Effect of Protective Behaviour of Biofilm Formed By the Anaerobic Sulfate-Reducing Bacteria on the Corrosion Resistance of the API X42 Microalloyed Steel

In this study, the protective behavior of the biofilm produced on the surface of the API X42 micro-alloyed pipeline steel by the bacterium clostridium sp. as an anaerobic sulfate-reducing bacteria (SRB) is evaluated in a saline simulated soil solution in comparison with the sterile medium. Microstructure and surface morphology was examined by field emission scanning electron microscopy (FESEM) coupled with energy dispersive spectroscopy (EDS). Corrosion properties were investigated using linear polarization and electrochemical impedance spectroscopy (EIS). The results approve the formation of a biofilm consisting of bacterial cells, extracellular polymeric substance (EPS), and corrosion products. In this relatively dense biofilm, semiconductive iron sulfide which is destructive to the corrosion behavior of biofilm is not observed. In addition, the biofilm produced on the metal surface at immersion time of 21 days in the bacterial inoculated medium improves polarization resistance to 7330 Ω.cm2, while at this time the polarization resistance of the protective corrosion products layer created in the sterile condition is about 1421 Ω.cm2. This comparison shows a 5-fold improvement in corrosion resistance as a result of the biofilm's protective behavior.