Research On The Mechanical And Sealing Performance Of Oil Tubing And Casing Conical Threaded Connection With Sealing Shoulder Face

The oil tubing and casing threaded connection with sealing shoulder face is widely used in practice. In the past, the researches on the mechanical performance of threaded connection almost did not analyze on the connection with the sealing shoulder face and consider the influences of the force on the sealing shoulder face on the mechanical performance of threaded connection. The sealing mechanism of threaded connection is not investigated deeply, and most of the researches focus on qualitatively analyzing the relationship between contact stress on thread tooth and sealing performance. However, a generally recognized sealing mechanism system has not established. In this dissertation, the mechanical performance of conical threaded connection sealing shoulder face under tightening is deeply studied, and numerical calculation and experiment on sealing performance parameters between two contacting surfaces are carried out.The main contents and conclusions of this dissertation include the following aspects.The total load and deformation for the pin and the box are investigated respectively, as well as the load and deformation for the individual pin and box thread. The expressions of axial deformation on the pin and box are developed. According to the matching relation between two corresponding points of the pin and box, the deformation compatibility equations are derivated for the conical threaded connection under tightening. The expressions of bending deformation and axial displacement on the pin and box thread tooth are developed. Then, the equations of displacement for a certain matching point on the thread tooth are derivated. On this basis, a calculation approach to extrusion force on the sealing face, axial load and deformation on pin and box thread and maximum contact pressure on thread tooth surface for conical threaded connection in tightening is developed.By using the above calculation approach established, an API conical threaded connection is taken as the sample and its mechanical performance is calculated. Some regular variation curves are obtained.Based on the analytic mechanical model, a finite element model is obtained. By using the non-linear finite element software MARC, mechanical performance of an API conical threaded connection is calculated. Comparing finite element results with analytic results, rationality and reliability of two methods are validated.3D topography of rough sealing surface is simulated by using index autocorrelation function. Metal surface micro-contact model is established and simplified into micro-contact model for single asperity. Based on Hertz contact theory, a calculation approach is set up for analyzing the influences of the external load on the interfacial separation, contact area and interfacial stress in the process of contact for the two metal surfaces.A simulation approach to micro-contact performance of sealing surface for conical threaded connection is established. Base on this, the influences of tightening cycles on interfacial separation, contact area and maximum interfacial stress are investigated in different initial sealing clearance and surface roughness conditions.Conical threaded connections with different initial sealing clearance and surface roughness are made. Experimental equipment is developed to test the sealing performance of conical threaded connection. The influences of initial sealing clearance and surface roughness on leakage rate are investigated in different make-up torque and gas pressure conditions.The research and conclusions obtained in this dissertation can provide some theoretical foundations for further researches and practical application on mechanical performance and sealing performance for conical threaded connection with sealing shoulder face.