Comparison of the Corrosion Behaviour of 9-12 % Cr Steels in H2O, H2O-CO2 and H2O-CO2-O2

Abstract The development of a new high efficient power plant generation with higher combustion and steam temperatures demands corrosion resistant steels. The environmental need to establish CO2 capture technology influences the flue gas composition due to oxyfuel combustion. To conserve necessary resources, higher process efficiency is a must. Consequently, the oxidation behaviour of the power plant steels T92 and B was investigated for 1000 h in the main environments of future power plants: steam, H2O-CO2 and H2O-CO2-O2 atmospheres at a pressure of 80 bar and in a temperature range between 550°C to 625°C. The corrosion rates were distinctly different in the investigated gas compositions. In steam, the oxide scales were thicker compared to those in the other gas compositions, which is a well known effect of the accelerated corrosion by H2O. In the three test atmospheres a general phase sequence was observed consisting of (Fe,Cr)2O3 in FeO, Fe-Cr-Spinel and Fe3O4 starting from the steel oxide interface. The Fe-Cr-Spinel was enriched in Cr near the steel interface. In a H2O and H2O-CO2-O2 atmosphere an additional Fe2O3 layer (hematite or maghemite) was observed on the oxide/gas interface.