某油田直井气井在正常产气56 d（天）后发生油管本体断裂失效。通过宏观检验、化学成分分析、力学性能测试、金相检验、扫描电镜及能谱分析，对该油管的失效原因进行了综合分析。结果表明：该油管的断裂性质属于腐蚀疲劳断裂；外表面脱碳降低了油管的耐腐蚀能力，在服役过程中管材外表面接触水及空气的位置发生氧腐蚀，形成腐蚀坑，腐蚀坑底部产生应力集中成为疲劳裂纹源；在外力作用下疲劳裂纹不断扩展，最终导致了油管的断裂失效。

A tubing used in an oilfield for a vertical gas well fractured after 56 days regular gas production. Macroscopic examination, chemical composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy and energy spectrum analysis were used to comprehensively investigate the failure reasons of the oil tube. The results show that:the fracture of the oil tube belonged to the corrosion fatigue fracture; and the decarburization on the outer surface reduced the corrosion resistance of the oil tube; during the service process, the oxygen corrosion occurred on the outer surface where the water and air contacted, and the corrosion pitting formed; the stress concentration generated in the bottom of corrosion pitting, and induced the fatigue crack source; under the action of external force, fatigue cracks propagated constantly, and finally led to the fracture failure of the tubing.