Vibration of a high-pressure piping system due to flow in a spherical elbow

During the commissioning of a 400 MW coal-fired power plant with supercriti cal steam parameters, severe vibration and intense noise at approximately 4 kHz were produced by the high-pressure piping used to by-pass the steam tu rbine. This vibration caused fatigue damage to several components attached to the piping; including the stem of the main by-pass valve. Since the vibr ation frequency was within the frequency range of valve noise, attention wa s first focussed on modifications of the by-pass valve to alleviate its cou pling with any other possible sources in the piping system. however, all mo difications of the valve design alone influenced neither the level nor the frequency of vibration, and therefore modifications in the layout of the hi gh-pressure piping became unavoidable. Tests on a one-third scale model of the piping system without the valve indicated that the strongest excitation source in the system is a sphere-shaped elbow located upstream of the valv e, after eliminating this spherical elbow and reinstalling the original ver sion of the by-pass valve, the system operated without any vibration proble ms and the noise level was reduced to the design value. (C) 2001 Academic P ress.