Question:
Vibration measurements were collected from motor – in between bearings pump as shown in pictures. It was found high overall vibration levels in radial directions up to 20 mm/s in horizontal direction and 11 mm/s in vertical direction. The dominant is only 1X in all spectra of 4 points (MNDE, MDE, PDE, PNDE). If you have a single channel analyzer and there is not any opportunity to use another tool like cross phase, how do you scientifically analyze this issue and identify the fault(s)?
Answer:
In fact, the dominant 1X in the spectrum is the most ambiguous diagnosis pattern specifically in case of lack of using other tools. However, we still have some criteria to diagnose this type of pattern. If we move back to the phenomena of rotating equipment structure regarding the nature of fixation in vertical direction, it was found that the equipment is stiffer in vertical direction compared to horizontal direction. This effectiveness appears when the equipment suffers some variation in the fixation/toughness of external structure, and this can be translated as a high difference between vertical and horizontal vibration readings.
Based on this analysis, the following items represent how to avoid confusion between different faults which have the same 1X pattern:
- Unbalance:
Has similar or near 1X values for horizontal and vertical direction based on the centrifugal force that would be generated in radial directions due to unbalance.
- Structural Looseness:
High vibration reading, 1X dominant, in horizontal direction compared to vertical one. This can be detected by checking the ability of tightening for base bolts.
- Soft Foot:
High vibration reading, 1X dominant, in horizontal direction compared to vertical one. Another pattern is to find directional vibration due to 2X of electrical line frequency. This can be detected by live mode measurement during releasing/tightening for each one of base bolts till reaching the defected foot.
- Structural Weakness:
High vibration reading, 1X dominant, in horizontal direction compared to vertical one. This can be detected visually by observing signs of fatigue stress (cracks in concrete, broken elements) around the equipment area.
