Vibration diagnostics in rotating equipment: decision tree from spectral analysis to root cause

1. Problem Description and Scope

This is a guide to diagnosing excessive vibrations in rotating equipment, including pumps, compressors, fans and generators. Vibration can be critical, leading to equipment failure, damage to bearings or danger to personnel. It is necessary to determine the root cause — imbalance, incorrect alignment, bearing defect or resonance.

2. Precautionary Measures for Safety

Turn off the electrical supply and perform the locking/tagging procedure before carrying out any diagnostic actions.
Use personal protective equipment: gloves, safety glasses, protective helmets.
Check for the presence of stored energy voltages in electrical circuits.

3. Required diagnostic tools

4. Initial assessment: check-list

5. Systematic Diagnostic Scheme

1. Measure the vibration level in the appropriate range (0–100 mm/s).
1. If the vibration level exceeds 4,5 mm/s — perform a spectrum analysis.
2. If the vibration level does not exceed 4,5 mm/s — check the condition of the bearings.
2. Perform vibration spectrum analysis.
1. If harmonics are detected at the rotational frequency — returns to imbalance.
2. If harmonics at the frequency of 2×rotation — returns to incorrect alignment.
3. If harmonics at the bearing frequency — return to the bearing defect.
4. If harmonics at the resonance frequency — returns to resonance.
3. Perform thermography.
1. If bearing overheating is detected — returns to the bearing defect.
2. If overheating of the rim is detected — returns to imbalance.
4. Check the electrical connections.
1. If a leak or disconnection is detected - return to electrical problems.

6. Vibration Cause Matrix

7. Root Cause Analysis

7.1 Imbalance

Imbalance occurs due to uneven mass distribution on the rotating element. This leads to vibration at the rotational frequency. To confirm, perform a spectrum analysis. If harmonics at the rotational frequency are detected, it can be considered that the problem is due to imbalance. If imbalance is not corrected, it may result in damage to the bearings or the rim.

7.2 Improper Alignment

Incorrect alignment occurs when the axes of rotating elements are not aligned. This leads to vibration at the frequency of 2×rotation. To confirm, perform a spectrum analysis. If harmonics are detected at the frequency of 2×rotation, it can be considered that the problem is due to incorrect alignment. If alignment is not corrected, it may result in damage to bearings or the rim.

7.3 Bearing Defect

A bearing defect may occur due to wear, lack of lubrication or oil leakage. This leads to vibration at the bearing frequency. To confirm, perform thermography. If overheating of the bearings is detected, it can be considered that the problem is due to a bearing defect. If the bearing defect is not corrected, it may result in damage to the rim or mechanism.

7.4 Resonance

Resonance occurs when the vibration frequency coincides with the natural frequency of the system. This leads to a significant increase in the amplitude of vibration. To confirm, perform a spectrum analysis. If harmonics are detected at the resonance frequency, it can be considered that the problem is due to resonance. If resonance is not corrected, damage to the rim or mechanism may occur.

8. Step-by-step correction procedure

8.1 Imbalance

1. Balance the rotating element using the balancing device.
2. Set the weight on the rotating element at the points determined by the balancing device.
3. Check the vibration level after balancing. If the vibration has decreased to 4,5 mm/s, consider the problem resolved.

8.2 Improper Alignment

1. Align the axes of rotating elements using an alignment device.
2. Set the alignment of the shafts at the points determined by the alignment device.
3. Check the vibration level after balancing. If the vibration has decreased to 4,5 mm/s, consider the problem resolved.

8.3 Bearing Defect

1. Turn off the electrical supply and carry out the locking/tagging procedure.
2. Remove the bearing and check for wear, oil leakage, or damage.
3. Install the new bearing and perform alignment.
4. Check the vibration level after installing the new bearing. If the vibration decreases to 4,5 mm/s, consider the problem resolved.

8.4 Resonance

1. Determine the natural frequency of the system using spectral analysis.
2. Change the rotational speed of the rotating element to avoid resonance.
3. Check the vibration level after changing the rotational speed. If the vibration decreases to 4,5 mm/s, consider the problem resolved.

9. Maintenance Methods

10. Parts and Components

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11. References

• ISO 10816:1995 — Vibration — Measurement and evaluation of machine vibration
• EN 60034-16:2001 — Vibration of Rotating Electric Motors
• DSTU 3167-97 — Vibration of Rotating Equipment
• Technical Documents Catalog UNITEC-D