New CP Criteria for Elimination of the Risks of AC Corrosion and Overprotection on Cathodically Protected Pipelines

Abstract

Abstract The risks of AC corrosion and overprotection are increasing on cathodically protected buried steel pipelines, due to the increased cases of installing pipelines in proximity to high voltage AC power transmission lines and DC/AC powered rail transit systems. Based on field and laboratory studies as well as literature research, new cathodic protection (CP) criteria were developed based on AC and DC current densities measured using coupons, to eliminate those risks. Using these criteria, the design of CP systems for newly constructed pipelines, paralleling overhead high voltage AC power transmission lines, and in the proximity to DC powered rail transit systems, was successfully performed. Corrective measures to eliminate the risk of AC corrosion were taken by the use of distributed magnesium anodes and solid-state DC decoupling devices.