某井φ88. 9 mm×6. 45 mm外加厚P110油管接头发生脱扣，采用宏观观察、参数测量、化学成分分析、拉伸试验、金相检验以及不同扭矩下的实物拉伸试验等方法对脱扣原因进行了分析，然后采用有限元模拟进一步分析该P110油管的最佳扭矩。结果表明：采用较小的上扣扭矩时，会降低螺纹的连接强度，在遇阻时活动管柱，油管受到震动、井壁摩擦力及其他径向载荷，使螺纹产生反向滑动，发生松动形成脱扣。在不考虑螺纹几何公差配合、螺纹脂摩擦特性、螺纹表面镀层、上扣速度等因素影响的情况下，通过有限元模拟计算，认为在计算出的最佳扭矩下螺纹达到最佳状态（即过盈两圈时），考虑其他因素的影响，安全系数取1.25，实物上、卸扣试验也验证了该值的可行性。

The P110 tubing joint of φ88. 9 mm×6. 45 mmextra thickened tripped in a well. Macro observation, parameter measurement, chemical composition analysis, tensile test, metallographic examination and physical tensile test under different torques were used to analyze the tripping causes, and then finite element simulation was used to further analyze the optimal torque of the P110 tubing. The results show that the connection strength of the thread will be reduced when the smaller make-up torque was used. When the tubing string was blocked, the tubing will be affected by vibration, wall friction and other radial loads, resulted in reverse sliding of the thread, loosening and tripping. Without considering the influence of thread geometric tolerance fit, thread grease friction characteristics, thread surface coating, thread making speed and other factors, through the finite element simulation calculation, it was considered that the thread reached the best state under the calculated optimal torque (interference two turns). Considering the influence of other factors, the safety factor was 1. 25. The feasibility of this value was also verified by the actual loading and unloading tests.