Case Study: Corrosion Caused By an Inadvertent Short between a Cathodically Protected Pipeline Segment and a Large Plant Grounding System

Abstract This paper presents a case study of a cathodically protected gas line within a facility/plant setting which was found to be exhibiting external pitting corrosion. The 6” pipeline is a single 2.5 km isolated section between a metering station and a plant. Pipeline tie-ins were made of non-metallic materials and tracer wires were found to be properly isolated from the plant. The coating was fusion bonded epoxy (FBE). Line operation was found to be within industry best practice with a designed external corrosion mitigation system as well as a designed AC mitigation system. The Pipeline Operator proactively initiated an investigation of the possible causes of external corrosion to assess risks to pipeline integrity. The risk of most types of corrosion such as AC corrosion, stray current interference from foreign CP systems, microbiologically induced corrosion, and disbonded coating corrosion were found to be minor. The presence of low pipe to soil potentials and low coupon current densities lead to a suspicion of an inadvertent short to the grounded plant structures, which were not cathodically protected. Current mapping analysis identified a possible short to plant structures, which was excavated in 2025. The excavations uncovered a grounding cable which was directly in contact at the 6 o’clock position with the pipeline. The clearing of the short led to the immediate improvement of the CP potentials and current mapping confirmed that current loss was no longer present at this location. The remediation was deemed to be successful.