Age-hardened nickel-base alloys began to be seriously considered for power piping in the late 1990’s in the European Thermie project to develop materials technology for Advanced Ultra-supercritical (AUSC) coal-fired power boilers. It was recognized at that time that conventional ferritic and austenitic boiler tube would require unrealistically large wall thickness at the temperatures and pressures specified for AUSC. Only age hardened nickel-base alloys appeared to provide the required combination of creep strength, hot corrosion and oxidation resistance, and weldability. Over the next decade projects were initiated in many countries to characterize new and legacy alloys for this application. The results of this work were widely shared internationally and served as a material data basis for newer advanced energy technologies such as supercritical CO2, Gen 3 concentrating solar, and Gen 4 nuclear. Over the past decade full-scale component demonstrations and pilot plants designed for operation at or above 700°C have been constructed and operated in test mode. This paper summarizes achievements to date using primarily examples for UNS N07740 but with reference to published data on similar alloys. Specific challenges for future widespread use of these alloys are defined.

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