The oil analysis test results are broken down into wear metal concentration, oil condition, and contaminants. Each analysis normally has past results included.
The most important information the oil analysis lab will provide would be the overall comments made by the oil analysis technician. The technician takes past results and the existing results and formulates a course of action. The most important information the customer will provide is a thorough representation of the equipment being used and the oil being tested. Effort should be made to ensure that consistent and accurate information is provided.
Test results from previous analysis are important for comparison purposes. The past results help the oil analysis technician and the customer establish any trends that may be emerging and take the appropriate action.
Wear metal analysis tests for various elements found in the oil that may be from wear debris, contamination, or the additives found in the oil. When an oil-lubricated component begins to wear, small amounts of metal become suspended in the oil. These trace amounts of metal are the first indicators of component wear. If left unattended, the wear will increase and potential part failure will occur. In extreme cases, metal shavings from worn gear teeth can be found in the oil. If the wear is severe, metal shavings can be seen during the oil change and will contribute to more wear. This situation can occur in gearboxes, hydraulics, engines, and air compressors. Many components and parts are made up of several different metals. An oil analysis technician can determine which component is beginning to show signs of wear just by the type of metal and the concentration found in the test sample.
Wear metal analysis is performed by emission spectroscopy. This test provides the concentration of metals for wear, additive concentration, and contamination found in lube oils and is measured in parts per million (ppm) (1,000 ppm equals 0.1 percent). Emission spectroscopy measures metallic particles that are less than 10 microns in size. Many components have different levels of acceptable concentrations of wear metals. A transmission or gearbox can withstand higher levels of wear metals compared to a hydraulic pump or engine.
A trained oil analysis technician can determine critical levels and provide the appropriate recommendations. Keep in mind that all systems are different. Some systems, by their design, will produce high levels of wear metals. It is essential that periodic test results are compared in order to establish if any trends are emerging.
Oil analysis is helpful in understanding how fast a system is wearing. It is also helpful in understanding contaminants and even the performance ingredient levels in oils. Contaminants can be internally or externally generated. The only way to insure that the elements can be considered a contaminant is to compare the results against a reference sample of the oil being used.
When lubricants oxidize, they form reactive materials that can re-constitute into different deposits. Oil analysis can help to identify the degree of oxidation that has occurred. More sophisticated analysis may have to be performed in order to identify the exact contaminant. The following are several of the typical deposits that are formed and the problems that can occur when lubricating oil breaks down.
Contamination analysis tests for oil oxidation, sulfur, soot, fuel, antifreeze, and nitration, and is measured by an instrument called a Fourier Transform Infrared (FTIR) spectroscopy. The lab must know the type of oil in service to produce accurate results. Engine oils are tested for oxidation, nitration, and sulfur content. A baseline reference sample is required in order to compare the test sample against a baseline. The FTIR will scan the sample and look for a build-up.
Water contamination is typically screened using a hot plate technique, where the oil sample is dripped onto a hot plate. If the sample crackles, water is present. This method is used to quickly screen samples for further analysis. Positive results are confirmed and quantified using the Karl Fischer titration method. Results may be reported in ppm or by percent by weight. Water can be found in hydraulic and compressor oil samples due to large temperature swings and a large air cavity in the sumps.
In the early 1950s when particle counting was first employed, the particles were counted manually. This involved someone actually counting the particles under an optical microscope and then classifying them into size ranges. Optical microscopy techniques for particle measurement consist of the maximum particle diameter technique. This technique measures the maximum straight-line diameter of an irregular shaped particle. This technique is very effective and is still used today, but is very time consuming. Modern particle counters do not measure particle diameter. The instruments use a device called a light blocking sensor diode. The particle produces a shadow. The detector senses the shadow and determines the size, which is based on the surface area of the particle. The particles are counted by a computer and put into a size range standard. If a sample is too dark due to contamination, an accurate reading cannot be taken.
Many oils use various chemicals (additives) to obtain certain levels of performance. It should be noted that certain elements found in these additives (e.g., calcium) might not decrease as the oil begins to wear out. These elements continue to exist but may lose functionality. Keep in mind, the performance additives change into different compounds as they are used up and thus, are not as effective as their original design. In other cases, elements found in certain additives may actually decrease in concentration (e.g., zinc and phosphorous) because they are adhering to the surface of the metal and are no longer in the oil. The only way to truly know when the oil additives are being used up is the sharp rise in wear metal concentrations.
Viscosity is considered the single most important characteristic of lubricating oil. Viscosity is a fluid’s resistance to flow with respect to temperature. Oil will thicken in cold temperatures and thin out at high temperatures.
Viscosity is measured using a bubble viscometer and kept at 40 degrees Celsius (C) or 105 degrees Fahrenheit (F), depending on equipment application. Single weight or International Standards Organization-grade oils such as some gear and hydraulic oils are tested at 40 degrees C (105 degrees F). Multi-grade oils such as Society of Automotive Engineers transmission and engine oils are tested at 100 degrees C (212 degrees F). Results are reported in centistokes, or cSt. Other viscosity tests include Saybolt and Brookfield. Viscosity may increase or thicken due to oil oxidation or excessive particulate. Viscosity may also decrease or thin down due to fuel or contamination from solvents, another lighter oil, or thermal breakdown.
As oil begins to breakdown, various types of acids form that can lead to further oil degradation, metal wear, and additive depletion. It is important to establish a starting point in order to compare the oil that is being used. A baseline sample from the oil drum is essential. The total acid number (TAN) is used to check the acid neutralization of hydraulic, gear, and air compressor oils, which normally increases over time. The TAN of a reference sample should be tested in order to establish an oil’s initial TAN. If the used oil increases three points above the TAN number from the reference sample, the oil should be changed. The total base number (TBN), also referred to as the base number, measures the amount of basic (alkaline) materials in engine oil that will neutralize acids. The TBN decreases as it approaches the end of its useful life and is used to test the acid neutralization ability of engine oils. The lower the value, the less effective the oil will be at neutralizing acids. As acids increase, so do deposits. Deposit build-up will shorten engine life.
Getting Down on the Floor - June 2006 Render