Determination of Coating Deterioration with EIS: Part II. Development of a Method for Field Testing of Protective Coatings

Abstract

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 (ϕ_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 (ρ), while ϕ_min and the ratio f_b/f_min depended only on A_d. Recording of f_b, f_min, and ϕ_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.