Microbiologically influenced corrosion of carbon steel exposed to anaerobic soil

Microbiologicay influenced corrosion (MIC) of plain carbon steel in anaerobic soil was investigated using field survey, the electrochemical polarization technique, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) Coupled With energy-dispersive spectroscopy (EDS), a thin-film electrical resistance (ER) probe, and galvanic current measurement, The field survey revealed that the risk of MIC could be predicted by the analysis of environmental parameters such as soil resistivity, water content, the content of total organic carbon, reduction-oxidation potential, and the content of sulfate with the consideration of the effectiveness of cathodic protection (CP). From the results of conventional electrochemical experiments, it is evident that the presence and therefore the activity of sulfate-reducing bacteria (SRB) alter the corrosion mechanism of steel by the production of hydrogen sulfide (H2S) and iron sulfide (FeS) film on the steel surface, which reduces the polarization resistance and therefore increases the corrosion rate. SRB-induced MIC is a localized corrosion accompanying the breakdown of the biogenic FeS film. This fact is confirmed by SEM/EDS analysis and thin-film ER probe testing. The localized corrosion rate by SRB after the rupture of the sulfide film can be obtained by the zero-resistance ammeter (ZRA) technique and is comparable to that reported in field conditions.