双台肩钻杆丝扣粘扣失效的力学机制探究

The mechanism of the galling for double shoulder drill pipe joint

针对丝扣粘扣中接触压力过大引发的塑性变形的问题,基于双台肩钻杆接头的三维有限元分析,分析了上扣扭矩、轴向拉力、旋转扭矩作用下的钻杆接头接触压力分布规律和Mises应力分布规律。研究结果表明:当轴向拉力达到2500kN时,主台肩上的接触压力降为零,这将使得载荷主要由螺纹牙来承担,增加丝扣粘扣的风险。当旋转扭矩超过24000N m时,一方面提高了副台肩上的接触压力,增加了副台肩失效的风险;另一方面大幅提高了螺纹牙的承载比例,增加了丝扣粘扣的风险。适当增大副台肩间隙和副台肩处的接触面积可以降低大位移井中副台肩失效的风险。适当增大主台肩、副台肩的接触面积可以降低超深直井中丝扣粘扣的风险。本文计算的三种工况条件下,最大Mises应力同样均位于公扣大端第一个螺纹牙处,说明该处是最易发生粘扣的部位,在螺纹结构的优化设计中应予以重点考虑。

Galling is the most common failure pattern of drill pipe joint,which may cause great loss to the oil field.From the viewpoint of mechanics,plastic deformation caused by excessive contact pressure is the root cause of the galling of tool joint.Three-dimensional finite element analysis of double shoulder tool joint is carried out and the distribution law of contact pressure and Von Mises stress of tool joint under make-up torque,axial tension and rotation torque are analyzed.According to the analysis,when the axial tension exceeds 2500kN,the contact pressure of primary shoulder will reduce to zero,thus make the load undertake by the thread primary,which increases the risk of thread galling.When the rotation torque exceeds 24000Nm,contact pressure of the secondary shoulder will increased greatly,which increases the failure risk of the secondary shoulder.Moreover,excessive rotation torque increases the bearing ratio of the thread,which increases the galling risk of the thread.Increase the gap of secondary shoulder and the contact area of primary shoulder appropriately can reduce the risk of failure of secondary shoulder in the extended reach wells.Increase the contact area of the primary and secondary shoulder appropriately can reduce the risk of galling in the ultra-deep wells.In the three load cases,the maximum Von Mises stresses are all located at the first engaged thread of the pin,which means galling is the most likely occur case and should be taken more consideration in the design of the tool joint.Results obtained can be taken as references in understanding the mechanical mechanisms of galling and reducing the galling failure of tool joint.