Analysis of an Overestimation of the Long-term Creep Life for Alloy 617

Ni-base superalloys are used for high temperature applications such as turbine blades, structural materials for nuclear reactors, and a very high temperature reactor (VHTR) for a hydrogen production. Especially, since the VHTR components such as the hot gas ducts and intermediate heat exchanger (IHX) are operated during a design life of 30 to 60 years at 950 .deg. C and 3 ∼ 8MPa in He impurities, their components are required to have a good high temperature strength, creep-rupture strength, high-temperature stability, and a good corrosion resistance. Among them, above all, a long term creep strength is important, because the integrity of the components should be preserved during a design life of over 30 years at a maximum operating temperature up to 1000 .deg. C