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.