Abstract
AC mitigation has become an absolute necessity for pipeline operators due to safety concerns and the risk of through-wall corrosion leaks as a result of induced AC.
AC mitigation systems have evolved to use one of three grounding systems: zinc ribbon anode, bare copper cable and an engineered system utilizing a copper conductor with machine packed grounding backfill. All can be connected to solid-state DC decoupling devices.
This paper provides a comparison of these metallic grounding systems. A test bed was constructed at an electric and gas utility facility with intensive overhead electrical transmission and the site of a documented 2002 steel gas transmission pipeline AC through-wall corrosion leak.
The test bed was constructed to individually test the zinc ribbon anode, bare copper grounding and the engineered system to measure their ability to reduce the induced AC voltage. Field test data is provided and conclusions are made regarding the performance of the three grounding systems.
The test bed also provides insight regarding spatial effects of the grounding system, including lateral alignment and cover depth relative to the positioning of the steel pipeline. Field test data suggests that AC mitigation installed laterally at a distance of ten feet (3 meters) or more from the pipeline is more effective. This also results in an increased working space that provides a clear safety benefit to the grounding system installers.
