Vibration and oil analysis have been in the Philippine industry for a while.

While some reliability and maintenance professionals prefer one technique over the other, it is important to understand their strengths and weaknesses and their most appropriate applications to know when and how to use them.

Vibration Analysis

Many believe that vibration analysis is the best technique to use to detect machine failure. It can also detect the degree of failure severity and validate a newly adjusted machine.

Application of Vibration Analysis

  • electric motors
  • pumps
  • reducers
  • fans
  • power generators
  • compressors
  • turbines

Failure Mode Detection

  • misalignment
  • unbalance
  • mechanical clearances
  • belt defects
  • warped shafts
  • defective bearings and gears
  • cavitation
  • lubrication defects
  • identify resonance in static structures

Vibration analysis makes use of vibration analysis tools to be able to conduct non-invasive testing which means you don't have to open a machine to know what is going on inside which allows for the prompt implementation of improvements. With vibration analysis, you can monitor alignment, foundation conditions, balance quality, and other persistent machine problems.

Oil Analysis

Just like vibration analysis, many have used oil analysis as part of their condition monitoring program. This condition monitoring technique has contributed greatly to machine reliability through lubrication excellence.

Application of Oil Analysis

  • reducers
  • compressors
  • turbines
  • pumps
  • transformers
  • hydraulic systems

Just like vibration analysis, oil analysis has various test parameters you can use to detect the degree of severity and condition of lubrication-related problems. The most common oil analysis test parameters done in the laboratories are viscosity, nitration, oxidation, particle count, acid number, and machine wear analysis. Bear in mind that water contamination issues need urgent action as it hastens the oxidation process and increases metal-to-metal contact.

Case Study 1

A manufacturing plant that produces vegetable proteins in South America had machines that were situated outdoors which made them vulnerable to the harmful elements of the environment. The effects of these elements were visible in the oil analysis results from the get-go. Due to the presence of water contamination, they found out that machine wear started increasing as shown by the increase in the level of iron and chromium content in the oil samples. There were signals that wear is already happening in the bearing but there is no onset of vibration signal that states otherwise. It was not until a month later that the vibration result indicates shaft bearing failure. The maintenance personnel decided to stop the operation and conducted machine intervention. They replaced the damaged bearing and change the oil. Seeing the advantage of using the two technologies, the plant regularly conducts routine inspections using both technologies.

Case Study 2

When Palo Verde Nuclear Generating Station in Arizona implemented a transformative change in their approach to condition monitoring, their assessment showed that oil analysis was able to detect 40% of the bearing defects, vibration detected 33%, and when both technologies were used 27%of the defects were found. Monash University also conducted research in the correlation between oil analysis and vibration and found that the correlation was generally good, however, there are cases when one technique detects fault earlier than the other. For example, when there is a formation of sliding wear, oil analysis registers an increase in wear generation while vibration does not register any signal. As sliding wear generation increases the surfaces are slowly honed which results in looseness. This explains why vibration reduces as sliding wear formation increases. On the other hand, when a gear tooth fractures and when it is too large wear particle analysis is ineffective. This is because the debris finds its way into the bottom of the sump and eventually undergoes oxidization and leeches into the oil which could take months to complete. In this case, employing vibration analysis works early compared to oil analysis.

Oil Analysis versus Vibration Analysis: Two Techniques are Better Than One

To sum it up, both techniques are crucial to achieving reliability in order to get a holistic perspective on the condition of your machine. There have been many cases wherein both technologies were applied and were found to be complementary with each other. However, in cases of unbalance and misalignment, vibration analysis is a better technique for early detection. Likewise, contamination and oil degradation are easily detected through oil analysis.

  1. Oil analysis and vibration analysis can be used to detect the degree of severity of machine issues and their failure modes.
  2. It is possible for one technique to lead in the detection of incipient failure while the other serves as a confirmatory technique. Gearboxes, hydraulic systems, and reciprocating equipment are best monitored with oil analysis, especially with lubrication-related issues.
  3. High-speed journal bearing failures are generally best detected using vibration analysis. When it comes to localizing the location of the failure, generally vibration is stronger (depending on application).
  4. Oil Analysis works better in finding the wear mechanism that induces failure. To be able to pinpoint the root cause of the problem, both techniques have to be used. Both techniques can generate a good correlation but in some instances, the results may be contradictory.

 

Source: machinerylubrication.com