钻杆内螺纹接头纵向开裂机理及材料性能指标研究

近年来由于深井、定向井等逐渐增多，油气井钻井中钻杆内螺纹接头纵向开裂失效成为常发事故。大量失效分析发现钻杆内螺纹接头纵向开裂的裂纹源是外表面及螺纹表面的摩擦热裂纹、钳牙咬痕等各种损伤，这些裂纹以脆性断裂或应力腐蚀机理扩展。虽然裂纹源很难避免，但如果能够阻止裂纹的扩展，也能够防止钻杆内螺纹接头纵向开裂失效。应用钻杆失效评估技术研究表明，横向材料冲击功大于80 J将避免钻杆内螺纹接头纵向脆性开裂失效。对钻杆接头材料进行SSC试验，发现如果将材料硬度限制在HB310以内，将明显减少钻杆内螺纹接头纵向应力腐蚀开裂失效。失效案例统计数据验证了这些结果。建议有关标准规定钻杆内螺纹接头的横向材料冲击功，如可行同时限制材料的硬度，选用高性能钻具，以此提高钻具使用寿命，确保钻井速度。

STUDY ON LONGITUDINAL FRACTURE MECHANISM AND MATERIAL PROPERTY INDICATORS OF BOX-ENDED DRILLPIPE TOOL JOINT

Due to the increasing number of deep wells and directional wells being drilled,longitudinal fracture occurred on the box-ended drill pipe tool joint is often reported.A great deal of failure analysis shows the source of the fracture is various kinds of damage made on the outer surface and the thread surface of the box joint,such as the friction heat induced fracture,tong tooth bite,and etc.The fracture is further extended as a result of brittle fracture or stress corrosion.Although it is hard to avoid the sources of fracture,the longitudinal fracture failure on the box joint can be prevented if proper measures are taken to prevent further extension of the fracture.The drill pipe failure assessment demonstrates the longitudinal brittle fracture will be avoided when the transverse impact power of the material is over 80J.And the SSC test shows the stress corrosion crack of the drill pipe box joint will be reduced if the material hardness be restricted within HB310.The analysis of the failure cases also has verified these rules.This paper suggests that the corresponding standards stipulate the transversal impact energy of the drill pipe box joint,and control the material hardness of the drill pipe box within necessary range if practical,and choose high-performance drilling tools to ensure longer life of drilling tools and higher drilling rate.