Performance of industrial gas turbine materials at high temperatures

The Gas Turbine Efficiency in a combined cycle plant is a strong function of the Turbine Inlet Temperature (TIT) of the gases. Increasing the TIT is therefore one of the recommended means of achieving the 60% efficiency goal of Advanced Turbine Systems. Improvements in cooling of the hot gas components is required to keep the surface temperature of these components within the safe operating limits. Steam has been proposed as an alternative cooling medium because of its high specific heat and low kinematic viscosity. The objective of this paper is to study and evaluate the effects of steam on the performance of commercially used gas turbine superalloys. Even uncontaminated Steam was found to have a deleterious effect on IN 738 LC, which suffered extensive oxidation compared to that in air and the other alloys studied. CMSX-4 exhibited a tendency to undergo a healing phenomenon with prolonged exposures particularly at higher temperatures in steam. Both IN 738 LC and CMSX-4 showed greater oxidation in steam than in air. IN 617 showed greater degradation in air than in steam with a tendency for preferential grain boundary oxidation. X-45 exhibited better overall oxidation resistance in steam and air, but it did exhibit a tendency to undergo stress cracking in steam