This study aims to develop a practical measurement method for recording and assessing alternating current (AC)-induced corrosion on cathodically protected steel pipelines. Current field practices do not allow reliable in situ evaluation of metal loss. The proposed approach combines analytical modeling with experimental validation to establish boundary conditions and acceptable error tolerances for field application. The hypothesis assumes that capacitive phenomena at the steel/electrolyte interface can serve as indicators for detecting and quantifying metal loss. The capacity is calculated directly from the determined impedance, performing the model concept and the postulated assumptions and simplifications. Galvanostatic tests were conducted on electrical resistance probes and coupons with 1 cm2 coating defect at 50 Hz featuring various defect geometries, bedding materials, and electrolyte solutions under constant AC current densities (Jac) and varying cathodic protection (CP) levels (low, normal, and very high), using six parameter sets for 1 y. This study compares the correlation measurement method with conventional practice measurement methods and examines calculated capacitance as an indicator of progressive AC corrosion. The results show that corrosion rates and calculated capacitance increase with CP current density and Jac, with capacitance showing a linear dependence on Jac and correlating with corrosion. However, fluctuations in calculated capacities occurred, mainly because of environmental factors like diffusion conditions. These fluctuations were more pronounced in electrolytes with increased convection compared to soils. These findings highlight the potential of the correlation measurement method and calculated capacitance (Cs) for evidence-driven AC corrosion risk assessment. Although the method is theoretically applicable, practical implementation requires long-term monitoring and statistical averaging to minimize errors.
Houban et al. (Sun,) studied this question.