Based On Research On Sealing Characteristics And Leakage Prediction At The Micro-scale

This paper is based on the study of the sealing characteristics and leakage prediction of Oring in high-pressure wellheads,because of the high experiment pressure exist in the highpressure casing head,the sealing components not only need extremely high sealing performance,but also need strictly control the leakage amount.Considering the difficulty of high pressure experiments,this paper uses the finite element method to combine the experimental data of the surface profile of the metal parts in contact with the rubber ring to simulate the leakage of the seal.In this paper,a three-dimensional model of rough surface contour at the microscopic scale of metal parts and rubber parts is established by using W-M three-dimensional model in Fractal Theory,and use simulation analysis of the sealing characteristics of rough surface profiles under different parameters and different working conditions.At last,using the Persson seepage leakage theory to study the leakage prediction of contact surfaces.Specific steps are as follows:(1)Research the scale effect of the microscopic model and get the influence of different fractal parameters on the surface profile.The surface profile experimental data was obtained by scanning the surface of the metal parts with an optical profilometer,and the data was fitted according to the data to obtain the actual fractal parameters of the analysis:Ds=2.565,G=1.1102E-4.In this way,a three-dimensional solid model of rough surface contours is established.(2)Using the established three-dimensional microscopic model,the finite element model is established and the independence of the mesh is verified to ensure the accuracy of the finite element model;Using finite element analysis,the results found:the larger the magnification,the surface micro-convex is more detailed,and the stress and contact stress are uneven distributed,the scale effect brings the complexity of the surface;The larger the elastic modulus,the larger the maximum equivalent stress on the surface,the elastic strain gradually decreases,and the contact stress and contact area also show an increasing trend;As the Poisson's ratio increases,the maximum equivalent stress is increased,the elastic strain is decreased,and the contact behavior is less affected;As the ratio of yield strength to ultimate strength increases,the maximum equivalent stress on the contact surface decreases first and then increases,and the contact area and contact stress show an increasing trend.(3)For the change of working conditions in the run of the seal ring,select parameters to analysis:As the normal displacement increases,the more the stress distribution on the sealing surface is intensived,the maximum equivalent stress increases,and the contact stress and contact area also increase,but as the displacement increases,the rate of increase gradually decreases;As the displacement of the fluctuating rebound continues to increase,the maximum equivalent stress and strain on the contact surface is decreased,but both of them are larger than the same displacement in the compression stage,and the contact behavior also shows a decreasing trend.(4)Using Seepage theory to calculation and prediction of Leakage Rate on leakage channels of contact surface:under steady-state conditions,the critical leakage channel produces a corresponding magnification of 10 times;The leakage rate increases with the increase of the pressure difference,and uses the Persson leakage rate calculation formula to make numerical calculations for specific working conditions;The leakage rate increases with the increase of the elastic modulus of the metal part.The Poisson's ratio has little effect on the leakage rate.The effect of the ratio of the yield strength to the ultimate strength for the leakage rate is consistent with the influence on the contact behavior;The increase of normal displacement makes different critical magnifications exist under different displacements,the displacement increases lead to the contact gap of leakage points decreases,and the leakage rate decreases.Stress fluctuation has a great influence on the leakage rate,the larger the rebound displacement cause the larger the leakage rate.In summary,this paper analyzes and studies the sealing characteristics and leakage prediction at the microscopic scale.