Study On Thermal Stress And Fatigue Life Of Pipeline In Nuclear Power Plant Based On Fluid-solid Coupling

As an important component of nuclear power plants,pipelines are mainly responsible for the transmission of fluids.When the non-isothermal flow flows in the tube,the mixed flow will cause a sharp fluctuation in the temperature near the tube wall and generate a cyclic heat-induced stress on the tube wall.When the range of thermal stress is large enough,thermal fatigue damage is likely to occur.Thermal fatigue of nuclear power plant pipes seriously affects the safety of nuclear power plants.Aiming at the thermal fatigue problem of nuclear power plant pipelines,based on the ANSYS Workbench simulation platform,a one-way fluid-solid coupling analysis method was used to establish the finite element models of the solid-fluid domain of straight pipe,curved pipe and T-tube structures,respectively simulation research.The specific research content is as follows:(1)Based on elastic thermodynamics,finite element theory and fluid-solid coupling theory,the thermal stress states of three different types of pipes under the same conditions,such as straight pipe,bent pipe and T pipe,under the conditions of inlet velocity and inlet temperature are studied.The results show that pipelines are prone to stress concentration and fatigue damage at structural discontinuities.And under the same conditions,the thermal stress suffered by pipes of different structure types is quite different.Among them,the T-shaped pipe structure is most prone to stress concentration,and the stress value is also the largest.(2)Further,the effects of different operating conditions such as flow rate,temperature load and inner diameter of the branch pipe on the thermal stress of the T tube mixing area under cold and hot mixing conditions are studied.The results show that the increase of the cold flow rate of the branch pipe or the decrease of the main pipe heat flow rate can significantly reduce the maximum stress value of the pipe in the stress concentration area.The maximum thermal stress value of the pipe wall in the mixing area is affected by the average temperature more than the temperature difference.The smaller the inner diameter of the branch pipe,the smaller the stress on the pipe wall.(3)Finally,combined with the theoretical idea of the local stress-strain method,a thermal fatigue life prediction model of the T-shaped pipeline is established.The results show that the prediction model can directly correlate the magnitude of the thermal stress on the pipeline with the number of fatigue cycles,and the calculation is simple with fewer limiting factors.The thermal fatigue of the pipeline can be directly analyzed based on the thermal stress state of the pipeline.Overall,the results of this study can provide an important reference for fatigue failure protection and thermal fatigue monitoring of pipelines in nuclear power engineering,and have great important significance to improve the operation of the nuclear power plant safety,reliability andeconomy.