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

Abstract

Primary surface recuperators (PSR’s) for land-based industrial gas turbines are typically constructed from heat-resistant alloys such as austenitic stainless steels or nickel-base superalloys. 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 an extensive laboratory test program to characterize the performance of heat-resistant alloys will be summarized, outlining the different modes of attack and means for their mitigation. These results will be compared to an investigation carried out using sub-size recuperator components which were exposed to a full-flow exhaust stream during gas turbine operation for times ranging from a few weeks to over one year.

Effect of gas flow rate on oxidation behaviour of alloy 625 in wet air in the temperature range 900–1000 °C

“…The alloy has a large variety of applications for instance in aerospace industries, chemical processing, pollution control equipment, waste‐to‐energy boilers and recuperators . Recently, alloy 625 was considered as a potential construction material for gas turbine recuperators and its oxidation behaviour in water vapour containing exhaust gases was studied during long‐term exposures in a wide temperature range .…”

“…Refs. ) and its significance for the overall oxidation performance is well established when considering materials behaviour at temperatures around and above 900 °C . Especially from extensive studies carried out at Chalmers University of Technology (Göteborg, S) it was shown that the formation of volatile chromium species may also substantially affect materials performance at much lower temperatures around 600 °C.…”

“…For NiCr‐base alloys, this sudden change in oxidation kinetics does generally not occur due to the relatively low growth rates of the less protective oxides NiO and NiCr 2 O 4 . The change in oxidation kinetics upon occurrence of a critical Cr depletion occurs more gradually and therefore the expression ‘critical Cr‐depletion’ may be more appropriate than ‘breakaway oxidation’ .…”