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In an oxyfuel plant, heat exchanging metallic components will be exposed to a flue gas that contains substantially higher contents of CO2, water vapor, and SO2 than conventional flue gases. In the present study, the oxidation behavior of the martensitic steel P92 was studied in CO2‐ and/or H2O‐rich gas mixtures with and without addition of SO2. For this purpose, the corrosion of P92 at 550 °C up to 1000 h in Ar–H2O–SO2, Ar–CO2–SO2, Ar–CO2–O2–SO2 and simulated oxyfuel gas (Ar–CO2–H2O–O2–SO2) was compared with the behavior in selected SO2‐free gases. The oxidation kinetics were estimated by a number of methods such as optical microscopy, scanning electron microscopy with energy and wave length dispersive X‐ray analysis, glow discharge optical emission spectroscopy, X‐ray diffraction as well as transmission electron microscopy. The experimental results revealed that the effect of SO2 addition on the materials behavior substantially differed, depending on the prevailing base gas atmosphere. The various types of corrosion attack affected by SO2 could not be explained by solely comparing equilibrium activities of the gas atmospheres with thermodynamic stabilities of possible corrosion products. The results were found to be strongly affected by relative rates of reactions of the various gas species occurring within the frequently porous corrosion scales as well as at the scale/gas‐ and scale/alloy interfaces. Whereas SO2 addition to Ar–CO2 resulted in formation of an external mixed oxide/sulfide layer, the presence of SO2 in oxyfuel gas and in Ar–H2O–SO2 resulted in Fe‐sulfide formation near the interface between inner and outer oxide layer as well as Cr‐sulfide formation in the alloy. In the latter gases, the presence of SO2 seemed to have no dramatic effect on oxide scale growth rates.

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Modern gas turbine materials are subjected to increasing operating temperatures in service environments, which contain high concentrations of gaseous species originating from fuel impurities, e.g. sulfur. In the present study, the oxidation behavior of two commercially available nickel‐base alloys, Rene 80 and PWA 1483, was investigated for up to 500 h duration in synthetic air and synthetic air containing 2% SO2 at 1050 °C. In order to investigate the mechanisms of SO2 attack, specimens of the two alloys after different oxidation times were characterized using a number of surface analytical techniques such as scanning electron microscopy, XRD, and glow discharge optical emission spectrometry. The corrosion reactions in the presence of SO2 were found to be strongly alloy dependent and could not be explained simply in terms of the contents of the main scale‐forming alloying elements, Cr and Al. Severe internal sulfidation was observed underneath the chromium‐rich oxide scale on Rene 80, leading to breakaway oxidation after longer exposure times. For PWA 1483 sub‐scale formation of a near‐continuous alumina occurred, which resulted in substantial suppression of sulfidation. Consequently, no breakaway oxidation of PWA 1483 was observed up to 500 h exposure at 1050 °C in synthetic air with 2% SO2. The formation of a dense alumina sub‐scale on PWA 1483 is believed to be correlated with the Ta‐addition in this material. It is proposed that Ta can tie up Ti by forming a mixed oxide of the type TiTaO4. In this way, it prevents the incorporation of Ti into the chromia scale, which can lead to enhanced scale growth.

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