The role of Cr content on the corrosion resistance of carbon steel and low-Cr steels in the CO2-saturated brine

The selection of appropriate materials for the transportation pipelines is of vital importance to ensure the safety operation in Carbon Capture, Utilisation and Storage (CCUS). To clarify the effects of Cr content in steel on the resistance against general and localised corrosion, electrochemistry methods combined with pH measurements and various surface analysis techniques were implemented on X65, 1Cr, 3Cr and 5Cr steel samples in a CO2-saturated solution at 60 °C and pH 6.6 during 192 h of immersion. Additionally, thermodynamic and kinetic analyses of the formation of the corrosion products on carbon steel and low-Cr steels were performed. The results show that the general corrosion resistance increased with rising Cr content without the presence of significant corrosion products formation. However, with the formation and development of the corrosion products, the general corrosion resistance reduced with the increase in Cr content. The formation of the compact crystalline FeCO3 on X65 and 1Cr steel surfaces offered superior general corrosion protection, while cannot provide enough localised corrosion protection. By contrast, the double-structural corrosion product layers on 3Cr and 5Cr steels notably suppressed the localised corrosion, but providing poor protection against general corrosion over long immersion periods. This study reveals the contributions of Cr content on general and localised corrosion resistance at various periods, providing references for material selection and evaluation in CO2 environments relevant for CCUS.