ArticleCombining Vibration & Tribology Analysis To Detect Gas Turbine Main Bearing Failure – A Case History
by Eira Patriansyah Arief
This paper is a short case history where vibration analysis, oil analysis & tribology were used to detect a problem with a gas turbine generator. While both vibration & oil analysis results were stable, the author began noting a significant change in particle count from one of the magnetic chip detector (MCD) units installed along the gas turbine. Detection by the MCD of a problem prompted him to focus additional PDM efforts on the portion of the machine measured by the MCD in question. The decision was made to accelerate scheduled overhaul of the machine and a catastrophic failure of the machine was likely avoided. This paper provides an excellent example of how employing more than one predictive maintenance technology on a critical machine can aid in detecting problems earlier and more precisely.
An aeroderivative gas turbine drives a Centrifugal booster compressor. The compressor compresses Commercial Gas to end users, e.q.: LNG Plant, Fertilizer Plant, and for industrial fuel. The gas turbine is Avon Rolls-Royce MK1535-121G type (called Gas Generator, GG), free running power turbine DJ160R, and the booster compressor is Dresser-Rand Model 755B10-8. The gas turbine produces exhaust gas (gas generator) that propels power turbine. Power turbine and booster are directly connected by a one-shaft torque meter coupling. Maximum running speed for the driver is about 7650 rpm, and the driven is 5330 rpm.
Routine condition monitoring is done to the unit, vibration survey and oil analysis or Tribology survey. The vibration survey utilizes two Channel CSI2120 for hand held direct reading at the GG. And for continuous reading and protection system, in the GG permanently installed accelerometer transducers connect to BN7200 panel in control room. GG shut down is set at 1.2 ips rms. Hand held direct reading points are Gas Generator Forward horizontal (GGF) and Gas Generator Rear horizontal (GGR), Fig. 2. The undirect reading points are GGF, GGR, Power Turbine Forward Radial Y Direction (PFY), Power Turbine Forward Radial X Direction (PFX), Power Turbine Rear Radial Y Direction (PRY), Power Turbine Rear Radial X Direction (PRX), Compressor Forward Radial Y Direction (CFY), Compressor Forward Radial X Direction (CFX), Compressor Rear Radial Y Direction (CRY), and Compressor Rear Radial X Direction (CRX). GGF and GGR vibration sensor are accelerometer sensor. PFY, PFX, PAY, PAX, CFY, CFX, CAY, and CAX vibration sensors are proximity/displacement sensor.
Lube oil sample is done for both the turbine lube oil and the driven equipment. The schedule is for every one month. At the Avon engine there are three MCD for three main bearings and one for auxiliary drive governor, Fig. 3. Lube oil from external lubrication system via filter housing and connection block, is feed to front, center, and rear bearings. Each bearing has their feed oil line. Before return lube oil leave connection block, they will flow through a magnetic chip detector. Every 4000 hours service, all the chip detectors are inspected and the debris measured by a Debris Tester Special Device. The equipment is MCD detector. Then, the measurement results recorded. From that the trend of debris accumulation is monitored, reviewed, and evaluated. Every 1000 hours lube oil sample is taken and then tested on CSI Oil Analyzer Oilview Model 5100 & Digital Viscometer 52DV. Only for special or detail test Laboratory test will be done.”
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