| dc.description.abstract | In a centrifugal compressor, interactions between impeller blades and stationary parts such as diffuser vanes will generate high frequency pressure pulsations. The frequencies of these pulsations, so called “blade passing frequency� (hereafter BPF), depend on the rotating speed and number of impeller blades. The BPF of a centrifugal compressor is typically beyond 1 kHz, and the resulting pressure pulsations can excite high frequency vibrations in the compressor itself and in the adjacent process piping. In the piping system, generally, there are many natural frequencies around the BPF, and the accompanying vibration modes can be complex shell wall type. In some cases, excessive piping vibration and noise radiation can be observed due to excessive BPF pulsation amplitudes. In the worst-case scenario, cracks in the pipe and eventual failure can occur. Any pipe failure is a serious safety concern and can further cause downtime for the plant operation. It is, therefore, very important to control the piping vibration in the engineering phase of the design. The OEM experienced a pipe failure within its compressor package due to excessive piping vibration caused by pressure pulsation originating from a centrifugal compressor in a chemical plant. The root cause investigation and countermeasures were collaboratively discussed among the end-user, EPC contractor, and OEM with involvement of a 3rd party consulting company. The parties solved the high vibration problem in the piping by means of the following countermeasures. • Modified the compressor’s diffuser construction in compressor from vaned type to vaneless type in order to reduce the vibration source • Increased the pipe thickness in order to reduce the vibration response • Install a rubber expansion joint in order to isolate the piping system from vibration source (compressor) In addition to the above three major countermeasures, the fabrication methods such as welding, post-weld-treatment and inspection procedures were improved as well. After implementation of the countermeasures, their effectiveness was confirmed by on-site measurements. This paper discusses acoustic excitation in a centrifugal compressor, resultant high frequency vibration in the accompanying piping system, along with details surrounding the field case of pipe fracture and its countermeasures as well as root cause analysis. | |
