Corrosion of Hot-Dip-Zinc Galvanized Power-Transmission-Tower Caused by Asid Rain

Abstract

Recently, corrosion of Power-Transmisson-Towers made of hot-dip-zinc galvanized steel are accelerated by acid rain. Corrosion is localized at a lower part of the tower placed under an aluminum rail. This paper is aimed to find the mechanism of this corrosion. Test pieces were exposed to rain water flowing on the aluminum rail, that flowing on the galvanized-steel tower and that falling from the sky. After 9 months, change in weight and appearance of test pieces were examined. Laboratory tests were also performed immersing test pieces in the three kinds of rain water described above. It was found that pH of rain water increases flowing on a galvanaized-steel tower as a result of the reaction between zinc and the rain water. On the other hand, increase in pH of rain water flowing on an aluminum rail is little sinse corrosion resistance of aluminum is higher than zinc. Consequently, corrosion rate of galvanized steel exposed to rain water flowing on an aluminum rail is higher than that exposed to that flowing on a galvanized-steel tower.