核电厂高压缸进汽管道高频壳壁振动分析

High Frequency Shell-wall Vibration Analysis of High-pressure Cylinder Steam Inlet Pipes in Nuclear Power Plant

某核电厂机组启机过程中,对高压缸进汽管道和相连仪表管进行了振动加速度和应变的连续监测。通过振动信号时频分析、机组工况参数分析,发现进汽管道及相连仪表管的振动水平与机组状态及主调节阀的开度显著相关,当电功率达到核功率的 53%、主调节阀开度达到 13.7%时,管道振动水平明显下降。升速及低功率平台下,进汽管道及仪表管以 450 Hz 以上高频振动为主。经验公式和有限元计算表明,低功率下高压缸进汽管道可能以壳壁振动为主,并伴随有整体弯曲和扭转振动,且模态频率密集。进汽管道振动加速度高达 300 g,长期运行下易导致连接支管的振动疲劳失效。增加约束层阻尼是可能的高频壳壁振动缓解措施。

Continuous vibration acceleration and strain measurement of the high-pressure cylinder steam inlet pipes and instrumental pipes are implemented during the start-up process of a Nuclear power plant. Vibration signal analysis and plant condition parameters are analyzed,which shows that direct correlation exists between the vibration level of pipes and the plant condition. Pipe vibration level decrease dramatically when the electric power reaches 53% nuclear power,at which time the main steam control valve’s opening ratio arrives at 13.7%. During the speed-raising and low power stage,inlet pipes and instrumental pipes vibrate at frequency above 450 Hz. According to empirical shall wall modal frequency equation and FEM analysis,shell-wall vibration dominates within high frequency domain,at the same time,bending and twisting modes also make contribution. The actual vibration acceleration of the inlet pipe approaches 300 g,which is so high that can easily introduce fatigue failure of branch pipes during long time operation. To reduce the shell-wall mode vibration level,constrained-layer damping can be a potential method.