Analysis Of Flange Connection Tightness Under Complex Load

Flange connection is a common sealing device in process industry.The safe operation of equipment requires that flange connection has good sealing performance.But the flange accepts a variety of loads such as bolt load,high temperature,high pressure and axial force of pipe caused by internal pressure,and the force is very complex,which easily leads to sealing failure and leakage.Therefore,it is very necessary to study the sealing property of flange connection under complex load.In this paper,the Waters flange design method and the EN13445 Appendix G flange design method are discussed in detail.The parts where the flange bolt is liable to fail under various working conditions are analyzed by finite element simulation,and the stiffness and tightness of the flange are further discussed.The work and conclusions of this paper are as follows:(1)Based on the periodic symmetry characteristics of the flange connection,1/12 of the flange connection is taken to establish a three-dimensional simulation model.The steady-state temperature field of the flange connection is analyzed and the temperature distribution law of the flange connection is studied.The results show that there is an obvious temperature gradient along the radial direction of flange connection,and the temperature decreases gradually from inside to outside.(2)The thermal-structural coupling field of flange connection is studied,and the parts where flange bolts are prone to failure under various working conditions are analyzed.The results show that the structural discontinuity in the trapezoidal groove of the flange pressing surface and the inner side of the stud and nut connection are prone to failure under the preloading condition,and the structural discontinuity in the trapezoidal groove of the flange pressing surface is prone to failure earlier.Under pressure conditions,failure is easy to occur near the inner edge of the flange neck bolt hole and the inner side of the stud and nut connection,and failure occurs earlier at the inner side of the stud and nut connection.Under operating conditions,the outer side of the flange neck bolt hole fails earlier than the inner side,while the inner side of the stud nut connection fails earlier than the outer side of the flange neck bolt hole.According to the comprehensive analysis of the three working conditions,the inner part of the stud and nut joint is the earliest failure.(3)The stiffness of the flange and the sealing property of the gasket are checked.The results show that both the stiffness of the flange and the sealing property of the gasket meet the safety assessment conditions.Although the bolting load calculated by the two methods respectively can make the flange connection meet the safety assessment conditions,the EN method takes into account the influence of gasket creep,thermal deformation and other factors,which is closer to the actual situation.Therefore,the EN method is recommended to be used in the calculation of the bolting load of high temperature and high pressure pipe flange connection.