Formation mechanism and protective property of corrosion product scale on X70 steel under supercritical CO2 environment

The comparison of corrosion mechanism of X70 steel, as well as the formation mechanism of scale, at between 9.5 and 1 MPa were studied. The outer FeCO3 scale formed at 1 MPa presented better protectiveness than that at 9.5 MPa, while the protectiveness of inner layer was just contrary. Under supercritical CO2 condition, localized corrosion occurred at the transitional stage-the amorphous layer evolved into inner FeCO3 scale. General corrosion rate decreased in a logarithm tendency with the Young's modulus of FeCO3 scale. The fracture toughness of scale at 9.5 MPa was higher than at 1 MPa.