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Evaluation of protection against corrosion of thick polyurethane coating by electrochemical impedance spectroscopy

Abstract The protection performance of a thick polyurethane coating was studied by using an electrochemical impedance spectroscopy in 3% NaCl solution. Electrolytic penetration through the coating changes the dynamic characteristics of the conduction and resistance of the coating film of the protected system over time. Equivalent circuits were used to interpret the physical and electrochemical properties. The mechanism and kinetic of electrochemical systems were assessed by measuring the fluctuations in resistance, capacitance, percentage of water uptake and dielectric constant through coating. A series of accelerated test, e.g. salt spary, 100% relative humidity, cathodic disbonding and adhesion tests have been used to evaluate pipeline coatings. The results revealed that tested coating has very high protection efficiency and can be a very good alternative for conventional pipeline coatings. In the meantime, percentage of water uptake and dielectric constant through the coating were measured maximum 15˙9 and 3˙2% respectively.