AC Corrosion Evaluation of Cathodically Protected Pipeline Steel

The effect of alternating current (AC) on the corrosion rates of cathodically protected buried steel pipeline was investigated through mass loss testing. Results indicate that cathodic protection (CP) at potentials at or below the CP criteria of -780 mV(SCE) is adequate to prevent increased corrosion due to AC at AC densities up to 350 A/m(2). Further, the interfacial capacitance of the steel was theorized to be a controlling factor in the ratio of the capacitive to faradaic current portions of the AC and thus the corrosion rates due to AC. The value of capacitance was measured in various soil types to determine the effect of the bulk environment on this parameter. It was found that interfacial capacitance is much lower in artificial soils than in a soil-simulating solution but that the composition of the soils does not greatly affect the capacitance.