Oil condition monitoring as an early-warning system
A piece of heavy mining equipment breaks down due to undetected wear in critical components, holding up extraction for days. Repeated breakdowns in a manufacturing plant cause long downtimes and endanger perishable goods. Water contaminates the lubricant in critical power-generation equipment, putting reliable operation at risk. The high costs of machine failures highlight the importance of preventive maintenance and having key information about your machines’ health in advance [1].
Oil analysis is a valuable tool for preventive maintenance. In a sense, it’s like a blood test for machines. It tells us not only if the lubricant oil is deteriorating and ready to be changed, but it also gives us more general information about the machine’s condition. The presence of contaminants such as glycol from the coolant or fuel from the engine may indicate leaks or failures allowing these components into the lubricant. Oil analysis can also detect small metal particles that indicate if parts of the machine are suffering excessive wear.
However, the information we get from oil analysis is only as reliable as the measurements we make. Although a wide range of instruments and technologies is available to monitor lubricant oil condition, they need to be used consistently and under consistent conditions. This makes sure that any abnormalities or changes we see in oil composition come from the oil itself, and not from variations in how we measure it. Here is where standardisation comes into play.
Why standardisation matters in lubricant condition monitoring
Although consistency is always important when performing oil analysis, the level of analytical control required may vary depending on where and how the measurements are made. On-site technicians often work under less controlled conditions, while in-house laboratories may develop their own procedures to meet the needs of a particular operation.
However, when oil analysis is outsourced to a specialised laboratory, standardisation becomes particularly important. These laboratories may process lubricant oil samples from dozens of different customers. The samples may come from different machines, contain different oil formulations, and be analysed by different technicians using different instruments. Yet the results of these analyses are used to make important maintenance decisions. A misleading result could mean unnecessary maintenance or, worse, failing to detect a problem before it causes a costly breakdown.
This puts considerable responsibility on the laboratory. It is not enough to produce accurate measurements; they also need to be reproducible and, importantly, defensible and auditable. The laboratory needs to be able to demonstrate that its results reflect the condition of the oil rather than variations introduced by instruments or operators. It must also be able to systematically troubleshoot unexpected results and determine whether they reflect a genuine change in the oil or a problem with the analytical process.
This is where standardisation comes into play. By following clear, widely recognised standards, laboratories can ensure that their analyses follow consistent procedures, reducing variability between measurements, instruments and operators. Just as importantly, they can demonstrate to their customers (and to themselves!) that their analyses are performed according to established methods.
Luckily, laboratories do not need to develop these procedures from scratch. ASTM International has published standard practices covering different aspects of lubricant oil condition monitoring. Let’s see how.
ASTM E2412: Trend analysis for oil condition monitoring
Practices published by ASTM International are voluntary standards that cover how to perform different types of operations, including measurements, in a consistent and standardised manner. Although ASTM itself has no enforcing role, following established standards avoids having to develop new procedures from the ground up. Moreover, because ASTM standards are widely recognised, their use can help produce consistent and comparable results across instruments, laboratories and organisations.
ASTM practices include standards related to oil condition monitoring, such as ASTM E2412: Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry [2]. FTIR spectrometers measure the absorbance spectrum of a sample across the infrared range. Different chemical compounds absorb infrared light at characteristic wavelengths, producing bands in different regions of the spectrum. By analysing these bands, it is possible to obtain information about a sample’s chemical composition and how it changes over time.
ASTM E2412 explains how to apply FTIR spectroscopy to oil condition monitoring. It covers the evaluation of chemical degradation, additive depletion and contaminants such as ethylene glycol, soot, water, fuels or incorrect oil, as well as aspects of instrument configuration, sample handling, data analysis and interpretation. Importantly, the guidelines in ASTM E2412 recommend using trend analysis rather than isolated measurements. In trend analysis, samples of the same oil and from the same machine are taken at different time points. This gives important information on how the analysed oil evolves without necessarily needing to determine the precise concentration of each component.
FTIR trend analysis can evaluate the levels and rates of change of contaminants, degradation products, additives and extraneous oils. Based on historical data and knowledge of the equipment being monitored, technicians can establish warning and alarm levels that indicate when action may be required. But while E2412 covers many aspects of FTIR spectroscopy analysis, its main purpose is condition monitoring through trend analysis. A complementary ASTM practice, D7418, focuses specifically on standardising FTIR instrument setup and operation so that the data used for oil condition monitoring are acquired consistently.
ASTM D7418: Systematising measurements
ASTM D7418 exists to give more specific detail on the operational parameters of the spectrometer equipment itself [3]. The output of a spectroscopy instrument is an absorption spectrum: a measurement of how much infrared light at different wavelengths is absorbed by the sample. This is not a straightforward measurement and, without a systematic approach, unwanted variation can easily be introduced into the data. We may then be unable to tell whether a difference between measurements reflects a real change in the oil or simply a difference in how the measurement was performed.
This variation introduced by the instrument and user can have several sources, such as background noise that changes from day to day or differences in the measurement parameters set on the instrument. For spectroscopy measurements, a thin layer of sample is placed in a measurement cell. If the cell has not been properly cleaned between experiments, or the thickness of the sample layer (the optical path length) changes between measurements, the absorbance spectrum may change even if the sample itself is identical. Even with consistent experimental protocols, care is also needed when analysing the data so that results remain comparable between measurements, samples, users and instruments.
ASTM D7418 provides guidelines for controlling these and other sources of variation. Rather than requiring each technician to develop their own systematic approach to FTIR measurements, it provides a ready-made standard that can be applied across instruments, laboratories and organisations.
As a result, following this practice provides much greater confidence that any changes seen in the absorption spectra of samples taken from the same oil system at different times reflect actual differences in oil composition, rather than variation in how the measurements were performed. It also reduces variability when measurements are made by different people, on different instruments or in different labs. The increased reliability that comes from following ASTM D7418 is especially important in oil trend analysis, where multiple samples from the same system need to be analysed over months or even years, and small, gradual changes in oil composition need to be detected. This is why E2412 and D7418 are meant to work together.
Integrating different oil tests
Something ASTM E2412 makes clear from the outset is what FTIR analysis can and cannot measure. Although it is an effective tool for detecting contaminants and chemical deterioration, it can’t measure all the properties relevant to lubricant and machine condition. Therefore, a complete condition-monitoring programme does not rely only on FTIR.
As we saw in our previous article, other parameters, such as viscosity, acid or base number, or the presence of metal particles originating from machine wear, are also key indicators of machine health. They indicate whether the lubricant is protecting the machine adequately and can detect component deterioration before it becomes an issue. Moreover, these techniques not only fill information gaps in FTIR analysis, but also complement it. For example, oil oxidation can also affect viscosity, so consistent changes in both measurements provide stronger evidence of oil deterioration. Therefore, techniques such as viscometry or elemental analysis are also important parts of oil condition monitoring and, like FTIR, have their own dedicated ASTM standards. Examples include ASTM D5185 for elemental analysis of lubricating oils by ICP-AES and ASTM D664 for determining acid number by potentiometric titration.
Scaling up standards
Stringent standards and meticulous procedures are essential for reliable analysis, but applying them consistently in practice is not always straightforward. This is especially true in the case of large, specialised laboratories that handle hundreds or even thousands of samples every day, necessarily using multiple instruments and technicians. How can such a lab implement and enforce strict standards without slowing down the entire operation?
Having the right equipment can make a big difference. Instruments and accessories specifically designed to support ASTM-compliant measurements can simplify instrument setup, reduce the need for manual adjustments and reduce the burden on analysts. Adding automation further supports the implementation of these standards, allowing a laboratory to perform a high volume of analyses while helping ensure that established procedures are followed consistently and reducing the variability introduced by repetitive manual operations. Combined with systematic adherence to established ASTM practices, this equipment can help laboratories handle large numbers of samples without sacrificing the consistency and reliability that oil condition monitoring depends on.
Conclusion
Using FTIR and other analytical techniques to track the condition of lubricating oils over time as part of a maintenance programme can help prevent costly failures. However, all the data and measurements in the world are only as valuable as their reliability. This is especially true in trend analysis, where measurements must be sufficiently comparable to detect small or gradual changes.
From this perspective, standards such as ASTM E2412 and D7418 are not red tape that gets in the way of real work, but valuable tools for getting the most out of lubricant analysis. Sooner or later, any organisation that needs to repeatedly perform complex analyses is going to have to develop a methodology. ASTM standards save organisations from having to build these procedures from the ground up, with the added advantage of being developed through expert consensus. For specialised laboratories handling samples from multiple customers, this is especially valuable. Following recognised standards not only helps them obtain consistent results, but also gives both the laboratories and their customers confidence that those results are based on established, reliable methods.
Both performing preventive maintenance and incorporating ASTM standards for oil trend analysis can therefore be seen as putting in a small amount of work upfront to avoid failures, complications and headaches down the line.
References
- U.S. Department of Energy. Operations & Maintenance Best Practices: A Guide to Achieving Operational Efficiency. Release 3.0. Federal Energy Management Program, 2010, p. 6.16. https://www.energy.gov/sites/default/files/2020/04/f74/omguide_complete_w-eo-disclaimer.pdf
- ASTM International. ASTM E2412-23a: Standard Practice for Condition Monitoring of In-Service Lubricants by Trend Analysis Using Fourier Transform Infrared (FT-IR) Spectrometry. ASTM International, 2023. https://doi.org/10.1520/E2412-23A
- ASTM International. ASTM D7418-23: Standard Practice for Set-Up and Operation of Fourier Transform Infrared (FT-IR) Spectrometers for In-Service Oil Condition Monitoring. ASTM International, 2023. https://doi.org/10.1520/D7418-23
- ASTM International. ASTM D5185-26: Standard Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). ASTM International, 2026. https://doi.org/10.1520/D5185-26
- ASTM International. ASTM D664-24: Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration. ASTM International, 2024. https://doi.org/10.1520/D0664-24