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The problem associated with the development of an accelerated test for assessing the susceptibility of materials to microbiologically influenced corrosion (MIC) is an uncommonly difficult one, The usual methods of accelerating corrosion such as increasing the temperature and concentration of aggressive species cannot be used. Both these factors have to be maintained within relatively tight limits, otherwise unacceptable changes in the biology of the system will result. Conventional, anodic polarization techniques can produce misleading information because the very high fields produced at the metal surface during polarization are incompatible with the maintenance of viable microorganisms. Other methods of acceleration and detection must therefore be sought.
A combination of failure analyses, laboratory studies, and field simulations has been useful to determine the mechanism of corrosion of Ontario Hydro's freshwater cooled heat exchangers (HXs) and to identify the most detrimental operating conditions. During field simulations of the worst conditions, electrochemical noise monitoring has identified a reproducible response that could be an MIC signature. This signature may be used to verify the relevance of proposed accelerated MIC tests to field operation.
This paper describes the methods and results of field experiments using electrochemical noise monitoring and their implications for accelerated MIC testing.
electrochemical noise, sulphate-reducing bacteria, hypochlorination, stagnation, hydrogen sulphide oxidation
Research scientist, Ontario Hydro, Toronto, Ontario
Research scientist, Chalk River Laboratories, System Chemistry and Corrosion, Chalk River, Ontario