Comparison of MCI pit morphology with non-MIC chloride induced pits in types 304/304L/E308 stainless steel base metal welds

Two groups of corrosion pits were examined using scanning electron and optical microscopes: (1) MIC pits in Type 304/304L stainless steels and E308 stainless steel welds and (2) non-MIC chloride induced corrosion pits in the same materials. A faceted appearance is common to MIC and non-MIC pitting/crevice corrosion of Type 304/304L stainless steel base metal. Facets were found even in dendritic skeletons in MIC and non-MIC cavities of E308 stainless steel welds. Dendritic skeletons are common to MIC and non-MIC pits in E308 stainless steel welds. Thus, no unique morphological characteristics exist for MIC pits. Scanning electron and optical micrographs are presented to support the findings.