Threshold SRB populations for MIC of stainless alloys

The three CANDU reactor sites on the Great Lakes exhibit differences in susceptibility to microbially influenced corrosion (MIC) of heat exchanger tubes, despite similar colonization of sulfate-reducing bacteria (SRB). Therefore, it was suspected that bacterial activity, rather than numbers, is responsible for pit initiation. Accelerated corrosion tests are being used to examine the relationship between SRB colonization and pitting activity on stainless alloy heat exchanger tubes. Experimental conditions model those of the natural systems. At present, there appears to be little correlation between bacterial numbers and pit initiation. However, there does appear to be a correlation between bacterial activity (causing a decrease in corrosion potential, as a function of sulfide production), and pit initiation. Data are being collected to develop a model to predict MIC for the CHECWORKS service water module. (author)