❄️ Pour Point Temperature
Determination of pour point of petroleum products — lowest temperature at which product is still capable of flowing under standardized cooling conditions.
Overview
Pour point is the lowest temperature at which a petroleum product is still capable of flowing under standardized cooling conditions. Below this temperature, the network of paraffin crystals forms a gel that prevents liquid flow. Pour point is lower than cloud point — fuel first becomes cloudy (cloud point), and only at lower temperature stops flowing (pour point).
Pour point is a key parameter for lubricating oils, hydraulic and transformer oils, where low-temperature flow capability determines pumpability and lubrication under winter conditions. For engine and gear oils, pour point must be significantly lower than lowest operating temperature — otherwise oil will not reach lubricated surfaces during engine startup.
Standard PN-EN ISO 3016 describes manual and automatic methods. Sample is cooled in stages in baths of progressively lower temperature. Every 3°C test jar is removed and tilted — if sample does not move within 5 seconds, temperature 3°C higher is recorded as pour point. Standard describes separate procedure for residual fuels and heavy base oils (lower pour point).
Pour point is a mandatory parameter in lubricating oil specifications (SAE, ISO VG), transformer oils (PN-EN 60296), hydraulic and compressor oils. Oil producers use pour point depressants (PPD — Pour Point Depressants) — polymers that disrupt paraffin crystallization and lower pour point by 20–40°C.
Method principle
Sample is pre-heated to dissolve paraffin crystals, then cooled in series of controlled-temperature baths. Every 3°C test jar is removed from bath and tilted 90° for 5 seconds. If sample moves (flows), jar returns to bath and cooling continues. If sample does not move within 5 seconds, test is complete. Pour point = temperature of last movement + 3°C. In automatic apparatus, detection is based on optical monitoring of sample surface movement during tilting.
Applications
- Engine oil specification — SAE J300, winter pumpability limit
- Quality control of transformer oils (PN-EN 60296: pour point ≤ -40°C)
- Evaluation of hydraulic oils — pumpability at low temperatures
- Testing diesel fuel — pour point as informational parameter
- Quality control of crude oil — pipeline transport problems
- Evaluation of pour point depressant (PPD) effectiveness
- Testing gear and compressor lubricating oils
- Marine fuel specifications (ISO 8217)
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | from +51°C to below -60°C (automatic apparatus to -95°C) |
| Resolution | 3°C (result always multiple of 3) |
| Repeatability | ±3°C |
| Reproducibility | ±6°C |
| Sample volume | 45–50 mL |
| Determination time | 30–120 min (dependent on pour point) |
Standard
- Standard number
- PN-EN ISO 3016:2019
- Title (PL)
- Przetwory naftowe i produkty pokrewne pochodzenia naturalnego lub syntetycznego — Oznaczanie temperatury płynięcia
- Title (EN)
- Petroleum and related products from natural or synthetic sources — Determination of pour point
Step-by-step procedure
1. Sample pre-heating
Heat sample to temperature 12°C above expected pour point, not lower than 45°C. For samples with pour point > -33°C heat to 48°C in 48°C bath. Purpose is to dissolve paraffin crystals.
2. Test jar filling
Pour sample into clean, dry test jar to level mark (~45 mL). Insert thermometer and close with cork.
3. Cooling in first bath
Place jar in bath at temperature dependent on expected pour point. For pour point > -33°C: 0°C bath as first.
4. Flow test every 3°C
At each 3°C sample temperature drop remove jar from bath. Hold horizontally and observe for 5 seconds whether sample moves. If it flows — return to bath.
5. Bath change
When sample still flows in current bath — transfer to lower temperature bath (-18°C, -33°C, -51°C, -69°C). Continue tests every 3°C.
6. No flow determination
When sample does not move within 5 seconds when jar is tilted — determination complete. Record temperature at which sample stopped.
7. Pour point calculation
Pour point = stopping temperature + 3°C. For example: if sample did not flow at -21°C, pour point = -21 + 3 = -18°C. Result always multiple of 3.
8. Repeat determination
Repeat test on new sample portion (again pre-heated). Two results should agree within repeatability limits (±3°C).
9. Reporting
State pour point in °C (multiple of 3). State: PN-EN ISO 3016, sample identification, date. Clearly indicate whether result is "normal" or "lower" pour point.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Automatic cloud/pour point analyzer | PAC OptiCPP (ISL), Anton Paar CPA, Koehler K46100 | 60 000–130 000 PLN |
| Manual pour point apparatus | Cylindrical test jar + cooling baths per ISO 3016 | 5 000–15 000 PLN |
| Cooling baths | Bath set 0°C, -18°C, -33°C, -51°C, -69°C | 8 000–25 000 PLN |
| Low-temperature thermometer | ASTM thermometer range -80°C to +50°C, resolution 1°C | 300–800 PLN |
| Test jar | Cylindrical glass jar with flat bottom per ISO 3016 | 50–150 PLN/pc |
| Cork with thermometer hole | Cork or silicone stopper with central hole | 10–30 PLN/pc |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Acetone (for cleaning) | 67-64-1 | Purity ≥99.5%, for washing and drying test jars |
| Cooling mixture | — | Acetone + dry ice (CO₂) for -51°C and -69°C baths, or ethanol + liquid nitrogen |
| Liquid nitrogen (automatic apparatus) | 7727-37-9 | Or cascade cooling system to -95°C |
| Pour point CRM | — | Certified reference material with known pour point for apparatus verification |
Health and safety (OHS)
- Petroleum products — flammable, store away from ignition sources
- Baths with acetone + dry ice — flammable solvent at low temperature, dry ice causes frostbite
- Liquid nitrogen — risk of frostbite and asphyxiation in enclosed spaces, ventilation!
- Cryogenic gloves mandatory when handling low-temperature baths
- Safety glasses mandatory