某平台湿气压缩机法兰与钢管焊接接头焊缝发生开裂失效，采用宏观观察、化学成分分析、金相检验、力学性能试验、扫描电镜分析和能谱分析等方法对焊缝的开裂原因进行了分析。结果表明： 焊接接头结构的不合理和焊缝内部的未熔合缺陷造成局部应力集中，并导致焊接接头的疲劳极限下降，在应力作用下法兰一侧切口处焊缝根部与未完全熔合的法兰母材交界处形成裂纹源；在外部循环载荷作用下，裂纹逐渐向外表面扩展，当达到焊接接头的疲劳极限时，焊缝即发生开裂。

The welded seam on welded joint between flange and steel pipe of wet gas compressor of a platform cracked. The cracking causes of the welded seam were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, mechanical property test, scanning electron microscopy analysis and energy spectrum analysis. The results show that the unreasonable structure of the welded joint and the incomplete fusion defects in the welded seam caused the local stress concentration, which led to the decrease of the fatigue limit of the welded joint. Under the action of stress, the crack source was formed at the interface between the weld root of the notch on one side of the flange and the incomplete fusion flange base metal. Under the action of the external cyclic load, the cracks gradually expanded to the outer surface. When the fatigue limit of the welded joint was reached, the welded seam cracking occured.