Coupons simulating the coating defects have been used to evaluate cathodic protection level of steel structures. This paper aims to provide requirements for coupon AC current density as affecting AC corrosion of cathodically protected steel pipelines. The field investigation into the polyethylene coated 400 mm diameter natural gas transmission pipeline paralleling a 25 kV AC transit system which operated at frequency of 50 Hz was carried out. The steel coupon was connected to this pipeline with the cathodic protection applied. The four parameters, that is, coupon on-potential, coupon instant-off potential, coupon DC current density, and coupon AC current density were acquired by using the new coupon technology with high data sampling rate of 0.1 ms and 16-bit. It was thought that the requirements to regard the coupon AC current density for a single period of commercial current frequency as affecting AC corrosion could be: 1) polarity reversal; 2) consistency with commercial current frequency; 3) small distortion factor of a waveform.

Subject
Electric current, CP coupons, Piping, Cathodic protection, Steel coupons, Cathodic current, Distortion, Current densities, Cathodic current density, Alternating current corrosion, Corrosion coupons, Instant off potential, Coupons
Keywords:
buried steel pipeline, cathodic protection, AC corrosion, coupon AC current density
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2015
Association for Materials Protection and Performance (AMPP)
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