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In this study, the effect of sulfate reducing Citrobacter sp. strain on the corrosion behavior of API X70 micro-alloyed pipeline steel is evaluated in a simulated soil solution at different immersion times (varying from 3 days to 24 days) under both abiotic and biotic conditions. In this process, a soil sample containing sludge was used as a source of production sulfate reducing citrobacter sp. and a soil sample extracted from the Ahvaz 2nd area was used as the basis of the soil simulation solution. The corrosion behavior of steel in two medium of sterile and an inoculated solution was evaluated through series of electrochemical tests, including Open circuit potential (OCP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques. Furthermore, to investigate the corrosion mechanism and the analysis of the products formed on the surface of the steel, a field emission scanning electron microscope coupled with energy dispersive X-ray spectroscopy (FESEM/EDS) were used. The EIS results showed a considerable variations in charge transfer resistance of corrosion reaction in the both abiotic and biotic systems. Formation a protective layer of corrosion products on the metal surface in the sterile medium led to a slight increase in the corrosion resistance and decrease in the corrosion rate. Nonetheless, different findings were observed for the coupons immersed in the inoculated solution. Regarding the FESEM photographs, accumulation of bacteria on the steel surface after than 3 days was observed. For further immersed times, a biofilm comprised of the dense extracellular polymeric substances was formed. This microstructural variations is associated with a remarkable reduction in the charge transfer resistance from 956 Ω.cm2 at 3 days to 55.03 Ω.Cm2 at 21 days.

Keywords: X70 microalloyed steel, Sulfate reducing citrobacter sp. strain, Open circuit potential (LPR), Biofilm, Linear polarization resistance (LPR), Electrochemical impedance spectroscopy (EIS)

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