某天然气管道用直通球阀卡套螺母在服役期间发生开裂。采用宏观观察、断口分析、腐蚀产物分析、化学成分分析、显微组织分析等方法对该卡套螺母的开裂原因进行了分析，并进行了热模拟试验及晶间腐蚀试验。结果表明：化学成分不合格和固溶处理不充分是卡套螺母开裂的主要原因；大量非金属夹杂物的存在导致电化学腐蚀，是卡套螺母开裂的次要原因。

The ferrule nut of a ball valve used in natural gas pipeline cracked during the service period. Macroscopic observation, fracture surface analysis, corrosion product analysis, chemical composition analysis, microstructure analysis and so on were used to analyze the cracking reasons of the ferrule nut, and the thermal simulation experiment and intergranular corrosion test were carried out. The results show that:the main reasons for cracking of the ferrule nut were that chemical compositions were not qualified and the solution treatment was insufficient; the minor reason for cracking of the ferrule nut was that a large number of non-metallic inclusions caused the electrochemical corrosion.