Comparative electrochemical noise study of the corrosion process of carbon steel by the sulfate-reducing bacterium Desulfovibrio alaskensis under nutritionally rich and oligotrophic culture conditions

This paper describes the electrochemical behavior of SAE1010 carbon steel when it was exposed to a new isolate of Desulfovibrio alaskensis (strain IMP-7760) growing in nutritionally rich or oligotrophic conditions. The localization index (LI) from the electrochemical noise analysis was used to identify the type of corrosion mechanisms, which took place under the two different environmental conditions. In nutritionally rich conditions, steel first exhibited a uniform corrosion, followed by a short period of localized corrosion with values of LI near 0.3, and finally a mixed corrosion process. In contrast, under oligotrophic conditions, there were fluctuations among the three mechanisms during the first 100 h, then a long period of localized corrosion with values of LI reaching 1, and finally the corrosion process became uniform. The analysis of Rn was used to evaluate the corrosion rate when the corrosion process became uniform. Under nutritionally rich conditions, the average corrosion rate was low; it never exceeded 1.2 mpy. In contrast, a significant corrosion rate value of 8 mpy was obtained in oligotrophic conditions. The analysis of the time series for current and potential noise in nutritionally rich experiments showed that the signals did not present the characteristic transients of metastable pitting and did not change with time, even at the highest values of LI. On the contrary, in oligotrophic experiments, just before pitting was initiated as evidenced by the rapid increase of LI, a modulated amplitude signal in current noise, with a corresponding modulated potential noise response, was observed. At the highest values of LI, the time series for current and potential noise showed a typical pitting corrosion pattern.