Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/934530
8 | January - February 2018 | www . machinerylubrication.com contaminants in the oil for more than a month or two, then vibration analysis should be detecting wear on the bearings and gears as well. e reverse would also be true. If the vibration signature is showing bearing or gear defects, then the oil analysis results should reveal signs of wear metals in the oil samples. If these complementary condi- tions are not being found, then both analysts should question whether representative samples of either the lubricant or the vibration signature have been captured. e only caveats would be when contaminants in the lubricant have just appeared and have not had time to produce any signif- icant abrasive wear and therefore have not been seen in the vibration signature, or when subsurface fatigue occurs in bearings where no material has been liberated from the surface of the races and cannot be detected in the oil sample. Regardless, if these exceptional conditions exist, the analysts should be stating it in their reports to the asset owner. EXAMPLES OF POOR INTERACTION In the following example of poor interaction between oil analysis and vibration analysis, the trend plot offered by the oil analyst showed iron content in the oil samples as being high and rising for four months (see Figure 1). e analyst commented that the ferrogram revealed cutting particles, indicating abrasive wear in the gearbox, and recommended that the unit be checked for misalignment and high vibration. At the same time, the vibration analysis for the same unit found no identifiable defects. From the perspective of the asset owner, some questions at this point should have been: Why did the vibra- tion signature not show what the oil 0 3 6 9 12 15 18 21 24 4/5/2016 - 8/2/2016 - 10/18/2016 - 12/13/2016 - 9/14/2016 - 24 24 22 ISO PC>6 ISO PC>6 alarm ISO PC>6 alert 19 18 0 10 20 30 40 50 60 70 80 90 100 110 4/5/2016 - 8/2/2016 - 10/18/2016 - 12/13/2016 - 9/14/2016 - 96 84 94 Iron Iron alarm Iron alert 82 87 Figure 3. High ISO cleanliness for more than eight months Figure 4. High iron content in oil samples for more than eight months Figure 5. An example of leaking gearbox seals COVER STORY