某电厂300 MW机组锅炉运行过程中发现12Cr1MoVG钢屏式再热器发生爆管。采用宏观观察、化学成分分析、力学性能测试、硬度测试、金相检验、扫描电镜及能谱分析等方法对爆管原因进行了分析。结果表明:爆口属于长时超温开裂,爆口处的显微组织严重老化(球化级别为5级),爆口周围内、外壁有较多的纵向蠕变裂纹,且爆口内、外壁覆盖有很厚的氧化层;外壁氧化结焦导致弯头局部长时过热,过热处管子的组织、性能出现严重劣化,局部发生蠕变,产生蠕变裂纹,裂纹沿晶扩展,在内部介质的压力作用下最终发生蠕变开裂。

During the operation of a 300 MW unit boiler in a power plant, it was found that the 12Cr1MoVG steel plate reheater burst. By means of macroscopic observation, chemical composition analysis, mechanical properties test, hardness test, metallographic examination, scanning electron and energy spectrum analysis, the causes of tube explosion were analyzed. The results show that the crater belong to long-time over-temperature cracking, and the microstructure at the crater was seriously aged (nodulizing grade reached five). There were many longitudinal creep cracks in the inner and outer walls around the detonation, the inner and outer walls of the blast hole were covered with a thick oxide layer. Oxidation and coking on the outer wall led to the local long-time over-temperature of the elbow. The microstructure and properties of the pipe at the overheating point were seriously degraded, which made the local creep and produced creep cracks. The cracks propagated along the crystal, and finally creep cracking occured under the pressure of the internal medium.