Effectiveness of Cathodic Protection under AC Interference and Determination of the Optimum Protection Potential

Although the alternating current (AC) may cause corrosion on coated pipelines even when cathodic protection is applied, but experimental studies proved that impressed current cathodic protection system could have effectiveness to mitigate AC corrosion, if the protection potential has been selected correctly. The effect of AC interference on cathodic protection system was studied with a laboratory simulation device. Electrochemical experiments were used to characterize and quantify the AC corrosion of X70 steel under different protected potential. The polarization experiment results proved that protection voltage of –650mV to –1100mV may play a protective role. According to the electrochemical impedance spectroscopy (EIS) analysis of X70 steel with different AC interferences in soil environments, the corresponding equivalent circuits were proposed respectively. Based on EIS results, the Rt-Ee,c curves are obtained, from which the optimum protection potential of X70 steel in soil solution can be determined.