| Summary: | This research investigates the behaviour of microbiologically influenced corrosion (MIC) of sulfate-reducing bacteria (SRB) on API 5L X65 carbon steel in the presence of CO2 gas. The weight loss test, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation were implemented to determine the corrosion behaviours. Biofilms, corrosion products and pit penetration rate were characterised by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and infinite focus microscope (IFM). Findings from weight loss confirmed that specimens in the absence of SRB promote uniform corrosion with a higher corrosion rate value of 1.05 mm per yr compared to the pit penetration rate of 0.12 mm per yr. The IFM analysis shows that samples with the SRB presence promote localised corrosion due to the higher pit penetration rate value of 0.81 mm per yr than the uniform corrosion rate of 0.57 mm per yr. Furthermore, EIS measurements confirmed that corrosion products and biofilm formations affect the corrosion process. The surface analysis proved the presence of sulfur on metal specimens exposed to SRB in CO2 environments; this indication supports the formation of the FeS layer. Finally, the XRD test affirmed the formation of Fe3C and FeS in samples exposed to the SRB. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
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