超临界机组P91管道焊接接头IV型蠕变断裂分析

Analysis of IV Type Creep Rupture of Welded Joint of P91 Pipe in Supercritical Thermal Power Unit

采用宏观检查、金相组织检验、硬度检查、断口观察和能谱分析等手段对发生泄漏的超临界机组P91管道焊接接头失效原因进行分析。检验结果表明,长期高温运行使管道焊接接头细晶区大量(Fe、Cr、Mo)23C6相在晶界位置析出,大大减弱沉淀强化作用,并促进细晶区蠕变孔洞形成,孔洞聚集成孔洞链,形成微裂纹,最终造成P91管道焊接接头IV型蠕变断裂。

The macroscopic examination, metallographic structure examination, hardness test, fracture observation and energy spectrum analysis were used to analyze the failure reasons of welded joint of P91 pipe in supercritical thermal power unit. The results show that a large amount of(Fe,Cr,Mo)23 C6 phases precipitate at the grain boundaries of the fine grain zone of welded joint because of long-term high temperature operation, which greatly reduces the precipitation strengthening and promotes the formation of the creep holes in the fine grain region. The creep holes gather into a chain of holes and form the micro cracks. Finally, the type IV creep fracture occurs in the welded joint of the P91 pipe.