600MW锅炉12Cr1MoV末级再热器管失效原因分析

Failure Analysis on 12Cr1MoV Tube Final-stage Reheater for 600 MW Boiler

某电厂600 MW亚临界机组的12Cr1MoV末级再热器管运行50000 h后发生泄漏。在迎烟气侧弯头背弧出现裂纹。采用光学显微镜、扫描电镜和能谱仪等方法对失效管样进行分析。结果表明,弯头向火侧氧化层过厚,组织球化严重;弯头向火侧管壁存在明显的蠕变孔洞和沿晶裂纹,裂纹沿着晶界发展并充满氧化物;基体出现合金元素贫化,导致组织劣化。综上,12Cr1MoV末级再热器管失效是由长期过热造成管件向火侧组织老化,蠕变开裂而引起泄漏。

A 600 MW subcritical boiler final-stage reheater tube made by 12Crl MoV steel leaks after running for 50000 h. The crack appears in the gas side elbow. The cracked reheater tube was analyzed by optical microscope （OM）, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results show that a thicker oxidation film is coated on the fire-facing side of the elbow, and serious pheroidization of pearlite is found in metallographic structure. Many creep cavities and micro-cracks appear in the fire-facing side of the elbow. The micro-cracks extending along the grain boundaries, are filled with oxide. The alloying elements are depleted in the matrix, which can cause the deterioration of tube microstructure. In conclusion, the degradation of the microstructure caused by long term overheat is the main reason for the failure of 12Crl MoV hot stage reheater tube, and the creep cracking causes the leak.