engleski

Microbial pitting corrosion of stainless steel weldments in fresh water systems

A case of severe pitting corrosion of stainless steel pipes in a facility for fresh water treatment has been analysed. The phenomenon resulted in system's failure by water leakage. It is proven that the failure was the consequence of microbially induced corrosion under nodules formed by settlement of microbes on circumferential weldments and on adjacent heat tint zones. Microbiological testing revealed the presence of iron and manganese oxidising bacteria in the nodules. The presence of sulphides in corrosion products was also established that points at the activity of sulphate reducing bacteria under larger nodules. Accordingly, the process of damaging of stainless steel pipes is a combination of aerobic and anaerobic microbially induced corrosion. It is possible to achieve essential reduction of liability of such corrosion by acid pickling of the interior of welded stainless steel pipes that proves strong effect of surface state on damaging process. On the contrary the influence of the type of stainless steel is not significant.

MIC; Stainless Steel Weldments; Fresh Water; Surface State

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