How to Monitor Lubricant Cleanliness Levels in Lubricants Containing Antifoam Silicon

How to Monitor Lubricant Cleanliness Levels in Lubricants Containing Antifoam Silicon

ILD is sometimes asked this question as some Sinopec Lubricants are specifically formulated with silicon additives to reduce foaming.

Many lubricants have a silicon additive to help antifoam, but some people wonder if this impacts on the ability to tell the cleanliness of the oil because the silicon particles will show up as contamination. Sinopec prides itself on the cleanliness quality of its lubricants, so it is important for ILD customers to understand that some contamination reading may give a false read if the lubricant contains antifoam silicon.

Whenever there is silicon element in the oil, the laser light-blockage particle counter test (commonly used in laboratories such as Hastings Deering or ALS) will pick up the silicon particles. Even though the silicon is not dirt, the particle counter does not discriminate the source or type of silicon in the oil.  As a result, the particle counter will report a high ISO code giving the impression of dirty oil.

The light-blockage particle count method is the easiest and fastest way to evaluate the ISO code cleanliness and therefore the most common and easily available in test labs. However, there are other particle counter methods used to overcome this additive interference such as the “patch” or “membrane visual inspection” method - but many labs are not keen to do it because of its tediousness nature to get an accurate result.

A small presence of Silicon in oil will greatly distort the test ISO code when using light-blockage particle counters. A base oil that started off with ISO 13/9 when treated with 0.02% silicon antifoam additive (20 ppm) will cause an immediate increase of reading to ISO 22/21. Silicone antifoams are insoluble to allow them to disrupt the surface tension of foam formed in oil.  The insoluble nature of these additives can lead to the appearance of phantom counts in light-blockage particle counters.  You can read more about this study here:

This limitation of light-blockage particle counters is recognised by Caterpillar itself. In one of its SOS guides, it indicates that particle count reading will be affected by presence of water, entrained air, and oil additives (additive interference)- especially in engine oil. The additive interference is more apparent in new oil than in-service oil. As such, new oils taken directly from bulk tanks or IBCs can appear to be dirtier (by ISO code) than in service oils taken from equipment compartments although in actual both oils are at the same level of cleanliness. Below is the extract from the SOS guideline for further reading.

Relying on ISO code readings (via light-blockage particle counter) for oils with Silicon antifoam will not give an accurate picture of the oil cleanliness. A high reading of ISO 21/22 may mean the oil is heavily contaminated with dirt or possibly that additive interference has caused it.

ILD recommends taking the following steps whenever you get high ISO code particle count samples:

  • Check the metal elements for Silicon presence.
  • In case of oil that you know has an Silicon additive in it, take note of its level in ppm. If you know the oil does not have Silicon additive in its formulation, then very likely it is external contaminant such as dirt ingression.
  • Compare the Silicon ppm level with the additive concentration guideline for Sinopec oils given below.
  • If the ppm level is out of the range given in this guideline, the Silicon could be coming from different source(s). Even if it is within the range, it is also worth taking the next step to confirm that it is truly additive.
  • Identify the possible sources of silicon based on combination with other metal elements:
    1. Additive: Si high (and within the concentration range) but Al and other non-wear metal elements are < 1 ppm (this can also mean seal and gasket leaching).
    2. Dirt: Both Si and Al elevated, and their ratio (Si:Al) is between 4:1 to 2:1 (depending on soil type). Normally when you see this, Fe and/or Cu will also see an increase because of the abrasive nature of dirt.
    3. Coolant leak: Si and Na elevated but Al remains low.

The ISO code generated by Hastings Deering can still be relied upon for hydraulic oils including UTTO. However, for engine and transmission oils, the use of Silicon antifoam as an additive will make the ISO code reading inaccurate. ILD is aware of how important ISO cleanliness monitoring is to your business. Therefore we are currently looking into alternative methods of establishing baseline cleanliness for our oils to then offer this service for any contamination initiatives or monitoring that you have.