DEVELOPMENT OF AN ADVANCED INSTRUMENTATION FOR ASSESSING THE AC CORROSION RISK OF BURIED PIPELINES

Recently, in Japan like other countries in the world, pipelines are being constructed in parallel with HVAC electrical power lines and/or AC traction railways with thinner, high strength walls, high resistivity coating with little or no corrosion allowance. This means that more attention must be paid to new threats, that is, AC corrosion and overprotection on modern pipelines. To determine the AC corrosion risk, coupons should be installed where the AC current density reaches its maximum. The AC current density I_AC together with DC current density I_DC of a coupon are the primary determining factors in assessing the AC corrosion risk.

The authors have developed an advanced instrumentation for assessing the AC corrosion risk of buried pipelines. The most distinguished feature is the simultaneous computation in a measuring unit of 20ms regarding coupon DC current density I_DC and coupon AC current density I_AC (50Hz) corresponding to the commercial frequency of 50Hz that is the predominant frequency component on AC corrosion of buried pipelines. Immediately after computing the averaged I_DC and I_AC (50Hz) in measuring time, the results are referred to the coupon current density-based cathodic protection criterion established by the authors.