ASTM D5853 Standard Test Method for Pour Point of Crude Oils
9. Procedure
9.1 Procedure A for Maximum (Upper) Pour Point:
9.1.1 Pour the test sample into the test jar to the level mark. If necessary, reheat the test sample to a temperature at least 20°C above the expected pour point (8.2 and Appendix X1) but not higher than a temperature of 60°C (Warning - The vapor pressure of crude oils at temperatures higher than 60°C will usually exceed 100 kPa. Under these circumstances the sample container may rupture. Opening of the container may induce foaming with resultant loss of sample and possible injury to personnel.).
9.1.2 Immediately close the test jar with the cork carrying the high cloud and pour thermometer, or, if the expected pour point is above 36°C, the melting point thermometer. Adjust the position of the cork and thermometer so the cork fits tightly, the thermometer and the jar are coaxial, and the thermometer bulb is immersed to a depth that places the beginning of the capillary 3 mm below the surface of the test specimen.
9.1.3 Keep the test jar with the test specimen at room temperature (between 18 and 24°C) for at least 24 h.
NOTE 5 - The pour point of a crude oil is dependent on the state of crystallization of the wax in the test specimen. In crude oils, achieving equilibrium between crystallized wax and dissolved wax is a rather slow process. However, experience has shown that in a majority of cases, such an equilibrium is reached within 24 h.
9.1.4 If the expected pour point is greater than 36°C, heat the sample to 9°C above the expected pour point. If the expected pour point is less than 36°C, heat the sample to a temperature of 45 +/- 1°C. Maintain the water bath (6.2) to heat the sample at 48 +/- 1°C or at a temperature 12°C higher than the expected pour point, whichever is higher.
9.1.4.1 As soon as the test specimen has reached the required temperature, remove the cork carrying the thermometer and stir the test specimen gently with a spatula or similar device. Put the cork carrying the thermometer back in place (see 9.1.2).
9.1.5 Ensure that the disk, gasket, and the inside of the jacket are clean and dry. Place the disk in the bottom of the jacket. Place the disk and jacket in the cooling medium a minimum of 10 min before the test jar is inserted. The use of a jacket cover, while the empty jacket is cooling, is permitted. Remove the test jar from the water bath and dry with a tissue. Place the gasket around the test jar, 25 mm from the bottom. Insert the test jar into the jacket in the first bath maintained at 21°C and commence observations for pour point. Never place a test jar directly into the cooling medium.
9.1.6 Exercise care not to disturb the mass of test specimen nor permit the thermometer to shift in the test specimen; any disturbance of the spongy network of wax crystals will lead to a lower pour point and erroneous results (Note 5).
NOTE 6 - With dark colored materials, such as crude oils, it is impractical to observe, in the test jar, the onset of crystallization and network formation in the test specimen. Hence, it is presumed that network formation will begin at the very early stages of the cooling sequence.
9.1.7 Pour points are expressed in temperatures which are positive or negative multiples of 3°C. Begin to examine the appearance of the test specimen when the temperature of the test specimen is 9°C above the expected pour point (estimated as a multiple of 3°C). At each test thermometer reading which is a multiple of 3°C below the starting temperature, remove the test jar from the jacket. When necessary, remove moisture that limits visibility of the test specimen by wiping the surface of the test jar with a clean cloth moistened in alcohol at approximately the temperature of the test specimen in the jar. Then tilt the jar just enough to ascertain whether there is movement of the test specimen in the jar. When movement is observed, immediately return the test jar into the jacket. The complete operation of removal and replacement shall require not more than 3 s.
9.1.7.1 If the test specimen has not ceased to flow when its temperature has reached 30°C, transfer the test jar to the next lower temperature bath per the following schedule:
(a) If the test specimen is at +30°C, move to 0°C bath;
(b) If the test specimen is at +9°C, move to -18°C bath;
(c) If the test specimen is at -9°C, move to -33°C bath; and
(d) If the test specimen is at -24°C, move to -51°C bath.
9.1.7.2 As soon as the test specimen in the jar does not flow when tilted, hold the jar in a horizontal position for 5 s, as shown by an accurate timing device (6.4) and observe carefully. If the test specimen shows any movement, replace the test jar immediately in the jacket and repeat a test for flow at the next temperature, 3°C lower.
9.1.8 Continue in this manner until a point is reached at which the test specimen shows no movement when the test jar is held in a horizontal position for 5 s. Record the observed reading of the test temperature.
9.1.8.1 If the test specimen has reached -36°C and still shows movement, discontinue the test.
NOTE 7 - To determine compliance with existing specifications having pour point limits at temperatures not divisible by 3°C, it is acceptable practice to conduct the pour point measurement according to the following schedule. Begin to examine the appearance of the test specimen when the temperature of the test specimen is 9°C above the specification pour point. Continue observations at 3°C intervals as described in 9.1.6 and 9.1.7 until the specification temperature is reached. Report the sample as passing or failing the specification limit.
9.2 Procedure B for Minimum (Lower) Pour Point:
9.2.1 Pour 50 g of the test sample into a clean pressure vessel (6.3 and Note 8). When necessary, reheat the test sample to a temperature of at least 20°C above the expected pour point (8.2 and Appendix X1) but not higher than 60°C (Warning - The vapor pressure of crude oils at temperatures higher than 60°C will usually exceed 100 kPa. Under these circumstances the sample container may rupture. Opening of the container may induce foaming with resultant loss of sample and possible injury to personnel.). Check that the rubber ring is in place and screw the lid on tightly.
NOTE 8 - The pressure vessel may be cleaned by any appropriate solvent, provided the solvent is capable of dissolving remnants of high melting wax and asphaltenes. Hot toluene (100°C) has been found to be an appropriate solvent for this purpose.
9.2.2 Heat the pressure vessel in an oil bath or by any other suitable means to a temperature of 105 +/- 2°C and leave at that temperature for at least 30 min.
9.2.3 Take the pressure vessel from the oil bath, wipe and dry the surface of the pressure vessel, swirl gently to homogenize the contents, and leave the pressure vessel to cool at room temperature for exactly 20 min.
9.2.4 Carefully open the pressure vessel and transfer the sample into the test jar filling to the level mark of the test jar, preheated in a water bath (6.2) kept at a temperature of 48 +/- 1°C (Warning - After 20 min at ambient temperature, the temperature of the test specimen will be approximately 50°C. The vapor pressure at that temperature may still exceed 100 kPa. Under these circumstances, inattentive opening of the pressure vessel may induce foaming with resultant loss of sample and possible injury to personnel.).
9.2.5 Immediately close the test jar with the cork carrying the high cloud and pour thermometer, or, if the expected pour point is above 36°C, the melting point thermometer. Adjust the position of the cork and thermometer so the cork fits tightly, the thermometer and the jar are coaxial, and the thermometer bulb is immersed to a depth which places the beginning of the capillary 3 mm below the surface of the test specimen.
9.2.6 Proceed as described in 9.1.5-9.1.8.
