The microbiologically influenced corrosion (MIC) behavior of L360N pipeline steel was studied in simulated tight gas produced water mixed with condensate. The effect and mechanism of condensate on MIC behavior was explored by conducting experiments.Six groups of static immersion tests were carried out under different volume proportions of mixed condensate, and the condensate concentration dissolved in water was measured by gravimetric method. The MPN method was used to count sessile cells settled on coupon surface. The weight-loss and electrochemical measurements were applied to study the influence of condensate on the corrosion rate and mechanism of L360N pipeline steel. The laser microscope was used to analyze pit depth of coupons after removal of corrosion product. Investigation of the surface and cross-sectional morphology of corrosion product was conducted by SEM. EDS and XPS were used to analyze the composition of corrosion product.The MIC behavior was closely affected by the dissolution of condensate. And the condensate concentration in water increased as volume proportion of condensate rose. The general corrosion rates in the presence of condensate were much lower than those without it. But the occurrence of pitting corrosion was observed for all coupons under different conditions. It indicated that the presence of condensate had a limited inhibition effect on pitting corrosion. With the existence of dissolved condensate, there were still a large amount of sessile cells at above 104 cells/cm2 for both SRB and FB. The SEM analysis showed that all coupons were covered with biofilms with the composition of Fe2O3 and FeS. It suggested that the metabolic activity could not be completely prevented by the increase of condensate concentration, and the MIC was caused for all conditions. From EDS analysis, the significant difference in S mass fraction was found among different analysis regions for the same coupon. It indicated the increase of condensate concentration contributed to the formation of more heterogeneous biofilms because of inhomogeneous distribution of sulfide, which was one of the reasons for pitting corrosion occurrence. It could be seen from electrochemical measurements that although the electron transfer resistance (Rct) obtained under various conditions showed different levels, Rct and corrosion current density (Jcorr) for all conditions had similar orders of magnitude at the end of testing. It demonstrated that the increase of condensate might promote MIC inhibition at the start of immersion, but could not consistently hinder bacteria metabolism.The influence of condensate on MIC behavior of L360N pipeline steel in simulated tight gas produced water was revealed. The MIC occurred for all conditions and caused pitting corrosion. The reason for it was that the complete biofilm was formed on all coupons surface that exposed to simulated produced water with different concentration of condensate. Then the conformable environment under it was created for sessile cells to survive. Therefore, the metabolize of sessile cells was increasingly enhanced and localized corrosion battery was formed gradually. And the increase of condensate concentration led to the formation of biofilms with more heterogeneous structure, which could be one of mechanisms about pitting corrosion induced by MIC as well.
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