Over the years when training “new” vibration analysts, I stress for them to keep it simple. Many analysts believe that you must review time waveform data to analyze all machinery problems. This is not true. However, some problems are impossible to diagnose without it.
Common Machinery Problems in Industry
A majority of plant machinery problems can be found with a basic understanding of the vibration FFT. Look at orders and amplitude. Focus on learning the most common machinery faults in industry. In my opinion, these are:
- Bearing Faults
- Unbalance
- Misalignment
- Bearing Looseness
- Structural issues
If you follow the basics to a tee, it’s really not that difficult to diagnose 90% of these problems quickly and easily.
Tips on Tackling Machine Faults
Bearing faults:
Be detailed in entering RPM as always and get bearing numbers whenever possible. Compare “new” data to past data. If the suspect frequency is new to the FFT and non-synchronous, there is a good chance it’s a faulty bearing. Does it feel rough? Is the bearing excessively hot? Are there more than 2 or 3 harmonics of the frequency? Do you have high acceleration amplitudes? Also, when in doubt, strobe the frequency to ensure it is not a harmonic of other equipment in the area.
Unbalance:
Another quite common problem and easily detectable with vibration analysis. It will be 1X RPM usually in the horizontal plane. You should be able to feel the vibration if it is excessive.
Misalignment:
Misalignment or a worn drive coupling is typically a 2X or 3X RPM problem predominating in the axial or horizontal direction. Use a strobe light to do a visual inspection on couplings while in operation to inspect for wear and obvious grease loss. First, freeze the coupling, then slightly alter the frequency of the strobe so the coupling appears to rotate slowly. Look for signs of damage, wear or loose bolts, etc. This is not always easy to do due to guarding issues. A mirror can be helpful in some cases to look around the guard. Be safe! The coupling may appear to not be rotating but it is.
Bearing Looseness:
Also a high 1X RPM problem and has classic harmonics of the 1X frequency. This problem can be seen using a strobe light to observe the shaft spinning in the bearing or “walking” in the housing. This is often misdiagnosed as a faulty bearing; however, it is a fit issue and should be inspected as such. Shafts and bearing housings should be measured to ensure proper fits.
Structural Issues:
Will often be in the direction of least resistance to movement, frequently in the vertical direction, if base bolts are loose, cracked welds, raised platform bases, etc. Look with your strobe by setting it a few RPM off of rotating speed and inspect for cracks, loose bolts, etc. Many times, you can feel or see the crack with a little visual inspection.
Review and Focus on the Basics
Always review the basics with a new technician and with your more seasoned colleagues if possible. Learning to focus on the basics is easy and rewarding when applied slowly. Always double-check your data to ensure repeatability and use your strobe light. When problems are diagnosed and solved, take pictures, print out FFT spectrums to use as a reference, and show off your findings. These can make vibration analysis fun and prosperous.
