Microbiologically Influenced Corrosion (MIC) of stainless steel weldments on the pipe line in the sewage treatment plant

Abstract

Microbially Influenced Corrosion (MIC) of several types of stainless steel weld metal were examined by using the waste water which was extracted from sewage treating plant. An activated carbon was employed in this treatment. Experiments were done under controlled laboratory conditions. Weld metal samples were exposed to the test solution of waste water and kept in an incubator at 40 C (104 F). The turbercles developed on the surface of samples and grew gradually as a function of time. Such developed the turbercles were not hard. The corrosion sites were observed on the samples of 316L 308N and 308 stainless steel weld metal under the turbercles. It was estimated that corrosion behavior was affected by the microstructure of the weld metal. An unattached ferrite dendritic skeleton structure and a pit like penetration hole were observed. The bacteria attaching on the pits were observed by using Scanning Electron Microscopy (SEM). The types of bacteria will be identified in future work.

下水処理プラントから採取した廃水を用いて、数種類のステンレス鋼溶接金属の微生物誘起腐食を試験した。この処理には活性炭を用いた。実験は制御された実験室条件で行った。溶接金属試料を廃水溶液に曝してから40度C(104度F)の微生物培養器中に保持した。試料表面上に小粒が発生し、時間の経過と共にゆっくりと成長していった。このように発生した小粒は硬いものではなかった。316L,308Nおよび308ステンレス鋼の溶接金属試料で小粒の下に腐食箇所を観察した。腐食挙動は、溶接金属の微細構造の影響を受けているように思える。フェライト組織の樹枝状結晶は腐食されておらず、ピット状の浸透孔を認めた。走査電子顕微鏡を用いて、このピットを観察したところ、細菌による侵食が見つかった。細菌の種類の同定は今後の研究で行う。