The influence of soluble salts content on the performance of an epoxy coating system via accelerated corrosion tests

Abstract

It is generally accepted that surpassing a threshold value of water-soluble salts at the substrate/coating interface can impart premature failure in painted structures. The Coatings industry has an identified need in defining a maximum allowable soluble salts content, however, a variety of threshold values are found in published data. Based on that, this work aims at evaluate the effect on epoxy coating performance of three different ranges of soluble salts content taking into account the maximum allowable values specified by NORSOK M-501 and IMO PSPC MSC.215, two important standards of naval and offshore sectors.Blast-cleaned carbon steel specimens contaminated with sodium chloride solutions diluted in methanol ranging 20, 50 and 100 mg/m² NaCl were painted with two epoxy-amine paint coats. Samples were evaluated by cathodic disbondment, water immersion at 40 ºC, pull-off adhesion strength and cyclic corrosion tests.Larger blisters and loss of adhesion were observed as the soluble salts content at the interface increased. Although, it was not possible to find a critical level of soluble salts even considering data about similar coating systems. A safe soluble salt content must be chosen based on tests that closer reproduce service and environmental conditions to which a painted structure will be exposed.

Ship Painting Process Design Based on IDBSACN-RF

“…The rating film thickness of the primer for the outer plate above the waterline is 200 µm, as specified in the coating matching table for the H1127/7 type ship. According to the PSPC standard, the dry film thickness should satisfy the 90/10 principle [40]. That is, the dry film thickness of more than 90% of the test points is not less than the specified film thickness and the dry film thickness of the remaining test points is not less than 90% of the specified film thickness.…”