Analysis on Fatigue Life of Mixing Tee Weldments Subjected to Dynamic Loadings in Piping Systems

Thermal and pressure loading are subjects that have been studied to understand the fatigue cracking occurrence at mixing tee regions of piping systems. In order to quantitatively predict the fatigue life of a mixing tee, in this paper, computational fluid dynamics (CFD) coupled with finite element analysis (FEA) were employed to analyse the mixing flow of fluids in order to determine the effect of thermal and pressure loadings on the pipe structure. The stress distribution obtained from this analysis was then used for fatigue analysis to predict the fatigue life of the mixing tee. A modified S-N Goodman curve for AISI 304L stainless steel was employed to predict the fatigue life of the inner and outer walls of the mixing tee weldment. The analysis was carried out with various velocities of 0.76/0.78 m/s, 2 m/s and 3 m/s for fluid flow in the mixing tee. Based on the result, the fatigue life of the outer and inner walls of the mixing tee weldment could last up to an infinite number of cycles as the alternating stress contributed from pressure and thermal loading was very small.