What is Varnish? Varnish is a soft contaminant composed of lubricant degradation by-products that are less than 1 micron in size and is not measured by traditional particle count Varnish deposit is a thin-orange, brown or black insoluble film deposit occurring on internal of lubricant systems Varnish is a high molecular weight substance that is unstable in oil Varnish deposit is unable to remove by mechanical filtration What is sludge? Sludge is varnish which have higher water content Sludge look like a soft mud-like deposit that settles out of the oil Sludge is also a soft contaminant Sludge contaminant, if prolonged elevated temperatures will evaporate the moisture from the sludge contaminant

1. Varnish

2. • Varnish is a soft contaminant composed of lubricant degradation by-products that are less than 1 micron
in size and is not measured by traditional particle count
• Varnish deposit is a thin-orange, brown or black insoluble film deposit occurring on internal of lubricant
systems
• Varnish is a high molecular weight substance that is unstable in oil
• Varnish deposit is unable to remove by mechanical filtration
What is Varnish?
Varnish is a hard, lacquer-like oil-insoluble substance that is difficult to remove—great for wood, not so much for machinery.

3. • Sludge is varnish which have higher water content
• Sludge look like a soft mud-like deposit that settles out of the oil
• Sludge is also a soft contaminant
• Sludge contaminant, if prolonged elevated temperatures will evaporate the moisture from the sludge
contaminant
What is Sludge?
Sludge—often a varnish precursor—is a soft, pliable residue that’s less tenacious.

4. • Sticking or sized occurs in moving mechanical parts such as servo control valve
• Plugged or restricted small oil flow orifices
• Loss of heat conversion efficiency in heat exchangers due to varnish’s insulation effect
• Attract dirt and larger contaminants, increasing wears and component failure
• Encourage premature bearing failure
• Catalytic deterioration of turbine oils ( and hydraulic oils)
• Increased maintenance costs due to cleanup and disposal of oil
Potential Problems caused by Varnish
Spool and Bore

5. Varnish Formation
Thermal degradation
 Thermal degradation happens at temperatures above 299 C and leads to oxidation. There are four
potential sources of heat:
i. Full spark discharge
ii. Dark stream spark discharge
iii. Friction
iv. Adiabatic compression

6. Varnish Formation
Contamination
 Although contaminants come from a variety of sources, internal contamination is most often submicron
oxidized oil that agglomerates to leave deposits. Certain oil additives can create more varnish than
others—including some rust inhibitors. These contaminants agglomerate into sludge and varnish.
Oxidation
 Oxidation is accelerated by exposure to temperatures of 249 C and above. Elevated temperatures
accelerate the oxidation process; for every 10 C increase in operating temperature, the rate of oxidation
doubles. The present of aeration, water and metals accelerates oxidation. Once underway, oxidation by-
products develop into insoluble contaminants.

7. Electrostatic Discharge (ESD)
ESD is produced by friction that results when two surfaces move in relation to each other—this usually
means they must come in contact with each other, but not always. Common causes of electrostatic charge
in a system include one or more of the following:
• Fluid flowing through narrow passages
• Fluids passing through filters
• Fluids that travel through systems at high speeds and/or are highly agitated
• Fluids that are kept at lower temperatures
• Fluids that become aerated.
ESD leads to the formation of free radicals within the oil, which leads to uncontrolled polymerization
that culminates in the buildup of insolubles like varnish and sludge

8. Filtration and static
The transition to synthetic and glass filters with tighter pores coupled with higher filter flow rates has
created a perfect storm for ESD. A high flow rate creates high voltages that result in more powerful and
frequent spark discharges. If the filter is made of nonconductive materials like these, the charge will not be
able to dissipate into the filtration system. Then the filter will charge until the voltage reaches a certain
point and discharge to conductive parts such as the metal components of the filter housing—causing
significant damage. While grounding the filter system will prevent sparking, it will not prevent either the
filter or fluid passing through it from charging and causing damage.

9. How to detect Varnish?
Varnish can be vary difficult to detect. Standard oil analysis test may show no signs of varnish when it is
present. The best method for detecting varnish is via precision oil analysis (e.g., MobilServ Varnish
Analysis). The following are examples where varnish might occur in both gas and steam turbine systems:
• Black, curtsy deposits on mechanical seals
• Gold adherent films on valves
• Charcoal-like deposits on Babbitt sleeve bearings
• Gooey-brown accumulations on filters
• Black, scabby deposits on mechanical seal surfaces and thrust-bearing pads
• Carbonaceous residue on mechanical surfaces

10. Factors that Increase Varnish occurrences in Gas Turbines
Simplified representation of some of the causes of gas turbine varnish
Ref: Practical Approaches to
Controlling Sludge and Varnish
in Turbine Oils

11. Measuring Varnish: Setting removal targets
 Measurement of varnish potential does not indicate the actual amount of varnish deposited on the
surfaces of components
 It measures varnish precursors in the oil
 A system can be considered “varnish free” when varnish deposits have disappeared, not necessarily
when varnish potential is down.
 Removal of varnish precursors from the oil displaces the solvency equilibrium in the oil, forcing deposit
to “redissolve” in the fluid, then removed by varnish removal units. To be free of varnish, varnish
precursor measurements must be consistently low for an extended period.
 Actual clean up time depends on
• Efficiency of varnish precursor removal
• Amount of deposits already present in the system
• Solvency behavior of varnish in the system (site dependent –machine dependent –oil dependent…)

12. Varnish Removal
The electrostatic method (EST)
 Kidney-loop mode, off the main tank
 Oil is subjected to electrical field causing varnish particles to:
• charge / agglomerate to larger particles
• captured by filter mat or
• attach to charged, disposable surface
• As the oil is cleaned up, it lifts varnish deposits into the oil phase, cleaning the surfaces
Chemical cleaning/flushing
 Lube system flushing with chemicals / solvents
 Softens and removes insoluble materials and the flushing action suspends and helps remove the
material by fine filters
 Several hours to several days
 System is flushed with appropriate flush fluid to remove residual chemicals
 Intensive & costly process.
 Allows quicker removal of deposits.
 Continuous monitoring and turbine shut down

13. Varnish Removal
The adsorption method:
 Utilizes large surface area, high void volume
 Low fluxes allow proper residence time for adsorption
 Electro-chemical affinity of the filter media for varnish particles is a KPI

14. Prevention
Preventing varnish from developing in the first place with a well-balanced formulation of high-performance
base stock and advanced additives is a sound strategy. To that end, the following should be considered.
• Deposit control. As mentioned earlier, varnish can be generated by thermal degradation, oxidation
and contamination. Some oils generate more deposits than others, but advanced turbine oils are
formulated to limit the generation of sludge and varnish, while keeping deposits in suspension.
• Air release and foam control. Entrained air in oil with inferior air release performance may be
compressed in turbine bearings or high-pressure hydraulics, causing adiabatic compression (micro
dieseling). Adiabatic compression can cause localized elevated oil temperatures that may promote
the formation of varnish. Similarly, excessive surface-level foaming can accelerate oxidation. Oils
formulated for rapid air release and minimal foam formation will provide superior protection against
varnish.
• Filterability. This refers to a fluid’s ability to pass through a filter with minimal pressure drop. Oils
with poor filterability will pollute filters faster, which might require more frequent filter changes.
• Antirust and corrosion protection. Rust and corrosion contribute to oxidation and the formation of
contaminant-based varnish.
• Wear protection. Since wear metals act as an oxidation catalyst, wear material from machinery
components can lead directly to varnish formation

15. The 100% Varnish Prevention Solution
According to Fluitec International in Jersey City, N.J., it is possible to prevent all damage from gas turbine
lubricant varnish. Following is five-point varnish prevention program:
1. Choose a good oil
2. Monitor oil condition
3. Minimize sparking
4. Maintain the oil
5. Remove contaminants
Ref: STLE TLT Magazine

16. Turbine Oil System care and Maintenance
The Seven steps:
1. Keep the oil clean
2. Keep the oil dry
3. Analyze the oil periodically
4. Ventilation
5. Prevent leakage
6. Maintain Temperature Records
7. Keep operating records
Ref: Turbine Oil System Care and Maintenance
Mobil Technical Topic

17. Suggested Schedule for Oil Analysis of Turbine Systems
Taken from ASTM D4378

18. Oil Analysis
Figure courtesy of Lubrication Engineers, Inc.
A better approach is a combination of the
following three tests:
• Ultracentrifuge, which predicts
varnish.
• MPC identifies the contamination level
in used oil as it relates to oil
degradation and potential varnish
development.
• Remaining useful life evaluation
routine (RULER) identifies levels of
antioxidants

19. Compiled by: Aung Khaing Htun