Study On Middle Flange Sealing Performance Of Check Valve Under High Temperature And Temperature Fluctuation

In engineering practice,check valves are often used under high temperature and temperature fluctuation conditions,which leads to frequent failure of the middle flange sealing.At present,the research on the factors causing the failure of the middle flange sealing is less and not deep enough.For this situation,this paper studies the changes of sealing performance of the middle flange and mechanical behavior of each component in depth under high temperature and temperature fluctuation conditions.The main work is as follows:First,finite element simulation was used to study the sealing performance of the middle flange under pre-tightening and operating conditions with different internal pressure.The results showed that with the increase of medium pressure,the stress and deflection on the flange was increasing,while the gasket stress was decreasing.That resulted in the phenomenon of "external tightening and internal loosening" on gasket,which lead to the decline of the flange sealing performance.Second,based on the steady-state temperature field and structural-thermal coupling field,the change of mechanical behavior of each component on flange joint under high temperature was studied.The results showed that high temperature would increase the stress and deformation of the flange while decrease the stress on gasket.It can be concluded that the sealing performance of flange decreases at high temperature.Third,based on the Transient thermal and structural-thermal coupling field,the effects of different heating rates on gasket sealing performance were studied.The results showed that the faster the temperature rose,the faster the gasket stress decreased and the faster the deformation increased,which lead to the sealing performance decreases greatly.Meanwhile,the Transient thermal field was used to study the temperature fluctuation.The results showed that the temperature fluctuation caused the increase of deformation and decrease of stress on gasket,that lead to gasket sealing performance are irreversibly damaged.Fourth,orthogonal test method was used to study the influence of the three factors,such as preload,temperature and pressure,on the sealing performance of spiral-wound metal gasket with graphite and solid metal serrated gasket.The test results showed that the relative level of the three factors for spiral-wound metal gasket with graphite was: preload > pressure > temperature,and that for solid metal serrated gasket was: preload > temperature > pressure.Fifth,optimizing the gasket type for the middle flange in check valve was based on the orthogonal test results.The sealing performance of spiral-wound metal gasket with graphite and solid metal serrated gasket was compared by FEM simulations analysis.The results showed that compared with the spiral-wound metal gasket with graphite,the solid metal serrated gasket can be used in a larger range of preload.If the installation conditions were harsh,the solid metal serrated gasket was recommended to reduce the difficulty of bolt installation.Meanwhile,the bearing capacity of the two gaskets to pressure fluctuation was compared.The results showed that the solid metal serrated gasket was more suitable for pressure fluctuation condition.Replacing the gasket with the solid metal serrated gasket can improve the middle flange sealing performance greatly.