Evaluation of fatigue damage induced by thermal striping in a T junction using the three dimensional coupling method and frequency response method

Thermal fatigue cracking induced by thermal stratification, cycling and striping have been observed in several PWR plants. Especially, thermal striping, the highly fluctuating thermal layer, became one of the significant problems, since it can cause un predicted high cycle thermal fatigue (HCTF) at piping systems. This problem are usually found in T junctions of energy cooling systems, where cold and hot flows with high level of turbulence mix together. Thermal striping can cause the networks of fatigue crack at the vicinity of weld parts and these cracks can propagate to significant depth in a relatively short time. Therefore, thermal striping and fatigue crack initiations should be predicted in advance to prevent the severe failure of piping systems. The final goal of this research is to develop a rational thermal and mechanical model considering thermohydraulic characteristics of thermal striping and an evaluation procedure to predict the initiation of thermal fatigue crack. As a first step, we evaluated the fatigue damage in a T junction using two widely used methods. Then, we analyzed the results of each method and conducted comparisons and verifications