What is the Best Test for Used Lubricants?

You’ve pulled the oil samples, labeled the bottles, boxed them up and sent them off for testing. Play along with us now - suppose your lab could conduct only one test. What would it be?

Tough call? Consider your options. If you’ve implemented a rigorous proactive maintenance program, and keep your lubes extremely clean and dry, you’d probably opt for a particle count. Why should you choose the particle count?

The particle count is one of those catch-all tests. Almost anything that can go wrong in a machine will result, sooner or later, in an increased particle count. If misalignment, overloading, water contamination, viscosity breakdown or bearing failure occurs, the particle count will rise. But is a particle count the only “best-fit” test?

Maybe you’d pick different tests for different environments and applications. Some situations may call for wear debris, water or other tests. Do you have a favorite test for your applications? In a recent online poll of Lube-TipsTM subscribers, readers were invited to share their thoughts on which test is the most valuable oil analysis tool. And here’s what they had to say.

The primary test I would look at is an acid titration. This can give two pieces of information, acid number (AN) and pH. A low pH indicates ingestion of strong acids, which can attack bearings and result in corrosive wear. Measuring pH allows us to catch this type of problem before undue wear occurs. AN will give you the state of oxidation of the fluid and depletion of corrosion protection, allowing us to do condition-based oil changes.

Daryl Beatty Dow

I am involved in the predictive maintenance at our plant site. I do most of the vibration readings and run the oil analysis program for our maintenance department. I do a particle count four times a year, and on the fourth sample I also do analytical ferrography to try to determine the origin of any particulate matter in the oil. If I have a suspect machine I perform the ferrography more often. The particle count is an important tool as an early warning of a problem in the machinery reliability program, and combined ferrographic analysis, in my opinion, is the most valuable test.

Ken Lee Celanese/CA

We regard the glycol test as key to a lot of potential problems. Coolant intrusion, either salt water or antifreeze, is the leading problem maker for us. If there is no glycol present and the sodium (from sea water) or copper (from the cooling bundles) has increased from our elemental analysis, I assume a leak on the water side. Excess sodium can also indicate exhaust problems, a common failure.
Kip Wiley, Pilots Point Marina

If I had only one option, it would be the particle count. That is the first thing I look at when I get an oil analysis report back. Of course, different equipment merits looking at different tests. Our chiller turbines have a history of water, so I look at the water closely. Our generator turbines have oil that is more than 10 years old so I tend to look at AN and viscosity. Overall, however, the particle count test is the best at indicating problems in our otherwise very clean oil supply.
Robert Niehoff, Iowa State University

I like your suggestion regarding particle count, but a close second choice of preferred tests would be viscosity. Deviations in viscosity can reveal soot loading, fuel dilution, oxidation, lubricant misapplication/admixture, VI polymer additive shearing and certain contaminants. While the underlying cause of the change in viscosity may not be readily apparent, if you have some basic information about the system from which the sample was drawn and maintenance practices relating thereto, you can make educated inferences from the viscosity reading alone.

David Krause Parman Lubricants Corporation

Gravimetrically filtering fluid through a 0.8 micron Millipore filter will trap the vast majority of metallic and nonmetallic debris present. After drying the membrane filter, microscopically counting and examining the morphology of debris will provide much more diagnostic information from both a contamination and wear related standpoint. Gravimetric analysis with microscopic evaluation is the way I would go with one sample and one test.

Bob Broaddus Analysts, Inc.

Our first call is always FTIR. We have baseline spectra of all our lubricants and have routines whereby we subtract the new sample baseline from the used sample spectrum, allowing us to identify contaminants such as water, CO2 and glycol. It can also show the absorbance of plasticisers from seals and can identify fluid degradation when used in the hands of a skilled operator.

Dr. Gareth Fish GKN Technology Ltd