Determination And Safety Evaluation Of The Bolt Preload Of Pipe Flange

Due to the complexity of the working conditions of the structure,the flange connection system is easy to leak and cause many accidents.The correct application of bolt installation load is the key factor to avoid leaking.At present,Taylor-Waters method and EN13445-3 appendix G are the main methods for calculating bolt installation load,therefore,this paper mainly obtains empirical data through a large number of calculations,which is convenient for guiding the engineering application.This study took the PL flange and WN flange as the research objects,and adopted the calculation method EN13445 appendix G and Waters method to calculate the bolt preload of pipe flange under different working conditions.After the calculation,the data were fitted by formula.At the same time,the influence of different factors on bolt preload was studied.The results showed that the bolt preload of EN13445 appendix G increased with the increase of the ratio of nominal diameter to thickness of flange,external bending moments,temperature and pressure,while the bolt preload of Waters increased with the increase of the ratio of nominal diameter to thickness of flange,and temperature and pressure had little effect on it.In order to facilitate inquiry,a database of bolt preload was established according to the calculation results,and a Web query program was compiled to realize the numerical query function of bolt preload.Two completely different sizes and working conditions of pipe flange-bolt-gasket were randomly selected.The Design Modeler of the finite element software ANSYS Workbench was used to establish the 3D finite element model,which was analyzed for thermal stability and the temperature distribution on the pipe flange.And then the temperature field distribution of flanged connection system was obtained.The simulation results indicated that the temperature gradient of the flange connection system was obvious in the radial distribution,and they were basically symmetrical distributed.The highest temperature existed in the inner wall of flange and gasket.In order to verify whether the bolt preload of the pipe flange system calculated by the existing calculation methods could meet the requirements of sealing and ensure the integrity of the components.thermal-structural coupling was carried out on the basis of thermal steady state analysis.The bolt preload calculated according to EN13445 Appendix G and Waters method,as the initial one respectively,was applied to the corresponding pipe flange system,and the components under preloading and operating conditions were analyzed and the results were post-processed.According to the analysis,the safety identification was carried out.The results showed that the bolt preload calculated by two methods can ensure the sealing of pipe flange structure and the integrity of each component.Combining the results of finite element analysis and related data,using the method of fault tree in safety evaluation,the author analyzed the reasons that might cause leakage of flange-bolt-gasket system,and drew a reasonable fault tree.And then,the qualitative and quantitative analysis and structural importance analysis were carried out,and the possible causes were proposed.The basic events of the leakage and the relevant measures were put forward according to the analysis results at last.