上扣扭矩对圆螺纹套管连接强度的影响

INFLUENCE OF MAKE-UP TORQUE ON THE CONNECTING STRENGTH OF ROUND THREAD CASING

文章针对目前普遍存在的API圆螺纹套管易于发生滑脱失效的现象,分析了这种套管在拉伸载荷作用下滑脱失效的特点,并通过弹塑性有限元方法研究了各牙螺纹的受力。在此基础上,系统地研究了上扣扭矩对这种套管连接强度的影响,并利用全尺寸试验验证了有限元计算结果的可靠性。研究结果表明,上扣扭矩对圆螺纹套管的连接强度有较大影响,在API推荐扭矩的基础上,适当增大上扣扭矩,将上扣扭矩从API最佳值提高到最佳值的1.5倍,可明显提高圆螺纹套管的连接强度。

In light of the commonly existing phenomenon that the API round thread casing is easy to be failed because of slippage at present, the characteristics of this kind of casing failure under the action of tensile load are analyzed in the paper. The forces acting on each tooth of the round thread were investigated by use of elasticoplastic finite element method, then the influence of make-up torque on the connecting strength of round thread casing was systimatically studied, and then the reliability of the calculation results by the element method was verified through a series of tests of full gauge samples. The study results indicated that this kind of influence was notable; and, on the basis of the make-up torque recommended by API, the connecting strength of the round thread casing will be obviously raised through suitably increasing the value of the make-up torque to 1.5 times that of the one recommended by API.