Localized corrosion initiation and inhibition of carbon steel in CO ₂ –Cl ⁻ –HCO ₃ ⁻ environment

Internal localized corrosion of carbon steel pipelines severely threatens the service safety of oil and gas transportation facilities in CO 2 -containing aqueous environments. In this work, the corrosion evolution and localized corrosion initiation mechanisms of carbon steel in CO 2 –Cl − –HCO 3 − coexisting environments were systematically investigated under varying temperatures and HCO 3 − concentrations. The results demonstrate that the initiation of localized corrosion is primarily attributed to the formation of loose and porous FeCO 3 films, which fail to block the permeation of aggressive Cl − and expose the steel substrate to continuous corrosion. In contrast, the synergistic effect of elevated temperature and appropriate HCO 3 − concentration significantly improves FeCO 3 supersaturation and promotes the formation of dense, uniform, and protective FeCO 3 films, which effectively isolate the substrate from corrosive media and inhibit localized corrosion. Furthermore, this study quantitatively clarifies the optimal matching relationship between temperature and HCO 3 − concentration for the growth of high-quality protective FeCO 3 films. The findings provide fundamental mechanistic insights and practical guidance for the targeted regulation of HCO 3 − to mitigate localized corrosion of carbon steel in CO 2 -saturated oil and gas production systems.