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.

It is very likely that you have encountered the RPVOT (Rotating Pressure Vessel Oxidation Test), a laboratory test developed in the 1960s and later standardized by ASTM D2272. It measures the antioxidant stability of lubricating oils by accelerating oxidation in a rotary pressure vessel.

The most common result is an integer expressed in minutes that measures the time until the pressure drops by 25 psi from the initial maximum (T0 to T1) under conditions of 150°C, oxygen at ~90 psi, and a copper catalyst. Some labs include the graphic that most closely resembles one of the most famous drawings in Antoine de Saint-Exupéry’s book, An Elephant Inside a Boa Constrictor.

Although this laboratory test has a lot to say about the state and condition of the oil, it has been assumed that the result depends only on the numerical value, being that it is much more than a simple number, and knowing this test in slightly more detail can be very useful when planning the lubricant. In this article, we will analyze the oil’s behavior during this test from an energy perspective. We will examine the relationship with other laboratory tests and, finally, the application of new methodologies to assess the test’s performance.

Let’s look at three samples of the same type of oil, a zinc-free mineral oil designed for gas and steam turbines with antioxidant additives, rust and corrosion inhibitors, and anti-foaming agents. According to the technical sheet, the RPVOT test of the new oil reports 1000 minutes.

Remember that the objective of the test is to force the oxidation of the oil.

RPVOT Regions

PART 1: Graph Analysis

Oxidation Induction Region, Gas Heating and Expansion

An initial period where antioxidants (phenolics, amines, phosphorus) neutralize free radicals (ROO-, O2-) formed by temperature (150°C) and Cu, H2O, and O2 catalysts. In this phase, the gas’s thermal expansion predominates, water evaporates, but oxidation is still low.

• Graphically: Low slope (<0.05 psi/min), stable pressure ~192 psi.​
• Entropy: minimum ΔS (+10-19 J/mol· K); under molecular disorder.
• Gases: Very few volatiles (residual H2O).
• Duration: ~35-100 min; longer in sample 2 (additives in good condition).

Region of Propagation of Quasi-Stationary Oxidation

The primary antioxidants are exhausted; the oxidative chain begins when free radicals attack the hydrocarbons of the base oil, initiating a sequence of peroxide formation, aldehyde formation, and acid formation, leading to varnish (degradation byproducts). In this phase, O2 is rapidly consumed.

• Graphically: Tipping point, average slope (-0.05 to -0.2 psi/min), drop ~192→175 psi.
• Entropy: High ΔS (+25-32 J/mol· K); Disorder increases due to the increase in molecular fragments of the hydrocarbon chain.
• Gases: CO, CO2, volatile hydrocarbons cause ~10-20 psi drop.​
• Sample 3 has a steeper curve due to the consumption or condition of additives.

 Region of Termination or Pressure Drop

The secondary inhibitors present in this oil, such as phosphates, recombine the remaining radicals, and in this phase, the oxidation slows, but the presence of residues is evident, which can increase viscosity and AN.

• Graphically: Low slope (<-0.2 psi/min), stabilization ~170 psi.
• Entropy: moderate ΔS (+16-22 J/mol· K); residual disorder.
• Gases: Minimal, but there is evidence of varnish or accumulated sediment.
• Sample 2 is more stable; this is evidenced by a flat curve.

Analysis by Sample

Sample 2 (more stable, total ΔP ~22 psi in ~300 min): Low degradation, additives are efficient and limit clutter.​

• Induction Region (t≈48-100 min, 192.1→190.5 psi): ΔS = +10.2 J/mol· K and phenolic antioxidants intact.
• Propagation Region (100-220 min, 190.5→182 psi): ΔS = +24.8 J/mol·K. With a moderate concentration of peroxide.
• Termination Region (>220 min, 182→170 psi): ΔS = +16.5 J/mol·K. Total: +51.5 J/mol·K.

Sample 1 (mean degradation, ΔP ~23 psi): a higher initial additive consumption.​

• Induction Region (46-90 min, 192→183 psi): ΔS = +14.7 J/mol·K.
• Propagation Region (90-230 min, 183→173 psi): ΔS = +27.1 J/mol·K.
• Termination Region (>230 min, 173→169 psi): ΔS = +19.2 J/mol·K. Total: +61.0 J/mol·K.

Sample 3 (the most degraded, ΔP ~25 psi): High early oxidation.​

• Induction Region (35-80 min, 192→167 psi): ΔS = +18.9 J/mol·K. The exhausted phosphate additive is exhausted.
• Propagation Region (80-260 min, 167→160 psi): ΔS = +32.4 J/mol·K. Increase in volatile compounds and acid production.
• Termination Region (>260 min, 160→155 psi): ΔS = +22.1 J/mol·K. Total: +73.4 J/mol·K.

PART 2: Relationship with Other Laboratory Tests

The relationship between RPVOT and other laboratory tests is very weak and unreliable, and it is unlikely to predict a low RPVOT result.

Following our case study, we have:

On the other hand, the repeatability and reproducibility of the RPVOT is low and this greatly reduces its reliability when making a decision in case of results that do not meet the expectations of the end user.

So, what laboratory analysis can be a good ally when performing the RPVOT? As Table 2 shows, traditional tests do not correlate with RPVOT results. However, there are two analyses that do show potential problems and can be used to work in conjunction with this test; Differential pulse voltammetry (DPV) is a powerful electroanalytical technique designed to measure the concentration of redox-active species with high sensitivity and resolution, often allowing the detection of analytes at concentrations as low as 10^-8 to 10^-9 molar. The next is FTIR, which allows identifying compounds in the fluid.

PART 3: Price Matters and Goes Hand In Hand with Innovation

Depending on the country and laboratory, the cost of an RPVOT analysis is usually between 150 and 650 $US, with an estimated turnaround time for results easily exceeding 10 days, not only because of the time it takes to test but also because samples may be on hold. If it is simply to comply with the oil manufacturer’s recommendations or the turbine OEM’s warranty, the end user will pay little attention to the result or the graph in the report.

The analytical tools available to us today have facilitated many aspects of our lives, including data analysis and the detection of patterns that help us identify future behaviors. Within the scope of RPVOT, in mid-2024, I was fortunate to develop an analytical tool that I called RPVOT_[SYN]. Its function basically aims to minimize two key aspects of this laboratory test: time and cost.

Thus, by applying a Bayesian analysis, it is possible to determine with a degree of confidence greater than 75% what the expected result of the RPVOT of a turbine oil will be. For a fraction of the cost of the laboratory test and in less than 6 hours, you get a result very similar to this:

RPVOT_[SYN] : 180 – 200

Some Recommendations: What Is Important When Receiving the RPVOT Results?

We said before that the numerical result matters, but it is not the only thing that should matter in this test. If you work with a respectable laboratory with sufficient technical knowledge, they will be able to report the graph (even in csv format) in such a way that it can be analyzed from the point of view of their regions.

Remember, the regions say much more than the simple numerical result. Cross-referencing this information with FTIR and DPV can yield much more insight into the condition of the lubricant. And it can help plan, in conjunction with other tests, a possible intervention on the lubricant, whether it’s a partial or complete change, or finding a solution due to problems related to the lubricant’s chemistry.

Don’t miss the opportunity to get the most out of an analysis of this caliber; it can tell you a lot about the condition of your lubricant.

The EGR (Exhaust Gas Recirculation) system recirculates a fraction of the exhaust gases into the intake manifold to lower combustion temperature, reduce NOx emissions, and, in some cases, improve fuel consumption in both diesel and gasoline engines. This recirculation of hot gases introduces more soot, acids, and contaminants into the lubricant, accelerating its degradation and reducing engine life if not controlled with proper design, oil, and maintenance.

In diesel engines, the EGR valve diverts a portion of the exhaust gases before or after the turbocharger. It reintroduces them, often after cooling in an exchanger, into the intake to reduce effective oxygen and flame temperatures, thereby decreasing NOx formation.

The valve is governed by the ECU (Engine Control Unit) based on load, temperature, and rpm, opening primarily at partial loads and closing at cold idle or full load.

In gasoline, EGR can be hot or cooled. It is used to reduce part-load pumping losses and to lower NOx emissions. By recirculating inert gas, the valve can be opened wider at the same torque, reducing intake vacuum and improving efficiency. In GDI (Gasoline Direct Injection) and turbo engines, external or internal EGR (through valve overlap) is adopted to control combustion temperature and mitigate knock.

The latter refers to reducing the mixture’s tendency to detonate spontaneously before or just after the spark, a common problem in high-compression gasoline engines. Recirculating inert gases lowers the combustion temperature and slows the reaction rate, reducing the likelihood of knocking and allowing greater advance or load without damaging the engine.

Typical EGR Failure Modes

No precise statistics indicate exact percentages of EGR valve failure modes. However, there are two failure modes that, depending on the engine type (diesel or gasoline) and the OEM, account for a high percentage of total failures. (1)

Open seized EGR valve ~ 65%

Excess recirculated gases, loss of power, smoke, possible increase of soot in the manifold and in the combustion chambers of the engine cylinders.

When the EGR valve is seized open, it recirculates excess exhaust gases (with soot and contaminants) into these chambers, diluting the fresh mixture too much, reducing power, and causing incomplete combustion that generates more soot accumulated on the walls of the chambers, pistons, valves, and intake manifold.

Excess soot in combustion chambers tends to raise temperatures, increase wear, and complicate gas flow in subsequent cycles, aggravating failures such as compression loss or excessive emissions.

In open-valve failure, the vicious cycle of soot obstructing the intake reduces airflow, forcing more fuel to compensate, increasing consumption and emissions. In contrast, NOx is reduced by excessive dilution. In diesel engines, it triggers frequent DPF regeneration due to low soot levels.

DPF regeneration is the automatic or manual cleaning process of the Diesel Particle Filter, which burns the soot accumulated in its ceramic channels to prevent clogging and keep emissions low, converting carbon particles into CO₂ and ash at temperatures of 500-600°C.

Closed seized EGR valve ~ 15%

High NOx, possible detonation, higher temperatures, and risk of thermal damage to metal components.

In a closed-valve failure, the ECU detects high NOx and enters safety mode (reduces power, limits rpm), accelerates piston thermal wear, and saturates the DPF due to insufficient dilution. In this failure mode, lubricating life degrades dramatically, reducing TBN at an accelerated rate.

In some post-2021 diesel engines, or Boxer-type engines with high-pressure EGR, a mixture of soot and light-fraction oil vapors from the combustion chamber forms dense sludge in the manifold, valve, and cooler, thereby aggravating EGR-system failures.

EGR failure identification opened by oil analysis

The failure mode of EGR valve seized open, excess recirculation introduces high volume of soot (carbon particles) and acidic contaminants (SOx, NOx dissolved) to the crankcase via blow-by, drastically raising the soot content (>2-5% wt), increasing viscosity and TAN (total acid number), and lowering TBN (total basic number) in an accelerated manner. This indicates incomplete combustion and dirt in intake – combustion chambers; oil detergents-dispersants become saturated, forming sludge and accelerating abrasive wear (Fe, Al, Pb high in iron, aluminum).

Closed EGR failure identification by oil analysis

In the closed-seized EGR valve failure mode, combustion is hotter. It generates greater oxidation/nitration of the oil, reflected in a high oxidation index (IR spectrum >30 Abs/cm), an increase in viscosity is evidenced by polymerization, and TBN is depleted by neutralization of the excessive load of NOx acids.

On the other hand, rising temperatures cause thermal wear due to thermal expansion. Increasing wear is measured by metal loss (chromium and iron from bearings/pistons). A low soot concentration (<2%) may be observed, possibly due to ECU injection adjustments that increase fuel dilution. In some cases, this dilution can cause the absence of soot despite high temperatures.

Global market for the sale of used and new cars

There is no accurate global data for annual sales of new and used cars worldwide. On the other hand, used markets vary significantly by region and country, and there is no unified source like OICA for used. But the data shows a worldwide trend where the sales of used cars exceed new cars by at least 3:1, according to the estimated data:

According to the data, it is very likely that, at some point, you will have to buy a used car; specifically, there is an 80% chance (equivalent probability) that you will do so.

At the same time, you’ve likely never done an oil analysis on your car. But if you’ve paid some attention to this article, chances are you’ve understood the value of a simple oil analysis—an analysis with a cost of nearly $30.

Over the years, I have helped several friends choose a second-hand car. Where the exterior can be very presentable, clean and very well maintained; But inside, where many times not even today’s computers can identify the problem unless it is very advanced states, a simple analysis of the oil in service can be the difference between buying a problem or making sure that the car’s engine – the heart of the machine – is working properly.

“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 remains one of the main causes of premature failure in lubricants in service in turbines and compressors, and with a highly harmful effect on the mechanical components of the system.

It is estimated that the failure of a gas turbine caused by the presence of varnish has an estimated average cost of US$760 per hour, which includes the costs for unscheduled shutdown, the removal of the varnish present, and the replacement of at least 10% of the oil in service.

Varnish can quietly drain hundreds of thousands of dollars before a single visible failure occurs.

Although varnish is not a new problem, the increasing number of plants and machinery affected by it makes it clear that, on the one hand, analyzing oil in service is becoming increasingly necessary. On the other hand, laboratory analytical methods must be accurate to identify this problem in time.

Why Standard Varnish Tests Often Miss the Problem

At the commercial level, the methods for determining the presence of varnish have been standardized and it is very common for lubricant analysis labs to offer a package that usually includes at least the following test: determination of suspended solid particles ASTM D7647 (reported with ISO 4406), FTIR ASTM E2412, acid number ASTM D664/974,  ASTM D445 viscosity determination, ASTM D6304 water determination, ASTM D5185 element determination, ASTM D6810 organic additives determination, and ASTM D7843 patch colorimetry membrane MPC.

In many cases, all these values may be within an apparent normality; however, the internal components of the machine can show a completely different reality that becomes evident when the temperature of the oil in service shows an erratic and increasing trend. On the other hand, during general maintenance, the machine reveals an excessive amount of material adhered to the metal surface, which is varnish.

How is it possible that the oil shows no signs of degradation or physicochemical changes, at least at the surface level, while internally the components of the machine show clear signs of those degradation by-products called varnishes?

Are current laboratory analytical methods not well defined and have standardization undergone accepted by both end users and machinery manufacturers?

The above graph clearly shows the reality of many machines that, under the magnifying glass of standardized analysis for the determination of varnishes, do not show signs of the presence of these by-products. At the same time, the internal components tend to fail for this reason.

Anti-Varnish Products Market Trend

Since 2000, at least 16 different types of fluids have been developed and put on the market, specifically designed to reduce or eliminate the effect of varnish in gas turbines and compressors, depending on the type of definitions and technical terms. This figure includes both lubricants with advanced formulations and specialized cleaning products.

Examples of these fluids include:

• Group II base oils with improved additives for solubility and varnish control.
• Varnish remediation systems that remove varnish precursors in the oil.
• Turbine oils with proprietary additives.
• Polyglycol lubricants, which do not form varnish and remove the existing varnish in compressors.
• Specific cleaning fluids that keep degradation byproducts and varnish precursors in suspension.
• Synthetic and mineral oils with anti-varnish
• Lubricants with state-of-the-art additives.
• Cleaning products for varnish flushing in lubrication systems.

In many cases, the development of these fluids has been driven by the increased operational demands of machinery, higher oil temperatures, and the need to extend both lubricant and equipment life.

While in others it is mainly due to changes in the formulation of base oils, especially the shift from Group I oils to Group II oils with lower solvency, this facilitates the formation of varnish because these oils tend to keep the polar substances less dissolved as degradation by-products and responsible for the varnish, causing it to fall into the components.

On the other hand, there are factors specific to the end user:

• There is Greater Industrial Awareness: industry is increasingly recognizing the detrimental effect of varnish and the need for proactive (not just corrective) strategies for its prevention and removal.
• Increase in Varnish Reported Failures: Leading lubricant analysis laboratories in the industrial market report an increase in the presence and recognition of varnish-associated problems of around 600% over the past decade, especially in sectors such as power generation and oil & gas.
• Demand for higher Availability and Reliability: The need to maintain operational efficiency in critical turbomachinery motivates operators to invest in advanced lubrication and varnish management solutions. 

Case Study: A Typical Situation

The most typical situation is one in which the client performs an analysis with a relatively adequate frequency, quarterly, and the results of the standard analysis are reported as normal:

However, after a few months, the customer observes an abnormal trend in the temperature of the oil, with clear signs of erratic behavior and a potential internal problem.

On the one hand, the temperature has increased by 7°Celsius compared to usual. On the other hand, a marked trend of sawteeth shows an anomaly that coincides with the presence of polar elements adhered to the surface of the components.

When the scheduled shutdown arrives, the presence of varnishes in the system is evident; the seals, the cooling system, and parts of the tank show this presence. However, if the system shows an imminent presence of this type of by-product, what is the reason why there are no traces of these in the lubricant, and on the other hand, what improvements can be made at the laboratory level to identify this presence in advance?

Can traditional laboratory tests determine the presence of dissolved varnish?

Laboratory Analytical Improvements

The traditional or standardized methods of commercial laboratories for the determination of varnishes in lubricated systems do not cover the entire spectrum; they aim rather at those varnishes that precipitate and not those that tend to remain in solution.

In many cases, this condition of degradation byproducts is precisely due to the application of at least one of these 16 different types of fluids developed in the last 25 years; In any case, the system maintains the presence of by-products that at some point will tend to adhere to the metal parts of the system, causing in many cases production losses and unscheduled stoppages.

Let’s first analyze color. On the left, the oil before service, and on the right, after two thousand hours in service.

Let’s look at this same color change under the magnifying glass of the absorbance spectrum:

The color is an indicator of a chemical change in the oil that physically affects the molecular structure. In this case, the change is both measurable and quantifiable, as we have a starting point and a point where the oil is after a few hours of being in service.

New compounds formed. It is evident that the change in color indicates a change in the chemistry of the lubricant, which is not detectable by traditional means, but is detected under an advanced FTIR analysis, the same that is used with little judgment to measure the oxidation of an oil of this type.

That color is due to the formation of intermediate compounds such as alcohol, aldehydes, and others. On the other hand, the loss of anti-foam characteristics of the lubricant is evident.

Concentration of Organic Additives. The most accurate technique for the determination of this type of additives is by Differential Pulse Voltametry (DPV). This technique enables the clear determination of low concentrations or incipient changes that other techniques cannot detect.

The Rosetta Stone. Egyptian culture could not have been discovered had it not been for Champollion being able to decipher the Rosetta Stone. In a simile, temperature plays a key role in this entire analysis and is the missing piece that, in many cases, can help to understand and determine the present state and future condition of an oil that has dissolved degradation byproducts, varnish precursors.

We thus have a combination of three laboratory analyses that determine the condition of the oil at a specific time and the temperature, which tells a much longer story and, once modeled, serves to determine the future condition of the oil.

Achieving the modelling of temperature data, without having known any failure, can be a titanic task. However, applying mathematical models such as Time Series Analysis or Neural Networks allows us to predict a future state based on the condition of the oil in service. The next step is to create connectivity between the lab and the machine, using gateways such as IoT platforms or directly from the Scada system.

When labs connect directly with machines, oil analysis shifts from reactive testing to true failure prediction.

Integration allows for determining not only those potential lubricant failures but also serves as a trigger that indicates the best time to take a sample.

For many industrial lubricant analysis laboratories, integrating operational data has become a reality that enables the prediction of potential lubricant failures, as illustrated in this case.

The Industry 4.0 trend has knocked on many doors, will it be the case that commercial laboratories open a window and breathe this air?

Will end users be able to allow access to their data to improve the service?

As an end user of turbines or compressors, would you be willing to take the next step and start a new type of analysis that helps you identify problems early?

In industrial maintenance and reliability engineering, few concepts are as intuitively powerful as the Pareto Principle—also known as the 80/20 rule. Originating from Vilfredo Pareto’s observations of wealth distribution, this principle has evolved into a universal heuristic for identifying and prioritizing key contributors to outcomes in various systems.

When applied to oil analysis and lubrication in industrial sites, the Pareto Principle becomes a strategic lens for uncovering the few root causes that contribute to the majority of lubrication-related failures, inefficiencies, or costs.

This article explores how the 80/20 rule can be harnessed to improve lubrication practices, interpret oil analysis data more effectively, and drive proactive maintenance programs that prevent catastrophic failures and optimize equipment uptime.

Understanding the Pareto Principle in Maintenance Context

The Pareto Principle suggests that 80% of the consequences come from 20% of causes. In maintenance, this often manifests as:

• 80% of downtime comes from 20% of the assets.
• 80% of failures arise from 20% of the failure modes.
• 80% of lubrication problems stem from 20% of systemic causes.

It’s not always a perfect 80/20 split—it might be 70/30, 90/10—but the essence remains: a minority of inputs drive most results.

The Relevance of Pareto in Lubrication and Oil Analysis

In lubrication management, problems such as excessive wear, contamination, oxidation, or varnish are typically not evenly distributed across all assets. Often, a handful of machines or poor practices are responsible for most lubrication issues.

By applying Pareto thinking to oil analysis reports and failure data, organizations can identify:

• Which machines cause the most oil-related problems.
• Which contaminants or degradation modes (e.g., water, particles, oxidation) are most responsible for wear.
• Which human errors or process gaps (e.g., over-greasing, delayed oil changes) create recurring lubrication issues.

Common Lubrication Problems on Industrial Sites

Before diving into Pareto-based solutions, let’s categorize common lubrication problems observed in industrial environments:

Contamination

• Particulate contamination (dust, wear particles)
• Water contamination (condensation, seal failures)
• Cross-contamination (mixing incompatible lubricants)

Degradation

• Oxidation due to thermal stress or long drain intervals
• Thermal degradation due to temperature
• Varnish formation in turbine and hydraulic systems
• Additive depletion in modern synthetic oils

Human and Procedural Errors

• Improper lubricant selection
• Over or underlubrication
• Lack of lubrication schedules or documentation
• Incorrect oil sampling methods, leading to misleading analysis

Equipment Design or Condition

• Poor seals or breathers
• Inaccessible lubrication points
• Aging machinery with high internal clearances or hotspots

These problems create a web of interlinked failure causes—but applying a Pareto analysis can clarify which issues deserve immediate, focused attention.

Applying Pareto Analysis to Oil Analysis Data

Oil analysis laboratories and CMMS (Computerized Maintenance Management Systems) often collect thousands of data points. The challenge is prioritizing corrective actions based on this overwhelming data. Here’s how the Pareto Principle helps.

Step 1: Aggregate the Data

Collect a year’s worth of oil analysis reports across all critical assets. For each sample, extract flagged issues, such as:

• Particle Count > ISO 18/16/13
• Water Content > 500 ppm
• TAN > 2.0
• Wear Metals above alarm thresholds

Step 2: Categorize Failures

Group issues into categories:

• Wear (Iron, Lead, Copper)
• Contamination (Water, Dirt)
• Degradation (Oxidation, Nitration)
• Additive Depletion (ZDDP, Ca/Mg levels)

Step 3: Quantify Occurrence

Tally how many times each issue occurred. You may find, for example:

• % of reports show particle contamination
• % shows elevated wear metals
• % shows high oxidation
• % shows water ingress

Step 4: Visualize with a Pareto Chart or Table

Create a bar chart from most frequent to least frequent issue, with a cumulative percentage line.

This visualization immediately shows you that 80% of your oil analysis alerts may stem from just 2 or 3 primary causes.

Step 5: Target the 20%

Now focus efforts on reducing these top causes by investigating:

• Source of contamination (Are breathers effective? Is filtration adequate?)
• Lubrication schedules (Are intervals too long?)
• Training gaps (Do technicians know how to sample or top off correctly?)

Real-World Example – Pareto in Action

Steel Manufacturing Plant, Case Study

At a steel plant running 250 hydraulic systems, the maintenance team struggled with chronic equipment downtime linked to hydraulic fluid failures. They implemented a two-year oil analysis program and categorized around 1000 samples, 2 samples per asset per year.

One of the first problems the site must address is the report from the lubricant analysis service provider. The report does not identify the type of failure the oil is suffering from; simply, like most providers, they flag a value that is above normal or outside the limits and mention said value in the report.

Thus, all the results from the nearly 1,000 samples had to be uploaded to an expert system we designed together with the support of state-of-the-art data analysis tools. After data processing and correct application of the fundamentals of oil analysis, the results were as follows:

• 38% flagged for particulate contamination
• 24% for water ingress
• 9% for oil oxidation
• 7% for oil thermal degradation
• 8% for viscosity improver modifier degradation
• 14% excessive wear

Many of the samples shared at least two of the identified conditions, in some cases due to the creation of a vicious cycle between them. For example, the presence of water generates wear, and wear can generate more wear.

Applying the Pareto rule, the three main factors that affect the availability of the plant’s hydraulic systems are particulate contamination, water ingress, and excessive wear.

If this analysis were to stop here, and this is what happens in 90% of cases due to a lack of application of knowledge of the fundamentals of lubrication, the first thing that would be done would be to work on improving the filtration, handling, and storage methods of the plant, which is not bad and would have an immediate impact on the degree of cleanliness of the oils.

At the same time, water ingress, in this case and in many systems, is due to inadequate vent points and seals, which leads to water ingress into the system and consequently to the lubricant.

Let’s take a closer look at particulate contamination for a moment. Let’s look at this from several perspectives:

• Lubricant oxidation
• VI improver additive loss
• Thermal degradation

In all three cases, the result is an increase in the concentration of soft solid particles present in the oil.

And yes, the answer, dear reader, is in that word that has gone unnoticed before your eyes, soft, which is not hard, is not abrasive. The method used for particle counting must be appropriate, eliminating organic compounds and water. Once this first problem has been overcome and the count verified, it is necessary to determine what type of particles are present in the oil.

Thus, having corrected the particle counting method, changed oil analysis providers, and analyzed a set of samples under a microscope, it is evident that solid but soft particles are present in higher concentrations than abrasive ones. These soft particles do not have an abrasive effect on components and do not cause wear. They do reduce heat transfer, increase oil temperature, and induce premature oxidation.

Actions Taken:

• The 4 types of hydraulic oils used in the plant are replaced by others with better IV characteristics and a slightly higher working temperature range.
• Added breathers to some units
• Trained technicians in clean oil handling

Results After 6 Months and 220 Samples

The results in just six months show that 69% of the samples are under perfect conditions, compared to the previous situation where almost every sample has been flagged for a reason.

The Pareto principle is a tool used to identify those situations that cause the most problems. However, its applicability must be based on the context in which it is used; in this case, a simple analysis of the fundamentals of lubrication and oil analysis.

Lubricating oils play a critical role in rotating machinery’s efficient and safe operation. However, these fluids are exposed to various factors that can deteriorate their performance over time. Two of the most common degradation mechanisms are oxidation and thermal degradation, each with distinct causes, effects, and failure modes.

This article explores the differences, from a chemical point of view, and the physical changes between the two processes, their consequences on machinery, and their early identification.

On many occasions, both terms are misused as synonyms when in reality, the processes are entirely different.

Oxidation: The Chemical Chain Reaction That Starts It All

Oxidation is a chemical process in which oil reacts with oxygen present in the air. The concentration of the air in the oil varies depending on variables such as flow rate, viscosity, or temperature. The percentage of air in oil, for example, in the return line of a gas turbine tank can be between 6 and 12%, while that same oil in the bearing area can have an air concentration of less than 2% [1]

Oil oxidation in the presence of oxygen is a complex chemical process that involves a series of chain reactions. Additionally, these reactions can be catalyzed by heat, pressure, metals, and contaminants.

Factors that influence oxidation:

• Temperature: At higher temperatures, the rate of reaction with oxygen increases exponentially.
• Presence of catalyst metals: Iron and copper wear particles can accelerate oxidation.
• Exposure time: The longer the oil is in contact with the air, the greater the oxidation.
• Working load: In gas turbines and engines, high load generates temperatures that can induce premature oxidation.

Oxidation follows a clearly defined process where the following stages are identified:

Initiation

The process begins with the formation of free radicals in the molecules of the base oil. This can occur for various reasons, including time, improper storage, and more aggressive factors in the machine.

Propagation

Free radicals react rapidly with molecular oxygen (O2) to form peroxide radicals (ROO•).

Degradation of Hydroperoxides

Hydroperoxides (ROOH) are unstable and break down thermally or catalytically into organic acids, aldehydes, and ketones that can be monitored by advanced analysis.

Formation of Insoluble Compounds

Over time, radicals and secondary oxidation products (such as aldehydes, ketones, and carboxylic acids) react with each other to form insoluble polymers, often called varnish and sludge. These reactions are known as cross-polymerization and result in high molecular weight compounds.

• Varnishes: Semi-solid and brittle compounds that adhere to metal surfaces.
• Sludge: Sticky rubber-like materials that clog filters and ducts.

Byproducts such as aldehydes, ketones, and carboxylic acids can be determined and quantified long before they impact the acid number (AN), as in many cases, this can be a late indicator of chemical reactions in the oil.

On the other hand, although it may seem contradictory, one of the indicators of lubricant oxidation is precisely the determination of the degree of oxidation by FTIR. In the oxidation analysis of lubricating oil by FTIR (Fourier Transform Infrared Spectroscopy), the degradation of the oil is mainly measured in the absorption region corresponding to the carbonyl groups (C=O), which appear when the oil is oxidized, region: ~1,710 cm⁻¹ (±10 cm⁻¹).

Other bands that may indicate secondary oxidation:

3,400 cm⁻¹ → Hydroxyl (-OH) groups of advanced oxidation products.

1,230 – 1,150 cm⁻¹ → Oxidized esters and additive degradation products.

The figure above shows that the variation in the oxidation of turbine oil is minimal after having been in service for about 12000 hours, with a variation of less than 3% in oxidation.

Thermal Degradation: When Heat Breaks Oil at the Molecular Level

Unlike oxidation, thermal degradation is when base oil molecules and additives are chemically broken down or transformed due to high temperatures or constant exposure to medium-high temperatures without oxygen. This happens when temperatures exceed the thermal stability of the lubricant, causing the breakdown of molecular chains and the formation of undesirable byproducts.

Factors that influence thermal degradation:

• Temperature spikes: Contact with surfaces that are at a high temperature (such as bearings).
• Extreme workload: Natural gas engines and turbines operating at full capacity for an extended period of time generate excessive heat.
• Oil residence time: The longer the oil is exposed to extreme heat without proper cooling, the greater the degradation.

Chemical Mechanisms of Thermal Degradation

At high temperatures, the chemical bonds in the base oil molecules can break; this phenomenon is known as cracking, which leads to two factors in parallel.

Homolytic rupture

C−C or C−H bonds break down by generating free radicals:

Additive breakdown

Certain additives such as antioxidants, antifoam, and dispersants, among others, have thermal limits. At extreme temperatures, additives degrade, forming inactive compounds or even secondary compounds that contribute to the formation of deposits.

Thermo-oxidation

Also, at high temperatures, a phenomenon called Thermo-oxidation. Although oxidation usually requires oxygen, at very high or prolonged temperatures, oxidation can occur without the need for atmospheric oxygen due to the internal breakdown of hydroperoxides (ROOH):

The figure above shows that the variation in the oxidation of turbine oil is about 7% after having been in service for about 2500 hours. However, due to a hot spot effect on the turbine, the ester-based defoamer additive drops drastically below 30% of the initial concentration, causing a Microdieseling problem in the oil.

Oxidation Failure Modes

One of the primary debates in both cases is oil filtration. Inevitable degradation byproducts can be removed using filtration technologies. However, can the source of the byproduct generation problem be eliminated? In many cases where thermal degradation is the primary failure mode, a filtration system will systematically remove internally generated byproducts, but will it solve the root cause of the problem?

[1] JAlarcon Turbine Oil Analysis 2024

Microdieseling is a term often associated with changes in lubricant color and the formation of harmful byproducts within lubricated systems. It occurs when microbubbles of air (smaller than 5 microns) in the lubricant transition from a low-pressure environment to a high-pressure one, triggering implosions.

The size of these bubbles plays an important role, as these micro-explosions not only degrade the oil but can also damage machinery components where they occur.

The process of how the compression of air bubbles implodes in the high-pressure zone is very well defined, and it is possible to calculate, at least theoretically, the temperature at which this phenomenon can easily exceed 1000°C.

Microbubbles imploding at over 1,000°C cause more damage than meets the eye.

The best-known case of this phenomenon is OceanGate in 2023, which had to withstand around 4000 atmospheres of pressure when imploding.

Lubricated systems such as turbines or hydraulic systems should suffer from this phenomenon at some point in their life in service, since they have air in the lubricant due to the operating conditions. A new turbine oil has around 8% air, while an oil in service in areas such as the reservoir can reach a concentration of 18%.

Microdieseling: cause or effect?

In lubricated systems such as turbines or hydraulics, Microdieseling is the effect caused by the partial or total degradation of an additive, a very special one…

Let’s look at a power generation plant case study:

Day 1: Everything was going well!

A high percentage of gas turbine oils work with groups I and II, mainly because of the cost-benefit ratio these provide. These oils can reach specific areas of high temperature that exceed 100°C. In these areas, the lubricant suffers a lot, but we are talking about thousands of liters in the system—8, 12, or 20 thousand liters. In this case, the temperature and temperature variations do not have an immediate effect on the oil; it takes some time.

Day 2: Change the filters!

For some reason, the filters of both turbines were clogged a couple of days apart, a strange coincidence, of course.

Something is already out of the ordinary, and the maintenance team has begun to pay attention to this situation. During their research, they observed that the temperatures of both oils have increased in recent months, still below the recommended limits to put on standby the group but above normal. Something is happening, it’s already obvious. After a more in-depth check of the lubrication circuit, it was observed that there is also a material similar to that of the filters in other areas of the system, especially in low areas, in discharge pipes, and in the tank.

Day 3: The oil goes dark!

For some reason, the oil began to lose the typical color it had to acquire an increasingly darker tone. The images below show the color difference between both oil samples.

Laboratory analysis showed an advanced degradation (AN) problem.

Day 4: Filtering the oil is the solution!

The matter found in the filters and the low and cold areas of the system are lacquers or sludge, and the presence of varnishes in other areas was also evidenced. The decision was immediately made to install a varnish filter by choosing a supplier who ensured their system could remove those unpleasant byproducts without any problems.

The lab reports didn’t reveal anything unusual – you can’t ask for much more for a $75 analysis – so no further investigation was done. After 3 months of filtration, the consumption of filters from the system and organic matter removal equipment (varnishes, sludge, etc.) exceeded the 5-year filter budget.

Turbine Oil Temperature

Day 5: Change of supplier and imminent stoppage!

Degradation byproducts continued to clog the filters, and the filtration system was replaced with another supplier. The problems remained, and the shutdown of both turbines was imminent. The costs of changing the oil, not only the volume but also the logistics of the change, greatly impacted the plant’s budget.

Due to the number of byproducts present, chemical and physical flushing had to be done on the entire system. In total, there were 16 days of unscheduled stoppage. Imagine the production losses!

Advanced Analysis Techniques for Identifying Microdieseling

The trend towards a dark color of turbine oil is mainly due to an air compression problem in high-pressure areas, yes, Microdieseling!

Air is usually just one piece of this reaction puzzle, so blaming excess air in the lubrication system alone is not the solution.

Air in the oil is a piece of the puzzle, but not the whole story.

The vast majority of turbine mineral oils have in their formulation a modified silicone additive in a base that can be ester or ether, whose primary function is to break the wall of the bubbles, minimize their presence, and eliminate the accumulation of air bubbles. This molecule comprises a silicone backbone (polydimethylsiloxane) with branches or modifications of polyether or polyester side chains.

This hybrid structure allows the compound to retain the unique properties of silicones (such as low surface tension and thermal stability) while becoming more compatible with the hydrocarbon chain. Compared to traditional silicones, the modified one offers better compatibility at a lower concentration, it is dissolved, which makes it present throughout the fluid. This makes it preferable when robust defoaming performance is needed without compromising system stability and uniformity.

Modified silicone additives are the hidden heroes—and villains—in turbine oils.

But like any compound, this one is also susceptible to degradation. The main cause of degradation is due to the reduction or loss of its thermal stability caused by extreme temperature peaks.

Their degradation generates fragmented polymers, esters, aldehydes, organic acids, and very low concentrations of silicates. One of these elements is the key to identifying Microdieseling problems.

Microdieseling Analysis, Control, and Recommendations

Traditional analyses on turbine oils cannot identify this failure mode until it is well advanced. In general, the problem is evident when the concentration of the Acid Number (AN) exceeds >3 times that of the original oil, when the color gives away the problem, with an increase in temperature, or when the filters are changed more frequently.

Late tests, such as the determination of varnishes, also known as MPC, are very close to the end of the P-F curve of this type of failure. On the other hand, the concentration of silicates or silicon oxides is so small that it goes unnoticed by atomic emission spectroscopy, so the silicon element is not an indicator of failure.

The only way to identify both the concentration of this additive and its degradation and the formation of byproducts is achieved through the analysis of Fourier Transform Infrared Spectroscopy (FTIR). This is the only laboratory technique that allows the chemical cause of Microdieseling to be accurately identified.

However, this analysis requires particular knowledge and a lot of experience in the FTIR technique applied to industrial oils, only a couple of laboratories and individuals worldwide can determine this problem, so it is very important to choose your lubricant analysis provider wisely.

One last comment: If your oil is suffering from a Microdieseling problem, do not waste time looking for the source of air entry into the system. Identify the area or hot spots that have caused the degradation of the aforementioned additive; that is the real cause of the problem.

The global natural gas and landfill gas engine market is growing at annual compound rates of 6% to 8%, and these segments are expected to increase their share in the coming years, supported by technological advances and circular economy policies.

Currently, and depending on the source consulted, power generation with gas engines represents between 8% and 10% of global generation. In 2023 and part of 2024, natural gas generation accounts for approximately 60% of the market, while landfill and natural gas occupy 25% and 15%, respectively.

The natural gas engine market is consolidated and led by emission-efficient technologies, while landfill gas and biogas are gradually gaining traction as more sustainable options thanks to clean energy policies and increased investment in value-added infrastructure.

In regions such as Europe and North America, strict regulations and government incentives have accelerated the adoption of engine technologies that use landfill gas and biogas.

These gases, composed mainly of methane, are increasingly used for electricity generation in waste treatment plants and landfills. Companies are improving the efficiency of biogas-powered engines, although they face technical challenges, such as corrosion and lubricant contamination due mainly to the sulfur content in biogas.

Demanding Conditions Require High-Performance Lubricants

Lubricating stationary engines that run on gas requires specialized oils due to each type of gas’s combustion characteristics and contaminants.

Natural gas engines typically have cleaner and more stable combustion, which allows for longer intervals between oil changes and makes it easier to anticipate chemical changes that may occur. They require low-ash lubricants to minimize deposit formation and protect critical components such as valves.

On the other hand, these oils must have high thermal stability and resistance to oxidation due to the high temperatures and pressures in the engine.

Natural gas engines benefit from low-ash lubricants that protect critical components like valves.

The combustion gas can vary depending on the geographical location and conditions of production. However, it is mainly composed of methane and carbon dioxide and can contain pollutants such as hydrogen sulfide and siloxanes.

These contaminants generate acidic byproducts and abrasive particles affecting oil performance and lubricated components. For this reason, biogas engine lubricants need higher detergency and higher BN (Base Number) to neutralize acids and minimize the effect of corrosion.

As for landfill gas engines, the gas has a greater variability in its composition, with high levels of contaminants.

Oils must be able to handle a higher load of residues and offer a strong neutralization capacity for acidic byproducts. As with biogas engines, gas pre-treatment, and regular lubricant monitoring are crucial to maintain engine performance and protect internal components.

In all three cases, a proper in-service oil analysis program is vital in preventing failures and optimizing the engine’s life and the lubricant.

Tribological Conditions in Power Generation in Gas Engines

If you’ve been in the lubrication area for a while, you’ve probably heard of the Stribeck curve. The Stribeck curve is a fundamental tool in tribology as it describes how the coefficient of friction varies depending on lubrication conditions.

It was developed by Richard Stribeck in 1902 (although the same study is also attributed to Mayo Hersey in 1914) and is critical to understanding lubrication regimes in mechanical systems.

This curve includes three main regions:

1. Limit lubrication: when there is direct contact between surfaces due to a shortage of lubricant or an unfavorable lubricant condition.
2. Mixed lubrication: Some areas are separated by a lubricant film, while others have direct contact.
3. Hydrodynamic lubrication: the surfaces are completely separated by a fluid lubricant film.

In gas engines, this curve serves to optimize the selection and formulation of lubricants, as well as the determination of the wear suffered by the components under the effects of lubrication.

In these engines, factors such as viscosity, relative speed between components, and load affect the lubrication regime, influencing the efficiency and service life of the components.

In the limit and mixed lubrication regime, there is a high degree of contact between the moving parts of the lubricated system, which causes premature aging or wear of these components.

This can become evident when comparing major maintenance on these engines, where an engine running on landfill gas receives maintenance at half the hours that an engine running on natural gas does.

Let’s look at the Stribeck curve adapted to the three main types of gases. Natural, landfill, and biogas. What is the reason for this situation?

Let us ask the same question from a tribological point of view. What is the reason for an engine that works with landfill gas to work under a limited lubrication regime?

The lower values of the Stribeck parameter in a Landfill Gas engine are due to the particular characteristics of this type of engine and the conditions in which it operates, which affect the behavior of the lubricant and the frictional forces in the system. The main factors for the landfill gas engine to work at a limit regime are:

Composition of Landfill Gas

Landfill gas and biogas can have varying concentrations of contaminants, such as H₂Sand ammonia, which can affect operating temperatures and engine efficiency.

Operation at Low Load Levels

Engines operating at higher loads generate more heat, raising engine and oil temperatures.

Low Speed and Viscosity

Landfill gas may have less control in terms of operating speed and temperature, which can affect the oil’s viscosity. If the lubricant’s viscosity is lower than expected, the system tends to be closer to a limit lubrication state.

Impact of Particulate Matter and Contaminants

Landfill gas, a less refined fuel, can contain solid particles or water contaminating the lubricant. These impurities can alter the viscosity and ability of the oil to form a suitable lubricant film. As a result, the system could operate in a mixed lubrication condition or even at a limit, leading to a low Stribeck parameter.

Lower Operating Temperatures

Engines that run on landfill gas often fail to reach the optimal temperatures for oil operation, which can cause the lubricant not to flow efficiently, favoring limit lubrication. This can result in a higher coefficient of friction and a low value for the Stribeck parameter.

One of the products that are present in landfill gas is siloxanes. These organic compounds containing silicon atoms, oxygen, and alkyl or aryl groups (usually methyl) are primarily generated by the degradation of silicone-containing products.

Due to the high temperatures and pressure generated in the chamber during combustion, siloxanes are usually broken down into compounds such as formaldehyde, solid silicon oxides, and acids such as orthosilicic. The latter, when precipitating, forms highly abrasive particles that damage the components, causing accelerated wear.

Abundance Of Data to Generate Specific Knowledge

Due to the impact of lubricant quality on this type of engine, oil analysis programs are generally quite mature, and there is a lot of information, including operating data such as generated production.

However, it is important to know the composition of the engine components’ residues to determine the most common causes of accelerated wear caused by three-body abrasion.

The table below shows the average results of a set of residue samples collected near the pistons of different gas engines, analyzed by scanning electron microscopy (SEM).

The most common laboratory analyses are usually viscosity, AN, BN, ipH, water in ppm, and FTIR. Of these, the least exploited is the analysis of compounds by FTIR. A correctly performed analysis can determine the presence of siloxane-derived compounds that can become abrasive as the lubricant is in service. These values can be analyzed to anticipate wear problems in engine components.

On the other hand, the correlation between the hours in service of the oil and the formation of byproducts derived from siloxanes is almost perfect. This allows a more exhaustive analysis of the concentrations of formation of byproducts derived from siloxanes, both precursors of the formation of abrasive elements and those that promote the generation of acids.

One of the first theoretical lessons you learn when you dive into the world of lubrication and lubricant analysis is that temperature generally harms these compounds. This is true, and many trainers in the area have at least a few slides dedicated to this point in their presentations.

To further elaborate on the subject, the certifying bodies also include questions about the effect of temperature on lubricants and even refer to Arrhenius’ law, a mathematical expression used to check the dependence of the speed constant of a chemical reaction on the temperature at which that reaction takes place, described by the Swedish scientist Svante Arrhenius in 1889.

The most widely spread myth about the effect of temperature on lubricant based on the Arrhenius rule is that for every 10 degrees Celsius increase, the life of the lubricant is cut in half. To what extent is this true, and to what extent is it an echo of a past when the chemistry of lubricants was very different from today?

Of course, as do operating conditions, the operating environment, and previous storage, chemistry plays an important role. Therefore, to generalize a concept to the wide range of lubricants in service would be to assume that they are all the same, which is far from reality.

Within the industrial oils market, consumption is distributed, depending on the source consulted, as follows:

• Hydraulic oils: 35-40%
• Gear oils: 20-25%
• Compressor oils: 10-15%
• Turbine oils: 5-10%

These oils work at different temperatures depending on their application; the most common are:

• Hydraulic oils: The average operating temperature is between 45°C and 65°C. In well-designed hydraulic systems, the temperature is prevented from exceeding 80°C to avoid oil degradation and ensure oil performance.
• Gear oils typically work between 60°C and 90°C, although they can reach up to 100°C under high load or speed conditions. A good system design should keep the temperature below 100°C to prevent the lubricant from oxidizing.
• Compressor oils: The operating temperature varies depending on the type of compressor. Air compressors can be between 85°C and 100°C, while refrigeration compressors can be lower, around 50°C.
• Turbine oils: They usually operate from 50°C to 60°C. Although they can easily reach 90 °C in hot spots, this is only for very short periods of time.

On the other hand, another critical piece of information that is related to the consumption and service of these oils is the replacement rate of oils in the plant, which, in its simplest form, is calculated based on the following formula:

ε: Oil substitution or replacement rate (dimensionless)

Vs: Oil volume in service

Vk: Volume of oil stored

Rf: Replacement by year or management, which is ƒ operating conditions, the type of lubricant, operating environment, and the type of lubricated component 

The lower the ε, the higher the cost related to replacing the oil. This calculation allows inferring many conclusions when an audit of the plant is carried out. In my last audit of a production center with its power generation capacity, the typical values were as follows:

But let’s return to the subject of temperature. Of the oils mentioned above, the gear oils exert the greatest mechanical and temperature effort, and this article focuses on this set.

The temperature of the gears in this plant varies depending on production and time of year between 75°C and 87°C. The hypothesis raised is simple: does the operating temperature of oil have the expected effect based on the Arrhenius rule? In other words, does the temperature increase reduce the oil’s life?

The in-service gear oil is classified as an ISO VG 320 with the following characteristics.

1. Synthetic base
2. ISO L-CKD (ISO 12925)
3. New oil viscosity of 356 cSt
4. Viscosity Index 181
5. AN 0.99 mg KOH/g
6. Phosphorus additive 373 ppm

However, the main characteristics of this oil are easily identifiable by the infrared spectrum.

The FTIR identifies, for example, the antifoaming characteristics (of the base, not the additives), the organic antioxidants such as amines and phenols, esters, and other compounds, that will be the ones on which this analysis was carried out since the changes in these are precise, easily identifiable and, above all, an early indicator of the changes undergone by the lubricant that could have an effect of reducing its expected life.

Initial Results

The oil is subjected to the same environmental and operating conditions but at a temperature of 120°C or 248°F, and samples are taken over periods of time based on a frequency established based on the estimated service life.

The most important part of this process is determining the variable or set of variables that best indicate the remaining life or loss of lubricant characteristics that show a reduction in service life.

The variables most commonly applied by any commercial lab are viscosity, acid number, additives, and oxidation.

Which variable or variables in the table above should be used to determine if the life of the oil has been reduced by a percentage after being subjected to a temperature increase?

There are different points of view on which we should choose one over the rest. For example, the viscosity in sample five is 7.5% above and very close to the gears’ design limit. However, in this same sample, the AN barely exceeds 14%, oxidation is in a safe zone, and additives measured as phosphorus are 55%.

Except for viscosity, these results are lagging indicators of the lubricant’s condition since the main indicators are those that actually change and subsequently give rise to those in Table 1 in compounds measured using the infrared spectrum.

Why Test These Compounds?

In this case, there are no longer just four variables to consider; we are talking about twenty different types of compounds present in this oil that can be characterized, measured, and subsequently determined by their impact on reducing the oil’s service life.

These compounds tend to change and give rise to new compounds, which can be harmful in many cases. For example, carboxylic acids, when they reach a certain concentration, can be measured indirectly logically by AN or oxidation.

Alcohols

Degradation-derived alcohols in industrial lubricating oils are organic compounds containing one or more hydroxyl (-OH) groups bonded to carbon atoms. These alcohols are formed as intermediates during the oxidation and thermal degradation of lubricating oil under extreme operating conditions, such as high temperatures, the presence of oxygen, and mechanical stress.

Lactones

Lactones in industrial lubricating oils are chemical compounds formed as byproducts during oil degradation and oxidation. They are cyclic esters derived from carboxylic acids and alcohols. In the context of lubricating oils, lactones are mainly generated when the hydrocarbons present in the oil are oxidized, and closed-ring structures are formed.

• Effect of lactones on oils: The presence of lactones is an indicator of advanced oil oxidation. These compounds can contribute to the oil’s acidity and negatively affect its lubricating properties, which can lead to the formation of sludge, varnishes, and corrosion on metal surfaces.

Aliphatic Acids

Aliphatic acids in industrial lubricating oils are organic compounds made up of linear or branched hydrocarbon chains that contain a carboxyl (-COOH) functional group.

• Formation of aliphatic acids in lubricating oils: Lubricating oils are subjected to extreme conditions (temperature, pressure, and exposure to oxygen) that cause the breakdown of the hydrocarbon molecules present in the oil base. This degradation leads to the formation of oxygenated compounds, such as aldehydes and ketones, which can subsequently react to form carboxylic acids, including aliphatic acids.
• Effect of aliphatic acids on oils: Increased acidity. The formation of aliphatic acids contributes to the increase in the lubricating oil’s total acid number (AN). A high AN indicates that the oil has oxidized and degraded, which can lead to corrosion of metal surfaces and negatively affect the oil’s lubricating properties.
• Wear and corrosion: Aliphatic acids can be corrosive to the metal components of the lubricated system, accelerating wear and damage to the equipment.

Olefins

Olefins are unsaturated hydrocarbons formed when oil molecules break down due to extreme temperature conditions and mechanical stress, a byproduct of thermal degradation in industrial lubricating oils.

• How olefins are formed during thermal degradation: When lubricating oil is exposed to high temperatures, the chemical bonds of the hydrocarbon molecules (which form the base of the oil) begin to break. This process is known as “thermal cracking” and results in the fragmentation of longer hydrocarbon chains.

  During thermal cracking, molecular fragments containing carbon-carbon double bonds (C=C) are generated, resulting in the formation of olefins (alkenes). Due to their double bonds, these compounds are more reactive, which can lead to more side reactions, such as deposit and sludge formation.

• Effects of olefins as degradation byproducts: Increased oxidation: The olefins generated are chemically more reactive and prone to oxidation, which can lead to the formation of additional oxidation products, such as acids, varnishes, and sludge. These oxidation byproducts can damage metal surfaces and negatively affect oil performance.

  Deterioration of oil properties: The presence of olefins and other thermal degradation products can change viscosity, decrease thermal and oxidative stability, and affect the oil’s lubricating properties.

Excellent Information. As An End User, When Do I Change the Oil?

It’s the million-dollar question! Let’s take it one step at a time.

First, what does an end-user in the maintenance area who struggles every day with spare parts, work planning, scheduling, orders, etc., do with this purely chemical information?

One of the most common questions in maintenance is precisely when to change the oil. Based on the analyses shown above, this same question was asked to 3 commercial laboratories.

Two of them agreed that the oil should be changed after the analysis of sample 5 based on the sample viscosity result. Most service providers have a +/- 10% limit for viscosity.

The third lab did it in sample four, based on the loss of phosphorus additive.

Draw your own conclusions from these recommendations.

Second, is traditional oil analysis useful? Of course! And a lot. The problem is that neither end users nor service providers are willing to spend time identifying that red line at which oil should be changed because its properties have been compromised or because degradation from that point will become exponential.

As has been observed, finding the lubricant failure mode is not easy, but it cannot go unnoticed. Otherwise, your lubricant condition monitoring program has not reached the degree of maturity it should and is not contributing to the maximization of the reliability and availability of plant assets.

From the third sample onwards, the degradation problem tends to become a non-linear growth trending to exponential.

The primary or early indicators of the thermal degradation reaction are closely related to those of traditional and purely commercial analysis. However, these chemical changes occur before they can be measured by a physical change, such as viscosity, for example.

In the case of service providers who perform the AN analysis manually, the problem is much greater. Assess whether it is worth working with these methods of low analytical quality.

However, we invoked the Swede Arrhenius, and his rule applied to lubrication, which must be taken with a grain of salt. We will have to see if we can apply it without putting data on the game table. Does the increase in temperature reduce the life of the oil?

In this case, you can check the characteristics of this gear lubricant above for this type of oil. The rule is not fully enforced. The temperature has increased 3 times 10°C, and even so, the oil was able to reach up to 35% above what was expected, and if we leave it in the hands of the service providers, it could reach 46%.

In a similar case, but for turbine oils, the results were the same: the lubricant could easily work ten degrees above without showing signs of degradation or loss of its remaining life.

Can Arrhenius’ rule be applied to lubrication?

Maybe, but not in all cases, and especially in new formulations where the lubricant’s nature makes it resistant to factors such as temperature or contamination.

How should I answer this question in a lubrication certification exam?

My friend! If you have come this far, I am sure you know the answer. But I advise you to answer yes or true.

What about the analytics service provider?

Value analytical quality above all else. Look for the supplier’s intensity (industrial or fleet), their expert knowledge, and how they can help you find the failure modes of your lubricants, not just issue a simple report. Choose wisely.