3 use cases of vibration analysis to detect machine problems

The following typical real-life cases illustrate the importance of using vibration analysis to detect and troubleshoot equipment problems.

• Use case 1

  Routine vibration checks on critical equipment in a large gas processing plant revealed excessive vibration in a centrifugal air compressor. Subsequent vibration analysis of the machine revealed misalignment between the compressor and the speed increaser. In addition, a high-frequency vibration in the gearbox indicated that the main gear of the speed increaser was damaged. Further, a visual inspection revealed a hairline crack in the gearbox.

  As a replacement gear was not available at the time, containment holes were drilled at both ends of the crack to prevent it from spreading further. After the unit was completed, the equipment was returned to full service until a new gear could be assembled.

  When the new gear was ready, the unit was shut down for only enough time to replace the gear. Even though this took four days, a total lack of effort could have forced the unit to shut down for six months.

• Use case 2

  Three identical, gear-driven, centrifugal cooling compressors, which were used for air conditioning in a large office building, had just been reconditioned and shortly after the commissioning of the three units, a high-pitched, annoying sound began to be produced. Soon the noise level became very loud and could be clearly heard throughout the building. The owner of the building refused to pay for the refurbishment work until the noise problem was corrected.

  A noise and vibration analysis immediately identified the source of the problem in the gearbox of one of the units, even though an earlier visual inspection had indicated that the gears were in good condition. A vibration analysis confirmed the origin and frequency of the noise and revealed the presence of a high level of vibration in the output bearing of the gearbox.

  This fact, together with the frequency of noise and vibration, indicated that the bearing was the cause of the problem. Mechanical measurements showed that the bearing clearance exceeded tolerances by several thousandths. Replacing the bearing with one having the specified clearance completely eliminated the annoying vibration noise.

• Use case 3

  This incident involved a 7000 rpm ammonia compressor used in fertiliser production. Periodic checks showed the presence of increasing vibrations in the turboexpander used to drive the compressor. A vibration analysis identified the origin of the problem in a faulty coupling between the expander and the compressor.

  At this point, the vibration had reached a high level that would have justified an immediate shutdown of the equipment; however, production requirements absolutely do not allow this. Five days after the diagnosis was made, the suspected coupling failed.

  Even with a spare coupling available, the forced failure of the coupling and continued operation at excessive vibration levels caused extensive damage to the shafts and bearings, requiring four days of continuous 24-hour work for repairs.

  If the coupling had been replaced at the recommended time, extensive damage could have been avoided and downtime reduced to as little as eight hours.

If you are interested in learning more about vibration analysis to detect problems in machines, we invite you to find out which are the most common vibration analysis methods. practical methods for vibration analysis of rotating equipmentor also a example of application of vibration analysis on pumps and fans.

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