The causes of exceptionally high localized corrosion rates in steels may be difficult to diagnose. In
recent years the cause has commonly been ascribed to microbially-influenced corrosion (MIC). This
paper looks at two water-bearing piping systems, one stainless steel, the other carbon steel, and uses
them to develop criteria by which MIC could be recognized.
Corrosion in the stainless steel piping was taking place at or near welds, producing through-wall
penetration of 0.25-inch (~6 mm) thick piping in six months; Micromorphology of the corrosion sites,
plus their location with respect to the weld, allow identification of the process as MIC.