Donald L. Gibbon and Mehrooz Zamanzadeh

MATCO Inc
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. This  corrosion produced through-wall penetration in six months; Micromorphology  of the corrosion sites, plus their location with respect to the weld, allow  identification of the process as MIC.
Corrosion in the carbon steel pipes took place hidden from view in joints  made with  Victaulic-couplings.. On opening the joints it was found that corrosion had eaten away as  much as one quarter inch of schedule 20 steel at the ends of the pipe. The system had already been shut down and dried out, making traditional culturing of the microbes in the joints impossible. Polymerase chain reaction techniques were used to recreate the DNA of the bacteria responsible for the corrosion, allowing their identification.