350MW超临界锅炉水冷壁管爆管原因分析

利用宏观检查、金相组织分析、力学性能检测、化学成分分析以及断口扫描电镜分析等对失效管段进行了全面检测,分析某超临界锅炉水冷壁管的爆管原因。结果表明:安装人员将原设计的柔性连接改为刚性焊接连接,同时,施工质量较差,连接焊缝中存在未熔合缺陷导致严重的应力集中;顶棚过热器管与水冷壁管膨胀量及膨胀方向不一致,且反复变化,使水冷壁管与加强筋的搭接焊缝在锅炉运行过程中长期承受疲劳载荷,是导致本次水冷壁管开裂的直接原因。

Cause analysis on water-wall tubes bursting of 350 MW super-critical boiler

By the means of the macroscopic examination, metallurgical analysis, mechanical properties detection, chemical composition analysis and fracture scanning electron microscope, the failed tube was fully analyzed. The causes of the water-wall tubes bursting of 350 MW super-critical boiler were analyzed. The results show that the flexible connection of original design was changed by mistake to rigid welding-connection during the build process, and the construction quality is poor, the incomplete fusion defect was left in the weld resulting in serious stress concentration in this area. The direct reason of the failure was that roof superheater tubes were inconsistent with the expansion and expansion direction of water-wall tubes, which are liable to vary repeatedly resulting in the lap weld of stiffener and water-wall tube bearing fatigue load for a long time during boiler operation.