Analysis of the creep rupture data of alloy 617 for a high temperature gas cooled reactor

Since very high temperature gas-cooled reactor (VHTR) components for a hydrogen production are designed for a lifetime of 30 to 60 years at a high-temperature of 950 degrees C, a material selection is important, and also one of the most important properties in these metallic components is their long-term creep behavior. In this study, for selecting a suitable material for the intermediate heat exchanger (IHX), the high-temperature strengths of several candidate alloys approved for use by ASME VIII (boiler and pressure vessel code) were reviewed. From this review, alloy 617 was immediately selected as one of the best materials. In addition, to provide design data for a long duration for alloy 617, lots of creep data was collected through world-wide literature surveys of European Alloy-DB and available literature surveys. Using these data, a long-term creep life for alloy 617 was predicted for up to 10(6) hours based on the Larson-Miller (LM) parameter. Also, the creep rupture data was analyzed by a statistical treatment. Creep master curves for the creep-life prediction were presented for various standard deviations; 1 sigma, 1.65 sigma, 2 sigma and 3 sigma. A minimum design value for the creep-rupture time was found to be 10 times lower than the average value. Failure probability of the creep rupture data followed a lognormal distribution well.