The Basics Of Oil Analysis For Equipment Maintenance
Due to its physical/chemical properties, low cost, and availability, oil is the most common lubricant around, used to slow down wear and tear caused by friction. It is to no surprise then that oil analysis plays an important role in equipment maintenance.
How does the process work and when it is applied? Find out by scrolling below.
What is oil analysis?
Oil analysis forms an important part of tribology – the study of wear in machinery. It employs various tools and techniques to reveal the properties of lubricating oil. The idea is that the oil condition reflects the condition of the machine. In other words, it is like a blood test for your machinery.
Oil analysis programs are used to lower maintenance costs, improve reliability, and prolong the useful life of bearings, gearboxes, and other rotating equipment. Hence, fleet managers have a strong incentive to perform frequent engine oil analysis.
The first step in oil analysis is taking the oil sample – collecting a small quantity of lubricant from the machinery with minimal disturbance. The oil is drawn to a clean container and the sample is sent to the laboratory to perform oil analysis through various physical and chemical tests.
Which test will be done is determined by the specific use case. While the test can be a one-time thing, the properties of lubricating oil are usually checked at regular intervals as a part of condition monitoring and predictive maintenance.
The need for oil analysis
Laboratory testing is performed to:
identify the physical and chemical properties of oil
study contaminants present in the oil
analyze machine wear and tear
In other words, oil analysis helps us understand the conditions of the machinery that is being tested. It reveals important information without the need to cut open or disassemble the machine.
Non-destructive testing (NDT) methods are generally employed to evaluate the health of machines in operation. But there are many machines where NDT tests are difficult to perform due to difficulty in access.
In such instances, oil analysis can be the saving grace because lubricating oil contains plenty of information about different machine components.
The oil analysis reports can be used to determine whether the machine is operating according to expectations. If any abnormality is identified through the analysis, corrective maintenance can be performed to eliminate the identified problem(s) and prevent equipment failure.
Who performs the testing?
Oil analysis requires specialized equipment and qualified professionals. It is conducted at specialized laboratories by trained oil analysis professionals (unless you have the budget to build an in-house lab or call in a mobile laboratory).
An individual oil analysis test costs between $10 and $30.
International Council for Machinery Lubrication (ICML) is a widely recognized non-profit organization that regulates everything related to machine lubrication. ICML conducts certification examinations and accredits lubrication professionals across the globe.
Oil analysis certifications issues by ICML adhere to the standards of the International Organization of Standards (ISO) and include:
STLE has its own set of standards and procedures to certify oil analysis professionals and analysts.
How to perform oil analysis?
Oil analysis report reveals information on oil health, oil contamination, and machine wear. It informs future maintenance actions.
To get a clearer picture of the process, let’s discuss the key aspects of performing oil analysis.
Taking an oil sample
The collected sample needs to be representative of the oil flowing through the machine. The three things to keep in mind while taking oil samples are:
ensuring maximum data density
minimizing data disturbance (the sampling process should ensure that we do not add any contaminants before the sample gets to the lab)
setting the right sampling frequency (choosing an appropriate oil drain interval is important because of the P-F interval – you want to have enough time to spot trends and eliminate issues before they lead to serious issues)
Oil samples have to be taken in clean containers using equipment like a vacuum suction pump and other types of sampling pumps (often come as a part of different oil analysis kits).
The ideal oil sample is the one taken while the machine is in operation. However, that is not always the safest or easiest approach. Instead, you can collect the sample right after the machine is turned off. If the lubricating oil is allowed to rest, the sediments will also rest and potentially ruin the quality of the sample.
There are a plethora of tests that can be done on the collected sample. Routine oil analysis procedures will repeat the same battery of tests.
In the case of a one-off test, the type of test is chosen based on the following considerations:
The oil analysis tests should match the oil type and the failure modes of the machine that are being monitored.
The flagging levels for the analysis have to be set according to the corrective response plan in place.
An application-specific approach (separate package of tests for each machine) or a single test package for all assets are both viable options. The decision is made after evaluating the cost efficiency and other critical test considerations.
When performing an unscheduled oil analysis, the tests should be mapped to incidents that triggered the analysis.
The most common oil analysis tests are:
Viscosity: it is caused by the friction between the various layers in a fluid. A viscosity test is conducted to analyze whether the lubricating oil falls within the required range for the particular machine.
Elemental analysis (Spectrometry/Spectroscopy): one of the oldest techniques used to analyze the contaminants in lubricating oil. When it was introduced, it was only able to detect the presence of iron and copper. Today, test results can identify up to 25 different elements present in the oi.
Ferrography: particles larger than 5 microns are difficult to detect by spectroscopy. Analytical ferrography can be used to examine wear particles and solid contaminants in lubricating oil without any particle size limitations.
Acid number:the acid number (AN) test is one of the methods available in the oil analysis field used to estimate the amount of additive depletion, acidic contamination and oxidation.
Base number: similar to acid number, but specifically used for combustion engines. It represents the ability of the engine oil to neutralize acids created due to combustion and oil degradation.
Interpreting the oil analysis report
Oil analysis reports do not give cut-and-dry recommendations. We need oil analysts to interpret the test results based on their expertise and experience.
The ideal oil parameters for each machine are specified in the manuals provided by machine OEMs. This is used as a benchmark for reading the oil analysis report. The three common properties of lubricating oil from the report are:
Viscosity: excessive viscosity dampens machine performance. As contaminants and elements in the machine increase, the viscosity of lubricating oil increases accordingly.
Elements: spectral analysis or ferrography helps determine whether the present elements are contaminants or part of normal wear and tear. According to the number and quantity of materials present, expert oil analysts can provide specific maintenance recommendations.
Acid number: high acid number indicates a high chance of corrosion. The acid number should be kept within the range advocated by the OEMs.
The importance of trends for oil sample analysis
A single oil sample report doesn’t do much on its own.
Oil sample analysis at consistent intervals performing the same test package is way more useful for equipment maintenance. The increasing number and quantity of elements in the oil analysis reports indicate more wear and tear – which warrants further investigation.
Similarly, the changes in viscosity and acid number also give clues to potential equipment problems. Experienced oil analysts can find the causal factors affecting changes in oil analysis reports while plotting and tracking trends.
Performing machine maintenance
The value of oil analysis lies in the maintenance actions taken in response to the interpretation of the oil analysis report. Common recommendations include oil filtration, oil change, or further monitoring.
To ensure these tasks are carried out in a timely fashion, maintenance managers should use CMMS software to allocate the necessary resources, schedule preventative maintenance work, and assign it to a trained technician. Similarly, CMMS is a perfect tool to schedule and track tasks for taking oil samples in the first place.
Of course, the criticality of equipment, the impact of failure, and the impact of machine downtime are factors in determining the exact maintenance actions. If the report suggests a big capital expenditure, more tests are done to confirm the oil analysis results.
Oil litmus test
Oil analysis is useful to monitor the health of machines without any invasive procedures. It can act as a litmus test for machine health and performance.
Conducting oil analysis at regular intervals gives insights into machine reliability and remaining useful life. These insights can be used to improve maintenance schedules and extend the lifetime of engines and other machines.
And with that, we are wrapping up this article. If you have any questions, start a discussion in the comments below!
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