Capabilities and limitations of direct current and electrochemical impedance mapping in measuring the cathodic disbondment of coatings using multi-electrode array

© 2016 Curran Associates Inc. All rights reserved. An electrochemically integrated multi-electrode array has been used to monitor and evaluate the cathodic disbondment of a coating by means of (i) measuring the local electrochemical impedance and (ii) measuring local direct current during its exposure to an aggressive solution under a cathodic protection (CP) potential. The performance of these two measurement methods in determining the disbonded area of the coating has been evaluated by comparing the impedance and current maps measured using the multi-electrode array under different CP potential and different environmental resistivity conditions. The results demonstrate that both current mapping and electrochemical impedance mapping are capable of evaluating the disbonded area of coating at higher level of CP potential (e.g. -1400 mVAg/AgCl) during exposure to a solution with a low resistivity. However, the current mapping has shown limitations because current maps measured at lower CP potential (e.g. -950 mVAg/AgCl) and measured in a solution with higher resistivity (e.g. 20 Mohm-cm) did not accurately correlate with the cathodic disbondment area of the coating. The electrochemical impedance maps measured at the same conditions, nevertheless, accurately determined the disbonded area of the coating. According to results from this work the electrochemical impedance mapping is found to be more capable of evaluating the cathodic disbondment of coating under different conditions.