Influence of substrate characteristics on cathodic delamination of anticorrosive coatings

P. A. Sørensen, S. Kiil, K. Dam-Johansen, C. E. Weinell

Despite improvement in coating technologies, problems continue to exist in long-term protection of steel structures (e.g. offshore oil rigs, wind turbines and ballast tanks) against their environments. For organic anticorrosive coatings in electrolyte solutions (e.g. seawater), cathodic delamination is one of the most severe types of failure. Although significant advances in understanding the mechanisms and modes of failure have been made, the detailed mechanism of cathodic delamination remains unknown.

 The purpose of this work is to investigate the mechanism of cathodic delamination. Experimental investigations, with selected coating system, show that disbondment of organic coatings is mainly controlled by diffusion of cations from a defect to the delamination front and not through the intact or disbonded coating. Furthermore, an ongoing delamination process was found to be inhibited, when the anodic reaction was suppressed. The influence of substrate surface characteristics on the rate of cathodic delamination was also investigated. Steel substrates with a higher degree of roughness were found to decrease the rate of delamination. Through experimental analysis of the surface characteristics, the disbondment results are related to effective diffusivity of cations at the coating-steel interface.