某电厂主蒸汽管道的三通与上连接管的焊接接头处多次发生开裂。采用无损检测、硬度测试、金相检验、管系应力计算分析、管系推力计算分析和有限元分析等方法对焊接接头开裂的原因进行了分析。结果表明：该管道三通附近管系布置不合理，焊接接头处弯曲应力较大并存在应力集中，最大应力超过了焊接接头的高温持久强度，加之裂纹处显微组织老化，焊接接头的力学性能降低，从而发生蠕变开裂。

Several crackings occurred at the weld joint between the main steam pipe tee and the upper connecting pipe in a power plant. The causes of cracking of the welded joints were analyzed by means of non-destructive testing, hardness testing, metallographic examination, pipe system stress calculation analysis, pipe system thrust calculation analysis, finite element analysis and so on. The results show that the pipe system arrangement near the tee of the pipe was unreasonable. The bending stress at the welded joint was large and there was stress concentration. The maximum stress exceeded the high temperature endurance strength of the welded joint. In addition, the aging of the microstructure at the crack site decreased the mechanical properties of the welded joint, which led to the creep cracking of the welded joint.