GB/T 6986-2014 Determination of Cloud Point of Petroleum Products

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Card type: Test method

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

• Standard number: GB/T 6986—2014
• Chinese name: Determination of Cloud Point of Petroleum Products
• English name: Standard test method for cloud point of petroleum products
• Replacement relationship: replaces GB/T 6986—1986 "Determination of Cloud Point of Petroleum"
• Adoption relationship: modified adoption using the redrafting method of ASTM D2500-11 "Standard Test Method for Cloud Point of Petroleum Products"; the automatic method content is based on ASTM D5771-12 "Determination of Cloud Point of Petroleum Products (Optical Detection with Stepwise Cooling Method)"
• Publication/implementation: published on 2014-02-19, implemented on 2014-06-01
• Custodianship: Subcommittee on Petroleum Fuels and Lubricants of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280/SC 1)
• Main drafting organization: Maoming Branch of China Petroleum & Chemical Corporation

2. Scope of application and non-applicability

• This standard specifies manual and automatic methods for determining the cloud point of petroleum products, biodiesel, and biodiesel blended fuels; the manual method is the arbitration method.
• This standard is only applicable to determining the cloud point of petroleum products, biodiesel, and biodiesel blended fuels that are transparent at a layer thickness of 40 mm and have a cloud point lower than 49 °C.
• The color of the test sample determined by this standard is ≤3.5 (determined according to GB/T 6540); this standard may also be used for cloud point determination of samples with color >3.5, but the precision of this standard does not apply.
• Non-applicability: the source text does not clearly list other non-applicable objects.

3. Method principle

Place a clear and transparent test sample into the apparatus and cool the sample by stepwise temperature reduction. Determine whether wax crystals have formed by visual observation or continuous monitoring with an optical system. The highest sample temperature at which wax crystals first appear at the bottom of the test tube, causing a misty or cloudy appearance, is the cloud point of the sample, expressed as °C.

4. Reagents and materials (purity / preparation)

• 4.1 Dehydrating agent: anhydrous sodium sulfate, analytical reagent. It should be dried in an oven at 100 °C–105 °C for 1 h–2 h to constant weight, then placed in a desiccator for use. Drying immediately before use is better.
• 4.2 Filter paper: qualitative or quantitative filter paper. It should be dried in an oven at 100 °C~105 °C to constant weight, then placed in a desiccator for use. Drying immediately before use is better.
• 4.3 Coolant:
  • Ice and water
  • Sodium chloride crystals, chemically pure
  • Solid carbon dioxide (dry ice)
  • Acetone: chemically pure (Warning: extremely flammable)
  • Solvent naphtha: meets the requirements of No. 3 in GB 1922—2006 (Warning: flammable, toxic vapor)
  • Anhydrous ethanol: chemically pure (Warning: flammable)
  • Anhydrous methanol: chemically pure (Warning: flammable, toxic vapor)
• 4.4 Cleaning reagents (automatic method, used for cleaning and drying the test unit):
  • Solvent naphtha: meets the requirements of No. 3 in GB 1922—2006
  • Hexane: meets the requirements of GB 17602
  • Note: Other non-corrosive reagents may also be used to clean and dry the test unit, including reagents recommended by the instrument supplier.
• 4.5 Cooling bath medium (automatic method, used as the cooling medium in the circulating bath):
  • Anhydrous methanol: chemically pure (Warning: flammable, toxic vapor)
  • Anhydrous ethanol: chemically pure (Warning: flammable, toxic vapor)
  • Note: Anhydrous media that can achieve the bath temperature specified in the method and do not corrode the equipment, including reagents recommended by the instrument supplier.

5. Apparatus and equipment

5.1 Manual method apparatus (the manual cloud point tester is shown in Figure 1)

• Thermometer:
  • Thermometer used for the constant-temperature bath (bath temperature): total immersion type, meets the technical requirements of thermometer GB-38 in GB/T 514—2005. Temperature measurement range −80 °C~+20 °C, scale division 0.5 °C.
  • Thermometer used in the test tube (for measuring the sample): partial immersion type, meets the technical requirements of thermometers GB-36 and GB-37 in GB/T 514—2005. No. GB-36 low-temperature-range thermometer, temperature measurement range −80 °C~+20 °C, scale division 1 °C; No. GB-37 high-temperature-range thermometer, temperature measurement range −38 °C~+50 °C, scale division 1 °C.
  • Note: Low-temperature thermometers should be stored upright at low temperature.
• Test tube: flat-bottomed, cylindrical, made of transparent glass, inner diameter 30.0 mm–32.4 mm, outer diameter 33.2 mm–34.8 mm, height 115 mm~125 mm, wall thickness not greater than 1.6 mm. A mark line is provided at 54 mm±3 mm from the inner bottom of the test tube, and the volume at the mark line is 45 mL±0.5 mL.
• Sleeve: flat-bottomed metal or glass cylinder, inner diameter 44.2 mm~45.8 mm, height about 115 mm. The sleeve should be able to maintain an upright position in the cooling bath, and its height above the cooling medium must not exceed 25 mm.
• Cork stopper: used together with the test tube, with a hole in the center of the stopper through which the thermometer can be inserted.
• Gasket: made of cork or felt, thickness 6 mm, diameter the same as the inner diameter of the sleeve.
• Ring: annular, thickness about 5 mm, required to fit tightly against the outer wall of the test tube and to be loose within the sleeve. The ring may be made of cork, wool, or other suitable material, as long as the ring has sufficient elasticity to fit tightly against the test tube and sufficient hardness to maintain its shape. The purpose of the ring is to prevent the test tube from contacting the sleeve.
• Cooling bath: must achieve the temperature specified in this standard and firmly fix the sleeve in a vertical position. The required bath temperature should be maintained as much as possible by a refrigeration device or a suitable coolant. The bath temperature of the cooling bath is required to be maintained within the range of ±1.5 °C of the specified temperature.

5.2 Automatic method apparatus

• Optical cloud point tester: consists of a microprocessor controller, which can control one or more independent test units. The instrument should have the following functions: individually control the temperature of each unit according to a specific cooling program; continuously monitor the sample temperature; detect the appearance of cloud point at the bottom of the test tube without removing the test tube from the sleeve, and display the result accurate to 0.1 °C or 1 °C (see Figure 2).
• Temperature probe: should meet Class A of standard JB/T 8622 PT100: ΔT=±(0.15+0.002|T|), measurement range −50 °C~+80 °C, and the temperature probe should contact the bottom of the test tube.
• Test tube: cylindrical, made of transparent glass, with a mirrored bottom, outer diameter 34 mm±0.5 mm, wall thickness 1.4 mm±0.15 mm, height 120 mm±0.5 mm, bottom thickness 2.0 mm±0.5 mm, and a mark line at 54 mm±0.5 mm from the inner bottom of the test tube to indicate the sample height.
• Sleeve: made of brass, cylindrical, flat-bottomed, depth 113 mm±0.2 mm, inner diameter 45 mm±0.1 mm. The sleeve is cooled according to a specific cooling program.
• Circulating cooling bath: equipped with a circulation pump (either internally or externally equipped), capable of maintaining a temperature at least 10 °C lower than the lowest required sleeve temperature (see Table 3 and Figure 2).
• Cork gasket: 6 mm±0.2 mm thick, loose within the sleeve. Felt gaskets may also be used, but special attention should be paid to the possible presence of moisture in felt gaskets. The felt gasket should be dry before each test.
• Cork ring: can fit tightly around the outside of the test tube and is loose within the sleeve. Its purpose is to prevent the test tube from contacting the sleeve.

6. Recommended operating conditions

• Environmental conditions: the environmental conditions during testing require humidity not greater than 75% (see 6.3).
• Manual method cooling bath temperature control: the bath temperature of the cooling bath is required to be maintained within the range of ±1.5 °C of the specified temperature.
• Manual method cooling bath medium and bath temperature (Table 1):
  • Ice and water: 0 °C±1.5 °C
  • Crushed ice and sodium chloride crystals, or solid carbon dioxide added to acetone or solvent naphtha or ethanol or methanol to obtain the required temperature: −18 °C±1.5 °C
  • Solid carbon dioxide added to acetone or solvent naphtha or methanol or ethanol to obtain the required temperature: −33 °C±1.5 °C
  • Solid carbon dioxide added to acetone or solvent naphtha or methanol or ethanol to obtain the required temperature: −51 °C±1.5 °C
  • Solid carbon dioxide added to acetone or solvent naphtha or methanol or ethanol to obtain the required temperature: −69 °C±1.5 °C
• Manual method cooling bath and sample temperature (Table 2):
  • Bath number 1: bath temperature set at 0 °C±1.5 °C, sample temperature range start~9 °C
  • Bath number 2: bath temperature set at −18 °C±1.5 °C, sample temperature range 9 °C~−6 °C
  • Bath number 3: bath temperature set at −33 °C±1.5 °C, sample temperature range −6 °C~−24 °C
  • Bath number 4: bath temperature set at −51 °C±1.5 °C, sample temperature range −24 °C~−42 °C
  • Bath number 5: bath temperature set at −69 °C±1.5 °C, sample temperature range −42 °C~−60 °C
• Automatic method sleeve and sample temperature (Table 3):
  • Sample temperature (ST) ST>+10 °C: sleeve temperature 0 °C±0.5 °C
  • +10 °C≥ST>−7 °C: sleeve temperature −17.2 °C±0.5 °C
  • −7 °C≥ST>−24 °C: sleeve temperature −34.2 °C±0.5 °C
  • −24 °C≥ST>−41 °C: sleeve temperature −51.2 °C±0.5 °C
  • −41 °C≥ST>−58 °C: sleeve temperature −68.2 °C±0.5 °C
  • −58 °C≥ST>−75 °C: sleeve temperature −85.2 °C±0.5 °C
• Automatic method temperature precision: general laboratory practice is 1 °C; if higher requirements are placed on the results, 0.1 °C may be selected.
• In the automatic method, the time to move from one sleeve temperature to the next sleeve temperature shall not exceed 200 s; this time is suitable for sleeve temperature decreasing to −52 °C; for lower sleeve temperatures, the time to move from one sleeve temperature to the next sleeve temperature shall not exceed 300 s.
• After the automatic method detection is completed, the sleeve temperature shall be adjusted to 23 °C±2 °C before the test tube can be removed.

7. Sampling and specimen preparation

• Sampling: unless otherwise specified, sampling shall be carried out in accordance with GB/T 4756.
• At room temperature, the specimen shall be fluid, transparent, and free of impurities.
• If the specimen contains water, one of the following may be used for dehydration treatment. Throughout the entire treatment process, the relative humidity of the environment shall be maintained at not more than 75%; during filtration, the specimen temperature shall be maintained at least 14 °C above the expected cloud point, but shall not exceed 49 °C.
  • If the specimen is not transparent at room temperature, the specimen temperature shall be adjusted to at least 14 °C above the expected cloud point, and it shall be filtered with dry filter paper until the specimen is completely clear.
  • For diesel fuel, if the haze that appears is relatively dense, take 100 mL of a new specimen and 5 g of anhydrous sodium sulfate, shake for at least 5 min, let stand until clear, and filter with dry filter paper; as long as sufficient time is allowed, this method will remove or sufficiently reduce water haze, making it easier for the operator to correctly observe the turbidity caused by wax crystallization.
  • Note: The amount of anhydrous sodium sulfate may be increased or decreased as appropriate according to the water content in the specimen; the main goal is the amount that best allows clear observation of the cloud point.
  • Note: The turbidity or haze formed by wax crystals always appears first at the bottom of the test tube, where the temperature is lowest. Usually, slight haze caused by trace amounts of water in the oil will spread throughout the entire specimen and will gradually become more obvious as the temperature decreases. Generally speaking, this kind of water haze does not interfere with the determination of the wax cloud point. If there is interference, filtering with dry filter paper is sufficient.

8. Analysis procedure

8.1 Manual method test procedure

• Inject the specimen into the test tube up to the marked line.
• Stopper the test tube tightly with a cork stopper fitted with a thermometer. If the expected cloud point is higher than −36 °C, use thermometer GB-37; if the expected cloud point is lower than −36 °C, use thermometer GB-36. Adjust the position of the cork stopper and thermometer so that the cork stopper tightly seals the test tube, the thermometer and test tube are on the same axis, and the mercury bulb of the thermometer just touches the bottom of the test tube.
  • Note: The thermometer may occasionally show a break in the liquid column that cannot be detected immediately. The thermometer may be checked periodically. It may be used only when the reading is room temperature when not immersed in a bath, and the reading is 0 °C±1 °C when immersed in an ice bath. Alternatively, check the thermometer by immersing it in a cold bath of known accurate temperature.
• The gasket, washer, and sleeve shall all be clean and dry. Place the gasket at the bottom of the sleeve. Before placing the test tube, the gasket and sleeve shall first be placed in the cooling medium for at least 10 min. When the empty sleeve is cooled, the cover may be put on. Fit the washer onto the test tube about 25 mm from the bottom, and insert the test tube into the sleeve. Under no circumstances shall the test tube be placed directly into the cooling medium.
  • Note: If the gasket, washer, and sleeve are not clean and dry, wax formation may result, which may cause erroneous results.
• The cold bath shall be maintained within the range of 0 °C±1.5 °C.
• Whenever the test tube thermometer reading is observed to decrease by 1 °C, without stirring the specimen, quickly remove the test tube, observe the cloud point, and then place it back into the sleeve. Completing the entire process shall not exceed 3 s.
  • Note: When the test tube temperature is very low and the test tube is taken out to observe the cloud point phenomenon, the outer wall of the test tube will be covered by a thin film of water haze; at this time, the test tube may be quickly wiped with anhydrous ethanol to facilitate observation.
• When the specimen has cooled to 9 °C and no cloud point has yet appeared, transfer the test tube into a second bath sleeve maintained at −18 °C±1.5 °C. During the transfer of the test tube, the sleeve shall not be transferred. If the specimen has cooled to −6 °C and no cloud point has yet appeared, transfer the test tube into a third bath sleeve maintained at −33 °C±1.5 °C. In order to determine very low cloud points, several baths need to be added, and the bath temperature of each bath shall be consistent with Table 2. In all cases, if no cloud point appears in the specimen in the test tube and the bath temperature currently used for the identified specimen has reached the lowest temperature in the corresponding specimen temperature range in Table 2, the test tube shall be transferred to the next cold bath.
• When wax crystals appear at the bottom of the continuously cooled test tube, record the thermometer reading as the cloud point, read accurately to 1 °C.

8.2 Automatic method test procedure

• Set the instrument parameters according to the requirements of the instrument manual, such as sensitivity or threshold and set temperature precision, etc.
  • Note 1: Temperature precision, general laboratory practice is 1 °C; if higher requirements are placed on the results, 0.1 °C may be selected.
  • Note 2: For specimens with color of 0 or ≥3.5, such as bright stock produced by solvent-refined lubricating oil processes (BS), naphthenic base oils, and hydrotreated oils produced by secondary processing, if the determination results are not ideal during cloud point testing, this can be achieved by adjusting the sensitivity or threshold.
• Inject the specimen into the test tube up to the marked line.
• Place the cork gasket at the bottom of the sleeve, and fit the cork washer onto the test tube. If necessary, make final adjustments according to the instrument manual. The cork washer shall be 25 mm±3.0 mm from the bottom of the test tube.
• Place the test tube into the sleeve. Connect the temperature probe according to the instrument manual.
• Start the test according to the instrument manual. The instrument will automatically adjust the sleeve temperature as in Table 3 and begin monitoring the cloud point of the specimen with light. During the test, the instrument will monitor and display the sleeve temperature and specimen temperature.
• The instrument will continuously monitor and adjust the sleeve temperature according to Table 3. The time to move from one sleeve temperature to the next sleeve temperature shall not exceed 200 s; this time is suitable for sleeve temperature decreasing to −52 °C.
• For lower sleeve temperatures, the time to move from one sleeve temperature to the next sleeve temperature shall not exceed 300 s. Maintain the temperature of the cooling system as low as possible so that these sleeve temperatures can be reached in the shortest time. The cooling capacity of the cooling system can achieve the lowest temperature required for the test.
• The instrument shall be able to detect the temperature at which turbidity appears at the bottom of the test tube. The highest displayed temperature at which turbidity appears at the bottom of the test tube is the cloud point of the specimen, and it shall be recorded accurately to 0.1 °C or 1 °C.
• The instrument shall have an alarm so that when the cloud point is detected, it will immediately alert the operator. This function can also allow the operator to remove the specimen from the instrument and observe whether the specimen is turbid, to further confirm the cloud point result of the specimen.
• After detection is completed, the sleeve temperature shall be adjusted to 23 °C±2 °C before the test tube can be removed.
  • Note: Removing the test tube under low temperature conditions may cause damage to the temperature probe.

8.3 Preparation of automatic method instrument

• Prepare the instrument according to the instrument manual.
• Select a suitable cleaning solvent to clean and dry the test probe and test tube.
• Adjust the setting of the recirculating chiller to a suitable temperature, and cool the sleeve to the required temperature (see Table 3).

8.4 Automatic method calibration and standardization

• Ensure that the instrument is calibrated, checked, and operated in accordance with the instrument manual.
• A simulator with known resistance is used to calibrate the instrument. This may be carried out according to the calibration instructions in the operation manual.
  • Note: The test probe simulator can be obtained from the instrument supplier; the simulator can help confirm the correctness of temperature measurement.
• Specimens with mutually agreed cloud points, such as specimens verified by multiple laboratories, may be used for checking instrument performance.
  • Note 1: Certified reference materials (CRM), reference materials (RM), interlaboratory comparison samples, and proficiency testing samples may be used to check the instrument.
  • Note 2: For new instruments or instruments used at least once a year, the samples in "Note 1:" may be used for checking, and the measured cloud point results shall be within ±1 °C of the nominal value or median value.

9. Qualitative and quantitative determination and calculation formulas

• Manual method: take the temperature recorded in 7.3.7 as the cloud point, accurate to 1 °C.
• Automatic method: take the temperature recorded in 8.6.8 as the cloud point, accurate to 0.1 °C or 1 °C.
• Note: The precision requirements for the determination results are related to customer needs or product technical specifications, etc.
• Calculation formula: not provided in the available source.

10. Precision

Use the following provisions to judge the reliability of test results (95% confidence level). Note: The precision of this standard is derived from statistical analysis of results from multiple laboratories. In the manual method, participants analyzed 13 kinds of samples; these samples consisted of various distillate fuels and lubricating oils with cloud point ranges from −1 °C to −37 °C, and 8 participating laboratories used manual instruments. In the automatic method, participants analyzed 11 kinds of samples; these samples consisted of various distillate fuels and lubricating oils with cloud point ranges from +34 °C to −56 °C. 10 participating laboratories used automatic instruments, and 8 participating laboratories used manual instruments.

10.1 Repeatability (r)

For the same operator, using the same instrument, on the same specimen, the difference between two repeat determination results shall not be greater than the repeatability values shown in Table 4 and Table 5.

Table 4 Precision of the manual method

Table 5 Precision of the automatic method

10.2 Reproducibility (R)

In different laboratories, by different operators, using different instruments, on the same test sample, the difference between two single and independent results obtained shall not be greater than the reproducibility values shown in Table 4 and Table 5.

10.3 Bias

• Bias of the manual method: because the cloud point result is defined by only one method. The bias of the cloud point in the manual method has not been determined.
• Bias of the automated method: because there is no suitable reference material for defining bias, the bias of the cloud point in the automated method has not been determined, including the bias for biodiesel.
• Relative bias: the relative bias of the automated method: it is the relative bias of the automated method compared with the manual method as tested by multiple laboratories. Although a statistically significant bias has been recognized, the measured value is too small (−0.56 °C) to have practical significance.

11. Report

The test report shall include at least the following contents:

• a) state the reference to this standard;
• b) the type and identification of the test sample;
• c) whether the test sample was filtered and dehydrated;
• d) the test results;
• e) whether the automated method or the manual method was used for the test results;
• f) any differences from the test procedure of this standard as specified by agreement or other provisions shall be stated;
• g) the test date.

12. Normative references

• GB/T 514—2005 Technical conditions for glass liquid thermometers for petroleum product testing
• GB 1922—2006 Solvent naphtha for paints and cleaning
• GB/T 4756 Manual sampling of petroleum liquids (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 6540 Determination of color of petroleum products
• GB/T 15000.3 Directives for the work of reference materials (3) General principles and statistical methods for value assignment of reference materials (GB/T 15000.3—2008, ISO Guide 35:2006, IDT)
• GB/T 15000.7 Directives for the work of reference materials (7) General requirements for the competence of producers of reference materials (GB/T 15000.7—2012, ISO Guide 34:2009, IDT)
• GB 17602 Industrial hexane
• JB/T 8622 Technical conditions and graduation tables for industrial platinum resistance thermometers (JB/T 8622—1997, neq IEC 751:1983)

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 for questions and answers