Reliability Prediction of Long-term Creep Strength of Gr. 91 Steel for Next Generation Reactor Structure Materials

This paper focuses on reliability prediction of long-term creep strength for Modified 9Cr-1Mo steel (Gr. 91) which is considered as one of the structural materials of next generation reactor systems. A "Z-parameter" method was introduced to describe the magnitude of standard deviation of creep rupture data to the master curve which can be plotted by log stress vs. The larson-Miller parameter (LMP). Statistical analysis showed that the scattering of the Z-parameter for the Gr. 91 steel well followed normal distribution. Using this normal distribution of the Z-parameter, the various reliability curves for creep strength design, such as stress-time temperature parameter reliability curves (sigma-TTP-R curves), stress-rupture time-reliability curves (sigma-t(r)-R curves), and allowable stress-temperature- reliability curves ([sigma]-T-R curves) were reasonably drawn, and their results are discussed.