When it comes to preventative maintenance with oil analysis, information is key. That’s why the best lubrication management programs include sampling, testing and analysis of in-service lubricants.
It’s important to maintain an acceptable fluid cleanliness level at all times. Oil analysis can help determine when filter or oil changes should be scheduled, when inspections should occur, and when equipment should be repaired. In turn, this can help you to avoid downtime, reduce repair and replacement costs, increase safety, maximize lubricant life, and reduce the chance of catastrophic failure to keep operations running smoothly.
Conducting an Oil Analysis
Oil analysis looks for a variety of contaminants as well as signs of fluid degradation, that could reduce the life of the lubricant. This includes particle count, element analysis, viscosity, water content, TAN (total acid number) rating, and more. Here are some of the most common testing methods utilized in a good lubrication management program.
Visual Patch
A patch test is a visual inspection of oil through a microscope to identify the types and quantity of contamination present in a sample. In most cases, this test comes with a picture on the report so you can visually see the results. The fluid power industry standard for this test is ISO 4406.
Particle Count
A particle count rating indicates how many small, medium, and large particles are present in a sample. These particles are counted and measured using a laser. ISO 11500/4406 is the industry standard for particulate size and quantity in a sample.
Water Content
Added water reduces lubricity and may look like premature wear, which is why it is important to test for water content using ASTM D6304. Most oil analysis reports will display a specific value (in ppm) which you can then compare to the acceptable range.
Conductivity
ASTM D2624 provides a measure of conductivity in pS/m. This test is particularly important for systems with very high flows that are at risk of electrostatic discharge.
Element Analysis
ICP (inductively coupled plasma) analysis identifies the elemental breakdown of contaminants in ppm. This makes it easier to determine which components are currently subject to excessive wear. For example, if you have elevated levels of Cu (copper) in a hydraulic system, you may be dealing with a worn piston pump. If you have elevated levels of Fe (iron), you may be looking at worn gears, bearings, shafts, or cylinders/liners.
Viscosity
Viscosity that is too high or too low can cause catastrophic issues for systems that are hydraulically driven. Different systems may have different operating parameters, but in any case, it’s crucial to know the ideal oil viscosity for your system. A good rule of thumb is to ensure that you are operating within +/- 10% of what is outlined in the material data sheet.
MPC (Membrane Patch Colorimetry)
This test looks at insoluble particles suspended in your lubricant, commonly known as varnish. These contaminants can discolor equipment and harm components. Equipment running in extreme temperatures (or large temperature variations), or where water egress is a problem, is particularly susceptible to these issues.
TAN (Total Acid Number)
As acidity levels increase due to oxidation, your system becomes more at risk of damage from corrosion and buildup of oxidized materials. This test is particularly important for the ester-based fluids that often break down over time.
Related article: The Importance of Oil Analysis | PTE (powertransmission.com)