Analysis of Abnormal Vibration and Sound in the High-Pressure Control Valve Due to Silencer Cracks

Failure of the high-pressure control valve will lead to unbalanced regulation of the steam inlet volume of the turbine, resulting in unplanned shutdown and serious economic losses. The high-pressure control valve of a nuclear power plant turbine unit showed abnormal vibration and sound, along with the presence of cracks at the bottom of silencer. The paper analyzed and compared the vibration data of normal and abnormal valve, obtaining the characteristic frequency of abnormal valves. The causes of abnormal vibration were studied through simulations of silencer model, including modal simulation and fluid-structure interaction simulation. Then a modal simulation of the gas column between the silencer and the positioning ring was used to analyze the cause of abnormal sound. The results showed that the silencer of the high-pressure control valve cracked at the bottom due to metal fatigue. The cracked silencer model undergone 3rd order resonance at small opening degrees and the cracked silencer model undergone 6th order resonance at large opening degrees (>35%), resulting in abnormal vibration. Abnormal vibration caused steam leakage, and then the steam excited the gas column between the silencer and the positioning ring to resonate, causing abnormal sound. Finally, according to the analysis results, replacing the silencer resolved the problem of abnormal vibration and sound.