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The presence of active microorganisms on piping and components in cooling water systems can have a profound effect on the corrosion performance of such systems. Microbiologically influenced corrosion (MIC) can result in premature failures of critical and support systems, increased downtime of equipment for repairs and maintenance, and increased operating costs associated with mitigation measures. In some cases, MIC has forced premature replacement of tanks, heat exchangers, and piping systems with a severe effect on plant availability.
Monitoring methods that alert plant operators that biofilm formation is occurring on pipe work and components permit the operators to initiate mitigation actions before biofouling becomes severe or MIC has occurred. The effectiveness of common water treatment chemicals is also increased substantially by prompt actions. Unfortunately, most monitoring activities rely upon process controls or batch methods that are too slow or of insufficient sensitivity to permit reliable control and implementation of mitigation techniques. Those methods are also too slow to be utilized for process controls of biocide additions, hence, mitigation activities are often excessively costly, both environmentally and in terms of direct costs of antimicrobial chemicals.
An electrochemical probe to permit on-line monitoring of biofilm activity under power plant or other industrial exposure conditions is under development. This device, the BIoGEORGE electrochemical biofilm monitor, permits on-line evaluations of the effects of biofilm formation upon the surfaces of passive alloys such as stainless steels exposed to cooling water environments. Benchtop experiments have shown that biofilm formation on stainless steel surfaces can be detected by an electrochemical indication well in advance of any visual evidence of biofilm or corrosion on the electrodes. The probe may be used to provide an early warning to plant operators to take appropriate actions such that biofouling and MIC may be avoided. The simplicity of the design and operation sequence are such that probes may be installed and left to operate unattended for extended periods with only minimal operator interaction.
The design of the probe, results of benchtop experiments, and a description of its installation at the Browns Ferry Nuclear Plant are described.
monitoring, microbiologically influenced corrosion (MIC), electrochemical methods
Associate, Structural Integrity Associates, San Jose, CA
President, Corrosion Failure Analysis and Control, San Ramon, CA
Engineer, Tennessee Valley Authority, Browns Ferry Nuclear Plant, Decatur, AL