1. PT. HYPROWIRA ADHITAMA
JL. Raya Kebayoran Lama 17D
Jakarta
Telp. 021 5361105
Fax. 021 5361517
www.hyprowira.com

2. 1. Overview varnish
2. Varnish and its consequences
3. Formation: Precursors and Varnish
4. Measurement
5. Varnish removal

3. How many of you have not experienced the
following due to varnish?
1) Darkened color of lube oil
2) Increased temperatures due to cooler coatings
3) Plugged oil filters
4) Sluggish operations / sticking control valves
5) Accelerated rises in acid levels
6) Expensive system flushes and clean-out
Reff: Analyst Inc .

4. Thin, insoluble film deposit that forms on surfaces inside the turbine lube
system (pipes, tank, bearings heat exchanger, servo-valves, etc)
Comprised of a wide range of oil additive and thermo-oxidative
breakdown, high molecular weight compounds. Varnish precursors are
the result of breakdown from mainly:
◦ Oxidation: water, air and metallic contamination from wear
◦ Thermal stress from extreme temperatures in cases of:
static discharge
Micro dieseling: adiabatic compression of air bubbles
The chemical compositions of varnish precursor vary depending on the
turbine type, operating conditions and the oil type. Varnish precursors are
>75% soft particles, <1 micron
Varnish precursors are polar, and their solvency is temperature dependent
◦ Over time migrate from the oil to machine surfaces - depending on system and
oil conditions.
Reff: Pall Corp.
Varnish Precursors +
+ -- +
-
Varnish

5. Compressor/Turbine Shaft
Main bearings ( roller or journal)
Cooler
Main filter Solenoid valve
Main
pump
3500 psi Control oil filter
To Hydraulic control
Lube Oil Reservoir circuit
little/no flow at turning
Control oil circuit
Hydraulic circuit:
High VPR impact
Lube circuit Low Reff: Analyst Inc .
VPR impact Inlet Vane Control Fail open valve Gas valve

6. Contamination of critical GT control hydraulic components
◦ Fuel control valves
◦ Safety fail open valves
◦ Vane control valves
Inability to control operation, high maintenance cost for
◦ Replacement of contaminated valves
◦ Cost of chemical clean and flush
Fail to start condition: Loss of flexibility
Trip during operation: Loss of production
Downtime and lost production represent a large share of the
costs associated with poor varnish control in GT installations
Reff: Pall Corp.

7. Reff: Pall Corp.

8. All turbine oils create varnish precursors under normal operating
conditions.
The rate of generation is higher under severe / unusual operating
conditions.
◦ Oxidation
◦ Additive depletion
◦ Filter related electrostatic discharge
◦ Micro-dieseling, adiabatic compression
Recent increase in varnish related problems is attributed to:
◦ Higher operating temperatures
◦ Smaller reservoirs
◦ More peaking and cyclic service
◦ Highly refined base-stocks (Group II - lower solvency for varnish)
◦ Finer filtration resulting in electrostatic discharge
The solvency of varnish in oil is temperature dependent
◦ Transition point 54 - 57 °C
◦ Temperature falls below 54 - 57 °C in the hydraulic section
Reff: Pall Corp.

9. Oil has limited solvency for varnish
◦ Majority of the varnish in a turbine lube system
is in the form of deposits
◦ Small portion of the total is suspended in the oil
◦ As the oil is cleaned up, it dissolves more
varnish
◦ Lube system is clean when all removable
varnish deposit is gone
Varnish deposits cause
◦ Restriction and sticking of servo valves
◦ The cost of valve replacement due to varnish is
~$30,000 + turbine down time costs
Reff: Pall Corp.

10. Inside filter housing
Contaminated trip relay piston
Reff: Pall Corp.

11. Pencil Filter, contaminated with varnish deposits
Servo valve spool: heavily contaminated
Reff: Pall Corp.

13. Have You Seen This?
Varnish formation on a turbine bearing
Reff: Analyst Inc .

14. Shuttle Valve
Plugged Filters
Compressor Gears
Gas Turbine
Bearing
Reff: Analyst Inc .

15. Oil test for visc., TAN, RPVOT, metals, foam, etc will not
indicate varnish potential
Varnish forming potential of oil can be measured by:
◦ FTIR - nitration procedure
◦ Gravimetric analysis (Toluene soluble)
◦ Ultracentrifuge (~17,500 RPM for 30 minutes)
◦ 0.2 – 2.0 um Particle Count (Modified ASTM D312) OR
Color patch - Quantitative Spectrophotometer Analysis (QSATM) –
Analysts Inc)
◦ Most commonly used – Draft stage ASTM procedure
◦ Measures discoloration / stain on patch
◦ Proprietary calculations determines varnish potential rating (VPR)
◦ Significant variation in VPR values between labs
◦ VPR of <35 normal - no action
◦ VPR of 38-58 - active monitoring
◦ VPR 60-79 - abnormal
◦ VPR >79 - critical - immediate action
Reff: Pall Corp.

16. Reff: Pall Corp.

18. 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…)
Reff: Pall Corp.

19. 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
Reff: Pall Corp.

20. 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
◦ Cost of flushing: $50,000 to $60,000.
Reff: Pall Corp.

21. 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
Particles captured by adsorption, eg
varnish precursors
Particles captured by direct
interception, eg wear metals
Reff: Pall Corp.