A PARAMETRIC CORRELATION FOR STRESS RUPTURE DATA INCORPORATINq HEAT TO HEAT VARIATIONS AND ITS APPLICATION FOR 9Cr-1Mo STEEL PART I: DEVELOPMENT OF THE CORRELATION AND NUMERICAL ALGORITHM

摘要

A novel semi-empirical parametric correlation for stress rupture that incorporates heat to heat variations is proposed. It stipulates that (i) two heat-sensitive material parameters, scaling respectively stress and rupture life, are adequate to describe the teat to heat variations in stress rupture properties; and (ii) both stress and rupture life require temperature-scaling through heat-independent apparent activation energies. A fully numerical nonlinear least-square fitting algorithm is developed for determining the optimal values for the unknown material constants in the stress rapture equation for an arbitrary number of heats. The algorithm proved successful in simultaneously correlating stress rupture data (from literature) for eleven heats of 9Cr-1Mo steel, a steel that is widely used in boilers and heat exchangers. The superiority of our multiple heat correlation to earlier correlations which ignore heat to heat variations is also demonstrated.