AC Corrosion on a Pipeline Located in an HVAC Utility Corridor

Abstract

Abstract Corrosion of a pipeline that had been laid in HVAC utility corridors was investigated. Severe AC corrosion occurred resulting in four holes in the pipeline after only five months life and before operation had begun. This represents a corrosion rate of over 400 mpy. An “intelligent” pig survey identified 18 additional locations with over 50 percent wall penetration. These damaged areas were all replaced. The AC voltage on the pipeline, which was originally as high as 90 volts, was subsequently grounded and reduced to below 10 volts using a combination of deep ground beds and a series of zinc anode installations. The pipeline was also cathodically protected and there have been no leaks after 3 years operation. Research is needed to determine the mechanism of AC corrosion, why AC corrosion does not always occur, and to determine the rate of corrosion as a function of AC voltage. Guidelines are needed to set mitigation standards.