GB/T 3535-2025Determination of pour point for petroleum products (English PDF)

3.1 Pour point

The lowest temperature at which a cooled specimen can flow under specified conditions.

3.2 Lower (minimum) pour point

The pour point observed after the sample underwent a specific treatment designed to delay the gelation of wax crystals and the solidification of the specimen.

5.1 Manual pour point tester

5.1.1 Test Tube. Made of flat-bottomed, cylindrical transparent glass, with an outer diameter of

33.2 mm to 34.8 mm, a height of 115 mm to 125 mm, an inner diameter of 30.0 mm to 32.4 mm, and a wall thickness not exceeding 1.6 mm. A long graduation mark indicating the volume of the contents (45 mL ± 1 mL) is marked 54 mm ± 3 mm from the bottom of the test tube. See

Figure 1.

9 - Cold bath (5.1.7).

Figure 1 -- Manual pour point tester

5.1.2 Temperature measuring device. Meets one of the following requirements.

a) Contact digital thermometer (DCT), meeting the requirements of A.1 in Appendix A.

b) Glass liquid thermometer. Partial immersion type, meeting the requirements of A.2.

Because liquid thermometers sometimes experience liquid column separation, which may be missed; the thermometer shall be checked before the test, and its accuracy shall be within ±1 °C.

5.1.3 Cork. Used for test tube, with a hole in the center for mounting a temperature measuring device.

5.1.4 Sleeve. Made of flat-bottomed, cylindrical metal, leak-proof, washable, with an inner

diameter of 44.2 mm to 45.8 mm, a wall thickness of approximately 1 mm, and a height of 115 mm ± 3 mm. The sleeve shall remain upright in the cold bath (5.1.7), with the portion protruding above the liquid surface not exceeding 25 mm, and shall be washable.

5.1.5 Disc. Made of cork or felt, approximately 6 mm thick, with a diameter matching the inner diameter of the sleeve. Its size shall allow for easy removal after installation within the sleeve.

5.1.6 Washer. Made of rubber, leather, or other suitable materials. Ring-shaped, approximately

5 mm thick, with a certain degree of elasticity; it shall fit snugly against the outer wall of the test tube while maintaining a loose fit against the inner wall of the sleeve. It shall also possess sufficient rigidity to maintain its shape.

NOTE. The purpose of the ring-shaped washer is to prevent direct contact between the test tube and the sleeve.

5.1.7 Cold bath. Capable of holding the sleeve firmly in a vertical position at a specified temperature. The bath temperature can be obtained through refrigeration or a suitable mixture of refrigerants. Appendix B lists commonly used mixtures of refrigerants.

5.1.8 Timer. The maximum error for a 30-second measurement shall not exceed 0.2 s.

5.2 Automatic pour point tester

5.2.1 Automatic pour point tester. Consists of a computer control system, cooling system, monitor, sensor, and a robotic arm (optional) for lifting and tilting the pour point tube, etc.

Thereof, the computer control system shall be able to control one or more independent testing units; the monitor shall be able to continuously monitor the specimen temperature; and the sensor shall be able to measure slight movements of the specimen during tilting.

5.2.2 Pour point tube. A transparent cylindrical glass tube with a flat bottom, an outer diameter of approximately 32 mm, and a height of approximately 120 mm. It shall have a graduation mark indicating the height of approximately 45 mL of specimen.

NOTE. The outer diameter and height of the pour point tube may vary slightly between different manufacturers and must be matched with an automatic pour point tester.

5.2.3 Pour point tube sleeve. A cylindrical metal product with a flat bottom, an inner diameter of approximately 45 mm, and a height of approximately 115 mm.

NOTE. The inner diameter and height of the pour point tube sleeve may vary slightly between different manufacturers and must be matched with an automatic pour point tester.

5.2.4 Temperature probe. Capable of measuring within the range of -80 °C to 70 °C, with a resolution of 0.1 °C. The temperature probe shall be inside the pour point tube being tested; and the top of the temperature sensing area shall be immersed below the specimen surface.

5.2.5 Cooling system. An internal cooling system or an external cooling system equipped with a circulating pump; capable of maintaining the bath temperature to meet the requirements of

Table 1.

7.1 Manual method

7.1.1 Pour the specimen into the test tube (5.1.1) up to the graduation mark. If necessary, the sample may be heated to flowability in a water bath before being poured into the test tube. If it is known that the specimen has been heated to above 45 °C within 24 h before the start of the test, or if its heating history is unknown, it must stand at room temperature for 24 h before the test can be conducted.

7.1.2 Stopper the test tube with a cork fitted with a high cloud point and high pour point thermometer (see A.2) or a contact digital thermometer with a nominal temperature range of high pour point (see A.1). If the expected pour point of the specimen is above 36 °C, use a melting point temperature measuring device (5.1.2), such as the GB-35 glass liquid thermometer (see A.2) specified in GB/T 514-2005 or a contact digital thermometer with a nominal temperature range of melting point (see A.1). Adjust the position of the cork and temperature measuring device so that the cork tightly seals the test tube. The temperature measuring device and the test tube shall be on the same axis; and the temperature measuring device shall be immersed to a suitable depth below the specimen liquid surface.

For glass liquid thermometers, the capillary tip of the thermometer shall be immersed 3 mm below the specimen liquid surface.

For contact digital thermometers, the tip of the probe shall be immersed 10 mm to 15 mm below the specimen liquid surface.

7.1.3 Pretreat the specimen in the test tube according to 7.1.4 or 7.1.5.

7.1.4 Specimens with a pour point higher than -33 °C shall be treated as follows.

a) Place the specimen, without stirring, in a bath maintained at 12°C above the expected pour point, but at least 48°C. Heat the specimen to 45°C or 9°C above the expected pour point (whichever is higher).

b) Transfer the test tube to a bath maintained at 24°C ± 1.5°C and begin observing the pour point. If using a liquid bath, ensure the liquid level is between the graduation mark on the test tube and the top surface of the test tube.

c) When the specimen reaches 9°C above the expected pour point (estimated as a multiple of 3°C), begin observing the flowability of the specimen as specified in 7.1.7.

d) If the specimen is still flowable at 27°C, carefully remove the test tube from the bath;

wipe the outer surface of the test tube with a clean cloth dampened with wiping solution;

and then place the test tube in a cold bath at 0°C (5.1.7) as specified in 7.1.6.Observe the fluidity of the specimen as specified in 7.1.7; and cool it according to the procedure specified in 7.1.8.

7.1.5 Specimens with a pour point of -33 °C or lower shall be treated as follows.

a) Heat the specimen to 45 °C in a 48 °C ± 1.5 °C bath without stirring; then cool it to 27 °C in a 24 °C ± 1.5 °C bath.

b) If using a liquid bath, ensure the liquid level is between the graduation mark on the test tube and the upper surface of the test tube. When the specimen temperature reaches 27 °C, if using a glass liquid thermometer, remove the thermometer with high cloud point and high pour point, replace it with one with low cloud point and low pour point; place the test tube in a cold bath, and cool it according to the procedure specified in 7.1.8.

7.1.6 Ensure the inner walls of the disc (5.1.5), washer (5.1.6), and sleeve (5.1.4) are clean and dry; and place the disc at the bottom of the sleeve. Before inserting the test tube, the disc and sleeve shall be placed in a cold bath (5.1.7) for at least 10 min. Place the washer on the outer wall of the test tube, approximately 25 mm from the bottom; and insert the test tube into the sleeve. Except for a 24°C bath, the test tube shall not be placed directly into the cooling medium.

7.1.7 Observe the flowability of the specimen.

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