Mitigating Manganese-Induced Pitting Failures on a Stainless Steel Surface Condenser

In early 2005, the 4-unit, 1200 MW Cottonwood Energy facility on the Sabine River in Deweyville, TX experienced a sudden increase in condenser tube failures and eddy current pit indications. Metallurgical analysis of failed tube specimens revealed the presence of a thin, hard manganese-rich coating, with intense pits propagating at breaks in the deposit. Successful mitigation of manganese-induced pitting and repassivation of the condenser tubes requires that the surface and pits first be thoroughly cleaned prior to implementing a manganese deposit control program. This paper reviews the successful cleaning process developed and implemented by Cottonwood Energy to remove manganese deposits from four stainless steel surface condensers. The cleaning procedure employed several novel features to ensure complete manganese removal, minimize environmental impact, reduce costs, control attack on the base tube metal, and ensure personnel safety. The paper also includes a discussion of corrective actions taken to prevent re-occurrence.