In order to verify whether the pre-tightening force calculated by different methods can meet the sealing requirements,two kinds of pipe flange-bolt-gasket models at different sizes and under different working conditions were selected for finite element analysis.A three-dimensional model was built by using ANSYS Workbench finite element software,and the temperature load was applied to obtain the temperature field distribution of the flange system.The bolt pre-tightening force was determined according to EN13445 Appendix G and Waters method,and was applied as the initial pre-tightening force to the corresponding pipe flange system for thermalstructural coupling.The flange system under pretightening condition and operating condition was simulated and analyzed,and the sealing and strength properties were evaluated.The results show that the bolt pretightening force calculated by EN13445 Appendix G method and Waters method can meet the sealing requirement of flange system,and can meet the safety assessment requirements.However,the bolt pre-tightening force determined by EN13445 Appendix G method can ensure more uniform distribution of stress and lower stress level of the flange,and the EN13445 Appendix G method takes into account the sealing requirements and strength requirements of the whole flange joint,which is more comprehensive than the Waters method