LONG-TERM TESTING OF EPOXY-COATED STEEL IN ASTM SEAWATER USING ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY

Laboratory-prepared samples of four types of epoxy coatings on 1010 (UNS(1) G10100) carbon steel were immersed in aerated ASTM(2) seawater for up to 4 years. Quantitative visual coating degradation via blistering was correlated to coating and corrosion parameters as determined by electrochemical impedance spectroscopy (EIS) modeling and measurements. The data indicate EIS parameters allow identification of subfilm disbondment long before surface evidence of coating deterioration is apparent. An equivalent circuit model suggests disbondment areas as small as 0.0001 percent can be measured.