An 18-year exposure test of thermal-sprayed Zn, Al, and Zn-Al coatings in marine environment

The thermal spray committee of the Japan Association of Corrosion Control (JACC) has been conducting a marine corrosion test of thermal-sprayed Zn, Al, and Zn-Al coatings since 1986. Me coating was applied to twelve steel pipes by arc- and flame-spraying to varied thicknesses and subjected to various post-spray treatments. The samples were set vertically into seawater at a port located approximately 80 km south of Tokyo. The corrosion performance of these coatings has been inspected annually by recording their appearance and thickness at the sea-air, splash, and tidal zones. No significant changes were observed for the first several years of exposure. After 7 years, however, Zn coatings with and without sealing started to suffer degradation in the immersed portion. Contrary to this, most of the At and Zn-Al coatings still exhibit superb corrosion performance. In order to place the test in a proper perspective, a special team of about 20 members was formed to conduct a survey on corrosion prevention through thermal spray technology in fiscal year 2001, collecting more than 170 published reports and asking experts to contribute reviews on various aspects of this technology. In this paper, the corrosion performance of sprayed coatings in the exposure test during 18 years will be summarized, and discussion will be made by comparing the test results with the published data collected by the survey.