Marine Exposure Tests of Thermal Sprayed Coatings in Japan

Abstract

Abstract 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 1985. Twelve kinds of sprayed coating were deposited onto steel pipes by arc- and flame-spraying to varied thickness and subjected to various post-spray treatments. The samples were set vertically into seawater at a port 80 km south from Tokyo. Corrosion performance of these coatings has been inspected annually by recording the appearance and coatings’ thickness at sea air-, splash- and tidal-zones. No significant changes were observed for five years exposure. After 7 years, however, Zn coatings with and without sealing started to suffer degradation in the immersed portion. Contrary to this, Al and Zn-Al coatings still exhibit superb corrosion performance. The test will continue till 2006 to complete the test period of 20 years. In order to place the test into a proper perspective, we also conducted a survey on the corrosion prevention by thermal spray technology in 2001, collecting more than 170 published reports and asking experts to contribute reviews on various aspects of the technology. This paper first describes several topics from the survey report to explain the past and the present situation of thermal spraying for corrosion prevention in Japan. Then, the corrosion performance of sprayed coatings in the exposure test during 15 years will be summarized.