Are you experiencing problems with the solubility of oxidation products in turbine oil at low temperatures? Many clients have contacted us with similar issues where it dissolves within operating temperatures (i.e. 60 – 80 degrees C) while at slow temperatures (i.e. below 25 degrees C); they become insoluble and begin to deposit on working surfaces. This is a difficulty faced by many users of hydraulic piston pumps regardless of the type of turbine (gas/steam/etc.) and/or the operating time.

Upon reading their issues, I have come to a conclusion that these issues are related to varnish formation. This is a problem which commonly occurs in high-temperature and high-pressure systems such as steam turbines, high-performance hydraulic systems or lubrication systems .

What is varnish?


Varnish results due to the buildup of oil oxidation and degradation compounds on machine surfaces or its parts. There are many causes of such accumulation which includes high temperatures, lubricant degradation, electrostatic discharges, and micro dieseling. There are many problems that can occur due to the production of varnish. These include trouble with machine operation such as valve stiction, as well as clogged filters and constraint in lubricant flow, etc.

The process of varnish begins as dissolved pollutants. When these contaminated particles buildup and reach a point where they start to saturate, they migrate to the surfaces of the lubrication system. If these particles remain on the surfaces, they harden with time resulting in the malfunction of the lube system and its components.

The two significant properties of lubricant are

  • Oxidation resistance
  • Oxidation solubility

The oxidation resistance process refers to the way molecules combat the chemical reaction with the oxygen in the air.  The oxidation degrades the oil which is the primary reason to adjust it. The greater the oxidation resistance, the longer the life span of oil will be.

The oxidation solubility allows the lubricant to hold polar substances like varnish in suspended mode without harming the machinery and its components. Oil solubility is bound to increase at high temperatures. The oils that are part of group III have low solubility than those that belong to oil groups I and II. Many users have experienced varnish deposits due to the lower solubility of oil. This was also a result of making change from Group I oil to a Group II or III oil.

If you are also facing difficulty with varnish deposits, there are two ways to control it. First, figure out the root cause which is leading to the accumulation of varnish. Then remove the existing varnish from the machine. This can be done by mixing solvent or particles of detergent to the oil and removing using a synthetic material. A varnish removal system can also be installed to achieve the desired result. Of course, in the case of varnish which has hardened a solution will provide no benefits and changing the components will be recommended.