[en] A test program was conducted under contract to Sandia National Laboratories to investigate water/steam effects on elevated temperature low cycle fatigue and creep-fatigue of Alloy 800. This report presents interpretation and analysis of the test results. Tubular specimens with water sealed inside were cycled to failure under strain control. Tests were conducted to 616K (650⁰F) and 922K (1200⁰F); some at 922K included tensile or compressive hold periods to simulate creep-fatigue conditions. The tubular specimens showed significantly lower lives than solid bar specimens cycled at equivalent strain ranges. Rough internal surfaces contributed to early crack initiation with these specimens. Inclusion of hold periods caused further large reductions in cycles to failure

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[en] Alloy 800 (Sandvik-Sanicro 31) has been subjected to fully reversed push-pull strain controlled tests at 600⁰C. High and low strain rates were imposed by controlling the test frequency. The conditions for these strain rates were chosen on the basis of fracture analysis. The failure at the low strain rate was entirely intercrystalline whereas that at the high strain rate was completely transcrystalline and striated. Tests were carried out by mixing sequences of cyclic creep (intercrystalline) and fatigue damage. On considering the accumulation of damage in a non-linear manner, it was found that this approach gave a unified explanation to the observed results. It is shown that interaction occurs between the cyclic creep and fatigue mechanisms after a certain amount of prior damage has been imposed. (author)

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[en] The influence of precipitation (ν') on the cyclic behaviour of alloy 800 is studied with the help of the analyze of microstructures. The precipitation (ν') induces an increase of the maximum strain and the most important cyclic hardening is obtained for the material with the biggest precipitates. With the consideration of this microstructural data, the strenghtening stage of the alloy is described in the behaviour law from two different theorical concepts

[en] The AMSE Boiler Code development of design stresses and their optimization for alloys 800 and 800H for conventional and nuclear power plants have coincided with many successful trial installations of these grades of alloy 800. These trial installations, along with laboratory tests, have shown that alloy 800H can be used for long times with a retention of good mechanical properties, including ductility. While gamma prime can be formed, it soon loses its detrimental effect on ductility in service. Sensitization of the alloy also occurs but it, too, has a decreasing effect on corrosion resistance with time in service, especially at elevated temperatures. The authors discuss all of these aspects and conclude that alloy 800 perhaps with low carbon control in the annealed (1800 to 1950degF)(982 to 1066degC) condition gives the optimum combination of properties to 1050degF(566degC) and alloy 800H (.05 to .10%C) solution annealed at 2100 to 2200degF (1149 to 1204degC) has optimum properties above 1050degF (566degC). The effects of aluminium and titanium and the benefit of keeping these within the ASTM limits of .15 to .60% are also stressed. (author)

[en] The evolution of the various grades of Alloy 800 is described in relation to both nuclear and non-nuclear applications, and comments are made on relevant service experience. The significance of the behavior characteristics of this alloy in relation to design and analysis methods is reviewed with particular emphasis on elevated temperature nuclear construction, where cyclic (creep-fatigue) as well as monotonic loads must be considered. The influence of fabrication factors, such as environment, on the properties of this material is also noted, and some comments on the potential applicability of probabilistic design methods are included. (Auth.)

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