Abstract
Early corrosion investigations in New York City were concerned with electrolysis caused by stray currents leaking from elevated and trolley lines. This problem was solved by installing insulating joints in the gas mains. Attention was then given to mitigating soil corrosion which is responsible for many of the leaks being experienced. Test data at 472 field excavations showed that the most severe corrosion usually occurred in the poorly aerated clay soils containing organic matter. Bacterial action was indicated in 81 percent of the locations of severe corrosion. This revelation prompted a detailed investigation of the bacterial influence in underground corrosion. Population counts of five types of anaerobic and aerobic bacteria were determined at corrosive locations, concurrently with measurements of moisture content, organic matter, aeration and pH of the soil and the presence of sulfide in the corrosion product. Seasonal variations in the soil moisture, aeration and population of anaerobic bacteria were found to be associated with the underground corrosion cycle. Following a discussion as to the probable mechanisms of bacterial corrosion, the need for further improvement of the soil redox probe developed in the American Gas Association investigation is indicated. This probe measures the reducing intensity of the soil and thus locates corrosion areas prior to. installing the pipe,
