Once established, such programs enable users to confirm that the proper lubricant is being used; prevent potential over- or under-lubrication; track lubricant use and waste; raise flags about quality (including inorganic contamination, debris from wear, or lubricant degradation); and contribute to the desired cleanliness of machines and systems.

Like other predictive maintenance processes, lubricant analysis can satisfy two objectives: detecting a problem and diagnosing the problem source. Many lubricant suppliers often provide a basic lubricant analysis as an added-value service for using their lubricants. However, these suppliers may only quantify whether the lubricant meets the specification as a lubricant. Unfortunately this service offers little information in regards to the health of the machinery. For this reason, one of the first steps in establishing a predictive maintenance program for lubricants is to identify the lubricant testing technology employed to make analytical assessments.

While lubricant monitoring and subsequent analysis may be essential in helping users manage their machinery assets more effectively, the good news is that not all lubrication inspection has to be performed in a laboratory. Many of the characteristics of working lubrication can be examined visually or with the aid of very simple tools.

For example, clarity and water contamination can be observed in a standing sample. Ferrous materials – filings, metal dust – can be detected using a magnet drawn up the side of a glass jar containing lubricant diluted with a solvent. Flow and discoloration can be noted in a bulls eye sight glass. Viscosity can be monitored using simple in-plant tools. These are good day-to-day observations.

On a broader and more in-depth scale, industry experience tells us that several critical machine and lubricant parameters should be routinely evaluated as part of a lubricant monitoring and analysis program. These include machinery wear particles, contamination, and lubricant and/or additive degradation.

Machinery Wear. All machines normally experience inorganic contamination resulting from wear. Test and measurement techniques for small wear contamination are based largely on the predominant lubrication regime.

In machines where the operating regime largely is hydrodynamic (full fluid film) and the wearing components are nonferrous bearing surfaces (such as with sleeve and pad bearings), Rotrode Filter Spectroscopy is appropriate. For machines with rolling element or steel gear component wear as the primary failure modes, direct-reading ferrography will prove most suitable. These techniques also can be used periodically to measure large severe wear particles.

Contamination. Contamination can be present in four different forms: gaseous, fluid, semi-solid, or solid. Selection of the analytical method for contamination ultimately will depend on the machine, lubricant and environment.

The best practice selects test methods relevant to the probability that a specific contaminant can enter the machines lubricating system or be produced within the machine. Users should inspect the machine to be sampled and list likely contaminants that should be detected in the lubricant analysis program. (The list could include fluid, dirt, water, fibers, coolant, and others.) Once the contaminants to be measured are identified, the appropriate analytical techniques can be chosen to measure their presence at a minimum threshold level.

Lubricant Degradation. All lubricating oils contain additives to delay the natural process of degradation. Since lubricants will lose their serviceability (and must be replaced) when required additives for an application become depleted, measuring the degradation process can help prevent related problems before they can occur.

Standard analytical methods for measuring degradation include increases in viscosity or changes in alkalinity and/or acidity. When changes in viscosity, alkalinity and/or acidity occur (from degradation instead of contamination), it is a reliable sign that sludge and varnish have already begun to form in the machine and that the oil is overdue for changing.

Typical Tests and Values

Truly meaningful lubricant analysis programs will encompass testing a wide range of parameters using a variety of methods. Some of the most common test areas:

Color and Appearance. These characteristics should be noted as part of routine evaluation, although some oils may be too dark for effective appraisal. If this is the case, the volume of oil observed can be reduced to a constant depth for proper observation.

Viscosity. Oils found to be outside the lubricant specification are always considered abnormal. However, a change within a grade also can be a sign of trouble. Users should be alert for changes of 10 percent from new oil.

Base Number. Alkalinity values (base number) of new diesel engine oil can be compared to the used oil. A general rule for oil change is when the alkalinity value of the used oil is 50 percent of the new oil.

Acid Number. Acidity varies in new unused lubricating oils, based on the concentration of antiwear, antiscuff and extreme pressure (EP), or antirust additives. Increases in acidity above the new oil reference will indicate oil degradation. Lubricants having additives such as ZDDP and EP agents will generally exhibit higher acidity to start than those containing only rust and oxidation additives.

Water Content. In new and used refrigeration oils, less than 50 ppm water content is preferred, and the water content of diesel engine oil can be substantially higher (500 ppm). Stern tube oils containing water emulsions often are in excess of 50 percent water.

Emulsion. Water separability testing is primarily used to evaluate steam turbine, hydraulic and circulating oils susceptible to high water contamination.

Foam. In systems where foam is perceived to be a problem, a foam test should be performed to confirm whether the lube oil is the source. If the oil is not the problem, attention must turn to other parameters – such as mechanical or operational influences – to resolve the issue.

Fluid Sampling and Handling

The validity of any lubricant program will hinge on proper sampling and handling techniques. Without them, results and conclusions may be questionable. Here are five suggested guidelines to advance the cause of reliability:

1. Users should have written procedures to follow for taking samples consistently and according to good maintenance practices. Samples should be taken in the same manner each time to allow accurate trending of oil properties.

2. Representative sampling can only be reliably obtained either from an agitated tank or a free-flowing turbulent line. A sample line should always be flushed before a sample is taken, and the system should be in steady state operation. An agitated tank is one currently in use or within 25 minutes of shutdown.

A fluid sample will probably not prove representative if the system fluid normally operates hot but the sample is drawn cold; if the fluid in the system is one color or clarity in an in-line sight glass but the sample is a different color or clarity; or if the fluid viscosity of the reservoir fluid is different from that of the sample when both are at the same temperature.

3. Sample containers (usually supplied by an analysis facility) should be:

Clean: If in doubt about its cleanliness, use another container. If this is not possible, flush it out with the fluid to be sampled.

Resistant to the material being sampled: For example, fire-resistant phosphate ester fluids will dissolve certain plastics, including the liner in some bottle caps. To verify a containers resistance, if time permits, allow the sample to stand in the container and observe its effects.

Appropriate for required handling: Containers with leaking tops and improperly protected glass containers are unsuitable for shipment.

Appropriate for the analyses required: Some plastic containers may not be acceptable for flash-point testing, because volatile materials may leak through the container walls. Containers should be either glass or polyethylene for wear debris analysis samples, to avoid material leaching.

4. A sample should be properly marked in order to track the history of a particular piece of equipment.

5. Plan for preservation. Samples should be tested as soon as possible. Users should store samples away from strong light and as close to room temperature as possible. If samples are to be retained for extended periods of time, special arrangements should be made to safeguard the integrity of the sample. (This may include storing in dark amber glass bottles in a cool area.)

When any lubricant analysis is completed, expert data interpretation will point users in the right direction toward understanding the root causes of a problem and suggesting remedies.

Results should be documented and shared with appropriate personnel. Reports should at least cover minimum and maximum alarm limits (when available), detailed analysis of wear, contamination and oil or additive degradation, and information identifying the particular machinery.

One final note: The very first step in establishing an effective lubricant program involves specifying and using the correct lubricant for an application.

Although standardization of a single lubricant plantwide may be appealing in order to increase purchasing power by buying in quantity, production machines operate as highly specialized rotating assemblies, and in many cases their lubrication requirements are quite specific. Mixing types will prove long-term fatal and should be avoided at all costs.