Monitoring Corrosion in Sacrificial Anodes With Pulsed Eddy Current and Electromechanical Impedance: A Comparative Analysis

Measuring the extent of corrosion of sacrificial anodes used in cathodic protection systems would enable real-time monitoring of the efficacy and remaining useful life of the cathodic protection system. This article presents a comparison of the sensing capabilities of pulsed eddy current (PEC) and electromechanical impedance (EMI) based techniques for measuring extent of corrosion of zinc sacrificial anodes. Experiments were conducted with a lead zirconate titanate (PZT) transducer attached to the sacrificial anode as well as with a PEC probe placed in the vicinity of the sacrificial anode. Accelerated corrosion tests were performed on the anode and the corrosion was quantified by the root mean square deviation (RMSD) of the conductance spectra for the EMI based measurement and area under the curve (AUC) method for the pulsed eddy current based measurement. The experimental results show good agreement with finite element method (FEM) simulations. We report that the EMI method has large sensitivity to onset of corrosion in the anode, with sensitivity reducing nonlinearly over time due to delamination of corrosion by-products. In contrast, the PEC method shows excellent linearity over the entire duration of the accelerated corrosion experiment. A key insight from this work is that an effective monitoring strategy could combine the merits of both sensing mechanisms, with EMI used for identifying incipient corrosion and PEC used for tracking the extent of corrosion over the life of the sacrificial anode.