The Influence of Chemical Cleaning Methods on Pitting Morphology Attributed to Microbially Influenced Corrosion of Stainless Steels

Chemical cleaning methods are frequently used for the removal of biofilm/corrosion products from metallic materials to evaluate the type and severity of microbially influenced corrosion (MIC) damage. The study described here investigates the effect of commonly applied cleaning treatments on the dissolution of stainless steel surface inclusions and emphasizes the potential impact of such treatments on MIC diagnostics. Polished 304 grade stainless steel coupons were ultrasonicated for 1 min, 3 min, and 7 min in each of the three commonly applied agents, i.e., Clarke’s, nitric acid, and hydrofluoric acid-based solutions. Post-treatment analyses of steel surfaces revealed pitting attack. For each treatment type and duration, the morphology and quantitative measurements of pits were recorded. Shape, size, and depth of examined pits closely resembled damage that, in many laboratory-based studies, have been attributed to MIC. The investigation herein demonstrates that caution ought to be exercised when implicating MIC as the cause of stainless steel pitting damage.