GB/T 2430-2008 Freezing point of aviation fuels

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: GB/T 2430-2008
• Chinese name: Aviation Fuel Freezing Point Determination Method
• English name: Standard test method for freezing point of aviation fuels
• Replacement relationship: replaces GB/T 2430-1981 "Jet Fuel Freezing Point Determination Method"
• Adoption relationship: modified adoption of ASTM D2386:2006 "Standard Test Method for Freezing Point of Aviation Fuels"
• Publication/implementation: published on 2008-08-25, implemented on 2009-02-01
• Custodian: Subcommittee on Petroleum Fuels and Lubricants of the National Technical Committee for Standardization of Petroleum Products and Lubricants
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafters: Zhang Ji, Zhang Cuijun

2. Scope of application and non-applicability

• 1.1 This standard specifies the determination method for the freezing point of jet fuels and aviation piston engine fuels; below the freezing point, solid hydrocarbon crystals will form in aviation fuels.
• Note: The precision verification of this standard does not include aviation piston engine fuels.
• 1.2 This standard uses International System of Units [SI] units.
• 1.3 The use of this standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and protective measures and to determine the applicability of regulatory limitations prior to use.

3. Method principle

• 3.1 Freezing point freezing point: Under specified conditions, aviation fuel is cooled to form solid hydrocarbon crystals, then the fuel is warmed; the lowest temperature at which the hydrocarbon crystals disappear is the freezing point of the aviation fuel.
• 4.1 The freezing point of aviation fuel is the lowest temperature that ensures no solid hydrocarbon crystals appear in the fuel. If such crystals are present in the aircraft fuel system, they will obstruct the passage of fuel through filters. Because the temperature of the fuel in aircraft fuel tanks usually decreases during flight, the extent of the decrease depends on flight speed, altitude, and flight duration. Therefore, the freezing point of the fuel must always be below the minimum operating temperature of the fuel tank.
• 4.2 The freezing point is a technical specification in product standards such as GB 1787 and GB 6537.

4. Reagents and materials (purity / preparation)

• 6.1 Acetone: If no residue remains after evaporation to dryness, chemically pure acetone may be used as a coolant. Warning—flammable.
• 6.2 Ethanol: Industrial or chemically pure anhydrous ethanol is used as a coolant. Warning—flammable.
• 6.3 Isopropanol: Industrial or chemically pure anhydrous isopropanol is used as a coolant. Warning—flammable.
• 6.4 Dry ice: Dry ice is used as a coolant. Warning—extremely cold, −78°C. The gas released by carbon dioxide (solid) can cause suffocation, and contact with skin can cause burns and frostbite.
• 6.5 Liquid nitrogen: When the freezing point is below −65°C, industrial or chemically pure liquid nitrogen may be used as a coolant. Warning—extremely cold, −196°C. The gas released by liquid nitrogen can cause suffocation, and contact with skin can cause burns and frostbite.
• Other materials: absorbent cotton (see 5.6, used to fill the space between the brass tube and the stirrer); dry atmospheric-pressure nitrogen or air (see 5.1, fills the space between the inner and outer tubes of the double-walled glass test tube).

5. Apparatus and equipment

• 5.1 Double-walled glass test tube: a double-walled, unsilvered container similar to a Dewar flask, with the space between the inner and outer tubes filled with dry atmospheric-pressure nitrogen or air. The mouth of the tube is stoppered with a stopper fitted with a thermometer and a moisture guard tube (or compression cap), and the stirrer passes through this moisture guard tube (see Figure 1). Dimensions (Figure 1): outer tube outer diameter 30.0 mm±0.7 mm, wall thickness 1.90 mm±0.30 mm; inner tube inner diameter 18.7 mm±1.1 mm, wall thickness 1.68 mm±0.35 mm; the space between the inner and outer tubes is at atmospheric pressure; minimum length 280 mm (requires confirmation against the source standard (source-text extraction), the original text is marked as "minimum 280").
• 5.2 Moisture guard tube: see Figure 2, to prevent condensation of moisture. Alternatively, the compression cap shown in Figure 3 may be used. Figure 2 dimensions: outer diameter φ12, φ5, length 100.0 mm, 10.0 mm, glass wall thickness 1 mm±0.1 mm; filled with glass wool and desiccant (silica gel); Note: cover the top to prevent loss of silica gel.
• 5.3 Stirrer: a brass rod with a diameter of 1.6 mm, the lower end bent into a smooth three-turn spiral. Note: A mechanical stirring device may be used for the stirrer.
• 5.4 Vacuum flask: an unsilvered vacuum flask, minimum dimensions see Figure 1, capable of holding a sufficient amount of coolant to allow the double-walled glass test tube to be immersed to the specified depth. Warning—risk of implosion. Figure 1 label: minimum inner diameter 70 mm.
• 5.5 Thermometer: total immersion type, temperature range −80°C~+20°C. Meets the specification requirements for thermometer No. GB-38 in GB/T 514. Note: The accuracy of this thermometer shall be verified according to the thermometer verification method, with verification point temperatures of 0°C, −40°C, −60°C, and −75°C (requires confirmation against the source standard (source-text extraction), the original text is "0°C, 40C, 60CC and 75°CC").
• 5.6 Compression cap: During low-temperature testing, to prevent moisture condensation, the compression cap shown in Figure 3 may be installed. The compression cap is tightly inserted into the cork stopper, and absorbent cotton is used to fill the space between the brass tube and the stirrer. Figure 3 dimensions: φ8, drilled hole φ2.4, 13, knurled, M5 thread, 10, 27, drilled hole φ2.4, φ6.

6. Recommended operating conditions

• Stirring speed: 1 (times/s)～1.5 (times/s), moving the stirrer up and down (see 8.3).
• Thermometer sensing bulb position: 10 mm~15 mm from the bottom of the double-walled glass test tube, located in the center of the test tube, not touching the wall (see 8.1).
• Sample liquid level position: should be about 15 mm~20 mm below the coolant liquid level (see 8.2).
• Coolant: acetone, ethanol, or isopropanol; for samples with a fuel freezing point below −65°C, liquid nitrogen may also replace dry ice as the coolant; mechanical refrigeration may also be used (see 8.2 Note).
• Observation conditions: This test requires bright light in the laboratory (see 8.1 Note 2).
• Time for removing the double-walled glass test tube for observation: no more than 10 s (see 8.3 Note 1).

7. Sampling and sample preparation

• 7.1 Unless otherwise specified, sampling shall be carried out in accordance with GB/T 4756.
• 7.2 At least 25 mL of sample is required for each test.
• 7.3 The sample is stored in a sealed container at room temperature, minimizing the introduction of moisture. The sample should be kept as far away from heat sources as possible.

8. Analytical procedure

• 8.1 Measure 25 mL±1 mL of sample and pour it into a clean, dry double-walled glass test tube. Tightly stopper the double-walled glass test tube with a cork stopper fitted with a stirrer, thermometer, and moisture guard tube (or compression cap), adjust the thermometer position so that the sensing bulb does not touch the wall and is located in the center of the double-walled glass test tube, with the thermometer sensing bulb 10 mm~15 mm from the bottom of the double-walled glass test tube.
  • Note 1: During the test, bubbles formed by the sample in the double-walled glass test tube immersed in the coolant may interfere with observation, and crystals of the sample may appear in various forms and be difficult to identify.
  • Note 2: This test requires bright light in the laboratory. Some crystals are very faint and difficult to observe when light is insufficient.
• 8.2 Clamp the double-walled glass test tube so that it is immersed as deeply as possible in the vacuum flask containing the coolant (Warning: prone to implosion) (see Note). The sample liquid level should be about 15 mm~20 mm below the coolant liquid level. Unless mechanical refrigeration is used for cooling, dry ice must be continuously added throughout the test to maintain the coolant liquid level in the vacuum flask.
  • Note: The coolant may be acetone, ethanol, or isopropanol, but all these reagents must be handled with care. For samples with a fuel freezing point below −65°C, liquid nitrogen may also replace dry ice as the coolant. Mechanical refrigeration may also be used.
• 8.3 Except during observation, the sample must be continuously stirred throughout the test, moving the stirrer up and down at a speed of 1 (times/s)～1.5 (times/s), and care must be taken that the brass ring of the stirrer does not touch the bottom of the double-walled glass test tube when moving downward and remains below the sample liquid level when moving upward. During certain steps of the operation, momentary stopping of stirring is permitted (see Note 1), and the sample is continuously observed to detect hydrocarbon crystals. Due to the presence of water, when the temperature drops to near −10°C, a cloudiness will appear; if the cloudiness does not increase upon further cooling, such cloudiness may be disregarded. When crystals visible to the naked eye begin to appear in the sample, record the temperature at which hydrocarbon crystals appear. Remove the double-walled glass test tube from the coolant, allow the sample to continue warming at room temperature while still stirring at a speed of 1 (times/s)～1.5 (times/s), continue observing the sample until the hydrocarbon crystals disappear, and record the temperature at which the hydrocarbon crystals completely disappear.
  • Note 1: Because gases released by the coolant may obstruct the line of sight, the double-walled glass test tube may be removed from the coolant to facilitate observation. The time for removing the double-walled glass test tube shall not exceed 10 s; if crystals have already formed, record this temperature. Allow the sample to warm at room temperature with stirring, and the temperature should rise to at least 5°C above the crystal disappearance temperature, then re-immerse the sample in the coolant for cooling. Remove the sample at a temperature slightly above this recorded temperature and observe the crystallization point.
  • Note 2: It is recommended to compare the crystal appearance temperature with the crystal disappearance temperature. The crystal appearance temperature should be lower than the crystal disappearance temperature. Otherwise, it indicates that the crystals were not correctly observed and identified; the difference between these two temperatures is generally not greater than 6°C.

9. Qualitative and quantitative determination and calculation formula

• The observed freezing point value determined in Chapter 8 shall be corrected according to the corresponding correction value of the thermometer as described in the Note to Clause 5.5.
• If the observed freezing point value lies between two calibration temperatures, linear interpolation shall be used for correction.
• Report the corrected crystal disappearance temperature, accurate to 0.5°C, as the freezing point of the sample.
• Calculation formula: not provided in the available source.

10. Precision

• Determine the reliability of the test results according to the following rules (95% confidence level).
• 10.1 Repeatability (r): In the same laboratory, by the same operator, using the same apparatus, on the same test sample, the difference between two test results shall not be greater than 1.5°C.
• 10.2 Reproducibility (R): In different laboratories, by different operators, using different apparatus, on the same test sample, the difference between two test results shall not be greater than 2.5°C.
• 10.3 Bias: Because there is no hydrocarbon mixture with a known freezing point that can be used to simulate aviation fuel, the bias cannot be determined.

11. Report

• The observed freezing point values measured in Chapter 8 shall be corrected according to the corresponding correction values of the verification thermometer as described in the note to clause 5.5. If the observed freezing point value lies between two correction temperatures, correct it using linear interpolation. Report the corrected crystallization disappearance temperature, to the nearest 0.5°C, as the freezing point of the test sample.

12. Referenced Documents

• GB/T 514 Specification for liquid-in-glass thermometers for petroleum product testing
• GB 1787 Aviation piston engine fuels
• GB/T 4756 Manual sampling of petroleum liquids (GB/T 4756—1998, eqv ISO 3170:1988)
• GB 6537 3 jet fuel

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference Q&A