Initial corrosion mechanism for API 5L X80 steel in CO2/SO2-saturated aqueous solution within a CCUS system: Inhibition effect of SO2 impurity

In the present study, the effect of an SO2 impurity on the electrochemical behaviour of X80 steel in CO2-saturated solution was evaluated within a carbon capture, utilization and storage system. In the initial stage of corrosion, although SO2 dissolved in water reduced the pH of the solution, the inhibition of corrosion by SO2 and its hydrolysate adsorbed on the surface of X80 steel dominated the corrosion behaviour. Under anaerobic conditions, SO2 was converted to S− and S2−, which reduced the adsorbed SO2 molecules. The FeS and FeS2 corrosion product scales which took shape on the surface of X80 steel had poor adhesion and could only provide limited protection. However, the corrosion product scale occupied the adsorption region of SO2 and its hydrolysate, resulting in an increase in the corrosion rate. The adsorption of SO2 molecule and the hydrolysate and the protective properties of the corrosion product scale affect the corrosion mechanism of X80 in CO2/SO2-saturated solution. [Display omitted] •SO2 impurity inhibited corrosion at the initial stage in CO2-saturated solution.•Product scale with poor protectiveness occupied the adsorption zone of SO2.•SO2 is mainly converted to FeS and FeS2 in the anaerobic-CO2 solution.•Both the product scale and the adsorption of SO2 molecules affected the corrosion.