I was watching this video that in my first experience on Varnish in PDO in Oman that I was a SKF Lubrication consultant there , Peter Dufresne EPT Clean Oil presented to us.
Why “Keeping Varnish Dissolved” with Aftermarket Chemistry Can Become a Reliability Risk
The problem is not varnish color. The problem is varnish inventory.
The classic mineral turbine-oil beaker demonstration is powerful because it shows a basic truth: varnish is not only a contamination problem; it is a temperature-dependent solubility and saturation problem. In the demonstration, two samples from the same gas turbine oil reservoir behave differently as temperature changes. The “as-found” oil can hold pre-varnish compounds while warm, but when it cools during shutdown or outage conditions, the oil loses solvency and the pre-varnish compounds crash out of solution. EPT Clean Oil describes the oil in that demonstration as approximately three years old with an MPC value of 35, and specifically notes that the as-found sample demonstrates how pre-varnish can be soluble or insoluble depending on fluid temperature. (Machinery Lubrication)
This is the central issue with aftermarket chemicals designed to keep varnish dissolved. They may make the oil look better by MPC, but they do not necessarily remove the oxidation products from the system. They can simply move the varnish problem from the visible or filterable phase into the dissolved phase. That is not removal. That is chemical masking unless proven otherwise.
1. Varnish begins dissolved, then becomes insoluble when saturation is exceeded
Sludge and varnish products often begin as dissolved lubricant degradation products. They accumulate until the oil reaches its solvency limit, or saturation point. Once that limit is exceeded, the surplus converts into insoluble degradation products and deposits on machine surfaces. (Machinery Lubrication)
This matters because a turbine oil system is not one uniform temperature. Bearings, reservoirs, control-oil lines, servo valves, last-chance filters, coolers, stagnant pipework, and shutdown conditions all create different solvency environments. A varnish precursor that is soluble in the reservoir at 50–60°C may become insoluble in a cooler hydraulic control section, a standby line, or during an outage. One Machinery Lubrication article notes that varnish solvency in turbine oil is temperature-dependent and that control sections frequently fall below the transition region, causing deposits on control valves and last-chance filters. (Machinery Lubrication)
That is why “keeping varnish dissolved” is not the same as controlling varnish. The system can remain apparently clean while warm and still deposit material where the oil is cooler, slower, and closer to critical clearances.
2. A near-zero MPC after chemical addition may be a solubility artifact
MPC is useful, but it must be interpreted correctly. ASTM D7843 is designed to extract insoluble contaminants from in-service turbine oil onto a membrane patch and report the patch color as a ΔE value. ASTM describes it as a guide and trending tool for lubricant-generated insoluble deposits, not as a complete mass balance of all varnish-forming chemistry in the machine. (ASTM International | ASTM)
That distinction is crucial. If an aftermarket chemical keeps oxidation products dissolved during sampling and testing, fewer colored bodies may be captured on the membrane. The MPC value can collapse toward zero even though the total chemical inventory of varnish precursors has not been removed. The number improves, but the system may still be carrying a high dissolved load.
This is why MPC should not be treated as a single concrete “varnish amount.” Machinery Lubrication has explicitly warned that MPC measures varnish potential, not direct varnish level, and that MPC values must be interpreted as part of the bigger picture of saturation, soluble contamination, oxidation and breakdown. (Machinery Lubrication)
The same problem appears in temperature-sensitive testing. STLE summarized field observations where warm turbine oils filtered through membrane filters looked clean, but the same oils produced colored patches after cooling at room temperature for several days. (STLE) In another discussion of MPC methodology, precipitation time was shown to be critical: longer precipitation time after standardized heating produced significantly higher MPC results. (Machinery Lubrication)
So, a near-zero MPC after adding solubility chemistry can mean one of two very different things:
Good case: oxidation products were actually removed from the oil.
Risky case: oxidation products were chemically hidden in the dissolved phase and may reappear under colder, stagnant, or overloaded conditions.
Only additional testing can separate those two cases.
3. Cold temperature is the real audit
The uploaded video shows the practical failure mode: warm oil may look clear; cooler oil can turn cloudy as pre-varnish comes out of solution. This is exactly what happens in real turbine systems during shutdowns, peaking service, cold starts, standby periods, or low-flow control-oil operation.
Chevron’s varnish guidance explains the same mechanism: hotter oil holds varnish in solution more readily, but when the system cools or becomes stagnant, the risk increases that varnish will stick to surfaces. (Chevron Lubricants)
This means that aftermarket solubility chemistry may create a false sense of security. At operating temperature, the treated oil may show low MPC and good visual clarity. But as the oil cools, the solvency balance changes. The oil can become supersaturated. When that happens, the material that was being held in solution can crash out quickly, especially in the coldest, lowest-flow, tightest-clearance areas: servo valves, last-chance filters, hydraulic manifolds, actuator lines, reservoir walls, and coolers.
The technical risk is not only that varnish returns. The risk is that more material may be available to deposit at once because the chemical has been holding an overloaded inventory in the oil instead of removing it.
4. Why aftermarket solubility chemicals can create their own deposit risk
The strongest technical objection is this: aftermarket chemistry does not enter a turbine oil as neutral magic. It enters as another chemical system.
Modern turbine oils are carefully balanced formulations. Their base oil, antioxidants, rust inhibitors, demulsifiers, anti-foam agents, and other components are selected to work together. Adding an aftermarket package can disrupt that balance through concentration imbalance, additive competition, settling, and incompatibility. Fluid Life notes that formulated lubricants already contain additive packages and warns that aftermarket additives can disrupt the balance of the existing formulation, compete for metal surfaces, and exceed the oil’s ability to dissolve added chemistry. (Fluid Life)
That is where “they make their own varnish” becomes a defensible technical argument. The issue is not that every aftermarket product instantly creates deposits. The issue is that repeated addition of non-OEM polar chemistry can introduce new deposit precursors and new incompatibility pathways.
There are several mechanisms:
First, added polar chemistry can disturb water separation. Turbine oils must shed water. Many solubility improvers, cleaners, and dispersant-like chemistries work because they are polar or surface-active. But polar constituents can damage demulsibility. Precision Lubrication notes that even very small amounts of polar molecules can severely affect turbine-oil water separability, and that detergents or cleaners introduced through maintenance activities can destroy demulsibility at very low concentrations. (Precision Lubrication)
Second, incompatible additive chemistry can trigger varnish formation. Chevron specifically warns that introducing oil with a different additive formulation can upset lubricant stability and start a degradation process that leads to varnish. (Chevron Lubricants) Aftermarket chemical addition is not identical to oil cross-contamination, but the compatibility principle is the same: new chemistry can interact with the existing additive system.
Third, additives themselves can degrade. Turbine varnish is not only degraded base oil. Machinery Lubrication notes that varnish material can include oil additives and high-molecular-weight thermo-oxidative breakdown compounds, and that the additive package and its interaction with the base stock can play a significant role in varnish formation. It also notes that a type of amine antioxidant is known to form deposits of its own when it depletes. (Machinery Lubrication)
Fourth, dissolved varnish is still reactive contamination. Oxidation products, acids, polar bodies, and depleted additive fragments do not become harmless just because they are dissolved. Varnish-related deposits can contribute to servo-valve sticking, filter plugging, impaired cooler performance, wear, and even autocatalytic lubricant deterioration. (Machinery Lubrication)
Therefore, the question is not: “Did the chemical lower MPC?”
The correct question is: “Did the chemical remove the oxidation products, preserve the original lubricant properties, and remain stable under hot, cold, wet, dry, stagnant, and high-flow conditions?”
5. Repeated 5% annual dosing is not maintenance. It is uncontrolled reformulation.
A one-time, engineered cleaning step with a defined exit plan is very different from adding 5% treatment chemistry every year to keep MPC low.
If 5% of the system volume is added every year, the chemical inventory becomes significant very quickly. If the system is “bled and fed” by replacing 5% of the oil volume annually with treatment chemistry, and assuming perfect mixing with no consumption or removal, the cumulative treatment fraction becomes:
| Year | Approximate treatment fraction in system |
|---|---|
| 1 | 5.0% |
| 3 | 14.3% |
| 5 | 22.6% |
| 10 | 40.1% |
| 15 | 53.7% |
The formula is:
If the chemical is simply added without removing oil, the gross addition is even simpler: 5% per year equals 25% of the original sump volume after five years and 50% after ten years.
That is not a small additive correction. That is a major change in the lubricant formulation.
This is especially important because steam turbine and compressor oils typically use a relatively low additive concentration compared with engine or gear oils. Fluid Life lists steam turbine and compressor oils as generally containing R&O, demulsifier, and anti-foam chemistry in the approximate range of 0.1% to 5% by volume. (Fluid Life) Therefore, an annual 5% treatment dose can be the same order of magnitude as the entire original additive system.
After several years, the plant may no longer be operating the OEM-approved turbine oil. It may be operating a hybrid blend of base oil, depleted antioxidants, dissolved oxidation products, treatment chemistry, reaction by-products, and whatever top-up oils or contaminants entered during service.
At that stage, an MPC number by itself is a weak defense.
6. Saturation still wins
A solubility enhancer can raise the apparent holding capacity of the oil, but it cannot eliminate thermodynamics. The system still has a finite saturation limit. That limit changes with temperature, oxidation state, water, particle contamination, additive depletion, base oil type, and residence time.
Highly refined turbine oils can have excellent oxidation stability while still having lower solvency for polar varnish precursors. Machinery Lubrication notes that hydrotreated base stocks are less polar than Group I base stocks, and varnish is usually less soluble in Group II base stocks. (Machinery Lubrication)
So, if oxidation continues and the treatment chemical is repeatedly added, the system can enter a dangerous condition: high dissolved varnish load, low MPC, and poor cold-temperature margin. It appears controlled until the next trigger occurs: shutdown, cold weather, water ingress, additive incompatibility, extended standby, filter change, top-up with different oil, antioxidant collapse, or localized overheating.
When the trigger arrives, the crash-out can be sudden.
That is why the claim “MPC is near zero, therefore varnish risk is near zero” is technically incomplete. Near-zero MPC is meaningful only if it is supported by evidence that the varnish precursor inventory has been removed or chemically neutralized without damaging the lubricant’s critical properties.
7. What a serious technical audit should demand
A responsible varnish-control program should not accept annual chemical dosing based only on MPC improvement. It should require proof of total fluid health.
At minimum, the audit should include:
- MPC at controlled conditions, including cold-soak or extended precipitation evaluation, not only standard warm-handled samples.
- RULER antioxidant testing for phenolic and aminic antioxidant depletion.
- FTIR oxidation / carbonyl trend, acid number, and possibly ultracentrifuge or gravimetric patch testing.
- Demulsibility, foam, air release, water content, and filterability before and after treatment.
- Hot and cold particle counts, because varnish precursors can appear differently at different temperatures.
- Deposit analysis from servo valves, filters, reservoir walls, or coolers using FTIR, SEM-EDS, or other suitable analytical methods.
- Compatibility testing with the in-service oil, intended top-up oil, seals, paints, filters, and water contamination scenarios.
- Mass-balance evidence showing that oxidation products are being removed from the system, not merely kept dissolved.
The most important question is simple: after treatment, where did the varnish-forming material go?
If it was removed, the program has technical merit.
If it was only dissolved, the problem has been postponed.
If 5% must be added every year to keep the number low, the chemistry is managing the symptom, not eliminating the root cause.
Conclusion: Low MPC is not enough
Aftermarket solubility chemicals can produce impressive short-term MPC results. That does not automatically mean the turbine oil is clean, unsaturated, or safe.
The technical risk is that these chemicals can:
- keep varnish precursors dissolved instead of removing them,
- mask the true saturation level of the oil,
- release deposits when the oil cools,
- carry varnish precursors into colder control circuits,
- disturb demulsibility, foam, air release, and additive balance,
- degrade into their own deposit-forming by-products, and
- gradually reformulate the lubricant if repeatedly dosed at 5% per year.
The strongest reliability position is this:
Varnish control should be based on removal, oxidation control, temperature management, contamination control, and verified lubricant health — not on chemically forcing a saturated oil to look clean by MPC.
P.S.
While writing this article , saw below award hanging in my office wall as one of the biggest achievements of my career
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