Comparative Study on High Temperature Oxidation of T92 Steel in Dry and Wet Oxyfuel Environments

Fireside oxidation of T92 steel was studied after exposure times up to 1000 h in the temperature range of 580-650 A degrees C in simulated dry (CO2-27 % N-2-2 % O-2-1 % SO2) and wet (CO2-20 % H2O-7 % N-2-2 % O-2-1 % SO2) oxyfuel environments. Water vapour addition to the oxyfuel gas substantially increased the oxidation rate. The oxide scales developed under wet environment contained more defects, resulting in higher access of oxidants to the substrate material and enhanced oxidation. In addition, the oxide scales had lower chromium enrichment in the inner layer as compared to that in the dry condition. The oxide scales consisted of hematite and magnetite in the outer layer and a mixture of (Fe, Cr)-spinel, sulphides and wustite in the inner layer. The sulphur distribution differed between the oxide scales developed in dry and wet oxyfuel environments. Sulphur was mainly concentrated in the inner layer and at the oxide/alloy interface. In contrast to the wet oxyfuel gas, very high sulphur concentration was measured in the inner oxide scale formed in the dry oxyfuel gas. Additionally, Fe-sulphide was formed at the interface of inner and outer oxide layer in the wet condition.