Turbine Engineer asked me : All companies like Shell, TOTAL, Mobil , Chevron etc are global lubricant manufacturer , do we need to really care about technical comparison or leave it to the procurement to buy the cheapest among all ? Khash , How would you compare them technically.

Khash: By looking at Datasheet only we can not predict performance and yes — this is not only possible, it is very difficult to compare turbine oil formulations without knowing the formulation and without performance testing.

The idea is:

Test new oil before oxidation stress, then intentionally stress the oil using RPVOT, then test the stressed oil residue with RULER, MPC, FTIR, TAN, viscosity, and patch photo.

This gives you a much deeper comparison than the normal Technical Data Sheet.

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1. First: What Are We Really Comparing?

When comparing new turbine oils by FTIR, RULER, and RPVOT, we are not fully reverse-engineering the formulation.

We are comparing the formulation fingerprint and formulation behavior under stress.

In simple terms:

Test	What It Tells You
FTIR	Chemical fingerprint of base oil/additive/degradation products
RULER	Antioxidant type and remaining antioxidant reserve
RPVOT	Resistance to oxidation under accelerated oxygen/water/copper/high-temperature stress
MPC	Tendency to generate insoluble color bodies / varnish potential
TAN	Acid generation tendency
Patch photo	Visual nature of degradation products

ASTM D2272 RPVOT uses an oxygen-pressurized vessel to evaluate oxidation stability of new or in-service turbine oils of the same composition in the presence of water and copper catalyst at 150°C. This is important because RPVOT is an oxidation stress test, not a complete field-life simulation. (ASTM International | ASTM)

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2. How to Compare FTIR of New Turbine Oils

Purpose of FTIR

FTIR gives a molecular fingerprint of the oil.

For new turbine oils, FTIR can help compare:

• Base oil chemistry similarity
• Synthetic ester presence, if applicable
• Additive-related absorption patterns
• Oxidation baseline
• Aromatic / paraffinic character differences
• Wrong oil or cross-contamination
• Similarity between current oil and candidate oil

ASTM E2412 is commonly associated with FTIR trend analysis for in-service lubricants, including molecular signatures related to oxidation, nitration, sulfation, water, glycol, soot, additives, and other condition-monitoring indicators. (eralytics)

How to Compare New Oils by FTIR

For Shell vs TotalEnergies, or any two turbine oils, the lab should do this:

1. Run FTIR on Oil A new
2. Run FTIR on Oil B new
3. Run FTIR on the current in-service oil, if available
4. Overlay all spectra
5. Compare peak positions, peak intensity, and baseline shape

What to Look For

FTIR Area	What It May Indicate
Hydrocarbon region	Base oil fingerprint
Carbonyl region	Ester chemistry or oxidation products
Oxidation region	Starting oxidation baseline
Additive-related peaks	Different additive chemistry
Water region	New oil moisture contamination
Overall spectral match	Chemical similarity or mismatch

Important Practical Point

FTIR should be used as a comparative fingerprint, not as a standalone “good/bad” test.

For example:

• Oil A and Oil B may both be excellent, but FTIR may show they are chemically different.
• Oil A and current oil may look close, while Oil B may look very different.
• A different FTIR does not automatically mean worse oil; it means compatibility and behavior must be verified.

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3. How to Compare RULER of New Turbine Oils

Purpose of RULER

RULER, based on voltammetric antioxidant measurement, is very powerful for turbine oils. ASTM D6971 covers voltammetric determination of hindered phenol and aromatic amine antioxidants in new or in-service non-zinc turbine oils.

RULER helps compare:

• Phenolic antioxidant reserve
• Aminic antioxidant reserve
• Antioxidant balance
• Antioxidant depletion behavior
• New oil baseline for future trending

Many turbine oil antioxidant packages use mixtures of amine and phenolic antioxidants, and antioxidant packages can differ by type and blend ratio; this is why the new-oil baseline is critical.

How to Compare New Oils by RULER

The lab should not only report “% remaining useful life.”

For new oils, the lab should provide:

• RULER voltammogram
• Phenolic peak
• Aminic peak
• Peak area
• Peak height
• Total antioxidant response
• Relative oxidation potential / voltage location
• Comparison with product-specific new oil baseline

Example Interpretation

Oil	Phenolic Response	Aminic Response	Possible Interpretation
Oil A	High	Medium	More phenolic-dominant formulation
Oil B	Low	High	More aminic-dominant formulation
Oil C	Medium	Medium	More balanced antioxidant system

But be careful:

Higher RULER peak does not automatically mean better oil.

Why?

Because performance depends on:

• Antioxidant chemistry
• Base oil quality
• Additive synergy
• Thermal stress resistance
• Depletion rate
• Deposit formation tendency
• Compatibility with existing oil

The real question is not only:

“Which oil has more antioxidant?”

The better question is:

Which oil consumes antioxidants more slowly and generates fewer harmful degradation products under stress?

That is why RULER must be compared before and after RPVOT stress.

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4. How to Compare RPVOT of New Turbine Oils

Purpose of RPVOT

RPVOT gives an accelerated oxidation stability result. It measures how long the oil resists oxidation under severe test conditions.

But RPVOT should not be used alone.

A high RPVOT value does not automatically guarantee:

• Low varnish tendency
• Low MPC
• Good servo valve cleanliness
• Good demulsibility
• Good filterability
• Good field life in every turbine

ASTM D2272 is specifically an oxidation stability test for turbine oils, using oxygen pressure, water, copper catalyst, and elevated temperature. (ASTM International | ASTM)

How to Compare RPVOT Correctly

For new oil comparison:

Item	Requirement
Same lab	Avoid inter-lab variation
Same method	ASTM D2272
Same oil grade	ISO VG 32 vs 32, 46 vs 46
Same sample condition	Fresh, sealed, uncontaminated
Same interpretation basis	Do not mix supplier TDS data with independent lab data
Repeatability check	Consider duplicate testing for critical decisions

Weak Comparison

Oil A RPVOT = 1600 min
Oil B RPVOT = 1400 min
Therefore Oil A is better.

This is too simple.

Strong Comparison

Oil A has higher RPVOT, but after RPVOT stress it generated higher MPC, higher TAN, darker patch, and more RULER depletion. Oil B had slightly lower RPVOT but produced fewer insoluble color bodies and showed better post-stress cleanliness. Therefore, Oil B may present lower varnish risk in this specific application.

This is a much stronger MLE-style interpretation.

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5. Is It Possible to Compare RULER, MPC, and FTIR of New Oils vs Used Oil After RPVOT?

Yes.

And technically this is very valuable.

But we need to be precise in wording.

You can compare:

1. New Oil A before RPVOT
2. New Oil A after RPVOT
3. New Oil B before RPVOT
4. New Oil B after RPVOT
5. Used in-service oil before RPVOT
6. Used in-service oil after RPVOT, if enough sample is available and the lab agrees

This gives a powerful view of how each oil behaves under accelerated oxidative stress.

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6. Recommended Test Matrix

Before RPVOT

Test each fresh oil before stress:

Test	Purpose
FTIR	New oil chemical fingerprint
RULER	Antioxidant baseline
RPVOT	Oxidation resistance baseline
MPC	Initial varnish potential
TAN	Initial acidity
Viscosity	ISO grade confirmation
ICP	Additive/contamination fingerprint
Karl Fischer water	Water contamination
Particle count	Cleanliness
Color	Visual fingerprint

After RPVOT

After RPVOT is completed, collect the stressed oil residue and test:

Test	Purpose
RULER	How much antioxidant was consumed
MPC	How much insoluble color body / varnish potential was generated
FTIR	Oxidation by-product formation
TAN	Acid generation after oxidation
Viscosity	Polymerization / thickening tendency
Color	Thermal/oxidative darkening
Membrane patch photo	Visual deposit character
Insolubles / sludge if possible	Deposit tendency
Filterability if enough sample	Plugging tendency

This is the key comparison.

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7. Best Comparison Format

Oil A: New vs After RPVOT

Parameter	New Oil A	Oil A After RPVOT	Change
RPVOT	1600 min	End of test	—
RULER phenolic	100% baseline	25% remaining	-75%
RULER aminic	100% baseline	45% remaining	-55%
MPC	3	28	+25
TAN	0.05	0.35	+0.30
FTIR oxidation	Low baseline	High oxidation band	Increased
Viscosity 40°C	32 cSt	34.5 cSt	+7.8%
Patch photo	Clean/light	Brown deposit	Varnish tendency

Oil B: New vs After RPVOT

Parameter	New Oil B	Oil B After RPVOT	Change
RPVOT	1350 min	End of test	—
RULER phenolic	100% baseline	40% remaining	-60%
RULER aminic	100% baseline	60% remaining	-40%
MPC	2	12	+10
TAN	0.04	0.18	+0.14
FTIR oxidation	Low baseline	Moderate oxidation band	Increased
Viscosity 40°C	32 cSt	33.0 cSt	+3.1%
Patch photo	Clean/light	Light yellow deposit	Lower deposit tendency

Interpretation

Oil A had higher RPVOT, but after oxidation stress it produced more MPC, more TAN, stronger FTIR oxidation, and darker patch deposits.

Oil B had lower RPVOT, but it produced fewer insoluble oxidation products and lower varnish tendency.

So for a turbine with a history of varnish or servo valve sticking, Oil B may be the lower-risk choice even if its RPVOT is lower.

That is why RPVOT alone is not enough.

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8. How to Interpret RULER Before and After RPVOT

RULER before RPVOT tells you the starting antioxidant fingerprint.

RULER after RPVOT tells you how the antioxidant system survived the oxidation stress.

What to Compare

RULER Observation	Interpretation
High phenolic depletion	Phenolic antioxidants consumed rapidly
High aminic depletion	Aminic antioxidants consumed rapidly
Balanced depletion	More even antioxidant consumption
One antioxidant disappears completely	Possible weak point in antioxidant strategy
Low depletion but high MPC	Antioxidants remain, but deposits still form
High depletion but low MPC	Antioxidants sacrificed but controlled deposits better

Very Important Point

Do not only compare “% RULER remaining.”

Compare the voltammogram shape.

The shape can reveal that two oils have completely different antioxidant systems.

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9. How to Interpret FTIR Before and After RPVOT

FTIR before RPVOT is the oil’s chemical fingerprint.

FTIR after RPVOT shows what oxidation stress created.

Compare These Changes

FTIR Change	Meaning
Increase in oxidation band	More oxidation products
Carbonyl growth	Acid/ester/oxidation products
Additive peak reduction	Additive depletion or transformation
New peaks	New degradation chemistry
Baseline shift	Insolubles, degradation, contamination
Water-related changes	Water retained or reaction products

The strongest method is to overlay:

• New Oil A vs RPVOT-aged Oil A
• New Oil B vs RPVOT-aged Oil B
• RPVOT-aged Oil A vs RPVOT-aged Oil B

Then compare oxidation growth, not just absolute spectra.

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10. How to Interpret MPC Before and After RPVOT

MPC before RPVOT gives initial varnish potential.

MPC after RPVOT shows how much varnish-type material the oil generated under stress.

ASTM D7843 is the standard method for measuring lubricant-generated insoluble color bodies in in-service turbine oils using membrane patch colorimetry. (Lovibond)

Important

MPC after RPVOT is not exactly the same as field MPC.

Why?

Because RPVOT is an artificial accelerated oxidation test. Field conditions include:

• Hot spots
• Air entrainment
• microdieseling
• electrostatic discharge
• water ingress
• catalytic metals
• residence time
• filtration
• cooling cycles
• deposit dissolution/redeposition

But MPC after RPVOT is still very useful for relative comparison.

If Oil A and Oil B are stressed under identical RPVOT conditions, and Oil A produces much higher MPC after stress, that is important evidence.

What to Compare

MPC Result	Interpretation
Low new MPC + low aged MPC	Good deposit resistance under test
Low new MPC + high aged MPC	Hidden varnish tendency after oxidation
High new MPC + higher aged MPC	Higher concern
High MPC but light patch	Possible mild soluble color bodies
High MPC with dark/brown/black patch	Stronger concern; examine deposit type

Always ask for:

• MPC number
• Patch photo
• Delta L
• Delta a
• Delta b

The patch tells the story.

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11. Can Used Oil Also Be Compared After RPVOT?

Yes, but with caution.

Used oil already contains:

• Depleted antioxidants
• Oxidation products
• dissolved varnish precursors
• contamination
• wear metals
• water history
• possible mixed top-ups
• degraded additives
• system-specific degradation products

So used oil after RPVOT may oxidize very quickly and generate high MPC/TAN.

This can be useful, but interpretation must be careful.

Useful Comparison

Sample	Reason
Current used oil before RPVOT	Real system condition
Current used oil after RPVOT	Remaining oxidation resistance under stress
New candidate oil before RPVOT	Candidate baseline
New candidate oil after RPVOT	Candidate stress response
New candidate + used oil mixture before/after RPVOT	Changeover compatibility risk

This is excellent for deciding whether a new oil can safely replace the existing oil.

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12. Best Advanced Study: New Oil + Used Oil Mixtures

This is where the lab comparison becomes very powerful.

Prepare mixtures:

Mixture	Purpose
100% used oil	Current condition
90% used / 10% new	Small top-up simulation
75% used / 25% new	Partial replacement
50% used / 50% new	Worst-case mixing
25% used / 75% new	Major replacement
100% new oil	New oil baseline

Then test before and after RPVOT:

• FTIR
• RULER
• MPC
• TAN
• viscosity
• filterability
• patch photo

This can reveal:

• Incompatibility
• additive clash
• varnish release
• sludge formation
• demulsifier conflict
• antioxidant instability
• high MPC generation after mixing
• poor response to top-up

For field conversion, this is more useful than comparing only two fresh oils.

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13. Proposed Laboratory Protocol

For a professional end-user comparison, use this protocol.

Step 1: Collect Samples

Use:

• Fresh sealed Shell turbine oil sample
• Fresh sealed TotalEnergies turbine oil sample
• Current used oil from turbine, hot and representative
• Optional: another approved reference oil

Step 2: Baseline Testing

Run:

• FTIR
• RULER
• RPVOT
• MPC
• TAN
• viscosity
• ICP
• water
• particle count
• color
• demulsibility
• foam
• air release

Step 3: RPVOT Stress

Run RPVOT on:

• New Oil A
• New Oil B
• Used oil
• Optional: 50/50 used/new mixtures

Step 4: Post-RPVOT Testing

On RPVOT-aged residues, run:

• RULER
• MPC
• FTIR
• TAN
• viscosity
• color
• patch photo
• insolubles if possible

Step 5: Interpretation

Compare:

1. Starting antioxidant fingerprint
2. RPVOT life
3. Antioxidant depletion after RPVOT
4. MPC generation after RPVOT
5. TAN increase after RPVOT
6. FTIR oxidation growth
7. viscosity increase
8. patch color
9. used/new compatibility
10. field application risk

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14. Technical Scoring Example

Evaluation Factor	Weight	Oil A	Oil B
RPVOT life	15%	9/10	8/10
RULER reserve new oil	10%	8/10	8/10
RULER retention after RPVOT	15%	6/10	8/10
MPC after RPVOT	20%	5/10	9/10
TAN increase after RPVOT	10%	6/10	8/10
FTIR oxidation growth	10%	6/10	8/10
Viscosity change	5%	7/10	9/10
Patch photo severity	10%	5/10	9/10
Compatibility with used oil	5%	6/10	8/10

This type of scoring is much better than “RPVOT is higher, so this oil is better.”

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15. Key Technical Warning

ASTM D2272 says the test is for evaluating oxidation stability of oils having the same composition.

This is important.

When comparing different formulations, RPVOT is still useful as a screening tool, but interpretation must be careful.

Why?

Because different antioxidant chemistries can respond differently in the RPVOT vessel.

So for Shell vs TotalEnergies, or any different brands, RPVOT should be interpreted as:

“Comparative oxidation response under ASTM D2272 conditions”

not as:

“Guaranteed field life ranking.”

That is why post-RPVOT RULER, MPC, FTIR, TAN, and patch photo make the comparison much stronger.

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16. Final Khash Recommendation

Yes, it is absolutely possible to compare RULER, MPC, and FTIR of new oils versus the same oils after the end of the RPVOT test.

In fact, this is one of the best ways to expose the hidden difference between turbine oil formulations.

A normal TDS may show two oils are very similar.

But after RPVOT stress, one oil may show:

• higher antioxidant depletion
• higher MPC
• darker patch
• higher TAN
• stronger FTIR oxidation
• more viscosity increase
• more sludge tendency

while the other oil remains cleaner.

That difference is very important for turbine oil selection.

So the strongest technical comparison is not:

“Which oil has higher RPVOT?”

The strongest comparison is:

“After the same oxidation stress, which oil still has better antioxidant reserve, lower MPC, lower TAN increase, lower FTIR oxidation growth, cleaner patch, and better viscosity stability?”

That is the MLE way to compare turbine oils.

RPVOT tells you how long the oil resisted oxidation.
RULER tells you how the antioxidant system survived.
FTIR tells you what chemistry changed.
MPC tells you what varnish-type material was generated.
TAN tells you how acidic the degradation became.
The patch photo tells you what the oil is trying to deposit inside the turbine.