Executive Summary
About half of TLT readers reported lubricant compatibility as a pain point in their work. Challenges involved in lubricants compatibility include limited information from manufacturers, chemical reactions in certain applications and lack of knowledge among customers or end-users. Some of the most popular technical improvements that readers would like to see are more data from lubricant manufacturers and more standardization in testing for compatibility.

Q.1. Please describe the technical challenges you are facing when dealing with lubricant compatibility.

Grease compatibility testing is labor intensive/expensive.

Sometimes the fresh lubricants are compatible, but the combination between a degraded lubricant and a new, different fresh lubricant leads to formation of soft contaminants, foam, etc. For large systems it is impossible to completely flush the old lubricant before switching to another brand.

Marketing forces blur the lines between science and the need to increase market share. This leaves the issue of compatibility in the hands of suppliers, even as customer relationship departments are being reduced or removed.

Oils—synthetic base stocks versus conventionals; lack of readily available info or misinformation on product data sheets, particularly when evaluating private label products. Greases—the length of time and limited options for grease compatibility testing prevents timely resolutions on issues where comingling has occurred, changes in product or upgrades from one thickener to another (based on the application).

Many people don’t understand that just because lubricants are comparable doesn’t mean they are compatible.

There is a big range of seal and polymer materials with very different properties. Even for nominal the same polymer from different suppliers one can see different behaviors. There are many test methods and within those methods are different parameters that can vary, like temperature, time, complete immersion, partial immersion, etc. Also, there are many different mechanical tests of the materials before and after the test or the lubricant itself, making testing extremely complex and scattered. Having better-framed industry recognized tests would help. The other difficulty is that many quite inert seal materials or polymers are more expensive than those ones that are suffering more from fluid impact, but these are the ones OEMs want to use because of price.

In the progression of my career through three lubricant companies, I noticed increasing attention to lubricant compatibility. Better equipped facilities can handle lubricant compatibility much better than others. Ideally, you would like to have as much dedicated equipment as possible.

Laboratories that are not aware that an ASTM method D7155 exists to test lubricant compatibility. New oils may be perfectly compatible, but an in-service oil with a fresh oil can have compatibility issues that need to be measured in advance.

Our lubricants for the oil and gas drilling sometimes may have incompatibility with emulsifiers and oil wetting agents.

Yes, customers often do not want to dump tanks of rolling emulsion, so they seek to add on top of the old chemistry. You can sometimes see issues with lubricity, wetting or emulsion stability.

Slugging and dropout.

Don’t really have a problem other than in rare circumstances when troubleshooting misapplications. Simply need to understand the application, OEM specifications/recommendations and then match lubricant to specs.

Additive compatibility used to formulate.

Finding adequate technical documentation to compare lubricants.

None—I understand compatibility and materials chemistry.

Based on my experience some important factors must be considered: 1.) solubility of additives and base oils, 2.) avoiding phase separation (formation of two phases), 3.) chemical interactions with specific metals, 4.) stability over temperature and pressure variations, 5.) consideration about compatibility with sealing systems and 6.) risk of deposit formation or sludge.

Unexpected results. When operating an efficient plant, unexpected results create havoc in your system. Quality systems require you to contain the suspect material and then conduct a root cause analysis. This can lead to rejected parts at your customer, stains, rust, part cleanliness, modifying systems and retraining employees. People who monitor cost of quality have to ensure that this does not happen.

I refer to the OEM.

1.) Knowing what the old lubricant really is. 2.) Trying to learn whether lubricants are really compatible can be time consuming and expensive. I understand that manufacturers publish compatibility charts, for example, between lithium complex greases, but that doesn’t guarantee compatibility between the additives in the two greases.

When formulating lubricants, being able to balance performance without destroying the intended use is primary. Next would be choosing the right additives from the myriads of choices to match the application would be next.

Formal compatibility testing seems expensive unless you are dealing with a significant and critical asset. Compatibility issues are not readily understood by end-users and users rely on change and flushing when part change could be reasonable. Grease compatibility is even less well understood.

Chemical incompatibility—different lubricants have different base oil and additives leading to unwanted chemicals combination. Viscosity mismatch—this results in poor lubrication due to improper film thickness. Temperature variation—this is due to thermal variation, hence temperature fluctuations.



Is lubricant compatibility a headache in your specialized lubricant application?
Yes 54%
No 46%
Based on an informal poll sent to 15,000 TLT readers.
Additive chemistry, type of base oils.

Constant product consolidations and moves to multipurpose greases and oils.

PFAS.

Everything must be backward compatible.

Additives and base oils blend together to form the lubricant. Blending of additives into a specific base oil requires knowledge and sometimes testing. The blending sequence of which additive goes in first and which additive goes in last has to be carefully tested. Then comes storage and weather of the blended lubricant. Base oil solubility with the additives could sometimes be influenced by weather, humidity and temperatures. Each batch of base oils and additives needs tests to verify they are compatible.

In my area, we have internal methods to ensure compatibility short and long term.

The biggest concern is personnel; anyone who is involved in a lubrication program needs to be fully educated about lubricant compatibility and incompatibly. The people who are using lubricants need to understand which oils and greases are compatible with each other and also the lubricants that are incompatible with other lubricants. Also, the compatibility issues concern more things than oils and greases which do not mix well with each other. Seal elastomers, gaskets and sealants must be compatible with the lubricants that they are in contact with, or failure and break downs are going to occur. Correct training is very much needed in today’s lubrication field.

Compatibility with seals and paints since sometimes we do not know the type that has been used. Also, additives compatibility.

Changes of the behavior; are there any differences which can cause problems?

Is there an established test method for compatibility in your specialized lubricant application?
Yes 51%
No 49%
Based on an informal poll sent to 15,000 TLT readers.

Hardening of grease causing blocking of tubes of central lubrication systems, softening of grease causing excessive grease consumption and lack of sealing.

Inform (and convince) operators about the importance of performing accurate washings when they have to switch from a lubricant to another.

Additives, regulation, PFAS issues, thermal behavior, cleanliness.

Some base oil has an issue when mixed with current base oils.

Ensuring that the lubricant will be compatible with the seals and the paint of gearboxes, while simultaneously lubricating the gears and bearings in an efficient way. This is true for both oil and grease lubricated gear lubricants.

For lubricating grease, there are too many published “guides” to make compatibility decisions. However, there is specific testing that can be done to measure grease compatibility.

You can face a number of challenges for oils from phase separation of the oil to haziness, to additive drop out. With grease you can also encounter hardening or softening of the grease.

Sometimes, despite the basic information provided by the grease manufacturer on the packaging, it is not possible to precisely predict the interaction with another grease when mixing them, even if this is permitted by the manufacturers of both greases. While chromatographic analysis can be helpful in determining the composition of the base grease, in the case of the presence of refining packages, there is often a lack of standards for chromatographic analysis.

Seal compatibility due to the difficult nature to change some of those out.

Improper mixing can cause the lubricant to become more viscous and even turn asphaltic, causing damage to the metallurgy of the machine, as well as corrosive attacks, and damage to gaskets and seals.

Understanding the different additive chemistries used between major oil companies for the same type of oil/application.

One of the biggest ones is lubricant manufacturers constantly changing product names. 

Q.2. Please describe the technical improvements you would like to have when dealing with lubricant compatibility.

Smaller scale/less grease needed.

Manufacturers of lubricants to provide materials explaining compatibility with different oils, fresh and after aging.

Truthful product data sheets (PDSs) help to relieve compatibility challenges which present themselves in the field. Yes, it is a simple solution. Yes, it is a solution that is easily used and very reliable.

Better guidance from formulators and distributors.

Good defined test methods and boundaries of testing regimes. Same for mechanical and chemical testing. Ideally fewer polymers and maybe normed test materials.

Unless we can get to “one size fits all” with lubricants, the compatibility challenge has to be met with more dedicated equipment.

Compatibility test.

Is there a need for a new technique or new instrument for a compatibility test?
Yes 48%
No 52%
Based on an informal poll sent to 15,000 TLT readers.

It would be good if there were an agreed upon standard or at least a method for each customer approval.

How compatibility is tested.

Have the technical resources needed when called for to sort out issues.

More info from manufacturers on types and compatibilities.

Access to compatibility test results for various lubricants.

1.) Better predictive models for solubility and miscibility. 2.) Advanced analytical techniques for early detection of incompatibility. 3.) Improved additives to enhance compatibility with a wider range of materials. 4.) Standardized industry guidelines for compatibility testing.

Tests that can determine if two lubricants are compatible, though many lubricants applications are process dependent. That is why we conduct trials and monitor production to ensure that issues do not arise, and if they do, address them quickly.

I would like to know grease equivalence better.

Compatibility data.

With the variety of lubes available, I don’t see any great advances on the near horizon.

Corrosion protection.

Performing oil analysis, knowing your lubrication needs, being productive.

Technology that allows you to do small batch testing.

I would like to see more compatibility testing from the lubricant vendors.

Nearly impossible to introduce something new, because of requirements for backward compatibility.

Each lubricant component needs to be tested beforehand. Samples of the lubricant should be tested in the windowsills as a monitoring sample while the lubricant is sold. But if the windowsill sample begins to degrade, then some modification should be considered.

Surface engineering, application of nanocomposite and other advanced materials including light alloys, ecological lubricants additives.

Technical issue whether different types and brands. Compatibility with the machine materials. Looking for universal grade to most lubricating applications.

I think practices that exist have proven to be effective for marketers and additive companies. For engine oils, there are some standardized tests, but most companies do additional work that is more severe to ensure there are no problems.

It would be a great help to have easy-to-understand charts that would show what lubricants are compatible and incompatible with other lubricants and sealing materials.

Awareness is key to improvements, and understanding the concept is key.

Improvement of the compatibility test by reducing the duration. 
 
Improvements for different cases of combinations, such as combination of base oil and additives.

A database would be advantageous, where you can find basic data about the miscibility of different thickener types and base oils.

Besides the usual “compatibility charts,” more in depth knowledge about the “if” and “what” when it comes to mixing of different thickener and base oil type while changing over from one to another.

Small lab at customer end to show basic examples of compatibility or incompatibility.

Sustainable solution without compromising the performance.

Need to include co-solvent.

The choice of seals and sealing material are driven mostly by getting basic performance at the minimum cost. This usually makes solving the compatibility problem more difficult to solve and adds cost to the lubricant formulation and to the overall cost of the system. If a sensible approach to treating seals like an engineering component was taken, the lubricant formulation would be simpler, and better performance would result without increasing the overall cost.

More published information about the specific tests to measure compatibility.

If the lubricant company is proposing the change in lubricant, I want them to have the compatibility data completed and ready to share when they present their proposal for a lubricant change.

Uncompromised purity even of mixed lubricants, their increased stability and prolonged duration.

I would love to have a very simple cheat sheet, which I used to have, that is easily accessible to all current fluid and seal types.

Oil analysis and compatibility.

Knowledge of compatibility of different additive chemistries.

Make more of the lubricants compatible with each other. Many of the formulation changes appear to focus on marketing new fluids through compatibility issues. 

Editor’s Note: Sounding Board is based on an informal poll sent to 15,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.