Calculation And Analysis Of The Heat Transfer,Thermal Stress And Life Of The Main Steam Tee

Main steam pipe is an important part of the power plant. Because the tee is stress concentration relatively large area and the weak link of the main steam pipe and reheat steam pipe, so we need to give the tee special attention. Because of the complexity of the geometry of the tee, when the transient convective heat transfer of the fluid within the tee occurs, a separation zone will be formed near the pipe wall and the secondary flow will be produced in the cross section of the tee, so the velocity field and pressure filed of the tee will change and significant changes of the convective heat transfer coefficient will occur. While studying the thermal stress and life of the tee, we used to obtain convective heat transfer coefficient of the main pipe and the branch pipe of the tee according to the forced convective heat transfer correlation of the round straight pipe, and use them as boundary conditions of the tee. Then, a detailed analysis and verification of the effect about the thermal stress and life of the tee caused by the complexity of tee geometry-induced the change of convection heat transfer coefficient along the pipeline should be obtained.Relying on the ’the key technology research accident prevention of(ultra) supercritical power plant boiler accident prevention based on a typical failure mode’ subject and taking a 300 MW unit for example, this article studied the resultant stress intensity curve of internal pressure and thermal stress over time and confirmed the corresponding time of low and peak points during start-stop process of boiler according to strength calculation criteria of pressure parts for water tube boilers; The variation of convection heat transfer coefficient along the pipeline at the low and peak time was obtained, and the variation law of the convective heat transfer coefficient was also analyzed by conjugate heat transfer numerical simulation of FLUENT software; Using the convective heat transfer coefficient by FLUENT numerical simulation and by the forced convective heat transfer correlation of the round straight pipe as the tee’s wall boundary conditions respectively, thermal stress was calculated at tee check point of peak and low time by applying ANSYS software; Internal pressure stress also was calculated at tee check point of peak and low time by applying ANSYS software; Both wall heat transfer conditions were compared and analyzed by using ASME fatigue life calculation method and fatigue-creep intercourse life calculation method respectively. The differences and the impact of the tee fatigue-creep life and the thermal stress between changeable convective heat transfer coefficient in the tee because of the complexity of geometry and constant convective heat transfer coefficient calculated through the experimental relation of forced convective heat transfer were studied, thus can provide a reasonable basis for the amendment and perfection of creep-fatigue life engineering practice calculation in future.