Electrochemical Characterization of Microbiologically Influenced Corrosion on Linepipe Steel Exposed to Facultative Anaerobic Desulfovibrio sp.

In-situ electrochemical techniques were used to investigate the microbiologically influenced corrosion (MIC) of API 5L X52 linepipe steel by Desulfovibrio sp. (sulfate reducing bacteria; SRB) cultivated from a sour oil well in Louisiana, USA. These techniques include electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) and linear polarization resistance (LPR). OCP trend showed anodic polarization shift of 100 mV between the biotic medium with reference to abiotic medium (control). These positive polarization shifts have been attributed to complex deposits of bacterial cells, extra-cellular polymeric substances and associated structures that synergistically altered the electrochemical environment of the system and increased the corrosion rate. Through circuit modeling, EIS results were used to interpret the kinetics and real time interactions between the electrode, biofilm and solution interfaces. The results confirmed that extensive localized corrosion activity of SRB is due to a formed biofilm and a porous iron sulfide layer on the metal surface.