Comparison And Research Between Conventional And European Calculation Methods Of Bolt Preload For Flange Joints

Bolted flange connections system is a commonly used chemical equipment connection device.A lot of research has shown that the failure of flanged connections is mainly caused by leakage,and the failure caused by strength is few.So the research for flange bolt connection sealing performance should pay enough attention.Therefore,it is important to improve the sealing performance of flange joints by research different methods of flange connections.As the calculation of bolt preload have mainly used ASME method in domestic,while the European bolt preload calculation method have few used in researches and applications.Therefore,in this paper to calculation the required bolt load by two methods of flange connection design,and the finite element software is used to simulate the flange connection structure.The effect of different flange design methods on strange and sealing performance of flange connection were analyzed.In this paper,different calculation methods of bolt load of flange connections is more completely,more deeply and more objectively studied by means of theoretical analysis,numerical calculation and finite element simulation.First of all,in this paper there are two types of commonly used design methods for flange connections are introduced.One is the traditional Taylor-Forge method,represented by ASME VIII-1 flange connections design rules,and the other is the European flange design method EN13445 Annex G-Alternative design rules for flanges and gasketed flange connections as the representative.The method based on Taylor-Forge is design flange connection system by the strength.While,the European alternative design method aims at the sealing to make sealing and integrity calculations for each condition.It is shown that EN13445 Annex G method to calculate the bolt load is more accurate,more to ensure the flange connections sealing by comparing the theoretical basis,the calculation process and the parameters involved and so on of the ASME VIII-1 flange connections design rules(hereinafter referred to as ASME)and EN13445 Annex G(hereinafter referred to as Annex G)methods.So it will provide theoretical guidance for the bolt load calculation in practice.Then,according to the actual operation parameters of the equipment provided by a petrochemical company,the bolt load of the flange joints is calculated by ASME and Annex G.The bolt loads calculated by above two methods were Compared and analyzed.The results show that the bolt loads in bolting-up and operating conditions calculated by Annex G are generally less than which calculated by ASME method.While,some actually maximum bolt loads of Annex G are more than the loads of bolting-up condition of ASME and some are opposite.Finally,using finite element software,the stress-strain of bolted flange connections under the bolt loads calculated by the two methods were analyzed.Through analyzing steady temperature field and thermal structure coupling field of the flange joints under the two load cases,the results show that applied the bolt load calculated by the Annex G the flange joints components are not out of the material yield limit,while applied the bolt load calculated by ASME method the maximum stress of the flange bolt hole exceeds the yield limit of the flange material.If the flange material were in the yield state in a long term,it will cause the flange failure.In addition,uneven stress phenomenon of gasket is obviously when subjected to ASME bolt load,and it will also lead to flange seal failure caused by leakage.