Abstract
Stainless steel pipes whose inner surface is electro-polished have become applied as the pipings for purified gases used in the semiconductor processing. In order to maintain the purity of the gases, the piping is required not to release particles and impure gases from its surface and to have excellent resistance to corrosive gases such as chlorine, hydrogen chloride and so on. The corrosion behavior of the electro-polished SUS 316L pipe was investigated in a moist chlorine environment. The heat affected zone (HAZ) of its weldment preferentially suffered pitting corrosion. The results of the pitting corrosion test using ferric chloride solution revealed that the pitting resistance of the HAZ was deteriorated as compared with the base metal. The chemical compositions at the inner surface of the pipe were analyzed by the secondary ion mass spectrometer (SIMS). The surface film was composed of Cr rich oxide on the base metal, but the Cr concentration in the film on the HAZ was decreased because of the enrichments of Si and Mn. The relationship between the film formation and the corrosion resistance on the HAZ was discussed in relation with the previous work on the pitting corrosion of the tinted HAZ of stainless steels.
