Fluid structure interaction simulation of thermal striping in a t-junction pipe made of functionally graded material

In a nuclear power plant, thermal striping occurs at the T-junction, where high-temperature steam and low-temperature processed fluids mix. The non-uniform temperature distribution and temperature fluctuation in the pipe produced by thermal striping may lead to cracks and high cycle thermal fatigue failure. The use of a thermal sleeve can prevent this issue to a certain extent, but delamination is a major concern in such thermal striping. Functionally graded materials (FGMs) in which the material properties are graded along the thickness direction can relieve the thermal stress gradient in the pipe, eliminating the delamination problem. In this study, a one-way fluid structure interaction simulation of ceramic and structural steel functionally graded T pipes under thermal striping was performed using the detached eddy simulation method. The initial condition of velocity and temperature was used based on the “WATLON” experiment conducted by the Japan Atomic Energy Agency. Spectral analysis was performed to evaluate the temperature fields for both the fluid and the pipe, as well as to determine the temperature fluctuation characteristic. The temperature variation in the pipe was then used in the transient structural analysis to evaluate fluctuations in the thermal stress. Finally, the rainflow counting method was employed to determine the stress cycles of the pipe. The thermal stress cycles of homogenous, composite, and FGM pipes were compared. The reduced amplitude of the stress cycle of the FGM pipe confirms a higher fatigue life and potential application of the FGM at the T-junction.