Effect of Chromium and Molybdenum on Corrosion Resistance of Super 13CR Martensitic Stainless Steel in CO2 Environment

Abstract The effect of Cr and Mo on the corrosion resistance of super 13Cr stainless steel in CO2 environment has been investigated by the electrochemical technique and the surface film analysis. The corrosion rate in CO2 environment at elevated temperatures is reduced with the increase in the effective Cr content. The pitting resistance is improved by the addition of more than 0.25 mass% Mo, because Mo is effective to stabilize the passive film in the CO2 environment. The effect of the Mo content on the SSC susceptibility in CO2 environment with a little amount of H2S has been also studied. Mo is also effective to improve the SSC resistance by the formation of Mo sulfide in the outer layer of the surface film, because the Mo sulfide film can assist the formation and/or stabilization of the Cr oxide passive film in the inner layer even in the CO2 environment with a little amount of H2S at room temperature. Based on these results, 0.01C-13Cr-5.2Ni-0.7Mo steel chemical compositions has been determined to improve the corrosion resistance of 13Cr martensitic stainless steel. The applicable environment of the developed steel will be discussed compared with super 13Cr stainless steel containing 2mass% Mo and conventional 13Cr steel.