API圆螺纹接头连接强度的影响因素研究

Research on the Factors Influencing the Connection Strength of API Knuckle Thread Joint

API圆螺纹接头经常发生滑脱失效事故，严重影响了这种接头油套管的应用。为此，利用有限元法研究了API圆螺纹接头发生滑脱失效的过程与机理，同时分析了螺纹参数和上扣扭矩对接头连接强度的影响。通过对17个圆螺纹套管接头试样进行全尺寸试验，对有限元模拟结果进行了验证。试验和计算结果表明，圆螺纹油套管滑脱失效最先发生在啮合大端的第1、第2牙螺纹上，螺纹参数尤其是不匹配的锥度对接头滑脱失效影响很大，同时上扣扭矩也有显著影响。建议将上扣扭矩在API扭矩的基础上再提高（15～20）％，这样有利于接头连接强度的提高。

Slippage failure often happens to API knuckle thread joint, which seriously affects the further ap- plication of tubing and easing with this joint. Therefore, the finite element method was used to study the process and mechanism of joint slippage failure. Meanwhile, the effeets of thread parameters and make-up torque on the connec- tion strength of the joint were analyzed. Through the full-seale test of 17 knuckle thread easing joint samples, the fi- nite element simulation result was verified. The test and calculation findings show that the knuckle thread tuhing and casing slippage first takes place on the I st and 2nd pitch threads of gearing big end. The thread parameters, espe- cially the unmatehed taper, have remarkable effect on joint slippage failure. Meanwhile, make-up torque has con- siderable effect. It is suggested that tire make-up torque should be improved by （ 15 ～ 20） % on the basis of API torque. This helps improve the connection strength of the joint.