某电厂高压调汽门EH油（抗燃油）管发生断裂并造成机组非计划停机，通过宏观观察、金相检验、显微硬度测试等方法对EH油管的断裂原因进行了分析。结果表明：4号高压调汽门VP（阀位）卡接线端子松动引起高压调汽门波动，造成了EH油管支管振动，在EH油管三通与支管连接角焊缝的应力集中区域形成较大的交变应力；循环交变应力使得正常奥氏体组织转变成形变马氏体，从而导致该部位硬度升高、脆性增大；同时三通设计上的缺陷以及打磨线性缺陷的存在，使得EH油管最终发生脆性断裂。

The EH oil (fire resistant oil) pipe of the high pressure steam regulating valve in a power plant fractured and caused unplanned downtime of the unit. The causes of fracture on EH oil pipe were analyzed by means of macro observation, metallographic examination and microhardness test. The results show that the loose connection terminal of No. 4 high pressure steam regulating valve VP (valve position) card caused the fluctuation of high pressure steam regulating valve, causing the vibration of EH oil pipe branch pipe, and forming large alternating stress at the stress concentration area of the fillet weld between EH oil pipe tee and branch pipe. The cyclic alternating stress caused the transformation of normal austenite structure into deformed martensite, which led to the increase of hardness and brittleness. At the same time, the existence of design defects of tee and grinding linear defects made EH oil pipe brittle fracture finally.