ELECTROLYSIS AT NEW BEDFORD.
Abstract of Report of
The question of electrolysis upon water and gas mains in many places continues to cause much concern among those who are responsible for the safety of such properties. A recent report made by A. A. Knudson, electrical engineer, of New York city, upon the piping system of the city of New Bedford, Mass., and also upon the important forty-eight-inch steel conduit through which water is supplied from the lakes to that city, contains features of more than usual interest, and, through the courtesy of Superin tendent Coggeshall, of New Bedford, is given the following abstract of the report, which consists of two parts. The first portion gives the results of a preliminary examination upon the steel main in May; the second, the complete details of a more thorough examination of that conduit and also of the piping system of the city in July. The results discovered upon the steel main are first considered. Referring to map A, this main, beginning at the pumping station at C, on Little Quittacas lake, runs southwest through the country about eight miles to the reservoir at D. It is constructed of five-sixteenths-inch riveted steel. At E, Beaver Dam, a suburban electric railway line passes over it. This line runs between New Bedford, Middleboro, and other towns, and its power house is located at P H. A thirty-six-inch cast iron main delivers water from the reservoir, D. to the city, and is connected to the steel main through a forty-eight-inch by-pass at the reservoir. Portions of the tracks of this road were unbonded, and there are no track-feeders. It was found that, when cars on the electric road were south of Beaver Dam, or in the vicinity of the terminus of the city’s main (located at F), some of the returning current would pass by this main south to the city mains, where a connection to the thirty-six-inch main is found; thence to the reservoir and by-pass to the steel main; thence through that main to the crossing at Beaver Dam, where the most of it was delivered to the rails. At times the current measurements upon the mains ltaken at different places), which were uncovered, showed a maximum flow north through the steel main of 19.2 amperes, with an occasional reversal, which accounts for the arrows on the map pointing, in some cases, in both directions. Immediately north of the crossing, at a gate-vault, the highest current reading obtained was six amperes, which left a delivery of current from the main to the rails of 13.2 amperes at different times of the day. The voltmeter readings between the main and rails at this point showed the main positive to the rails as high as twelve volts, and negative twenty-six volts, with frequent reversals. The six amperes which slipped past the crossing was a remnant that passed on to about two and one-half miles north, and followed a two-inch wrought iron service pipe, which crossed under the same tracks not far from the power house at G. This service pipe had frequently been destroyed at this point by electrolysis. The water was turned off from this pipe, and the pipe was uncoupled at a point just before it passed under the rails. A current reading by the direct method was then made, and a flow of three to seven amperes was found passing towards the rails to which it was delivered, which fully accounts for the pipe’s frequent destruction. It will be seen that the test by the drop of potential method just north of Beaver Dam, where six amperes were discovered, and the test at G by the direct method upon the service pipe of three to seven amperes, compare quite closely. As the current readings on the main and potential tests at the Beaver Dam crossing pointed strongly to electrolysis upon the main at this point, the main was uncovered at each side of the tracks and under the rails. The conditions discovered are illustrated in Fig. 1. Electrolytic pittings were found upon the main immediately under the tracks upon the top, and extending down the sides for some distance; the deepest, however, did not exceed one-eighth of an inch. But the tops of the three flanges showed the results of more severe action. Upon one of them a depth of one-quarter of an inch was found, and the others were similarly damaged. These flanges were riveted to the main, and extended five inches from its surface. They were so placed to give additional strength to the main, under the tracks and roadway. When the above facts became known to the city authorities of New Bedford, a conference was help at the office of the superintendent, composed of the mayor, members of the water board, the electrical engineer of the railway company, and Mr. Knudson, representing the city. These discussed the question of remedy. The railway company’s representative advised bonding the steel main to the rails at tne boint where the damage was found. This was objected to by the engineer for the city, on the ground that probably twice the amount of current would be brought upon the six miles of steel main and about four miles of the thirty-six-inch cast iron main, with conseqnent electrolytic action at some of the numerous joints in both. He added that such a plan would, in effect, convert these valuable properties into a return conductor for railway currents to their future detriment, and could not be allowed. It was, however, finally suggested upon the part of the railway representative, that a system of auxiliary track-feeders should be coustructed upon this line, and the rebonding of the tracks, which had Deen Degun, should be completed. He claimed that this plan would remove all current from these mains It was, therefore, decided to await the construction of this work, when further tests are to be made to ascertain its effect in relieving the dangerous conditions discovered.
The survey and examination in the city of New Bedford did not reveal any very serious cases of electrolysis. This is largely due to unusually good track-return found in a city of this size. The most important case found was on the four-inch service pipe just outside of the power house. This pipe belongs to the railway company, ami furnishes the sole supply of water to the steam plant. An underground copper cable track-feeder passed over it at right angles and about three feet above it. Electrical measurements in the vicinity pointed to electrolysis on this pipe under the cable, and, when uncovered, it was found so badly damaged that its immediate removal and the substitution of a new length were deemed necessary to avert a sudden stoppage of water if the pipe should burst. To prevent future damage at such an important place, the position of the cable was changed to nearer the surface of the ground and more carefully insulated; at the same time a second pipe was run into the station from another main. The chief engineer reported to Mr. Knudson that the condenser pump in the station was being badly damaged at the interior iron parts, and was asked to make an examination, as electrolysis was suspected. Trolley current was found flowing through it and other parts of the steam plant. This was carefully traced, and its entrance to the building was discovered through the four suction-pipes where they enter the river. A current reading on these pipes showed a maximum current of twenty amperes passing from the river into these pipes and through the steam plant and pumps. When these facts became known to the manager, means were at once adopted to cut this current out of the steam plant and avoid further damage to the machinery.
In the second part of the report it was noticed that a number of lengths of six-inch cast iron pipe recently removed from the river bed, where it crossed, were being heated and re-dipped at the department yard preparatory to again being relaid in the river. Examination of some of the lengths showed they were badly softened at the spigot ends by electrolysis, as indicated in Fig. 3, where nails can be seen driven in the soft material. There were pittings and soft spots at other places on these lengths; but the greater damage was at the spigot ends, near where the joints were made, and were doubtless caused by the railway current flowing through them from spigot to bell. The pittings and furrows at the ends of some of these lengths were from one-eighth to three-eighths of an inch deep. Some of these lengths were condemned by the superintendent as unfit for further use, owing to their weakened condition. The joints, it may he added. were of the hall and socket type. This evidence of damage at the joints of mains caused by currents flowing through them is regarded as an apt illustration at this time, and serve as an indorsement of the action of the water board, under Mr. Knudson’s advice, in refusing to allow the railway company to “bond” the steel force-main to the rails of their tracks, where the result of such a method, as stated, would be to divert a stronger current of electricity through this and other mains, thus increasing joint damage and weakness of the same in both the steel and cast iron mains. The report concludes with the suggestion that from time to time voltmeter tests should be made with instruments belonging to the water department, not only upon the steel conduit, but upon other mains in the city, where the tabulated readings in the report indicate current movements upon the mains in more or less degree. It is also regarded as fortunate for all concerned that the examination upon the steel conduit was made before electrolytic action had progressed farther than was discovered, as it is quite certain that this main would have burst in the near future at the point mentioned if the conditions found had continued. The same may also be said of the power house service pipe in the city of New Bedford.