The evolution and characterisation of the corrosion scales formed on 3Cr steel in CO2-containing conditions relevant to geothermal energy production

The corrosion behaviour of 3Cr steel at CO2 partial pressures (pCO2) of 2.7/28.5 bar and 200 °C was investigated. The evolution of double-layered corrosion scales was analysed by surface analysis to identify physical and chemical nature and results are combined with an analysis of thermodynamic calculations. Both experimental and thermodynamic results show that the corrosion scales comprise a crystalline FeCO3 outer layer and an inner Fe3O4, FeCr2O4, and Cr(OH)3 at 2.7 bar pCO2. At 28.5 bar pCO2, the inner layer evolves to be a mixture of FeCr2O4 and Cr(OH)3 containing concentrated Cl− ions, and this induces an enhancement of localised corrosion.