Thermal-mechaniacal Coupling Analysis Of Pressure Vessel By Finite Element Method

The pressure vessel is a kind of pressure-bearing airtight container,which is used for the production processes of chemical reaction,mass transfer,heat transfer,separation and storage.It's a common structure in the petrochemical industry,power,nuclear energy,machinery manufacturing and other industries.In addition to mechanical stress,it also bears thermal stress due to the variable temperature distribution under fluctuating temperature conditions.The cyclic thermal stress may reach a considerable value to cause structural excessive plastic deformation or fatigue fracture failure due to the obvious change of transient temperature in the startup and shutdown process.Therefore,it has a great theoretical and practical significance to study the structural temperature field,the coupling thermal stress and the heat transfer between components.Based on a practical vessel structure,through reasonable simplifying,a 3-D finite element model of pressure vessel is set up in this paper combined with the requirement of finite element modeling.The startup and shutdown process of steel pressure vessel and inhomogeneous material pressure vessel is simulated by sequential coupling method.Finally,the temperature change and the structural coupling thermal stress are obtained.Then according to the results of numerical simulation and the relevant criterion of this industry,the safety status of each part of the pressure vessel is determined.The changing law of the structural coupling thermal stress is given.The stress state of the main bolt is shown,and the difference of heat transfer and coupling thermal stress between the two kinds of pressure vessel are compared.In this paper,the real engineering structure is simulated and the accurate numerical simulation results are given,it has an important guiding significance to practical engineering application.According to the result of the numerical simulation,the following conclusions are drawn:(1)Under the certain working conditions,the coupling thernal stress values of each part of the steel pressure vessel are large when starting,leading to the partially damage on the top cover and the nozzle belt and the plastic deformation on main bolt and main nut.During the shutdown process,the top cover of the steel pressure vessel has plastic deformation,and the nozzle belt has been partially damaged,the main bolt and the main nut are in a safe stress state.While the coupling thermal stress values of each part of the inhomogeneous material pressure vessel are small and each part is in a safe stress state during the startup and shutdown process.(2)In the process of heat conduction,the heat transfer rate of the steel pressure vessel is faster than that of the inhomogeneous material pressure vessel,which shown the inhomogeneous material has a better heat insulating property.(3)In the startup process,the structural coupling thermal stress of the two kinds of pressure vessel increases with the thickness of the wall,While in the shutdown process,the structural coupling thermal stress of the two kinds of pressure vessel is decreases.with the thickness of the wall.The coupling thermal stress values of the two kinds of pressure vessel are axially symmetric in the circumferential direction.(4)The exact values of axial force and bending moment on main bolt of the two kinds of pressure vessel during the startup and shutdown process are given,which provide a theoretical basis for the design and safety check of the main bolt of the pressure vessel.