某电站锅炉再热蒸汽管道的开裂原因

Cracking Cause of Reheat Steam Pipe of a Power Plant Boiler

某电站服役约10万h锅炉在检修时发现,其再热蒸汽管道排空管的承插焊支管座内壁和母管承插孔附近发生龟裂,采用宏观与微观形貌观察、化学成分分析、力学性能试验、显微组织观察、微区成分分析等对开裂原因进行了分析。结果表明:再热蒸汽管道排空管结构设计不合理,导致排空管后端一次阀前水平管段易集聚大量冷凝水;在逆流冷凝水和高温蒸汽的共同作用下,再热蒸汽管道排空管的承插焊支管座内壁、母管内壁靠近承插孔下游位置及承插孔内壁萌生热疲劳裂纹。在蒸汽压力、循环热应力和碳酸盐腐蚀物质的综合作用下,热疲劳裂纹扩展,并最终导致管道的开裂。

It was found that cracking occurred on the inner wall of the socket welding branch outlet in the evacuation pipe and the location near the socket of the header pipe of reheat steam pipe in a power plant boiler during overhaul after service for over 100,000 h.The causes of cracking were analyzed by macro-and micro-morphology observation,chemical composition analysis,mechanical property test,microstructure observation,and microcomponent analysis.The results show that the structure design of the evacuation pipe of the reheat steam pipe was unreasonable,leading to the accumulation of a large amount of condensate in the horizontal pipe section in front of the first valve of the evacuation pipe back end.Thermal fatigue cracks initiated at the inner wall of the socket welding branch outlet in evacuation pipe,inner wall at down stream part of the header pipe close to the socket and inner wall of the branch outlet of reheat steam pipe under the combined action of countercurrent condensate and high temperature steam.Under the combined effect of steam pressure,cyclic thermal stress and corrosive carbonate substances,thermal fatigue cracks expanded,eventually resulting in the cracking of the pipe.