Enzyme-induced ennoblement of AISI 316L stainless steel: Focus on pitting corrosion behavior

The use of purified enzymes in microbial influenced corrosion (MIC) studies is increasingly recognized as a powerful tool to understand electrochemical interfacial processes, especially the ennoblement of stainless steels (SS) in natural waters. The ennoblement has attracted the interest of many researchers as the consequences in terms of pitting corrosion are still not well understood. In the present study, the ennoblement of AISI 316L SS was induced by glucose oxidase (Gox) catalyzed reaction or by adding hydrogen peroxide (H2O2) in synthetic fresh water, on the basis of previous work. The corrosion behavior of the sample was studied using potentiodynamic and galvanostatic polarization tests. When the ennoblement occurs. the pitting potential (E-p) becomes nobler as well. The involvement of H2O2 to enhance pits repassivation seems to be a key consideration in this respect. Results obtained using this enzymatic system enable us to reappraise the commonly acknowledged hypothesis that the ennoblement increases the risk of localized attacks. (C) 2009 Elsevier Ltd. All rights reserved.