采用断口形貌观察、化学成分测试、显微组织分析及力学性能测试等方法对某核电站汽轮机旁排阀紊流罩的开裂原因进行了分析。结果表明：该紊流罩的开裂形式为疲劳脆性开裂；材料化学成分不符合标准使其强度降低，安装时紊流罩上端面的定位孔没有对中，工作时气流通过产生的磨损及震动使得该处应力集中较大，导致裂纹在紊流罩的外侧凸缘表面萌生；在长期循环热应力作用下，裂纹沿最小承载力的截面扩展，最终紊流罩开裂。建议采取材料复验措施，减少不合格材料的流入，对安装过程严格要求，避免定位不中，减小磨损及震动引起的应力集中。

The cracking reason of the exhaust valve turbulent hood at turbine side of a nuclear power plant was analyzed by fracture morphology observation, chemical composition test, microstructure analysis and mechanical performance test. The results show that the cracking mode of the turbulent hood was fatigue brittle cracking. The chemical composition of material did not meet the standard, which reduced its strength. The positioning holes on the upper end of the turbulence hood were not centered during installation. The wear and vibration produced by the airflow during working process made a relatively large stress concentration in this location, leading to crack initiation in outer flange surface of the turbulence hood. Under long-term cyclic thermal stresses, the cracks propagated along the section with the smallest bearing capacity, leading to cracking of the turbulent hood. It was suggested to take material re-inspection measures , thereby reducing the inflow of unqualified materials and to take strict requirements for installation process to avoid misalignment, thereby reducing stress concentation caused by wear and vibration.