Design Considerations of Inductive AC Interference Mitigation Techniques

Electromagnetic induction is the primary interference effect of a high-voltage transmission line on a buried steel pipeline during normal steady state operation. The operating current directly affects the level of electromagnetic interference, which can induce an alternating current (AC) voltage and corresponding current in the pipeline. This induced AC potential may present a safety hazard to personnel and can contribute to AC corrosion of the pipeline. Problems arise when alternating currents above the defined limits are present on a pipeline, even if the cathodic protection (CP) levels are satisfactory and meet the criteria defined in ISO 15589-11 and ISO 218572. Much effort has been made in the last decades to define acceptable AC interference levels for carbon steel under CP conditions.3, 4, 5, 6, 7, 8, 9, 10, 11 This article discusses CP design considerations for pipelines when AC interference is present.