Localized corrosion, such as pitting and crevice/underdeposit corrosion, is responsible for the majority of plant equipment corrosion failures. However, the assessment of localized corrosion in plant operating conditions is often overlooked, partly because none of the techniques commonly used today can provide realistic and effective monitoring of localized corrosion. Research has resulted in the development of the localized corrosion monitor (LCM) as a solution to this problem. The LCM is based on a new, patented electrochemical method capable of in-situ, real-time, online determination of underdeposit corrosion rates. Experimental results have shown that the LCM technique can be used accurately, sensitively, and reliably to determine the rate of propagation of localized corrosion in mild steel. It ideally is suited to monitor the performance of corrosion inhibition programs in industrial systems. In this paper, the scientific principles behind the LCM are described. Usefulness of the LCM were demonstrated by results obtained in two refinery cooling water system trials. The results demonstrate clearly that the LCM localized corrosion rate was far more sensitive to process variable changes than general corrosion rate, and real-time, online, localized corrosion monitoring was most effective for treatment optimization to minimize the damaging effects of process variations.

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