Mitigation and Assessment of Small Branch Piping Vibration in Nuclear Plants
In nuclear power plants,small branch pipings(Φ<2 inches)such as steam turbine lubricant pipelines,instru-ment pipelines and gas exhausts frequently encounter mechanical vibration-induced fatigue fractures,which can further lead to system interruption or even unit/reactor shut down.In view of over-standard vibration of lubrication,top shaft and cranking system(GGR),this paper investigated the real fact and established an appropriate assessment method as well as retrofit scheme for mitigating vibrations.First the combination of on-site vibration measurement and modal test clarified that the fundamental cause of the small branch piping excessive vibration was structural resonance.Based on this,the cor-responding retrofit scheme for mitigating vibration was formulated to avoid the resonance zone of the structure.The effec-tiveness of the retrofit scheme was then verified from the perspective of vibration amplitude.The modified small branch pipings were standard-qualified in transient strain and vibration fatigue according to test results,which can ensure the long-term safe and stable operation of the system.