Design And Study Of New Type Airtight Buckle

Tubing is an indispensable special pipe in oil and gas exploitation,the connection strength and sealing performance of the tubing joint directly affect the success of oil and gas operations.With the development of petroleum industry,the API thread can not meet the requirements of deep well,ultra deep well,high temperature and high pressure oil and gas wells due to the limitation of the structure,being replaced by high bonding strength,excellent sealing performance of airtight buckle.Therefore,it is of great practical significance to study the design of high performance airtight buckle in China to improve the performance of the oil pipe.In this paper,the sealing mechanism,load and failure mode are analyzed.Based on the classical mechanics theory,the mechanical model of the airtight buckle under makeup condition is established,and the distribution of contact stress is calculated.The 3D finite element model of VAM TOP and NK3 SB was established by Hypermesh and ANSYS,the sealing and connecting performance under the load of makeup,stretching and bending were simulated,research shows: there is a serious stress concentration in the transition zone between shoulder and sealing surface,and it is the weakest link in airtight buckle structure.The thread stress distribution of NK 3SB is more uniform under tensile condition,and the thread stress fluctuation of VAM TOP is smaller in bending condition.When it comes to tensile and bending loads,NK 3SB spherical / conical sealing performance is more excellent,VAM TOP reverse shoulder sealing performance is more excellent.In order to solve the problem of serious stress concentration in the transition area between the shoulder and the sealing surface,a new type of airtight buckle with stress release slot structure was designed.The influence of the main structural parameters on the performance of the air seal was studied by simulation.It provides a theoretical basis for optimizing the structure parameters.The main features of the design are:(1)Thread design: The thread taper is 1:16,the thread pitch is 5TPI,the guide surface angle is 10 degrees,the bearing surface angle is 0 degrees,the tooth height is 1.575 mm,the complete thread quantity is a circle of 10.7,it can guarantee the thread tensile strength to achieve the 100% pipe body strength level.(2)Metal seal design: The main seal with cone/cone seal structure,the sealing surface of the cone angle is 12 degrees,the reverse torque shoulder angle of 10 degrees,a stress release slot is designed in the transition region between the torque shoulder and the sealing surface,The utility model is favorable for reducing the stress concentration at the shoulder,making the stress distribution more uniform,improving the compression resistance and the stress corrosion resistance of the air tight buckle.