Effect of temperature on the critical water content for general and localised corrosion of X65 carbon steel in the transport of supercritical CO2

An assessment of both the general and localised corrosion behaviour of X65 carbon steel in water-containing CO2 environments representative of CO2 transport in Carbon Capture and Storage (CCS) applications is presented. Autoclave experiments were conducted at a pressure of 80 bar and temperatures of 35 °C and 50 °C in environments where the CO2 phase was either saturated or under-saturated with water. Such an approach enabled identification of the minimum water content for each system, below which no general or localised attack was observed. At 50 °C in the water-saturated environment, material dissolution was localised, with approximately only 10% of the surface showing signs of attack after 48 h immersion. In water-saturated tests at 35 °C after 48 h, almost the entire carbon steel surface showed signs of corrosion and regions of more significant localised attack were also visible. Iron carbonate (FeCO3) was shown to precipitate onto the steel surface in both experiments, and appeared to offer better protection to the substrate at higher temperature due to the formation of a more extensive layer. In under-saturated tests at 50 °C, no corrosion was observed at a water content below 1600 ppm, whilst small level of corrosion were recorded with 300 ppm of water present at 35 °C. The results reflect that temperature drops within the system can promote corrosion at lower water concentrations (on a molar basis) and that localised corrosion is a fundamental consideration in such systems.