钻杆接头表面裂纹的断裂性能研究  

Fracture behaviors of surface cracks in the toll joint

作　　者：赵广慧[1] 赵莉[1] 石健[1] 唐松[1] 李举[1] 

机构地区：[1]西南石油大学机电工程学院,成都610500

出　　处：《应用力学学报》2016年第5期838-844,937,共7页Chinese Journal of Applied Mechanics

基　　金：国家自然科学基金(51134004;11102173);石油天然气装备教育部重点实验室资助项目(OGE201403-10);西南石油大学研究生创新基金(CX2014SY28)

摘　　要：定向井的钻井作业中,受到最大拉力的井口附近以及交变弯矩作用的造斜段是钻杆发生断裂的危险范围;接头螺纹及加厚过渡段的截面形状变化比较大,结构复杂,是疲劳裂纹产生的最主要的区域。以API NC50钻杆接头为例,建立了公螺纹根部含半椭圆表面裂纹的接头有限元模型,通过研究拉力、弯矩分别作用下裂纹前缘的断裂性能发现:公螺纹中完整啮合第一扣的根部最容易产生疲劳裂纹;拉力作用下量纲为一的应力强度因子大于弯矩单独作用的情况。另外,得到了螺纹根部裂纹扩展至不同深度的临界形状比,拟合出拉力和弯矩分别作用下量纲为一的应力强度因子随着裂纹扩展的变化规律,为研究位于井口附近以及造斜段的钻杆接头螺纹的疲劳寿命提供依据。In the course of the drilling operation of a directional well, the drill string near the surface stands the largest tension and the drill pipe in the angle buildup interval is subjected to the alternating bending moment. As a result, the drill pipe in these two regions is most prone to failure. For a single drill string, fatigue cracks usually generate in the joint-thread and the upset end, whose cross-section shapes change greatly and the structure is complicated. Based on the API NC50 tool joint, the finite element model of the joint that contains a semi-elliptical surface crack located at the root of the pin-thread joint is established, and the fracture characters of the crack under tension and bending are analyzed respectively. It is found that a fatigue crack occurs at the root of the first engaged tooth more likely. The dimensionless stress intensity factor under tension is larger than the one under bending. Then the transition aspect ratios of the crack are determined corresponding to different crack depths. Finally, the equations for dimensionless stress intensity factors as a function of crack depth and forces are fitted under tension and bending. It provides a basis for further study on the fatigue life of the joint-thread that is near the well head or in the angle buildup interval.

关 键 词：钻杆接头 螺纹 半椭圆表面裂纹 断裂性能 应力强度因子 

分 类 号：TE921[石油与天然气工程—石油机械设备]