Microbiologically influenced corrosion on weld of stainless steel

The influence of welding defects, water compositions and microbiological species on MIC (microbiologically influenced corrosion) was studied. The open circuit potential (OCP) was measured during MIC test. It was found that OCP shifted to a higher level when the system was inoculated with bacteria and it decreased dramatically when MIC started. As a contrast, the OCP kept stable in the system without bacteria. Among a series of welding defects the golden heat tint was found to be the most susceptible to MIC. It was found that pitting corrosion happened when Cl(-)content in the water was high. The tubercles over pitting were observed with SEM. Some elements inside of the tubercles were measured with EDXA. Microbiological analysis of a corroded and a non-corroded samples revealed the significant difference to be number of the Mn-Fe oxidizing bacteria between them.