- Buyer's Guide
When a company decides to instigate on-site oil analysis, obvious questions such as: “What tools and equipment are we going to use?” and “What types of tests do we want to perform on-site?” are typically asked. These questions are quickly answered with another question: “What kind of budget do we have for this project?”
While with unlimited funds, the decision would be far simpler; the reality for most, if not all individuals just beginning an oil analysis program, is that the budget is most likely undersized. With an undersized budget and oversized ambitions for an on-site oil analysis program, deciding which tools to procure and in what order to do so can be critical to the on-site oil analysis program’s success.
Categories of Oil Analysis Testing
When spending budgeted money on an oil analysis program, choosing which tests should be performed on-site and which test slates are best deployed by the off-site lab is the most important decision. Typical test slates can be divided into three categories: on-site screening, routine laboratory analysis and exception testing.
On-site screening tests can be performed at various frequencies, depending on machine, lubricant stressing conditions and the reliability objectives of the asset owner. Machines and lubricants that operate at high loads/speed and/or are exposed to high temperatures and environmental contaminants need more frequent screening. The type of screening test needed is machine- and application- dependent. For instance, oil exposed to steam would need to be screened for water. High temperature lubricants, however, don’t need water assessments but rather tests that indicate thermal distress, such as viscosity or blotter spot tests.
Routine tests are also application- and machine-dependent. They are either performed on-site by a fully equipped laboratory, or by an off-site commercial laboratory. Common routine tests include particle counting, elemental spectroscopy, viscosity, infrared spectroscopy, acid number and moisture analysis, among many other possibilities.
Just as the name implies, exception tests are triggered by a nonconforming inspection or test result coming from a screening test or a routine test. Tests that are performed on exception in some applications are performed routinely in others. Basically, the idea behind exception testing is to perform expensive and sometimes manually intensive tests only when needed. Exception tests enable the oil analysis practitioner to explore more deeply into the oil’s database. Analytical ferrography, demulsibility, XRF and scanning electron microscopy are examples of exception tests. An exception test might also be a test that was not included on a routine test slate for streamlining or budgetary reasons.
On-site Oil Analysis Strategy
With rare exception, the goal of on-site oil analysis is not to replace the commercial lab. Commercial labs can invest millions of dollars in state-of-the-art scientific instruments. A reputable commercial lab gives the on-site lab the flexibility to have numerous exception and lubricant property tests performed when needed without having to carry the associated costs of hardware and training. Except when a large number of samples need to be routinely analyzed, it is unrealistic for an on-site lab to be sufficiently equipped with the range of analysis instruments typically needed.
Consider the following key points when selecting on-site tests:
Many view a particle counter as the most beneficial on-site tool and believe it should be acquired first. The data from this instrument will provide critical information regarding the equipment health and will call attention to associated exception tests when needed. The benefits of having this tool on-site are numerous. Early detection of increased particle levels can be a powerful indicator of both wear and contamination-related problems.
Making the Most of Every Last Dollar
So what is the best approach to on-site analysis with a limited budget? The following is a list of candidate tests that might be preformed on-site:
ISO Particle Count
Moisture Detection Devices
This list we can be reduced by removing tests that are not required on-site because they are seldom performed and/or because the equipment and training costs are exorbitant.
For example, when analyzing a gearbox oil, elemental analysis and FTIR are removed from the on-site analysis list strictly based on the initial costs. Foam, demulsibility and rust tests can also be removed from the on-site list based on the expected limited frequency at which they will be performed. Also, Karl Fischer moisture involves wet chemistry, which may not be suitable for an on-site lab because chemicals must be handled and a lot of training is required to accurately perform these tests. Because it’s a gearbox, soot and fuel tests are also not needed. The abridged on-site list of tests for a gearbox and the estimated associated costs are illustrated in Table 1.
As the table illustrates, there are several effective ways to utilize even the most modest budget. Given a budget of only $5,000, several tools that will provide significant information regarding lubricant and equipment health can be procured. Tests for water, viscosity, acid number and solid contamination are possible with a $5,000 budget. As the budget increases, so does the arsenal of tools.
There are several makes and models of particle counters on the market today. Most models are laser-based instruments and a couple are pore blockage (mesh obstruction) instruments. Although most models cost more than $10,000, a particle counter should be at the top of the shopping list when the budget is available. When performing ISO particle counts of any kind, it is crucial for the sample to be violently agitated by an industrial paint shaker. These two items need to be procured at the same time to ensure accurate results.
Hot plates are a simple way to identify the presence of water in a system. Hot plates can be procured from any lab supply vendor for as little as $150. This pass/fail method will identify free and emulsified water in the oil and allow the oil analysis practitioner to make educated decisions on necessary exception testing. Because free and emulsified water pose a significant risk to equipment health, a small investment has substantial return potential. This item should be included for purchase in all budget categories.
As with particle counters, there are several viscometers on the market today. There are automatic lab viscometers, simple bench-level viscometers and field-use manual viscometers. Manual viscometers such as the viscosity comparitor, allow for a quick comparative measure of a lubricant’s viscosity, but do not provide the same accuracy as more sophisticated instruments. For low-budget on-site screening, an inexpensive viscometer is a must and can be used to determine if the correct grade of oil is in use. When a larger budget is available, a more accurate lab-style viscometer should be included.
Acid Number Kits
Acid number kits are designed for use by nontechnical individuals in an on-site environment. These kits provide premeasured, nonhazardous reagents in ready-to-use ampoules. Within minutes, an accurate measure of acids in the oil can be recorded. Although accurate, these test kits only approximate lab titration methods such as ASTM D664 and the two should not be compared quantitatively.
Ferrous Density Testers
Ferrous density testers measure ferromagnetic metal debris (iron or steel) in a given sample. Usually reported by an index number, some results are reported as a percentage of the overall particle count of the same sample. Others simply provide a gravimetric concentration such as micrograms per milliliter. Ferrous density testers can be powerful tools for identifying mechanical failures and for prompting exception tests such as analytical ferrography.
The instruments needed to perform ferrogram analytical ferrography include a slide maker and a microscope. Although different slide makers are available, all produce a glass slide by holding ferrous particles in place with a magnet as the fluid is passed over. Typically, the microscope will have a 100X to 1,000X resolving power with a digital camera to capture ferrogram images. These items go hand-in-hand and typically carry a large price tag. A significant amount of training and education must accompany a successful on-site ferrography program. These instruments are often left to mature on-site programs with significant resources.
Patch Test Kits
Alternatively, lower cost filtergram makers, also called patch kits, are valuable tools that offer high return on investment when used routinely. They can be used to provide data on contamination concentration and source, and ferrous and nonferrous wear debris. They are similar to analytical ferrography, even with some superior features, and they should be a part of all on-site oil analysis programs of all budget levels. Patch testing can also enable microscopic particle counts in lieu of automatic particle counters.
There are several moisture meters based on different measurement principles on the market today. Some of these instruments measure the relative humidity of water in oil and provide results in percent saturation (or dew point). Regardless of the technology deployed, a reliable means to detect and quantify free and emulsified water is nearly always justified for on-site analysis.
Even the most modest on-site oil analysis budget can provide the resources necessary for significant instrument inclusions. With as little as $5,000, a strategically important part of an oil analysis program can be brought on-site. The immediate benefit to bringing oil analysis on-site is that machine reliability information is provided as soon as it’s needed. Timely and significant on-site data combined with data from quality commercial laboratories and an entire menu of available routine and exception tests is a recipe for a world-class oil analysis program.