A Study on Vibration Control for Reheater Spray Piping

Abstract

Piping vibration sometimes occurs resulting from the mechanical excitation sources like an unbalanced force of a rotating machine. But it usually occurs due to a pressure pulsation generated from vortex shedding in the piping or from pumps. Generated vibration energy is amplified according to the structural or acoustic characteristics of the piping, which cause high vibration and excessive noise in the piping. During a startup test, high frequency shell mode vibration with severe noise (96.5 ∼ 106.7 dB, RMS) was generated at the reheater spray piping, and beating was also detected in the sound and vibration signals. The function of reheater spray piping (OD 3.5 inch, Sch 80) is to control boiler temperature. It receives water from feedwater pumps and supplies it to attemperator installed in the cold reheat line. It regulates boiler temperature by injecting feed water into the reheater when the boiler is overheated, but the line is not activated during the normal operation. The object of this study is to analyze a root cause of the piping vibration and to establish possible corrective actions to mitigate high frequency shell mode vibration and associated high level sound in the reheater spray piping.