Deeper Technical Review: All Synthetic Oil Types Used in Turbomachinery

Synthetic oils are not one family. They are several different lubricant chemistries, each with very different strengths, weaknesses, compatibility limits, and turbomachinery applications.

In turbomachinery, the word synthetic can include:

1. PAO — Polyalphaolefin
2. Synthetic esters
3. PAG — Polyalkylene glycol
4. Phosphate esters
5. Polyol esters
6. Diesters
7. Alkylated naphthalenes
8. Silicone fluids
9. PFPE — Perfluoropolyether
10. Synthetic hydrocarbon blends
11. Synthetic compressor oils
12. Synthetic gas turbine oils
13. Synthetic fire-resistant hydraulic fluids

The most important point is this:

The base oil chemistry decides the behavior.
Two oils can both be called “synthetic,” but one may be excellent for a gas turbine, another for an ammonia compressor, another for EHC fire resistance, and another completely unsuitable for the same machine.

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1. PAO — Polyalphaolefin Synthetic Oils

What PAO is

PAO is a synthetic hydrocarbon. Chemically, it is made by polymerizing alpha-olefin molecules into a very controlled hydrocarbon structure.

PAO is often considered the closest synthetic alternative to mineral oil because it is still hydrocarbon-based.

Main properties

PAO has:

• Excellent oxidation stability
• Excellent thermal stability
• High viscosity index
• Very good low-temperature flow
• Low volatility
• Good hydrolytic stability
• Good compatibility with many mineral oils
• Good compatibility with many seals, when properly formulated

Where PAO is used in turbomachinery

PAO-based oils are common in:

• Gas turbines
• Centrifugal compressors
• Screw compressors
• Integrally geared compressors
• High-speed gearboxes
• Turboexpanders
• Offshore rotating equipment
• Cold-climate turbomachinery
• Long-drain industrial rotating equipment

Why PAO is useful

PAO is very useful when the machine has high temperature, high speed, long oil-life expectations, or cold-start requirements.

Compared with mineral oil, PAO usually gives better oxidation resistance and better viscosity control across temperature.

This is important in gas turbines and compressors where oil can see high bearing compartment temperatures and hot drain-back conditions.

PAO weakness: poor natural solvency

This is a major point.

PAO is chemically clean and non-polar. That gives it excellent stability, but it also means PAO has relatively poor natural solvency.

In simple words:

PAO does not naturally dissolve polar degradation products as well as ester-based oils.

This can affect:

• additive solubility
• deposit control
• varnish behavior
• seal swelling
• sludge suspension

For this reason, many PAO lubricants contain a small amount of ester or alkylated naphthalene to improve solvency and additive response.

PAO and varnish

PAO can reduce oxidation rate compared with mineral oil, but it is not automatically varnish-free.

PAO-based oils can still form varnish if:

• antioxidants deplete
• oil runs hot
• air entrainment is severe
• electrostatic discharge occurs
• microdieseling occurs
• water contamination exists
• oxidation by-products accumulate
• oil residence time is poor

PAO may slow degradation, but it does not remove varnish already in the system.

Best use of PAO

PAO is often the best synthetic choice when the plant wants a synthetic oil with good compatibility and relatively low changeover risk compared with more polar synthetic chemistries.

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2. Synthetic Esters

Synthetic esters are a very important lubricant family, but they must be understood carefully.

There are two major families relevant to turbomachinery:

• Diesters
• Polyol esters

Both are synthetic esters, but their performance is not the same.

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3. Diester Oils

What diesters are

Diesters are made by reacting dibasic acids with alcohols. They were among the earlier synthetic lubricants used in aviation and high-temperature applications.

Main properties

Diesters generally have:

• Good thermal stability
• Good low-temperature properties
• Good lubricity
• High natural solvency
• Good deposit control
• Good additive solubility

Where diesters are used

They may be found in:

• Older gas turbine oil formulations
• Aviation turbine oils
• Compressor lubricants
• High-temperature circulating oils
• Synthetic blends

Strength: excellent solvency

Diesters have better solvency than PAO. This means they can help keep polar degradation products suspended or dissolved.

This can improve system cleanliness, but it can also create a risk during conversion.

If a dirty mineral oil system is converted to an ester-containing oil, the ester may dissolve existing deposits and release them into the circulating oil. This can lead to:

• filter plugging
• valve sticking
• sudden discoloration
• increased particle counts
• movement of old varnish
• deposit relocation

This is why ester conversion must be controlled.

Weakness: hydrolysis risk

Diesters are more sensitive to water than PAO.

In the presence of water and heat, ester fluids may hydrolyze. Hydrolysis can form acids and alcohols. This can increase acid number and affect oil life.

Therefore, ester oils require strong water control.

Compatibility concerns

Diesters can affect:

• seals
• paints
• gaskets
• adhesives
• elastomers
• sight glass materials
• old residual deposits

They are not “drop-in” fluids without compatibility study.

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4. Polyol Ester Oils

What polyol esters are

Polyol esters are made by reacting polyhydric alcohols with fatty acids. They are generally more thermally stable than diesters and are widely used in demanding high-temperature applications.

Main properties

Polyol esters offer:

• Excellent high-temperature stability
• Very good oxidation resistance
• Very low volatility
• Excellent lubricity
• Good cleanliness
• High natural detergency/solvency
• Good low-temperature performance

Where polyol esters are used

Polyol esters are used in:

• Aviation gas turbines
• Industrial gas turbines in special cases
• High-temperature compressors
• High-temperature circulating systems
• Some refrigeration compressor oils
• Severe-service synthetic turbine oils

Why polyol esters are important

Polyol esters are excellent for very high-temperature applications because they resist thermal breakdown better than many other lubricant chemistries.

They are especially valuable where coking, deposits, and volatility are concerns.

Weaknesses

Polyol esters may have:

• higher cost
• compatibility concerns
• water sensitivity compared with PAO
• stronger solvency effect on old deposits
• need for careful elastomer evaluation

Polyol esters and varnish

Polyol esters can help reduce deposits because of better thermal stability and solvency. However, they can still oxidize and form acidic degradation products if water, heat, and oxidation stress are not controlled.

Their solvency can also mask early varnish behavior because degradation products may remain dissolved longer. This means oil analysis interpretation must be adapted.

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5. PAG — Polyalkylene Glycol Oils

What PAG is

PAG stands for polyalkylene glycol. PAGs are synthetic fluids made from alkylene oxide monomers.

There are different PAG types:

• Water-soluble PAG
• Water-insoluble PAG
• EO/PO copolymer PAG
• Butylene oxide-based PAG
• High-temperature PAG
• Food-grade PAG variants

PAG is not one chemistry. PAG design can be adjusted significantly.

Main properties

PAG oils can offer:

• Excellent thermal stability
• Excellent deposit control
• Very low varnish tendency in some applications
• High viscosity index
• Good lubricity
• Low friction coefficient
• Good heat transfer
• Good performance in some gas compressor applications

Where PAG is used in turbomachinery

PAG may be used in:

• Screw compressors
• Reciprocating compressors
• Some centrifugal compressors
• High-temperature gearboxes
• Worm gearboxes
• Process gas compressors
• Certain refrigeration compressors
• Some severe industrial applications

PAG and compressor applications

PAGs are very important in compressor lubrication.

They can perform well where mineral oil or PAO has limitations related to gas solubility, deposit formation, or high operating temperature.

In some gas compressor applications, PAG can reduce hydrocarbon gas absorption compared with mineral oil. This helps maintain viscosity and reduce dilution effects.

PAG and varnish

PAGs are often associated with low deposit and low varnish tendency. Their polarity and thermal behavior can help reduce deposit formation in some severe applications.

However, PAG selection must be exact. The wrong PAG chemistry can cause major issues.

Major warning: compatibility

PAG oils are often not compatible with mineral oils and PAO.

This is one of the biggest risks.

A PAG conversion may require:

• complete drain
• flushing
• seal review
• paint compatibility review
• filter compatibility review
• residual oil analysis
• OEM approval
• startup monitoring
• oil analysis baseline

Mixing PAG with mineral oil can cause separation, haze, deposit formation, or performance loss depending on the formulation.

PAG weakness

Potential weaknesses include:

• poor compatibility with mineral oil
• compatibility concerns with seals and paints
• water interaction depending on PAG type
• limited OEM approval in some turbomachinery
• difficult conversion procedure
• different oil analysis interpretation

Best use of PAG

PAG is excellent where the application has been designed or approved for PAG, especially severe compressors and high-temperature gear applications.

It should not be selected casually.

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6. Phosphate Ester Fluids

What phosphate esters are

Phosphate esters are synthetic fire-resistant fluids. They are not selected mainly as normal bearing lubricants. They are selected where fire resistance is critical.

Where phosphate esters are used

The most famous turbomachinery application is:

Steam turbine electrohydraulic control systems — EHC systems

They are used to operate:

• turbine control valves
• stop valves
• intercept valves
• governor valves
• servo valves
• hydraulic actuators

Why phosphate esters are used

They have excellent fire resistance compared with mineral oils.

In steam turbines, hydraulic control systems are often located near high-temperature steam lines. A mineral oil leak in such an area could create serious fire risk.

Therefore, phosphate ester fluid is selected as a safety-critical fluid.

Main properties

Phosphate esters have:

• high fire resistance
• low flammability
• good hydraulic performance
• good lubricity in hydraulic components
• high density compared with mineral oil
• special electrical properties
• special contamination sensitivity

Key failure mechanisms

Phosphate ester fluids are sensitive to:

• water contamination
• acid formation
• low resistivity
• chloride contamination
• metal contamination
• thermal degradation
• hydrolysis
• oxidation
• particulate contamination

Important EHC tests

For phosphate ester EHC fluids, the critical tests include:

• Acid number
• Resistivity
• Water content
• Particle count
• Chlorine/chloride
• Color
• Viscosity
• Specific gravity
• Air release
• Foam
• Metals
• MPC or deposit tendency when applicable

Why resistivity matters

Low resistivity can disturb servo valve control and increase electrochemical activity. In EHC systems, resistivity is not just a laboratory number. It can be linked to hydraulic control reliability.

Phosphate ester and servo valves

Servo valves have very small clearances. Any varnish, acid degradation product, particulate, or gel-like deposit can create:

• sluggish valve response
• hysteresis
• instability
• hunting
• failure to stroke
• actuator movement problems
• turbine trip risk

Maintenance philosophy

Phosphate ester systems need a dedicated fluid management approach. You cannot treat them like normal mineral turbine oil systems.

They often require:

• acid scavenging media
• full-flow fine filtration
• water control
• resistivity control
• dedicated sampling
• strict cleanliness
• compatibility-controlled top-up fluid
• avoiding cross-contamination with mineral oils

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7. Alkylated Naphthalene Synthetic Oils

What alkylated naphthalene is

Alkylated naphthalene is a synthetic aromatic hydrocarbon.

It is often used as a co-base stock with PAO. It helps improve the weaknesses of PAO.

Why it is used

PAO is excellent but has poor solvency. Alkylated naphthalene improves:

• additive solubility
• seal compatibility
• deposit control
• oxidation stability
• varnish resistance
• sludge handling
• polarity balance

Where it is used

It may be used in:

• synthetic turbine oils
• compressor oils
• high-temperature circulating oils
• synthetic gear oils
• PAO-based blends

Why it matters in turbomachinery

A PAO oil with alkylated naphthalene can behave differently from a pure PAO formulation.

It may provide better cleanliness and deposit control while maintaining good synthetic hydrocarbon stability.

Practical point

When reviewing a synthetic oil data sheet, it may simply say “synthetic hydrocarbon.” That can include PAO, alkylated naphthalene, or blends. The actual formulation matters.

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8. Silicone Fluids

What silicone fluids are

Silicone fluids are synthetic fluids based on siloxane chemistry.

Common types include:

• polydimethylsiloxane
• phenyl methyl silicone
• fluorosilicone variants

Main properties

Silicone fluids can offer:

• very high viscosity index
• excellent low-temperature behavior
• good thermal stability in some environments
• chemical inertness
• low surface tension

Where they are used

Silicone fluids are not common as main lubricants for large turbomachinery bearings.

They may be used in:

• specialty high-temperature equipment
• damping fluids
• instruments
• vacuum-related equipment
• special applications requiring low volatility or temperature stability

Major limitations

Silicone fluids usually have poor boundary lubrication compared with hydrocarbon and ester oils. They can also have poor additive response.

In turbomachinery, where bearings, gears, and hydraulic components need strong antiwear, oxidation, demulsibility, and cleanliness performance, silicone fluids are generally not a common first choice.

Practical warning

Do not assume silicone oil is suitable just because it is synthetic and temperature-resistant.

For most turbomachinery lubrication systems, silicone is a specialty fluid, not a standard turbine or compressor oil.

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9. PFPE — Perfluoropolyether Fluids

What PFPE is

PFPE stands for perfluoropolyether. It is a very high-performance fully fluorinated synthetic fluid.

Main properties

PFPE fluids can offer:

• exceptional chemical inertness
• excellent oxidation resistance
• very high thermal stability
• very low vapor pressure
• nonflammability
• compatibility with aggressive gases
• excellent performance in vacuum or oxygen service

Where PFPE may be used

PFPE is used in highly specialized rotating equipment, such as:

• vacuum pumps
• turbomolecular pumps
• oxygen compressors in special designs
• semiconductor equipment
• aerospace mechanisms
• aggressive chemical environments
• high-purity process systems

Why PFPE is not common

PFPE is very expensive and not always a good lubricant for standard industrial turbomachinery.

It may also have limited additive solubility and special compatibility requirements.

Best use

PFPE is selected where chemical inertness, oxygen compatibility, vacuum performance, or nonflammability is more important than normal industrial lubricant economics.

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10. Synthetic Compressor Oils

This is a very important group because compressors often need special synthetic lubricants.

Synthetic compressor oils may be based on:

• PAO
• PAG
• diester
• polyol ester
• alkylbenzene
• alkylated naphthalene
• blends of the above

Why compressors are special

Compressor oil is exposed to gas. That changes everything.

The gas can:

• dissolve in the oil
• reduce viscosity
• increase volatility
• change flash point
• cause swelling
• promote oxidation
• create deposits
• react with additives
• create safety issues

Gas type matters

The required synthetic oil depends on the gas:

Hydrocarbon gas

Oil dilution and viscosity loss may occur. PAO or PAG may be considered depending on compatibility and OEM approval.

Hydrogen

Small molecule, leakage risk, seal design sensitivity, and oil/gas interaction must be reviewed carefully.

Ammonia

Oil selection must consider chemical compatibility and refrigerant interaction.

CO₂

CO₂ solubility can affect viscosity and phase behavior.

Sour gas

H₂S and corrosive species create special chemical and safety concerns.

Refrigerant gases

Oil miscibility and return behavior are critical.

Compressor oil decision

For compressors, the question is not only:

“Can this oil lubricate the bearings?”

The real question is:

“Can this oil lubricate the machine while exposed to this specific gas at this pressure and temperature?”

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11. Synthetic Gas Turbine Oils

Gas turbine oils may be based on:

• high-quality mineral oil
• PAO
• ester
• PAO/ester blends
• other synthetic hydrocarbon blends

Why gas turbines are severe

Gas turbine oils face:

• high bearing compartment temperature
• hot shutdown soakback
• rapid start-stop cycles
• high air exposure
• high oxidation stress
• coking tendency
• deposit sensitivity
• servo/control system sensitivity

What synthetic gas turbine oil must provide

It must offer:

• oxidation resistance
• thermal stability
• deposit control
• air release
• foam control
• demulsibility
• filterability
• elastomer compatibility
• additive stability
• long service life

Gas turbine oil failure modes

Even synthetic gas turbine oils can fail by:

• antioxidant depletion
• varnish precursor accumulation
• coking in hot zones
• servo valve deposits
• filter plugging
• oil darkening
• TAN increase
• RPVOT decline
• MPC increase
• sludge formation

Practical Khash-style point

For gas turbines, the oil may not fail uniformly in the tank. It often fails first in the hottest, smallest, most stressed areas of the system.

This is why oil analysis must be connected to machine symptoms.

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12. Synthetic Gear Oils in Turbomachinery Packages

Some turbomachinery packages include gearboxes, especially:

• integrally geared compressors
• turbo gearboxes
• high-speed reduction gearboxes
• pump/turbine gear drives
• compressor gear couplings
• expander-generator gearboxes

Synthetic gear oils may be based on:

• PAO
• ester
• PAG
• synthetic hydrocarbon blends

Why gear oils are different

A bearing turbine oil may not be enough for a gear mesh.

Gear oils may need:

• higher film strength
• antiwear properties
• micropitting protection
• scuffing protection
• EP performance
• shear stability
• high-temperature oxidation stability

Risk of wrong oil

Using a pure R&O turbine oil in a gearbox that requires antiwear or EP performance can lead to:

• gear tooth wear
• micropitting
• scuffing
• bearing damage
• high temperature
• vibration increase
• oil degradation

Synthetic gear oil benefit

Synthetic gear oils may reduce:

• churning losses
• operating temperature
• oxidation rate
• deposit formation
• energy losses
• oil change frequency

But the oil must match gear design, speed, load, metallurgy, and OEM requirement.

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13. Fire-Resistant Synthetic Hydraulic Fluids

Besides phosphate esters, fire-resistant hydraulic fluids can include:

• water-glycol fluids
• polyol ester fire-resistant fluids
• HFDU synthetic fluids
• HFD-R phosphate ester fluids

In turbomachinery

These may be used in:

• hydraulic control systems
• turbine control systems
• valve actuation systems
• high-fire-risk auxiliary systems

Important difference

Not every fire-resistant fluid is suitable for every EHC system.

Some systems are specifically designed for phosphate ester. Others may use different fire-resistant hydraulic fluids.

The selection must consider:

• pump type
• servo valve compatibility
• seal compatibility
• fire risk
• water tolerance
• filtration
• operating pressure
• air release
• resistivity
• OEM approval

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14. Synthetic Refrigeration Compressor Oils

Refrigeration and process cooling compressors often use special synthetic lubricants.

Common chemistries:

• POE — polyol ester
• PAG
• alkylbenzene
• PAO in some cases

Why refrigeration compressors are special

Oil must work with refrigerant.

Important factors:

• miscibility
• oil return
• evaporator behavior
• viscosity after dilution
• chemical stability
• wax-free behavior
• moisture sensitivity
• compatibility with refrigerant type

POE oils

Polyol ester oils are very common with HFC refrigerants because of good miscibility.

But POE oils are hygroscopic. They absorb moisture. Water control is extremely important.

PAG oils

PAG oils are common in some refrigeration and automotive compressor applications.

They also require strict compatibility and moisture management.

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15. Synthetic Blends

Many commercial synthetic turbomachinery oils are not one pure chemistry.

They may be blends of:

• PAO + ester
• PAO + alkylated naphthalene
• PAO + mineral oil
• ester + additives
• synthetic hydrocarbon + special solvency improvers

Why blends are used

Blends are designed to balance:

• oxidation stability
• solvency
• seal compatibility
• additive solubility
• low-temperature performance
• deposit control
• cost
• OEM approval

Practical point

A data sheet may say “synthetic technology” or “synthetic hydrocarbon.” This does not fully explain the chemistry.

For critical turbomachinery, ask the supplier:

• What is the base oil family?
• Is it PAO, ester, PAG, or blend?
• Is it compatible with current oil?
• Is it OEM-approved?
• What seals were tested?
• What is the varnish/deposit tendency?
• What is the changeover procedure?
• What field references exist?

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16. Comparison Table

Synthetic type	Best strength	Main weakness	Common turbomachinery use
PAO	Oxidation stability, low-temperature flow	Poor natural solvency	Gas turbines, compressors, gearboxes
Diester	Solvency, cleanliness, lubricity	Hydrolysis, compatibility	Compressors, turbine blends
Polyol ester	High-temperature stability	Moisture sensitivity, cost	Gas turbines, aviation, refrigeration
PAG	Low deposit tendency, lubricity	Poor mineral oil compatibility	Compressors, gears
Phosphate ester	Fire resistance	Water/acid/resistivity sensitivity	Steam turbine EHC systems
Alkylated naphthalene	Solvency, additive support	Usually used as blend component	PAO turbine/compressor blends
Silicone	Temperature range, inertness	Poor boundary lubrication	Specialty applications
PFPE	Chemical inertness, nonflammability	Very high cost, special use only	Vacuum, oxygen, aggressive gas
Alkylbenzene	Refrigerant compatibility	Specialized use	Refrigeration compressors
Synthetic gear oil	Load capacity, thermal stability	Must match gear design	Integrally geared compressors

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17. Synthetic Oil Selection by Turbomachinery Type

Steam turbines

Usually mineral or Group II/III turbine oils are common. Synthetic may be considered if:

• high temperature exists
• varnish is chronic
• oil life is poor
• special OEM requirement exists
• fire-resistant EHC fluid is required

For EHC systems, phosphate ester may be used separately from the main bearing oil.

Gas turbines

Synthetic oils are more common due to thermal severity.

Likely synthetic types:

• PAO
• PAO/ester blend
• ester-based turbine oil

Focus:

• oxidation
• varnish
• coking
• bearing compartment temperature
• hot shutdown behavior

Centrifugal compressors

Synthetic oil may be selected depending on gas, temperature, pressure, and OEM approval.

Likely types:

• PAO
• PAG
• ester
• synthetic hydrocarbon blends

Focus:

• gas dilution
• deposits
• seal compatibility
• viscosity retention
• oxidation stability

Screw compressors

Synthetic oils are very common.

Likely types:

• PAO
• PAG
• ester

Focus:

• discharge temperature
• carbon deposits
• oil carryover
• air/oil separation
• oxidation

Integrally geared compressors

Likely types:

• PAO gear/turbine oils
• synthetic gear oils
• special OEM-approved compressor oils

Focus:

• gear mesh load
• bearing speed
• air release
• foam
• micropitting
• thermal stability

Turboexpanders

Likely types:

• PAO
• ester
• special low-temperature synthetic oils

Focus:

• low-temperature performance
• gas compatibility
• bearing lubrication
• seal behavior

Vacuum turbomachinery

Likely types:

• ester
• PAO
• PFPE
• silicone in selected cases

Focus:

• vapor pressure
• volatility
• oxidation
• process contamination

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18. Oil Analysis Differences for Synthetic Oils

Synthetic oils need oil analysis, but interpretation changes depending on chemistry.

PAO

Monitor:

• viscosity
• TAN
• RPVOT
• RULER
• MPC
• FTIR oxidation
• particle count
• water
• foam
• air release

Ester

Monitor:

• TAN carefully
• water very carefully
• viscosity
• FTIR
• RULER
• MPC/deposit tendency
• seal condition
• filter debris

TAN interpretation may differ because ester chemistry can influence acid number behavior.

PAG

Monitor:

• viscosity
• water behavior
• TAN
• FTIR trend
• contamination by mineral oil
• particle count
• wear metals

Mineral oil contamination in PAG systems is a major concern.

Phosphate ester

Monitor:

• acid number
• resistivity
• water
• particle count
• chlorine/chloride
• viscosity
• color
• metals
• deposit tendency
• servo valve performance

PFPE

Monitor:

• viscosity
• contamination
• wear metals
• process contamination
• acidity if applicable
• volatility-related changes

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19. Synthetic Oil and Seal Compatibility

This is one of the most underestimated topics.

Synthetic oils can interact differently with:

• NBR
• HNBR
• FKM/Viton
• EPDM
• PTFE
• silicone rubber
• polyurethane
• neoprene
• gaskets
• O-rings
• paints
• tank coatings

Possible effects

• swelling
• shrinkage
• hardening
• softening
• leakage
• cracking
• loss of elasticity
• coating lift-off
• sight glass crazing

General warning

PAO may cause seal shrinkage if not properly formulated with seal-swell agents. Esters may cause swelling. PAG may be incompatible with some paints and elastomers. Phosphate esters require special seal materials.

Never convert oil chemistry without checking elastomer compatibility.

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20. Synthetic Oil Changeover Strategy

A synthetic oil conversion should be treated as an engineering project.

Step 1: Confirm OEM approval

No discussion should continue without this.

Step 2: Identify current oil chemistry

Do not only check brand name. Identify:

• base oil type
• additive system
• viscosity grade
• years in service
• contamination condition
• degradation condition

Step 3: Analyze current oil

At minimum:

• viscosity
• TAN
• RPVOT
• RULER
• MPC
• water
• particle count
• FTIR
• elemental analysis
• foam
• air release
• demulsibility

Step 4: Inspect system

Check:

• reservoir
• bearing drains
• filters
• coolers
• servo valves
• sight glasses
• tank coating
• elastomers
• sample points

Step 5: Compatibility test

Laboratory compatibility should evaluate:

• current oil + new oil mixture
• deposit formation
• haze
• separation
• filterability
• foam
• air release
• water separation
• seal compatibility where possible

Step 6: Clean system if required

If the system has varnish, sludge, or degraded oil, a simple drain and fill is risky.

The system may need:

• flushing
• chemical cleaning
• varnish removal
• reservoir cleaning
• filter upgrade
• cooler cleaning
• servo valve inspection

Step 7: Control startup

After conversion, monitor:

• differential pressure across filters
• particle count
• oil color
• TAN
• MPC
• water
• foam
• leakage
• temperature
• vibration
• servo valve response

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21. Khash Practical Summary

PAO

Best “safe synthetic” for many turbomachinery applications. Excellent stability, good compatibility, but needs solvency support.

Ester

Excellent high-temperature and cleanliness performance, but water and compatibility must be controlled.

PAG

Excellent in selected compressors and gear applications, but conversion risk is high due to incompatibility with mineral oils.

Phosphate ester

Not a normal turbine oil. It is a fire-resistant EHC hydraulic fluid requiring special monitoring.

Alkylated naphthalene

Very useful as a hidden hero in synthetic blends because it improves PAO solvency and deposit control.

Silicone

Specialty fluid, not common for main turbomachinery lubrication.

PFPE

Extreme specialty fluid for chemical inertness, vacuum, oxygen, and aggressive environments.

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Final Conclusion

Synthetic oil selection in turbomachinery is not about choosing the most expensive oil. It is about matching the fluid chemistry to the machine stress.

For turbomachinery, the selection must consider:

• bearing temperature
• gear load
• gas exposure
• fire risk
• oil life target
• varnish tendency
• seal compatibility
• water contamination risk
• OEM approval
• flushing requirement
• oil analysis interpretation
• failure consequence

The deepest mistake is to say:

“Synthetic oil is better.”

The correct engineering statement is:

“This synthetic chemistry is better for this specific machine, under this specific operating condition, with this specific risk profile.”

For turbomachinery reliability, synthetic oils are powerful tools — but only when selected by chemistry, not by marketing name.