某超临界锅炉运行1.2万h后，在其吹灰器罩壳内水冷壁管背火面发现密集横向裂纹。通过资料调研、材料成分检验以及开裂部位显微组织、断口形貌和拉伸性能分析，研究了水冷壁管表面裂纹产生的原因。结果表明：水冷壁管材料正常，其背火面管外壁裂纹为热疲劳裂纹；吹灰器套管外径偏大顶在吹灰孔周边水冷壁管上，温度偏低导致吹灰蒸汽带水，水沿着水冷壁管和吹灰套管间的缝隙滴到水冷壁管背火面，导致此处长期承受冷热交变应力而发生热疲劳开裂。

Dense transverse cracks were found on the backfire surface of the water-wall tube in the soot blower cover after the supercritical boiler ran for 1.2×10⁴ h. By data investigation, material composition inspection, and analysis of microstructure, fracture morphology and tensile properties, the causes of surface cracks of the water-wall tube were investigated. The results show that the material of the water-wall tube was normal, and the cracks on the tube outer wall of the backfire surface were thermal fatigue cracks. The outer diameter of the soot blower cover was too large, making the cover being topped on the water-wall tube around the soot blowing hole. Meanwhile, the temperature was low, making the soot blowing steam carrying water. The water dropped along the gap between the water-wall tube and the soot blowing sleeve to the backfire surface of the water-wall tube, causing the bearing of long-term heat and cold alternating stresses, and finally thermal fatigue cracking occurred.