Corrosion Behavior of Austenitic Stainless Steels in Oxidizing and Reducing Gases Relevant to Oxyfuel Power Plants

The oxidation behavior of three austenitic stainless steels was studied at 650A degrees C up to 1000 h. The selected materials (S304HCu, TP347HFG, and Sanicro 25) were exposed to an atmosphere simulating oxyfuel combustion, and the results compared with the behavior in a test gas with addition of CO, thus simulating locally occurring reducing operating conditions. For the 18% Cr steels (S304HCu and TP347HFG), lower corrosion rates were generally found in reducing than oxidizing gas. As might be expected based on its substantially higher Cr content, Sanicro 25 showed lower oxidation rates than the two 18% Cr steels in the oxyfuel gas. However, the opposite was the case in the reducing gas. The higher Ni content resulted in formation of a mixed sulfide/oxide outer layer, which adversely affected the formation of a protective chromia scale, resulting in a higher corrosion rate than for the 18% Cr steels.