Temperature is a dominant factor influencing lubricant degradation, machine reliability, and overall asset performance. The widely accepted heuristic that lubricant life is reduced by half for every 10 °C increase in temperature is rooted in the Arrhenius equation, which describes the exponential relationship between temperature and chemical reaction rates.

This article presents a comprehensive analysis of thermally driven degradation mechanisms, supported by graphical interpretation, and discusses the implications for reliability-centered maintenance strategies.

Lubrication is a fundamental pillar of machine reliability, directly influencing friction, wear, and thermal stability. However, its effectiveness is strongly dependent on operating temperature.

Heat speeds up oil failure and quietly reduces its ability to do its job.

In industrial systems, even moderate temperature increases can significantly accelerate lubricant degradation while simultaneously reducing its load-carrying capacity creating a compounded reliability risk often underestimated in maintenance strategies.

Thermokinetic Fundamentals: The Arrhenius Equation

The degradation of lubricants follows chemical kinetics governed by the Arrhenius equation:

This equation demonstrates that reaction rates increase exponentially with temperature, forming the scientific basis for the widely used engineering rule:

For every 10 °C increase, lubricant life is reduced by approximately 50%.

The exponential nature of this relationship is illustrated below:

Technical Interpretation:

• Reaction rates remain relatively low at moderate temperatures
• Beyond a threshold, degradation accelerates sharply
• Small temperature increases result in disproportionately high chemical activity

This explains why oxidation, additive depletion, and oil breakdown escalate rapidly in elevated temperature conditions.

Thermally Driven Lubricant Degradation Mechanisms

Elevated temperatures initiate multiple degradation pathways:

• Oxidation acceleration (acid formation, sludge, varnish)
• Additive depletion (loss of antioxidants and anti-wear protection)
• Thermal cracking (molecular breakdown of base oil)
• Volatilization (loss of light fractions)
• Deposit formation (varnish and carbon residues)

These mechanisms are not independent – they interact synergistically, amplifying degradation rates.

Viscosity-Temperature Relationship and Lubrication Regimes

While temperature accelerates chemical degradation, it also directly affects lubricant physical properties, particularly viscosity.

Technical Interpretation:

• Viscosity decreases exponentially with increasing temperature
• Reduced viscosity leads to thinner lubricant films
• Increased risk of metal-to-metal contact

This directly impacts lubrication regimes:

• Hydrodynamic → Mixed → Boundary lubrication

As viscosity drops, the lubricant loses its ability to separate surfaces, dramatically increasing wear rates.

Combined Effect: The Dual Degradation Mechanism

One of the most critical insights from reliability engineering is the simultaneous occurrence of two degradation processes:

1. Chemical degradation accelerates (Arrhenius effect)
2. Mechanical protection decreases (viscosity loss)

Key Insight

Temperature does not create a single failure mechanism it creates a compound failure environment.

This dual effect significantly increases failure probability, particularly in:

• High-load systems
• High-speed machinery
• Thermally stressed applications (compressors, turbines, hydraulics)

Impact on Machine Components

Bearings:

• Reduced film thickness
• Increased asperity contact
• Accelerated fatigue

Bearing life may be reduced by up to 50% under poor thermal and lubrication conditions.

Seals and Elastomers

• Thermal hardening
• Loss of elasticity
• Increased leakage and contamination

System-Level Effects

• Filter clogging (due to varnish/sludge)
• Reduced heat transfer efficiency
• Increased internal friction

Thermal Feedback Loop in Failure Development

A critical reliability concept is the self-accelerating failure cycle:

1. Temperature increases
2. Lubricant degrades
3. Friction increases
4. Heat generation increases
5. Further degradation occurs

This feedback loop explains many catastrophic and unexpected failures in industrial systems.

Reliability Engineering and Maintenance Strategy

To mitigate thermal effects, organizations must adopt a proactive approach:

Monitoring

• Temperature sensors
• Infrared thermography
• Online oil condition monitoring

Predictive Maintenance

• Viscosity tracking
• TAN and oxidation analysis
• Particle counting (ISO 4406)

Prescriptive Actions

• Improve cooling systems
• Use synthetic lubricants with high thermal stability
• Control contamination
• Optimize lubrication intervals

Strategic Implications for Asset Management

Temperature control must be treated as a critical reliability variable, not a secondary parameter.

Organizations that integrate thermal management into lubrication strategies achieve:

• Increased MTBF
• Reduced downtime
• Lower maintenance costs
• Improved operational efficiency

Temperature is one of the most influential factors affecting lubricant performance and asset reliability.

The Arrhenius relationship and viscosity-temperature behavior clearly demonstrate that thermal effects simultaneously:

• Accelerate chemical degradation
• Reduce mechanical protection

This dual mechanism significantly increases failure risk.

Effective temperature control is not optional; it is essential for achieving high reliability and operational excellence.

References

• Bannister, K. (2007). Practical Lubrication for Industrial Facilities.
• Bloch, H. P. (2004). Machinery Failure Analysis and Troubleshooting.
• Fitch, J. (2012). Lubrication and Reliability Handbook.
• Harris, T. A. (2006). Rolling Bearing Analysis.
• Mortier, R. M. (2011). Chemistry and Technology of Lubricants.
• Moubray, J. (1997). Reliability-Centered Maintenance.
• Stachowiak, G. (2014). Engineering Tribology.
• ISO 4406 – Cleanliness Code
• ISO 55000 – Asset Management

Crude oil prices have fluctuated significantly over the past 12 months, with a recent sharp increase in 2026 due to the crisis in the Middle East, while global lubricating oil prices remain relatively stable and do not directly track crude oil volatility.

An analysis of the monthly average crude oil prices (spot average of Brent, WTI, and Dubai in USD per barrel) and price estimates per liter for lubricants such as ISO 46 mineral hydraulic, engine synthetic, ISO 320 mineral and synthetic current shows that now there is no significant variation and depends more on brands and volumes.

Lubricants do not immediately reflect changes in oil due to long-term contracts and stocks.

Why is there no rise in lube oil prices if there was a rise in oil prices?

Lube oil prices have not risen immediately despite the recent increase in crude oil (from ~60 USD/barrel to 95 USD in March 2026) due to several structural factors in the industrial supply chain.

Main reasons

• Delay in the production chain: The oil is refined into base oils, a process that takes 2 to 6 months. Lubricants use stocks purchased at previous prices, cushioning rapid rises.
• Long-term contracts: Lubricant manufacturers sign fixed agreements (3 to 12 months) for base oils and additives, which represent between 70 and 80% of the final cost of the product, but are not adjusted daily like spot crude.
• Low proportion of crude oil: Only 50 to 70% of the lubricant is petroleum-derived base oil; the rest are imported additives (20-40%), packaging and margins, diluting the impact a little more, 10 to 20% of the final price.
• Isolated volatility: The oil base markets have their own dynamics (refinery supply, technical shutdowns, scheduled maintenance); they do not follow Brent/WTI 1:1.
• Stable demand and competition: Industrial, hydraulic, or gear lubricants, for example, are sold in large volumes with negotiated prices, without the “rocket-feather effect” as marked as in fuels.

Comparison with fuels

•  The stability of oils reflects robust supply chains and low spot volatility, although gradual increases may be beginning to be felt in some countries and may soon become a practice globally.
• The war in the Middle East (which began on February 28, 2026) has caused significant disruptions in the global production of petroleum derivatives, including lubricants such as those in the table above, although the effects on lubricants are more indirect and later than on fuels.

Confirmed impacts on petroleum derivatives

• Fall in crude oil supply: Up to 8 million barrels per day less (IEA, March 2026), due to the closure of the Strait of Hormuz (20% of world oil), cuts in the Persian Gulf (Saudi Arabia, Iraq, etc.), and attacks on Iranian and regional refineries.
• Affected refineries: Shutdown of complexes in Iran, Qatar, and others, reducing capacity to produce base oils (raw material for lubricants). These impact derivatives such as gasoline, diesel, and lubricants.
• Lubricants specifically: what we can expect in the following months

• • Price increase announced (not immediate shortages)
  • Rising energy, transport, and raw material prices
  • Lubricant refining process (vacuum distillation + hydrogenation) depends on stable crude
  • Outages lead to delays of 1 to 3 months

 Table of effects by product type

Impact of the rise in oil prices on these economies

The rise in oil prices generates energy inflation, but the large economies can cushion through diversification and reserves.

• Importers (China, India, Japan, Germany, Brazil, UK, France): Cost increase by 10 to 20% in transport/industry.
• Exporters (Russia, Indonesia): They will generate extra profits and have plans to invest in local refining.
• USA: Minimal impact, less than 2%, refiners increase their profit margins.

Effect on demand and stock of lubricants

Although most countries have not yet seen a direct impact on end-user prices, the situation is not stable, and the impact is expected to materialize sooner or later.

Conclusions and recommendations

If you can negotiate the prices and purchase volumes of your plant and depend on the region where you are located, you can apply any of the following recommendations:

• The stock in Europe, the US, and China in the next 2 to 6 months is stable and there will probably not be a price increase, unless producers take advantage of this scenario; but if the conflict continues for more than months, there is a possible strangulation of the production chain with an immediate impact and increases in industrial oils starting in the summer.
• The 10 largest economies in the world and the surrounding countries are facing possible inflation, but they maintain a lubricant demand, as the industry is inelastic. This means that even though lubricant prices are likely to rise, the industry needs to buy what it needs.
• Secure short- to medium-term stocks with your lubricant supplier, or prioritize advanced purchases of the most-consumed products in your plant.
• Invest wisely in training for your maintenance personnel, in applications and tools that allow you to keep the lubricant in proper conditions and in lubricant analysis with which you ensure that when discarding oil it is because it no longer fulfills any of its main functions for which it has been designed and can have a negative impact on the lubricated component and the availability of the machine.

Sometimes we can spend hours poring over technical data sheets, comparing oil performances, and finally selecting the “right” oil which aligns with the needs of our equipment. Then, within 2 months, the oil degrades, our machines shut down, and we have a bunch of maintenance repairs lined up. What went wrong? We clearly had the “right” oil in the equipment; everything should have worked beautifully. This is where the awareness of lubrication and its practices becomes critical.

Having the correct oil is only one part of the puzzle. Being able to deliver that oil in its purest, cleanest form to the machine is often one of the other pieces that go missing. Another piece is selecting the right oil, not just based on the sales guy’s advice, but on the actual operating conditions of your machine. In this article, we dive a bit deeper into ways you can align the right oil with the proper practices, or avoid the wrong ones, to help extend the life of your asset.

Spec Sheet vs Strategy

For this example, we will consider a turbine oil selection. If a customer wants to change the oil in their turbine, then they may consider the following:

• What are the OEM specifications that need to be met?
• Is this oil available from the local supplier?
• How does it compare to other oils on the market?
• Does the cost justify the value? (or will the purchasing department want something cheaper?

For most of these questions, engineers or the person tasked with selecting the oil can readily find the answers in the oil’s technical data sheet and by talking to their sales representative. But if we dive a bit deeper, are we selecting the right oil for the operating and environmental conditions? Let’s examine the selection of a turbine oil for the Siemens SGT 200 Gas turbine that meets the Siemens TLV 9013 04 specification.

As seen in this document from Shell Lubricants, a few of their products meet that specification, namely Shell Turbo T, Turbo S2GX, Turbo S4X & Turbo S4GX.

On the other hand, Mobil provides some solutions as well, namely, Mobil DTE 732, 746, or DTE 832, 846

Chevron also provides an option of Chevron GST as follows:

With so many options, how can one choose the “right” oil? They all meet the required Siemens specification, TLV 9013 04. This is where the data sheets, OEM manual, and knowledge of the equipment’s operating conditions play a crucial role.

As per the manual, there are preset conditions for temperatures and pressures, but if your actual system runs hotter (or production is being pushed a bit more), it is functioning outside the operating envelope.

The spec sheet tells you what the oil can do. Your operating conditions tell you what it must do.

Additionally, if your surroundings are harsh (close to the sea or in a corrosive environment, or in a non-ventilated area where heat can build up), these can place additional stress on the equipment. For these harsher conditions, a synthetic oil might be more appropriate than a mineral oil, albeit more expensive in terms of the initial investment.

The manual also specifies which tests/characteristics should be used to monitor the condition of the oil, namely: viscosity, particle count, water content, demulsibility, air release, foaming characteristics, RULER®, and MPC. Based on the performance of your current oil in the system, you can determine whether these values fluctuate toward the higher warning zones. This can also influence your decision about which oil to choose.

It’s not just about the right oil or one that aligns with OEM requirements. The selection should also be based on the environmental conditions of the oil and the equipment, and on whether the oil is suited to perform in these conditions. A mineral oil will not withstand the temperatures that a synthetic oil can for extended periods without degrading. Similarly, given the “right” conditions, synthetic oils can also degrade. By cross-examining your spec sheet, OEM manual, and actual conditions, you can determine the best-suited oil for your operations.

Common Modes of Failure

Regardless of the oil selected, common modes of failure can occur with every lubricant. These include: contamination, improper storage and handling practices, and environmental factors, as shown in Figure 4.

Contamination can be defined as any foreign particle entering the system. This includes any gases, liquids, or solids. Especially when the lubricant system runs alongside the process side, process gases and liquids can leak into the oil. These contaminants can influence the oil’s degradation, leading to deposits or chemical reactions that break it down. Common process contaminants include ammonia or treated water.

 The biggest threat to the right oil is often what gets added to it – whether it’s process contamination or the wrong oil during a top-up.

Another liquid that can contaminate oil is another oil. During top-ups, operators can add the wrong oil to the system, causing contamination and, depending on the oil, a possible shutdown. Adding motor oil to hydraulic oil can be catastrophic, as the additive packages work differently and the motor oil additives may counteract the hydraulic additives, removing them from the oil, leaving the asset open to wear and failure. Despite selecting the correct lubricant for your system, adding the wrong oil (mistakenly) will shorten its lifecycle and cause the asset to fail. 

Bad storage and handling practices can also erode your oil, regardless of the oil you choose. Turbine and hydraulic oils are used in precise equipment. As such, they need to be clean and free of dirt or other contaminants. However, if oils are not stored correctly, contaminants can enter and contaminate the oil.

Simple techniques, such as transferring oil from larger storage containers (pails, drums, or totes) into smaller, more manageable containers (2-3 liters or less), can introduce contaminants into the oil if not done correctly. If oils are to be transferred to another storage container, the storage container must be clean. The transfer process should use clean hoses (not previously used for another lubricant) and be completed in a dust-free environment.

If you wouldn’t use a dirty needle for a blood transfusion, why would you use a dirty hose for an oil transfer?

The transfer of oils from one container to the next can be thought of as a blood transfusion. Would you use dirty needles or vials to transport the blood to be placed into another human? Similarly, oil can be likened to the equipment’s lifeblood and should be treated accordingly. Just as we observe sterile practices for blood transfusions, we should also observe similar types of practices for oil transfers.

Environmental and operational factors can also influence lubricant degradation. As stated earlier, all lubricants can degrade over time under harsh conditions. The lubricant formulation largely influences this, as does whether it was blended to withstand those conditions.

Oxidation can easily occur when temperatures increase, free radicals are present, or when wear metals are present. Thermal degradation occurs when the temperatures exceed 200°C. On the other hand, microdieseling occurs in the presence of entrained air, despite the lubricant used in the system, as shown in Figure 5.

Any of these degradation mechanisms can occur regardless of the type of oil chosen. Hence, it is essential to remember that operational conditions and environmental factors can heavily influence oil degradation, even when the oil is appropriate for the system.

Role of Condition Monitoring

As mentioned earlier, choosing the right oil for the system is just one part of the puzzle. How do we know the oil is performing when it’s in the system? This is where condition monitoring can work hand in hand to help ensure that the oil does not fail the asset.

If a proper oil analysis program does not exist, operators will not know whether the oil is properly lubricating the asset. They will also not be aware of whether the oil is breaking down too quickly and failing to protect the asset. Oil analysis can also alert operators to signs of wear in the asset, so they can fix them before they turn into functional failures.

An oil analysis program that lives in a drawer protects assets about as well as no program at all.

There is also the possibility that an oil analysis program exists but is not top of mind, or that its results are put in a drawer. This can also cause the asset to fail even though the correct oil is being used. Apart from the aforementioned factors, if operators are not warned of the impending failure of the oil, this can result in production losses, increased downtime, and, in some extreme cases, the complete loss of the asset if it has failed beyond repair. 

Incorrect sampling is another area in which the actual condition of the asset is not reported. Even with the correct oil used, if a sample is collected from a dead leg or an area that is not truly representative of the conditions inside the component, its actual condition will not be known. With incorrect data about the component, the asset can be misdiagnosed or treated for symptoms that do not exist, which can lead to its detriment.

Human and Organizational Factors

Not all failures occur at the equipment level; human and organizational factors can also cause the asset to fail even when the correct oil is used. If humans aren’t properly trained in oil sampling techniques or storage and handling practices, these can affect the asset’s functionality. We often forget that, at the heart of it all, lies the human factor, which is partially governed by the organization’s systems.

Training needs are an organizational factor that is often overlooked when considering how an asset can fail. However, if operators have not been trained in condition monitoring techniques, they will not be able to read oil analysis reports or take appropriate actions to protect the asset. Training can help bridge some competency gaps that directly impact asset performance.

It doesn’t matter what oil is in the system if no one is trained to monitor it – or motivated to care.

Culture is another factor swept under the rug. If the culture doesn’t exist to look after the assets, it doesn’t matter what type of oil is placed in the system; the asset will fail eventually. The performance of the asset does not only rely on using the correct oil. By implementing a culture of Asset ownership, where operators look after the asset and are accountable for its performance, assets are optimized to provide the functionality they should. This is one way to ensure the right oil is used to enable the assets’ performance.

Another area of concern is the documentation of maintenance procedures. If maintenance procedures are not adequately documented, someone new to the operation may not be aware of the correct practice. This, coupled with a lack of training, can spell disaster for the equipment. In these cases, even though the right oil was selected, the wrong practice or lack thereof can fail the asset.

Turning the “Right oil” into the “Right Outcome.”

As explained in this article, improper practices can jeopardize the asset’s health, even when the right oil is used. However, if all the right things align, we can have an asset that lasts for its expected lifetime or beyond.

This starts with selecting the right oil based on the application, environmental conditions, and OEM recommendations. If we follow this up with good storage and handling practices, proper condition-monitoring programs, documentation, and training, we can look toward a longer-lasting asset. The right oil enables reliability – but only disciplined practices deliver it.

What’s the Right Number of Lubricants for Your Plant?

Over the years, I have been to sites with either too many or too few lubricant types.

Both scenarios are potentially costly.

On the one hand, too many types of lubricant are costly in terms of purchase price and ultimately risk downtime due to the wrong lubricant being used.

On the other hand, too few lubricant types are costing the company due to overzealous consolidation, leading to a possible substandard lubricant specification in use.

Why Do Lubricant Inventories Get Out of Hand?

Generally, I find that where too many lubricant types exist, usually differing brands, is the result of procurement blindly following the Original Equipment Manufacturer (OEM) insistence on a brand for “Warranty reasons”.  Legally, the OEM should provide a recommended lubricant specification and include a list of brands.  However, if a non-recommended brand can be shown to meet or exceed the required specification, the warranty issue is no longer a concern, especially if the OEM is contacted and obtains written approval. 

I have been through this process on several occasions, especially on new builds, where various electric motor and pump suppliers will try to enforce a particular brand, sometimes for commercial rather than technical reasons.

Where too many lubricant types exist, usually differing brands, is the result of procurement blindly following the OEM insistence on a brand for warranty reasons.

Another possibility is that the procurement team is shopping around for the best pricing, resulting in numerous brands in the storeroom.  This has happened in both small, family-run businesses and in larger operations where a procurement contractor is responsible and is shopping for the best deal. 

What Makes Lubricant Consolidation Worth the Effort?

Primarily, the main reason is cost-benefit.

Purchasing fewer lubricant types means each remaining type in use is purchased in greater volumes, thereby realizing potential cost savings through negotiated discounts for higher volumes. 

This goes further: particularly with oils, these can be bought in larger container sizes, further reducing the purchase price, as typically the larger the container, the cheaper the unit cost.  However, while handling small pails is cheap, handling drums is more complex. Still, with the installation of a “best practice” bulk storage system, the oil can be purchased in drums but handled and transferred via smaller, more easily managed, sealable, and refillable containers that also meet “best practice” guidelines.

A secondary cost reason is the reduced risk of using the wrong lubricant and the resulting damage from cross-contamination.

This latter issue, however, is also the result of a lack of “best practice” with no tagging of the machines and no internal company policy of colour-coding the lubricants, either, allied to poorly written work orders that lack detail.

Is There a Business Case for Consolidation?

Yes…and no.

Be careful of being penny-wise and pound-foolish, as we say in the UK, or should that be cents-wise and dollars-foolish?

Let’s clarify.  In the late 1990s, working with BP, they stated that the average customer will spend less than 1% of their annual maintenance budget buying lubricants, but will spend more than 40% of it dealing with the outcomes of poor lubrication practices on site.

To put that into context, with a $10 million annual maintenance budget, less than $100,000 is spent on lubricants, while $4 million is spent on repairs, rebuilds, and other downtime costs associated with poor lubrication management.

So, would you rather chase a $20,000 savings or deal with an internal issue costing $4 million and recover at least $1 million of that?

The average customer will spend less than 1% of their annual maintenance budget buying lubricants, but will spend more than 40% of it dealing with the outcomes of poor lubrication practices.

In my opinion, the cost-benefit of a lubricant consolidation exercise will also depend on the industry type.  In some instances, certain industries, such as Food & Beverage and Pharma, have limited lubricant ranges, with consolidation already underway, particularly for NSF-approved Food-Grade lubricants, and limited asset types. 

On the other hand, Oil & Gas, mining, Pulp & Paper, for example, not only have a larger range of lubricants to suit a wide variety of asset types, but these industries will also utilise greater quantities, especially in fluid power systems, engines, transmissions, and turbine trains for compressors or power generation.

The Right Way to Consolidate Your Lubricant Program

Lubricant consolidation, in my opinion, is again an essential first step in implementing a world-class lubrication management programme.  Apart from getting a handle on all the lubricants on site, it will help identify obsolete stock, address issues arising from product name changes, and create a plan for the discontinued and hard-to-obtain products still on the list.

Ideally, using internal or sub-contracted, independent expertise, a list of the lubricants in use should be compiled at the beginning.  This is a useful exercise, as I often find multiple duplicates in Enterprise Resource Planning systems (SAP, Maximo, etc.) for lubricant accounting codes.  While each container size of a lubricant type should have its own accounting code, there are often instances where procurement has inadvertently added another, but under a slightly different term, for example, as 15-40 instead of the original 15W-40.

Once the duplicates have been removed, the list should be tabulated in a spreadsheet with columns denoting the brand, product, and then further itemized by column headings not only for the base oil type, thickener type, and intended application, but also relevant to the lubricant type, showing the physical, chemical, and performance properties.

 I would then prioritise the lubricants, with the highest priority given to those used in critical assets or specialised equipment that must remain, and the lowest to those in general applications and low-criticality assets.

However, be aware that, for greases. At the same time, it is tempting to use a multi-purpose grease for the motors; the base oil’s viscosity may be too high compared to a specialist electric motor bearing grease, which can increase power consumption.

In addition, gearboxes and transmissions need investigation, as Sulphur-Phosphorus-based Extreme Pressure oils may not suit all designs. In fact, apart from the chemical issue with the S_P EP oils, which require a solid-suspension type physical EP oil, some gears may only need an Anti-Wear oil.

Rather than dumbing down to the cheapest level, take the opportunity to raise the bar to the highest level.

A final comment here is that rather than dumbing down to the cheapest level, take the opportunity to raise the bar to the highest level.  For example, switching from mineral to synthetic base oils may seem counterintuitive in terms of cost; however, there are several benefits.  The higher VI of the synthetic base oils may help consolidate into different Viscosity Grade oils, while potential cost benefits include longer oil change intervals and reduced energy consumption.

What Comes After Consolidation?

While the consolidation may be your only objective, the cost-benefit of such a process will be limited and, in fact, incur additional costs due to downtime resulting from uncertainty about the new lubricant range and cross-contamination. 

In addition, it is simply not possible to start topping up with a revised oil grade, such as an ISO VG 22 synthetic oil, on a gearbox currently using an ISO VG 320 mineral oil. Hence, the likelihood is that the consolidation won’t happen.

Further, even if consolidation reduces the number of lubricant types in use, it may still result in a variety of container sizes or require purchasing smaller containers at a higher unit cost unless steps are taken to address processing with larger containers in the lubricant store.

Simply put, the real benefit comes from a structured process of improvement across the whole lubrication management strategy.

Should You Let Your Supplier Run the Consolidation?

It is, of course, possible, and increasingly, lubricant vendors are going down this road with their clients.  A strong supplier with your best interests as the end user at heart is the ideal approach.  Unfortunately, I have seen too many instances of a cursory review of the lubricants resulting in over-consolidation to the detriment of the machinery.

One outcome of creating a spreadsheet, as mentioned earlier, is the generation of an internal lubricant specification document.  With actual product names removed, the folder of specifications for each lubricant can be shared with all suppliers as part of a single-source procurement process.  This means that, without the current product name, the lubricant supplier must review the specification document in detail, note its properties and performance criteria, and recommend a suitable lubricant.

What Are the Benefits of a Single Lubricant Supplier?

Just as there is a cost-benefit to lubricant consolidation, rationalising the supplier base can also realise cost savings.  Buying all the lubricants from one source will also help push for discounts beloved of bulk purchasing.

There are other benefits to single sourcing, too.  When evaluating responses to the tendering process, a single-source supplier is more likely to support the process once in place.  Naturally, this depends on the volume of business, but a single-source supplier is more likely to commit to your process of improving the lubrication management strategy.

With actual product names removed, the folder of specifications for each lubricant can be shared with all suppliers as part of a single-source procurement process.

Of course, a single-source supplier may not be able to cover all lubricants, so some allowance will need to be made for specialist lubricants.

What’s the Big Picture Here?

While a cost-benefit, the desire for lubricant consolidation should not be driven by procurement looking to maximise short-term savings, especially by avoiding the temptation to err on the side of cheaper, lower-performing products. 

Lubricant consolidation should be driven by reliability professionals looking to improve the overall lubrication strategy, in which knowledge of future improvements in storage and handling will enable more effective consolidation decisions, maximising the cost-benefit.

Compressors are integral to many of our operations. They are used to compress gas, increasing its pressure, and to power tools. They can also be used as vacuum pumps or blowers, but each application is different. As such, they require various types of lubrication, particularly for applications that use specific refrigerants and come into contact with the lubricant.

In all these applications, the functions of the oil remain largely the same: it must lubricate the surfaces, prevent wear and corrosion, maintain the required viscosity, and provide proper sealing.

In this article, we will dive into the various types of compressor oils and explain why they are suited to these applications. We will also discuss monitoring the health of these oils and the tests that should be performed to ensure your compressor oils remain healthy.

Types of Compressors

Essentially, there are two main types of compressors: Displacement and Dynamic. For displacement compressors, gas is drawn into a chamber, compressed, and expelled by a reciprocating piston. On the other hand, for dynamic compressors, turbine wheels accelerate a medium, which is then abruptly accelerated.¹

Positive displacement compressors include Reciprocating and Rotating compressors. These can be further subdivided as shown in Figure 1. For Dynamic (Turbo) compressors, these are further subdivided into Centrifugal, Axial, and Mixed types (also shown in Figure 1).

Depending on the type of compressor, the required lubricant will vary. For example, positive-displacement compressors use rolling or sliding motion and include bearing and sealing components within the compression chamber. On the other hand, dynamic compressors use hydrodynamic journal and thrust bearings, or rolling-element bearings, to support the main shaft, which is isolated from the compression chamber.

Working pressures, temperatures, and the type of gas being compressed also play a significant role in determining the appropriate lubricant.²

As with most applications, there can be a dry-sump or a wet-sump. Wet sumps are typically seen in reciprocating and rotary screw compressors.  In a wet sump, the gas usually contacts the oil, lowering its viscosity. This is where it is essential to note the gas’s solubility in the system oil. Natural gas and other hydrocarbons are more soluble in mineral oils and PAOs than in PAGs and diesters. Thus, PAGs may be preferred in some cases to avoid lubricant failure.

Compressor Oils

Most of the major global lubricant OEMs have classified their oils based on:

• Rotary vane and screw air compressor oils
• Reciprocating (piston) air compressor oils
• Refrigeration compressor oils

As seen below in Figure 2, Shell Lubricants³ has a line of lubricants, particularly for air compressors, which are further classified into mineral oils, PAOs, and PAGs for Rotary vane and screw air compressors or Reciprocating (piston) air compressors.

In reciprocating air compressors, cylinder design dictates the lubrication type, as this is the most severe application. Compressing the gas usually results in high temperatures, which can easily lead to oxidation. The compressed gas must be free of contaminants, as contaminants can accelerate oxidation. Typically, for reciprocating air compressors, mineral oils or PAO- or di-ester-based lubricants in the ISO VG 68 to 150 range are preferred.

Rotary vane compressors can experience pressure extremes as the vanes slide to compress the gas, and oil is continuously injected into the compressor chambers. Typically, ISO VG 68-150 oils are used in this application.

For screw compressors, the oil must perform several functions, including lubricating the meshing rotors and the plain and roller bearings that form part of the geared coupling. ISO VG 46 mineral oils are usually used in these compressors, but the viscosity can be increased to ISO VG 68 or to synthetic PAO or PAG lubricants at higher ambient temperatures. Similarly, Group III base oils of these viscosities can be used in this area. Most screw compressor oils contain mild EP/AW performance additives and require an FZG failure load≥10.

Ideally, reciprocating piston compressors will use higher viscosities (ISO VG 100-150) with extremely low carbon residue and no or mild EP/AW additives. Conversely, screw compressors will use lower viscosities (ISO VG 46 or 68) with excellent oxidation stability and mild/high AW/EP additives1, as shown in Figure 3.

Other Industry Standards

Some other classifications which users may see when dealing with compressor oils (even though some of these standards may be dated) include:

ISO 6743-3, which uses the following acronyms for associated compressors:

• DAA, DAB, DAG to DAJ: Air compressors
• DVA to DVF: Vacuum pumps
• DGA to DGE: Gas compressors
• DRA to DRG: Refrigeration compressors

In this standard, the “D” family includes detailed classifications of lubricants used in air, gas, and refrigeration compressors. The second letter usually indicates the type of compressor, and the third letter indicates the application severity or type, especially for gas or refrigeration compressors.

For instance;

DAJ represents:

D -> Compressor Lubricant

A -> Air compressor

J-> Lubricant drain cycles of >4000 hours

DVB represents:

D-> Compressor Lubricant

V->Vacuum pumps, Positive Displacement Vacuum pumps with oil lubricated compression chambers, Reciprocating and rotary drip feed, Rotary oil-flooded (vane and screw)

B-> Low vacuum for aggressive gas (10² to10^-1kPa or 10³ to 1 mbar)

DGD represents:

D-> Compressor Lubricant

G-> Positive displacement reciprocating and rotary compressors for all gases, Compressors for refrigeration circuits or heat pump circuits, together with air compressors, are excluded.

D-> Gases that react chemically with mineral oil, usually synthetic fluids, HCI, CI2, O2, and oxygen-enriched air at all pressures. CO₂ at pressures above 10³ kPa (10 bar) with O2- and oxygen-enriched air: mineral oils are prohibited, and very few synthetic fluids are compatible.

DRB represents:

D-> Compressor Lubricant

R-> Compressors, refrigeration systems

B-> Ammonia (NH3), Miscible, Polyalkylene glycol, Commercial and industrial refrigeration, For direct expansion evaporators; PAGs for open compressors and factory-built units.

Another standard which is also used in this industry is DIN 51506, which defines:

• VB, VC: Uninhibited mineral oils (no oxidation inhibitors)
• VBL: Mineral oil-based engine oil (additives that protect from corrosion and oxidation and air compressor temperatures up to 140°C)
• VCL: Mineral oil-based engine oil (additives that protect from corrosion and oxidation and air compressor temperatures up to 160°C)
• VDL: Inhibited oils with increased aging resistance (additives that protect from corrosion and oxidation and air compressor temperatures up to 220°C, recommended for compressors with 2-stage compression)

One more standard is DIN 52503, which has these classifications:

• KAA: Not miscible with ammonia
• KAB: Miscible with ammonia
• KB: For carbon dioxide (CO2)
• KC: For partly and fully halogenated fluorinated and chlorinated hydrocarbons (CFC, HCFC)
• KD: For partly and fully fluorinated hydrocarbons (HFC, FC)
• KE: For hydrocarbons (e.g., propane, isobutane)

These standards are referenced when discussing certain compressor oils, and their definitions are helpful for navigating acronyms.

Refrigeration Lubricants

For industrial refrigeration systems, there are a couple of essential pieces of information to consider before selecting the most suitable oil. The user must know the refrigerant in use, the evaporator type (dry or wet; carryover < 15%), the evaporator temperature, the compressor type, and the outlet temperature.⁴

The refrigerant fluids are classified as per the ASHRAE classification (ANSI-ASHRAE Standard 34-2001):

• R717 — Ammonia
• R12 — Chlorofluorocarbon (CFC)
• R22 — Hydrochlorofluorocarbon (HCFC)
• R600a — Isobutane
• R744 — Carbon dioxide (CO2)
• R134a, R404a, R507 — Hydrofluorocarbons (HFC)

It should be noted that CFCs were banned under the Montreal Protocol (1989) due to their Ozone Depletion Potential, and HCFCs are being phased out due to their Global Warming Potential.

Chevron provides some general guidelines for selecting the appropriate refrigerant, as shown in the table below.⁵

(But you should always follow the guidelines of your OEM when selecting the appropriate lubricant.)

ExxonMobil classifies its refrigeration lubricants based on refrigerant type, evaporator temperature, and compressor type (Piston, Screw, or Centrifugal). This is very helpful when determining the best-suited lubricant for your refrigerant compressor: 

PDF

Critical Condition Monitoring Tests for Compressor Oils

To ensure these oils remain healthy (and not contaminated or degraded), a few basic tests can be performed on all compressors, regardless of type (reciprocating, screw, refrigerant, etc.). These include:

• Viscosity – this is key as some of the gases can easily affect the viscosity, which (if decreased) will not provide adequate separation for the interacting surfaces and cause wear. Generally, a ±10% limit is used (though OEMs may use different values).
• Acid Number – if this begins increasing, then we have an accumulation of acids in the oil, which can be because of contamination. For most compressors, a 0.2 mg KOH/g increase is the warning limit, but for refrigeration compressors, the limit is tighter at +0.1 mg KOH/g. Always check with your OEM for these limits.
• Water content – changes by OEM and refrigerant type, as the different gases will have varied tolerances.
• Wear metals – these values will vary as per OEM, as well, since they are all designed with different types of metals. Users should look for trends or significant increases in these values to indicate wear.

Some specialty tests for compressors include:

• MPC (Membrane Patch Colorimetry) – this helps to measure if there is any potential for the oil to form varnish. Given the high temperatures these types of equipment endure and the potential for contamination, the oil is at risk of forming varnish. While limits will vary by OEM, some general guidelines to follow are 0-20 Normal, 20-30 Warning, >30 Action required
• RULER® (Remaining Useful Life Evaluation Routine) – this quantifies the remaining level of antioxidants in the oil. When oxidation occurs, the antioxidants get depleted. As such, by monitoring antioxidant levels, one can easily determine whether oxidation is happening in the oil. The general rule of thumb is that if the level falls below 25%, there are not enough antioxidants to keep the oil healthy and prevent degradation.  
• Air Release (DIN ISO 9120) – measures the ability of the oil to allow air to escape and not keep the air in the oil. If air bubbles remain in the oil, this can be devastating, as it can lead to micropitting, cavitation, or increased oxidation. Users can trend the values; if they increase, it indicates that the air is taking longer to be released, which means it is staying in the oil and in the system longer.
• Particle Count – this can identify if there are any contaminants in the system. These oils must be kept clean, and OEMs typically specify target cleanliness levels.

Compressors are critical equipment, and we must understand how they work and the lubricant specifications required. Monitoring their health can also help us avoid unnecessary downtime and keep our facilities running.   

References

1. Mang, T., & Dresel, W. (2007). Lubricants and Lubrication. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA.
2. Totten, G. E. (2006). Handbook of Lubrication and Tribology – Volume 1 Application and Maintenance – Second Edition. Boca Raton: CRC Press.
3. Shell Lubricants. (2025, November 08). The Shell Corena range. Retrieved from Shell Lubricants Compressor Oils: https://www.shell.com/business-customers/lubricants-for-business/products/shell-corena-compressor-oils/_jcr_content/root/main/containersection-0/simple_1354779491/promo_1484925192/links/item0.stream/1759302155345/17be2a9a74057f321bb209128933f68f8b88ca70/s
4. ExxonMobil. (2025, November 08). Refrigeration Lubricant Selection for Industrial Systems. Retrieved from ExxonMobil Lubricants: https://www.mobil.com/lubricants/-/media/project/wep/mobil/mobil-row-us-1/new-pdf/refrigeration-lubricant-selection-for-industrial-systems.pdf
5. Chevron Lubricants. (2025, November 08). Optimizing compressor performance and equipment life through best lubrication practices Chevron. Retrieved from Chevron Lubricants: https://www.chevronlubricants.com/content/dam/external/industrial/en_us/sales-material/all-other/Whitepaper_CompressorOils.pdf

When the lube room resembles a crime scene – chaotic storage, unlabeled containers, questionable handling tools, inconsistent transfer practices – it becomes a hidden driver of accelerated wear, additive depletion, ingress-driven contamination, and component life variability that will never show up cleanly in maintenance reports.

The condition of the lube room often mirrors the true reliability culture more accurately than any KPI dashboard. These conversation starters expose the systemic, upstream issues that quietly undermine asset reliability long before oil ever reaches a machine.

25 Lube Room Conversation Starters

1. Why do unlabeled or ambiguously labeled containers still circulate – and who verifies contents before use?
2. What process ensures transfer equipment is flushed, capped, and stored correctly to maintain cleanliness targets per the ISO 4406 cleanliness standard?
3. Why does incoming oil fail our cleanliness specifications – and are we actually verifying ISO 4406 codes instead of relying on supplier paperwork?
4. Who is accountable for lubrication storage standards – and why is “nobody” still the default?
5. Are lubricants grouped by base oil, viscosity grade, and additive chemistry – or simply by whichever shelf is empty?
6. Why are new desiccant breathers sitting idle while storage containers exchange unfiltered air?
7. Why are open funnels or unsealed top-off containers still acceptable when they are proven contamination pathways?
8. If drums are stored horizontally, are the bungs positioned at 3 and 9 o’clock to maintain seal integrity?
9. Do we routinely verify incoming lubricant quality (particle count, viscosity per ASTM D445, AN/BN) against the OEM Certificate of Analysis – or assume delivered product meets specification?
10. Why is moisture control reactive when water accelerates oxidation, depletes additives, and destabilizes boundary films?
11. Have we consolidated lubricant options to the lowest reasonable minimum?
12. Why is the filter cart treated as an emergency tool instead of being used as part of a repeating task to filter all critical sumps routinely?
13. How often do we audit lubricant shelf life – especially for products nearing manufacturer-recommended limits (typically 2–5 years depending on chemistry and storage conditions)?
14. What ISO 4406 cleanliness code targets do we require for stored lubricants – and do we confirm incoming product meets those targets before use?
15. Are grease cartridges stored to prevent temperature cycling and oil separation – or do we assume the sealed packaging eliminates all risks?
16. What controls prevent “clean” top-off containers from becoming contamination sources after weeks of exposure?
17. Why is faded Sharpie still our primary labeling method instead of standardized, controlled identification?
18. Do we maintain a documented lube room SOP – or rely on tribal knowledge that evaporates with personnel turnover?
19. Why do spills persist long enough to become permanent floor features despite OSHA 1910.22 housekeeping requirements and slip-risk implications?
20. Why do we allow partially used containers to sit uncapped, accelerating airborne particulate ingress?
21. How many lubrication-related failures begin right here in the lube room long before a technician touches a machine?
22. Are the open-stores containers protected from temperature extremes, high atmospheric pollution, and high humidity to help maintain additive stability and prevent condensation?
23. What is our process for removing expired or degraded lubricants – before they become “mystery blends” applied during outages?
24. Is the lube room organized as a contamination-control system – or just as a more efficient way to store lubricants?
25. If a new hire walked in today, would the lube room reinforce excellent lubrication practices – or accelerate the spread of bad habits?

A modern lube room isn’t a storage closet – it’s a contamination-control and quality-assurance environment. When lubricants are stored under controlled conditions, verified for cleanliness, transferred with discipline, and protected from environmental stressors, machine reliability increases before any wrench is turned.

Cleaning up the lube room is not cosmetic work; it’s one of the highest-leverage steps a plant can take to stabilize lubrication quality, extend asset life, and reduce avoidable failures. These conversation starters expose the upstream weaknesses that sabotage reliability – and point the way toward transforming the lube room into a controlled, engineering-grade operation.

 When I go into industrial plants and tell the Lubrication Team, aka, oilers and greasers, that they are Tribologists, I usually get a look of confusion on how they would fit in. When you first think of Tribology, your thoughts may immediately go to all the great PhD scientists who have excelled in this field, starting from the coining of the term by Dr. Peter Jost, the Father of Tribology.  

In a review by Enrico Cuilli of the University of Pia titled “Vastness of Tribology Research Fields and Their Contribution to Sustainable Development,” you see a graph that outlines all the areas that spin off from the original explanation of Tribology as shown in Figure1.  

At its core is the definition of Tribology as the science and engineering of interacting surfaces in relative motion, with a focus on friction, wear, and lubrication. It applies to everything from R&D to mechanical systems such as bearings and gears.

Industrial Tribology brings the maintenance and reliability teams into the Tribology family, putting to work “all the applications of tribology to the industrial products, manufacturing, and maintenance. CONGRATS, YOU ARE A TRIBOLOGIST!”

Looking at the areas that deliver the best R&D in Tribology and how they fit the production floor, there are three main areas of focus: lubrication, friction, and Tribochemistry.

Lubrication includes bearing selection, proper fluid film, and Machine components, requiring the gearbox, electric motor, or hydraulic system that best fits the application.

Friction is determined by the type of rolling, sliding, or static contact, the industry, what you are manufacturing or designing, and the Tribofailures, to determine the root cause of failure.

Lastly, as a tribochemistry field lubrication specialist, you must evaluate many products to determine the best lubricant for your application.

The table below (Figure 2) provides additional explanation of the various branches of tribology and the main subjects they cover. 

In Industrial Manufacturing Tribology, it also includes metal forming, maintenance, maintenance monitoring (KPI’s), and condition monitoring of lubricant health with oil analysis. The lab tribologist reviewing oil reports to determine additive strength, wear metal and contamination concentrations and sources, and oxidation levels can advise users on getting the full value and life from their lubricant. 

This will also assist your team in managing time to extend drain intervals, reduce labor costs, and allocate time to other lubrication/reliability projects. Tribology affects everything and everyone.

The goal for Tribologists on the research side is to understand, on the nano-level, the three main components of friction (lower), wear (eliminate), and lubrication (best formulations) to improve energy efficiency, life span of the asset, and increase performance.  This will not only make your company profitable (the cake) but also lower your carbon footprint (the icing on the cake).

If maintenance teams embrace this concept and communicate to management that they are one of the plant’s best assets, they could receive buy-in and support to expand and grow their proactive maintenance program with new equipment and training. The key to this is making sure you are documenting all increases in your production KPI’s and decreases in downtime to keep the management philosophy of “what have you done for me lately” concept addressed.

As we welcome you, the heroes of maintenance and reliability, please know that, as an Industrial Tribologist, you must have a desire to learn and grow every day in this field, and that you are a very important part of the company. You not only make them profitable but also lead the way in energy efficiency for every electric motor, gearbox, and hydraulic unit, and you create the “icing on the cake” as good stewards of the environment. To learn more about Tribology connect or join the Society of Tribologists and Lubrication Engineers. 

Reference:

Ciulli, E. Vastness of Tribology Research Fields and Their Contribution to Sustainable Development. Lubricants 2024, 12, 33. https://doi.org/10.3390/ lubricants12020033

“I want to obtain a certification in the area of…” is often one of the goals set by maintenance personnel, especially those working in predictive maintenance. One of the certifications in the predictive area that has seen significant growth is the lubrication certification. However, doubts arise from the very first moment an individual considers ​​obtaining such a certification.

Lubrication, oil analysis, and tribology share common ground – but each follows a completely different science, purpose, and career path.

For inappropriate reasons, primarily for marketing purposes, the terms “lubrication,” “oil analysis,” and tribology have been mistakenly treated as synonyms or words that share the same purpose. Thus, when individuals seek certification, they face a rather complex task in making the appropriate choice and, above all, in responding to their initial need, which is obtaining knowledge and a certificate to back it up.

Are the terms Lubrication, Tribology, and Oil Analysis similar? No! That’s the first thing to consider when seeking certification in this field. A survey of 86 people seeking certification clearly revealed the lack of awareness and confusion in the market.

Thirty-two of the respondents (37%) were seeking certification in tribology. Of these, only one actually took a tribology course after further researching the topic.

26 of the respondents (30%) were seeking certification in lubrication, while 28 (32%) were interested in oil analysis.

Understanding the Practical Differences Between Oil Analysis and Tribology

Let’s examine the real situation from these perspectives. Oil analysis involves a laboratory where lubricant samples (oil or grease) are received, their physicochemical characteristics are analyzed and compared with a reference, and a result is issued. A tribology laboratory, on the other hand, not only works with lubricants but also has a much broader scope.

It can extend to component surfaces, lubricating media that are not necessarily industrial lubricants, and the analysis of wear suffered by parts based on previously determined conditions. While an oil analysis laboratory analyzes hundreds of samples per day, a tribology laboratory primarily works on projects where a component, fluid, or surface goes through a series of analytical phases that can take weeks or even months.

And what about lubrication? Are there lubrication laboratories? Can lubrication be simulated in a laboratory? In this case, lubrication refers to a series of stages in which the lubricant passes through the plant.

What Role Do Training Providers Play?

Of course, one of the key links in this chain is those responsible for training. In this area, there is an invisible classification that is often not obvious to the candidate. If we return to the three initial terms, trainers generally have experience in at least one of the areas. That is, they know, have experience, and can transmit what they know in the areas of tribology, lubrication, and oil analysis.

If you are a potential candidate, it is very likely that the previous lines have already clarified your doubts somewhat, or perhaps, on the contrary, have generated much deeper ones, simply because you assumed the three terms were interchangeable and similar.

Clarity begins when you stop treating lubrication, oil analysis, and tribology as interchangeable – and start seeing them as distinct disciplines.

If you already know the area in which you want to obtain certification, it is logical that you should look for a trainer who has knowledge and experience in that area. Let’s go a little deeper. I was fortunate enough to grow professionally in one of the world’s best lubricant analysis laboratories, while one of the world’s best tribology laboratories was located just down the floor.

Have you heard of Professor Peter Jost? He was the author of the eponymous “Jost Report,” the report of the Working Group established in 1964 to investigate the state of lubrication training and research in the United Kingdom. For the next five decades, until his passing in 2016, he continually emphasized the importance of tribology for manufacturing efficiency, energy conversion, and environmental sustainability.

This magnanimous gentleman was a thesis advisor for some of my colleagues in the tribology laboratory. Let’s apply simple logic: if you were looking for a certification in tribology, which of the two laboratories would you go to?

What Certification Alternatives Are Available on the Market?

At least for now, there are two recognized entities that issue certification in the areas of dispute. In this article, we will not analyze whether they meet the requirements of international certification regulations, but simply the certification options.

STLE, the Society of Tribological and Lubrication Engineers. Founded in 1944 initially as the American Society of Lubrication Engineers (ASLE), it changed its name to STLE between 1987 and 1988. It offers four certifications:

• Certified Lubrication Specialist – covers a broad area of ​​field lubrication, the mechanical principles of lubricated machinery, and lubricant analysis.
• Certified Oil Monitoring Analyst – aimed at certifying knowledge in the area of ​​lubricant and fluid analysis, such as coolants. It covers primarily a basic or initial level.
• Certified Oil Monitoring Expert – similar to the previous one, but aimed at a more advanced level.
• Certified Metalworking Fluids Specialist – focuses solely on fluids such as cutting fluids or coolants. If this is your area, this is the certification you’re looking for.

ICML, the International Council for Machinery Lubrication, founded in 2001, is a non-profit organization. It offers certifications in the following areas:

• Machinery Lubrication Technician, two levels
• Machine Lubricant Analyst, three levels
• Machinery Lubrication Engineer
• Laboratory Lubricant Analyst, two levels

Both types of certification fully cover two of the three terms in dispute. What about tribology? Although the trainers, or at least the material they provide, mention something about tribology, it is very brief and insufficient, considering its scope.

Apparently, it is the science that studies surfaces interacting in relative motion, as well as any aspect related to the design and operation of a machine concerning friction, wear, and lubrication. This has a pending issue: certification.

Aspects to Consider When Seeking Certification

• The trainer’s experience in the selected field. Do they know about lubrication, oil analysis, and tribology? 3 out of 3 is a checkmate.
• The trainer’s depth of knowledge. Does he or she work in a lubricant analysis laboratory? Does he or she work in a tribology laboratory? Does he or she know about lubrication?
• What certifications does the trainer have?
• Will the certification you are seeking be helpful to you professionally or personally?
• Does your employer value certifications in this field?
• Will the certification have an impact on your professional work and work environment?

Remember, the ignorant buy trinkets, the wise acquire knowledge.

Varnish formation is one of the most critical and often overlooked challenges faced by industrial lubrication systems, especially in high-performance applications such as steam turbines, gas turbines, compressors, and precision hydraulic systems. Even when invisible to the naked eye, varnish compromises the reliability, efficiency, and service life of key components in industrial plants.

What is Lubricant Varnish?

Varnish is an insoluble by-product of the thermo-oxidative degradation of oils. Over time, these residues, usually brown to reddish-brown in color, adhere to metal surfaces, forming a thin, hard, and resistant film, similar to the varnish used on wood.

This deposit is composed of hydrocarbon oxidations, degraded additives, carbonized particles, and other byproducts of lubricant decomposition. The formation of this film occurs gradually and almost imperceptibly, making early diagnosis essential.

1. Studies published by turbine manufacturers, oil analysis companies, and organizations such as STLE (Society of Tribologists and Lubrication Engineers) indicate that More than 70% of the turbines that experienced recurrent failures had varnish buildup in the lubrication systems. In many cases, the varnish went unnoticed for years, silently accumulating until it interfered with the operation of servo-controlled valves and high-precision bearings.
2. Training and accession mechanism Laboratory research has shown that varnish arises from the thermo-oxidative degradation of lubricants, catalyzed by elevated temperatures, the presence of water, oxygen, and metal contaminants. These factors lead to the formation of free radicals and insoluble compounds that, over time, adhere to metal surfaces through electrostatic and chemical forces, particularly in areas with limited oil circulation or stagnation points.
3. Studies on behavior under different conditions. Experiments conducted by laboratories such as Chevron and ExxonMobil have shown that oils with different additive packages exhibit varying behaviors in varnish formation. Oils with higher phenolic antioxidant and amino content tend better to resist oxidation and the formation of insoluble byproducts. However, even with high-quality oils, if the rate of by-product generation exceeds the oil’s ability to keep them dissolved, varnish will inevitably form.

Consequences of the Presence of Varnish in Industrial Systems

The presence of varnish compromises not only performance, but also the safety and useful life of the assets. Among the main operational impacts, the following stand out:

• Locking of control valves and servo valves;
• Increased operating temperature in bearings and rotating components;
• Reduction of thermal efficiency by thermal insulation of the system;
• Increased energy consumption;
• Loss of operational reliability and increase in unscheduled downtime;
• Difficulty in maintaining the stability of the hydraulic system.

How to Identify the Presence of Varnish

Early detection depends on a structured analytical approach. Among the main laboratory methods, the following stand out:

ASTM D7843 – MPC (Membrane Patch Colorimetry)

This method measures the propensity of a lubricating oil to form insoluble deposits. By extracting and filtering a sample onto a membrane, filter browning is quantified numerically. MPC values above 30 are considered critical – an early and direct indication of the tendency to varnish formation.

ASTM D2272 – RPVOT (Rotating Pressure Vessel Oxidation Test)

This test evaluates the oil’s resistance to oxidation under accelerated conditions. The longer the time until pressure collapses, the longer the remaining life of the fluid. It is essential to indicate the degradation of antioxidant additives. Helps plan oil replacement before failure.

ASTM D6971 – RULER (Remaining Useful Life Evaluation Routine)

It uses voltammetry to measure the residual concentration of antioxidants in the oil. It provides an accurate analysis of the lubricant’s “chemical lung” by separating the types of antioxidants (phenolics and aminates). Quantitative indication of the chemical health of the lubricant.

ASTM D664 – TAN (Total Acid Number)

The TAN test measures the total acidity of the lubricant. The increase in this index indicates the presence of acidic products resulting from the oxidation of the oil, which are precursors of the formation of varnish and deposits. A continued increase in NHS may signal the need for intervention, even before visible contaminants form.

Other relevant tests include:

• FTIR (Infrared Spectroscopy): Identification of oxidation products, thermal degradation, and presence of polar contaminants;
• Particle Count (ISO 4406): Evaluation of fluid cleanliness and the presence of insoluble particles;
• Karl Fischer: Verification of the presence of free and dissolved water;
• VPR – Varnish Potential Rating: Composite index that combines MPC, FTIR, and operational data to predict the varnish formation trend.

 Varnish Prevention and Control Strategies

The most effective approach involves continuous monitoring combined with specific preventive and corrective actions:

• Off-line filtering with absolute elements or nanofiltration, ensuring removal of solid contaminants and varnish precursors;
• Strict humidity control, reducing the water content in the fluid to avoid hydrolytic reactions;
• Use of soluble varnish removal systems, such as ionic dry resin, treated cellulose, or electrostatic purifiers (ECR);
• Selection of lubricants with a high index of resistance to oxidation, preferably with modern antioxidant additives;
• Efficient thermal management, avoiding hotspots and stabilizing operating temperatures;
• Condition-based oil change planning and analysis instead of fixed intervals.

Tip: Implement critical varnish indicators in the reliability plan and integrate them into your predictive monitoring system.

Varnish is more than just waste: it is a marker of advanced lubrication system degradation. To ignore its presence is to accept the risk of serious failures and unexpected operating costs.

The solution? Adopt a predictive and proactive posture, with regular analysis, contaminant control, and use of modern technologies. This ensures performance, reliability, and longevity of industrial assets.

Understanding Electrostatic Spark Discharge and Its Impact on Lubrication Systems

Electrostatic Spark Discharge typically occurs when static is built up in an oil at a molecular level, causing it to discharge in the system and create free radicals, which increase the opportunity for varnish to form. This usually occurs at temperatures of around 10,000 °C.

If we were to liken this to an everyday situation, we could think about walking around a carpeted room where the static builds up in our body. When we touch a metallic object (more than likely a door handle), we get a bit of a shock as the built-up static is discharged through us and the door handle.

Inside a lubricant system, static doesn’t just build – it ignites microscopic sparks powerful enough to scar filters and start the chain reaction that leads to varnish.

Similarly, in lubricants, static exists at a molecular level, and in areas of tighter clearances, some molecules are forced to rub against each other, causing a buildup of static. When it accumulates to the point of becoming a full charge, it dissipates at the first opportunity, usually at the filter membrane or some sharp-edged object along the way. These are seen as burnt patches on the filter membrane.

When this spark occurs, it creates a chemical reaction that generates free radicals. Free radicals are highly reactive species that need to engage with other substances. These are the initiators of varnish, and their presence can accelerate reactions, leading to deposits forming in the lubricant. Eventually, this will lead to a system that has experienced both ESD and oxidation.

In this article, we will discuss various identification methods and ways to prevent ESD in modern lubrication systems. We will also spend some time identifying typical root causes for ESD by developing a logic tree as a guide for future investigations.

How to Identify Electrostatic Spark Discharge in Lubrication Systems

Every degradation mechanism produces varying results in the form of deposits or in how these are formed. For ESD, some tell-tale signs alert the user to its occurrence. These include:

• Crackling sounds / buzzing outside of components – This noise is representative of sparks as they discharge on part of the media/asset. Typically, this occurs when the fluid is in motion, allowing it to be heard near the filters when the system is operating.  
• Burnt or pinhole filter membrane – The filters usually feel the full effect of ESD, and small burn patches or even pinholes are created when ESD occurs. When changing filters, the membranes should be examined for these patches to determine if ESD is occurring.

Free radicals are produced when ESD occurs. As such, this leads to polymerization of the lubricant, which produces varnish and sludge. This is part of the oxidation process, and the antioxidant levels will begin to decrease. During ESD, certain gases are also released in the oil. Some of the lab tests which can be used for identifying where ESD has occurred include:

• RULER® – Remaining Useful Life Evaluation Routine test, which quantifies the presence of antioxidants in the oil. By trending this over time, one will be able to determine whether the levels of antioxidants are decreasing or not. Typically, this test can be performed twice annually on larger sumps (such as turbines) or the frequency can be increased according to the criticality of the equipment. If the value gets below 25% then this is the critical limit, and methods to regenerate the oil or change it should be explored.
• MPC – Membrane Patch Colorimetry – this measures the potential of the oil to form varnish or deposits. Depending on the equipment, the warning limits will vary, but a good rule of thumb is to treat results below 10 as normal, those above 15 as within the monitor range, and those above 20-25 as the critical range. Be sure to double-check these levels with the OEM of the equipment.
• FTIR – Fourier Transform Infrared Spectroscopy can identify various molecules in the oil. It is likened to identifying the fingerprint of the oil, where each molecule has a specific characteristic spectra representative of that molecule. This test can be used to identify the presence of oxidation or any deposits that may have formed.
• DGA – Dissolved Gas Analysis – this test can be used to identify the presence of particular gases that are released during ESD, such as acetylene, ethylene, and methane.

Those above are just some of the methods that can be used to identify the presence of ESD in a lubrication system.

Effective Strategies to Prevent ESD in Lubrication

ESD occurs when there is a buildup of static in the oil; therefore, one of the best methods of preventing it is to ensure that the static levels remain low or are dissipated before they have a chance to wreak havoc on the system. The simplest and most common way of reducing this static is the installation of antistatic filters. These filters can help to remove static from the system before it builds up to dangerous levels, where it can burn the membranes or develop varnish.

Static in oil is inevitable – how you control and discharge it determines whether your system runs clean or burns itself from within.

Ensuring that the system is grounded correctly is another way to guarantee that any built-up static is removed. This is where your electricians can perform checks and install proper grounding devices for your equipment to safeguard against this buildup of static in the system. Therefore, if static charges get built up in the system, they can be dissipated without the effects of ESD.

If oils experience high levels of conductivity, they can conduct static. Typically, if the conductivity is above 100pS/m, there is potential for the fluid to conduct the charge and allow it to be discharged along the system without causing harm.

Unfortunately, there are base oils with low conductivity (below 100pS/m) that cannot carry the charge and dissipate more easily. As such, these types of oils will see an increase in the presence of ESD if not formulated correctly for modern lubrication systems.

As the viscosity of the oil decreases, more force is required to pass through the filters, which can lead to a buildup of static at a molecular level. Additionally, as temperatures decrease, the viscosity also decreases. In these cases, keeping the oil at the system temperature (designed for that particular viscosity) can help to reduce the buildup of static charge in the oil.     

Identifying the Root Causes

Thus far, all the prevention methods have focused on the physical roots of ESD. We did not explore some of the human or systemic roots that are also accountable for ESD. In this section, we will develop a logic tree designed to address a critical failure occurring in a plant. This will be used as an example of the logic tree, which can be developed when investigating the root causes of ESD.

Let’s start with the top of the logic tree, where we define the event or the reason we care. In this situation, it is an unplanned shutdown for 4 hours. An unplanned shutdown will impact the plant’s production, which is why we care about conducting this investigation.

We will assume that the failure mode occurred on one of the critical pumps, and we are investigating how that failure could have happened. Note, we did not ask the question “Why?” because it can be misleading to an opinion, and we are trying to stay as factual as possible.

A disciplined root cause analysis doesn’t start with ‘why’ – it starts with evidence. Each degradation mechanism tells its own story, and Electrostatic Spark Discharge is just one of them.

For this investigation, we will investigate the hypothesis of a critical bearing failing due to lubricant degradation. Since we are focused on ESD for this article, we will have only one hypothesis regarding the degradation mode being ESD. However, in the real world, if this logic tree were being developed, we would be investigating the six various lubricant degradation mechanisms: oxidation, thermal degradation, microdieseling, ESD, additive depletion, and contamination.

As shown in Figure 1, at the top of the logic tree, we start by placing our hypotheses on the tree, and then using evidence/facts, we can rule them out afterwards. This is a critical step as the investigation should be able to stand on its own in the court of law (even if it may not reach that point). The next hypothesis is the buildup of static in the oil. There are three possible ways for this to occur;

• Clearances too tight (as discussed earlier, this can lead to molecular friction, which can induce static)
• Less than adequate grounding system (if a proper grounding system doesn’t exist, then there isn’t an option for the static to dissipate)
• Less than adequate conductivity of the oil (if the conductivity of the oil is too low, then the charge can build up and cause it to be dissipated along the system, such as the filters)

Now, we need to investigate each of the three main hypotheses stated and find out the root causes for them.

Let’s begin with the Clearances being too tight hypothesis.

For this hypothesis, we will ask the question, “How can clearances be too tight?”. In this case (and we will have to keep it general and in broad buckets, so we can drill down into these later and eliminate as necessary), there are three possible reasons:

• The OEM could have designed the system such that it was less than adequate (LTA)
• The flow rate could have been increased above the recommended threshold
• Incorrect viscosity of the lubricant could cause additional friction (we will dive into this one later).

We will develop the other two hypotheses in Figure 2. 

If we further investigate where the OEM did not design the system effectively, we can determine that the operating conditions were probably not adequately considered before implementation. This is a systemic root cause and one that needs to be addressed with the OEM.

On the other hand, if we investigated the flow rate, there could be two main reasons for the adjustment. One could be because of system changes, which forced adjustments to the flow rate. Since a decision was made here, it is a human root cause. Someone decided to change the flow rate based on the variables involved. However, if we investigate why these changes were made (once a human is involved, the question moves from how to why), we can determine that the system was not designed to accommodate these changes. This is a systemic root. 

Similarly, if the operational conditions change (such as when a higher output is required, which is different from system changes), then the flow rate must be adjusted. Again, a decision must be made here, and a human is involved. Then we ask the question, “Why?”. In this case, we have the same systemic root, and the design is inadequate to accommodate the necessary changes.

For this part of the tree, we have found some human root causes where decisions were made, as well as systemic root causes. Both need to be addressed when we perform the final root cause analysis. For the human root causes, we can think about the procedures that guided them to make those decisions (if they existed) and amend these accordingly. 

On to the next hypothesis, which we have yet to investigate (still under the clearances being too tight), the incorrect viscosity of the lubricant, which is shown in Figure 3. There are a couple of ways in which this can happen:

• OEM recommendations were not followed
• There was an unavailability of the specified viscosity of the lubricant
• There was a less-than-adequate procedure for selecting the correct viscosity of lubricant

If we investigate why the OEM recommendations were not followed, we can find two main reasons. Either they were not documented and therefore could not be followed, or the internal best practice was used instead to replace the OEM recommendations. In both cases, these would be systemic root causes, and we should investigate why these were not documented or why they were replaced.

When investigating the unavailability of the specified viscosity of the lubricant, we can find two main causes. Either there was an issue with the restocking of this lubricant at the warehouse due to their forecasting, or appropriate checks were not carried out. This is a systemic root cause that should be investigated further.

Another hypothesis could be that the specified lubricant was unavailable from the supplier. This is another systemic root cause and should be addressed with the supplier to ensure it is resolved in the future. 

When lubricant viscosity errors trace back to missing stock or missing training, the problem isn’t the person or the product – it’s the system that allowed both to fail.

On the other hand, if we examine the procedure for selecting the correct viscosity of the lubricant, we identify a human root cause, as someone would have made the decision on which viscosity to use. But in this case, we need to investigate why the person was not trained to determine this value.

There are two main reasons why a person does not receive training: either it doesn’t exist, or it was not followed. In both cases, these are systemic roots that need to be further investigated and addressed.

Now, we will investigate the next major hypothesis, “LTA grounding of the system” in Figure 4.

When investigating the grounding of a system, we can identify two major classes: either it doesn’t exist, or it didn’t meet the requirements. If grounding did not exist, then this is an inadequate system design and therefore a systemic root cause. On the other hand, if the grounding did not meet the OEM requirements, we need to determine how this was possible.

There are two possibilities: the site’s best practices were used to replace the OEM standards, which is something we often see, especially if these requirements have worked in the past. This is a systemic root cause that should be investigated. Or there were fewer than adequate components to achieve grounding.

In this case, we can have components that are not designed for the system (do not meet the system’s requirements) or components that were not OEM-recommended and are being used (such as aftermarket products that do not meet the necessary specifications).

Finally, on to the last major hypothesis, “LTA conductivity of the oil,” as shown in Figure 5.

Figure 5: Investigation of the hypothesis, “LTA Conductivity of oil”

As noted earlier, if an oil has a conductivity of more than 100pS/m, it will be able to dissipate any accumulated charge easily. However, if it falls below this value, the charge will be dissipated in the system at the earliest opportunity.

How can oil have less than adequate conductivity? Perhaps the elements of the oil have a less-than-adequate conductivity. If that is the case, then there can be two plausible reasons for this. Either the formulation was not appropriately designed, or the materials (base oils, additives) were not of a particular standard. Both causes are systemic root causes and should be investigated further to determine if anything can be done to correct these. 

If we were to summarize a list of the root causes, we would see that many are systemic, while a few are human, as shown in Figure 6.

This further reiterates the need to develop a comprehensive logic tree when investigating any failure, as many root causes are not physical or surface-level. If these are not adequately addressed, the failure mode will recur in the future. The entire logic tree can be found here under additional support material, along with logic trees for other degradation mechanisms.

References

Mathura, S. (2020). Lubrication Degradation Mechanisms: A Complete Guide. Boca Raton: CRC Press.

Mathura, S., & Latino, R. (2021). Lubrication Degradation: Getting into the Root Causes. Boca Raton: CRC Press.