A 25 year exposure test of thermal sprayed Zn, Al, and Zn-Al coatings in marine environments

摘要

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. Coating was applied to twelve steel pipes by arc- and flame-spraying to varied thickness and subjected to various post-spray treatments such as sealing and painting. The samples were set vertically into seawater at a port located approximately 80 km south from Tokyo. Corrosion performance of these coatings has been inspected annually by recording the appearance and coatings' 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 Al and Zn-Al coatings still exhibit superb corrosion performance. After 18 years, heavily damaged portions of three pipes were removed and new pipes were welded to the sound portions. The repaired regions were spray coated with Al-5%Mg. In this paper, the corrosion performance of sprayed coatings in the exposure test during 25 years is summarized.