通过宏观检查、化学成分分析、力学性能测试、显微组织观察等,对某600 MW亚临界机组分隔屏过热器管换位弯内弧外表面裂纹的产生原因进行分析。结果表明:腐蚀性S元素的富集浓缩腐蚀了分隔屏过热器管基体,形成“显微缺口”,萌生微裂纹;外表面脱碳层的存在,为裂纹扩展提供了有利条件;微裂纹在S腐蚀环境和热疲劳循环载荷协同、交互作用下不断扩展,最终产生腐蚀性热疲劳裂纹。

The causes of surface cracks on the outer surface of inner arc of a transposition bend of partition platen superheater tube of a 600 MW subcritical unit were analyzed through macroscopy examination, chemical composition analysis, mechanical property testing, microstructure observation, etc. The results showed that the enrichment concentration of corrosive S element corroded the substrate of the tube, forming “micro notches” and initiating microcracks. The presence of a decarburized layer on the outer surface provided favorable conditions for crack propagation. Microcracks continued to propagate under the synergistic and interactive effects of S corrosion environment and thermal fatigue cyclic loads, ultimately resulting in corrosive thermal fatigue cracks.