某火电厂主蒸汽管道取样管多次发生开裂。通过管道及支吊架布局分析、管道应力计算分析等方法对取样管开裂原因进行了分析。结果表明：主蒸汽管道取样管和支吊架的布局不能有效承受母管及管道自身的热位移，造成二次应力严重超标，接管座焊缝区应力最高，当局部应力超过断裂强度时，材料将产生裂纹，造成取样管开裂泄漏。

The sampling pipe on main steam pipeline in a thermal power plant cracked many times. The cracking cause of the sampling pipes were analyzed by layout analysis of pipes and support hangers, and the calculation of pipe stress. The results show that the layout of sampling pipe and support hanger of main steam pipeline could not effectively support the thermal displacement of main steam pipeline and the pipe itself, resulting in the secondary stress seriously exceeding the standard, and the highest stress in the weld area of nozzle seat. When the local stress exceeded the fracture strength of material, cracks would produce and eventually led to the cracking and leakage of the sampling pipe.