Abstract
Soluble salt contamination of the substrate prior to coating application will cause premature coating failure at the coating/steel interface as well as underfilm corrosion of the steel substrate, especially when the surface concentration of the soluble salts exceeds a critical level. So, in order to prevent this salt-induced premature coating failure IMO’s PSPC regulation adopted recently for ship’s water ballast tank specified the allowable NaCl limit to be 50 mg/m2 or less for primary and secondary surface preparation. The finalized criterion on the salt contamination, however, can be still subjected to argument mainly due to lack of reasonable technical justification for coating systems of ship’s water ballast tank. In this study, coating performance of epoxy coatings for ship’s water ballast tank were evaluated with soluble salt levels, especially NaCl, in terms of adhesion strength and blistering resistance test in immersion, condensation, and cathodic protection environment to propose reasonable soluble salt criterion. The results based on the coating performance tests for 6 months suggested the maximum allowable NaCl of 70 to 100 mg/m2, depending on epoxy coating formulation used. It is recommended that blistering resistance should be evaluated to determine the criterion of soluble salt since the maximum allowable salt level does vary with coating formulation.
