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You may be surprised to learn that there are no less than five lubrication performance properties that are missing from nearly all in-service oil analysis reports. These are not esoteric properties that are of limited value or interest to those in charge of machine reliability. Instead, they represent the core foundation of a lubricant’s formulation and purpose. In other words, they relate to the essence of what we expect and need from a lubricant. And, these are the properties that are imparted by additives and commonly found on a lubricant’s product data sheet (spec sheet).
Don’t get me wrong; I am not suggesting that commercial oil analysis labs are duping their clients by shortchanging testing services. Many of these missing tests cannot be practically performed on routine oil samples because they are expensive, involve prolonged test periods and/or require large sample volumes. Yet it is important that the user community fully understand what they get and what they don’t get when they pay $35 for oil analysis.
Below is a list of “performance” tests that are often used to portray the quality and performance capabilities of a new lubricant. Unlike ordinary used oil analysis tests that report physical and chemical properties such as viscosity, acid number, flash point, elemental analysis and contamination, performance tests work by challenging a lubricant in some way similar to the actual machine work environment. The reported results characterize or measure how the lubricant responded to the challenge. The following are typical examples of performance tests:
Film Strength. There are numerous ASTM test methods that attempt to depict or measure a lubricant’s ability to reduce friction and control wear under wide-ranging rolling and sliding conditions. Adhesive wear, contact fatigue and two-body abrasion are examples of wear modes affected by a lubricant’s film strength. Antiwear and extreme pressure (EP) additives are added to many lubricant formulations for this purpose. These additives are subject to depletion and impaired performance as a lubricant ages and becomes contaminated. Conventional used oil analysis tests do not measure film strength.
Air-handling Ability. The quality of a lubricant’s basestock and the use of certain additives can define its air-handling abilities. We want a lubricant to release entrained air rapidly and to suppress the formation of foam. Air handling is nearly impossible to interpret from ordinary oil analysis.
Water-handling Ability. Like air handling, the lubricant’s ability to efficiently shed water during static conditions is difficult to anticipate from the usual slate of oil analysis tests. Yet for most lubricants, a loss of water-handling ability not only reveals risks from oil-water emulsions but also signals faltered performance of other important properties. This property too often goes unnoticed by the used oil analysis community.
Corrosion Control. Corrosion control is a fundamental lubricant formulation objective. There are many additives used to neutralize corrosive agents or form protective barriers on sensitive machine surfaces. These are sacrificial additives that lose their effectiveness over time. Nonetheless, no conventional used oil analysis test, other than the base number, reports the residual effectiveness of the corrosion-protecting qualities of an in-service lubricant.
Oxidation Stability. With rare exception, nearly all lubricants are formulated with oxidation inhibitors to stem the rate of oxidation. The most robust and superior lubricants on the market today emphasize this important lubricant property. These include premium turbine oils, long-mileage motor oils and synthetic lubricants of all types. While post-oxidation by-products can be detected and measured by ordinary oil analysis tests (after the fact), the residual oxidation stability of a lubricant is far more difficult to assess. That said, some success has been reported with techniques such as linear-sweep voltametry and infrared spectroscopy (additive spectral bands). These tests are becoming increasingly common in commercial oil analysis, although used on less than five percent of all samples tested.
Besides those properties listed above, there are numerous other performance properties that are application- and lubricant-type specific. These include volatility, resistivity, biodegradability and thermal stability. And there is a slew of properties relating specifically to grease formulation including consistency, dropping point, separability, water wash-out, pumpability, etc.
While it is true that commercial oil analysis labs will not be conducting performance tests on in-service oils any time soon, the need and application are still very real. The following are examples of when performance testing is both practical and vitally needed:
After oil reclamation or oil reconditioning (especially when dehydrators and acid scavengers have been used)
After in-machine additive reconstruction
When the compatibility of two mixed oils is in question
After extreme exposures (for example, radiation, heat, chemical, etc.)
After prolonged storage
Before or after a major outage
After a long shutdown period
Before starting standby equipment in critical applications
After a chemical flush where there is risk of residual chemical mixtures
For lubricants exposed to extremely long service life
When a defective and faulty new oil formulation is suspected
There are probably numerous other instances when performance testing can be justified. In general, when in doubt, consider running tests that can help confirm performance properties you need and expect from the lubricant in question. Although expensive and time consuming, the benefits can far outreach the costs and hassle to perform.