MULTIPHYSICS INVERSE ANALYSIS METHOD FOR REDUCING TRANSIENT THERMAL STRESS IN A THICK-WALLED PIPE

When high temperature fluid flows into a pipe, a temperature distribution in the pipe induces a thermal stress. It is important to reduce the thermal stress for managing and extending the lives of plants. In this problem heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of multidisciplinary nature. In a previous paper the present authors proposed an inverse method for determining the optimum thermal load history which reduces the transient thermal stress considering the multidisciplinary physics. The optimum temperature history of inlet fluid may be useful for designing and operating plants. Analytical solutions of the temperature and stress distributions for a thin-walled pipe were used in the analysis. In the present study the reduction of transient thermal stress in a thick-walled pipe is considered. The finite element techniques are employed in the optimization for obtaining the temperature distribution and the thermal stress in the thickwalled pipe. The maximum hoop tensile stress is minimized for the case where inner surface temperature is expressed in terms of a polynomial function of time. The effect of the ratio of inner radius to outer radius on the optimum temperature history is examined. It is found that when the ratio of inner radius to outer radius is larger than 0.8 the optimum temperature history for the thin-walled pipe gives a good estimate. For thicker pipes the optimum temperature history for the thin-walled pipe can be an initial guess for searching the optimum temperature history.