N80钢级油管接箍纵向开裂失效分析

Failure analysis on N80 steel tubing coupling

通过力学性能测试、化学成分分析、显微组织和微观断口分析,对N80钢油管接箍纵向开裂失效原因进行分析。结果表明,该油管接箍的热加工工艺不当,组织中存在带状分布的马氏体,导致其冲击功明显低于标准要求。裂纹起源于接箍外表面上扣大钳的夹痕处,在腐蚀性介质H2S的作用下脆性扩展,最终导致接箍发生应力腐蚀开裂。

Failure reasons of the longitudinal cracking N80 tubing coupling were researched through mechanical properties test,chemical composition,microstructure and micro-fracture surface analysis.The results show that the hot working technology of the tubing coupling is not proper and there is banded martensite in microstructure,its impact energy is much lower than requirement of the standard.Under the effect of H2S corrosive medium,cracks originate from the clamp mark in couplings out surface and extend quickly.In the end,they lead tubing coupling to stress corrosion cracking.