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What Are the Causes of Varnish in Hydraulic Oil?

Wed, Nov. 07, 2012

The Problem of Varnish Contamination 

Varnish contamination is the inevitable byproduct of many degradation processes in hydraulic and lubrication systems. The effects of varnish on industrial and manufacturing systems range from the nuisance of minor downtime and routine maintenance to, worst case scenarios, multi-million dollar catastrophic failures of major capital equipment. 


Causes of Varnish in Hydraulic Oil

The building blocks of varnish come from oxidation byproducts that overcome the solubility of the oil, and thermal degradation from system hot spots, element sparking or pressure induced dieseling (micro-dieseling). 

Varnish in Turbine Oil

AW type hydraulic oils are suceptible to varnish deposit formation (common in plastic injection molding machinery).

Varnish and Solubility

Warmer oil can hold more oxidation byproducts in solution but as the oil cools, oxidation byproducts (feedstock for varnish deposit formation) come out of solution and can form deposits in servo valves and other critical components. The first video below shows two oil samples from the same gas turbine with 3-year-old oil which had MPC value of 35 (common for gas turbines). The sample on the left was treated with SVR® Lubricant Conditioning System technology to remove soluble oxidation byproducts; the sample on the right was left untreated as found in the turbine. The solubility of oil is directly related to oil temperature. 

At the beginning of the video, both samples show oil with acceptable solubility indicated by clear oil appearance and no visible insoluble contamination above a temperature of 40C / 104F.  As the oil is allowed to cool (simulating turbine off-peak or shutdown), the solubility of the oil decreases and the soluble oxidation byproducts previously held in solution in the untreated sample on the right are rejected by the oil and become insoluble as the building blocks for varnish deposit formation (cloudy appearance of the oil). 

The SVR® treated sample on the left has no soluble oxidation by-products in solution and thus it can safely cool without releasing varnish causing contaminant which will result in successful turbine start without varnish related unit trip or fail-to-start condition. 

Download one of our Soluble Varnish Removal Case Studies!

Written by Aaron Hoeg


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