Effect of Impurities on the Corrosion Behavior of CO2 Transmission Pipeline Steel in Supercritical CO2-Water Environments

The corrosion property of carbon steel was evaluated using an autoclave under CO2-saturated water phase and water-saturated CO2 phase with impurities (O-2 and SO2) at 80 bar CO2 and 50 degrees C to simulate the condition of CO2 transmission pipeline in the carbon capture and storage (CCS) applications. The results showed that the corrosion rate of carbon steel in CO2-saturated water was very high and it increased with adding O-2 in the system due to the inhibition effect of O-2 on the formation of protective FeCO3. It is noteworthy that corrosion took place in the water-saturated CO2 phase under supercritical condition when no free water is present. The addition of O-2 increased the corrosion rates of carbon steel in water-saturated CO2 phase. The addition of 0.8 bar SO2 (1%) in the gas phase dramatically increased the corrosion rate of carbon steel from 0.38 to 5.6 mm/y. This then increased to more than 7 mm/y with addition of both O-2 and SO2 center dot SO2 can promote the formation of iron sulfite hydrate (FeSO3 center dot 3H(2)O) on the steel surface which is less protective than iron carbonate (FeCO3), and it is further oxidized to become FeSO4 and FeOOH when O-2 is present with SO2 in the CO2-rich phase. The corrosion rates of 13Cr steel were very low compared with carbon steel in CO2-saturated water environments with O-2, whereas it was as high as carbon steel in a water-saturated CO2 phase with O-2 and SO2.