Materials Property Requirements for Steam Generator Components in the Creep Range

The design of steam generator components operating in the creep range often involves sophisticated methods of analysis requiring a variety of test data. Creep, relaxation, stress rupture, and fatigue data are required, and in many cases it is necessary to extrapolate the data to the long-term service conditions. The 9% Cr—1% Mo steel in the normalized and tempered condition has a relatively high proof strength and good creep rupture strength and ductility properties; furthermore, its fatigue strength is little affected by creep. The % Cr—1% Mo steel is not so strong, and its creep-fatigue properties have not yet been sufficiently well defined to provide reliable design guidance in this area. Alloy 800 has a good rupture strength, and although design guidance for creep fatigue is available, recent results suggest that the values may need to be reviewed.