Many industries have a problem of mixing up lubricants in a given application. A recent study surveyed lubricant users and found that using different types and viscosity grades that deviate from the standard manufacturer lubricant is the largest cause of equipment failure and increased manufacturing costs.
Whilst a lack of training, supply chain issues and poor laboratory/factory housekeeping are the main reasons for lubricant mix-ups, there are many simple oil analysis techniques that can be employed to identify when a mix-up has occurred.
Lubricants are used across many different industries and in many different types of machinery and moving part. Some examples of where lubricants are commonly used includes engines, compressors, drive-trains, turbines, ships, trains, generators, offshore platforms and industrial machinery.
The most common tests to determine the quality and correct mixture of lubricants are through measuring the viscosity of the lubricant, elemental spectroscopy, infra-red spectroscopy and gas chromatography. Some techniques are sufficient on their own, whilst others are not, and require at least one other technique to effectively analyze the lubricant. Here, we take a look at the above techniques and how they apply to lubricant testing.
Viscosity is the easiest way to identify an incorrect lubricant by human eye, as a well-trained user will be able to tell the difference between different viscosities. However, whilst the user can immediately tell if it is the wrong gradient of oil, viscosity alone cannot determine what type of lubricant oil is being used. For a full determination, kinematic viscosity measurements need to be coupled with another technique.
The need for an accompanying technique is mainly due to two reasons. The first is the variation of viscosities that can be exhibited by the same type of lubricant, and a deviation of 20% against the named viscosity is considered to be within the normal range. The second, is that some lubricants have the same (or very similar) viscosity ranges and physical properties, making them hard to distinguish using viscosity alone.
Despite needing another technique to clarify the lubricant in a system, it is the most commonly used technique for analyzing lubricants as it is cheap, easy to perform and tests the most fundamental property of a lubricant.
Elemental analysis, or elemental spectroscopy, is an excellent way of detecting trace contaminants within the lubricant. Industry uses a combination of inductively coupled plasma (ICP), rotating disc electrode (RDE) spectroscopy and X-ray fluorescence (XRF) techniques to identify trace amounts of common additive elements– such as phosphorus, zinc, calcium, magnesium, barium and potassium.
Contaminants can enter the lubricant in a number of ways, although the most common is through being picked up into the system when the oil circulates and splashes off different machine components and surfaces. Contaminants can also enter the lubricant during manufacturing, routine service, faulty seals, poor breathers or open hatches.
Regardless of how the contaminants get into the lubricant, it is a serious issue and one that can cause a lot of damage. So, the ability to test the lubricant is crucial. The presence of ‘wear metals’ within the lubricant also gives a good indication of abnormal wear with the machine.
The main advantages of using an elemental analysis approach is that ash-type additives can be easily identified, and the elemental ratios can be deduced easily. However, it does have its pitfalls. Non-ash-type additives do not have an elemental signature and cannot be identified using this technique, and currently, basestock mismatch has not been addressed.
Infra-red (IR) is used in two forms in the analysis of lubricants – through direct IR spectroscopy and Fourier transform infra-red spectroscopy (FTIR). IR is a highly regarded technique for analyzing lubricant mix-ups, as it allows for the comparison of an unknown sample to be compared against a known reference. By analyzing the lubricant that should be in the machine, against the lubricant present, it allows the differences to be distinguished by superimposing the two spectra. Any unusual or uncharacteristic peaks within the lubricant can then be identified.
Overall, IR-based techniques are most useful when a mix-up is either expected or is in an environment where a mix-up is likely. FTIR is most commonly adopted in condition monitoring laboratories and a common misconception is that the technique can recognize a mix-up in real-time, it cannot. Direct IR is often used in a situation where the mix-up is known (and environment) is known and can be modeled beforehand.
The main advantage of using FTIR is that it can easily detect, search and identify functional groups and additive packages within the lubricant. Whereas, the main advantage of direct IR is its ability to validate a known oil. However, using IR still has some drawbacks. Many of the basestocks and/or additive packages supplied by manufacturers are often very similar in nature and the formulation can change from time to time. This makes it inherently difficult to be decisive on an unknown sample, especially if the internal composition of the lubricant often changes.
Gas chromatography-based techniques are less commonplace but are still worth mentioning. Gas chromatography analysis takes two forms for lubricant analysis and is considered to be a non-routine procedure. Standard gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) are the two techniques utilized in lubricant analysis.
Gas chromatography can be advantageous because different molecules in the lubricant elute at different (and known) times. This is often utilized for oils with clear ionization signals. Gas chromatography techniques currently have the ability to measure 0.05% of lubrication mix-up. However, compound oils are difficult to separate with many GC columns and several common compounds co-elute, making it harder to reach a decisive conclusion.
In all, the various types of lubricant testing provided by companies allows many industries to minimize costly down-time and repairs, by recognizing early and developing problems before they become big and costly issues.
Spectro Scientific: https://www.spectrosci.com/default/assets/File/SpectroSci_OilAnalysisHandbook_FINAL_2014-08.pdf
Machinery Lubrication: http://www.machinerylubrication.com/Read/30443/oil-analysis-reports