Combined impurity effects on carbon steel corrosion in supercritical CO 2 systems

The presence of water and impurities in supercritical CO 2 (sCO 2 ) can significantly increase corrosion risk for carbon steel used in carbon capture, utilisation and storage (CCUS) systems. Acidic impurities such as SO x , H 2 S and NO x may dissolve in condensed water to form corrosive species, while brines can originate from residual formation water or operational carryover. This study investigates the combined effects of H 2 O, HNO 3 , SO 2 , H 2 S and NaCl on the corrosion behaviour of 1Cr carbon steel in sCO 2 –brine environments (100 bar, 35–55 °C) under both full-immersion and limited-wetness conditions. Corrosion was characterised using weight-loss measurements, SEM, AFM, XRD and contact angle analysis. Corrosion behaviour was controlled by impurity interactions, corrosion product stability, chloride content and water availability rather than pH alone. At 35 °C, HNO 3 -containing systems produced the highest corrosion rate (3.4 mm y −1 ), while SO 2 and H 2 S systems showed rates below 0.5 mm y −1 . At 55 °C, corrosion rates in NaCl-containing multicomponent systems increased from 1.6 to 8.6 mm y −1 after 7 days. Continuous immersion caused higher corrosion rates, whereas thin films promoted localised attack. The novelty lies in directly comparing bulk immersion and thin-film corrosion under identical multicomponent impurity conditions.