⛽ Demulsibility properties of oils
In short
Assessment of oil ability to separate from water (demulsification). Critical parameter for turbine, hydraulic and circulating oils. The test is performed according to PN-EN ISO 6614:1994; Oil volume: 40 mL. The procedure comprises 10 steps (about 2 h 44 min–3 h 29 min in total); it is used for: Quality control of turbine oils (PN-EN ISO 8068, DIN 51515), Testing hydraulic oils (HLP, HVLP) — demulsifying properties, Assessment of circulating oils in central lubrication systems.
At a glance
- Standard: PN-EN ISO 6614:1994
- Category: Petrochemistry
- Procedure steps: 10
- Total time of stages: 2 h 44 min–3 h 29 min
- Oil volume: 40 mL
- Water volume: 40 mL (distilled or 1% NaCl)
- Test temperature: 54 ± 1°C (or 82 ± 1°C)
Overview
Demulsibility properties define an oil's ability to rapidly and completely separate from water after mixing. This is one of the most important quality parameters for turbine, hydraulic, circulating, and transformer oils, which under operating conditions may come into contact with water (condensation, cooling leaks, moisture from air).
The PN-EN ISO 6614 method (equivalent to ASTM D1401) involves mixing 40 mL of oil with 40 mL of distilled water (or 40 mL of 1% NaCl solution for some specifications) in a graduated cylinder, vigorous stirring with a stirrer for 5 minutes at controlled temperature, then observing the emulsion separation rate.
The result is expressed in format X/Y/Z (T), where X = oil layer volume [mL], Y = water layer volume [mL], Z = emulsion volume [mL], T = time [min] to achieve this state. Ideal result is 40/40/0 (30) — complete separation in 30 minutes. Acceptable result is emulsion ≤3 mL in 30 min (for oils with viscosity <90 cSt) or in 60 min (for oils with viscosity >90 cSt).
Poor demulsifying properties lead to maintaining emulsion in oil system, causing: corrosion of metal elements, worse lubrication (water is a poor lubricant), microorganism growth in emulsion, and accelerated oil aging. In steam turbines, presence of stable water-oil emulsion is unacceptable.
Method principle
40 mL of test oil and 40 mL of distilled water (or NaCl solution) are introduced into a 100 mL graduated cylinder placed in a thermostatic bath at 54 ± 1°C (for oils with viscosity <90 mm²/s at 40°C) or 82 ± 1°C (for oils with higher viscosity). After temperature equilibration, the cylinder contents are mixed with a rotating stirrer at 1500 rpm for 5 minutes. After turning off the stirrer, layer separation is observed and oil phase, water phase, and emulsion volumes are recorded every 5 minutes. The time to achieve complete separation or maximum time of 60 minutes is noted.
Applications
- Quality control of turbine oils (PN-EN ISO 8068, DIN 51515)
- Testing hydraulic oils (HLP, HVLP) — demulsifying properties
- Assessment of circulating oils in central lubrication systems
- Control of transformer oils — water separation
- Monitoring oil degradation in service (demulsibility deterioration)
- Testing effect of contaminants on oil properties
- Formulation and development of new lubricants
- Turbine OEM specifications (Siemens, GE, Alstom)
Key parameters
| Parameter | Value |
|---|---|
| Oil volume | 40 mL |
| Water volume | 40 mL (distilled or 1% NaCl) |
| Test temperature | 54 ± 1°C (or 82 ± 1°C) |
| Mixing time | 5 min (1500 rpm) |
| Ideal result | 40/40/0 (30) — full separation in 30 min |
| Acceptable result | Emulsion ≤3 mL in 30 min (or 60 min) |
Standard
- Standard number
- PN-EN ISO 6614:1994
- Title (PL)
- Przetwory naftowe — Oznaczanie wlasciwosci rozdzielania wody od olejow naftowych i cieczy syntetycznych
- Title (EN)
- Petroleum products — Determination of water separability of petroleum oils and synthetic fluids
Step-by-step procedure
-
Cylinder preparation
Wash cylinder with chromic acid or detergent, rinse with distilled water, then acetone. Dry.
-
Bath preparation
Heat bath to 54°C (or 82°C if oil viscosity >90 mm²/s at 40°C). Wait for temperature stabilization.
-
Oil introduction
Measure 40 mL of test oil and pour into graduated cylinder.
-
Water introduction
Add 40 mL of distilled water (or 1% NaCl solution).
-
Thermostating
Place cylinder in bath. Wait for temperature equilibration (approx. 15–30 min to reach 54°C).
-
Mixing
Insert stirrer into cylinder. Mix at 1500 rpm for exactly 5 minutes. Turn off stirrer and remove from cylinder.
-
Separation observation
Start stopwatch. Every 5 minutes read and record oil layer, water layer, and emulsion volumes (X/Y/Z).
-
Test completion
End observation when emulsion = 0 mL (full separation) or after 60 minutes (if separation did not occur).
-
Result recording
Record result in format X/Y/Z (T min): e.g., 40/37/3 (30) = after 30 min: 40 mL oil, 37 mL water, 3 mL emulsion.
-
Cleaning
Wash cylinder and stirrer with detergent, rinse with water and acetone. Dry. Check for no oil residues on walls.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Demulsibility testing apparatus | Normalab NDE 710, Koehler K18400, Stanhope-Seta | 15,000–35,000 PLN |
| Thermostatic bath | Water or oil bath 54°C / 82°C, stability ±1°C | 5,000–15,000 PLN |
| Graduated cylinders 100 mL | Glass cylinders with 0.5 mL graduation, ground stopper | 100–300 PLN / pc |
| Stirrer with impeller | Electric stirrer with speed control, impeller per standard | 2,000–5,000 PLN |
| Stopwatch / timer | Digital stopwatch for timing mixing and observation | 50–200 PLN |
| Thermometer | Pt100 contact thermometer, accuracy ±0.5°C | 200–1,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Distilled water | 7732-18-5 | Freshly distilled, conductivity <2 µS/cm, 40 mL per determination |
| Sodium chloride (NaCl) | 7647-14-5 | For preparation of 1% solution — used in some marine specifications |
| Chromic acid or detergent | — | For washing measuring cylinders (removing oil layers from glass surface) |
| Acetone | 67-64-1 | For final rinsing of cylinders and stirrer |
Health and safety (OHS)
- Hot bath (54°C or 82°C) — risk of burns, use heat-resistant gloves
- Chromic acid — highly toxic and carcinogenic (CMR), use only if necessary, prefer detergents
- Oils — avoid prolonged skin contact, use nitrile gloves
- Rotating stirrer — do not insert hands in working zone, watch for splashing
- Safety glasses and laboratory coat required
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 6614:1994 — “Petroleum products — Determination of water separability of petroleum oils and synthetic fluids”.
How does this method work?
40 mL of test oil and 40 mL of distilled water (or NaCl solution) are introduced into a 100 mL graduated cylinder placed in a thermostatic bath at 54 ± 1°C (for oils with viscosity <90 mm²/s at 40°C) or 82 ± 1°C (for oils with higher viscosity). After temperature equilibration, the cylinder contents are mixed with a rotating stirrer at 1500 rpm for 5 minutes.
What is the measuring range and accuracy?
Oil volume: 40 mL; Water volume: 40 mL (distilled or 1% NaCl); Test temperature: 54 ± 1°C (or 82 ± 1°C); Mixing time: 5 min (1500 rpm).
How long does the test take?
The times given for the individual stages add up to approximately 2 h 44 min–3 h 29 min. The procedure comprises 10 steps.
What equipment is required?
Demulsibility testing apparatus, Thermostatic bath, Graduated cylinders 100 mL, Stirrer with impeller, Stopwatch / timer, Thermometer. Indicative cost of the core instrument (Demulsibility testing apparatus): 15,000–35,000 PLN.
Where is this test used?
Quality control of turbine oils (PN-EN ISO 8068, DIN 51515); Testing hydraulic oils (HLP, HVLP) — demulsifying properties; Assessment of circulating oils in central lubrication systems; Control of transformer oils — water separation; Monitoring oil degradation in service (demulsibility deterioration); Testing effect of contaminants on oil properties; Formulation and development of new lubricants; Turbine OEM specifications (Siemens, GE, Alstom).
What safety precautions apply?
Hot bath (54°C or 82°C) — risk of burns, use heat-resistant gloves; Chromic acid — highly toxic and carcinogenic (CMR), use only if necessary, prefer detergents; Oils — avoid prolonged skin contact, use nitrile gloves; Rotating stirrer — do not insert hands in working zone, watch for splashing; Safety glasses and laboratory coat required.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 6614.