Tagged: viscosity

Measuring Oil Viscosity

The viscosity of oil is one of its most essential characteristics. Thus, it is important to understand how this is measured and quantified. There are two main types of viscosity, dynamic (or absolute) and kinematic viscosity.

The dynamic viscosity measures the force required to overcome fluid friction in a film and is reported in centipoise (cP) or in SI units Pascal Seconds (Pa s) where 1 Pa s = 10 P (Poise). It can also be considered the internal friction of a fluid. This is usually used for calculating elastohydrodynamic lubrication related to rolling element bearings and gears.

On the other hand, the kinematic viscosity of a fluid is the relative flow of a fluid under the influence of gravity. Its unit of measure is centistokes (cSt) which in SI units is mm2/s, 1cSt = 1 mm2/s. (Mang & Dresel, 2007).

Kinematic Viscosity = Dynamic Viscosity / Density

Other units of measure for viscosity include; Saybolt, Redwood, and Engler, but these are less widely used than the cSt or cP, especially for lubricants.

Oil Viscosity Grades and Standards

One of the best-kept secrets about viscosity is that a particular grade often represents a range. When oils are classified, one may see an ISO 32 or ISO 220 and believe that the oil will have this exact viscosity (32 cSt or 220 cSt). However, this is not the case.

There are three general classifications where viscosity grades have particular ranges based on the fluid type. The fluid may behave differently in each application, hence the need for these three scales. However, there is a chart that allows users to convert the various scales into the one needed.

Engine Oil Classification (SAE J300)

As per the Society of Automotive Engineers (SAE), the SAE J300 standard classifies oils for use in automotive engines by viscosities determined at low shear rates and high temperature (100°C), high shear rate and high temperature (150°C) and both low and high shear rates at low temperature (-5°C to -40°C) (Pirro, Webster, & Daschner, 2016).

Engine manufacturers have widely used this system to aid in designing lubricants suited for these applications. As such, oil formulators also adhere to these classifications when engineering lubricants.

One will note the use of the suffix letter “W” in some of the grades below. These oils are intended for low ambient conditions, whereas those without the “W” are intended for oils that will not encounter low ambient conditions.

These are commonly described as multigrade (where the “W” is found between two numbers) and monograde oils (where the “W” is at the end or the grade is identified by a number only) in the table below.

The table shows that the viscosities must fall within a particular range to be classified. For instance, a 5W30 oil should meet the specifications of:

  • Low temperature, Cranking viscosity of 6600 cP at -30°C
  • Low temperature, Pumping Viscosity Max with No Yield Stress of 60,000 cP at -35°C
  • Low shear rate Kinematic viscosity at 100°C should be between 9.3 -12.5 cSt
  • High Shear rate viscosity at 150°C Max at 2.9 cP

One will notice the range of 9.3 to 12.5 cSt (at 100°C). This is where oils can be blended to either end of this scale but still achieve the classification of a 5w30 oil.

Axle and Manual Transmission Lubricant Viscosity Classification (SAE J306)

As per the SAE recommended practice J306, automotive manual transmissions and drive axles are classified by viscosity, measured at 100°C (212°F), and by the maximum temperature at which they reach the viscosity of 150,000 cP (150 Pa s) when cooled and measured in accordance to ASTM D2983 (Method of Test for Apparent Viscosity at Low Temperature Using Brookfield Viscometer). (Pirro, Webster, & Daschner, 2016).

The table below shows that for an SAE grade of 190, the kinematic viscosity must fall within the range of 13.5 to 18.5 cSt at 100°C. While most viscosities tend to fall mid-range of these values, it also indicates that if the lubricant achieves 18 cSt at 100°C, it can still be classified at an SAE grade 90.

The most common multigrade lubricants within this grade fall within the 80w90 or 75w140 classifications.

Another factor for these types of lubricants is API GL4 or GL5 ratings. It must be noted that a GL5 lubricant is recommended for hypoid gears operating under high-speed, high-load conditions.

On the other hand, a GL4 lubricant is usually recommended for the helical and spur gears in manual transmissions and transaxles operating under moderate speeds or loads. These should not be used interchangeably as the GL5 lubricants tend to adhere to the surfaces and may cause more damage in a GL4 application.

Figure 5: Automotive Gear Lubricant Viscosity Classification. Source: Lubrication Fundamentals, Third Edition Revised and Expanded by Pirro D. M., Webster M., and Daschner E. pg 52

Viscosity System for Industrial Fluid Lubricants

This classification was jointly developed by the ASTM and STLE (Society for Tribologists and Lubrication Engineers). Initially, the system was based on viscosities measured at 100°F but converted to viscosities measured at 40°C.

ASTM D2422 and ISO 3448 are the references for this system. In this system, it is clearer to see the variances in the ranges of viscosities. In this case, the mid-point of the range is used as the ISO viscosity. To determine the range of any ISO viscosity, one can calculate ±10% of the mid-point value to get the minimum and maximum values of the range.

Figure 6: Viscosity System for Industrial Fluid Lubricants. Source: Lubrication Fundamentals, Third Edition Revised and Expanded by Pirro D. M., Webster M., and Daschner E. pg 52

All of these systems can be represented in the figure below, where it is easy to calculate the oil viscosity using another system:

Figure 7: Various viscosity systems in one chart.

Factors That Affect Oil Viscosity

Similar to the molasses and water examples above, different factors can affect the viscosity of a liquid. For instance, water can assume other states depending on the temperature.

If water is at its freezing point (0°C), it can turn to ice but remains liquid at room temperature (around 20-30°C). Then, at 100°C, it can turn into a vapor. Its viscosity can change depending on the influencing factors.

Four factors affect oil viscosity:

  • Temperature
  • Pressure
  • Shear rate
  • Oil type, composition, and additives

Temperature

As seen with the example of the water above, when the temperature decreases, the water can turn to ice. Similarly, for lubricants, as the temperature drops, the viscosity increases. This means the oil will get thicker or more resistant to flow at lower temperatures. Likewise, as the oil heats up, it can become thinner.

This is similar to a block of ice melting as temperatures increase. Its viscosity will decrease, and the ice will turn to water. In this case, the internal molecules gain more energy with the increase in temperature, lowering the internal friction within the fluid. As such, the viscosity also decreases.

Since the oil’s viscosity will change with temperature, most OEMs will supply a temperature–viscosity chart for their equipment to help ensure the correct viscosity is used depending on the operating temperature.

In the figure below, gear oils of varying viscosities are plotted against the temperature for a particular piece of equipment. OEMs will typically specify the optimum operational viscosity range for their equipment.

It is then up to the lubrication engineers to determine the ideal viscosity based on the conditions of their equipment (this can vary depending on the application).

Figure 1: Temperature – Viscosity chart for Shell Omala S2 G (Source: Shell Lubricants TDS)
Figure 1: Temperature – Viscosity chart for Shell Omala S2 G (Source: Shell Lubricants TDS)

From the figure above, one can see that at 40°C, most of the gear oil grades correspond with their viscosities (ISO 68 corresponds with a 68 viscosity). However, at 0°C, an ISO 68 gear oil can become 1000 cSt, while at 90°C, this same grade of oil is around 11cSt.

Interestingly, all of the oils listed here can achieve a viscosity of 100cSt but at different temperatures, as shown below:

  • 32°C – ISO 68
  • 40°C – ISO 100
  • 47°C – ISO 150
  • 55°C – ISO 220
  • 63°C – ISO 320
  • 68°C – ISO 460
  • 75°C – ISO 680

Temperature is a significant influencing factor of viscosity, but it is not the only factor.

Pressure

The effects of pressure on a lubricant’s viscosity are often overlooked. However, the viscosity-pressure behavior has become part of the calculation for elastohydrodynamic films. In these cases, oil viscosity can rapidly increase with pressure.

One such instance occurs with metal-forming lubricants, which are subjected to high pressures such that the oil’s viscosity can increase tenfold (Mang & Dresel, 2007). As the pressure increases, viscosity also increases, protecting the surface in these lubricant films.

The very definition of viscosity alludes to pressure’s impact on Newtonian and non-Newtonian fluids. For example, with Newtonian fluids (regular lubricating oils), the shear rate is proportional to the applied shear stress (pressure) at any given temperature.

As seen above, the viscosity can be determined once the temperature remains the same. However, Non-Newtonian fluids, such as greases, only flow once a shear stress exceeding the yield point is applied (Pirro, Webster, & Daschner, 2016).

Hence, this is why the observed viscosity of grease is called its apparent viscosity and should always be reported at a specific temperature and flow rate.

Shear Rate

For Newtonian fluids, viscosity does not vary with shear rate (Pirro, Webster, & Daschner, 2016). In fact, per the definition of viscosity for Newtonian fluids (regular lubricating oils), viscosity is a constant proportionality factor between the shear force and shear rate. Thus, even when subjected to greater shear forces, the viscosity will not change for Newtonian fluids.

On the other hand, for non-Newtonian fluids, the viscosity is influenced by the shear rate. Some non-Newtonian fluids can include; pseudoplastic fluids, dilatant fluids, and a Bingham solid, the effects of shear rate on these fluids are shown in the figure below.

A Bingham solid is a plastic solid such as grease that only flows above a particular yield stress. It can be seen that pseudoplastic fluids decrease viscosity with an increasing shear rate, while dilatant fluids show an increase in viscosity with an increasing shear rate. (Hamrock, Schmid, & Jacobson, 2004)

Figure 2: Characteristics of different fluids as a function of shear rate vs. viscosity (a) and shear rate vs. shear stress (b). Source: Fundamentals of Fluid Film Lubrication by Hamrock, Schmid & Jacobson, page 102.
Figure 2: Characteristics of different fluids as a function of shear rate vs. viscosity (a) and shear rate vs. shear stress (b). Source: Fundamentals of Fluid Film Lubrication by Hamrock, Schmid & Jacobson, page 102.

The shear of a lubricant can influence its shear rate. Typically, longer-chain polymer viscosity index improvers can shear over time. When this happens, it can result in a decrease in oil viscosity. Similarly, non-Newtonian fluids, such as grease, experience a decrease in viscosity as a function of shear rate (Totten, 2006).

Another essential characteristic to note is whether a material is thixotropic or rheopectic. For a thixotropic material, if it is placed under a continuous mechanical load over a period of time, the viscosity will appear to decrease over this time.

However, the original viscosity is restored after a specific rest period, as shown in the figure below. On the other hand, for rheopectic materials, continuous shearing causes the viscosity to increase. (Mang & Dresel, 2007).

Figure 3: Flow characteristics of a thixotropic lubricant (Source: Lubricants and Lubrication edited by Theo Mang and Wilfried Dresel, page 30)

Oil Type, Composition, and Additives

Various oil types, compositions, and additives can influence a lubricant’s viscosity. For instance, the five groups of base oils all have varying characteristics, as shown in the figure below. One can note the differing viscosities for the various groups.

Figure 4: Base Stock property comparison (Source: Lubricants and Lubrication edited by Theo Mang and Wilfried Dresel, page 13)
Figure 4: Base Stock property comparison (Source: Lubricants and Lubrication edited by Theo Mang and Wilfried Dresel, page 13)

When a finished lubricant is made, it usually consists of a base oil and additives. Hence, the base oil will have a significant role in determining the final viscosity of the oil. However, with the advent of Viscosity Index Improvers, desired viscosities can be engineered regardless of the base oil type being used.

 

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

What is Oil Viscosity?

Oil viscosity is the internal friction within an oil that resists its flow. It measures the oil’s resistance to flow and is one of the most important factors in lubricants. Viscosity is also defined as the ratio of shear stress (pressure) to shear rate (flow rate).

Understanding Oil Viscosity

Imagine walking through a swimming pool filled with water. While walking through the pool, your body experiences some resistance from the water. Now imagine walking through the same swimming pool, filled with molasses this time!

It takes someone much longer to wade through a molasses-filled pool than one filled with water. In this case, the molasses is more viscous than the water. Thus, it has a higher viscosity than water.

Viscosity_600x300_AMRRI

You can also apply this to using a straw for drinking water from a glass. Pulling the liquid from the cup will be easy using a big straw. However, getting the same liquid to the person using the straw would take longer if a thinner straw were used.

Engine Oil Analogy

We can draw this analogy to car engines over the last 30-40 years. These engines had larger clearances for the oil to flow throughout the engine. As such, most of these engines used a 50-weight (or straight 50) oil.

As the technology evolved, the size of the engines got smaller. The clearances also got smaller, and the engine oil was now required to flow faster, control the transfer of heat and contaminants and keep the engine lubricated.

A straight 50 oil could not pass through the smaller straw at the speed it should. This would be equivalent to the user using a smaller straw for drinking molasses. It could take a while!

However, if a lighter weight (or less viscous) engine oil was used (such as a 0w20 or 10w30), then this is like someone trying to drink water (0w20) with a smaller straw.

It will flow much faster than molasses (straight 50) with the same straw! The lighter-weight oil would also transfer heat and flow much faster than the heavier-weight (more viscous) oil.

 

Future Developments and Research in Oil Viscosity

As explained at the beginning of this article, the changes in technology (such as smaller engines) will demand more from lubricants, especially in viscosity. Thirty years ago, a 0w16 engine oil was unfathomable, but today, it is being integrated into our newer model vehicles.

Some of the concepts which will continue in the future can include:

  • Reducing viscosity – as seen in the examples above, with most pieces of equipment getting smaller, the need for lighter weight (lower viscosity) oils will continue as OEMs constantly evolve and push the boundaries of their equipment.
  • Measuring viscosity – traditionally, viscometers have always been used where the difference in the height of the liquid at particular temperatures (or under certain conditions) is measured. Given the advancements in technology, this may be subject to change very shortly into a more reliable and even more accurate method.
  • Viscosity-dependent parameters – temperature and pressure have the most significant impacts on the oil’s viscosity. However, some of these challenges can be overcome with the advent of viscosity index improvers. With enhancements in the formulation of viscosity index improvers, one can expect oils of varying viscosities to be used in parameters they could not have used in the past.
  • Alternative oils – more sustainable options are constantly being explored. Whether this lies in using plant-based oils or other alternative bio-based oils, these may introduce new ways or conditions under which different viscosities can exist.

Overall, viscosity is one of the most important characteristics of a lubricant. It can easily influence the impact of the oil on the internal surfaces of the equipment and its overall energy efficiency.

It is important to remember that oil viscosity should be determined by the application in which it is being used. Parameters such as temperature, pressure, and shear rate should all be considered when selecting the lubricant’s viscosity.

 

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

Mixing viscosities

mix_viscosities

Can I mix different viscosities of oils to get the viscosity that I want?

It can be done but this is not an ideal situation.

There are times when the only available viscosity is an ISO 46 (on a rig) but the equipment requires an ISO 68 and the new stock will not be delivered in time to avoid shutdown. Can the ISO 46 be used instead?

An ISO 46 oil is lighter in viscosity than an ISO 68 however, for most oils, there is a chart that depicts the viscosity of the oil at operating temperature. In these cases, one can consult this chart and determine if the viscosity at operating temperature will still fall within operating limits.

If we mix an ISO 46 with an ISO 68 oil we cannot be certain of where the new viscosity will fall especially if we do not know the ratios that are being used. There is a viscosity calculator that can help guide this decision available at: https://www.widman.biz/English/Calculators/Mixtures.html

This can be used as a guide and the actual values of the oil should be verified via oil analysis.

 

While this situation is not ideal, we need to remember that compatibility is also key.

As such, we should stick with the same line of lubricants that we being used. Typically, lubricant suppliers have the same formulation but change the viscosities for lubricants of the same line.

Mixing oils

mix_oils

Can I mix hydraulic oils with engine oils?

Oils should never be mixed!

Every oil is designed with its application in mind. As such, they are blended with varying concentrations and types of additives. For instance, a typical engine oil has at least 30% additives while a turbine oil may have only 1% additive.

Hydraulic oils are designed for applications where power has to be transmitted through the lubricant. On the other hand, engine oils are designed to withstand varying temperatures (gasoline engines have a different temperature range compared to diesel engines. Diesel engines generally run at higher temperatures than gasoline engines).

Always pay particular attention to what the OEM recommends. Usually, the OEM will recommend that a lubricant meets a particular global standard (API SN or CK4). These standards were developed to ensure the best performance of an engine and should be adhered to when choosing lubricants.

Multigrade vs Monograde

multi_mono

Why use multigrade instead of monograde oils?

A monograde oil does not provide the same level of protection on start-up as a multigrade oil.

With the multigrade oil, it is designed to reduce the time it takes to get from the bottom of the sump to the top of the engine (this is indicated by the number in front of the “w”).

However, the monograde oils have not been adapted for this type of technology. Thus, it takes longer to get to the top of the engine and to all the components compared to a multigrade oil.

Most wear occurs on start-up. Before we start the car on a morning, all of the oil is at the bottom of the sump, so it takes some time to get to the top and the other components. However, once we start the engine, all the parts will begin moving. If they are moving without any lubrication, then a significant amount of wear will occur!

Typically, when driving, we start the car, go to our destination and stop. Then come back and start the car again. During this time, the oil would have drained back to the bottom of the sump and now has to get back to the top. Before it gets to the components, these are still moving without lubrication, inducing wear! If we think of the number of times that we start and stop for the day (or for the month!), we will realize the amount of wear that we put our engines through.

Hence, this is one of the main reasons, that we choose multigrades over monogrades.

Recommended oil – Automotive

oil_car

What type of oil should I use in my car?

Always follow what the OEM recommends! A quick google search can help you find the required lubricant if you don’t have the owner’s manual.

Most modern vehicles use lighter weight oils compared to older vehicles. Let’s think about cars back in 1950. They were larger, with big engines. With a big engine, it would mean that the lines carrying the oil would be larger. Thus, a heavier oil (50 weight) would be the most appropriate.

Now, fast forward to cars today. The engines are smaller, (albeit with a lot more horsepower as well!). If the size of the engine has changed, then the size of the lines carrying the lubricant will change as well. These lines will get smaller. If the lines are smaller, then the liquid that has to flow through them, should be lighter (thinner).

We can use an analogy of a straw trying to pull up molasses.

With a large straw, we could pull up the molasses faster than with a thinner straw. This is similar to the older cars, they would have thicker “straws” (lines) that would have allowed them to adequately pump the lubricant.

In the newer cars, the straw has gotten thinner, so it can’t pull up the molasses anymore. If we tried to pull up water instead, it would definitely flow faster than the molasses and not have as much strain on the person pulling up the water (pump in the engine). Hence, lighter oils are used in modern cars.

Most recommendations can be found by contacting the OEM or even doing a bit of Google searching with the year of manufacture for the car and of course the model.

ICML 55 – the revolution in the lubrication sector

icml_stds

What is ICML 55?

ICML 55 is revolutionizing the lubrication industry! It is so exciting to be around at this time when it has started its implementation. For those who aren’t aware of ICML 55, here are a couple of notes on it.

ICML 55 was born out of ISO 55000 which speaks to Asset Management. From this standard, 3 standards were developed to guide the lubrication industry since no previous standards existed within the lubrication industry.

  • ICML 55.1 - Requirements for the Optimized Lubrication of Mechanical Physical Assets
  • ICML 55.2 - Guideline for the Optimized Lubrication of Mechanical Physical Assets
  • ICML 55.3 - Auditors' Standard Practice and Policies Manual

ICML 55.1 has already been completed, while 55.2 should be done at the end of this year and 55.3 scheduled for 2020.

These are exciting times!

Here’s the official press release:

https://info.lubecouncil.org/2019/04/04/icml-introduces-icml-55-asset-management-standards-mle-engineer-certification/

While ICML 55.1 was only launched in April of this year (2019), it is a standard that the lubrication industry has been in need of for several years. It addresses the “Requirements for the Optimized Lubrication of Mechanical Physical Assets”.

What exactly are the assets covered? Here they are:

  • Rotating & Reciprocating Machines, Powertrains, Hydraulic Systems and lubricated subcomponents
  • Assets with lubricants that reduce friction, wear, corrosion, heat generation or facilitate transfer of energy
  • Finished products from API categories I-V
  • Non Machinery support assets (Personnel, policies, procedures, storage facilities and management)
icml_55

There are also fluids and assets which are NOT covered:

  • Fuels, coolants, metal-working fluids, pastes, fogging agents, preservative fluids, coating materials, heat-transfer fluids, brake fluids, cosmetic lubricants
  • Solid lubricants (e.g., powders and surface treatments used as coating rather than to reduce friction between surfaces in motion)
  • Additives independent of the finished lubricant
  • Electrical transformer oils and anti-seize compounds
  • Fluids and materials derived from a petroleum or petroleum-like base
  • Fluids that do not serve a lubrication function
Photo Credit: https://info.lubecouncil.org/icml-55-standards/
Photo Credit: https://info.lubecouncil.org/icml-55-standards/

ICML 55.1 speaks to the “Requirements for the Optimized Lubrication of Mechanical Physical Assets” it also describes and defines 12 interrelated areas that can be incorporated in a lubrication program. This has never been officially documented before, nor has any standard been published as a guideline for lubrication programs.

The 12 areas are outlined below:

  1. SKILLS: Job Task, Training, and Competency
  2. MACHINE: Machine Lubrication and Condition Monitoring Readiness
  3. LUBRICANT: Lubricant System Design and Selection
  4. LUBRICATION: Planned and Corrective Maintenance Tasks
  5. TOOLS: Lubrication Support Facilities and Tools
  6. INSPECTION: Machine and Lubricant Inspection
  7. LUBRICANT ANALYSIS: Condition Monitoring and Lubrication Analysis
  8. TROUBLESHOOT: Fault/Failure Troubleshooting and RCA
  9. WASTE: Lubricant Waste Handling and Management
  10. ENERGY: Energy Conservation and Environmental Impact
  11. RECLAIM: Oil Reclamation and System Decontamination
  12. MANAGEMENT: Program Management and Metrics

As per ICML's website, here's a list of people that the new standard can benefit:

Photo Credit: https://info.lubecouncil.org/icml-55-standards/

 

Check out the ICML 55 standards today and apply it to your organization!

Oxidation

oxidation

What is Oxidation?

One of the major types of oil degradation is Oxidation. But what is it exactly, as applied to a lubricant?

Oxidation is the addition of oxygen to the base oil of the lubricant to form either of the following:

  • Aldehydes
  • Ketones
  • Hydroperoxides
  • Carboxylic Acids

Wow… too many chemical names right?! These help to pinpoint the conditions responsible and then we can address them accordingly. Each of these by products are produced by different types of reactions or in some cases different stages of the oxidation process. It is key to note the type of by product as it gives us a clue to the root of the issue through which oxidation occurs.

For instance, the presence of Carboxylic acids can result in the formation of Primary Amides which can lead to heavy deposits. Early detection of the Carboxylic acids can help us prevent this. Once we determine the source of oxidation to produce the carboxylic acids, we can in turn remove this from the system.

 

Oxidation Stages

Oxidation does not happen in an instant. Usually, it follows a series of events which eventually lead to oxidation. Like any process in life, there are different stages for Oxidation:

  • Initiation – Production of the free radical via the lubricant and catalyst.
  • Propagation – Production of more free radicals via additional reactions
  • Termination – Continuation of oxidation process after the antioxidants have been depleted or the antioxidant stops the oxidation process.
Stages of Oxidation

Results of Oxidation

Why is Oxidation bad for the lubricant? What can it ultimately result in?

Well, oxidation can result in the formation or lead up to the following:

  • Varnish
  • Loss of antifoaming properties
  • Additive depletion
  • Base oil breakdown
  • Increase in viscosity
  • Sludge

None of these are good for the lubricant!!!!!!!!! If you see any of these signs be sure to test for oxidation and identify the root cause for the introduction of oxygen in your system.

tests for oxidation

Oxidation Tests

Now that we know more about oxidation… what tests can be performed to prevent it?

There are 6 main tests that can be performed:

  • RPVOT (Rotating Pressure Vessel Oxidation Test)
  • RULER (Remaining Useful Life Evaluation Routine)
  • MPC (Membrane Patch Calorimetry)
  • FTIR (Fourier Transform Infrared)
  • Colour (ASTM D1500)
  • Acid Number (ASTM D974)

One must be careful in selecting which test to apply, this is heavily dependent on the type of lubricant and its application.

For instance, if we perform the RULER test and the antioxidant levels have depleted significantly, we can suspect that oxidation is occurring or has stopped. Charting the rate of antioxidant depletion, can determine the rate of oxidation. This can assist us to forecast the time remaining before antioxidants have been depleted and can no longer protect the base oil.

Lubrication failures in Ammonia plants

Quite often, when lubrication failures occur, the first recommended action is to change the lubricant. However, when the lubricant is changed, the real root cause of the lubricant failure has not been solved. As such, the cause of lubrication failure will continue to be present and may escalate further to develop other problems.

Essentially, this can cause catastrophic future failures simply because the root cause was not identified, addressed and eradicated. Moreover, the seemingly “quick fix” of changing the lubricant, is usually seen as the most “cost effective” option. On the contrary, this usually becomes the most expensive option as the lubricant is changed out whenever the issue arises which results in a larger stock of lubricant, loss in man hours and eventually, a larger failure which can cost the company at least a month or two of lost production.

In this article, we investigate lubricant failures in Ammonia plants and their possible causes. Some Ammonia plants have a developed a reputation for having their product come into contact with the lubricant and then having lubrication failures occur. As such, most Ammonia plant personnel accept that the process materials can come into contact with the lubricant and usually change out their lubricants when such issues occur. However, there are instances, where the ammonia is not the issue and plant personnel needed to perform a proper root cause analysis to determine the root cause and eradicate it. Here are a couple of examples of such instances.

Livingstone (1) defies the Lubrication Engineers Handbook in their description of ammonia as an inert and hydrocarbon gas that has no chemical effect on the oil, stating that this is incorrect. Instead, Livingstone (1) lists the number of ways that Ammonia can react with a lubricant under particular reactions such as;

  • ammonia being a base that can act as a nucleophile which can interact with any acidic components of the oil (such as rust/corrosion inhibitors)
  • reaction of ammonia with carboxylic acids (oil degradation products) to produce amides which cause reliability issues
  • transesterification of any ester containing compound to create alcohol and acids and the reaction of ammonia with oxygen to form NOx which is a free radical initiator that accelerates fluid degradation.

As such, one can firmly establish that ammonia influences the lubricant and can lead to lubrication failures should that be the cause of the lubricant failure.      

The Use of Root Cause Analysis     

Van Rensselar (2) quotes Zhou as saying the best method for the resolving varnish is to perform a root cause analysis. Wooton and Livingstone (3) also advocate for the use of root cause analysis to solve the issue of varnish. They go on to explain that the characterization of the deposit aids in determining the root cause of the lubricant degradation. As such, Wooton and Livingstone (3) have developed a chart to assist in deposit characterization as shown below.


Deposit Characterization graphic from Wooton and Livingstone (3)

Wooton and Livingstone (3) discussed that with the above figure, once the deposit can be characterized then the type of lubricant degradation can be more accurately identified. As such, the root cause for the lubricant degradation can now be firmly established thereby allowing solutions to be engineering to control and reduce / eliminate lubricant degradation in the future. 

Case Studies

A case study from Wooton and Livingstone (3) was done with an Ammonia Compressor in Romania which experienced severe lubricant degradation. In this case study, they found that when the in-service lubricant was subjected to two standard tests namely MPC and RULER, both tests produced results within acceptable ranges. As such, there was no indication from these tests that the lubricant had undergone such drastic degradation as evidenced by substantial deposits within the compressor. Thus, it was determined that the deposits should be analysed as part of the root cause analysis.

For the deposits from the Ammonia compressor, Wooton and Livingstone (3) performed FTIR spectroscopy to discover that its composition consisted of mainly primary amides, carboxylic acids and ammonium salts. It was concluded that the carboxylic acids formed from the oxidation of fluid while in the presence of water. 

In turn, the carboxylic acids reacted with the ammonia to produce the primary amides. These amides consisted of ammonium salts and phosphate. As such, the onset of carboxylic acids within the system eventually leads to the lubricant degradation. Thus, an FTIR analysis for carboxylic acids was now introduced to this Ammonia plant as well as MPC testing to monitor the in-service lubricant.

Additionally, chemical filtration technology was implemented to remove carboxylic acids within the lubricant. These two measures allowed for the plant to be adequately prepared for lubricant degradation and avoid failures of this type in the future.

Another case study was done in Qatar with an ammonia refrigeration compressor which was experiencing heavy deposits due to lubrication degradation. For this Ammonia plant, high bearing temperatures and deposits were found on the bearing. 

Upon investigation, it was realized that the lubricant had been contaminated externally and there was restricted oil flow to the bearings. After a FTIR was performed it was deduced that that the deposits were organic in nature and there were several foreign elements including high levels of carbon and primary amides. 

From further root cause analysis, it was determined that the high temperatures observed were due to the lubricant starvation. Due to these high temperatures, oxidation initiated and with the high levels of contamination (mainly from ammonia within the process) this lead to degradation of the lubricant in the form of heavy deposits.

The bearing oil flow was increased and reduction in external contaminants were implemented. Oil analysis tests of Viscosity, Acid Number, Membrane Patch Calorimetry and Rotating Pressure Vessel Oxidation tests were also regularized in the preventive maintenance program. Thus, for this failure, some operational changes had to be made in addition to increased frequencies of testing. With these measures in place, there would be a reduced likelihood of future failures.

From the case studies mentioned, it can be concluded that ammonia systems have a higher possibility of undergoing lubricant degradation due to the contamination of the lubricant by ammonia gas / liquid due to its properties. However, it must also be noted that the ingression of ammonia into the lubrication system is not the only cause for lubrication failure.

Therefore, it is imperative that a proper root cause analysis be carried out to determine the varying causes for lubrication failure before the ingression of ammonia accepts full responsibility for any such failure.

References:

  1. Livingstone, Greg (Chief Innovation Officer, Fluitech International, United States America). 2016. E-mail message to author, March, 08.
  2. Van Rensselar, Jeanna. 2016. “The unvarnished truth about varnish”. Tribology & Lubrication Technology, November 11. 
  3. 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.