Evaluation of thermal fatigue failure probability at mixing tee subjected to random fluid temperature fluctuation

Calculation of fatigue damage and fatigue life of a mixing tee considering uncertainty on loading and strength parameters has been achieved by conducting Monte Carlo simulations with the aim of clarifying the effect of the uncertainties on the prediction of fatigue damage and quantifying the level of safety of mixing tee designs. In fact the uncertainties concerned 3 parameters: heat transfer coefficient, stress factor and life factor. The correlation between the COVs (Coefficient of Variation) on the input and output variables was analyzed by performing linear or quadratic regressions on the results of multiple simulations. In the present condition, the uncertainty on the stress factor appeared to be dominant over the two other uncertainties. When considered on its own, the initial COV on the input variable is multiplied by about 10 times while propagating towards the fatigue damage distribution. The uncertainty on the heat transfer coefficient h was found to increase the initial COV on the input by about 1.5 times when calculating the fatigue damage. The uncertainty on the life factor was the most harmless one, as it propagated without increasing the COV values or distorting the scattering distribution shape. Furthermore, quantification of the level of safety of mixing tee designs were successfully achieved by calculating the probability of thermal fatigue failure