1S4b: (20 min.) Case Study: Sub-synchronous Vibration and Compressor Rotor Instability

Ahmad Fadzli Ismail , Staff Engineer, MLNG Sdn. Bhd.


During commissioning of Boil-Off Gas (BOG) Compressor train, the compressor tripped three times due to high vibration while compressor discharge pressure being raised up. Root Cause Analysis (RCA) was formed to analyze the vibration data and other observation. Sub-synchronous frequency vibration was observed in forward and reverse direction. The orbit also indicating rubbing phenomena. Compressor was dismantled and fact finding inspection revealed rubbing marks on the impellers and diaphragm. Several corrective actions were implement. During first verification run the compressor tripped again on similar vibration behavior but at higher discharge pressure than before. The compressor was dismantled and later reassembled with swirl brake labyrinths. The compressor was restarted for the second verification run according to defined procedure. The verification run was successfully performed and the specified discharge pressure of 78.6 was achieved. Later it was also further increase to design discharge pressure and vibration level still remain low. This presentation will cover the vibration analyze done, rotor stability study and root cause to this vibration problem.


More than 11 years experience in LNG plant maintenance of rotating equipment. Spent almost 3 years in project as Lead Rotating Equipment Engineer building world first on-shore Boil Off Gas Reliquefaction plant. Certified as Mobius Vibration Analyst Cat III and Machinery Lubrication Analyst (MLA II). Involvement in reliability study, major maintenance activities, condition monitoring, troubleshooting and root cause failure analysis of GE Frame Heavy Duty Gas Turbine, Siemens SGT-700 gas turbine, Mitsubishi steam turbines, Siemens-Dresser Rand centrifugal compressor, Nouvo Pignone Centrifugal and axial compressor, Instrument Air oil free screw and intergral gear centrifugal compressor, API 610 pumps and Cryogenic submersible centrifugal pump. Heavily participate in organization capability development by conducting training and coaching session to junior and senior engineers.