DETERMINATION OF COATING DETERIORATION WITH EIS .2. DEVELOPMENT OF A METHOD FOR FIELD TESTING OF PROTECTIVE COATINGS

A theoretical analysis of the impedance of polymer-coated steel was performed to identify parameters for assessing coating performance in a short time without rigorous analysis of data from electrochemical impedance spectroscopy. Results of the analysis applied to nine coating systems suggested the breakpoint frequency (f(b)), the frequency f(min) of the phase-angle minimum observed at high frequencies (PHI(min)), and the ratio of the impedance recorded at two frequencies could be used for this purpose. Analysis also showed f(b) and f(min) depended on the delaminated area (A(d)) and the coating resistivity (rho), while PHI(min) and the ratio f(b)/f(min) depended only on A(d). Recording of f(b), f(min), and PHI(min) allowed determination of coating damage and, therefore, was recommended for the design of a commercial device for field testing of the remaining lifetime of protective coatings.