ALS Tribology eSource
September 6, 2011

Which Test Package Should I Use?
by Ambrose Hughey
Business Manager, Northwest

One of the questions I often get asked when training is “Which test package should I use?” Often, test packages are designed to focus on parameters that are component specific. For example, we would not recommend the same test slate for an engine sample as a hydraulic sample. We also would not recommend the same test package on a natural gas engine as a diesel engine.

Also contributing to which test package is the most effective, is why the sample is being sent to the laboratory.   Is this a routine oil sample for trend analysis? Was this sample pulled due to an operating issue/concern?  Did the unit fail and there is the need to gain insight on why it failed?  Selecting the correct package and additional testing can provide additional value to your oil analysis program. A routine oil analysis package does not contain the appropriate tests for a failure analysis such as analytical ferrography by using our microscopic particle evaluation (MPE).

Basic testing is often selected for economic reasons, but when maintenance professionals start asking questions, answers are not always available with the limited test data provided by the most basic packages. The savings on upfront costs can lead to expenses down the road.

Below are some value added tests not typically provided in basic oil analysis packages:

Base Number - Generally specific to crankcase oil, the base number measures the alkalinity reserve which is the oil’s ability to combat the acidic byproducts formed during the combustion process. Knowing the amount of reserve alkalinity is a key parameter for monitoring drain intervals.

Acid Number – The acid number measures the amount of acidic constituents in the oil, which can provide an indication of the amount of oil degradation or acidic contaminants ingressed into the system. Too high of an acid number and the oil will actually begin to attack the oil wetted components as opposed to protecting them. Measuring acid number provides an indication as to the remaining life of the oil and suitability for continued use.

PQ – Specific to monitoring ferrous particles, PQ has an advantage over traditional spectrochemical analysis.  Spectrochemical analysis has size limitations of particles while the PQ does not. Using PQ to compliment spectrochemical analysis provides insight in the size and degree of iron wear.

Particle Count – Critical for monitoring the cleanliness of filtered industrial systems. Clean systems require a minimum level of cleanliness to operate reliably, and the particle count gives maintenance professions a measure of the oil cleanliness in order to determine if actions are necessary to maintain cleanliness targets to increase machine reliability.

Varnish Potential – With typical routine oil analysis, varnish precursors will go undetected. A system may potentially have a serious varnish problem, and routine oil analysis reports indicate a “Normal” condition giving the end-user only part of the overall condition of their lubricant. There is not a direct measurement or specific test for varnish precursors in hydraulic and turbine lubricants, but ALS’s comprehensive test package can predict the lubricant’s potential to create varnish buildup.

Filter Patch Test - A common method for making a more detailed determination of wear occurrence, and debris, especially for non-ferrous materials, is to employ a Filter Patch Test examination using a microscope for Wear and Debris Analysis. A measured portion of used oil is filter through a membrane filter patch and visually examined microscopically for a qualitative report on the material captured. Observation will generally be accompanied by a photo of the filtered debris material on a test report.  

MPR / Analytical Ferrography – MPE or Analytical Ferrography utilizes a skilled analyst examining a prepared ferrogram slide with a computer aided microscopic to identify the composition of the material present in a used lubricating oil sample. Wear material and other debris suspended in a lubricant is deposited and separated onto a ferrogram slide maker. The sample is diluted to improve particle separation onto the ferrogram slide. Magnetic separation of wear material from the lubricating fluid attracts ferrous particles out of the oil onto the ferrogram slide maker. Though the method is biased to ferrous material, other nonferrous wear particle and contaminants are also captured and identified. The slide is examined under a microscope to distinguish composition, morphology, particle size and relative concentration of the ferrous and non-ferrous wear particles. Treatment of the ferrogram with heating and chemicals will further distinguish identification of the metallurgical composition of the wear material. The skilled analyst performs the analytical ferrography to provide a root cause for wear mechanisms based on the morphology and composition of the particles.

While only a few of our value added tests are discussed above, ALS Tribology has an extensive offering of testing capabilities. Please contact your local laboratory for any additional testing needs.


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