Research On Comparison Of Flange Design Method And Determination Of Bolt Preload

A large number of experimental studies have shown that failure of flanged systems is mainly due to seal failures,while strength failures are only a minority.Once failures occur,the environment,personnel and economy will be greatly affected.One of the important factors to ensure that the flange joint does not seal failure is to apply a suitable preload to the bolt.Currently,the method for calculating the bolt preload is the Taylor-Waters method?hereinafter referred to as the Waters method?.This method has a long history of use,rich design experience,and extensive engineering applications.However,the EN calculation EN 13445-3 Appendix G flange design method?hereinafter referred to as EN method?is less used,but this method is more comprehensive in terms of strength and tightness when calculating.Meanwhile,the two methods will be made in-depth comparative study.In this paper,a comparative analysis of EN method and Waters method is carried out through theoretical introduction,calculation of examples and finite element analysis.At the same time,the influence of the parameters such as nominal flange diameter,design pressure,design temperature,and gasket type on the results of the preloading force of the two calculation methods was analyzed.The development process and research status of EN method and Waters method are elaborated.The calculation processes of the two methods are introduced in detail.It is found that EN method is more comprehensive in consideration of the strength and tightness of flange joints in the calculation process.The VB.NET programming tool in Visual Studio 2012 was used to prepare the flange design and bolt preload calculation software.The software integrates flange design methods such as the EN method,Waters method and the ASME PCC-1 bolt installation load determination method.The standard flange and non-standard flange can be calculated by the EN method and the Waters method.Meanwhile,the recommended range of bolt preload,the strength check of the flange parts and the automatic generation of the result report can be given.The calculated calculation software is used to calculate the standard A-type socket-weld flange,standard B-type socket-weld flange and standard Welding neck flange by EN method and Waters method,respectively.And the two methods are compared to calculate the preload.At the same time,the influence of the parameters such as nominal flange diameter,design pressure,design temperature and gasket type on the results of the preload of the two calculation methods was analyzed.The results show that the bolt preload of the EN method is smaller than that of the Waters method,and the bolt preload increases with the increase of the nominal flange diameter,design pressure,and design temperature.The finite element simulation of the initial bolt preload was performed using the calculated results of the EN method and the Waters method bolt preload.The stress distribution of the flange system and the degree of deflection of the flange was analyzed and checked.Study the reliability of the flange strength and sealability and the feasibility of the method when the two methods are used to guide the flange joint bolt installation.The results show that the pre-tightening force of the EN method can ensure the strength,rigidity and sealing performance of the flange joints.The pre-tightening force of the Waters method can ensure the strength and rigidity of the flange joints,but there is the possibility of the gaskets leaking.The bolt preload is optimized based on the stress classification design assessment criteria,ASME's requirements for the flange deflection angle,the minimum gasket compressive stress(Q_0,min)required to ensure sealing as specified in Annex G of EN13445 and the maximum compressive stress(Q_max)to ensure that the gasket is not crushed.Determine the nominal diameter of 1200 mm standard with neck butt welding flange in the design pressure of 3.4 MPa,the design temperature of 300°C working conditions to meet the flange strength,stiffness and sealability of the bolt pre-tightening force range of 27.43%⁴4.17%?_S??_S is the yield strength of the bolt material at room temperature?.