Category: Lubricant Degradation

Lubricant Degradation

How do I know if Oxidation is occurring?

What Evidence is needed to prove that oxidation has occurred / is occurring?

However, understanding the oxidation process is just one part of the puzzle. When performing an investigation, we also need to know what factors or characteristics should be present. Additionally, we need to prove that their presence confirms our hypothesis of whether or not oxidation is occurring. This is where the line of evidence-based questioning plays a significant role.

When oxidation occurs, it is usual to see the presence of aldehydes, ketones, hydroperoxides, and even carboxylic acids. These can be confirmed using the FTIR (Fourier Transform Infrared test).

Typically, one will also find some deposits in the system. These deposits can be further characterized and tested to determine their nature using FTIR. Their presence, however, may be confirmed using the MPC (Membrane Path Colorimetry, ASTMD7843) test.

Identifying the presence of the deposits and/or the compounds listed above can lead to the conclusion that oxidation has occurred.

Another critical characteristic of oxidation is the depletion of antioxidants. This can be easily identified by utilizing the RULER® (Remaining Useful Life Evaluation Routine) test. This test quantifies the remaining antioxidants in the oil and gives the value for the amines and phenols (which is very important, especially in synergistic mixtures).

As such, one can detect the trend in the depletion of antioxidants and implement measures to prevent this before they become depleted.

The main tests to assist in determining the presence of Oxidation include:

RULER (Remaining Useful Life Evaluation Routine) levels less than 25% compared to new oil. This value represents the level of antioxidants in the oil. Hence, low levels indicate that the antioxidants are decreasing, possibly due to oxidation. This test can accurately give information on whether oxidation is currently occurring in the oil before deposits are formed.

An increase in acid number indicates the presence of acids resulting from oxidation. However, it must be noted that this change in acid number only occurs after oxidation has taken place. Hence this test is not a good indicator to determine if oxidation is occurring; instead, it is more definitive in letting us know that oxidation has already occurred.

Rapid color changes – darkening of the oil due to the deposits being present. While color is not the best indicator, in some instances, the darkening of the oil can provide a bystander to ask whether something is occurring in the oil. It is not a definitive test for the presence of oxidation.

FTIR test (Fourier Transform Infrared) for the presence of insolubles formed during the oxidation reaction. This can accurately determine the presence of any compound to assist us in determining whether oxidation is occurring.

MPC (Membrane Patch Colorimetry) levels outside the normal range (above 20). This lets us know that insoluble deposits are present in the oil. One must note that there may be instances where the deposits might not appear in the MPC test. As such, this should not be a standalone test to determine the presence of deposits.

RPVOT (Rotating Pressure Vessel Oxidation Test) levels are less than 25% compared to new oil (this is the warning limit). This is the industry standard, but this test does not have a high repeatability value in that if the same test were performed on identical samples, the values would be different. Additionally, the value (reported in minutes) is not easily translated into the environment of the components.

These tests provide us with the evidence we need to determine the presence of oxidation when performing the root cause analysis on the component’s failure.

 

Find out more in the full article, "Here's a more comprehensive approach to revealing oxidation root causes" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
April 13, 2024
Lubricant Degradation

How Can Oxidation Occur in Lubricants?

Typically, when an oil undergoes degradation, the first culprit to be blamed is oxidation. We often hear that the oil has oxidized, producing varnish, leading to its degradation. While this simple statement may seem plausible, it is not the only way oil can degrade.

If an oil has undergone oxidation, the real question we should be asking is not how much varnish has been produced but what caused the oxidation in the first place?

In this article, we will explore the various ways in which an oil can degrade via oxidation. However, as you know from previous articles, other degradation methods exist.

How Can Oxidation Occur?

Before diving further into the root cause of oxidation, one must first fully understand how oxidation occurs. When truly investigating a root cause for a failure, we should start with the question “How could?” rather than “Why?”.

This line of questioning heavily influences the answers. The “How could?” responses stem from a more evidence-based approach.

On the contrary, if we question “Why?” this is more opinionated and can mislead the investigation towards a biased opinion rather than the facts.

This leads us to the main question, “How can oxidation occur?”.

According to Ameye, Wooton, and Livingstone, 2015, oxidation occurs when there is any reaction in which electrons are transferred from one molecule. Ideally, in oxidation, during the initiation phase, free radicals are formed, which in turn produce more free radicals.

A free radical is a molecular fragment with one or more unpaired electrons which are accessible and can easily react with other hydrocarbons, as explained by Ameye, Wooton, and Livingstone, 2015.

After the initiation phase, which has the free radicals, the propagation phase follows, in which the antioxidants react with these free radicals to make them more stable. This is part of the reaction in which there is usually a drastic depletion of antioxidants or where the oil becomes sacrificial.

The antioxidants act as a barrier to protect the base oil from oxidizing. However, they can no longer protect the base oil once they become depleted. This leads to the termination phase, where the remaining free radicals attack the base oil.

As a result, this gives rise to the condensation phase, where we begin to physically notice the changes in the oil’s viscosity and the presence of insoluble by-products. These are the deposits that are known are lube oil varnish to some but can further be defined by their chemical composition.

Understanding how oxidation occurs can assist us in determining the root cause when an oil degrades. It allows us to identify the different stages to further help us determine if it is indeed oxidation that is occurring or not.

Find out more in the full article, "Here's a more comprehensive approach to revealing oxidation root causes" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
April 13, 2024
Lubricant Degradation

The Influence of Lubricant Selection on Degradation

Guidelines should always be followed when selecting a lubricant for a particular application. OEMs will have specific criteria ranges for specialty applications that must be satisfied. Some general guidelines which should be considered can be summarized in the table below based on the listed mechanisms above.

Based on the three listed mechanisms above, one can identify that choosing a lubricant can impact the type of degradation which occurs during its lifetime. As such, when selecting lubricants, it is critical to note their applications and the conditions they will endure.

Having a history of lubricant failures for particular equipment can also assist in this regard by informing users of past failure trends. Therefore, when selecting a lubricant, operators can be more mindful of the properties which should not be compromised during the selection process.

The process of troubleshooting degradation in lubricants has been covered in detail in the book, “Lubrication Degradation – Getting Into the Root Causes” by Bob Latino and myself, published by CRC Press, Taylor and Francis.

 

Find out more in the full article, "How lubricant selection impacts degradation and machine failure" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
February 24, 2024
Lubricant Degradation

Which Degradation Mechanism Is Affected?

My previous article published in Precision Lubrication covered six degradation mechanisms: oxidation, thermal degradation, microdieseling, electrostatic spark discharge, additive depletion, and contamination.

Upon further investigation, there are only three mechanisms where selecting the correct lubricant will impact the degradation mode. These are; oxidation, microdieseling, and electrostatic spark discharge. The properties of the lubricant can easily influence each of these degradation mechanisms.

When selecting a lubricant, especially for rotating equipment, one of the critical areas of importance is the performance of the antioxidants. When formulated, oils must be balanced to protect the components in various aspects.

Thus, some oils that boast a high level of antioxidants may suffer from low levels of antiwear, or these increased levels can react with other components to reduce the performance of the oil. During oxidation, antioxidants are depleted at an accelerated rate which can lead to lube oil varnish. Hence, the choice of lubricant can influence this degradation mechanism.

A good trending test, in this case, would be the RULER test to accurately quantify and trend the remaining useful antioxidants for the oil. This test can easily distinguish and quantify the type of antioxidant rather than providing an estimate of the oxidation, as with the RPVOT test.

It has been noted that oils with an RPVOT of more than 1000 mins have a low reproducibility value which can mislead users during trending of lubricant degradation. Corrosion inhibitors, not just antioxidants, have also influenced the RPVOT values. Thus, there are better tests for monitoring the presence of antioxidants and helping operators to detect the onset of possible lube oil varnish.

On the other hand, during microdieseling, entrained air can lead to pitting the equipment’s internals and eventually the production of sludge or tars depending on whether the entrained air experiences a high or low implosion pressure.

If bubbles become entrained in the lubricant and do not rise to the surface, this can directly result from the lubricant’s antifoaming property. The antifoaming property is essential when selecting an oil, especially for gearboxes. Typically, OEMs will have recommendations for their components that should be followed.

Another degradation mechanism that can be influenced by lubricant selection is electrostatic spark discharge. This mechanism occurs when the lubricant accumulates static electricity after passing through tight clearances. These then discharge at the filters or other components inside the equipment, providing sharp points or ideal areas to allow static discharge.

This is frequently seen in hydraulic oils due to the very tight clearances within the equipment. If fluid conductivity is above 100 pS/m, the risk of static being produced is reduced. Some OEMs also provide particular values the lubricant should meet for this property.

 

Find out more in the full article, "How lubricant selection impacts degradation and machine failure" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
February 24, 2024
Lubricant Degradation

Has the Lubricant Failed the Equipment, or Has the Equipment Failed the Lubricant?

Many lubrication engineers are faced with finding the most appropriate lubricant for an application. Therefore, they are tasked with selecting the “right” lubricant; subsequently, their decision can influence several outcomes.

A lot of the positive results are in the realm of extending the life of the oil, providing better energy efficiency, and even saving costs associated with downtime. However, can the choice of an “incorrect” lubricant impact its degradation process or lead to the presence of lube oil varnish?

Has the Lubricant Failed the Equipment, or Has the Equipment Failed the Lubricant?

Lubricants provide many different functions. These can range from moving heat or contaminants away from the components, minimizing wear and friction, improving efficiency, providing information about the status of the lubricant, or even transmitting power, as is the case with hydraulic oils.

There has been the time aged question of whether a lubricant fails the equipment or the equipment has failed the lubricant. If a deeper dive is performed into this question, one can deduce that lubricants are engineered to withstand particular conditions.

Once those conditions are met, lubricants can perform their intended functions. However, if the conditions exceed the tolerances of the lubricant, then one will notice a faster degradation. In this case, the environment and its conditions have failed the lubricant.

On the other hand, lubricants are designed to be sacrificial and are used up while in service. Hence, it is normal to see additives’ values deplete when trending oil analysis values, especially for turbine oils. Quite notably, additives responsible for antiwear or extreme pressure will decrease over time as they protect the components.

For this instance, the lubricant would have been performing its function until it could no longer do so or has reached its end of life. The conditions in the environment cannot be blamed for the lubricant failing. This is the nature of the lubricant.

Lubricant condition monitoring lets analysts detect whether a lubricant is undergoing degradation and can even help determine some areas where it has begun to fail. For instance, if the RULER® test can quantify the remaining antioxidants in an oil. Analysts can easily interpret its results to determine if the process of oxidation is occurring within that lubricant.

Similarly, an FTIR test can detect whether contaminants are present in the lubricant or if the additive packages have become severely depleted. These tests all aid in allowing analysts to successfully determine whether or not a lubricant is performing at its full functional capacity.

 

Find out more in the full article, "How lubricant selection impacts degradation and machine failure" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
February 24, 2024
Lubricant Degradation

Can Lube Oil Varnish be Eliminated? 

Varnish can be likened to cholesterol in the human body. It can build up in our arteries and eventually clog those, causing restrictions in blood flow to our heart which may lead to a heart attack.

Humans cannot simply change their blood to remove the cholesterol build-up. However, cholesterol is controlled through proper diet, exercise, and with some condition monitoring in the form of blood tests to help gauge the presence of it in the bloodstream. Similarly, a couple of approaches can be used to reduce the varnish build-up or eliminate it.

As per Livingstone et al. (2011), the lifecycle of varnish is critical. Particular attention should be paid to the double arrows between the stages of Solubility to Varnish formation in the figure below.

This means that even after varnish has been deposited, it can be solubilized back into the oil. This can only occur if conditions are met per Hansen’s Solubility principles where the solvent and degradation products meet using the three parameters of Polarity, Hydrogen Bonding, and Dispersive Forces as discussed in “The Hansen Solubility Principles and Its Relation to Varnish” (2022).

mechanisms-oil-varnish-formation

The Varnish Lifecycle as per Livingstone et al. (2011)

Varnish exists in various forms and can consist of differing compositions. Hence, it is essential to understand the characteristics of the varnish being formed in a system before attempting to eliminate it.

There are certain technologies, such as solubility enhancers or specifically engineered filtration media, which can be effective at removing lube oil varnish. However, this technology is heavily reliant on the type of varnish being formed and can be customized as per the system accordingly.

Solubility enhancers can solubilize the varnish back into the oil solution. When these deposits are reintroduced into the oil, they can be removed using resin-based filtration. In this method, the media is specifically designed to allow for the adsorption and removal of the varnish which presently exists in the oil.

When these methods are used together, they can prove quite effective and prevent manufacturing plants from experiencing unwanted downtime.

To summarize, it is of utmost importance to first understand the characteristics of the varnish being produced in your equipment before attempting to remove it from your system.

There is no cookie-cutter method to eliminate varnish from a system as it is a complex deposit. Similar to practices we observe with our bodies in the instances of cholesterol build-up, we can employ methods of dissolving the varnish and removing it while monitoring for possible recurrences in the future.

 

References:

Livingstone, Ameye, & Wooton. (2015.). Antioxidant Monitoring as Part of Lubricant Diagnostics – A Luxury or a Necessity? OilDoc, Rosenheim, Germany.

Livingstone, Overgaag, & Ameye. (2011). Advanced removal Techniques for Turbine oil Degradation Products. Powergen Milan.

Mathura, S. (2020). Lubrication Degradation Mechanisms (CRC Press Focus Shortform Book Program) (1st ed.). CRC Press.

The Hansen Solubility Principles and its Relation to Varnish. (2022, July 31). Fluitec International. https://www.fluitec.com/the-hansen-solubility-principles-and-its-relation-to-varnish/

 

Find out more in the full article, "Lube Oil Varnish Detection and Control" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
December 23, 2023
Lubricant Degradation

Is Oil Analysis the Only Method of Varnish Detection?

Varnish will deposit in layers and adhere to the metal surfaces inside the equipment. As it continues to deposit, the layers will eventually accumulate until it reaches a point whereby it can cause significant changes to the clearances of the components.

There have been instances where shafts in rotating pieces of equipment have been moved due to the build-up varnish. This is where vibration analysis can be instrumental.

When the vibration analysis method is used, it can detect any small changes in the alignment of the shaft in rotating equipment. As varnish continues to build on the inside of the component, vibration analysts can detect if the shaft observes some misalignment over a period.

This may be easy to miss as sometimes the varnish which has built up can be wiped away, causing the shaft to resume its proper alignment. Thus, these technologies should be used in tandem before conclusions are made about the presence of varnish.

Another detection method that can be employed is the monitoring of temperature fluctuations. As stated earlier, varnish can form an insulating layer trapping heat. There have been case studies that demonstrate that bearings experiencing varnish tend to display temperature increases.

Typically, these temperature patterns assume a saw-tooth pattern where temperatures rise continuously as the varnish builds up. The varnish becomes wiped away, and the temperature is reduced drastically.

This saw tooth pattern of temperature variation is characteristic of varnish formation. In some cases, the formation of localized deposits on bearing surfaces may cause temperature escalations without a corresponding MPC increase. In this case, the bulk oil may not show any degradation, yet temperature excursions may be experienced at the bearing surface.

 

Find out more in the full article, "Lube Oil Varnish Detection and Control" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
December 23, 2023
Lubricant Degradation

Can Lube Oil Varnish be Detected? 

Detecting something is the first step towards formulating a solution to minimize its effects or eliminate it from a system. In the case of varnish for lubricated assets, a few technologies are currently being used to detect its presence.

As seen at the beginning of this article, varnish can exist with various characteristics depending on the degradation mechanism which aided in its formation. For this article, the degradation mechanism of oxidation will form the main focus as it is the most prevalent pathway to lube oil varnish formation.

During oxidation, the first chemical change which can be observed in the lubricant is the depletion of the antioxidant additives. This is where the knowledge of phenols and amines is critical.

As per Livingstone et al. (2015), these antioxidants can form synergistic mixtures in mixed antioxidant systems. When the free radicals react with the phenols, they become depleted but can regenerate amines. Thereby, the phenols are sacrificial.

Thus, when performing the RULER analysis, one can find that the concentration of the phenols will typically deplete quicker than the amines. This provides the analyst with a good overview of the amount of oxidation that has taken place in the lubricant.

The RULER analysis is one of the oil analysis methods which can provide early detection of the occurrence of oxidation.

It has been shown that the physical changes, such as polymerization, will only begin after this chemical change of the depletion of antioxidants. It is at this point that the actual deposits will begin formation.

Unfortunately, oil analysis tests such as viscosity and acid number only show significant changes after the deposits have been formed. At this time, it may be too late to implement technologies to mitigate varnish formation.

The Membrane Patch Calorimetry (MPC) oil analysis test (ASTM D7843) can offer analysts insight into the estimated amount of insoluble varnish currently within the system. These results have three main ranges which identify the severity of the varnish, namely, 0-20 (Normal), 20-30 (Abnormal), and >30 (Critical). Oil analysis tests can effectively provide the operators with some awareness of the current condition of the lubricant and its tendency to form varnish.

 

Find out more in the full article, "Lube Oil Varnish Detection and Control" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

 

by
December 23, 2023
Lubricant Degradation

The Six Forms of Lubricant Degradation

oil-degradation-modes_800x300-2

Oxidation

The most common form of degradation is oxidation. While this is the most recurrent form of degradation, the term is often misused to describe all forms of degradation. During Oxidation, a free radical is formed, which is highly reactive. Its primary purpose is to create other free radicals which can attack the base oil.

However, lubricants have been formulated with antioxidants. These knights in shining armor react with the free radicals to neutralize them and protect the base oil. As such, during the oxidation process, one will notice a decline in the concentration of antioxidants typically evaluated using the RULER® (Remaining Useful Life Evaluation Routine) test.

Eventually, the antioxidants become depleted, and the free radicals begin attacking the base oil. During this stage, polymerization can occur, which leads to the formation of deposits within the lubricant. Not every deposit is chemically similar.

The deposit will gain its characteristics from its environment and the products present during the chemical reaction. When these deposits occur, they can get lodged in the smaller clearances (particularly servo valves), which leads to possible malfunctioning of the equipment. Due to the nature of lube oil varnish, it can act as an insulating layer that increases the temperature throughout the equipment.

Thermal Degradation

Another form of degradation is called thermal degradation. As its name suggests, heat is one of the environmental conditions required for this degradation mechanism. During thermal degradation, the oil can experience temperatures over 200°C.

The Arrhenius equation is one of the industry’s rules of thumb whereby for every 10°C rise over 60°C, the life of the oil is essentially halved. At 200°C, the oil is cooked and produces carbon-based deposits, which is this mechanism’s characteristic type of deposit. The FTIR (Fourier Transform Infrared) test is instrumental in identifying the presence of these deposits.

Microdieseling

One can argue that microdieseling is a form of thermal degradation and should be classed as such. However, during microdieseling, air becomes entrained in the oil and moves from a low-pressure zone to a high-pressure zone.

If the oil does not have good air release properties, then the entrained air will not make its way to be dissipated at the surface. This entrained bubble in the oil can cause temperatures to rise to 1,000°C.

The bubble interface usually experiences some carbon accumulation and then implodes. This can be through a high implosion pressure which results in soot, tars, or sludge, or through a low implosion pressure which can form carbon insolubles such as coke, tars, or resins.

Electrostatic Spark Discharge

Electrostatic spark discharge may be classified under thermal degradation as it involves temperatures over 10,000°C. During this mechanism, oil builds up static electricity at a molecular level when the dry oil passes through tight clearances in the equipment.

Eventually, the static will build to a point where it produces a spark, and free radicals are formed. This can lead to uncontrolled polymerization producing varnish, sludge, or other insoluble materials. One of the tell-tale signs of this mechanism is the presence of burnt patches of membranes on the filters.

Additive Depletion

Additive depletion is often a form of degradation which gets left behind. As stated earlier, additives are sacrificial and will be depleted over time. Their purpose is to protect the lubricant and the machine, but they can be significantly depleted in some instances, leaving them vulnerable.

This type of degradation can produce two types of deposits, organic or inorganic. During degradation, rust and oxidation additives can become reacted with other components. These types of reacted additives can form organic deposits.

Alternatively, inorganic deposits such as ZDDP (Zinc dithiophosphate) can deplete and form a tenacious layer. The Depletion of ZDDP will impact the wear rate as this is the antiwear additive.

Contamination

Often, the most unrecognized form of degradation is contamination. Some may argue that this is not a form of degradation. On the contrary, this degradation mode can be the initiator for other mechanisms such as oxidation, thermal degradation, or even microdieseling.

Essentially, contamination occurs when foreign material is present in the lubricant. Often, this foreign material can become a catalyst for one of the other forms of degradation. Therefore, it must be acknowledged separately, as only the degradation mode can be eliminated by removing the contaminant.

 

 

Find out more in the full article, "Lube Oil Varnish Detection and Control" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

by
December 23, 2023
Lubricant Degradation

What is varnish or oil degradation?

Varnish is a type of deposit that forms on the surface of equipment in lubrication systems. It is caused by the oxidation of the base oil and the buildup of additives in the oil over time, forming a sticky, varnish-like substance. Lube oil varnish can cause problems in equipment operation by clogging filters, reducing oil flow, and leading to valve sticking and pump failures.

Lube oil varnish is no stranger to the manufacturing industry. It constitutes the substance of most operators’ worst nightmares and plant managers’ ultimate fears. For those who have been in the industry for the last decade, varnish is the sticky subject that unites all facility departments.

It can cause an entire manufacturing plant to shut down while sending the finance department into a frenzy trying to balance production loss with incoming repair costs. In the fight against lube oil varnish, all teams need to work together to ensure that it can be managed and possibly eliminated from the system.

What Is Oil Degradation?

Before diving into the world of varnish, one must first understand how it forms and the circumstances which have led to its existence. Within the industry, the term varnish is used loosely to define any form of lubricant-derived deposit found in industrial.

However, oil can degrade by several mechanisms, which require various conditions for degradation—as such, using the term varnish to describe any deposit formed within a machine does not suggest its mechanism of formation.

The lubricant begins its degradation journey from the moment the lubricant enters the machine.

A lubricant is composed of base oil and additives, of which infinite combinations exist. Additives are carefully engineered to protect the base oil and the equipment. As such, they can become depleted over time, leading to the degradation of the lubricant.

This becomes concerning when the additive levels have depleted to a threshold where they can no longer protect the base oil or the machine. At this stage, degradation is the most serious concern because its rate is greatly accelerated.

According to Mathura (2020), there are six major forms of degradation under which a lubricant can undergo. While some may argue that these can be grouped, some characteristics set these mechanisms apart.

Each mechanism has unique environmental factors which contribute to producing different types of deposits. It is critical to note that identification of the type of mechanism can assist operators in performing remedial works on their equipment to aid in preventing the formation of varnish.

 

Find out more in the full article, "Lube Oil Varnish Detection and Control" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd. 

 

by
December 23, 2023