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

The development of a new power plant generation with higher combustion and steam temperatures demands corrosion resistant steels. The need of establish CO₂ capture technology influence the flue gas combustions due to oxyfuel combustion and implicate higher process parameters. Consequently the oxidation behaviour of the power plant steels B and P92 was investigated for 1000 h in the main constitutions of future power plants: steam, H₂O-CO₂ and H₂O-CO₂-O₂ atmospheres at a pressure of 80 bars and in a temperature range of 550°C to 625°C.
The corrosion rates are distinct different in the investigated gas compositions. In steam the oxide scales were thicker compared to the other gas compositions, which is a well known effect of the accelerated corrosion by H₂O.
In all atmospheres a general phase sequence is observed consisting of Cr₂O₃ in FeO, Fe-Cr-Spinel and Fe₃O₄ starting from the steel/oxide interface. The Fe-Cr-Spinel is enriched in Cr near the steel interface and enriched in Fe close to the gas side. In H₂O and H₂O-CO₂-O₂ a Fe₂O₃ layer (hematite or maghemit) was observed on the oxide/gas interface.