Pour point

Pour point

The pour point of a liquid is the lowest temperature at which it will pour or flow under prescribed conditions. It is a rough indication of the lowest temperature at which oil is readily pumpable.

Also, the pour point can be defined as the minimum temperature of a liquid, particularly a lubricant, after which, on decreasing the temperature, the liquid ceases to flow.

Measuring the pour point of petroleum products

The specimen is cooled inside a cooling bath to allow the formation of paraffin wax crystals. At about 9oC above the expected pour point, and for every subsequent 3oC, 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 secs. If it does not flow, 3oC is added to the corresponding temperature and the result is the pour point temperature.

It is also useful to note that failure to flow at the pour point may also be due to the effect of viscosity or the previous thermal history of the specimen. Therefore, the pour point may give a misleading view of the handling properties of the oil. Additional fluidity or pumpability tests may also be undertaken. An approximate range of pour point can be observed from the specimen's upper and lower pour point.

Measuring the pour point of crude oils

Two pour points can be derived which can give an approximate temperature window depending on its thermal history. Within this temperature range, the sample may appear liquid or solid. This peculiarity happens because wax crystals form more readily when it has been heated within the past 24hrs and contributes to the lower pour point.

The upper pour point is measured by pouring the test sample directly into a test jar. The sample is then cooled and then inspected for pour point as per the usual pour point method.

The lower pour point is measured by first pouring the sample into a stainless steel pressure vessel. The vessel is then screwed tight and heated to above 100oC in an oil bath. After a specified time, the vessel is removed and cooled for a short while. The sample is then poured into a test jar and immediately closed with a cork carrying the thermometer. The sample is then cooled and then inspected for pour point as per the usual pour point method.

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