What is Pour Point?
The pour point is the lowest temperature at which oil flows in a specified lab test. Specifically, the pour point is 3℃ (5℉) above the temperature at which the oil shows no movement when a lab sample container is held horizontally for 5 seconds.
Pour point is an indication of the cold temperature properties of oil. But we should not select a lubricant product based solely on its pour point. The cloud point is also a very important factor for choosing any lubricant for any application. Cloud point is approximately the low temperature at which the oil becomes cloudy due to the formation of wax crystals within the oil. ASTM D97 (ISO 3016 or IP 15) covers the standard methods to measure the pour point of petroleum products. In addition, several methods are used to determine cloud points, including ASTM D5772.
How to Measure Pour Point of Lubricants?
- The Seta Cloud and Pour Point Bath give the required cold bath to liquid to take them to the necessary stage.
- It utilizes the current and with the help of conditioners and couples present in them. They cool the fluids up.
- They hold four test positions.
- They can supply the temperature range from 9°C to -69°C.
- The equipment identifies the minimum safe operating temperature.
- The bath accommodates four jackets and a steel cover, and a drain tap.
These are the most common methods that are used to determine the pour point of a product:
- D97 – Pour Point of Petroleum Products
- D5853 – Pour Point of Crude Oils
- D5949 – Pour Point of Petroleum Products (Automatic Pressure Pulsing Method)
Measuring the pour point of petroleum products
ASTM D97, Standard Test Method for Pour Point of Crude Oils. The specimen is cooled inside a cooling bath to allow the formation of paraffin wax crystals. At about 9 °C above the expected pour point, and for every subsequent 3 °C, the test jar is removed and tilted to check for surface movement. When the specimen does not flow when tilted, the jar is held horizontally for 5 sec. If it does not flow, 3 °C is added to the corresponding temperature, resulting in the pour point temperature.
ASTM D5949, Standard Test Method for Pour Point of Petroleum Products (Automatic Pressure Pulsing Method) is an alternative to the manual test procedure. It uses automatic apparatus, and yields pour point results in a format similar to the manual method (ASTM D97) when reporting at a 3 °C.
Under ASTM D5949, the test sample is heated and then cooled by a Peltier device at a rate of 1.5±0.1 °C/min. At either 1 °C or 3 °C intervals, a pressurized pulse of compressed gas is imparted onto the sample’s surface. Multiple optical detectors continuously monitor the sample for movement. The lowest temperature at which motion is detected on the sample surface is the pour point.
|Test||Objective/Summary||Applications||Typical results High/Low|
|Pour Point ( ASTM D97 – 96a)||1) This is the test to determine the lowest temp at which oil will flow under the influence of gravity.
2) The oil sample is placed in a beaker along with a thermometer, sealed with a cork, heated to 46℃ (115℉), and then progressively cooled. The jar is removed at progressive 3℃ (5℉) intervals & tilted to determine fluidity.
3) The pour point is 3℃ (5℉) above the temperature at which the oil shows no movement when a lab sample container is held horizontally for 5 seconds.
|All lubricants exposed to cold start or cold operating temperatures.||-10℃ or -32℃.
Low is better
What is Pour Point Depressant?
Pour point depressant is an additive (polymer) that allows oils and lubricants to flow at very low temperatures without the heavy wax formation at these cold temperatures and enables the oil to remain pumpable (flowable). They are typically used in paraffinic base oils in applications where extremely low machine startup temperature conditions are possible. Most paraffinic motor oils use pour point depressors. Pour Point Depressants work as modifiers & modify the interface between the crystallized wax and the oil.
Pour Point of Various Lubricants and Oils
Pour points for Crude oils range from 32 °C to below −57 °C (90 °F to below −70 °F). Some typical values of Pour Point are provided below in the table:
|Multi-grade engine oil||-35 Deg. C|
|Monograde engine oil||-23 Deg. C|
|Turbine Oil||-18 Deg. C|
|Synthetic Polyol ester||-32 Deg. C|
|Castor Oil||-33 Deg. C|
|Coconut Oil||21 Deg. C|
|Groundnut Oil||3 Deg. C|
|Mustard Oil||-18 Deg. C|
|Sunflower Oil||-18 Deg. C|
|Olive Oil||-9 Deg. C|
|Kerosene||-69 Deg. C|
Table: Typical Pour Point Values for Oils
|Typical properties of commonly used classes of synthetic lubricants (oils).|
|Lubricants||Thermal stability, (◦C)||Specific gravity at 20◦C||Flash point (◦C)||Pour point (◦C)|
|Neopentyl polyol esters||230||0.96||250||−62|
Adapted from PRINCIPLES AND APPLICATIONS OF TRIBOLOGY, Bharat Bhushan, 2013
Due to the presence of high molecular weight components, such as wax, asphaltene, and resin, heavy and extra-heavy crude oils usually have higher pouring points. The pour point of the liquid can be improved by using depressants like polymethacrylates, alkylated wax fennel, alkylated wax naphthalene, etc.