Abstract
Localized corrosion of SAE1010 steel exposed to Desulfovibrio vietnamensis strain 7760 under oligotrophic conditions was characterized through an electrochemical noise analysis. Once the sulfate-reducing bacteria were inoculated, three evolution patterns of localization index (LI), were observed. From the start of the experiment to 135 h, LI values varied between 0.1 and 0.4. Then, the LI raised near to 1 and fluctuated between 0.1 and 1 for a long period of time (140 to 560 h). Finally it decreased and remained stable up to the end of the experiment at 0.01. This situation could indicate two different processes. After 140 h, mainly a localized corrosion process took place over the steel surface and after 560 h, a general corrosion process occurred.
According to the transients in current noise, a modulated amplitude signal with a correspondent modulated potential noise response for the initiation of pitting was observed just before LI increased near 1. At the highest LI values, the time records for current and potential have shown a typical behavior of pitting corrosion process.
In contrast, experiments with lactate as energy and carbon source for the sulfate reducing-bacteria exhibited a moderated localized corrosion process (LI, 0.1-0.3). In this case, the current and potential series did not present the characteristic signal of pitting corrosion.
The increase in LI and the presence of typical signal of pitting was discussed in terms of the utilization of cathodically produced hydrogen as a consequence of oligotrophic conditions.
