Why Should You Perform Oil Analysis?
The most evident reason to undergo oil analysis is to understand what the condition of the lubricant is but it also can be used to assess the condition of the asset that the lubricant has been taken from. There are 3 categories of oil analysis:
- Fluid Properties
- Wear Debris
The Fluid Properties analysis identifies the oil’s current physical and chemical state. It also defines its remaining useful life (RUL).
By doing this test, the following questions are able to be answered:
- Does the sample match the specified oil identification?
- What is the oil’s RUL?
- Is the correct oil being used?
- Are the correct additives present and active?
- Have any of the additives depleted?
- Is the viscosity of the oil as expected? If not, why?
It is important to detect the presence of contaminants as they can be destructive. Under oil analysis will identify destructive contaminants and specify their potential sources, whether these are internal or external.
The kinds of questions that can be answered from oil analysis are:
- What is the cleanliness of the oil?
- What types of contaminants can be found in the oil?
- What is the source of the contaminants?
- Are any other lubricants or fluids detected?
- Is there any evidence of any internal leakage?
Wear Debris oil analysis identifies the existence of particles produced as a result of mechanical wear, corrosion or other machine surface degradation.
The types of questions that it may answer are:
- Are there any abnormalities to the machine degradation?
- Is wear debris produced?
- Which components are the most likely source of the wear materials?
- What is the type of wear and what is its cause?
- What is the severity of the wear condition?
It is imperative to know whether any actions need to be undertaken to ensure the health of the machine and to elongate the life of the oil.
Oil is the “lifeblood” of a machine and can be compare to blood in the human body, therefore oil analysis can be treated as the same as a blood test. These are completed to detect any abnormalities and to breakdown the overall health of the lubricant and the asset that the lubricant is being used. One test type alone doesn’t have the capability to detect all the functional elements that may be affected. Therefore the three types are used. In the same way the blood taken from a human is analysed, studied and a conclusion is made of the treatment needed to be taken, a full report can be made from analysis with a comprehensive action plan of any “treatment” that may need to be done on either the oil or the asset.
Oil Analysis Basics
To complete successful oil analysis, samples need to be taken in a careful manner.
All samples are subjected to several tests using highly complicated and advanced machinery. It is then down to qualified laboratory technicians to interpret the data. This is more effective the more that the technicians know about the assets that the samples have been taken from. Without this information, the results may be imprecise.
Here is a list of the information that would be advantageous for the technician to know:
- Anything that may affect the machine. This is most commonly the machine’s environmental conditions. This can be any extreme temperatures, high humidity, high vibration, etc.
- The originating component (steam turbine, pump, etc.), make, model and oil type currently in use
- The permanent component ID and exact sample port location
- Proper sampling procedures to confirm a consistently representative sample
- Occurrences of oil changes or makeup oil added, as well as the quantity of makeup oil since the last oil change
- Whether filter carts have been in use between oil samples
- Total operating time on the sampled component since it was purchased or overhauled
- Total runtime on the oil since the last change
- Any other unusual or noteworthy activity involving the machine that could influence changes to the lubricant condition
An oil analysis report can display a large amount of information that may not be easy to digest. It takes a good level of understanding to be able to interpret the data. Oil analysis can be costly and the equipment and machines used to undertake the tests are very expensive. Many companies have a large budget to deal with the cost of oil analysis to help as part of their condition monitoring strategy but unfortunately many staff are unable to understand, to the full extent, what the reports identify, therefore not benefiting the company.
What to Look for When Reviewing an Oil Analysis Report
- Read and check the data on the oil type and machine type for accuracy
- Verify that reference data is shown for new oil conditions and that trend data is at an understood frequency (preferably consistent)
- Check the measured viscosity
- Verify elemental wear data and compare to reference and trended data. Use a wear debris atlas to match elements to their possible source
- Check the elemental additive data and compare to reference and trended data. Use a wear debris atlas to match elements to their possible source
- Verify elemental contamination data along with particle counts and compare with reference and trended data. Use a wear debris atlas to match elements to their possible source.
- Check moisture/water levels and compare to reference and trended data
- Verify the acid number and base number and compare to reference and trended data.
- Check other analysed data such as FTIR oxidation levels, flash point, demulsibility, analytical ferrography, etc.
- Compare any groups of data that are trending toward unacceptable levels and make justifications based on these trends
- Compare written results and recommendations with known information on the oil and machine, such as recent changes in environmental or operational conditions or recent oil changes/filtration
- Review alarm limits and make adjustments based on the new information
When an oil analysis report is created, the technician may include a summary section that is intended to put the results and any recommendations in less complex terms. As the technicians who complete the analysis may have never been in to contact with the asset that the sample has been taken from or have no knowledge of the history of the asset, many recommendations will be generic and may not be tailored to the individual circumstances.
With this being in mind, it can be the responsibility of the person receiving the analysis report to take any actions from their knowledge of the asset, the lubrication or the environment.
Oil Analysis Tests
For a standard piece of equipment undergoing the normal recommended oil analysis, the test slate would consist of “routine” tests. If more testing is needed to answer advanced questions, these would be considered “exception” tests.
Routine tests vary based on the originating component and environmental conditions but should almost always include tests for viscosity, elemental (spectrometric) analysis, moisture levels, particle counts, Fourier transform infrared (FTIR) spectroscopy and acid number. Other tests that are based on the originating equipment include analytical ferrography, ferrous density, demulsibility and base number testing.
Several methods are used to measure viscosity, which is reported in terms of kinematic or absolute viscosity. While most industrial lubricants classify viscosity in terms of ISO standardized viscosity grades (ISO 3448), this does not imply that all lubricants with an ISO VG 320, for example, are exactly 320 centistokes (cSt). According to the ISO standard, each lubricant is considered to be a particular viscosity grade as long as it falls within 10 percent of the viscosity midpoint (typically that of the ISO VG number).
32% of lubrication professionals would not understand how to interpret an oil analysis report from a commercial laboratory, based on a recent poll at MachineryLubrication.com
Viscosity is a lubricant’s most important characteristic. Monitoring the oil’s viscosity is critical because any changes can lead to a host of other problems, such as oxidation, glycol ingression or thermal stressors.
Too high or too low viscosity readings may be due to the presence of an incorrect lubricant, mechanical shearing of the oil and/or the viscosity index improver, oil oxidation, antifreeze contamination, or an influence from fuel, refrigerant or solvent contamination.
Limits for changes in the viscosity depend on the type of lubricant being analysed but most often have a marginal limit of approximately 10 percent and a critical limit of approximately 20 percent higher or lower than the intended viscosity.
Acid Number/Base Number
Acid number and base number tests are similar but are used to interpret different lubricant and contaminant-related questions. In an oil analysis test, the acid number is the concentration of acid in the oil, while the base number is the reserve of alkalinity in the oil. Results are expressed in terms of the volume of potassium hydroxide in milligrams required to neutralize the acids in one gram of oil. Acid number testing is performed on non-crankcase oils, while base number testing is for over-based crankcase oils.
An acid number that is too high or too low may be the result of oil oxidation, the presence of an incorrect lubricant or additive depletion. A base number that is too low can indicate high engine blow-by conditions (fuel, soot, etc.), the presence of an incorrect lubricant, internal leakage contamination (glycol) or oil oxidation from extended oil drain intervals and/or extreme heat.
FTIR is a quick and sophisticated method for determining several oil parameters including contamination from fuel, water, glycol and soot; oil degradation products like oxides, nitrates and sulfates; as well as the presence of additives such as zinc dialkyldithiophosphate (ZDDP) and phenols.
The FTIR instrument recognizes each of these characteristics by monitoring the shift in infrared absorbance at specific or a range of wavenumbers. Many of the observed parameters may not be conclusive, so often these results are coupled with other tests and used more as supporting evidence. Parameters identified by shifts in specific wavenumbers are shown in the table below.
Elemental analysis works on the principles of atomic emission spectroscopy (AES), which is sometimes called wear metal analysis. This technology detects the concentration of wear metals, contaminants or additive elements within the oil. The two most common types of atomic emission spectroscopy are rotating disc electrode (RDE) and inductively coupled plasma (ICP).
Both of these methods have limitations in analyzing particle sizes, with RDE limited to particles less than 8 to 10 microns and ICP limited to particles less than 3 microns. Still, they are useful for providing trend data. Possible sources of many common elements are shown in the table below.
The best way to monitor this type of data is to first determine what is expected to be in the oil. An effective oil analysis report will provide reference data for the new oil so any amounts of additive elements can be easily distinguished from those of contaminants. Also, because many types of elements should be expected at some level (even contaminants in certain environments), it is better to analyse trends rather than focus on any specific measurement of elemental analysis data.
Particle counting measures the size and quantity of particles in the oil. Many techniques can be used to assess this data, which is reported based on ISO 4406:99. This standard designates three numbers separated by a forward slash providing a range number that correlates to the particle counts of particles greater than 4, 6 and 14 microns. Here’s an illustration of how different particle counts are assigned specific ISO codes.
Moisture content within an oil sample is often measured with the Karl Fischer titration test. This test reports results in parts per million (ppm), although data is often shown in percentages. It can find water in all three forms: dissolved, emulsified and free. The crackle test and hot-plate test are non-instrument moisture tests for screening before the Karl Fischer method is used. Possible reasons for a moisture reading being too high or too low would include water ingression from open hatches or breathers, internal condensation during temperature swings or seal leaks.
Interpreting Oil Analysis Reports
The first thing to check on an oil analysis report is the information about the customer, originating piece of equipment and lubricant (see Section A of the sample report below). Including these details is the customer’s responsibility. Without this information, the effectiveness of the report will be diminished.
Knowing which piece of equipment the oil was sampled from affects the ability to identify potential sources of the measured parameters, especially wear particles. For example, the originating piece of equipment can help associate reported wear particles with certain internal components.
The lubricant information can provide a baseline for several parameters, such as the expected viscosity grade, active additives and acid/base number levels. These details may seem straightforward but are often forgotten or illegible on the oil sample identification label or request form.
What Is an Oil Analysis Kit?
An oil analysis sampling kit should include everything required to obtain a representative sample from a piece of equipment. Generally, the lab performing the analysis will offer this kit with their service. It should contain disposable tubing, a sample label, a vessel for mailing back the sample and a sample bottle.
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