The Leakage Mechanism Research And Simulation Analysis Of Pressure Vessel Lifting Hole Sealing Structures

In the fields of nuclear power,aerospace,shipbuilding and so on,there are a large number of pressure vessels.In order to ensure the normal operation of the system,the pressure vessels are usually required to have good sealing performance to prevent the leakage of working substances into the external environment.The local sealing structure such as the lifting hole on the pressure vessel is the main way to produce leakage.However,some previous studies mainly focus on the strength criterion of the sealing structure,and lack of quantitative analysis on the leakage mechanism.In this paper,a prediction model of leakage rate independent of empirical parameters is established from the point of view of tightness,and the analysis scheme of leakage rate for the sealing structure of pressure vessel lifting holes is given by combining the finite element macroscopic mechanics simulation.Firstly,the interface microscopic leakage mechanism of the static seal is studied,and the principle and deficiency of the existing leakage rate prediction model is introduced.Based on the smooth plate flow,two important dimensionless parameters,roughness flow factor and height flow factor,are introduced,and a leakage rate prediction model based on three-dimensional numerical rough surface is proposed.Then,the accuracy of the model was verified by comparing the experimental results with the theoretical model in the literature.Secondly,the macroscopic mechanical properties of lifting hole bolted flange gasket seal structure and O-ring seal structure were obtained by using ABAQUS finite element software.Combined with the leakage rate prediction model,the influence of different parameters on the sealing structure is analyzed.The results show that for gasket seal,the leakage rate under high medium pressure can be effectively controlled by increasing the preload,the thickness of gasket and the number of bolts.The influence of flange width is small,while the influence of bolt diameter can be almost ignored.For O-ring seal,the elliptical trapezoid section with lower hardness and high compression rate has better sealing performance.Finally,the definition and mechanism of generalized creep are introduced,and the influence of creep on gasket seal of lifting hole and O-ring seal of lifting hole under long-term working conditions is discussed respectively.The results show that after 10000 h,the size and distribution of the stress of the sealing structure have a great change,and the contact stress significantly decreases,resulting in a great increase of the leakage rate,which indicates that the creep effect has a great influence on the sealing integrity of the sealing structure.In this paper,leakage mechanism model for the lifting hole of pressure vessel is presented,all the micro numerical results are fitting for the dimensionless parameter.At the same time,combined macro mechanics simulation,any seal structure under the condition of leakage rate can be predicted without relying on any empirical formula.The research results can be applied to the design of the sealing structure such as the lifting hole of the pressure vessel and predict its sealing performance under any working conditions.