ELECTROLYSIS ON WATER MAINS.
Mr. F. B. Kelsey. C. E., who has been investigating the effects of electrolysis on the water mains at Salt Lake City, Utah, reports that :n the case of one pipe examined there was considerable electrolytic corrosion—the action being more marked along a longitudinal crack in the side of the pipe, where the current had flowed from the pipe where the water oozing from the pipe had moistened the ground. Farther along the line the pipe was nearly destroyed; the shell being in some places less than three-sixteenths of one inch thick, and some corroded portions of the pipe resembling graphite, while the iron could be easily cut with a knife. Measurements taken with a volt meter showed the pipe in that locality to be positive to the ground; consequently there was a flow of electric current from it, with the resulting electrolytic action. In this case the corrosion was caused by the return currents of the electric railways, accelerated by the soluble salts contained in the ground round the pipes. This shows, (i) that, on all single trolley railways where the current leaves the rail for the ground, it will flow to, and along the underground pipes, and vhere it leaves them corrosion is sure to result; (2) that ample eturn metallic conductors, provided by thoroughly bonding he rails and connecting them every 200 or 300 feet with overlead or underground conductors extending to the power house, vill reduce the action to a great extent, but will not entirely ire vent it.
At Salt Lake City the rails within the paved district arc well /■v l Oil. 11 i-clUC V, I ly lilt I aiu numii mv • vv. M.V onded, and, in addition, a supplemental bare copper wire is … t . i * 11 .1 _ 1 _ _ J _ __ Ann aid between the rails and connected with the bonds every 200 eet. Outside the paved district the only return conductor irovided besides the rails is an insulated overhead wire on Sec>nd East street, extending from the power house and having ,ne connection each with the tracks where it crosses them on iecond, Third, and Fifth South streets. Outside the paved listrict the rails are bonded with a number four copper wire astened to the flange of the rail with rivets. The street railays, therefore, are not provided with ample return conduc>rs; outside the paved districts they are not sufficiently well snded; and the return wires are a protection to the pipes only , the district which they cover.
, To determine the oause and discover indications and location of electrolytic action, Mr. Kelsey advises taking voltage measurements,between the pipe itself and the damp earth immediately surrounding it with a volt meter and two wooden rods, in whose lower ends are brads connected with wires, leading to the volt meter, which is better than the ammeter for determining whether or not there is a flow of current and the direction. A fraction of volt difference potential between pipes and the damp earth surrounding them is sufficient to induce the action. Less than one-half volt destroyed a telephone cable in a few months; the amount of current flowing is the measure of the rapidity of the action. An electro-motive force, even so low as .002 volts is sufficient to cause injurious action from electrolysis. A very small difference in potential, as little as .001 a volt will cause the electrolytic action; in fact, it needs an extremely low potential, not exceeding .01 of a volt, coupled with other favorable conditions, to produce electrolyiic action, though it may take considerable time to cause the results to become apparent.
Corrosion will take place (1) where the pipes are positive to the earth, in which case electric currents will flow from the pipes to the earth: (2) it occurs at the places where the electric current leaves the buried metal for the earth, as there is a tendency for the metal to do to the negative pole of the generator; (3) where, owing to certain conditions of the railway system, abnormal currents are flowing through the earth; (4) where the measurements at the hydrants indicate a tendency of electricity from the pipes to the earth; (5) whenever a volt or ampere shows a flow of electricity from gas or water main? to tn the 1 L roile rails or along fliaco these mains; points becomes positive to adjacent or parallel construction, in which case the extent of destructiveness will depend upon the low resistance offered by the earth and upon the amount of soluble salts, the electrolysis of which is injurious to the iron contained thereicontained therein.
One result has been established by investigations into the subject—namely, that cast iron pipe remains intact, while the wrought iron and lead pipe are at once affee’ed by electrolysis. Some engineers hold that white casting is perfectly indestructible under the action of ordinary oxidizing influences. Certain wrought iron clamps and bolts employed to fasten a cap upon the end of the pipe were seriously injured by corrosion Lead sewer pipes also, immediately attached to the uninjured cast iron and exposed to the same condition showed unmistakably the expected electrolytic corrosion. Wherefore, it is suggested that at low potentials cast iron of such quality as exists in the water mains which were examined will endure* practically unharmed, a flow of current into the earth, which under the same conditions, is totally destructive to wrought iron and lead.
To prevent electrolysis: Extend 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 branches—to be of such a size as to carry the current properly and maintain the return path at a comparatively low resistance. For a track extending three miles in any one direction from the power house a number OOO copper wire would give a resistance of but one ohm from the most distant point. From this return wire frequent connections should be made to the track—about every 200 feet—of such size or shape as to cause the same resistance from the rail at all connections. The rails should be thoroughly bonded and no ground connections must be allowed on the dynamo or any direct connections to the rails without the proper resistance. In addition to the bonding a continuous supplemental rail should be laid in the centre of each track and connected to each rail at least every 300 feet extending the whole length of the road from the power house,and equal in area to that of all the feed wires that supply power over the section, allowance being made for the bond wire; no wire less than a number O to be used, and every wire to be connected to the negative side of the generator. With the rail circuits carefully bonded and reinforced by insulated return wire, or cables from central points, such increase of current on any water pipe is not easily possible, as the resistance offered by the water pipe is very low—the metallic section of a six-inch water pipe being one and one-half time* that of seventy-pound rail, while that of an eight-inch pipe i# two and one-quarter, and of a twelve-inch pipe three and onequarter times as great. Therefore, the perfecting of the circuit from the pipe to the generator in such cases is generally sufficient provision against electrolysis.
No amount of bonding, however, will wholly prevent a portion of the current from following the pipes. To use buried rails for conduits, if ordinary copper bonds are used for connections is not good. Even when new, it in impossible to get the full conductivity of the rail, and the contacts get worse and worse as time passes. The copper, when covered with the damp earth, will oxidize at a rate determined by the composition of the soil and the amount of current transmitted. The rail on any street railway should be a continuous rail electrically welded at the joints, or. if separate or distinct rail* are used, they must be bonded or connected at the rail joints as follows: For rails of forty or sixty |>ounds to the yard, one bond of number OOOO B. W. G. copper wire at each joint; from sixty to ninety pounds, two bonds; where that wire is joined to the raiis. the holes through the rails must be carefully drilled, and the copper wire made to fit the hole carefully. A thread must be cut in the end of the wire, and a copper nut or a copper washer with iron nut used, and the surface of the rail so smoothed and dressed that, when the nut is made tight, there shall be a thorough contact with the rail. The contact of the wires with the rails to be made on bright surfaces, and the end of the copper wire enlarged so as not to have less than ten times the area of the bonding wire in contact with the bright surfaces of the side and hole of the rail, so as to make a waterproof joint—the whole to be at once painted with the best electrical insulating paint. At each alternate rail the track must be cross-bonded with a number O wire; connection being made to the loop of the nearest bond with a wrapped joint and solder _the same method being adopted on double track construction.
The rails which it. the first instance receive the return current unquestionably possess, if of ample section and without joint, sufficient conductivity to return all the current to the generator, except what in any case, under the law of divided circuits, is certain to escape to other conductors, if such exist; therefore, all that is necessary to obtain the most | erfect insulated and available conductor is to reduce >11 possible resistance at the rail ends by producing a most perfect bond between them equal to the rail in conductivity, or, in other words, by riveting a copper bond of twelve inches in length to the end rails, the section and number of these bonds to increase as the power house is being approached, supplemented by similar cross-bonds connecting the four rails to each other every 100 to 120 feet.
Frequent connections with the water pipes should be avoided, as they will increase the action in other parts of the city, though they may reduce it near the house. A large conductor, extending from the grounded side of the dynamo entirely through the danger territory and connected at every few hundred feet to such pipes as are in danger, will usually insure their protection. It is better to use a separate conductor lor each set of pipes to be protected; connections at the power station only to water or gas pipes will not insure their safety. Connections between the pipes and rail or rail return wires outside of the danger district should be carefully avoided. Tests show that,if a large current is flowing longitudinally in an Iron pipe, even with good points, an injurious action is likely to occur at the joints, and the flow of an electric current along an iron pipe will increase the rate of decay to some extent. It has been objected in this connection that any plan permitting the attachment of conductors from the pipes to the return systems of the railroad would, by promoting the increased flow of current along the pipes, cause a very serious corrosion at the joints in the pipes through an indefinite extent of the city. In one case where the water pipe was examined the drop in potential round the joints in the main was found to be from one to two volts; and there were no evidences of electrolysis is to be found. Under no condition should the current be grounded by means of wires or rods at any point near the gas or water mains or the iron or lead pipe connections. If, after return conductors have been provided the pipe is still positive, the rail bonds at such points should be perfected, and,if the connections are such that an increase of the section or number of such bonds will not entirely remove the difficulty, proper and suitable metallic connections shou d be made at such places between the pipe and rail, so as to permit the return of the current to the rail; but they should be made only where the pipe is positive,in order to receive the pipe—and for no other purposes.
The positive pole of the dynamo should be connected to the trolley lines. Frequent voltage measurements between pipe and earth should be obtained and such changes in return conductors made as the measurements indicate. If the current is kept from flowing in the buried metal or if it can be prevented from flowing into the earth from that metal, the corrosion can be stopped To get rid of electrolytic action it is, consequently, necessary eithci to make the regular return circuit of sut h low resistance that there will be no flow in the pipes (which is practically Impossible) or so to arrange return feeders that the current will not leave the pii>es for the earth. It is impracticable to eliminate electrolytic action except by a constant inspection of the water system as a whole, with a view to locating points where difficulty is likely to occur and applying such remedies as are well known. Thus the danger can be minimized. At the same time a means of absolute prevention of injury, so long as the pipes are of a kind liable to corrode ,is as yet unknown. The e$ca|>e to the earth of a portion of the current discharged into the rail is a condition inseparable from the single trolley system, all tending towards electrolysis.