Some levels (normal) of vibration in machines are expected as various forces influence the dynamic behavior at normal operating conditions. However, this becomes a challenge when the expected vibration amplitude levels (especially at known fault frequencies) deviate significantly from the normal. In most cases, the vibration issues that show up on machines are because of the imperfections in the practices carried out during various aspects of operation and usage.
Imperfections
Some of the common causes of high vibration levels in machines stem from imperfections attributed to:
- Design: Errors in design can lead to higher vibration levels than normal in machines. We have experienced some field cases where poor design layouts of suction and discharge lines caused pipe strain in centrifugal pumps.
- Manufacture: Inherent defects such as metal casting flaws or even machining errors during manufacturing processes can lead to significant deviations from normal vibration levels at the onset of a machine’s life.
- Assembly: Improper assembly of machine parts can lead to eccentricity issues with parts out of alignment from the beginning of operations.
- Installation: Installation of misfit bearings / bearing housings is a common cause of high vibration since such improper fits can lead to play and out of specification tolerances.
- Operation: Operating machines out of the manufacturer’s specified limits can lead to severe increase in vibration amplitude levels. From experience, operating a pump outside its designated limits can cause cavitation (visible from vibration spectral plots) which significantly reduces the life of the asset.
- Maintenance: Wrong maintenance practices can result in higher-than-normal machinery vibration levels. Practices such as hammering a bearing, use of wrong replacement spares and poor lubrication practices will lead to high vibration and early wear of machine parts.
- Wear: Machine parts will eventually wear and deteriorate due to age, usage and length of service causing high vibration amplitude levels.
Issues that Cause Machine Vibration
Furthermore, at the machine level, common faults show up as the consequences of any shortcomings in dealing with above mentioned practices. Listed below are the primary causes of abnormal machine vibration.
- Imbalance: A heavy spot in a rotating component creates a centrifugal force when the unbalanced weight rotates around the component’s axis. The faster the rotation, the more significant the imbalance.
- Misalignment: Occurs when the axes of a machine’s motor and pump shafts are out of line and can be either angular (shafts meet at a point, but not parallel) or parallel (shafts are parallel, but not in line).
- Looseness: Occurs when a component vibrates due to loose bearings, structural issues (e.g. loose bolts, machine not properly attached to its mounts) or corrosion.
- Bearing deterioration: roller bearing vibration can be caused by damage to the inner ring, outer ring, housing, or rolling elements. Sleeve bearing vibration can be caused by shaft position or fluid film issues (resulting in oil whip or oil whirl).
- Gear-related issues: vibrations can occur because of damaged or worn-out gear teeth.
Other issues that can cause machine vibration include:
- Damaged Belts and Pulleys
- Bent Shafts
- Load / Process Variation
- Electrical related issues
- Flow related issues
- Rub
Vibration Resonance
All machines and components vibrate at a natural frequency. Vibration resonance is the tendency of an external vibration force amplifying a component’s natural vibration frequency. While not necessarily the cause of abnormal vibration, resonance can result in severe damage to equipment and components, significantly reducing their lifespan if not corrected.
Mitigating Issues with Abnormal Machine Vibration Levels
If you’re seeing machine vibration levels increasing past normal, it can indicate the need for an assessment of the causes or trigger immediate action to prevent catastrophic failure. It’s important to understand how abnormal vibration occurs so you can decide on the most effective ways to mitigate its effects. Some best practices include:
- Creating a Strong Maintenance Culture: Following good maintenance practices during design manufacture, assembly, installation, operation, and maintenance will ensure that issues of abnormal vibration levels are kept to a minimum. An environment that fosters a well-defined maintenance culture should be encouraged. The use of technology and other non-intrusive maintenance techniques (vibration analysis, oil analysis, thermography, etc.) should be utilized where possible.
- Training: Personnel associated with operations and maintenance of machines should be properly trained in best practice techniques to improve how they interact with critical machines.
- Measure and analyze vibration data routinely: Measurement and analysis of vibration data will help in spotting the onset of a change in the machine’s condition. It also helps to specify the likely faults and reasons for any deviations observed. This in turn means that proper measures can be recommended and implemented to prevent any secondary damages or catastrophic in-service failures.
Find out more about incorporating vibration monitoring in your operations. Contact a Reliability specialist today.