Diagnostics of excessive vibrations in rotating equipment: from spectrum analysis to determining the cause

1. Problem description and scope

This tip is dedicated to diagnosing excessive vibrations in rotating equipment. Vibration can be of different nature: harmonic, pulsed or cutting. It can occur in equipment of various types: electric motors, pumps, compressors, turbines. Vibration is determined using a vibration meter or a thermal camera. Depending on the vibration level, it is classified as critical (more than 12 mm/s), medium (5–12 mm/s) or small (up to 5 mm/s). Critical vibration can lead to rapid bearing wear, housing chipping, or equipment failure.

2. Preliminary safety measures

Stop the equipment before diagnosis. Use a lockout and signout (LOTO) system to eliminate a hazardous power connection. Disconnect the wiring, open the bearing assemblies and gain access to the internal parts of the equipment. Use special protective equipment: gloves, glasses, manicure, means to protect against high temperatures and high pressure.

3. Necessary diagnostic tools

4. Preliminary review

5. Systematic diagnostic scheme

1. Measure the vibration in three planes (X, Y, Z) at a distance of 10-20 mm from the bearing.
   1. If the vibration is more than 12 mm/s:
      1. Measure the vibration spectrum.
         1. If the harmonic frequency is detected:
            1. Balance diagnosis.
               1. Check the level balance.
                  1. If the balance is incorrect:
                     1. Perform balancing.
                     2. Check the vibration after the fix.

6. Matrix of determination of causes

7. Analysis of reasons

7.1. Negligence

Reason: Negligence in balancing rotating equipment. During balancing, the central moment should be less than 0.1% of the mass of the rotating element. Carelessness leads to harmonic vibrations in the corresponding frequency.

Diagnosis: Use vibration spectrum analysis to detect harmonic frequencies. If the vibration increases from 1 to 10 kHz, this may be a sign of carelessness.

Potential damage: Carelessness causes rapid wear of bearings, failure of equipment, loss of energy.

7.2. Incorrect centering

Reason: The eccentricity between the shafts in the rotary equipment does not meet the permissible standards (up to 0.1 mm). This results in vibration at a frequency that is a multiple of the rotation frequency.

Diagnosis: Measure the runout with a measuring tool. If the eccentricity is greater than 0.1 mm, it may be the cause of vibration.

Potential damage: Improper centrifugation leads to rapid wear of bearings, failure of equipment, loss of energy.

7.3. Violation of bearings

Reason: Bearings lose their wear properties or internal defects occur. Vibration can occur due to uneven surfaces or cracks.

Diagnosis: Measure the temperature of the bearings with a thermal camera. If the temperature is higher than 40°C, this may be a sign of a defect.

Potential damage: Bearing failure leads to equipment failure, bearing wear, energy loss.

7.4. Resonance

Reason: Resonance occurs when the frequency of rotation of the equipment coincides with the equivalent frequency of the equipment elements. This results in vibration at different frequencies, which increase the vibration.

Diagnosis: Use vibration spectrum analysis to identify resonant frequencies. If the vibration occurs at a frequency that coincides with the rotation frequency, this may be a sign of resonance.

Potential damage: Resonance leads to equipment failure, bearing wear, energy loss.

8. Step-by-step solution procedures

8.1. Balancing

1. Balance the rotating equipment with a balancing tool.
2. Measure the vibration again after balancing.
3. Check that the vibration does not exceed 5 mm/s.

8.2. Centering

1. Measure the eccentricity of the rotating equipment.
2. Center the shaft in the appropriate plane.
3. Measure the vibration again after centrifugation.

8.3. Repair of bearings

1. Measure the temperature of the bearings.
2. Unclip the old bearings and install the new ones.
3. Measure the vibration again after correction.

8.4. Correction of resonance

1. Use vibration spectrum analysis to identify the resonant frequency.
2. Change the frequency of rotation of the equipment or remove the nodes that cause resonance.
3. Measure the vibration again after correction.

9. Preventive measures

10. Replacement parts and components

Go to the UNITEC-D e-Catalog for details on available components.

11. Links

• Certificates: CE, UkrSEPRO
• Standards: DSTU 3109-96, EN 13445, ISO 10816
• Additional links: Rotary Equipment Repair Manual, UNITEC-D Maintenance Guides