φ139.7 mm×10.54 mm G105钻杆刺穿失效分析

Failure Analysis on Piercement of aφ139.7 mm×10.54 mm G105 Drill Pipe

采用宏观分析、化学成分分析、力学性能试验、金相检验、扫描电镜断口分析及能谱分析等手段对某规格为φ139.7 mm×10.54 mm的G105钻杆的刺穿原因进行了分析。结果表明:钻杆刺穿的实质是早期疲劳失效;蹩钻、跳钻等钻柱振动引起钻杆上产生的严重交变应力是导致钻杆失效的主要原因;钻井液中的溶解氧对钻杆外表面造成氧腐蚀并形成腐蚀坑,促进了疲劳裂纹的萌生;钻铤直接过渡到钻杆,截面变化突然,使应力集中加剧,也是导致钻杆发生疲劳失效的原因之一。建议在钻井液中添加除氧剂和缓蚀剂,并适当降低钻压,调整钻井参数,避免钻柱剧烈振动。

The reasons to the piercement of drill pipe with grade of G105 and size of φ139.7 mm× 10. 54 mm were analyzed through morphology analysis, chemical components analysis, mechanical property test, microstructure examination, SEM analysis and energy spectrum analysis. The results show that the essence of drill pipe piereement was early fatigue failure, and the main reason of which was severe alternating stress induced by vibrations such as bit bouncing. Dissolved oxygen in drilling mud caused the pitting on the outer surface. Just those pits accelerated arising of fatigue crack. Moreover, direct transition from the drill collar to the drill pipe, the sudden change of the section led the exacerbation of the stress concentration which was also one reason causes for the occurrence of drill pipe fatigue failure. Scavenger and inhibitor were suggested to add in the drilling mud. In addition, a lower bit weight and optimum drilling parameters were good ways to avoid drill string vibration strenuously.