Stress Simulation Analysis And Gas-sealing Capacity Researching Of Casing Threaded Connection

The drilling pipe used in slim borehole drilling performs great potential due to its lower cost and higher efficiency.However,the slim drill joint torque is subjected to torque,axial tension force and the frictional force acting on the shaft wall in the drilling process.The insufficiency of the strength of the screw thread part can cause the seal failure,which causes the leakage.The stress intensity and distribution of the stress of the thread is the key of improving air tightness.To solve this problem,we carry on the research of the slim joint.We design joint with an diameter of ф68 according to the drilling needs.Using the lame thick walled cylinder theory,we established the contact stress model under the axial tension force,torque and the contact stress model under differential pressure of drill pipe.In order to ensure the air tightness,the contact stresses should be higher than the differential pressure,and the contact surface must be smooth.Based on 3D modeling software SolidWork and finite element analysis platform Ansys Workbench we construct the 2D simulation model.The simulation results on the distribution of contact stress between the surface shows that the effect of joint sealing was predicted and the key factors that affect the air tightness.Through the design calculation, we can get the Optimum Makeup Torque and the related parameters of the experiment.The experiment was verified with results from various states in the model.Testing results are compared with simulation.The results show that, the makeup torque plays a decisive role in ensuring the sealing of the joint and the sealing performance is affected with the increasing of axial force.By comparing the experimental and simulation results.We verify that the gas tightness criterion,and the flatness of contact surface has also play a big role on the air tightness.So,the machining precision need to be controlled strictly.The research results of the paper intended to lay the groundwork for future research of optimizing the structure of the tool joint connection.