某电厂超临界机组锅炉末级过热器钢管在弯头处发生泄漏。采用宏观检查、化学成分分析、金相检验、扫描电镜及能谱分析、力学性能试验等方法对钢管泄漏原因进行了分析。结果表明：钢管弯头在弯制中变形过大且其外弧侧因环境温度过高造成应力集中，随着钢管显微组织的变形和老化，晶界附近产生贫铬区，晶界强度降低，当应力集中达到晶界开裂的程度时，晶粒交界处产生楔型裂纹，裂纹迅速扩展最终导致钢管在运行时发生泄漏。

Leakage occurred at the elbow of steel pipes of final superheater of supercritical unit boiler in a power plant. The leakage causes of steel pipes were analyzed by means of macroscopic examination, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis, and mechanical property test. The results show that the deformation of steel pipe elbows were too large in bending, and the ambient temperature of the outer arc side was too high, which resulted in stress concentration. With the deformation and aging of the steel pipes microstructure, there were chromium poor area near the grain boundary, and the strength of the grain boundary decreased. When the stress concentration reached the degree of grain boundary cracking, wedge-shaped cracks appeared at the junction of the grains. The rapid expansion of cracks eventually led to the leakage of the steel pipes during operation.