Hours to failure Positive Negative 1 Neponset watei-dyke felt and com- pound do 3 layers 2 layers 1 layer 3 layers 2 layers 1 layer 3 layers 2 layers 3 layers 2 layers 1 layer 1 2 3 4 5 9 10 11 12 17 18 19 20 25 26 27 28 29 33 34 35 35 41 42 43 44 49 50 51 52 57 58 59 60 65 66 67 68 73 74 75 76 Positive do do Negative 9200 5040 6000 2160 ? do Positive do Negative 7600 4200 9200 do 3600 3... do Positive do 10000 10000 10000 3100 4 do PosiHve do do. Negative 16000 14700 ' 14000 420O . . do 3200 5.. . do do. 5000 2000 do do Positive do 10000 10000 290O 6 3040 do Positive do do Negative Positive 10000 3800 14700 5700 2000 7 8 do 4300 Barrett specification pitch and tar paper do 5000 9 Positive do Negative 3500 4800 3900 do 2100 10 Positive do 2100 2100 do 720 do 720 11 Positive do Negative 3400 3400 ) 552 do 48 ' No breakdown after the givea number of hours. 22 Technologic Papers of the Bureau of Standards TABLE 2— Continued Tests of Pipe Wrappings, Dips, Etc., as Insulating Coatings — Continued Coating Material Layers or dippings Speci- men Polarity ol cone Hours to failure Positive Negative 12 Barrett pitch (sample 1) and muslin Barrett pitch (sample 2) and muslin Barrett pitch (sample 3) and muslin Barrett pitch (sample 4) and muslin Sarco-mineral rubber-pipe dip and muslin do Slayers do do do 4 layers.... 3 layers 2 layers 1 layer 2 layers 1 layer 3 layers 81 82 83 84 89 90 91 92 97 98 99 100 103 106 107 108 113 114 115 116 121 122 123 124 129 130 131 132 137 138 139 140 145 146 1« 148 154 155 156 157 162 163 164 165 Positive do Negative 12500 3400 3900 .do 3900 13 Positive do Negative 12500 12500 5590 14 do Positive do Negative 4400 4400 3400 1400 do 3000 Positive do Negative 12000 '12000 • '1200O 16 do do 12000 2100 . ..do 2100 Positive do Negative 10000 10000 17 1400 do do Positive do Negative 10000 2100 336 18 1200 do . . do 300 Positive do Negative 300 2900 19 2100 Mogul repairing compound and muslin do do Positive do do do Negative 300 2100 1600 1600 300 20 1600 do 1000 21 Positive do Negative 768 1600 S. P. Co. cold cementing compound and treated burlap 1600 do 1000 22 Positive do Negative 7200 '7200 7200 do 7200 ' No breakdown after the given number of hours. Surface Insulation of Pipes 23 TABLE 2— Continued Tests of Pipe Wrappings, Dips, Etc., as Insulating Coatings— Continued Coating Material Layers or dippings Speci- men Polarity of cone Hours to failure Positive Negative 23 S. P. Co. cold cementing compound and treated burlap do . ... 2 layers 1 layer 3 layers 2 layers 1 layer 2 dippings.. do 170 171 172 173 178 179 180 181 186 187 188 189 . 194 19S 196 197 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 Positive do Negative '7200 7200 480 do 7200 24 Positive do Negative '7200 '7200 S. P. Co. cementing compound (grade A) and treated burlap do 7200 do '7200 25 Positive do '7200 '7200 ' 7200 do '7200 26 Positive do Negative '7200 '7200 .do '7200 do. . '7200 27 Positive do Negative '7200 7200 Sarco-mlneral rubber-pipe dip Barrett pitcll (sample 1) '7200 do 7200 28 Positive do do do do do 24 5 96 9000 29.. ...do 360 30 do Positive do Negative 336 do. do 1056 31 Positive do Negative 672 4400 do 1680 do 4400 32 Positive do Negative 6000 2 layers 672 do .. 336 33 PosiHve do '3192 '3192 ' 3192 do ' 3192 . T No breakdown after the given number of hours. 24 Technologic Papers of the Bureau of Standards The manner of failure of the coatings was similar to that of the paint coatings, i. e., craters of rust formed at points in anode specimens if they were allowed to run long enough, while cathode specimens showed large blisters. The failure of these coatings was, however, much slower than the paint coatings after the first appearance of current flow. This is probably due to the thick- ness and rigidity of the coatings. VI. TESTS OF WRAPPED PIPES BURIED IN EARTH In view of the fact that the laboratory tests might be open to criticism on account of the continual presence of moisture in con- tact with the coatings, whereas if the specimens were buried in earth they might be partially dry at times and their useful life; thus be greatly increased, it was deemed advisable to conduct a few tests under conditions such as would be met with in actual practice. To this end a number of specimens of wrapped pipe were obtained and a test carried out, as described below. 1. GENERAL DESCRIPTION OF SPECIMENS In this test 26 specimens of wrapped pipe were used, 24 of which were furnished by commercial firms. Twelve of these 24 speci- mens were of 4-inch wrought-iron pipe, 5 feet in length, which had been wrapped with two alternate layers of pitch and burlap. The other 12 were of i^^-^T^ch. wrought-iron pipe, 5 feet in length, which had been covered with 4 alternate layers of tar and paper. This paper was not impregnated with tar before being applied, but consisted of what appeared to be rather heavy wrapping paper wound on spirally over a coat of tar while the tar was still hot, the tar containing 3 or 4 per cent lime. The finished coating in this case was about one-eighth of an inch in thickness. This coating is of the t3^e known as the Nichols coating and has been used to a considerable extent in actual service. The pipes de- scribed above were covered and supplied to the Bureau by a large gas company that has been using this t3rpe of coating for several years. The bturlap and pitch coating was a little thicker than the pitch and paper coating, or about three-sixteenths of an inch. In preparing the specimens for burying in the earth. Ter.hiiok.-i-. P:i[.^r N Fig. 4. — Specimens of pipe with muslin and paint couering Surface Insidation of Pipes 25 leads of rubber-covered copper wire were first soldered to the inside of the pipes and the ends of the pipes closed with wooden plugs, the wire leads being drawn out through small holes made in the plugs. The ends of the pipes were then capped with several thicknesses of tarred paper and pitch, this cap extending about 4 inches over the end of the pipe. The ends of the pipe were thus thoroughly reenforced against dampness by a cap which made a good union with the wrapping itself. This made it certain that the wrapping would show current leakage first, as the' thickness of the cap was several times that of the wrapping. The two remaining specimens of wrapped pipe spoken of above were made up with muslin and the paint given under ntunbers 21 and 22 in Table 2. These specimens were very carefully pre- pared in the laboratory, the coating being placed on pieces of clean iron pipe iX inches in diameter and 18 inches long after having plugged their ends and arranged the leads as described in the preceding paragraph. The coating was applied as follows: Two coats of paint were brushed on 3 days apart and allowed to dry. A third coat was then put on. Whenth is third coat had become tacky, a strip of muslin which had been painted and allowed to dry was wound on spirally over the tacky coat so as to make two layers, the muslin being painted a second coat as it was woimd on. This was given 10 days in which to dry, at the end of which time the specimens were given two more coats of paint about three days apart, as was done in the case of the first two coats. The specimens were then allowed to dry for another month before placing them in the ground. Fig. 4 shows the appearance of the finished specimens. 2. DESCRIPTION OF TEST The specimens were buried in earth and connected up to the positive side of a 15-volt direct-current circuit in such a way that the pipes were about 4.5 volts positive to the surrounding earth. Current readings were taken at intervals of about one month. The ground was quite wet during the spring and fairly moist during the rest of the year. The temperature ranged from about 0° C in winter to 17° or 18° in siunmer. 26 Technologic Papers of the Bureau of Standards 3. DISCUSSION OF RESULTS Table 3 gives the results of the tests. As before, the data in the column headed "Time to failure" indicates the time to the first appearance of current flow. TABLE 3 Tests of Wrapped Pipes Buried m Earth Specimen Wrapping used Time to failure Total time oltest Current in milliamps. at end ol test 1 Wtrh rtnA f>^ir1np Days 10 7 7 10 10 10 13 13 13 56 56 56 29 29 29 29 29 29 29 75 2 29 29 29 63 63 Montlis 18 18 18 18 18 18 18 18 18 13 18 18 10 10 10 10 10 10 10 10 10 10 10 10 13 13 10 2 do 12.0 3 do 13 4 do 8 5 do 6 do 8.0 7 .....do 9.0 8 do 8.0 9 do 8.0 10 do 4.0 11 do ... . S 12 do 5.0 13 Tar and paper 2.0 14 do 2.0 15 do 1.5 16 do 1.5 17 do 2.0 18 do 2.0 19 do 1.5 20 do 1.5 21 do 1.5 22 do 4.0 23 do 2.0 24 do 2.0 25 1 4 26 do -* ... 1.0 The total time of the test and the current at the time the specimens were dug up are also given. When the pipes were removed from the earth and the wrapping stripped off they were found to be covered with rust spots, and here and there were pits of considerable depth. An illustration of these pits is given in Fig. 5. The pipes longest in the ground i- ~ >.■-• --- -^r- --■-,—. w.- . ■ — . . Surface Insulation of Pipes 27 were buried about one and one-half years, and in that time pits were formed extending ahnost through the iron. The currents were not large, but the high-current density resulting from local failure of the coating resulted in very rapid corrosion of the iron wherever breakdown occurred. The longest period during which any specimen of the lot remained insulated is seen to be 75 days, which is very insignificant, indeed, compared with the total life of a pipe under normal conditions. VII. CAUSE OF THE FAILURE OF THE COATINGS A careful study of the conditions under which the failure of insulating coatings under electric stress takes place shows that it is due to the combined action of the moisture and electric stress. Repeated experiments have shown that if any paints or membranes herein referred to are carefully weighed when dry and then immersed in water they will markedly increase in weight, showing that they all absorb moistxure in greater or less degree. This is also borne out by the electrolytic measmrements already described in this paper. The failure of the coating has been found to be invariably preceded by a slight flow of electric cturent, which in itself is proof that a slight amount of moisture has penetrated throi"^h the coat to the smrface of the coated metal. The actual rupture oi the coating is due to the fact that when the water once penetrates through to the surface of the metal a slight flow of electric current first takes place, and this results in a small amount of electrolysis, which invariably produces more or less gas. This gas being confined soon develops sufficient pressure to ruptiure the coating, giving rise to the peculiar appearances illustrated in Fig. 3. While in the experiments above described the failure of the coating has usually taken place only locally, this is undoubtedly due to the fact that the experiments were dis- tinued as soon as rapid pitting of the covered pipes had taken place. If the coatings were to be left in service, as they would be in any practical case, moisture would undoubtedly continue to penetrate the coating at many points, which would in time give rise to a continued increase in the mmiber and size of the blisters, so that ultimately the coating would be entirely destroyed. 28 Technologic Papers of the Bureau of Standards The time required for such destruction would, of course, depend upon the thickness of the coating. But coatings of the thickness commonly used for covering service pipes and similar structures can hardly be expected to last more than a few years. At most, under ordinarily severe electrolysis conditions a majority of the paints and coatings which we have tested would undoubtedly fail within a short time, their usefiol life probably not exceeding a year in the majority of cases. There remain two other classes of surface insulations which we have not discussed in this paper, for the reason that the experi- mental work in regard to them has not yet progressed far enough to justify us in making definite statements as to their value. These are the methods already referred to in the introduction of this paper, viz, inclosing the pipes within some sort of fiber con- duit either with or without pitch filler, or covering the pipe with some sort of instdating enamel similar to those used in the manu- f actm-e of numerous kinds of enameled ironware that are now on the market for a great variety of purposes. Experiments relating to the effectiveness and value of both of these methods of protection of pipe are now in progress and will be reported on as soon as conclusive results have been obtained. Vin. CONCLUSIONS Summing up the results of the foregoing experiments it is evident that they indicate that such pipe paints, dips, and wrap- pings as have been brought to our attention are, with practically no exception, of no value whatever for protecting pipes from elec- trolysis when appHed in the positive areas near the power houses. If, however, they are applied in negative areas they may be of considerable temporary value in reducing the current picked up by the pipe, and in that way indirectly they may reduce damage in positive areas. We wish to emphasize the fact that the results of these tests are not to be considered as throwing Ught on the value of these coatings for protecting various metals from natural soil corrosion, as the tests were designed solely for the* ptirpose of testing their value as a means for protecting against electrolysis from stray currents, where the forces tending to corrode the pipes Surface Insulation of Pipes 29 are of much greater magnitude than those producing galvanic action, which is largely responsible for slow corrosion of iron in soil. Whatever use may be made of such coatings in the nega- tive areas for reducing the amoiuit of ctuxent flow in the pipes it should always be looked upon as a secondary means of mitiga- tion only and not depended upon as a chief means of protecting pipes. In any case, where electrolytic action becomes serious, the first and most important step to be taken is to provide a proper nega- tive return for the stray railway currents so that the potential drop in the rail will be reduced to so low a value that there will be no serious tendency for stray currents to pass in transit from the tracks on to the pipes. When adequate measiures are taken in this direction it will, as a rule, not be necessary to go to great expense in providing exterior protection on the pipe systems themselves; were such protection necessary, we think that there are other and much more effective means available than siurface insulation. It is not within the scope of the present paper, however, to discuss such methods, as they are discussed in considerable detail in Technologic Paper No. 27, by the Bureau of Standards, dealing with the general subject of electrolysis mitigation, Washington, January 5, 1914. APPENDIX EXPERIENCE AND OPINIONS OF PIPE OWNING COMPANIES WITH RE- GARD TO THE PREVENTION OF ELECTROLYSIS AND SOIL CORROSION BY MEANS OF INSULATING COATINGS. With a view to obtaining information as to the experiences of a large number of pipe-owning companies with insulating coatings for undergrovmd pipes 28 letters, each containing a list of ques- tions, were' addressed to as many companies in cities of impor- tance throughout the United States. Replies were received from 19 of these companies. The list of questions was as follows: (i) What kind of coatings have you used and what was the manner of their application ? (2) In what kind of soil was the pipe laid after coating ? (3) Was the coated pipe subjected to soil corrosion only, or to both soil and electrolytic corrosion ? (4) For what length of time did these coatings appear to suc- cessfully prevent corrosion ? (5) What was the character of the damage to the pipe and coating where damage occtirred ? (6) What is your opinion of such coatings, in general, as pre- ventives of either soil corrosion or electrolytic corrosion ? Table 4 shows the results of this correspondence in a brief manner. It is there seen that nine of the correspondents reported actual experience with insulating coatings used for the purpose of pre- venting damage to pipes by electrolysis. The substance of their replies is quoted verbatim below, the numbers showing answers corresponding to the questions given above. 30 Surface Insulation of Pipes 3r s •0 3 a a-a I- 23 5-S VI a o a-s to OS > 9 rn ^ -at s » « g §J a g >3 o sua ID ^ a ^-6 sa > -s r at OJ ■sg e •33 ■ga 5 ^•3 •O CO "m 9 go ■sa ^" Hi S-S ^S ii II si •31" a'3 o £ a a "m" -a H^S a o C S nog a 'It Zi o < A'CJ §9 -Sou •ON 41 Pi*" '0'3 o a Pi VI Qi as J*" O » o a II •alg ill •S-S* w 4} U is S g to U al o .as > ^ is .3 Sb sI so S3 n e* ^ ■s (0 Hi 0] 32 Technologic Papers of the Bureau of Standards •a V •I O U w pq < ! 1 i^ S I ■0 |a •S _ « 11 s S o 5tf oT t « bO l1 n III Qi boa ^ll •a 4 1 ||i i e o n CO h O 01 s" fe o s fe-O "3 ; 2 "3 Is ■§« -d •a ft ■*^p. 0) •g i SI ^1 1 a 1 1 ! 'SI i sii 1 o « • ss-l .!< ^»i •o & s g«s a a o o ■< o M i 0) ^ o. « ji-a iji! 1" g S 4 [ 1 •§ a d i a> , •S 3 o "o 0) at o ^ g u OS u o "o i ' i =3 m (0 !/■ CO tn i CO 1" il ■0 & B 1 i •c 1 , -3 • { s ■2 g u J ' 1 . a SB oS •s • ill lis p< o H o a o , ^ ^ . ■ , , in I 3 01 §. & t te n ^ §2 "S 1 « 1 1 ^ m .s g <« 1 I- t* o d 5 o'O S id Ss " s 3 S "a s ■a o«- "2 S 1 la u Is Is Si 5« > 1 nil IS 15 n H a tl isr t- 1 Surface Insulation of Pipes 33 a. metropolitan water and sewerage board, boston. mass. Wm. E. Foss (i): "Burlap saturated with hot asphalt; and slaked lime and Portland cement mortar. Both of these coverings were applied after the pipes were laid. [The burlap and asphalt covering was applied to a forty-eight inch water main at points where it was thought that considerable damage by electrolysis was being done. One section 26 feet long, another 77 feet long and another 39 feet long were treated in the following manner: The pipes were first moroughly cleaned with scrapers and wire brushes. A coat of asphalt paint was then applied and over this a layer of Warren's " Kiola rock asphalt wire composition " was applied hot. A sheet of burlap was then wrapped aroimd the pipe, and over this another layer of the hot asphalt was put on. The insulation was applied in short sections, which overlapped about 6 inches at the junction lines, and when completed was from % inch to ^ inch in thickness. As the trench was refilled, three lines of old tram rails were laid in the trench parallel with the axes of the pipes, and about 6 inches from the bells at the nearest point. These rails were connected to the pipe line by means of "0000" copper bonds soldered to the pipe bells near the ends of each insulated section. The rails were also connected at the ends with similar copper bonds. Where the pipe line was located under the car tracks, the rails were placed in a horizontal plane directly over the pipes, and opposite the power station where there are no tracks in the street they were placed in a vertical plane. Arrangements have been made so that the amount of electricity flowing off from the rails can be measured, and also the amount flowing on the pipes. All of the pipes insulated show the effects of the electrolytic action, and some of them have been very badly damaged. On one pipe there were about 80 pittings, varying in size from circles X of ^^ inch to i}4 inches in width, and from -^ of an inch to -j^ of an inch in depth. Extract from second annual report of metropolitan water and sewerage board, Jan. i, 1903.] "The lime and cement covering was first used last fall (19 12). A ^2 inch coat of slaked lime was applied to the outside of the pipe and over this a i X "ich protective coating of mortar, composed of equal parts of Portland cement and sand, was applied. (2): "The soil in which the 48-inch pipes covered with burlap and asphalt were laid was partially made ground containing miscellaneous materials, including some ashes and clayey gravel, which had been filled over the original marsh mud. The groimd water usually stood 3 or 4 feet below the surface of the ground. The 24-inch pipes covered with lime and cement mortar were laid in a brick lined tmmel 6 feet in diameter, located tmder an arm of Boston Harbor. The coated pipes are surrounded by salt water which leaks into and fills the tunnel. (3) : ' 'The pipes covered with burlap and asphalt were probably subjected to electrolytic corrosion only, as they were laid near a large power station where the street railway return current flowed through the soil at all times. The pipes covered with lime and mortar have been insulated from the remainder of the pipe system by a wooden joint at each end of the tuimel, in order to prevent electrolytic corrosion as far as possible. 34 Technologic Papers of the Bureau of Standards (4) and (5) : "The condition of the pipes coated with lime and cement mortar has not been determined since the recent appUca- tion of the coating. [On April 6, 1904, the burlap and asphalt covering which was applied in November, 1902, was removed from one length of 48-inch pipe for the purpose of examination. Before the covering was applied the pipe was carefully cleaned and the pits dug out and located. Upon removing the covering many new pits were found, and in some cases one large pit was found where there were two or three separate pits before the covering was put on. The number of pits in the pipe had increased from 80 in 1902 to 496 in 1904. The railway engineers suggested that possibly the pits were not all dug out before the pipe was covered, and therefore re-covered it for a fiu'ther test. They have since made the following experimental tests, which indicate that the covering has little if any value under some circumstances. A short piece of 4-inch pipe, covered in the same manner as the large pipe, was buried in dry earth in a box, and a cast iron plate was buried 1.25 feet from the pipe. In one test tar was used in the covering, and in another asphaltum. The pipe and plate were connected in the regular trolley circuit of 500 volts. While tiie earth was dry the resistance between the pipe and plate witi the tar covering was 700 megohms, and with the asphaltum covering 34 megohms. The earth was then sat- urated with salt water, and the resistance quickly diminished, and after seven to ten days disappeared. Extract from report of metropolitan water and sewerage board, Jan. i, 1905.] (6) : "Our experience would indicate that it is not practicable to successfully apply and maintain protective coatings to under- ground pipes in general. Whether or not the lime and mortar covering will be successful under the special conditions where it has been applied on our work has not yet been determined." The conditions of the tests of the covering used on the 48-inch pipe seem to be fair enough, but the voltage used in the tests on the 4-inch pipe is abnormally high. It is imsafe to draw conclusions from the results of such forced tests. The coatings were presumably put on with considerable care, but inasmuch as the coating of the 48-inch pipe was probably put on while the pipe was full of water, it would be very difficult to obtain a continuous coating of the asphalt. That is, the rapid cooling would tend to leave the coating full of pinholes instead of allowing the asphalt to run together after it had been brushed on and thus form an impervious layer. B. NEW YORK STATE RAILWAYS, SYRACUSE, N. Y.. A. N. Brown (i): "The pipe in question was a 6-inch gas main, cast iron, leaded joints, and at this particular intersection had been giving considerable trouble; in fact every two years this pipe would fail. In 1908 it became necessary to make a renewal of some loo feet of pipe, and before putting it in the grotmd each length was given a Surface Insulation of Pipes 35 good thick coating of asphalt paint and then served with an insu- lating tape about 6 inches in width and in make-up very much like the ordinary friction tape. Another coat of asphalt paint was then applied and this was allowed to set before being installed in the ground. The joints were made up and a similar applica- tion was then made around each joint as on the pipe itself. (2) : "The soil was not damp and contained considerable gravel and some clay. (3) : "The pipe at this location was subject to electrolytic cor- rosion only, there being nothing about the soil which would lead one to believe that soil* corrosion was taking place. (4): "The pipe, coated as outlined above, has been in service five years and has given no trouble. (5): "There has been no damage observed on either pipe or coating. (6) : "To prevent electrolytic action on pipes by such a method and make it applicable to a whole system is out of the question on account of the excessive expense. The approximate cost to cover this 100 feet of pipe, including labor and material was 30 cents per foot." The principal objection to be brought against the coating de- scribed above at present is its first cost, as stated imder (6). Five years is also too short a time to judge of its ultimate behavior under the conditions of the test, because the soil in which the pipe was laid is described as being not damp, which would have a ten- dency to lengthen the life of the coating over what it would be in a damp soil. In view of the excessive cost of covering the pipe in this way it seems that the life of the pipe ought to be at least doubled over that under ordinary conditions where not subjected to electrolysis, because there are a number of comparatively inexpensive ways in which the damage by electrolysis could be prevented, or at least very much reduced. C. KINGSTON GAS & ELECTRIC CO., 611 BROADWAY, KINGSTON, N. Y. F. TOBEY, Jr. (i) : "The coating used was coal tar pitch. For ordinary pur- poses the tar is applied by dipping the hot pipes into a trough con- taining the melted tar. On larger pipes it is applied with brushes to the steam heated pipe. (2) : "These pipes are laid in a variety of soils, ranging from clay to clean sand. (3): "When coated as above, the pipe was not intentionally subjected to electrolysis. Where electrolysis is suspected the pipe is encased by a wooden box, and the box is filled with hard 36 Technologic Papers of the Bureau of Standards pitch, which forms a coating at least one inch in thickness at the thinnest part. (4) : "We have had some experience of electrolysis on the light coated pipes, sometimes within two years. Those with the box covering have not been affected after an exposure of five years, so far as we can learn. (5) : "The damage generally took the form of deep pitting, often involving the whole thickness of the pipes, and causing leakage. In appearance these pits could not be distinguished from rust spots. (6): "We would say that the first mentioned coating has con- siderable value in preventing ordinary corrosion, but very little if any value in the prevention of electrolysis. The box coating appears to be of value for the latter purpose. "In addition I would say that this matter of pipe coating has not been taken up by our company, imtil within the last ten or twelve years, and in passing I will state that we still have in use a number of miles of pipes, both cast and wrought iron, which have been in the earth for fifty 'years, and occasional removals have shown that some of these were still in condition to last some years longer. These old pipes were put into the ground with no treat- ment whatever, and I am inclined to believe that in the absence of electric currents, and in sandy soil, neither cast nor wrought iron pipes require any protective covering." The box covering described above is evidently of such a character that it would last for a long time. There are no threads of fabric to form a path for water to creep through the pitch mass, and if trouble does not develop by the pitch flowing into the manholes or down inclines and leaving portions of the pipe exposed, the pro- tection ought to be very good. No mention is made of cost but it would probably be approximately 35 cents per foot for a 6-inch pipe for materials. This would almost make it out of the question as a means of preventing electrolysis, but in the light of the results described previously in this paper it seems that the only hope of permanent protection by an insulating coating is to be found in coatings approaching in thickness that of the one described above. d. water department of atlantic city, n. j. Lincoln Van Gilder (i) : " Pioneer Mineral Rubber used as a hot dip on 30-inch steel pipe over which a wrapping of burlap was placed. A brand of asphaltum rubber called ' Marco ' was used on f^-inch wrought iron bonds for a wood stave pipe. The latter received two hot dip- pings and in both cases a cold brush coat was applied to all abraded places. Surface Insulation of Pipes 37 (2) : " These pipes were both laid in a sandy field and across salt marsh, partly under the surface of the latter, the exposed portion being backfilled with a meadow sod. (3): "Principally soil corrosion. Various tests show slight electrolytic action. (4) : " Both brands have given good service to date in the sandy soil and both were but partially satisfactory in salt marsh. The steel pipe coated with Pioneer Rubber began to fail within two years and is today, after 12 years, nearly worn out. The wrought iron. bands on the wood pipe are now about 3 years old. They have not seriously deteriorated. The coating, where intact, ap- pears to have considerable elasticity but some has flaked off. (5): "On the steel pipe, blisters would appear in the coating and the pipe would pit under the blisters. The burlap covering did not appear to be beneficial. "A section of this pipe recently examined by the writer shows the coating of the top and sides to be valueless and the pipe badly pitted. The bottom third of this section is in fairly good condi- tion. The burlap is destroyed but the mineral rubber adheres well, has considerable elasticity and the pipe shows but slight pitting. At this point the bottom part of pipe lies in solid meadow that is constantly saturated. " At some points on this Hne the worst pitting occurs at the bot- tom of the pipe, at others the top pits and the bottom rarely shows a leak, the latter condition occurring nearest the thoroughfare where the marsh is subject to overflow with very salt water. The bottom pitting occurs nearer the shore where the soil is fresher but fairly salt. The ' Marco ' coating has not been on long enough to give an authoritative opinion. (6) : " For soil corrosion, the writer's experience with protective coatings has been rather unsatisfactory. For the prevention of electrolysis his experience has not been sufl&cient to warrant an opinion." e. philadelphia sttburban gas & electric co. Chari,es Wilde. (i) : " During the last five years we have used two coatings for protecting our pipe. The formula of the first of these coatings is as follows: Five gallons of coal tar boiled from 4 to 5 hours at a temperature not exceeding 550° F, this boiling to continue until the tar is sticky but is not brittle when dropped into cold water. "To the tar which is being boiled add for every gallon of tar one pound of quicklime which has been slacked to a powder; also i pound of tallow and ^ pound of powdered resin. 38 Technologic Papers of the Bureau of Standards "The lime, resin and tallow may be added at any time before or during the boiling. "After the boiling is finished 13 ounces of a solution of crude rubber in turpentine is added to every gallon of tar. This solu- tion is made by dissolving two pounds of rubber in 7 gallons of turpentine. The rubber should not be added until the tar is almost cool, as it will not do to boil the rubber. The rubber may be added after the mixture is heated ready to go on the pipe. "The other coating which we have been using later is simply 600° F coal tar pitch, or in other words, nothing more nor less than a coal tar boiled to 600° P, in order to drive off the acids and as much oil as possible without making the pitch brittle. "We apply these coatings as follows: First, see that the pipe is thoroughly clean and free from rust, and also remove any burrs or projections of metal. " Put the coating in a trough with a steam coil in the bottom. Pass steam through the pipe from ten to thirty seconds until the pipe is thoroughly heated and dry. The pipe is then to be dipped in the coating and allowed to remain in long enough to completely coat the pipe, after which it is taken out and wrapped with muslin or manila paper which has been torn or cut into strips five inches wide. After being wrapped the pipe is again dipped and wrapped as before, thus securing a quite heavy coating, and if it is known that the pipe is to be used in a district particularly affected by electrolytic conditions, it would be advisable to give it a third treatment as above outlined. (2) : "Our pipe is, as a rule, laid in a dry yellow clay, but we have nearly all soil conditions to contend with. When laying pipe in a fill where cinders or any other material has been used that would prove destructive to our pipe, the pipe is protected by placing in the ditch below the pipe, and also over the pipe, a suffi- cient covering of good earth to prevent the corrosive materials from coming in contact with the pipe. (3) : " Our pipe has been principally subjected to electrolytic corrosion. (4): "In answering this questional would say that in some instances where we have been formerly in constant trouble, we have not up to the present time (on service pipe renewed about five years ago) had any further trouble. In some other localities, it does not seem to have been so efficient, as we have had in some instances service pipe to be destroyed in a period of a little over one year, even with the pipe coated as above specified. (5) : "The character of the damage to the pipe has always been in the nature of pits, which in some cases are in clusters and in others may be in one deep pit, in very many instances leaving a Surface Insulation of Pipes 39 deposit in the pits of hard carbon. The damage to the coating is always a complete destruction of the coating at the place where the trouble occurs. At other parts of the pipe, possibly not more than a foot distant, the coating may be in perfect condition. (6) : "Our opinion is that with either of these coatings applied to the pipes as above specified we have secured a much longer aver- age life to our pipe than would otherwise be the case. We do not hesitate to say that either of the coatings as above outlined is an absolute necessity where any steel or wrought iron pipe is exposed to soil or electrolytic corrosion, and beUeve that the pipe thus protected should show an average hfe at least 50 per cent longer than pipes which are not coated." f. the chuctunda gas light co., amsterdam, n. t. Geo. D. Conlee (i) : "The coatings used were coal tar pitch — coal tar pitch over a coating of graphite paint — and pitch painted on hot. All service pipes laid in the last twelve years have been coated. (2): "Services have been laid in all sorts of ground, including blasted rock, gravel, sand, hard pan and loam. (3) : " In a number of cases there were stray currents shown in the pipes by test. (4) : " Pipes have lately been exposed after being in the ground for more than ten years with no signs of corrosion. (5) : "We have not found any coated pipe that has been seriously damaged. (6) : "We coat all wrought iron pipe that we put under ground as we consider that the increased life of the pipe pays the increased cost several times over. " In July 1909 we made some tests for Mr. A. F. Ganz of Stevens Institute on a six-inch line coated with tar and having a Dresser coupling every three hundred feet. This pipe passes the sub- station which supplies the street railway current. It was dug up after having been in the ground for about ten years and found to be in good condition, the coating being perfect and without signs of rust under it. "We coat with hot pitch at the present time, the first coat of graphite paint having been discontinued." G. THE PEOPLES GAS LIGHT & COKE CO., CHICAGO, ILL. J. H. Eustace (i): "Experimentally we have used about 40 coatings for the prevention of soil and electrolytic corrosion of underground iron pipe. A complete description of these tests, their results and 40 Technologic Papers of the Bureau of Standards conclusions drawn appeaxs in the Proceedings of the Illinois Gas Association for 1909, p. 108 to 192, in a paper entitled 'The Com- parative Values of Various Coatings and Coverings for the Pre- vention of Soil and Electrolytic Corrosion of Iron Pipe,' by R. B. Harper. "Prior to 1909 we used a coating known as 'Cremo.' This preparation was based upon the formula of Mr. Hickenlooper and was similar in many respects to the Hickenlooper coating used by many gas companies at that time. The preparation of that coat- ing as made by us prior to 1909 was as follows (description given in Illinois Gas Association Proceedings for 1909) : A 50-gallon barrel of clean, water free, coal tar is placed in an ordinary portable tar kettle and gradually heated up by a slow fire. When sufficiently fluid, 25 pounds of freshly slaked lime are sifted over the top and well stirred into the tar, which is now brought to a boil. When the mixture shows a consistency of a soft pitch upon cooling a sample to ordinary temperature, the fire is drawn and the whole allowed to cool somewhat. The maximum temperature of the mixture when the fires are drawn is usually 500° F. The hot pitch is transferred to settling and cooling tanks. As the mixture cools to about 350° F, 3 pounds of powdered resin and about 8 pounds of tallow are added and worked in until well dissolved and incorporated with the pitch. When a temperature of about 200° F is reached, 5 gallons of rubber cement (containing rubber and turpentine in the ratio of 4 pounds of pure rubber to 7 gallons of turpentine) are added and stirred in until a thoroughly homogeneous mixture results. Cremo, when fresh, is a brownish-black, soft material that possesses tenacity, and, when stretched by pulling apart two siufaces to which it is attached, presents a fibrous or ropy appearance. Even when made with the greatest care, it contains particles of rubber which appear as minute lumps. It has a specific gravity of from 1.2 to 1.25 and often contams over 3 % by weight of lime. It becomes fluid at about 180° F. Cremo remains soft for a considerable time, but gradually hardens, apparently by volatilization and oxidation of some of its constituents. "Owing to numerous examples of failure of pipe coated by ' Cremo,' tests were started in 1907 on the protective values of this and other coatings. As a result of nearly two years of testing, the conclusion was reached that, all things considered, a clean coal tar pitch with requisite physical properties was vastly superior as regards cost, durability, etc., to 'Cremo' or Hickenlooper coating and to many of the paints or dips on the market. Therefore, since 1909, a clean coal tar pitch free from water, acids or soluble mineral matter has been in use by us. "At present we prepare our pipe covering as follows: "A 50-gallon barrel of clean, water ffee, coal tar is placed in an ordinary portable tar kettle and gradually heated by a slow fire, as was done in making 'Cremo.' This is done under a special draft hood, so that the distilling vapors are drawn from the kettles, through an exhaust fan, into a brick stack which acts as a condenser. In this way objectionable vapors are not breathed by the workmen and danger of fires is reduced to a minimum. "The tar is then gradually boiled until the hot liquid residual pitch shows temperatures of from about 525 to 550° F. The Surface Insulation of Pipes 41 temperature reached depends upon the consistency of the pitch at that time. Pitch coating of the proper consistency has a spe- cific gravity at 60° F of about 1.28. When a small sample taken from the kettle and chilled in water at ordinary temperature may be rolled into a ball which will not stick to the fingers, the material is about finished. A final test, by coating a small piece of pipe, cooling same to ordinary temperature and examining for adherence of coating, lack of undue tackiness and freedom from brittleness, is considered the best indicator of a finished preparation. When the pitch meets the foregoing requirements, the fires are at once withdrawn from the kettles and the hot pitch transferred to galvanized iron cooling tanks. When cooled to about 300° F the pipe covering is poured into 50-gallon barrels, in which it is shipped to the various pipe covering sheds throughout the city. ' ' At these shops the pipe covering is placed in a long wooden trough having a cross section of a symmetrical trapezium. At the bottom of this trough, which is about 12 inches wide and 8 inches deep, are several lengths of pipe constituting a steam coil for keeping the pipe covering liquid during application. One end of the trough is provided with a crank and geared device for revolving the pipe in the trough. "The process of covering the service pipe in sizes from i}4 inch to 4 inches is preceded by a thorough cleaning, so that all mill scale, rust, foreign material, moisture, etc., is removed prior to placing the pipe in the bath of pitch. ' ' After heating the clean pipe by means of a steam jet placed in one end and the allowing of steam to blow through, the hot pipe is capped at one end and fastened to the revolving device at the other. It is then let down into the bath of liquid pitch and, as it slowly revolves, a spindle carrying a roll of muslin 4 inches wide is moved parallel with the pipe, wrapping it snugly with an over- lap of about I inch. In this manner the entire pipe is wrapped with muslin which is saturated with coal tar pitch. The excess pitch is removed by a block which follows the winding device. "The whole operation occupies but a few minutes. " The completed pipe is then removed and laid on a rack to cool and allow the covering to harden. (2) : "Our pipes have been buried in almost every conceivable type of soil as much of this city is built on filled ground. The soils include gravel, sand, blue and yellow clays, loam, cinders, plaster, brick, refuse of all kinds and mixtures of any of those mentioned with one another. In many cases it would be most difiicult to classify the soil surrounding a given pipe. (3): "Our underground coated pipes have been subjected to both soil and electrolytic corrosion. 42 Technologic Papers of the Bureau of Standards (4): "The protective life of our coatings is quite variable. In some cases the coating shows destruction in spots after a few months and in others no deterioration is noticeable after years. Cases of failure are usually found in ground under electrolytic conditions. Whether these failures are due to some poorly satu- rated spots in the covering which are initially permeable to soil waters and hence readily corroded, or are attributable to exces- sively destructive conditions existing in the surrounding soil, we are unable to state. (5) : " In most cases of damage to coated pipe, the corrosion localizes itself in several spots where the cloth appears to be more or less rotted and the pitch disintegrated or melted away by the heat at the stuface corroded. The pipe itself usually shows deep and locaHzed pittings which in numerous cases have resulted in large holes or perforations to the interior. (6) : " In general, we feel that while the coating which we have adopted as the best shows failures from time to time, due doubt- less to the practical impossibiUty of covering each and every pipe in an absolute perfect manner, yet much protection is afforded our service pipes from ordinary soil corrosion and mild conditions of stray electric currents." H. THE CITY OF NEW YORK DEPASTMENT OF WATER SUPPLY, GAS, AND ELECTRICITY I. M. DE Verona (i) : "Cast-iron pipe. — ^The coating used upon cast-iron pipe is the customary dead oil of coal tar coating, and generally in accordance with the following specifications : 38. After such inspection and examination by the engineer, both as to cleaning and rust, all pipes and special castings shall be heated in an oven to a temperature of about 300 degrees Fahrenheit, and shall then, and at this temperature, be coated inside and out by dipping into a tank filled with coal tar pitch as hereinafter specified. Every casting shall be entirely free from rust when the coating is applied. If the casting can not be heated and coated immediately after being cleaned, the surface shall be covered with linseed oil to prevent rusting until such time as it may be coated. 39. The coal-tar pitch shall be made from coal tar, distilled until the naptha is entirely removed and the material mixed with oil so as to make a smooth, tough and tenacious coating, neither sufficiently soft to flow when exposed to the summer sun nor brittle enough to crack and scale ofE^hen exposed to temperature below freezing. The pitch shall be carefully heated in a suitable vessel to a temperature of 300 degrees Fahrenheit, and shall be maintained at this temperattire during the time of dipping the pipe. Should this pitch thicken and deteriorate after a number of pipes have been dipped, fresh pitch or some of its original ingredients shall be added to maintain the qualities of the dip. The vessel shall be entirely emptied of its old contents and refilled with fresh pitch, when deemed necessary bjr the Engineer. Every casting shall remain in the pitch for such time as the Engineer may direct, and shall then be slowly removed and laid on skids to drip. "Steel pipe. — ^The only steel pipe laid by this Department which has been laid for a reasonable length of time, and which has been Surface Insulation of Pipes 43 at all examined since laying, is coated in accordance with the following specifications : 85. After such tests, the pipes, after being heated and cleaned, are to be coated by- dipping vertically in a bath of Mineral Rubber Asphalt Pipe Coating, equal to that manufactured by the American Asphalt and Rubber Company of Chicago. The pipe must remain in the dipping tank until it shall have attained the temperature of the bath. The coating must be durable, smooth, glossy, hard, tough, perfectly waterproof and strongly adhesive to the metal, and must show no tendency to flow when exposed to the sun in summer or become so brittle as to scale in winter. All pipe must be thoroughly covered and protected by the coating. The dipping material must be kept pure and free from sand, grit or any other foreign material. To attain this the Contractor must, as often as is necessary, in the opinion of the Engineer, empty the tauks of their contents, clean and refill them with pure material. The consistency of the material must also be kept uniform by the addition from time to time of suitable flux . (2): "Cast-iron pipe. — Cast-iron pipe has been laid by this Department in soil of practically every nature, both wet and dry ; and has been subject in some cases to the action of sewage and of salt water. "Steel pipe. — ^The steel pipe in question, amounting to about 25 miles in length, was laid mostly in sandy soil and generally above the ground water table. (3): "Cast-iron pipe. — ^The cast-iron pipe in this city has been only slightly affected by electrolysis, so far as this Department has information. The only places noted where cast-iron pipe has been acted upon electrolytically have been in the vicinity of electric power stations, and there the action has not been serious. "Steel pipe. — The steel pipe in question has not been subject to electrolytic action as far as we know. (4) : " Cast-iron pipe. — ^The minimum age at which tuberculation and marked corrosion occur is generally about ten years, and the protection of the pipe by the coating is of more or less value up to 50 years or more. "In Brooklyn, a comparison of the condition of uncoated pipe laid in 1858-9 with coated pipe laid in 1860-5 shows that the corrosion of the uncoated pipe is several times as great in area and amount as that of the coated pipe. But in Manhattan there is some pipe which has been in service for about 70 years, and remains in good condition, although it probably was never coated. "Steel pipe. — ^The steel pipe in question, part of which was laid in 1907 and the remainder in 1909, was uncovered in several places during the past year. The coating in all places was found to be intact, except in a few cases on the under side of the pipe at field joints where settlement had occurred, and the consequent leakage had produced incipient rusting over small areas. (5) : " Cast-iron pipe. — The corrosion of cast-iron pipe, especially in the interior, takes the form of tubercles, beneath which small pits are formed in the iron. 44 Technologic Papers of the Bureau of Standards (6): "Cast-iron water pipe. — ^The purpose of coating cast-iron pipe is not so much to prevent soil and electrolytic corrosion as to prevent the corrosion of the interior of the pipe and thus preserve a smooth and unobstructed waterway. The application of a preservative coating such as above described prevents to a large degree corrosion due to the action of the soil for a period of ten years or more. Such few observations as we have tend to show that the coating is also of some slight advantage in resisting electrolytic corrosion. "Steel pipe. — We have no information regarding the action of steel pipe coating other than that given above. "It is impossible for us to answer your questions in detail, as no systematic observations have been made by this Department with regard to the effect of protective coatings in preventing corrosion." I. WATER DEPARTMENT, CITY OF SPRINGFIELD, MASS. E. E. IvOCKElDGE This letter mentions a 42-inch steel main which was subjected to electrolysis at a certain portion of its length. In order to pro- tect this part it was covered with from one to eight thicknesses of tar paper laid alternately with the same general kind of tar which was applied hot to the pipe as it lay in the trench. This coating has been in service since December, 1909, and in September, 19 13, had shown no signs of failure or deterioration. Eight of the remaining correspondents had used dips, consisting of hot tar and mixtiu-es of hot tar, turpentine, rubber, and rosin, for the prevention of soil corrosion with a fair degree of success, but were generally of the opinion that an attempt to prevent electrolysis in any such manner would result in failure. Two correspondents had had no experience . with insulating coatings in any way. The results of these practical tests seem, in a general way, to bear out the results of the laboratory tests described in the foregoing paper. In one or two cases mentioned trouble from stray currents had not yet developed, but there is also some uncertainty as to whether the conditions were present which would develop trouble. From three to five years is also rather a short time for serious trouble to appear if coated pipe is buried in a rather dry soil, as mentioned in one or two of the letters. There appears to be nothing in the above replies to change the conclusions drawn from the laboratory tests previously described, which lead to the conclusion that insulating coatings heretofore used should not be depended on to protect pipes from corrosion by stray currents. DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON, Director No. 25 ELECTROLYTIC CORROSION OF IRON IN SOILS BY BURTON McCOLLUM, Associate Physicist and K. H. LOGAN, Assistant Physicist Bureau of Standards [JUNE 12, 1913] WASHINGTON GOVERNMENT PRINTING OFFICE 1914 ELECTROLYTIC CORROSION OF IRON IN SOILS By Burton McCoUum and K. H. Logan CONTENTS Page I. Introduction 3 1 . Arrangement of apparatus 6 ■J . Cleaning of anodes 7 3. Check specimens 8 4. Determination of ampere hours 8 II. Factors Affecting Efficiency of Corrosion 9 1. Effect of current density 9 .i. Effect of moisture on the rate of corrosion 15 3. Effects of temperature 18 4. Effect of depth of burial on efficiency of corrosion 19 5. Effects of oxygen on corrosion of iron 22 6. Effect of oxygen on the end products of corrosion 25 7. Relative electrolysis in different kinds of iron 28 8. Effect of certain chemicals on the corrosion of wrought iron in earth . 33 9. Corrosion in soils from different sources 39 10. Causes of variation in efficiency of corrosion 45 (a) Formation of new galvanic couples 46 (6) Depolarizing effect of oxygen 50 (c) Nonuniform corrosion of the iron 51 (d) Circulation of the electrolyte 51 11. Effect of very low voltage S3 III. Earth Resistance 54 1. Effect of moisture content on earth resistance 56 2. Effect of temperature on earth resistance 59 3 . Effect of mechanical pressure on earth resistance 60 4. Other factors affecting current flow 62 5. Resistance of soils from different sources 63 IV. Conclusions 66 I. INTRODUCTION The term "electrolytic corrosion" is most frequently used to indicate corrosion caused by the discharge of an electric current which enters the metal from external sources. During recent years, however, the theory has been widely accepted that all cor- rosion in water solutions is essentially electrolytic in its nature, 3 4 Technologic Papers of the Bureau of Standards and in consequence there have come into use a variety of terms such as "galvanic action," "stray current electrolysis," "self-cor- rosion," etc., to distinguish between the cases of corrosion origi- nating from different causes. Thus, corrosion of buried iron may be due to galvanic action caused by physical or chemical differ- ences between adjacent points on the surface of the metal, to the presence of foreign substances in the soil, such as coke cinders, iron oxides, etc., which set up local galvanic action, or it may be due to the discharge of electric cm-rents that have entered the structure at some remote point. In the present paper the terms "electrolysis" and "electrolytic corrosion" are used to designate corrosion caused by the discharge of electric current which has entered the metal from some outside source, while all other forms of corrosion in which the electric currents originate within the corroding system itself from whatever cause are referred to as " self-corrosion." It should be pointed out at the outset, however, that these two general classes of corrosion are by no means inde- pendent of each other, since the presence of either kind of corrosion generally affects in marked degree the nature and extent of the other under a given set of conditions. This mutual influence is such as to be of considerable practical importance, and in particular it often greatly increases the difficulty of obtaining trustworthy experimental data in regard to electrolytic corrosion proper. The data herein presented represent a portion of the work done by the Bureau of Standards in connection with a more general investigation of the subject of electrolysis and electrolysis mitiga- tion, which has been in progress for some time past. The present paper is designed to deal only with the fundamental laws govern- ing electrolytic corrosion under practical conditions, and relates to self-corrosion only in so far as it is necessary to distinguish between the two classes. The stlbject of the prevention of elec- trolytic damage is referred to only incidentally, when occasion requires, in order to interpret the significance of results obtained. This matter of electrolysis prevention has been given much atten- tion and will be treated at some length in a report which will be issued shortly by the Bureau of Standards, deaUng exclusively with the subject of electrolysis mitigation. Electrolytic Corrosion of Iron in Soils 5 In studying the phenomena of electrolytic corrosion in soils under practical conditions many variables are encountered which tend in greater or less degree to affect the results. Among these may be mentioned the current density at the surface of the metal, the moisture content of the soil, the presence of oxygen either in the gaseous state or dissolved in soil waters. The latter not only affects the rate of corrosion but also affects the character of the end products of the reactions, and thus to some extent has a bearing on the question of diagnosing the cause of particular cases of corrosion. The temperature of the soil is also important, par- ticularly because of its effect on the current flow. In the case of iron, the formation of oxids as a result of the initial corrosion may complicate matters because of their possible action in stimu- lating galvanic action. Other factors, such as the mechanical and chemical properties of the soil, the depth of burial of the metal, the limitation of current flow due to polarization, the formation of high resistance films on the surface of the metal, and the pitting of the surface, due to a variety of causes, may likewise act to increase or decrease the rate at which damage may progress, and therefore require special investigation. Finally, since it is not practicable to carry on all experiments in the field under practical conditions, it is necessary to study the possible differences in results that may in some cases occur between experiments per- formed in the laboratory and in the field. It is these factors that are dealt with in the following pages, and while the investigations have in most cases not yet been completed, we believe that the data thus far obtained will be of sufficient interest to justify a report of progress at this time. While the corrosion of iron by electric currents may be influ- enced by a variety of causes, the data to be presented later show that under most practical conditions the extent of the corrosion is to a large extent a function of the quantity of electricity that is discharged from a given surface. This is a quantity that can be readily measured under laboratory conditions and we have there- fore determined, in all cases, the corrosion as a function of the ampere-hour discharge from the anode. The results are expressed in terms of the "corrosion efficiency." If the corrosion of the 6 Technologic Papers of the Bureau of Standards anode is the sole reaction involved at the anode, then, according to Faraday's law, 96 540 coulombs are required to corrode i gram equivalent of the metal and the corrosion efficiency is said to be 100 per cent. In most cases, however, the actual corrosion noted is either greater or less than this amount, and the percentage which the actual corrosion in any case is of the theoretical amount may be called the "efficiency of electrolytic corrosion," or more briefly, ' ' corrosion efficiency, ' ' under those conditions. The experi- mental data presented in the first part of this paper show how the efficiency of corrosion is affected by the varying physical conditions encountered in practice. The corrosion efficiencies are in all cases calculated on the assumption that the iron is divalent. The experiments presented show that in most cases at least this was true, since, as a rule, the corrosion efficiencies observed have been near or above 100 per cent. This is therefore the logical basis on which to figure the efficiency of corrosion. In those cases where the corrosion efficiency was very low it may be due in part to the iron taking the ferric state, and such tendency, when it exists, may therefore be regarded as one of a number of possible causes of low efficiency of corrosion. The various factors enumerated above which affect the efficiency of corrosion of iron in soils are discussed in detail in a later part of this paper. 1. ARRANGEMENT OF APPARATUS The methods of conducting the experiments recorded below were, in general, the same, and may therefore be described once for all. The local earths used in the laboratory tests were from virgin soil near the laboratory, sifted to remove stones and to insiure uniformity. This earth was mix^ with the desired amount of distilled water and placed in tin cans, which served as cathodes. The bottoms of the cans were separated from the earth by a thick layer of paraffin or other insulating material, so that the discharge from the anode placed in the center of the can would be substantially uniform and only toward the sides of the can. The outside of the cans were insulated from each other by several layers of heavy paraffined paper. In a number of experiments, Electrolytic Corrosion of Iron in Soils 7 however, the test specimens were buried in virgin soil out of doors in order to compare directly the corrosion found imder these conditions with the corrosion which resulted when the tests were made in the laboratory. 2. CLEANING OF ANODES In cleaning the anodes and determining their losses, a number of precautions are necessary. It has been shown that many solutions render iron at least temporarily passive. Such solu- tions are, of course, not desirable for cleaning iron previous to a test. The iron used was filed and sandpapered to remove dirt and scale, cut into suitable lengths, stamped on one end with steel numbers for identification, and weighed. Rubber-covered leads were then soldered to the unnumbered ends of the anodes and both ends covered with paraffin or pitch. To make these stick to the iron it is necessary that it should be rather hot when they are applied. The specimens were then thoroughly washed with gasoline to remove any grease due to handling and finally dried with a towel. At the close of the experiment the specimens were washed and brushed to remove all loose dirt and then made cathode in a 2 per cent solution of sulphuric acid with a high- cmrent density. To prevent plating a noncorrodable anode should be used. This method of cleaning was developed after various mechanical and chemical methods had been tried with inconsistent results and has proven very satisfactory.* The speci- mens came from the solution perfectly clean within 10 to 30 minutes and careful tests have shown that clean iron subjected to the treatment suffers no loss. The method seems very much preferable to any mechanical method we have tried, since when the rust sticks very tightly or the iron is rough it is impossible to remove the corrosion products without scraping off some of the iron with them. In a few instances where it was not convenient to clean the iron electrolytically, as in the case of hollow anoaes too small to permit the interior to be protected by inserting an anode, a solution of ammonium citrate has been used. This latter method is satisfactory, except in the case of deep pits, especially if a warm solution is used. * For cleaning wrought iron and steel. Note. — Cast-iron specimens should not be cleaned electrolytically with an acid electrolyte after a corrosion experiment, as the acid attacks the iron. An alkali solution may be substituted for final cleaning, but the alkali may render the iron passive, and so is unsuitable for use before a test. Electro- lytic cleaning with alkali electrolytes is not as rapid or satisfactory as with acid. The ammonium citrate solution is recommended for small specimens of cast iron. 8 Technologic Papers of the Bureau of Standards The paraffine protecting the ends of the specimens was removed by gasoUne and the pitch by toluol. The solder attaching the leads was melted and carefully wiped off. We have also tried dissolving the solder by mercury, but the process is slow tinless heat is used, and the result no better than the easier method. 3. CHECK SPECIMENS Correction for the loss by the anodes due to self-corrosion was made by placing a check specimen inside each can and screening it from the anode by a shield of glass or paraffined paper. Fig. I shows the arrangement of the anode and check specimen. The loss of this check specimen has been de- ducted from the loss of the anode and the difference used as the loss due to electrolysis. It will be shown later that the loss of check specimen in a can with an anode is considerably greater than that of a similar check specimen in a separate vessel of the same earth and it seems therefore that part of the loss in the former case is due to some effect of the current and should be charged against it. The cor- rosion efficiencies found are conse- quently lower than if check specimens in separate cans were used. However there are several advantages in keeping the check specimen in the can with the anode and the increased loss on this account is usually small compared with the total loss of the anode. Fig. 1. — Showing arrangement of ap- paratus for corrosion tests A, anode; T, containing vessel; B, insulation; I, insulating bottom; P, paraffin coating on ends of anodes; L, lead; C, check specimen; S, in- sulating shield 4. DETERMINATION OF AMPERE HOURS To obtain the corrosion efficiency it is of coiu-se necessary not only to determine accurately the loss of the anode, but equally essential to know the quantity of electricity discharged by it. To Electrolytic Corrosion of Iron in Soils 9 obtain this the specimens were so arranged that the current could be read at frequent intervals, compensation being provided where necessary for the resistance of the milliammeter. Curves were plotted showing the relation between the current and time, and the area between the curve and the axes determined with a planimeter. While the exact current values between times of observation are unknown, the areas represent a value of the ampere hours suffi- ciently accurate for practical purposes, and the large number of circuits operating at one time made the use of more accurate recording instruments out of the question. II. FACTORS AFFECTING EFFICIENCY OF CORROSION 1. EFFECT OF CURRENT DENSITY A number of investigators have reported experiments showing that the amount of corrosion which results from a given ampere hour discharge varies greatly from the theoretical amount. Among these may be mentioned the work of Hayden,' and of W. W. Haldane Gee,^ who worked with high current densities, and observed that there was a marked tendency for the iron to become passive, the resulting corrosion being considerably less than the theoretical amount. In general this tendency toward passivity was much more marked when the current density was very high. These experiments were carried out with test specimens immersed in liquid baths, however, so that the conditions were very different from those which prevail in ordinary street soils. Ganz^ has re- ported the results of experiments carried out in certain soils, which showed that the actual corrosion observed was much greater than the theoretical amount, in some cases the loss in weight being as much as several times the loss calculated from Faraday's law. In these experiments very low current densities were used and the earth contained considerable quantities of salt, and this may have affected the result. The authors have carried out several series of experiments in which the aim has been to maintain con- ditions as nearly as possible approximating those which will be encountered in practice, both as regards soil conditions and cur- 1 Jour. Franklin Inst., Vol. 172, p. 29s. 2 Jour. Municipal School of Tech., Manchester, Vol. z, 1910. 8 Proc. A. I. E. E., Jxuie, 1912, pp. looi-toio. lo Technologic Papers of the Bureau of Standards rent densities. The soil used was a virgin soil taken from a sparsely settled portion of the residential district of Washington. An analysis was made of a typical sample of the soil for those ingre- dients which are most likely to affect corrosion, the results being shown at the top of Table i along with the data on efficiency of corrosion. In determining the current densities to be used values were chosen of such magnitude as could give rise to considerable injiny within a period varying from a few months to 15 or 20 years. For example, the highest value used was about 5 milli- amperes per square centimeter, which under uniform distribution and at 100 per cent efficiency of corrosion would cause the corro- sion to progress inward at the rate of about 5.7 centimeters per year, which corresponds to a rate rarely exceeded under practical conditions. The minimum current density used was 0.05 milli- amperes per square centimeter, which corresponds to a normal rate of corrosion of about i centimeter in 1 7 years. These extreme ranges represent therefore the limits between which the corro- sion is of much practical importance. Several series of experiments were made, the data presented in Tables i and la being typical of the series. The corrosion effi- ciencies under Table i are for a soil containing considerably less moisture than those under Table la, which are obtained on a soil practically saturated with water. In the former the test speci- mens were all imbedded in samples of earth placed in tin cans as described above, while in the second series half of the tests were run with specimens buried to a depth of about 2}4 feet in the ground out of doors. The data in Table i are plotted in Fig. 2, and those of Table I a are plotted in Figs. 3 and 4, the curve of Fig. 4 being a con- tinuation of that of Fig. 3, but on,, a smaller scale. While the points do not lie on a smooth curve, because of a number of dis- turbing factors to be discussed later, the trend of the curves is nevertheless unmistakable. They show corrosion efficiencies vary- ing greatly with the current density, the ranges being from about 20 to 140 per cent for the range of current density varying from about 5.0 to 0.05 milliamperes per square centimeter, the lower Electrolytic Corrosion of Iron in Soils II corrosion efficiencies being obtained at the higher current den- sities. All of the data in Tables i and i a are plotted as a single curve in Fig. 5, which, in spite of the irregularities in the individual points shows clearly the decided falling off in efficiency of corro- • • • 120 100 \ \ \ \ • \ X • • 80 ^^ • \. • \ X 60 X \ • v "S \ i ^ " 40 • n 0.4 o.e 1.2 1.6 CURRENT DENSITY — MILLIAMPERES PER SQ. CM 2.0 Fig. 2. — Effect of Current Density on Efficiency of Corrosion sion with increase in current density. It is interesting to note here that the points in Fig. 5 marked with an x were taken out of doors in native earth while those marked with dots and cir- cles were two separate series taken indoors, using small samples of earth in cans. The agreement between the different groups is 12 Technologic Papers of the Bureau of Standards fully as good as that between different points of the same group which indicates that the results obtained on small samples in the laboratory are substantially the same as those obtained on specimens buried in the earth out of doors. This gradual change 100 I > o z 60 40 X ^^ !<__ X X ^ . ■ X :: X .05 .10 .15 .20 .25 CURRENT DENSITY— MILLIAMPERES PER SQ. CM Fig. 3. — Effect of Current Density on Efficiency of Corrosion in corrosion efficiency with current density does not appear in accord with the results of Hayden, Haldane Gee, and others, whose work with liquid electrolytes seemed to indicate an abrupt change in efficiency of corrosion from loo per cent to zero at a critical current density. Electrolytic Corrosion of Iron in Soils 13 160 1« 120 100 BO J 40 120 100 I 80 o JS X X \ X X \ K X^ o "V o o N. ^^ o O X. e Fig. 4.- 1. 2. 3. 4. CURRENT DENSITY— MILUAMPERES PER SQ. CM -Effect of Current Density on Efficiency of Corrosion c 40 Ix : ^v X X >vB o ■~~ .^ ° o 3 Ui 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 CURRENT DENSITY -MILLIAMPERES PER SQ. CM Fig. 5. — Effect of Current Density on Efficiency of Corrosion 4.2 4.5 4.8 14 Technologic Papers of the Bureau of Standards TABLE 1 Relation between Current Density and Efficiency of Corrosion [Partial analysis, per cent of moisture-free sample Oil WO3 CO3 SO< . 0.002 0.002 0.003 O.OO4' No. Density, milliam- peres per square centimeter Efficiency of corro- sion No. Density, milliam- peres per square centimeter Efficiency of corro- sion 1 2.0 57.6 10 .8 75.0 2 1.8 37.4 11 .7 88.3 3 1.7 ■ 69.2 12 .6 79.1 4 1.6 43.2 13 .5 75.2 5 1.5 84.3 14 .4 102.1 6 1.3 75.8 15 .3 142.2 7 1.2 72 ■< 16 .2 96.2 8 1.1 83.8 17 .1 148.4 9 1.0 89.2 18 .05 142.9 TABLE 1 a Current Density and Corrosion Efficiency — Outdoor Tests [Area of anodes 70.9 square centimeters. Time of run, 115 hours] Current Current density. density. Nou milliam- Corrosion Ho. milliam- Corrosion peres per efficiency peres per efficiency square square centimeter centimeter 19 0.034 124.1 24 .163 118.3 20 .064 115.0 25 .206 125.8 21 .088 141.5 26 .222 117.1 22 .129 123.6 27 .258 101.8 23 ISO 104.6 28 .279 113.4 [) 2-liour run In saturated soil in laboratory 4-27-13 to 4-30-13. Exposed anode area 11.78 square centimeters] 29 0.48 102.5 • 34 2.50 78.1 30 1.01 98.1 35 3.45 52.9 31 1.26 78.3 36 4.27 43.6 32 1.84 102.2 37 4.29 27.4 33 2.28 63.6 38 4.72 20.4 It will be noted that these results do not show as high effi- ciencies of corrosion as those reported by Prof. Ganz/ who fovind * Proc. AI. E. E.. June, 1911. Electrolytic Corrosion of Iron in Soils 1 5 values ranging over 500 per cent. It should be noted, however, that the results obtained by Prof. Ganz were for the most part obtained on much lower current densities than were used in the present experiments. It is seen also from Fig. 5 that as the lower current densities are approached the curve tends rather strongly upward, indicating that if the current density had been reduced to the low value used by Ganz the corrosion efl&ciencies might have reached the high values found by him. As pointed out above, however, lower current densities than those used in the present series, although of great theoretical interest, are of little consequence from the practical standpoint. 2. EFFECT OF MOISTURE ON THE RATE OF CORROSION The following experiments were tried to determine whether the amoimt of moisture in the soil affected the corrosion efficiency of iron buried in it. A quantity of red clay soil was air dried and then distilled water was added, a can of earth taken out, more water added, etc., till six cans of earth had been obtained. The ends of the specimens and the bottom and outside of the cans were insulated as in previous tests and small dishes of water placed inside the can to retard evaporation. The six cans were connected in series, the sides of the cans serving as cathodes and a current of 10 milliamperes giving about i milliampere per square centimeter was maintained by daily adjustments for 18 days. At the end of this time the resistance had increased so much that it was difficult to maintain the current and the specimens were there- fore removed, cleaned, and weighed. The efficiency of corrosion was then computed, corrections being made for self-corrosion. While the current was flowing, samples of the earth taken when the specimens were placed in the cans were dried for about a week in an oven at a temperatiu-e of 105° and the percentage of moisture computed from the loss of weight. The per cent of moisture is expressed in terms of the earth before drying. The experiment was repeated, using 12 samples of earth. In order to run the entire set in series it was necessary to use a current of 2 milliamperes instead of 10 milliamperes as in the first trial. This may account for the difference in the results obtained in the two series. The methods were the same in each case. The 44126° — 14 2 I6 Technologic Papers of the Bureau of Standards results of these tests are given in Table 2 and those for the second series are plotted in Fig. 6. 100 ) "X -'^'^^ X A, 60 40 / X / / ^ SO k/ y t /2 y • L- e\ -<^^' 0— ?— ^- T 6 12 IS 24 30 36 MOISTURE-PER CENT Fig. 6. — Effect of Moisture Content of Soil on Efficiency of Corrosion TABLE 2 Effect of Moisture on Corrosion 42 S No. Per cent moisUire Loss In grams Per cent efficiency Total Self -corrosion Electrical corrosion ot corrosion 1 2 3 4 5 6 7 8 9 10 11 12 15.9 20.0 22.5 23.8 26.0 27.6 28.9 31.1 33.3 35.7 37.0 39.4 0.090 .110 .623 .715 2.002 1.579 3.192 4.182 4.217 4.545 4.463 4.218 0.044 • .040 .039 .080 .073 .145 .160 .121 .265 .207 .335 .125 0.046 .070 .584 .635 1.929 1.434 3.032 4.061 3.952 4.338 4.132 4.093 1.1 1.6 13.7 14.9 45.3 33.7 71.2 95.4 92.8 101.9 97.0 96.2 Electrolytic Corrosion of Iron in Soils 1 7 Looking at the curves of self and electrolytic corrosion, it will be seen that where a point on one curve is too high, the corresponding point on the other curve is too low. Since the electrolytic curve was obtained after natural losses had been deducted it is evident that some of the irregularities are due to incorrect values of the natural loss. However, the natural loss is so small that in most cases it could not account fo.r the entire variation in the electro- lytic curve. Since all wrought iron contains more or less slag, it is probable that the presence of minute slag particles explains, in part at least, the pitting and variations of results from expected values. The results of these tests show that the corrosion efficiency varies greatly with the moisture content of the soil, being so small as to be practically negligible when the soil is fairly dry, but approaching values of the order of loo per cent when the soil becomes saturated. In these tests there was very little corrosion when the moisture content was below 20 per cent. It should not be assumed, however, that the numerical values given here will hold for all soils, since there is considerable uncertainty as to the conditions which actually prevail. In the first place, the percentage of moisture required to pro- duce a wet condition of the soil varies greatly with different soils so that the percentage of moisture can not be taken as a measure of the condition of dryness. In the red-clay soil used in these tests the soil appeared to be barely moist at 1 5 or 20 per cent moisture, whereas we have since encountered numerous soils in which 10 per cent of moisture caused it to appear quite wet. There may also be variations due to differences in soil composition which affect the efficiency of corrosion. Further, while the average current density in these experiments was maintained practically constant it is not improbable that the actual current density varied considerably. When the soil is practically saturated with water the current density is probably nearly uniform, but as the moisture content is reduced and some of the pores in the soil become voids, there is a tendency for the current to discharge locally at the points of contact between earth and iron, and it appears possible that this may give rise to great variation in the actual current density of the discharge. It has already been seen 1 8 Technologic Papers of the Bureau of Standards that at high current densities the efficiencies of corrosion tend to become smaller, so that the variations in efficiency of corrosion here observed as due to changes in moisture content may after all be due in large part to changes in current density. However this may be, the important fact is that the amount of corrosion per ampere hour is hkely to be quite low in the case of fairly dry soils, while as the percentage of moisture approaches that corresponding to saturation the corrosion efficiency approaches lOO per cent for the particular value of current density used in this series, namely, i milliampere per square centimeter. 3. EFFECTS OF TEMPERATORE In order to study the effects of temperature on the efficiency of corrosion of iron in soil, three series of experiments were carried out. In the first of these the temperature of the cans containing the earth samples was maintained practically constant at between zero and i° C by means of an ice bath; the second was run at between 24° and 27° C, which corresponds to about average sum- mer temperature in soils; and the third group was maintained at between 35° and 40° C by means of an automatically regulated oven. Four specimens were used in each group, and the ctu-rent density was maintained practically constant at about 0.84 milli- amperes per square centimeter. The tests were all run in the same kind of earth, which was kept practically saturated with moisture. The results of these tests are given in Table 3. An examination of the values of efficiency of corrosion will show that they are practically independent of the temperature. It appears, therefore, that it is safe to assume that throughout the range of temperatures that are likely to be encoun- tered under practical conditions temperature variations have no marked effect on the corrosion e|^ciency of iron in soils. This does not mean, however, that temperature is not an important factor in electrolysis under practical conditions, for the reverse is true; but this grows out of the effect of temperature on the resist- ance of the soil rather than on the efficiency of corrosion. It is shown in a later part of this paper that the resistance of soils varies with temperature in a very remarkable manner even within the ranges of temperature that are likely to occur in soils tmder Electrolytic Corrosion of Iron in Soils 19 ordinary conditions, and that the effect of this change in resistance on the current flow is such as to make the actual amount of elec- trolysis which may be expected vary greatly with temperature. This matter is discussed later under the head of earth resistance. TABLE 3 Effect of Temperature on Corrosion Efficiency [Average cunent density, 0.84 milliamperes/cm^] No. Temperature Corrosion efficiency 1 2 35 to 40° C 98.2 J 103. 4 3 4 Average 97.0 98.4 99.2 5 6 24 to 27° C . 98.2 97.6 7 8 97.9 97.6 97.8 9 10 lo to 1° C .. f 93.8 j 95.7 11 I 99.1 96.2 4. EFFECT OF DEPTH OF BURIAL ON EFFICIENCY OF CORROSION Inasmuch as the efficiency of corrosion is found to vary greatly under different conditions, it was deemed advisable to investigate whether the depth to which a pipe is buried below the surface would have any effect on the efficiency of corrosion. Accordingly a number of specimens were prepared and buried in earth to dis- tances varying from a few inches to about 6 feet. A check speci- men was provided in each case to permit correction for self- corrosion, and it was so shielded as to prevent the passage of any current through it. The anodes and check specimens alternated with each other in the order given in Table 4. In correcting for self-corrosion the mean of the losses on the check specimens on both sides of each anode was used. The specimens were buried in virgin red clay soil and were run at an average current density 20 Technologic Papers of the Bureau of Standards of about 0.056 milliamperes per square centimeter for about 1490 hours. The results of the tests are shown in Table 4 and plotted O 80 ^^x"^ X X ^"^r- X X 1 X ELF CORROSION -DEPTH X -X ^ — « " X 16 32 43 DEPTH OF BURIAL-INCHES 80 Fig. 7. — Effect of Depth of Burial on Efficiency of Corrosion in Fig. 7, which gives curves of both self-corrosion and efl&ciency of corrosion as a function of depth. Electrolytic Corrosion of Iron in Soils 21 TABLE 4 Effect of Depth of Burial on Natural and Electrolytic Corrosion [Wrought-iron cylinders 5,1 cm long and 4.4 cm in diameter polished. Odd numbers carried current; even numbers are for natural corrosion. Area ol surface, 70.9 square centimeters. Mean current den- sity, about 0.056 mllUamperes per square centimeter] No. Total loss Electrical loss Theoretical loss Per cent efficiency oi corrosion Depth g E g Inches 1 9.260 7.972 6.990 114 75 2 1.288 72 3 9.475 8.319 8.119 102 69 4 1.024 66 5 7.630 5.685 6.280 91 63 6 .875 60 7 10. 862 9.929 8.785 113 57 8 .991 54 9 9.422 8.512 7.890 103 51 10 .829 48 11 8.505 7.593 6.959 109 45 12 .995 42 13 8.822 7.866 6.942 113 39 14 .916 36 15 8.225 7.341 6.618 HI 33 16 .852 30 17 6.899 5.913 5.385 110 27 18 1.120 24 19 7.331 6.424 5.780 HI 21 20 .694 18 21 4.667 3.993 3.732 107 15 22 .654 12 23 5.092 4.420 4.226 105 9 24 .690 6 It will be seen that the results, while somewhat irregular, indicate that there is but slight variation attributable to depth, although there seems to be a trend upward in the case of self-corrosion. The variation in efficiency of corrosion with depth is probably due to the fact that the moisture content varied with depth. The fact that no greater variation was observed is doubtless due to the fact that the tests were carried out at a time when the soil was fairly wet both near the surface and at greater depths. The results given above on the effect of moisture content indicate that if the experiments had been made in a fairly dry time, when there was 22 Technologic Papers of the Bureau of Standards considerable variation of moisture content with depth, the corro- sion efficiency would probably have shown a corresponding varia- tion. When conditions are such that there are considerable variations in moisture content with depth, as in a moderately dry time, for instance, the preceding data indicate that the efficiency of corrosion would probably also vary greatly with depth, being in general greater the greater the depth. 5. EFFECTS OF OXYGEN ON CORROSION OF IRON Since, according to the electrolytic theory of corrosion, the presence of oxygen is an important factor in the production of self- corrosion of iron in the presence of water, it might be expected that the electrolytic corrosion of iron by stray currents would be affected in a marked degree by the content of dissolved oxygen in soil water. In order to investigate this point lo anodes and a corresponding number of check specimens having an exposed area of 90 square centimeters each were prepared in the usual way, connected in series, and run on a practically constant current density of 0.056 milliampere per square centimeter. Five of these jars were so arranged that oxygen bubbled through the liquid continuously throughout the entire experiment, and the other five were immersed in the water without oxygen being passed through them. At the end of 183 hours the experiment was completed, the anodes were weighed, and the efficiencies of corrosion calcu- lated. The data are given in Table 5, from which it will be seen that there is considerable variation in the efficiencies of corrosion for the individual specimens. These variations are so large that the difference between the average of the five specimens in the jars through which oxygen was passed (98.5 per cent) and the average for those specimens in the remaining jars (91 per cent) has but little significance. It is of course fiecessary to bear in mind in interpreting these results that even the water through which oxygen was not passed contained a good deal of oxygen in solution, se that any differences in efficiency of corrosion that might be indi- cated would be those due to a somewhat indefinite difference in the oxygen contained in the water. Electrolytic Corrosion of Iron in Soils TABLE 5 Effect of Oxygen on Efficiency of Corrosion [Current density, 0.056 milliampere/cm'!; time, 183 hours; area of anodes, 90 cm^] A. OXYGEN ADDED 23 No. Total loss Self -corrosion Electrical loss Efficiency of corrosion e S g Per cent 1.248 0.182 1.066 110.7 1 1.251 .312 .939 97.5 2 1.296 .330 .966 100.5 63 .993 .067 .929 96.5 4 1.128 .327 .801 87.0 B. NO OXYGEN ADDED s5 0.886 0.030 0.873 90.6 6 .940 .027 .913 94.9 7 .913 .029 .884 91.7 8 .889 .030 .859 89.0 9 .895 Average .040 .855 88.7 91 ^ Buried in sand. TABLE 5a Effect of Oxygen on Efficiency of Corrosion {Tlieoretical loss, 0.730 gram; area of anodes, 15.2 square centimeters; current density, 1.45 mUllamperes/cm^] WITHOUT OXYGEN No. Solution Weights in grams Loss Original Final efficiency 1 H2O g 51. 326 51. 570 52. 361 5L642 g 50. 624 50. 871 51. 651 50. 935 g 0.702 .699 .710 .707 Per cent 96.2 2 HsO 95.8 3 4 10%Na!SO< 10%NasSO< 97.3 96.9 96.5 24 Technologic Papers of the Bureau of Standards TABLE 5a— Continued WITH OXYGEN No. Solution Weights in grams Loss Corrosion Original Final efficiency 5 HjO g 51. 852 52. 725 51. 467 51. 034 g 51. 154 52.044 50. 759 50. 317 g 0.698 .681 .708 .717 Per cent 95.7 6 HjO 94.7 7 8 10%NajSO, 10%Na2SO, 97.0 98.2 96.4 In order to check this result more carefully, two series of experi- ments were carried out, in which a much larger difference in the oxygen content in the two cases was maintained. In each series four specimens were used, two being placed in tap water and the other two in a lo per cent solution of sodium sulphate. In one series the liquids were first boiled down to about half their original volume in Erlenmeyer flasks to remove oxygen and the iron elec- trodes inserted during boiling. After the boiUng an atmosphere of hydrogen was introduced into the flasks as they cooled down, so that practically no oxygen could have access to the liquid. In the other series air was caused to bubble through the liquid throughout the experiment, so that an abundant supply of oxygen was always present. The results are given in Table Va. From this table it will be seen that there is no appreciable difference between the efficiencies of corrosion in the presence of oxygen and in the absence of oxygen, at least in the liquid electrolytes here used. We have reason to believe, however, that this is not the case when the anodes are buried in soils, although just why a difference should exist here is not %lear. That there is a differ- ence is borne out by a number of tests we have made with anodes buried in earth in hermetically sealed cans and others bvuied in cans exposed to the atmosphere, conditions as to moisture con- tent, current density, etc., remaining the same. Whenever the tests were continued for a considerable time, it was found that the efficiency of corrosion in the sealed receptacle was in nearly all cases considerably lower than when the container remained open. This effect is shown in Table 6. Electrolytic Corrosion of Iron in Soils TABLE 6 Corrosion Efficiencies in Open and Closed Cans [Aveiage current density, 0.494 mllUampere per cm^; area of anodes, 9.4 cm^] 25 No. Efficiency of corrosion No. Efficiency of corrosion Closed cans Open cans Closed cans Open cans 1 87.9 77.4 95.2 79.9 95.4 77.2 85.8 8 9 10 11 106 5 2 105.5 3 4 105 5 85.5 7 The average corrosion efficiency in the closed cans was 85.5 per cent, while that in the open cans was 107.5 P^r cent. Whether or not this difference is due to the difference in the amount of oxygen or CO2 present or to other causes, it affords another indi- cation of the danger of drawing conclusions from experiments made in liquid electrolytes as to what would occur in the case of electrodes buried in soils. 6. EFFECT OF OXYGEN ON THE END PRODUCTS OF CORROSION One very marked effect of oxygen on corrosion, however, is its influence on the final products of electrolysis. There is a very common impression extant that the final products of corrosion of iron due to stray currents are the black oxids, whereas in the case of self-corrosion red oxids are produced. This is not in accord with accepted theories of corrosive processes, and the following experiments have been carried out in order to demonstrate that in general this is not the case, although under certain circum- stances the tendency may be in that direction. Four tests were made in which ingot iron was allowed to cor- rode naturally in the absence of oxygen, one test being in distilled water, two in tap water, and one in 10 per cent NajSO^ solution. Four tests were made in which the iron was allowed to corrode naturally in the presence of oxygen, two tests being in distilled water and two in tap water. Four tests were made in which the iron was allowed to corrode electrolytically in the absence of 26 Technologic Papers of the Bureau of Standards oxygen, the electrolyte being tap water in two of the tests and lo per cent Na2S04 solution in the other two. Four tests were also made in which the iron was allowed to corrode electrolytically in the presence of oxygen, two tests being in tap water and two tests in lo per cent NajSOi solution. The solutions were prepared practically free from oxygen by boiling down to about half their original volume in Brlenmeyer flasks. The iron test pieces were introduced during the boiling, and after the boiling was stopped the flasks were closed off from the air and a current of hydrogen free from oxygen was allowed to pass into the flasks as they cooled down, thus keeping the solutions under an atmosphere of hydrogen. In the case of the natural corrosion tests in the absence of oxy- gen, the iron showed no corrosion at first, but after a day or two a a few spots of greenish-black rust were noted, which gradually became larger as time went on, with the formation of a small amount of yellow ferric oxide. This was probably due to the fact that the air gradually diffused in through the rubber connec- tions. In the case of the natural corrosion tests in the presence of oxygen, the rust was soon apparent and consisted almost entirely of the yellow ferric oxide. Thus we see that when oxygen is almost entirely excluded, the ferrous oxide predominates, and when oxygen is present, the ferric oxide predominates. In the case of the electrolytic corrosion tests, the eight flasks were connected up in series, and a current of about 0.025 amperes allowed to pass for about 27 hours. At the end of this time the current was stopped and the anodes were taken out and weighed and the loss in weight determined. It was foimd that the corro- sion efficiency was practically 100 per cent in all cases, calculating with iron having a valence of two. In the case of the four flasks' from which air was excluded, the i]«>n was practically all in the ferrous condition, the corrosion products having the pale green color of the hydrated ferrous oxide. Analysis of the corrosion products in one of the flasks gave 98.9 per cent ferrous iron, the slight oxidation being probably due to the unavoidable introduc- tion of air into the flask during the removal of the electrodes for weighing. Through two of the other four flasks a current of air was allowed to bubble during the course of the electrolysis, and Electrolytic Corrosion of Iron in Soils 27 in those two flasks the corrosion products had the reddish-yeltow color of the hydrated ferric oxide, showing that the iron was largely oxidized to the ferric condition. The other" two flasks were left open to the air, but air was not bubbled through, and in these flasks the corrosion products had a darker color and when filtered off, dried, and tested with a magnet showed the presence of considerable magnetic oxide. Evidently then, the corrosion had proceeded so fast that there was not enough oxygen present to oxidize the oxide completely to the ferric condition, but in the other case, where air was bubbled through the solution, the solu- tion was kept saturated with oxygen and so the oxide was con- verted completely to the ferric condition. These results show that when iron corrodes electrolytically, it corrodes as the ferrous oxide, and that the formation of higher oxides is due to the oxidation of the ferrous oxide by the oxygen of the air, the degree of oxidation depending on the rate of corro- sion and the concentration of the oxygen. If the rate of corrosion is relatively rapid and the concentration of the oxygen is rela- tively low, there will be predominance of the lower oxides, i. e., the ferrous oxide and the magnetic oxide. On the other hand, if the reverse is the case, i. e., if the rate of corrosion is relatively low, there will be a predominance of the ferric oxide. The same explanation will apply to natural corrosion. In this case the rate of corrosion is very slow, and so the ferric oxide pre- dominates ; and even when the oxygen is almost entirely excluded, the rate of corrosion is so slow that there is a slight formation of ferric oxide, although the ferrous oxide predominates. From the foregoing it will appear that the character of the end products of corrosion does not depend essentially on the cause of the corrosion, but that either of the oxides may be produced, both in the case of self -corrosion and in the case of electrolytic corrosion. It may, however, throw some light on the question in many cir- cumstances, for the reason that the rate of natural corrosion of pipes embedded in earth may usually be expected to be so low that practically nothing but the ferric oxides would be produced, there being enough oxygen in the soil waters to oxidize any ferrous iron that may be formed. In the case of electrolytic corrosion, however, this will not always be the case, the corrosion being so 28 Technologic Papers of the Bureau of Standards rapid, especially under bad electrolysis conditions that the suji ply of oxygen in the ground waters will -not be sufficient to oxidize all of the ferrous iron, and the result will be the formation of a considerable amount of magnetic oxide. This, however, will no doubt be largely affected by the depths of the pipe below the surface. The deeper the pipes, as a rule, the less would be the available supply of oxygen, and the greater would be the tendency for the formation of the magnetic oxide. Pipes very close to the surface even though corroding very rapidly by stray currents, might still form little, if any, magnetic oxide, because of the abun- dant supply of oxygen that would be available. Nevertheless, wherever a large preponderance of magnetic oxide exists, while it does not definitely prove that the corrosion has been due to stray currents, it may usually be regarded as a good indication that the rate of corrosion has been so great as to make it altogether probable that stray currents have been largely responsible, unless soil con- ditions, such as the presence of cinders, coke, chemicals, etc., are such that extremely rapid self-corrosion may be indicated. 7. RELATIVE ELECTROLYSIS IN DIFFERENT KINDS OF IRON The question as to relative tendencies of different kinds of pipe to suffer damage due to electrolysis has often been discussed, and there appears to be a well-defined feeling in many quarters that a marked difference of this sort exists. It seems to be the general impression that cast-iron pipes are much less susceptible to elec- trolytic damage than wrought-iron or steel pipes. Experience indicates that cast-iron pipe does show less trouble from electrolysis than other kinds under most conditions. It has often been con- tended that certain kinds of iron are more resistant to self -corro- sion than others, cast iron suffering less than either wrought iron or steel. Since the experimental data presented later in this paper show that the natural corrosion is affected in a marked degree by the presence of stray currents, it might reason- ably be supposed that different kinds of pipes would also suffer in widely varying degrees from stray-current corrosion. In order to determine to what extent this might be the case, a considerable number of experiments have been carried out, using different kinds of iron that are employed in commercial service for under- Electrolytic Corrosion of Iron in Soils 29 ground pipes. Four kinds of iron were used, namely, ingot iron, which is the purest commercial iron known, wrought iron, machine steel, and" cast iron. Two series of experiments were run on cast iron, in one of which the cast iron was machined to a clean surface and in the other the iron was used just as it came from the mold, without removal of the scale. The test specimens, weighing about 30 grams each, were placed in a red-clay soil practically saturated with water and rim in series on a constant current, so that the same number of ampere hours was discharged from each test specimen. The results are shown in Table 7. Since the current in all specimens was the same, and the size of the test specimens practically the same, giving about 0.2 milliampere per square centimeter, the figures shown in the column under " electrical loss " are directly comparable for the different kinds of iron and show the relative tendency of the iron to corrode electrolytically under conditions of the test. TABLE 7 Comparative Corrosion Efficiency for Ingot, Wrought, and Cast Iron, and Machine Steel 1. INGOT IRON . No. Total loss Self-corrosion Electrical loss % e i 1.704 0.015 1.689 3 1.678 .033 1.645 4 1.848 .051 1.797 5 1.669 .031 1.638 6 1.791 .043 1.748 7 2.243 .046 2.197 8 1.665 .041 1.624 9 1.583 .074 1.509 10 1.688 .036 1.652 11 1.713 .060 1.653 12 1.706 .033 1.673 13 1.676 .042 1.634 14 2.167 .055 2.012 15 1.661 .028 1.633 16 1.679 .076 1.603 17 1.674 .046 1.628 18 1.648 .058 1.590 19 1.647 .057 1.590 Average ^046 1.695 30 Technologic Papers of the Bureau of Standards TABLE 7— Continued 2. MACHINE STEEL No, Total loss Self-corrosion Electrical loss K S e 20 1.658 0.052 1.606 23 1.734 .076 1.650 24 1.827 .062 1.765 25 1.721 .066 1.655 26 1.672 .064 1.608 27 1.694 .076 1.618 28 1.684 .113 1.571 29 1.756 .087 1.669 30 1.644 .031 1.613 31 1.653 .046 1.607 32 1.792 .066 1.726 33 1.761 .059 1.502 34 1.686 .033 1.653 35 1.695 .063 1.632 36 1.808 .066 1.742 37 1.734 .066 1.668 38 1.818 .109 1.709 39 1.694 .059 1.635 .066 1.652 3. WROUGHT IRON 40 1.713 0.160 1.533 43 2.203 .077 2.126 44 1.789 .065 1.724 45 1.712 .063 1.649 46 1.689 .117 1.572 47 1.842 .094 1.748 48 1.756 .116 1.640 49 1.693 .069 1.624 50 1.659 .048 1.611 51 1.201 .114 1.087 52 1.701 .124 1.577 53 1.661 .068 1.593 54 1.852 • .055 1.797 55 1.634 .068 1.616 56 1.646 .050 1.596 57 1.712 .073 1. 639 58 1.713 .076 1.637 59 1.840 .080 1.760 .084 1.696 Electrolytic Corrosion of Iron in Soils TABLE 7— Continued 4. CAST IRON SURFACED 31 No. Total loss Sell-corrosion Electrical loss S K E 60 1.807 0.120 1.687 63 1.700 .305 1.395 64 1.846 .108 1.738 65 1.757 .283 1.474 66 1.769 .177 1.592 67 1.746 .079 1.667 68 1.808 .136 1.672 69 1.939 .082 1.857 .161 1.635 5. CAST IRON UNSURFACED 70 1.712 0.136 1.576 71 1.435 .255 . 1.180 74 1.810 .047 1.763 75 1.709 .060 1.649 76 1.863 .245 1.623 77 1.710 .135 1.575 78 1.662 .252 1.410 79 1.712 .060 1.652 .149 1.553 An examination of these figures shows that there is but little difference in the amount of corrosion in the different kinds of iron. This is particularly true of the wrought iron, machine steel, and machined cast iron, which show, respectively, 1.641, 1.656, 1.635 grams loss. The ingot iron showed a somewhat higher electrolytic corrosion than any of the others, which seems to be somewhat svuprising in view of the fact that it has fre- quently been found that the self-corrosion in the case of ingot iron is less than others. The least corrosion of all was in the case of the imfinished cast iron, and this is probably due to the protective effect of the scale, but even here the difference is hardly great enough to be considered of practical importance. The conclusion that must be drawn from these figiu-es is that the efficiency of electrolytic corrosion of the different kinds of iron pipes is practically the same. If we examine the columns show- 44126°— 14 ^3 32 Technologic Papers of the Bureau of Standards ing the self-corrosion in different kinds of iron we find very sur- prising differences. These check specimens were placed in the can along with the anodes and carefully shielded from the flow of current as in all previous cases. An examination of these data shows that ingot iron gave the least corrosion of all, the average for all the specimens being 0.046 grams. Machine steel came next with a total natiural loss of 0.066 grams; wrought iron is third with 0.084 grams; and last, and most surprising of all, the self -corrosion of the cast iron is very much higher, being 0.161 for the machined iron and 0.149 for the unfinished iron. This shows but little difference between the finished and unfinished cast iron in the matter of self-corrosion in the presence of current flow. The relatively high rate of self -corrosion of cast iron as compared to the other kinds of iron tested is contrary to the generally accepted idea that cast iron is more resistant to self- corrosion than wrought iron. It is not improbable that this impression in regard to the superiority of cast iron has grown out of the fact that cast iron structures are usually made rela- tively heavy and they also tend to corrode more uniformly than wrought iron or steel, both of which factors would tend greatly to increase the life of the former. The principal cause of the greater rate of self -corrosion of cast iron appears to be the galvanic action set up between the free carbon and the iron. The carbon is distributed so uniformly throughout the mass, however, that no appreciable pitting results, and hence the corrosion is less conspicuous and also less important than the same amount of corrosion would be if not uniformly distributed as is usually the case of most other kinds of commercial iron. It should be pointed out here that these tests were carried out in the same kind of soil as that used in securing the data of Table i, and the partial analysis there given shows it to 1»e low in chlorides, sulphates, carbonates, and nitrates. It was also free from cinders, coke, etc., and hence is not to be regarded as a very corrosive soil. It is shown later in this paper that the chemical constituents in the soil have a marked influence not only on the total corrosion but also on the pitting, or uniformity of the corrosion, so that it should not be assumed that the relative values given here will hold for all soils. Electrolytic Corrosion of Iron in Soils 33 The foregoing results show that the dif3ferent kinds of iron do not in themselves differ materially as regards their tendency to corrode electrolytically. It would appear from this that the differences noted in practice, particularly in favor of cast iron, are due to various other causes, as has already been pointed out by Prof. Ganz and others, namely, higher resistance joints, higher specific resistance of the iron, the heavier walls, and a tendency to corrode more uniformty. 8. EFFECT OF CERTAIN CHEMICALS ON THE CORROSION OF WROUGHT IRON IN EARTH When pipes are buried in the streets, they are subject not only to the action of the moisture and various natural constituents of the soil, but also to the effects of such chemicals as may result from the traffic on the streets, or from other sources. A large amount of work has been done by other investigators on strips of iron immersed in aqueous solutions, and it has been shown that the resulting corrosion is a function of the amount as well as the character of the chemical used. In many cases the tendency toward self-corrosion first increases with the con- centration and later diminishes very rapidly, possibly to zero, when the concentration is sufficiently increased. It is well known also that certain solutions, such as alkalies, chromates, etc., tend strongly to inhibit electrolytic corrosion, at least when such solutions are practically pure. Hayden has shown that solutions of chromates, for example, tend to produce passivity in iron and thus prevent electrolytic corrosion, but that this passivity is destroyed by the addition of a few hundredths of I per cent of a chloride or a somewhat greater quantity of sulphate. It was considered advisable to carry out a series of experiments with iron .embedded in earth to which various chem- icals had been added. For these experiments a number of acids, bases, and salts as indicated in Table 8 were secured and 2 grams of each were added to 300 g of distilled water. The solution was added to 700 g of air dried red clay, which had been sifted through a 20-mesh sieve. This earth contained initially about 5 per cent of moisture, so that the resulting mixture contained about 33 per cent water, which 34 Technologic Papers of the Bureau of Standards produced a fairly wet earth. The whole was thoroughly mixed and placed in a quart tin fruit can provided with friction top. The anodes were prepared as in experiments already described and vessels of water were placed in the cans as in previous experi- ments and the cans connected in series ; first, in one group ; finally, on account of increased resistance, in three. The current was adjusted daily to 0.005 ampere, which gave a current density of discharge of about 0.45 milliampere per square centimeter. At the end of 85 days the experiment was discontinued, the cylinders cleaned as previously described, and the losses computed. In Table 8 the substances have been grouped according to the anions formed. Since in a number of cases more salt was used than the water could dissolve, the solubility of each chemical has been indicated. This is followed by the number of grams of the anhydrous salt used per liter of water. Then follows the chemical value of the solution, i. e., the number of grams of salt per liter of water multiplied by the hydrogen value of the anion and divided by the molecular weight of the salt. TABLE 8 Effect of Chemicals on Corrosion 1 2 3 4 5 6 7 8 9 10 Corro- Chemical Can No. Solu- billly (gper liter) Solu- tion (gper liter) Chem- ical value Critical value Limiting value (g per liter) Effi- ciency ol corro- sion at (0.55 m. a. per sq. cm.) Self- corro- sion loss (Mg per sq. cm. 4i sion effi- ciency ob- Uined ^w Hayden 1 psr cent sol. (0.22 m. a. sq. cm.) CHjCOOH 2 28 5.715 5.715 o.ras? .0364 102.5 0.109 .166 ITMnO, 63.4 Ba{NOj)j 34 92. 5.175 .0441 (NH<)NOi 10 1924. 5.715 .0719 0-500 H55 116 3 265 37.8 TXtNOa 16 880. 5.715 .0677 KNOt 22 4 316. 5.715 5.715 .0571 .0914 89.6 85.4 .238 .506 HHOi ATtrage 103.7 .262 Electrolytic Corrosion of Iron in Soils TABLE 8— Continued 35 1 Chemical 2 Can No. 3 Solu- bility (gper liter) 4 Solu- tion (gper liter) 5 Chem- ical value 6 Critical value (gper liter) 7 Limiting value (g per liter) 9 Effi- ciency of corro- sion at (0.55 m. a. per sq. cm.) 9 Self- corro- sion loss (Mg per sq. cm. d'a" BS 10 Corro- sion effi- ciency ob- tained by Hayden iper cent sol. (0.22 m. a.) sq, cm.) BaCk (2 HiO) 31 25 1 7 19 13 357. 427. 4.874 2.890 5.715 5.715 5.715 5.715 .0479 .0526 .1579 .1076 .0772 .0985 374 106.0 101.8 101.6 101.4 98.6 97.8 .136 .159 .270 .496 .222 .239 CaCUi2'RtO'\ HCl. NHiCl 372. 340. 3582. 1.0 50.0 290 299 395 102.3 KCl.. 102. 2 NaCl 101.2 .253 NajSOi (10 HjO) KsSO) 18 24 36 6 12 30 194. 111. 0.002 2.520 5.715 5.175 5.715 5.715 4.520 .0260 .0661 .0494 .1174 .0873 .0669 10.0 400 108 89.2 88.9 87.7 87.4 86.0 85.9 .136 .170 .231 .329 .316 .174 102.8 BaSOj H3SO4 (NHils SOi 754. 2. 0-200 534 102.7 CaSOi (2 H2O) 87.5 .226 Ba (OH)j (8 HjO) 32 8 20 14 3&33 26 39. 526. 1120. 1090. 3.104 11. 770 3.480 3.942 .0365 .6965 .0348 .0993 3.1 93.1 88.7 85.6 81.7 73.9 73.5 .322 .591 .611 .608 .268 .195 KOH (2 HiO) . . NaOH(lH!0) .1 1.0 HOH(Av).. Ca(OH)i 1.6 5.715 .1556 . 67-1. 35 Average 82.7 .431 KzCOb 21 15 9 27 1120. 275. 1000. 0.01 5.715 2.107 5.715 5.715 .0834 .0201 .1225 .0719 1.0 1.0 1-10 10 89.3 85.4 81.7 66.2 .306 .394 .561 .348 2 75 NasCOj (1 OHiO) (NHi)iCOa CaCOa .0003 .28 80.6 .402 BaCiO<.. .. 35 11 29 23 17 5 0.004 405. 142. 632. 813. 657.5 5.715 5.715 4.643 5.715 2.829 5.715 .0455 .0762 .0640 .0593 .0354 .1143 45.0 0.4 0.3 0.3 0.3 -0.2 .189 .003 .136 .163 .082 .122 CaCrOi (2 H2O) KsCrO« . 1 up NaiCrOj (10 HjO) CrOs . 01-. 05 .116 36 Technologic Papers of the Bureau of Standards Then follow two columns of values obtained from Hein and Bauer's "On the attack of iron in water and aqueous solutions." ^ The first is the concentration of solution giving maximum corrosion; the second the concentration producing passivity or minimum corrosion. Hein and Bauer suspended small iron plates in beakers of solutions of concentrations from zero to satura- tion. Their researches in this line are more extensive than any other work so far reported. While their experiments can not be compared with the one now recorded on account of differences in conditions, the values quoted may indicate at what part of the corrosion-concentration curve the present tests were made, from which we may form some esti- mate as to the manner in which the corrosion would have changed if the concentration were varied. The efficiency of corrosion is given in the following column, and this is followed by the natural loss in milligrams per square centimeter of surface of the iron per day. Referring to the efficiencies of corrosion given in column 8, it will be seen that with the exception of chromate compounds the efficiencies of corrosion are comparatively high. All of the soluble chromates seem to protect the iron from elec- trolytic corrosion, though this protection is not quite complete. In the case of chromium trioxide the loss at the anode was slightly less than that of the check specimen. No significance should be attached to this result until after further investigation. The comparatively slight protection shown by barium chromate is no doubt due to its very slight solubility. None of the other chemicals which Friend, Hein and Bauer, or Hayden have found to render iron passive in solutions seem to have been effective. Indeed, excepting the chromates there are but two values less than the average conlDsion efficiency when distilled water was used. The anodes in cans containing chromates were blackened, and making the iron cathode in 2 per cent H2SO4 for half an horn- did not remove the discoloration. The check specimens were not discolored in this way. s Mittellungen aus dem Koniglichen Material-priifungsamt. rgoS Berlin 26, i. Electrolytic Corrosion of Iron in Soils 37 That the hydroxids did not protect the iron may have been due to the presence of materials in the soils which neutralized them. There was no doubt considerable CO2 in the soil since it had been dried, crushed, and sifted in the laboratory and had stood there in an open barrel for some time, and this may have been sufficient to counteract the effect of the hydroxids. As will be seen by comparing columns 4 and 7 the concentrations used in the case of the hydroxids and carbonates were in nearly every case greater than those producing passivity when the solution alone acts on the iron. The difference in the results may be due to the effect of the earth on the solution or to the effect of the current. It seems clear, however, that the conditions which prevent self-corrosion are not in general those which will maintain passivity in the case of anodes discharging current at moderate current densities. There does not appear to be any very definite relation between the corrosion efficiency observed and the self-corrosion. The nitrates and chlorides for instance show respectively 103 and loi per cent efficiencies of corrosion with corresponding value of self-corrosion of 0.262 and 0.263 ^ig per square centimeter per day. The hydroxids and carbonates show lower corrosion efficiencies, namely, 82 and 80 per cent, respectively, but the self-corrosion is much higher, being 0.431 for the hydroxid and 0.402 for the carbonate. The soluble chro- mates show almost a complete absence of electrolytic corrosion, whereas the self-corrosion, although smaller than in the other cases, is by no means so small in proportion. It will be seen, also, that the corrosion efficiencies observed do not agree with the values found by Hayden,^ and shown in column 10. While a part of this difference may be due to the differences in solution strength and current density, it is probably due for the most part to the fact that the tests in the present instance were carried out with anodes embedded in earth, whereas the experiments of Hayden were carried out in water solutions. It does not seem probable that a sufficient quantity of inhibiting chemicals can be added to the soil surrounding a buried pipe to protect it indefinitely at a reasonable cost. To render the pipe ^ Jour, of the Franklin Institute, v. 172, p. 295. 38 Technologic Papers of the Bureau of Standards passive is one problem; to maintain it passive against fluctuating, or even reversing cturents regardless of the action of the soil and the constantly changing soil waters on the soluble chemical, is quite another. A phenomena of importance which is not shown in the tabulated data, is the pitting of the iron. This is usually attributed to particles of impurities in the surface of the iron or to variations in the soil. In these experiments the virgin soil was dried, rolled, and sifted through a 20-mesh sieve. Enough solution was added to nearly saturate the soil. All of the cylinders were cut from the same piece of Norway iron rod. It might be expected, there- fore, that the pitting would be very similar in all cases. This, however, was by no means the case. The anodes from the nitrate cans were covered by a dark cheese-like layer which maintained the original form of the anode. When this was pared off the surface of the iron was nearly smooth, showing the fibrous struc- ture of the wrought iron but no pits. The anodes in the cans containing sulphates were corroded almost as uniformly; the surface of the cleaned anodes was brighter and somewhat uneven but showed no marked pits. The surface of the anodes from the car- bonate cans was more uneven. Pitting is noticeable in the case of the hydroxids and very marked in anodes from the cans con- taining chlorids. As has been stated the soluble chromates blackened the surfaces of the anodes but did not materially attack them otherwise. There are no marked differences in the appearance of the check specimens except that those from the chromate cans remained bright. So marked are the differences in the anodes that in most cases it is possible to classify them by their appearance without reference to their numbers. As underground pipes are almost^always destroyed by pitting rather than by the amount of iron lost, a satisfactory means of preventing pitting would be of great value. The remedy most commonly suggested is the use of a more homogeneous iron. Without doubt this would reduce the corrosion due to local galvanic action, but the above experiments indicate that pitting of buried iron is very largely influenced by the natiue of the electrolyte in the soil. Electrolytic Corrosion of Iron in Soils 39 It may seem that for comparing the effects of different chemicals quantities which are chemically equivalent should be chosen. A glance at columns 5 and 8 will show that in a number of cases practically equal corrosion efficiencies occur when the chemical values are very different. Indeed, so far as the tables go, there seems to be no relation between chemical values and corrosion efficiency. It appears from these experiments that solutions which produce passivity when iron is immersed in them do not protect the iron against electrol}rtic corrosion when the solutions are in earth, and with the exception of the chromates, no chemicals here tried are of marked value in reducing corrosion. Also, the action of iron in a solution is not a safe criterion of its behavior when the iron is made anode in earth containing these solutions. 9. CORROSION IN SOILS FROM DIFFERENT SOURCES While the foregoing experiments show the effect of the different factors which influence electrolytic corrosion in soils, it naturally raises the question as to what extent these various factors are acting in the case of iron pipes subjected to electrolysis under practical conditions. This question seems to be best answered by actually carrying out experiments on electrolytic corrosion in a great variety of soils of different kinds and gathered from widely different sources, at the same time maintaining the conditions as near to practical conditions as possible. In order to do this, cor- rosion tests were made on a large number of samples of soils which were gathered from various cities and sent to the Bvu-eau of Standards at Washington for test as to their various physical properties. Ninety-seven such samples were used for these cor- rosion tests which were taken from various places in Philadelphia, Pittsburgh, Erie, and Apollo, Pa.; St. Louis, Mo.; Butte, Mont.; and Albuquerque, N. Mex. Practically all of these soil samples were taken from excavations made for the ptupose of examining pipes and were taken at about the same depth as the pipe in most instances. In all cases the samples were put at once into her- metically sealed cans and kept therein until ready for test. For the purpose of making the corrosion tests the soils were divided into two classes. Those soils from Philadelphia, St. Louis, Butte, 40 Technologic Papers of the Bureau of Standards and Albuquerque were saturated with distilled water and kept so throughout the tests. The current density of the discharge aver- aged about 0.0002 ampere per square centimeter. The soils from Pittsbtugh, Erie, and Apollo, Pa., were tested with the same moistiu'e content which they had when taken from the ground, and the cmrent density was maintained at about o.ooi ampere per square centimeter. We thus have for one set a very wet soil and a rather low cmrent density, and in the other a rather high current density with what may be considered as roughly average moistiure content, since at the time the samples were taken the soil was neither unusually wet nor unusually dry. The results of these efi&ciency of corrosion tests are given in Table 9. An exami- nation of specimens i to 85, in which the earth was very wet and the cturent density low, shows quite high efficiencies of corrosion, the extreme ranges being 87.9 per cent for specimen Nq. 2 and 126.3 P^r cent for No. 30. All but four show values exceeding 100 per cent, while the great majority fall between 100 per cent and 115 per cent, the average of all being about 107 per cent. TABLE 9 Corrosion Efficiency Tests on Soils from Different Sources Rod N0.8 Total laS3 Self-corrosion Electrical loss Theoretical loss Corrosion efficiency 1 i 2. 294 ' 1.811 2.147 2.244 2.327 2.203 2.156 2.244 2.273 2.363 1.881 2.103 g 0.114 .170 .062 .195 .090 .117 ,075 .175 .089 .133 .064 .174 i 2.180 1.641 2.085 2.049 2.237 2.086 2.081 2.069 %084 2.230 1.817 1. 929 % 1.867 Pet cent 116.8 87.9 3 111.9 4 110.0 5 119.8 6 7 112.1 111.9 8 111.0 9 116 7 10 118 8 110.0 11 97 3 12 103.4 ^Nos. I to 37, inclusive, taken from Philadelphia, Pa.; Nos. 38 to 47, inclusive, taken from Norristown, Pa.; Nos. 48 and 49 from Albuquerque, N. Mex. ; Nos. 50 to 84 from St. I^ouis, Mo. Electrolytic Corrosion of Iron in Soils TABLE 9— Continued 41 Hod No. Total loss Seli-corrosion Electrical loss Theoretical loss Corrosion efficiency 13 14 K 2.173 1.992 2.052 2.584 2.186 2.207 2.052 1.804 2.058 s .126 .025 .308 .280 .041 .032 .086 .103 .091 i 2.047 1.967 1.744 2.304 2.145 2.175 1.966 1.701 1.967 g 1.876 Per cent 109.2 104.8 15 16 122.8 17 114.4 18 115.9 19 104.8 20 21 104.8 22 23 2.187 2.168 2.091 2.220 2.239 2.398 .130 .203 .044 .045 .078 .112 2.057 1.965 2.047 2.175 2.261 2.286 1.871 109.9 105.0 24 109.4 25 26 120.9 27 122.3 29 30 2.091 2.497 2.190 2.130 2.068 2.310 2.114 2.362 2.375 2.300 2.313 .068 .108 .044 .079 .061 .170 .097 .085 .193 .025 .155 2.023 2.389 2.146 2.051 2.007 2.140 2.017 2.277 2.182 2.275 2.158 1.895 107.0 126.3 32 103.6 33 108.4 34 106.0 37 113.2 38 106.4 39 102.4 40 115.6 41 120.2 42 113.7 43 44 2.161 2.148 2.202 2.105 2.257 2.489 2.126 2.177 2.188 2.305 2.200 2.250 2.108 2.330 2.252 2.206 2.258 2.194 1.318 2.201 .150 .094 .031 .182 .101 .351 .022 .121 .122 .104 .148 .228 .052 .117 .115 .156 .247 .133 .054 .143 2.011 2.054 2.171 1.923 2.156 2.138 2.104 2.056 2.066 2.201 2.052 2.022 2.056 2.213 2.137 2.050 2.011 2.061 1.264 2.058 1.913 105.0 107.3 45 113.4 46 100.7 47 112.8 48 111. 7 49 110.2 50 107 3 51 107.9 52 116.1 S3 107 3 54 105.7 55 107.4 56 115.6 57 58 107 2 59 105.2 60 107 8 62 66.2 63 107 6 42 Technologic Papers of the Bureau of Standards TABLE 9— Continued Rod No. Total loss Self -corrosion Electrical loss Tlieoretical loss Corrosion efficiency 64 65 g 2.242 2.224 2.295 2.085 2.164 2.276 2.225 2.210 2.152 2.070 2.190 2.062 2.200 2.089 2.063 2.286 2.152 2. 330 1.706 2.062 s .068 .157 .060 .045 .060 .181 .096 .156 .020 .096 .100 .038 .072 .151 .114 .064 .157 .135 .188 .003 e 2.174 2.067 2.235 2.040 2.104 2.095 2.129 2.054 2.132 1.974 2.090 2.024 2.128 1.938 1.949 2.222 1.995 2.195 1.518 2.059 B 1.866 Per cent 117.2 116.3 66 121.0 67 109.9 68 113.4 69 112.9 71 114.7 72 110.8 73 104:9 74 106.4 75 112.6 76 109.2 77 114.6 78 104.4 79 105.1 81 119.8 82 107.5 83 108.3 84 81.8 85 111.0 PITTSBURGH, PA., SOILS Total loss Self-corrosion Electrical loss Theoretical loss Corrosion efficiency 4.600 5.100 e 0.207 .177 .295 .220 .030 .005 .140 .270 .140 .145 .546 .545 E 4.393 4.923 3.658 2.560 5.180 4.363 5.055 2.552 2.865 4.290 2.973 3.727 •- 4.969 Per cent 88.4 99.2 3.953 74.7 2.780 51.6 5.210 104.3 4.368 87.8 5.195 101.6 2.822 51.4 3 005 57.7 4.435 86.4 3 519 67.2 4.272 72.0 ERIE, PA., SOIL 4.932 0.185 .260 .255 .129 .245 1.451 .040 4.747 3.249 4.437 3.466 4.532 17. 729 7.491 4.750 99.9 68.2 94.0 72.9 74.4 80.7 36.3 4 692 3 595 4.777 18.180 7.531 Current density, 1 milliampere per square centimeter. Electrolytic Corrosion of Iron in Soils 43 The figures in the second group show much lower values, the extreme range being between 36.3 per cent and 104.3 P^r cent. Most of the values fall between 60 and 100 per cent, with an average for all specimens of about 76 per cent. The difference between the efficiencies of corrosion shown by the two series is evidently due partly to the lower moisture content and higher current density in the latter case. These results are in accord with the data already presented in which the effects of moisture and cuixent density have been studied separately. It should be pointed out here that while the current density in the second series is higher than may be expected under average conditions in practice, it is no higher than would frequently be encountered under moderately severe prac- tical conditions. From these and the preceding tests it will be evident that under average practical conditions we may expect the corrosion efficiency to be of the order of 100 per cent when the earth is very wet and the current density quite low, while as the moisture content is reduced or the current density increased the corrosion efficiency falls off and will usually be found to range between 50 and 100 per cent, while in quite dry soils, such as might at times be encountered in practice, a much lower figure might occur. We are convinced that under average conditions of soil moistiure, and with current densities that may be expected in localities where electrolysis conditions may be considered moder- ately severe, a corrosion efficiency between 50 and 1 10 per cent, will usually prevail. It will be seen also from the foregoing data that the decrease in corrosion efficiency due to increased current density is by no means as rapid as the increase in current, so that within the limits of current density that will usually be encountered in practice the actual amount of corrosion will be found to increase with increase of current. The question may well be raised as to the reliability of corrosion efficiency experiments carried on in earths in the laboratory, and the extent to which such results may be considered as representing what would take place in the earth under normal conditions. In general, however, it will appear that experiments made in the laboratory are much more satisfactory for studying the laws of corrosion because conditions can then be much more readily con- 44 Technologic Papers of the Bureau of Standards trolled, and it is simply necessary to determine whether or not the laws of corrosion are substantially the same in the case of experi- ments on iron embedded in small samples of soil as they would be if the iron were embedded in the earth out of doors, all other con- ditions being the same. This would probably not be true if the experiments were continued over a great length of time during which certain soluble constituents of the soil in the laboratory specimens might become exhausted by the corrosive processes, but we have ample reason to believe that experiments thus made and extending over a comparatively short time represent quite closely what may be expected to take place in the case of pipes under actual conditions. Numerous experiments have been made on specimens of iron embedded in the earth out of doors in order to check this conclusion and to guard against any serious error that might be introduced by possible conditions of the soil. Some of the data bearing on this have aheady been given in the earUer part of this report relating to the effects of depth of burial and of current density on efficiency of corrosion, which show that for similar conditions the results for the outdoor tests do not give results materially different from the laboratory tests. Another series is given in Table lo. In this case a number of specimens of iron were buried in the earth out of doors and caused to carry cur- rent for several months, and the efficiency of corrosion was deter- mined. The current density varied considerably during the experi- ments, due largely to change in resistance of the soil, but on the whole the range of current density averaged about the mean of the values used in the tests on effect of current density given above. The moisttue content, of course, varied considerably from time to time. An examination of Table lo shows that the efficiencies of cor- rosion in these outdoor tests ranged^between approximately the same limits as those carried on indoors for similar ranges of moisttire and current density. These data afford additional evi- dence that the results of the corrosion efficiency experiments car- ried on on samples of iron embedded in soils in the laboratory are of substantially the same order of magnitude as they would be if the iron had been buried out of doors. Electrolytic Corrosion of Iron in Soils TABLE 10 Efficiency of Corrosion, Specimens Buried in Ground out of Doors 45 No. Total loss Self-corrosion Electrical loss Efficiency of corrosion S S g Per cent 1 15. 719 0.286 15. 433 74.9 3 12. 159 .286 11. 873 72.8 5 4.425 .282 4.143 61.5 6 5.879 .282 5.597 73.9 7 5.894 .280 5.614 80.0 10 6.374 .280 6.094 96.3 11 2.364 .278 2.086 83.3 12 3.310 .278 3.032 76.8 77.9 10. CAUSES OF VARIATIONS IN EFFICIENCY OF CORROSION The causes which give rise to corrosion less than the theoretical amount according to Faraday's law have been the subject of much investigation by numerous investigators in connection with studies of passivity in iron. Numerous theories have been evolved, but comparatively little is definitely known in regard to this subject. The subject is too complicated and would lead to too much theo- retical detail for discussion here. On the other hand, no attention has been given to the influences that may be responsible for corro- sion efficiencies greater than loo per cent, and in view of the frequency with which these high efficiencies of corrosion occur it seems well to present here very briefly a few comments as to the possible causes that may be responsible for these high values. It has been seen that the efficiency of corrosion of iron embedded in earth in many cases exceeds loo per cent, although we have not been able to confirm the results of other investigators previously referred to in this paper who have reported electrolytic corrosion amounting to several times the theoretical value. The highest values which we have found in our experiments have been of the order of 1 50 per cent, but for the most part the corrosion has not been greater than 20 per cent in excess of the theoretical amount. The very large number of cases, however, both among the tests already described and among those that follow, in which the corro- sion efficiency exceeds 100 per cent, even after careful correction 46 Technologic Papers of the Bureau of Standards has been made for self-corrosion, indicate quite clearly that the loss of iron due to the discharge of electric current is in many cases appreciably greater than the theoretical amount. This is a matter of great importance and is being given special attention with the viev/ of throwing further light on its. causes, but much yet remains to be done before the phenomena can be properly understood. Several causes suggest themselves as possible factors in pro- ducing this high efficiency of corrosion, some of which are dis- cussed below. (a) Formation of New Galvanic Couples. — It is well known that when iron corrodes in the presence of water and oxygen oxids of iron are formed as end products. Under most underground conditions these will be deposited at the surface of the iron in more or less irregular contact with the iron. These oxids are fairly good conductors and are also electronegative against iron, so that when a particle of iron oxid comes in actual contact with the iron, a galvanic element is formed which tends to corrode the adjacent iron. It seems not improbable, therefore, that when a clean piece of iron is subjected to the discharge of electric current the forma- tion of the iron oxid which results from the initial corrosion may set up galvanic couples which did not before exist and thus greatly increase the self-corrosion on the specimen. The following experiments were carried out to gain an idea of the effect of the initial corrosion products on subsequent electro- lytic corrosion and on the self-corrosion of the specimen. In this experiment twelve 2 -quart tin cans were coated outside with paraffin, and a layer of heavy paraffined paper placed over the sides. The cans were then nearly filled with red clay which had been air dried two months and sifted through a 20-mesh sieve; 300 g of distilled water was added to 700 g of this sifted earth, and the whole thoroughly mixed befor^it was packed in the cans. This earth was nearly saturated with water. For anodes and check specimens cylinders of % inch Norway iron 2 inches long were used. The cylinders were carefully cleaned and placed vertically in the cans, the anodes in the center and the check specimens close to the side, and carefully shielded from current flow. A small vessel of water was placed within each can to retard evaporation of the moisture in the earth. Electrolytic Corrosion of Iron in Soils 47 The 12 cans were then connected in series on a 1 15-volt circuit; the cans serving as cathodes. The current was kept practically- constant at 10 milliamperes. At the end of 429 hours 8 cans were removed from the circuit. Four of these were set aside unopened. From the other four the cylinders were removed, cleaned, weighed, and replaced, and the 4 cans were then replaced in circuit. At the end of 686 hours more the cans were opened, the cylinders cleaned, weighed, and the losses computed. When the cylinders were washed in warm water, practically all of the rust came off, so that it was necessary to clean them electrolytically for but a few minutes to obtain a bright surface. The corrosion of the anodes was more uniform than in most previous experiments, but the corroded surface was nevertheless somewhat imeven, the loss being greatest near the centers of the cylinders. There was practically no pitting of the check specimens. The results of the experiments are shown in the following Table 11: TABLE 11 Effect of Initial Products on Subsequent Corrosion Aiea o( exposed metal, 7.6 cm'; current density, about 1.2 milliamperes per cm<; moisture in soli, about 30 per cent] GROUP A No. Total loss Self -corrosion Electrical loss Efficiency of corrosion 2 6 7 12 i 4.270 4.408 4.365 4.370 i 0.085 .085 .085 .085 i 4.185 4.323 4.280 4.285 J/er cent 102.8 106.3 105.2 105.3 Average 104 8 GROUP B, FIRST PERIOD 1 4.230 0.045 4.185 102.8 3 4.226 .045 4.181 102.7 13 4.225 .045 4.180 102.7 14 4.273 .045 4.223 103.8 44126° — 14- 48 Technologic Papers of the Bureau of Standards TABLE 11— Continued GROUP B, SECOND PERIOD No. Total loss Sell-corrosion Electrical loss EfBcienc; of corrosion 1 3 13 14 g 6.316 6.645 6.475 6.823 g 0.080 .080 .080 .080 K 6.236 6.565 6.395 6.743 Per cent 87.8 92.5 90.1 95.0 91.4 GROUP C 4 11. 185 0.149 11.036 99.0 5 10. 658 .149 10. 509 94.3 8 10. 275 .149 10. 126 90.8 9 10. 945 .149 10. 796 96.9 Average 95.2 Here the specimens are divided into three groups — ^A, B, and.C. In group A the current was kept on the specimens during the first period of 429 hours and then switched off, but the specimens were permitted to stand in the soil undisturbed during the second period of 686 hours, after which they were taken out and weighed and the efficiency of corrosion determined. In this case if the initial corrosion due to the electric current tended to accelerate self-corrosion we should expect a higher efficiency of corrosion than if the specimens had been removed as soon as the current was shut off. In group B the specimens also carried current dur- ing the first 429 hours, but were removed from the earth, cleaned, and weighed as soon as the current was shut off, and then put back in circuit again. If the self-ctrrosion is greater due to the initial electrolysis, we should expect that the efficiency of corro- sion would be smaller for the first period in group B than was obtained for group A. The table shows that such was the case, although the difference is quite small and may possibly be due to other causes. By cleaning these specimens and putting them back in the same soil in which they had previously nm and maintain- ing the same current flow as before diuing the second period we Electrolytic Corrosion of Iron in Soils 49 could determine whether there was any marked change in the efficiency of corrosion due to changes in the soil caused by the flow of current. The table shows that there was a marked differ- ence here, the efficiency of corrosion being much lower during the second period than during the first. In group C the specimens were permitted to remain in circuit during both the first and second periods without interruption. In comparing the results obtained from these three groups it is significant that the highest apparent efficiency of corrosion was obtained when the current was allowed to flow for a time and then removed and the specimen allowed to remain in the earth subjected to the action of self -corrosion during the second period. The next largest apparent efficiency was obtained when the specimens were cleaned and weighed at the ends of the first period . immediately after the stopping of the current. The lowest effi- ciency was obtained when the cleaned specimens of group B were returned to the same earth which had been previously used and again connected in circuit during the second period. Further, group C, which ran continually throughout the first and second periods, showed an intermediate value of corrosion efficiency. These results appear to show that there are two opposing tenden- cies at work, one of which is to increase the corrosion efficiency, as in group A, due to some cause associated with the flow of cur- rent, and the other a tendency to decrease the corrosion efficiency, as in group C, due perhaps to depletion of certain ingredients in the electrolyte. Other experimental data given in this paper indicate that this tendency for the efficiency of corrosion to de- crease with time may be due either to the exhaustion of dissolved oxygen or to a loss of moisture by the earth. The check specimens used in these experiments also show the effect of current flow on the self-corrosion of check specimens placed in the cans along with the anodes. Examining the data for group B under the column headed " Self -corrosion," we find that during the first period the rate of corrosion was less than after the check specimens had been cleaned and rettu^ed to the same cans. By comparing the self -corrosion in group A with those in groups B and C the tendency is seen to be the same and even more marked. Further, by comparing the self-corrosion of group B with that of 50 Technologic Papers of the Bureau of Standards group C we find that, although the total flow of current is the same, the corrosion is considerably greater in the latter. Since those of group B were removed once and cleaned, while those of group C were not, this result seems to support the theory that the presence of a small amount of initial corrosion tends to stimulate the self- corrosion throughout the remaining period of the test. It should be borne in mind, however, that the figures on which this state- ment is based are subject to such large variations that they should not be accepted as conclusive until they have been repeatedly verified. (b) Depolarizing Effect of Oxygen. — According to the electro- lytic theory of corrosion all iron contains sufficient differences in physical or chemical structure at different points on its surface to set up local galvanic elements which are supposed to be respon- sible for self corrosion. Under ordinary conditions of self corro- sion, therefore, there will be certain points on the surface which will be anode points discharging current into the electrolyte and corroding the iron, and there will also be near by cathode points at which the current reenters the iron. The amount of corrosion which results from these couples will, of course, depend upon the resistance of the local circuit as well as on the effective difference of potential which exists between adjacent points. When cur- rent flows in these local paths there is a tendency to form a film of hydrogen at the cathode points which diffuses but slowly, and this not only sets up a counter electromotive force, but it Ukewise introduces a large amount of additional resistance into the local circuit. In consequence of this the self corrosion may be said to inhibit itself to a very considerable extent. If now we superpose on this specimen an electric current, making the specimen anode, more or less oxygen will be liberated near the surface of the metal which may react with the hydrogen, ihus in effect depolarizing the local galvanic elements and permitting much greater self corro- sion in the case of a specimen discharging current than in a case of a similar specimen not discharging. This excess of self corrosion would always appear due to the main current flowing and would thus increase the apparent efficiency of corrosion. It is easy to see how this effect could increase the efficiency of corrosion from a low value up toward loo per cent, although it would not in general tend to make the corrosion efficiency greater than loo per cent. Electrolytic Corrosion of Iron in Soils 51 (c) Nonuniform Corrosion of the Iron, — When iron corrodes it is always with greater or less irregularity. Pits may be formed in which a small hole on the surface may communicate with a large chamber below, and this pitting may pursue such an irregu- lar course as to eat entirely around particles of iron, causing them to fall away from the test specimen. This seems particularly likely to happen in the case of very impure metals, which often exhibit a more or less honeycombed aspect after long-continued corrosion. Since the efficiency of corrosion is always determined from the net loss of weight, any particles of iron that might be dis- lodged in this manner would be charged against the current, and in this way the corrosion efficiency might easily be made to appear larger than 100 per cent. (d) Circulation of the Electrolyte. — It is well known that if the electrolyte surrounding a piece of iron be kept in constant cir- culation, the amount of self corrosion which results will be greater than if the electrolyte remains practically still. When an electric current flows through an electrolyte it causes a migration of the ions, which may increase the self corrosion of the iron in a manner analogous to circulation of the electrolyte. Particularly, in the case of an anode there is a tendency for the acid radicals such as CI, SO4, etc., to concentrate near the anode surface, and it is well known that liquids containing large amounts of these radicals, particularly the chlorine, produce very rapid corrosion of the iron. Here, again, any excess of self corrosion which would be produced would be charged against the electric current, and a high efficiency of corrosion would result. It is not improbable that any or all of the above-mentioned causes may be operating in certain cases to produce a high efficiency of corrosion. However that may be, it has been definitely established that if a check specimen is em- bedded in the earth along with the anode the self corrosion will always be much higher than if the check specimen is embedded in the same earth but in a separate vessel. This is true even when ample precautions are taken to shield the check specimens from the flow of electric current. This is shown by the following series of experiments, which is typical of a great many which have been carried out. The anodes were buried in the center of a quart tin can filled with earth, the can itself serving as the cathode. The 52 Technologic Papers of the Bureau of Standards check specimen was placed in the earth near the cathode and shielded from current flow by means of a glass shield, semicylin- drical in form and of considerably greater diameter and length than the check specimen. The arrangement is shown in Fig. i. In many of these experiments, in addition to the check specimens placed inside the can, a second check specimen was also placed in the same kind of earth with the same moisture content, but placed in a separate vessel, through which no current passed. A few of these data, which are typical of all, are given in Table 12. TABLE 12 Effect of Current Flow on Self Corrosion Check No. Loss of check with iron carrying current 49 days Loss of check In separate vessel 83 days Check No. Loss of check with iron carrying current 49 days Loss of check in separate vessel 83 days 7 14 21 28 35 42 g 0.075 .025 .091 .038 .048 .155 g 0.041 .022 .025 .022 .045 .057 63 83 84 Average.. i 0.143 .135 .118 S 0.063 .018 .014 .092 .034 From this table it will be seen that the average self-corrosion on the check specimens, placed in the can carrying current- was roughly 2.7 times that on the specimens in the cans through which no current passed, while the time in the latter case was 1.7 times that in the former, thus making the average rate of self- corrosion about 4.6 times as great in the can carrying current as in the one which carried no ciurent. Further, it seems alto- gether probable from the foregoing discussion of causes of in- creased corrosion efficiency that thi self-corrosion on the anode itself would be considerably greater than that on the check speci- men placed inside the same can, so that even though the electro- l3rtic corrosion proper were to take place strictly in accordance with Faraday's law we should nevertheless obtain an experimen- tal result indicating an efl&ciency considerably greater than 100 per cent. Electrolytic Corrosion of Iron in Soils 53 In view of the foregoing, therefore, it does not appear that we have any reason to suppose that the electrolytic corrosion proper does not take place in accordance with Faraday's law, even though a corrosion efficiency of much more than 100 per cent is indicated. Nevertheless, in computing corrosion efficiency it is proper to charge all of this excess of self-corrosion against the electric cur- rent, since in the absence of the cturent it would not have occurred, and the corrosion directly chargeable to the current includes all of that which results from the passage of the current, whether due directly to the current or to secondary causes brought into action by the current flow. 11. EFFECT OF VERY LOW VOLTAGE In all of the foregoing experiments, although the current den- sity has often been reduced to quite low values, the voltage impressed upon each pair of electrodes has in general been some- what high, being of the order of several volts in most instances. This has been due to the fact that the small size of most of the electrodes used gave rise to so high a resistance in the earth that voltages of this order were necessary in order to produce the desired current density. Although there is no theoretical reason why the efficiency of corrosion should vary with voltage, except in so far as it affects the current density, nevertheless it seemed very desirable to carry out a few experiments on very low voltages, particularly below i volt, in order to determine whether the effi- ciency of corrosion would be materially different with such ex- tremely low voltages from what it is on the higher values. Ac- cordingly three cells were made up using tap water as an electro- lyte and thin sheet-iron electrodes separated by several sheets of filter paper. This gave very low resistance between the electrodes and made it possible to secure sufficiently large current on much lower voltages than had been possible in the case of specimens buried in soil. One of these cells was run on a constant potential of 0.1 volt, another on 0.6 volt, and the third at i volt. Current measurements were made at frequent intervals and the ampere hours determined. The results are shown in the table following. 54 Technologic Papers of the Bureau of Standards TABLE 13 Low Voltage Test [Aiea of anode, 47.47 square centimeters; average natural loss o( anode, 40 mg] Plate No. Loss total Electrical loss Theoretical loss Corrosion efficiency Current density (mil. amps./cm2) Voltage 1 2 3 0.496 .153 .062 0.456 .113 .022 0.467 .127 .024 97.7 89.0 91.7 0.051 .014 .003 1.0 .6 .1 It will be seen by reference to this table that the efficiencies of corrosion are comparatively high, being highest in the case of the I -volt cell and lowest in the case of the 0.6- volt cell and interme- diate in the case of the o.i-volt cell. The current densities are given in the table and are seen to be extremely low, the lowest being but 0.003 of ^ milliampere per square centimeter. These results show quite clearly that there is no reason to expect that the corrosion efficiency changes materially at any critical value of voltage within a range that is of any practical consequence in the negative return of street railway systems. III. EARTH RESISTANCE The foregoing experiments show what may in general be expected under different conditions as to the discharge of current from iron electrodes buried in soils. In practice, however, when investigating electrolysis conditions, we are not dealing with known conditions of current flow, since it is in most cases imprac- ticable to measure directly leakage currents at any point in the soil without resorting to meastu-es that are too tedious and expen- sive for most work. We have, on the contrary, certain easily determined voltage conditions thrqughout the negative railway return system, and hence, in order to properly interpret the data above presented relating to laws of corrosion, it is necessary to take into consideration the effect of earth resistance on the stray cur- rents that may be carried by the pipes and discharged by them into the earth under known conditions as to potential differences in the network. It is not the pxurpose of this paper to go into detail in regard to the matter of earth resistance, as this is to be Electrolytic Corrosion of Iron in Soils 55 treated somewhat fully in another paper by the authors in a publication of the Bureau of Standards. The great importance of the subject of earth resistance, however, in relation to electro- lytic corrosion in soils makes it desirable to present here very briefly a few fundamental principles in regard to the resistance of soils and its relation to stray-ctu^rent electrolysis. It is obvious that if the soil surrounding the pipe network possessed infinite resistance there would be no trouble from electrolysis, since in that case no stray current could leak off of the tracks and hence find its way into the pipes. On the other hand, if the earth possessed zero resistance, we would also have no electrolysis, since in that case the earth would short circuit the pipes and prevent them from taking up the stray cturents. Some- where between these two extremes we will obviously have a value of earth resistance which in any given case would produce a maximum of electrolysis trouble. The value of this resistance required to give a maximum electrolysis undoubtedly varies greatly with conditions, such as geometrical form of the pipe and track networks, kinds of joints used in pipes, size of pipes, resistance of rail return, and numerous other factors. We feel confident, however, from observations made under practical conditions that in most if not all cases the resistance of the earth will be found much higher than that required to produce maximum electro- lysis, so that in general we may expect the electrolysis to be greater the lower the resistance of the earth. With a view of giving an idea of what may be expected in the way of earth resistance in practice, we present below a summary of some investigations which we have made in regard to variation of earth resistance with varying conditions, and following that we have given the results of a considerable number of earth-resistance measurements made on a variety of soils taken from widely scattered sources. In making these earth-resistance meastuements several different methods were used, in some of which the earth was measured in place without being disturbed, while in other cases the samples were taken to the laboratory, packed in glass cylinders, and the resistance measmred between plastic amalgam electrodes pasted on the ends of the cylinder, the voltmeter-ammeter method with alternating current being used. In a good many cases both 56 Technologic Papers of the Bureau of Standards methods were used and the results were found to check in a very satisfactory manner. In making the earth-resistance measure- ments in place two excavations were made side by side to a depth of several feet, leaving a portion of undisturbed earth several inches in thickness between the two excavations. The sides of this undisturbed portion were made approximately parallel and fairly smooth, and small electrodes a few inches in diameter placed on the opposite sides. These electrodes were then sur- rounded by guard rings of sufficient diameter to assure practically parallel lines of ciurent flow between the two electrodes. The resistance of the earth between the electrodes was then measured by means of the voltmeter-ammeter method as in the laboratory, alternating current being used for the purpose. In making these measurements care was taken to keep the electrodes and the guard rings not only at the same potential, but also to see that there was no displacement of phase between the emf's applied to them. In making the tests in the laboratory preliminary experiments showed that much more satisfactory results could be obtained by compressing the earth in the testing machine to such a point that further increase in pressure caused practically no variation of resistance. It was found, and will be shown by the curves below, that with increase of pressure a point is soon reached beyond which the resistance varies but slightly with further increase in pressure. Careful comparison of results obtained by first meas- uring the resistance in place in the ground, and later in the same earth in the laboratory, indicated that they were practically the same whichever method was used, and since the method of meas- uring the resistance in the laboratory was so much more rapid and convenient this method was used for the great majority of of measurements that are presented bf low. 1. EFFECT OF MOISTURE CONTENT ON EARTH RESISTANCE Moisture content is one of the controlling factors in earth resistance. In Table 14 are given a series of resistance measure- ments taken on a sample of red-clay soil with varying moistiu-e content, which may be regarded as more or less typical. Electrolytic Corrosion of Iron in Soils 57 TABLE 14 Relation Between the Amount of Moisture in the Soil and its Specific Resistance Per cent moisture (In terms of dry earth) Specific resistance (ohms per centimeter cube) Per cent moisture (in terms of dry earth) Specific resistance (ohms per centimeter cube) 5.0 2 340 000 44.5 4725 11.1 237 400 55.5 4870 16.7 13 880 56.7 5197 22.2 6835 77.8 5045 33.3 5400 For making each measurement a new sample of thoroughly dry earth, dried at 105° C, was taken and the required amount of moisture added, the percentage of moisture being expressed in terms of the dry earth. It will be seen that above about 22 per cent of moisture the resistance remains practically constant, but below this , value the resistance rises very abruptly with decrease of moisture content, and at 5 per cent of moisture the resistance has risen to considerably over 400 times its value when the soil is saturated. This shows that the actual current flow to and from a pipe embedded in soil is dependent in vastly greater degree on the moisture content than on the potential difference between the pipe and surrounding structm-e, and points to the fact that a potential difference which might be perfectly safe in a high and well-drained locality might be sufficient to give rise to a great deal of damage in a low and damp locality. This tendency has of course been well recognized, but it has not been given the con- sideration which it deserves. Cases frequently arise in which this fact might well be treated as an important factor in determining the location of a railway substation, and particularly the points at which insulated radial return feeders might best be connected to the tracks. Another important practical aspect of this change in resistance with moistture content is its effect on the distribution of potential drops throughout the negative railway return area. Since the various parts of the pipe systems are buried at different depths and are very irregularly located with respect to the tracks, it is 58 Technologic Papers of the Bureau of Standards evident that changes in the moisture content with depth will exert a marked influence on the distribution of the resistance in the path of the leakage current, which in tturn will greatly affect both the magnitude and distribution of the potential gradients through- 48 O30 §24 X T o \ \ \ X \ \ \ \ \ \ \ \ V. * n T* -20 -16 -12 -8-4 4 8 TEMPERATURE-DEGREES C 20 Fig. 8. — Effect of Temperature ok Earth Resistance out the system. For this reason not as much reliance should be placed on voltage surveys made at extremely wet, and more espe- cially at very dry periods, as on those taken under more nearly average moisture conditions. Electrolytic Corrosion of Iron in Soils 59 2. EFFECT OF TEMPERATURE ON EARTH RESISTANCE The effect of temperature on the resistance of soil was deter- mined throughout the range from about 18° C to - 18° C (o to 65° F). For this purpose a moist soil was used and was placed in a vessel surrounded by an ice chamber in which a mixture of ice and salt was placed, and the whole was allowed to stand until the temperature had reached about - 18° C, the resistance being measured from time to time by means of electrodes which were embedded in the sample of earth and brought out by rubber- covered leads. The temperature of the earth was taken at the same time each resistance measurement was made, an ordinary mercury thermometer inserted in the center of a hollow electrode being used. The results of these resistance measurements as a function of temperature are given in Table 15 and are plotted in Fig. 8. By reference to the curve it will be seen that the resist- ance varies throughout very extreme ranges, even within the ranges of temperature variation that commonly occur in this country. Above freezing the resistance variation is much less marked, but even here we find that the resistance at 0° C is is approximately 2% times its value at 18° C. At about the point at which the soil water begins to freeze there is a tremen- dous increase in the temperature coefficient of resistance, and as the temperature becomes lower the resistance rises enormously, and at — 18° C the resistance is seen to be over 200 times as great as at 18° above zero. TABLE 15 Effect of Temperature on Resistance of Soil [Soil No. 32; molstuie, 18.6 per cent; specific resistance at 20°, 6260 ohms/cm'] Temperature Resistance Temperature Resistance "0 Obms °C Ohms IS.O 224 - 3.0 1185 13.0 286 - 5.5 4340 8.5 398 -12.0 21700 1.5 458 -13.0 24 600 1.0 462 -15.0 36 200 O.Q 542 -18.0 45 000 -2.0 940 -19.0 48 900 6o Technologic Papers of the Bureau of Standards This enormous variation of earth resistance with temperattireis of considerable practical importance and indicates that in moderately cold weather such as prevails in the northern cities comparatively- little trouble from electrolysis may be expected. This is due not primarily to the higher resistance of the earth immediately siur- rounding the pipes, since the pipes are usually located at a sufficient depth so that the temperature of the earth immediately siurround- ing will not reach the lower values used in this experiment. The real reason for the diminution of electrolysis trouble with the fall in temperature is the reduction of leakage current from the rails. It will be evident that when the ground is frozen even but a few inches deep the resistance of the earth immediately surrounding the rail is enormously increased, and the leakage of stray currents into the earth is thereby correspondingly reduced. And since the rise in resistance with even a few degrees of frost may be many- fold, it is apparent that but a thin layer of frozen earth about the rail would be necessary in order to produce a very marked in- crease in the total resistance of the path of the leakage current. This reduction in electrolysis troubles in cold weather due to increase in resistance of the earth is further augmented by the increase of the conductivity of the rail return which takes place at the lower temperature, which may amount to as much as 15 or 20 per cent, and is sufficient as a rule to compensate for the increased load which usually prevails dtuing the cold period. It should also be pointed out here that the effect of variations in temperature with depth on the resistance of earth will have an effect on the distribution of potential gradients in the earth very similar to variations in moisture content referred to above. For this reason it is preferable not to make voltage surveys at times when extremely low temperatures prevail. • 3. EFFECT OF MECHANICAL PRESSURE ON EARTH RESISTANCE Of considerable interest, although of much less practical impor- tance, is the effect of mechanical pressure on the electrical resist- ance of earth. As already stated, when presstire is applied to a sample of earth its resistance is but little affected, as a rule, after a certain relatively low value of pressure is reached. This is shown in Fig. 9, which gives resistance-pressure curves for a ntmi- Electrolytic Corrosion of Iron in Soils 6i ber of different soils from various sources. The range of pressures here are for the most part between 20 and 1000 pounds per square inch, and the variations in resistance between these Umits are sur- prisingly small. Numerous measurements of the resistance of 3000 2800 SPEC IFIO RESISTANCE — PRESSURE CURVES OF EARTHS N0.I -BLUE CLAY SAMPLE No.51 " 2-BLACK HUMUS " " 52 " 3-BLACK HUMUS " " 69 " 4-YELLOW CLAY " " 66 " 5-SAND AND HUMUS " " 64 " 6— YELLOW CLAY AND SAND " " 83 2200 2000 1800 \ ■ -^ % 1600 -6 — ~~ -2 1 1400 1200 1000 -— r \ ^ -6 800 -1 600 400 200 100 200 300 400 500 600 700 800 PRESSURE IN LBS. PER SQ. IN. 900 1000 Fig. 9. — Effect of Mechanical Pressure on Earth Resistance earth 2 or 3 feet below the surface before being disturbed, using the guard-ring method, and subsequent measurements of the same earth in the laboratory under pressure show that the resist- ance at a few hundred pounds' pressure per square inch is substan- tially the same as the undisturbed earth. 62 Technologic Papers of the Bureau of Standards 4. OTHER FACTORS AFFECTING CDRRENT FLOW There are other factors also which aflfect the resistance of soils, such as its mechanical properties and chemical constituents, and these may have an important bearing on current flow to and from the buried pipes. The character of the street railway roadbed is also an important factor in determining the extent of leakage of stray current into the earth. A well-drained rock or concrete roadbed may in general be expected to offer much higher resist- ance to the leakage of current than one in which the construction is such that a large amount of moisture is retained. Polarization 35 « S O 30 I ^-inch auger to a depth approximately twice the distance apart of the holes. A small quantity of damp clay was then tamped in the bottom of each hole and a contact piece consisting of a bare sleeve i % inches long and a plug screwed 8 Technologic Papers of the Bureau of Standards to the end of a }4-vich pipe which had been painted and vsrapped with insulating tape was thrust or driven firmly into the damp clay. After the first set of data was taken the terminals were removed and some damp clay was packed in the holes and the measure- ments were repeated. The terminals were again removed, inter- changed, and replaced, and the measurements again made. In this way 9 sets of observations were made to determine the effects of the contacts and the accuracy with which the measure- ments could be repeated. Table i gives the results of the 9 observations. Trial showed that it was very difficult without a jig to bore a set of holes at equal distances apart and get them placed accu- rately enough to use the simplified equation given in Dr. Wenner's paper. In nearly all cases the error introduced was sufficient to necessitate working out the entire formula. TABLE 1 Observations Ohms per centimeter cube Per cent of deviation from mean Observations Ohms per centimeter cube Per cent of deviation from mean 1 7006 7286 7858 7339 7534 7250 -5.6 -1.8 +5.9 -1.1 + 1.5 -2.3 7. . . 7385 7400 7737 5 2 8 3 9 +4-3 Average 7420 6 It will be seen that the results check within 6 per cent, a much higher degree of precision than is required for practical purposes. Where an alternating current source is available and the soil is free from rock, measurements are^not difficult, though the re- quired transportation of the apparatus from place to place is an objection to the method. After the measurements had been completed a number of sam- ples of earth were taken in the immediate neighborhood and presstu-e-resistance curves run on them, using the testing machine, as is explained later. It is there shown that the resistivity ob- tained by Dr. Wenner's method corresponds to resistivity with Earth Resistance and Electrolysis the compression method at pressures of from 30 to 75 povmds per square inch, depending on the soil. (c) Guard-Ring Method. — ^This method, which hkewise measures the resistance of soils in situ, has also been developed at the Bureau of Standards. In this method two parallel trenches large enough for a man to work in and a few inches apart are dug to any desired depth and the separating wall trimmed until the sides are smooth and parallel. Against one side of the wall is pressed a circular metal plate. Opposite this, against the other side of the Fig. I. — Diagram of corrections and apparatus. D, disk; A, ammeter; R, guard ring; P, plate; E, voltmeter; r. resistance in series with guard ring; d, resistance in series with disk; and T, telephone receiver or vibration galvanometer. wall, is pressed a disk of half the diameter of the first, surrounded by a wide ring of the same external diameter as that of the plate. The disk and ring are separated by a narrow insulating ring and held in position by being screwed to an insulating block of hard rubber or paraffined wood. The connections and apparatus are shown in Fig. i . Contact was made to the earth wall by plaster- ing on a thin coating of clay paste and the surface of each elec- trode pressed into the paste and held by clamps while the read- ings were being taken. In order to determine what portion of 39282°— 16 2 lo Technologic Papers of the Bureau of Standards the current indicated by ammeter (A) was being carried by the central circular plate, a noninductive resistance r was placed in series with the guard ring, and another resistance d in series with the disk D. The resistance r was variable, and with the current on the contact was moved back and forth until the vibration galvanometer T showed no deflection, or at least a well-defined minimum. The currents in the two paths would then be inversely proportional to the resistances, or j — . = --j where / is the total current and i is the current passing between the disks; then Ir i = . This method of determining the current in the central plate was devised by O. S. Peters. Now, the resistance of the cylinder of earth between the disk and the plate equals -r — d.- Substituting the above value of i, the resistance R of the earth E(d+r) then equals j d, where E is the impressed voltage and I is the total current flowing. From the area A of the disk D and the distance between the disks ./ the specific resistance can then be calculated, since R= ~t'' P = ~j-- The contacts were generally good, but occasionally a bad one would throw the results off from what they evidently should be- The causes of these bad contacts are probably air bubbles on the surfaces of the plate and loose soil at the contact point into which the paste did not press properly. The thickness and resistance of the paste used did not greatly affect the results. Its total thickness was usually about 3 or 4 mm, and its resistance 2000 or 3000 ohms per centimeter cube. In measuring the length of the current path, about 2 mm were ususily deducted from the total length to allow for the paste if the soil was of high resistance. No other correction was made. In calculating the area of the disk the mean diameter was taken; thus in one apparatus the diameter of the disk was 7.46 cm, while the internal diameter of the guard ring was 7.78 cm. The diameter used in calculating the area of disk A was 7.62 cm. Some moisture from the paste diffused into the soil, but as the resistance change came into the machine measurements too, it did not affect the check, although Earth Resistance and Electrolysis 1 1 the original resistance may have been reduced. To avoid adding moisture to the soil, a paste of an amalgam of solder and mercury- may be used. In checking up on the testing machine, enough measurements were made to use all of the earth measured by the guard ring, and the average of all such measurements were taken in plotting the curve. No corrections for temperature effects were made until the last 1 2 measurements were made, which may account in some measure for the fact that in some cases the values obtained by the compression method were considerably less than the values obtained with the guard ring, as would be the case if the machine temperature was higher than that in- the other test. The following example illustrates the application of this method and gives an idea of the order of magnitude of the quantities entering into the measurement : Soil, disintegrated rock. Electromotive force = £ = 1 7.0 volts. Total current =/ = 0.101 amperes. Resistance in series with disk = whence p= '- — =4140 ohms per centimeter cube. 341 If a large number of measurements are to be made, it is more convenient to compute R graphically. On a large sheet of finely subdivided cross-section paper lay off BA (Fig. 3) proportional to the reactance of the instrument and BO proportional to its resistance. Continue OB to C and mark the scale of ohms per 14 Technologic Papers of the Bureau of Standards division along OC with the zero at 0. Cut a strip from the top of the sheet and indicate a similar scale along one edge of the strip and place the zero on the point A. It is most convenient to fix the papers to a drafting board and to let the strip revolve about A as a center, using a pin through the zero point as an axis. E Determine -f and place the strip in such a position on the paper that the distance AG-- GO will then be proportional to the value of the resistance of the soil. Fig. 3. — Graphical determination of R With a little care the results so obtained will be as accurate as the data justify. The results of three measurements of soil samples from practi- cally the same point are shown in Table 3, and indicate how nearly results can be duplicated. TABLE 3 • Sample No. Pressure Specific resistance Per cent dif- ference from average Pounds 1000 1000 1000 Ohm/cm 3 4140 4200 3970 +0.90 2 +2.36 —3.24 4103 Earth Resistance and Electrolysis 15 2. MEASUREMENTS OF SPECIFIC RESISTANCE OF SOIL BY THREE METHODS For the purpose of showing how nearly the different methods check, Table 4 has been prepared. Figs. 4 and 5 illustrate the relation between the results by the compression method, Wenner's method, and the guard-ring method, respectively. The varia- 6000 3 O BOOO 5 4000 X O \ \ Nsr^^ ■WENN IR'S ME "HOD S ^l^e k> NOTE; EARTH NSITU ''«f5? ^^ ^~s?i^ ■^ewTof^"^^^" — »yACff( V£ 31.B 127.2 159.0 198.8 222.6 POUNDS PER SQUARE INCH 254.4 2S6,2 31S. Fig. 4. — Comparison of earth resistivities by Wenner's and compression methods tions in the results are more likely to be due to differences in soil than to errors in method, as the soil used was very heterogeneous, the color and texture sometimes changing very radically within a few feet. Such variations in the character of the soil occur in many locali- ties. As will be shown later, even the soil in any one locality i6 Technologic Papers of the Bureau of Standards will change greatly in resistivity from time to time. It is not important, therefore, to obtain an accurate measurement of the soil resistivity at some particular time, but the approximate value of this resistivity will serve quite as well. This being true, any of the methods described will give satisfactory results and the ui 6000 I- z 5JJ 5000 s X 3000 ^ \^ GUARD RING CORRECTION TO 22° «s% ^^^^ ^^^^^^^;^?i?;;r-s 31.8 63.6 95.4 127.2 POUNDS PER SQUARE INCH Fig. 5. — Comparison of earth resistivities by guard ring and compression methods most convenient one may be chosen. For most purposes, where rapidity of working is important the compression method is preferable. Table 5, taken from another publication of the Bureau of Standards,' contains the results of measurements of specific 1 Burton McCoUum and K. H. I,ogan, Electrolytic Corrosion of Iron in Soils, Technologic Paper No. 25, Bureau of Standards. Earth Resistance and Electrolysis 1 7 resistance of soil saiftples from various localities. These samples were for the most part taken from around gas or water mains or from ditches where new mains were being laid. Care was taken to obtain soil from the bottom of the excavation and that it should be free from any ususual contamination from the street. Where pipes were laid in made ground, the samples, of course, contained more or less foreign material; indeed, a great variety of materials has been identified in some of these samples. The samples were removed from the stirrounding earth and trans- ferred immediately to glass jars or tin cans and sealed at once to prevent loss of moisture. At least two samples of soil were taken at each place, and throughout the experiments care was taken to prevent contamination and loss or absorption of moisture. The measurement of specific resistance were made at ordinary room temperatures by the use of alternating current and a volt- meter and milliammeter. Care was taken not to allow the current to flow longer than necessary, so that there should be little heat- ing due to the current. As has been said, the results could be duplicated only approximately. Their values serve very well, however, to show the range of soil resistances likely to be encoun- tered in practice. For convenience, the moisture content of these soil samples is given in the same table. 39282°— 16 3 i8 Technologic Papers of the Bureau of Standards B o O •a a a •o o a I U vi S H Tl I-) O ^ 1 H S .a o o a B o U 1 3 1 p. i a s S, o ;il s o o i O O O O lO O in fM CO (M (£> o **- m T^ m m o o Th CO •* CM S o o Ol o S S g g S S 5 S 1 ii las ■n- tM VO 3 O O U3 lO CN] crv ^o to s s s s 7235 4950 4320 4030 4900 2865 5120 5150 2880 6865 7250 10 370 10 200 56 700 68 200 52 300 58 700 35 400 o o o o- in 5640 5700 2960 7235 7750 11 180 11 050 58 800 71 830 54 800 60 870 35 500 5185 3399 1720 VO o o o t-^ VO K) oooomoomooooooooomoo 0«S§fO°^OCO^O^S22°°^^ co-Mr^iOt^covo" .-H i-H \D r-. m W3 CO CO o o o sis c*inin>r>tnxoi>.coooo u3cot-h .-I'-t-inc^incftc^vD ■-H >-i xD CO m ^o CO s OOOOOOOO o a n s S; s s g S r4 i i s Character of soil i 1 f 11 i 1 1 s ■g 2 1 5 i 1 s 5 5 T 1 g a t- S Q 1 •i I 1 s u 1 s 5 s ; .2 S ■s 2 1 o a ■d o en •§ •e i m c S 1 ii i 1 CO 1 '"' O) CO ■* lO XO '^ as CTi O ' fM M ' in \c t^ K o\ s w r.j CO rg O s s Earth Resistance and Electrolysis 19 omooooooo en no»n O O CTl (M Tf 00 CO ■<*• m t>- ■^ \n 0000000000 ■^r'.OOi/liOi-H'^i-kD ^ ^ -n '"' '"' IM ^ •■■4 fM CO I fl a 20 Technologic Papers of the Bureau of Standards TABLE 5 Specific Resistance of Soils PHILADELPHIA SOILS No. Cliaracter Moisture Specific resistance Per cent Ohms/cm > 11.7 651 14.8 3850 16.1 3036 7.6 2700 17.4 8820 4.7 156 400 16.2 5930 17.9 595 13.1 2830 15.3 1605 17.2 5340 13.4 6280 11.0 24 550 9.5 2600 17.4 2060 12.9 12 100 16.8 5000 19.4 4825 17.3 3820 19.3 21 200 15.6 25 900 15.7 13 700 13.7 1494 20.0 821 18.7 1774 16.7 2490 16.2 2585 0.3 610 000 16.8 2250 18.5 2455 23.8 4410 18.6 6260 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Moist gray clay Moist yellow clay Moist blue clay Near dry red sand Moist red clay Nearly dry mica schist Nearly dry gray clay Nearly dry clay rock and cinders Moist blue clay and gravel Moist blue clay Moist yellow clay Moist yellow clay and sand Wet gravel Wet bumus and clay Moist clay sand cinders Damp disintegrated schist Wet clay cinders gravel Moist yellow clay do Moist red clay Moist yellow clay Moist red sand and clay Moist clay cinders sand Moist clay and sand do Damp clay and humus do Near dry disintegrated schist Damp yellow clay Moist yellow clay Saturated clay and cinders Moist clay and sand PITTSBURGH SOILS Damp sand Moist yellow clay. Moist clay and humus Blue clay Moist gray clay Damp sand do Loam and cinders Near dry sand 13.4 4506 16.5 2819 20.5 2300 26.5 14 025 26.3 619 13.0 1335 10.2 8709 21.8 1074 12.3 2908 Earth Resistance and Electrolysis TABLE 5— Continued ERIE SOILS 21 No. Character Moisture Specific resistance 42 43 44 45 46 47 Moist clay and gtavei Clay coal gravel Wet blue clay Moist blue clay and sand . Moist gravel Wet blue clay and sand... 6.0 16.7 19.3 11.9 5.7 19.6 18 080 1796 3779 3080 14 025 2462 ST. LOUIS SOILS 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 Wet clay Blue clay Moist virgin soil Moist yellow clay Yellow clay ....do do ....do do Virgin black soil Yellow clay do do... do Sand and humus do Blue clay Virgin yellow clay do Yellow clay Virgin yellow clay Virgin soil Yellow clay Blue clay do do Moist blue clay Near dry yellow clay. . Blue clay Yellow and blue clay. . do Blue clay Clay and loam Sandy clay Yellow clay 20.4 600 21.1 700 20.8 1500 21.5 1250 19.0 1800 1600 21.1 1800 22.8 1400 21.3 1400 21.2 1700 16.0 1800 23.4 990 18.4 700 21.9 950 17.8 925 20.0 900 22.0 470 19.1 1450 22.5 484 22.0 700 20.0 1700 22.9 840 23.3 900 26.1 400 19.1 600 24.2 830 23.1 500 16.4 1100 17.1 650 26.9 600 19.7 820 20.0 750 19.2 1450 19.5 1600 22.6 1200 22 Technologic Papers of the Bureau of Standards TABLE S— Continued APOLLO, PA., son, No. Character Moisture Specific resistance 48 30.5 1796 ALBUQUERQUE, N. MEX., SOILS 85 15.3 11.1 11.9 43 960 86 59 475 87 41 908 WASHINGTON, D. C, SOILS 89 90 91 93 Air -dry red clay Near dry Moist loam Wet yellow clay and sand. . . Wet liumus, clay, and sand. 4+ 10 20 30 30 2 340 000 14 660 8729 41 490 24 060 Two samples of soil from 20 to 50 grams each were removed from the jars of earth, placed in evaporating dishes and weighed, and then transferred to an oven maintained at abojit 105" C. From time to time the samples were reweighed until they showed no further loss of water. The per cent of moisture was then computed in terms of the original weight of the soil. The signifi- cance of the moisture content of the soil is discussed in a later paragraph. III. FACTORS AFFECTING THE SPECIFIC RESISTANCE OF SOILS The wide range of resistances shown in Table 5 at once raises the question of the cause of these differences. A number of experiments have been tried to determine the causes of the differ- ences in specific resistance and to determine the effect of each. 1. EFFECT OF PRESSURE It will be seen from Figs. 4, 5, and 6, showing the specific resistance of soil at different pressures, that the resistance of the soil decreases as pressure is applied until about 100 pounds per Earth Resistance and Electrolysis 23 square inch is reached. Beyond this point there is but a sUght change in resistance with pressure. Fortunately, the results of outdoor measurements check fairly close with this limiting value. It seems, therefore, that a satisfactory idea of soil resistance may be obtained without taking apparatus into the field. 3000 2800 2600 2400 2200 SPECIFIC RESISTANCE — PRESSURE CURVES OF EARTHS No. 1 -BLUE CLAY SAMPLE No.51 " 2-BLACK HUMUS " " 52 " 3-BLACK HUMUS " " 69 " 4-YELLOW CLAY " " 56 " 6-SAND AND HUMUS " " 64 " 6— YELLOW CLAY AND SAND " " 83 \, ^ 1800 . \ 1600 -8 ' -2 K 1400 (0 1'200 1000 ^- \ V ■-^ -5 800 -1 600 400 200 1 00 200 300 400 500 600 700 800 PRESSURE IN LBS. PER SQ. IN. 900 1000 Fig. 6. — Specific resistance of soil at different pressures Certain precautions must be observed, however, chief among which is to apply the pressure slowly enough to permit the earth to adjust itself to the pressure applied before readings are taken. The time required for this adjustment will range from a few minutes to several hours, according to the change in pressure and 24 Technologic Papers of the Bureau of Standards the character of the soil. Fig. 7 shows this change of resistivity with time for two samples of soil. It will be noted that the total change in resistivity even after standing from one to two hours amounts to only about 5 per cent, so that for ordinary purposes it is not necessary to wait long before taking the measurement. As will be seen by reference to Figs. 4 and 5, a resistivity corre- sponding to that of the earth in place is obtained by bringing the pressure up to about 50 to 75 pounds per square inch. o (J 4000 3 U _--^ 5PEClM^NjiS:L ^.^^ — ^/ X ■ 1. 1.5 TIME IN HOURS 2.5 Fig. 7. — Resistance-time curves of wet red clay standing under a load of 1, 600 pounds Usually water will be forced from the soil before the limiting pressure is reached, and of course this excess of water must be carefully removed to prevent leakage of the testing current. On account of the loss of water mentioned above the moisture con- tent of the soil tested in the machine is not the same as that of the soil in the field, with which it is compared as to resistivity. What is obtained, therefore, is not identity of condition but an equivalent resistivity. The earth in the machine will evidently Earth Resistance and Electrolysis 25 be saturated, since it has given off excess water, while the earth in the field may be far from satm-ation. The temperature coefii- cient of soil is high, and care must be taken not to heat the soil by the current used in measuring its resistance. 2. EFFECT OF MOISTURE As was stated in the introduction to this paper, the conduc- tivity of the soil is electrolytic, and the passage of a current through it is by means of the soil moisture and the salts or other materials in solution. Table 6, taken from Technologic Paper No. 25 (Biureau of Standards), gives the results of an experiment illustrating this fact. It consists of a series of resistivity measurements taken on samples of a red clay soil. A quantity of this soil was dried at 105° until it ceased to lose weight. Various quantities of distilled water were then thoroughly mixed with samples of the dried earth to obtain the desired moisture contents. At the close of the experiment the moistiue content was also determined by the loss of weight method. From the table it will be seen that when the earth is nearly dry its resistivity is very high. The resistivity falls rapidly as the per cent of moisture is reached. Further addition of water has little effect. The slight rise in resistivity when the moisture content became more than 50 per cent may be due to a dilution of the conducting solution due to a lack of soluble material in the soil, but it is difficult to work with soil containing so much water, and the apparent small rise in resis- tivity may be due to these difficulties. TABLE 6 Relation Betweeu the Amount of Moisture in the Soil and its Specific Resistance Per cent moisture (in tenns of dry eartii) Specific resistance (otuns per centimeter cube) Per cent moisture (in terms of dry earth) Specific resistance (ohms per centimeter cube) 5.0 2 340 000 44.5 4725 11.1 237 400 55.6 4870 16.7 13 880 56.7 5197 22.2 6835 77.8 5045 33.3 5400 26 Technologic Papers of the Bureau of Standards While a similar set of data may be obtained with any soil, the point at which the resistivity reaches a nearly constant value will of com-se depend upon the sample measured. We may think of each particle of soil as surrounded by a film of water of greater or less thickness and held in place by capillarity or by adhesion between soil and water. When the soil is saturated all the spaces between the earth particles are filled with water, and current flowing across the soil has its shortest and widest path. As the soil becomes dryer the layer of water surrounding each soil par- ticle becomes thinner, and the current which must pass through the soil by way of the water has, therefore, a narrower and more circuitous route. The soil resistivity consequently becomes greater as this water film decreases in thickness and as the length of the path over the surface of particles between points of con- tact increases. Probably it is this conducting moisture film that explains the effect of pressure noted above. The contact between the soil particles as they are first placed in the testing cylinder is poor, and the resistivity is consequently high. With the increase of pressure larger areas come into contact with each other, and moisture is forced from those regions where the pressure is great- est and fills voids, thus further reducing the resistivity. More pressure may cause a loss of water, but if gradually applied it is accompanied by a corresponding decrease in the length of the earth cylinder which remains saturated, and therefore the change in resistance will be approximately proportional to this change in length of the cylinder, which would be very small. 3. CHARACTER OF SOIL The experiments on the effect of pressure and of moisture show that while moisture is a determining factor in soil resistivity the amount of water (the number of f rams of water per kilogram of earth) is not a definite criterion of the conductivity of the soil, if its condition as to compactness is unknown. A given quantity of water in a hard-packed road will produce much greater con- ductivity than the same amount in a soil recently loosened by freezing and thawing. Earth Resistance and Electrolysis 27 It is evident, too, that the character of the soil will largely determine the effect of a given quantity of water. If the soil, due to its location or composition, contains large quantities of soluble salts, absorption of moisture will greatly decrease its resistivity; while if practically all soluble material is absent, the water absorbed will remain nearly pure, and consequently a poor conductor. I/ikewise the physical character of the soil has a great influence. If the particles are fine, it will require a much larger quantity of water to cover their surfaces with a conducting film than if the soil is composed chiefly of large grains of sand, since in the latter case the ratio of surface to mass will be much smaller, the volume increasing as the cube and the surface as the square of the dimen- sions of the particles. Thus saturated sand may show a much higher resistivity than unsaturated clay, because the sand may contain less soluble material to make the water a conductor and because the amount of -water may actually be less. Often the soil beneath the pavements of the streets receives much organic matter in solution due to traffic. In some alleys and streets this is augmented by refuse thrown upon them and the overflow of or absorption from drains and sewers. The con- ductivity of such soil is usually high. In many cities large areas consist of made land, the material of v/hich is composed largely of refuse of many kinds, both organic and inorganic. The conductivity of such land is usually especially high, due partly to the amount of soluble material it contains and partly to the fact that it is usually lower than the neighboring regions, and consequently contains more moisture. Often it not only receives the drainage of the higher land, but seepage water from the river or bay from which it has been reclaimed. Salt marshes and moist alkali soils in general may be expected to exhibit very low resistivity. In such regions we may expect not only a maximum damage from any stray current which may be discharged from buried pipes, but also a maximum natural corrosion due to chemical action. 28 Technologic Papers of the Bureau of Standards 4. EFFECT OF TEMPERATURE ON SOIL RESISTANCE Since the conductivity of soil is electrolytic, we would expect soil samples to show a temperature coefficient similar to that of other electrolytes. This temperature effect is described in Tech- nologic Paper No. 25 (Bureau of Standards). To obtain data on the subject a fairly moist soil was packed in a glass vessel and the resistance measured between a metal cylinder on the outside of the soil and a hollow cylindrical electrode in the center. The soil was placed in a chamber which was siu-rounded by salt and ice and allowed to remain tmtil a steady temperature of — i9°C was reached, the resistance being measured by means of the electrodes with an alternating current and the temperature being observed by means of a mercury thermometer in the hollow central electrode. The change in temperature was quite gradual and the diameter of the cylinder about 3 inches, so there was probably no large difference of temperature between the outer and the inner elec- trode. The data are given in Table 7 and plotted in Fig. 8. TABLE 7 Effect of Temperature on Resistance of Soil [Soil No. 32; moisture, 18.6 per cent; 5peci£c resistance at 20°, 6260 olims/cm^] Temperature Resistance Temperature Resistance °C Olmis °C Olims 18.0 224 - 3.0 1185 13.0 286 - 5.5 4340 as 398 -12.0 21 700 1.5 458 -13.0 24 600 1.0 462 -15.0 36 200 0.0 542 —18.0 45 000 -2.0 940 -19.0 48 900 An interesting phenomenon occurs when the electrolyte is cooled below the freezing point of water. Here the data indicate a very rapid rise in resistance. The increase may be attributed to the freezing of the solution and the consequent deposition of parti- cles of ice of high resistance throughout the mass. While the change is very rapid just after the freezing point of water is reached, the continued rise in resistance as well as the Earth Resistance and Electrolysis 29 rate of change in resistance with time indicate that the solution has no definite freezing point, but that, due to the salts in solu- tion, the freezing is gradual, and the proportion of frozen material LJ 21 \ \ \ X \ \ \ \ \ \ \ \ \ \ \ \ \ V. -6-4 4 3 TEMPERATURE-DEQREES C Fig. 8. — Effect of temperature on earth resistance is a function of temperature. A number of tests of which data recorded are typical have been made on different soils with similar results, although the specific resistance of the different earths at a given temperature varied greatly. 30 Technologic Papers of the Bureau of Standards 5. RESISTANCE LAYERS BETWEEN PIPES OR RAILS AND SOIL While the specific resistance determines the conductivity of the soil itself, the soil resistance is only one of the factors which determine the quantity of electricity which escapes from a street railway system. That the conductance of the track and the relative conductances of the track and undergromid structures, as well as the roadbed resistance and distance between the track and pipes, affect the leakage is self-evident. We may now con- sider still other factors which influence the resistance between pipes and rails to a greater or less extent. These may be termed interposed resistances. Wrought-iron and steel pipes are covered more or less com- pletely with a coat of mill scale, which has a much higher resist- ance than the pipe itself and may also act to som.e extent as a noncorrodible electrode. Moreover, the pipes are frequently covered with one or more coats of paint, which also tends to reduce the amount of current picked up or discharged. There is little doubt that a continuous paint coating will offer a high resistance, but the life of the coat depends upon the soil, mois- ture, and the electromotive force impressed upon it as well as on the constituents of the paint itself, and has been shown to be very uncertain.^ Cast-iron pipes usually contain on their stuface more or less sand from the mold, and there may be some alloying of the sand and the iron. It is possible that this surface layer might either be of high resistance or noncorrodible. Preliminary experiments, however, with similar cast-iron pipes, half of which had the original surface machined off, fail to show any resistance, due to the surface coating. We may also add that we have failed to find material differences in the rate of elec- trolytic or nattaral corrosion of surf^ed and unsurfaced cast-iron specimens. If pipes are buried when the ground is dry, there is a possi- bility that when the ditch is first filled there will be a poor con- tact between earth and pipes in certain localities. We would expect, however, that as water found its way down to the pipes 2 Burton McCoUum and O. S. Peters, Surface Insulation of Pipes as a Means of Preventing Electrolysis, Technologic Paper No. 15. Bureau of Standards. Earth Resistance and Electrolysis 31 the joint action of the moisture and pressure of the earth above would pack the earth firmly against the pipe in a short time. No experiments have been made in the field to date to deter- mine either the magnitude or the duration of resistance due to poor contact between earth and rails or pipes. The following laboratory experiment, however, indicates that with fairly homogeneous moist soil the contact resistance between a pipe and the soil will be small. A box of paraffined wood 10 cm square and 35 cm long inside was filled with a rather dry clay collected from the side of a hill. Sheet-iron electrodes 10 cm square were placed in the box 6. 5. ^ ^ ^^ ^^ ^ -J. 2. 1. ^^ ^ .^^ .^■ .---' .^^ ^' 40 80 120 160 200 240 280 DISTANCE BETWEEN ELECTRODES IN MILLIMETERS Fig. 9. — Relation of earth resistance to distance between electrodes 30 cm apart, the earth tamped thoroughly and the resistance measured with a voltmeter and milliammeter using alternating current. One electrode was then removed, a few inches of the earth shaved away, the electrode replaced, and the earth tamped in behind it. The tamping of the earth between the electrodes was thus maintained constant. The box was kept covered during measurements to conserve the moisture in the soil. The results of a series of these measurements are given in Table 8 and plotted in Fig. 9. A continuation of the curve passes through the origin of coordinates and indicates that there was no appreciable contact resistance between the earth and the elec- trodes. The curve also indicates a linear relation between the resistance and the distance between the plates. The deviation 32 Technologic Papers of the Bureau of Standards of two points from the ciirve may be due to variations of tempera- ture in the soil or to errors in determining the distance between the plates since it was difficult to get them exactly parallel. TABLE 8 Soil Resistance — Distance Data Distance between electrodes Resistance oi soil MUlimeters 155 213 260 305 OhnT? 3210 4430,4265 5370 6320,6640 While the resistance between two conductors biu-ied in the earth would usually be much less than that measxured in the laboratory, the area of contact between earth and conductors would be much larger, and the relation of contact to earth resist- ance may be expected to remain about the same. A soil contain- ing insulating materials might, of course, give different results if a number of the insulating particles happened to come between the metal and the earth. Dryer soil might make a poorer con- tact with the metal, but the soil resistance would also be increased, so that we would expect the relative resistance of contact and soil to remain about the same. 6. POLARIZATION AND SURFACE FILMS Polarization voltage is the change in voltage between an electro- lyte and an electrode immersed therein due to the flow of electric ciu-rent to or from the electrode. When a potential difference exists between two electrodes in an electrolyte the positive ions migrate toward the negative elec|rode and the negative ions toward the positive electrode. Thus, with aqueous electrolytes hydrogen and oxygen may be liberated at the electrodes, and where no chemical reaction with the electrolyte occurs these gases collect on the electrodes, forming fihns of high resistance. Hence it happens that if one attempts to measure the resistance of a soil sample by means of direct current, the apparent resistance is found to be a function of the time and the amoimt of current employed. Earth Resistance and Electrolysis 33 The same phenomenon occurs when current flows between two buried conductors. The following experiments illustrate the character and magnitude of this effect. Two current electrodes 5 cm square were set vertically about lo cm apart in a stone jar of earth. Just back of each electrode, and insulated from it by a . POTENTIAL ELECTRODE I 1 1 1 1 Fig. io. — Apparatus for determining polarization potentials layer of pitch, similar potential electrodes were placed. Current was passed between the inner electrodes, and the potential differ- ence between each electrode and the adjacent potential electrode was measured by means of a high-sensibility voltmeter, which required very little current. Fig. lo represents the arrangement of the apparatus. 34 Technologic Papers of the Bureau of Standards The current density at the electrodes was varied and the polarization potentials at each electrode read when a steady value was obtained. Figs. II, 12, 13, 14, 15, and 16 show the results of these obser- vations. From Fig. 11, which shows the results with iron elec- trodes and a virgin red clay soil obtained near the Bureau of Stand- ards, it will be seen that the polarization at the anode is nearly proportional to the current density employed, while the polariza- tion at the cathode increases less rapidly. Comparing these curves with those shown in Fig. 12, which were obtained with lead electrodes, we see that the polarization with lead electrodes is much greater than with iron electrodes. The shape of the curves is the same, but the slope of the curves is much greater with lead electrodes. The data for the above curves were obtained in soil which had not previously carried current. To obtain the curves in Fig. 13, current was permitted to flow between the electrodes all night, and then the cell was short-circuited until no polarization could be detected at anode or cathode. Data was then obtained as for Fig. 12. It will be seen by comparing Figs. 12 and 13 that the effect of the long continued flow of current has been to reduce the polari- zation potentials, especially at the cathode and for the higher current densities. The curves seem to indicate that the polari- zation potential decreases with time. Fig. 14 shows the results of an experiment with iron electrodes and with a solution of NajCOj added to fine clean quartz sand. Here the polarization at the cathode is seen to be slightly more than one-half that when clay was used for the electrolyte and the polarization at the anode has been reduced somewhat more. It is not evident whether the chang| is due to the NaCO, or to the substitution of sand for the clay. However, since the sand was considerably more porous than the clay, it would allow any gases to escape more readily, and this would tend to reduce the polari- zation potential. Fig. 15 shows the results of a similar experi- ment with lead electrodes and a solution of NajNOj in sand. The cathode curve is similar to that in Fig. 14. The anode curve is very peculiar, showing a critical value at a current density of Earth Resistance and Electrolysis 35 O P N 0.8 01 3 p 0.6 0.2 ^^ CATHODE ^ ^ "ANODE y ^ X ^ y A ^ -^ / / ^ ^ ^ ^' 0.08 0.16 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.88 0.96 1.04 1.12 1.20 CURRENT DENSITY- MILLIAMPERES PER CM^ Fig. II. — Polarization voltage — Iron electrodes in natural soil 4.0 3.6 3^ 2.8 J J 2.4 : 52.0 I 5 1.6 3 1. 1.2 0.8 0.4 y y y /Inc OE > --- ^ y CAT r HODE X ^ y y" ^ y y / / ^ -^ / y y 0.08 0.16 0J24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.88 0.96 1.04 1.12 1.20 CURRENT DENSITY-MILLIAMPERES PER CM'' Fig. 12. — Polarization -voltage — Lead electrodes in natural soil 36 Technologic Papers of the Bureau of Standards 3.2 2.8 2.4 in t3 2.0 g z O 1.6 g M §1.2 O CL 0.8 / ^ ANCIDE ^ / ^ V y / 1 J, CATHODE ^^ 1 / ^ ■^ ^- / 0.16 0.32 0.48 0.64 0.80 0.96 1.12 1.28 1.44 1.60 1.76 1.92 CURRENT DENSITY-MILLIAMPERES PER CM'' Fig. 13. — Polarization voltage — Lead electrodes in natural soil — Current on all night before observations 0.55 0.50 0.45 40 CATH( )DE ^ J ^ 0.36 =* 0.30 z M 0.25 a. 3 0- 0.20 0.15 0.10 0.0 / / i / / / • ANODE ^^ , ^ / X 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0,32 0.36 0.40 0.44 CURRENT DENSITY-MILLIAMPERES PER CM = Fig. 14. — Polarization voltage iron electrodes — 2 per cent Na^C(y in fine sand Earth Resistance and Electrolysis 37 11.2- 3 O0.5 . : ' ANOCE ^ ^^^ _ ■ — ■ — ' CATHODE -^ "^^ ^ -^ -■^"x c J 0.08 0.16 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80 0.83 0.96 1.04 CURRENT DENSITY- MILLIAMPERES PER CM^ Fig. 15, — Polarization ■voltage — Lead electrodes 2 per cent NaCO^ in fine sand 0.9 IRON -* — -1 __ ' "^^^^ ^ 0.8 0.7 ^ r / 0.6 : 0.5 0.4 0.3 0.2 ■ 0.1 LEAD — 1 — ■ i ■ ^ ^^-'oS^ 3 1 2 1 6 2 2 4 2 8 3 2 3 6 - LEA ) ) 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.35 0.40 - CURRENT DENSITY- MILLIAMPERES PER CM ^ Fig. i6. — Polarization voltage iron and lead electrodes NaOH in fine sand 38 Technologic Papers of the Bureau of Standards O.I 2 milliampere per square centimeter. Fig. i6 shows the anode polarization voltage with lead and iron electrodes when a solution of NaOH was used. With the iron electrode a curve was obtained as the current density was increased and then as it was decreased. The polarization is higher for the latter curve, as would be ex- pected if the cell did not fully recover from the effect of polariza- tion at the higher current density. The polarization for lead is seen to be much less than for iron. This is the reverse of the results shown in Figs, ii and 12. 40 ^^^,— -^ + 30 40 TIME— MINUTES Fig. 17. — Effect of polarization on resistance between buried pipes It will be seen from the curves shown that the polarization voltage at an electrode is a function of the electrolyte, the char- acter of the electrode, the current density at the electrode, and the time the current has flowed. The phenomena of polarization voltage are under investigation, and*the results of the experiments will be reported later. Fig. 1 7 shows the decrease in current between two 4-inch cast- iron pipes buried in a wet clay soil, as previously reported.^ It represents the effects of polarization on the current flowing between two cast-iron pipe lines buried in clay soil. The lines were about ^ Burton McColIum and K. H. Logan, Electrolytic Corrosion of Iron in Soils, Technologic Paper No. 25, Bureau of Standards. Earth Resistance and Electrolysis 39 50 feet long and the soil very wet. The resistance of the earth between the pipes was about 18 ohms at the beginning of the experiment. As will be seen from the figine, the apparent resist- ance of the circuit was practically doubled in half an hour. IV. RELATION OF SOIL RESISTANCE TO ELECTROLYSIS 1. TRACK LEAKAGE AS A SOURCE OF STRAY CURRENTS From the data given above it will be seen that the specific resistance of soils varies through a very wide range, and that this resistivity depends on a number of factors which are difficult or impossible of accurate determination with respect to soils between buried conductors. When one attempts to deal with the total resistance between a portion of a track network and a neighbor- ing pipe line, the problem is of course much more complicated. It is important, however, to make a thorough study of resistance conditions and to determine as accurately as practicable their effect on the leakage current. (a) Bonding and Track Network. — It should be pointed out in the first place that in so far as practicable the return currents of street railways should be confined to the tracks and return feed- ers. To this end the conductivity of the grounded return system should be as good as can be procured for the permissible invest- ment. This means, first of all, that the bonding of the rail joints should be kept in the best condition by frequent thorough tests of all bonds and the prompt repair of any found defective. Pres- siu-e wires for measuring potential drops in the earth return will also be of great service in determining track conditions. Under service conditions track resistance is found to vary between wide limits, according to the weight of rail and the effectiveness of the bonding. For a well-bonded track of 100-pound rails the resist- ance will be approximately 0.0045 obxa per 1000 feet of single track. Owing to bad bonding, however, actual track resistance will often reach several times this figure. A more neglected factor is the number of tracks returning ciu-- rent directly to the power house. Frequently a substation is 40 Technologic Papers of the Bureau of Standards located with not more than a single track passing near it when shifting the location of the substation a few blocks would afford a return path of two or even four tracks. Since a 90-pound rail has approximately the conductivity of i 000 000 circular mils of copper, the advantage of the larger number of tracks becomes apparent as soon as an attempt is made to limit the current density in the return portion of the circuit. (b) Roadbed. — Another factor so far as the railway system is concerned is the conductivity of the roadbed. In so far as the roadbed is given a high resistance leakage current is of course prevented. For interurban roads wood ties and good rock ballast, well drained, will do much toward preventing electrolysis. In city streets the same degree of insulation is more difficult to attain. We may point out, however, the fact that stone has a much higher resistance than moist concrete. In fact, moist concrete has a specific resistance but little higher than clean earth, ranging from about 4000 ohms per cubic centimeter up, depending upon the character of the concrete and the amount of moisture it con- tains. The specific resistance of dry rock is very high, and many kinds of rock absorb much less water than concrete. The con- ductivity of a rock-ballast roadbed is due, therefore, largely to the conductivity of the films of moisture and dirt on the surfaces of the stones. While only a little data is at hand relative to the resistances of different kinds of roadbeds, such data as is available show that the resistance of a rock ballast is higher than a bed of concrete or cinders, moisttue conditions being equal. A number of measure- ments made on several different kinds of roadbed in actual service show that the leakage resistance varies between wide limits, but for the most part will be found to range between 0.2 and 12.0 ohms per 1000 feet of single track, the values for double track being approximately 70 per cent of those for single track. The practice in many cities of frequently flushing the rails to prevent the formation of a high-resistance scale on the head of the rail due to dirt from the street must add considerably to the leakage currents, since this flushing is most necessary with dirt roads, a condition frequently, though not necessarily, coupled with Earth Resistance and Electrolysis 41 poor roadbed and loose rail joints. The situation presents an excellent opportunity for cooperation between the city and rail- way company in diminishing electrolysis damage as well as in improving conditions generally. It not infrequently happens that the street railway company delays relaying an old track on an unpaved street because the street is to be paved within a few years, at which time extensive changes in the tracks would prob- ably be necessary. When the city is in a position to do so, it may be advisable for the city to pave the street somewhat sooner than was planned that the railway company be put to no unnecessary expense. This is especially true if the railway company is required to bear a share of paving expense. 2, EFFECT OF DISTRIBUTION OF UNDERGROUND STRUCTURES After the consideration of track conditions comes the question of the number of uridergroimd conductors in the street, their size, and their location with respect to the rails. In most cases, per- haps, these things must be fixed without regard to electrolysis conditions, but in some cases the danger from stray currents may be minimized by a careful study of local conditions. It is our experience that in the majority of cases gas lines pick up less current than water mains of the same size, probably because of the greater depth of burial, lighter material used, and the intro- duction of high resistances, such as cement joints or expansion joints with rubber gaskets. Usually, too, the distributing pipes for a gas system are smaller than the water pipes serving the same neighborhood. It would seem advisable, then, that if the two systems of pipes must be on the same side of the street that the water mains be placed nearer the curb. Lead-sheath cables of all kinds may well go between the rails and the gas mains, both on account of the insulating properties of the ducts through which they run, although this resistance is not very high, and because the lead sheaths can be relieved of current more easily than the pipes. It must be said in this connection, however, that lead is much more easily destroyed by electrolysis than iron and that a judi- cious draining of the lead sheaths is in most cases necessary for their protection. 42 Technologic Papers of the Bureau of Standards In cities where the density of population warrants the expense, gas and water mains may be run along both sides of streets occu- pied by street railways. While the conductivity of the pipe net- work is thus somewhat increased, the necessity of running service pipes beneath the rails is avoided. When service pipes run under the tracks, the highest gradient is usually between the rails and these services, and in areas where the pipes are positive to the tracks corrosion is concentrated on these small pipes. While, of course, a leaky service is not so expensive to replace as a leaky main, the thinner material in the former case and the fact that the pipes run at right angles to the rails causes a con- centration of corrosion and a very rapid destruction of the pipe. The damage to the street is practically the same whether a main or a service is replaced. A great deal of inconvenience and prob- ably a considerable expense for renewals is therefore avoided by the double-main system. Our measurements of current in gas and water mains have con- vinced us that the cement joint frequently used in gas mains, even when installed with no attempt to keep the pipe ends apart, very materially reduces the current collected by these mains. The subject of the proper use and the effectiveness of insulating joints in preventing electrolysis is considered in another paper.* In locating a new car track or a new supply main it may in some cases be possible to prevent electrolysis trouble by shifting the location somewhat to avoid paralleling an important main or heavily loaded track. 3. son- CHARACTERISTICS AND ELECTROLYSIS Just what portion of the total resistance of the leakage circuit the earth forms depends, of course, upon a number of factors, and while no such variations in tjje total resistance are to be expected as are found in the table of specific resistances, neverthe- less the soil resistance and the factors influencing it are doubtless very important. (a) Soil Resistivity and Electrolysis. — ^The table of specific resistances referred to above serves to call our attention to the * E. B. Rosa and Burton McCollum, Electrolysis and its Mitigation, Technologic Paper No. 5:;, Bureau ol Standards. Earth Resistance and Electrolysis 43 wide range of resistivities which have been found to occur in actual field work. Certain kinds of soil, especially those containing a large percentage of sand or gravel, are almost invariably of high resistivity and of low moisture content. A study of the samples of clay soils shows a wide variation in resistivity which can not be closely connected with the physical appearance or the amount of moisture and which is due no doubt to its chemical properties. We might add here that the appear- ance of soil as to moisture, while indicating roughly its relation to the saturated condition, is not an indication" of the amount of moisture present. A sand which feels quite moist will actually contain less moisture than a clay or loam much drier in appear- ance. It would seem unnecessary to point out the fact that sam- ples of soil taken for resistivity measurements must be so treated as to prevent any change in this moisture content, but we have experienced considerable difficulty in impressing the importance of this upon some who have collected soil samples for us. It is, of course, absolutely essential that the moisture content shall not change if the sample is to indicate the resistivity of the soil from which it was taken. On account of the wide variation in soil resistivity it is impor- tant to include measurements of soil resistivity in any study of electrolysis conditions. Samples of soil should be obtained in the immediate neighborhood of the power house and along the tracks throughout the positive and negative areas. For this purpose a I j4-mch soil auger is convenient. If at any point three or four holes are bored and samples taken at, say, 2, 4, and 6 feet below the surface of the earth and all of the samples well mixed, a single measurement of the specific resistance of a part of the mixture should afford a fair idea of the conductance of the soil in that region. How many such measurements should be made will, of course, depend on the extent of the track network and the diversity of the soils within the city. An idea of the latter can often be obtained from the officials of the local gas or water company, as well as by surface indications along the tracks. (b) Effect of Pressure. — ^The experimental data show that little variation in soil resistance is to be expected, due to the hardness 44 Technologic Papers of the Bureau of Standards with which the soil is packed, except in so far as this influences the moisture content. We would not, therefore, expect any- material change in electrolysis conditions due to the packing of the earth by traffic over the road in which the pipes are buried. (c) Effect of Soil Moisture. — ^The importance of soil moisture can scarcely be overestimated and every effort should be made by street railways and by pipe owners to keep the earth in the neigh- borhood of their conductors as dry as possible. Well-drained tracks in the suburbs and well-ballasted tracks in the cities, drained streets with good pavements, and tight joints in water mains will do much toward reducing leakage cxurents. The influence of moisture in the soil must be kept in mind in interpreting the results of electrolysis stuveys. Readings taken after a prolonged season of wet weather will tmdoubtedly show lower over-all potentials and greater currents on pipes than those taken under dry conditions. On account of the excellent con- ductivity of salt water or water containing quantities of vegetable matter the location of power houses along water fronts is to be avoided in so far as consistent with other operating conditions, and if it seems desirable to choose such a location on account of the coal or water supply it is only fair that the increased expense of track feeders and track insulation due to the high conductivity of the soil in such localities should be charged against the advan- tages of the situation. Especial precautions must also be taken that the insulation of the track be as high as practicable when interurban roads cross marshy land. (d) Effect of Temperature and Freezing. — Two important phenomena occtu with respect to the effect of temperature on soil resistance, as is indicated in Fig. 8. The temperattue coefii- cient of the soil is negative and rilatively high. This and the positive temperature coeflicient of the rails produce a shifting of the relative amounts of current carried at different seasons of the year. It will be observed that at even a few degrees below zero the resistance of the soil is largely increased, and we may expect, therefore, that if the ground is frozen only to a depth of a few inches the leakage current from tracks will be materially dimin- Earth Resistance and Electrolysis 45 ished, due to the increased resistance, and the danger from elec- trolysis proportionally reduced. In the cities in the northern half of the United States the time during which the frost is in the ground is sufl&cient to make this phenomenon of some impor- tance. The dirfect determination of the effect of temperature on leakage currents by tests of current on water pipes is made difficult by the changes in conditions of pipe lines, tracks, and station outputs which are almost sure to take place between two sets of readings taken six months or more apart. Some data have, however, been obtained on the relative currents in underground pipes in a num- ber of places during the winter and surmner months, all of which show that such pipes generally carry more current in proportion to the railway load in summer than in winter. The data obtained in the neighborhood of the Ann Avenue substation in St. Louis, Mo., given in Table 9, will serve to illustrate this effect. These figures represent currents reduced to the average stunmer-load conditions. TABLE 9 Currents on Water Pipes in the Neighborhood of Ann Avenue Substation, St. Louis, in Summer and Winter Mississippi and Ann Avenues Mississippi and Russell Avenues Mississippi and Allen Avenues Eighteenth Street and Russell Avenue.. Eighteenth Street and Ann Avenue Total. " Winter current is ^o per cent of the summer current. The temperature of the earth when the last readings were taken was about 32° F,but there had been several weeks of cold weather previously and the frost was not entirely out of the groimd. Indeed there was snow on the groimd in many places though the weather for the previous two days had been quite warm for winter. The condition of the ground at the base of the rails and 46 Technologic Papers of the Bureau of Standards below is, therefore, somewhat in doubt, and the increase in earth resistance is probably less than it might have been had the read- ings been taken a few days earlier. On the other hand, we can not be sure just what changes had occurred in track and pipe conditions or that the assumed corrections for the time of day or the increase of the winter load are exactly correct. The table is therefore not an exact index of the magnitude of the change, but these data, as well as a considerable amount of similar data obtained elsewhere, leaves no doubt as to the character of the change and to temperature variations, although some of the changes found have been less marked. It will be seen that the current in moderately cold weather has been reduced to approximately one-third of its value during the fall months, when the earlier measurements were taken. No doubt if fall measurements had been taken immediately after a period of wet weather the difference would have been much larger. These changes must, of course, be taken into account in con- sidering electrolysis sm-veys made during cold weather. (e) Effects of the Flow of Current on the Resista-nce of the Leak- age Path. — We have seen that as a unidirectional current flows through the earth there is an increase of resistance due to polariza- tion and the collecting of gas about the electrodes. The polari- zation depends partly upon the difference of potential and partly upon the character of the medium surrounding the electrodes. In cinders the polarization electromotive force is high and persists for a long time. The amount of gas collected about the electrodes will depend somewhat on the porosity of the soil. Another possible effect of the passage of current is an increase in the resistance of the soil due to the decrease in the soluble salts or to chemical changes taking place in connection with the migration of the ions. With large currents there may be some drying of the soil due to the electrolysis of the water and to the heating effect of the current. Under most circumstances, how- ever, it seems probable that the supply of soluble materials will be renewed by diffusion and from the surface of the ground, and that no protection can be expected from these phenomena. Earth Resistance and Electrolysis 47 (f) Other Possible Sources of Resistance. — ^While it is possible that there are a number of other causes which may increase the resistance between rails and buried pipes, we have so far been unable to determine them. Our experiments show that in some cases at least there is no appreciable resistance due either to a poor contact between soil and pipes or to the slag on the surface of cast-iron pipes. Although the paint applied to pipes while in good condition often offers a considerable resistance to the pas- sage of a current, the experiments of the Bureau on insulating paints ^ indicate that the period of time that a paint film will withstand even a low potential when exposed to moisture is com- paratively short, and that the failure of the coating in spots con- centrates corrosion, causing the life of the pipe to be less than it would have been if the paint had not been used. It seems better, therefore, not to make any allowance for the resistance of paint films in estimating resistances between pipes and r^ils, since though the resistance of the leakage path is increased the danger of damage by the escaping current is also increased. V. SUMMARY In the foregoing sections the resistivity of the soil in which metallic structures are buried is shown to be of much importance with respect to electrolysis of these structures. Three methods of measuring the specific resistance of the soil, two of which do not require the removal of the soil from its original position, are described. Results of soil-resistivity measurements by each method are compared, and it is shown that any of the described methods is satisfactory for practical purposes, although each has advantages over the others under certain conditions. The results of a large number of measurements of resistivity of soil samples from widely separated points in the United States have been tabulated. These data show great variations in soil resistivity, and indicate the desirability of a study of local soil conditions in connection with any complete electrolysis survey. The majority of soils tested show resistivities of between 1000 and 5000 ohms per centimeter cube. ' Burton McCoUum and O. S. Peters, Surface Insulation of Pipes as a Means of Preventing Electrolysis, Technologic Paper No. is. Bureau of Standards. 48 Technologic Papers of the Bureau of Standards A number of factors have been found to influence the resis- tivity of the soil. Increasing the pressure on a sample of soil under test tends to increase the conductance of the sample slightly, especially if the original pressure is low. Increase in moisture increases the conductance of the soil if it is not saturated with water. The amount and kind of soluble material in the soil affects its resistivity. The resistivity of soil is found to increase as its temperature falls, especially when the freezing point of water is reached. The flow of current through the soil has been found to produce an apparent temporary increase in soil resis- tivity in the neighborhood of the electrodes. The relation of soil resistivity to electrolysis is considered from the standpoint of leakage from street railway lines using the track as a return current. The importance of good rail bonding and of well-drained roadbed is pointed out. The refetions of the various factors affecting leakage resistance, namely, character of the soil, pressure, moisture, freezing, and polarization, and surface films to the electrolysis problem are described, and it is shown that a knowledge of the resistivity of the soil is of importance in estimating the danger indicated by potential difference and potential gradient measurements. It is also shown that the moisture and temperattue of the soil mate- rially affect the amount of current escaping from a grounded track used as a return circuit, and that these factors must be given due consideration in the interpretation of data obtained during an electrolysis survey. In conclusion the authors wish to express their appreciation of the assistance of their colleague, O. S. Peters, who did a large amount of work in connection with the development of the guard ring and compression methods of soil-resistance measurements, and rendered valuable assistance iir connection with the measure- ment of the resistivity, of earth samples. Washington, September 9, 191 5. ^ DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON, Director No. 27 SPECIAL STUDIES IN ELECTROLYSIS MITIGATION 1. A PRELIMINARY STUDY OF CONDITIONS IN SPRINGFIELD, OHIO, WITH RECOMMENDATIONS FOR MITIGATION E. B. ROSA, Chief Physicist and BURTON McCOLLUM, Associate Physicist Bureau of Standards [JUNE 19, 1913] WASHINGTON GOVERNMENT PRINTING OFFICE 1914 PREFACE. The accompanying report on the electrolysis situation in the city of Springfield, Ohio, has been prepared in the course of a general investigation of the subject of electrolysis from stray earth currents which is being carried out by the Btueau of Stand- ards. In connection with this investigation an examination of conditions in Springfield was made and in the prosecution of this work the Biu-eau had the cooperation of the Springfield Railway Co., the City Water Department, and the Springfield Gas Co. SPECIAL STUDIES IN ELECTROLYSIS MITIGATION: 1. A PREUMINARY STUDY OF CONDITIONS IN SPRINGHELD, OHIO, WITH RECOMMENDATIONS FOR MITIGATION By E. B. Rosa and Burton McCoUum CONTENTS Page Introduction 3 Part I. Methods of Electrolysis Mitigation. A. Methods applicable to pipes 7 1. Surface insulation of pipes 7 i!. Insulating joints in pipes 10 3. Pipe Drainage Systems 13 (a) Direct taps between pipes and rails 13 (b) Negative feeders to pipes 13 B. Methods to be applied to the railway system 18 4. Construction and Maintenance of Way 19 5. Uninsulated negative feeder system 21 6. Insulated negative feeder system 22 (a) Boosters in separate feeders 24 (6) Insulated negative feeders without boosters 27 (c) Single booster system 32 (d) Inverted booster systems 34 7. Number and location of power stations 37 Part II. Recommendations for Electrolysis — Mitigation in Springfield, Ohio. . . 40 I. Improvement in rail joints 41 ' i; . Interconnection of tracks 42 3 . Cross tying of tracks on East Main and High Streets 45 4. Negative feeder systems 46 Summary 54 INTRODUCTION The investigation by the Btireau of Standards into the electrolysis situation in the city of Springfield, Ohio, was undertaken primarily because it afforded an opportunity for making a study of the effec- 4 Technologic Papers of the Bureau of Standards tiveness of the insulated negative feeder system at present installed by the Springfield Railway Co. as a means of mitigating damage to pipes and other buried structures by stray currents from the street railway. For this reason the experimental investigation was of a somewhat restricted character, only such data being taken as had a direct bearing on the influence of the negative copper feeders as now installed. For this purpose several series of measurements were made, including potential differences between pipes and rails and potential gradients along the rails from which current densities in the rails could be determined, and also the distribution of cur- rent between the different rails which also gave information in regard to the condition of the rail joints. The ctirrent flow in the taps connecting the insulated feeders and the rails was also meas- ured ; current flow in pipes was determined at a number of points, and over-all potential measurements between a number of points scattered over the city were also taken. These different series of measurements were taken first with the insulated feeders connected to rails in accordance with the plan adopted by the Springfield Railway Co., and then these feeders were temporarily removed, all connections being made the same as they had been prior to the installation of the present feeder system and the same series of measurements was repeated. A comparison of the data of the two series gives an indication of the extent to which the installa- tion of the present feeder system has influenced electrolysis condi- tions. While these measurements showed that the system as now installed has greatly improved electrolysis conditions, it was found that a number of changes could be made in the system which would improve its operation, both from the standpoint of cost and also its effectiveness as a protection against electrolysis. Such addi- tional information was therefore oUtained from the railway com- pany in regard to their traffic and physical condition of plant as was necessary to determine what changes should be made in the feeder system in order to insure adequate protection at a reasonable cost. A study of the conditions at present existing in the negative return systems in Springfield shows that a readjustment of the insulated negative feeders, together with other changes as indi- cated later, will give considerably better voltage conditions in Electrolysis Mitigation in Springfield, Ohio 5 the negative return throughout the city, and at the same time prove considerably more economical to the railway company. In the first place the over-all potential measurements between remote points in the city were found to fluctuate between rather wide limits, due primarily to the high resistance in the negative feeders. It is evident that the potential between any two points of connec- tion of the feeders to the rails will be equal to the difference in the total voltage drops on the two feeders between points of connec- tion on the track and the bus bar. Further, since owing to the constantly shifting character of the load, the current in the sepa- rate feeders will necessarily vary considerably, it follows that the actual variation in potential drop of the feeders will also vary, and this variation will be larger the higher the resistance of the feeder, and consequently the difference of potential between points of connection of the feeders to the track will be corre- spondingly high. If the size of the feeders were increased and the total drops thus reduced, a given percentage variation in the load would produce much less difference of potential between points of attachment of the feeders to the tracks, and such a change would therefore bring about considerable improvement in voltage conditions throughout the city. It will be shown later that this reduction in the total drop of potential on the feeders can be accomplished, however, without increasing the annual cost of the system, but that on the contrary, a considerable saving can be secured. Another condition of importance in the present system is revealed by the potential drops taken on short lengths of rails in various parts of the city. A great many of these measurements were taken and it was found that the ciurent distribution in the different rails at any one point was often very unequal. This showed that some rail joints were not in good condition, thus giving rise to a relatively high resistance of the track with conse- quent larger potential gradients than would occur if the rail joints were maintained in better condition. However, conditions in this respect can not be considered as particularly bad. It may further be pointed out that the present negative feeder system is so designed that the current returns to the power house by a much 6 Technologic Papers of the Bureau of Standards more indirect route than is necessary or desirable. It was found . in fact that not only was all of the cturent from the central part of the city returned over negative feeders, but that there was a general flow of current from the entire eastern part of the city west as far as Limestone Street, whereas in a properly designed system all of the current from the eastern part of the city should be intercepted at about Sycamore Street, and the tracks farther westward utilized for carrying a moderate amount of cturent toward the power house instead of away from it, as is now the case. This change would not only improve potential conditions, but it would afford a considerably cheaper installation to the railway company. Means for accomplishing this result are set forth in detail later. Another defect in the present system grows out of the fact that the rails of the Springfield Railway Co. and of the Ohio Electric Co. are not properly connected at crossings. As a result of this the current can not divide between the various rails in such a manner as to utilize the maximum conductivity of the track and local potential differences are therefore made considerably higher than would otherwise be the case. A proper intercoiinection of the rails of the two companies with the consequent interchange of current on the negative side would be of great value to both com- panies from the standpoint of electrolysis protection and also of operating cost. It was further found that the continuity of the rails of the Ohio Electric Co. was very tmsatisfactory, a large part of their current being returned through the city as far as Isabella and North Streets by way of the Springfield Railway Co.'s tracks. This, we understand, is a temporary condition due to reconstruc- tion work now going on, and with the completion of this work will disappear. • In the following report we give a very brief general discussion of the various possible methods of electrolysis mitigation, setting forth which methods we consider best adapted in general for reducing electrolysis troubles. This is followed by a somewhat detailed discussion of conditions in Springfield, with recommenda- tions in regard to a permanent system of electrolysis mitigation applicable thereto. Electrolysis Mitigation in Springfield, Ohio 7 PART I. METHODS OF ELECTROLYSIS MITIGATION In the effort to reduce or eliminate damage to pipe systems and other subsurface structures due to stray earth currents from street railways, a great many methods have been proposed and tried. Some of these have been widely used with more or less benefit in many instances and apparent failure in others. In the case of most of these but little systematic effort has been made to develop them to meet the requirements of practical service in the most advantageous manner. We present below a very brief discussion of the different methods of electrolysis mitigation that have been proposed, together with our conclusions as to their relative merits. The majority of these methods are either of no value or of such limited application that it has not been deemed worth while to discuss them in any detail, and they have there- fore been passed by with merely a brief statement as to their limitations. A few of those methods which have special merit as methods of electrolysis mitigation in general or in special cases are treated at somewhat greater length. We have not attemped to discuss in great detail, however, even these latter methods, since all methods of electrolysis mitigation are discussed at some length in a publication that will shortly be issued by the Bureau of Standards. Methods of electrolysis mitigation are here treated under two heads: First, those that may be applied to the pipe system for protection of the pipes without regard to the extent of stray cur- rent leaking from the rails; second, those which are applied directly to the negative return of the street railways system and have for their object the prevention of the leakage of electric current into the earth or the reduction of such leakage to so low a value as to do practically no harm. A. METHODS APPLICABLE TO PIPES 1. SURFACE INSTJLATION OF PIPES Painting or otherwise insulating the surface of pipes, as by the use of treated papers and textiles, was early resorted to as a possible means of protecting pipes from electrolysis, and this method is still used in some instances. It is doubtful, however, whether 44128° — 14 2 8 Technologic Papers of ihe Bureau of Standards there exists any instance in which it has been definitely proved that insulating paints have effectively protected pipes from elec- trolysis for any considerable period of time, while there are many instances where they have failed utterly and where their presence has actually done harm. This statement may seem somewhat surprising to some who are familiar with instances where paints have withstood the action of soils for a long period and when uncovered both paint and pipes appeared to be in practically as good condition as when they were laid down. Practically all paints are classed as insulators and it is quite natural that the impression should be more or less prevalent that these paints ought to prove effective as a protection against self-corrosion in the soil. In practice, however, such paints behave in a very uncertain manner at best. A given paint may endure for a long period in some places, while in other places in the same city it may deteriorate rapidly and become worthless in a comparatively short time. This is due partly, no doubt, to differences in soil conditions, but the general failure of these paints under conditions where electrolysis was to be expected indicate that the stray currents themselves have much to do with the destruction of the coatings. With a view of throwing further light on this point and also of determining if possible something of the relative value of different coatings as a possible protection against electrolysis, the Bureau of Standards has undertaken a series of experiments, which, while as yet uncompleted, have yielded considerable definite information. In all about 40 different kinds of paints have been tested and of these not a single one has withstood the action of the very moderate test voltage of 4 volts for any con- siderable length of time, failure of the coating with consequent pitting of the pipe occuring withi* a few months in all cases. The explanation of the failure lies in the fact that none of the paints tested are absolutely impervious to moisture, and when brought into the presence of water a slight trace of moistvire ultimately permeates the coating. When this occurs at any point the coating becomes slightly conducting, and if an elec- tromotive force is applied, a trace of current flows at first, giving rise to slight electrolysis which is accompanied by the formation of more or less gas beneath the coating. As this gas increases in Electrolysis Mitigation in Springfield, Ohio 9 amount and expands, the coating is 'ruptured, after which the current flow is greatly increased at the point of breakdown and rapid electrolysis of the exposed iron follows. In some cases, if the coating is sufficiently porous to permit the gases to escape, it may remain intact and electrolysis may continue beneath the coating, eating through the metal without any superficial evidence of failure of the paint. This phenomenon is frequently observed in practice. The vital weakness of all the paints thus far tested is due to the fact that none of them are entirely nonabsorbent. If a paint could be secured which is absolutely impervious to soil moisture and which would remain so for an indefinite period, it would prove an effective preventive of electrolysis, and all efforts to produce such a protective paint should be directed to this one point of making it absolutely and permanently moisture proof. The maimer in which these paints usually fail under electric stress shows that they may under certain circumstances increase the troublefrom electrolysis. Breaking down as they do at isolated points, the discharge of current from the pipes is concentrated at those points and the pitting is likely to be more serious than if the paint were not used at all. In all areas, therefore, where the pipes are strongly positive to the earth, these paints are likely to do more harm than good, and it would be better to omit them alto- gether. But in places where the pipes are practically neutral, or negative to earth, they can do no harm even if they do fail in spots, and in such places they may be of value in reducing current flow in pipes and in preventing soil corrosion. The method of coating pipes with treated textiles or tarred paper is open to the same objections that have been given to the use of insulating paints, the only difference being that the time required for their initial failure is usually somewhat greater than in the case of paint. The principal reason for this is the greater thickness of the coating that usually results from this method of insulation. We have tested a considerable number of such coatings with uni- formly disappointing results. Among these may be mentioned the coating consisting of four alternate layers of tar and paper as now appHed by the Laclede Gas Co. of St. Louis to all their services. A number of samples of this coating have been tested by us under a pressure of 4 volts, as in the case of the paints mentioned above. lO " Technologic Papers of the Bureau of Standards A number of pipes coated in this way were buried in damp soil, their ends having been carefully plugged to prevent contact between the metal and the soil. A rubber-covered wire was soldered to each pipe and brought to the surface. When first laid the application of a difference of potential of 4 volts between the pipe and the ground gave* no indication of current, thus show- ing that the coating was continuous and free from flaws. Current readings taken from time to time showed when the coating failed, and it was found that within a few weeks the coatings had been punctured in many places. After about two months some of the specimens were removed for examination and it was found that characteristic blisters had appeared in spots, and beneath these faults serious pitting of the pipes had occurred. The rate at which this pitting progressed indicated that the life of the pipes would not have exceeded a year under the conditions imposed, and it can not be said that these conditions were severe, since a difference of potential of 4 volts between pipes and ground may often be exceeded under practical conditions. The result of the tests of this coating is in line with those made on a great many similar coatings during the past two years, in which the surface coatings have uniformly failed locally, giving rise to severe pitting of the pipes. Where no electromotive force is impressed on the pipes provided with this tar and paper coating it appears to remain in good condition for several years and for this reason it appears to be of at least temporary value as a preventive of self-corrosion. Its use is probably justified in neutral or negative areas, but in all positive areas it would tend to aggravate rather than reduce the rate of deterioration of the pipes. Its use is not, therefore, to be recommended except in neutral or negative areas where it would undoubtedly be beneficial, the onlyiquestion being whether or not it is worth the cost. As a means of preventing or even reducing electrolytic damage in positive areas this method of surface insulation does not appear to be practicable at the present time. 2. INSULATING JOINTS IN PIPES Another method of reducing current flow m pipes and one which has found rather extensive application within the last few years is that of breaking up the continuity of the pipe lines by Electrolysis Mitigation in Springfield, Ohio 1 1 the use of insulating or resistance joints. In ordinary wrought iron or steel mains with screwed or riveted joints the resistance of the joints is usually small in comparison with that of the pipes, and when such pipes are laid in localities where there is an appre- ciable potential gradient in the direction of the pipe cmxents of considerable magnitude will usually be carried by the pipes. In the case of cast-iron mains the resistance of the joint is often as great or greater than that of a section of pipe and it is not uncom- mon to find a lead joint having a resistance equal to that of several hundred feet or more of pipe, and it is due largely to this high joint resistance and to some extent also to the higher specific resistance of cast iron that cast-iron mains usually carry less cur- rent under similar conditions than wrought iron or steel mains. Experience has shown, however, that the resistance of lead joints is not sufiicient to reduce the current to a safe value, and attempts have been made to still fmther increase the resistance of the pipes by the introduction of specially designed joints of high resistance. Following the earlier attempts to prevent electrolysis by this method very strong claims were made for it by some of its advo- cates, some of them claiming that they had completely solved the problem of electrolysis by means of insulating joints. Within a few years, however, a noticeable reaction set in; many engineers criticized the method, and some of those who were its warmest advocates in the beginning, abandoned it. It is but natiu-al how- ever, that the initial attempts to apply this method should have resulted in some disappointments, and it is not safe to consider these early failures too seriously in judging the value of the method when properly applied. At that time no experience had been gained in regard to the frequency with which such joints should be used, the proper location of the joints, the kind of joints best suited to certain conditions, and the complications arising from the presence of other pipe systems not so insulated. All of these are important factors and must be carefully considered if adequate protection is to be secvired. Despite the criticism it has received in some quarters, the method has, in recent years, steadily gained in favor, and is more frequently encountered at the present time than ever before. 12 Technologic Papers of the Bureau of Standards "We can not here go into detail in regard to the merits of this method, or the proper procedure in applying it, as this will be fully treated in another publication of this Bureau, and it is sufficient to state here some of the conclusions at which we have arrived as a result of our investigation of this method. If pro- perly installed, with joints of proper construction and used with sufficient frequency, it can be made very effective in minimizing electrolysis troubles. The higher the potential gradients in differ- ent parts of the system the more frequently the insulating joints must be used. In most cases it would not be necessary to make every joint insulating, one-third or one-fourth of the joints being usually sufficient even under severe voltage conditions, while in many parts of the system a much smaller percentage would suffice. Where new hnes are being laid it is a comparatively simple matter to insert the necessary number of such joints, but in the case of old systems the expense becomes great, unless the potential gradients in the earth are first reduced by other means, so that a comparatively small number of insulating joints will be sufficient. Chiefly, for this reason, we do not in general recommend this method as the principal means of protecting pipe systems already laid with the lead joints. When, however, proper precautions are taken such as those described in detail in a later part of this report to reduce potential gradients to a comparatively low value, such, for example, as i volt per looo feet or less, this method of insulat- ing joints may well be applied for the purpose of eliminating such residual electrolysis as might otherwise still occur if the system were not so protected. With potential gradients reduced to approximately the limit mentioned, a comparatively small number of insulating joints not exceeding 5 or lo per cent of the total ntunber would be sufficient to give tactically complete protection to the pipes. We wish to emphasize, however, that we regard this method as valuable chiefly as an auxiliary method which may be used in connection with, and supplementary to, a negative retturn system of proper design. Electrolysis Mitigation in Springfield, Ohio 13 3. PIPE DRAINAGE SYSTEMS A system of electrolysis mitigation which has received wider application in this country than any other method is that which is best characterized as the "Pipe drainage system." This method has taken a variety of forms, the principal ones being as follows : (a) Direct Taps Between Pipes and Rails. — In this form no extensive negative feeder system is used, but at various points throughout the positive areas where the pipes are close to the tracks, short heavy cables are connected between the pipes and rails with the view of keeping the pipes at nearly the same poten- tial as the tracks. It is true that by the use of a sufl&cient number of such taps it would be possible to prevent any considerable difference of potential between pipes and tracks, but this does not insure relief from electrolysis. In order that such equality of potential may exist it is necessary that the potential gradients along the pipes throughout the region affected shall be the same as in the rails and under the conditions which commonly prevail in the positive areas this potential gradient is quite high, usually reaching several volts per 1000 feet and often 5 to 10 volts per 1000 feet, and even higher. Such gradients are sufficient to produce heavy current flow in the pipes and in case occasional high-resistance joints are encountered the heavy fall of potential across the joint will generally cause large leakage of current around the joint and rapid injury to the pipes. In case of local defects developing in the track bonding, practically all of the rail- way current may be forced to return via the pipes and the danger of excessive leakage is largely increased. (b) Negative Feeders to Pipes. — ^Another form of pipe drainage consists in rtmning negative feeders direct from the negative bus to various points of the pipe system. This form of pipe drainage has three practical embodiments. In one of these tminsulated negative feeders are run from the bus bar and tied to the pipes, some directly at the power house and others at more remote points. In this case the longer feeders have to have a very large cross section or else the resistance will be so large that they will draw very little current from the pipes and their purpose will be 14 Technologic Papers of the Bureau of Standards thus defeated. In some cases it has been proposed to run these long feeders parallel to the pipes and tap them to the pipes at fre- quent intervals. It will be quite evident that this arrangement is open to the same objection as the plan of using uninsulated nega- tive feeders to rails, in that it leads to large expense for copper, particularly in case it becomes necessary to carry the feeders to points far from the power house. In order to overcome this diffi- culty in some installations boosters have been connected to the longer feeders, in which case they can be made much smaller and by proper excitation of the booster any desired amount of current can be taken from the pipes by each feeder. There seems to be no reason why the same results can not be obtained by omitting the boosters and inserting resistance in the power house tap and in the short feeders, since in this way any desired distribution of current in the feeders can be obtained without the complication and oper- ating cost of the boosters. The advantages of this latter plan would be very great in the case of a large system, since with the booster system a separate booster would be required for each feeder. The use of resistance taps can, as a rule, be made both economical and effective when used in connection with a somewhat similar system applied to rails, as described later. We can not here go into detail in regard to the advantages and disadvantages of the pipe drainage system but will mention a few of the more important considerations respecting it. First, it has been objected that it is not a permanent system, re- quiring constant watching and changing when the distribution of the street railway load or of the pipe systems undergoes any marked change. This objection is no doubt an important one where the insulated system of pipe feeders is used, but it would not be of serious moment in the ca^ of the insulated feeders with resistance taps, since by the insertion of proper resistances in the various feeders they could be adapted to widely varying conditions as regards load distribution. A second objection, already referred to, is the fact that any form of pipe drainage will necessarily increase to a greater or less degree the amount of current carried by the pipes, which is accompa- nied by the ever-present danger of trouble developing on high- 1 & ^ Electrolysis Mitigation in Springfield, Ohio 1 5 resistance joints at obscure and unlooked-for places. This objec- tion is much more serious in the case of direct taps between pipes and rails and uninsulated pipe feeders than yrh&a. boosters or re- sistance taps are used, since in the latter cases a proper distribution of current can be maintained that will greatly reduce this danger, although it can not eliminate it to a satisfactory degree. A third objection is that the connection of the pipe system to the bus bars or rails lowers the potential of the pipes and tends to make them negative to other pipe and lead cable systems, thereby en- dangering the latter. The advocates of this system attempt to avoid this objection by recommending that all pipe and cable systems be included in the installation. This is sometimes prac- ticable and sometimes not, depending on local conditions; but in any case it would greatly extend the area in which acute troubles might be expected and the expense of watching and guarding against trouble would be largely increased. A fourth objection, resulting from the great tendency of this system to increase the current flow in the pipes, is the increased life and fire hazard which it introduces, particularly in connec- tion with gas systems. The failure to properly bond the pipes before making any disconnections, or the accidental opening of the bond while the pipe line is broken, is likely to ignite escap- ing gas with more or less disastrous results to both Hfe and property A fifth objection, and an important one, is that the applica- tion of this system requires that all pipe systems to which it is applied shall be electrically continuous throughout. In addition to the possibility of high-resistance lead joints already pointed out we are confronted with the fact that in a great many installa- tions, cement joints, rubber gasket joints, and other insulating joints are now largely used. Where used, these will usually be found distributed to a greater or less extent throughout the system, and if the drainage plan were applied to a pipe system containing any considerable number of these insulating joints it would result in the certain destruction of many of them within a comparatively short time. As a rule the points at which isolated insulating joints occiu", or those in which the insulating jointed sections connect to the lines having lead joints, would be the 44128°— 14 3 1 6 Technologic Papers of the Bureau of Standards ones that would be in greatest danger. For these reasons the application of a general plan of pipe drainage as the chief means of electrolysis mitigation would be particularly tmforttmate in case any one of the pipe systems contained any considerable number of insulating joints. A sixth objection to the general application of the pipe drainage system as a means of electrolysis mitigation arises from the tendency toward the production of an excessive amount of alkali at the surface of a negative electrode imbedded in earth. This will occur to a much greater extent in some soils than in others, depending on the chemical content of the soils. The concentra- tion of alkali at the negative terminal will have no detrimental effect in the case of iron pipe, but may tend considerably to increase the self-corrosion in the case of lead service pipe. If the soil is of such a nature as to present favorable conditions for the pro- duction of alkali at the negative terminal, considerable increase in the corrosion of lead services may be expected from this source provided the pipes are maintained too strongly negative through- out a large part of the day. Further, the application of the pipe drainage system makes the pipes more strongly negative throughout the entire system, and it is undesirable to create this condition unless it is known that local soil conditions are such as not to give rise to any serious increase in alkalinity under the voltage conditions that would exist. What appears to us, however, as being the greatest objection to the pipe-drainage system, and this applies also to all the other methods mentioned above, is the fact that they are designed to relieve the symptoms rather than to remove the cause of the trouble. They are, therefore, fundamentally in the nature of palliatives, rather than remedies. In general, our study of the pipe-drainage method has convinced us that while it may tmder certain conditions be useful as a secondary means of lessening trouble, its installation as the principal means of electrolysis miti- gation is an unwise procedure, not so much because the immediate consequences are bad, because the contrary is quite the rule, but because of the ultimate consequences to which this method, when once resorted to, must inevitably lead. In its practical working out it exhibits two opposing tendencies, viz, (i) the reduction of Electrolysis Mitigation in Springfield, Ohio 1 7 the difference of potential between pipes and rails in the positive areas, with consequent reduction of damage at those points, and (2) an increase of the danger to the pipes throughout the entire system, as indicated above. As a rule, in the early stages of its application the effect is apt to be apparently beneficial, reducing the danger in positive areas more than it increases it elsewhere. As the system grows, the load increases; more and heavier bonds or cables become necessary, and the current in the pipes may become so great that the consequent damage due to the causes above mentioned will be of greater moment than the reduction of troubles in the positive areas, and any further extension of the drainage becomes a menace to the system. It is due largely to this slow and obsciire manner in which trouble develops that has caused this method to be so widely used. Since it transfers the trouble from where it has been most evident to a new locaUty, where perhaps it may require several years to manifest itself anew, there is sure to be a lull in the storm which creates a favorable impression very difficult to dispel even when trouble later recurs. In some more recent installations it has been proposed to limit these secondary effects by placing a limit on the amount of current taken from the pipes by the drainage cables, the plan being that when this total drainage current reaches, say, 10 per cent or there- abouts of the total railway load, the track conductivity is to be increased by copper cables in order to keep the drainage current below the prescribed limit. In some systems which we have inves- tigated in which the unlimited pipe-drainage system has been applied, it has been found that in order to reduce the potential condition to the desired limits it was necessary to draw from the pipes from 40 to 50 per cent or more of the total railway load. It is evident that if we attempt by means of ordinary tminsulated negative copper cables to decrease the total leakage to 10 per cent, the cost of the copper required will be so great as to render the plan wholly impracticable. We confidently believe that a system worked out on these lines will ultimately lead to much greater expense and less satisfactory protection than will result from other installations designed along the lines outlined in a later section of this report. 1 8 Technologic Papers of the Bureau of Standards Among other methods that it has been proposed to apply to pipe systems for protecting them from electrolysis may be men- tioned (a) chemical protection, which contemplates siorrounding the pipes with certain chemicals, such as lime, etc., which are known to have a tendency to inhibit corrosion under certain circumstances, (b) the use of cement coatings on the pipes, (c) cathodic protection, or protection of pipes by maintaining them negative to certain structures by means of battery, motor generator, etc., (d) favorable location of pipes with respect to rails, (e) the use of noncorrodable conducting coatings, and (f) what may be termed electric screens which are sheets of metal placed near to or surrounding a portion of the pipe and electrically connected thereto. It is not necessary to discuss these at length here, as such a discussion will be found in publications of the Bureau of Standards to be issued shortly, and it need only be said that our investigations have convinced us that none of these methods can be considered seriously in connec- tion with the permanent mitigation of electrolysis. B. METHODS TO BE APPLIED TO THE RAttWAY SYSTEM None of the systems of electrolysis protection mentioned above have to do with the nature or condition of the street railway rettim system, and in the practical working out of such methods the rail- way return system is usually ignored. The currents are permitted to stray from the tracks without restriction, and the sole purpose of the methods outlined is either to prevent their entrance into the pipes, or, if they are permitted to enter, the aim is to provide means for their exit with as little injury to the pipes as possible. It would appear more logical to attack the problem by beginning at the source of the evil and to prevent, to a large extent at least, the leakage of the currents from ^e railway return conductors into the earth. This is the more emphasized by the fact that in the past where such mitigating measures have been appUed to the pipes the burden of providing the protection has usually fallen where it does not properly belong, namely, on the injured party and not on the party causing the injiuy. We shall now consider what measures may be applied by the street railway companies to their own systems with a view of removing or at least greatly relieving the cause of the trouble. Electrolysis Mitigation in Springfield, Ohio 19 Of the various methods that have been proposed for appUcation to the negative return of the railway system, the majority are either inadequate or unsuited to the situation in Springfield. Among these may be mentioned alternating-current traction, three-wire systems, the use of negative trolley, groimding of tracks and bus bars, periodic reversal of trolley polarity, and the use of the double-trolley system. There is no question, of course, but that the double-trolley system, if properly installed, would eliminate entirely electrolysis from railway currents. This system as at present used in Cincinnati, Ohio, and Havana, Cuba, and the corresponding underground conduit systems as used in Wash- ington and parts of New York City eliminate almost completely the danger of electrolysis, the small leakage which does occur being of no practical consequence. The chief objections to its use are the cost of installation and the increased operating difficulties which it involves. The cost of installation in fact does not appear to be justified merely as a means of electrolysis protection, inas- much as a very satisfactory degree of protection can be obtained by other and much more economical means. 4. CONSTKUCTION AND MAINTENANCE OF WAY. Proper maintenance of the track in order to secture high con- ductivity is everywhere recognized as a necessary condition in electric railway operation, but it does not always receive the atten- tion that its importance justifies. In the matter of joints alone there is a very wide diversity of practice. In recent years, how- ever, engineers have rapidly come to recognize the futility of trying to maintain a proper state of track conductivity by merely bridg- ing the joints with short copper bonds. Such construction is still used, but it is finding much less favor than' formerly, and in most of the larger and better maintained systems these methods of shunting the joints are used, if at all, chiefly as secondary expe- dients. The tendency now is to make the joint itself electrically continuous rather than to shunt around it, although both methods are not uncommonly combined. The methods whereby more or less perfect continuity of the joints is obtained embrace the various types of welded joints such as electric welds, thermit welds, etc., and those joints in which a 20 Technologic Papers of the Bureau of Standards second metal such as zinc and its alloys are employed to form the junction. Of these latter the well-known Nichol joint made by pouring molten zinc between the fishplates and the rail ends is one of the most effective, and has given very satisfactory service for a number of years. The zinc is poured in after the fishplates are bolted on and the expansion of the zinc which takes place on solidifying makes a firm and permanent contact between the fish- plates and rail ends. Joints made either in this way or by any of the various welding processes have, as a rule, a lower resistance when new than an equal length of rail, and for the most part have given good satisfaction in service, although some trouble has been experienced, -particularly in welded joints, due to parting of the rails at the weld. Experience to date, however, indicates that these joints are very satisfactory in all cases where the tracks are laid in paved streets, or otherwise suitably reenforced. As a pre- cautionary measure, however, some engineers prefer to bond over all joints also. In the case of welded joints we believe this to be good practice, but experience seems to make it appear unnecessary in the case of the Nichol joint. Cross bonding between the rails is also much resorted to as a precaution against the troubles arising from bad joints. If such cross bonds are properly installed and maintained at sufficiently frequent intervals, the deleterious effect of occasional bad joints is almost entirely eliminated. These cross bonds are usually placed at intervals of from 200 feet to 500 feet and those distances are sufficient if the cross bonds and rail joints are fairly well maintained. All special work should be shunted by copper cables capable of carrying all of the current passing over the tracks at that point. In many places this is the regular pActice, but it is often neglected entirely or poorly maintained, and in some cases the drop across special work has given rise to very serious electrolysis. The remedy is so simple and effective that only carelessness can ac- count for the existence of trouble of this nature. A properly drained roadbed is also a very effective aid in reduc- ing the leakage of stray currents from the rails. The amoimt that can be accomplished in this way will of course vary greatly with varying conditions so that no specific recommendations can Electrolysis Mitigation in Springfield, Ohio 2 1 be made here, other than to point out that since the conductance of the leakage path is largely dependent on the amount of moisture which is contained in the material forming the roadbed and the earth beneath, any construction which tends to reduce the average moisture content therein will reduce in corresponding degree the magnitude of the leakage currents. Indeed, we have made tests on long lines of track without intersections to cause complications, in which it was found that leakage from the rails had been almost entirely eliminated, the reason being that the road was so con- structed that the leakage path from rails to earth was on the whole of high resistance. We believe that much more could be accomplished by this means than is commonly supposed, without materially increasing the cost of construction, although it must not be regarded as a satisfactory primary means of electrolysis mitigation. S. UNINSULATED NEGATIVE FEEDER SYSTEM This system has been much used in this country as a means of increasing the conductance of the track, especially in the regions near the power houses where, as a rule, the current densities become high. The benefits that accrue from its use are three- fold, viz, the reduction in potential drops on the rails, thereby lessening damage due to electrolysis; the saving in power; and the maintenance of a more uniform voltage on the cars, especially at times of peak load, thus giving rise to improved car service and car lighting and reducing the maximum demand. When these benefits are carefully considered it seems somewhat surprising that the use of negative feeders is not more common than it is. While we do not regard this as being in general an economical system, it is proper to consider here its merits as compared with systems in which no feeders are used. In the matter of the second item — the saving in power — it is easy to show that in this feature alone much can be gained by the addition of negative copper. With feeders costing $4000 per mile installed for cables of i 000 000 circular mil section, the most economical potential gradient to allow in the rails is about 3 volts effective per 1000 feet (root mean square for 18-hour period) with power costing i cent per kw-hr Wherever the potential gradient exceeds that figure the addition 22 Technologiq^ Papers of the Bureau of Standards of copper in parallel with the rails produces an annual saving more than sufficient to pay all proper charges, including interest, taxes, and depreciation on the copper required to reduce the potential gradient to 3 volts. With energy costing 2 cents per kw-hr the most economical gradient limit is a little over 2 volts per 1000 feet. When these values are exceeded in any locality, that section of the track is not only being operated at an unnecessary loss, but con- ditions as regards electrolysis are tmnecessarily bad, much worse in fact than they would be under the more economical installa- tion. If we attempt to carry the voltage limit below this value, the cost of the necessary copper increases very rapidly and soon becomes prohibitive. On the other hand, it is generally recog- nized that a potential gradient of 3 volts per 1000 feet is much too high to permit a reasonable degree of immimity from elec- trolysis, so that some other method must be employed if a fair degree of economy is to be maintained. Such economy is afforded in varying degree by the insulated negative feeder systems which we shall now consider. 6. INSULATED NEGATIVE FEEDER SYSTEM In this system, instead of tying the tracks directly to the nega- tive bus and depending on the tracks, and such copper as may be in parallel therewith to retvim the current to the power house, the connection at the power house is either removed or given a suitable high resistance and insulated feeders are nm from the negative bus to various points of the track, as shown in Fig. 4. By this means two important results may be achieved. In the first place, the cur- rent being taken off of the rails at numerous points, high-current densities, and consequently high potential gradients in the rail are avoided. In the second place, it is p^sible, by so designing the sys- tem that the drop of potential on all of the feeders is the same, to so subdivide the current flow in the tracks that the direction of the flow will be frequently reversed, thus preventing the accumulation of large potential differences between points on the tracks some dis- tance apart. It will be evident that in this case the actual drop of potential on the different feeders is of secondary importance so long as it is practically the same in all, in so far as the potential differences in the track are concerned. We can thus impose any desired potential restrictions on the track and still be free to Electrolysis Mitigation in Springfield, Ohio 23 design the feeders to give maximum economy, something we can not do when the feeders are connected in parallel with the tracks as is most commonly the case. RAIL DROP Fig. 5 Figs. 3, 4, 5. — Effect of insulated feeders in reducing rail gradients A graphic representation of what can be accomplished by using a system of insulated feeders of this sort is shown by Figs. 3 . 4, 44128° — 14 ^4 24 Technologic Papers of the Bureau of Standards and 5.^ Fig. 3 shows the arrangement of a negative return in which no negative feeders are used and the rails are tied directly to the negative bus at the power house, a uniform distribution of load being assumed. The curve at the top shows how the poten- tial of the rails vary from point to point. Fig. 4 shows the same system with insulated negative feeders run to a number of points on the track, and so organized as described later that the drop of potential is the same on all during average condition of load. It is seen that the current flow in the tracks is here so subdivided that the total differences become very small, and consequently the tendency to set up large differences of potential between rails and surrounding structures is practically eliminated. An examination of the two curves shows that the maximum potential difference in the rails has been reduced to one-sixteenth of its former value by the installation of only two negative feeders on each side of the station. It is evident, however, that these great reductions in potential differences in the tracks are obtained at a sacrifice of the track conductivity, of which very little use is made in the latter case. Between these two extremes any desired compromise can be obtained; that is, if instead of making the drop on all of the feeders the same we make the drop on the feeders smaller as we approach the power house, we shall have a continual gradient in the rails all the way to the station, thus utilizing the conductivity of the tracks to any desired extent. This will result in a more economical installation but at the expense of somewhat greater potential differences in the track return system, as shown in figure 5. These insulated-feeder systems embrace a number of modifications, chief among which are the following: (a) Boosters in Separate Feeders. — A method that has found considerable application in Europ# but is comparatively little used in this country is that of carrying insulated negative feeders to various points on the track and inserting a booster in each feeder or group of feeders. The advantage of this method is that by varying the voltage of the individual boosters, almost any desired potential conditions can be obtained in the track network. ^ The figures are reproduced from a more comprehensive report previously issued, and figs. I and 2 of that report are irrelevant to the present test and are therefore omitted. Electrolysis Mitigation in Springfield, Ohio 25 To offset this advantage we have, among other things, the large first cost of the boosters and an increased depreciation and opera- tion cost. In a large district as many as a dozen or more negative feeders may be required, and the use of a booster with each of these would obviously introduce considerable complication in the operation of the station. Figure 6 shows in diagrammatic form an insulated negative feeder system with multiple booster control. MULTIPLE BOOSTER SYSTEM POSITIVE BUS + + .NEGATIVE BUS 0-^ @-P Fig. 6 In this, as in all other insulated negative feeder systems, the most important characteristic is the fact that the potential grad- ients may be kept low without regard to the total drop on the negative return between cars and bus bar. If the voltage of each booster is kept about equal to the total drop on the cable to which it is connected, the potentials of the various points of tap to the rails will be approximately the same, so that large differences in 26 Technologic Papers of the Bureau of Standards potential between different points in the track will not occur. In consequence of this the copper feeders can be designed solely from the point of view of economy and thus a much more economical installation can be obtained than would be possible with an insu- lated feeder system, in which the drop on the cable must be no greater than the drop on the rails. When it is desired to reduce the potential gradients in the tracks to i volt per looo feet or lower this method is much more economical, all costs considered, than the uninsulated negative feeder system mentioned above, the saving of first cost of copper being more than sufficient to com- pensate for the cost of the boosters and the capitalized value of the annual depreciation and increased energy loss. These boosters are usually driven by one or more constant- speed motors, and the fields of the boosters are separately excited, a certain range of hand control being provided. The ideal excita- tion would be to have each booster excited in proportion to the load delivered to the district drained by the cable to which the booster is connected, but this, as a rule, is not practicable, and best results will usually be secured by making the excitation of each booster proportional to the total load on the system. One arrange- ment for accomplishing this is shown in Fig. 7, in which a booster equaUzing bus is introduced on the negative side. A similar arrangement can be used on the positive side if desired, and in some cases where local conditions warrant it, the different boosters may be excited separately by individual feeders or groups of feeders supplying power to the region corresponding approximately to the region drained by each particular booster. While this system is capable of giving very satisfactory results, so far as potential conditions in the tracks are concerned it is to be seriously ques- tioned whether the expense and complication of it is justified, particularly in view of the fact that practically as good results can be obtained by other methods which are simpler to install and oper- ate and at the same time much cheaper in point of both first cost and maintenance. The sole advantage of this system over those described below is that a somewhat more flexible control over the individual feeders is obtained, but this is of doubtful value, since the simpler methods afford practically all that is needed in this respect, as will presently appear. Electrolysis Mitigation in Springfield, Ohio 27 (b) Insulated Negative Feeders Without Boosters. — In this system the layout of the negative feeder system will be very similar to that in the case of the booster system described above, the chief difference being in the elimination of the boosters. The potential necessary to force the required ciurent through MULTIPLE BOOSTER SYSTEM SHOWING REGULATION Fig. 7 the negative feeders without the use of additional copper is obtained by removing the direct tie between negative bus and rails at the power house and substituting in its place a properly designed resistance tap. The layout then becomes substantially as shown diagrammatically in Fig. 8. 28 Technologic Papers of the Bureau of Standards In designing the feeders a careful study is made of the load distribution over the entire territory supplied by the station under consideration, and from this study the most natiural points for taking off the current are selected and the number of amperes to be taken off at each point determined. A preliminary value of potential drop on the first feeder is then assumed and from this drop and the cvirrent to be carried by the feeder together with RESISTANCE TAP SYSTEM POSITIVE BUS ^NEGATIVE BUS RESISTANCE TAP Fig. 8 ^ its length the cross section of the feeder must be designed con- sistently with this, so as to avoid potential gradients in the tracks greater than the value determined upon as the limiting allow- able average gradient. Beginning thus with feeder No. 2 its drop is the drop on No. i minus the allowable drop on the dis- tance (a) between the points at which the two feeders tap the rails. For instance, if the assumed drop on No. i is 15 volts Electrolysis Mitigation in Springfield, Ohio 29 and the distance between the two taps is, say, 1200 feet and we are permitting a maximum drop of i volt per 1000 feet in the tracks, the average gradient between C and D will, in general, be less than this figure, depending on the amount of load originating between these points. The average value of this can be determined from the car schedule. Assuming it to be 0.7 volt, for example, the total drop between C and D will be 0.84 volt. The total drop on feeder No. 2 will therefore be 15 — 0.84=14.16 volts. From this value and the ctirrent assigned to this feeder its cross section can be calculated, the length being, of course, already- fixed. We proceed in a precisely similar manner for the other feeders and the resistance taps near the power house. Sometimes the cross section of the feeders as thus calculated will be too small to carry the required current without overheating, and when this is the case the feeder must be made sufficiently large to carry the current and an additional resistance inserted, preferably at the power house, to give the necessary voltage drop. When this calculation is completed we are ready to determine whether the original assumption made in regard to voltage drop on the first feeder was the one that would give approximately the most economical installation. To determine this we sum up the total cost of the feeders installed, and determine the proper annual charge, including interest, taxes, and depreciation, and also calcu- late the total annual value of the energy lost in the feeders and re- sistance tap. If these are approximately equal, the voltage drop assumed was the proper one. If, however, the annual charge on the feeder system is less than the cost of lost energy, the voltage assumed is too high and vice versa, and a correction must be made. This correction can be very easily and simply applied without recalculating the feeder system, as in the first instance. For example, if the annual cost of the feeders is found to exceed that of the energy lost by 20 per cent, we must increase the mean voltage drop by 10 per cent and reduce the area of the feeders by about 10 per cent which change will bring the costs to approximate equality, the condition for most economical instal- lation. If £1 is the original voltage drop calculated for any given feeder and E^ is the mean voltage drop for all feeders, weighted ac- cording to the current in the feeders, then the increase of voltage on 30 Technologic Papers of the Bureau of Standards any feeder being i/io E^ we must reduce the cross section of the feeder by the factor ~- The value of E^ in each case is the E, + ^ lO initial voltage drop calculated for that particular feeder, so that each feeder is corrected by a different factor. When the correc- tion is made in this way there is no appreciable change in the poten- tial gradient assumed for the rails. At first thought it might be considered that the introduction of feeders of this sort, together with a resistance tap at the power house, over which a considerable potential drop is allowed, would cause an objectionable increase in the power lost, with consequent reduction in voltage on the cars. This would be true iii some cases where the voltage drop on the rails is already low, but on the other hand there are many practical cases where the present drop on the rails is large, in which the reverse is the case. With power costing i cent per kw-hr the most economical drop of potential on the copper cables is nearly the same as the value given in the case of uninsulated feeders, viz, 3 volts per 1000 feet. If the power lost in the resistance tap is a large part of the total, the most economical gradient will be somewhat smaller. Detailed calculations show that if the initial potential gradients in those portions of the track to be paralleled by the feeders is much above 3 volts (root mean square for 18 hours), an actual saving of power will result from the installation of the negative feeders, the saving in the rail loss being more than sufficient to compensate for the loss in the feeders and resistance tap. For the same reason the average potential at the cars will be increased. It has been pointed out above that the rail gradients in many instances greatly exceed this value, and in such places there woul^ be a substantial saving in power resulting from the installation of this system. In other places there will be some increase in the loss, and as a rule it is be- lieved that the total negative losses will not be greatly affected by the installation of a feeder system of this character. Only a de- tailed calculation for each individual case can determine whether the net effect as regards power loss will be a loss or a gain. The simplicity of this system as compared with the negative booster system is obvious. In fact the chief objections that have Electrolysis Mitigation in Springfield, Ohio 31 been urged against the negative booster system are overcome, viz, the cost of booster equipment, together with elaborate switchboard apparatus for controlling the same, the space occupied by the boosters, which is out of all proportion to their kilowatt capacity (because of the large number of small machines required) and, finally, the time and expense involved in caring for these machines. In the matter of power loss there is probably little to choose be- tween the two methods. In either case the loss in the cables would be approximately the same, since all but the very short cables would be designed for maximum economy. The difference in power loss would be approximately the difference between the losses in the boosters and the loss in the resistance tap. The efficiency of such small motor-driven boosters, operating at a low load factor would hardly exceed 60 per cent, so that if the loss in the resistance tap is less than 40 per cent of the total feeder loss, the latter plan would give rise to even less power loss than the booster method. Against these decided advantages of the resistance tap method over the booster method must be set the objection that the former is less flexible than the latter, and can not be made to re- spond as readily to meet the exigency of shifting loads. The importance of this objection i* greatly minimized by two consid- erations, the first of which is that the really important considera- tion is to take care of average normal conditions, and this the system will do automatically if properly designed. Abnormal conditions, such as blockades or other temporary bunching of the load in one locality are usually of so short duration that such dis- titfbances in the rail gradients as would result therefrom would have no appreciable influence on the electrolysis problem. The second consideration is the fact that a large measure of flexibility can be imparted to the system by providing means for varying to a slight extent the resistance of the individual feeders at the power house. Since the voltage drop on any feeder will, as a rule, be of the order of ten or more times the voltage drop on the rails be- tween adjacent feeder taps, a change of lo per cent or less in the resistance of a feeder or group of feeders would take care of a shifting of the load tending to produce local variations of 100 per cent in the rail currents. Such resistance control can be 32 Technologic Papers of the Bureau of Standards accomplished in a comparatively simple and economical manner, and throughout sufficient range to meet most practical require- ments, although it will not be possible in this way to secure the same degree of flexibility in the feeder control as by the use of separate boosters in each feeder. However, this method is a thoroughly practical one, and if properly installed can be made to reduce potential gradients in the rails to any desired degree, and under many circumstances it is the most economical effective means that can be installed for preventing electrolysis. Under certain conditions, however, as in the case of a power house or substation located in the center of a dense network of rails in which a large amount of current can be brought close to the bus bar on the rails or very short feeders, the power lost in the resist- ance tap might become so large as to be an important matter, and to make this system less economical as well as less flexible than the systems described below. (c) Single Booster System. — This system is designed to eliminate to a large extent the disadvantages of two systems just described, namely, the insulated negative feeder systems with and without boosters. As pointed out above, the chief objections to the use of the direct boosters in the negative feeders arise from the large mmiber of machines that will be required in most cases, the con- sequent increased depreciation, operating difficulties and space requirements, and to the fact that the small size of the individual machines render a high efficiency of operation out of the question. This will still be true as regards the generator part of the boosters even though all of them are driven by a single motor, as can often be done. In the case of the insulated system without boosters the elimination of these difficulties is accomplished through the sacrifice of a considerab^ measure of the flexibility of the booster system, and at the expense of the added power lost in the resistance taps, which latter may become serious under the conditions pointed out above. The single booster system occu- pies a somewhat intermediate position between these two extremes, preserving to a large degree the flexibility of the one and simplicity of the other, while yielding under some conditions an economy oi operation greater than either. The system is represented dia- grammatically in Fig. 9. It will be seen that all of the negative Electrolysis Mitigation in Springfield, Ohio 33 feeders except the power house tap are brought to a feeder bus and that a single large booster is connected between this bus and the negative bus of the generators. In this case the proper dis- tribution of current between the different outlying feeders is secured by a proper proportioning of their resistances, as in the case when boosters are not used. Here, however, the power house tap, instead of being connected to the negative bus through a resistance, SINGLE BOOSTER SYSTEM Fig. 9 is led through the field of the booster. In consequence of this the voltage tending to force current through the feeders is propor- tional to the current in the power house tap, and hence the proper division of current between the two sections is automatic. It will of course be obvious that very short feeders such as those running to various street intersections adjoining the power house would be combined with proper ratios of resistance and led to the 34 Technologic Papers of the Bureau of Standards field of the booster as a single feeder, as indicated in Fig. 6. The advantages of this over the method without boosters is that the power loss in the resistance tap is eliminated and the distribution of current between the outlying feeders and those near the power house can be controlled throughout any desired range by properly shunting the booster field. Further, and this is of special impor- tance, the distribution being thus adjusted to any desired ratio, it will automatically be maintained at approximately that ratio regardless of the magnitude of the load, and in this way overloading the rails approaching the power house, even temporarily, is ren- dered practically impossible. The importance of this will be readily appreciated when it is considered that it is this local over- loading that is responsible for the rapid fall of potential in the rails which in tium is chiefly responsible for the large differences of potential which often occur between pipes and rails in the regions near the power house. (d) Inverted Booster System. — ^This system is represented diagrammatically in Fig. lo. It will be seen that this differs from the insulated feeder system without boosters only in the substitu- tion for the resistance tap of an "inverted booster"; that is, a booster so arranged as to produce a counter emf in the power-house tap sufficient to cause the proper amount of current to flow over the insulated feeders and prevent excessive currents from flowing over the tracks. In its practical embodiment this inverted booster consists of a series motor coupled to a practically constant- speed generator connected to either the D. C. bus bars, or the A. C. system, in the latter case an ordinary induction motor being satisfactory. The cotmter emf of the series motor gives the drop required on the feeders, and the power consumed by the motor in excess of the losses is returned to the ^stem through the generator end of the unit. By a proper design of the field characteristic of the series motor the coimter emf of the machine may easily be made practically proportional to the current taken from the tracks by the motor, and it will be obvious, therefore, that the drop on the feeders and consequently the current taken by them will be nearly proportional to the motor current, which is approximately the condition desired. The operation is therefore entirely automatic Electrolysis Mitigation in Springfield, Ohio 35 for normal load conditions, and such special control as may be necessary because of changes in track conditions near the power house, or to other causes, can readily be secured by an adjustable shimt on the series field or by providing a certain amotmt of sepa- rate excitation in addition to the series field. It will be evident that as long as the railway load is sufficiently large, so that the input into the series motor exceeds the losses in INVERTED BOOSTER SYSTEM Fig. 10 the unit, the generator will return the excess to the system, but if the input into the motor is less than the losses, both machines act as motor, the generator end carrying the excess of the losses. If the generator consists of an ordinary shimt-wound D. C. machine, or a properly designed induction machine, only a slight drop in speed accompanies this change from generator to motor action, so that the counter emf of the series motor remains practically pro- 36 Technologic Papers of the Bureau of Standards portional to the current input. By a proper design of the D. C. generator, such as by compound windings, working well up on the saturation ciurve, it would be practicable to make the cotmter emf of the series motor rise either faster or more slowly than the cturent input wherever such special conditions might be made desirable by local conditions, but this will not, as a rule, be neces- sary. Considering the relative merits of the last three methods, it will be seen that in so far as the distribution of current between the different outlying feeders is concerned, they are all on a par, depending as they do on the resistance of the feeders for such dis- tribution. As regards the distribution of current between out- lying feeders and those near the power house, both the single booster and the inverted booster methods give greater range and flexibility of control of the ratio of these currents than the resist- ance tap, although a fairly satisfactory degree of control can be obtained by the latter method by using a variable resistance in this tap. As to first cost, the resistance tap will of course be the cheapest under all conditions while the relative first cost of the booster methods will depend on local conditions. If the distribu- tion of the load and the character of the track network are such that more than half the total station load is taken from the track via the power-house taps, then a smaller and cheaper machine can be used in the case of the single booster than if an inverted booster be used. If, however, less than half of the current be taken from the tracks at or near the power house, the inverted booster will be the smaller and, in general, the cheaper. In the matter of net cost, however, we are concerned not alone with the cost of installation but also with numerous other charges, such as the cost of energy lost, deprecation, and operating charges. If the character of the system be such that the greater part of the power of the station be taken from the taps at the power house, the single direct booster method would show to advantage over the inverted booster, and in most cases the saving in annual value of energy lost as compared with the loss in the resistance tap would more than pay all proper charges against the booster, as will be shown later. If, however, the cturent taken from the Electrolysis Mitigation in Springfield, Ohio 37 tracks near the power house is less than half the station load, the inverted booster will be cheaper both in first cost and in operation than the direct booster and, except for quite small capacities, will show a saving in operating costs over the resistance tap. However, as the amount of ciurrent taken from the power house tap becomes smaller, a point is finally reached at which saving in power no longer compensates for the additional cost of the booster and the resistance tap becomes the cheaper. It will be seen, therefore, that the relative merit of the three systems depends on conditions which must be determined for each individual case, but in most cases either the inverted booster or the resistance tap will prove to be the most economical installation. Combinations of two or more of these systems may often be found desirable, as, for instance, in the case of a number of compar- ative short feeders going to nearby points and one or two very long feeders extending much farther from the station. In such a case any one of the above feeder systems may be applied to the shorter feeders as a group, and a direct booster inserted in the long feeder to provide the voltage necessary to bring the average current flow in the cable up to the most economical value. 7. NUMBER AND LOCATION OF POWER HOUSES AND SUBSTATIONS In a general way the effect of the number of feeding points on the potential drops in the rails and the consequent leakage of current from the tracks is obvious but some of the more important aspects of this problem are obscture and often not appreciated. The economic aspect of the question is also more complex than is generally recognized. In the broadest terms we may consider the matter under two heads, namely, (i) the effect of the number and location of the stations on the tendency of the pipe systems to pick up stray currents from the earth, and (2) the effect on the total drop of potential on both sides of the line. As to the first of these we have to consider the fact that as the number of stations is reduced the capacity of each must be increased, with the result that the current flow in the rails approaching the power house will be greater, and the increased potential gradients resulting there- from cause correspondingly increased leakage of current from the tracks. Further, as the distance between stations is increased 38 Technologic Papers of the Bureau of Standards the tendency of pipe lines to take up current from the earth under a given potential gradient increases much more rapidly than the distance of transmission. In fact it can be shown that the cur- rent picked up by the pipes may increase either as the second, the third, or even a higher power of the distance between feeding points, according to the character of the system imder consider- ation. Any increase in the number of feeding points, or more properly speaking, the number of "drainage points" or points at which current is taken from the track, will reduce in much greater degree the flow of stray currents in the pipes. The num- ber of drainage points can be increased to any extent desired by the proper use of insulated negative feeders as above out- lined, but the fewer the stations the longer and heavier the feeders must be, and in consequence of this an increase in the number of stations may often prove to be in the interest of economy, considering only the negative return; this economy will become much more pronovmced when we consider also the distribution of the power on the positive side as well as its return on the negative. When we come to consider the question of total drop of potential in the distribution and return of the current, we have many com- plex factors to consider. One of these factors is the loss of power resulting from such drop of potential, but the calculation of the value of this lost power is by no means so simple as might at first appear. It is not sufficient simply to determine the total energy loss during any given time and multiply this by the cost of power per kw-hr in order to determine its value. We must consider that the loss of power is proportional to the square of the load and hence is greatest at time of peak load when the capacity of the power station is usually taxed to its utmost. The capacity of the generating plant and hence the fixed ^arges on the cost of power are thereby increased; or, if the power be pmrchased, there is usually a fixed charge imposed on the maximum demand. In any case if the operation of the system is such that the line losses give rise to an increased demand for power at time of peak load, the cost of the lost power wiU be greater than the cost of the power utilized at the cars. Besides the question of lost power due to line drop we have to consider also the effect of this drop of potential on the character of Electrolysis Mitigation in Springfield, Ohio 39 the car service and the cost of operation of the car system. Low- voltage means lower average car speed, with a consequent increase in the number of cars required to operate at a given headway, which in turn increases both fixed charges and operating costs. Any change in the distribution system, therefore, whether a change in the number of stations or any other change which affects mate- rially the line losses will exert a marked effect on the cost of opera- tion of the system. In designing a system of electrolysis mitiga- tion, therefore, many things have to be taken into account quite apart from the technical points regarding the electrical condition of the negative return if a proper balance is to be maintained be- tween the cost of making the proposed changes and the benefits resulting therefrom. In the foregoing brief review of the various methods that have been proposed for reducing troubles from electrolysis, a number were stated to be of little value for extensive application to net- works of any considerable size, and certain of them were stated to be actually detrimental because of their tendency to accelerate deterioration of the pipes. The method of insulating joints and the pipe drainage system were stated to be of some practical value, but it was recommended that their use be restricted to auxiliary measures used in connection with certain of the track drainage systems. A more logical and at the same time a more effective and economical procedure is to attack the source of the trouble by applying remedial measures to the railway system. A num- ber of methods are available for this piurpose, but as pointed out in the foregoing review, the majority of these, viz, the "alternating current system," the "double trolley system," "three wire system," "negative trolley," "periodic reversal of trolley polarity," and "uninsulated negative feeders to rails," considered solely as methods of electrolysis mitigation were either impracticable or else open to the objection that the expense and operating difficulties attending their application were rendered unnecessary, because of the fact that there are other adequate methods available for general application which are comparatively cheap to install and which introduce but slight complication into the operation of the system. These latter methods are the four types of insulated negative feeder systems outlined above. It is 40 Technologic Papers of the Bureau of Standards possible by the proper application of any of these methods to reduce the potential gradients in the earth to almost any desired degree, and they can consequently be made very effective in relieving electrolysis troubles. In special cases, however, it may sometimes be better, where conditions are favorable, to combine one of these methods with either the insertion of a moderate num- ber of insulating joints in pipes, or with the use of a very limited amoimt of pipe drainage, the insulated feeder system being applied to reduce potential gradients throughout the system to a very low value, and one or the other of the auxiUary systems used to prac- tically eliminate any residual electrolysis that might still remain. An additional advantage that would result from the proposed installation grows out of the more uniform voltage available at the cars. The rail drop being reduced to a small fraction of its former value the variation of car voltage will be chiefly that due to the drop on the positive side, and hence the voltage regulation at the cars will be materially improved. This gives rise to much more satisfactory car lighting, a matter of considerable impor- tance to the traveling public. In a later section of this report we present a summary of a plan of electrolysis mitigation that we deem best suited to existing con- ditions in Springfield. A study of these conditions has shown that the insulated feeder system without boosters offers the most economical effective solution of the problem. The plan has been worked out in detail, the size and location of each feeder being given, and the first cost of the installation and the economies resulting therefrom are carefully estimated. Conclusions drawn from these detailed calculations are that the economies resulting from this initial outlay make it, from the start, a dividend-paying investment, the saving being sufl&cieig: in itself to justify the in- vestment qtiite apart from its effect in eliminating electrolysis troubles. PART II. RECOMMENDATIONS FOR ELECTROLYSIS MITIGATION IN SPRINGFIELD, OHIO As pointed out in the foregoing section, the most logical and effective method of securing protection against electrolysis troubles consists in eradicating the cause of the trouble by eliminating to a Electrolysis Mitigation in Springfield, Ohio 41 large extent the escape of stray currents into the earth. It was shown that this can be very effectively accomplished by any one of a number of insulated negative feeder systems applied to tracks, and the relative value of the different types of these systems, both as to effectiveness and economy of installation and operation, was very briefly discussed. It has also been pointed out that the Springfield Railway Co. has already installed a feeder system of this kind, consisting of a number of insulated overhead copper feeders running directly from the bus bar to various points in the track return. The experimental data secured by the engineers of this Bureau show that this feeder system has brought about a material improvement in electrolysis conditions in Springfield; but, as already stated, some modifications of this system will be necessary before a satisfactory degree of protection will be assured. A study of the system as it now exists shows that with certain modi- fications, which are set forth in detail below, not only can trouble from electrolysis to the water and gas pipes be very satisfactorily eliminated, but that considerable economy in the operation of the system will likewise be secured. An examination of the present system also reveals the fact that certain other changes in the neg- ative return circuit should be made in order to bring about the most satisfactory conditions from both the standpoint of elec- trolysis mitigation and economy and simplicity of operation. These various changes are discussed in detail below. 1. IMPROVEMENT IN RAIL JOINTS The electrical measurements taken on the rails of the Spring- field Railway Co.'s tracks and also the tracks of the Ohio Electric Co. show that it is desirable to give some attention to improving the continuity of the tracks, in order to secure the maximum benefit from the conductivity of the rails. It has already been stated, however, that the condition of the Springfield Railway Co.'s tracks on the whole is not considered particularly bad, but it is nevertheless important that the tracks be gone over and all bad joints carefully rebonded. The Ohio Electric Co.'s tracks at present are particularly bad, it being found that the Ohio Electric Co.'s current in large part returns over the tracks of the Springfield Railway Co.'s lines to the junction of Isabella and 42 Technologic Papers of the Bureau of Standards North Streets, the double track on North Street east of Isabella carrying practically no current. We understand this is due to the reconstruction work which is now going on on the Ohio Electric Co.'s lines, and that within a short time this reconstruction work will be finished and the present bad condition of the track con- ductivity will be eliminated. This matter should be given careful attention, however, in order to insm-e that a good condition of the track is secured and maintained. Of the several other inter- urban lines running into Springfield, the power houses are so located and the load so light that they will not contribute appreciably to electrolysis troubles, provided their rails are properly bonded, the rails themselves being capable of affording all the conductivity that is needed for the light loads carried. With all the railway systems, however, it is very important that periodic tests be made on the tracks and immediate steps taken to improve the con- ductivity of any joints that are found to be of high resistance. In general the resistance of the joint should not be permitted to exceed that of two or three feet of continuous rail, it being entirely practicable to secure and maintain this condition with any one of a variety of rail joints without prohibitive expense. 2. INTERCONNECTION OF THE TRACKS OF THE OHIO ELECTRIC RAILWAY AND SPRINGFIELD RAILWAY COS. A very important n;atter in connection with the elimination of the electrolysis troubles in Springfield is the proper inter- connection of the tracks of the Springfield Railway Co. and the Ohio Electric Co. at all crossings. This is of prime importance not only because of the marked economy that would result from such interconnection, but also because of the fact that it would be prac- tically impossible by any means to secure satisfactory electrolysis conditions if these railway tracks y^re not electrically intercon- nected. The importance of such a connection can readily be understood by reference to Chart I, which shows in diagramatic form the railway tracks of the two systems on North and Main Streets between the two power houses and also the cross tracks on Isabella, Wittenberg, Limestone, and Syracuse Streets and Lagonda Avenue. The tracks on North Street will have, when the present rehabilitation work is complete, rails weighing 90 Electrolysis Mitigation in Springfield, Ohio 43 pounds per yard, having a resistance of 0.00 24 ohms per 1000 feet, or about 0.024 ohms total between Isabella and Sycamore Streets, the distance being approximately 10 000 feet. The Spring- field Railway Co.'s tracks on Main will be for the most part 60- pound rails, having a resistance of 0.0037 ohms for the entire distance between Isabella and Sycamore. The cvirrent of the Ohio Electric Co. which may be considered as originating at D east of Lagonda Avenue, amounts to approxi- mately 400 amperes on the average. The cvirrent of the Spring- field Electric Railway line coming from west of Lagonda is during the average day load of the order of about 1000 amperes. This is, of cotuse, distributed over the entire city, but for purposes of illus- trating the advantage of the interconnection of the two railway track systems, we may assume that a load of 500 amperes con- centrated on west Main Street in the vicinity of Western Avenue. This will of course not represent an actual condition, but would give a total drop on the Main Street tracks to the power houses which is approximately equal to that produced by the distributed load which actually exists there. Under these assumptions the drop on the Ohio Electric tracks along North Street between D and the Ohio Electric power house at B would be the current multiplied by the resistance which equals 400 times 0.024 = 9.6 volts, the gradient being from east to west. The drop on the Springfield Railway tracks along Main between C and the power house A would be 500 times 0.037 = 18.5 volts. Since these drops are in opposite directions it will be impossible to prevent large differences of potential between the tracks on Main and North Streets. If, for instance, rails at both power houses are at zero potential, then the Ohio Electric tracks near Columbia and North will be 9.6 volts positive to the rails of the Springfield Railway Co., giving rise to large leakage of current through the earth between the two systems which would cause serious injury to the pipes. Further, the potential between the Springfield Railway tracks west of Main and the tracks on North Street near the Ohio Electric power house would be about 18.5 volts, producing an even more serious condition than the former. The distance between the tracks here being only about 1000 feet, the potential gradient will be seen to be enormous, and it would inevitably result in serious 44 Technologic Papers of the Bureau of Standards injury to the pipes in that locality. If, however, the tracks are tied together at all streets on which cross tracks now exist, namely, at Isabella and Western, Wittenberg, Limestone, Sycamore, and Lagonda the current from the two directions would divide between the tracks and since they would flow in opposite directions, the resultant current would be the difference between the two, or only about loo amperes, which would be directed eastward and toward the Springfield Railway Co.'s power house. The combined resistance of the two tracks in parallel is only 0.015 ohm, giving a drop of 1.5 volts over the entire 10 000 feet. It would thus be impossible to produce any large difference of potential between any two points on the tracks. Further, the drop would in this case be in the same direction on both tracks instead of the opposite direction as would be the case if the tracks were not interconnected, so that they would be almost absolutely at the same potential throughout their entire length. It will thus be seen that the voltage conditions will be enormously improved by tying the tracks together, and what would otherwise be a very dangerous condition along the entire Une between the two power houses would be converted into a condition of comparative safety. It is thus clearly seen that tying the tracks together at various points amounts, in effect, to an interchange of current on the nega- tive side between the two power houses. The Springfield Railway Co.'s power house would then intercept the Ohio Electric's cur- rent coming from the east beyond Lagonda, while the Ohio Elec- tric Co.'s station would take a corresponding amount of current from the Springfield Railway tracks in the western part of the city, only the difference between the Ohio Electric load and the Springfield Railway load being taken from the west back to the Springfield Railway power house. ^ In addition to the improvements in the electrolysis conditions above noted, there will also be a large saving in power. With the tracks separated the loss on the Ohio Electric tracks between La- gonda and Isabella will be the cmrent multiplied by the voltage drop, or 400 times 9.6 = 3840 watts = 3.84 kw, and on the basis of an i8-hoiur day this gives a total of about 25 000 kw-hr per year. On the Springfield Railway tracks between Lagonda and Western Avenue the loss would be 500 times 18.5 = 9250 watts = 9.25 kw, Electrolysis Mitigation in Springfield, Ohio 45 giving a total annual loss of 60 000 kw-hr. The total loss on both tracks would therefore be 85 000 kw-hr per year. At I cent per kilowatt hour this is $850 per year. As seen above, however, if the tracks are tied together, the average current in this same section is reduced to approximately 100 amperes, and the total drop to only 1% volts, hence the loss is but 150 watts, giving an annual loss of 972 kw-hr per year, which at i cent per kw-hr would be worth but $9.72. The saving, therefore, resulting from tying the tracks together would be over $840 per year, the capitalized value of which would at least be $14 000. It thus appears that the interconnection of the tracks at the various points on which cross lines already exist would have a very large monetary value to both companies, and would be very desirable from an economic standpoint regardless of any consid- eration of electrolysis protection. When, also, we consider the great improvement in voltage conditions that would accompany such interconnection, it is evident that such interconnection of the tracks is the only wise course to pursue. The electrical measturements obtained by the engineers of this Bureau show that at certain places at least, such interconnection does not now exist, as at Columbia and North Streets, for example, where large differences of potential were found to exist between the tracks on the Ohio Electric and Springfield Railway lines at the crossing. In view of the considerations pointed out above it is obvious that this condition should be corrected as soon as prac- ticable. We have also been informed that one of the rsiilway compa- nies contemplates insulating the tracks of the two systems from each other at all crossings. As pointed out above this would greatly increase the danger of electrolysis troubles due to stray cmrents as well as materially increase the operating cost because of the increased power loss, and we very strongly urge that this plan to isolate the two systems be not carried out, but on the, contrary, special precautions should be taken to insure thorough bonding between the tracks of the two systems at all intersections. 3. CROSS TYING OF TRACKS ON EAST MAIN AND fflGH STREETS Another matter of importance in addition to the installation of properly designed insulated feeder system is the placing of a proper crosstie between the tracks on east Main and east High 46 Technologic Papers of the Bureau of Standards Streets at or in the vicinity of Sycamore or Lagonda Avenue. The reason for this is that these tracks run approximately parallel and qtiite close together for a long distance ■without any cross lines to produce an electric connection between them. It will be evident that the potential difference between the two lines at adjacent points will be due to differences in the drop along the two tracks extending eastward from Limestone Street, at which point they are practically tied together by the rails on the Lime- stone Street Une. Thus, if the drop along Columbia between Lagonda and Limestone should be lo volts and the drop on east Main Street over the same distance should be, say, 5 volts, then the potential drops between the tracks at Lagonda would be 5 volts, and since the distance here is very short this would give rise to a very high potential gradient between the two lines which would be sufficient to cause dangerous leakage of current into the earth, and consequently, serious damage to the pipes. In order to overcome this difficulty a heavy copper cable should connect the two Knes on High and Main Streets to serve as an equalizer and prevent any large differences of potential of this sort from arising. 4. NEGATIVE FEEDER SYSTEMS The above recommendations while important and necessary to the securing of satisfactory immimity from electrolysis troubles must nevertheless be considered as secondary in importance to the installation of a properly designed and maintained system of insu- lated negative feeders connecting the negative bus bar to various points in the rail retirni. The system of negative feeders already installed is shown in Chart II. By reference to this chart it will be seen that this system comprises a feeder running from the power house at Sycamore and Wardipr up to the comer of Main and Limestone, at which point it branches and rebranches and ties to the tracks at a ntunber of points on west Main, west High, west Pleasant, and South Limestone Streets, thus draining the tracks in a large part of the center of the city. Another feeder ex- tends from the power house along Warder and College Avenues to the comer of Limestone and College. A third feeder runs south along Sycamore to east High Street, thence east and taps to the rails at East and High and at Glenn and High, also Electrolysis Mitigation in Springfield, Ohio 47 south on Bast to Kenton Street. A fourth feeder runs along War- der and Lagonda Avenue, thence along Lagonda to James Street, thence along James to Columbia Avenue with taps to rails at Pauline and Lagonda, James and Lagonda, and James and Columbia Avenue. As at present constituted, this feeder system, while undoubtedly greatly improving electrolysis conditions, is not altogether satisfactory for several reasons. In the first place the arrangement of the feeders is such that comparatively little current is taken from the feeders ruiming east from the power house on Lagonda and east High Streets, while a relatively large amotmt of current is taken from the feeders running to Limestone and beyond. As a result of this the direction of current flow in the rails on Columbia and east Main and east High between Syca- more and Limestone Streets is actually away from the power house. This tends to produce the lowest potential up in the heart of the city, and causes a complete loss of the conductivity of the double track lines on these streets, which could be utilized if the feeder system were so proportioned as to cause a considerable amount of current to flow eastward on those streets and be taken off in the region of Sycamore Street. A redesign of the cables so as to take less ctirrent from the terri- tory surrounding Limestone Street and a greater proportion from feeders draining the region to the east of Sycamore Street would at once produce better potential conditions and likewise give rise to much greater economy because of the more direct route by which the current would be returned to the power house. Another disadvantage of the present feeder system is the relatively large potential drop which now occurs on these feeders, thus giving rise to a large energy loss. As will be shown later by a detailed calculation, a redistribution of the feeder copper would result in large economies in this direction. A further defect growing out of the high drop of potential of the feeders is the fact that the poten- tial difference between the different points at which the feeders are connected to the tracks depends on the differences in the poten- tial drop in the various feeders themselves. Since the load is con- stantly fluctuating from point to point the drop on these feeders will necessarily change, so that it is impossible to maintain the terminal points of the various feeders always at the same potential. 48 Technologic Papers of the Bureau of Standards It will be evident that a given shifting of load producing a certain percentage variation in the drop on an individual feeder, will cause a greater potential difference between termini of the feeders if the total drop on the feeders is large, than the same percentage variation of a load would produce if the total drop on the feeders were relatively small. For this reason a redistribution of the feeder copper such as to reduce considerably the total drop on the negative feeder would result indirectly in much smaller potential differ- ences between those points on the track to which the feeders are connected, and consequently the earth gradients throughout the city would be much smaller, and electrolysis correspondingly improved. In order to show how the system can be redesigned to over- come these objections, we have worked out a detailed plan for changing the present negative feeder system in such a manner as to secure at once adequate protection of the pipe systems and the greatest economy in installation and operation. This plan of reorganizing the negative feeder system is outlined in detail below. A complete plan of the proposed feeder system is shown in Chart III, showing the size and location of the feeders required and the points at which they should be tapped to the rails. We have also given a careful estimate of the cost of converting the present sys- tem into the system proposed, together with an estimate of the economies resulting therefrom. It will be found that while the proposed changes contemplate the expenditure of about $4900, the change will be accompanied by certain operating economies which will result in a saving sufficient to pay large retmns on the cost of making the necessary changes. In making the calculations for the negative feeder system it was necessary first to secure data as^^o the average distribution of load in the track network. In order to do this the car schedtde of the entire system was obtained from the Springfield Railway Co., and from this schedule the average car distribution was laid out on a map of the railway system, as shown in Chart III. The average current per car is foimd to be very close to 40 amperes, and this value has been used in all calculations. In making the calctdations the normal average load car distribution is determined from the car schedule as represented in Chart III. A careful study of the load and track layout was made and the approximate dis- Electrolysis Mitigation in Springfield, Ohio 49 tribution of the current in the rails determined, beginning in the outlying portions and gradually tracing the cturent distribution as the station was approached. Where it was foimd that the cur- rent density at any point was such as to give a potential greater than one-half volt per looo feet, a feeder of suitable size was con- nected to the rails to carry off the excess cturent. In this way the potential gradient throughout the entire negative return of the rail- way is maintained below one-half volt per looo feet. This is but a small fraction of the potential gradient existing in the rails prior to the installation of any negative feeder system, and will of course give rise to a corresponding reduction in electrolysis troubles. It is believed that this figure is sufficiently low to practically eliminate any serious electrolysis trouble. The result of the calculations shows that a total of four feeders are required, together with a suitable number of taps as hereinafter described. These feeders and their routing are described in detail below and a condensed statement of all the essential data in regard to them is given in Table I. TABLE 1 Insulated Negative Feeders for Springfield Railway Co. liOcfltion Length, 1 Cur- rent, amp Cross section, M. C. M. Potent drop, volts Loss, KW Copper, weight Copper, added. Tap 2 Tie 3 Tap 4 Tap 4 Tap Con Limestone, Pleasant to Main. . Main-Limestone to power house At Limestone and Main Columbia to power house,Syca- more Sycamore-High to Main Sycamore Main to power house. Main-East to Sycamore Main and Sycamore James-Lagonda Lagonda and James Nelson-Lagonda to Warder. . . Lagonda and Warder Warder-Lagonda to power house 0.60S 1700 1050 2220 1160 200 80 310 240 380 140 300 40 40 .413 3.410 .837 .605 1270 11.04 3.67 12.72 .74 11.04 2.69 1.95 10.4 6.25 3.20 9.24 2.208 .294 3.9 .178 4.6 ,.377 .585 .416 .250 .256 1.20 8360 2130 10 850 5640 2130 2130 9540 2750 820 .794 1870 Total., 49 260 28 041 Aimual energy loss —101 200 kw-hours. Annual energy loss =$1012.00 Copper value =$12 315.00 Aimual interest on copper=$985.20. Aimual saving in energy loss =$2805.00 50 Technologic Papers of the Bureau of Standards Feeder No. i. — This feeder extends from the negative bus at the Springfield Railway Co.'s power house to the comer of Main and Limestone Avenue; throughout this length it has a cross section of I GOO GOO circular mils. At this point a suitably designed resistance tap connects the feeder to the rails , taking off 80 amperes . The feeder then continues south on Limestone Street to the comer of Pleasant, the cross section of this portion of the feeder being 605 000 circular mils. At Pleasant a cmrent of 120 amperes is taken from the tracks, the total drop of potential on this feeder between Pleasant and Main is 4.48 volts (calculated), and between Main and Lime- stone and power house the drop is 1 1 .04 volts, giving a total poten- tial drop of 15.52 volts, and a total power loss diiring average con- ditions of load of 2.8 kw. The total weight of copper in this feeder will be 21 190 pounds, but since there is already a large amount of copper installed on this route the additional copper required will be but ID 525 poimds. Feeder No. 2. — ^This feeder runs from the power house to the comer of Sycamore and Columbia, a distance of about 1700 feet. It here taps to the rails, taking off an average of about 310 amperes ; the cross section reqtiired is calculated at 413 000 circular mils, giving a drop of 12.72 volts, and an average power loss of 3.9 kw. The total weight of copper required is 2130 potmds. Cross tie between High and Main at Sycamore Street. — ^This is the cross tie referred to above designed to prevent large differences of potential arising between the tracks on east Main and east High. Its length wiU be about 1050 feet and the cross section 3 410 000 circular mils. It is depended upon to carry 240 amperes average from east High Street, which would give a potential drop of 0.74 volts, and an average power loss of o. 1 780 kw. The total copper required is 10 850 pounds. ^ Feeder No. 3 — This rtms from the power house to the comer of Sycamore and Main, which section has a cross section of 837 000 circular mils. At Sycamore and Main the feeder is tapped to the rails through a resistance tap designed to take off 300 amperes. The feeder also continues east on Main Street to Lincoln Street, where it is tied directly to the rails. This latter section has a cross section of 605 000 circular mils and is designed to carry 140 amperes. The length of this latter section is about 11 60 feet Electrolysis Mitigation in Springfield, Ohio 51 and the length of the section between the power house and Syca- more and Main is about 2220 feet. The total weight of the copper required will be 2130 and 5640 pounds, respectively, for the two feeders, giving a total of 7770 pounds, of which a considerable por- tion is already in place. The total power loss of this feeder, in- cluding the loss on the tap at Main and Sycamore, will average about 5.5 kw. Feeder No. 4. — This feeder runs from the power house along Warder to Lagonda, thence along Lagonda to James, thence along James to Columbia. It will be seen that the route of this feeder is identical with that already in place, and the cross section is the same from the terminus at James and Columbia to the corner of Lagonda and Nelson. The current carried on this cable is small and the energy loss only about 0.4 kw. There is a resistance tap at Lagonda and James designed to take about 40 amperes from the rails at a potential drop of 6.25 volts, giving a power loss of 0.25 kw. From Nelson to Warder the cross section of the feeder is 317 000 circular mils, thus requiring the addition of 406 pounds of copper in this section. A tap at Lagonda and Warder designed to take 130 amperes from the track has a drop of 9.24 volts and a power loss of 1.2 kw. From Lagonda and Warder to the power house the current carried is 210 amperes, requiring a cross section of 794 000 circular mils, and the distance 1060 feet, which requires a total of 2560 pounds in this section, or an addition of 1870 pounds to the copper already there. Summing up, we find that the proposed feeder system would require a total of 49 260 pounds of copper, of which, however, 21 220 povmds are already in place. The total power loss as seen from Table i is 15.4 kw, which gives an annual loss of loi 200 kw-hr, having a value at i cent per kw-hr, or $1012 per year. In order to determine the cost of the system, however, we must deduct the value of copper which can be removed in making the change, and also determine the saving in power that results. A study of the proposed layout shows that the following copper that is now in place can be removed. The feeder running from the power house to College and Limestone, on Main from Limestone to Lowry, on High from Limestone to Center, on Pleasant from Limestone to Center, on Limestone south of Pleasant, and a short section on 52 Technologic Papers of the Bureau of Standards east High street. All of these are 4/0 cables and have a total weight aggregating 8590. There is also a section on East Street of 420 000 circular mils weighing 3040 which is not required tinder the proposed plan. This gives a total of 1 1 630 pounds of copper to be removed. The value of this is figured at 18 cents a pound after allowing for the cost of removal, which gives a value of $2095 as the value of the copper recovered. From Table i it is seen that the total copper required to be added is 28 040 pounds, the cost of which estimated at 25 cents per pound is $7010. The net initial investment required would therefore be $7010, minus $2095 = $4915. The annual cost of the copper added reckoning 8 per cent on the initial investment amounts, therefore, to $393. From this annual cost, however, we must deduct the annual value of the power saved by changing to the proposed installation. To determine this we must calculate the power loss in the present system of negative feeders. Measurements of the total drops of potential on these feeders shows that the average drop on all the feeders during the average day load amounts to about 44.3 volts, and since all the current returns over these feeders under the present system the average power loss is equal to the average drop on the cables multiplied by the average current, which gives 44.3 times 1310 times 10 — ^ = 58.1 kw. This gives an annual loss of 381 700 kw-hr, which at i cent per kw-hr has an aimual value of $3817. It was shown above that the annual energy loss under the proposed system would amount to $1012, so that the net saving in power loss reaches $2805 per year. Deducting from this saving in power the above figure of $393, which was the annual cost of the necessary changes in the copper feeders, we get a net saving of $2412 per year under the proposed plan. Another way of looking at it is that the total ^paving in power amounting to $2805 per year yields 57 per cent on the total cost of reconstructing the negative feeder system. It appears, therefore, that from the standpoint of economy alone it is highly important to make the changes recommended. It will be evident also that since the total drop on the feeders, as shown by Table i, has been reduced to not more than one-fourth of the drop under present conditions, any fluctuations in load distribution will produce very much smaller potential differences between the termini of the feeders Electrolysis Mitigation in Springfield, Ohio 53 than at present and consequently the tendency for high potential gradients in the earth will be very greatly reduced, and electrolysis conditions through the city correspondingly improved. It will be noted that in the proposed plan there is no direct con- nection between the rails and the negative bus out of the power house. Such connection is omitted primarily for the reason that this district is in low ground that is likely to be comparatively damp, and consequently of low resistance, so that to make this the most positive part of the system as would be the case if any considerable current were taken off at the power house, would be to throw the positive area in a region where it would do the great- est amount of damage. On the other hand, by removing the power-house connection the positive areas are thrown out at the termini of the feeders which are located on relatively high ground, where owing chiefly to lower moisture content, the average resist- ance of the soils will be much higher than down near the power house, so that the given difference of the potential between pipes and rails would be much less serious. This is an important point which should always be considered in the design of insulated nega- tive feeder systems. In considering the need for negative feeder system at the Ohio electric station, it is found that owing to the comparatively small current taken from the tracks east of the substation the tracks alone will have ample carrying capacity up to the corner of Isa- bella and North Streets, providing the tracks of the two railway systems are interconnected, as recommended in the foregoing. In order, however, to facilitate the interchange of current on the nega- tive side and to reduce the potential gradient in the tracks between Isabella and North, and the substation, it is very desirable to run a short feeder directly across South from the Ohio electric sub- station to the Springfield Railway tracks on west Main Street. This feeder will need to carry only about 120 amperes, so that the section should be about 400 000 circular mills. The distance would be about 950 feet, giving a weight of 1 1 50 pounds of copper. In order to make proper use of this and to prevent too large gra- dients in the tracks on North Street, it would be necessary to install a very low resistance tap between the negative bus bar and the North Street tracks at the power house, such as would give a 54 Technologic Papers of the Bureau of Standards drop of potential of about 0.85 volts between the tracks and bus bar. This would probably not require much additional resistance above that possessed by the tap already in use. The total cost of this feeder installed would not exceed about $285. SUMMARY. Reviewing the recommendations in the foregoing report it will be seen from the discussion of the various proposed methods of electrolysis mitigation that those methods which are intended to be applied to the pipe system are regarded as unsatisfactory in general, and particularly so for conditions as they exist in Spring- field. This is the more emphasized by the fact that there are in the pipe systems at Springfield, especially the gas system, a con- siderable number of insulating joints, the gas company, we are informed, having several hundred Dresser couplings scattered throughout its system. So long as these insulated couplings are in place the application of negative feeders to either the gas pipes or the water pipes, or to both, would prove disastrous to the gas system in the vicinity of these insulating couplings. On the other hand, if the system of insulated negative feeders be applied to the tracks as recom- mended in the report so that the potential difference between different parts of the networks are reduced to the comparatively low value, the presence of these insulating joints would be decidedly beneficial, since they would tend still further to reduce the current flow in the pipes, while the potential gradients would be so small that dangerous potential drops across the insulating joints could not arise. The life and property hazard would also be increased by the installation of a system of feeders connected to the pipes, because of the dangers from fires alld explosions already pointed out in this report. After a full consideration of the relative merits of all the different systems available, we strongly recommend that the insulated negative feeder system applied to tracks be adopted as the primary means of electrolysis mitigation in the city of Springfield, and the system hereinabove proposed and worked out in detail is believed to be entirely adequate to take care of the situation for some time Electrolysis Mitigation in Springfield, Ohio 55 to come, and can readily be modified and extended to take care of any situation that may arise as the system grows. It is fm-ther recommended that the joints in all the railway systems operating in the city of Springfield be tested at intervals not exceeding six months or a year, and all joints showing resist- ances exceeding that of 3 feet of rail should be immediately rebonded so as to maintain perfect continuity of the tracks throughout the city. It is also of very great importance to have the railway tracks of the Ohio Electric Co. and the Springfield Railway Co. inter- connected electrically at all crossings, both for the sake of economy of operation and for the safety of the pipe system. To neglect this interconnection, or to deliberately insulate the two systems from each other, would invite certain disaster to the tmderground pipes. It appears from the calculations set forth above that the pro- posed system of insulated track feeder will not only greatly im- prove voltage conditions throughout the entire negative return, but will also bring about large economies in power which will pay large returns on the small investment required for putting the proposed plan into effect. As compared with the arrangement of insulated track feeders that is now in service, the proposed system would give considerably smaller drop on the negative return, which in turn would give a higher average voltage on the cars with consequent improvement in the car service and car lighting. We are confident that this system if properly installed and maintained will prove to be the most effective means of affording permanent relief to the pipe owning companies of Springfield from damage due to stray ciurents from the street railways. Washington, June 19, 19 13. DEPARTMENT OF COMMERCE Technologic Papers OP THE Bureau of Standards S. W. STRATTON, Director No. 32 SPECIAL STUDIES IN ELECTROLYSIS MITIGATION, No. 2 ELECTROLYSIS FROM ELECTRIC RAILWAY CUR- RENTS AND ITS PREVENTION— AN EXPERI- MENTAL TEST ON A SYSTEM OF INSULATED NEGATIVE FEEDERS IN ST. LODIS BY E. B. ROSA, Chief Physicist BURTON McCOLLUM, Associate Physicist and K. H. LOGAN, Assistant Physicist Bureau of Standards [DECEMBER 27, 1913] WASHINGTON GOVERNMENT FEINTING OFFICE 1914 SPECIAL STUDIES IN ELECTROLYSIS MITIGATION NO. 2: ELECTROYSIS FROM ELECTRIC RAILWAY CURRENTS AND ITS PREVENTION— AN EXPERIMENTAL TEST ON A SYSTEM OF INSULATED NEGATIVE FEEDERS IN ST. LOUIS By E. B. Rosa, Burton McColIum, and K. H. Logan I. General Discussion. Introduction. .. . CONTENTS Page 3 3 Purpose and plan of investigation 5 2. Rail Gradients 11 3. Current Flow in Pipes 14 Effect of Pipe Drainage on Current Flow in Pipes 16 4. Potential Differences between Pipes and Rails 20 5. Over-all Potentials 24 6. Significance of Test Data 26 7. Discussion of Costs 27 Comparison of costs of insulated and uninsulated feeder systems as actually installed 27 Comparison of costs of the two systems for the same voltage conditions in both cases 30 8. Applicability of Insulated Feeder Systems to Old Stations 32 9. Summary 33 1. GENERAL DISCUSSION INTRODUCTION In a recent paper * the authors have discussed briefly the rela- tive merits of some of tlie more important possible methods of electrolysis mitigation, and have drawn from that discussion the conclusion that insulated negative feeders should provide an economical and effective means of reducing electrolysis troubles to a practically negligible minimum. This discussion, however, was based mainly on theoretical considerations, and there has been ^Electric Railway Journal, Jan. 3, 1914. 3 4 Technologic Papers of the Bureau of Standards up to the present time an almost complete dearth of quantitative experimental data bearing on the practical working out of systems of this character. While it is true that insulated feeders have been used abroad for many years, they have found no applica- tion in this country until within the last few years, and no compre- hensive experimental data as to their operation has been pub- lished. Moreover, the feeder systems that have been used abroad have for the most part been used in connection with boosters, and the use of insulated feeders has usually been associated with the use of boosters in the minds of most engineers in this country. It is only natural, therefore, that engineers should be. reluctant to install feeder systems of this character in the absence of any experimental data showing their effectiveness for accomplishing the purposes intended. It has, therefore, been necessary, in order to get adequate experimental data bearing on these problems, to install some experimental systems expressly for the pturpose, and work of this sort has already been done in a few places, with the cooperation of electric railway companies. In making these installations localities were selected -where conditions may be considered as normal and fairly representative of average condi- tions in American cities. The systems installed have been designed in accordance with the demands of service conditions, and are, therefore, of such nature that the experimental data obtained in connection with them is of a very practical character. Additional work of this kind is contemplated, and it is hoped through these investigations to accumulate evidence which will establish beyond doubt the practical possibilities of insulated negative feeder systems as a means of taking care of electrolysis troubles. In connection with the general investigations that have been carried out by the Bureau of Standards for the past two or three years a considerable amount of preliminary work was done during the summer of 191 2 in the city of St. Louis, as well as in other places. It was found that conditions in St. Louis were not excep- tional, but that, in common with many other American cities, more or less trouble from electrolysis was experienced, and the tests showed that there was need for improvement in this direc- tion. As a result of these preliminary tests a full report was Test on Insulated Negative Feeder System 5 prepared by the engineers of the Bureau of Standards and sub- mitted to the United Railways Co., of St. Louis. In that report the conditions as to danger from electrolysis were fully set forth, and recommendations were made for removing the cause of the damage. In making these tests the engineers of the Bm-eau of Standards had the active cooperation of the officials of the United Railways Co., who furnished all necessary data in regard to track layout, feeder installations, car schedules, etc., which were required in order to design in detail a suitable system for the transmission of the ciurent and its return to the power stations in a manner to take care of the traffic adequately and at the same time eliminate in a large measure future trouble from electrolysis. Based on these data and the experimental data obtained by the Bureau of Standards a thorough study of the whole situation was made, and the conclusion was arrived at that the best way to take care of electrolysis troubles was through the installation of insulated negative feeders. When this report was submitted to the United Railways Co. an arrangement was made with them for the actual carrying out of the recommendations in the case of one of the substations of the company for the ptirpose of demonstrating the effectiveness of the proposed plan. The work of installing the negative feeders was done by the United Railways Co., and throughout the entire investigation the representatives of the Btu-eau of Standards had the cordial cooperation of the engineers and officials of the com- pany, and the services of several of the company's men to assist in carrying on experimental work. PDRPOSE AND PLAN OF INVESTIGATIONS The purpose of the test was twofold — first, to demonstrate the effectiveness of the insulated retiurn feeder system as a means of mitigating electrolysis troubles; and, second, to determine the relative cost of securing equally good electrolysis conditions by the use of insulated and uninsulated negative feeders. In order to obtain data on the relative merits of the uninsulated and insulated systems it was necessary to install a system of negative feeders complete and in such a way that they could be converted into an 6 Technologic Papers of the Bureau of Standards insulated or uninsulated feeder system at will. Since the negative feeders of the substation selected for the test were on poles or in fiber ducts, this could readily be accomplished by tying the bus bar to the tracks near the power house for the uninsulated system and removing such ties and inserting suitable resistance taps for the insulated system. In both cases the feeders themselves were insulated from the tracks between the point at which they were tied into the tracks and the bus bar, but since in the uninsulated system the feeders were at the same potential as the tracks at both ends, the potential drops on the feeders were, of cotuse, the same as the potential drops on the tracks which they parallel, and hence electrical con- ditions were substantially the same as they would be if the feeders had been uninsulated, and the relative electrolysis conditions and costs would also be identical. In the present case the tests were first made on the uninsulated feeder system ; then suitable resist- ance taps were placed at the power house and at certain points out on the line to give proper distribution of current between the feeders, and the tests were repeated to show the change in conditions. A complete record of both of these series of tests is given below. The station selected for this experimental investigation was the new Ann Avenue substation, located at the corner of Mississippi and Ann avenues. The rated capacity of this station is 4000 kilowatts at the present time, and the peak load (average for one hour) was at the time the tests were made about 7540 amperes. The average load for 24 hours was 3500 amperes, giving a load factor of about 46 per cent. It will therefore be seen that condi- tions at this station as regards size and character of the load are fairly representative of average conditions in a moderate-sized city substation. The track networlf, in the district fed by the sta- tion is shown in Figs, i and 2. These show that only one single track passes immediately by the station, and another single track passes along the street one block to the east. This is therefore an unfavorable location with respect to returning the ciurent to the station, because the cross section of rails approaching the station is unusually small. However, this was not the governing factor in determining the location of this station. On this account a Kg. l.-Original , feeder system. Ann Avenue district Bg-2 ^Insulated negate * ■ system, Ann Aveme district Test on Insulated Negative Feeder System 7 relatively large amount of copper would have to be installed in any case, whether the insulated or uninsulated system be used, and therefore the cost of returning current to this station, per kilo- watt of capacity, would be expected to be considerably higher than the average, and this fact makes the test of the insulated system a more severe one from the economic standpoint, although it has no appreciable bearing on the effectiveness of the system in reducing electrolysis troubles. The station in question is a new station which was just nearing completion at the time arrangements were made for the proposed tests. A considerable amount of negative copper was already in place, and in designing the proposed insulated feeder system this copper was allowed to remain; extensions were made where neces- sary and the ctirrent distribution was adjusted by means of resist- ance taps. The cross-sectional area of the feeders is not, there- fore, just as it would have been if a new insulated feeder system had been installed throughout ; and this also tends to make the cost run somewhat higher than would otherwise have been the case. The original feeder layout designed by the engineers of the United Railways Co. for the negative return is shown in Fig. i, and the system as finally completed for the insulated feeder layout is shown in Fig. 2. An examination of these two figvires shows that changes were made in three cases. In one case a feeder of i 000 000 circular mils cross section had been designed to run from the negative bus eastward along Ann Avenue and tied to the tracks at both Eighteenth Street and Ann Avenue and Twelfth Street and Ann Avenue. The change made here was merely to remove the tie at Eighteenth Street and Ann Avenue and install a pair of 0000 cables running directly from the tracks at Eighteenth Street and Ann Avenue to the bus bar, thus giving two separate feeders to those two points instead of one common feeder. The length of each of these 0000 feeders was about 760 feet. A second change will be noted on Gravois Avenue. The original feeder layout contemplated running one feeder of i 000 000 cir- cular mils to Victor Street and Gravois Avenue, and another to Jef- erson and Gravois avenues. The feeder at Jefferson and Gravois avenues was allowed to remain, but the feeder running to Victor 29786°— 14 2 8 Technologic Papers of the Bureau of Standards Street was cut loose from the tracks at this point and extended to CaUfomia and Gravois avenues, a distance of about 2300 feet. The third extension was in one of the feeders running north on Mississippi Avenue. The original plan contemplated running one I 000 000 circular mil cable to Mississippi and Gayer avenues and a similar cable to Mississippi and Lafayette avenues. A resistance was put in series with the feeder extending to Geyer Avenue, and the Lafayette Avenue feeder was extended to Lafay- ette Avenue and Grattan Street, and a resistance was inserted in the tap to Mississippi and Lafayette avenues. The amount of copper added in extending the feeder from Mississippi Avenue to Grattan Street was 1300 feet of i 000 000 circular mil cable. The total weight of copper added in the three places was therefore about 1 2 1 1 3 pounds. The original plan called for the installation, in addition to the above-mentioned feeders, of a i 000 000 circular mil cable running east on Ann Avenue to Ninth Street, a distance of 2900 feet, and two i 000 000 circular mil feeders running east from the power house along Ann Avenue to Broadway, a distance of 3800 feet. The total weight of copper under the original plan would have been 60 100 pounds, all of it in i 000 000 circular mil cables, while in the system as actually completed there were, as is shown later, 72 213 pounds of copper, all of which was of I 000 000 circular mils cross section except the two short 0000 feeders running to Eighteenth Street and Ann Avenue. The excess cost of the actual system over that of the original system was about $3147, exclusive of the cost of the resistances which is negligible, figuring the cost of overhead feeders at $750 per 1000 feet of I 000 000 circular mil cable installed. All of the additional feeders were installed overhead, except the two 0000 cables, which were in fiber conduit. The cost of the latter feeder is figured at $1400 per 1000 feet of million circillar mils of cable. In designing these extensions the object was to reduce the potential gradient in the rail retiurn at all points of the system to a value not exceeding i volt per 1000 feet, average for one hour at peak load, which at 46 per cent load factor would correspond to an average of about 0.46 volt per 1000 feet during the 24-hour period. In making the tests the system was first arranged as an uninsulated feeder system by tying the tracks at Mississippi and Ann avenues Test on Insulated Negative Feeder System 9 and Eighteenth Street and Ann Avenue as directly to the bus-bar as the connecting cables would permit. A complete electrical sur- vey was then made to determine the electrical conditions existing in the negative return and pipe systems. These measurements include the following : 1. Rail-Gradient Measurements.— th&se. for convenience com- prised measurements with a millivoltmeter of the drop of potential on a fixed length of 4 feet of rail, the measurements on all the rails on any particular street being taken at each point. This method involves the assumption that all joints are as good as equivalent length of rail. Numerous preliminary tests of joints were made to determine the condition of the joints and all bad joints found were repaired before final measurements were begun. 2. Current Flow in Pipes, Including Both Gas and Water Mains. — For this pvtrpose excavations were made at a number of points and rubber-covered leads were fastened to the pipes 4 feet apart, the leads being brought underground to service boxes located inside the curb. These points were for the most part located within a half- mile of the station. Meastirements of the millivolts drop on the pipe at these points permit the calculation of the actual value of the ciurent flow in the pipes at those points, the size and kind of pipe being known. In addition to these, potential meastuements were made between adjacent fire plugs at a number of outlying points considerably beyond the terminals of the feeders. While these do not permit the calculation of the actual current flow in those localities the ilieasurements taken under the insulated and uninsulated systems gave values proportional to the current flow under the two conditions, and thus afford a means of determining the relative ctirrent flow in the two cases. 3. Potential Difference Measurements Between Pipes and Rails. — These measurements were taken throughout a large part of the area affected by the station, including a considerable portion of the region where the pipes were negative to the rails, in order that any tendency of the insulated feeder system to extend the positive area could be determined. 4. Over-all Potential Measurements. — These measm-ements were made between a point on the rails adjoining the power house and a number of remote points near the extreme limits of the feeding districts. These measurements were made with the. cooperation lo Technologic Papers of the Bureau of Standards of the Kinloch Telephone Co., which connected the telephone wires to the points at which potential measurements were desired, so that the measurements could all be made at the telephone exchange. 5. Current in the Various Feeders. — These data were taken in order to determine the correctness of the current distribution and the economy with which the copper was being worked in the different parts of the system. After all of the above measiurements were completed the sys- tem was converted into an insulated feeder system, as mentioned above, and the same measurements repeated at the same points. In taking the electrical measurements at any one point the readings were taken every 1 5 seconds for a period varying from 5 to 1 5 min- utes, according to local conditions, and the average of all these readings is taken as the reading at that particular time of day. Since readings at different points were necessarily taken at differ- ent hours of the day, when the station load differed, the readings as observed are not directly comparable, and in order to get a basis on which the readings under different conditions could be directly compared it was found most satisfactory to reduce all the readings to the average 24-hour values. This was done by dividing the average observed reading at any point by the ratio of the station load at that particular time of day to the 24-hour average station load. It is this reduced 24-hour average value that is recorded in the tables in each instance. Careful study of a large amount of test data shows that this affords a very satisfactory basis of comparison. In converting to the insulated feeder system, the different exten- sions outlined in detail above were installed and the feeders were adjusted for approximately equal drop by the insertion of suitable resistances where necessary. The ftumber and location of these resistances are shown in Fig. 2, which gives the final layout of the insulated feeders. It will here be seen that there are three resistances at the substation in the cables running to the tracks at Mississippi and Ann avenues. Eighteenth Street and Ann Avenue, and Twelfth Street and Ann Avenue. There is also a resistance in the feeder running north on Mississippi Avenue to Mississippi and Geyer avenues, the resistance being at the outer end of the feeder. The feeder running north on Mississippi Ave- Test on Insulated Negative Feeder System ii nue to Lafayette Avenue is connected to the tracks at Lafayette and Mississippi avenues through a resistance tap designed to give about 4 volts drop at peak load. There is also a resistance tap at Ann Avenue and Ninth Street. This is not, however, in series with any feeder, but is connected between the feeder which is connected to the tracks at Ninth Street and the two feeders which run on to Broadway. It, therefore, affords a certain measure of paralleling between these feeders. A comparison of the measurements taken under the insulated and uninsulated feeder systems shows clearly the relative danger from electrolysis under the two systems. Although the amount of copper in the feeder systems under these two series of tests is not the same in each case, the difference was not great enough to pro- duce any marked change in electrolysis conditions under the uninsulated feeder system. This was shown in advance by careful calculations and was borne out by experimental data obtained later, so that although some copper was added for the insulated feeder system, such copper, because of its outlying location, would have exerted practically no influence when used in connection with the uninsulated system. The results show the changes due to conversion from an uninsulated to an insulated system with substantially the same amount of copper. 2. RAIL GRADIENTS In determining the rail gradients measurements were taken on a fixed length of 4 feet of rail. The points for measurement were selected so as to give the maximum gradients that existed in each case. This means that gradient measurements were taken on all sides of each point at which a negative cable was tapped to the tracks under both the insulated and uninsulated feeder systems. It is obvious that at more remote points the gradients tend to become less than the values recorded at these places, except under very special conditions, which did not exist in this installation. The value of these rail gradients consists chiefly in that they per- mitted the determination of whether or not the gradients calculated in advance had been approximately realized, and they also afforded a definite indication as to the condition of the track. Since the gradients were measured on all of the rails on a given street, if the tracks were in good condition and properly cross bonded, the 12 Technologic Papers of the Bureau of Standards rail-gradient measurements should be substantially equal on all of the rails. If, however, there was a marked difference in gradients on different rails, it indicated that the current was not equally- distributed between the rails, which in turn indicated a bad con- dition of the joints somewhere in the vicinity. The latter was found actually to be the case, and it was necessary to make a considerable number of repairs of the track before satisfactory conditions were finally realized. The location of the points at which potential gradient measurements were taken, and also the values obtained under both the insulated and uninsulated systems, are shown in Table i . TABLE 1 Rail Gradients Uninsulated feeders Direction of flow Gradient volts per 1000 feet Insulated feeders Direction of flow Gradient volts per 1000 feei Grattan north of Lafayette Lafayette east of Grattan Lafayette west of Grattan Lafayette east of Mississippi. . . Lafayette west of Mississippi. . Mississippi north of Lafayette. . Mississippi south of Lafayette. . Mississippi south of Geyer Geyer east of Mississippi Geyer west of Mississippi Mississippi south of Ann Gravois south of Victor Victor east of Gravois , Gravois west of Jefferson Jefierson north of Gravois JeffersonsouthofGravois Gravois west of California California north of Gravois California south of Gravois Broadway north of Aim Broadway south of Ann Ninth north of Ann Ninth south of Ann Twelfth north of Ann Twelfth south of Ann Eighteenth north of Ann Eighteenth south of Ann West.. East... South.. South.. South.. West.. East... North.. North.. East... East... South. North.. 1.90 0.16 0.90 1.87 2.89 0.91 1.17 1.35 1.77 0.29 0.98 0.69 0.44 South.. North.. South-. North.. South.. North.. South- North.. Average. 0.59 0.35 0.69 0.14 0.33 0.80 0.60 0.75 0.93 South 0.47 West. 0.15 West 0.34 West 0.59 East 0.48 South 0.72 South 0.75 South 0.57 West . . 0. 29 West 0.60 North.... 0.21 North 0.17 East 0.03 South 0.68 North.. . 0.22 East 0.59 South 0.33 North 0.15 South North 0.90 South.... 1.28 North 39 South.... 0.25 North 0.30 South.... 0.80 North. .. 43 0.46 Test on Insulated Negative Feeder System 13 By comparing the figures point by point in the columns show- ing average gradients under each system we get the effect pro- duced by the change from uninsulated to insulated feeders. An examination of these columns shows that in many places the gra- dients have been greatly reduced, this being particularly true in the region near the power house where the gradients were rather high under the uninsulated system. It will be noted that there is but one point which shows a potential gradient greater than i volt per 1000 feet under the insulated feeder system, whereas the average of all points is but 0.46 of a volt. Since the station-load factor is about 46 per cent, this means that the average potential gradient at peak load is almost exactly i volt, and most of the readings will not vary much from this mean value. These figures show that the in- stallation of the insulated return feeder system has substantially fulfilled the conditions that it was designed to .accomplish in the way of potential gradients, in that the mean value at peak load does not exceed the calculated value of i volt per 1000 feet. Under the uninsulated feeder system, however, there are a con- siderable number of readings which run above i volt average, the highest being 2.89 volts per 1000 feet, which corresponds to a peak-load value of about 6.2 volts per 1000 feet. The average for all points under the uninsulated feeder system is 0.93 volt for the 24-hour period, which corresponds to a mean value of 2 volts during peak load. "While it is important that rail gradients should be kept low, this figure is only of indirect importance, since low gradients in gen- eral mean small leakage and consequently reduced current flow on the pipes. Of even greater importance, however, than low gradients is the direction of the gradient. Under the tminsulated feeder system this gradient is necessarily continuous from the out- lying districts clear into the power house; whereas, under the insulated feeder system, the current flow can, if desired, be made to flow from all directions toward the points of tap of the insu- lated feeders to the rails, and since these points are- distributed through a considerable portion of the feeding area, the direction of current flow in the rails can be frequently reversed, so that the gradient in any one direction will extend over only a compara- 1 4 Technologic Papers of the Bureau of Standards lively short distance, and hence large differences of potential be- tween different points in the earth can not be set up. It will be evident, therefore, that the improvement in electro- lysis conditions caused by the installation of insulated feeders will in general be much greater than the ratio of reduction of the rail gradients. This is borne out in a very marked manner by the data given below. 3. CURRENT FLOW IN PIPES One of the best criteria for determining the relative amounts of damage from electrolysis under different conditions of track return is afforded by determining the current flow in the pipes. Since, as in the present case, where there were no metallic connec- tions to pipes, all the current flow carried by the pipes must ulti- mately be discharged into the earth, the total amount of electroly- sis will be approximately proportional to the current flow on the pipes. Table 2 shows the current flow, as measured at a number of points tmder the insulated and uninsulated feeder systems. The ctirrents in all cases were calculated from measurements of milli- volt drop on a 4-foot length of pipe, the resistance of the pipe being determined from the size and kind of pipe and known con- stants as determined from numerous laboratory tests. This method of determining ciurrent in the pipes, while not strictly accurate, because of variations in the kind and weight of the pipes, has, nevertheless, been shown to be sufficiently accurate for most practical purposes when used with care. Referring to Table 2, the first column, headed " Location," gives the points at which current measurements were made; the second coltmm, headed " Size of pipe," gives the diameter in inches of the pipe on which the cimrent was mensured, and in each case this figtue is followed by the letter W or G, indicating whether the pipe was a gas or water main. In the third and fourth columns the cm-rent flow average for the 24-hour period is given for the two systems. Test on Insulated Negative Feeder System TABLE 2 Current in Gas and Water Pipes. Not Drained 15 Location Size of pipe, inches Uninsu- lated system Current In amperes Insulated system Russell, west of Thirteenth Russell, west of Mississippi Ann, west of Twelfth Ann, west of Eighteenth Ann, east of Mississippi Ann, east of McNair Ann, east of McNaii Gravois, west of Eighteenth Gravois, west of Shenandoah Shenandoah, west of Thirteenth. . Shenandoah, east of McNair Ljmch, west of Indiana Eighteenth, north of Shenandoah. Eighteenth, north of Victor Lemp, north of Victor Mississippi, south of Lafayette Mississippi, south of Allen Mississippi, south of Russell Mississippi, south of Ann Salena, north of Shenandoah Salena, north of Victor SOW 6W 4G 6W 4G 6W 4G 6W 4G 20 W 20 W 66 6W 20 W 6G 6G 20 W 20 W 20 W 20 W 6W 46.80 0.60 0.16 3.24 6.93 2.35 0.17 11.80 0.08 9.42 43.10 0.15 6.97 23.40 O.U 0.06 1.40 56.40 19.60 40.20 0.31 3.78 0.00 0.17 1.86 2.16 0.05 0.03 1.63 0.03 0.62 12.50 O.U 3.62 7.48 0.05 0.03 1.70 19.30 3.06 7.02 0.10 Total. , 273. 25 65.30 An examination of the columns headed. "Current in amperes" shov7S that there has been a very marked reduction in the current flow in practically all cases. The general average ratio of reduc- tion is best determined by summing up the total current flow in the pipes at all points and determining the ratio of these total currents under the insulated and uninsulated systems. It will be seen from these figures that the total current flow at all observation points under the uninsulated feeder system was 273.3 amperes, whereas the corresponding figure under the insulated feeder system was 65.3 amperes, which gives an average ratio of reduction of about 4.2 to I. This represents the average reduction in the rate of electrolytic corrosion throughout the system, as indicated by these 29786°— 14— 3 1 6 Technologic Papers of the Bureau of Standards measurements. In some localities, particularly near the power station, the reduction will be greater than this, whereas in the more remote districts it will be correspondingly less, but these figures may be taken as a fair indication of the general improve- ment that is effected by the insulation of the feeders. EFFECT OF PIPE DRAINAGE ON CURRENT FLOW IN PIPES While no attempt was made in the present investigation to install a complete pipe-drainage system, it was deemed worth while to temporarily tie in the pipes at points near the station in order to determine the effect of such tying in on the general magnitude of current flow in the pipes, and particularly the relative increase of current produced by such tying in under the insulated and tminsulated feeder systems. For this purpose temporary ties between the water and gas pipes at Mississippi and Ann Avenues and the tracks were installed, and likewise a direct tie between the water pipes and tracks at Twelfth Street and Ann Avenue was installed. Measurements of current flow at the same places as shown in Table 2 were made with the pipes thus tied in and with the feeders insulated and uninsulated from the ground. The results of these measurements are shown in Table 3 . Here the columns have the same significance as in Table 2, the columns 3 and 4 repre- senting the ciurents in the pipes under the uninsulated and in- sulated feeder systems, respectively. It will be seen by com- paring these figures with those of Table 2 that there has in general been a marked increase in current flow in the pipes, and this is particularly true in the case of the uninsulated system. The sum of all the currents at different points of measurement is 844 amperes for the uninsulated system and 84.8 amperes imder the insulated system, showing^ that under these conditions of tying in the current flow in the uninsulated system is, on the average, about 10 times as great as under the insulated feeder system. It will also be observed by comparing the totals of Table 2 with those of Table 3 that the tying in of the pipes with the uninsulated feeder system causes an increase in the current flow in the ratio of about 3.1 to i, whereas under the insulated feeder system the increase in current due to tying the pipes in is increased only in the ratio of 1.3 to i. Test on Insulated Negative Feeder System TABLE 3 Current in Gas and Water Pipes. Pipes Drained 17 Size of pipe, inches Uninsu- lated system Current in amperes Insulated system Huasell, west of Thirteentli Russell, west of Mississippi Ann, west of Twelfth Ann, west of Eighteenth Ann, east of Mississippi Ann, east of McNair Gravois, west of Eighteenth Ann, east of McNair Giavois, west of Shenandoah Shenandoah, west of Thirteenth. . Shenandoah, east of McNair Lynch, west of Indiana Eighteenth, north of Shenandoah. Eighteenth, north of Victor Lemp, north of Victor Mississippi, south of Lafayette Mississippi, south of Allen Mississippi, south of Russell Mississippi, south of Ann Salena, north of Shenandoah Salena, north of Victor 30 W 6W 4G 6W 4G 6W 6W 4G 4G 20 W 20 W 6G 6W 20 W 6G eG 20 W 20 W 20 W 20 W 6W 108.00 4.90 0.24 5.04 9.20 4.79 21.63 0.34 0.30 8.82 83.00 0.11 9.26 42.80 0.10 0.11 8.17 301.00 105.40 128.40 2. 55 5.02 0.71 0.32 3.15 3.53 0.05 1.98 0.35 0.08 2.20 20.60 0.11 3.37 2.57 0.05 0.05 1.20 22.20 6.94 10.23 0.11 Total. , 844. 16 84.82 This shows that the tying in of the pipes has a much smaller tendency to increase the current flow in the case of insulated feed- ers than it has in the case of uninsulated feeders. The total cur- rent flow with the pipes tied in under the insulated-feeder system is only 84.8 amperes, whereas the ctirrent flow under the uninsu- lated system with the pipes not tied in is 273 amperes, which means that draining the pipes at these two points under the insu- lated-feeder system results in only thirty-one per cent as much current flowing in the pipes as the flow in the pipes without such drainage under the uninsulated-feeder system. . These various ratios are summarized in Table 4 and show in a very striking manner the marked reduction in current flow that in every case accompanies the insulated-feeder system, and they 1 8 Technologic Papers of the Bureau of Standards form an excellent illustration of the value of the insulated feeders as against the uninsulated-feeder systems as a means of reducing electrolysis trouble. ' TABLE 4 Summary of Current in Pipes and Current Flow Ratios CURRENT IN PIPES Amperee Uninsulated system, pipes drained, total current 844. 1 Uninsulated system, pipes not drained, total current 273. 2 Insulated system, pipes drained, total current , 84.8 Insulated system, pipes not drained, total current 65.3 CURRENT FLOW RATIOS Pipes not Pipes drained drained With insulated feeders 65.3 84.8 = ■ = 0. 239 = 0. 101 With uninsulated feeders 273. 2 844. 1 Insulated Uninsulated feeders feeders With pipes drained 84. 8 844. 1 = = 1. 30 = 3. 09 With pipes not drained 65. 3 273. 2 Insulated feeders, drained pipes 84. 8 - = 0. 31 Uninsulated feeders, pipes not drained 273. 2 The above figures show the current flow in the pipes in the region within approximately a quarter of a mile radius of the power station. It was deemed advisable also to determine the relative current flow under the different conditions at points more remote from the power house, and for this purpose, in order to avoid the labor of additional excavations, potential measure- ments were made between adjacent fire hydrants at suitable places, the potential differences under the insulated and uninsu- lated systems being taken as representing the relative cmrent flow in the two cases. Under each feeder systefn also these measure- ments were taken with the pipes diftined at the two points men- tioned above near the station, and also with the pipes not drained, so as to show the tendency, if any existed, of pipe drainage to increase current flow in the pipes at very remote points. These data are given in Table 5. Test on Insulated Negative Feeder System TABLE 5 Potential Differences Between Fire Plugs 19 Location Average volts From— To— Uninsulated feeders Insulated feeders On— Pipes not drained Pipes drained Pipes not drained Pipes drained Kennett Allen Sidney Menard Jefferson Indiana Lynch Lafayette. ... Geyer Victor Eleventh.... Indiana Missouri Sidney 0.685 .211 .646 .320 .132 .394 .156 0.908 .425 .735 .624 .308 .648 .333 0.042 .150 .229 .159 .060 .159 .001 0.C59 .137 260 Gravois Ann 023 219 McNair .007 Total 2.544 3.983 O.80O POTENTIAL DIFFERENCE RATIOS With insulated feeders With uninsulated feeders With pipes drained With pipes not drained Insulated feeders, drained pipes Uninsulated feeders, pipes not drained Pipes not drained Pipes drained 0.800 - - 0. 314 2.544 0.913 - 0. 229 3.983 Uninsulated Insulated feeders feeders 3.983 = - 1. 56 2.544 0.913 = 1. 14 0.800 0.913 = = 0. 359 2.544 In this table are shown the voltage drops between hydrants, under both the insulated and uninsulated feeder systems, and under each system are shown also the voltage drops with the pipes drained and not drained. The ratio of the sums of the voltage drops with the insulated and uninsulated systems is 0.3 14 with the pipes not drained. Under pipe drainage the difference is still more marked, the ratio of the sums of the volt drops being here only 0.229. With the insulated feeder systems the ratio of current flow with the pipes drained and not drained is 1.14. With the uninsulated feeder system the ratio is i .56, indicating that even in these more remote points the current flow shows a marked increase when the pipes are tied in, but that this increase is much less marked in the case of the insulated feeder system than it is in the case of the uninsulated feeder system. The last ratio given in 20 Technologic Papers of the Bureau of Standards the summary of Table 5 also shows that at these outlying points the current flow in the pipes, under the insulated feeder system combined with pipe drainage at the points near the power house, is but little over a third of the current flow without pipe drainage under iminsulated feeder systems. We wish to emphasize here the fact that in making the above tests with the pipes tied in, no attempt was made to install a scientific pipe drainage system with a view of obtaining minimum current flow in the pipes. If this had been done, the current flow under pipe drainage could no doubt have been materially reduced, particularly at points near the power house, but such reduction would not have occurred in the outlying points referred to under Table 5. The results as presented, however, while they do not show conditions that would exist under an ideal pipe drainage system, show, nevertheless, the tendencies which exist, and that conditions in regard to cmrent flow in the pipes are invariably much better under the insulated feeder system than under the uninsulated system. One point of special interest in connection with the data on ctu- rent flow in the pipes should be mentioned here. By reference to Tables 2 and 3 it will be noted that those points marked Win column 2, indicating water mains, show in general a much higher current flow than the points marked G, which indicate gas mains. The reason for this is that the gas mains in this vicinity have a con- siderable number of cement joints, and this undoubtedly is re- sponsible for the comparatively low current flow. It is probable that those points which show almost no cmrent flow are sections which contain cement joints, whereas those points that show small yet appreciable current flow are older and lead- jointed sec- tions, since both kinds are known to exist in this territory. 4. POTENTIAL DIFFERENCES BETWEEN PIPES AND RAILS Another criterion for determining the relative danger to pipes under different conditions is the potential differences between pipes and rails. Such measurements do not give altogether reliable indications as to relative danger when made in different localities, because of differences in soil resistance and other local conditions, but when such measurements are made at the same Test on Insulated Negative Feeder System 21 points under different physical conditions of the negative return the values afiford an accurate measture of the relative danger from electrolysis. Such potential difference measurements were, there- fore, made between fire hydrants and rails at a considerable number of points under both the insulated and uninsulated feeder systems, and the results are given in Table 6. TABLE 6 Potential Differences Between Pipes and Rails A. POTENTIALS ORIGINALLY OVER ONE VOLT Potential difference Location Potential difierence Location Uninsulated system Insulated system Uninsulated system Insulated system Twelfth and Russell... Eighteenth and Geyer. . Eighteenth and Allen. . . Eighteenth and Russell. Eighteenth and Ann Eighteenth and Shen- 1.80 1.38 2.02 3.00 2.15 2.02 1.69 2.63 0.70 0.29 0.67 0.24 0.08 0.70 0.55 0.86 Mississippi and Allen. . Mississippi and Russell. Mississippi and Gravois. Gravoig and McNair Gravois and Victor McNair and Geyer Average 3.45 4.22 3.60 3.20 1.13 1.91 0.37 0.17 0.16 -0.84 0.53 0.15 2.44 0.33 Eighteenth and Victor.. Mississippi and Geyer. . Ratio of average values=7.4. B. POTENTIALS ORIGINALLY LESS THAN ONE VOLT Ninth and Lafayette Twelfth and Shenan- 0.62 0.56 0.25 0.38 0.69 0.62 0.71 0.02 0.59 0.30 0.05 0.25 0.37 0.35 McNair and Victor Salena and Victor Jefferson and Lafayette. . Jefferson and Geyer Jefferson and Aim Jefferson and Gravois.. . Jeff erson and Pestalozzi. Average decrease . . 0.94 0.71 0.22 0.06 0.00 0.77 0.39 0.52 0.40 -0.01 Grattan and Lafayette. . . Eighteenth and Lafay- ette -0.04 —0.01 0.77 Eighteenth and Sidney. . 0.32 Mississippi and Lafay- ette 0.49 0.28 Lemp and Victor Ratio of average values=1.75. C. POTENTIALS ORIGINALLY NEGATIVE Broadway and Victor. . . Broadway and Russell. . Ninth and Russell -0.70 -0.01 -0.23 -0.33 -0.37 +0.48 +0.80 +0.80 +0.62 +0.33 Grattan and Park California and Geyer California and Gravois. . -0.51 -0.01 -0.33 +0.35 +0.29 +0.84 Ninth and Victor -0.31 Eleventh and Park 22 Technologic Papers of the Bureau of Standards An examination of these data reveals that for the most part there has been a marked reduction in potential differences, par- ticularly in the region near the power house where such potential differences were originally high. In order to facilitate the inter- pretation of these data they have been divided into three groups with subheads A, B, and C. The data for all points at which original potential differences were greater than i volt are placed in group A ; all those at which the pipes were positive but less than I volt are placed in group B ; and all those points at which the pipes were originally negative but have become somewhat positive under the insulated feeder system are placed in group C. On examination of group A, which includes the points of high original potential and therefore covers the area in which the original danger was greatest and the need for improvement most urgent, we find that there has been a very large reduction of potential differences between pipes and rails. In one case, notably at Gravois and McNair avenues, where the pipes were originally strongly positive to rails, they have become slightly negative, and in all the other points in this group a marked re- duction is apparent. The average potential difference at all points tmder the uninsulated system was 2.44 volts, whereas under the insulated feeder system this average was reduced to 0.33 volt, giv- ing a mean ratio of reduction of 7.4 to i. Referring to group B, where the original potential differences were less than i volt, we find there is still a very considerable reduction. The average for all of these points is 0.49 volt, whereas the average for the corresponding points under the insulated feeder system is 0.28 volt, giving a ratio of reduction of 1.75 to I. Even here, in the intermediate region, where the danger was comparatively small under the original conditions, there has still been a considerable improvement, the average value of 0.28 volt being so small as not to involve any considerable danger to the pipes. In group C we find that eight points which were originally negative have become more or less positive. This is to be expected in general because of the tendency to form positive areas in the region near the points where the negative feeders are tied to the Test on Insulated Negative Feeder System 23 track. At these eight points there existed originally a mean value of potential difference of —0.31 volt, whereas under the insulated feeder system this has been converted into a mean value of +0.56 volt. In the more remote districts the potential differences were negative under both insulated and uninsulated systems, and are therefore of no consequence here. These data show that under the insulated feeder system the reduction of danger is greatest at those points where there is greatest need for improvement, and the foregoing figures indicate very clearly that in the present instance the potential differences have been reduced to so low a value as to make the pipes com- paratively safe. They also show that although the installation of a negative feeder system does tend to increase the area of the positive zone the positive potentials are so low as to lead to no serious consequences. One of the principal objections to the installation of insulated negative feeders that has been urged by some engineers has been that it creates a large number of positive areas covering a much greater territory than is the case with the ordinary uninsulated system. Although it is true that there is a tendency for the insulated feeder system to extend the positive area, and this is clearly indicated by the foregoing data, these data nevertheless show that comparatively few new positive points have been created, and that where they have appeared, the potential differences are so low as not to give rise to any serious corrosion of the pipes under ordinary conditions. The figures show conclusively that this objection to the insulated negative feeder system is not valid, at least in the present case, whereas the reduction of the potential differences in the regions where the conditions were originally bad is so great as to completely over- shadow the effects of the slight tendency to broaden the positive zone. All of the foregoing potential difference measurements were taken between water pipes and rails because of the greater con- venience of making such measurements, since meastirements could be taken between fire hydrants and tracks. In order to determine whether or not the potential differences between gas pipes and the tracks differed materially from the corresponding 24 Technologic Papers of the Bureau of Standards voltages between water pipes and rails, a considerable number of measurements were taken between water and gas mains at ac- cessible places. These measturements are shown in Table 7. These figiures show that potential differences between water and gas mains are in nearly all cases very low, the maximum observed anywhere being 0.56 volt average for the 24-hour period, and the great majority being much smaller than that figure, the mean of all the measurements taken being 0.147 volts average for 24 hours. These figiu-es show that potential differences between the gas pipes and rails are not much different from the values observed and recorded above for the water pipes. TABLE 7 Potential Differences Between Water and Gas Pipes ^ Location Uninsu- lated feeders, average volts Location Uninsu- lated feeders, average volts 0.00 0.05 0.05 0.27 0.17 0.02 0.16 0.09 0.16 0.44 0.56 0.21 Eighteenth and Russell Gravois and Victor 22 Eighteenth and Victor MrNnir HTid Allen 04 I,/ ^|HKB^nHH|PpK/ \- ^HH 5.--.-- '-" ■ '■ - Ibk i; ' C J, 'f r '- n Hfti^taK, im^g i IP Fig. I. — Example of elect lolylic corrosion Fig. j. — Example of self corrosion Electrolysis Mitigation 1 1 of the iron itself, or due to differences in the electrolyte in the soil near to adjacent portions of the iron surface. Unfortunately, self-corrosion generally manifests itself in a manner very similar to that caused by stray currents. This is shown quite clearly in Fig. 2, which is a photograph of two pieces of cast-iron pipe corroded under conditions such that no stray currents could exist. It will be seen that the pipe exhibits pitting very similar to that caused by electrolytic corrosion. Be- cause of this similarity in appearance it is not possible in general to determine by inspection of a corroded pipe whether or not the corrosion was caused by stray currents or by local galvanic action. Owing to this fact it not infrequently happens that cases of pipe corrosion are charged to the railway companies when the damage was actually due to local causes arising from the nature of the soil or of the pipe, or both. The only sure way of determining whether or not stray currents are causing corrosion in any particular case is by making proper electrical tests to determine whether or not the pipes are actually discharging current into the earth. In a case where serious cor- rosion has been caused by stray currents and the cause of these stray cturents later removed, the only certain way of determining whether or not the previous corrosion was caused by stray cur- rents or by local influences is by making actual corrosion tests in the soil under the same average conditions of moisture and using the same kind of iron as was previously found corroded. In the absence of a test of this kind it is not possible to fix with cer- tainty the cause of the damage. 4. TROUBLES FROM STRAY CURRENTS OTHER THAN CORROSION While it is no doubt true that by far the greater portion of damage caused by stray cturents takes the form of corrosion of underground pipes and cables there are certain other dangers resulting from these stray cturents that deserve consideration. Among these may be mentioned overheating of pipes in buildings due to the flow of excessively heavy currents therein. Cases of this kind have been brought to otir attention in which service pipes and their connections have been heated to a red heat by stray railway currents flowing through them, and where lead service 12 Technologic Papers of the Bureau of Standards pipes have been melted off. Such extreme cases are of course rare, but when they do occur the fire hazard accompanying them may at times be serious. Another danger from the presence of stray currents on pipes is that due to the possibiUty of explosion of gases. Wherever any considerable amount of stray current is found on a gas pipe it is necessary to bond around any contemplated break in the continuity of the pipe, otherwise the arc which would occur be- tween the pipe sections when disconnected would be likely to ignite escaping gas with possibly serious consequences. These various dangers will be referred to again later. 5. ELECTROLYSIS IN CONCRETE AND IN STEEL BUILDINGS i (a) Anode effects. — Diuring the last few years it has been observed that when an electric current flows through reinforced concrete certain effects are produced which may result in the destruction of the concrete structure. The first of these to be observed is known as the anode effect, first described by A. A. Knudson,^ which occtu-s under certain circumstances when current passes from the reinforcing material out into the concrete. The action here is essentially the same as when current is discharged from a pipe into the earth, namely, the surface of the iron is corroded; but the effects of this case are even more serious than in the cor- rosion of pipes because of the secondary actions which take place. As soon as iron is carried into solution by the electric ciuxent it comes in contact with oxygen in the concrete and there is formed a precipitate of iron ojiide. This occupies a volume of about 2.2 times the volume of the original iron, and there results a swelling action which in time may become sufficient to split even very large masses of concrete. The character of the results of this action are shown in Fig. 3, which shows a block of concrete with an embedded iron electrode which has been exposed for some time to the flow of ciurent from the iron mto the concrete. It is very important from the practical standpoint to bear in mind, however, that the disastrous results shown in Fig. 3 occur only tmder special conditions which are not likely to be frequently 1 iFor a full discussion of the subject of electrolysis in reinforced concrete, see Technologic Paper No. i8 of the Bureau of Standards. 2 Electrolytic Corrosion of Iron and Steel in Concrete, trans. A. I. E. E., Vol. 26, p. 231, 1907. Bureau of Standards Technologic Paper No. 52 Fig. 3. — A node cf/vcl in coiicrcic ]''iG. 4. — Callwdc effect in concrete Electrolysis Mitigation 13 encovintered in actual practice. Extensive investigations have shown that in the case of ordinary concrete this rapid corrosion of the embedded iron with the resultant cracking of the concrete takes place only when the potential gradient impressed on the specimen is quite high — much higher, in fact, than would generally be encountered from stray railway currents. If the voltage on specimens of ordinary size such as might be used in buildings is kept as low as 2 or 3 volts or less, long time experiments have shown that practically no damage to the concrete results. It is therefore only under very extreme conditions that serious trouble of this kind is likely to be met in practice. However, it may occur ; as for example, when an electric light wire becomes grounded on a metallic conduit embedded in concrete. The voltage here would generally be high enough to cause corrosion of the conduit and any reinforcing material that might be electrically connected there- with, which would result in ultimate splitting and more or less complete local destruction of the concrete structure ; this is there- fore a danger which under certain conditions should be guarded against. For this reason it may be well not to embed metal con- duit in concrete structures where the character of the building is such that this is not necessary, nor should the conduit be elec- trically connected to the reinforcing material. It is important to call attention to the fact that while, as above stated, in ordinary normal concrete with only 2 or 3 volts or less acting on concrete structures of the sizes usually encountered in practice, serious corrosion or cracking of the concrete will not occur, such corrosion and cracking will develop if any appreciable amount of salt is added to the concrete either during or after con- struction. It has been conclusively shown by years of experience that ordinary concrete affords a good protection for iron against natural corrosion, and recent investigations have shown that under ordinary circumstances it also affords a fair degree of protection against electrolytic corrosion. The addition of a small quantity of salt, however, has been found to destroy completely the protec- tive effect against electrolytic corrosion. For this reason it is very important that no salt be used in the erection of reinforced con- crete structures wherever there is any likelihood of stray currents from any soiu-ce getting into the reinforcing material. 14 Technologic Papers of the Bureau of Standards (b) Cathode Effect.— Another effect of electric currents on rein- forced concrete has only recently been discovered. This is the cathode effect, and it occurs only where the current flows from the concrete toward the reinforcing material. In this case there is no corrosion of the iron at all, but there is a gradual softening of the concrete at the surface of the reinforcing material, due to the gradual concentration of alkali at the cathode. This softening begins at the surface of the iron and very slowly progresses out- ward into the concrete, often requiring many weeks or months to progress a distance of a sixteenth of an inch. The practical im- portance of this phenomenon lies in the fact that the softening of the concrete at the surface of the reinforcing material, although usually confined to a thin layer, is nevertheless sufficient practi- cally to destroy the bond between the iron and the concrete, and in this way a structure may be weakened or destroyed. The cathode effect has been found to occur not only on high voltages, as in the case of the anode effect above described, but also on relatively low voltages, the rate at which it progresses being roughly proportional to the voltage applied in any particular case. Examples of trouble of this kind are shown in Fig. 4, which shows very definite regions of softened concrete surrounding the embedded iron. Because of the fact that this softening of the concrete near the cathode progresses at a much lower voltage than is generally required to produce the anode effect previously described, this cathode effect is likely to prove of greater practical importance than the cracking of the concrete at the anode which had previously been observed. In regard to the actual dangers to which reinforced concrete structures in practice are subjected as the result of these phenom- ena, it should be emphasized that while cases of actual damage of this sort have been encountered in practice in a few instances, they are comparatively rare, and only in exceptional cases have condi- tions been such as to produce any appreciable amount of damage in actual building structures. We have had occasion to investi- gate numerous cases in which reinforced buildings or bridges have been damaged in which the damage was attributed to stray cur- rents, but in most cases it has been found that the trouble was not in any way due to the presence of electric currents. In fact only Electrolysis Mitigation 15 one case has up to the present time come to our attention in which any serious damage to a reinforced concrete structure has occurred in actual practice, except in those instances where salt was present in the concrete in considerable quantity. This emphasizes the importance of omitting salt in the construction of reinforced con- crete buildings wherever there is any likelihood of stray currents getting into the structure. III. METHODS OF MITIGATION APPLICABLE TO PIPES The various methods of electrolysis mitigation that have been proposed are here treated broadly tmder two heads — first, those that may be applied to the pipe systems for protection of the pipes without regard to the extent of stray current leaking from the rails; second, those which are applied directly to the negative retiu-n of the street railway system and have for their object the prevention of leakage of electric current into the earth or the reduc- tion of such leakage to so low a value that it will do practically no harm. 1. SURFACE INSULATION OF PIPES Painting or otherwise insulating the surface of pipes, as by the use of treated papers and textiles, was early resorted to as a possible means of protecting the pipes from electrolysis, and this method is still used in some instances. It is doubtful, however, whether there exist any instances in which it has been definitely proven that insulating paints have effectively protected pipes from elec- trolysis for any considerable period of time, while there are many instances where they have failed utterly and where their presence has actually done harm. This statement may seem somewhat surprising to some who are familiar with instances where paints have withstood the action of soils for a long period and when uncovered both paint and pipe appeared to be in practically as good condition as when they were laid down. Practically all paints are classified as insulators, and it is quite natural that the impression should be more or less prevalent that these paints ought to prove effective as a protection against self -corrosion in the soil. In practice, however, such paints behave in a very tmcertain man- ner at best; a given paint may endure for long periods in some 2456°— 15 2 1 6 Technologic Papers of the Bureau of Standards places while in other places in the same city it may deteriorate rapidly and become worthless in a comparatively short time. This is due partly, no doubt, to differences of soil conditions. General failure of these paints under conditions where electrolysis was to be expected indicate that the stray currents have much to do with the destruction of the coatings. With a view to throwing fturther light on this point and also to determine if possible some- thing of the relative value of these coatings as a possible protection against electrolysis, the Btrreau of Standards has carried out a considerable number of experiments with different types of com- mercial pipe coatings and protective paints which have yielded considerable definite information. (a) Work of Previous Investigators on Paint Coatings. — A con- siderable amount of work relating to surface insulation of pipes has been done by many pipe-owning companies as well as in special investigations by individuals. The most extensive work in this direction carried on by individual investigators was that reported by R. B. Harper before the Illinois Gas Association in March, 1909. In this investigation more than 38 different com- pounds, including paints, dips, and wrappings, were tested. The conclusions given in the report state that no insulating coating was foiuid that would resist the attacks of electrolysis for any considerable length of time. Against the results of these tests, however, there has been directed a criticism that the voltage used on the coatings was abnormally high (no volts), and therefore would not represent actual working conditions, where the voltage might average but a few per cent of the above value. This criticism would appear to be more or less well founded, because it is not desirable as a rule to accept an intensive test as conclusive, and this is particularly true in a case where a breakdown voltage may be involved. It is not safe to assume that because a coating will not withstand the action of no volts it is therefore not suitable for insulating pipes at 10 volts or less, and since the voltages to which a pipe coating would be subjected tmder most practical conditions would not exceed a few volts, tests made on no volts would not appear to fimiish altogether reliable data as to the value of the coatings as a protection against electrolysis. Electrolysis Mitigation 1 7 In addition to the work mentioned in the previous paragraph that of various other investigators also points to the fact that at least a large proportion of the paints sold for the purpose of preserving metals from corrosion are not impervious to water, and as will be shown later this is a vital point in the protection of pipes from electrolytic corrosion by such means. From the standpoint of soil corrosion the access of a slight amount of mois- tinre to the siu^ace of the iron may not be a serious matter, pro- vided the paint is an inhibitor of corrosion, or at least does not form a galvanic couple with the iron, but if there is a difference of potential of even a few volts between the pipes and soil, the results may be very serious, as shown by the experimental data presented later in this paper. (b) Materials Available for Insulation of Pipes. — The materials which are commercially available for this particular kind of insulation work and which are practicable commercially may be divided into four general classes: (i) Paints or compounds which are to be applied at ordinary temperatures, depending on oxidation or other chemical action, drying, etc., for their setting properties. (2) Dips or compounds intended to be melted at a high temper- ature and the iron immersed and left until bath and iron are at the same temperature, when the iron is removed and allowed to cool, the compound hardening with decreasing temperature. These dips include asphalts, coal tar, pitches, and allied products. (3) Wrappings which consist of alternate layers of compound and fabric, the compounds used including the classes mentioned under both (i) and (2), while the fabric may be either felt, cloth, or paper. These may be treated or untreated, according to the ideas of the manufacturer or the person making the test. (4) Coverings consisting of some sort of conduit, or a large pipe inclosing the pipe or cable to be protected, the intervening space between pipe and conduit being sometimes filled with an insulating material such as pitch. (c) Tests on Pipe Coatings. — Coatings of the first three classes — namely, paints, dips, and wrappings — have been tested in consider- able number during the course of these investigations. The 1 8 Technologic Papers of the Bureau of Standards details of the experiments thus far completed relating to pipe coverings are reported in full in Technologic Paper No. 15 of the Bureau of Standards, so that only a summary of the results need be presented here. In making these tests the coatings were carefully applied in accordance with instructions of the manufacturers, and in all cases a sufficient number of coatings were appHed to give perfect con- tinuity and insure the absence of pinholes over the entire surface. In order to determine whether or not there were any flaws in the finished coating, the coated surface was immersed in salt water, and an electromotive force of 80 volts was applied between the coated iron and the salt solution for a period of 30 seconds. A very sensitive milliammeter was placed in series with the electric circuit and gave a deflection in case there was a minute flaw at any point of the coating. After 30 seconds the electromotive force was removed and the electrical resistance of the coating measured by a special method. The coating was then placed under a life test by immersing the coated surface in a suitable electrolyte, usually Potomac River water, and impressing on the coating a low potential difference between the iron and the sur- rounding water. As a rule, five specimens of each kind were used, in two of which the coated iron was made positive and in one negative, and in the remaining two no electromotive force was appHed. The electromotive force permanently applied during the Ufe test was 4 volts in all cases for the painted pipes and 15 volts in the case of the dips and wrappings. Table i gives the condensed data for the tests on the pipes covered by paint coatings. This table shows the number of coat- ings given each specimen, the resistance in ohms per square centi- meter before the test was started, the electrolyte used, which in most cases was water from city m^ns, and the voltage of the time test. The polarity of the coated iron, hours elapsing before the first appearance of ctirrent flow in positive, negative, and neutral specimens, and the weeks of drying prior to testing are also given for each specimen. Electrolysis Mitigation TABLE 1 Tests of Metal-Preservative Paints as Insulating Coatings 19 Name of paint g 1 Resis., ohms per cm" Electrolyte 1 1 Polarity of cone Hours to failure bO 1 a 1 1 1 Antakwa, heavy Antakwa, metal pro- tection. R. I. W., number not known. Carbonkote, interior Mindura, brine-re- sisting finish. Mindura, ordinary finish. Nev-a-Rust 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 2. X 10 11 2. X 10 11 >2. X 10 11 >2. X 10 11 >2. X 10 11 2. X 10 11 1. 6 X 10 9 >2. X 10 " >2.0xlO" >2. X 10 11 2. X 10 11 >2. 0X10" >2. Ox 10 11 >2. Ox 10 11 >2. Ox 10 11 3. X 10 19 3. 6 X 10 10 >2. X 10 11 >2.0xl0" >2. X 10 11 7. X 10 9 3. 2 X 10 9 >2. Ox 10 11 >2. Ox 10 11 >2. X 10 11 10. 8 X 10 9 3. 2 X 10 9 >2, X 10 11 >2. X 10 " >2. X 10 " 1. 7 X 10 9 7. 7 X 10 8 1. 6 X 10 9 1. 6 X 10 9 2. 1 X 10 9 2. X 10 1" 5. 5 X 10 19 >2. 0X10" >2.0xlO" >2. X 10 " 3. 1 10 9 1. 6 X 10 9 1. 1 X 10 11 1. 1 X 10 11 5. 5 X 10 1" 2. X 10 11 3. 4 I 10 ' 9. 2 X 10 8 1. 2 X 10 8 1. X 10 6 4. 5 X 10 8 3. 6 X 10 8 6. 2 X 10 9 5. 4 X 10 9 5. 6 X 10 9 2%NajC03... Water 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Pes... Pos... Neg. . . 312 384 ? 2 do 2000 1400 do Neut 8 do Neut.. 2 2%NasCOa... Water Pos... Pos... Neg 192 ? 2 do. 2000 1466' 1400 g do Neut. . do Neut.. 3 J%H2SOi Water Pos... Pos... Neg. . . 312 5000 2 do 600 "(M 1350 do Neut.. g do... Neut g 4 I^at?r^°-:::: Pos... Pos... Neg 528 ? do... C) "n 8 do Neut.. do Neut.. 5 3%NaCI Water Pos... Pos... Neg. 840 120 2 2 do 760 "576' 570 do Neut 8 do Neut.. 6 2%NazCOs.... Water Pos... Pos... Neg... 5 7 2 do 2000 '2800' 2800 do Neut g do Neut 8 7 2%Na!C03.... Pos... Pos... Neg 5 240 Carbonall, No. 10... Carbonkote, No. 100. Sarco do... 120 "336' 902 8 do Neut.. do Neut . 8 J_%H!S04 Water Pos... Pos... Neg 5 552 7 2 do 3144 iioo 1100 8 do... Neut 8 do Neut.. 9 2%NasC03... Pos... Pos... Neg... 72 1368 ? R do 6000 '2806" 2800 R do do 4%HjSOj.... Water Neut.. 8 Neut.. R 10 Pos... Pos... Neg 312 2 AeOnite, preserva- tive paint. 8 do 1752 '336' 336 8 do do Neut.. Neut. . 11 do Pos... Pos... Neg... 5 2 do do do 2952 "336" 1208 8 Neut 8 do Neut.. R o No sign oi current after 10,000 hours. 20 Technologic Papers of the Bureau of Standards TABLE 1— Continued Name ot paint 1 1 is Resis., olims per cm Electrolyte ■s ii Polarity of cone Hours to failure I ! 1 1 a 1? Crysolite, No. 10 Neponset, Water- dyke paint. No. 107, H.F.Scott.. Insulite.. 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 , 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 M 2 3 4 .■> 4 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 1.0x109 6. 6 X 10 9 >2. X 10 11 1. 1 X 10 11 1. 1 X 10 11 1. 2 X 10 9 >2.0xlO" 1. 1 X 10 9 3. 5 I 10 ' 9. 2 X 10 » 1. X 10 10 2. 2 X 10 9 1. 8 X 10 " 6.8x109 2. X 10 I 1. X 10 6 2. 2 X 10 9 >2. X 10 " 4. 2 X 10 ' 1. 8 X 10 ' 1. 5 X 10 9 1. 6 X 10 9 1.6x109 3. 7 X 10 10 3. 7 X 10 10 5. X 10 10 5. 6 X 10 9 3. 9 X 10 9 >2. Ox 10 11 >2.0xlO" 5. 1 10 10 2. 5 X 10 10 2. 3 X 10 10 8. 5 X 10 10 1. X 10 6 4. 6 X 10 9 8. 4 X 10 9 >2. 0x10" 2. 5 X ID ' 4. 3 X 10 ' 7, 2 X 10 9 7. 2 X 10 9 5. 6 X 10 9 >2. Ox 10 11 >2. Ox 10 11 >2. X 10 " >2. Ox 10 11 3. 1 X 10 9 >2.t)xlOll 4. 2 X 10 9 4.0xl0» 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Pos . . . Pos... Neg 240 7 do 7 do do 860 'isoo" 600 8 Neut.. R do Neut 8 n do Pos... Pos... Neg. - . 2800 7 do do do 7 10000 '1752" 2376 8 Neut.. •R do Neut.. R 14 do do Pos... Pos... Neg. . . 5 6500 2 R do do do 912 "912' 3200 R Neut.. 8 Neut.. R ii do do do do do do do do do do do do do do do do do do.. .. Pos... Pos... Neg. 10000 48 R Bar-ox 7 2700 "336' 336 2 Neut.. 8 Neut.. R ifi Pos... Pos... Neg.-- 3300 816 R R.I.W.,No.S Gllddens, acid proof and graphite acid proof. Hydrex, preservative paint. R. I. W., No. 49, over Tocltoliai. R 206 "766" 1400 R Neut.. 8 Neut. 8 17 Pos... Pos... Neg. . . 1320 480 R 8 3900 "iioo' 1400 8 Neut.. R Neut.. 18 Pos . . . Pos... Neg 4500 5300 R R 2800 '2880' 2800 8 .do.. Neut 8 do do Neut. . 8 19 Pos... Pos... Neg... 2600 816 8 do do do 2600 "912' 912 R Neut- . 8 8 R do Neut do do Pos... Pos... Neg. 192 192 8 do do If do do do do do 100 'ieoo" 2000 8 Neut. . Neut. . 8 21 Pos... Pos... Neg... 100 1586 8 Insulator, Carman . . 8 2800 'im 900 8 8 Neut. . Neut-. 8 o22 do do do do do a Four holes eaten through cone in 48 hours. Ten specimens in all were required to obtain one which would withstand the first test. All were carefully treated and dried 8 weelis. t> Nos. 2 to 5 failed on 80 volts. Electrolysis Mitigation TABLE 1— Continued 21 Name of paint Resis., olims per cm Electrolyte Polarity of cone Hours to failure o23 Damp-proofer» Car- man. 29 32 Crysolite, No. 8. Dixon's graphite... S. P. C, flexible iron paint. P&B, No. 2. P & B, black, air- drying varnish. National, double K natural graphite paint. Des Moines, elater- ite. No. 40. Des Moines, elater. ite. No. 10. I. D. P., steel paint. 1. 2 X 10 ' Water. do.. do.. do.. do.. >2. X 10 " 7. X 10 8 1.0x10 = 1.0x10 = 1. X 10 6 9. X 10 ' 3. 3 X 10 8 1. 6 X 10 8 1.6x10 8 1. 8 X 10 8 1. 2 X 10 8 2. 3 X 10 ' 1. 8 X 10 8 1.0X108 2. 2 X 10 8 9. 8 X 10 ' 2. X 10 8 2. X 10 ' 2. 9 X 10 8 l.OxIO* .do., -do., .do., -do., .do.. -do., -do., .do., .do., .do.. .do., .do., -do., .do., .do.. .do., .do., -do., -do., .do.. ..do.. -do.. ..do.. -do., ..do.. 4. X 10 8 3.4x108 3. 4 X 10 8 3. 4 X 10 8 3. 4 X 10 8 2. 7 X 10 8 2. 2 X 10 8 1. 8 X 10 8 6. X 10 ' 4. X 10 8 9. 7 X 10 « 2. 1 X 10 ' 4. X 10 « 1. 8 X 10 ' 9. 7 X 10 8 4. X 10 « 6. 5 X 10 ' 6. X 10 ' 5. 7 X 10 ' 1. X 10 « .do., -do., -do., .do., -do.. .do., .do.. -do., .do., -do.. .do., -do., .do., .do., .do.. -do., .do., -do.. ..do., .do.. Pos . . . Pos . . . Neg. . . Neut.. Neut.. 150 1032 1032 1032 Pos.. Pos.. Neg.. Neut. Neut. Pos... Pos . . . Neg... Neut. . Neut.. 48 2300 120 120 672 672 Pos.. Pos.. Neg.. Neut. Neut. Pos.. Pos.. Neg.. Neut. Neut. Pos... Pos.. Neg. Neut Neut Pos... Pos... Neg. Neut Neut 6500 912 912 912 6500 6500 10000 10000 912 912 10000 10000 2440 2000 Pos... Pos. Neg. Neut Neut 120 3300 Pos . . . Pos.. Neg. Neut Neut Av.= 120 120 120 -2900 96 96 3112 <• Five holes eaten through would withstand the first tesi !> Nos. 2 to 5 failed on 80 vol ° Resistance very low, about 1,000 ohms. cone in 48 hours. Ten specimens in all were required to obtain one which . All were carefully treated and dried 8 weeks is. 22 Technologic Papers of the Bureau of Standards The general appearance of the data under the columns "Hours to failure," which is of course the most important, indicates that a paint is not to be depended upon as a preventive of electrolysis in the presence of moisture, even though the voltage between the pipes and earth be only 4 volts. Here and there an individual specimen appears which seems to have withstood the action of the water for a considerable period of time, and in coating No. 4 only one of the four specimens has been broken down after a little more than a year. It may be said of No. 4, therefore, that it gives far greater promise of good results in practice than any of the others. The average of the hours to failure seems to indicate that positive specimens lose their insulating power first, with negative specimens second, and those not subjected to a difference of potential third; but the differences are too small to be conclusive on this point. On the contrary, an examination of the data, specimen by specimen, shows quite clearly that the low electric stress applied had very little effect toward reducing the insulation resistance of the paint. The time of the breakdown evidently depends more upon characteristics of the individual specimens than on the action of the water. The manner in which failure of the coating occurred depended upon the direction of current flow. The anode specimens showed rust spots at the places where the breakdown first took place. These rust spots would grow to craters in some places if the paint coating was brittle and easily broken, or bubbles would form if the coating was elastic. The removal of this crater or bubble would reveal a pit filled with iron rust, the pits in time extending clear through to the sheet iron. The cathode specimens failed in an entirely different way. No rusting of the iron occurred under the paint coating, but gas was liberated, which lifted the film tmtil a blister was formed which would sometimes break and leave a large area of iron exposed. These forms of failure are illustrated in Fig. 5, the specimen on the right being the anode specimens, while the one on the left is a cathode specimen. The specimens having no electromotive force applied showed no deterioration of the coating which was visible to the eye, except in one or two cases where the paint blistered somewhat, as it did when the specimens were made cathode. Coating No. 6 showed this type of failure in the greatest degree. Bureau of Standards Technologic Paper No. 52 Fig. 5. — -Shoioiiuj ilKiiatlcn.^lw fiuhdr of j^a'nit ioatunjs 1 ^^9 1 1 _^ 4 • -ws-" K .^^ ' > ^¥^. E < --«^^^fe^. , * -n» ■^:r 41^ -v^^ ' ' , '." . f^~ i '% . * ^ - * . ' 4 Fig. 6, — Shoeing pilliiujs on loiikj fipcs Electrolysis Mitigation 23 It is evident from the rapid failure of practically all of these coatings that they can not be depended upon even for a few months effectually to protect btuied pipes from electrolysis due to stray currents. The tests on pipes covered with dips and wrappings show some- what more favorable results. The data on these tests are given in the following table : TABLE 2 Tests of Pipe Wrappings, Dips, Etc., as Insulating Coatings [Water served as electrolyte in all cases. Voltage= 15 except in i-i and 4-1 where V= 4, and also 206 to 225] Coating Material Layers or dippings Speci- men Polarity of cone Hours to failure Positive Negative 1 Neponset water-dyke felt and com- pound do Slayers 2 layers 1 layer 3 layers 2 layers 1 layer 3 layers 2 layers 3 layers 1 2 3 4 5 9 10 11 12 17 18 19 20 25 26 27 28 29 33 34 35 36 41 42 43 44 49 50 51 52 57 58 59 60 Positive do 9200 5040 6000 do 2160 do 2 Positive do 7600 4200 do 3600 3 do PosiUve do 10000 10000 10000 Negative. . 3100 do 4200 Positive do do 16000 14700 014000 do 5 do do 5000 2000 do do Positive do 10000 10000 2900 g NegaHve 3040 do 2000 Positive do do 10000 3800 14700 7 Negative 3 Positive Negative . 5700 Barrett speclflcstion pitch and tar paper 5000 9 Positive do 3500 4800 do 2100 a No failure after the given number of hours. 24 Technologic Papers of the Bureau of Standards TABLE 2— Continued Coating Material Layers or dippings Speci- men Polarity of cone Hours to failure Positive Negative Barrett specification pitch and tar paper .do.. Barrett pitch (sample 1) and muslin Barrett pitch (sample 2) and muslin Barrett pitch (sample 3) and muslin Barrett pitch (sample 4) and muslin Sarco-mineral rubber-pipe dip and muslin .do.. .do.. Mogul repairing compound and muslin 2 layers ... 1 layer.. Slayers.. .do.. .do.. 4 layers.. Slayers.. 2 layers.. 1 layer.. 2 layers.. .do llayer. 65 66 67 68 73 74 75 76 81 82 83 84 89 .90 91 92 97 98 99 100 105 106 107 108 113 114 115 116 121 122 123 124 129 130 131 132 137 138 139 140 145 146 147 148 154 155 156 157 Positive... ....do Negative.. ....do Positive... ....do Negative.. do Positive... do Negative.. do.... Positive... do.... Negative.. do.... Positive... do.... Negative.. do.... Positive... do.... Negative. . do.... do.... do.... Positive... do.... Negative.. do.... Positive... do.... Negative.. do.... Positive... do.... Negative.. do.... Positive... do.... do.... do.... Negative.. do.... Positive... do.... Negative.. do.... 2100 2100 3400 3400 12500 3400 12500 12500 4400 4400 12000 a 12000 10000 10000 10000 2100 300 2900 300 2100 1600 1600 768 1600 720 720 552 48 3900 3900 5500 3400 1400 3000 a 12000 12000 2100 2100 1400 336 1200 300 2100 300 1600 1000 1600 1000 o No failure after the given number of hours. Electrolysis Mitigation TABLE 2— Continued 25 Coating Material Layers or dippings Speci- men Polarity of cone Hours to failure Positive Negative 23. 24. 25., 29. 31. S. P. Co. cold cementing compound and treated burlap Slayers.. .do. .do.. 2 layers.. 1 layer.. S. P. Co. cementing compound (grade A) and treated burlap .do.. 3 layers . 2 layers.. .do.. 1 layer.. Sarco-mineral rubber-pipe dip.. 2 dippings. Barrett pitch (sample 1).. Barrett pitch (sample 2).. .do.. Barrett pitch (sample 3).. .do.. Barrett pitch (sample 4).. Minwax and cloth. 2 layers.. 162 163 164 163 170 171 172 173 178 179 180 181 186 187 188 189 194 195 196 197 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 Positive... do.... Negative.. do.... Positive... do.... Negative.. do.... Positive.. 40.... Negative., do.... Positive.., do.... Negative., do.... Positive... do.... Negative.. do.... Positive... do.... Negative.. do.... Positive... do.... do.... do.... do.... do.... Negative. . do.... Positive.., do.... Negative., do.... Positive... do.... Negative.. do.... Positive. . . do.... Negative.. do.... Positive... do.... Negative.. do.... 7200 07200 07200 7200 07200 07200 07200 07200 07200 07200 07200 7200 24 5 96 9000 336 672 4400 6000 3192 3192 7200 7200 480 7200 7200 07200 07200 07200 07200 07200 07200 7200 360 1056 1680 4400 672 336 3192 3192 "No failure after the given number of hours. 26 Technologic Papers of the Bureau of Standards It is seen from this table that 82 per cent of the total number of specimens under test had failed after the tests had been in progress about 7200 hours. Coatings Nos. 25, 26, and 33 seem to remain intact, but they were among the last ones put in circuit, so their behavior had not been definitely determined when it became necessary to discontinue the tests. No. 27, however, which is of the same material as 25 and 26, shows two individual specimens which have broken down. These are of one layer of compound and burlap, and it seems reasonable to say that they forecast the future behavior of the others of the same material, but having a greater number of coatings. The results taken as a whole do not indicate that the life of insulating coatings of this character can be expected to be more than two or three years, even when carefully put on the pipes and btuied in perfect condition; in most cases failure may be expected to occur within a few months. The attempts to dip specimens appear to have yielded very poor results, and it is questionable whether coating pipes in this way is any better than painting. The manner of failure of the coatings was similar to that of the paint coatings described above. Failiure of the covering was much slower than in the case of the paint coatings after the first appearance of current flow. This is probably due to the greater thickness and rigidity of the coatings. The characteristic failure of the coating is very strikingly shown in Fig. 5. Explanation of the phenomenon lies in the fact that none of the paints tested are absolutely impervious to moisture, and when they are brought into the presence of water a slight trace of moisture ultimately permeates the coating. When this occurs at any point the coating becomes slightly con- ducting, and if an electromotive force is applied, a trace of current flows; this gives rise to slight elec1*-o lysis, which is accompanied by the formation of more or less gas beneath the coating. As a rule much more gas is formed if the iron surface is cathode than if anode, so that when current once begins to flow the forma- tion of craters or bubbles in the coating takes place more rapidly if the iron be negative than if it be positive. As this gas increases in volume and expands, the coating is ruptured, after which the current flow is greatly increased at the point of breakdown; in Electrolysis Mitigation 27 case the pipes are positive rapid electrolysis of the exposed por- tion follows. In some cases if the 'coating is sufficiently porous to permit the gases to escape they remain intact and electrolysis may continue beneath the coating, eating through the metal with little or no superficial evidence of failure of the paint. This phenomenon is frequently observed in pipes in actual practice. The vital weakness of all paints and wrappings thus far tested is due to the fact that they are not entirely nonabsorbent. If a paint could be secured which is absolutely impervious to soil moisture and which would remain so for an indefinite period of time, it would prove an effective preventive of electrolysis; all efforts to produce such paint should be directed to this one end of making it absolutely and permanently moisture proof. A considerable number of tests were also made on wrapped pipes buried in earth. A number of these pipes were coated by a method in use by a gas company in a large western city, and the specimens actually tested were supplied by the company in question. A considerable number of others were supplied by a large manufacturer of iron and steel pipe, the coatings having been put on primarily for the purpose of reducing soil corrosion. When the pipes were removed from the earth after the test and the wrappings stripped off they were found to be covered with rust spots and here and there were pits of considerable depth. An illustration of these pits is given in Fig. 6. The pipe longest in the groimd had been birried about one and a half years, and in that time pits were formed extending almost through the iron. The currents were not large, but the high-current densities resulting from the local failure of the coating resulted in very rapid corrosion of the iron wherever a failure occurred. The test voltage on these buried pipes was about 4^^ volts, a voltage of the order of magnitude frequently encountered in practice. The protection of pipes by laying them in conduit filled with pitch would appear to be effective for a much greater length of time, and in special cases this method would be useful; but the expense would be high if used on a large scale, and at present it appears very questionable whether or not the protection secured would be worth the cost. A large amount of work needs to be done in this direction before definite results on this subject will 28 Technologic Papers of the Bureau of Standards be available. As far as paints, dips, and wrappings are con- cerned, however, there can be no question but that as they are at present applied they are not only of no value when applied only in the positive areas, but they may do actual harm by con- centrating the current discharge on a comparatively small por- tion of the pipe sm-face, thus giving rise to rapid pitting. On the other hand, such coatings are unquestionably of great value in preventing self-corrosion in the case of pipes not subject to elec- trolysis from stray ciurents. Further, in cities where electrolysis is taking place, if such coatings are placed on the pipes in the negative or neutral areas, they would not only protect against self -corrosion, but owing to the increased resistance between pipes and earth the current which would be picked up by the pipes would be greatly reduced, and electrolysis in the remote positive areas would be corre- spondingly reduced. It may be said, therefore, that such coat- ings should never be used in the positive districts where the pipes tend to discharge current into the earth; but they may, if circumstances justify, be applied in the neutral or negative areas. However, for reasons pointed out later in this report, such protec- tion from electrolytic corrosion as might be obtained by the use of these coatings in negative areas should be regarded as of an auxiliary character, to be ultimately superseded by more effective mitigative measures along the Hnes suggested in a later part of this paper. 2. CHEMICAI- PROTECTION The corrosion of iron due to discharge of electric current is dependent not alone on the amount of the current discharge, but also to a very large extent on the chemical nature of the medium into which the discharge takes place and on a number of other factors. The results of a* great many experiments car- ried out by the Bureau of Standards ^ show that in case of ordi- nary street soils the amount of corrosion of iron per ampere hawc varies considerably with the chemical composition of the soil and also with the physical properties of the soil, such as moisture content, temperature, density, etc. * Burton McCoUuin and K. H. I^ogan, "Electrolytic Corrosion of Iron in Soils," Tedinologic Paper No. 25. Electrolysis Mitigation 29 Certain chemicals, as, for example, soluble hydroxides, tend to render iron passive — that is, prevent the corrosion of iron when it is made anode — whereas other chemicals, particularly the chlorides and sulphates, have the opposite tendency. Partly as the result of such opposing tendencies the "coefficient of electrolytic cor- rosion," or amount of corrosion of the iron which actually takes place in a given soil expressed as a fraction of the theoretical amount, according to Faraday's law, varies between wide limits. Moderately strong solutions of sodium, potassium, or calcium hydroxides alone will entirely prevent the corrosion of the iron by electric currents, and attempts have been made to prevent electrolysis under practical conditions by this means. Sodium and potassium hydroxides are obviously not well suited for this purpose because of their great solubiHty, which would cause them to diffuse and disappear very quickly. Calcium hydroxide or ordinary hydrated lime is much less soluble, and a soil thoroughly satiurated with Ume will remain so for a considerable length of time unless soil conditions are such that an abnormal amount of seepage occurs. This material has therefore been used in the attempts that have been made to prevent electrolysis by this method. We have found, however, that while a saturated solution of lime will, when practically pure, completely prevent electrolysis with ordinary current densities, it loses its power entirely when mixed with any considerable amounts of certain salts, such as chlorides, sulphates, carbonates, etc., which occur to a greater or less extent in practically all soils, and which always tend to con- centrate about an electrode discharging current into the soil. The protection afforded to pipes by laying them in lime, therefore, is of a transient character, and with the diffusion of the earth salts into the lime its protective property ultimately disappears. The temporary protection afforded by this means is too short lived to justify the expense of its application, except, perhaps, in very special cases where conditions are pecuUarly suited to its use. 3. CEMENT COATINGS Cement coatings have been used on pipes for many years, and the claim has been made, and is still made, by certain manufac- turers of cement-Uned and cement-coated pipes that their product 3° Technologic Papers of the Bureau of Standards is immune from, electrolysis. In so far as we have been able to observe, however, in all those cases in which these pipes have withstood moderately severe electrolysis conditions without injury for any considerable length of time the pipes have also been laid with cement joints, and it appears certain that the immunity which has been claimed for these pipes has been due to the high resistance joints rather than to the cement coatings. This conclusion is borne out by the results of tests which we have made on experi- mental lines of these cement-covered pipes on the grounds of the Bureau of Standards. Two experimental lines of these pipes were laid 20 feet apart, one being laid with calked lead joints and the other with cement joints. These were subjected to identical con- ditions, such as would under ordinary conditions give rise to con- siderable electrolysis. After about two years excavation revealed the fact that the Hne having lead joints had already suffered con- siderably from electrolysis, while the one having cement joints showed practically no evidence of trouble. From theoretical considerations we might expect that a cement covering would exert a temporary protective influence, since the cement contains a considerable amount of Ume, and, as pointed out above, this has a tendency to prevent corrosion of the iron. In fact we have repeatedly demonstrated that iron pipes em- bedded in cement and kept free from contaminating influences will not corrode to any great extent, even when discharging cur- rent at densities which are usually found in the case of under- ground pipes in practice. When, however, a pipe is covered with a layer of cement an inch or so in thickness and buried in the earth, it requires but a comparatively short time for the earth salts to diffuse into the cement, particularly if the pipes be dis- charging ciurents into the earth. This migration of the negative ions into the cement is due largely to the flow of electric cturent, the negative ions migrating in all cases in the opposite direction from that in which the current is flowing. As a result of this entrance into the cement of the acid radicals contained in the soil, the protective effect of the calcium hydroxide is in time destroyed. It has been claimed by some that the resistance of a cement coating is enough higher than the resistance of earth to bring Electrolysis Mitigation 31 about a material reduction in the current flow to and from the pipes. Otir experiments regarding this point do not, however, bear out this claim. We have found that the specific resistance of water-soaked cements, mortars, and concrete will vary as a rule from 2,000 to 8,000 ohms per centimeter cube, which is but little greater than the average specific resistance of a large number of samples of soil obtained from a number of widely scattered cities throughout the country. Further, experiments described, in Technological Paper No. 18 of the Bureau of Standards show that if a small amount of corrosion occurs under the cement coat- ing the expansive forces which develop will shortly cause cracking and splitting off of the cement. We are, therefore, convinced that the protective effect of cement coatings, Hke that obtained by burying pipes in lime, is but a temporary one and can not be seriously considered as a practical means of permanent electrolysis mitigation. 4. CATHODIC PROTECTION Since corrosion of pipes occurs only where the current flows from the pipes into the earth, it is obvious that if we could devise some means of always maintaining the pipes negative to the earth at all points of the system electrolysis could not occur. A great many attempts have been made to utilize this principle, and a number of pateUted methods of electrolysis prevention are based upon it. Broadly speaking, the principle of cathodic protection involves also another factor in addition to keeping the current always flow- ing toward the pipes. In some systems where this protection has been proposed, efforts have been made to produce and maintain a passive state of the iron by the production and concentration of alkali, which, under certain circumstances, takes place at a cathodic surface. One method that has been proposed for accomplishing this consists essentially in impressing an unsymmetrical alternating current on the pipe system in such a way as to make the average unidirectional current approximately zero. Under certain soil conditions this alternating current will produce a strong hydroxide solution in the soil adjacent to the pipes, which would tend to produce a passive condition of the iron, tending to protect it from corrosion. 2456°— 15 3 32 Technologic Papers of the Bureau of Standards The objections to this latter system are several. In the first place the apparatus required for automatically maintaining a proper unsymmetrical alternating current flow into the pipes involves considerable complication and expense. In the second place it is only under certain soil conditions that a sufficient amount of alkali could be produced to induce the passive state in the iron, and consequently in most cases protection by this method would not be had. In the third place even if those conditions under which strong alkalinity in the soil could be produced, a serious danger would be introduced because of the tendency of such alka- line soils to attack lead service pipes forming a part of the system, or the lead sheaths of power and telephone cables. We have no hesitation in saying that the system would not only be ineffective in most cases but would actually become a menace in others, and it is therefore not to be considered seriously as a means of elec- trolysis mitigation. Another method of applying cathodic protection, and the one most commonly thought of when such protection is proposed, consists in connecting a low-voltage generator between the pipe system to be protected and the adjoining rails in each positive area, and so exciting this generator as to maintain the pipes always at a lower potential than the rails. This is very closely related to certain forms of the common pipe-drainage system described below and possesses all of the disadvantages of the latter together with the additional drawbacks of extra expense and complication. At the same time it appears to offer no material advantage over the usual types of pipe-drainage system. A patented modification of the above method that has been developed abroad consists in substituting a large metallic electrode buried in the earth for the tracks as thfe positive electrode, the pipe system being as before maintained negative to earth. This plan of substituting a buried electrode for Ae tracks as the positive terminal has two marked disadvantages, namely, the increased cost of providing the electrode and the relatively small radius of the protected zone. Experiments carried out by us show that the extent of the region protected depends very much on the size of the buried positive electrode and also to a large extent on its position with respect to the pipe system. Electrolysis Mitigation 33 Figure 7 shows in diagrammatic form a layout of experimental pipe lines used for studying this problem. Two parallel pipe. lines {D and E, Fig. 7) were buried about 20 feet apart, one of 4-inch cast-iron pipe and the other a 3-inch steel pipe. Between these pipe lines a 5-volt battery, F, was connected in such a way as to make the cast-iron pipe positive, so that it would tend to discharge current into the earth and thence to the steel pipe. A motor generator set was then connected between the pipe line D and one of the small buried electrodes A, B, C, the connection being such as to cause current to flow from the buried electrode A, for example, into the earth and thence into the pipe line D. It will be seen, therefore, that the small 5-volt battery F tends to cause cmrent flow from the pipe line D into the soil; whereas the motor generator set G tends to cause current to flow into the pipe line D. The motor generator set, therefore, tends to protect the pipe line D from corrosion by the current from the battery F, and if the protective tendency of the motor generator set could be made everywhere sufificiently great, it would entirely prevent corrosion of the protected pipe. In order to determine to what extent such protective tendency existed, careful exploration was made throughout a considerable length of the pipe line D in order to ascertain to what points and to what extent it was discharging current into the earth under various connections of the protecting motor generator set G. In order to make these explorations a series of holes H were drilled in the ground immediately beside the pipe line D. These holes were drilled in pairs to the same depth as that of the pipe. One hole of each pair terminated immediately beside the pipe and the other about a foot farther away. With suitable non- polarizable electrodes the potential difference between the bottoms of the holes of each pair could be measured, and this was, of coiurse, proportional to the surface intensity of the current discharged from the pipe siurface assuming uniform soil resistance throughout, which was substantially the case. By measuring the potential difference between the bottoms of the different pairs of holes we could then plot a curve showing the intensity of the current discharged along the length of the pipe. 34 Technologic Papers of the Bureau of Standards A series of such meastirements were first made with the motor generator set connected between the buried pipe line D and the buried electrode A. The motor generator set was then con- nected between D and the btnied electrode B, and the series of measurements on all the holes repeated, after which a similar series of measurements was made with the motor generator set con- nected between D and C. The results of these measurements are plotted in etudes shown in Fig. 8, shown on the same sheet, both figures being drawn to the same scale. In this figure curve D shows the potential difference between the bottoms of the test holes when the motor generator G was disconnected entirely — in other words, when there was no tendency whatever to protect the pipe line D from corrosion. The ordinates of this ciu-ve show roughly, the relative danger of corrosion of the pipe at any point along its length, and it will be seen that the pipe is positive throughout. The motor generator set was then connected between the pipe line D and the buried electrode C, which was buried at a distance of 40 inches from the pipe line D. It was found necessary in the preliminary experiments to impress about 50 volts from the motor generator set in order to get any appreciable amount of protfection even in the immediate vicinity of the buried anode, ajid this voltage was therefore maintained throughout the test. With the 50 volts impressed between the anode C and the pipe Hne the series of potential measurements between the bottoms of the test holes gave the curve C. It will be seen that in the immediate vicinity of the buried anode there is a marked reversal of polarity, the pipe being strongly negative to earth for a distance approximately equal to the length of the anode. As we proceed along the pipe, however, the negative condition of the pipe diminishes with great rapidity, and at a distance of about 4 feet from the end of the buried mode it will be seen that the pipe has become positive, and as we proceed farther away from the anode along the pipe we find that the pipe becomes more and more strongly positive to the soil until at a distance of about 20 feet from the buried anode the potential of the pipe against the earth is practically the same as it was without the motor generator connected to the anode. The remaining length of the Electrolysis Mitigation 35 pipe as far as explored was in practically the same condition. The motor generator set was then connected between the pipe line D to the buried anode B, which was located at a distance of "o ^^• w Q tv y ^^ S< oa V X33^ o 80 inches from the pipe line D, or twice as far as anode C. The series of potential measurements was then repeated and the data plotted as curve B. 36 Technologic Papers of the Bureau of Standards It will be seen here that the negative condition of the pipe D immediately opposite the buried electrode is less pronounced than in the case where the electrode is buried nearer the pipe, but the negative condition persists for a greater distance along the pipe line to be protected, in this case the pipe line remaining negative to earth for a distance of about i5 feet. Throughout its remaining length the pipe was positive to earth, although its positive condition was much less pronounced than in the case of the unprotected pipe. The motor generator set was next con- nected between the pipe line D and the buried anode A, which was located about i6o inches from the pipe line, or four times as far as the anode C. Potential measurements taken in the bot- toms of the test holes under this condition are plotted as curve A. Here it will be seen that the extent of the protected zone is greatly increased, the pipe line remaining more or less negative to earth for a distance of more than 50 feet, beyond which it became positive, and consequently very little protection could be expected beyond a hundred feet or so from the buried electrode. It appears from these tests that making a pipe system negative against a buried anode will protect the pipe only in a very small area immediately surrounding the anode. Even in this present case, where the protecting voltage was 10 times the normal potential difference between the buried pipe lines, we find the area of the protected zone to be almost insignificant, and it is very evident that if the protecting voltage were reduced, the area of the protected zone would be reduced correspondingly. In any actual case it would be impracticable to use so high a protective voltage as was used in these experiments, because of the large expense involved, both for the generator units and for the power wasted, so that the results obtained here, although wholly inadequate to afford any appreciable protection, are nevertheless better than could be explcted from any practical application of this method of protection. When, however, the rails are used as positive terminals instead of a small buried anode, the anode is in effect spread over a very large area, and consequently the radius of the protected zone would be much larger than in the case above considered. It appears, therefore, that these patented modifications involving the use of small bmied anodes are without merit. Electrolysis Mitigation 37 Another form of cathodic protection consists in bvirying near the pipes a metal which is electropositive to the pipes, such as zinc, and connecting this metallically to the pipes. This tends to protect a small area of pipe near the point of connection, but from the experiments described above it will be obvious that the radius of the protected zone will be extremely small. It has the further disadvantage that a greater number of such connections are required to protect the pipe line, and the zinc or other protecting metal rapidly wastes away. Further, there is no cheap metal which is electropositive to iron, and the expense of this method is therefore prohibitive, except perhaps in extreme cases. All of the above modifications which employ a booster to lower the mean potential of the pipes tend to cause increased current flow in the pipes, and they also lower their potential with respect to stirrotmding structures, thereby increasing the danger to the latter. They are, therefore, open to the same objections as the pipe-drainage system described later yi this report, besides being as a rule more complicated and more expensive to install and operate. S. FAVORABLE LOCATION OF PIPES WITH RESPECT TO TRACKS The location of pipe lines with respect to tracks has a very important bearing on the danger of electrolysis. In general, it may be said that the farther the pipes are from the tracks the less current they will pick up, and hence the total damage will be correspondingly reduced. A more important matter, how- ever, is the distribution of the discharge, it being desirable as far as practicable to distribute the discharge over as large an area as possible. If the pipe in the positive area be brought near to the tracks at one point, as by crossing immediately under it, the tendency is to concentrate the discharge at that point and thereby cause rapid destruction locally. The location of the pipes is therefore more important within the positive area than outside this zone, although in both cases it is important. In laying new pipes, or replacing old ones therefore, the pipes should be placed as far as practicable from the rails and the cross- ing of service pipes under the tracks should be avoided if cir- cumstances permit. Some companies make it their regular 3^ Technologic Papers of the Bureau of Standards practice in the more densely built up districts to lay mains on both sides of the street, in which case the crossing of services under tracks is rarely necessary. In many cases this is not practicable, however, but something can always be accomplished by laying the pipes as deep as possible where they pass under the tracks. The practice of putting mains immediately tmder the tracks tends greatly to increase damage by electrolysis and should be avoided wherever possible. It has been contended by some investigators that it is feasible to eliminate altogether damage by electrolysis by taking pre- cautions to keep all parts of the pipe system more than 4 or 5 feet distant from the railway tracks. This plan has been advocated rather strongly by some European engineers, notably Messrs. J. G. and R. G. Cunliffe,* who have concluded from extensive experi- ments on the resistance of groimd plates that the tendency of the earth to short-circuit the pipes is so great that if a pipe hue is everywhere more than 4 or 5 feet distant from the tracks it will pick up practically no current from the earth. We are convinced, however, that this deduction is in error. In the first place, the experiments on which this conclusion was based were carried out on very small ground plates in which, obviously, the greater part of the resistance between the electrodes would be within 2 or 3 feet of the electrodes themselves, because of the relatively small cross section of the path of the current in those parts. If, however, we are dealing with very large electrodes, we find that a large part of the resistance between the electrodes is to be found at points much farther from the electrodes. Con- sequently, if current is being discharged from a very large electrode, the pipe line would have to be removed much farther from the vicinity in order not to pick up any current from it. In any actual case, we may consider a railway system as con- stituting a large network forming a dmgle anode discharging current into the earth, and in such a case we can not apply the conclusions that would be drawn from comparatively small anodes, such as used in the experiments above referred to. On the contrary, our own experiments have convinced us that it is 1 J. G. and R. G. Cunliffe, "Electric traction vagabond currents," Jour. Inst, of Elec. Eng., Vol 43, p. 449. Electrolysis Mitigation 39 wholly impracticable to so locate the pipes that they will not be in danger of picking up considerable amounts of current from the earth under conditions which in the past have usually prevailed in most cities in this country. As evidence of this we may cite the fact that quite frequently when investigating voltage conditions in various cities we have encountered localities where even at a distance of 200 yards from the nearest railway line the potential gradients in the earth were as high as several volts per mile. It is very obvious that a pipe line placed in earth in which such large potential gradients exist, must of necessity pick up large amounts of current. While, therefore, the method of reducing electrolysis troubles by careful location of the pipe lines can never be more than partly successful, we are nevertheless convinced that a good deal can be accomplished in laying new lines by keep- ing theln as far as practicable from the street railway tracks. The advantage of this, as pointed out above, is more because it tends to distribute the current discharge over a large area than because of actual reduction of current in the pipe systems, although the latter is, of course, of some consequence. The limitations of the method of pipe location are, however, very obvious. The major part of the electrolysis problem has to do with the protection of pipe systems where both the pipes and the tracks are already in place; hence this method should be regarded merely as presenting certain feattues, of which advantage can and should be taken in special cases, and not as a general method of electrolysis mitigation. 6. CONDUCTING COATINGS If it were practicable to provide a continuous conducting coat- ing for the pipes which would not corrode tmder the discharge of electric currents, there would be less need of trying to prevent the flow of current in the pipes. Numerous attempts have been made to utilize this principle in electrolysis mitigation. In general, the aim has been to provide on the surface of the pipe a conducting material which is noncorrodable, and which is in metallic contact with the pipe, the idea being that the cmrent would pass from the pipe to the noncorrodable material by metallic conduction, and thence be discharged into the earth without injury. The diffi- culties of this method lie in the fact that all noncorrodable metals 4° Technologic Papers of the Bureau of Standards available for this purpose are too expensive for commercial appli- cation, so that attempts to use this method have necessarily been confined to nonmetallic coatings. Here, however, a difficulty is encountered, owing to the impracticability of maintaining a con- tinuous coating by means of any nonmetallic conducting material. In one attempt to utilize the method of conducting coatings the iron was covered by a layer of black oxide, either by subjecting it to the well-known Bower-Barff treatment or by various other means. Black oxide is a very good conductor of electricity and is noncorrodable imder most soil conditions, and at first sight this method might appear promising. It has, however, two serious drawbacks which combine to make the method utterly ineffective in practice. The first is the fact that it has been impossible to to provide a coating of this kind that was entirely free from cracks or other flaws reaching through the coating to the iron -below. The second difficulty is due to the fact that iron oxide is electro- negative to iron, and wherever a fault develops in the coating per- mitting soil waters to enter and make contact with the iron, galvanic action is set up which speedily produces severe pitting in the iron. In fact, it is this phenomenon which is in large meas- ure responsible for the unequal corrosion of iron in practice which results in pitting of the surface. The initial corrosion results in the formation of iron oxides at certain points, and these areas at once become electronegative, forcing the current to discharge else- where and thus aggravating the rate of deterioration of the pipes. A patented modification of this method consists essentially in providing a coating of conducting particles such as coke, for ex- ample, embedded in a continuous nonconducting binding material, such as pitch, the theory being that the particles of coke would afford a metallic path for the current through the coating, and thus prevent corrosion of the iron. In practice it has been found that the insulating coating soon breaks down after the manner described above for paint coatings, and when this takes place the particles of coke in contact with the iron set up galvanic action, which causes rapid deterioration of the pipe. It is safe to say that conducting coatings as applied up to the present time have invariably been harmful in their effects because of this tendency to produce a greatly increased amoimt of self-corrosion. Electrolysis Mitigation 1. ELECTRIC SCREENS 41 A method that has been used in some cases to reduce cases of local electrolysis consists in interposing between the pipes and the structtne to which it is discharging current a mass of metal which LJ LJ Track. M I. i\ >>. ik J< J< J< J^ j\ A Cast Iron plate or .screen CanneoHng wire Fig. 9. — Plane screen is electrically connected to the pipe or other structure to be pro- tected. The ciurrent is then carried from the pipe to the metal screen by way of the metallic path, and thence discharged into the earth, the corro- sion taking place on the screen instead of on the pipe. The screen can be of heavy cast-iron plates or grids. In order to be effective the screen must be placed on the side of the pipe toward which it tends to discharge current, and if the pipe is discharging current Outer pipe. Fig. 10. — Circular screen in all directions, the screen must take the form of a larger pipe inclosing the pipe which is to be protected. The principle of such screens is shown in Figs. 9 and 10. Fig. 9 shows diagrammatically a plain screen interposed between the 42 Technologic Papers of the Bureau of Standards pipe line and the railway track where the pipe crosses under the track. In this case the tendency would be for the pipe to discharge current upward into the track, so that a small slab of metal, such as cast iron considerably longer than the width of the track and having a width several times the diameter of the pipe inter- posed between pipe and tracks and connected to the pipe elec- trically, would take off the greater part of the ciurrent on the pipe without injury to the pipe itself; and if the iron slab were very heavy, it would in most cases last almost indefinitely. Fig. lo shows a circular screen surrounding a pipe which tends to dis- charge current locally in several directions. The chief advantage of such a screen over a direct bond between the pipe and the structure to which it is discharging current is that the screen has an almost negligible tendency to increase the magnitude of the current flow in the pipes, and therefore can not induce a dangerous condition to the pipes or other structures at remote points, where they are not electrically continuous. It is obvious that this method is not adapted for extensive use throughout the pipe system, but it may be useful in special cases for relieving severe cases of corrosion in very restricted areas, as, for example, where an important pipe line passes under or very near a street railway line or other pipe system which is strongly negative to the pipe to be protected. At best, however, it should be regarded as a temporary expedient to be resorted to only in emergency, while more adequate mitigative measures are being applied elsewhere in accordance with principles set forth in a later part of this report. 8. INSULATING JOINTS IN PIPES (a) General Discussion. — Another method of reducing current flow in pipes which has found rather extensive application within the last few years, in some cases for the |#imary purpose of reduc- ing electrolysis, but in most cases for other reasons, is that of breaking up the continuity of the pipe lines by the use of insulating or resistance joints, particularly cement joints. In ordinary wrought-iron or steel pipes with screwed or riveted joints the resistance of the joints is usually small in comparison with that of the pipes, and when such pipes are laid in localities where there Electrolysis Mitigation 43 is an appreciable potential gradient in the direction of the pipe current of considerable magnitude will usually be carried by the pipe. In the case of cast-iron mains the resistance of the joints is often as great as or greater than a section of the pipe, and it is not uncommon to find a lead joint which has a resistance equiva- lent to that of several hundred feet or even several thousand feet of pipe, and it is due largely to this high joint resistance and to some extent also to the higher specific resistance of cast iron that cast- iron mains usually carry less current under similar conditions than wrought-iron or steel mains. Experience has shown, however, that the resistance of lead joints is not sufficient to reduce the current to a safe value, and attempts have been made still further to increase the resistance of the pipes by the introduction of specially designed joints of high resistance. Because of the wide use that is now being made of insulating joints, both for the purpose of protecting against electrolysis and for other reasons, we give below a rather full discussion of the use of such joints and the precautions that should be taken in installing them. It should be emphasized, however, that in general we regard the use of insulating joints as valuable chiefly as an auxiliary measure which may often be used to advantage to supplement measures applied to the railway tracks to reduce voltage drops therein to reasonably low values. Following the earlier attempts to prevent electrolysis by this method, very strong claims were made for it by some of its advo- cates, some of them claiming that they had completely solved the problem of electrolysis mitigation by the use of insulating joints.. Within a few years, however, a noticeable reaction set in. Many engineers criticized the method, and some of those who were its warmest advocates in the beginning abandoned it. It is but natural, however, that the initial attempts to apply this method should have resulted in some disappointments, and it is not safe to consider these early failures seriously in judging the value of the method when properly appUed. At that time no experience had been gained in regard to the frequency with which such joints should be used, the proper location of the joints, the kind of joints best suited to certain conditions, and the complications arising from the presence of other pipe systems not so insulated. 44 Technologic Papers of the Bureau of Standards All of these are important factors and must be carefully con- sidered if adequate protection is to be secured. On account of the very great number of systems, particularly gas systems, which now use cement or other insulating joints, this subject has become a very important one and requires somewhat extended discussion. We therefore give below a rather full state- ment of the principles underlying the design and construction of the resistance- joint systems where electrolysis mitigation is the primary consideration and also give an account of some of our own investigations that have been completed to date in regard to the use of such joints. A number of cases have come to our attention where systems in which insulating joints have been installed for the express purpose of preventing electrolysis have, nevertheless, suffered severely from corrosion by stray currents. In every case that we have examined, however, there has been good reason for believing that the trouble was due either to the use of an insuf- ficient number of joints, or joints of improper design, or to the fact that they were not located in such places as to be rhost effective in reducing danger. A very common procedure has been to insert insulating joints at infrequent intervals of from 200 to 500 feet or to insert a single insulating joint on either side of the track, and a few feet therefrom, and to assume that these insulating joints should prevent current from getting from the railway tracks into the pipes beyond the joint. The reason why such an installation might fail to protect the pipes in many instances will be evident if we consider the con- ditions which exist in many places. In the course of voltage surveys in various cities we have often encountered localities where the potential difference over distances of a few hundred feet reach 5 or 6 volts or more during tie average all-day load, and considerably higher values during peak load. At times potential gradients of this magnitude have been found to prevail continuously over distances of a thousand feet or more. In a case of this kind, where the difference of potential is, say, 10 v6lts per thousand feet, and a pipe line is located in a direction approximately parallel to the electromotive force, heavy cur- Electrolysis Mitigation 45 rents will, as a rule, be picked up by the pipes, and if this is discharged into the earth, serious damage will, of course, result. If, now, we break up the continuity of the pipe by inserting insulating joints at intervals of, say, 300 feet, these joint resist- ances, being high compared with the resistance of the pipe, practically all of the potential drop will be concentrated at the joints and across each joint a potential drop of about 3.3 volts will occur. Since, as usually made, the leakage path arotmd such joints is very short, the metal parts on opposite sides of the joint being brought within an inch or less of each other, it is evident that the potential gradient across this short distance will be ex- tremely high, and as a consequence heavy leakage currents will flow around the joints sufficient to destroy them within a comparatively short time. It is evident that in order to prevent this a sufficient number of insulating joints must be used so that the drop of potential across each joint will not be sufl&cient to injure the joiat within a long period of years. In other words, the total resistance of the line must be so much increased by the addition of the joints that the current flowing through it luider the total potential difference will be too small to do serious damage. This points to the importance of governing the num- ber and location of the joints by the local potential conditions, a subject which is taken up in detail in a later part of this paper. (6) Tests on Insulating Joints in Service. — In attempting to determine by actual experiment imder practical conditions just how effective insulating joints may be in reducing cxurrents in pipes, difficulties are met with owing to the complex and uncer- tain ramification of the pipe networks. In connection with other lines of field work we have made excavations and measured the flow of current in pipe lines provided with insulating joints at more or less frequent intervals, and by comparing these with similar measurements on lines not provided with insulating joints but otherwise similarly situated, an approximate idea has been gained as to the extent to which the currents are reduced by the joints. In making such measiurements the method used was the one most commonly employed by engineers for this 46 . Technologic Papers of the Bureau of Standards purpose, viz, to expose a portion of the pipes between adjacent joints and with a millivoltmeter measure the drop of potential between two points a measured distance apart. The size, type, and class of pipe being known, and the specific resistance being obtained from tables prepared for this purpose, the current in the pipe could be calculated with a sufficient degree of accuracy for work of this kind. Wherever practicable the current measurements were made in cities where one pipe system only (either water or gas) was pro- vided with insulating joints, and by selecting places where the pipes of the two systems lay parallel and near together for some distance it was possible to obtain points at which the two systems were subjected to somewhat similar conditions except for the insu- lating joints, and in this way a fairly definite idea of the effect of insulating joints could be obtained. Such readings are of course not altogether satisfactory, for there was often a difference in the material of the pipe and in some cases a difference in size also, and allowance should be made for these. There was also the uncer- tainty in regard to the ramifications of the network to which the lines were connected, but in general the conditions were sufficiently similar to indicate clearly the tendency of the joints. A number of these current readings in parallel mains is shown in Table 3. In test No. i, the measurements were taken on an 8-inch water main provided with very infrequent leadite joints, and on the same street measurements were taken on a 6-inch gas main provided with lead joints throughout. As shown in the table, the current in the former was 0.93 ampere and in the latter 1.57 amperes, showing an appreciable reduction, although the difference is small. It is important to note, however, that in this case the leadite joints were at a considerable distance apart, averaging several thousand feet, and further, they were not installed with the idea of making them insulating, so that in many cases the joints were of low resistance owing to con- tact between the bell and spigot ends of the pipes. In test No. 2 measurements were taken on a 1 2 -inch main provided with a leadite joint every 12 feet and on a parallel 16-inch main with lead joints throughout. The difference here is very marked, the current in the lead joint line being over one hundred times that in the line Electrolysis Mitigation 47 having leadite in ever>' joint. Similarly, in test No. 3, where also one line was provided with a leadite joint every 1 2 feet, the differ- ence is more marked, the cmrent in the case of lead joints being about a hmidred and twenty times that in the pipes having leadite joints. In test No. 4 the difference is much less, but this is partly due, no doubt, to the difference in size of the pipes, as shown by the table. The chief factor, however, is the distance between the leadite joints, this being in the present instance about 300 feet. TABLE 3 E£Fect of Insulating Joints on Cuirent Flow in Parallel Mains Test Mains "^i^t"' Distribution of insulating Section in which drop was measured Average potential across section Amperes No. Kind Class Size joints in mains Distance to joint Length in pipe Inches Feet MUlivolts (Cast Do... D 8 Leadite.. Isolated.... Adjacent. 9 0.2 0.93 A 6 Lead None 6 .4 1.51 2 C Do... Do:.. A C 12 16 Leadite . . Lead 12 feet None ....do... Hi 3 .013 .2 .062 7.27 3 f Do... Do... D C 12 16 Leadite . . Lead 12 feet None j....do... lOJ 8 .013 .83 .094 11.31 r Do... Do... D 12 Leadite . . 300 feet j....do... 1 ^^ .02 .138 C 4 Lead None 6 .3 .86 5 (Wrought, least Standard. 6 No. 6D.. Isolated.... |....do... r 3 .005 .037 C 6 Lead None 3J .8 6.13 6 f Wrought. Cast Standard. 4 No. 6D.. Irregular... |....do... J 2^ .01 .062 C 4 Lead None 10} 8.0 12.85 7 (Wrought. Cast Standard. 6 No. 6D.. Irregular... I ^ .0025 .0185 C 20 Lead None lOi 1.9 28.22 8 Wrought. Standard. 4 No. 6D.. Irregular... ....do... f 2i .01 .056 Cast C 4 Lead None 7 .15 .371 9 Wrought. Cast Standard. 6 No. 6D.. Irregular... |....do... I '* .0025 .042 C 6 Lead None 1 11* .02 .048 f Wrought, {cast Standard. 8 No. 6D.. Irregular... |....do... f 2i .0025 .031 C 6 Lead None [ 11} 2.4 5.47 U Wrought. Cast Standard. C 3 6 No. 39D. Lead 20 feet None ....do... 22 lOJ .005 2.0 .0024 3.U 12 Wrought. Cast Standard. C 3 10 No. 6D.. Lead Irregular... None 1000 feet.. 10 10 1.2 .3 1.26 1.62 fWrought. Standard. 3 No. 6D.. Irregular... f * .01 .026 13 I Cast C 12 Lead None Il300feet.. 10 .5 3.50 I. ...do... C 12 do... do 1 10 .2 1.40 14 [Wrought, least Standard. C 3 10 No. 6D.. Lead Irregular... None 500 feet... 1 10 .015 5.0 .016 27.0 2456°— 15- 48 Technologic Papers of the Bureau of Standards TABLE 4 Small Cuirents Flowing in Mains Protected by Insulating Joints Mains Kind Class Size Joints Type Age Distribu- tion of in- sulating joints in mains Section in whicli drop was measured Distance from insU' lating joints Length Average potential across section Amperes in pipe Cast Do-... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Wrought. Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do.... Do-... Cast Wrought. Cast Wrought. Cast Do Do D D D D D D D D D D Standard ....do. .. ....do.... ....od.... ....do.... ....do.... ....do.... ....do.... ....do.... ....do.... ....do.... ....do.... ....do.... ....do.... ....do.... C. Standard. C Standard. C C c Inches 12 12 12 12 12 12 12 12 12 12 4 6 4 6 4 6 8 3 3 3 4 4 4 4 4 6 3 8 4 6 6 e Leadite . do... do... do... do... do... do... do... Wood... do... No. 6 D. do... do... do... do... do... do... No. 39D. N0.6D.. ...do... ...do... ...do... ...do... ...do... ...do... ...do... ...do... ...do... ...do... Cement . do... do... Years 3 3 3 2 2 3 4 4 3 3 4 4 4 4 4 4 4 4 2 2 2 2 2 2 2 2 2 2 2 10 10 10 12 feet... do... do... do... do... do... Isolated.. 300 feet.. Isolated.. do... 20 feet... Isolated.. Irregular do.-- do... do... do... 20 feet... Irregular do... do... do... do... do... do.. do... do... do... do... 12 feet... do.. do... Adjacent. do.... do.... do.... do.... do.... do.... do.... do.... 100 feet.., Adjacent. do.... do.... do.... do.... do.... do.... do.... 1000 feet.. 1300 feet.. 200Ieet.., Adjacent . 1200 feet.. 600 feet... Adjacent. ... .do.... 500 feet... 2500 feet., 750 feet... Adjacent, do... do... * Feet 12 lOi 11 8 11 11 lOi 11 6 6 S 3 225 3 2i n 2i 2i 10 4 10 3 6 6 4 3i 10 6 6 11 11 11 Millivolts 0.013 .013 .013 .01 .041 .01 .02 .02 .01 .03 .0025 .005 .01 .0025 .01 .0025 .0025 .005 .0025 — .01 .015 .025 .02 .01 .0025 .01 .015 .2 .1 .0025 .015 .05 0.082 .094 .090 .095 .283 .069 .148 .138 .127 .38 .0044 .037 . 00063 .0185 .056 .043 .031 .024 .0026 — .0263 .0211 .1175 .047 .0235 .0088 .0765 .0157 1.30 .235 .0061 .0365 .122 Tests No. 5 to 1 1 , inclusive, were made on wrought-iron gas mains provided with Dresser couplings at irregular intervals and on par- allel cast-iron water mains provided with lead joints. In compar- ing these figiures it should be borne in mind that cast iron has a much higher resistance than wrought iron, and further that the lead joints themselves introduce considerable resistance into the Electrolysis Mitigation 49 circuit, so that the real effect of the Dresser joints is much greater than the figures would indicate. While considerable variation exists in the ratios of current in parallel mains in the different tests of this series, they show without exception considerable reduc- tion in current due to the insulating joints. Taking the average of the series we find that the current in the lines having lead joiilts is about thirty-six times that in the lines having insulating joints. TABLE 5 Current Mains in Mains When Joints are Infrequent Mains Joints Distribu- tion of in- sulating joints in mains Section in which drop was measured Average potential across section Amperes in pipe Kind Class Size Type Age Distance from insu- lating joints Length Cast Do.... Wrought. Do.... Do.... Do.... Do.... Do.... Do-... Do.... D C Standard. ...do ...do ...do Casing... Standard. ...do ...do Inches 8 30 6 6 4 4 5f 6 8 4 leadite ...do... N0.6D ...do... ...do... ...do... ...do... . .do... ...do... ...do... Years 4 3 4 4 4 2 2 2 2 2 Isolated.. d.... Irregular do... do . . . do... do... do... do... do... Adjacent. do.... 1000 feet.. 600 feet. . . 300 feet... 200 feet... 2500 feet.. 1200 feet.. 300 feet... 1200 feet.. Feet 9 11 3 2J 2 19 6 2 3 2i Millivolts 0.2 .2 .04 .25 .11 1.0 .05 .4 .6 .4 0.926 5.45 .296 , 2.02 .775 .742 .78 4.44 6.18 2.25 In all of these cases, except in test No. 11, the insulating joints- were irregularly spaced, the distance between joints in various parts of the system varying from three hundred to several thousand feet. This fact being considered, the relatively low values of current in the lines provided with insulating joints is quite re- markable. In the last two tests shown in Table 3 (Nos. 13 and 14) the ratios of current in the lead jointed lines to that in the lines with insulating joints are, respectively, 134 and 168, but in these tests considerable allowance must be made for the relatively large size of the cast-iron mains as shown by the table. In Table 4 is shown a series of current measurements on lines having insulating joints under conditions where, in most cases, it was not possible to obtain similar readings on lines not so insu- lated, and they are presented here merely to show that in general 50 Technologic Papers of the Bureau of Stcmdards if oil 4 « tl i- if G-) 4 V I ■a s 1 •^ these currents have been found to be very low. These figures may be regarded as typical of what may be expected under ordinary _^ conditions where a considerable number of insulating joints are used. That the current in these systems was not invariably small, however, is shown in Table 5, which gives a number of tests showing current of considerable magnitude flowing in the pipes. It is "to-he noted, however, that in all such cases the insulating joints were widely separated, as shown by the column giving the distance from the nearest insu- lating joint to the point at which the measurements were taken. The distance between joints be- ing at least double these values, they range, therefore, from four hundred to several thousand feet. These figures emphasize the fact pointed out above that if the joints are placed too far apart in places where potential gradients in the earth are high, enough current may continue to flow through the pipes to cause serious damage. In all of the cases above re- ferred^ to the resistance joints were either spaced at consider- able distances apart or were not carefully enough made to insure a high resistance; they do not therefore show what may be ac- "'■ complished by the use of insulat- ing joints when installed at very frequent intervals and when proper care is taken to eliminate defects in the joints. In order to secure ^ -^ is 0, •8 ■*-, s "s- I ■d Electrolysis Mitigation 51 ftirther and more exact data on this point two experimental lines of 4-inch cast-iron pipe were laid at the Bureau of Standards under conditions which insured identical conditions except for the joints. The lines were laid parallel, 100 feet long and 40 feet apart, one line being provided with ordinary lead joints and the other with carefully made cement joints. The arrangements of these pipes is shown in Fig. 11. At the center of each line the pipes were separated by a large insulating plate and to the ends of the pipes adjoining this plate insulated leads were attached, and these were brought to the surface and short-circuited, an ammeter being inserted in these leads when it was desired to measure the current in the pipes. A difference of potential of 15 volts was impressed on the pipes and measure- ments of the current flowing in the pipes were made. The results are given in Table 6, and are a most striking illustration of the effect of carefully installed insulating joints in keeping the currents off the pipes. It will be seen that the current flowing in the line provided with cement joints was, when last measured, less than one twenty-two thousandth part of that flowing in the line having lead joints, and is decreasing. This current is so small as to be entirely negligible, in so far as electrolysis effects are concerned. TABLE 6 Current in Parallel Cement and Lead Joints Date Voltage Current Ratio, lead to cement Cement Lead Mflv 8. 1911 15 15 0.0032 .0011 29.1 24.2 9 100 Nov. 2, 1911 22000 It is very important to note that in the systems mentioned above not only have the currents in the pipes been reduced to relatively small values by means of insulating joints, but the systems thus protected have been singularly free from electrolysis troubles since the joints were installed. Although they have been in service for periods varying from 2 to 10 years or longer no serious cases of trouble have arisen, although in some instances other systems laid in the same streets and not so protected have suffered considerable 52 Technologic Papers of the Bureau of Standards damage from electrolysis. As an example, we may cite the ex- perience of the Cambridge Gas Co., of Cambridge, Mass. This company uses cement joints exclusively in their gas mains and they have had but little trouble from electrolysis, while the water pipes occupying the same region and not so protected are reported to have suffered severely for years. (c) Resistance of Various Types of Insulating Joints in Practice. — While the foregoing shows that insulating or resistance joints when properly installed and used in sufficient number will very greatly reduce the flow of current in pipes, there are certain features in connection with such installations, which, if not guarded against, may give rise to considerable trouble. In the first place, joints designed and installed as insulating joints may or may not be insulating when completed, and this is especially apt to be true after the joints have been in service for a considerable length of time. A little carelessness in making the joint may permit the two ends of the pipe to make metallic contact, in which case, of course, the joint becomes worthless as a protection against elec- trolysis. This is particularly apt to occur in making joints where cement or leadite is substituted for lead, but it can easily be guarded against with a little care. But even when every care is exercised in making the joints, they will often show surprisingly low resistances after having been in service for a considerable time. Table 7 shows the resistances of a number of so-caUed insulating joints in actual service selected at random, and these are typical of what may be expected. In measuring these resistances, a joint and a portion of the pipe were uncovered and the drop across the joint compared with that across a measured length of pipe either by means of a voltmeter or with a slide wire bridge. The size, weight, and material of the pipe being known, the resistance of both pipe and joint in ohms could also be calculated with a fair degree of accuracy. It is to be noted that a number of joints show an extremely low resistance, comparable with that of an ordinary lead joint, thereby indicating metallic contact of the pipes. This is particularly true of some of the leadite joints. It is important to note that the leadite joints were made without any attempt to make them insulating and this may be largely responsible for the large proportion of very low resistance joints. Kind Electrolysis Mitigation TABLE 7 Resistance of Joints in Service 53 Mains Class Joints Type Age Average potential across joint Resistance of joints Ohms Length of pipe with same re- sistance Cast... . D Do D Do D Da D Do D Do D Do D Do D Do D Do D Do D Do C Do C Do D Do D Do D Do D Do D Do D Do D Do D Do D Do D Wrought DO Do Do Do Do Do Do Do Standard ...do ...do ...do ...do ...do ...do ...do ..do Cast C Do C Inches Leadite. do... .do., .do., .do.. .do., .do., .do.. .do., .do., .do.. .do., .do., -do.. .do., -do., .do.. .do., .do., .do.. .. -do do 18-foot wood stave . N0.6D do .do... .do... .do... .do... do... do... ....do... ....do... Cement. Years 4 4 3 3 3 3 3 3 2 2 2 3 3 3 3 3 3 4 4 4 4 4 3 4 4 4 4 4 4 4 2 2 2 10 MUIlvolts 0.8 20.0 8.0 .02 .3 1.0 5.0 S.D .15 4.0 11.0 60.0 5.0 3.0 3.0 .6 .12 40.0 30.0 40.0 3.0 6.0 4000.0 57.0 60.0 1300.0 400.0 100.0 800.0 750.0 400.0 200.0 80.0 0.01 0.00133 .033 .123 .0003 .004 .014 .03 .03 .002 .018 .051 .015 .0012 .0052 .0052 .0113 .226 .357 .268 .357 .028 .057 40.0 2.64 .36 4.96 4.65 .425 5.35 9.0 10.65 9.5 .286 .002 Feet 36 897 7230 18 235 824 1760 1760 118 1060 3000 3350 269 306 306 665 13 300 21000 15 700 21000 1650 3350 2 350 000 155 000 37 600 292 000 480 000 25 000 560 000 1 400 000 626 000 558 000 60 800 42 Perhaps the most stirprising feature of Table 7 is the low resist- ance shown by the Dresser coupHngs which had been in service for a number of years. Although these joints are provided with rubber gaskets and doubtless had a very high resistance when new, the resistances have now fallen to a few ohms. A joint hav- 54 Technologic Papers of the Bureau of Standards ing a resistance of this magnitude, however, is practically as good as one of much higher resistance, since only ciurrents of negligible value can flow through such a resistance under the differences of potential that would commonly prevail across the joint in prac- tice. In the case of the joints having a resistance of a few hun- dredths of an ohm or lower, cmxents of considerable magnitude may be found, and these can not be regarded as satisfactory resistance joints. With reasonable care in the making, however, all joints whether made of cement or wood or some special joint provided with rubber or other insulating gasket will have ample resistance, and if properly located and used in a proper manner any of these joints should prove effective. Leadite joints when new also have ample resistance, comparing favorably with cement joints in this respect, but their resistance appears to decrease rapidly with age. This is very strikingly shown in Table 8, which shows the variation of the resistance of some leadite joints with time. A pipe line about loo feet long Tvas laid with leadite joints, care being taken to make all joints free from metallic contact between the ends of the pipe. At the center of the line the pipes were separated and an insulating plate inserted, and the two ends of the pipe on either side of the insu- lating plate were provided with insulated leads, in which an amme- ter could be inserted for the purpose of measuring from time to time the current flowing in the pipes. A difference of potential of 15 volts was impressed on this Une continuously for several months; this was sufficient to give a drop of potential of about 0.8 volt on each joint. TABLE 8 Showing Variation of Resistance of Leadite Joints with Time July 7, 1911 July 14, 1911 July 21, 1911 July 28, 1911 Aug. 11, 1911 Aug. 25, 1911 Sept. 8, 1911 Sept. 19, 1911 Feb. 19, 1915 Current Resistance.. - 0. 0069 2,174 0. 0076 1,990 0.046 326 0.268 56 0.064 23 0.360 41 1.24 12 1.88 8olims 132.0 0.113 The readings show that the current was very small when the pipe was first laid, but increased rapidly with time, and after being laid 4 months the resistances had decreased to about one two-thousandths of their initial value and were still decreasing. Electrolysis Mitigation 55 At the end of that time the current was discontinued and the pipes were allowed to stand in earth for about 14 months, when the resistance of the line was again meastired. It was then found that the resistance of the entire line had fallen to 0.25 ohm, and after about 4 years the resistance was only 0.113 ohm, or less than one nineteen thousandths part of its value at the beginning. This resistance is still high enough to have an appreciable value in reducing current flow in the pipe, the resistance of the joints being still nearly twenty times that of the pipes, but the results indicate that leadite joints can not be depended upon to remain permanently insulating, and their permanent value as a preventive of electro- lysis is at least questionable. At first it was supposed that the apparent decrease in the resistance of the joints might be due to increased leakage around the joints, but measurements made of some of the joints when uncovered show that the resistance of the joint itself has decreased. It was fotmd that the leadite contains a large amount of sulphur, and when placed in wet soil this gradu- ally oxidizes forming sulphuric acid which appears to be chiefly responsible for the steady falling off of the resistance of the joints. {d) Number of Insulating Joints Required. — A condition already referred to that is likely to cause trouble is a too infrequent use of insulating joints, and this condition is probably responsible for a good deal of the disfavor into which this method has fallen with some people. Obviously, if the join-^ are placed far apart, the long stretch of intervening pipe may pick up considerable ciurrent, and since most of this current must flow out of the pipe as it ap- proaches the insulating joint, serious electrolysis may occur on the positive side of the joint. The more frequently the joints are placed the less the danger from this source. It is of course impos- sible to lay down any very definite rules in regard to the frequency with which such joints should be used, since that must be deter- mined in each case by local conditions. In general, however, it may be said that the resistance joints should not be confined to the positive area as some have supposed, but should be distributed throughout the negative and neutral areas also. All lines which run near by, or cross under street railway tracks, are generally most in need of resistance joints. 56 Technologic Papers of the Bureau of Standards In many cases where there is good reason for believing that the drop of potential is fairly uniformly distributed throughout the entire region in which the insulating joints are to be placed, it is sufficient simply to determine the total difference of potential between the ends of the line affected and use this value in deter- mining the number of insulating joints that are needed in order that the drop of potential across each joint shall not exceed a pre- determined value. It usually happens, however, that the poten- tial gradient may vary greatly in different portions of the line and if the joints were uniformly spaced in such cases, the joints would either be more frequent than necessary in some places, or too few in others, and the condition of maximum of protection at a mini- mum cost would not be realized. This condition is very likely to occur where a pipe line nms at right angles to railway lines, in which case the potential gradient along the pipe will often be many times greater at points within a short distance on either side of the track than at more reihote places. Other conditions, such as the presence of other pipe systems, may also disturb the uniformity of the potential drop. In some instances, as in laying new lines where some cheap type of joint is being used, it may often be less expensive to allow a liberal factor of safety and install enough joints to be safe under any conditions that may arise; but in other cases, as, for instance, where insulating joints arerto be inserted in large and important mains already laid, where the cost of each joint is an important matter and where interruption of the service is of serious moment, it is important that no unnecessary joints be used, and that these be so placed that they will be most effective in reducing current flow in the pipes, and so that there will be no danger of developing a high enough difference of potential across the joint to cause trouble. For this reason, before attempting to install a series of insulating joints for the purpose of preventing electrolysis in cases where it is important for economic or other reasons to use as few joints as possible, it is important, first, to make a careful potential survey of the district to be affected and determine the magnitude of the potential gradients in a direction parallel to the pipe Hues. This will enable one to determine in advance the approximate number of joints that will be necessary and also the proper loca- Electrolysis Mitigation 57 tion of the joints, so that the drop of potential across any joint may not exceed a certain amount. If a new line is to be laid, it is safe to assume that the average potential gradient after the pipe has been laid will not differ greatly from that which prevails beforehand, provided the joints are used at proper intervals ; btit the distribution of this potential gradient will be greatly altered, practically all of the fall of potential occiur- ring at the joints. The average drop of potential across joints in any given portion of the line will be approximately equal to the total drop divided by the number of joints. When insulating joints are to be placed in old Hues it is well to bear in mind that the insertion of the joints in the pipe will, in general, increase the po- tential gradient along the pipe due to reduction of ciurrent flow in the pipes. This increase may reach as much as loo per cent or more, and allowance should be made for this. In actually measuring the potential gradients in the earth special precautions must be taken if trustworthy results are to be ob- tained. The best procedure to be followed in work of this sort is discussed in detail in Technologic Paper No. 28 of the Bureau of Standards, entitled "Methods of making electrolysis surveys. " After a series of joints are installed the only method of deter- mining experimentally whether or not a sufficient number of joints has been installed is by measuring the drop of potential across each joint and by measuring current flow in the pipes. If the joints are too few in number in any locality, there will be too high a voltage across the joints, and the consequent heavy leakage current may injure the pipe on the positive side of the joint. As to the voltage that can be safely permitted, that is a matter which depends on a variety of conditions, such as the nature of the soil, kind of joint used, etc., and can only be roughly indicated here. Careful observation of joints under average conditions for a considerable period, together with experiments to be described later, indicate that in cast-iron mains a drop across the joint of from 0.1 to 0.4 volt can usually be regarded as safe, while in wrought-iron pipes a voltage not exceeding about one-third of these values should be allowed. The lower Hmit applies to pipes located in low, wet places and to joints having a short leakage path between the sections of the pipe, and the upper Umit to pipes in 58 Technologic Papers of the Bureau of Standards comparatively dry soils and to joints having a long leakage path. This matter of the length of the leakage path around the joint is an important one and is treated later in discussing the relative value of different kinds of joints. If the joints used have not a very high resistance, as when leadite is used, for instance, consid- erable current may flow through the joints without making a dangerous drop across the joint, and the ciurents thus collected in a large number of branch Hnes may ultimately be carried to a few lines in a remote quarter and there give rise to serious damage. In order to guard against this, current measurements in the pipes should also be made. If in any Une a considerable current is found to be flowing, or if the voltage across the joints exceeds consid- erably the limits mentioned above, additional joints should be installed, or measures should be taken to reduce potential drops in the railway return systems. The latter course should be fol- lowed where practicable. One of the problems encountered in attempting to protect a pipe system by the use of resistance joints is the effect of other pipe systems in the same territory not so protected. Gas and water systems, for instance, are often brought into metallic con- tact with each other in many places, and this greatly increases the difficulty of protecting either system alone by the use of resistance joints. This difficulty could be largely avoided by inserting an insulating joint in the service pipe inside of the buildings in which metallic connections with the other system is made; This would usually be expensive, however, and there are other complications which are not so easily dealt with; where an uninsulated pipe system occupies the same territory with an insulated system, isolated cases of electrolysis are likely to occur. When a line having insulated joints must be connected to another line not so insulated trouble may be experienced, due to the tend- ency to develop high potential drops across the joints in such places, particularly if the insulated pipe line is at a potential con- siderably different from that of the earth, either positive or nega- tive. This condition is especially likely to occur if the uninsulated main is connected to negative return feeders, and those joints near which the negative feeders are attached, are often subjected to imavoidable differences of notential that may be sufficient to Electrolysis Mitigation 59 destroy the joint in a short time. For this reason the use of insu- lating joints and negative return feeders in the same system should be avoided. The difference of potential that can safely be permitted across a joint presents a problem of great importance and one to which comparatively little study has been given. Some of the factors governing this are mentioned above and one of the most important of these is the type of joint used. It is well recognized that the actual damage due to the discharge of current from a pipe depends not so much on the total quantity of electricity discharged but mainly on the distribution of the discharge. If the current leaves the pipe uniformly over a large surface, a much longer period must elapse before serious damage will result than if the intensity of cxorrent discharge is much greater at some points than others, so that conditions which tend to prevent concentration of discharge will correspondingly reduce the danger. As already shown, even pipes provided with insulating joints will carry some current, and especially if the joints are not very frequent; and since with high resistance joints most of this current must leave the pipes at every joint, it becomes important to determine as accurately as possible what the distribution of this discharge may be and to find how this distribution may be made most nearly uniform. (e) Effect of Form of Joint on Distribution of Leakage. — To e Fig. i8. — Construction of Wyckoff stave pipe, showing connection to iron pipe The Metropolitan Water Board of Boston has used a type of wooden joint shown in Fig. 19. This joint is simple in construc- tion, consisting of a one-half inch wooden liner made of overlapping sections of wood, the ring thus formed being wound with canvas impregnated with paraffin. The purpose of this is to prevent possible metallic contact between the ends of the pipes. The Pine Wedges 2& \//yj'y////^^/ /yy^//^l/ ^ Wooden Ring ;^\\^\v\\\\\^vvwxr Fig. 19. — Type of insulating joint used by Metropolitan Water Board of Boston. wooden staves are of clear white pine, planed to fit the curvature of the pipe, and are driven in by a special driver to prevent splinter- ing. Any leaks that may develop are stopped with white-pine Electrolysis Mitigation 69 wedges. These joints have been found to be very satisfactory up to about 75 pounds pressure. Higher pressures sometimes cause moderate leakage through pores of the wood, and this has been overcome by dipping the inner ends of the staves in red lead. In some cases the staves are reinforced by an iron band clamped around the spigot end of the pipe. Usually a slight change is made in the castings where this joint is to be inserted, the spigot end being cast without bead and the inside of the bell smooth without groove. The cost of these joints has been given as ranging from $5 to $12 when installed in new lines, but when installed in old mains the cost would be much higher. The resistance of this joint is Russian hemp lafhe ya^riy Yarn WMy//////mzm m^^T^/////////////. ^^^2^^^^^^^SZ2^ ^^^^^^^^^^^ Roman or-chard cement. Fig. 20. — Cement joint used by Cambridge Gas Light Co. ample under all circumstances that may arise, but the relatively short leakage path would often make it necessary to use the joint with greater frequency than would be necessary with joints having a long leakage path. Cement joints have been given a variety of forms, and one which has been used successfully for years by the Cambridge Gas Light Co. is shown in Fig. 20. In making this joint the inner ring of hemp is chosen exactly the right size to fill the annular space between bell and spigot, and this is rolled in when the pipes are set together and driven hard with the calking tool. As usually made by the Cambridge company no special attempt is made to keep the metal of the two adjacent lengths of pipe apart; not- 70 Technologic Papers of the Bureau of Standards withstanding this fact, the resistance of the joints has, on the whole, been high enough to prevent the accumulation of any con- siderable amounts of stray currents, and as a consequence this system has never been troubled by electrolysis, although the pipes of the Cambridge Water Co. are said to have suffered severely. After thoroughly tamping the ring of hemp into place the cement is carefully worked into the joint with trowel and calking tool until the space between bell and spigot is filled flush with the face of the bell. Another turn of hemp the same as the first is then laid against the cement and driven in with the calking tool just under the edge of the bell. The cement is in this way ren- dered very compact, and it is claimed that on this feature depends in large measure success of the joint. A collar of cement is finally laid over the outer ring of hemp to protect it from rot. If success is to be achieved with this joint, great care must be exercised in the making of the joints. Perfect cleanliness of the inside of the bell and outside of the spigot is necessary, and all loose scale and sand should be removed before the cement is put in place. Only the best quality of cement should be used and this should be thoroughly mixed and tamped into the joint with the greatest care. In some cases careful bedding of the pipes is important, as the cement joint is much less yielding than lead, and if any consider- able lateral movement of the pipes takes place it is liable to break the pipe, the strength of a well-made joint being as a rule greater than that of the pipe itself. In some instances, instead of making every joint of cement, every third or fourth joint only is made of cement, the others being lead. Except in extreme cases this seems likely to prove practically as effective in minimizing elec- trolysis troubles, and it has the great advantage that the lead joints impart a flexibility to the system that will greatly reduce troubles due to lateral motion of the pipes. The principal defect of the joint just described from the point of view of protection against electrolysis lies in the fact that no provi- sion is made for preventing metallic contact between the bell and spigot end of the pipe. In order to guard against this a modified construction, shown in Fig. 21, can be used. This is the same as Fig. 20 except that an insulating ring A of rubber or fiber or other suitable material is inserted to prevent actual metallic contact Electrolysis Mitigation 71 between the ends of the pipe. Such a joint should answer all requirements for ordinary service where joints are used at very frequent intervals, so that the drop of potential across the joint is not great enough to require a long leakage path. The use of leadite for joints has been confined chiefly to water mains, and for such service some prefer it to any other material, although it has not always met with favor. This material is melted and run into the joint after the manner of a poured-lead joint. It is cheaper than lead and some claim that it makes a better joint mechanically, but many dissent from this view. It often happens that when the joints are first made a large pro- portion of them will show considerable leakage, but in the presence Hussiari hsmp lathe yarn. y/ ///////////// / ///^m .Y«rn V////y////////////////y. WMMmm^//^M^^/^y/^^7P^ ym/A Fig. 21. — Cement joint '•Cemenf of water they seem to have a tendency to seal themselves up and the leaks will usually cease entirely within a day or two. It is very important to see that a dense mass completely fills the joint, and it is lack of care in this respect that is probably responsible for most of the trouble with leaky joints. The runner used in .pouring the joint should be so designed that there will be a head of 8 to 10 inches above the joint. If the material is at proper temperature this head is usually sufficient to insure a dense homogeneous mass of leadite in the joint. As already noted, the resistance of leadite is very high when first run, but after lying in the ground for some time its resistance decreases greatly, and until further experience has been had we would not recommend 72 Technologic Papers of the Bureau of Standards them unreservedly as suitable for preventing electrolysis, although they may be foimd valuable for this purpose. {h) Increasing the Length of Leakage Path Around Joint. — Inasmuch as short insulating joints are much easier and cheaper to build than long joints, it is well to discuss here some possible means whereby a long leakage path may be given to a short insulating joint and thus combine in one joint a certain measure of the economy and ease of construction of the short joint and the greater protective tendency of the long joint. A joint embodying these featmres is shown diagrammatically in Fig. 22. In this case the insulating joint proper between the bell and spigot is made with cement in the usual way, care being taken to prevent metallic y-n c fiegaHye Bus Another objection lies in the fact that should any discontinuity occur in the track between two adjacent ties, the entire railway current would be compelled to flow around through the pipes, and in case there were any high-resistance joints in that portion of the pipe, rapid destruction of the pipes would inevitably occur. A fourth objection to this type of pipe-drainage system Hes in the fact that it is impossible to control the distribution of cmrent flowing on the pipe system so that excessive cturent flow in certain portions of the pipe network can not be prevented. Taken altogether, the objections to this type of pipe drainage far outweigh the single advantage of low cost of copper and we do not consider it a desirable system to install under any circumstances. (c) Drainage by Uninsulated Feeders. — A modified form of pipe drainage which has frequently been used and which is less objec- tionable than the one just described is shown in Fig. 24. In this 82 Technologic Papers of the Bureau of Standards system instead of tying the pipes directly to the tracks at frequent intervals a copper cable is run from the negative bus along the pipe line and tapped to it at frequent intervals by taps a, a. This has the advantage over the system just described in that the pipe system is entirely independent of the tracks, so that the bad joints either in pipe or tracks between taps would in most cases be less serious. The total current drawn from the pipes can be controlled by installation of the booster B in series with a negative feeder at the power house or, to some extent, by varying the resistance of the cable. Here, as in the preceding case, it is not practicable to con- trol the distribution between the different sections of the pipe. The control of the total current by means of the booster will, Negative Feeders w'lih Resistance Taps to Pipes. riiiiaiiiiiimniiiiiiiiimiiiiKiiiiliiiiiiiiiniifiiiiiiiMiiiiiiiiiiiiiii Negative F'eeder Negaflye Bus Fig. 25 however, be objectionable because of the complication and cost of the necessary booster equipment. Another objection to this form of pipe drainage lies in the fact that the potential gradient on the pipe is the same as on the nega- tive feeder, and because of this the current density in the copper cable will be very low unless the potential gradients along the pipe system is objectionably high. The result would be a very uneconomical use of copper, leading to high cost of installation in comparison with the benefits obtained. (d) Drainage by Insulated Feeders. — In order to overcome certain of the objections mentioned above the modification shown in Fig. 25 might be used, although so far as we are aware, a system embodying these features has not heretofore been installed. In Electrolysis Mitigation 83 this case a cable is run along the pipe Une as before, but instead of tying the cable directly to the pipe line at frequent intervals, a direct connection to the pipe is made at the extreme end of the cable, a, and then at intermediate points b, b, connections are made between the cable and the pipe through suitably designed resist- ance taps. These might take the form of short steel cables prop- erly proportioned to give the desired resistance and similar in construction to those described later in connection with the dis- cussion of track drainage systems. It is possible by properly adjusting these resistances to secure a fairly equal distribution of current between the different taps regardless of the size of the feeder cable. In this way a better distribution of the current in the pipe system can be secured whereby a heavy current on the pipes at any point can be to a large extent avoided and at the same time the copper cable can be designed for maximum economy, and this greatly cheapens the installation. In such a case, however, the drop along the cable will, as a rule, be much greater than the drop along the pipe, and this will result in gradually increasing drop on each of the taps as we approach the power house. By the time the power house is reached, the drop between the pipes and the negative bus may become quite large. We can not, therefore, connect the tracks directly to the bus bar, as in Fig. 24, as in that case the pipes near the power house would become strongly positive to the tracks and there might be a large discharge of current from the pipes to the tracks in that locality. In order to avoid this, it is necessary to raise the potential of the track above the bus bar by about the same amount as the pipes, and this is accomplished by the installa- tion of a low resistance tap between the tracks and negative bus bars and at the power houses, as shown in Fig. 25. Still another modification of pipe drainage by means of insulated feeders is shown in Fig. 26. In this case, instead of running a single feeder along the pipe line to be protected, separate feeders are run from the power house to various points on the pipe line. These feeders must either be given sufficient cross section to carry the desired current with a total drop no greater than the rail drop between the power house and the extreme point at which the feeders run, or else boosters must be installed in the feeder in order 84 Technologic Papers of the Bureau of Standards to force the desired current through" them. In the latter case, a considerable economy in copper is secured, but at the expense and compUcation of the booster equipment. This difficulty is eliminated in the modification shown in Fig. 27. In this case the different feeders are designed to have practically the same resist- ance so that substantially the same current will flow in each one without any great difference of potential between the points at which they are connected to the tracks and, subject to this con- dition, the feeders are designed to give maximum copper economy. This, as a rule, involves a much greater drop on the feeders than is permissible along the tracks, and in order to prevent a large difference of potential between pipes and tracks near power :«= =0: Tracks Pipe Line ^ , ( D= 30: :5D=' 00=3 ■<2H h^gofiye Bus Fig. 26 house and also to seciu"e the necessary drop of potential to force the desired current over the drainage cables a resistance tap C is installed the same as in Fig. 25. For reasons given in detail later in connection with the discussion of the cost of insulated feeder systems in general, the pipe drainage systems shown in Figs. 25 and 27 wil^prove the most economical of any that can be installed, and at the same time they permit an accurate determination of the distribution of current in the different parts of the pipe network, and also permit a considerable amount of regulation of such current distribution through the adjustment of the individual feeders or resistance taps. This control feature is of the greatest importance, since only in this Electrolysis Mitigation 85 way can dangerously heavy currents in the pipes at certain points be avoided. Even these systems, however, possess the drawbacks that must be common to all pipe drainage systems, namely, that unless the potential drops in the tracks are kept within reasonable limits, large currents may have to be drawn from the pipes in order to keep them from becoming too strongly positive to the earth. Hence, the pipe drainage system even in its best form can not be expected to give satisfactory results unless installed with due regard to its influence on neighboring structures, and particularly unless potential drops in the tracks are first reduced to such low values that only a very small amount of current needs to be taken iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii II ■■■iiiiiiiiii Ill Tracks ^ Pipe Line tiegaUve- Bus Fig. 27 from the pipes. The means whereby such low voltage drops in the negative return may be secured in the most economical manner are discussed in a later section of this paper. 10. SUMMARY OF DISCUSSION OF METHODS OF MITIGATION APPLICABLE TO PIPES The discussion presented above relating to methods of mitiga- tion applicable to pipe systems leads to the conclusion that of the various methods that have been tried none are suitable for general use as primary means of preventing electrolysis troubles. The methods of chemical protection, cement coatings, cathodic pro- tection, and conducting coatings should be regarded as substan- 86 Technologic Papers of the Bureau of Standards tially worthless in their present state of development. Surface insulation of pipes by means of paints or dips is not much more reliable, but insulation by putting the pipes in troughs or conduits filled with pitch may be used in special cases where the expense would be justified. The practice of .placing all pipes as far as possible from railway tracks affords a certain measure of protection of which advantage should always be taken wherever practicable in laying new lines or relaying old ones, and the use of electric screens is often a valuable expedient in taking care of acute local cases of trouble in existing mains. These methods, with the exception of that relating to the proper location of pipes in new work, are suited only to special conditions, however, and are not usually to be considered as important factors in any general plan for electrolysis mitigation. Pipe drainage is sometimes useful but should be used with proper restriction and with due precautions against setting up any dangerous condition either in the system drained or in neighboring systems. In general, in city networks where there are a number of independent underground systems to be protected, pipe drainage should be used as little as possible, the chief reliance being placed on mitigative measures applied to the railway negative return. The drainage of lead cable systems will, however, usually be desirable, but these should always be drained by means of suitable insulated-feeder systems so arranged as to drain the least prac- ticable current from the cables in order that neighboring struc- tures may not be. subjected to imnecessary danger thereby. The most valuable mitigative measure that can be applied to pipe systems consists in the proper use of insulating joints, and the extensive use of such joints should be encouraged in new work and in making repairs. Precautions are necessary in their use, however, as set forth in the preceding discussion. None of the methods of mitigation available for application to pipe systems are, except in special cases, to be recommended as principal means of mitigation, but rather as auxiliary or emergency measures, which may be used in connection with, and supple- mentary to, measures applied to the railway return systems for reducing stray currents to the lowest practicable minimum. Methods for accomplishing this end will be discussed in the next section. Electrolysis Mitigation ■ 87 IV. METHODS OF MITIGATION APPLICABLE TO RAILWAY NEGATIVE RETURN None of the systems of electrolysis protection mentioned above have to do with the nature or condition of the street railway return circuits, and in the practical working out of such methods the railway return system is often ignored. The currents are per- mitted to flow away from the tracks without restriction, and the sole purpose of the methods outlined is either to prevent their entrance into the pipes or to provide means for their exit with as little injury to the pipes as possible. It would appear more logical to attack the problem by beginning at the source of the evil and prevent, to a large extent at least, the leakage of the currents from the railway return conductors into the earth. This is the more emphasized by the fact that in the past, where such mitigative measures have been applied to the pipes, the burden of providing the protection has usually fallen where it does not properly belong, viz, on the injured party and not on the party causing the injury. We shall now consider what measures may be applied by the street railway companies to their own properties with the view of removing, or at least greatly reducing, the cause of the trouble. 1. ALTERNATING-CIJRRENT SYSTEMS The proposition to use alternating current for street-railway traction purposes need hardly be discussed here. If alternating current were used, the amount of electrolysis that would occur would in most cases be not more than i per cent of what it is with direct current. In the case of lead pipes the corrosion may be greater than this, but the experimental data available show that there is little likelihood of its exceeding this percentage under practical conditions. The objections to the substitution of alternating current for direct current in the case of systems already installed in large cities are so obvious and so serious that the question needs no discussion, particularly since the problem of electrolysis protection can be taken care of by other means. In the case of suburban or interurban systems, on the other hand, where alternating current possesses certain advantages which for other reasons often justify its use, the fact that such a system will be comparatively free from electrolysis troubles is an additional argument in favor of its use. 88 Technologic Papers of the Bureau of Standards This question of electrolysis, due to stray currents from inter- urban roads, is becoming increasingly important as pipe -systems are installed or enlarged in small towns along the route, and par- ticularly because of the steadily increasing number of pipe lines being installed throughout the coimtry. In such cases the alter- nating-current system of traction may well be regarded as a satisfactory solution of the electrolysis problem, although at the present time the importance of this protection along interurban lines is not great enough to be by any means a deciding factor in the choice of systems. 2. DOUBLE-TROLLEY SYSTEMS The double-trolley system of electric traction as at present used in Cincinnati, and the corresponding underground conduit sys- tems as used in Washington and in parts of New York City, elimi- nate almost completely the danger of electrolysis, the' small leak- age which occurs being of no practical consequence. The chief objections to its use are the cost of installation and the increased operating difficulties which it involves. The cost of installation, which is very great, does not appear to be justified merely as a means of electrolysis protection, inasmuch as a very satisfactory degree of protection can be obtained by other and much more economical means. 3. USE OF NEGATIVE TROLLEY Practically all street-railway systems in this coimtry are oper- ated with positive trolleys. Under such conditions the stray cur- rent is taken up by the pipes over a relatively large area and dis- charged within a comparatively small area, commonly called the positive area, near the power house. It is obvious, therefore, that the current density within this small positive area will be much greater on the average than in the mifth larger negative area. If the polarity of the trolley were reversed, the positive and negative areas would be interchanged without affecting to any considerable extent the intensity of the current at any point. We should then have a comparatively low average density of current discharge from the pipes throughout a much larger positive area. The total amotmt of corrosion would not be materially affected, but its dis- Electrolysis Mitigation 89 tribution over the larger area would tend to reduce the intensity of damage at any particular point, so that the average life of the pipes would be increased and trouble would be much slower in developing. Aside from the fact that in some cases the increased life of cer- tain of the pipes might be such that they would endtue until they would have to be removed anyway for reasons other than their failure, about all that can be said in favor of this proposal is that it postpones the time when serious trouble will develop. On the other hand, most engineers would prefer to have the trouble more localized, as it is under present conditions, where it can be more carefully watched and more effectively controlled. Furthermore, this reversal of trolley polarity will generally impose serious hard- ship on cable-owning companies which have already installed a drainage system for the protection of their cables. This method does not, therefore, appear to be worthy of serious consideration in the present instance. 4. PERIODIC REVERSAL OF TROLLEY POLARITY Another proposal that has been advanced has for its object the attainment, as far as practicable, of the electrolytic conditions which prevail with alternating currents, without discarding the direct-current method of electric traction. If an alternating cur- rent flows from iron into soil, there is, during any half cycle in which the iron is positive, corrosion of the iron just as in the case of direct current, but during the succeeding half cycle the corroded iron is again plated out as metallic iron on the surface of the pipe. If the efl&ciency of both corrosion and deposition is 100 per cent, there will be no perceptible corrosion of the metal surface, and in the case of ordinary alternating currents this condition is very nearly reaUzed in practice. Experiments have shown that even with very low frequencies of reversals, such as once in 24 hours, a large measure of this effect persists, and the ultimate amount of corrosion is much less than would occur if the polarity is maintained always the same. It has therefore been proposed to reverse the polarity of the trolley at stated intervals, as, for example, once every 24 hours, as a means of reducing electrolysis troubles. If the reversals are made 90 Technologic Papers of the Bureau of Standards with sufficient frequency to give effective protection, the method is open to the objection that it introduces a complication into operating conditions that does not appear to be justified by the benefits that would result, particularly where several substations are being operated in parallel. Where only a single substation is used, a reversal of polarity once in 24 hours would be entirely practicable and would undoubtedly be decidedly beneficial. Extensive experiments at the Bureau of Standards show that with daily reversals of polarity the corrosion in the case of iron pipes at any particular point will be only about one-fourth as much as when the current flows continuously in the same direction. For lead pipes and cables the polarity would have to be reversed much more frequently in order to reduce the corrosion at any point to less than 50 per cent of that which would occur with uni- directional current. 5. REDUCING POTENTIAL DIFFERENCES IN THE UNINSULATED PORTION OF NEGATIVE RETURN Turning now to a consideration of what may be accomplished in the way of providing an adequate return circuit for the railway currents we find a number of possibilities available. In consid- ering these methods it is necessary to bear in mind that the ftmda- mental condition to be realized in order to reduce the leakage of stray currents into the earth is not the maintenance of the lowest possible resistance in the negative return hut the minimum differ- ences of potential between different parts of the grounded track network. The two conditions are not necessarily identical, depending as they do on the character of the negative retvun system used. The various possible methods of thus reducing track gradients to a satisfactory value all have for their primary object the taking of the ctnrent direct from the track through the agency of negative feeders, and they are therefore classed in one general group under the name of "track-drainage systems." These track-drainage systems present several separate practical embodiments, the chief of which are (a) the proper construction and maintenance of track to secure the full benefit of the conductivity of the rails, (b) ground- ing of tracks and negative bus, (c) the use of iminsulated negative Electrolysis Mitigation 91 feeders in parallel with the rails, (d) the use of insulated negative feeders without boosters, (e) the use of insulated negative feeders with boosters, (/) the three-wire systems, and {g) the use of a proper number of substations so located as to take the current from the tracks so as to combine in greatest degree economy of distribution of power and reduction of leakage current from the rails. These different systems are discussed separately below. 6. CONSTRUCTION AND MAINTENANCE OF WAY Proper maintenance of the track in order to secure high con- ductivity is everywhere recognized as a necessary condition in electric railway operation, but it does not always receive the atten- tion that its importance justifies. In the matter of joints alone there is a very wide diversity of practice. In recent years, how- ever, engineers have rapidly come to recognize the difficulty of maintaining a proper state of track conductivity by merely bridging the joints with short copper bonds. Such construction is still widely used, but it is finding much less favor than formerly, and in many systems, particularly where the traffic is heavy, these methods of shunting the joints are used, if at all, chiefly as second- ary expedients. The tendency in such cases is to make the joint itself electrically continuous rather than to shunt around it, although both methods are not uncommonly combined. The methods whereby more or less perfect continuity of the joints is obtained embrace the various types of welded joints such as electric welds. Thermit welds, etc., and those joints in which a second metal such as zinc and its alloys are employed to form the junction. Of these latter the well-known Nichol joint made by pouring molten zinc between the fishplates and the rail ends is one of the most effective, and has given very satisfactory service for a number of years. The zinc is poured in after the fishplates are bolted on and the expansion of the zinc which takes place on solidif5dng makes a firm and permanent contact between the fish- plates and rail ends. Joints made either in this way or by any of the various welding processes have, as a rule, a lower resistance when new than an equal length of rail, and for the most part have given good satisfaction in service, although some trouble has been experienced, particularly in welded joints, due to parting of the 92 Technologic Papers of the Bureau of Standards rails at the weld. Experience to date, however, indicates that these joints are very satisfactory in all cases where the tracks are laid in paved streets or otherwise suitably reinforced. As a pre- cautionary measure, however, some engineers prefer to bond over all joints, also, and we understand that this is being largely done in St. Louis. Cross bonding between the rails is also much resorted to as a means of maintaining track conductivity, and this is a very neces- sary precaution against the troubles arising from bad joints. If such cross bonds are properly installed and maintained at suffi- ciently frequent intervals, the deleterious effect of occasional bad joints is almost entirely eliminated. These cross bonds are usually placed at intervals of from 200 to 500 feet and these distances are sufficient if the cross bonds and rail joints are fairly well maintained. All special work should be shimted by heavy cables capable of carrying all of the current passing over the tracks at that point. In many places this is the regular practice, but it is often neglected entirely or poorly maintained, and in some cases the drop across special work has given rise to very serious electrolysis. The remedy is so simple and effective that only carelessness can accoimt for the existence of trouble of this nature. The question of weight of rails is one that has not usually received the consideration which it deserves, particularly in the case of the T rails. At the present price of girder rails there is very little difference between the cost of rail and copper of the same conductivity. The conductivity of steel rails varies consid- erably, but on the average it will be about one-tenth to one- twelfth that of commercial copper. Hence, at the former figure with copper at 1 7 cents per pound and rails at $39 per ton the cost of a given conductance will be about 10 per cent greater if obtained by using copper cables in parallel with th^rails than if it is obtained by the use of heavier rails. In the case of T rails costing $28 per ton the cost of a given conductance in steel rails will be about two-thirds that for copper. This is on the assumption that the extra labor cost of laying the heavier rails will about equal the cost of laying the copper cables. As to whether or not this is true will depend largely on local conditions, so that the above figures are only approximate. Electrolysis Mitigation 93 An important factor which should be considered here, however, is the reduction in track and rolling stock maintenance charges that accompany the use of heavier rails. This is often sufficient to justify the extra expense of the heavier rails quite apart from any consideration of their higher conductance, and largely for this reason there has been a general tendency in recent years to use heavier rails. When we consider this fact in connection with the increased conductance of such rails there would appear to be good reason for using somewhat heavier rails than traffic condi- tions would usually call for in those regions near the power houses where it is important to secure higher conductance than would be afforded by the usual weight of rails. The rail weights used in most large cities range for the most part between 80 and 1 20 pounds, so that we may consider that the approximate average weight is but little more than 100 pounds per yard. A double track of these rails having good joints has a conductance equivalent to about 4.5 million circular mils of copper. Standard rails are now rolled and in practical use weighing 137 to 139 pounds per yard and would have a con- ductance of about six and one-quarter million circular mils, or an increase over that of the average rails equivalent to about one and three-quarter million circular mils. It would therefore appear to be worth while in some cases, when tracks are being relaid near the power stations, to consider seriously the advisability of using much heavier rails than are usually adopted, the combined effect of improved track conditions and increased conductance being sufficient to justify the additional expense. A properly constructed and drained roadbed is also a very effective aid in reducing the leakage of stray currents from the rails. The amount that can be accomplished in this way will, of course, vary greatly with varying conditions so that no specific recommendations can be made here, other than to point out that since the conductance of the leakage path is mainly dependent on the amount of moisture which is contained in the material forming the roadbed and the earth beneath, any construction which tends to reduce the average moisture content therein will reduce in corresponding degree the magnitude of the leakage currents. Indeed, we have made tests on long lines of track without inter- 94 Technologic Papers of the Bureau of Standards sections to cause complications, in which it was found that leakage from the rails had been almost entirely eliminated, the reason being that the road was so constructed that the leakage path from rails to earth was on the whole comparatively dry. We believe that much more could be accomplished by this means than is commonly supposed without materially increasing the cost of construction, although it must not be regarded as a satisfactory primary means of electrolysis mitigation. 1. GROUNDING OF TRACKS AND NEGATIVE BUS The grounding of the negative bus or the tracks near the power house was one of the earliest expedients resorted to for the purpose of reducing the resistance of the negative return. Because of the decided tendency for such grounds to increase the flow of leakage current from the tracks it was early recognized that they might tend to increase electrolysis troubles, and in the majority of cases these ground plates have been abandoned. There are, however, a good many cases where such grounds still exist, so that their bearing on the electrolysis situation is an important matter. During the last few years, also, it has been seriously recommended by certain well-known engineers that this expedient of grounding tracks be carried much further, and, in fact, used as a means of eliminating electrolysis. The method of procedure proposed by the advocates of this sys- tem is to lay ground plates several feet below the track and at frequent intervals throughout the stystem so as to secure as nearly as possible the perfect grounding of the tracks at all points. This proposal has been based chiefly on experiments which have been performed with small electrodes buried in the earth which showed that most of the resistance between such electrodes and the earth was found to be in the region very near to the electrode, owing to the small cross section of the%urrent path at such points. From these experiments the conclusion was drawn that at a dis- tance of 3 or 4 feet from such an electrode the cross section became so great that the resistance practically disappeared. It was there- fore thought that if frequent ground plates were laid 3 or 4 feet below the track and connected thereto, the large cross section of the path offered for the discharge of current into the earth would Electrolysis Mitigation 95 cause the resistance of the negative return practically to disappear, and consequently the drop of potential in the earth would be so small that no aopreciable current would be picked up by the pipes. Oiur own investigations on this subject, which have comprised experiments with electrodes both of the size used in the investiga- tion above referred to, and also with much larger ones, which are more comparable with conditions which actually exist in railway systems, and also the results of voltage surveys made remote from electrodes that might serve as sources of stray currents, have con- vinced us that the theory on which this method of protection is based is erroneous, and that the stray currents that would be introduced into the earth by the proposed ground plates along the track would greatly aggravate the trouble from electrolysis. We would strongly urge, therefore, that grounds of all kind, whether along the track or the negative bus, be altogether elimi- nated in every case. 8. UNINSULATED NEGATIVE FEEDERS A typical form of uninsulated negative feeder system is shown in Fig. 28. It will be seen that this consists essentially in running n rt I SOS D//?scT r/es ro T/?ACJt/s^ system are rapidly becoming appreciated by railway companies throughout the country. (6) Types of Insulated Negative Feeders. — In the insulated negative feeder system, instead of tying the tracks directly to the negative bus and depending on the tracks and such copper as may be in parallel therewith to return tlfe current to the power house, the connection at the power house is either removed or given a suitable resistance, and insulated feeders are rim from the negative bus to various points on the tracks, as shown diagramatically in Fig. 30. By this means several important results may be achieved. In the first place, the current being taken off the rails at numerous points, high current densities, and consequently high potential gradients in the rails, can be avoided to any desired degree. In the second place, by so designing the system that the drop of Electrolysis Mitigation 99 potential on all of the feeders is the same, the current flow in the tracks can be so subdivided that the direction of the flow will be reversed, thus preventing the accumulation of large potential differ- ences between points on the tracks which are some distance apart. Ojstonce />am ^tv er //pose Further, it will be evident that in this case the actual drop of potential in the different feeders is of little importance so far as electrolysis protection is concerned, so long as it is nearly the same in all. We can thus impose any desired potential restriction on the track and still be free to design the feeders to give maximum economy, which we can not do when the feeders are connected in /'otver/fovse £>/s/oj7ce />-om fbtver //ai/ss Fig. 31. — Effect of insulated feeders in reducing rail gradients parallel with the tracks, as has been the common practice in the past in practically every American city. A graphic representation of what can be accomplished by using a system of insulated feeders of this sort is shown in Figs. 29, 30, and 31. loo Technologic Papers of the Bureau of Standards Fig. 29 shows the arrangement of the negative return in which any feeders that are used are connected directly in parallel with the track throughout, and a uniform distribution of the load on the line is assumed. The arrows show the direction of the current flow, and the curved line AB shows how the potentials of the rails vary from point to point, the potential curve becoming steeper and steeper as the power house is approached. With tmiform distribution of the load, as here assumed, and uniform track con- ductivity it can be readily shown that this potential curve is the segment of a parabola. Fig. 30 shows the same system with insulated negative feeders run from the negative bus to four points on the track, two in either direction, and so designed that the drop of potential is the same on all during average load conditions. Here also the curved lines represent the potential of the tracks from point to point, and, as in Fig. 29, the curves are segments of parabolas. The portion DE of Fig. 30 corresponds exactly to' the portion BC of Fig. 29. It is seen that the current flow in the tracks is here so subdivided that the total over-all potentials become very small, and consequently the tendency to set up large differences of potential between the rails and surrounding structures is practically eliminated. An examination of Figs. 29 and 30 shows that the maximum potential difference in the rails is reduced to one-sixteenth of its former value by the installation of only two negative feeders on each side of the station. It is evident, of coiirse, that this great reduction in the potential difference in the tracks is obtained at the sacrifice of track conductance, of which little use is made in the latter case. Between these two extremes any desired compro- mise can be obtained; that is to say, instead of making the drop on all of the feeders the same, We may make the drop on the feeders lower as we approach the power hotise, thus making a continuous gradient equal to the maximum allowable gradient all the way to the station. We can thus utilize the conductance of the tracks to the limiting extent consistent with satisfactory electrolysis con- ditions. This will result in a more economical installation but at the expense of greater over-all potential differences in the track return system, even though the Umiting potential gradients in Electrolysis Mitigation loi the track may be the same. This type of feeder system is shown diagramatically in Fig. 31. This latter plan is often more economical than the plan shown in Fig. 30, and it is sometimes to be recommended where condi- tions are such that there is a large track conductance to be availed of. Wherever the track conductance is small, however, so that most of the current will have to be returned by the feeders anyway, the equal-drop system is to be preferred, since electrolysis condi- tions will be better and the difference in cost not very great. A still further modification of the insulated feeder system will gen- erally be found to be desirable. In this modification, instead of running several independent feeders in one direction from the power house, a single large feeder is run along the line and connected to T/r-j^CHS BUS Fig. 32. — Diagrammatic representation of insulated negative feeders the tracks at suitable points by means of resistance taps. This system is shown diagrammatically in Fig. 32 . It has the advantage of simplicity of line construction, cheaper first cost and mainte- nance, due to running one large feeder instead of several small ones (where the total feeder area is not great) , and it also has the advan- tage of bringing back a much larger load on the single feeder, which results in a less variable current, and this makes possible a more economical use of the negative copper. From the foregoing it will be apparent that the economy of using insulated negative feeders as compared with uninsulated feeders in parallel with the tracks is so great, particularly when it is necessary to maintain the voltage drops in the track at very low figures, such as is usually necessary for electrolysis protection, I02 Technologic Papers of the Bureau of Standards that only insulated negative feeders can be considered seriously, and they should always be installed in lieu of uninsulated feeders when the conductance of the tracks is not in itself suflficient to carry the current without excessive voltage drop. (c) Calculation of Insulated Negative Feeder System. — It is desir- able to state briefly here the methods of procedure in laying out the design of insulated negative feeder systems. A careful study is first made of the load distribution over the entire territory sup- plied by the station under consideration, and from this study the most natural points for taking off the current are selected and the number of amperes that must be taken off at each point in order that the current in the rails shall not exceed a predetermined value is determined. NEGAT/VS" BLfS Fig. 33. — Diagram illustrating calculations of insulated negative feeders A preliminary value of potential drop in the first feeder, which is usuallv one of the largest and most important ones, is then assumed, and from this drop and the current to be carried by the feeder, together with its length, the cross section of the feeder is calculated. When this is done, all of the other feeders must be designed consistently with this so as to avoid potential gradients in the tracks greater than the value determined upon as the limiting allowable average gradient. Beginning thus with feeder No. i, I^. 33, we find that the volt- age drop to be allowed on feeder No. 2 is the drop on No. i less the allowable drop on the tracks over the distance (a) between the points at which the two feeders connect to the rails. For instance, if the assumed drop on feeder No. i is 15 volts and the distance between the two taps is, say, 1200 feet and we are per- mitting a maximum drop of one-half volt per 1000 feet in the tracks, the average gradient between C and D will in general be Electrolysis Mitigation 103 less than this figure, depending upon the amount of load origi-' nating between these points. The average value of this can be determined from the car schedule. Assuming it to be 0.4 volt per thousand feet, for example, the total average drop between C and D will be 0.48 volt. The total drop on feeder No. 2 will therefore be 1 5 — 0.48 = 14.52 volts. From this value and the current assigned to feeder No. 2 its cross section can be calculated, the length of course, being already fixed. We proceed in a precisely similar manner to calculate any other feeders on this same line between feeder No. 2 and the power house, including the resistance tap B at the power house. It is then necessary to work outward from the power house in calculating the remaining feeders. For example, if the voltage drop on the power house tap has been fotmd by the above-described procedure to be 12 volts, the drop on feeder No. 4 will be 12 volts plus the allow- able drop on the tracks between the power house tap and the point E at which the feeder is connected to the tracks, and so on for other feeders more remote from the power house. Sometimes the cross section of the feeders as thus calculated will be too small to carry the required current without overheating, and when this is the case the feeder must be made sufficiently large to carry the current and an additional resistance inserted prefer- ably at or near the power house in order to give the necessary voltage drop. When this calculation is complete for all the feeders, we are ready to determine whether the original assumption made in regard to the voltage drop on the first feeder was the one that would give approximately the most economical installation over the entire system. To determine this we sum up the total cost of the feeders installed and determine the proper annual charge, including interest, taxes, and depreciation, and also calculate the total annual value of the energy lost in the feeders and resistance taps. If these are approximately equal, the voltage drop assumed was the proper one. If, however, the annual charge on the feeder system is less than the cost of lost energy, the voltage assumed is too high (and vice versa) and a correction must be made. This correction may be very easily and simply supplied without recalculating the feeder system as in the first instance. For ex- ample, if the annual cost of the feeders is found to exceed that of I04 Technologic Papers of the Bureau of Standards the energy lost by 20 per cent, we must increase the voltage drop by approximately 10 per cent, and reduce the area of the feeders by about 10 per cent, which change will bring the cost to approxi- mate equality, a condition for the most economical installation. If E^ is the original voltage drop calculated for any given feeder and E2 is the weighted mean voltage drop for all feeders, then the E increase of voltage on any feeder being — we must reduce the cross section of the feeder by the factor „ E^. The value of E.^ ' ID in each case is the initial voltage drop calculated for that particular feeder, so that each feeder is corrected by a diflferent factor. When the correction is made in this way there is no change in the poten- tial gradients and current distribution assumed for the rails. (d) Effect of Concentrated Loads on Effectiveness of Insulated Feeders. — The view has been taken by some engineers that while the insulated negative feeder system works out very well when appUed to a fairly well distributed load it fails to show any appre- ciable advantage when applied to conditions where the load is concentrated at a few points, such as is usually the case on an in- frequent schedule. While this is true when we consider the maximum values of potential drop between different points of the negative return, it is not true if we are considering the effectiveness of the electrolysis protection afforded. The significance of this statement will be made more clear by reference to Fig. 34. Let us assume, as shown diagramatically in Fig. 34, that we have a linear railway system to which a number of insulated feeders are connected at distributed points, the feeders being so designed that the resistances of all of the feeders are substantially the same. Let us assume also that we have a single train oper- ating on the line in which case the Itad will be delivered to the tracks at one point which will be moving back and forth on the line. Consider first the conditions that prevail when the car is at the point A. It will be evident that the current delivered to the rails will divide at the point A, a portion of it going over feeder No. I and the remainder going in the direction of S, as shown by the arrows. Electrolysis Mitigation 105 Since the current going in the direction of B will find several parallel paths by which to return to the negative bus, each path having approximately the same resistance as path No. i, it will be evident that in this position of the train the greater part of the current will remain on the tracks between A and B, the track current being reduced somewhat at B and again at C and also at D, and finally the remainder going off on feeder No. 5 at E. Under these conditions the drop of potential in the tracks will be continuous from A to E, the point A being that of highest and / /' /' ^ / Ax {J / / / / C.-^ ^ \ \ \ 'X7.-^l \ — • ^1 I / T / / / £.^ \ \ y aX\ ^■*- 3.< ^■ y Fig. 34. — Reversal of leakage current with concentrated load and insulated negative feeders point E that of lowest potential. Under these conditions the leakage currents tend to leave the track in the region of A and B and rettun to the track again in the region of D and E. The general direction of this leakage current is shown by the curved dotted lines and attached arrows. Since only a small part of the current is taken off on the insulated feeder at A , it is evident that if this condition were to be perma- nent electrolysis conditions would be nearly as bad as if feeder^ No. I did not exist. However, the load which was originally at A progresses along the track in the direction of E, and when it arrives at C it is evident that this is the point of highest potential, and in this position part of the current is going off over feeder No. 3, part of it is flowing on toward D, and a portion flowing back toward B and going on feeders Nos. i and 2. io6 Technologic Papers of the Bureau of Standards The direction of current flow under these conditions is shown by the arrows in Fig. 35, and the leakage currents, as shown by the curved lines, tend to flow off in the region around C and enter the tracks again at the ends of the line in the vicinities of A and E. It will thus be seen that the direction of the potential gradient in the section between A and C has become reversed. Thus, as the load progresses in the direction of E the direction of the current flow in the tracks to the left of the load will always be the reverse of what it was in the beginning, and finally when the load reaches the point E the voltage conditions of the entire line are exactly the reverse of what they were in the beginning. The conditions at this time are shown in Fig. 36. The point E is now the point of highest potential and A is the point of „--^ 'r^\i^?2 B. t- M . r I \ /. •s._ '^■. '1/^ Fig- 3S lowest potential, and the leakage currents tend to leave the tracks in the regions around A and B. It will be evident, therefore, that if there is a pipe system paralleling the railway line, and the load is concentrated at A, the pipes in this vicinity will be negative to the tracks, and a certain amount of corrosion will take place at the latter point. When the load is shifted to E, however, the pipes become negative to the tracks in the vicinity of E and positive around A. It will therefore be evident that as the con- centrated load moves back and fortMl along the line it gives rise to cyclical variations in the potential difference between the pipes and tracks at any given point, the pipes becoming alternately positive and negative as the load is remote from or near to the point under consideration. This fact is of very great importance in determining the magnitude of electrolysis damage that will result. Electrolysis Mitigation 107 Extensive expennents have shown that the process of electro- lytic corrosion of iron when embedded in the soil is to a limited extent a reversit^le process. During any interval when the iron is discharging a current into the earth the iron will be corroded and go into solution. If conditions are such that the iron remains in solution near the surface of the pipe tmtil the direction of the current is reversed, there will be a tendency for the metallic iron to be plated back on the pipe. This will usually be deposited in a more or less spongy form that will have no value mechanically, but it is nevertheless in the form of metallic iron in contact with the outer surface of the pipe, and when the iron again becomes ■* . ^v \ \ \ ■i- — ^-* — -"' D.-A \ \ l i ' ) 1 ^v77 Fig. 36 positive this same iron must again be corroded before the deeper layers can be affected. If this process were entirely reversible, an alternating current would do no damage at all in the way of corrosion, but unfortu- nately the process is not entirely reversible. Oxygen dissolved by the soil waters coming in contact with the dissolved iron salt tends to precipitate the insoluble iron oxides, and when this occurs the iron can not entirely be plated back on the pipe upon the reversal of the current flow. For this reason an alternating cur- rent will produce a certain amount of electrolytic action, and the slower the frequency of the reversal the more oxidation of the dis- solved iron will take place and consequently the greater the amount of the corrosion. io8 Technologic Papers of the Bureau of Standards Experiments have shown however, that if the period of the cycle is made quite long, as much as lo to 15 minutes, or even longer, the actual amount of corrosion that occurs, while it may be very considerable, is nevertheless very much less than would be the case if voltages of the same magnitude existed in the nega- tive return and always in the same general direction. For this reason this negative feeder system, when used in connection with a concentrated load, will always give much greater reduction in the actual amount of the electrolysis damage than it does in the actual voltages which exist from time to time between different points in the negative return. In consequence of this fact, it may be stated that so long as improvement in electrolysis conditions is the object sought, the insulated negative feeder system may be regarded as being quite as applicable to a system having concen- trated loads moving back and forth along the line at frequent intervals as to a system in which the loads are more or less uni- formly distributed along the Hne. When, however, the period of the load cycle becomes half an hour or an hour or even longer the corrosion becomes much greater, and may then become quite serious unless the voltages are kept very low. To be siure, the energy loss can be shown to be greater with the concentrated load than with a distributed load, but this is true exactly in the same ratio on both positive and negative feeders and in the uninsulated rail return; and this fact can not, therefore, be considered in any sense whatever a defect in the insulated negative retiurn feeder system when appUed to loads of this character. 10. INSULATED NEGATIVE FEEDERS WITH BOOSTERS (a) Direct Boosters. — The insulated negative feeder system described above, because of its simplicity and economy will be found most suitable for practicall}* all cases where the feeding distances are not too great. Cases are frequently encountered, however, in which one or more of the Hnes are suppHed over such a great distance that serious difficulites are encountered. For instance, if the power house is suppl}ning a network of lines near the station, insulated feeders may be made to take care of this area without requiring a voltage drop on the feeders or the power-house tap of more than perhaps 10 to 20 Electrolysis Mitigation 109 volts. At the same time one or more very long and perhaps heavily loaded lines may extend from the network, and if an insulated feeder, as above described, is to be used to take care of this line also, it would be necessary to use a very heavy feeder in order to keep the voltage drop comparable with that on the feeders running to the local network, or else a high resistance would have to be inserted in series with the latter. The former alternative would involve a prohibitive charge for copper, while the latter, by making all of the ciurent from the network return over a relatively large voltage drop in the power- house tap, would give rise to large power losses. These difficul- ties can be avoided by designing both the local feeder system and the long line on the basis of the most economical size of cables and connecting in series with the long line a booster designed to supply the voltage necessary to force the required currents over the long feeder. This booster will consist of a direct-cturent generator of suitable voltage to take care of the peak-load drop of the feeder, coupled to either a 6oo-volt D. C. motor or an induction motor, according to circumstances. By the use of such a booster it will sometimes be possible to save enough in copper investment or power losses to more than compensate for the losses in the booster and the installation cost and complication which attend its use. Such a booster system is shown diagramatically in Fig. 37, and this arrangement is called a direct-booster system. (6) Inverted Boosters. — Instead of connecting a direct booster in series with the long feeder, as above described, a similar result can be accomplished by insertion in series with the shorter feeders supplying the local network an "inverted" booster. This would consist of a series-wound motor connected in series with the local feeder system, this motor being used to drive a constant-speed generator connected to either the D. C. or A. C. bus bars. If the latter, an induction generator would be preferred. With this arrangement the speed would be held substantially constant, and hence the counter emf of the series motor would be proportional to the current, which condition would be necessary for maintaining the proper balance between the two feeder systems. Such a sys- tem is shown diagrammatically in Fig. 38. A little consideration will show that when such an inverted booster is used in lieu of a no Technologic Papers of the Bureau of Standards resistance tap, instead of the energy being dissipated in the re- sistance tap the excess energy over that required to supply the booster losses is delivered back to the D. C. or A. C. bus bars through the generator driven by the series motor. It is evident that the operating characteristics obtained from these two booster systems will in general be substantially the same. The choice between them will therefore depend mainly on the relative load in the two parts of the system. It is evident Positive Bus Neffotive Bus iii i i i / i i i niii iii -mtMititt Mimwi'iii iiii iii i l i iii i iiii li im w iii i i i i ii Iiiiihu- iiii iii iilinniii Fig. 37. — Direct booster system that if the greater part of the load is%n the long feeder, the use of a direct booster in this feeder would require a larger and more expensive machine as well as greater power losses in the machine itself than if the inverted booster were used in series with the relatively small load in the local network. Hence, if the load in the local network is the smaller an inverted booster would be cheaper, while if the greater part of the load originates in the local Electrolysis Mitigation III system a direct booster in the long feeder would be indicated. In the majority of cases, however, the insulated feeder system without boosters as described in the preceding section is found to be as cheap or cheaper than either of the booster systems, and is gen- erally to be preferred because of its greater simplicity. •Positive 3uS' @-@| + -JVe^ative Bi/S\ Fnyer/ed Booster' Fig. 38. — In-verted booster system 11. THREE-WIRE SYSTEMS A method that has received some consideration for railway work, partly as a means of securing greater economy in the dis- tribution of power and partly as a means of reducing electrolysis troubles is the three-wire system using the tracks as neutral. By this means the cmxent flow in the rails could in general be greatly reduced, but the practical value of this method under average conditions remains yet to be demonstrated. Aside from the cost of converting to this system which would in any case be consider- able and in many cases prohibitive, there are certain operating 2456°— 15 8 112 Technologic Papers of the Bureau of Standards disadvantages, such as greater variations in the car voltage, resulting in less satisfactory car operation and inferior car lighting. There is also the condition that one-half of the trolley wire network will be at a high difference of potential against the other half, and in one form of the three-wire system this increases the cost of construction and maintenance and the difficulty and danger of making repairs. In many cases, also, where single-track lines run on separate streets, with a long distance between track crossings, it would be necessary to install either a double trolley on each street or to run heavy and expensive cross bonds from one street to another in order to prevent large potential differences from developing between the two tracks. 3 A^£GATIV£: m: IIIMMIIIM ~SOJWO > yy^^cKs i 600 K G£-A/. 600V. ■^OS/r/V£- TffOJ. Fig. 39. — Parallel three-wire system (a) Parallel Three-Wire System. — The three-wire system may take two different forms the same in principle but differing radi- cally as to the arrangement of the feeder system. One of these is directly analogous to the ordinary three-wire system of lighting and is called the parallel three-wire system. The typical arrangement for the case of a double-track line using this system is shown in Fig. 39. Here one trolley is negatifre and the other positive, the tracks being neutral. It is evident that only the difference in the load on the two sides of the line returns to the power house on the track, although there may at times be heavy circulating cur- rents flowing between cars in short sections of track. If the cars run at frequent intervals, however, such circulating currents will not have to flow over sufficiently great distances in the tracks to set up nearly as large potential differences therein as would exist Electrolysis Mitigation "3 with the same loads under the ordinary track-return system. The result would be that where load conditions are reasonably favorable for the work of the three- wire system large reductions in potential drops in the negative return could be secured. ■f=osir/ve reecETfi Fig. 40. — Sectionalized three-wire system A single-track line with two overhead trolleys, one positive and one negative, can also be used, or the two tracks may be on differ- ent streets, the trolley on one street being positive and that on the other negative. The latter, however, is open to the objection that since the current would generally tend to flow in one direction in the tracks on one street and in the opposite direction on the other, frequent cross-bonding becomes very important, and unless the two lines are close together this would become quite expensive. (b) Sectionalized Three-Wire System. — The other form of three- wire system is shown diagramatically in Fig. 40. In this form the feeding district is divided into sections, and alternate sections are supplied by feeders rimning directly from the positive bus, while the remaining sections are supplied by feeders from the nega- tive bus, the difference of potential between the two busses being 1200 volts. In this way the existence on the same portion of the street of two trolleys having a high difference of potential between them is avoided. The tracks as before serve as the neutral and convey the current from the cars in one section to those in' the adjoining section and return the unbalanced current to the power house. The advantages of this form of three- wire system are (i) that it separates the positive and negative trolley sections, keeping them on different portions of the line, and (2) any system in which the substations have two positive busses and two or more genera- tors can quickly and cheaply change to this system, the only 114 Technologic Papers of the Bureau of Standards requirement being to sectionalize the feeding and trolley system in such a way as to properly balance the load. Both of these three-wire systems require for satisfactory opera- tion a fairly well balanced load, and hence they will operate more satisfactorily in sections where the schedule is frequent. For infrequent suburban or interurban service, voltage fluctuations at the cars would be serious, giving rise to unsatisfactory car service and car lighting and imdoubtedly increasing the maintenance cost of the car equipment. The system would also require a number of generators in each substation or their equivalent in three-wire generators, which have not as yet been built for 6oo-volt service. On the other hand, it would, if properly arranged and operated, unquestionably greatly reduce the average potential drops in the tracks. It would have the further advantage that the shifting of the car loads would frequently reverse the polarity of the leakage currents, and this tends still further toward reducing electrolysis damage for reasons explained above under the discussion of insulated return feeders. As pointed out at the beginning of this section the three-wire system has sometimes been considered as a means of increasing the economy of power distribution. While it does accomplish something in this direction, it does not possess the advantage that is at times claimed for it. A little consideration will show that a perfectly balanced three-wire system operating with 600 volts on each side is identical with a 1200- volt, double-trolley system in so far as the amount of feeder copper required is concerned. Since in any double-trolley system the amount of copper required on the return portion of the circuit would be in general equal to that on the outgoing lines, the total copper for a 1200- volt, double- -trolley system would be substantially the same that is required for a positive feeder system of a 6oo^olt track-return system. It follows, therefore, that a three-wire system requires the same amount of copper and the same energy loss in the feeders when we consider both positive and negative sides as is required in the positive-feeder system of the ordinary 600- volt network. The only economy resulting from the installation of the three- wire system, therefore, is the saving in track losses, which are greatly reduced, although not entirely eliminated. Track losses, Electrolysis Mitigation 115 however, are generally much smaller than the losses in the positive- feeder systems, so that the economy in this feature, while important in some cases, would be very small compared with the economy that would result from doubling the voltage on the ordinary track- return system. The relatively small saving in the track losses would, however, be largely offset, if not more than counterbalanced, by the increased station costs due to the more expensive and less efficient units required. Judged solely from the standpoint of electrolysis protection the three-wire system must be said to possess considerable merit, and its adoption along with proper precautions regarding load balance, track bonding, and cross bonding, would undoubtedly take care of the electrolysis problem in a very effective manner. Thorough tests of these systems under conditions to which they are best adapted would be very valuable. As yet, however, so little experience has been had with the operation of these systems that it is not possible to say how satisfactory this would prove under average conditions from the operating standpoint. A section- alized three-wire system has been in operation in Nurnberg, Ger- many, for 1 2 years, and appears to be giving satisfactory service. Experiments have been made with the system in this country, but it was abandoned because of operating difficulties encountered. At the present time, so far as we are aware, only one three-wire system is being experimented with in America. This is a section- alized system in operation on a portion of the lines of the Pacific Electric Railway Co. in Los Angeles, Cal. It has only recently been installed, and its success has not yet been determined. 12. NUMBER AND LOCATION OF POWER HOUSES AND SUBSTATIONS In a general way the effect of the number of feeding points on the potential drops in the rails and the consequent leakage of current from the tracks is obvious, but some of the more important aspects of this problem are obscure and often not appreciated. The economic aspect of the question is also more complex than is generally recognized. In the broadest terms we may consider the matter under two heads, namely, (i) the effect of the number and location of the stations on the tendency of the pipe systems to pick up stray currents from the return, and (2) the effect on the total drop of potential on both sides of the line. 1 16 Technologic Papers of the Bureau of Standards As to the first of these we have to consider the fact that as the number of stations is reduced the capacity of each must be in- creased, with the result that the current flow in the rails approach- ing the power house will be greater and the increased potential gradients resulting therefrom cause correspondingly increased leakage of current from the tracks. Further, as the distance between stations is increased the tendency of pipe lines to take up current from the earth under a given potential gradient in- creases much more rapidly than the distance of transmission. In fact, it can be shown that the current picked up by the pipes may increase either as the second, the third, or even a higher power of the distance between feeding points, according to the character of the system under consideration. Any increase in the number of feeding points, or, more properly speaking, the number of "drainage points" or points at which current is taken from the track, will reduce in much greater degree the flow of stray currents in the pipes. The number of drainage points can be increased to any desired extent by the proper use of insulated negative feeders, as above described, but the fewer the stations the longer and heavier the feeders must be, and in consequence of this an increase in the number of stations may often prove to be in the interest of econ- omy, considering only the negative return. This economy will become much more pronounced when we consider also the dis- tribution of the power on the positive side as well as its return on the negative. When we come to consider the question of total drop of poten- tial in the distribution and return of the current we have many complex factors to consider. One of these factors is the loss of power resulting from such drop of potential, but the calculation of the value of this lost power is b)^no means so simple as might at first appear. It is not sufficient simply to determine the total energy loss during any given time and multiply this by the cost of power per kilowatt hotir in order to determine its value. We must consider that the loss of power is proportional to the square of the load and hence is greatest at time of peak load when the capacity of the power station is usually taxed to its utmost. The capacity of the generating plant and hence the fixed charges Electrolysis Mitigation iij on the cost of power are thereby increased; or if the power be purchased, there is usually a fixed charge imposed on the maxi- mum demand. In any case if the operation of the system is such that the line losses give rise to an increased demand for power at time of peak load, the cost of the lost power will be greater than the cost of the power utilized at the cars. Besides the question of lost power due to line drop we have to consider also the effect of this drop of potential on the char- acter of the car service and the cost of operation of the car system. Low voltage means lower average car speed, with a consequent increase in the number of cars required to operate at a given headway, which in turn increases both fixed charges and oper- ating costs. Any change in the distribution system, therefore, whether a change in the number of stations or any other change which affects materially the line losses, will exert a marked effect on the cost of operation of the system. In designing a system of electrolysis mitigation, therefore, many things have to be taken into account quite apart from the technical points regard- ing the electrical condition of the negative return, if a proper balance is .to be maintained between the cost of making the proposed changes and the benefits resulting therefrom. In considering the installation of a new system of electric power distribution for street railways complete, without regard to exist- ing power stations, it would be a comparatively simple matter from a detailed study of the system in question to determine the proper number of stations and the best location of the same in order that best results might be secured, all things considered. But even if such a system were installed which answered in an ideal manner the requirements of present-day service, it would be but a few years until the growth of traffic and shifting of business centers would require increases in the size of the plants and other changes which would make the system much less economical than the ideal. In studying a system already installed we may be able to show that the feeding distances for some or all of the various stations are too great for economy and that a greater number of stations with reduced feeding distances would provide a much more econom- ical system of distribution. It does not follow, however, that an 1 18 Technologic Papers of the Bureau of Standards increase in the number of stations in such a system will actually improve its economy, but on the contrary the reverse might be the case, for, although the present feeding distances may be con- siderably too great for maximum economy, the location of the stations with respect to each other may be such that the placing of a new station in between will overstep the point of most economical feeding distance and even raise the net cost of operation, whereas the cost of moving old stations to more desirable locations might be altogether prohibitive. In dealing with existing conditions, therefore, we must work tmder considerable restriction, and many things must be taken into account before it can be determined definitely whether or not a proposed substation will prove desirable from an engineering and economic standpoint. 13. SUMMARY OF METHODS OF MITIGATION In the foregoing review of the various methods that have been proposed for reducing troubles from electrolysis those treated in the first section relate solely to protective meastires to be applied to the pipes. Of these the first seven are found to be o* little value for extensive application to networks of any considerable size, and certain of them are shown to be actually detrimental because of their tendency to accelerate deterioration of the pipes. The method of insulating joints, and a properly designed pipe-drainage system are of practical value, but it is recommended that their use be restricted to auxiliary measures used in connection with certain of the measures described in the second section for application to the track-return system. This recommendation is made for two reasons — first, because the practical working out of these systems applied to the pipes usually places an undue part of the burden of mitigation on the pipe-owning companies, and second, because the adequate protection of all subsurfac* structures by either of these means in cities where potential gradients are allowed to remain high will in general prove a difiicult and expensive matter. A more logical, and at the same time a more effective and often more economical, procedture is to attack the source of the trouble by eliminating in a large measure the leakage of the electric currents into the earth. Numerous methods applicable to the Electrolysis Mitigation 119 railway return system are available for this purpose, but, as pointed out in the foregoing review, the majority of these, namely, the alternating-current system, the double-trolley system, the use of negative trolley, the periodic reversal of trolley polarity, and the use of uninsulated negative feeders in parallel with the rails, when considered solely as methods of electrolysis mitigation, are either impracticable or else open to the objection that the expense or operating difficulties attending their application are rendered unnecessary because of the fact that there are other adequate methods available for general application which are comparatively cheap to install and which introduce but slight compUcations into the operation of the system. The importance of proper construction and maintenance of track return is emphasized. Thorough bonding and cross bonding are urged, and it is pointed out that at times it may be desirable on the ground of economy to use somewhat heavier rails than would be called for solely by traffic conditions. The drainage of roadbed where practicable is also ttrged, and where track is laid on private right of way the rails and ties should be kept, as far as possible, out of direct contact with the earth in order to reduce leakage of the current to a minimum. Good well-drained rock ballast is very effective for this purpose. It is also pointed out in the foregoing that a three-wire system, when viewed solely from the standpoint of electrolysis mitigation, possesses large possibilities, and experiments with these systems under favorable conditions are urged. Attention is called to the fact, however, that up to the present time sufficient experience has not been had with these systems to show whether they are prac- ticable from the operating standpoint under average conditions of service. At the present time it must be regarded as an experi- mental system which may under favorable circumstances be found of value in relieving electrolysis troubles. The most effective methods that have been thoroughly tried out in practice over long periods are the use of insulated negative feeders, either with or without boosters, as described above. It is pointed out that in most cases where the feeding distances are not too long an insulated feeder system without boosters will prove cheapest and at the same time more satisfactory because of its 1 20 Technologic Papers of the Bureau of Standards greater simplicity. It is possible by the proper application of either of these insulated feeder systems to reduce the potential gradients in the earth to such low values that in most cases little damage would result, and they can consequently be made very effective in relieving electrolysis trouble. In many cases, however, it may be better where conditions are favorable to combine one of these methods with either the inser- tion of a moderate number of insulating joints in the pipes or with the use of a very limited amount of pipe drainage, providing conditions are favorable to its use. The insulated-feeder system would be applied to reduce the potential gradients throughout the system to very low values and one or the other of the atixiliary systems used to eliminate largely any residual electrolysis that might still remain. By the proper use of the measures set forth above it is in most cases possible to secure sufficiently low-voltage drops in the nega- tive return to afford adequate protection to underground pipes, so that there will be little need for resorting to the use of any auxiliary measures, such as pipe drainage or insulated joints in the pipes. In fact, it has frequently been found that a careful study of the power distribution system, such as should always be made ih. connection with the design of an electrolysis mitigative system, will show that changes in the distribution system could be made that would yield operating economies which quite apart from any considerations of electrolysis protection are more than sufficient to justify the expense involved. We have found this to be true in so many cases that we are convinced" that the adop- tion by the railway companies of the best measures for reducing voltage drops to such low values as substantially to eliminate electrolysis trouble would in very few cases result in financial hardship. V. REGULATIONS REGARDING ELECTROLYSIS MITIGATION 1. NEED FOR REGULATIONS The many conflicting interests involved in the electrolysis problem make it imperative that some sort of regulations govern- ing the procedure of the various parties in interest be adopted if Electrolysis Mitigation 121 a permanent and just settlement of the problem is to be secm-ed. It is true that conditions vary greatly in dilBferent localities, and always to attain a complete solution would require a separate in- vestigation for each case. In general, however, it is not practi- cable to make a detailed engineering investigation of each locality, such as would be necessary in order to prescribe regulations es- pecially adapted thereto. As in all other cases where diverse in- terests come into conflict the interests of all will be best safe- guarded by the adoption by a proper authority of more or less specific regulations defining the responsibilities, rights, and limi- tations of the parties to the dispute. In the case of electrolysis, long experience both in America and abroad has shown that some sort of regulations are neces- sary for protecting undergrotmd pipes and cables and that such regulations can be made very effective. To be sure, any set of regulations drawn to meet average conditions might in special cases fail to give sufficient protection, and in other cases might cause somewhat greater expense than would be necessary if each case could be considered in detail by itself. Such regulations would, however, insure fair and adequate treatment of all parties concerned imder general average conditions, which would be a great improvement upon present practice in most places. Such regulations wisely drawn would not alone protect pipe-owning companies, but would often benefit the railway companies also. In the absence of such regulations a single serious case of trouble traceable to electrolysis such as might occur, or the activity of in- terested or overenthusiastic individuals, may lead to hasty and ill-considered legislation, resulting in rules much more drastic than conditions call for, and lead either to undue hardship on the railway companies or to long and costly and perhaps fruitless liti- gation. Regulations would also define definitely what is expected of the railway companies and enable them to treat the matter as one of the definite engineering problems connected with the opera- .tion of the railway system. They could thus plan and build definitely and with the assurance that they would not be con- tinually harassed by agitation of the subject of electrolysis. 122 Technologic Papers of the Bureau of Standards 2. PROPER AGENTS FOR DRAWING PROPOSED REGULATIONS It is very important, however, that such regulations should be drawn with the greatest care and with due consideration of the interests both of the railway and the pipe-owning companies. They should not be drawn by persons unfamiliar with require- ments, nor by the representatives of any one of the interests con- cerned, but by all of such interests acting jointly. It is hoped that such joint action may be taken in the near future as a result of the work of the National Joint Committee on Electrolysis now at work on the general subject of electrolysis. The work of that committee is primarily educational and is not concerned at all with the legal aspect of the question. Nevertheless, a careful scientific and engineering study and report will lead at least to a partial definition of the requirements and responsibilities of the various utilities interested in this problem. 3. PRINCIPLES ON WHICH REGULATIONS SHOULD BE BASED It is not our purpose to present here anything in the way of a set of regulations suitable for enactment into law. We shall, however, discuss briefly the fundamental principles on which we believe such regulations should be based. The various factors which determine the electrolytic conditions of underground structures, such as overall potentials and potential gradients in the track or pipe network, potential differences be- tween pipes and tracks, and between various pipe and cable sys- tems and the earth, current flow in the pipes, current density of discharge from the surface of pipes, etc., while important in any complete electrolysis survey, are for the most part subject to such a variety of influences that they are not suitable for use as a basis for regulations. The factors selected must not only afford a fair criterion of the general electrolysis |^tuation, but they must at the same time be susceptible of easy measurement, and they must lend themselves to ready and fairly accurate predetermination, so that the railway return system can be designed to meet the regulations with a minimum of uncertainty. All of the above-mentioned factors except the overall potential measurements, and potential gradients in the track return, are affected to a great extent by the character of the pipe systems. Electrolysis Mitigation 123 and changes in the latter may produce marked changes in most of the former; and hence these factors are only partially under the control of the railway company. Further, none of these other factors except the potential drops on the pipe systems afford an accurate criterion of the danger from electrolysis. They are there- fore unsuitable for use as a basis of specific regulations designed to protect imderground structures. The overall potential and potential gradient measurements, on the other hand, particularly those taken on the pipe systems, afford practically as good a criterion of the danger existing when inter- preted in the light of general experience as any other measurable factors. They are fairly definite, readily measurable, and in very large degree under the control of the railway company ; hence they are best adapted for use as a basis of rules and regulations. In all laws and regtilations that have up to the present time been adopted, so far as we are aware, the over-all potentials and potential gradients have been specified as those taken between various points on the railway tracks. This is true of the various European ordinances as well as those adopted in this country. These are very good criterions in many respects and have proven successful, particularly in Europe, in reheving electrolysis troubles. There is much to be said, however, in favor of limiting potential drops on the earth or on pipe networks rather than on the railway track. Such voltages afford the most accurate criterion of all, as to the actual danger to the underground structures, and would also prove more advantageous to the railway companies. If potential drops on the earth or pipes be made the subject of limitation, higher voltages could be allowed in those tracks having a high resistance to earth. This would apply to tracks laid on a well-drained roadbed, for example, and with still greater force to tracks on private right of way where the rails are set up on ties out of contact with the earth. On the other hand, relatively low voltages would have to be maintained in tracks in which the rails are much of the time in intimate contact with moist earth, or otherwise constructed so as to give a comparatively low resistance to ground. Under tliis plan low voltages in the track would be required only where most needed and the railway company would be encouraged to so construct the tracks as to give a liigh leakage 1 24 Technologic Papers of the Bureau of Standards resistance to ground. It is evident that if the leakage resistance to ground be made high, practically all of the current will be com- pelled to return to the negative bus by way of the railway negative return and thus increase the voltage drop on the tracks, although reducing electrolysis troubles. If, however, the voltage drop on the tracks is limited by regulations any construction of roadbed that would reduce leakage would increase the difficulty and cost of complying with the regulations. On the other hand, if the voltage drop on the pipes is made the basis of the regulations, the railway companies would profit by any construction which tends to reduce leakage instead of suffering by it, as in the case where voltage drops in the tracks are Hmited. If this plan were adopted, it would of course be necessary to prescribe lower voltage Umits than would be applicable to tracks in order to secure the same freedom from electrolysis. 4. VOLTAGE LIMITS IN TRACKS (a) Previous Experience Regarding Voltage Limitations. — In this country little experience has been had until recently with railway installation in which voltage drops in the negative retimi have been maintained low enough to give substantial freedom from electrolysis trouble. The prevailing practice in a majority of the cities of America has been to permit rather high voltage drops in the return circuit, and it is for this reason mainly that electrolysis troubles have assumed much more serious proportions in this country during the past decade than in almost any other country. There has, therefore, been but little experience in this country that can be used as a reliable guide as to just what voltage limits can be considered safe, although there is abundant and incontrovertible evidence in regard to what voltage limits may, under many circumstances at least^be considered unsafe. On the other hand, in Great Britain and many parts of conti- nental Europe much experience has been had with installations in which quite low voltages have been maintained over a period of many years; and this long experience has shown that the volt- ages which have been maintained in these countries are such as to insure, under average conditions, substantial freedom from electrolysis. This experience, therefore, is a valuable guide in Electrolysis Mitigation 125 determining what voltage limits can be considered safe under similar conditions here. (&) Voltage Limits Prevailing in Great Britain. — -In Great Britain the maximum allowable voltage drop between any two points of any railway system, near which underground metallic structures are laid, is limited by law to 7 volts. This law has generally been complied with by the railway systems of Great Britain, and where this 7-volt limit has been substantially complied with there has been comparatively little trouble from electrolysis of underground structures. In some instances this legal limit has been considerably ex- ceeded, due primarily to the fact that the British Board of Trade, which is charged with the responsibility of administering the law, has not made it a practice to make investigations of electrolysis conditions on its own initiative, but only on the complaint of interested parties. For this reason isolated cases can be found in which the prescribed voltage limits are for a time exceeded, and it is doubtless due largely to this fact that most of the elec- trolysis trouble, that has been experienced in Great Britain, has occurred. On the other hand, in many cities in Great Britain the limits prescribed by the ordinance have not only been met, but the prevailing voltage drops under ordinary traffic conditions have been found to be considerably below the maximum limit prescribed by law. The accumulated experience with the voltage limits which pre- vail in Great Britain appears to show quite conclusively that voltages of the order of the magnitude of those maintained in the railway systems there are none too low to assure adequate pro- tection to underground structures; and it is the opinion of some competent engineers that even lower limits are desirable and commercially practicable. This attitude was taken by the engi- neers who drew the regulations that are now in effect in many cities of continental Europe. (c) Voltage Limitations in Germany. — The so-called German regulations, which are in effect in many cities in continental Europe, while differing radically in the manner in which the voltage limits are defined, were designed by the framers of the regulations to yield somewhat lower average voltage conditions 126 Technologic Papers of the Bureau of Standards than those demanded by the British law. The German regula- tions prescribe a voltage limit oi 2.}4 volts throughout any city network of street railway lines, and they further prescribe a limit of I volt per kilometer (0.3 volt per 1000 feet) on interurban lines. These limits are applied to the period of average scheduled traffic instead of to the peak-load period, as in the case of the British law. In both of these sets of regulations, the definition of voltage limits is indefinite and unsatisfactory. The British law limits the maximum drop to 7 volts, but does not specify whether it is the momentary maxinium that is subject to limitation, or the sus- tained maximum during some definite interval of time. In ap- plying the law, however, the British Board of Trade has found it necessary to adopt for administrative purposes a more specific definition of the term "maximum voltage." In determining this maximum voltage, the average value for the half hour of highest load is determined, and also the maximum momentary drop during this period, and the mean of these two values is taken as the maximum voltage within the meaning of the law. In the German regulations a similar ambiguity exists. While it is stated that the voltage under average scheduled traffic should not exceed certain values, it is debatable whether or not it is intended that the momentary value of voltage drop tmder ordinary schedule traffic is to be kept within the prescribed limit or whether the average value of voltage drop under normal operating con- ditions is the value to be considered. If we place the latter interpretation on the question, the limit appears to be reasonable and practicable, and one that would, imder many circumstances, be applicable in this country. If, however, it is intended to limit the momentary voltage under average load conditions in street railway networks to 2>^ volts, the regulation would be altogether too severe for general application ,^as a voltage limitation of this severity is not needed for providing reasonable protection to un- derground pipes and the cost of meeting such limitations would be altogether out of proportion to the benefits that would accrue therefrom. If we assume, then, that this over-all voltage limit oi 2}4 volts is to be taken as the average value under normal scheduled traffic, it would be foimd to compare very well, so far as ultimate results Electrolysis Mitigation 127 are concerned, with the voltage Hmits in effect in Great Britain. It will be apparent that the maximum value of 7 volts, defined as the mean value between the average for the maximum half hour and the highest momentary value for that hour would cor- respond to a mean value for the maximum half hoiu- of approxi- mately 4 to 6 volts under most traffic conditions. On a basis of 50 per cent load factor, this would give a mean value under average load conditions of 2 to 3 volts, which is of the same order as the lyi volts average limit named in the German regulations. The above discussion relates only to the over-all voltage limits prescribed by the regulations in question. The German regula- tions make no provision for restricting the potential gradient within the city network proper, the gradient limits of these regu- lations applying only to interurban lines. The British law, however, contains a provision which limits the current density in any street railway rail to 9 amperes per square inch of cross section. This, in effect, prescribes a potential gradient limit, which, how- ever, is variable according to the resistivity of the rails; and for rails of average resistivity this gradient limit would yield a maxi- mum potential gradient of approximately 0.9 volt per 1000 feet, exclusive of the drop on the joints. This would correspond to an average all-day gradient of from 0.3 to 0.4 volt in the case of most railway loads. It is very desirable to have both the overall voltage limit and the potential gradient limit, the latter to prevent too rapid change in the potential of the tracks in any locality, which makes it diffi- cult to prevent large potential differences between pipes and rails from developing locally, and the former to prevent the use of exces- sively long feeding distance, which, even with a small gradient, would permit the accumulation of large potential differences between pipes and tracks. {d) Manner of Specifying Voltage Limits. — As to the manner of specifying the limiting voltages that should be allowed, there is a good deal of difference of opinion. Some prefer to specify a limit for momentary voltages, and others advocate restricting the maxi- mum value for some definite short period, such as 10 to 30 minutes during the peak-load period, while many prefer to follow the prac- tice of specifying an upper limit for the average voltage during the 2456°— 15 9 128 Technologic Papers of the Bureau of Standards operating period. We have become convinced that the last plan is in general to be preferred. Our investigations have shown that the actual amount of corro- sion which takes place is much more nearly proportional to the average all-day load than it is to any short-time peak value. In fact, investigations made at the Bureau of Standards,' show that as the load increases and the current density is thereby increased the actual amount of corrosion does not increase as fast as the current increases. For this reason it is undesirable to place a heavy penalty on a high peak of short duration, provided the average current is small. This objection is avoided entirely by specifying the average value of the voltage instead of some short time peak-load value. To specify a limiting value of voltage during from lo to 30 min- utes would probably not be a serious matter in the case of a con- gested city district, where the railway loads are comparatively steady and the load curve shows a comparatively flat maximum. In case of suburban or interurban lines operating an infrequent schedule, particularly where multiple car passenger trains and heavy freight trains are operated, any short-time voltage limita- tions will almost always impose upon the railway company a hard- ship that is altogether out of proportion to the benefits that could possibly result from such a method of defining the maximum. In the case of interurban railway systems, any voltage limita- tions based upon momentary maximum values would be practi- cally prohibitive, unless the voltage limit were placed so high as to be of no real value for general adoption. It seems best, there- fore, that any voltage limitations that may be applied be based upon the all-day average value of the voltage rather than on any short-time period. Investigations have shown that if the polarity of the pipes reverses frequently, as, %)r example, every few minutes or oftener, the actual amount of corrosion which results is practi- cally proportional to the algebraic average value of cmxent due to the fact that for short periods of reversal the corrosive process is in large degree reversible. If, however, the frequency of reversal is very low, the reversal taking place once an hour, or at longer 5 Burton McCollum and K. H. Logan, "Electrolytic corrosion of iron in soils," Bureau of Standards Technologic Paper No. 25. Electrolysis Mitigation 129 intervals, the corrosion increases and tends to become more nearly proportional to the average value of current during the time when the pipe is positive to earth, the average being of course reduced to a 24-hour basis. Owing to the imcertainty of the length of the periods of reversal that may occtu- under average operating conditions, it is best in fixing voltage limits in practice to base the limiting values on the 24-hour average value of voltage during those periods when the pipe frequently becomes positive to earth. In interpreting the significance of voltage readings actually taken, however, where the frequency of reversal is always approximately known, it is best to bear in mind that for periods of reversal of a few minutes or less the algebraic average affords a better criterion of the damage that will result than the arithmetical average. A careful study of the local conditions in this country, in the light of the extended experience in European countries with the voltage limits that have prevailed there for many years, indicates that the average all-day voltage drop in the railway tracks tmder average conditions should be restricted to a value not exceeding about 2 to 4 volts, the lower value applying to localities such as business centers in large cities where the underground utilities are highly developed and of great value, and the higher value to those regions in which the utilities are developed to a lesser extent, such as the average residential districts in cities. In very sparsely settled districts still higher voltage drops may be permitted, and in many cases, especially where tracks are on private right of way and substantially insulated from earth, thoughout their entire length the voltage limits may even be dis- pensed with altogether. Thus, in fixing regulations for any given city, some sort of a zone system is desirable, different voltage limits being prescribed for different zones, according to the value of the undergroimd utilities and other local factors. These all-day average values of 2 to 4 volts would, in the case of the majority of railway loads, correspond to an average dmring the maximum hour of from 3 to 10 volts, there being a greater variation in the values for the shorter than for the longer period. The average gradient corresponding to this over-all limit will 130 Technologic Papers of the Bureau of Standards depend in large measure on the means that are adopted for com- plying with the limitation and on the feeding distance. A study of the best methods available for reducing voltage drops indicates that the average 24-hour gradient at any point in the rail should under average conditions not be permitted to exceed about 0.3 to 0.4 volt per 1000 feet. These limits of 0.3 to 0.4 volt per 1000 feet for the 24-hour period correspond roughly to 0.4 to 0.5 volt per 1000 feet for the 18-hour operating period. If the drop of potential on pipes or earth is made the basis of limitation, lower values would have to be used. Experience indicates that, on the average, over-all potentials and potential gradients in the earth should be maintained at about one-half the figures given above in order to insure the same free- dom from electrolysis. We do not wish to be understood as taking the view that the average voltage for the maximum hour or even half hour can not be made a satisfactory basis for voltage regulation. Experience has shown that either plan can be made to work out very well in practice. Recent investigations, however, show that the use of the longer period is a more rational basis of fixing voltage limits, since it gives a factor which is more nearly proportional to the actual danger involved than any other. Cases continually arise in the operation of street railway systems where local traffic congestion will cause very excessive voltage drops locally for short periods of from 5 to 15 minutes or longer, but these occur so infrequently that they have but slight effect on the average all-day values, and hence on the total damage from stray currents. To adopt any rule which would limit these transient rises of voltage to very low values would involve an expense to the railway company which would be out of all proportion to the benefits that would accrue to the (^ners of underground utilities. On the other hand, if the voltage limit is placed high enough so that it can reasonably be applied to lines having very heavy transient loads, it would be altogether too high for other lines having comparatively steady loads. If the all-day average value is used, however, the cost of meeting the limit, as well as the degree of protection, will be independent of the character of the load on different lines. Electrolysis Mitigation 131 As to the convenience of determination of the voltage limits prescribed there is little to choose between the two plans. Even if a short period be adopted, it will be necessary to use recording voltmeters, and records would have to be taken over practically the entire day to make sure that the limiting values were being recorded, and when the all-day record is at hand, the all-day average value can be obtained with practically the same facility as the average for shorter periods. The all-day average value of voltage would therefore appear to be the most natural and logical criterion to use as the basis of voltage regulations. What- ever method may be ultimately adopted for defining any maximum allowable limits that are to be prescribed for any particular locality, extended experience both in this and in foreign countries shows that the average values must not greatly exceed the figures mentioned, provided reasonable and permanent protection is to be accorded to the undergroimd pipe system. S. GENERAL SCOPE OF REGDIATIONS (a) Voltage Limitations. — From the foregoing it will appear that one of the most essential things to be incorporated in elec- trolysis regulations is an appropriate limitation of the potential drops in the railway track network, or in the earth and pipe systems, and that such limits should be applied in the case of railway tracks to both the over-all potential drops between remote parts of the system and also to potential gradients in relatively short portions of the track network, the former being necessary to guard against the accumulation of large potential differences which might occur even with low gradients, provided the feeding distances are very long, and the latter to prevent the very rapid change in the voltage of the track in any portion of the system which might give rise to bad local conditions even though the over-all potentials were kept comparatively small. In fixing voltage limits for regulation it is desirable to specify the manner in which the voltages are measured and potential drops computed. In determining the potential gradients the voltage drop on a distance of 1000 feet is generally better than a much shorter length. This length is long enough to give a fair average condition over a considerable length of track, and at the 132 Technologic Papers of the Bureau of Standards same time short enough to prevent any serious accumulation of potential difference at any point, provided the limits mentioned above are substantially complied with. In calculating the potential gradient it is best to measure the distance in an air line between the terminal points, provided the region crossed by this line is occupied by pipe networks ; but if the pipe networks follow an indirect course, measurements should be made by way of the pipes. (&) Potential Wires. — In order to facilitate the determination at any time of the voltage drop, it is very important that perma- nent potential wires be installed running from a suitable terminal board at some central point and connected to the tracks or pipes at those points between which potential measurements are to be made. These should always be run to the more outlying points and also to the point in the system of approximately lowest poten- tial so that the maximum over-all potential drops can be directly measured. It is desirable also in most cases to have some wires run to intermediate points, so that any high potential drop that may be observed can be approximately localized by measure- ments with the potential wires. Such wires may either be especially installed for the purpose of taking potential measure- ments, or wires for this piupose may be leased from a telephone company. When satisfactory terms can be arranged, the leasing of wires is preferable, since the maintenance of these wires would, in general, be less than of special wires nm separately for this purpose. In view of the fact that the purpose of the potential wires is not primarily for the protection of the pipe systems but rather to supply information to all parties concerned as to the conditions which exist, it seems preferable that the expense of installing and maintaining or of leasing such potaitial wires should be borne jointly by all of the utility companies directly concerned in the electrolysis mitigation problem. If this were done, the cost to any particular company would be practically negligible and it would remove any material objection which the railway company might otherwise have to the installation of such potential wires. Graphic voltmeters should also be provided for measuring and recording the potential differences required. Electrolysis Mitigation 133 (c) Connections Between Tracks and Pipes. — Metallic connec- tions between underground metallic structures and the street rail- way tracks should never be permitted at any point where the pipes might become negative to the tracks and such ties deliver current into the pipe system. Such connections are sometimes advocated as a means of reducing voltage drops in the negative return, but the objections to such procedure are too obvious to be discussed here., It is not desirable in general to prohibit all metallic connections between pipes and railway negative return in the regions near the power stations, although in general in city systems such connections are not desirable, except in the case of lead cable systems where properly restricted drainage may be used. There are, however, special cases in which it might be desirable to install such ties on pipe systems, and this should not be entirely prohibited by the regulations. {(£) Interconnection of Tracks. — Wherever two or more railway systems operate in the same territory it is of the greatest impor- tance that the tracks should be electrically connected together at all intersections and such interconnection should be required by regulations. In special cases where tracks, either of the same or different railway lines, parallel each other for a considerable dis- tance, such as half a mile or more, and where the tracks are only a block or so apart, it is important that occasional crossties between the lines be installed to prevent wide fluctuations of voltage between them. This would be a special provision designed to meet local conditions rather than a general rule. (e) Track Maintenance. — If the voltage drops in the tracks be limited by regulation and if a sufficient number of potential wires are installed not only to the remote points of the system, but also to intermediate points so that the potential gradients on practically all sections of the track of lengths from 1000 to 3000 feet can be readily measured, it would not appear desirable to superpose on this any additional regulation in regard to track maintenance, leaving that matter entirely to the railway company. If, however, potential wires are connected only to the remote portions of the network, they would not give sufficient data in regard to elec- trolysis conditions at intermediate points, and in such cases it would be desirable to have some sort of regulation covering track 1 34 Technologic Papers of the Bureau of Standards maintenance. This might take the form of a rule requiring periodic tests and reports of the condition of the track bonding, and definitions regarding what may be considered a good or bad bond. Practice in regard to the latter point varies considerably in this country, but in general where the resistance of a joint (including 3 feet of rail) exceeds the resistance of a length of from 6 to 10 feet of rail the joint is considered defective. Cross bonding between tracks should also be required at frequent intervals. The best practice in this country at the present time calls for cross bonds at intervals of from 200 to 500 feet of track, according to traffic conditions, and bonding at shorter distances is required where the traffic is heaviest. Such bonds should be designed to carry the maximum ciurrent to which they can be subjected in use. (/) Exemptions. — ^Where railway lines operate in a territory remote from pipe systems exemptions from stringent regulations should generally be made. The German regulations exempt entirely railway lines which operate at a distance exceeding 200 meters (650 feet) from any pipe systems. Such an exemption undoubtedly involves no danger to the underground structures. Where the railway line is so constructed that the rails are practi- cally insulated from the earth, such, for example, as a railway line on a private right of way on which the rails are set up on wooden ties entirely out of contact with the earth, exemption from rigorous voltage regulations regarding track potentials should also be made. {g) Insulated Negative Feeders. — If the regulations prescribe certain specific and definite voltage limitations that must be compKed with, it will not be best to specify the manner in which such regulations are to be met. In order, however, to make it readily possible to further improve conditions at a later date, if such improvement should be foufid necessary, and to accom- plish this without any appreciable extra cost to the railway companies, it would be well to require that in any future con- struction wherever negative feeders are installed at all they should be installed as insulated feeders in such a way that they may, when necessary, be converted into what has been defined in this paper as an insulated negative feeder system. The insu- lation of negative feeders in this way is practically no more Electrolysis Mitigation 135 expensive than the installation of uninsulated feeders, so that no hardship would be imposed on the railway company by such requirements; on the other hand, in case future experience showed it to be necessary to still further reduce voltage drops, it would be a decided advantage to the railway company to the have feeders installed in this way. 6. RESPONSIBILITIES OF OWNERS OF UNDERGROUND UTILITIES REGARDING ELECTROLYSIS In considering the subject of regulations for the mitigation of electrolysis, it should be borne in mind that while the railway companies are chiefly responsible for reducing stray currents to as low values as are commercially practicable, the owners of underground utilities also must be considered to have certain responsibilities, particularly in so far as new construction work is concerned in territory already occupied by electric railways. There are a number of things that pipe and, cable owning com- panies can do at a very sHght additional expense that will go very far to reduce electrolysis trouble, provided such measures are taken at the time the pipes or cables are installed. For example, in new work or repairs, pipe lines should be laid as far as possible from railway tracks. Where the density of service connections is sufficient to justify the use of two mains, one on each side of the street, these should be laid down in order to eliminate the necessity for running services across under the railway tracks. This is quite common practice in many places where the utilities are highly developed, and it could frequently be extended in many instances with considerable improvement in local electrolysis conditions. Further, in laying new mains or repairing old ones, it is very simple and inexpensive to install a sufficient number of insulating joints largely to reduce stray currents in that portion of the pipe network, and such construc- tion should be encouraged in every practicable way. Wherever it is necessary to run service pipes across the street under railway tracks, care should be taken either to lay them as far as practicable below the tracks or else to provide substantial insulation between the service pipe and the track or between the service and the main by means of insulating joints; the latter will generally be found cheapest and most effective. 136 Technologic Papers of the Bureau of Standards 7. LIMITATION OF PIPE DRAINAGE In view of the fact that excessive drainage of current from one pipe system may set up a condition of serious danger in a neigh- boring system, meastires should be taken to so restrict the drain- age of cmrent from any one underground metallic structure that it will not be maintained at a potential sufficiently lower than sur- rounding structiu-es to cause any serious injury thereto. 8. ADMINISTRATION OF REGULATIONS Where regulations governing electrolysis mitigation are neces- sary, they should preferably be enacted and administered by State authority, where the necessary administrative machinery is available. In the absence of such administrative authority, however, the cities in which the utilities operate, should take the initiative. The Federal Government, while competent to carry out engineering investigations bearing on the problem as it is now doing, can not undertake to prescribe or administer regulations. Where State public utility commissions are in existence, they con- stitute the most logical and competent authority to deal with this subject. Such State commissioners are not only able to deal with the subject in a broader and more comprehensive way than the majority of local bodies, especially in smaller cities, but then- freedom from the influences of local interests will often enable them to deal more wisely and justly with all companies involved. It is in the highest degree desirable that regulations be made as few and as simple as possible, to the end that the various util- ities concerned may enjoy the greatest freedom of action consist- ent with safety to the undergrotmd structures. The present apparent necessity for regulations governing this subject is due to the lack of cooperation in the past between the railway companies and the owner^ of underground utilities. If the various interests concerned, and particularly the railway com- panies, would show a greater disposition than they have com- monly done to meet the issue, and instead of practically ignoring the subject, as has been too often done, would treat the matter as one of the engineering problems connected with the operation of street railways, the need for stringent regulations would be largely eliminated with advantage to all concerned. In the ab- Electrolysis Mitigation 137 sence of such a far-sighted policy, however, compulsory and per- haps more or less burdensome regulations will become inevitable. VI. SUMMARY Among the more important conclusions brought out in the fore- going paper are the following : 1. The electrolysis problem was for a long time neglected in America, and partly as a result of this, is now more serious than in those European countries which early met it by Government regulations. During the last few years, however, much greater attention is being given to this subject by railway companies generally. 2. Electrolysis may give rise to a number of different classes of injury, such as fires, explosions, and damage to concrete struc- tures. However, the damage from these effects is in the aggre- gate relatively small. By far the greater portion of the damage due to electrolysis is that arising from corrosion of imderground pipes and cables. In particular, electrolytic damage to concrete structures is to be feared only where voltage conditions are excep- tionally severe, or in the case of comparatively low voltages when salt has been added to the concrete either dtaring or after construction. 3. In general, those remedial measures that are applicable to pipe systems should be regarded as secondary means of mitiga- tion of electrolysis trouble, the principal reliance being proper construction and maintenance of the railway return circuit. In •special cases, however, mitigative measures may be applied only to the underground structures. 4. Of the mitigative measures applicable to pipes only a few of those that have been advocated have found much application. The two most commonly applied are the installation of insulating joints and the use of pipe drainage. Both these methods are valuable under certain conditions, the former particularly where new pipes are being laid and the latter for application to isolated pipe systems without insulating joints and where no other under- ground utilities are present to cause complications. In most cases, however, these systems should be restricted to use as auxiliary means of protection, after reasonable precautions have 1 38 Technologic Papers of the Bureau of Standards been taken to reduce potential drops in the tracks to as low values as are economically practicable. In any case where pipe drain- age is used, the drainage should be through the medium of insulated feeder systems, so adjusted as to take the minimtmi possible current from the pipes at all points. 5. Of the methods applicable to railways the most important of those which have been thoroughly tried out are the adequate maintenance of track bonding, the use of a proper number and location of power houses or substations, and, where the carrying capacity of the rails is not sufficient to return current to stations without excessive drop, the use of insulated negative feeders for the return of such current, these latter being much more econom- ical than uninsulated feeders where large reductions of potential drop are required. The three-wire system has proved effective in relieving electrolysis and should prove satisfactory from the electrolysis standpoint where operating conditions are favorable to its use. Thus far, however, too little experience has been had with this system to justify more than tentative conclusions. 6. Such remedial measures as have been adopted in this country have usually been applied to the pipes, and in general they have proven much less effective than measures used in certain foreign countries where regulations liniiting voltage drops in the nega- tive return have long been in effect and have been accompanied by substantial freedom from electrolysis troubles. Experience both here and abroad indicates that such limitation of voltage drop is necessary to a satisfactory solution of the problem. 7. In defining the voltage limitations either the all-day average value or the average value for a period not less than one-half hour may be used; the former, however, is preferable, since it affords the best criterion of the actual danger involved and is also more satisfactory from the standpoint q^ the railway companies. A shorter period than half an hour is too short to give a satisfactory basis for voltage regulations that are to be applied to the railway systems. 8. In fixing voltage limitations some plan analogous to the zone system should be adopted, the voltage limits prescribed for the various zones being determined largely by the degree of develop- ment of the underground utilities in the various zones. Electrolysis Mitigation 139 9. The voltage drops either in the tracks or in the pipes, and earth may be used as the basis of fixing Hmitation, but in general the latter is to be preferred. ID. Under most conditions over-all voltages in railway tracks should be limited to about 2 to 4 volts, and the potential gradients should in general be restricted to about 0.3 to 0.4 volt per thousand feet, these figures being all-day average values, or to corresponding values based on averages for a period of not less than half an hour. The higher over-all voltage limit will generally apply to the longer feeding distance and outlying districts, while the higher potential gradient limit can be permitted where feeding distances are relatively short. Potential drops on pipe systems should be, roughly, half of these figures. 11. In order that ready determination of voltage drops can be made at any time, potential wires should be installed rtmning from some central point to selected points on the railway or pipe networks. These points should include the points of approxi- mately highest and lowest potential, and preferably also some intermediate points. 12. Exemption from any regulations regarding track voltages should be made in special cases as set forth in this paper, where local conditions make it improbable that any serious damage would result. 13. Any regulations governing electrolysis mitigation should be made to apply not alone to the railway system, but should also define the responsibilities of the owners of underground utilities, since the latter can often contribute materially to the diminution of the trouble at a practically negligible cost. Washington, April 9, 191 5. APPENDIXES APPENDIX 1.— EXTRACT FROM PAPER ON "MEANS FOR PREVENTING ELECTROLYSIS OF BURIED METAL PIPES " a * * * Having referred to the method of preventing electrolysis, which has been employed on a portion of the pipes in Boston and in some other American cities for sev- eral years, and to some of the erroneous ideas on the subject, we may now present the outline for another method of minimizing the danger. No description of this plan has ever before appeared in print. It is furthermore attractive as lying entirely within the power of the railway companies to adopt. It is not excessively expensive and it does not involve connections with other companies' property, nor the mutual coopera- DYNAMO Qy^ DDDDDDO \^ -f- PLATE GJSOUAtD Fig. 41. — Diagram showing the difference in potential along an electric railway tion of cities or corporations. By this method the tracks of the railway will also be preserved from electrolytic action. In order to bring the principle clearly before ttie reader, the writer would call atten- tion to a fact generally known, but often ignore * In all cities where electric railways operating the single-trolley system are in use, and especially where trouble from elec- trolysis has been discovered, it is found that the earth in one section of the city has a different electrical condition from that in certain other sections. If an insulated wire, having included in its length a suitable galvanometer or voltmeter, is extended between a ground plate located near the railway power house and another ground plate located a mile distant from the first plate, as shown in the diagram marked Fig. i [identified o By Isaiah H. Famham, published in Cassier's Magazine for August, 1895. 140 Electrolysis Mitigation 141 as Fig. 41 in this publication], a difference of potential will be found to exist between these plates. If the dynamo is connected with its positive pole to the trolley, the ground plate situated at the greater distance will be positive to the plate near the power house. Some of the fire underwriters recognize this difference of potential as a danger, and they attempt to rule against it. The writer has known such difference of potential to reach 50 volts and more. The earth in the distant territory is, so to speak, saturated with positive electricity, while near the station it is being "pumped out" or made negative by the dynamo. This want of a level, or balance, in the electrical condition of the earth, leads to a flow of the current fromlhe higher to the lower electrical level, much as would occur if water should replace the electricity. In flowing, the elec- tricity finds its way into pipes and cables, and, on leaving them at the lower level, causes the electrolytic action. Fig. 2 [identified as Fig. 42 in this publication], on the next page, will, by analogy, fairly illustrate this want of electrical balance or level in the earth. The line A repre- sents the surface of the earth; B, the surface of a flood of water produced by a heavy rain, and flowing to a low plane where a pump is drawing the water from the earth in a limited district. ::-"MfU/Al/>-^- ■'■ ~. Fig. 42. — Diagram illustrating the want of electrical balance in the earth If, now, we can preserve a level or balance in the electrical condition throughout the city, or, in other words, prevent a difference of potential, there will be no disposition for a current to flow from one portion of the city to another. It is the purpose in the plan now proposed to accomplish this equalization of potential as nearly as possible. To illlustrate by the water analog)'. Fig. 3 [identified as Fig. 43 in this publication] shows the flood of water being pumped from many points on the surface of the earth by pipes of proper size, so that there is substantially no difference of water level, and therefore no flow from one distant point on the earth to another. A comparison of this figure with the one above it will render the point clearer. As may be anticipated by a study of the principles already set forth, the new method consists in extending from the negative or rail side of the dynamo an insulated return wire, either on poles or underground, throughout the entire length of the railway, including all cross-town or branch tracks. This return wire is to be of such size as to properly carry the current and to maintain the return path at a comparatively low resistance. For a track extending 3 miles in any one direction from the power house a No. 0000 copper wire would give a resistance of but i ohm from the most distant point. Two such wires, about one-third inch in diameter each, would not seem excessive in cost, and would render the maximum resistance but one-half ohm from car to power house. 142 Technologic Papers of the Bureau of Standards In large railway systems a still heavier main return may be employed. From this general return wire or system of wires frequent connections would be extended to the track system, say one at every other pole (200 feet). Let these connections between the general return wire and the rails be of such size, or shape, as to cause the resistance from the rail at the nearest point to the power house to be the same, no more nor less, than from the most distant rail connection to the power house ; that is, with such a system, if the resistance of the circuit from the rail, 3 miles distant, to the power house Fig. 43. — Diagram illustrating an example of electrical balance is one-half ohm, the resistance from any other point along the route of the track shall also be one-half ohm to the power house. Allow no ground connection on the dynamos and no direct connection to the rails without the proper resistance. Fig. 4 [identified as Fig. 44 in this publication] roughly represents such a system. It should be under- stood that the rails are to be suitably bonded under this, as other systems using the rails for a portion of the electric circuit. f/fo cueecf^r) Fig. 44. — A system, with which electrolysis of buried pipes is avoided If, now, we imagine an approximately uniform distribution of cars, there can be no rise or fall of potential in the earth except at the very limited areas between the several points where the rails are connected to the general return wire system. Cars are not, of course, equally distributed over a city, and, therefore, perfect results can not be reached by carrying out this plan, but to adopt it is certainly working in the right direction, and as the distribution of cars approximates uniformity, the advantages of the system will approach the maximum. On the other hand, with Electrolysis Mitigation 143 the present usual manner of connecting the return wires to the tracks there never can be a condition where a. difference of potential will not exist between different sections of a city, no matter how nearly perfect the rail system is constructed as a return conductor, and, therefore, there can be no elimination of current passing from a higher to a lower potential throughout a city; and, of course, as the currents pass through the earth, pipes are brought into the path, and constitute a portion of the electric conductor, with all the possibilities of electrolysis wherever, from a. poor joint or for other reasons, the currents leave the pipes for the damp earth on their way to the negative side of the dynamo. This system of returning the railway current will accomplish several desirable ends: (r) It will allow but very'little current to enter the earth and flow therein; (2) the current through the earth being minimized, electrolysis will to that extent be prevented; (3) having by this means reduced the danger of electrolysis to small proportions, it will be comparatively easy to take care of the remaining danger, if such be found, by resorting to the means described in the previous paper; (4) in addition to practically overcoming the danger of electrolysis, the annoyance to tele- graph, telephone, btirglar alarm, and other grounded circuits, due to difference of potential in different sections of a city, will be incidentally removed. The equi-potential return system just described has so far been tried in a New England city as to indicate practically that the benefits claimed for it may be con- fidently expected. APPENDIX 2.— PDBLICATIONS OF THE BUREAU OF STANDARDS RELATING TO ELECTROLYSIS Technologic Paper No. 15: Surface Insulation of Pipes as a Means of Preventing Electrolysis; by Burton McCollum and O. S. Peters. Technologic Paper No. 18: Electrolysis in Concrete; by Dr. E. B. Rosa, Biuton McCollum, and O. S. Peters. Technologic Paper No. 25: Electrolytic Corrosion of Iron in Soils; by Burton McCol- lum and K. H. Logan. Technologic Paper No. 26: Earth Resistance and its Relation to Electrolysis; by Burton McCollum and K. H. Logan. Technologic Paper No. 27: Special Studies in Electrolysis Mitigation, No. i; by Dr. E. B. Rosa and Burton McCollum. Technologic Paper No. 28: Methods of Making Electrolysis SiuT^eys; by Burton McCollum and G. H. Ahlbom. Technologic Paper No. 32: Special Studies in Electrolysis Mitigation, No. 2; by Dr. E. B. Rosa, Burton McCollum, and K. H. Logan. Technologic Paper No. 52: Electrolysis and Its Mitigation; by Dr. E. B. Rosa and Burton McCollum. 2456°— 15 DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON. Director No. 54 special studies in electrolysis mitigation in. A REPORT ON CONDITIONS IN SPRINGFIELD, OHIO, WITH INSULATED FEEDER SYSTEM INSTALLED BY BURTON McCOLLUM, Electrical Engineer and GEORGE H. AHLBORN, Assistant Physicist Bureau of Standards ISSUED FEBRUARY 5, 1916 WASHINGTON GOVERNMENT PRINTING OFFICE 1916 ADDITIONAL COPIES OP TmS PUBLICATION MAT BE PKOCUEED rROM THE SUPEKINTEiroENT OE DOCUMENTS GOVEENMENT PBINTING OFFICE WASHINGTON, D. C. AT 26 CENTS PER COPY CONTENTS Page I. Introduction 7 A. Previous surveys in Springfield 7 B. Reasons for present survey 8 II. Discussion of general conditions on the various systems 8 A. Railway systems of Springfield 8 I. Details of construction 9 A. Repaired sections 9 B. Other utilities lo III. Description of insulated return feeder systems ii A. Constructional details ii B. Current, resistance, and losses in feeders 12 C. Resistance taps 15 D. Operating costs without return feeder systems 15 E. Operating costs with return feeder systems 19 F. Annual charges on insulated negative feeders 19 IV. Pressure wire system 21 A. Location of pressure wires 21 B. Construction of presstu'e wire system 22 V. Results of measurements 22 A. Methods of measurement 22 B. Corrections and reduction factors 23 C. Description of tables 27 1 . Potential differences 27 (a) Water mains to rails 27 (6) Gas to water mains 30 (c) Lead sheaths to other structures 3r 2. Potential gradients 33 (a) Springfield Railway Co. lines 33 (6) Ohio Electric Railway Co. lines 35 (c) Outside tap points 36 3. Over-all potentials 38 (a) Springfield Railway Co. lines 38 (5) Interurban lines 39 4. Stray current in undergroimd structures 41 (o) Current in water mains 4a (i) Current in natiural gas mains 43 (c) Current in artificial gas mains 45 (d) Current in lead cable sheaths 46 5. Cross connections 47 6. Cost data 48 7. Significance of data 49 3 4 Contents V. Results of measurements — Continued Page D. Comparative data— winter and summer stu-veys 50 1 . Power-house loads 51 2. Comparison of winter and summer electrical measurement. 53 (a) Comparative potential differences 53 (6) Comparative current on mains 55 (c) Ciurent in lead sheaths 58 (d) Comparative rail gradients 58 (e) Comparative over-all potentials 59 VI. Recommendations 60 A. Insulated return feeders 60 B. Immediate rail bonding 60 C. Interconnections 61 D. Extension and maintenance of pressure wire system 61 E. Drainage methods 61 F. Underground structures 62 G. Voltage limitations 62 H. Standards of bonding 62 I. Annual tests and reports 63 J. Supervision of tests and reports 63 VII. Summary 63 ILLUSTRATIONS 1. Map showing repairs and extensions 10 2. Map showing insulated return feeder lines 11 3. Twenty-four-hour smoked chart 22 4. One-hour smoked chart 23 S- Load and ratiocurves, Springfield Railway Co 25 6. Load and ratiocurves, Ohio Electric Railway Co 25 7. Map showing potential differences, water mains to rails 27 8. Potential difference chart Burt and Kenton Streets, July 23, 1914 30 9. Potential difference chart Burt and Kenton Streets, August 6, 1914 30 10. Map showing potential differences, telephone sheaths to other structures ... 31 11. Map showing potential gradients on tracks 35 12. Map showing over-all potential differences 41 13. Map showing stray cunent in water and gas mains 41 TABLES 1. Insulated return feeder data .^ 14 2. Insulated return resistance units 15 3. Power losses, uninsulated return 18 4. Power losses, insulated feeder return 20 5. Telephone pilot wire resistance 26 6. Permanent pilot wire length and resistance 26 7. Potential differences, water mains to rails 28 8. Potential differences, gas to water mains 31 9. Potential differences, lead sheaths to other structures 32 10. Potential gradients, Springfield Railway Co. lines 34 Contents . 5 Page 11. Potential gradients, Ohio Electric Railway Co. lines 36 12. Additional potential gradients 37 13. Over-all potentials, Springfield Railway Co 39 14. Over-all potentials, intemrban lines 40 ij. Current in water mains 43 16. Current in natural gas mains 44 17. Current in artificial gas mains 46 iS. Ciurent in telephone sheaths 47 ig. Comparative load, Ohio Electric Railway Co 51 20. Comparative load, Springfield Railway Co 52 21. Comparative potential differences 54 22. Additional potential differences, gas to water mains SS 23. Comparative current in water mains 56 24. Comparative current in natural gas mains 57 25. Comparative current in artificial gas mains 58 SPECIAL STUDIES IN ELECTROLYSIS MITIGATION: 1. A REPORT ON CONDITIONS IN SPRINGFIELD, OHIO, WITH INSULATED FEEDER SYSTEM INSTALLED By Burton McCoUum and George H. Ahlbom I. INTRODUCTION A. PREVIOUS SURVEYS In an earlier report^ there was given a brief discussion of the subject of electrolysis mitigation and a description of the negative feeders which the Springfield Railway Co. had already installed, and recommendations were made concerning the methods to be pursued in Springfield. These included improvement of the Springfield Railway Co.'s system of insulated return feeders, redis- tribution and addition of negative copper, one crosstie between tracks, the installation of one cable at the Ohio Electric Railway Co.'s substation (chart No. Ill, opposite p. 49 of above report), careful testing and bonding of track and thorough interconnection of tracks at all intersections whether of the same or different rail- ways. The insulated return feeder system installed in Springfield was designed and built by the American Railways Co., which operates the Springfield city railway system. During a joint investigation carried on by the utilities and the Bureau of Standards in Decem- ber, 1913, and January, 1914, certain changes were made, includ- ing the disconnection of pipe drainage copper from the pipes and its connection to the tracks on North Street as negative return feeders, and the installation of a cable on East Main Street between Sycamore Street and Belmont Avenue. As pointed out in a spe- cial report,^ other work remained to be done, including the installa- ^ Technologic Paper No. 27, Bureau of Standards. ^ Joint Investigation Report on Electrolysis Conditions in Springfield, Ohio. 8 Technologic Papers of the Bureau of Standards tion of pressure wires running to the end of every trolley line or the point where the line crossed the city Umits, and a considerable amount of track repair work. B. REASONS FOR PRESENT SURVEY Because the condition of the track was unsatisfactory at the time of the previous survey and the weather had interfered with measurements and probably affected the values, more detailed measiurements were made by the Bureau in July and August of 1914. It is the purpose of this report to discuss the results obtained in these measurements, to describe the insulated return feeder system as finally installed, to make comparison between the conditions shown by the various siurveys, to present certain rec- ommendations regarding the improvement and maintenance of the track network, and to draw conclusions as to the effectiveness of the mitigation system in its present form. II. DISCUSSION OF GENERAL CONDITIONS OF THE VARIOUS SYSTEMS Before taking up the discussion of the data, a brief description of the conditions existing in Springfield, Ohio, which aflfect the elec- trolysis situation will be of interest. Springfield is a city of varied manufacturing interests, having a population of 50 000 and a rid- ing habit of 0.55 per inhabitant, the number of passengers per car mile being 6 and the power required 0.17 kwhrs. per ton mile on the city lines. The country is rolling, there being no very steep grades on either city streets or interurban right of way. A. RAILWAY SYSTEMS OF SPRINGFIELD Five railway companies operate witlftn the city limits of Spring- field. The Springfield Railway Co. operates 33 miles of single track and normally 29 cars weighing from 12 to 16 tons with an average running current of 35 amperes each. The Ohio Electric Railway Co. operates heavy interurban cars weighing 34 to 43 tons and using an average ctuxent of 300 amperes, running on an hourly schedule in three directions and carried by the substation Electrolysis Mitigation in Springfield, Ohio g in Springfield on a total of i8>^ miles of line. Freight service, irregular schedule, is handled on these lines. The single-track mileage within the city is 1 1 .6 miles. The power stations of these two lines are fortunately situated, viewed from the electrolysis standpoint, as has been pointed out in previous reports, since they are toward opposite ends of the city load area, and since the inter- connection of tracks interchange of current on the negative side takes place very effectively. The other three interiurban lines, the Springfield, Troy &. Piqua Railway Co., the Springfield & Washington Railway Co., and the Springfield & Xenia Railway Co., have a combined length of 5.3 miles of single track, have no power houses within the city, and the cars (generally only one to each line in the city at any one time) run on an hourly schedule and draw an average current of about 75 amperes per car. Con- siderable freight service and motor load, especially on the Spring- field, Troy & Piqua line, increase the load on these lines. 1. DETAILS OF CGNSTRTJCTIGN The tracks are mainly T rails of weight varying from 35 to 100 pounds per yard, on wooden ties embedded in rock ballast or con- crete, new construction being mainly 90 or 100 poiuids per yard. A new type of construction already laid on West Pleasant Street and at several other points consists of loo-pound girder rails, laid on steel channels and I sections with a beam of concrete under- neath the rail. The joints are connected by an electric pencil weld, and are also welded to the channels at the joints. This provides frequent and effective cross bonding. The stray cturent leakage from this type of construction will probably be greater than with wooden ties, but the steel ties are spaced 6 feet, and the drainage from the concrete beams should be good. A small amount of track on private right of way is raised above the surface, so that only the ties are in contact with the earth or ballast. 2. REPAIRED SECTIONS All sections of track mentioned in the second report as defective, except on Limestone Street between McCreight Avenue and Grube Road and on High Street between Belmont Avenue and Biumett 5696°— 16 2 lo Technologic Papers of the Bureau of Standards Road have been repaired. Work on these two sections was in progress during this survey, and the discussion of the data will have to include consideration of the effect of these sections. Track repair work is so necessary that it seems undesirable to delay or interrupt it on account of a survey, and some track work will be in progress on a system of this size at all times. To get consistent results there should be a minimum number of discon- nected tracks. In addition to the above, new work and repairs were planned or in progress at the following points: East High Street from Biumette Road to the Detroit, Toledo & Ironton tracks; West Pleasant Street from Yellow Springs Street to Dayton Road; on Cedar Street and Broadway to Isabella Street; Yellow Springs Street from State Street south; and on North Fountain Avenue from McCreight Avenue to Home Road. These sections are shown by colors on the accompanying map (Fig. i, opposite p. id). B. OTHER UTILITIES The underground structures consist of cast-iron mains with lead joints and services operated by the city water department, cast- iron and steel mains with lead, screw, and Dresser joints, and steel or wrought iron service pipes belonging to the Springfield Gas Co., and lead sheath cables of the Central Union Telephone Co. and the Springfield & Xenia Telephone Co. Gas mains are laid from 2 to 4 feet below the stu^face, and the ratio of the mileage of cast iron to that of wrought iron and steel is about I to 2. The many lead joints showing gas leaks may indi- cate high resistance joints as on the steel mains do the frequent Dresser couplings, the location of which is very irregular and imcer- tain. The mains lie in the streets rather than in the alleys, and there is only one supply main to eack street, the services crossing under the car tracks. This is also true of the water mains which are all cast iron laid at a depth from 3 to 5 feet. Frequent water heaters make good metallic connections between the gas and water systems. No regular attempt to protect the surfaces by paints, other than the standard practice by the manufacturers, has been made, although some special preparations have been tried. The 1 J < r « 1, ^- l\ ; fi « i "' a / ^'^ ^-inch steel strand cross bond with copper terminals welded to the rails will often be more permanent and is effective and of sufficient conductivity. I. ANNUAL TESTS AND REPORTS The companies operating the railway lines should be required to submit annual reports showing the location and resistance in equivalent feet of rail of all bad joints. Since such resistances expressed in equivalent feet of rail can be obtained with any of the standard bond-testing instruments on the market, they should be given and not the drop across the joint which is a function of the ctuxent flowing as well as the resistance of the joint. J. SUPERVISION OF TESTS AND REPORTS It is very desirable that the city retain some one competent to pass on these bonding reports, check up the values given in the report, to measure the over-all potentials, and suggest any other desirable tests. This would greatly assist in maintaining good electrolysis conditions, and the employment of such an expert is recommended. VII. SUMMARY The foregoing report discusses previous electrolysis sirrveys and the physical conditions which affect electrolysis conditions of the city and public utilities. The present insulated return feeder system is described in considerable detail showing size, location, etc., of feeders, resistance taps, power losses, and the cost of opera- tion of the railways as affected by this mitigation system. It is shown that the cost of operation is slightly greater than before any system was installed but less than with the first insulated 64 Technologic Papers of the Bureau of Standards return system. The pressure wires by which the over-all poten- tial differences may be measured are described and resistance given. The data of the most recent smrv^ey are given in detail showing the potential differences between the various structiures and along the tracks, and the stray current in the undergrotmd pipes and cable sheaths. These data are also compared with those taken the preceding winter, and it is noted that low temperatures, slightly below the freezing point, do affect conditions consider- ably, reducing the amount of stray current and increasing the potential differences between the tracks and the pipes, both these effects being due to the increased soil resistance. Recommendations are made concerning the constructional details of the utilities and the administration of electrolysis regu- lations by the city. It is recommended that the insulated feeder system be continued in operation, that certain improvement in track bonding and interconnection be made, that the pressmre wires be maintained, that no pipe drainage be resorted to, and that the pipes laid in the future be kept as far as practicable from railway tracks and have enough insulating joints to mate- rially increase their resistance. Definite over-all voltage limits are suggested as a reasonable requirement and also a suitable standard of bond maintenance, these conditions to be determined by annual tests and reports to an expert employed by the city. In connection with the work in Springfield, the Bureau wishes to acknowledge the cooperation and assistance of the city manager and other city authorities, including the water department; also of the Springfield Gas Co., Central Union Telephone Co., Spring- field Railway Co., Ohio Electric Railway Co., Springfield, Troy & Piqua Railway Co., Springfield & Washington Railway Co., Spring- field & Xenia Railway Co., and of Prof. E. O. Weaver, professor of physics, Wittenberg College. Washington, July 17, 191 5. DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON. Director No. 62 modern practice in the construction and maintenance of rail joints and BONDS IN electric RAILWAYS E. R. SHEPARD, Associate Electrical Engineer Bureau of Standards ISSUED MARCH 10, 1916 WASHINGTON .GOVERNMENT PRINTING OFFICE 1916 ADDITIONAL COPIES OF THIS PUBLICATION MAT BE PEOCUBED FROM THE SOTEKINTENPENT OF DOCUMENTS OOTEKNMENT PRINTING OFKCE WASHINGTON, D. C. AT 35 CENTS PER COPY MODERN PRACTICE IN THE CONSTRUCTION AND MAIN- TENANCE OF RAIL JOINTS AND BONDS IN ELECTRIC RAILWAYS By E. R. Shepard CONTENTS Page I. Introduction S II. Historical and general discussion of bonds and joints 7 1. Bond requirements 8 (o) Intimate and permanent contact with rail under service conditions 8 (6) Durability 8 (c) Ease of installation under service conditions 9 (d) Low resistance 9 (e) Proof against theft 9 (/) Reasonable cost 9 z. Types of bonds 10 (o) Old types 10 (6) Soldered bonds 11 (c) Compressed terminal and pin terminal bonds 12 (d) Brazed or welded bonds 15 (e) Mechanically applied head bonds 17 (/) Tubular bonds 18 3. Cross bonding and special work bonding 18 (a) Cross bonding 18 (6) Special work bonding 19 4. Welded and special joints 19 (o) Cast weld ig (6) Thermite-welded joints 20 (c) Electrically-welded joints 21 (d) Arc-welded joints 21 (e) The Nichols composite joint 22 (/) Mechanical joints 22 III. Compilation of information submitted by operating companies 22 1. Questions submitted and natiu-e of replies 22 Rail bonds 23 Welded and other types of rail joints 24 3 4 Technologic Papers of the Bureau of Standards III. Compilation of information submitted by operating companies— Contd. Page. i!. Compilation of data submitted by operating companies on bonds. . 27 (a) Questions i, 2, and 3. Number and types of bonds 27 (6) Question 4. Inspection of bonds 30 (c) Question 5. Criterion for replacement 31 {d) Question 6. Average life of bonds 32 (e) Question 7. Intervals for cross bonding 38 (/) Question 8. Size of cross bonds 38 (9) Questions 9 and 10. Bonding around special work 38 {h) Question 11. Theft of bonds 39 (j) Question 12. Grade of labor for bonding 39 {j) Question 13. Bonding tools 40 (fe) Questions 14 and 15. Drilling 40 {I) Question 16. Cost of bonding 40 (to) Question 17. Causes of failure 45 (») Question 18. Resistance of bonds, new and old 47 3. Compilation of data submitted by operating companies on welded and other types of rail joints 4$ (o) Question 1. Number of joints in use 49 (6) Question 2. Types of construction 50 (c) Question 3. Electrical efficiency of joints 50 (i) Questions 4 and 6. Life of joints and causes of failure 50 {e) Question 5. Cost of joints 52 (/) Question 7. Temperature variation in welded joints 54 {g) Question 8. Expansion joints 55 IV. Analysis of data 55 1. The mechanical joint 55 (a) Defective roadbed 56 (6) Nonuniformity of rail sections 56 (c) Defective rail ends 56 (d) Failure to grind joints 56 (e) Loose bolts 57 (/) Improved bolts 57 {g) Joint plates 59 (Ji) Room for concealed bonds 59 (i) Examples of bond failures 51 (j) Special plates 62 {h) Improved joint plates 62 2. Types of bonds and featiures of installation 64 (o) Comparison of compressed an^pin terminal bonds 64 (6) Stranded v. ribbon bonds 73 (c) Use of solder and alloys with mechanically applied bonds. . 74 id) Mechanically applied head bonds 79 (e) Electric-weld bonds 83 (j) Oxy-acetylene welded bonds 88 {g) Bonding of manganese and other special work 90 (A) Bonding of converted steam roads gj (i) Double v. single bonding 94 Rail Joints and Bonds 5 IV. Analysis of data — Continued. 2. Types of bonds and features of installation — Continued. (j) Economic and other considerations for the replacement of Page. bonds I02 (fe) Standards for replacement 104 3. Welded and special joints 106 (a) The cast weld 107 (6) The thermite-welded joint 108 (c) The electrically-welded joint no (rf) The arc-welded joint 112 (e) The Clark joint 117 (/) The Nichols composite joint 117 V. Experimental tests 118 VI. General conclusions 121 Bibliography 123 I. INTRODUCTION While studying electrolysis and electrolysis mitigation dtiring the past five years the subject of rail bonding and track conduc- tivity has been brought forcibly to our attention by observations on railways where electrolysis surveys have been made, by a vast amount of discussion of the subject in the technical press, and by conversation and correspondence with railway engineers. This keen interest in track bonding originated largely through the necessity of mitigating electrolysis, and while electrolysis continues to be the greatest stimulus for bond maintenance, it is as a rule justifiable solely from the standpoint of good operation, and is an absolute necessity for the successful operation of block signals. In view of the great variety of bonds and bonding practices in use at the present time, and the large percentage of failures after 25 years of experimentation on the part of the operating and manufactming companies, and after repeated calls for informa- tion and advice on the subject from railway engineers, the Bureau of Standards deemed it advisable to institute a thorough investi- gation regarding the present status of bonding and joint mainten- ance with the idea of disseminating information that will aid the companies in selecting bonds and joints, and in methods of apply- ing and installing them, as well as of calling attention to the im- portance of good track conductivity and its true relation to elec- trolysis and its effect upon electric railway operation. 6 Technologic Papers of the Bureau of Standards Owing to the peculiar nature of the services that rail bonds and joints are called upon to perform and the great variety of condi- tions under which they operate, it was recognized that informa- tion obtained under service conditions over a period of years would be far more reliable and satisfactory than any laboratory or short-time tests that could be conducted. Many laboratory tests have been made by the manufacturers on the durability and resistance of different types of bonds and joints, and while such tests are valuable in determining the characteristics of a bond, they can not be taken as a criterion for the performance of the average bond under service conditions. The personal element which enters so largely into the installa- tion of bonds, and the variety of conditions under which they op- erate made it necessary to obtain information from a large num- ber of sources and to base conclusions only on testimony sub- mitted by a great many witnesses. Accordingly, data were col- lected through a large number of circular letters and other corre- spondence, by personal visits to some 50 operating companies, as well as to practically all of the manufacturers of bonds and rail joints. Owing to the rapid growth of the electric railways, the numerous changes in the standards of construction, the improvements in materials and methods, the franchise and street-paving require- ments, the changes in organization and administration, and the transient nature of the engineering staffs, it was found difficult to get definite and consistent information regarding the operation of any type of bond or joint over a period of years. Many of the companies consulted had kept only meager, if any, records of their bonding, and their replies, of necessity, were based largely on opinions. Few engineers were able to give with any degree of certainty the average Ufe of a given "type of bond. Either the bond had not been in service long enough to warrant a statement or else no definite records were available. New inventions and recent improvements in the manufacture and installation of bonds and joints, as well as changes in the types and composition of rails, all contribute to an unsettled con- dition at the present time, which means that a great number of bonds and joints now in service are in the experimental stage. Rail Joints and Bonds 7 While the larger operating companies have the engineers and resources with, which to meet the bonding problem with more or less success, the smaller companies must depend in a large measure upon these and other external sources for their standards. This has not always been to their advantage, as many practices em- ployed by the larger companies are not applicable to the smaller systems. Local conditions or city restrictions frequently limit the types of bonds that might be employed. The result is that many companies have been confused by the apparent inconsis- tencies in adopted standards, not realizing that each has been worked out to meet peculiar conditions. A great many railways have settled on certain bonding stand- ards and are apparently satisfied with the results they are obtain- ing, not that they believe they have the one and only best stand- ard, but they are tired of experimenting and are willing to let well enough alone. Others, and perhaps the majority of the com- panies, are not satisfied with their present practices, and are looking for something better suited to their requirements. In view of the conditions described above it can not be expected that this investigation will clear up a most vexatious question, nor in any way purport to be the last word on the subject. The Biu-eau of Standards hopes, however, in tabulating and analyzing the data which have been collected, to discern and interpret the present tendencies and to reconcile some apparent inconsistencies and differences of opinion. Its aim will have been fulfilled if it succeeds in laying before the electric railway companies, and par- ticularly the smaller companies with Umited resources, informa- tion which will be a guide to the selection of bonds and joints; and, what is of still more importance, in pointing out the best methods of application and maintenance and in emphasizing the necessity of adhering to them. II. HISTORICAL AND GENERAL DISCUSSION OF BONDS AND JOINTS Although early attempts were made to operate cars on unbonded tracks, relying upon the joint plates and the earth for conductance, it soon became evident that a metallic bond was necessary both from the standpoint of good operation and for the prevention of 8 Technologic Papers of the Bureau of Standards stray currents, which were early found to have a corrosive action on underground structures. Numerous types of iron and copper bonds came into use, many of which are now obsolete, and a description of which would be of no particular value to this paper. Those types which have found general use will be discussed with reference to their features of installation and the conditions under which they operate. No academic classification of bonds will be attempted. The great number of different types of bonds which have appeared in the past years is largely the result of attempts to better meet the exacting requirements which this piece of appa- ratus is called upon to fulfill. While these requirements and the different types of bonds which they have called forth are familiar to the majority of rail- way engineers, the most important of them are here briefly described by way of introduction to a. later part of the paper, where, in connection with testimony submitted by the operat- ing and maufacturing companies, a more detailed account of the manner in which the various types of bonds are meeting the requirements of service will be discussed. 1. BOND REQUIREMENTS (a) Intimate and Permanent Contact With Rail, Under Service Conditions. — Perhaps the first and most important requirement of a rail bond is that it make good electrical contact with the rail and that this contact remain good over a period of years while subjected to the mechanical vibrations of traffic, changes of temperature, the action of soil and moistiu-e, and to the mechanical injuries from workmen and vehicles. In general, three methods of making contact with the rail have been employed, viz, soldering, mechanical, and brazmg or welding. Combina- tions of these have also been used. Each method will be treated under the types of bonds employing it. {b) DuRABiuTY. — The diurabiUty of the bond itself depends, first, upon its ability to withstand the bending and vibration incident to expansion and contraction of rails and the deflection of the rail joint imder traffic, and, second, upon its ability to withstand electrolytic and soil corrosion. Rail Joints and Bonds 9 The first action is by far the more severe and has resulted in the failure of more bonds than has any other one cause. Loose rail joints are the chief cause of such failures, and the problem of bonding is therefore intimately related to the problem of joint maintenance. The second cause of deterioration, that of corrosion, is rarely important, although in extreme cases it may be serious. Iron bonds buried in the earth and copper bonds in soils of certain character, or on tracks from which large leakage currents are escaping, have been, known to corrode at a very rapid rate. (c) Ease of Installation Under Service Conditions. — For the greatest practical value a bond should be of such a nature that it can be safely and quickly installed under service conditions ; that is, while traffic is being maintained over the tracks. For new work this may not be required, but for repair and replacement work its importance is obvious. While bonds are frequently installed at night and traffic is sometimes diverted for the purpose of installing bonds, such practices are decidedly objectionable. Moreover, it is possible for bonding apparatus to offer a hazard to the safe operation of cars. Though not of prime importance, these features can not be neglected in the selection of a bond. (d) lyOW Resistance. — Under ordinary conditions the resist- ance of a bond within moderate limits is subordinate to its other qualities. Obviously, it must have a cross section sufficiently large to carry the track current without undue heating, but as a rule its length will be determined by other considerations. Where the resistance of bonded joints is limited by ordinance, or where for special reasons a high conductance is required, this feattue may be a determining factor in the selection of a bond. (e) Proof Against Theft. — In many localities the theft of rail bonds has become so prevalent and the losses from this soiu-ce so heavy that the resoiurces of the railways have been seriously taxed to cope with the problem. To-day no bonding of suburban track can be undertaken without due consideration of this feature, and either bonds designed to overcome this trouble must be selected or some other preventive means employed. (/) Reasonable Cost. — While the consideration of cost can not be neglected in the selection of apparatus and material, its promi- lo Technologic Papers of the Bureau of Standards nence may in some instances be entirely overestimated. It is not always apparent that ultimate economy may result from a high first cost, and with the difficulty in securing approval of estimates for bonding from those who do not always appreciate the impor- tance and necessity of this work the more expensive bond is likely to be seriously handicapped in its bid for consideration. Although the general manager who wants to know why bonding is necessary when the cars are operating under existing conditions is rather the exception, there are many who place bonding at the end of the budget, so that the engineer is sometimes forced to employ material and methods for the sake of economy which are against his better judgment. It is quite evident, therefore, that the first cost of a bond, which of course includes the cost of installation, although having httle relation to its ultimate economy, in many cases might be the determining feature in its selection. 2. TYPES OF BONDS (a) Old Types. — Early bonding was accomplished by riveting or bolting soUd iron or copper wires to the web or base of the rails. This general practice was not long employed, as it was soon found that such contacts rapidly deteriorated from corrosion. Practi- cally none of these bonds are in use at the present time and the types can be considered as obsolete. Channel-pin bonding, as shown in Fig. i, consists in driving a grooved plug into a hole in the rail with a round wire fitted into the groove in the plug, found early favor with the railway com- panies owing to its low cost and ease of installation. It is still to be foimd in service on old tracks and has a very limited sale at the present time for temporary use in mines and for other special purposes. These special conditions, however, are being met by modern and more satisfactory types, fhus leaving this bond with a very limited field. Originally steel plugs and solid copper wires were used, but the practice has been varied by the use of copper instead of steel plugs and in other cases by copper-plated or tinned plugs. Sometimes the plug entirely encircles the wire in the form of a sleeve. Although there are cases on record where this type of bond maintained good electrical contact with the rail for many years Bureau of Standards Tec hnoloj^'ic Paper No. 62 (f% I'll.. I. -A';;i/ii/ Liiiil Lhaiiiul j'ui buihls l^ Ihc. 2. — ■Loiiipic.'^.ycd icininial (ypt Rail Joints and Bonds 1 1 under service conditions, the results obtained in general were poor. Moisture invariably found its way between the plug and the rail, or between the wire and the plug, thereby causing corrosion and an increasing contact resistance. Channel pins and iron bonds still find a Hmited application on subtu-ban tracks where the theft of copper bonds excludes that type, and where the rail and joint plates are of such dimensions as not to permit the use of concealed bonds. Under such conditions they are admittedly a makeshift and are employed only as a last resort and in the absence of any satisfactory method of bonding. (6) S01.DERED Bonds. — With the failure of the riveted, bolted, and channel-pin bonds the necessity of a bond making a more perfect and permanent contact with the rail became apparent. The soldered contact early came into use to meet this demand and found universal adoption. With the exception of the most modem installations practically every electric railway company in the country has employed the soldered bond in one form or another. Its low cost and ease of application were in its favor and appealed to the operating companies. It can be applied to either the head, web, or base of the rail, requires no drilling, and can be installed without interruption to trafl&c. The one serious objection to this type of bond is the difficulty in seeming a permanent and low-resistance contact. The failures of soldered contacts are due to inherent defects in the method as well as to poor workmanship in installation. Copper has a coefficient of expansion nearly twice that of steel and somewhat less than lead-tin solder. It is evident, therefore, that with the diurnal temperature variations that steel rails undergo the soft film of solder connecting the two different metals is subjected to continual alternate strains which, in the presence of moisture and under the vibrations due to traffic, will eventually result in failure. There are few mechanical processes in which the personal ele- ment enters so largely as in the application of bonds, and this is particularly true with respect to the soldered bond. As a rule, skilled mechanics are not employed for this work and the ordi- nary track laborer is slow in mastering the apparently simple feat of soldering a rail bond. In fact, he is a rare workman if he ever does learn the intricacies of this process and conscientiously ap- 12 Technologic Papers of the Bureau of Standards plies his knowledge at all times. The soldered contact between bond and rail frequently corrodes without exhibiting any external signs of such deterioration. The bond might even resist a mod- erate blow from a hammer and still show a very high resistance when tested with a bond tester. Inspection therefore is not a reliable means of determining the condition of soldered bonds. Another inherent defect of the soldered, bond is the compara- tive ease with which it can be removed from the rail by copper thieves. A short bar is all that is necessary to remove these bonds from the head of a rail, and enormous losses of this type have occurred where the labor and time necessary to remove other types would have saved them. While there are some engineers who still retain faith in the soldered bond, and a few companies employing well-trained and careful workmen continue to install them, their inability in gen- eral to meet the requirements of service have led to their abandon- ment by the majority of operating companies. (c) Compressed Terminai. and Pin-Terminai, Bonds. — Com- pressed terminal bonds, shown in Figs. 2 and 3, are those having cylindrical terminals which are compressed with a screw or hy- drauhc compressor into holes drilled or punched in the web or base of the rails. They are referred to by the various manufac- turers as compressed terminal, solid terminal, and compressed stud terminal bonds. Pin-terminal bonds are those having tubu- lar terminals which are expanded into holes drilled or punched in the web or base of the rail by driving a steel pin into the hole in the terminal. They are referred to by the various manufacturers as pin-terminal, tubular-terminal, and pin-driven bonds. They will be referred to in this paper simply as pin-terminal bonds. The term "stud terminal" will be used to include both of the above types. These bonds are made either in the solid, stranded, or ribbon type, and are designed either for concealed or exposed applica- tion. Although a great diversity of opinion exists regarding the merits of these bonds, they have found wide application and for more than 15 years have remained the standards for numerous companies. Owing to their wide use at the present time and in view of the general interest manifested by the companies in them. Bureau uf Standards Technologk Paper No. 62 Fig. ^ — Piii-icrminnl bonds Rail Joints and Bonds 13 a somewhat detailed account of their properties will here be in order. Some difficulty was at first experienced by the manufactm-ers in secviring a perfect union between the terminal and the strands or ribbons of these bonds. The successful welding of copper re- quires certain precautions in the exclusion of oxygen, and until improvements were made in their fxumaces and methods the bond manufacturers fotmd difficulty in tiurning out bonds with properly welded terminals. This defect has been entirely overcome, so that it is now possible to obtain bonds which are perfect in this respect. To overcome thi:5 trouble some manufactxurers have forged the terminals from the wire strand of the bond itself. Another improvement in the construction of stud-terminal bonds which has come into use only in recent years is that of ma- chining the terminals. Before this practice was employed the in- equalities in the stud made it difficult to obtain a perfect contact over the entire surface of the terminal. This gave a chance for the entrance of moisture between the copper and steel, with re- sulting corrosion and rapid deterioration. A film of moisture on the contact acts as an electrolyte, and with the passage of electric current rapid corrosion took place. A number of manufacturers now machine all bond terminals, while others do so only when specifications require it. The additional expense is small and most companies are willing to meet it for the increased life of the bond. Other improvements in the nature of annealing or soften- ing the copper have added to the value of stud-terminal bonds by permitting a better flow of copper and consequently a better union with the steel. Failtu"e of the bond itself, due to the crystallizing and breaking of the wires and ribbons, has been largely overcome by increasing its length and by using a size of wires which experience has shown will withstand the maximum amornit of mechanical vibration. Attention has also been given to the matter of forming bonds to conform to the joint plate and rail sections. While the manufacturers have been active in their efforts to reduce the failiures of the stud-terminal bonds, by introducing improvements and refinements in their methods of construction, the utility of these, as well as all other types of bonds, has been 14 Technologic Papers of the Bureau of Standards greatly increased by improved methods in their installation. The importance of great care in the installation of stud-terminal bonds was, at first, not always appreciated by either the engineer or the workman. The many precautions and refinements now known to be imperative for best results were not known, in the early days of electric railway engineering. Electric roads were springing up like mushrooms in every city. In many cases they were built by contract at so much per mile and concealed bonds received scanty attention. Indeed, cases are on record where bonds have been removed from such roads after a period of years and were found not to have been compressed or expanded at all but simply driven in the holes drilled to receive them and covered up by the joint plates. Bonds poorly installed frequently gave good service for a short time; sometimes for a few years. Even if they did not, the joint plates and the earth roadbeds frequently suflBced to re- turn the current to the generators, and until water and gas leaks began to develop, or until the necessity for better service called attention to the poor retium circuit, the bonds often received no consideration. It is Httle wonder, therefore, that years were re- quired to establish the facts regarding the proper methods of bonding. The high percentages of failures that have been recorded in the past were apparently, therefore, on bonds which were manu- factured and installed under conditions far different from those existing at the present time or even in recent years, and they can not be considered as an index to the performance of modern bonds installed under more favorable conditions. Some of the featin-es of installation which have contributed to the failure of stud- terminal bonds are here recounted: (i) The drilling of too large holes, thus requiring too great compression or expansion to make good contact. Holes are now usually drilled having the same diameter as that of the bond terminals. (2) Rough or irregular holes caused by dull or imperfectly ground drills. (3) Instalhng bonds in old, corroded, or wet holes. Bonds are now installed in only freshly drilled holes, perfectly clean and dry. (4) The use of oil in drilling. A film of oil between bond terminal and steel impairs the contact. Holes are now, as a rule, drilled dry. (5) Failtire to clean web of rail around hole. Rust or scale on the web of the rail with which the face and button of Rail Joints and Bonds 15 the bond comes in contact is likely to permit the admission of moistm-e to the contact. The best modem practice requires the grinding of the rail adjacent to the hole. (6) Incomplete com- pression or expansion of terminals. (7) Old or wrongly shaped compressor face. (8) Carelessness in driving expanding mandrel or pin. (9) Failxu-e to clean bond terminal before installation. As with the soldered type the personal element enters largely into the installation of stud-terminal bonds, evidence of which is given by reference to the numerous details recounted above. The foregoing is considered a sufficient introduction to the discussion and comparison of the pin terminal and compressed- terminal bond which is to follow in connection with the reports of the operating companies. (J) Brazed or Wei/DEd Bonds. — ^This type includes all bonds in which either the copper terminal of the bond is welded directly to the rail or in which a third metal, such as brass or some other hard solder, is used to effect the union. Heat may be applied by any means, the most common being the passage of an electric current through the members being united, the electric arc, and the oxy-acetylene flame. The pouring of molten copper into a mold around the bond terminal has also been employed. The following definitions are in common use and will be adhered to in this paper. Electric Weld. — Though commonly called a brazing process this term is used by the Electric Railway Improvement Co. in reference to the operation in which current passing through carbon electrodes in contact with the bond terminal generates the welding heat. It will here be employed in that connection. Arc Weld. — A weld or brazing process affected by heat gener- ated by an electric arc. Oxy-Acetylene Weld. — A weld or brazing process affected by the use of the oxy-acetylene flame. Copper Weld. — A weld or brazing process affected by pouring molten copper into a mold surrounding the bond terminal. Up to the present time the use of the welded or brazed bonds has been confined almost entirely to that of the electric-weld type. These bonds are more modem than the soldered and mechani- cally applied types described above, and their manufacture and 14985°— 16 2 1 6 Technologic Papers of the Bureau of Standards use has been greatly stimulated by the high percentage of failures attributed to the imperfect contacts of the latter-named types. A greater stimulus, however, was the growing need for a short exposed bond which could be applied to the head of the rail without removing the joint plates and which would make such tenacious contact as to discourage the attempts of copper thieves to remove it. The need for such a bond was so strong and the brazed or welded bond met the requirements so admirably that it at once sprang into extensive use, particularly on open track, even before time had demonstrated its lasting qualities. To guard against theft on suburban tracks and also to reduce its cost the bond was of necessity made comparatively short. This feature led to a rather high rate of failure from the breakage of the wires or ribbons, particularly on roads having poorly maintained rail joints. Imperfect methods of application and carelessness in installation also contributed to the failures of this type. Like the stud-terminal bonds, therefore, the electric-weld bond had to go through an experimental stage. Improvements in construction, adoption of new t5rpes, as well as education of the railways in the methods of installation have progressed tmtil to-day most of the early defects have been overcome and the bond is supplying a wide and growing demand. The chief objections to the electric-weld bond are, first, as usually applied, their installation requires the purchase of rather an expensive bonding car, and, second, the bonding car is incon- venient to operate on tracks over which traffic is being main- tained. The first objection is a serious one for small roads having limited means, and the second objection applies to all tracks on which the headway is of the order of 30 minutes or less. It is necessary to derail the bonding car to let regular trains pass, and this is obviously impracticable uAier a short headway. These objections are not pertinent to other types of welded bonds, and for this reason they are now making a strong bid for recognition. Figs. 4 and 5 show two types of electric-weld bonds in common use. The ET type, which is the newer of the two, was recently designed to overcome defects in the EA type The manner in which the conductors of the EA type met and joined the bond terminal permitted of considerable bending and vibration at that Bureau of Standards Technologic Paper No. 62 Fig. (j.—L ai fur ul'plyii'il chrliii-i.ril I'omls :^^^.,^ I'IG. <,,l.—roitdirc-:eni sej^aralioi of uhhoiis ^■SL-r' \- ■ . ..^ _ \:iitT^'Z ^X^^^BM ^Bt.. ■■-^ j^AUUJI^I yp.t,- ^'•- "- . .'^C '^^ .■-'rf"-,v." .J ^V |p>'- "'■ "' J ^ --^-■.--,#- , '•'--' ;;-•■■-,,.:*.:*•-■■■ /■^M m^M^M^^':'^- 't^-^^.^i^.';^?^^!^ ..^M -*~Sj r f 4-^W' '«i m: •# n t ■* ^^-s&i^ , ^^^P^ 1 .- -^•^ '■"tg*- Sg^ >-^ !-.-#-. »a nn||M| »-i^ !'■ ^l£^ «pr~ - ^ '?A^ '^^ Fig. 22.~'Coii:pU/i\l ( 'hnk joint Rail Joints and Bonds 6 » On badly worn and loose joints of the type shown in Fig. 13 the entire vertical motion of the bond is confined to the short region between the bolts nearest the rail ends and in bonds which are hugged tightly by the plates to a still more restricted length. Such a condition results in the breaking of the strands, not at the bond terminals, as would happen with no restrictions, but at the juncture of the rails or near thereto. Even upon well-maintained joints in which there is practically no vertical motion the continual lengthening and shortening of the bond resulting from expansion and contraction, and which is confined to a comparatively short length, will produce the same effect. Such failm-es have been more prevalent on open track, where rails experience the full effect of temperature variations, than in city streets. This may be par- tially the result of better ballast and heavier rails in the latter type of construction, but it is quite reasonable to suppose that the linear expansion and contraction which takes place on the open track is largely responsible for the crystalUzation and break- ing of the strands and ribbons. (i) Examples oif Bond Failures. — Companies 2 and 14 specifi- cally state that expansion and contraction in rail joints is respon- sible for bond failures, and Company 16 says that the failure of concealed bonds is confined to those joints in which expansion and contraction of the rails takes place in the joint. The Boston & Worcester Street Railway Co. presents a striking example of this t3rpe of bond failure on their suburban line between Boston and Worcester. It is reported that only a small per cent of the origi- nal 12-inch concealed-wire bonds are now in service, a large ma- jority of them having failed by the wires breaking in the middle near the jimcture of the two rails. Engineers of the American Railways Co., which operates a num- ber of properties, state that they have had difficulty in obtaining room for concealed bonds on rails of 60 pounds per yard and smaller. On large rails they report ample room and state that they will permit of very loose joints without breaking bonds, while the slightest motion in the joints of the smaller rail sections will quickly result in broken strands or ribbons. Some of the bond manufactiurers have attempted to meet this problem by providing the operating companies with stranded Fig. ij. — Standard joint plates, showing quale space for bond 62 Technologic Papers of the Bureau of Standards bonds having a triangular section. A sectional view of such a bond installed is shown in Fig. 15. While this may be an improvement over a bond having a circular section, its very necessity is an ac- knowledgment of a condition which requires a more drastic remedy. (/') Special PIvATES. — Some of the larger and more progressive companies have called on the steel manufacturers to roll special plates for them which have been designed to give room for concealed bonds. This has been done in some cases and in a few instances such plates have become standard with the manu- factiu-ers. This is particularly true with re- spect to the manufacturers of some of the patent joint plates, such as the continuous joint and the Bonzano joint. Fig, 16 shows a sectional view of continuous joint plates applied to a 40-pound rail. It is seen that ample room is provided for concealed bonds. The j oint plates recently adopted as standard by the Amerian Electric Railway Association were designed to give ample clearance for bonds and are now being rolled. These standards, however, were adopted for only the 7-inch and g-inch rails, on which the problem of bond- ing was not so diffi- cult as on the smaller sections. {k) Improved Joint Pirates. — Not only do some of the improved joint plates materially in- FlG. 16. — special plates, showing ample provision for bond crease the life of concealed bonds by giving ample clearance for them, but their ability to better support and maintain the joint than the old types of plates is sufficient justification for their use. Among the improved bolted joints the continuous joint seems to be the most popular with the operating companies. Figures submitted in Table 6 show that 19 companies reported the use of this type of joint, whereas the largest nimiber using any other Rail Joints and Bonds 63 type of improved plates is 3. The total number of continuous joints reported is 68 669, which is more than twice the number of all other types of improved joints reported. This type of joint plate when properly installed with bolts hav- ing a high elastic limit grips the rail so firmly that expansion and contraction within the joint is largely eliminated, particularly on city tracks. We quote Company 3 with reference to this point: We think if the bolts in continuous joints are drawn tight there is very seldom any slipping of the joint, due to expansion or contraction, as this joint grips the rail very firmly, so that a well-bolted continuous joint gives nearly the same effect as welding. The type of bolted joint referred to under "Mechanical joints" in Section II of this paper, wherein a shop fit is obtained by ream- ing holes and using machine bolts and in which no expansion and contraction is allowed, has, to otu- knowledge, not been used on open track, although welded joints have been used in a number of installations for this purpose, expansion and contraction being taken care of by expansion joints at regular intervals of about 500 to 1000 feet. If such improved bolted joints were used on open track in connection with expansion joints, a great reduction in the maintenance cost of both bond and joint would be affected, to say nothing of the economy of operation and improved operating con- ditions generally. The ultimate economy of such construction would have to be carefully considered for any given project, but that it would be fully justified on heavy traction lines is firmly believed. If installed according to the best modem practice, bond failures would be reduced to a minimum, being relieved of the con- tinued lengthening and shortening so prevalent ia the ordinary joint. Maintenance would consist of occasionally going over the joints and tightening the bolts. If in time the rail ends began to cup, they could be inexpensively built up by applying new metal with the arc welder or acetylene flame and then ground to a true surface alignment. Such joints with the comparatively slight maintenance here mentioned would undoubtedly have a useful life equal to that of the rail and at the same time provide a continu- ous and permanent return circuit for the electric current. We believe the type of construction here described to be not only practicable but of ultimate economy, and urge its adoption by the operating companies at least on an experimental basis. 14985°— 16 5 64 Technologic Papers of the Bureau of Standards 2. TYPES OF BONDS AND FEATURES OF INSTALLATION (a) Comparison OP Compressed and Pin Terminal Bonds. — Stud-terminal bonds according to our definition on page 12 in- clude both compressed-terminal and pin-terminal bonds, and each of these types comprise ribbon and wire bonds for both concealed and exposed application. The tabulation on page 29 shows that 929 600 compressed- terminal bonds were reported as against 362 800 of the pin-ter- minal type. These figtures, together with a majority of testimony as to preference, indicate that the compressed terminal is easily the favorite among a majority of the operating companies. On the other hand, however, must be considered the fact that the pin-terminal bond has been adopted as standard and is being em- ployed with phenomenal success by a number of the largest oper- ating companies, including the New York Central & Hudson River Railroad Co. and the Pennsylvania Railroad. While it is not pos- sible to say in general that one of these types is better or worse than the other it is hoped that a careful analysis of all information available will aid in reconciling the differences in opinions regard- ing these two types, and establish the fact that each type has characteristics and properties which makes it peculiarly adaptable for certain classes of work or under certain special conditions. One of the arguments put forward in favor of the compressed- terminal bond is as follows: The contact resistance between cop- per and steel decreases as the pressiure increases up to about 30 000 to 40 000 pounds per square inch. As copper reaches its elastic limit and begins to flow at about 20 000 potmds per square inch, the minimum contact resistance is not reached with the pin- terminal bond since the copper is not confined during the driving of the pin, but is free to flow out around the pin, forming a button on the opposite side of the rail as is fllustrated in Fig. 3. With the compressed-terminal bond, it is argued, the copper is confined between the terminals of the compressor, and not beiug able to escape is subjected to a pressure Umited only by the design of the compressor or the diligence of the workmen. This argument, which at first may appear to be tenable, is un- doubtedly fallacious. It is true that very soft and thoroughly Rail Joints and Bonds 65 annealed copper has an elastic Umit of about 20 000 pounds per square inch, but upon undergoing a very small amount of manip- ulation it rises rapidly to from two to three times this value. As the action of the compressor or even the driving of the expanding mandrel produces a distortion in the copper more than sufficient to bring about this change in the elastic limit it is obvious that the pressure required for minimum contact resistance is reached in both the compressed and pin terminal type of bonds. If there is any difference in the contact resistance of these two types it appears to be so slight as to have practically no effect upon the total resistance of a bonded rail joint. The average of 32 tests on each type conducted by the Chicago Board of Super- vising Engineers in 191 1 shows the pin-terminal bond to have a conductivity of 96.65 per cent of that of the hydraulic-compressed bond and 98 per cent of that of the hand-compressed bond. As the double contact resistance of a 4/0, lo-inch, copper bond is only about 20 or 25 per cent of the total resistance of the bonded joint the slight difference in the contact resistance of the two types would affect the total resistance of the joint in the order of a fraction of i per cent, which is so small as to be entirely negligible for practical purposes. The contact resistance of a stud-terminal bond when newly and properly installed is often quite a different thing from the resist- ance of the average bond after being subjected to several months or years of service. That the two may be quite different is evi- denced by the greater part of the testimony recorded in answer to question 18, although several companies beHeve that bonds show Httle if any increase in resistance if the joints are properly maintained. The increase in the resistance of a joint in some instances may be solely the result of the loosening of the joint plates. Tests recently conducted by the Btureau of Standards, the results of which are given on page 1 1 9 of this paper, show that newly bonded and bolted joints have a much lower resist- ance with the plates on than with the plates removed, indicating that tightly bolted plates add very materially to the conductance of a rail joint. Also recent tests of joint resistances on unbonded tracks which have been in service for a number of years show 66 Technologic Papers of the Bureau of Standards that only about 5 per cent of unbonded joints have a resistance less than 1000 feet of rail. While these tests might in some cases account for the apparent increase iu resistance of bonded joints, it is undoubtedly true that a large number of the mechanically applied bonds slowly increase in resistance and may or may not reach a stage, within the life of the joint, where corrosion becomes so serious as to require the replacement of the bond. While contact deterioration has been attributed to the differ- ence in the coefficients of expansion of copper and steel and to other uncontrollable causes, it is imdoubtedly true that by far the most prevalent cause of such deterioration is natural and electrolytic corrosion resulting from the entrance of moisture between the two metals. Considerable evidence is at hand to show that, as a rule, on compressed-terminal bonds moisture finds admission to the bond terminal between the head of the bond and the steel on the bond side of the rail. Engineers of the American Railways Co. state that they have removed hun- dreds of compressed-terminal bonds after being in service for a time and that on nearly every one the corrosion had started on the shoulder of the terminal on the bond side of the rail. Experiments conducted by bond manufacturers have demon- strated that, under the action of a compressor, a bond terminal will begin to expand at the end opposite the head of the bond, and will gradually fill the hole toward the head as the pressure is increased. It is evident, therefore, that such failures as those reported by the American Railways Co. are the result of incom- plete compression and emphasize the necessity of careful atten- tion to this featiure. The life of poorly compressed bonds is possibly lengthened by grinding or otherwise cleaning, af the time of installation, the web of the rail with which the bond terminal comes in contact. Company 10 reports that they have greatly increased the life ot their compressed-terminal bonds by this operation and attrib- ute it to the good contact between the head of the bond and the web of the rail, which they believe delays the entrance of the moisture to the terminal proper. Rail Joints and Bonds 67 A few complaints have been registered against the pin-ter- minal bond on accomit of the steel pin being subject to corrosion when allowed to come in contact with the earth. It is claimed that corrosion of the steel pin takes place and rapidly rusts it out, thereby relieving the compression on the copper terminal. The great advantages of' the pin-terminal bond as claimed by the friends of that tjrpe are, first, that it can be installed with imiform and consistent results by ordinary labor, whi].e the compressed-terminal type requires careful and expert labor for satisfactory results; and, second, it can be installed without interruption to traffic or the danger of a derailment, which is possible when using a compressor across the rail. Regarding the first point there appears to be a division of opinion, some claiming that the compressed-terminal type is more nearly "fool proof" than the pin-terminal bond. It is claimed by advocates of the compressed type that the big New York companies, who are having such phenomenal success with the pin-terminal bond, were forced to the adoption of that type by company rules which forbid the use of a compressor or any other tool which might cause a derailment; and the rigid specifi- cations and extreme refinements which they have adopted in con- nection with the purchase and application of their bonds inclines one to the conclusion that this, rather than the first-mentioned reason, was the determining factor in making their selection. It is significant that the principal advocates of the pin-terminal bond are to be fotmd among the larger operating companies. The Philadelphia Rapid Transit Co. and the Bay State Street Railway Co., both operating extensive systems, may be added to the list of New York companies already mentioned. The observations of J. B. Taylor, engineer of way for the Philadelphia Rapid Transit Co., may throw some light on this point. Mr. Taylor states that in a system of the size of that in Phila- delphia a number of repair jobs are usually in progress at the same time and it would not be practicable to have expert bonding men at every job at the proper time. When the rails are ready the bonds must be applied, and as pin-terminal bonds can be installed quickly and with a fair degree of uniformity by an ordinary trackman, they are foimd to be better suited for this 68 Technologic Papers of the Bureau of Standards class of work than the compressed-terminal bond, which should not be installed by any but an experienced and careful workman. The Bay State Street Railway Co. has a thousand miles of track in and around Boston. They adopted pin-terminal bonds five years ago because of the ease and uniformity with which they can be applied and for their "fool-proof" qualities. All bonds are piirchased under rigid specifications based on their own drawings. Many of them, consequently, are not standard products of the manufacturers. Types and sizes are selected by laying out on the drawing board the rail and joint-plate sections and then prescribing a bond that has plenty of clearance. The extreme care with which the New York Central & Hudson River Railroad Co. installs their pin-terminal bonds has already been referred to. The reported price of 35 cents per bond for labor on installation is an indication of the grade of labor and the care employed. It is said that bonds are installed in only freshly drilled or reamed holes, and that the bond terminals are cleaned and polished before they are expanded. A driving fit must be secured and if a hole is fotmd to be larger 'than the bond terminal it is reamed out and a larger terminal inserted, or if the difference is small a larger expanding pin is used. Finally, the expanding mandrel and pin must be of the correct diameter to insure proper expansion. Too large a pin will tear the metal, while too small a pin will not insure complete expansion. Three companies are manufacturing the standard 16-inch 500 000 cir. mil stranded bond employed by this road, which is a special product, as no other operating companies use the same bond. That the careful and expensive methods of bonding employed by this company are fully justified is indicated by the extremely small percentage of failures recorded on page 36 of this paper. The following set of specifications whiat are required by the Bay State Street Railway Co. are similar to those required by other large companies employing pin-terminal bonds and may prove of interest to bond purchasers: RAIL BOND SPECIFICATIONS. Definition of terms. — The word "company" where occurring in this specification shall mean the purchaser of the material hereinafter referred to, or its duly authorized representative. Rail Joints and Bonds 69 The word "contractor" where occurring in this specification shall mean the party accepting the order to furnish the material hereinafter referred to, or its duly author- ized representative. General description. — ^The materials required under this specification are 4/0 A. W. gauge capacity bonds, for bonding around track joints. The completed bonds and the materials of which they are made shall conform in design and dimensions to the company's standard drawings, hereby made a part of this specification and to the following requirements and tests: Conductor. — ^All bonds shall consist of the required number of annealed copper wires or ribbons, free from splints, flaws, or other defects, and having an aggregate cross sectional area, when measured at right angles to the axes of the individual wires, at least equal to that of 4/0 American wire gauge. Each of the individual wires or ribbons shall have a conductivity of not less than 98^^ per cent of standard annealed copper at 20° C. Where stranded bonds are required the wires shall be concentrically stranded together in spiral layers having at least one complete turn in each j inches of con- ductor. The copper wires shall not vary more than i per cent from the nominal diameter. The copper ribbons shall not vary from the nominal widths and thickness more than the amount shown in the following table : Thickness, Variation, Width, in Variation, in inches in inches inches in inches u. oio-o. 050 o. 001 o. lo-o. 250 o. 003 Terminals. — Where copper terminals are required they shall be in effect a imit with the conductor. This may be accomplished by upsetting the head from a portion of the conductor or by welding drop-forged terminals on the conductor, in which case the tmion between terminals and the cable shall be a clean weld, free from oxide. The terminals shall be of uniform size and shape, free from cracks, bttrrs, fins, slivers, and hard spots, and any machining on terminals shall be followed by careful annealing. The surface of the terminals as called for on the drawing shall be milled smooth or otherwise finished, the resulting surface to be strictly eqiiivalent to that obtained by careful milling. Where steel terminals are required they shall be made of steel of good quality, soft, and carefully shaped to the dimensions specified, and shall be thoroughly tinned inside and out tfefore soldering to the conductor. The soldered joints between the terminals and cable sHall be carefully made with half-and-half solder and shall be free from imperfections of adhesion, excess of solder, or any other defects. Tests — Union between conductor and terminals. — ^All bonds with copper terminals may be tested as follows to determine the character of the union between the head and conductor: The stud of the bond shall be sawed lengthwise into four equal segments, allowing the saw to cut to but not into the conductor: These segments shall then be bent back, tending to separate the welded parts. If a clean, bright fracture is exhibited, with a surface entirely free from dark oxide, the weld shall be considered satisfactory. It is not essential that the lines of the individual wires or ribbons be entirely obliterated. 70 Technologic Papers of the Bureau of Standards Flexibility. — ;The test for flexibility hereinafter described is not made a condition of acceptance, but may be made at the option of the company and accorded due weight in the determination of the relative excellence of the bonds submitted. This test shall be made by holding rigidly one terminal of a bond while the other end is given a longitudinal movement of three-sixteenths of an inch, and a transverse movement of three-sixteenths of an inch, and continuing the movement until the first ribbon or wire breaks. Inspection. — Samples shall be selected at random from each type and kind of bond received for inspection and determination if they comply with the specification; the samples shall consist of two bonds from each loo and at least two bonds if there are less than loo bonds. Rejection. — If lo per cent of the selected samples fails to comply with the require- ments of the specification all bonds represented by these samples may be rejected and returned at the expense of the contractor. Method of shipment. — All bonds shall be so packed for shipment that they will be suitably protected from injiuy, each package being plainly marked with the number, type, and length of bonds, and the number of the company's order upon which ship- ment was made. The argument that it is easier to obtain uniform results with the pin-terminal than with the compressed-terminal bond is largely based on the assumption that it is easier to drive a pin into a bond terminal than to properly adjust and manipulate a com- pressor. This is no doubt true, but it is also a fact that workmen frequently drive the pins in crooked and thereby fail to get a uniform expansion. In the installation of compressed-terminal bonds not only must the compressor be properly adjusted so as to get an even bearing on the bond terminal but the maximum compression must be obtained in order to secure the best results. It is also important to keep the point of the compressor in good condition, and the axis of the screw should be at right angles to the opposite face of the compressor. The difficulty of knowing when complete compres- sion has been obtained has led sorrie of the operating companies to the practice of testing each bond at the time of installation. If it does not come up to the proper sAndard the compressor is appHed again or a new bond installed. One of the manufactming companies is attempting to provide for this insurance automatically by building a compressor which will shear out a button of sheet metal when the proper pressure has been reached. Workmen will then be required to turn in a button for each terminal compressed at the close of each day. Rail Joints and Bonds 71 Granting that attention to these details is obtained only by conscientious and experienced workmen, it is also true that a greater variation in the size of holes is permissible with the compressed- terminal than with the pin-terminal bond. The great care exer- cised in getting holes of exactly the right size and the rigid speci- fications regarding the diameter of pin-terminal bond studs is necessary on account of the small amount of expansion that can be obtained in this type of bond. On the other hand, although not good practice, pressure can be applied with a screw or hydrauHc compressor imtil a comparatively loose bond terminal has been made to fill the hole. Summing up the arguments we are incUned to believe that honors are about even respecting the two types, and we are led to the following conclusions: Excellent results are obtained with the compressed-terminal bonds when they are carefully installed by experienced men. Inexperienced, untrustworthy, or careless workmen should not be employed for their installation. The compressor should be kept in good condition in order that complete and even compression may be obtained. The testing of bonds immediately after instal- lation is also a good practice. Failure to comply with these requirements is Hkely to result in poor contacts, followed by corrosion and rapid deterioration. Results equally as good as those obtained under the best condi- tions with the compressed-terminal bond may be seciu-ed with the pin-terminal type when careful attention is given to the details of installation, particularly to obtaining a driving fit for the bond terminal before driving the pin. This condition can be controlled within narrow limits by specifying only machined-terminal bonds and giving close attention to the grinding of drills. The reaming of all holes with a straight reamer is a good practice and will add greatly to the uniformity of results. Moderate and fairly imiform results can be obtained with the pin-terminal bonds when installed by ordinary inexperienced laborers if they are provided with uni- form bonds and pins as well as drills which have been ground at the shop. This is owing to the fact that under these conditions the personal element has been largely eliminated, and so long as 72 Technologic Papers of the Bureau of Standards the pin is driven home there is a fair assurance that a good and permanent contact exists. Compressed-terminal bonds are often excluded from use on rapid-transit Unes where the compressor over the rail would offer a hazard to the safe passage of trains, also from special work where the sharp angles of the frogs sometimes prevent its use. Pin-terminal bonds are excluded from use on elevated roads and other tracks where wooden or steel guard rails prevent the use of a hammer in driving the pins. The steel pins in pin- terminal bonds are subject to corrosion and should be used with caution where they are likely to be subjected to excessive moisture. The following code of instructions for the installation of pin- terminal bonds is given by Howard H. George in the Electric Railway Journal of September 19, 19 14. It represents the best modem practice and has been incorporated in Prof. Richey's Electric Railway Handbook. All of the 13 rules, with the excep- tion of 10 and II, apply equally well to compressed-terminal bonds. CODE OF INSTRUCTIONS FOR INSTALLING RAIL BONDS I. Every roadmaster and foreman should see that one or more men in each gang are taught the proper way of installing bonds, and should be sure that any bonding done thereafter is performed by these men. u. When renewing rail or joint plates on single track in operation, care should be taken not to open or disconnect both rails at the same time, as this would open the return circuit by which the current returns from the cars to the power house. When it is absolutely necessary to open both rails, a long copper jumper should be installed to connectthe open ends so that the path of the return circuit shall not be interrupted. This applies more particularly to road ends and interurban lines. 3. Whenever any track is opened up and any ground wires for electric lights, lightning arresters, or other electrical apparatus which should be connected to the rail are found disconnected, they should be reported at once to the bond inspector, or distribution department, so that they may be repaired before the track is closed up. This is very important and should receive careful attention. 4. No bond holes should be drilled until just l^fore the bonds are ready to be put in. There are, of course, times when it is desirous to have the holes drilled before the rail is placed on the ties. When this occurs, it is necessary to place a tight-fitting plug in the hole as soon as it is drilled to avoid any possible introduction of moisttire. To drill a hole a day or two before and not protect it from moisture means a film of rust in the hole, which will greatly increase the resistance of the joint. S- Old bonds should never be used again, because they become battered up in driving them out. Then, when they are put in again they will not make good con- tact with the rail, which means a poor bond. Where a bond is removed from the rail it is not advisable to use the same hole in putting in a new bond, unless some pre- Rail Joints and Bonds 73 cautionary methods are used. The proper way is to drill a new hole, but as this is not allowable in some types of rails, ream out the old hole and use a bond with a special large size terminal. 6. Great care should be taken with the drills used in making bond holes. If an improperly ground drill is used the hole will be irregular and oval shaped, thus giving a poor contact between the terminal and the rail. All dull and broken drills should be carefully boxed, labeled, and sent to the shop to be reground, where the company has installed a special machine for the purpose to do the work perfectly and at much less expense than could possibly be done by hand. 7. In drilling bond holes never use oil to lubricate the drills. It is better not to use anything, but where it is absolutely necessary to use a lubricant, nothing more than a soda solution, should be employed. 8. Holes, after being drilled, should be carefully cleaned of any chips and wiped dry of any solution that may have been used to lubricate the drills. The holes must have a smooth and dry siuface, so that the bond terminal will make a good contact all around. 9. With a proper size hole, the bond terminal will make a very snug fit, not small enough to have to be driven with a heavy maul nor large enough to be put in easily with the hands. It should require a couple of taps with a hammer weighing about 3 pounds. With a heavy hammer or spike maul the head of the bond terminal is very likely to be battered and the taper punch struck on the slant, causing it to split and bend the terminal. 10. After the bond terminals are in position, always drive the long steel taper punch entirely through the terminal, taking care to strike the punch squarely on the head. The small end of this punch should be dipped in some kind of heavy grease, such as track grease, just before it is driven through each terminal. The grease will lubricate the sides of the punch, thereby expanding the terminals and not drawing the copper with the punch. 11. Drive into each of the expanded terminals one of the short drift pins, thus expanding the copper a little more. This pin should be driven in until it is just flush with the head of the bond terminal. 12. The bond should then be shaped by straightening out the bond conductors, and forming them so that they will not be cut by either the track bolts or the splice bars. If it is a 36-uich bond, it should be so shaped that it will in no way interfere with the removal of the splice bars. 13. The bond, and particularly the bond terminals on both sides of the rail, are to be painted with some good weatherproof paint, care being taken to see that the paint fills the space back of the terminal heads. (6) Stranded v. Ribbon Bonds. — Referring to the tabulation under question 3, on page 29, we find that a total of 579 200 stranded concealed bonds were reported, as against 214 200 ribbon bonds. Considering that the section of the ribbon bonds is much better proportioned for the space usually provided for concealed bonds, this apparent preference for the stranded type may seem surprising. Manufacturers who have conducted laboratory life tests on the two types differ as to their relative abilities to with- 74 Technologic Papers of the Bureau of Standards stand vibrations. The American Steel & Wire Co. states in their general catalogue that the stranded bond will remain intact longer than the ribbon bond, while the Electric Railway Improvement Co. affirms that many vibration tests on short head bonds have demonstrated that the ribbon bond will outlast the wire type. This seems to be another case where theories and laboratory experiments offer little evidence as to what will happen under the peculiar exigencies of service. The fact is that the majority, though not all, of the operating companies are using and prefer the stranded bond for concealed work and say that it is giving better satisfaction than the ribbon type and is not so sensitive. to vibrations and the corrosive action of the joint plates. The secret of the matter no doubt Hes in the fact that the con- ductors of the ribbon bond, not being twisted or woimd together, are easily separated and isolated. The space provided for con- cealed bonds is wedge shaped, as seen in Fig. 15, and the movement of the plates tend to work the ribbons and strands upward under the fishing surface of the rail head. This is a common complaint, and has been mentioned by a number of engineers. The wires of the stranded bond, being twisted together, are not so likely to become separated and broken by this action. The effect of loose joints on head bonds installed in macadam or earth streets is similar to that on concealed ribbon bonds described above. Dirt works in between the ribbons, which are gradually separated and brought to the surface by the continual motion of the joint. This trouble has been recognized, and is now being largely overcome by the application of a clip aroimd the body of the bond, which. prevents the separation of the strands. This clip is illustrated in Fig. 17. (c) Use op Soi^der and Ali^oys with Mechanicai.ly Ap- plied Bonds. — ^The large number of bdid failures in past years resulting from corrosion of mechanically applied terminals have led a number of companies to adopt the use of solder or a plastic mercury alloy as a third or intermediate metal between the copper and steel. In some cases compressed-terminal and twin-terminal bonds have been installed with solder, in other cases the terminals have been tinned either at the factory or on the gromid before installation, while in still other installations both the steel of the Rail Joints and Bonds 75 rail and the bond terminal have been amalgamated. While these various practices have found rather wide application and have many adherents, the manufacturers of bonds are a unit in their belief that the copper to steel contact can not be improved upon. They argue that the introduction of a third metal, having a spe- cifically high resistance, between the copper and steel will not only add to the contact resistance but might also be the source of a chemical action which will hasten rather than delay corrosion. To the argument that a third and soft metal is needed to take up the difference in expansion between copper and steel, they reply that the process of expanding or compressing a copper ter- minal so hardens it as to give it sufficient elasticity to take up this slight difference in expansion itself. In the absence of experi- mental data to substantiate these theories we are again forced to base our conclusions upon the best modem. practice resulting from years of experience and upon the opinions of prominent engi- neers. We will consider the practices of soldering, tinning, and amalgamating in the order in which they are named. The several methods of soldering compressed-terminal bonds which have been used are well described in the following extract from a letter received from the Ohio Brass Co., which developed the thermobonding process, in answer to an inquiry requesting information on the subject: The compressed-terminal type of rail bonds has had the most general use in the past, due principally to the fact that it can be installed in a satisfactory mamier with the comparatively low grade of labor that must be relied upon for work of this kind. One of the chief objections to the compressed-terminal type of rail bond has been the rather small contact area between the terminal of the bond and the rail. In case the bond is not properly compressed, the contact surface would corrode, further reducing the efficiency of the bond. In order to overcome this difficulty many railroads make a practice of soldering the head of the bond to the rail after it has been compressed. With this method it is customary to tin the bond terminals before they are compressed and after the compression to heat them with an ordinary blow torch, applying solder, so as to form a perfect contact between the head of the bonds and the rail, thus supple- menting the contact secured by the compression and excluding the moisture from the plug portion of the bonds, at the same time giving an electrical contact which is not liable to deteriorate. The soldering process, however, adds considerable to the expense of the installation. The 0-B thermobonding process was developed with a view of securing the advan- tageous results of soldering compressed-terminal bonds, at the same time furnishing a simple and cheap method of making this application. The charge of thermite is set ofE on the opposite side of the rail from the bond head and generates sufficient heat so 76 Technologic Papers of the Bureau of Standards that the bond head can be soldered to the web of the rail. Many of the largest roads in the country using compressed-terminal bonds with solder changed over to the thermo process as soon as it was put on the market, and a great many bonds have been installed in that manner. However, it is an added refinement which is not considered essential, and as it adds considerable to the expense of the installation it has not had a universal use. The process requires some care in the installation, and for this reason, where a low grade of labor is used, further difficulties are encountered. Where a railway wishes to secure a very high grade of bonding and is willing to take the pains to use the proper care in installing the bonds by the thermo process, it is a very excellent method and is quite successful. The thermobonding process here described has fallen into dis- repute, and disuse so that at the present time it is employed very- little, if at all. This has been the result, not only of the causes mentioned in the above quotation, but because of the injury done to the bond terminal and the web of the rail by the excessive heat generated by the thermite. We quote Company 1 6, on whose tracks a few bonds were soldered for demonstration purposes : After three years the bonds were removed for inspection, but we are sorry to say that they were in bad condition. The terminals were black and not soldered to the rail at all in the hole, and the excessive heat from the thermite had burnt the rail, which made it brittle and caused the steel to rust and depreciate. Conditions similar to these were also reported by A. P. Way, electrical engineer for the American Railways Co. Company 15 says regarding the thermobonding process : About four years ago a thermosoldering process developed by the Ohio Brass Co. was made a part of the standard process of installing a bond. It is supposed to make a complete union between the copper bond and the rail. In most cases it appears to do so, but there have been cases where such bonds were removed several months after installation and the contact between bond and rail has been black instead of bright, thus showing poor contact. This may have been due to poor workmanship in the installation, particularly since bonds installed by this process test good after installation. A test made by the Chattanooga Railway & Light Co. in November, 1910, shows the resistance of the thermo process bond contact to be approximately one-half the resist- ance of the compressed type without soldering. ^ In addition to Companies 14 and 15, which have employed the thermobonding process, may be mentioned Companies 7, 20, and 26, which solder their stud and twin terminal bonds by the aid of a blow torch. The following letter from Company 20, describing the method as practiced in Tacoma, Wash., will be fotmd of interest: We are sending you, parcel post, one of our standard 250 M c. m. twin-terminal bonds. The American Steel & Wire Co. have made a special die for the bonds they Rail Joints and Bonds 77 . furnish us. You will notice that the face of the terminal which comes in contact with the ball of the rail is a flat smooth surface. In applying these we are very careful to see that the ball of the rail is chipped smooth and deep enough so that all rust spots are cut out. Although the terminals are tinned, we redip them immediately before they are applied. We also are careful to see that the holes in the ball of the rail and the chipped surface is perfectly clean and well turned. The bond is driven with the rail hot and the solder fluid. After the bond is in place, solder is applied to the upper edge of the bond with an iron which makes a reinforcing fillet. Before adopting this type of bond as a standard, we applied a number of them without solder. Resistance measurements were taken immediately after the bond was applied and at intervals thereafter. We noticed in a number of cases that the resistance of the bonds increased, in some cases slightly and in some cases materially. Since we have been using solder in the application of this bond, we have made a large number of resistance measurements and have not noticed any change in the resist- ance of the bond. The bond here described is similar to the Form C twin-terminal bond, but having a broader face and a square shoulder to hold the fillet of solder. There seems to be a fairly general agreement that solder improves the contact of mechanically appUed bonds, but that when applied by the thermo process the chance of burning both the bond ter- minal and the rail are so great as to offset the benefits that might accrue therefrom. In view of the excellent results which are being obtained with the compressed-terminal bond under the present improved methods of manufacture and installation, the additional expense of soldering this type appears to be hardly justifiable. The soldering process requires skilled labor, addi- tional time, and extra material. If half this time and expense be devoted to careful and improved methods of drilling holes and compressing the bond terminals, equally good results could be obtained. The use of solder in connection with twin-terminal bonds will be further discussed when considering that type. The process of tinning stud-terminal bonds before installing them has been employed by a number of companies, and appar- ently with general success. One of the strongest advocates of this practice is found in E. Hey den, superintendent of overhead construction for the Indianapolis Traction & Terminal Co., who is very positive! in his belief regarding its value. Mr. Heyden states that he has used tinned- terminal bonds for years, and that in removing bonds from old rails he has invariably observed that corrosion has been much worse on bonds which had not been 78 Technologic Papers of the Bureau of Standards dipped. He goes further and says that with a bond tester he is able to distinguish between dipped and undipped bonds when testing the resistance of rail joints. Tinned bonds are also being used by the Empire United Rail- ways, of Syracuse, where it is stated they show less corrosion than undipped bonds. The process of amalgamating bond terminals before compress- ing them is now finding favor with. a number of operating com- panies, among which is Company 25, from whose report the fol- lowing quotation is taken: After using many types of bonds and rail joints, the writer has standardized on the use of compression bonds in connection with which is used the so-called H. P. Brown pastic and solid alloys. These alloys have proved very valuable, in that they take care of any grooves which may be cut in the bond hole when drilling the rail for a bond, and also, being live materials, take care of the difference in coefficients of expan- sion as between copper and steel at the connection of the bond to the rail. These alloys also form a protective coating over the copper and steel, preventing corrosion near the point of contact. These alloys have also been used by the American Railways Co., which believes them to be valuable in excluding moisture from the bond terminal. These alloys are useful only where they are confined, as they soon corrode and lose their effectiveness when exposed to the atmosphere. In the New York power stations, where they were used on copper switches to reduce the contact resistance, they were effective for about three months, after which time the switches showed a higher resistance than before the application of the alloys. Although the practice of tinning and amalgamating stud- terminal bonds has not been very extensively employed and com- paratively Httle information regarding it is available, it appears that in some installations they have«proved very valuable. Both processes are quite inexpensive, and on installations where cor- rosion of terminals has been a chronic trouble they can, no doubt, be used to advantage. The utility of many materials and prac- tices of this nature depends largely upon the personal element of the workmen involved. One man may learn how to apply compressed terminal bonds and obtain good and uniform results by his indi- vidual methods. The same man may utterly fail to get results Rail Joints and Bonds 79 with pin-terminal bonds or with soldered or amalgamated com- pressed-terminal bonds. Splendid results obtained with the use of any type of bond or material are usually the result of the indi- vidual efforts of some person who has mastered that particular problem. (cQ Mechanically Applied Head Bonds. — ^The twin-terminal bond and tubular-terminal, or 0-B, type J bond, shown in Figs. 7 and 8, are included under this heading and are so similar in con- struction and with reference to their features of installation that they may well be considered together. These types were developed as the result of a demand for a bond that could be installed without removing the joint plates and without undue interruption to trafl&c. Experience had demon- strated that long bonds which spanned the joint plates were sub- ject to theft, and the types here mentioned were made as short as possible in order to reduce this loss as well as for the sake of economy. The short length has naturally resulted in considerable breakage from vibration, particularly on loose joints, and this is perhaps the most prevalent cause of failure. While these types are best adapted to open track where they are not subjected to vehicle traffic they have been used to some extent in earth and macadam streets. The cost of renewing a concealed bond in city streets is shown by figures in Section III to range from $1 to $3, depending upon the nature of the pavement. It is argued that the cost of installing a short head bond is so small in comparison to this that a company is justified in its use, although the depreciation in city streets may be high. Very Httle testimony has been secured regarding the use of the tubular-terminal bond, as this type has been on the market but a short time. The extent to which it is being adopted on new roads, however, is not only evidence of the general demand for a short head bond but an indication of faith in this particular type. The following information is pertinent regarding its use. In answer to an inquiry on the subject the Northern Ohio Trac- tion & Light Co. says : Replying to your letter of the 2d instant, I wish to advise you that the O-B type J rail bond which we have used has given us very satisfactory service. 14985°— 16 6 8o Technologic Papers of the Bureau of Standards The Detroit Railway has the following comment to make : Replying to yoiirs of the 2d instant, relative to our experience with the O-B type J rail bonds, I beg to state that we have used a great many of these bonds on suburban work and they seem to be working out very well. I do not recommend them for city street work or for places where vehicles can in any way strike them, as they, like all other bonds of this character, are liable to shear off from the rail. George F. Silvia, electrical superintendent for the Albany South- em Railroad, states that a systematic rebonding of all the tracks on that road will soon be commenced and that the O-B type J bond will be used exclusively. He believes that where these bonds fail others should be installed by drilUng new holes in the head of the rails, as it would not be practicable to attempt to drill out the old terminals. Recent technical press notices state that on the new Grand Rapids-Kalamazoo line, 50 miles in length, and in the construction of the Fort Wayne & Northwestern Railway the O-B type J bonds are being used. The testimony relative to twin-terminal bonds is more abundant. Company 11 employs 60 000 and Company 42, 33 000 of the total 113 700 bonds of this type reported. On both roads its use is con- fined to open track. As these companies are among the largest users of twin-terminal bonds in the country their experience should be significant. Company 1 1 says in answer to question 6 : Twin terminal and compressed terminal bonds usually last as long as the track; the percentage of failtu-e is very small. Company 42 reports that in the seven years of operation 7357 bonds on an original installation of 33 000 have been replaced. Of these 800 had been stolen. This is equivalent to an annual failure of approximately 3 per cent. Good results have also been secured by the Cincinnati Traction Co., where a suburban line of 25 mil^ in length has been bonded with twin-terminal bonds. Practically no failures have been experienced and the bond is said to be easily installed by ordinary unskilled labor. In the May, 1915. issue of Electric Traction is a description of the new Waterloo-Cedar Rapids line in Iowa; 4/0 twin-terminal bonds are employed and were installed at the rate of 100 bonds per day by four men with electric drills. Rail Joints and Bonds 8i In contrast to the complimentary experience of these companies is to be found the opinions of a number of engineers who for one reason or another have not been pleased with this bond. The Bay State Street Railway Co. reports that they have used some twin- terminal bonds but found them short lived on accoimt of breaking at the terminals or loosening of the studs. Company 24 reports that of a trial installation in 1910 of 1000 twin-terminal bonds 75 per cent were stolen in 1913-14. With a number of these the studs, as well as the body of the bond, were removed showing that the contact was poor. The Virginia Railway & Power Co. installed a few of these bonds but was not entirely pleased with the results obtained. Several engineers have been consulted who object to drilling into the heads of rails, saying that it is likely to weaken them and increase the chance for cupping. This argument, however, does not appear to be founded on definite facts. That the contact resistance of twin-terminal bonds, as ordi- narily installed, increases gradually with time seems to be a well- established fact. Some of the answers to question 18 giving information on this point are here repeated. Company 7 says: A new twin terminal bond will equal about 3 feet of rail, when the old ones will average about ^% or s feet. Company ii. — We have found no difference in resistance between old and new bonding, so long as the bonds remain unbroken and their terminal contacts are unimpaired. This statement is made with reference to twin-terminal and compressed-terminal bonds. Company 26. — ^Tests of compressed-terminal bonds and twin-terminal bonds are practically the same, 4 to 4^ new, 5 to 6 when old. The letter from Company 20, quoted above, also states that the resistance of unsoldered twin-terminal bonds increases after installation, in some cases slightly and in some cases materially. The Bureau of Standards recently tested 40 joints on the Wash- ington, Baltimore & Annapolis Railroad near Washington. These joints were bonded with 4/0 twin-terminal bonds which had been in service about seven years on 80-pound rails. The test was made on 3 feet of joint, and the highest and lowest resist- 82 Technologic Papers of the Bureau of Standards ances were 9.9 feet and 6.0 feet of adjacent rail, respectively, the average being 6.90 feet, or 0.0000828 ohm. A test made by the Bureau of Standards on a single-rail joint, newly bonded by the American Steel & Wire Co., with one 4/0 twin-terminal bond, showed a 3-foot joint with plates bolted in place to have a resistance of 0.0000349 ohm or 2.91 feet of 80-pound rail and with plates removed to have a resistance of 0.0000745 ohm, which is equivalent to 6.2 feet of the adjacent 80-pound rail. While this latter figure is not materially less than the resistance of the average old joint it is much lower than that of individual joints. The joint plates undoubtedly add somewhat to the con- ductance of joints even on old installations but just how much it is difficult to say. The tests conducted by the Bureau of Stand- ards on unbonded joints which have been referred to before indi- cate that on old joints the function of the plates as far as aiding the return circuit is concerned is practically nil. It is altogether possible that observed changes in the resistance of bonded joints have frequently been attributed to deterioration in contacts when as a matter of fact they have been largely the result of loosen- ing and rusting of the joint plates. Considering all of the information at hand it appears to be more than probable that twin-terminal bonds as well as other mechanically appUed bonds gradually increase in resistance with time. This increase in resistance with the twin-terminal type, though small in some cases, becomes quite appreciable in others, and on the average remains within the limit of good practice for a period of years, on joints which have been carefully installed. That the use of solder in connection with these bonds will fore- stall this contact depreciation is undoubtedly true. Its adop- tion, however, should depend upon local conditions and the per- sonnel of the force of workmen. • Summing up the features of the mechanically appHed head bond we find the following to be applicable to both types here discussed. These bonds are short and therefore comparatively inexpen- sive. They can be rapidly installed with very little interruption to traffic, the total cost of installation, including bond, being about 50 cents each on new work. When used on city streets they can Rail Joints and Bonds 83 be installed without removing joint plates, but on this type of construction they are subjected to vehicle traffic, which is likely to shear them off of the rail. On open track they are subject to theft, but this loss is much smaller than with longer bonds. It can be reduced by painting with black paint, thus rendering the bonds less conspicuous. In some cases they have been protected by iron plates bolted to the joint. Owing to the shortness of the bond, failures frequently occur from breaking of the strands, par- ticularly on poorly maintained joints. The contact between cop- per and steel slowly, though as a rule not seriously, depreciates. This may be prevented by soldering and to some extent by tinning the terminals. (e) EI/Ectric-WeIvD Bonds. — ^The practically tmiversal demand for something better than a soldered contact and a substitute for the purely mechanical contact has been responsible for the wide adoption of the electric-weld bond within the past few years. The 720 000 of these bonds reported by the operating companies is an indication of the extensive use which it has found during the comparatively short period of its manufacture. Although it has been used for the most part as a head bond it is now coming into use more and more for concealed application to the web of the rail. There seems to be practically no question regarding the per- manency of the contact that these bonds make with the rail, but some criticism has been directed against some of their other features, particularly to the breaking of the ribbons and to the inconvenience of using the bonding car on tracks over which traffic must be maintained. The question has also been raised as to what effect if any the welding heat has on the steel of the rail. The following quotations from written reports and conversations, it is hoped, will throw some light on these questions. The New York State Railways, of Syracuse, are using large numbers of electric-weld bonds where they are believed to be the best bond available. The engineers state that they can be installed in paved streets by removing a couple of bricks and the expense is not over 60 cents per bond, while the replacement of a concealed bond on similar construction would cost about $3. When installed in macadam streets a wire is twisted about the iniddle of the bond to prevent the ribbons from separating and 84 Technologic Papers of the Bureau of Standards working to the surface. The need of this precaution has been recognized by the manufacturers, who now provide bonds with a clip as shown in Fig. 17. The company has been using the EA type and has experienced> a rather high percentage of failures from breaking of the ribbons. Recently, however, the ET type has been adopted from which much better results are expected. These two types are shown in Figs. 4 and 5 and have been pre- viously discussed. The New York Railways, of Rochester, are using practically nothing but electric-weld bonds. On new work where there is heavy traffic a concealed bond is welded to the web of the rail and an EA and an EB type to the head, making three bonds per joint. Very little trouble from traffic is experienced in paved streets, but in macadam and earth streets a number of bonds have been broken by vehicles. This company has also recently substituted the ET for the EA type. The Hudson & Manhattan Railroad Co. is using 600 000 cir. mils electric-weld bonds and finds them satisfactory for new work. They are not so satisfactory for maintenance as the bonding car can not be derailed in the tunnels, and the expense of operating it at night for small repair jobs is excessive. This company claims that if the carbon electrodes are kept well back on the bond terminal and not allowed to fuse the ribbons near the bend in the bond that good results may be obtained with the EA type. Company 14. — After a great deal of experience here and elsewhere with various types of bonds, we have come to the conclusion that an electric-weld bond of con- siderable length to give the bond the proper flexibility is the only type of bond to use. The experience of Company 13, which has been quoted under answers to question 6, is similar to that of other companies ui that the ET bond has been substituted for the EA type and better results are expected from it. Unfortimately, this new type has not been in service a great while and the companies are not prepared to make definite statements regarding it. The fact, however, that no complaints have been heard concerning it is good evidence that it is an improvement upon the EA type and will show a much smaller percentage of failures. Rail Joints and Bonds 85 Regarding injury to the rail by heat there seems to be very little definite information. A number of engineers have ex- pressed a question or fear regarding this point, but with possibly one or two exceptions no company has definitely reported any broken rails from this cause. The Cleveland Railway Co. states that several rails have cracked where bonds have been copper welded to the web of the rail. The Los Angeles Railway, which has over 300 000 electric-weld bonds, writes the following letter in reply to an inquiry on this question : In reply to your letter of the 3d instant regarding broken tmIs as a result of heating the web in applying bonds, wish to advise that in the several thousand brazed bonds we have installed under the plates or concealed on the web we have never had a broken rail caused by heating the web. It is reported that some fractures have occurred in rails through holes which had been punched in the web, but that such failures are easily prevented by reaming out the holes, thus relieving the strain around them. In the absence of more definite complaint on this score it is safe to say that the injury to rails resulting from the heat generated in welding rail bonds is so small as to be negligible and can be practically disregarded in the selection of a type of bond. The matter of interruption to traffic is something that will depend upon local conditions and will have to be met by each company in a manner depending upon a variety of circumstances. A number of companies operate their bonding car at night on tracks from which it is difficult to divert the day traffic. Upon suburban tracks, for maintenance work, it is usually possible to sidetrack the bonding car, or if not it may be derailed to accommo- date infrequent traffic. The following is a summary of the properties and features of the electric- weld bond: The bond is made for either head or concealed application. Either type can be installed on new work for from 50 cents to 60 cents. The head bond is short and has experienced a rather high percentage of failures from the breaking of the ribbons, as well as from ignorance and carelessness in its application. Mod- em improvements are materially reducing these failures. 86 Technologic Papers of the Bureau of Standards The bond makes a very low-resistance contact with the rail, which does not depreciate with time. The shortness of the bond and the strength of the contact has made the theft of this type, on interurban lines, far less than that of other types. The bond is used successfully in paved and other types of city streets, where it can be cheaply installed. Being subjected to vehicle traffic, however, occasional failiu-es must be expected. Where used in earth or macadam streets a clip should be employed to prevent the ribbons from working to the street surface. The installation of this bond is accomplished with the aid of a bonding car, the first cost of which is not justified on small prop- erties. Maintenance bonding can not be accomplished without inter- ruption of traffic or considerable inconvenience in derailing the car or operating it at night. Some fear has been expressed regarding the heating of the rail webs, but the failures from this cause have been so infrequent that no great importance shotild be attached to them. The following account of the apparatus and methods used in connection with the electric-weld and the copper-weld rail bonds was furnished by the Electric Railway Improvement Co. Some of the apparatus referred to is shown in Figs. 6 and 6a. ELECTRIC-WELD RAH, BONDS On direct-current lines electric- weld rail bonds are installed with a small car meas- uring 6 feet 10 inches in length and about 5 feet 10 inches in width. The frame of the car is of structural steel covered with an oak floor and carried on four 20-inch wheels. The electrical apparatus consists of a rotary converter and transformer with the nec- essary switches, circuit breakers, controller, resistances, etc., for its safe and con- venient operation. The rotary converter is provided with a clutch and is used as a motor for the propul- sion of the car along the track. The bonding clamps for electric welding are located at both sides at one end of the car over the rails and have adjusting screws with hand wheels for bringing the same into position for service. To avoid interference with traffic , a screw jack with bevel-gears termination in cranks at each side of the car, is fixed under the center of the car frame. By means of this jack the car can be raised for the ptupose of turning and rolling from the track to avoid interference with traffic. Depending on conditions, the car can be removed from the track in from one to one and a half minutes and may be replaced on the track in a similar length of time. Rail Joints and Bonds 87 The entire car is covered with a canopy top which carries the trolley pole. On alternating-current lines the car is not necessary, and the AC voltage is carried directly from the trolley to a portable transformer. The welding clamp is attached to the transformer, which is provided with wheels for rolling along the track. This apparatus may be lifted from the track in a few seconds. On high-tension lines the trolley voltage would pass through a step-down trans- former before entering the portable. For electric welding, a current of from 25 to 50 amperes is drawn from the trolley; this varies, depending on the trolley voltage and the size of bond to be attached. For welding a 4/0 rail bond to the rail, an alternating current of about 2500 amperes at 5 volts is employed, which is obtained on a direct-current line by converting and trans- forming about 25 amperes at 550 volts taken from the trolley. To make a weld, the current is applied for a period of from 45 seconds to 2 minutes, depending on condi- tions. An average of 100 4/0 bonds per 10 hours may be installed with the car operated by a bonder and two helpers. For best results the bonder should be a man of average intelligence, while the two helpers may be laborers. The welding apparatus is not sold by the manufacturer, but is put out under a lease. The clauses of most importance in the lease are those stipulating that during the life of the patents all rail bonds installed with the apparatus shall be purchased from the manufacturer at prices given in schedules attached to the lease, that the prices for bonds as given in the schedules are guaranteed by the manufacturer and the only change in the prices is due to the fluctuation of the market price of lake ingot copper in the bonds, that the manufacturer will furnish an expert to instruct the railway company's men in the proper operation of the apparatus, and at the expiration of the patents, under which the apparatus is leased, the manufacturer will transfer title in the apparatus to the lessee. COPPER-WELD RAIL BONDS The bonding cars as put out by the manufacturer carry a melting furnace suspended from the rear of the car for copper welding. This type of welding is especially adapted to the installation of large conductors around special work, and for attaching feeder cables, etc., to the rails. Bonds and cables of any capacity may be attached by this method. It is also used for joining third rails both electrically and mechanically together. Copper welding is effected by pouring molten copper. A mold of suitable refractory material is employed, the size of the same depending on the section of the conductor and the size of the terminal or contact area desired. The end of the conductor lies in the terminal mold. A short channel connects the terminal mold proper with another chamber or reservoir. The rail having been properly cleaned at the point of weld, the mold with the bond wires is clamped in position. The molten copper, on being poured into the mold, impinges on the ends of the bond wires and the steel at the point of weld, and flows on into the reservoir, which finally becomes filled; continuing to pour the molten copper, it backs up into and fills the terminal mold. The excess of copper poured over that required to form the bond terminal proper has the effect of raising the temperature of the steel within the area of the bond ter- minal, to a proper welding; heat; the steel then readily unites with the molten copper present. 88 Technologic Papers of the Bureau of Standards The mold is then removed and the block of copper formed by the reservoir is taken ofi by cutting with a chisel the small section of copper which connects it with the bond terminal. Copper welding may be used to electrically and mechanically join third rails. The copper-welding outfit is also ftumished independent of the bonding car. This particular apparatus is operated with kerosene oil, the crucible containing the copper being placed in a furnace similar to the one used in the coke outfits. The copper-weld ftunace car is equipped with from three to five kerosene furnaces and is designed for use on large installations. The copper- welding apparatus is put out imder a lease similar to that used in the case of the electric-weld cars. This method of bonding, while being adapted for installing large cables, etc., is especially suited for bonding steam-road electrifications and new electric lines where the electric power is not available at the time of installation. For this type of work it is not necessary to have any of the apparatus on the tracks while operating. In fact, the single kerosene-furnace outfit may be carried along by two men, and need never occupy the track. A modification of the Electric Railway Improvement Co.'s bond- ing car has been devised by the Cleveland Railway Co., and em- ployed by them with considerable success, particularly for their special work bonding. In this process, which is described in the Electric Railway Journal of August 7, 19 15, silver solder is used for a brazing metal instead of brass, and the union of the bond with the steel is therefore affected at a much lower temperature than is necessary with the standard equipment. It is claimed that the lower temperature and a different arrangement of elec- trodes enable the bond to be appKed with a much smaller current than is used by the regular bonding car. This smaller current is obtained by a small rotary converter which can be motmted on a motor truck and connected to a step-down transformer by flexible conductors. The transformer is carried about from joint to joint over an entire intersection and with no interruption to trafhc. It is claimed in Cleveland that this modified equipment and method has made possible the landing of special work on a daylight schedule and with no broken rails or interruption of traffic. ( / ) Oxy-Acetyi,EnB-Wei.dEd Bonds. — This type of bonding is accompUshed by welding bonds with forged or cast terminals to the rail, usually the head, and employing pure or fluxed copper to build up the terminal of the bond along the rail head. So far, it has not found a very wide application, although it has been used in Minneapolis and St. Paul for a number of years with Bureau of Standard; Technoloiric Paper No. 62 I'lG. iS. — Apl'tUiilus for applying I'OiitL- icilh tJic oxy- acii yloic Jlai/ic |rrk.J£ii^ I'iG. iq. — Appaialus for a[^plyiiig joint plates liith till clccliic (lit Rail Joints and Bonds 89 marked success. It possesses practically all of the advantages of the electric-weld bond and is free from the objection of requiring an expensive equipment and of interfering with traffic. Although it does not make quite as strong a contact with the rail as does the electric-weld bond, the contact is permanent and does not deteriorate with time. No injuries to rails have been reported from the use of the flame which apparently does not produce a higher temperatiu'e in the rail than is generated by the electric weld. The Minneapolis Street Railway Co. has the following to say with respect to their practice of bonding : The only type of bonds used during the past three or four years is a 250 000 cir. mils, U shaped, T head, bond welded on the side of the head of the rail, and in special cases on the side of the flange of the rail or on the base of the rail, using acetylene torch for welding. We use this type of bond on all types of construction from the light rail in earth streets to 100-pound guard rail on special work in paved streets, and on heavy T rail construction laid on concrete base with block, asphalt, or stone paving. We have at present between 14000 and 15000 such welded bonds in service. Unskilled labor is used for bonding work; that is, the laborers are instructed in the proper handling of the tools and are then competent to do the work. It is found unnecessary to do any cleaning of the steel before welding bonds. For acetylene welding we use compressed acetylene in acetone tanks and compressed oxygen in tanks, with torch specially developed for this class of work. Pure copper is used for welding and no flux is required. Complete cost of installing welded bonds of 250 000 cir. mils capacity in large numbers is between 50 and 60 cents per. bond including cost of tools and machinery. The failure of this method of bonding to have found more extensive use is apparently not the result of any defects or dis- advantages connected with the process, but is more than Hkely the result of other causes. The recent concerted action of the manufacturers of both bonds and acetylene in providing and advertising proper bonds and material for this method of bonding will no doubt act as a great stimulus to its further adoption. The following statements regarding this method of bonding rail joints have been abstracted from information submitted by the Ohio Brass Co. The apparatus referred to is shown in Fig. i8. OXY-ACETYLENE-WELDBD BONDS For applying rail bonds the equipment consists of the necessary tanks of com- pressed oxygen and dissolved acetylene, which may be ptirchased by the railway companies direct from the manufacturers, who have warehouses and factories quite generally distributed over the country, thus insuring prompt and convenient service. 90 Technologic Papers of the Bureau of Standards A pressure regulator and set of gauges are provided for both the oxygen and acety- lene tanks. These are changed from tank to tank as they become empty, the empty tanks being returned to the manufacttirers of the gas. A hose extends from each set of pressure regulators and is connected to a blowpipe or torch by means of which the gases are mixed and adjusted to give the proper condition of the flame. A grinder for cleaning the rails will also be required and may be either of the elec- trical or hand operated type. A pair of colored goggles to protect the eyes of the operator will be found advisable for constant work, although the rays of light from the oxy-acetylene flame do not affect the eyes and skin as do the rays from the electric arc. A small truck provided with handles will be found convenient for conveying the tanks of gas in service and can be purchased from the manufacturers or built from blue prints furnished by them. Clamps for holding the bond to the rail while welding on one terminal will be sup- plied by the manufacturers, as will also the necessary flux wire. The latter is a metal especially prepared for the purpose of attaching the bond to the rail and for building up the head of the bond. It is three-sixteenths of an inch in diameter and is fur- nished in coils of about Jo pounds, which the customer should cut into suitable lengths. For the proper application of bonds the work of only three or four men is required; a working foreman who watches and assists the blowpipe operator; blowpipe operator; and one or two grinders, the number depending on whether an electric or hand grinder is used. The grinders have time for other necessary duties as well. The bonds require on an average about 3 cubic feet, at atmospheric pressure, each of oxygen and acetylene, and the actual time required to apply a bond is from foin- to five minutes. {g) Bonding op Manganese and Other Special "Work. — The recent use of manganese steel for special work which is too hard to drill has led to some difficulties in bonding. On this point Com- pany 3, in speaking of electric-weld bonds, says: This method of bonding manganese special work and steam-raihoad crossings has been the only one that we have had any success with so far, on account of not being able to drill the manganese steel for compressed type. Some of the steel companies have undertaken to insert a soft-steel plug in the rail which can be reamed out to re- ceive the bond terminal, but we find that the contact between the plug and steel is in- sufiicient to carry current for any time. Other companies report no such trouble from inserts in manga- nese steel, and the failures in this particular instance may have been due to the fact that the plugs were inserted in the rails by the aid of an oxyacetylene flame rather than having been cast in as is customary. Company 27. — We bond around all important special work where any quantity of current is to be provided for by welding (with an oxyacetylene flame) heavy copper lugs to the web or base of the rail joint. To these lugs are attached stranded weather- proof covered cables of from 500 coo to 2 000 000 cir. mils, cross section, which spans the entire special work. Rail Joints and Bonds 91 Question E-W-84 in the May issue of the A. B. R. A. asks what is the best method of bonding manganese special work and raihoad crossings other than by using the plug holes provided. The fol- lowing answers to this question as fornid in the June and July num- bers are given below: Chas. E. Fritts, Electrical, Engineer, Metropolitan Street Railway Co., Kansas City, Mo. — We use copper cables tuidemeatli the special work and single bonds by brazing. Edw. J. Blair, Electrical Engineer, Metropolitan West Side Elevated Railway Co., Chicago, III. — The best way of bonding manganese special work and railroad crossings is to jump around them with copper-cable conductors, making the connection to ordinary rails behind the manganese special work. A. V. Brown, Engineer Maintenance o* Way, Lake Shore Electric Railway Co., Sandusky, Ohio. — Run cable around manganese special work. H. P. Bell, Electrical Engineer, San Francisco-Oakland Terminal Rail- ways Co., Oakland, Cal. — In bonding special work and railroad crossings," we have found, after much investigating, testing, and experience, that it is cheaper and more efficient to bond around crossings and special work (unless electrically continuous and easily drilled) witli such size cables as the current density and voltage drop allowed demand at that particular location. We place such cable or cables in trunking filled with tar compound and bury them about 6 inches below the tie, connecting them to the through rails by means of seven-eighths-inch separate compression-bond terminals. Thus the track special work may be repaired or replaced without necessary repairs to bonding. C. L. Cadle, Electrical Engineer, New York State Railways, Syracuse, N. y.— -The New York State railways' practice has been for the last seven years to install welded bonds on all track joints needing electrical connections. From our experience the welded bond adheres to manganese rail and special work as well as open-hearth and Bessemer steel. At railroad crossings in addition to bonding the joints each crossing is jumpered by placing a piece of 4/0 copper cable, or larger, around the crossing, so that in case the bonds on the joints of the special work are broken off the current will be carried through the jumper cable. C. D. Emmons, General Manager, Chicago, South Bend & Northern Indi- ana Railway Co., South Bend, Ind. — We use brazed bonds for all of our work. H. G. Throop, Superintendent Line and Buildings, New York State Rail- ways, Syracuse, N. Y. — I believe that the best method of bonding manganese special work is to use welded bonds to the head of the rail, double bonding, using a lo-inch and 18-inch bond. The special work should also be cabled, i. e., one 500 000 cm. cable installed for each track, attaching the ends of this cable to two 4/0 cross bonds welded to the rail at a point back of the special work each way from the crossing. H. F. Merker, Engineer Maintenance op Way, East St. Louis & Suburban Railway Co., East St. Louis, III. — On account of the fact that special work with heavy cables carrying current around it may be considered dead for all the time except when a car is passing over it, there have been various methods of bonding used. In fact, some engineers have gone so far as to leave all bonds off of such special work. We know of no better way to bond special work than to leave a soft plug for drilling a 92 Technologic Papers of the Bureau of Standards bond hole, but this hole may be placed at any convenient part of the special work piece and need not be in line with the bolt holes or near them, as all that is really necessary is one tap connecting it with the return circuit to keep the switch piece alive, and it is not necessary that each joint be bonded. E. H. ScHOPiELD, Engineer Power and Equipment, Minnbapolis Street Railway Co., Minneapolis, Minn. — In addition to cables spanning special work and bonded to rails, bonds may be welded by acetylene torch to the side of the head or guard of special work parts. H. A. Clarke, General Manager, Ithaca Traction Corporation, Ithaca, N. Y. — ^My experience has been that it is the best practice to bond around such spe- cial work, using bond terminals of whatever type may be in use, soldered to sufficient length of oooo copper wire. J. B. TiNNON, Engineer Maintenance op Way, Chicago & Joliet Electric Railway Co., JoliET, III. — I know of no better method of bonding manganese steel special work than by using the plugs in the castings. It is almost impossible to weld any kind of bond to the manganese casting and the heating of the casting would no doubt tend to destroy the value of the manganese steel. It is also nearly impossible to drill the casting, so I think that the method of using the plug holes and bonding to a through cable is the best method that has yet been developed. H. E- Gough, Engineer, Elmira Water, Light & Railroad Co., Elmira, N. Y. — We double bond all connections in special work, drilling the bond holes on the ground. Better connections are insured if drilling is done on the ground rather than in the shop. It is also generally wise to provide supplementary bonding around special work where the traffic is heavy. Geo. H. Pegram, Chief Engineer, Interborough Rapid Transit Co., New York, N. Y. — We find it most convenient and satisfactory to have all bonded holes provided by the manufacturers with copper plugs for signal bonding. We do not use manganese rail for negative return, as we have an opportunity to make use of the open- hearth steel guard rail for that purpose. The guard rail is bonded to manganese rail by means of clipped bonds. In a paper presented at the annual convention of the South- western Electric and Gas Association, Galveston, Tex., May, 1915, G. W. Smith, engineer, San Antonio Traction Co., San Antonio, Tex., said: Otir experience with rail bonds as ordinarily applied has not been such that we felt justified in depending on them to carry the current around the special work. We tried to get information as to whether or not copper cables could be welded to the steel rail by the thermite process, but in so far ^we were able to find out this had never been done, so we proceeded to do some experimenting. The result was that we succeeded in making a weld which gives a contact area equal to or greater than the cross-section area of the rail. The cable used, which is 800 000 cir. mils, is welded to the lower side of the flange of the rail, and a section cut through the weld shows a shading in color from steel at the top to copper color at the bottom of the weld. The cable enters the weld at the bottom and is therefore in contact directly with the cop- per film at the bottom of the weld, which insures minimum contact resistance. We are using this method of bonding on all reconstruction work. Rail Joints and Bonds 93 The opinions here expressed are overwhelmingly in favor of bonding around special work. In several answers no mention is made of bonding the individual members of the special work. Although they are called upon to carry current only when a car is passing over them, it is obviously good practice to provide for at least Ught bonding to the main retinm circuit. Although the consensus of opinion seems to be in favor of weld- ing or brazing bonds to manganese steel, a number of engineers are apparently having good results from the bonds installed in the soft plugs provided by the steel companies. Only one answer refers to the possibility of injuring the manganese steel by weld- ing bonds to it. Experience, however, seems to be sufficiently complete to show that any fear regarding such injury is unwar- ranted. {h) Bonding op Converted Steam Roads. — ^The bonding of steam railroads in preparation for electrification presents some problems somewhat different from those obtaining on the ordinary city or suburban track. The conditions which are, as a rule, similar, are briefly as follows: (i) Joint plates are in place and the removal of them would not only be expensive but unsafe with, the passing of high-speed trains; (2) the location is usually such as to invite theft of exposed bonds; (3) safety is of prime impor- tance, and the adoption of any bonding method from which a broken rail might possibly result could not be permitted. These conditions have forced several railroads to the adoption of a special type of bond which, so far, has been confined to this class of work. The objection to the removal of joint plates ex- cludes the concealed type of bonds and necessitates the use of either a short bond or one long enough to span the plates. Objec- tion has been made to the short head bonds both on account of the breakage of the strands and ribbons under heavy traffic as well as to the alleged injury done the rail by the welding heat and the drilUng of the head. As the adoption of a long exposed bond would mean continual loss and trouble from theft, a long compressed or pin terminal bond has been devised and adopted by several railroads which can be inserted tmder the joint plate and locked in position by the removal of a single bolt. This bond 94 Technologic Papers of the Bureau of Standards is provided with one terminal attached and one detached, and a sharp crimp or loop is put in the body of the bond near the end containing the fixed terminal. One of the end bolts of the joint plate is removed and the bond is threaded under the plate from this end. When the bond is in its proper position the bolt is replaced, which engages with the loop and locks the bond. The loose terminal is then soldered to the end of the bond and expan- sion or compression of the terminals is then affected in the ordinary manner. It is stated that in the electrification of the Chicago, Milwaukee & St. Paul Railroad this type of bond will be used and that it was adopted only after an exhaustive study of the subject. The Pennsylvania Railroad and the New York, New Haven 8c Hartford Railroad are also using this or similar types. (i) D0UBI.E V. Single Bonding. — ^The proper size and number of rail bonds per joint appears to be a subject regarding which very little definite knowledge exists, and the present practices of the operating companies seem to be based upon arbitrary and irrational rules rather than upon theoretical considerations.' W. A. Del Mar, in a letter published in the Electrical World of ^pril I, 1909, comments upon the absence of information and standard practice upon this point, and gives the following four rules as having been used by the operating companies to deter- mine the capacity of bonds : (i) Making the conductor equal in capacity to the rail. (2) Asking advice of manufacturers. (3) Doing what other people have done. (4) Guessing. Realizing the irrational character of these rules, Mr. Del Mar attempted to determine the proper capacity of bonds by the following three more logical considerations: (i) Determine the magnitude of ^e continuous and maximum currents in the rail and make the bond large enough to prevent imdue heating. (2) Make the bond large enough to give at least 90 per cent efficiency to the return circuit; that is, make the conductance of the bonded rails at least 90 per cent of the conductance of a 1 The Bureau of Standards is now making preparations to conduct experiments on tlie carrying capacity of different types of bonds tmder various conditions. The results of these experiments will be published at a later date. Rail Joints and Bonds 95 theoretically contiijuous rail. The following equation is given by Mr. Del Mar for the efficiency of the return circuit: Eff. = ^' L,+L,ii-K) K where K = average efficiency of bond, or the ratio of the con- ductance of the bond to the conductance of an equal length of rail. Li = length of rail, L2 = length of bond between terminals. (3) Make the bond large enough to conform to proper mechanical conditions. The author of the letter states that he was immediately frus- trated in his attempts by having no data on the capacity of bonds, and after a thorough search through trade Uterature and scientific abstracts he came to the conclusion that no work was available as to the amount of current that short bonds would carry under various conditions without undue heating. He suggests this as a splendid field for research by the colleges and coromercial lab- oratories and scores the manufacturers for not having data on the capacity of their various bond products. That this subject is of immediate and practical interest, and one on which a great diversity of opinion exists, is shown by the following answers submitted to question E-W-88, asking for the practice of the companies regarding single and double bonding, published in the June and July issues of the A. E. R. A. : C. D. Emmons, Generai, Manager, Chicago, South Bend & Northern Indiana Railway Co., South Bend, Ind. — We single bond our track in all cases excepting in city streets where leading to power stations. H. F. Merker, Engineer Maintenance op Way, East St. Louis & Suburban Railway Co., East St. Louis, III. — Where the return current is large and where a bad electrical joint would be serious, or where paving conditions make the opening of joints a serious matter, there is no doubt that double bonding is to be preferred. Remember the old maxim, "Do not carry your eggs all in one basket." John LEisenring, Signal Engineer, Illinois Traction System, Springfield, III. — ^This company has adopted the practice of double bonding all track in pave- ment or other forms of streets. The tracks on private right of way are only single bonded. 14985°— 16 7 g6 Technologic Papers of the Bureau of Standards H. P. Bell, Electrical Engineer, San Francisco-Qakland Terminal Rail- ways, Oakland, Cal. — We practice both double and single bonding of rails, depend- ing upon the current density, allowable voltage drop, size (conductivity) of rail, and capacity of bond. Charles E. Fritts, Electrical Engineer, Metropolitan Street Railway Co., Kansas City, Mo. — Double bonding. A. H. Babcock, Consulting Engineer, Southern Pacific Co., San Francisco, Cal. — Tracks are both single bonded and double bonded, according as the load re- quirements change with varying localities. No hard and fast rule can be laid down, but bonding should be done always with reference to the potential gradient in the rail. A. V. Brown, Engineer Maintenance of Way, Lake Shore Electric Rail- way Co., Sandusky, Ohio. — Double bond all tracks in pavements. Edward J. Blair, Electrical Engineer, Metropolitan West Side Elevated Railway Co., Chicago, III. — it is our practice to single bond our tracks, but this is rather a matter for local conditions to determine. Whenever the resistance of the return circuit can be kept within bounds by single bonding, it should be done. C. L. Cable, Electrical Engineer, New York State Railways, Syracuse, N. Y. — ^The practice of this company has been to bond each joint with at least one 4/0 bond. At locations where the current density is such that the size of this bond will not carry the current imposed on it, as high as five bonds are installed at each joint to take care of the additional current. H. A. Clarke, General Manager, Ithaca Traction Corporation, Ithaca, N. Y. — I would state it is the practice of this company to single bond our tracks. George L. Wilson, Engineer of Maintenance of Way, Minneapolis, Minn. — The Twin City Lines use only single bonds. It has never been the practice of this company to double bond its tracks. H. G. Throop, Superintendent Line and Buildings, New York State Rail- ways, Syracuse, N. Y.— It is a good practice to double bond tracks which are heavy carriers of return current to the power house from congested districts and also to double bond in congested districts. In both Utica and Syracuse this practice is followed throughout the central portions of the city and on lines to which the greatest amoimt of negative cables, which lead back to the power houses, are attached. This method also gives some insurance for good bonding, as of course the two bonds give greater life than a single bond. George H. Pegram, Chief Engineer, Interborough Rapid Transit Co., New York, N. Y. — We double bond oiu: rail joints. H. E. GouGH, Engineer, Elmira Water, Light & Railroad Co., Elmira, N. Y. — We double bond our tracks in the central portions of the city and where trafiSc is heavy. In outlying sections single bonding is used. We are using a pin-terminal bond for this purpose. * J. B. Tinnon, Engineer Maintenance of Way, Chicago & Joliet Electric Railway Co., Joliet, III. — We single bond tracks except where the return flow is very high, and then we double bond. The practice of double bonding for the pur- pose of having one good bond in case the other fails is, I think, a waste of money, as the same condition that causes one bond to fail will also cause the other ta fail in most cases. J. C. Donald, General Superintendent Asheville Power & Light Co., AshEvillE, N. C. — Bonding both track rails with cross bonds located every 200 feet is considered good practice. Rail Joints and Bonds 97 F. M. Richards, Electricai, Engineer, Atlantic Shore Railways, Kenne- BUNK, Me. — It has been our practice to single bond our tracks, installing cross bonds between rails every thousand feet. These answers throw absolutely no light on the question as to just what is the safe carr}dng capacity of rail bonds. That a short copper bond attached to heavy masses of cold steel can not attain a dangerously high temperature is obvious even when carrying ctirrents of the magnitude fotmd on heavily loaded tracks. The contact resistance of one terminal of a mechanically applied bond in good condition is in the order of 0.000005 ohm. When carrying a current of 500 amperes, which is greatly in excess of currents ordinarily found in rails, there would be a dissipation of only 1}^ watts, and with 1000 amperes a dissipation of 5 watts per terminal. This is, of coiurse, in addition to the heat generated in the copper of the bond, but as far as the contact is concerned there seems to be no practical limit to its capacity to carry current. Parshall in Bngland, in an article on " Earth returns for electric tramways," published in the Journal of the Institution of Elec- trical Engineers, April 28, 1898, stated that experience with pres- sure contacts in central station work had demonstrated that 100 amperes per square inch was the safe Umit, but suggests that 50 and even 25 amperes per square inch would be found more advis- able for rail bonds. As these figures are exceeded in practically all installations in this country they can not be regarded in any way as a practical limit for current density. A reference to the above answers will show that a number of companies, including some in large cities, install only single bonds and that several employ double bonding only when necessary to reduce the potential gradient on the tracks. This would indicate that double bonding is not necessary solely from the standpoint of capacity, but that its adoption is demanded by other considera- tions. One of the usual causes for its use is to insure safety, and not place reliance on a single bond in a permanent track where the repair of a bond would mean tearing up the pavement. Under extreme conditions double bonding is justifiable solely from the economic standpoint, and the factors which determine these conditions may also be used to determine the economic 98 Technologic Papers of the Bureau of Standards replacement of deteriorating bonds. These conditions can be determined when the constants of a given system are known and the cost of power and the average current in the rails are obtainable. Let F7= weight of rail per yard, 7= root-mean-square current in rail over a 24-hour period, ^ = cost of power per kilowatt hoiu: in dollars, P =cost of installing a bond, n = number of years bond will last, L = reduction in joint resistance resulting from installation of bond, expressed in feet of adjacent rail, »'=rate of interest paid on invested capital; then the resistance of the rail is very close to 0.001 jW ohm per foot and the annual saving of energy in dollars due to installing a bond would be P x ""-^ x ^- X 24 x 365 = °°°^ t^'^^ W 1000 ^ -> -^ \\r The annuity ^ required to retire the investment, P, on a new bond at the end of n years, its period of usefulness, is \R«-i) f where R = i -\ 100 When the annual power loss without the bond exceeds this annuity, it is obvious that the installation of a new bond would be a matter of economy. The limiting condition would be obtained when the energy charge is equal to the annuity. Equat- ing these two we get: 0.00876 -^ =P f „„_ y from which any quantity may be obtained provided the others are known. If we employ the equation to determine at what current double bonding becomes economical, we have ^ WP ^(R-i) 0.00876 Lp i?»-i In order to apply this equation with six independent variable factors it will be necessary to assume a set of values which would obtain under normal conditions. ' American Handbook for Electrical Engineers, p. 830. Rail Joints and Bonds 99 Let it be required to determine whether one or two 4/0, lo-inch compressed-terminal bonds should be used on loo-pound rails being newly installed under the following conditions: p =cost of energy =$0.01 per kw. hr. P = cost of installing bond = . 60 n = life of bond =12 years. r = rate of interest = 5 per cent The resistance of one lo-inch 4/0 bond, including contact resistance, is very close to 0.000055 ohm, and would probably average more. Two such bonds in parallel would have approxi- mately one-half of this, or 0.0000275 ohm, which is also the decrease in the resistance of the joint resulting from the installa- tion of the second bond. As a loo-pound rail has a resistance very close to o.ooooi ohm per foot, L would be 2.75 feet. Substituting these values in the above equation we find that /' is equal to 15 660 or / = 125 amperes. The Bureau of Standards has examined numerous railway load curves and has found that the ratio of the root-mean-square current to the all-day average, ranges from 1.25 to 1.4. If we use the lower of these values, which is more applicable for the heavily loaded Unes with which we are concerned in this discussion, we get 100 amperes as the all-day average value of the current. With a load factor of 40 per cent this would give 250 amperes per rail as the value at the peak period. While the values here assumed are normal in every respect, they are undoubtedly on the side tending to make the Umiting current small. A lower cost of energy, a shorter life of the bond, and a higher cost of installing a bond will all tend to give a larger ciurent where double bonding becomes economical. As the values assumed for these three variables are obviously near the limit in the other direction, it is difficult to conceive how the economy point would be reached at any aU-day average current value much less than 100 amperes. While a current of 100 amperes all-day average is entirely possible and undoubtedly exists on the rails of many properties, it is far in excess of what good electrolysis conditions would dictate. One hundred amperes on a loo-pound rail would give a drop of i loo Technologic Papers of the Bureau of Standards volt per looo feet, and as 0.3 to 0.4 of a volt per 1000 feet, average for the 24-hour period, is considered the limiting potential gradient, consistent with good electrolysis conditions, it is seen that the latter condition would limit the current in the rails long before economy would demand double bonding. It is true that double bonding will reduce the potential gradient in rails, and several of the engineers quoted above seem to con- sider this as a determining factor for this practice. Its influence in this respect is quite small, however, as will be seen from the following calculations : Consider lo-inch 4/0 concealed bonds on 100-pound rails as before. With 60-foot rails we have approximately 59 feet of rail in series with the bond and the resistance of the two are 0.00059 ^^^ 0.000055 ohm, respectively, or a total of 0.000645 ohm. Adding a second bond would reduce the resistance by 0.0000275 or to 0.0006175 ohm, which is 95.73 per cent of the resistance of the rail with one bond. With 30-foot rails the effect would be more marked, and the maximmn effect on the potential gradient resulting from the addition as a second bond would be where a short-head bond is installed on a joint previously bonded with a long-cable bond around the joint plates. A 30-foot rail bonded with a 36-inch 4/0 compressed terminal bond will have a resistance made up as follows: 27 feet of rail, 0.00027 ohm, 3 feet of 4/0 copper, 0.00015 ohm, two contacts, 0.000013 ohm, or a total of 0.000433 ohm, of which 0.000163 ohm is due to the bond. If now a 4/0 electric-weld bond having a resistance, including contacts, of 0.000045 ohm be applied to the head of the rail the long bond will be shunted by approximately 2}4 feet of rail in series with the short bond or by 0.00007 ohm. The two bonds in parallel will have a resistance of 0.0000487 ohm, making the resistance of one rail lengfti of circuit 0.0003187 ohm, which is 73.6 per cent of the resistance before the application of the second bond. With 80-pound rails, 60 feet in length the corresponding figure would be 87.3 per cent. These calculations will substantiate the statement that, except perhaps under extreme conditions, double bonding in lieu of single bonding has only a secondary effect upon the potential gradient in return circuits and therefore upon electrolysis condi- Rail Joints and Bonds loi tions. When the potential gradient therefore begins to approach the maximum allowable limit, or the limit set by good practice, other and more effective means should be employed to reduce it. In all of the above calculations the effect of the joint plates has been neglected. Their effect would be to increase the con- ductance of the joint and therefore reduce the necessity of double bonding. Considering only tracks in which the potential gradient does not greatly exceed the values considered safe from the stand- point of electrolysis we find that neither carrying capacity, econ- omy, nor voltage drop will justify the practice of double bonding under ordinary conditions. The only factor remaining, therefore, which might justify the use of two or more bonds is that of insur- ance against the total failure of a bonded joint. It is difficult to say to what extent the probability of a joint failure is reduced by the addition of a second bond. If the failures are the result of loose joints the second bond is not much of an insurance, while if failures are the result of imperfect work- manship in installation the value of the insurance is much greater. It is altogether possible that two bonds of different types could be used to advantage for this pmpose rather than bonds of the same type. A long bond around the joint plates might act as an insurance against the failure of a concealed bond and a con- cealed bond might insure the joint against theft of the exposed type. In employing a second bond as an insurance against the total failure of a joint it, of course, acts to improve operating and electrolysis conditions as well, to say nothing of reducing the power loss in the return circuit. These advantages when con- sidered together will ordinarily justify the use of the second bond on new and permanent tracks which are being installed in paved streets, where inspection of bonds is difficult and repairs expensive. The additional expense of installing the second bond at the time the new track is being laid is relatively very small and, in general, will be returned in reduced maintenance costs. The practice of double bonding would, perhaps, not ordinarily be justified on open track where the inspection and repair of bonds is less expensive and where the traffic as a rule is lighter. I02 Technologic Papers of the Bureau of Standards (J) Economic and Other Considerations for the Repi^acb- MENT OF Bonds. — ^The installation of a bond on a joint already bonded may be considered either as a replacement or as double bonding, and no sharp line of distinction between the two con- ceptions can be said to exist. The term "double bonding" has been used with reference to joints on which two bonds are origi- nally installed or where a second bond is installed to supplement a new or old bond in a practically perfect condition. The term "replacement" will be used with reference to bonds installed to supersede or supplement old bonds which have failed or which are in a state of deterioration. The value of the resistance which a deteriorating bond must reach before economy will justify its replacement can be deter- mined from the equation given on page 98 of this paper, in which the reduction in the joint resistance resulting from the installation of the new bond becomes the unknown quantity. Transforming the equation for this ptupose we find that ^^-^^^x(fe) WP 0.00876 Pp' The following concrete example will illustrate the application of this formula. Let us assume : W, the weight of rail per yard = 100 pounds. P, the cost of replacing a bond =$0.80. p, the cost of energy =0.0050 per kw. hr. n, the life of the new bond = 10 years. r, the rate of interest = 5 per cent. Let us also assume that the current is of such a value as to give a drop of 0.8 volt per 1,000 feet as an all-day average on a perfectly bonded rail. This is greatl;t in excess of the current permitted by good electrolysis conditions and is not ordinarily exceeded, even in regions where the problem of electrolysis does not exist. The resistance of a loo-pound rail is o.oi ohm per 1,000 feet, which would hmit the average current to 80 amperes. Taking 1.3 as the ratio between the root mean square a,nd the all-day average current we get for our equation / = i04 amperes. The replacement cost of a bond is usually greater than the cost on new work and is therefore taken at 80 cents. One-half cent Rail Joints and Bonds 103 per kilowatt-hotir for power may seem low, but as it is assumed to be the cost of energy which will be saved by the application of the bond, it would not be logical to load it with fixed charges and operating costs other than the fuel. Upon this basis it is high rather than low. A replacement bond is often installed on old track which is partially worn out and which may be entirely replaced within a few years. Ten years, therefore, is considered as a liberal life for the new bond. The srcap value of bonds is small and is neglected in this discussion. Substituting these values in the above equation we find that L = 13.4 feet. As the new bond itself will test equal to from 3 to 6 feet of rail this means that the old bond will test equal to about 18 feet of rail before a new one can be installed with economy. This is, of course, far beyond the point of deterioration which good practice has established for the replacement of bonds. Electrol- ysis and voltage conditions ordinarily, therefore, demand a better return circuit than economy itself can dictate. In fact, it is doubt- ful if economy alone in many circumstances will justify any but the cheapest and simplest type of bonding. The Bureau of Stand- ards ' and numerous independent investigators have demonstrated beyond a doubt that the character of most electric roadbeds is such as to shunt a large fraction of the ctirrent from the rails even when well bonded. With poor bonding the increased gradient along the track tends fiurther to increase the leakage current which might easily reach a large per cent of the total current, except in the immediate vicinity of the negative bus. Parshall, in an article previously referred to, makes the following statement: In tests recently carried out in a line some 8 miles long it was foimd, by cutting the track at the middle of the line and inserting an ampere meter, that some 60 per cent of the current was returning through the earth itself. Tests made as to the con- ductivity of the earth return showed as a whole that it was about one and a half that of the rails, bonds, and fishplates, which would indicate that on an average about S3 per cent of the current was leaving the rails. In other words, the voltage drop in the earth return was but two-thirds of what it would have been had the current been wholly in the rails. ' The Bureau of Standards is now engaged in investigating the resistance of different types of roadbeds under various weather conditions. Tests are being conducted on experimental tracks builtforthis purpose as well as upon city and suburban lines. A full account of this work will be published at a later date. I04 Technologic Papers of the Bureau of Standards In this connection the experience of the Virginia Railway & Power Co. is of interest. They report that several years ago the bonds on an alternating-current line of several miles in length were failing rapidly as the result of incorrect methods and poor work- manship on the original installation. A complete rebonding of the tracks meant a heavy expense which the road at that time was not prepared to meet. A careful study of the situation was made and after ascertaining that bonds were being omitted on a number of modem European alternating-current lines it was decided to continue operation without rebonding and to keep a careful record of the energy consumption from year to year. After three years of this practice, during which time practically all of the original bonds had failed, the road is in successful operation and no increase in energy consumption chargeable to poor bonds has been noted. Such a condition as here described would, of course, be utterly impracticable on an ordinary direct-current system on account of the pernicious electrolysis conditions which would obtain, to say nothing of poor operating conditions. The one thing which calls for and demands good bonding is good electrolysis conditions. Without the incentive to guard against trouble from this source it is difficult to say to what degree of deterioration a company is justified in allowing its return circuit to descend. {k) Standards for Rbpi.^acement. — ^The practices of the com- panies regarding the replacement of bonds, as recorded in Table i on page 32, indicate a wide variety of standards, ranging from 2,}4 feet of rail to 27 feet of rail as the limiting resistance of joints. Among the answers there was not a single suggestion as to the manner in which any particular standard was established. The selection of a standard for replacement should be governed almost wholly by local conditions. Tlere are so many elements to be reckoned with that it is practically impossible to suggest a hard and fast rule that would be applicable tmder all circum- stances. Even if such a rule or formula could be developed it would contain so many variable factors and qualifying consider- ations as to make its application impracticable. Frequent objection has been made to the universally adopted practice of referring to the resistance of a bond in terms of a Rati Joints and Bonds 105 length of adjacent rail. The practice is a convenient one but obviously irrational, as it gives no indication of the actual resist- ance of the bond unless modified by supplementary data. The length of the joint tested, the length of the bond, and the weight of the rail must be known before the resistance of the bond in ohms can be calculated. A logical standard of replacement should obviously include these several factors, which would, however, greatly compUcate the simple rule now in general use. It has been suggested that the replacement resistance of a bond should be defined in terms of its increase in resistance over that of a similar bond newly and properly installed rather than in some arbitrary length of adjacent rail, but this also has its objections. The in- crease in the resistance of a bonded joint results from breaking of strands and ribbons, corrosion of terminals, and loosening and rusting of plates, thereby reducing their ability to aid the bond. With welded bonds the deterioration from corrosion of the con- tact is nil while with the long cable bonds its effect on the total resistance of the bond is far less than in short concealed or head bonds. A standard therefore based upon, say, a 100 per cent increase in resistance, would be as irrational and arbitrary as one based upon a given length of adjacent rail. Moreover, with most of the standard bond-testing instruments, giving the resistance of a joint in terms of adjacent rail it would be difiicult to discontinue the practice of referring to bonds in these terms. A standard which is simple, definite, and workable, even though it does not always meet the demands based upon a rigid technical analysis of the subject, is much to be preferred to one which attempts to meet these demands but is clumsy, complicated, and impracticable. A standard of replacement based upon the resist- ance of a given length of adjacent rail possesses the advantages here enumerated and from the standpoint of practical consider- ations is not so irrational as may at first appear. After all, the factors which limit the resistance of bonded joints are, ordinarily, electrolysis and operating conditions, and both of these are de- termined by the potential gradient in the return circuit. If, there- fore, we assume the same current density in rails of different weights, which is by no means a violent assumption, we are con- sistent in basing our standard on a given length of rail, inde- io6 Technologic Papers of the Bureau of Standards pendent of its weight, thereby. Hmiting the voltage drop across the joint rather than its resistance in ohms. As to what this standard should be is a matter that should be determined largely by local conditions. Different standards might well be employed by a single company to meet the condi- tions on different types of construction or in regions requiring different degrees of electrolysis protection. It is altogether prob- able that it would be found advisable in some cases to employ different standards on city and suburban tracks. Answers to question 5 would indicate that the limiting resistance for a 3 -foot joint of from 6 to 10 feet of adjacent rail would ordinarily fall with- in the botmds of good practice. Greater lengths might be em- ployed in regions where no trouble from electrolysis is likely to exist, but on city streets these values should not be exceeded. 3. WELDED AND SPECIAL JOINTS It has been previously stated that the information available relative to the life and character of different types of welded joints is far less complete than that upon the subject of rail bonds. Some of the reasons for this lack of reliable information are set forth in the following quotation from one of the prominent electric railway engineers of the country : In my experience I will say that I consider the information gotten from the fur- nished answers from questions as above to be unreliable. There are but very few cities in which the engineering department has been in existence or that the engineer has held his position long enough to be able to make any statement about worn-out rails or worn-out joints. The intensity of traflSc and the weight of cars bears an im- portant relation to the life of rails and joints and the conditions vary in different cities, and have varied so from conditions of 10 years ago that very few men are capable of intelligently answering the questions. Also the change in the material of which rails are made has been so great that unless this is considered the information is unreliable, ^he first Bessemer rails of a girder type were rolled about 1884. These rails were sfructurally defective, and the rail mill did not know how to roll the girder rail. Girder rails at this period weighed 56 pounds to the yard and were about 4}4 inches high. By 1890 the girder rail had grown in height to 6 inches and some of the sections were such that they could be properly rolled, but many engineers were still using sections that could not get the proper treatment in rolling. About 1893 the 9-inch girder rail was coming into general use and girder rails commenced to be a success. The rails rolled from 1890 to about 1901 were Bessemer made from a good grade ore and gave a long life. About 1904 the grade of ore formerly used for making Bessemer rails was getting extremely scarce, so a lower grade was used, and for the next two or three years the rails furnished street railroad Rail Joints and Bonds 107 companies were not as good as formerly furnislied, and at tHis time the weight of cars had been materially increased, so that track life was short. About 1909 the open- hearth rail came into general use and apparently gives a very much better rail than that furnished previously, although the open-hearth rail has not been in use long enough to give absolute results on its life and durability. The increase in carbon in the steel used in rails has materially affected the reliability of the welded joint in some locality. Realizing as we do that the conditions here described are true to a large degree, we do not feel justified in attempting a close analysis of facts or in drawing any but the most cursory and gen- eral conclusions from the data and information at hand. The several types of welded and special joints will be taken up in turn and a brief summary of the facts available will be presented. Conclusions will be drawn and recommendations made only where the facts seem to warrant such. (a) The Cast Weld. — ^The compilation of figures under question 1 on page 49 show that of the 268 052 electrically continouus joints reported, 149 716, or more than 50 per cent of the total, are cast welds. In consideration of the fact that the installation of this joint has been practically discontinued these figures are an indi- cation of an early popularity at a time when the welding of rail joints was looked upon by many as a rather bold experiment. The excellent results and long Ufe obtained from this joint as reported by a number of companies, under questions 4 and 6, would seem to indicate that the discontinuance of its use in recent years is not the result of its inability to meet the conditions imposed upon it, but rather to the fact that other and more modern types of joints are meeting the requirements of service and installation in a more satisfactory manner. Several causes are given as responsible for the f ailtures of the cast weld. A frequent cause of complaint is that a true weld is not effected and the rails loosen up in the joint. This not only aug- ments wear and cupping but adds materially to the resistance of the joint. Some operators are inclined to the view that the cup- ping of the rails at the joint is frequently due to the softening of the steel, which is said to result from the excessive heat of the molten metal. This is apparently the most serious fault that has been foimd with the cast weld and is no doubt largely responsible for the almost total abandonment of this type of weld which has io8 Technologic Papers of the Bureau of Standards occurred in recent years. The large amount of molten metal used in the cast weld maintained the rail ends at a high temperature for a considerable length of time, and the slow rate of cooling had an anneaUng and softening influence which was later manifest in cupped and worn rail heads. None of the modern welding processes employ the large amount of metal that was used in the old cast weld, and the cooHng is con- sequently much more rapid. Moreover, the greatest heat is now confined to the web and base of the rail, and it is therefore extremely doubtful if the heads of modem steel rails are seriously injured by any of the welding processes in use at the present time. The cupping which so frequently develops in cast-weld joints may also have been augmented by a difference in the resilience between the joint and the adjacent rail or to imperfect surfacing, either of which would give rise to pounding and uneven wear on the rail. In 1908 Parshall, in an article already referred to, has the fol- lowing to say regarding the cast weld: Another method of somewhat the same nature as the process of welding is that known as the "cast weld, ' ' or the " Falk joint. ' ' This joint is made by pouring molten metal into a metal mold clamped round the rail joint. The surfaces of the cast metal that come in contact with the mold and with the rail joint are chilled, and are thus pre- vented from forming a perfect weld. I believe it has been asserted that a weld is effected. It seems, however, extremely doubtful, since without the use of a flux a weld is almost impossible between cold wrought steel and molten iron. The rail expands after the metal is poured around it, and remains expanded until after the cast iron has set, and finally resumes its former size. This affords a slight clearance for expansion and contraction, and accounts for the mechanical success of the joint, which, if carefully applied, makes when new a perfect mechanical track; although, in the writer's mind, the difference of resilience between the part surrounding the casting and the remaining part of the track may eventually cause uneven wearing away of the rail. The clearance above spoken of undoubtedly ataiits a certain amount of moisture, so that by the formation of oxide the resistance orthe joint increases in the cotirse of time. From the results of tests which I have at hand , it also appears that the electrical resistance of this joint, even when new, varies considerably; so that, considering the low voltage restrictions in this country, it should be used in connection with an efficient form of bond. Owing to the rigidity of the joint, however, copper bonds will undoubt- edly be found more durable in conjunction with it than with a fishplate form of joint. (6) The Thermite Welded Joint. — ^The failures of the thermite weld and the rather large percentage of cupped joints which have been reported from time to time have been for the most part on Rail Joints and Bonds 109 the old type of weld and should not be considered as evidence against the greatly modified and newer joint which is referred to on page 20. Very little evidence is at hand regarding this modified type of weld, but if it is successful in preventing the cupping of the joint one of the chief objections to the thermite weld will have been removed. In contrast to the old cast weld the thermite weld requires but a small amoimt of welding metal, and this metal actually unites with the steel of the rail to obliterate the joint. The small amount of metal and the perfect union contribute to give the joint a resilience practically the same as that of the adja- cent rail, and the wheel is thereby enabled to pass without encoun- tering a hard spot in the track. Moreover, the metal being continuous, the joint has a high conductance which does not deteriorate. Among the objections to the thermite weld has been recorded the facts that the process is comparatively slow and that in repair work where it is necessary to insert a short length of rail to take the place of a badly cupped railhead two distinct welds are neces- sary where other processes require only a modification of a single weld. These conditions are said to make the process less satis- factory on old rail than for new work. The San Antonio Traction Co. adopted the new thermite weld in the reconstruction of their tracks, which was begun in October, 1913. A full account of the work was given by G. W. Smith, engineer for the company, in a paper presented at the annual convention of the Southwestern Electrical and Gas Association, at Galveston, Tex., in May, 191 5. Mr. Smith made the following remarks : We have made a total of 3000 welded joints on track laid with concrete roadbed, and since the tracks have been put in operation we have had two breaks in the rails. One of these occurred at a crossover in the fall of 1914 and the other near a bridge in the winter of 1914. The first welds were made in the winter of 1913, and these have been through two winters and one summer. The joint which broke near the cross- over is in this lot. The joints which were put in in the summer of 1914 have been through one summer and one winter, and the joint near the bridge was in this lot. In so far as we are able to judge from our experience of the past 18 months, we are convinced that, from the mechanical as well as electrical standpoint, the best type of permanent construction is obtained by welding the joints in the rails and using steel ties in concrete. I lo Technologic Papers of the Bureau of Standards As the new type of thermite joint has been in operation for only about two years, it is too early to form definite opinions regarding it. That it is an improvement over the earlier types, however, there seems to be no question. Reports from other companies who have adopted it or who have installed it on an experimental basis will be looked forward to with interest. (c) The Ei> (2) (3) Equation (3) is the general equation giving the current strength at any point in the tracks distant x from the end of the railway line, and applies to both case I and case II, the difference in the two cases being only in the constants of integration A and B. Equation (3) shows that for a track of given length and origi- nating ciurent per imit length, the total current in the rails at any point depends upon three factors, namely, the distance of the point from the outer end of the tra(^, the resistance of the track per unit of length, and the leakage resistance per imit length between the tracks and earth at a considerable distance from the rail. The resistance of the rail varies with its temperature and depends also upon the size of the rail, the material from which it is rolled, and the treatment during manufacture. For rough calcu- Leakage Currents 7 lations we have assumed a resistance of 0.0 1 ohm per 1000 feet of 100-pound rail and taken the resistance of other rails as inversely proportional to their weights. This figure represents an average of a large number of values of resistances of rails of various sizes and from several makers. The resistance of the roadbed varies between wide limits, and experiments are now in progress for the study of roadbed char- acteristics. These experiments so far indicate that the roadbed resistance varies with the type of construction, the weather, and the kind of soil upon which it is laid. The leakage resistance of single track ranges between about 0.2 and 12 ohms per 1000 feet for constructions usually employed. In special cases, where the rails are laid in moist earth of high conductivity or crushed rock in a very dry region, the resistance may not fall within these limits. For double track the resistance may theoretically vary from 50 to 100 per cent of this, according to whether most of the resistance is near the rails or remote there- from, and in most practical cases it will vary from 60 to 80 per cent of that for single track of similar construction. Since the leakage current up to any point is equal to i^ — i, the effect of track resistance on leakage ciurent is seen from equation (3) to be exactly the inverse of the leakage resistance ; hence an increase in leakage resistance in any given ratio reduces the leakage currents in the same degree as increasing the conductance of the tracks in the same ratio. This emphasizes the importance of so con- structing the roadbed as to give the highest practicable leakage resistance. Since in the equations which follow the factor - /- occtu-s repeatedly, the equations will be simplified in form by letting ^_ = a. Making this substitution in equation (3) we get the simplified form : i = Ae"-F5e-" (3a) It is apparent that the form of the curves is determined not by the numerical values of S and r, but by the ratio of these factors. In order to facilitate the interpretation of the equations there is given in each case certain combinations of S and r which might 8 Technologic Papers of the Bureau of Standards be encountered in practice, and which would give the values of a used. The value of a will vary between wide limits. For example, if the track resistance be very low, such as when well-bonded 125-pomid rails are used, the value of 5 for a single track would be 0.004 ol™^ per 1000 feet. If, also, the leakage resistance has a high value, such as 12 ohms per 1000 feet, the value of a will be 0.018. On the other hand, if the track resistance be high, such, for example, 0.04 ohm per 1000 feet, due to very bad bond- ing, and if, at the same time, the leakage resistance be as low as 0.2 ohm per 1000 feet, the value of a would be 0.45. Under most practical conditions the value of a may be taken to range between 0.025 ^.nd 0.25, or in the ratio of about 10 to i. The quantity a is called the "leakage factor" of the railway line. It will be shown later in the discussion of the theory of leakage currents that it is very important that the value of a be kept as low as possible. This can be done either by maintaining good track bonding and by the use of heavy rails, or by so construct- ing the roadbed that the leakage resistance will be high. in. LEAKAGE CURRENTS FOR UNIFORM LINE We shall now proceed to examine in detail the application of equation 3a to the two cases encountered in practice, first with the negative bus not grounded, and next with the bus grounded. 1. (CASE 1) BUS NOT GBOUNDED At the outer end of the Hne x = o, and the current i = o. Since the bus is not grounded, all of the current which leaks off the track must return to the track. Hence, when x = L, the length of the line, the current in the tracks must be i^L. Imposing these conditions on equation 3a and solving for the constants A and B we get the following : * When ^ = A +B = o, ot A = -B. When x = h Ae^^ + Be-^^ = i^L ioL = (e^i'_e-aL)yl gaL — e-iL Leakage Currents From (3a) and the above relation A = — 5 we have : i = A[e*^-e-»^] = ioL eaL_g-aLi [ea._g-a.]^ •'• i = • 1° / T \ • sinh (a:K) smh {aL) ^ ' The total current originating in the tracks between the end of (4) (5) ^6 7 s 5 /o 7/ 7s 7s 7f 7F~~76 77 to /a zo (bus) Distance from the end of the Line in Thousands of Feet. Fig. 2 the line and any point x is i^x. Hence, the total leakage current up to any point x is ''"'"^'"sinh (aL)' sinh (ax) (6) The curves in Fig. 2 plotted from equation (6) show the magni- tude of the total leakage cturent at each point along a 20 coo- foot single track for three conditions of rail and leakage resistance, the originating current being assumed to be 25 amperes per 1000 feet of track. 16302° lo Technologic Papers of the Bureau of Standards In Fig. 2 three curves axe shown. Curve I shows the leakage current at various points on a line for which the track resistance 5 is 0.02 ohm per looo feet due to bad bonding, and the leakage resistance r is 0.4 ohm per 1000 feet, a value not unusually low. This gives a value of a equal to 0.2236. The maximum leakage current in this case is seen to occur at about 13 000 feet from the end of the line and amounts to about 220 amperes. The current originating in the tracks being 25 amperes per 1000 feet the total originating current is 25X20 = 500 amperes. Of this, 220 am- peres, or about 44 per cent, has leaked to earth. This represents a very bad leakage condition, but one not infrequently met with in practice. In curve // the value of S is 0.005 olioi P^'' 1000 feet, which corresponds to a well-bonded track of loo-pound rails, and the same value of r as in ctirve I. This gives a value of 0.112 for a, which represents a fair average value of the leakage factor. The difference between curves I and II shows the effect of reducing the track resistance from 0.02 to 0.005 ohm per 1000 feet, and it will be seen that the maximum leakage has been reduced to less than one-half of the value shown by curve /. Curve /// represents a very good condition regarding leakage, the track resistance being fairly low and the leakage . resistance 1.6 ohms per 1000 feet, which is a moderately high value, although one which may often be exceeded in practice. 5 is 0.005 ohm per looo feet, giving a. value of a = 0.01 78. Comparison of curves II and ///, which are for the same track resistance, shows the effect on the leakage ctnrent of increasing the leakage resistance. The leakage current decreases with decreasing values of a. The point at which the leakage current is a maximum is, of course, the neutral area in the electrolysis region at which point the earth and the tracks are at the same potential. This point is seen to shift toward the negative bus as the maximum leakage increases. This change in the size of the positive and negative areas wUl be shown more clearly by a later curve when its significance will be dis- cussed. For high values of the leakage factor a the leakage ctur- rent will be seen to increase more rapidly than the value of a, Leakage Currents 1 1 which emphasizes the importance of maintaining the value of a as low as practicable. For maximum leakage dx From (6) dii . ioLa , , . J^=^°-sinh(aL)-'=°'^('^^)=° sinh (aL) .-. cosh (ax) = — j^ — (7) ■■">^^-'[^^] («) = value of X for neutral zone. Substituting from (8) and (6) we get the value of maximum leakage. _^____^^_ sinh^ (aL) _ Max u = i - cosh-' rfE^LMIl bk / ^^ Max J, lo^ cosn \_ aL j sinh (aL) V a^ ; 1 r , I 1^; — 1 . . =^ cosh"' u -\ju'— I loL aLL M J '' '"^^ ' . — -. -. ^ /-. - . (9) , smh (aL) where u = j aL Equation 9 is plotted in Fig. 3 with length of line, L, as abscissae for to = 40 amperes per 1000 feet, 5 = 0.005, and r = o.^, which corresponds to a fair average condition. The curves indicate that the leakage cturent increases much faster than the length of the liae, especially for lines of moderate length, and shows the importance from an electrolysis standpoint of reducing the feeding distance as much as possible. Fig. 4 is the same as the lower part of Fig. 3 plotted on a larger scale, together with the dotted curve of a parabola. It indicates that for feeding distances up to about 10 000 feet the maximum leakage current increases approximately as the square of the feeding distance. 12 Technologic Papers of the Bureau of Standards JOOO £rf£i T Of TiaAi K l-t XViSTV ' ON Max 1 //M(//VI A-l EAK* GE C uieis£, vr-, -nT > ^ % ^0 ■? voo B-l EAy^ GE C u/eei HT- AMPi ■ess y / Bus UfVQK. our^L ■)ED / / / / ■y- a ■xi cc sy^'u -i/ / / B / i m'-/ u.-- S//V 7fa.i) Equ CS, / y / \^0O a L- A = 40 a = < / / / 1 """ zoo Joe / y / / ^ y / ^ y ^ ^ ■*s 2S /s )o s o ■<)■ e /S /6 eo 24- Z8 3Z 36 ■^O A4 A0 JZ Jf, eo I/ength of Line in Thousands of Feet. Fig. 3 /a 16 /4 Ert F- TBA \KAae -,K U. Cuee /GTH r/V7* ?/v Bus Unc eoui JDBD 'A <.oos r^ ■^o' / / / / -ify«. \x. ^[^ OSh' '^-i —1 ■Equ i9) Paeai tOLA'X i.zyJ / / ^ 4u^- / - aL / • y JO a Ok . • X y y ^ ^ s- e 7 e 9 JO Lengtli of Line in Thousands of Feet. Fig. 4 '/ /2 /3 /* /S Leakage Currents 13 For long feeding distances the rate of change of maximum leakage current is much less than for short feeding distances. Fig. 5 represents equation 9 with the rail resistance as the independent variable. The maxipium leakage ciurrent increases much less rapidly than the track resistance, except where the track resistance is very low. In Fig. 6, equation 9, is plotted with the leakage resistance as the independent variable. If the leakage resistance is small, E^f'E^ ZT Or Ta 'ACf< ^B SISTANl -e On A AXIMUM E cu/efs so 0.4-0 ENT BusUa &eouNi iED i- -^ ^f/HAX. ^«iH Sf^'u- Eeu. 19) ^ '-Ju--, -tl -i.^ u = . swh ( U) ^ ^^ £ ,-. ezL. s I ■^ • ^6 I / / / / / / ■004- 006 008 oj .o/e o/^- Track Resistance — Ohms per Thousand Feet. ■O/e, ■ 018 ■oz Fig. s such as that corresponding to an average concrete roadbed or track embedded in damp soil, the leakage current decreases very rapidly with increased leakage resistance. 2. (CASE n) BUS GROUNDED This differs from case I only in the terminal conditions. From case I. i=A(^^ ■^Be-''^ (10) when a; = o. z = o. :.A = —B (11) 14 Technologic Papers of the Bureau of Standards Where a;=L — ^that is, at the power house — ^we assume that the tracks are perfectly grounded so that the potential difference Bus UNo£:o / " y y \ / ' / y S- . . — /- ''/ y ,^^ .«-: \ / ,,-' ,--'" ^ "■-^^ -J, \ //y y _, 'j:^ '^ ^ ~^-. 3S / A ^ ^ ___,^ — — — - — •— — - -- ■JS ^ (a^ £ 90-0 7) ,^ 7 ■s/ri ^(CL ■) 3 — Volts pet ^' ---' / 3 ^^ -' / ^ -*«5. ^tNH rajc: B 9U.( >3) ^^ ■'' y ^ 2 l-ZS CLCi >Sh{ 0.1.) A *ZS J'= 0.0c S c = o-i IS ^' / y i. = ZO r- O-'H. ^^ ,f'' ^ ^ Potenti ^-■ ^■^' >- -^ ,-- -' ^ ^ -" -^ ^'' ^^ __ ^ ^■^ r:^ — e a /o /z y* Thousands of Feet from End of I,iiie. Fig. 9 bus ungrounded and grounded. The broken line indicates the gradient given by equation 18 when the entire cmrrent is con- fined to the rails. It will be seen that potential gradients in the tracks may be materially reduced due to leakage cturents, and this reduction is more marked if the bus is grotmded. Dividing equation 19 by 17 we get as the ratio of the gradients at any point mider the two cases. Leakage Currents 19 E2 tanh (aL) El aL (20) The ratio of the gradients in the two cases is thus independent of X, and for large values of L the ratio becomes practically in- versely as L. Thus, when the negative bus is ungrounded the potential gradients are greater than if the bus is grounded and the difference is very marked where the feeding distances are long. For very long lines the ratio varies practically inversely as the length of the Une. V. OVER-ALL POTENTIALS. 1. (CASE 1) BUS NOT GROUNDED The over-all potential drop is E = ^^edx. Hence, from (17) we have: E, = . , ° . , V ■ I sinh axdx » smh {aL) J„ = asinh(aL)L^°^^('^^)J, ••-^- = asinhiL) ["°^^^"^)-0 ^^'^ If there were no leakage, the over-all potential drop would be: ihdx=^i^b\ xdx = -^ (22) This value is also derivable directly from equation 2 1 by making r = 00 whence a = „. 2. (CASE n) BUS GROUNDED From equation 19 we have: fL L8 fL E, = I E^dx = u ^ T\ I sinh a xdx ^ Jo o cosh (aL) Jo E, ^"^ ]x = L x = „ "^ o^ cosh (oL) 20 Technologic Papers of the Bureau of Standards Dividing equation 23 by 22 we get as the ratio of the over-all potentials in the two cases : E^ tanh (aL) Ei'~ aL (24) This last result is, of course, deducible directly from equation 20, since if the ratio of the gradients at any point is constant through- 90 e^F -CT '^ L£ ya-TM OP L ^£ ■1 0Y£ <3AU. POT- TUTIA LS 7 / / / / jA - ■i.£A Mae C£ //I ■rtNn •£ 22) / / SO 7Q u5 B -Le/i •CAG£ eesi ^TANk :e >=7 wv£- '(0.4 '; B 'S U^ aeou •iDED / / / £; < SL \co& h(a J-/] E< >u.(i y 3 a VNh ^ai.) C -L£A <.(z i) ^ / '^ «. ishO ^0 -i.„ = 25- S-'O 00s a "an a / ^ 5-— "^ ZO to y '' ^ ^^ ^-'' '■' -^ c •*^ ^ ^ - — t 7 4 & / 3 / s 2 a ^ 4- £ e* s 2 b •« Length of Line in Thousands of Feet. Fig. 10 out the entire line the ratio of the over-all potentials must be equal to this constant ratio. The curves of Fig. 10 are plotted from equations 21, 22, and 23 and indicate the effect of the feec^g distances on over-all potentials. The reduction of over-all potentials due to leakage is relatively much greater in long lines than in short Knes and greater with grounded than with ungrotmded bus. For very long Hues and the moderate leakage and track resistance assumed in plot- ting these curves the over-all potentials are reduced in case of the ungrounded bus to about 40 per cent and in the case of the Leakage Currents 21 grounded bus to about 10 per cent of the values they would have if there were no leakage. If there be no leakage, the over-all potential drop is proportional to the first power of the track resistance and to the square of the feeding distance. If there is leakage and the bus is ungrounded, then, as either the track resistance or the feeding distance increases indefinitely, the over-all potential tends to become proportional to the square root of the track resistance and to the first power of the feeding distance. As the track resistance or the feeding distance increases indefi- nitely the over-all potential in the case of the grounded bus tends to become independent of both the track resistance and the feeding distance. VI. POTENTIAL DIFFERENCE BETWEEN TRACKS AND GROUND 1. (CASE I) BUS NOT GROUNDED di The intensity of current leakage at any point is equal to -3-I di and the potential difference between tracks and ground is r -7-I, r being as before the leakage resistance per unit length. From equation 6 we have diy . i^al cosh (a*) ■=lo dii dx dx ° sinh (at) ^1 _ . r al cosh (ax) "I x^*V sinh(aO J ^^5) The potential difference between tracks and ground is therefore „ dii . r al cosh (ax)~\ , ,. n'=^5^=4'--isrprj ('") The effects of leakage resistance and rail resistance on potential differences between tracks and the earth are shown by Figs. 1 1 and 12. If the bus is ungrounded, the intensity of the leakage current at the outer end of the Hne is less than at the power house 22 Technologic Papers of the Bureau of Standards end (current returning to the tracks may be regarded as negative leakage current) , and the difference is greater the lower the leakage resistance and the greater the rail resistance. It can be shown that the difference also increases with the length of track. Hence operating with the trolley negative would, in general, tend to reduce the rapidity with which trouble would become acute. The corrosion would, however, be distributed over a larger terri- tory and its total amount would be substantially unchanged. trrn T Ol eoA > B£. ' e£< ISTA. 'ce t W Pt TCN' •tAL I fjrfe* fS/'tCt s /6 f tso^-. ■> Bi 1 ec -OHf IS Pi -.B 7> •ous iNO t 'eET 7r» -ij- 1 '°- L)CO s^fA jc-;- £ 9t/-(S 6) / / / n iW/J 'aL.) s ^O.O IS 4-^ 5- L-2( } / V / e e A <♦> '4 / / //, '■■/ f y- / // / ^ y y^ ^ y ^ ^ x: ^ y^ .^ ■^ -2 — » -6 r= 0-/0 ^ ^ ■:.^^ ■^pf^ _- .-< ^ r^o 662 ^ --^ r=/- b Q Q /O /Z /^ Thousands of Feet from End of Line. Fig. II Although high leakage resistance lowers the leakage current and hence the danger from electrolysis, as is shown by Fig. 6, it also increases the potential difference between the tracks and the earth, and increases the size of the p^tive area as is shown by Fig. 1 1 . High potential differences are not in themselves, there- fore, a definite indication of leakage current, and they may even indicate good, rather than bad, electrolysis conditions, depending upon whether the high voltage is due to high roadbed resistance, high track resistance, or overloading of rails. This is shown by Fig. 12. Leakage Currents As the track resistance or the feeding distance increases indefi- nitely, the potential difference between the tracks and the ground at the power house becomes indefinitely large and the area of the positive zone becomes indefinitely small. This is shown in Fig. 12 and by equation 26 and less clearly in Fig. 2 where the point of maximum leakage — that is, the neutral zone — was seen to shift toward the power house with increasing values of o. Thus, with s to /e / TOF TJSAC OF T, /STA 7ACfr VC£- 7S f>. •JST/i 'Mi. L >/FF£- rfO F -E-r f^ ^ 1 B l/S c >v u / ^1 ^y' ^ ^ ^ / -2 ^^ ^^ ^ / 1 ,_^ >03 -— ^ ^ ^ y / Z--0. ^^ ^ y / / -a ■^ y / 10 "^ . ■ -^ ■^ 5 ^ £ > £ / 1 z 1 ■h / 6 / s Zo Thousands of Feet from End of Line. Fig. 12 high track resistance or long feeding distances there will be very severe trouble in a relatively small area. Long feeding distances, high track resistance, and low leakage resistance all tend to reduce the size of the positive area, although tending to increase the total amount of leakage current, and hence they greatly increase the severity of the electrolysis trouble near the power house. A relatively small positive area, there- fore, is an indication of bad electrolysis conditions generally. The length of the positive zone varies from a maximum of 42 per cent of the feeding distance under ideal electrolysis conditions (zero 24 Technologic Papers of the Bureau of Standards leakage) to an indefinitely small value where electrolysis condi- tions are particularly bad. This is indicated by Fig. 12. At the end of the line, where x = o, we get the maximum value of poten- tial difference which exists beyond the neutral point. Its value is n^'=^"^[^-s-EElk)] (^7) If either 6 or L is indefinitely increased, 11/ approaches as a limit the value ior. £f^£ z^ cr ce vcTV ' Of^ A AXit* Ufvl ^OT, -ftlT/. IL. C wyg> 'EHC ZS (q l) c ?sj7i 'ajJ^ (ai E^u.(2e) -^» ?-5- % o .2 *o /2 /« £0 2*- SB Length of Line in Thousands of Feet. FlO. 13 At the power house end of the line, where x=-L, the value of the potential difference is , 111 -V|^i sinh (aL) J' (28) Fig. 13 shows the variation in the maximum potential differ- ence between the track and the ground for various feeding dis- tances when the bus is not grounded. Three curves are given showing the effect of varying the track resistance. Leakage Currents 2. (CASE n) BUS GROUNDED From equation (13) we have cosh (c 25 dx Ix ~ 1' cosh {. ■•U3-t„r|^i cosh (aL) J- Ml aL)J (29) With the bus groxmded the potential difference at the power house is of course zero, and the increase in leakage current shown -1 -e -3 ~4 -S -6 -7 -e -9 f/rrc r OF ^tSACt AND l£Ak vse i t3«7 i^NCE PO'T. ■NT/A Oh L an Fsmt. NCCi r-7 e-AHA ■'TAN 3US ■> "1 f« U.C2 !) ^ s Cos t(aL 1 J \ ^> 2S .'-^ # ^// 4. ■? SO s f^ ''''^ y « r^ ^ / &. / / ^ ^ 'V / /' / ^ -0.; ee _ _- ^ :rr^ ;^ ^■^^ ^ ^ ^,-' V / / (K ._- .— 5 "^O.O 53" -^ ^ .'-' " V- ^'' /■ -^O:^ i — — ' ..,. .--• '" -^ y ^--^ ■' / u — 5^o7< S-T' ^^ ^ '' ^^ .- J^f ?-— -- r' ,^ — • -''' ______ 4=0. -:£^ r^ "< ) / 3 ■< s- 5 ' Th ' 6 ousa ndsc / fFe 1 ctfrc Fig f / mE . 14 nd fLin e. * / 7 / ff / in Fig. 7 indicates that the change in potential difference will also be most rapid in the region of the power house. Increasing either the roadbed or the track resistance increases the potential difference at the end of the Une, as is indicated by- Fig. 14. In this figure there are shown two sets of ctuves, one set in solid lines plotted for a constant value of track resistance of 0.005 ohm per 1000 feet and varying values of leakage resist- 26 Technologic Papers of the Bureau of Standards ance ranging from 0.286 to 0.667 ohm. The dotted curves show the effect of varying the track resistance from 0.003 to o.io ohm per 1000 feet with a constant leakage resistance of 0.4 ohm per 1000 feet. It will be observed that in this case leakage resist- ance is much more influential with respect to potential difference on the outer portions of the line than track resistance, a change in the leakage resistance in the ratio of 2.3 to i giving results of approximately the same order of magnitude as a change of 30 to I in the track resistance. At end of line where x=o, we have: n2'=io»' I - cosh {aL) (30) Here also for large values of 3 and L the potential difference approaches the limiting value of ior. VII. GENERAL EQUATIONS FOR LEAKAGE FROM ANY SECTION OF A TRACK NETV/ORK In this case both leakage resistance and track resistance may be discontinuous functions of the distance along tracks, and in general the bus will not be grotmded (Fig. 15). The differential equation for this case is derived in the same way as in case I and has the same form, the only difference in the solution being that in the present case the limits of the integration, instead of being throughout the line, are between the ends of the sections, the constants of the equation changing at each transition point. The equation for i, the current at any point in the n"* section from the outer end of line is j = Ae*n^ + 5e-»n^ (31) where x is the distance from the end|pf the line to any point in the w"" section xmder consideration. Applying this equation to the n*'' section where the limits of integration are Ln_i and L^ we have as the limiting conditions X = frn-l ^ ^^-'n-l X = /n i=In Leakage Currents 27 Substituting these limits in equation 31 and solving for A axidB, we get /„-, e^n (/^.,JJ -/„ ^ = e-n(2/^.^_y_g(an)(y /ne-/n'°-^>-/n-.e<'-'>(/n) Substituting these values of A and 5 in equation 3 1 , we get as the equation for the current in the tracks at any point within the «*'' section. . _ (In e-'KZn-i) - /n-1 e'^n Q g^r.^ - (J„ e^n (/„. J - /„,, g^^ /J g-,„x 2 Sinh (On) {In-ln-i) "^^ If there were no leakage within the n**" section, the current at any point X would be /n-i + t'n ix — l^-i). Hence the leakage current within the section up to any point x is il=In-i+in{x-ln-i)-i (SS) The value of i in this equation is given by equation 32. Equation 33 corresponds to equation 6 and furnishes a similar basis for the development of more general equations for leakage currents, gradients, potential differences, and over-all potentials when the track tmder consideration is made up of sections differing in weight of rail or in the construction of the roadbed. The equations already developed will serve, however, to show the general effect of variation in rail and leakage resistance. VIII. INTERPRETATION OF EQUATIONS An examination of the foregoing equations permits the follow- ing deductions in regard to the effect of track resistance, leakage resistance, and feeding distances, or on the current and voltage conditions in a uniformly loaded railway line. Most of these deductions have previously been set forth more in detail in con- nection with the discussion of the equations but are grouped and restated here for convenience. I. The voltage and current conditions in the return circuit are characterized by three constants, namely, the resistance of the 28 Technologic Papers of. the Bureau of Standards track per unit length, the leakage resistance between track and ground per unit length, and the feeding distance (equation 4 and following) . 2. The effect of track resistance on leakage currents is exactly the inverse of leakage resistance; hence an increase in leakage resistance in any given ratio reduces leakage currents in the same degree as increasing the conductance of the tracks in the same ratio. This emphasizes the importance from an electrolysis standpoint of so constructing the roadbed as to give the highest practicable leakage resistance (equation 6 and Fig. 2) . 3. The leakage current from any given line increases much faster than the length of the line (equation 6 and Fig. 3) . This shows the importance of reducing feeding distances as much as practicable. 4. Where the bus is not grounded there will be distinct positive and negative areas and the relative extent of the positive and negative areas is not a constant but varies with the length of the line, the track resistance, and the leakage resistance. 5. For short track lengths the percentage of the total current which leaks from the tracks increases practically as the square of the feeding distance (equation 9 and Fig. 4) . 6. For long feeding distances the rate of change of leakage current with distance is much less than for short feeding distances (equation 9 and Figs. 3 and 4). 7. The maximum leakage current increases less rapidly than the track resistance, except where the track resistance is very low (equation 9 and Fig. 5). 8. If the leakage resistance is small, such as that correspond- ing to an average concrete roadbed or track embedded in damp soil, the leakage current decreases very rapidly with increase in leakage resistance. For high values of leakage resistance, how- ever, the effect of increasing the leakfge resistance on the total leakage current is much less (equation 9 and Fig. 6) . 9. If the bus be grounded, as by connecting it to the buried pipe systems the total leakage current is greatly increased (equa- tions 9 and 13 and Fig. 7). Leakage Currents 29 10. With grounded bus the rate of increase in leakage current becomes relatively small as the power house is approached and becomes zero at the negative bus (equation 13 Fig. 7). 11. Where conditions are relatively good increase in leakage resistance has a greater effect in reducing leakage currents if the bus is grounded than when it is ungrounded (Fig. 7) . 12. When the conditions are such as to give rise to only mod- erate leakage currents, the maximum leakage may be more than doubled by grounding the negative bus (equation 13 and Fig. 7, curves III and III^. Where leakage conditions are bad the ratio of increase in leakage current due to grounding is less but the increase is still quite marked (Fig. 7, curves / and /j) . These cmves emphasize the importance of insulating the negative bus. 13. If the bus be grounded, the maximum leakage increases more rapidly than the feeding distance. For ordinary values of track resistance and leakage resistance this is particularly true for feeding distances up to about 15 000 or 16 000 feet (equation 16 and Fig. 8). 14. For very long feeding distances, such as are frequently encountered on interurban lines, practically all of the current may return by way of the earth (Fig. 8) . 15. Potential gradients in the tracks may be materially reduced due to leakage currents, and this reduction is more marked if the bus is grounded (equations 17, 18, and 19, and Fig. 9). Low potential gradients are not in themselves, therefore, a definite indication of good electrolysis conditions, but on the contrary may be due to excessive leakage of current from the tracks. Other factors must be considered, therefore, in interpreting gradient measurements. 16. For any given Une the relative value of the gradients for grounded and ungrounded bus is the same for all points on the line. For very long Hues the ratio varies practically inversely as the length of the line (equation 20) . 17. The reduction of over-all potentials due to leakage currents is relatively much greater in long lines than in short lines and greater with grounded bus than with ungrounded bus. For very long lines and the moderate leakage and track resistance assumed 30 Technologic Papers of the Bureau of Standards in plotting the curves of Fig. lo the over-all potentials are reduced in case of the ungrounded bus to about 20 per cent, and in case of the grounded bus to about 5 per cent of the values they would have if there were no leakage (equations 21, 22, and 23, and Fig. 10). It is evident, therefore, that low over-all potentials, like low potential gradients, are not a positive indication of good electrolysis conditions. It is necessary to know the cause of the low values before their significance can be determined. Certain measures, such as insulating tracks, that can be taken to reduce leakage currents may greatly increase both gradients and over-all potentials, although they would greatly improve electrolysis conditions. 18. If there be no leakage the over-all potential drop is pro- portional to the first power of the track resistance and to the square of the feeding distance (equation 22 and Fig. 10). 19. If there is leakage and the bus is ungrounded, then as either the track resistance or feeding distance increases indefi- nitely the over-all potential tends to become proportional to square root of the track resistance and the first power of the feeding distance (equation 21). 20. As the track resistance or feeding distance increases indefi- nitely the over-all potential, in the case of the grounded bus, tends to become independent of both the track resistance and feeding distance (equation 23 and Fig. 10). 21. If the bus is ungrounded, the intensity of the leakage cur- rent at the outer end of the line is less than at the power house end (current returning to the tracks may be regarded as negative leakage current); and the difference is greater the lower the leakage resistance and the greater the length. Hence, operating with trolley negative would, in general, tend to reduce the rapidity with which trouble would become acule. The corrosion would, however, be distributed over a larger territory and its total amount would be substantially unchanged (equation 26 and Fig. 11). 22. As the track resistance is increased indefinitely the poten- tial difference at the outer end of the line approaches a finite maximmn value which is ioS. A similar result follows from an indefinite increase in the feeding distance (equation 26). Leakage Currents 31 23. Although high leakage resistance lowers the leakage current, as shown by Fig. 16, it also increases the potential dijEEerence between tracks and earth. High potential differences are not in themselves, therefore, a definite indication of leakage current (equation 26 and Fig. 11). 24. As the track resistance or feeding distance increases indefi- nitely, the potential difference between tracks and ground at power house becomes indefinitely large, and the area of the posi- tive zone becomes indefinitely small. Thus, with high track resistance or long feeding distances there will be very severe trouble in a relatively small area (equation 26 and Fig. 12). 25. High track resistances and low leakage resistance both tend to reduce the size of the positive area, although tending to increase the total amount of leakage current, and hence they greatly increase the severity of the electroljrsis trouble near the power house. A relatively small positive area, therefore, is an indi- cation of bad electrolysis conditions generally. The length of the positive zone varies from a maximum of 42 per cent of the feeding distance under ideal electrolysis conditions to an indefi- nitely small value where electrolysis conditions are particularly bad (equations 8 and 26 and Fig. 12). 26. With the bus ungrotmded the potential difference at the power house is nearly proportional to the length of the line except for short lines (equation 28 and Fig. 13). 27. With the bus grounded the potential difference at the power house is zero and the change in potential difference is most rapid in the region of the power house. 28. Increase in either the roadbed or the track resistance increases the potential difference at the end of the line (equation 29 and Fig. 14). 29. Leakage resistance is much more influential with respect to potential differences than track resistance (equation 29 and Fig. 14) . Washington, September 8, 191 5. DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON, Director No. 72 INFLUENCE OF FREQUENCY OF ALTERNATING OR INFREQUENTLY REVERSED CURRENT ON ELECTROLYTIC CORROSION BY BURTON McCOLLUM, Electrical Engineer and G. H. AHLBORN, Assistant Physicist Bureau of Standards ISSUED AUGUST IS, 1916 WASHINGTON GOVERNMENT PRINTING OFFICE 1916 ADDITIONAL COPIES OF THIS PUBUCATION MAT BE PROCURED FROM THE SUPERINTEKDENT OF DOCUMENTS GOVERNMENT PRINTING OFFIcft WASHINGTON, D. C. AT 10 CENTS PER COPY A complete list of the Bureau's publications may be obtained free of charge on application to the Bureau of Standards, Washington, D. C, INFLUENCE OF FREQUENCY OF ALTERNATING OR INFREQUENTLY REVERSED CURRENT ON ELECTROLYTIC CORROSION By Burton McCoUum and G. H. Ahlbom CONTENTS p^g^ I. Introduction 4 1. Definition 4 2. Importance and scope of the present investigation 5 3- Work of previous investigators 6 4. Purpose of this paper 8 II. Discussion .* 8 i. Preliminary experiments on effect of circulation of electrolyte 8 2. Complete series of tests 12 (a) Arrangements 12 (6) Electrolyte 13 (c) Conditions of tests 14 (d) Chemicals 14 (e) Electrodes 14 (/) Frequency 15 (g) Ctxrrent density .' 15 (h) Length of run 16 (i) Accidental variables 16 (j) Cleaning electrodes 16 3. Equipment 17 (a) Current sources 17 (6) Commutating machine 17 (c) Resistance 17 (d) Current measurements 17 4. Correction and reduction factors 18 5. Accuracy of results '. 18 6. Description of each run 19 (o) Sixty-cycle tests 19 (6) Fifteen-cycle tests 19 (c) One-second period 19 (d) Six-second period 20 (e) One-minute period 20 (J) Ten-minute period 20 (g) One-hour period 20 (h) Forty-eight-hour period 20 (t) Weekly reversals 20 (j) Direct-current tests 21 3 4 Technologic Papers of the Bureau of Standards II. Discussion — Continued. Page 7. Discussion of results 21 (o) Indoor tests^Iron in normal soil 22 (6) Indoor tests — Iron electrodes in soil with sodium carbonate. ... 23 (c) Indoor tests — Lead electrodes in soil 24 (rf) Indoor tests — Lead electrodes in sodium carbonate 25 (e) Outdoor tests — Iron and lead electrodes in soil 26 8. Curves 27 9. Supplementary tests 28 III. Conclusions 30 INTRODUCTION This paper describes experimental work done to determine the coefficient of corrosion of iron and lead in soil with varying fre- quencies of alternating or reversed current with 60 cycles per second as the highest frequency and a two-week period as lowest, some direct-current tests being made as a check on the methods. The results show (i) that a decrease of corrosion occurs with an increase in frequency; (2) that there is a limiting frequency above which practically no corrosion occurs; (3) that the corro- sion is practically negligible below a five-minute period; (4) that certain chemicals affect the natural and electrolytic corrosion of the two metals quite differently; (5) that the loss of lead in soil on direct current is about 25 per cent of the theoretical loss; and (6) that alternating or reversed current with as long periods as a day or a week would in the case of iron materially reduce the damage to underground structures. The importance of these results grows out of the fact that there are large areas in practically every city in which the polarity of the underground pipes reverses with periods ranging from a few seconds to an hoiu: or more, due to the shifting of railway loads. The investigation shows that the corrosion under such conditions is much less than has generally been supposed. 1. DEFINITtoN The terms "electrolytic corrosion " and " electrolysis " have been used to designate corrosion caused by the discharge of electric currents which entered the metal from outside sotirces. In this paper the term " alternating-current electrolysis" applies not only to electrolysis from ordinary alternating ctirrents of commercial frequencies but also to alternating currents of much longer periods, such as several minutes or even a day or longer. Alternating currents of such long periods are very common on portions of underground pipe systems of practically every city, due to the continual shifting of railway loads which causes the pipes within Alternating Current Electrolysis 5 a large area, commonly called the neutral zone, to continually change their polarity with respect to the earth. In this paper the term " coefficient of corrosion " is frequently used in connection with the corrosion of an anode. This factor is the ratio of the actual corrosion observed to that which would have occurred if all of the electrode reactions' determined by Faraday's law had been in- volved solely in corroding the anode. Thus, if the theoretical corrosion in any case was 100 grams and the observed corrosion 46 grams, the "coefficient of corrosion" would be 0.46. This is sometimes called "efficiency of corrosion." 2. IMPORTANCE AND SCOPE OF THE PRESENT INVESTIGATION Since most of the electrolysis which occurs is due to stray cur- rents from electric railways, and since only a small percentage of these operate with alternating current, it might seem at first thought that altemating^current electrolysis is of rather infre- quent occurrence, and that the problems connected with it do not deserve much attention. However, in addition to the rail- ways which use alternating currents as motive power, such cur- rents often result as an incident of railway operation. These occur not only in the ordinary negative systems of railways men- tioned above, as the load shifts from point to point on the track with the movement of the cars, but they occur to a greater extent and in a much larger territory in the case of negative return systems in which insulated negative feeders are used. In such systems the potential differences between pipes and tracks can be greatly reduced, but this is accompanied by a large increase in the area of the so-called neutral zone, in which the polarity of the pipes is continually changing from positive to negative. With certain types of three-wire systems which are now being seriously considered in some places for the prevention of elec- trolysis, there will be large areas in which the polarity of the pipes will fluctuate between small positive and negative values. It has also been proposed that with the usual type of return that the trolley be made alternately positive and negative on succeeding days or weeks. All of these methods would have the effect of reversing the current flow on underground structures, and the period of the cycle would vary from a few seconds to a day or longer. Moreover, the frequent grounding of 60-cycle lighting circuits permits a certain amount of leakage from those systems, and the corrosion produced, especially in case of accidental grounds on other parts of the system, might be of considerable importance unless it is shown that alternating currents of such frequency do 6 Technologic Papers of the Bureau of Standards not give rise to serious corrosion. It is therefore of great practical importance to determine the extent to which periodically reversed currents of these long periods will produce corrosion on subsur- face metallic structures. 3. WORK OF PREVIOUS INVESTIGATORS A number of writers have advanced theories concerning laws governing alternating-current electrolysis and a considerable amount of experimental work has been done with frequencies of 25 to 60 cycles. One writer, discussing the phenomenon from the standpoint of the decomposition of the electrolyte/ arrives at cer- tain conclusions: (i) That the amount of chemical decomposition caused by alternating current is less than by direct current; (2) that it is proportional to the electrode current density; (3) that there is a limiting electrode current density below which no decom- position of the electrolyte occurs ; (4) that the quantity of corrosion decreases with an increase in the frequency of alternations, and that there is a limiting rapidity of alternation above which there is no decomposition. Conclusions (i) and (4) seem borne out by the experimental work described later. With reference to the dynamic characteristics of electrolytic cells, several writers have determined by experimental work,' chiefly with the oscillograph, that such cells affect the wave form. As one writer states, the chemical polarization in the cell causes it to behave as a variable condenser with a resistance in parallel and in series. With a very special set of conditions one experimenter ' has noted an amount of corrosion of the electrodes varying from zero to 35 per cent, with 60-cycle current, and he arrives at the conclu- sion that the corrosion is practically independent of the current density of the electrodes and temperature; and also that stirring of the solution has no effect. He s1<|tes that the corrosion does depend on the condition of the electrode surface, but does not attempt to state the principle of this variation. Experiments of more practical importance to the engineering world were conducted in 1905.* Twenty-five-cycle current was impressed on iron and lead pipes buried in soil and it was found 1 Dr. Guglielmo Mengarini, Electrical Worid, vol. i8, No. 6, p. 96; Aug. 8, 1891. 2 D. Ruchinstein. Electrolysis witli Alternating Current Dynamic Characteristic of an Electrolytic Cell. Zeitschriftfiir Electrochemie; Dec. i, i909;M. LeBlanc. The emf's of Polarization and Their Meas- urement by the Oscillograph. Deut. Bunsen Geselschaft, No. 3. Alternating Current Electrolysis Use of Oscillograph in Connection with Polarization. Zeitschrift fiir Electrochemie, 11, p. 707: 1905. ' G. R. White. Alternating Current Electrolysis with Cadmium Electrodes. * S. M. Eintner. Altemating-Cmrent Electrolysis, Electric Journal, vol. 2, p. 668; 1905. Alternating Current Electrolysis 7 that the corrosion was practically the same as that due to the soil alone. No figures of exact losses are given. Alternating current of 2 5 -cycle frequency was impressed on lead and iron plates in salt solution and direct current was impressed on other plates in a similar electrolyte, and it was found that the loss was negligible for the alternating current and very large for the direct current. Only a year or so later a large number of tests were conducted with 25-cycle, 60-cycle, and direct current on iron and lead plates.' The conditions were varied by using different soils, salts added to soils, varying the temperature and current density. The results show that although there is quite a large variation in the loss with different specimens and that the 25-cycle losses are uniformly greater than the 60-cycle losses, these losses never exceed i per cent under normal temperature conditions. The writer notes that some salts — ^for example, carbonates and alkaline compounds — reduce the electrolytic corrosion of lead plates. He found that an increase of temperattire to 40° C increases the corrosion to about I per cent. His final conclusions are that alternating- current electrolysis is more irregular than direct-cturent electrol- ysis; that nitrates increase corrosion and carbonates generally decrease it, but that the effect is not great enough to be of practical use for protecting lead cables; that lead is more attacked than iron} that the current density does not appreciably affect corro- sion except indirectly by increase of temperature; and that the corrosion increases with a decrease in frequency. He attempts to protect lead specimens by making them negative either by con- necting them to a zinc plate or with a small direct current, and finds that the loss is considerably less than with the alternating current alone. He finds that a current of i per cent of the value of the alternating current is sufficient to give practically complete protection, the corrosion in some instances being less than that due to natttral corrosion alone. It will be noted in the above experimental work that the different variables employed, such as current density, chemicals, temperature, etc., do change the action of alternating current, but that in practically no case did the losses exceed i per cent. When we consider the large variation of the electrochemical loss produced by direct current under identical conditions, it is evident that differences obtained between 25 and 60 cycle current are practically negligible. ' J. 1,. R. Hayden, Alternating-Current Electrolysis, Trans., A. I. E- E-, vol. 26, Part I, p. 201. 8 Technologic Papers of the Bureau of Standards Larsen has conducted some experiments on the corrosion effect of reversed currents of very long period using periods of two hours ajid two days. He found a marked reduction in corrosion, especially on the two-hour period. Prior to the present investi- gation, however, there have been no published results of tests on reversed currents of periods ranging from a few cycles per second to ten or fifteen minutes per cycle, a range of great practical importance in connection with the electrolysis of underground pipes and cables, as pointed out above. 4. PURPOSE OF THIS PAPER The data discussed in this paper were obtained as a part of the general investigation of electrolysis conducted by the Biu-eau of Standards. Its object is not to determine the laws which govern electrolytic corrosion at any one frequency, but to take a standard set of conditions approaching as nearly as possible those existing in practice; that is, wrought iron pipes and lead sheaths imbedded in soil and to determine the corrosion which will occm- in the range of frequencies mentioned above, namely, for frequencies ranging from 60 cycles per second to a week or more per cycle. These data will be of material assistance in determining the effectiveness of many of the proposed systems of electrolysis mitigation. II. DISCUSSION 1. PRELIMINARY EXPERIMENTS ON EFFECT OF dRCULATION OF ELECTROLYTE Before beginning the more complete series of tests to determine the effect of change in frequency a number of preliminary experi- ments were carried out in order to throw light on certain theo- retical aspects of the question under consideration. Theoretical considerations led to the belief that the corrosion of frequently reversed currents would be materiallytincreased by rapid circula- tion of the electrolyte and diminished by conditions which tended to restrict such circulation. If this were true, it was reasoned that in the case of metals buried in soils, in which the circulation of electrolyte is greatly restricted, relatively little corrosion would occur even with periodically reversed currents of long period. Accordingly, a number of experiments were carried out to deter- mine the effect of circulation of the electrolyte on the coefficient of corrosion. Alternating Current Electrolysis A set of four cells with wrought-iron electrodes and a i per cent NaCl solution as the electrolyte were connected in series on 60- cycle current. The electrolyte in cell No. i (see Fig. i) was stirred by a small turbine and in No. 2 the electrolyte was undisturbed; in No. 3 the lectrodes were wrapped with filter paper; and in No. 4 the electrolyte was prevented from mechanical circulation by gelatin. Iron electrodes, which were carefully weighed, were con- nected in the circuits and the current was maratained at about a half ampere for nearly 200 hours. At the end of the run the elec- trodes were again weighed and the loss determined by difference from the initial weight. Based on the theoretical loss.which would have been about 100 grams, the coefficients of corrosion (see Table 5 -- .0-^°^ 'l%NaCI5ol. r/oNaCISol.. IXNaCI5ol. 1% NaCl Sol. Thickened with Celatine Filter Paper Wrapping Quiet Stirred Fig. I. — First arrangement for testing effect of convection on electrolytic corrosion i) are 0.0034 for the stirred electrolyte; 0.002 in the stationary solution; 0.0009 when protected by filter paper; and 0.0007 in the gelatin. It seems evident that the chemical action is not as re- versible when the electrolyte is in motion about the electrodes as when stationary. In order to determine this effect, more exactly a single cell was connected, as shown in Fig. 2. Here there were two electrodes with no current impressed to determine the natural corrosion and two serving as current electrodes. One-of these was in the electrolyte stirred by the turbine and the other was wrapped in filter paper and buried in sand saturated with the solution. After correcting for the natural corrosion it was found' that the coefficient of corrosion was 0.0004 for the upper electrode and o.oooi for the lower. The results are shown in Table i . 34822°— 16 2 lo Technologic Papers of the Bureau of Standards TABLE 1 Effects Due to Variations in the Circulation of the Electrolyte [Siity-cycle cunent; wrought-iron electrodes; 1 per cent NaCl solution electrolyte] State of electrolyte Total corrosion Coefficient of corrosion Stirred Stationary Filter pajier separation . Gelatin Stirred Sand saturated Grams 0.344 .202 .088 .074 .065 .016 Amp.'hours 96 96 96 96 160 160 0. 0034 .0020 .0009 .0007 .0004 .0001 Stirring Turtlne Water Level "o Curren-I- Supply Sand Level Fig. 2. — Second arrangement for testing effect of convection on electrolytic corrosion « The same type of cell was operated on 20-cycle alternating current with the losses as shown in Table 2. TABLE 2 Effects due to Variation in the Circulation of the Electrolyte [Twenty-cycle current; wrought-iron electrodes; 1 per cent NaCI solution electrolyte] State of electrolyte Total corrosion Current Coefficient of corro- sion Stirred Sand saturaCsd . i Grams 0.079 .009 Amp.-hrs. 144.4 144.4 0. 0005 . 00006 Alternating Current Electrolysis II It will be noted that the corrosion is substantially negligible as in the case of 60 cycles under the same conditions. The same type of cell was placed in a direct-ctirrent circuit, which was reversed every 24 hours. As might be expected, the losses were very much greater as shown by Table 3, although the number of ampere-hours was considerably less than that used in the previous experiments. TABLE 3 Effects due to Variation in the Circulation of the Electrolyte [Twenty-lour-hour reversals; wrought-iron electrodes; 1 per cent NaCl solution electrolyte] State of electrolyte Electro- lytic corro- sion Current CoefflcienJ of corro- sion Stirred Sand saturated. Grams 45.45 32.45 Amp.-hrs. 97.1 97.1 0.45 .32 The electrode stirrounded by the moving solution had a loss corresponding to a coefficient of corrosion of 0.45, while the other gave 0.32, the difference due to stirring thus being even more evident on the slow reversals than on the high frequencies. If only the current discharged by each electrode as anode were considered, the coefficient of corrosion in the stirred solution was 0.90, and that in the confined electrolyte was 64 per cent. The foregoing results show that the free circulation of the elec- trolyte has a pronounced effect on the coefficient of corrosion, and that this effect is greater the lower the frequency of alternation of the current. They show that the low corrosion coefficient on alternating current is not determined solely by the speed of the reactions and the frequency of alternations. A more probable explanation is that the corrosion during any half cycle in which the electrode is anode takes place nearly in accordance with Fara- day's law, as in the case of direct current, but that during the succeeding half cycle when the electrode is cathode a large part of the corroded metal is electroplated back on the electrode. The increased corrosion due to circulation of the electrolyte would be expected under this theory, since the convection cturrents in the liquid would carry away from the electrode surface a part of the metal that has been corroded during the half of the cycle when the electrode is anode, thus preventing as complete a redeposition during the succeeding half cycle as would otherwise occur. In particular these convection currents in the electrolyte would bring 12 Technologic Papers of the Bureau of Standards into contact with the metallic ions, oxygen or other chemicals which would tend to form insoluble compounds, thus rendering the corrosive process irreversible. Accepting the above theory we would expect that in the case of iron or lead buried in soils, in which circulation of the electrolyte is greatly restricted, the corrosive process would be in large degree reversible even with much longer periods of reversal than in the case of liquid electrolytes, and it seemed possible that this con- dition might prevail even where the period of the cycle is several Leads Protected with GlassTubes Soil Level Electrodes Glass Cylinder' OpenTop Pilot Specimen Sera. Square Fig. 3, — Arrangement of electrodes and check specimen in A. C. electrolysis tests minutes or longer, as in the case of the polarity of buried pipes in many localities as mentioned above. This was found to be actually the case, as the following-described experiments show. 2. COMPLETE SERIES OF TESTS (o) Arrangements. — With the results of the above experiments in view, a more complete series of tests was planned. Since there is considerable variation among individual specimens, it was recognized that quite a number of specimens tmder each frequency Alternating Current Electrolysis 13 would be necessary in order to get a fair average. The specimens were arranged in cells having two current-carrying electrodes and one specimen subjected only to soil corrosion, this specimen being protected from the flow of cturent by a glass cylinder, as shown in Fig. 3. In a few cases the effect of adding sodium carbonate to the soil was studied. For convenience, the greater part of the tests were made in jars in the laboratory, but a number were made in specimens buried in soil out of doors, in order to check the results obtained in the laboratory. The agreement between the results under the two conditions was found to be satisfactory. The entire series is outlined in Table 4 below. TABLE 4 Summary of Tests (a) DIMENSIONS OF ELECTRODES Electrodes Indoor Outdoor cm 5 by 5 by 0.5 5 by 5 by 0.2 cm 20 by 20 by 0. 2 15 by 15 by 0. 4 Lead (b) FREQUENCIES USED AND NUMBER OF SPECIMENS USED FOR BOTH IRON AND LEAD Frequency of reversal Number of indoor specimens Natural BOU Soil with NaiCOa Outdoor tests 60 cycles per second.. IS cycles per second.. 1-second cycle 6-second cycle 1-mlnute cycle 5-minute cycle 10-mlnute cycle 1-hour cycle 2-daycycle 2-week cycle Direct current 3 large; iron only. 3 large; iron only. 18 18 Total.. 9 large. Grand total Jor Iron 297 Grand total for lead 291 Grand total for all tests 588 (6) Electrolyte. — In determining the coefficient of corrosion with different frequencies of current reversal it is desirable to simulate operating conditions as nearly as is feasible in a complete 14 Technologic Papers of the Bureau of Standards and general test. For this reason soil was selected as the elec- trolytic medium rather than water, which contains the soluble constituents found to exist in soil by chemical analysis. Condi- tions of circulation of the electrolyte and the electrolytic transfer in it are very different than in soil. The soil used was natural soil near the Bureau of Standards, a light clay having a resistance of 8000 ohms per centimeter cube at approximate saturation. It will support a good vegetable growth and is a fairly normal soil. Soil from the same locality was used in the experiments described in a previous Bureau of Standards' report" and a coefficient of corrosion of 100 obtained on iron at a definite current density. (c) Conditions of the Tests. — Some of the tests were run in the soil out of doors with natural drainage and aeration. Although it was considered very desirable to make a number of such tests, to run a complete series in outside soil would have been very difficult on account of interference by weather, difficulty of get- ting electrical connections to many electrolytic cells, and especi- ally the insulating of the various sets from each other, which would be necessary in order to determine the cmrent actually entering or leaving each specimen. The cells used in the inside laboratory tests were i gallon (3.8 liters) earthenware jars filled with soil to about 3 cm from the top (about 3 kg) , kept practically saturated by adding a quantity of distilled water every day. The tops were left open that evaporation and aeration might go on in a normal way. {d) Chemicals. — Since some soils vary widely in chemical con- stituents, and these may have a pronounced effect on the rate of corrosion, it seems desirable to vary those constituents in the soil which may be expected to affect the corrosion. As indicated by preliminary tests, sodium carbonate (Na2C03) has a very con- siderable effect on the electrolytic corrosion of both iron and lead; moreover, sodium is a common elem^pt in soil, as are carbonates, and this combination is quite soluble, which makes it a satisfac- tory compound to use in the soil, 0.5 per cent being added to certain cells, as shown in Table 4. (e) Electrodes. — Since iron and lead are the two metals com- monly serving as tmdergroimd electrical conductors exposed to soil they were selected as the materials for specimens in these tests. The above-mentioned report shows that the corrosion of different kinds of iron does not differ by large percentages under the con- ditions of these tests, and since "American iron," which is Besse- SMcCoUum and Logan, Electrolytic Corrosion of Iron in Soils, Technologic Paper No. 23. Alternating Current Electrolysis 15 mer-process steel, is obtainable in convenient form, it was adopted. This material was fine-grained and quite pm-e, having about one- tenth per cent carbon and no slag. The lead was conmiercially pxure and on analysis was found to contain traces of tin or anti- mony. Indoor specimens were 5 by 5 cm square, the iron being about 0.5 cm thick and the lead 0.2 cm thipk. The outdoor iron specimens were 20 cm square and about 0.2 cm thick. The mill scale and oxide left on the materials in the process of manufacture was not removed, since it was felt that with alter- nating current the siurface might affect the corrosion considerably more than with direct current. The leading-in wire was soldered to a comer of each specimen and a number stamped on the same comer. It was then weighed and a glass tube put over the lead and the tube was then sealed with pitch and the lead attachment and number covered with the same material. This type of con- nection failed in very few instances, due to corrosion, and the tube and pitch were easily removed with toluol before the speci- men was reweighed. (/) Frequency. — In determining the frequency of reversal of current two things must be considered : First, the frequencies fotmd in practice; and, second, the completeness of the series, so that a suitable curve could be obtained showing the relation between the corrosion coefficients and the frequency of reversal of current. The standard lighting frequency 60 cycles is available, and 15 cycle was adopted as about the lowest frequency proposed for power work. To obtain the slow reversals a reversing commu- tator machine was built which is described in detail later. It gave periods of i second, 6 seconds, i minute, 5 minutes, 10 min- utes, and I hour. The short periods of reversal were adopted because reversals of polarity of such frequencies commonly occtir in the usual operation of a street-railway system as pointed out above. Daily and weekly reversals and direct-current tests were also made. The direct-current specimens serve as a check on the theoretical coefficient of corrosion. (g) Current Density. — The density of the current flowing to or from the plates was intended to be such as to produce approximately 1 .00 as the coefficient of corrosion with direct-current electrolysis. This is shown in Technologic Paper No. 25 of the Bureau of Standards above referred to, to be about 0.5 miUiampere per square centimeter for iron, and approximately this value was used on both the indoor and outdoor specimens. 1 6 Technologic Papers of the Bureau of Standards (h) Length of Run. — The tests were continued until enough effect was produced to permit of accurate determination of the differences in weight of the specimens before and after test. It was also intended that one of the tests should be continued until a state of equilibrium was reached in the cell; that is, tmtil the rate of corrosion was not changing rapidly as might be the case during the first few cycles of current. Moreover, the cells should not be nm to an exhaustion of the soluble chemicals, their con- centration being probably closely related to the amoimt and rate of corrosion occurring on the electrodes. Since the current density is the same in all cases, this rate will depend on the frequency of reversal, and since the coefficient of corrosion is less on the higher frequencies, these must run fully as long as the lower frequencies in order to obtain sufficient weight differences. A period of 15 to 20 days has been found to produce sufficient differences in weight, and no indication that the composition of the soil except that very close to the electrodes had been changed decidedly. (i) Accidental Variables. — Other possible variables that have received attention during the experiments were maintained as nearly constant as possible. The temperature did not vary widely from 20°, there being very little heating by the current at the voltage and current density used. The depth was main- tained about ID cm below the surface in the indoor tests and about 40 cm in those outside the laboratory. (y) Cleaning Electrodes. — ^After each run was completed it was necessary to remove the end products of the corrosion process, and since they adhered firmly in some cases special methods were necessary. Iron specimens were cleaned by making them cathode on a 10-volt circuit in a 2 per cent sulphuric acid solution, as described in Technologic Paper No. 25 of the Bureau of Standards. This was found to be very effective and did not attack the iron enough to show on the balances used. The lead specimens were cleaned by immersing them in a solunon containing 5 per cent oxalic acid and i X per cent of nitric acid. The corrosion products became lead oxalate — a white flocculent substance which was easily removed by brushing. It was found in some cases where the amount of corrosion was large and adhered very firmly that this process was very slow and did not remove the corroded prod- ucts entirely. Unoxidized specimens weighed before and after immersion in this lead-cleaning solution were found to have lost less than 5 milligrams, the limit of the balances used. Alternating Cxwreni Electrolysis 17 3. EQUIPMENT (a) Current Sources. — Sixty-cycle current was obtained from the city power mains while the 15-cycle current came from a small inverted rotary converter. Transformers were used in both circuits to raise the voltage so that a number of cells could be operated in series and so that the primary side would be clear of ground. For the slower reversals of current on the indoor tests power was obtained from the regular three-wire lighting bus bar and commutated by the machine described below. For the outdoor tests for slower reversals and for direct current a small motor-generator set was used. A no-current indicator was used on the alternating-current circuits while a recorder showed what had occurred on the direct-current circuit and those of long period at all times. (6) Commutating Machine. — The commutating machine through which the intermediate frequencies were obtained consisted of a series of six commutators each having four brushes and two equal semicircular commutator segments, giving two complete cycles per revolution, driven by gears having such ratios that with the first or highest speed commutator rotating once in two seconds the succeeding commutators made complete current cycles in 6 seconds, i minute, 5 minutes, 10 minutes, and i homr. This machine was driven by a constant-speed motor. (c) Resistance. — In order to obtain the correct current density discharged from the electrodes the resistance of the circuits had to be varied. This was done in part by placing cells in series in groups and paralleling these groups. Rheostats or timgsten lamps were then used to get final adjustments, but no great effort was made to keep the current discharge at exactly 0.5 milliamperes per square centimeter since a small variation in current density does not affect the rate of corrosion. Tungsten lamps with their high positive temperattire coefficient are very satisfactory for use in such circuits, since within a certain range they tend to auto- matically maintain the current at a constant value. (d) Current Measurements. — Observations of cm-rent were made every day, and more frequently when the current values were changing appreciably. A standard milammeter having a resist- ance of 0.34 ohm was used for all frequencies above one second. For alternating-current measurements a thermoammeter consist- ing of a heating element, thermocouple, and millivoltmeter was used. The resistance of this meter amounted to about 7 ohms 1 8 Technologic Papers of the Bureau of Standards and was noninductive. When this meter was introduced in circuits, the effect on the current flow was negligible because of the high resistance of the circuits and it was very easy to correct for this small noninductive resistance by inserting an equal amoimt in each circuit when the meter was not in use. This meter was used to measure larger currents in the outdoor specimens by means of a shimt. A suitable ampere-hour meter was not available. > 4. CORRECTION AND REDUCTION FACTORS Since chemical corrosion, according to Faraday's law, is propor- tional to the average cturent flowing, and since all alternating- current values as observed are effective values rather than average, the current flow has been corrected by dividing the same by i . 1 1 , the ratio between effective and average values of sine-wave cur- rent. Since the current flowing with the longer time reversals is controlled by a commutating machine or switch the wave is flat- topped and no such correction is necessary. However, the cur- rent was off when controlled by the commutating machine 6 or 7 per cent of the time and this correction was applied to all such values. In order to correct any error due to a possible difference in the length of succeeding one-half cycles, the connections to the commutator controlling each test were reversed at regular inter- vals, e. g., the I -second commutator was reversed through the 10- minute commutator and the i-hour one by a switch every 24 hoin-s. In calculating the theoretical amount of corrosion, the corrosion products of both iron and lead were taken to be divalent and the quantity corroded per ampere-hour is then i .04 grams for iron and 3.86 grams for lead. 5. ACCURACY OF RESULTS The accuracy which can be obtained in corrosion experiments of this kind is limited by a numbei of factors: First, the con- sistency of the corrosion action itself, which it has been found may vary within wide limits under apparently similar conditions; and second, the limits of measurement. The electrical measure- ments are correct to about i per cent while the time meastirements are not in error more than a half per cent. The error due to weighing of single specimens was small, since it was carried to the fourth or fifth place, but in some cases the losses were small and this difference was correct to only the second or third place. This is true of practically all pilot specimens which were subjected only to natural corrosion. Therefore it is evident that the accu- Alternating Current Electrolysis 19 racy of the results is greater when the amount of corrosion is large. The combined accuracy of all measurements was much greater than the consistency to be expected in the corrosive processes. 6. DESCRIPTION OF EACH RUN The above description of the general condition of the tests is intended to apply to all the following data, and it will be necessary to describe each run only very briefly, deferring until later the presentation of the results. (a) Sixty-Cycle Tests. — ^The 60-cycle tests were nm with both iron and lead specimens for the indoor tests and iron for the out- door tests. Both natural soil and soil with 0.5 per cent sodium carbonate added were used for the indoor tests. It will be noted from the tables presented below in this as well as in other runs that the natural corrosion losses have been rather large on the iron pilot specimens. This is due to the fact that the mill scale was not removed from these specimens before the tests were started and that the cleaning process removed this scale as well as the oxide that was formed during the test. This rather obsctires the comparative effect of natural soil and sodium carbonate, but it is still evident, as in the earlier tests, that the natural corrosion loss of iron is greater in nattual soil while the electrolytic corro- sion is greater in the chemical soil. In fact, in almost every instance the natural loss was greater than the electrolytic loss in the natufal soil, and in 5 of the 1 2 specimens also in the chemical soil. With the three large specimens used in the outdoor tests the natural loss was considerably less than the electrolytic loss, and the coefficient of corrosion is only slightly less than i per cent. (b) Fifteen-Cycle Tests. — The 15-cycle tests were run with lead and iron in soil only, these cells being in series with about 310 volts, giving about 25 volts per cell. In every case except four iron electrodes the electrolytic losses were all greater than the natural corrosion in the same cells. (c) One-Second Period. — Iron and lead specimens in both nor- mal soil and soil with sodium carbonate were used in the tests with I -second period, the cells being divided into four groups of three each in series. In two cases the iron electrodes lost more than the pilot specimens, but on the average the losses were greater than in the preceding tests. Iron specimens were placed in outdoor soil for these tests, and in this instance the natural corrosion is un- usually high because the specimens were left in the ground without current for a considerable time. 20 Technologic Papers of the Bureau of Standards {d) Six-Second Period. — ^Normal soil alone was used in these tests, there being three groups of cells and four cells in each group. Approximately 12.5 volts existed across each cell in order to main- tain the current at about 30 milliamperes or 0.5 milliampere per square centimeter. (e) One-Minute Period. — In the one-minute reversals iron and lead electrodes were used in natural soil connected in three groups of four cells each. Approximately 9 volts were maintained across the cells containing the iron electrodes and 14 volts on the lead electrodes. In case of the iron electrodes there was a consistently greater loss on the odd electrode than on the even, the reason for which is not altogether evident since no such consistency exists on the lead specimens; and as the two sets were in series, it is therefore not due to unbalanced or unequal half cycles. (/) Ten-Minute Period. — Both iron and lead specimens in natural soil and soil containing sodium carbonate were used in the lo-minute period tests. The cells were divided into four groups of six each. It will be noted that the corrosion of iron in natural soil is here greater than in the chemical soil, and the reverse is the case with the lead specimens. {g) One-Hour Period. — Only natural soil was used in the one- hour reversals, about 15 volts being impressed on each pair of electrodes. {h) Forty-Eight-Hour Period. — Natural soil alone was used in the daily reversals (48-hour period) with iron and lead electrodes, the entire set being in series on 240 volts. The iron specimens had a voltage of about 15 volts on each pair and the lead electrodes about 13 volts. In the case of the iron specimens, the odd and even specimens, or those anode first or anode last in the test show no great or consistent difference as was noted in the preliminary tests, and the lead specimens show an opposite effect from that noted at that time; that is, the electrons which were anode dur- ing the first half cycle have lost more than those which were cathode initially. (i) Weekly Reversals. — Both natural soil and soil containing sodium carbonate were used in the weekly reversals (two-week period) and the entire set was connected in series on 240 volts. The voltage across the iron specimen cells in the natural soil was about 15 volts per cell and about 9 volts in the chemical soil. With the lead electrodes the average voltage was less than 12 across each cell in the natural soil and less ihan 4 in the chemical soil. Alternating Current Electrolysis 21 {j) Direct-Current Tests.- — The direct-current tests were carried on with iron and lead specimens both indoors and outdoors, and in the indoor tests with sodium carbonate in the soil as well as natural soil. The indoor cells were connected in fom- groups of six each with 230 volts impressed on them. The ampere-hours varied in the different groups from 8 to 12. With the iron speci- mens the anode losses are large, the coefficient of corrosion being approximate unity, while the cathode specimens lost less than the pilot specimens, evidently because of the protective effect of the current. In the lead specimens, however, the anode losses are far below what might be theoretically expected, while the cathodes lost less in the natural soil than the pilot specimens, but more in the soil containing sodium carbonate. This is due not so much to an increased electrolytic loss in the chemical soil, but to a greatly decreased natural loss. Since the loss in the lead specimens was so much less than might be expected, another set was run under practically the same conditions but with the current maintained more closely at 0.5 milliampere per square centimeter. These results, however, corroborate the work previously done. The outdoor tests were conducted on both lead and iron with the large plates mentioned above. The protective effect of the current is noted again on the iron specimens. In the lead specimens 12 anodes were used, the lead in this case being sections of lead- sheath cable, 6 of which contained about i per cent antimony while the other 6 contained only traces of tin and antimony. Two pilot specimens of each composition were used. These tests fmther corroborated the results of the indoor tests in that the coefficient of corrosion of lead on direct ciurent was low. 7. DISCUSSION OF RESULTS Tables containing the summary of the results of the above- mentioned tests are given below. These tables are arranged in halves with losses in grams above and the coefficient of corrosion below with the frequency or period of reversal in the first column, the average loss of six specimens in each of the three succeeding colunms (the first being the odd numbered electrodes and the second the even numbered electrodes and the third the pilot specimens). From these are calculated the electrolytic loss of odd or even electrodes shown in the fifth and sixth columns, and the seventh column contains the average electrolytic loss of all electrodes. Below the frequency is repeated and the next column contains the average quantity of electricity in ampere-hours flow- 22 Technologic Papers of the Bureau of Standards ing through the specimens. Following this are four columns giving the coefficient of corrosion. The coefficients of corrosion of the odd electrodes and even electrodes are first given, then the coefiicient of corrosion based on one-half the current or that while each electrode was positive, and last that based on the average loss and the total current through the cells. Since it is difiicult to draw any conclusions from the electrode losses shown without also considering the ampere-hours, the coefficients of corrosion will give us the best idea of results, and these are shown in both the tables and curves. (a) Indoor Tests — Iron in Normal Soil. — In Table 5 a summary of the results obtained using iron electrodes in indoor cells con- taining normal soil is given. TABLE 5 Summary of Alternating Current Electrolysis Tests — I [Variable, frequency of reversal; indoor tests; iron electrodes; soil electrolyte] Period of cycle Total loss Odd elec- trodes Even elec- trodes Pilot Electrolytic loss Odd elec- trodes Even elec- trodes Average 60-cycle 15-cycle 1-second 6-second l-minute 5-minute lO-minute 1-hour 2-day 2-week Direct-current. Grams 1.480 1.036 1.064 .960 2.024 1.907 2.522 3.134 5.490 8.349 9.697 Grains 1.289 .862 1.190 1.046 2.077 1.398 2.252 2.941 5.124 9.680 .139 Grams 1.645 .834 .640 .566 1.203 .748 .901 1.165 1.130 1.387 1.023 Grams -0. 165 + .202 .424 .394 .821 1.159 1.621 1.969 4.360 6.962 8.674 Grams -0. 356 + .028 .550 .480 .874 .650 1.351 1.775 3.994 8.293 Grams -0. 261 + .115 .488 .437 .848 .904 1.486 1.872 4.177 7.627 Period of cycle CoefQcient of corrosion Current dischargil (amp.^ Odd hours) elec- trodes Even elec- trodes On basis of anodic current On basis of total current 60-cycle 15-cycle 1-second 6-second 1-miaute 5-minute 10-nlinute 1-hour 2-day 2-week Direct-current 16.05 13.32 17.99 16.83 19.25 19.99 16.48 18.40 27.22 23.17 9.82 -0. 0198 + . 0292 .045 .045 .082 .111 .189 .206 .308 .58 .85 -0. 043 I- .0004 .059 .055 .087 .063 .158 .186 .282 .69 -0. 031 + .016 .046 .050 .084 .087 .173 .197 .295 .633 -0. 0156 -I- .008 .023 .025 .042 .043 .087 .098 .148 .316 .850 Alternating Current Electrolysis 23 As mentioned earlier, it will be seen that the pilot-specimen loss is quite large and that there is considerable variation under the different frequencies. This is evidently a real variation due to a difference in soil action, because it was found that in individual cases when the pilot-specimen corrosion varied considerably from the average the ctuxent-carrying electrodes would also vary in the same direction. The coefficient of corrosion only in the case of the 6o-cycle tests is negative. The electrodes were numbered consecutively, an odd number and a succeeding even number being grouped in each cell. The difference in the coefficient of corrosion between the odd and even electrodes is rather large in some cases; for example, in the 5-minute specimens the coeffi- cient is o. 1 1 6 for the odd electrodes and only 0.065 for the even, and in the 15-cycle test the per cent discrepancy is large, although the values in grams do not differ greatly. The direct-current test shows a coefficient of only 0.85, which is rather low, and this can only be explained as being probably due to the effect of the iron oxide serving as a protection rather than accelerating the corrosion. The next to the last column is simply double the one succeeding or an average of the odd and even electrode coefficients. (b) Indoor Tests — ^Iron Electrodes in Soil with Sodium Carbon- ate. — In Table 6, containing the results on iron electrodes in sodium carbonate soil, it will be noted that in the case of the 6o-cycle run the coefficient of corrosion is positive but that the values in the other cases of reverse currents are smaller than in the natural soil. In the 2-week test the odd-electrode loss is considerably less than the even, supporting the theory that in these longer time reversals the electrodes which are positive last suffer the greater loss. Under these conditions the direct-current loss is verv nearly 100 per cent. TABLE 6 Summary of Alternating Current Electrolysis Tests — II [Variable, frequency of reversal; Indoor tests; iron electrodes; soil and sodium carbonate electrolyte] Total loss Electrolytic loss Period oi cycle Odd elec- trodes Even elec- trodes Pilot Odd elec- trodes Even elec- trodes Average 60-cycIe .... Grams 1.390 .865 1.617 7.922 10. 423 Grams 1.373 1.146 1.532 9.081 .172 Grams 1.199 .677 .835 1.636 .819 Grams +0. 191 .188 .782 6.286 9.604 Grams 0.174 .469 .679 7.451 Grams +0. 182 10-minute 739 24 Technologic Papers of the Bureau of Standards TABLE 6— Continued Summary of Alternating Current Electrolysis Tests — tl — Continued Current dis- charge (amp, hours) Coefficient of corrosion Period of cycle Odd elec- trodes Even elec- trodes On basis of anodic current On basis of total current 16.05 17.99 16.48 23.17 9.82 0.023 .020 .091 .52 .94 0.021 .050 .081 .62 0.022 .035 .086 .57 Oil 1-second .018 .043 2-week .285 .94 (c) Indoor Tests — Lead Electrodes in Soil. — With lead electrodes in soil very regular results were obtained. In Table 7 the loss is shown to be increasing gradually frdm 60 cycles to 2 weeks with only one discrepancy, the loss on the even electrode (see p. 24) in 2-day reversals being considerably smaller than on the lo-minute and i-hour specimens. The products of cor- rosion seem to be increasing the effect on the pilot specimens, as it will be noted that the loss is increasing as the frequency decreases. However, the most remarkable facts concerning these tests is that the odd electrodes, those which were initially positive in the tests, lost considerably more than the even electrodes in both the 2-day and 2-week test. The other re- markable feature is the small coefficient of corrosion exhibited in the case of the direct-current test. Since in the first set weighed the losses were so small (only 22 per cent of the theoretical), a second run was made and a coefficient of 25.4 per cent obtained, practically the same as before. This indicates that under the conditions of these tests and probably xmder most soil conditions the corrosion of lead is very considerably less than it has been formerly considered to be# Alternating Current Electrolysis TABLE 7 Summary of Altemafing-Current Electrolysis Tests — HI • [Variable, frequency ol reversal; Indoor tests; lead electrodes; soli electrolyte] 25 Total loss Electrolytic loss Period of cycle Odd . elec- ' trodes Even elec- trodes Pilot Odd elec- trodes Even elec- trodes Average Grams 0.325 .342 .385 .518 2.860 3.868 3.468 5.886 8.719 13. 710 12. 319 13. 574 Grams 0.328 .332 .354 .528 2.845 3.634 3.738 5.771 5.072 7.789 Grams 0.124 .133 .118 .098 .652 .406 .341 .901 1.357 1.176 .937 .882 Grams -HO. 201 .209 .267 .420 2.208 3.462 3.127 4.985 7.362 12. 634 11. 382 12. 692 Grams +0. 204 .199 .236 .430 2.193 3.228 3.397 4.870 3.715 6.713 Grams 0.202 15-cycIe .204 .252 G-second .425 2.200 3.345 3.262 4.928 2-day 5.538 9.674 11. 382 Do . . Current dis- charge (amp. hours) Coefficient of corrosion Period of cycle Odd elec- trodes Even elec- trodes On basis of anodic current On basis oi total current 16.05 13.32 14.87 16.83 19.25 19.99 14.95 18.40 27.22 23.17 13.40 12.93 0.0065 .0082 .0093 .0129 .059 .089 .108 .140 .140 .282 .220 .254 0.0066 .0077 .0082 .0132 .059 .085 .118 .137 .071 .150 0.0065 .0080 .0088 .0131 .059 .086 .112 .139 .105 .216 0. 0033 .0040 .0044 .0065 l-minute .030 .043 .056 .069 2-da.y .053 .108 .220 .254 ((f) Indoor Tests — Lead Electrodes in Sodium Carbonate. — The losses of lead electrodes in sodium carbonate (Table 8) are greater than in the normal soil, the difference being especially noticeable in the longer reversals and in the direct-cmrent tests. For example, in the weekly reversals the coefficient of corrosion in normal soil was 0.108 while in the sodium carbonate it was 0.172; the direct-current coefficient of corrosion has risen from about 25 per cent to 34 per cent. 26 Technologic Papers of the Bureau of Standards TABLE 8 Summary of Alternating-Current Electrolysis Tests — IV [Variable, frequency of reversal; indoor tests; lead electrodes; soil and sodium carbonate electrolyte] Total loss Electrolytic loss Period of cycle Odd 1 Even elec- elec- trodes trodes Pilot Odd elec- trodes Even elec- trodes Average 60-cvcle Grams 0.555 .316 4.019 17. 356 17. 726 Grams 0.542 .630 3.844 13. 487 Grams 0.077 .062 .110 .111 .075 Grams 0.478 .254 3.909 17. 245 17. 651 Grams +0. 465 .568 3.734 13. 370 Grams 0.471 .411 3.822 15 307 17 651 Current dis- charge (amp. bours) Coefficient of corrosion Period of cycle Odd elec- trodes Even elec- trodes On basis of anodic current On basis of total current 16.05 14.87 14.95 23.17 13.4 0. 0154 .0088 .135 .386 .340 0. 0150 .0198 .129 .299 0. 0152 .0143 .132 .344 0076 .0071 2-week . 172 (e) Outdoor Tests — Iron and Lead Electrodes in Soil. — The out- door tests shown in Table 9 are not extensive, but the cases given show reasonably good agreement with the indoor tests given above. The coefficient of corrosion at 60 cycles is slightly less than 0.0 1 for iron electrodes and the direct-current loss is 0.70. Considering only the direct-current tests on iron, it was noted that as the voltage necessary to maintain the cmrent at 0.5 milliampere per square cen- timeter became greater the coefficient of corrosion decreased. For example, we find a coefficient of corrosion of 0.96 for iron electrodes in sodium carbonate soil and 0.85 in normal soil on the indoor tests and only 0.70 for the outdoor tests and the potential has varied from about 10 volts on the first to 35 on the last test. Alternating Current Electrolysis 27 TABLE 9 Summary of Alternating Current Electrolysis Tests — ^V [Variable, frequency of reversal; outdoor tests; iron and lead electrodes; soil and sodium carbonate electrolyte] Period of cycle Total loss Odd elec- trodes Even elec- trodes Electrolytic loss Odd elec- trodes Even elec- trodes Average 60-cycle 1-second Direct-current Do Grains 2.65 9.06 41.96 871.86 Grams 2.60 7.30 1.73 Grams 0.97 5.94 4.61 6.22 Grams 1.68 3.12 37.35 865. 64 Grams 1.63 1.36 37.35 Grams 1.65] 2. 24llron 37. 35J 865. 64 Lead Period of cycle Current dis- charge (amp. hours) Coefficient of corrosion Odd elec- trodes Even elec- trodes On basis of anodic current On basis of total current 60-cycle 1-second 13 irect -current Do 165.4 102.0 51.6 1034. 0. 0203 .0589 .700 0. 0197 .0256 .700 .217 0. 0192 .0431 .700 .217 8. CURVES The data shown in the above tables have been plotted in curves in which the ordinates are coefficients of corrosion expressed in per cent and the abscissas are the logarithms of the number of seconds required for one complete cycle. Fig. 4 shows the data obtained with iron electrodes, this being based on the average electrode loss and the total current flowing ia any one direction through the cells. The coefficient is therefore based on the total current discharged by one electrode. It will be noted that the curve for the coefficient in natural soil is above that for soil con- taining sodium carbonate, except the last point for direct current, when the latter shows the greater loss. The values begin to rise quite rapidly at about the lo-minute cycle, and reach a maximum in the direct-current test, the value for which is placed arbi- trarily as far as the time is concerned. It is very interesting to note that even in the case of a cycle of two weeks' duration the coefficient of corrosion is only about 0.6 and on a two-day cycle only 0.3 of its value for direct current. 28 Technologic Papers of the Bureau of Standards Fig. 5 contains the same data on lead electrodes, and here it is seen that the soil containing sodium carbonate produces a consist- ently higher coefficient of corrosion than the natural soil, just the reverse of the condition with iron electrodes. The tendency to rise is noticed at an earlier point or a higher frequency than with the iron, beginning with about the one-minute cycle, and at a cycle 100 60^ 15- IM 5M ION D.C ZDaya ZWeeks. Logarithm of Length of Time of One Cycle Fig. 4 ♦ of two weeks' duration the coefficient of corrosion has reached the same value as for direct current. 9. SUPPLEMENTARY TESTS Since certain authors have pointed out the fact that the wave form of alternating current is affected when passing through an electrolytic cell, and since a material change in such wave form would affect the current measurements, an oscillograph was used Bureau of Standards Technologic Paper No. 72 :*»^««'«*«W*g»« "0i|mt;.n i jp« t] ) . W!Br»!r ' luG. 6. — Wave shape for onc-sceond cycle Fig. 7. — IP'oi't shape for six-second cycle Alternating Current Electrolysis 29 to determine the wave form of current passing through the cell and its relation to the potential wave impressed on it. It was found that there was no appreciable distortion of the wave shape due to the presence of the cell. In order to determine the cycle of operation of the commu- tating machine exactly, the current wave was observed with the oscillograph. It is seen that on the one-second cycle (Fig. 6) too H z u O tr UJ a. I z. o 90 80. xr Gjefficient of Corrosion at Different Frequences • Soil o Soil + NajCOs Lead Electrodes Average Electrode Loss ZWeeks ^o.C. Logarithm of Length of Time of One Cycle Fig. s the current increases slightly during about the first one-fourth second and falls during the remainder of the half cycle. In the six-second cycle (Fig. 7) this rise and fall is seen, and the fall con- tinues for a considerable part of each half cycle, but the waves appear to be so nearly flat top in both the one-second cycle and the six-second cycle that no correction due to the variation between the average value and the effective value need be made. 30 Technologic Papers of the Bureau of Standards III. CONCLUSIONS From the above results certain conclusions may be drawn con- cerning the corrosion of iron and lead electrodes under usual soil conditions when exposed to the action of periodically reversed current. 1 . The corrosion of both iron and lead electrodes decreases with increasing frequency of reversal of the current. 2. The corrosion is practically negligible for both metals when the period of the cycle is not greater than about five minutes. 3. With iron electrodes a limiting frequency is reached between 15 and 60 cycles per second, beyond which no appreciable corro- sion occurs. No such limit was reached in the lead tests, although it may exist at a higher frequency than 60 cycles. 4. With peiriodically reversed currents, the addition of sodium carbonate to the soil reduces the loss in the case of iron and increases it in the case of lead. 5. The coefficient of corrosion of lead, imder the soil conditions described in the report, when subjected to the action of direct current, was found to be only about 25 per cent of the theoretical value. , 6. The corrosion of lead reaches practically the maximum value with a frequency of reversal lying between one day and one week. 7. The corrosion of iron does not reach a maximum value until the period of the cycle is considerably in excess of two weeks. 8. The most important conclusion to be drawn from these investigations is that in the so-called neutral zone of street rail- way networks, where the pipes continually reverse in polarity, the damage is much less than would be expected from a considera- tion of the arithmetical average of the current discharged from the pipes into the earth. Where pipes are alternately positive and negative with periods not excetding 10 or 15 minutes, the algebraic sum of the current discharged is more nearly a correct index to the total damage that will result than any other figure than can readily be obtained. 9. The reduction in corrosion due to periodically reversed cur- rents appears to be due to the fact that the corrosive process is in a large degree reversible; so that the metal corroded during the half cycle when current is being discharged is in large meas- ure redeposited during the succeeding half cycle when the current flows toward the metal. This redeposited metal may not be of Alternating Current Electrolysis 31 much value mechanically, but it serves as an anode surface during the next succeeding half cycle, and thus protects the uncorroded metal beneath. 10. The extent to which the corrosive process is reversible depends upon the freedom with which the electrol)rte circulates, and particularly on the freedom of access of such substances as oxygen or carbon dioxide, which may result in secondary reactions giving rise to insoluble precipitates of the corroded metal. It is largely for this reason that the corrosion becomes greater with a longer period of the cycle, since the longer the period the greater will be the effect of these secondary reactions. Washington, February 14, 1916. DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON, Director No. 75 DATA ON ELECTRIC RAILWAY TRACK LEAKAGE BY G. H. AHLBORN, Assistant Physicist Bureau of Standards ISSUED AUGUST 22, 1916 WASHINGTON GOVERNMENT PRINTING OFFICE 1916 ADDITIONAL COPIES OV THIS PUBLICATION MAT BE PKOCUKED FBOM THE STJPEKINTENBENT OT DOCUMENTS GOVEKNMENT PKINTING OFFICE WASHINGTON, D. C. AT 6 CENTS PEE COPY V DATA ON ELECTRIC RAILWAY TRACK LEAKAGE By G. H. Ahlbom CONTENTS Pace. I. Introduction ... 3 A. Definition of track leakage 3 B. Principles involved 4 II. Discussion 4 A. General method 4 B. Presentation of data 5 i. The Chevy Chase line, Washington, D. C S (a) General condition of line and test 5 (6) Current-leakage data 7 (c) Calculation of track ^ud roadbed resistance 10 2. The second line 12 (a) General condition of line and test 12 (6) Current-leakage data 14 (c) Calculation of track and roadbed resistance 16 3. The third line 17 (a) General condition of line and test 17 (6) Current-leakage data 18 (c) Calculation of track and roadbed resistance 19 III. Summary 21 I. INTRODUCTION A. DEFINITION OF TRACK LEAKAGE The stray currents which create the hazard from electrolytic corrosion and kindred dangers in our cities usually escape from the street railway tracks and return to the same circuit after having in many cases done more or less damage to the structures in their path. The amount of damage evidently depends not only on the amount of leakage from the tracks, but the per cent of this leakage that gets to the structures, the value of the latter, and their susceptibility to corrosion. 3 4 Technologic Papers of the Bureau of Standards B. PRINCIPLES INVOLVED There are two principal factors which govern the magnitude of the leakage current from any section of track. The first is the potential impressed on the leakage path. This potential depends on the magnitude of the return current flowing in the rails and earth and the resistance of this divided circuit. This resistance, in turn, depends on the conductance of the rails and connections and the condition of the bonding and cross-bonding and the resist- ance of the roadbed. The second factor is the resistance of the leakage path. This resistance is influenced by the area of con- ductors in contact with the groimd, the resistance of this contact, the conductance of the ties, and the length and conductivity of the earth path. Thus it is evident that the roadbed resistance is involved as a first and second order effect, influencing the potential impressed, as well as offering resistance to current flow from the track. This is made clear in equations shown imder the individual tests. McCoUum and Logan ^ have discussed in considerable detail the theory of track leakage and shown the effects on the magnitude of the leakage currents, of the length of feed, the track resistance, and the leakage conductance. It is the purpose of the following report to show in several actual cases the amounts of current that leak away from the track with load concentrated at the end of the line from which can be derived the constants of the track and roadbed. These constants can then be used in the equations given by McCoUum and Logan for further analyzing electrolysis conditions. The data here given were obtained in coimection with the Bureau's general investigations. IL DISCUSSION A. GENERAL METHOD In order to determine the amounl of leakage which actually occurs from trolley-line tracks, several lines of simple geometrical form were selected having no complication of track networks throughout the greater part of their length and having different physical characteristics as far as roadbed and soil conditions were concerned. It was arranged to impress a constant current on these lines dming the night when the regular car service was off. The ctuxent was then measured at regular intervals along the tracks, the difference between this current flowing in the rails > MeCollum and Logan, Technologic Paper No. 63, Earth Resistance and its Relation to Electrolysis. Electric Railway Track Leakage 5 and the impressed current being the leakage current. Since the current flow was calculated from the potential drop on a solid length of rail and the resistance of this length, which resistance may vary, due to difference in composition, heat treatment, or rolling of rails in manufacture or wear after being laid, the accuracy can not be greater than that of the potential measturement and consistency of rail resistance. Since only a short length of rail (lo feet or 4 feet) was used, a low reading, low-resistance milli- voltmeter was necessary and the accuracy of the readings was affected somewhat by the resistance of the contacts on the rail, readings being taken so rapidly that no great amount of time was spent in perfecting each contact. Two rail spanners having saw-blade contact points 4 feet apart were employed. These aided in expediting the tests, but even these contacts showed considerable variation in resistance and, in general, the results given below may have individual errors as great as 10 per cent, but the general tendency is shown and the average results are much better. B. PRESENTATION OF DATA I. The Chevy Chase Line, Washington, D. C. — (a) General Condition of Line and Test. — ^Although most of the trolley lines in the District of Colimibia are not grounded, there are several out- lying or interurban sections which use the track as retium. Among these is the Chevy Chase Une, running through the extreme north- west portion of the District of Coltmibia from Calvert Street Bridge to the District line at Chevy Chase, a distance of 3X miles, and from there to Chevy Chase Lake, about 2 miles farther. The country is rather rolling and the elevation is between 200 and 300 feet above sea level. The soil is generalty well-drained and there is considerable rock near the surface. Eighty-pound, T-rail, double-track construction is used throughout except on the first one-half mile where 83-pound girder rails are employed. The roadbed is of varied character, the first one-half mile with girder rails being concrete with asphalt street surface (Fig. i). The next 3.5 miles is rock ballast with ties and rails embedded, the surface being finished with "Tarvia" (Fig. 2). From the end of this section to the lake, 1.5 miles, the rails are raised above the ballast, as shown in Fig. 3. At the extreme end, where a network of car-bam tracks is embedded in soil, the power house is located, 6 Technologic Papers of the Bureau of Standards and the negative bus is connected to these tracks as well as the main-line tracks, and to a small ground plate in the lake. The test was made on this line on April 30, 191 1, from 2 a. m. to 5 a. m., when the regular car service was suspended. The ground was rather dry, no rain having fallen for some time. CONVENTIONS ^^^j^ asphalt soil mwm broken roQk i^^ concrete gravel Fig. I. — Roadbed consirtiction of first portion of Chevy Chase line Fig. 2. — Roadbed construction of second portion of Chevy Chase line 1 ^ :t Fig. 3. — Roadbed construction of third portion of Chevy Chase line After the cars stopped running the power was cut off and the trolley connected to the rails by a No. 0000 bond at Rock Creek Bridge. The generator voltage was then reduced and a current of 300 amperes was supplied to the track. This current was mattitained throughout the test. A record of the generator current and voltage is given in Table i. Electric [Apr Railway Track Leakage TABLE 1 Power-House Load . 30, 1911, Chevy Chase line] 7 Time Generatoi voltage Generator current Time Generator voltage Generator current 2.10 a.m 110 110 110 105 103 100 103 103 103 103 . 103 Amperes 300 300 300 290 300 290 300 300 300 300 300 4.00 a.m.. 103 104 103 103 103 103 105 103 103 103 Amperes 300 2.20a.m.. . 4.10 a. m 300 2.30 a.m 4.20 a. m 300 2.40 a.m 4.30 a. m 300 4.40 a.m 4.50 a. m 300 3.00 a. m 300 5.00 a. m 310 3.20 a. m 300 3.30 fl. m. . 5.20 a. m 300 3.40 a. m 5.30 a. m 300 3.50 a. m (6) Current-Leakage Data. — ^The citrrent in the rails was deter- mined by measuring the drop on a 4-foot length on each of the four rails at regular intervals. These data are shown in Table 2 and Fig. 4. In the table the first column gives the time and the second the distance from the power house. The next four col- umns contain the millivolt drop on each of the four rails, cotmting the north or east one as number one; the sixth colturtn totals these four columns, the values having been corrected for lead resistance, etc. The last column shows the total current in the four rails, based on a specific rail resistance of 0.000295 o^i™ per pound-foot and a weight of 80 potmds per yard. The current is quite evenly distributed among the rails, thereby indicating reasonably good bonding and cross-bonding on this line. The first set of readings was taken beyond the point where the trolley was connected to the rails and indicates that 50.5 amperes were flowing into the city network of tracks and thence through the earth back to grounded connections of the negative bus. Technologic Papers of the Bureau of Standards TABLE 2 Current Leakage [Apr. 30, 1911, Chevy Chase line] Distance from power house Millivolt drop on 4 ieet of rails Ttaie 1st rail 2d rail 3d rail 4th rail Cor- rected total Current 2.40 a. m Feet 28 600 28 400 27 900 27 400 26 900 26 400 25 900 25 400 24 900 24 400 23 900 23 400 22 900 22 400 21900 21400 20 900 20 400 20100 19 600 19100 18 600 18100 17 600 17100 16 600 16100 15 600 15100 14 600 14100 13 600 13 100. 12 600 12 100 8 500 5 900 2 600 0.0 4.0 6.6 6.0 8.0 8.0 6.0 6.0 6.0 7.0 7.0 6.5 6.0 6.0 7.0 7.0 7.0 8.5 6.0 6.5 7.5 6.5 6.5 7.5 7.0 6.0 6.5 5.5 7.0 7.0 6.0 6.0 5.8 6.0 7.5 7.0 7.0 8.0 0.8 9.2 6.8 6.4 5.0 8.0 5.0 5.0 6.0 7.0 6.0 5.5 8.0 6.0 6.5 6.5 5.0 5.5 6.5 6.0 6.0 6.0 7.0 7.0 6.0 6.5 7.0 7.0 6.5 6.0 7.0 5.5 5.5 5.5 6.0 7.0 2.3 7.4 6.2 5.5 7.0 7.0 5.0 4.0 4.0 7.5 6.0 7.0 6.5 6.0 7.0 6.0 7.5 7.0 7.0 7.0 6.0 6.5 6.5 7.5 7.5 6.5 7.0 6.0 6.0 7.0 7.0 5.0 6.5 7.0 7.5 6.0 7.5 7.5 2.4 6.5 5.8 6.3 5.0 6.0 6.0 5.0 5.0 6.0 7.0 6.0 6.0 7.0 6.5 7.0 6.5 7.5 5.0 7.5 6.5 6.0 6.0 6.5 7.0 7.0 7.0 6.0 7.0 6.0 5.0 7.0 6.5 7.5 7.0 7.0 6.5 7.0 6.1 30.1 28.2 26.8 27.8 32.2 24.4 22.2 23.3 30.5 28.9 27.8 29.4 27.8 30.0 29.4 28.9 31.6 27.2 30.0 28.9 27.8 28.9 31.6 30.5 28.9 30.5 27.2 29.4 28.9 27.8 26.1 27.0 29.4 31.6 28.3 30.0 32.2 Amperes 50.5 2.50 a. in 249.0 233.0 3.04 a. m. . 222.0 3.08a.m 230.0 .^.14 p. m 266.0 3.16 a. m 202.0 3.20 a. m 189.0 3.24 a. m 193.0 3.28 a. m 252.0 3.32 a. m 239.0 3.35 a. m 230.0 3.40 a. m 243.0 3.43 a. m 230.0 3.45 a. m 248.0 3.48 a. m 243.0 3.51 a. m 239.0 3.55a.ni. 261.0 225.0 4.13 a. m 248.0 4.15a.m 239.0 4.18 a. m 230.0 4.20 a. m 239.0 4.22 a. m 261.0 252.0 4.27 a. m 239.0 4.31a. m 252.0 4.34 a. m 225.0 4.38 a. m 243.0 4.41 a. m 239.0 230.0 216.0 4.48 a. m 223.0 4.50 a. m 243.0 4.53 a. m 262.0 234.0 5.12 a. m 248.0 5.27 a. m 266.0 Electric Railway Track Leakage 9 It is very evident from the ciirve in Fig. 4 that the current val- ues are quite irregular, not decreasing smoothly toward the center as they theoretically should do with uniform track resistance. This can be explained at some locations by a change in resistance of the return circuit, and this is emphasized by the potential gradient curve shown in Table 3, also plotted in Fig. 4. A small current and also low gradients are noted in the neighborhood of Kindle Run Bridge, where the rails are in contact with the steel structure which is carrying part of the cturrent, returning some of it to the tracks and discharging the rest to the earth. The last * 6 a /o /s /-f. /6 /a zo gz z4- Z6 za so PisTANCB FfiOM Power House — Thousands of Peet Fig. 4. — Track leakage, Chevy Chase line reading shows a difference of about 35 amperes between the total current and the current on the rails at a distance of 2100 feet from the power house. Most of this current must find its way to the bus through a ground in the lake, the switching and bam tracks, and the Kensington line tracks beyond the power house. With the exception of the place where the bridge structure paral- lels the track, the point of smallest cm-rent is near the center of the line (14 000 feet from the power house), the current here being 216 amperes. The loss of current to connecting tracks at the outer end of the line is 50 amperes, and returning to con- necting tracks on the other, 30 amperes. 43181°— 16 2 lO Technologic Papers of the Bureau of Standards TABLE 3 Potential Gradient in Rails, 500-foot spans [Apt. 30, 1911, Chevy Chase line] Time 3.04 a. m 3.07 a m 3.15 a m 3.20 a m 3.24 a. m 3.27 a. m. 3.30 a. m. 3.33 a. m. 3.36 a. in. 3.38 a. m. 3.41 a. m. 3.43 a. 3.46 a. 3.55 a. vn 4.10 a. 4.19 a. m Volts for 500 leet 0.31 .35 .35 .35 .36 .354 .33 .30 .32 .334 .336 .338 .35 .32 .34 .353 .336 .404 .34 .33 .334 .334 .34 .34 Distance to power house Feet 28 500 28 000 27 500 27 000 26 500 26 000 25 500 25 000 24 500 24 000 23 500 23 000 22 500 22 000 21500 21000 20 500 20 000 19500 19 000 18 500 18 000 17 500 17 000 Time 4- zS a. m. 4.42 a. m.. 4.54 a. m.. 5.00 a.m.. 5.25 a.m.. Volts lor 500 feet 0.33 .342 .34 .338 .35 .344 .344 .356 .356 .342 .34 .34 .376 .41 .36 .36 .36 .376 , .37 .358 .358 .376 .362 .364 Distance to power house Feet 16 500 16 000 15 500 15 000 14 500 14 000 13 500 13 000 12 500 12O00 11500 11000 10 500 10 000 9 500 9 000 8 500 8 000 7 500 7 000 6 500 6 000 5 500 5 000 (c) Calculation of Track and Roadbed Resistance. — The over-all potential drop was measured, using telephone lines for leads, and was found to be 2 1 volts. The foUowiag equations may be used to determine the track resistance and also the leakage resistance to earth, where: I A. = current at sending or receiving end Fa = potential to ground at sending or receiving end 2L = total length of track r= track resistance per unit length 9= track leakage conductance per tmit length 7b = current at center of track Electric Railway Track Leakage 1 1 The equations governing the relations between these quantities with fixed load delivered to the outer end of the line are given by Kennelly ^ and are: (i) /a =£a coth where to = jr, and 6=L -^rg n \g (2) Ib=Ea To sinh 9 Dividing (i) by (2) .-. 7a , ■zr =coth 6 sinh 9= cosh 6 =cosh L V''?- IB Taking as a particular case the Chevy Chase line, it is necessary to consider one half of the line as a unit. Considering first the power-house end, /a = 270 amperes /b = 2i6 amperes L =14 300 feet £a = io.5 volts .". /A = i.25=coshd 7^ Referring to hyperbolic tables, e =0.693 =L^ The equation involving the drop in potential on the line is, "■^B Ir sii in which all values except /7 are known, sinh d being obtained from cosh d in the above equations. Then substituting known values, we have ^=0.0648 9 We now have two equations and two unknown quantities. Solv- ing we get: r =0.00314 ohm per 1000 feet ^=0.748 ohm per 1000 feet ' A. E. Kennelly, The Application of Hyperbolic Functions to Electrical Engineering Problems. Ea=Ib Ir sinh 9 1 2 Technologic Papers of the Bureau of Standards Hence the resistance of looo feet of roadbed is 1/9=1.34 ohms. The value of track resistance, 0.00314 ohm per 1000 feet, is about 15 per cent greater than the calculated resistance of the continuous rail. This can be accoimted for by an average rail-joint resistance equivalent to 10 feet of rail on the basis of 60-foot rails, which is very low, especially since there were a number of high-resistance joints. We will find that a much greater effect due to bad joints exists on the other lines discussed below. The resistance of the roadbed, 1.34 ohms for 1000 feet, is a reasonable value as checked by other measvu"ements. Taking the other half of the Chevy Chase line, /a = 250 amperes /b = 2i6 amperes £3 = 10.5 volts L = i4 300 feet r and g unknown -^=coshLJ;^ = i.i55 /b * ^ 0.550 ^ ^ 14..' f4-3 and EK — I-B-ylrlg sinh 6 or -\lrjg = 0.084.1 Solving for r and g, r = 0.00323 ohm per 1000 feet. g = 0.4.58 mho per 1000 feet, or the resistance of 1000 feet of roadbed is 2.18 ohms. Both the rail resistance and roadbed resistance are higher than for the half nearer the power house, the rail resistance being 3 per cent higher and that of the roadbed 63 per cent. The averages for the entire length are 0.00318 ohm per 1000 feet and 1.76 ohms for each 1000 feet of double track. These average^values are probably the better since two assumptions were made in stating the conditions of each half of the line; that is, that the minimum cmrent occturs exactly at the center of the line and that the potential is also exactly divided between the two halves. Any error due to these approximations is practically eliminated when the average of the two is taken. 2. The Second Line — (o) General Condition of Line and Test. — The second trolley line runs a very straight course a distance of 1 1 Electric Railway Track Leakage 13 miles. The track is single with 48-pound rails and has two or three switches or turnouts. The base of the rails is only occasion- ally in contact with the soil, the type of construction being shown in Fig. 5. The soil is chiefly New Jersey gravel, well drained, and of rather high resistance. The elevation of the line above sea level is 123 feet at the highest point and 1 5 feet at the lowest, with an average of 75 feet. The power house is located at the western end, and the track at the eastern end is connected to a ground plate in the river near which the line terminates. Data as to trolley and feeders were obtained so that the potential difference of the different parts of the circuit could be calculated. The trolley wire was connected to the track after the cars stopped and the current adjusted to 150 amperes (Table 4), about Fig. 5. — Roadbed construction of second line 210 volts being required to maintain this current. Current read- ings were taken about every one-quarter mile by observing the potential drop in both rails with the 4-foot rail spanners or contact points. TABLE 4 Power-station Readings [Nov. 7, 1915, second line] Time Generator current 1a.m... 1.1s a. m 1.30 a. m 1.4S a. m 2.00 a. m 2.15 a. m Ampeies 150 150 150 150 145 ISO Generator voltage 215 215 215 215 205 215 Time 2.30 a. m 2.45 a. m 3.00 a. m 3.15 a. m 3.30 a. m 3.45 a. m Generator Generator current voltage Amperes 145 150 150 150 145 150 205 215 215 215 210 210 14 Technologic Papers of the Bureau of Standards (b) Current-Leakage Data. — ^The time, distance from power house, and potential drops on the 'rails are shown in Table 5, the calculations of current flow being given in the last column. These current values are plotted in Fig. 6. It will be noted that about 12 amperes are flowing into the grotmd plate at the extreme end of the line and that the city tracks at the power-house end are taking up about 50 amperes. The leakage curve is considerably /SO TOTfL Cm een-r ^ *30- r acroN 'Stati Track lbakagb ScCOf/O UNC t/0 / . y / f? •'I- \ *-"• § V __^ ■-^-r- ' ^ 1 ^ CVBRt rt-f in 4« <* t /. ^ / s z e 2 * ^ B S Z d « « ♦ * -tl 9 a 8 « ^/svywcc F/Bom Srivr/on—ThousAnos OF ^££,T Fig. 6. — Track leakage, second line smoother than that on the Chevy Chase line, but the percentage of loss is considerably greater, the rails at 1.5 miles from the power house are carrying about 80 amperes or 58 per cent of the total delivered to the track, and the remainder, 42 per cent, is leaking into the earth. As pointed out above, only a portion of the cur- rent escapes from or returns to the stmight track, 58 amperes escaping from the extreme half and 20 amperes returning to the other portion before it connects with the city networks. Electric Railway Track Leakage TABLE S Current Leakage [Nov. 7, 1913, second line] 15 Time Distance east of Eiwer ouse Millivolt drop on 4 feet of rail Northiail Southrall Total Weight of rail Current 1.07 a. m. 1.12 a.m. 3.50 a.m. 1.22 a. m 1.27 a.m. 1.37 a. m 1.42 a. m 1.45 a. m 1.49 a. m 1.50 a. m 1.52 a. m 1.54 a. m 1.56 a. m 1.57 a. m 1.59 a. m 2.02 a. m 2.04 a. m 2.06 a. m 2.09 a. m 2.12 a. m 2.14 a. m 2.15 a. m 2.17 a. m 2.19 a. m 2.21 a. m 2.23 a. m 2.25 a. m 2.27 a. m 2.30 a. m 2.33 a. m 2.35 a. m 2.37 a. m 2.40 a.m. 2.42 a.m. 2.44 a. m 2.46 a.m. 2.48 a.m. 2.50 a.m. 2.52 a.m. '2.55 a.m. 2.57 a.m. 3.00 a.m. 3.02 a.m. 3.06 a. m . Feet 56160 55 720 53 530 51400 50 590 49 400 48 240 47 000 45 745 44 500 43 270 41800 40 550 39100 37 900 36 700 35 560 34 300 33 030 31800 30 530 29 300 28 030 26 800 25 540 24 300 22 930 21700 20 020 18 800 17 330 16100 14 230 13 000 12 220 11000 9 720 8 500 7 220 6 000 4 717 2 582 788 0200 0.2 .6 10.0 6.3 .0 3.8 5.8 5.7 3.6 3.5 3.4 3.4 3.6 3.3 3.5 3.5 3.0 3.8 4.0 3.0 3.6 6.1 3.0 3.1 .1 3.3 2.8 3.6 2.9 4.0 3.0 .0 3.1 3.0 3.1 2.7 2.8 5.7 5.7 5.5 3.2 6.0 2.6 .1 0.4 7.3 .0 1.2 6.9 3.4 1.2 1.4 3.0 3.5 3.2 3.1 3.0 3.1 3.1 3.0 2.8 2.4 2.5 3.4 2.4 .0 2.8 3.1 5.9 2.6 3.1 2.2 3.0 1.8 2.8 5.8 2.7 3.0 2.7 3.0 2.6 .0 .0 .0 2.8 .0 2.6 .0 0.6 7.9 10.0 7.5 6.9 7.2 7.0 7.1 6.6 7.0 6.6 6.5 6.6 6.4 6.6 6.5 5.8 6.2 6.5 6.4 6.0 6.1 5.8 6.2 6.0 5.9 5.9 5.8 5.9 5.8 5.8 5.8 5.8 6.0 5.8 5.7 5.4 5.7 5.7 5.5 6.0 6.0 5.2 .1 Lbs./yd. 65 65 48 48 48 48 48 48 48 48 48 48 48 48 48 43 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 48 43 48 48 48 48 60 60 Amperes 6 11.5 150.0 149.0 105.0 97.0 101.0 98.0 99.0 92.0 98.0 92.0 91.0 92.0 90.0 92.0 91.0 81.0 87.0 91.0 90.0 84.0 85.0 81.0 87.0 84.0 83.0 87.0 81.0 83.0 81.0 81.0 81.0 81.0 84.0 81.0 80.0 76.0 80.0 80.0 77.0 84.0 84.0 91.0 1.7 o Beyond power bouse. ^ Flowing to ground plate at end o2 line. 1 6 Technologic Papers of the Bureau of Standards (c) Calculation of Track and Roadbed Resistance. — From the cur- rent and feeder data it is calculated that a pressiu-e of 66.7 volts was impressed on the track during this test. Referring to the table aiid curve it is seen that for the half of the track nearest the power house ^A = 334 volts Za = 100 amperes /b = 80 amperes L = 28 000 feet. Referring to the preceding equations Nos. i and 2 and substi- tuting numerical values, cosh 5 = -5— = 1.25 oO .•.e=L-yfrg^ 0.693 (3) r £'A=/B-t/-sinh^. Substituting known values, r = 0.556 . (4) 9 solving for r and g in (3) and (4) ^ = 0.0445 mho per 1000 feet or the resistance of 1000 feet of roadbed is 22.5 ohms r =0.01378 ohm per 1000 feet. For the outer half of the line -E^A = 33.4 volts /a = 143 amperes /b = 80 amperes* L = 28 000 feet as above cosh 6 = -^=-^— =1.788 /b 80 ' and l=i.i85=L -y/rg (5) ia=Ib-\ — sinh 6 V a V - =0.2817 (6) Electric Railway Track Leakage 1 7 solving for r and g in (5) and (6) 9=0.1503 mho per 1000 feet or resistance to ground = 6.65 ohms for 1000 feet and r =0.01 182 ohm per 1000 feet. The averages for the whole line are then : Resistance to ground i/gr = 14.57 ohms per each 1000 feet of single track r= 0.0128 ohm per 1000 feet. The apparent difference in the roadbed resistance between the two halves of the lines is probably much greater than actually exists, but the average value is reasonable when the t}rpe of road- bed is considered, the dry, sandy soil being in contact only with the ties. The resistance of the rails is increased about 40 per cent, or each joint has an average resistance of 12 feet of solid rail on a basis of 30-foot rails. 3. Thb Third Line — (o) General Condition of Line and Test. — This trolley line is a single track with 60-poimd rails, having a length of about 6.5 miles. The track has a short spur or Y about I mile from the extreme end, but it has no complicated network of tracks at either end, and the total current is easily measured. The roadbed is clay and New Jersey gravel, at many points in contact with or covering the baseof therail. Theelevation, compared to sea level, is the most striking feature of this line, the highest point being 15 feet above, the lowest 2 feet below, and the average 10 feet above. Salt marshes lie close to the track for the greater part of the distance, and the conductivity of this soil must be very high. There is probably a ground plate attached to the outer end of the track, but this is too small to materially affect the general leakage conditions. The rotary converter in the substation carried the load for this test, the machine voltage being reduced to 275 volts and the current being maintained at 205 amperes throughout the night, as shown by Table 6. The readings were taken every one-quarter mile on both rails, using the 4-foot spanners mentioned in the preceding test. 1 8 Technologic Papers of the Bureau of Standards TABLE 6 Substation Load (Nov. 8, 1913, third line] Time Ampeies Volts Time Amperes Volts 1.30 a. m 210 205 205 205 205 275 275 275 275 275 205 205 205 205 275 1.45 a. m 275 275 2.15 a. m 275 2.30 a. m (6) Current-Leakage Data. — In Table 7 are shown the results of this test arranged as in the previous tables, showing time, dis- T07 11. C JBBt fiT Ofn w 3£^ ' so iON 1 TmL lerl i^ / 8 ""' V TSACH LEAKAGE Third LmB k S N \ i \ / / ^ ^ \ ^ \ • BEN -IN 3/l»- ! -T f Br,aa J -^ ' i - £ I 4 » / t ■>■ * / i / s ^ £ 2 i * t t » J Fig. 7. — Track leakage, third line tance from substation, millivolt drop on rails, and the calculated current. It will be noted that 70 amperes is flowing into the earth at the outer end and that 85 amperes is finding its way to the track beyond the substation. T^e distribution of current between rails is very poor at times, as shown by zero readings on one and the total on the other, indicating bad bonding and cross- bonding on these sections. The curve (Fig. 7) shows very graphi- cally the small current left in the track at about the middle point, the lowest current recorded being 12.2 amperes, or only 6 per cent of the total and about 9 per cent of that actually flovdng in this direction. Electric Railway Track Leakage TABLE 7 Cunent Leakage [Nov. 8, 1913, third Une] .19 Time Distance irom sub- station Millivolt drop on 4 leet of rail Weight of rail Current East rail West rail Total 1.29 a. m Feet 33 415 33 100 32 300 31100 29 900 29 000 29 000 28 700 27 500 26100 24 900 23 650 22 400 21200 20 000 18 800 17 600 16 400 15 200 14 100 12 900 11800 10 800 9 700 8 500 7100 5 800 4 600 3 200 2 200 1000 150 50 4.0 6.2 1.8 1.6 1.6 1.6 .8 1.4 1.2 .8 .7 1.1 .0 •' .5 1.0 .0 .5 1.0 .9 .7 .9 .6 .0 2.0 2.2 3.1 2.3 3.0 4.2 7.3 3.4 3.5 0.0 1.6 2.0 1.8 1.8 1.6 .6 1.3 1.2 1.0 8.0 1.2 1.6 .8 .8 .0 1.0 .8 .0 .0 .0 .0 .4 1.0 2.0 2.3 3.2 4.6 3.2 2.5 .0 4.0 2.6 4.0 7.8 3.8 3.4 3.4 3.2 .2 2.7 2.4 1.8 1.5 2.3 1.6 1.5 1.3 1.0 1.0 1.3 1.0 .9 .7 .9 1.0 1.0 4.0 4.5 6.3 6.9 6.2 6.7 7.3 7.4 6.1 Lbs./yd. 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60 48 Amperes. O70.0 1.37 a. m 136.4 1.43 a. m 66.5 1.46 a.m 59.5 1.50 a. m 59.5 1.57 a. m 56.0 2.00 a. m 3.5 2.04 a.m 47.2 42.0 2.12 a. m 31.5 2.14 a. m 26.2 2.16 a. in , 40.2 2.18 a. m 28.0 26.2 2.22 a. m 22.7 2.24 a. m 17.5 17.5 22.7 17.5 2.52 a. m 15.7 12.2 15.7 3.12 a. m 17.5 17.5 3.19 a. m 3,22 a. m .' 70.0 78.8 3.24 a. jn 110.2 120.2 3.28 a. m 108.5 117.2 3.34 a. m 127.7 3.40 a. jn 129.5 85.0 a Beyond point of connection of trolley wire to track. Current flowing away from power house to earth. (c) Calculation of Track and Roadbed Resistance. — ^From the total current and voltage and resistance of the positive feeders the drop on the track can be calculated. This is found to be 87.4 volts. Using tlie same S3rmbols as before, the half of the track nearest the power house has these values. Ea = 43.7 volts /a = 135 amperes 7b = 14 amperes L = i6 600 feet 20 Technologic Papers of the Bureau of Standards Substituting these values in the equations previously used Cosh 0=^ = 9.64 = 2.957 =lV»^ (7) Ek = /b-» / - sinh Substituting above values, ^ ^=0.3254 (8) Solving for r and g in (7) and (8) ^=0.547 mho per 1,000 feet or resistance to ground is / = 1.828 ohms per 1,000 feet 9 ?'= 0.0580 ohm per 1,000 feet For the other half of the line the values are practically the same. £'a = 43.7 volts /a = 137 amperes 7b = 14 amperes L = i6 600 feet Substituting cosh 0=-i^ = 9.78 14 = 2.971 =L-^rg Substituting the above values ♦ £:A=/B-./^sinh0. (9) V^ -=0.321 (id) Solving for g and r in (9) and (10) ^ = 0.558 mho per 1000 feet or roadbed resistance i/gf = 1.79 ohms for 1000 feet r = 0.0573 ohm per 1000 feet Electric Railway Track Leakage 21 The averages for the two halves of the Ime are : 9=0.553 mho for 1000 feet i/g = 1.81 ohms for 1000 feet >' = 0.0576 ohm per 1000 feet. This line has a very low elevation, and is surromided by marshes, and its resistance to grotmd is tmusually low; while the rail resist- ance is very high, being 15.7 times that of soUd rail for this weight. In other words, the average resistance of each joint is equal to that of 470 feet of rail. For a considerable per cent of the distance only one rail was carrying any current, and it also undoubtedly had frequent high-resistance joints. III. SUMMARY Table 8 contains a summary of the above data and certain interesting conclusions may be drawn from it when the characteris- tics of the lines are considered. The Chevy Chase line is the shortest, of the three, and only 21 volts was required to maintain 300 amperes on this length. The total rail resistance of line No. 2 is about eight times that of the Chevy Chase line, and the poten- tial difference required per ampere is about six times as great, so that the greater length of line in No. 2 has about offset the effect of the much higher leakage resistance. City lines seldom have great feeding distances; the per cent of cvirrent leaking to earth will, therefore, generally be far less than in subtirban lines except in special cases where underground pipes are metallically connected to the track. TABLE 8 Stumnaiy of Track-Leakage Data Length Weight of rail Over- all poten- tial drop Current Resistance of return single track Leakage resistance Line Maii- mum in rails Per cent to earth Ohms for 1000 feet Total OhXQS Per cent of solid rail Ohms for 1000 feet Ohms for a mile Chevy Chase (double track) Line No. 2 (single track) Feet 28 600 56 000 33 200 Lbs./yd. 4-80 2-48 2-60 Volts 21.0 66..7 87.4 Amp. 250 143 136 13 42 90 0.00636 .0128 .0576 0.091 .717 1.913 115 140 1570 1.76 14.57 . 1.81 0.333 2.75 .343 Line No. 3 (single track) 22 Technologic Papers of the Bureau of Standards Although most of the joints on all these lines are better than indicated by the per cent increase of resistance, there are certain bad places on each line which bring this value up to a remarkably- high figure, especially on line No. 3. The need of occasional tests and of cross-bonding is emphasized by such conditions. The leakage resistance of line No. 2 is much higher than either of the others, being about eight times that of both the Chevy Chase line and line No. 3. This indicates that rails clear of soil, and ties embedded in well-drained sand and gravel have a higher resistance than any track with rails in contact with macadam- brick, or asphalt pavement. When it is considered that a leak- age resistance of 14.5 ohms for each 1,000 feet of roadbed indi- cates a leakage resistance of over 29 000 ohms for i foot, the high insulating properties of this roadbed are more evident. This line probably represents the upper extreme of roadbed resistance that will be found imder ordinary conditions. Washington, April 14, 1916.