Displacement Method for Determining Acceptable Piping Vibration Amplitudes   J. C. Wachel, 1995 ASME/JSME Pressure Vessels & Piping Conference, Honolulu, HI, July 1995. 

Methods are presented in the ANSI/ASME Operation & Maintenance Standards/Guides Part-3 1991, “Preoperational and Initial Startup Testing of Nuclear Power Plant Piping Systems” (OM-3) for determining if the vibration-induced stresses in a vibrating pipe span are acceptable. The displacement and velocity methods are presented in OM-3. These methods are applicable for piping spans vibrating at resonance in lateral bending modes. The background and theory necessary for understanding the lateral bending vibration modes of typical piping systems and the procedures for evaluating stresses are discussed.

The stress factors for characteristic spans given in OM-3 do not cover the entire range of configurations encountered in actual piping systems. In addition, data for calculating the lateral bending natural frequencies of piping spans and bends are not included in the OM-3 guidelines. Frequency factors, deflection stress factors and velocity stress factors for calculating the mechanical natural frequencies and the vibration-induced stress of most common piping spans have been published (Wachel, et. al., 1990). This information was used to develop a nomogram which can be used to calculate the natural frequency, the vibration-induced stress, and the allowable vibration amplitude of most piping spans.

The information presented herein on piping natural frequencies and vibration-induced stresses should allow the vibration analyst to evaluate piping systems under the OM-3 Vibration Monitoring Group 2 (VMG-2) category in less time and with increased confidence in the results.