Can Coverage of Alloy 800H in ASME Section III Subsection NH be Extended to 850°C?

Several solid-solution austenitic alloys are under consideration for the construction of components for high-temperature gas-cooled reactors of interest to the Generation IV nuclear reactor projects. However, coverage for these alloys in ASME Section III, Subsection NH is inadequate. Alloy 800H, for example, is included to 760°C whereas there is a need for coverage to 850°C. Efforts have begun to identify the existing database for Alloy 800H and, after evaluation, further identify the experimental and analytical research needed to extend coverage to 850°C. This paper summarizes progress in the first year of the effort. Emphasis is on the examination of the tensile, creep-rupture and fatigue database that exists worldwide. Also, the procedures used to set the allowable stress intensities and strain limits are being re-examined. Damage models to include environmental effects are included in the evaluation.