某井在勘探开发过程中,发生多起S135钻杆刺漏失效,对失效钻杆材料进行了化学成分、显微组织、力学性能等一系列理化检验,并对裂纹扩展面进行了详细的微观分析,获得了钻杆的失效模式为腐蚀疲劳失效.针对失效模式,对钻杆材料进行了圆棒小试样的拉压疲劳试验,获得了失效钻杆材料在高应力下的疲劳寿命,佐证了钻杆设计中设计系数的科学性,为钻杆失效原因判定提供了试验数据支持.分析结果表明:钻杆失效的主要原因是钻杆外表面发生氧腐蚀形成腐蚀坑,腐蚀坑底应力集中导致的局部高应力促使了疲劳裂纹的萌生,当裂纹扩展穿透整个壁厚后便形成刺漏失效.

Piercing failure had occurred in some S135 drill pipes in the process of a well drilling.A series of tests,such as chemical compositions analysis,metallographic examination,mechanical properties test and so on,were done to the failure drill pipes.According to these studies,the failure model of the drill pipes was regarded as corrosion fatigue.At the same time,tensional-compressive fatigue test was done to small round samples according to the failure model,which proofed the scientificity of design coefficient in the design of the drill string and provided data support for the failure cause.The analysis results show that it was the stress concentration of corrosion pits which located in outer surface of the drill pipes that resulted in the initiation and propagation of fatigue cracks,and the piercing failure occurred when the cracks propagated through the whole wall thickness.