Evaluating Corrosion Inhibitors as a Means to Control MIC in Produced Water

Film forming corrosion inhibitors are often selected to control CO₂ corrosion, and their effectiveness versus microbiologically influenced corrosion (MIC) is desirable in systems that suffer from both forms of corrosion.  Traditional corrosion inhibitor tests (e.g., bubble tests) have unfavorable conditions for microbial activity and are inadequate for evaluating MIC control.  Biocide screening test methods have been used to evaluate microbial kill with toxic chemicals added batch wise, providing very little direct information about controlling corrosion. Once-through flow cells containing corrosion coupons were inoculated with a field consortium enriched in synthetic produced water to simulate MIC field activity.  Maximum pitting rate on the coupons was the key performance indicator for screening inhibitors.  Results indicated that many of the corrosion inhibitors tested increased the maximum MIC pitting rates when compared to untreated controls. In at least one case, a less toxic inhibitor provided better MIC control than a more toxic inhibitor. Data suggest that the field microbial consortia used in the testing developed a resistance to an incumbent inhibitor that has been used for many years.  The results indicate that inhibitor selection based on MIC monitoring is not simply a function of their ability to control bacterial growth and activity.