The Effect of Cleaning Processes on External Coatings Performance

External coatings for corrosion protection are often used in severely corrosive environments. One major concern regarding coating performance is the negative effect of soluble salts on the steel substrate at the time of coating application, particularly for marine maintenance coatings. These salts impact the applied coating systems in several ways, including osmotic coating blistering, promotion of underfilm corrosion, and coating disbondment. CORROSION 2014 paper no. 4391, “The Effect of Four Commercially Available Steel Decontamination Processes on the Performance of External Coatings,” by M. Melancon, et al. focuses on removing soluble salts contamination by commercially available decontamination processes and the resulting effects on external coating systems. The researchers directly compared the effectiveness of four cleaning methods with the performance of ten coating systems. After cleaning, sample evaluation for chloride ion contamination levels was carried out using commercial chloride ion test kits for surfaces and the ion chromatography method. Additionally, scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX) and elemental surface mapping analysis were carried out. Laboratory testing of coating systems included adhesion, porosity, electrochemical impedance spectroscopy (EIS) analysis, and cyclic ultraviolet (UV)/salt fog exposure. The performance of the ten coatings on all substrates was good, but there were differences in gloss retention of the different coatings. The only significant difference in coatings performance compared to the substrate cleaning method was higher undercreep observed for most of the coatings applied over a substrate cleaned with an ultra-high pressure water jet system. This shows the importance of substrate preparation due to the sensitivity of the coatings to even low levels of salt.