[5A4] Instrumentation condition monitoring vibration and failure analysis of screw air compressor package in liquefied natural gas plant
E Pereira
Glasgow Caledonian University, UK
Instrumentation for conditioning monitoring on rotating equipment is vital for determining whether the equipment is running correctly or not. Measuring the bearing temperature or shaft vibration can identify any potential problems when running the equipment. Identification of a potential problem before it arises allows operating engineers to shut down the machine or make appropriate changes to the machine operation before the problem occurs. This is more economical, as shutting down a machine and making the relevant alterations is cheaper than allowing it to fail and performing the repairs. This paper investigates several sources of vibration on a screw air compressor package in a liquefied natural gas (LNG) plant. A root cause failure analysis (RCFA) approach is used to analyse historical failure and vibration analysis data. The main causes of vibration and consequent failures on the compressor are: resonance of the interstage condensate separator, important levels of dynamic pressure and vibration at low-pressure (LP) and high-pressure (HP) compression stage frequencies and harmonics, excessive axial force exerted on the main rotor shaft causing the bearing to run on the back edge and subsequently failing due to the excessive axial forces, inferior axial bearings, failing due to poor design or inferior material composition. In order to avoid other failures, the interstage condensate separator was redesigned to shift its natural frequency and cancel the resonance, two broadband mufflers were designed, one muffler for each stage, centred on 1244 Hz for the LP muffler (three times LP stage compression fundamental) and on 1816 Hz for the HP muffler (two times HP stage compression, harmonic 2). Condition monitoring graphs of vibrations and excitation sources are presented to give an overview of the acceleration, pressure and velocity root mean square (RMS) (mm/s), spectra on the compressor before and after the installation of the mufflers.
