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OVERCOMING THE NEW THREAT TO PIPELINE INTEGRITY - AC CORROSION ASSESSMENT AND ITS MITIGATION -

AC corrosion risk on gas buried transmission pipelines is increasing due to growing tendency to install the pipelines in proximity to overhead high-voltage AC power transmission lines and/or AC-powered rail transit systems. It has been generally recognized that the pipelines can suffer AC corrosion despite satisfying the conventional cathodic protection (CP) criteria based on pipe-to-soil potential which mandate a protection potential of -0.85 VCSE. Studies were therefore conducted to develop 1) new CP criteria to assess the AC corrosion risk and 2) AC mitigation methodology including the installation of grounding system. Consequently, new CP criteria were developed based on DC and AC coupon current densities. AC mitigation methodology was also established that included the grounding of pipelines using magnesium anodes and solid-state DC decoupling devices. The effectiveness of the new CP criteria and AC mitigation methodology was proven to be satisfactory through field tests conducted on pipelines buried in proximity to overhead high-voltage AC power transmission lines and AC-powered rail transit systems.