Executive Summary
TLT readers report using a wide range of lubricant tests in their work, including both standardized tests and in-house testing methods. While the specific tests chosen depend on the lubricant’s application, oxidation tests are among the most widely used. When lubricants fail before the end of their expected life, most readers say contamination is likely the reason, with oxidation as another likely cause.

Q.1. What tests do you use to choose a lubricant for a long life?

Rotating pressure vessel oxidation test (RPVOT), Fourier transform infrared spectroscopy (FTIR).

Depends on the lube’s chemistry, proposed usage and environment.

For lubricating oil: remaining useful life evaluation routine (RULER) test, total acid number (TAN), FTIR (ASTM D7414), oxidation test like ASTM D943, D2272 and D7098.

Oil analysis.

Oxidation.

Test in bearings: same bearings as application under similar loads, lambda ratio, etc.

Wear, oxidative stability, customer key life testing, field trials.

In my area of work (heavy duty axle lubricants), beside required performance tests, we run field tests to establish long life.

Generally, oxidation test. 

RPVOT and turbine oil oxidation stability test (TOST).

Bearing tests, oxidative stability testing, long term storage testing.

One may consider choosing one or more of the many thermo-oxidative stability tests that mimic the conditions in which the lubricant will function.

Oxidative and thermal aging, FTIR and Raman spectroscopy of lubricated test samples.

Oxidation, four-ball (wear and weld), viscometrics (viscosity, viscosity index [VI], etc.), additive package analysis.

Dry TOST, pressure differential scanning calorimetry (PDSC).

Full water analysis if it is a water soluble lubricant. Then biostability, foam, wear performance. If it is non-aqueous (straight oil), wear performance tests, oxidation stability tests, foam tests, corrosion tests, acid titration, viscosity stability and elemental analysis.

Oxidation tests.

Oxidation stability, TAN/total base number (TBN).

The type of test depends entirely on the application conditions.

RPVOT, water separability, foaming characteristics and air release.

Oxidation tests using various ASTM and in-house designs.

Oxidation, nitration (my job focuses mainly on heavy duty diesel).

TOST, RPVOT.

Test of oxidation stability.

In high-voltage substation circuit breaker applications, the bearings only run intermittently, maybe two or three times per year. The remainder of the time, the lubricant is static. I perform an oxidation induction test (OIT) on the lubricant. If it is exposed to sunlight, I may also use an ultraviolet (UV) light test. Secondary testing includes oil bleed and wettability (surface tension).

Viscosity, water content, shear stability, oxidative and thermal stability.

RULER and RPVOT.



Kinematic viscosity; water (crackle); additives; contaminants.

Oxidative stability.

Karl Fischer, particle count and filter debris analysis.

Oxidation stability, compatibility with contaminations.

Antioxidant.

Oxidation/thermal stability, wear/corrosion resistance, detergency and dispersancy.

None, when testing aged product, we use common quality control (QC) testing, acid value and infrared (IR) looking for oxidation and general condition.

Oxidation stability, wear protection, detergency/dispersancy.

I prefer isothermal thermogravimetric analysis (TGA) run in air.

Acid number, base number, RPVOT, metals for additive content.

I don’t do my own testing. I rely on supplier information, which is not standardized between suppliers. Base oil type can give a good indication of life, although formulation also influences life.
 
Depends on the application and then you choose the lubricant that will provide the best protection for the time frame needed.

Manufacturers case studies as proven example(s).

Viscosity at 40℃, acid number, FTIR, ASTM color.

TAN for our polyalkylene glycol oil (PAG)-based products as other testing doesn’t work well with it.

Component OEM specifications, operating conditions, supplier technical competence, lubricant availability survey, lubricant usage references, on site verification if similar/same lubricant is already in use (oil diagnostics review if available).

This completely depends on the application. Typically these are oxidation tests, but in certain applications, they can be wear tests.

1.) Field experience: survey users including operating and environmental conditions. 2.) Long term tests in ovens and environmental chambers. Tests to include moisture, particularly with ester lubricants. 3.) For temperature in cold applications, starting torque is a key factor.

Oxidative stability, viscosity index, TAN.

RPVOT and linear sweep voltammetry (LSV).

Viscosity.

Oxidation induction time ASTM D6186, then maybe TOST ASTM D943, water separability ASTM D1401.

RPVOT, TOST, PDSC, TAN.

It would depend on the type of lubricant and application.

The exact scope of tests depends on the application, but we always conduct tests to check tribological properties (effect of friction and wear) and rheological properties (study of flow under force) of a lubricant as these can often determine its lubricity and how long it will protect particular application. I would add to this oxidation stability testing as oxidation can affect lubricant’s lifetime and accelerated aging test.
 
TOST ASTM D943.

Oxidation tests depending upon the application.

Oxidation, TAN, TBN.
 
TAN, viscosity, RULER.
 
Elemental analysis, viscosity, base number and oxidation.

Oxidation.

Viscosity, TAN, TBN, water content, mineral content.

RPVOT (ASTM D2272).

Thermal and oxidation stability.

Oxidation stability.
 
High frequency reciprocating rig (HFRR) or mini-traction machine (MTM) reciprocating.

Oxidation, TBN and TAN.

Four ball, block on ring.

OEM in-house tests are best for this determination. Engine tests developed by accredited organizations (ASTM, CEC) for lubricant specifications are to be trusted also.

DIN 51821, DIN 51819, ASTM D8206.

Oxidation stability tests, viscosity tests such as kinematic and Brookfield viscosity ones, wear tests such as the four ball wear test. Additionally, thermal stability tests and pour point/flash point tests for applications in varying temperature conditions.
 
Application, cleanliness of area it is operating in, viscosity index, cost, availability.

FE9 to DIN 51821 and ASTM D3336 are used for greases, TOST testing is used for other industrial fluids.

Depends on situation.

What do you recommend to a customer who has a lubricant that is past the expiration date?
Discard         21%
Test and decide 79%
Use the lubricant 0%
Based on an informal poll sent to 15,000 TLT readers.
Oxidation stability, viscosity and wear test.

Oxidation and sonic shear in hydraulics.

Viscosity index.

We used tests to check condition of lubricants is oil cleanliness as per ISO, percentage of water in oil.

For a multigrade engine oil, its shear stability, environment protection and recommended drain interval.

Viscosity index, TAN, TBN.

Oxidation stability tests, viscosity testing, water tests and thermal stability analysis.

Four-ball weld.

Field test.

RULER, MPC, FTIR, air release.

Different aging tests, at various temperatures.

It is dependent on the requirements of the application, i.e., type of application, effect of surrounding environment, operating conditions. Typically, tests such as thermal stability, oxidation resistance and shear stability are required. However, other tests may be needed to understand the required properties of the lubricant.

That would highly depend on the application type, external working conditions (including working temperature), running conditions and possible OEM requirements. Upper temperature tests and oxidation behavior would be a good starting point.

Oxidation stability.

Q.2. What is the most common reason that a lubricant does not reach its expected life?

Contamination and heat.

The lube is insulted in some fashion: debris contamination, water contamination, etc.

Quality, contamination and operating beyond the design parameters like high temperature or pressure.

Mechanical failure.

Contamination.

The service that it’s in like hot weather or dirty environments.

Oil depletion due to chemical breakdown resulting from wear and particulate generation, shelf life question—answer depends on the lubricant in question. For lubricated parts, maintenance interval depends on the lubricant used.

Contamination.

Failure due to additive depletion.

Generally contamination. Of course the answer could fluctuate on whether you are talking about a lubricant in use or an unopened packaged product on the shelf.

A common shelf life for lubricants is five years; do you expect the actual shelf life to be longer?
Yes 61%
No 39%
Based on an informal poll sent to 15,000 TLT readers.

Contamination is by far the most common reason.

Overheating.
 
Contamination, misuse.

It is used in equipment for which it was not designed.

Heat stress-premature oxidation.
 
Oxidation, unable to handle contamination (particulate, water, etc.).

Contamination, or extreme conditions.

Contamination, oxidation, lack of maintenance, improper operation.

Oxidation, contamination.

Contamination, TBN depletion.



Lubricant properties changing over time due to wear particles or other contaminants in the lubricant.

Degradation due to contaminants/oxidation.

Contamination.

Contaminants such as silicon (dirt), fuel dilution, coolant leak.

Oxidation.

Additive depletion. 

The main reason is the fuel quality, especially diesel fuel.

Poor lubricant maintenance program and storage.

Adverse lubricating conditions, typically moisture, poor cleanliness or elevated temperature.

Oxidation.

Contamination (tramp oils), oxidation.

Our oil pumps, when in use, are subject to aeriation and oxidation due the engines be vented to the atmosphere at 14.7 lbs. per square inch. A common yard stick we use is 1% aeriation equals 3% negative lubrication properties. Anti-foaming additives are very important in lubrication of internal engines. Once again, oil adhesion at engine shut off must remain for the next start-up or dry start-up conditions will exist. Synthetic oil formulations are more dependable for consistency over natural crude oil.

Thermal shocking, entered contamination, improper use.

Contamination, cleanliness control.

Premature system compromises such as debris/fluid contamination via filter/seal leakage or component breakdown.

Storage conditions, contamination with opened containers.

Oxidation degradation.

Heat.

Under-engineering, thermal load, other lubricant contamination.

Severe operating environment and/or contamination.

Temperature, external contamination.

High heat applications will shorten the expected life.

Inadequate filtration.

Leakage, ingress of water and dust, mechanical or chemical aging.

With appropriate application it must be contamination. 

Contamination either from misuse or improper storage.

Environmental degradation.

Contamination, over heating, water ingression, not changing filters, cold temperatures.

Contamination with dirt or water. Secondly evidence of overheating—additive trend decline progress curve.

Oxidation, bleed and evaporation are all important in long life.

Contamination, or extreme operating conditions.

Contamination, do not use properly.

In my experience it has been the ingress of water.

Contamination and heat.

Usually it’s either the viscosity or acidity in the oil.

After a lubricated component has been sitting on a shelf, at what point would you require re-lubricating without testing before putting the component into service, assuming the component itself is not damaged?
5 years 89%
10 years     9%
15 years    2%
20 years    0%
Based on an informal poll sent to 15,000 TLT readers.

Field operating conditions are more severe and variable than any lab test to predict lubricant’s life.

Oxidation or volatilization. There are also contamination sources that can end the oil life too early, but oxidation and oil volatility are most common, in my opinion.

Very high temperatures, exposure to exhaust residues, contamination.

Contamination.

Not used within the time limit.

Contamination, especially commingling during compartmentalized bulk delivery.

Oxidation.

Contamination from improper storage.

Temperature, solid and liquid contamination.

Contamination.

Oxidation and water content.

Part materials, external environmental variables (temperature, air).

Improper storage of lubricants that does not prevent contaminants from getting into the products. These could include moisture and particle commination.

Overheat, contamination.

Water and dirt contamination, overheating.

Impurities of surroundings, decrease in viscosity.

Oxidation, degradation and decomposition.

Contamination.

Improper application; excessive operation temperature; wrong recommendation from start; contamination; ingress of sand and dust; leaking seals, gaskets and containers; ingress of water; fuel dilution.

Contamination, improper lubrication practices, additive depletion due to temperature.

Contamination, wrong selection of appropriate lubricant.

Oxidation and loss of oil content in grease.

Quality of the raw materials, method of manufacturing as the formulation itself. Next to this, the knowledge of the application (bad grease selection). Mainly it fails because it is seen as a cost by the purchasers, not seeing the lifetime benefits using a more expensive but suitable grease for the application.

Contamination.

Oxidation with greases and additive separation with oils.

The storage conditions.

Contamination and excessive exposure to heat.

Either manufacturing problem (low quality base oils and additives), operator mishandling or operating parameters.

Higher loads, temperature and vibration that actual capacity.

Contamination and improper storage and handling.

Moisture contamination.

Unbalanced formulation of antioxidants or lacking solubility to keep degradation products in solution.

Contamination with other products during application.

Poor storage conditions, poor lubrication routines, improper lubricant selection.

Incorrect lubricant-application combination.

Oxidation and contamination.

I think most likely contamination, chemical and/or physical.

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.