Abstract
The susceptibility to microbiologically influenced corrosion (MIC) of the 300 Series stainless steels has been well documented in the literature. MIC has occurred in Type 304 and 316 weld deposits, in the weld heat-affected zones and in base material. In the weld deposits either the austenite or ferrite phase can be preferentially attacked depending on whether the environmental conditions are either oxidizing or reducing, respectively. Attack in the base metal and the weld heat affected zone of the base metal has been assumed in the literature as due to the presence of sensitization, but sensitization has not been conclusively established by testing. One source which specifically checked for sensitization on a number of stainless specimens reported "there seems to be no correlation of sensitization to MIC".
This paper presents the results of tests performed with a number of specimens fabricated from Type 304, Type 316, and Type 316L stainless steel in both the welded, wrought, and furnace sensitized condition. Only the results of MIC in the base metal are presented. The results indicate that corrosion due to bacteria was not related to sensitization. The susceptibility to corrosion was found to be related to the microstructure produced during the manufacturing process. The resistance to MIC of the 300 series stainless steels could be improved easily by proper processing of the material and that the L grade stainless need not be specified to present MIC.
