Biofilm adhesion and microbially influenced corrosion of SUS304 welds exposed to dam water

Abstract

Microbially influenced corrosion (MIC) of stainless steel welds has been confirmed not only in natural sea water but also in fresh water recently. In this study, four kinds of SUS304 test coupons, like as base metal, as welded by GTAW without filler metal, as welded by GTAW with filler metal and polished after welding by GTAW, have been prepared. These test coupons have been exposed to the dam water, which caused the MIC failure on the SUS304 piping in the last few years, for 550 days in order to investigate the relation between the adhesion of biofilms and MIC. Visual inspection, measuring of adherent bacteria, proteins and corrosion potential have been executed on the immersed test coupons for each exposure times of 170, 420 and 550 days. The adhesion quantity of biofilms on the test coupons exposed for 170 and 550 days have increased much more than that on the test coupons exposed for 420 days. The effect on the adhesion of biofilms based on the difference of the surface treatments between polishing and as welded has not been confirmed. The ennoblement of the corrosion potential has a connection with not only the adhesion of biofilms but also algae and sedimentation. Furthermore, all test coupons have been observed by SEM. No corrosion pits has been observed on any test coupons of the base metal. On the other hand, some corrosion pits has been confirmed on the test coupons of welds regardless of reinforcement or oxide scale in this study.