Evaluation of Accumulated Fatigue in Metals Due to Random Oscillating Thermal Stresses

Abstract

A direct modeling calculation method was developed to improve the accuracy of metal fatigue life estimates. The procedures were developed for the evaluation of once-through steam generator tubes, but were intended to be generally applicable. Random thermal boundary conditions were first simulated, with specific consideration given to the cases of transition boiling and fluctuating coolant inlet temperatures. Subsequently, transient heat transfer rates were determined and wall stresses due to pressure and temperature oscillations were calculated. The resultant wall temperature and stress oscillation data were statistically analyzed to provide the effective parameters used to estimate the metal fatigue.