The Inconel 617 material was developed in the early 1970’s for high-temperature applications. It is a nickel-chromium-cobalt-molybdenum alloy with high strength combined with corrosion and oxidation resistance properties. Inconel 617 is one of the contenders for the Reactor Enclosure System (RXE) material of the Molten Chloride Reactor Experiment (MCRE). The properties of Inconel 617 are not available in the high temperature code ASME Boiler & Pressure Vessel Code (BPVC) Section III, Division 5 [1] but are given in Code Case N-898 [2]. However, for Inconel 617, the high temperature properties (stress to rupture and isochronous stress-strain curves) are available only up to 100,000 hours unlike stainless steels (SS) 304 and 316 for which properties are available for a time up to 300,000 hours. Consequently, the analyst must use 100,000 hours as the maximum creep life even for a very low stress value adding more conservatism to the already conservative elastic route of creep-fatigue lifing. This in turn limits the maximum operating temperature when the design curves are plotted. The purpose of this work is to identify a methodology to extrapolate the high temperature properties of Inconel 617 up to 300,000 hours. The two properties that need extrapolation are a) time to rupture and b) isochronous stress-strain behavior.

This work shows that for the time to rupture calculation, extrapolation of properties using the last two data points looks appropriate when evaluated against the Larson-Miller Parameter method [4]. For isochronous stress-strain curves, the same equations given in the ASME code case [2] can be extended up to 300,000 hours.

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