Yasushi Kikuchi1, Kenji Tomoto1, Chigo Okayama1, Fukuhisa Matsuda1,Masaki Nishimura2, Takeshi Sakane3 and Yoshinobu Kaneko4
1Joining and Welding Research Institute, Osaka University, Ibaraki 567
The failure in the weld joint occurred in as little as, two months from the start-up of the sewage treatment plant. At the beginning of the failure analysis, crevice corrosion was considered as the main reason since the welding defects. But, the estimated corrosion rate of the welds was too fast. Then, metallurgical failure analysis to understand this behavior was carried out. Finally, it was concluded that the localized corrosion on the welds was a kind of Microbiologically Influenced Corrosion (MIC).
The first stage of a laboratory scale test using the stainless steel welds and the residual liquid obtainable from the MIC -affected effluent treatment plant was performed.
The test samples were exposed in the liquid and kept in an incubator at constant temperature. Corrosion pits were found on 316L, 308N (0.2 mass% nitrogen approximately) and 308 weld metal. The colonies of bacteria several mm in size near the corrosion pits were observed and the types of the bacteria was identified. The evaluation test of corrosion ability of the identified bacteria was planned. MIC susceptibility of the stainless steels used was evaluated.
(Received January 31, 1997)
bacterial corrosion, stainless steel, weld metal
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