Mechanisms of Reproducible Microbial Pitting of 304 Stainless Steel by a MixedConsortium Containing Sulphate-Reducing Bacteria, Tri-Service Committee on Corrosion Proceedings

摘要

Pitting corrosion is characterised by the formation of small anodes andcorresponding large cathodes, which allow the formation of pits in the metal matrix. A number of mechanisms have been put forward to account for the involvement of SRB in this process including: cathodic depolarization of hydrogen, bacterial sulphide acting as the cathode, and changes in pH due to sulphate-reducing bacteria (SRB). To date there has been little success in reproducibly inducing SRB pitting of stainless steels in a laboratory system. A concentric electrode has been designed in which a small anode is artificially produced within a large cathode by applying a galvanic current of 12 muA /sq cm. During the application of this galvanic current, various consortia and axenic cultures of bacteria are allowed to colonise the surface of the stainless steel concentric electrode. After seventy-two hours the induced current is removed and the resultant current monitored. Electrochemical impedance spectroscopy (EIS) is carried out on both the anodes and cathodes in order to determine the charge transfer resistance (Rct values) and changes in phase angles with time. At the termination of the experiment viable counts of both SRB Vibrio sp. are recorded from the anodes and cathodes.