Tagged: contamination

The Six Forms of Lubricant Degradation

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.

Want to read the entire article? Find it here on Precision Lubrication Magazine!

Industrial / Strategic Tips

ISO 4406 rating

Is the ISO 4406 rating important?

Yes, it is very important!

The ISO 4406 rating tells us the cleanliness level of our lubricant. It tells us the number of particles that can pass through a 4, 6 and 14 micron rating.

However, the value on the ISO rating does not represent the number of particles. On the contrary, it represents the range in which the number of particles can lie.

One key point to remember is that the rating will always change from the time that the sample was taken to the date that the results were processed.

Therefore, it is a good idea to use the sample result as a guide as estimate a bit higher for the real value of your lubricant.

Check out our article which goes into more detail about ISO 4406.

Matt Spurlock CLS, CMRP, MLE explains further about redefining the ISO code in his article entitled; "A Twist on Particle Evaluation: Redefining the ISO Cleanliness Code".

Industrial / Strategic Tips

Filter rating

Is the filter rating important?

Yes! It is very important.

Usually, the OEM of the equipment specifies the filter rating (and even the filter material in some cases). These ratings help us to keep out particles of larger sizes that may cause damage to the equipment either through wear or clogging of fine clearances.

Some filters allow us to monitor the differential pressure. This is the pressure between the outside of the filters and inside and as this approaches the warning limits, we know that a filter change is needed in the near future.

However, there are times when there is no warning and the filter goes into bypass. When a filter goes into bypass, this means that the filter is no longer keeping back the larger particles. This can be catastrophic for the equipment as a higher concentration of contaminants can now enter the system and damage it.

It is common practice to change the oil filter when the oil is being changed. In some instance, (especially depending on the environment), OEMs recommend changing the oil filters twice or more before the actual oil change.

Always consult with your owner’s manual about the maintenance practices before adopting your own.

Lubricant Degradation / Storage & Handling of Lubricants

Conditions that affect lubricants

What conditions affect lubricants?

How are your lubricants currently stored?

Are you storing lubricants under the correct conditions?

These questions have come up a dozen times during audits and countless warehouse meetings!

To answer these questions, there are five main conditions that can affect lubricants. We have detailed them along with the effects of these conditions on the lubricant.

Temperature – if incorrect can lead to oxidation. For every 10C rise in temperature above 40C the life of the lubricant is halved.
Light – too much can lead to oxidation especially for light sensitive lubricants such as transformer oils. Hence the reason that most packaging is opaque.
Water – this usually works with additives to cause their depletion or contamination of the product. Water in any lubricant is bad (especially for transformer oils as they are involved in the conduction of electricity.
Particulate contamination – contamination can occur by air borne particles if packaging is left open or if dirty containers/vessels are used to transfer the lubricant from its packaging to the component.
Atmospheric contamination – this affects viscosity and promotes oxidation and can occur if packaging is left open. For instance, if a drum is not properly resealed or capped after usage or the most common practice of leaving the drum open with the drum pump on the inside.

Different types of lubricant degradation

Why is it important to know the types of lubricant degradation?

It’s important since it helps us to figure out why or in some instance how, the lubricant degraded! Usually degradation is the change that occurs when the lubricant can no longer execute its five main functions:

the reduction of friction
minimization of wear
distribution of heat
removal of contaminants and
improvement of efficiency.

Types of lubricant Degradation Mechanisms

There are 6 main types of Lubricant Degradation as detailed below. Each type produces various by products which can enable us to understand the reason for the degradation and eliminate that / those reasons.

Here are the 6 main types of Lubricant Degradation:

1. Oxidation
2. Thermal Breakdown
3. Microdieseling
4. Additive Depletion
5. Electrostatic Spark Discharge
6. Contamination

As discussed, each mechanism produces distinct results which help us in their identification! Check out our article on why lubricants fail for more info!

Used Oil Analysis

ISO 4406

A lot of people get confused when reading the ISO 4406 rating. The rating specifies a range of the number of particles of certain sizes that can pass through 3 particular sized filters namely; 4micron, 6 micron and 14 micron filters respectively.

For instance; a rating of 13/11/8 indicates:

13 represents 4000-6000 particles over the size of 4um
11 represents a range of 1000-2000 particles over the size of 6um and
8 represents a range of 130-250 particles over the size of 14um.

These values are actually the number of particles per milliliter. It does not mean that you have 13, 11 or 18 particles only in your oil, it's much more than that!

There are different ratings for different levels of cleanliness.

If your numbers are really high (25/22/19) then there’s definitely a high level of contamination!

Different components have different ISO cleanliness ratings. For instance, a roller bearing has a higher cleanliness target than a Variable Vane pump.

Understanding the ISO 4406 codes are crucial for determining the steps needed in “cleaning up” your system lubricants.

However, when we test for the cleanliness of an oil, there are a couple things that we need to consider:

When testing, we have exposed the oil to the elements (highly dependent on the method of sampling)
Results are not instantaneous (even with an onsite lab, there will be a timeframe between collecting the sample and processing it)

Since there are lag times involved, the value that is reported for the ISO4406 rating is never really truly representative of the oil. As such, when analysing the results of this test, it is important to consider that the actual value may potentially be higher than reported.

Matt Spurlock CLS, CMRP, MLE explains further about redefining the ISO code in his article entitled; "A Twist on Particle Evaluation: Redefining the ISO Cleanliness Code".

Lubricant Degradation / Used Oil Analysis

How can a lubricant fail?

This question has caused many sleepless nights and initiated countless discussions within the industrial and even transportation sectors. Before examining the causes for lubrication failure, one must first consider the definition of lubricant failure.

The composition of a liquid lubricant can be described as a combination of base oil and additives (Menezes, Reeves and Lovell 2013, 295). These two components work in tandem to define particular characteristics of the lubricant to perform its functions. According to Menezes, Reeves and Lovell (2013, 296) the five functions of a lubricant include;

the reduction of friction
minimization of wear
distribution of heat
removal of contaminants and
improvement of efficiency.

As such, lubrication failure can then be described as the failure of a lubricant to adequately perform any or a combination of its five functions as a result of the degradation of any of its two components; namely the base oil or additive package. Thus, it can be deduced that lubrication failure is as a result of lubricant degradation.

Now that we understand that a lubricant fails when it undergoes degradation which by extension results in the lubricant not being able to perform any of its functions properly, we need to explore further on the types of degradation that exist. Only then can we really answer the question of how a lubricant can fail.

Barnes (2003, 1536) focuses on three main mechanisms of lubricant degradation namely;

Thermal Degradation
Oxidation and
Compressive Heating (Microdieseling).

One may argue that these three types form the basis of all mechanisms of lubricant degradation.

However, Livingstone, Wooton and Thompson (2007, 36) identify six main mechanisms of degradation namely;

Oxidation
Thermal Breakdown
Microdieseling
Additive Depletion
Electrostatic Spark Discharge and
Contamination.

In this instance, the six identified mechanisms all produce varying identifiable characteristics which lend to these six forming the foundation of identification of lubricant degradation mechanisms. With these six in mind, one would need to be able to determine which degradation mechanism is at work in their facility. Afterwards, methods to treat with these mechanisms must be administered. Firstly, let’s understand each mechanism.

Oxidation

This mechanism involves the reaction of oxygen with the lubricant. According to Livingstone, Wooton and Thompson (2007, 36) oxidation can result in the formation of varnish, sludge, increase in viscosity, base oil breakdown, additive depletion and loss in antifoaming properties of the lubricant.

Barnes (2003, 1536) refers to this phenomenon as the addition of oxygen to the base oil to form:

Aldehydes
Ketones
Hydroperoxides and
Carboxylic Acids.

On the other hand, Wooton (2007, 32) explains that there are three main stages of oxidation namely initiation, propagation and termination. Fitch (2015, 41) explains that:

Initiation entails the production of a free radical via the lubricant and a catalyst.
Propagation involves the production of more free radicals via additional reactions.
Finally, termination entails either the continuation of the oxidation process after the antioxidants have been depleted or the antioxidant stopping the oxidation process.

Microdieseling

Livingstone, Wooton and Thompson (2007, 36) have characterized Microdieseling as a form of pressure induced thermal degradation. They describe it as the transition of entrained air from a low pressure to a high pressure zone which results in the adiabatic compression.

This type of compression results in localized temperatures almost on excess of 1000°C.As such, the lubricant undergoes dramatic degradation. Wright (2012, 14) explains that because of these high temperatures, the bubble interface becomes carbonized. As such, carbon by products are produced and the oil undergoes oxidation.

Electrostatic Spark Discharge

Livingstone, Wooton and Thompson (2007, 36) describe this phenomenon as the generation of static electricity at a molecular level when dry oil passes through tight clearances. It is believed that the static electricity can build up to a point whereby it produces a spark. This spark can induce localized temperatures in excess of 10,000°C which can significantly degrade the lubricant at an accelerated rate.

Van Rensselar (2016, 30) also advocates that Electrostatic Discharge contributes to the formation of free radicals in the lubricant which subsequently results in uncontrolled polymerization. This polymerization of the lubricant gives rise to the formation of varnish and sludge which may deposit on the surface of the equipment or remain in solution. Van Rensselar (2016, 32) indicates that the most common result of Electrostatic Discharge is an elevated rate of fluid degradation and the presence of insoluble materials.

Thermal Breakdown

This mechanism is largely dependent on temperature as one of its contributory factors even though dissipation of heat was highlighted above as one of the functions of a lubricant. However, during the operation of machinery particular components tend to develop increasing temperatures.

As described by Livingstone, Wooton and Thompson (2007, 36) once this temperature exceeds the thermal stability point of a lubricant, the consequences can include shearing of the molecules. This phenomenon is also called the thermal cracking of the lubricant which can result in the production of unwanted by products, polymerization and decrease in viscosity.

Subsequently, Barnes (2003, 1536) explains that thermal degradation usually occurs when the lubricant experiences temperatures in excess of 200°C. He also states that the by-products of thermal degradation differ from that of oxidation.

Wooton and Livingstone (2013) state that there are two main actions that can occur once a lubricant is thermally degraded.

Either the small molecules will become cleaved off and volatize from the lubricant. This does not leave any deposit in the lubricant.
On the other hand, there is the condensation of the remainder of the molecule in the absence of air thus dehydrogenation also occurs. Consequently, coke is formed as the final deposit with numerous types of deposits forming between the start of the condensation to its final deposit of coke.

The main contributing factor for thermal degradation can therefore be linked to dramatic increases in temperature or constant high temperatures.

Additive Depletion

Wooton and Livingstone (2013) indicate that additive depletion can result in either organic or inorganic deposits. The nature of the deposit is dependent on the type of additive that has been depleted and its reaction with other components in the oil.

For instance, if the rust and oxidation additives drop out of the oil, they typically react to form primary antioxidant species thus producing organic deposits. However, as Wooton and Livingstone (2013) explain, inorganic deposits can also be formed from additives that have dropped out of the oil but did not react with anything. This unresponsive reaction is typical of ZDDP (Zinc dithiophosphate) which is an additive that assists with reducing wear in the lubricant.

In cases of additive depletion, the FTIR test seeks to identify spectra relating to the reacted or unreacted additive packages for the lubricant in use (Wooton and Livingstone, 2013).

Contamination

This mechanism of degradation can include foreign material entering the lubricant and being used as catalysts for degradation mechanisms listed above. Contaminants can include a variety of foreign material, however Livingstone, Wooton and Thompson (2007, 36) have narrowed the list to metals, water and air. These main contaminants can significantly contribute to the degradation of the lubricant by oxidation, thermal degradation or compressive heating.

From the above, we can summarize these lubricant degradation mechanisms into the following table:

From this summary, we can now assess the methods in which a lubricant can fail. While this article may serve as a guide in determining various lubricant degradation mechanisms, each mechanism must be treated differently depending on the conditions (environmental and operational) that exist during the lubricant failure. A proper root cause analysis should always be done when investigating any type of failure.

References

1 Livingstone, Greg, Dave Wooton, and Brian Thompson. 2007. “Finding the Root Causes of Oil Degradation.” Practicing Oil Analysis, Jan – Feb.

2 Barnes, M. 2003. “The Lowdown on Oil Breakdown.” Practicing Oil Analysis Magazine, May-June.

3 Livingstone, Greg and David Oakton. 2010. “The Emerging Problem of Lubricant Varnish.” Maintenance & Asset Management, Jul/Aug.

4 Wooton, Dave and Greg Livingstone. 2013. “Lubricant Deposit Characterization.” Paper presented at OilDoc Conference and Exhibition Lubricants Maintenance Tribology, OilDoc Academy, Brannenburg, Rosenheim, Germany, United Kingdom, January 22-24, 2013.

5 Van Rensselar, Jeanna. 2016. “The unvarnished truth about varnish”. Tribology & Lubrication Technology, November 11.