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Oil Analysis - Turbine Oil Testing

Turbine Oil Testing

Turbine lube-oil systems are designed to cool bearings, flush contaminants away from rotating parts, prevent leakage of gases, provide hydrostatic lift for shafts and actuating valves in the hydraulic circuit and protect lube-system internals. Turbine oil formulations must handle large temperature fluctuations and the ingression of contaminants such as dirt and water. Monitoring in-service turbine oil condition for deterioration and degradation can significantly extend the life of both the lubricant and the turbine

The key to efficient turbine maintenance is routine monitoring of the oil, which ensures that decisions involving the turbine, including scheduling of oil changes and other maintenance, are based on what is actually happening inside the unit, instead of the number of hours, days or years of operation. Routine and in-depth monitoring can provide warning signs early enough to take corrective action.

What is Lube Oil Varnish?

Varnish is an insoluble film composed primarily of organic residue that coats the internal components of machines lubrication systems. Often comprised of degradation products associated with oxidation or thermal degradation, these soft contaminants are less than 1 micrometer in size.

Causes of Lube Oil Varnish


a chemical reaction of an oil molecule with oxygen to produce carboxylic acids.

Thermal degradation

a chemical change in the base oil molecules under elevated temperature.

Varnish Potential Analysis

Varnish is an insoluble film that coats the internal components of machinery lubrication systems. The specific lubricant degradation byproducts associated with varnish formation remain elusive so is the need for the special test for finding the VPI ( Varnish Potential Index).

Petrolab offers two packages for turbine oil testing - PEAS - Turbine Oil Quality (Annual) PEAS - Turbine oil monitoring ( Quarterly) confirms to ASTM D4378

Benefits of Varnish Potential Analysis Testing

  • Alerts customers of developing lube oil varnish problems
  • Measures oil’s propensity to drop out varnish deposits
  • Promotes proactive maintenance and contamination control
  • Provides turbine users confidence at start up

Damage Done By Lube Oil Varnish

  • Reduced clearance zones affecting lubrication regimes

  • Often, this means a transition from hydrodynamic lubrication to boundary lubrication, which increases wear rates of pumps, bearings and gears.

  • Increased friction in components

  • This friction will result in higher energy requirements and can cause valves to stick or seize.

  • Higher operating temperatures

  • Varnish acts as an insulator, lowering the effect of heat exchangers and lessening the ability of the lubricant to cool. The impact of friction and reduced clearance zones also contribute to higher temperatures

  • Restriction or impedance of oil flow

  • Varnish can cause valves, strainers and filters to clog.

  • Increased wear rates

  • Varnish captures hard contaminants creating an abrasive surface that will accelerate wear. Varnished surfaces often appear like sandpaper when examined under a microscope.