ELECTROLYSIS.

Press, Volume LXVI, Issue 19985, 21 July 1930, Page 10

ELECTROLYSIS.

WATER MAINS AFFECTED. due to tramway current. The effects of electrolysis—chemical decomposition caused bv the action of an electric current —on water mains, ferro-concrete structures, and underground metal pipes generally, formed the subject of an address by Mr D. E. Parton to the Canterbury College Engineering Society on Saturday evening. Mr Parton said that the problems raised were the concern, not only of electrical engineers, but also of civil engineers, anil that the lack ot knowledge at prebent existent was a matter uoeding attention.

"When it was discovered recently that electrolysis was playing bavou with the water mams." said Mr Parton, "one of the newspapers intimaceu mat some engineers who had been in cerviewed iitKi stated tftat eiectroiysio was practically unknown in tne Dominion, anu tuai the case mentioned was ttio uisi cowman under tlieir notice, j am sure that these authorities couiu not nave been electrical engineers, anu that the statements, were meant either to be comparative or were made W ignorance of the true position. It is quite true that the trouble is comparatively non-existent in Christ church, but this is due not to the possible absence of leakage from ine traction systems but rather to the fact mat preventive measures have < uut ed the danger not"*to be brought under notice. , "Corrosion has certainly affected underground structures in Christchurch, and in other City networks, but the cause has invariably been said to be anything but electrolytic action —chemical action perhaps, but not that associated with leakage currentIn Auckland probably the most serious cases have occurred, and in Australia water-mains and ferro-concrete structures have suffered similarly. "The same natural law which makes primary and secondary batteries useful also provides a menace for ' metal cable sheathings and for other metal conductors, for a current of electricity leaving them tends to dissolve them into any electrolyte that mav be present. Anv metal oipe buried in the earth follows the same law as that affecting the process of electroplating, and serves to carry current from one area to another. Where there exist single-trolley transport sy"tenia, such as the trams in Christchurch, in which the current passes from the overhead wire hy means of the trolley to the motors and then into the rails as a return circuit, part of the current is spread into the soil which act's like a conductor of very large area. This current is passing to the negative-bus-bars at the station and anv pipe if the earth is likelv to acquire a positive potential with*relation to it. so that electrolytic action is Ret up, and the pipe ultimately destroyed. "With electrolysis the earth acts as the electrolyte, and the mass of decomposed material, and consequently the proportion of metal attacked, depend primarily on the amount of current circulating in the electrolyte. Un derground distribution systems —networks of lead-covered cables water supply and gas mains and other underground metallic structures- offer, a much better conductive than does the surrounding earth. Where such distribution' systems are located in the vicinity of electric traction systems, strav currents of large and varying intensity are gathered up and carried for considerable distances "Metals such as lead, which resists many corrosive solutions well enough, are easily attacked bv the alkalis of the soil. The lead cable sheaths are also sometimes attacked at the points where the stray currents enter, the lead then playine the role of the cathode. In such a case a secondary reaction takes place- the more the current circulates the more alkaline bases are accumulated through electrolysis at the points of contact with the cables. When from any cause the current itself ceases to act, the corrosion of the cable continues throup.h the chemical action alone. Unless precautionary measures are taken in time the lead sheath will be pierced, the conductors exposed to humiditv. "nd the cable ultimately rendered useless."

f r Parton also outlined methods by which the action mi<»ht he checked, and method* of detectiha its oresence. At the conclusion of the meeting a hearts vote of thanks was accorded 4 he speaker.