Study on the effect of coexisting SO2 and NO2 on the electrochemical corrosion behaviour of P110 tubing material for CO2 sequestration

During CO 2 sequestration, the injected gas contains various non-CO 2 gases associated with carbonaceous materials, namely carbon source impurities. This study conducted in situ electrochemical tests on P110 tubing steel at 90 °C under conditions of zero carbon source impurities, 100 ppm SO 2 and 100 ppm NO 2 coexistence. Impedance spectroscopy and dynamic potential scanning polarography techniques characterised microstructural information concerning post-corrosion film layers, product film/substrate interfaces, and product film/corrosion medium interactions. Results indicate that under pure CO 2 conditions, a dense and protective FeCO 3 /CaCO 3 corrosion product film forms on the P110 steel surface. This film exhibits a large capacitive arc radius and a high charge transfer resistance (R t ) of 220.674 Ω·cm 2 , suppressing the anodic active area and resulting in low, uniform corrosion rates. The introduction of SO 2 and NO 2 significantly disrupted the integrity and stability of the corrosion product film, inducing dynamic enhancement and spatial expansion of local electrochemical activity. Within the CO 2 + 100 ppm SO 2 + 100 ppm NO 2 coupled system, the corrosion product film transformed into a loose, porous composite film comprising FeS, FeSO 4 , and Fe(NO 3 ) 3 . The capacitive arc radius markedly diminished, the corrosion current density (I corr ) increased, and R t plummeted to 5.270 Ω·cm 2 . Concurrently, the number of active anodic sites increased, with peak current density progressively rising over corrosion time, markedly enhancing localised corrosion susceptibility. This study first reveals the synergistic acceleration mechanism of localised corrosion in P110 steel under CO 2 storage conditions when SO 2 and NO 2 coexist at elevated temperatures and pressures. It provides crucial electrochemical evidence for predicting the service life and selecting materials for pipelines under impurity-containing CO 2 geological storage conditions. • SO 2 and NO 2 coexistence significantly accelerates the corrosion of P110 tubing steel in CO 2 sequestration environments. • FeCO 3 /CaCO 3 protective film is disrupted, forming a loose composite layer of FeS, FeSO 4 , and Fe(NO 3 ) 3 . • Electrochemical impedance and polarization data show a sharp decrease in charge transfer resistance and increase in corrosion current density. • Wire bundle electrode (WBE) mapping reveals dynamic expansion of localised corrosion sites over time. • Provides mechanistic understanding of multi-impurity corrosion for CCS material durability assessment.