超(超)临界锅炉水冷壁管泄漏失效分析

Failure Analysis of Water Wall Tubes' Leakage in(Ultra) Super-critical Boiler

利用故障树失效分析方法,从设计、制造、安装、运行等角度出发,对某超(超)临界锅炉水冷壁管泄漏事故可能性原因进行排除性分析,分析工作包括设计复核、运行参数检查、宏观形貌、断口形貌、显微组织分析、化学成分分析、室温拉伸性能试验、硬度试验等。结果表明:失效部件在设计、制造、运行方面无问题,水冷壁泄漏的直接原因为宽大的H型鳍片角焊缝裂纹扩展至水冷壁管。H型鳍片与水冷壁弯管的角焊缝质量差,存在未焊透、气孔、缩孔等缺陷,导致角焊缝的强度降低、局部应力集中、冷却效果差,在长期服役中过早形成裂纹。根据失效分析结果,给出了缺陷处理建议。

The leakage of water wall tubes was studied by using the fault tree analysis method from the views of design, manufacture, installation and running, which included the design review, the operation parameter inspection, the macroscopic morphology, the fi＇acture morphology, the microstructure analysis, the chemical composition analysis, the tensile test at room temperature, the hardness test and so on. The results show that the failed parts has no problems on the design, manufacture and running, and the direct reason of water wall leakage is that the weld crack of wide H type fin extends to the water wall tubes. The weld quality of H type fin and water wall tubes is poor, there is lack of penetration, pores, shrinkage defects, which results in the decrease of fillet weld strength, the local stress concentration and the poor cooling effect and early cracks in the long term service. According to the results of failure analysis, the suggestion of defects treatment was given.