This is a study of how Sulfate–Reducing Bacteria (SRB) intervene in the process of Microbiologically Induced Corrosion (MIC) of carbon steel. Specifically, the evaluation was centered on the part played by Desulfovibrio desulfuricans subs. desulfuricans in altering the kinetics of the cathodic reaction of hydrogen evolution using the hydrogen permeation cell developed by Devanathan and Starchuski. An evaluation of planktonic population growth was performed during the tests in the inoculated medium. In all cases, a typical growth curve was obtained, with counts ranging between 107 and 109 cell/mL at 24 hours. Sessile count was made by ultrasonic removal from the strip and biofilm characterization by Scanning Electron Microscopy (SEM). Bacteria with vibrio morphology were observed at a concentration of 107 cell/mL. The test determined hydrogen permeation 200 minutes after inoculation and an open–circuit potential reduction of the steel at values of –780 mV vs SCE, with high bacterial activity and the typical H2S attack morphology. These results, together with those obtained on a palladium strip, show that this SRB corrodes carbon steel through direct corrosive action of the H2S generated by the bacteria during their metabolic process of reducing sulfates to sulfides, accelerated by the formation of a non – protective iron sulfide film. Therefore, the Cathodic depolarization theory is not the chief action mechanism of D. desulfuricans in the MIC process.
Key words: Devanathan and Starchuski cell, hydrogen permeation, Cathodic depolarization, MIC, Desulfovibrio desulfuricans, sulfide corrosion.