varnish in turbine lube
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PT. HYPROWIRA ADHITAMAJL. Raya Kebayoran Lama 17DJakartaTelp. 021 5361105Fax. 021 5361517www.hyprowira.com
1.Overview varnish2.Varnish and its consequences
3.Formation: Precursors and Varnish4.Measurement
5.Varnish removal
How many of you have not experienced the following due to varnish?
1) Darkened color of lube oil2) Increased temperatures due to cooler coatings3) Plugged oil filters4) Sluggish operations / sticking control valves5) Accelerated rises in acid levels6) Expensive system flushes and clean-out
Reff: Analyst Inc.
Reff: Pall Corp.
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 dischargeMicro 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.
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Varnish Precursors
Varnish
Reff: Analyst Inc.
Lube Oil Reservoir
3500 psiControl oil filter
To Hydraulic control circuitlittle/no flow at turning
Solenoid valve
Control oil circuit
Inlet Vane Control Fail open valve Gas valve
Compressor/Turbine Shaft
Main bearings ( roller or journal)
Hydraulic circuit: High VPR impact
Lube circuit Low VPR impact
Main pump
Main filter
Cooler
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.
Reff: Pall Corp.
Reff: Pall Corp.
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.
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 goneVarnish 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.
Inside filter housing
Contaminated trip relay piston
Reff: Pall Corp.
Pencil Filter, contaminated with varnish deposits
Servo valve spool: heavily contaminated
Varnish formation on a turbine bearing
Have You Seen This?Have You Seen This?
Reff: Analyst Inc.
Shuttle Valve
Compressor Gears
Gas Turbine Bearing
Plugged Filters
Reff: Analyst Inc.
Oil test for visc., TAN, RPVOT, metals, foam, etc will not indicate varnish potentialVarnish 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) ORColor 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.
Reff: Pall Corp.
Reff: Pall Corp.
Measurement of varnish potential does not indicate the actual amount of varnish deposited on the surfaces of componentsIt 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.
The electrostatic method (EST)Kidney-loop mode, off the main tankOil 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.
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.
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 KPIParticles captured by adsorption, egvarnish precursors
Particles captured by direct interception, eg wear metals