Flow-Induced Vibration and Wear of Steam Generator Tubes

Potential tube fretting wear and fretting fatigue caused by flow-induced vibration are addressed in the design of nuclear steam generators. Flow-induced interactions of the tubes with the tube supports can cause localized tube wear and fretting fatigue effects if the system is not properly designed. The major flow-induced vibration mechanisms that can cause vibration of steam generator tubes are fluidelastic excitation, turbulence, and vortex shedding. Fluid-elastic excitation, rather than vortex shedding, is believed to have been the cause of large-amplitude vibration and rapid wear of heat exchanger tubes in the past. Fluidelastic vibration initiates when the flow velocity exceeds a critical value. For subcritical flow velocities, turbulence is the main excitation mechanism to consider in predicting the long-term wear of steam generator tubes. The various types of wear-producing forces and motions that can be generated between tubes and supports by flow-induced vibration have been identified, and some general procedures have been developed for predicting tube wear.