Environmental Degradation of Heat-Resistant Alloys During Exposure to Simulated and Actual Gas Turbine Recuperator Environments

Primary surface recuperators (PSR’s) for land-based industrial gas turbines are typically constructed from heat-resistant alloys such as nickel-base superalloys or highly-alloyed austenitic stainless steels. The water vapor present in gas turbine exhaust has been shown to increase the rate of chromium oxide volatility, which in turn can cause rapid oxidation of the underlying metal. As PSR’s are generally fabricated from thin foil materials, excessive degradation can cause perforation, leading to failure of components. The results of a field test program will be summarized, based on analysis of recuperator stand-in components which were exposed to a full-flow exhaust stream during gas turbine operation for times ranging from 500 hours to 21,500 hours. A significant effect of service on the materials of construction was observed, with near-surface chromium depletion and microstructural instability evident after the longest exposures. These results will be combined with those from an extensive laboratory test program to evaluate the performance of heat-resistant alloys during recuperator service, outlining the different modes of degradation and means for their mitigation.