Varnish contamination can cause havoc in a turbine lubrication system. Once it’s identified as the cause of the problems you’re facing, it’s not always easy to remove. For reliability and maintenance managers it can prove a real headache because traditional maintenance methods are simply not up to the job.
Oil changes, flushing or aggressive filtration may temporarily reduce symptoms, but they rarely address the underlying chemistry of varnish formation. In many cases, these approaches leave you facing unnecessary downtime, extra cost and increased operational risk.
Once you understand how varnish behaves, and which removal methods actually work, you have the knowledge needed to protect your turbine reliability and extend oil life.
Why Varnish Is Difficult To Remove
Varnish forms when turbine oil oxidises under thermal stress, producing polar degradation products. These compounds exist in two forms:
1. Soluble varnish – This remains dissolved in the oil at operating temperature
2. Insoluble varnish – This precipitates out and deposits on metal surfaces
The challenge is that soluble varnish often goes undetected by standard filtration and cleanliness testing. When temperature or pressure changes occur, these soluble compounds become insoluble, forming deposits on servo valves, bearings and heat exchangers.
This is why systems can appear clean on paper while still suffering from valve stiction, overheating and recurring reliability issues.
How Do Oil Changes And Flushing Fall Short?
If you suspect varnish-related problems, it’s quite common to order a full oil change or system flush as part of your oil contamination control process. While this may temporarily remove existing deposits, it comes with several drawbacks. Oil changes are expensive, time-consuming and require extended downtime. More importantly, they do not address the root cause of varnish formation. If operating conditions remain unchanged, oxidation will resume and varnish will return.
Flushing can also dislodge deposits unevenly, increasing the risk of re-deposition elsewhere in the system. In some cases, this can worsen valve sticking or block filters shortly after restart.
For high-value turbine assets, these reactive approaches rarely deliver long-term reliability improvements or acceptable return on investment.
Targeted Varnish Removal Technologies
Removing varnish from turbine oil requires solutions designed specifically to address oil degradation products without stripping healthy additives or disrupting system operation. A&S International supplies Fluitec technologies that combine two proven approaches: electrostatic separation and chemical dissolution.
Electrostatic Separation Process (ESP)
Electrophysical Separation Process systems utilise solubility characteristics to help remove deposits from the systems. The media used in the ESP filters targets the polar compounds responsible for varnish formation and removes these from the oil. This is done during a kidney-loop filtration process to effectively remove these precursors.
By selectively removing these degradation products, ESP systems reduce varnish potential and reduce turbine maintenance. Crucially, this process does not disturb the oil’s additive package, allowing the lubricant to remain in service for significantly longer periods.
ESP is particularly effective as a preventative solution, stabilising oil condition and protecting critical components from future varnish formation.
Chemical Dissolution With DECON™ And Solvancer® Technology
While ESP removes varnish from turbine oil, it does not dissolve deposits already adhered to metal surfaces. This is where chemical cleaning becomes essential.
Fluitec’s DECON product range uses patented Solvancer® technology to dissolve existing varnish deposits from internal surfaces. Applied at controlled treat rates of 3-5%, DECON™ breaks down deposits and returns them to a soluble state within the oil.
Once dissolved, these degradation products can be removed from circulation using ESP filtration, preventing re-deposition elsewhere in the system.
Why Combining ESP And DECON Works Best?
The most effective varnish removal strategy combines chemical dissolution and physical removal. DECON dissolves existing deposits, while ESP removes them from the oil permanently.
This dual approach offers you several advantages:
1. Removal of existing varnish from valves, bearings and heat exchangers
2. Prevention of re-deposition during operation
3. Extension of oil life without additive depletion
4. Elimination of the need for flushing or oil replacement
5. Minimal disruption to plant operations
Field case studies show that facilities using this combined approach have maintained turbine oils for 10 to 15 years while avoiding the valve failures and temperature excursions that previously drove monthly turbine maintenance costs higher than £40,000.
Reducing Downtime And Total Cost Of Ownership
From a reliability perspective, the key benefit of targeted varnish removal is predictability. By stabilising oil chemistry and eliminating deposits, plants reduce nuisance trips, improve control system response and maintain thermal efficiency.
From a financial perspective, avoiding oil changes and unplanned outages deliver a far stronger ROI than reactive maintenance. Reduced downtime, lower labour costs and extended lubricant life all contribute to a lower total cost of ownership.
If you’re under pressure to justify expenditure, varnish mitigation offers measurable, defensible results rather than short-term fixes.
When To Act
If oil analysis shows rising MPC values, servo valve issues are recurring or oil temperatures are trending upwards without a clear mechanical cause, varnish contamination is likely already impacting system performance. It is important to verify these values with your OEM as they may vary depending on the application. However, a good rule of thumb to observe for MPC values would be MPC<15 normal, MPC >25 Moderate, MPC > 30 Critical.
Addressing the issue early prevents escalation and protects critical components before damage occurs.
Ready To Remove Varnish And Protect Your Turbine Assets?
A&S International supplies proven Fluitec OEM approved technologies designed to remove existing varnish deposits and prevent future formation. By combining ESP filtration with DECON treatments, reliability teams can implement effective oil contamination control, extend oil life and protect rotating equipment.
Contact A&S International to discuss a varnish mitigation strategy tailored to your turbine systems.
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