Corrosion of buried or submerged metals is an electrochemical phenomenon in which direct currents usually are associated. However, reversing and alternating currents can cause corrosion, although at a lower rate than direct currents.
A brief review of the technical literature shows that numerous investigations have been made having a bearing on a-c electrolytic corrosion of iron, lead, copper, aluminum and other metals. These investigations have been concerned with such diverse ends as decomposition of water into hydrogen and oxygen, reduction of organic compounds, ascertaining the cause of pitting and corrosion in buried structures, reducing the shock hazard on pipelines due to induced voltages, determining the allowable levels of a-c voltage induced in cable sheaths, as well as attempting to determine under what conditions a-c electrolytic corrosion occurs, and the mechanism of rectification at the oxide film surfaces of metals.
No single investigation has been sufficiently comprehensive to permit a prediction as to what corrosion rate will result on buried structures. Taken together, however, the investigations suggest that a-c electrolysis is a complex phenomenon which depends on various factors, all of which probably exert influence on the rate of corrosion. 3.8.2
