The development of carbon capture and storage (CCS) technologies have helped facilitate the success of CO2-EOR injection operations. However, captured CO2 from anthropogenic sources can potentially contain oxygen which will increase the risk of corrosion. A preliminary study was conducted at 1 bar to investigate the effect of oxygen ingress on the iron carbonate (FeCO3) corrosion product layers generated during CO2 corrosion of mild steel. Carbon steel (UNS G10180) samples were immersed in a CO2- saturated 1 wt.% NaCl electrolyte for 7 days, with the tests being perturbed with 1 ppm O2 at different experimental times. Iron carbonate film-forming conditions (80°C and pH 6.6 ± 0.1) were maintained throughout experiments. Electrochemical measurements indicated a decrease in corrosion rate due to scale formation that conferred some degree of protection to the steel surface. Although the corrosion rates at the conclusion of all tests were relatively low, localized corrosion was observed. Surface analysis showed severe corrosion and confirmed the formation of iron (III) oxides and iron carbonate. A distinct feature of oxygen ingress is the formation of tubercles on the steel surfaces. The degradation of initially formed iron carbonate occurred concurrently with the development of localized corrosion features as deep as 100 µm. It can be concluded that oxygen ingress, even at low concentrations, can have a profound effect on sweet corrosion of mild steel.

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