In oxyfuel plants metallic heat exchanging components will be subjected to service environments containing high amounts of CO2 and water vapour. In the present paper, the oxidation behaviour of the ferritic/martensitic 9 % Cr steel P92 was studied in a model gas mixture containing 70 % CO2-30 % H2O in the temperature range 550 – 650 °C. The results were compared with the behaviour in air, Ar–CO2 and Ar–H2O. In the CO2- and/or H2O-rich gases, the steel formed iron-rich oxide scales which possess substantially higher growth rates than the Cr-rich surface scales formed during air exposure. The iron-rich oxide scales are formed as a result of a decreased flux of chromium in the bulk alloy toward the surface. This is the result of enhanced internal oxidation of chromium in the H2O-containing gases and carburisation in the CO2 gases. The oxide scales allow molecular transport of CO2 towards the metallic surface, resulting in carburisation of the alloy. The presence of water vapour induced buckling in the outer haematite layer, apparently as a result of compressive oxide growth stresses. Buckling did not occur in the H2O-free gas. This has been discussed in terms of the potential for H2O to increase growth stresses and accelerate crack propagation. The oxidation rates in CO2–H2O do not seem to be higher than those observed in flue gases of conventional fossil fuel fired power plants.
Fe-Cr alloys with variations in chromium content and additions of different elements were studied for potential application in intermediate temperature Solid Oxide Fuel Cell (SOFC). Recently, a new type of FeCrMn(Ti/La) based ferritic steels has been developed to be used as construction material for SOFC interconnects. In the present paper, the long term oxidation resistance of this class of steels in both air and simulated anode gas will be discussed and compared with the behaviour of a number of commercial available ferritic steels. Besides, in-situ studies were carried out to characterize the high temperature conductivity of the oxide scales formed under these conditions. Main emphasis will be put on the growth and adherence of the oxide scales formed during exposure, their contact resistance at service temperature as well as their interaction with various perovskite type contact materials. Additionally, parameters and protection methods in respect to the volatilization of chromia based oxide scales will be illustrated.
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