(eBook Version) Need: Induced AC on pipelines, despite the installation of AC mitigation facilities, can still produce deleterious effects involving the safe operation of the pipeline, the effective operation of the cathodic protection system, and the safety of personnel. One of the most serious consequences of steady state induced AC is that AC corrosion can occur, even though the induced AC voltage has been reduced to less than 15V as required by the standards and notwithstanding cathodic protection levels that also satisfy the standards.
Benefits: Implementation of the findings of this report will result in improved effectiveness of CP systems, longer useful pipeline operation life and a reduction personnel safety hazards.
Result: This project resulted in a report identifying and avoiding those situations where AC mitigation techniques may reduce the effectiveness of the CP system. DC isolators-AC couplers, such as zinc grounding cells, polarization cells, electrolytic capacitors, and isolation-surge protectors, used to protect isolating fitting from AC damage and to pass AC to ground, have certain operational characteristics that can affect the operation of the cathodic protection system and personnel safety. Under steady state AC conditions both zinc grounding cells and polarization cells allow cathodic protection current to pass, which can reduce the level of protection provided by galvanic anode systems. This can also cause polarization cells to corrode and fail in the open circuit mode and result in a possible voltage hazard.
