核一级先导阀探测波纹管泄漏原因分析

Cause Analysis on Detection Bellow Leakage of RCCP-1 Pilot Valve

某三代核电示范工程的稳压器安全阀采用热态结构设计,阀门由主阀和先导阀组成,主阀执行超压保护和关闭隔离功能,先导阀驱动主阀启闭动作,探测波纹管是先导阀的核心部件。在机组调试期间出现探测波纹管泄漏问题,会造成主阀异常关闭且无法恢复开启,导致阀门不可用和机组后撤。通过制定波纹管切割和分析方案,从SEM观察、基体成分分析、金相组织分析和应力分析等角度进行综合研究,发现波纹管泄漏原因为:小波纹管制造时焊接位置热影响区形成了裂纹,运行期间介质压力波动使裂纹发生疲劳扩展进而产生贯穿性裂纹,导致波纹管泄漏失效。在此基础上提出了波纹管成型后表面质量检验、波纹管动态弯曲试验和介质压力波动状态下的疲劳试验等改进措施,为后续波纹管质量控制提供参考,提升核电机组运行的安全稳定性。

The pressurizer safety valve of a third-generation nuclear power demonstration project is designed with hot structure.The valve consists of a main valve and a pilot valve.The main valve performs overpressure protection and closing isolation functions.The pilot valve drives the opening and closing of the main valve.The detection bellow is the core component of the pilot valve.During the commissioning of the unit,the problem of detection bellow leakage has occurred,which will lead to the risk that the main valve closed abnormally and cannot be reopened,leading to the unavailability of the valve and the withdrawal of the unit.Through formulating the cutting and analysis scheme of detection bellow and conducting comprehensive research from the perspectives of SEM observation,matrix composition analysis,metallographic structure analysis and stress analysis,it is found that the reason for the leakage of detection bellow is that cracks were formed in the heat affected zone of welding position during the manufacturing of inner bellow,and the medium pressure fluctuation during the operation led to the fatigue growth of the cracks and then to the formation of penetrating cracks,leading to the leakage failure of detection bellow.On this basis,improvement measures such as surface quality inspection,dynamic bending test of bellow and fatigue test under the condition of medium pressure fluctuation after forming of bellow are proposed,which can provide reference for subsequent quality control of bellows and improve the safety and stability of nuclear power unit operation.