Analysis Of Cylindrical Sealing Characteristics Of High Pressure Plug Valves Based On Fractal Theory

Plug valve is a hydraulic circuit control valve with convenient operation and sensitive response.It is widely used in the field of oil and gas exploitation,such as wellhead blowout prevention and fracturing circuit control.Its sealing performance directly affects the construction safety and economic benefits.Under the condition that the plug valve is subject to unilateral high medium pressure,the extrusion of the valve core and the sealing valve piece is easy to produce plastic deformation and damage the initial sealing surface formed by the interference fit.At the same time,the frequent opening and closing of the fracturing process and the penetration of hard particles may lead to the weakening of the valve sealing effect.Therefore,it is particularly important to analyze the sealing characteristics of the plug valve cylindrical surface.At present,the reliability design of the sealing pair is mainly based on the sealing specific pressure,and the sealing performance is evaluated by the contact pressure within the allowable range,which is different from the leakage standard of the pressure test,so it is impossible to estimate the leakage amount of the seal during the design process.In this paper,fractal theory is applied to the study of cylindrical seal characteristics,and a cylindrical contact leakage model is built,taking into account the influence of the real shape of rough surface,mechanical properties of seal and load conditions on the leakage.Based on the unit rough surface contact simulation,the relationship between the real contact area and the average contact pressure is fitted,and combined with the three-dimensional elastoplastic analysis of the actual working condition of the plug valve,the leakage of the cylindrical surface seal is calculated.The main research contents are as follows:(1)The leakage model of cylindrical seal is established.At present,the construction of leakage model based on fractal theory mainly focuses on low-dimensional plane pairs,and the cylindrical surface seal model considering microstructure is rarely reported.In order to expand the application of fractal theory in the field of leakage,a leakage model related to roughness,mechanical properties of materials and load conditions is established by combining the distribution function of surface contact micro-convex.(2)The two-dimensional contour curve and three-dimensional surface of rough surface are simulated,and the unit rough solid model is established.The W-M function covers many parameters,including fractal dimension,roughness amplitude and contour frequency coefficient.In order to understand the physical meaning of each parameter expression,the influence law of each fractal parameter on the characteristics of rough surface is summarized,the difference between two-dimensional contour curve and three-dimensional rough surface is compared,the value of relevant parameters in the fractal function is determined,and the unit rough solid model is established to provide technical support for the later numerical simulation.(3)The effects of fractal characteristic parameters,material mechanical properties and load conditions on leakage are summarized.Through three-dimensional elasto-plastic contact simulation of unit rough surface,the real contact area ratio of the sealing surface is extracted,and the Ra,H,E and η Influence of other parameters on leakage.(4)The leakage of cylindrical seal of high pressure plug valve is calculated.The functional relationship between the real contact area and the average contact pressure is fitted,and the real contact area of the sealing valve is estimated by combining the numerical simulation of the actual working condition of the high-pressure plug valve with the real contact area-average contact pressure function.Finally,the leakage amount is calculated by the cylindrical seal leakage model.