Effect of Adherent Bacteria on Microbially Influenced Corrosion (MIC) of Stainless Steel Welded Joints.

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  • ステンレス（３０４）鋼溶接部での微生物腐食に及ぼす細菌付着挙動の影響
  • ステンレス 304 コウ ヨウセツブ デ ノ ビセイブツ フショク ニ オヨボス サイキン フチャク キョドウ ノ エイキョウ

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Abstract

The failure cases in plants by microbially influenced corrosion (MIC) of stainless steels were often observed around the welded joints. It is significant to understand the underlying reasons that influence the susceptibility of weld regions of stainless steels to MIC. Experiments were carried out to investigate the effect of the shape of the weld bead on the adhesion of bacteria and the occurrence of pitting corrosion. Coupon exposure studies were conducted using Type 304 stainless steel including the weld bead with TIG using type 308 filler. Coupons were immersed in the bacterial culture medium and then the bacteria (Methylobacterium sp. or Bacillus sp.) were inoculated. After a fixed period of incubation, the bacteria adhered on the surface of the specimen were observed by epifluorescence microscope. In the case of reciprocal shaking condition, the adhesion area of bacteria at HAZ and the toe region were more than those at base metal and top of weld region. In the case of non-shaking condition, the bacteria were adhered uniformly at base metal, HAZ, toe and top of weld metal. After 60 days of incubation, the surface of the specimen was observed by SEM. Pitting corrosion was observed at the toe region. The austenite phase was preferentially attacked and δ-ferrite phase was retained like a skeleton. Bacterial adhesion correlated with the occurrence of corrosion. Therefore the weld bead shape is considered to have significant influence on bacterial adhesion and in turn, MIC occurrence in stainless steel. (250 words)

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