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What Is an Oil Analysis?

By Paul Scott
Updated May 17, 2024
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An oil analysis is a non-invasive and non-destructive diagnostic process used to establish the health of various mechanical or electrical devices by testing the quality of the oil that lubricates or insulates them. The oil analysis can be likened to a mechanical blood test as the oil in an engine or a transformer is as accurate a mirror of the overall health of the device as a human's blood is. Common oil analysis components include tests for insoluble contaminants such as abrasive solids and carbon which may indicate worn bearings and faulty compression rings. Tests for viscosity and spectral examinations for additives and metals are also common, and can indicate device conditions and the general quality of the oil. The oil in heavy current electric switchgear and transformers is regularly tested for the presence of carbon and moisture during oil analysis tests.

Mechanical devices such as internal combustion engines and gearboxes typically operate in a bath of oil or feature a sump from which oil is pumped up to lubricate the engine's moving parts. Electrical devices such as heavy circuit breakers, transformers, and resistance starters also operate within an oil-filled environment, although, in these cases, the devices rely on the oil for insulation rather than lubrication. Just as the blood in a human body can tell a pathologist a lot about the overall health of an individual, the oil in these devices is also a good indicator of how well, and how safely, they are functioning. In the case of mechanical devices, worn parts will cause metal shavings, water, or fuel, among other elements, to become suspended in the oil, giving a certain indication of the existence of a problem. The presence of excessive moisture or carbon contamination in the oil of an electrical device is a sure warning of the potential for a catastrophic failure of the device if the oil is not promptly recycled.

These tests are typically component parts of a comprehensive oil analysis and serve as a valuable non-intrusive diagnostic tool to identify problems without having to disassemble the device. The analysis will usually differ according to the device and environmental specifics, but several components are typical of most tests. These include spectral examinations that test for the presence of heavy metals and additives in the oil as a yardstick of its overall quality. An insolubles test will indicate the presence of suspended carbon, oxidation, and abrasive solids resulting from wear of engine or gearbox parts. A viscosity test is a indicator of both device health and the lubricant quality of the oil and, should it return a grade result below the specific oil's rating, may suggest general degradation of the oil, overheating of the device, or the presence of fuel or coolant in the oil.

Flash point tests carried out during an oil analysis measure the temperature at which oil vapors ignite. If the oil vapor ignites at a lower temperature than its rated value, it may have been contaminated, most commonly with fuel. As is the case with the blood test analogy used previously, early detection of problems is one of the strongest arguments for embarking on a regimen of periodic oil analysis tests and may improve the longevity, overall performance, and safety of the devices in question.

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