What is Varnish?
- Varnish is a soft contaminant composed of lubricant degradation by-products that are less than 1 micron in size and is not measured by traditional particle count.
- Varnish deposit is a thin-orange, brown or black insoluble film deposit occurring on internal of lubricant systems.
- Varnish is a high molecular weight substance that is unstable in oil. Varnish deposit is unable to remove by traditional mechanical filtration.
Why Test for Varnish?
- Varnish can cause sticking or seizing in moving mechanical parts such as servo control valves.
- Varnish can restrict oil flow in small orifices.
- Varnish can attribute to heat loss in exchangers due to varnish’s insulation effect.
- Varnish attracts dirt and other larger contaminants, increasing wear and potential component failure.
- Varnish acts as a catalyst in building more varnish. Deteriorating lubricant quicker.
How to Test for Varnish?
- Membrane Patch Colorimetry (MPC) is a scale used to measure the color bodies of insoluble contaminates in the lubricants.
- Ultra Centrifuge (UC) spins an oil sample driving varnish precursors to the bottom of test tube. The sediment uses a visual sediment rating scale.
- Remaining Useful Life (Ruler) is used to measure active antioxidants left in the lubricant.
- Acid Number (AN) Measures the total acid number in the lubricants. Acid depletes antioxidants leading to varnish.
- Varnish Potential Monitoring has evolved to include all of the tests listed above with normal lubricant analysis including:
- Particle Count (ISO Code) Measuring particulate contamination.
- Karl Fisher measuring Water %.
- IR Spectroscopy (FTIR) measuring wear metals and additive degradation.
There is no linear correlation across the Varnish predictions tests. A UC of 6 does not always correlate to an MPC of 30 and the Ruler at 45. These can be different due to life of the product, specific exposure to heat, temperature, additive package and the base product of the lubricants. Each test measures a different aspect to the current state of the lubricant. Which is why the labs offer the annual all-inclusive testing. Clients want as much data as possible to catch potential varnish issues prior to going into an unscheduled outage. Varnish Potential testing should be conducted annually at a minimum and more frequently for critical systems that are registering varnish potential.