GB/T 6533-2012 Determination of water and sediment in crude oil by the centrifuge method

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 title / English title / supersession relationship

• Standard number: GB/T 6533—2012
• Chinese title: Determination of water and sediment in crude oil by the centrifuge method
• English title: Test method for water and sediment in crude oil by the centrifuge method
• Supersession relationship: supersedes GB/T 6533—1986 "Method for determination of water and sediment in crude oil (centrifuge method)"
• Adoption relationship: modified adoption using the redrafting method of ASTM D4007-08 "Determination of water and sediment in crude oil by the centrifuge method (laboratory method)"
• Publication/implementation: published on 2012-12-31, implemented on 2013-07-01
• Custodianship: National Technical Committee for Standardization of Petroleum and Natural Gas (SAC/TC 355)
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, Zhoushan Entry-Exit Inspection and Quarantine Bureau, Daqing Oilfield Engineering Co., Ltd., Pipeline Science and Technology Research Center of PetroChina Pipeline Company
• Main drafters: Gu Jie, He Xin'an, Wei Yutong, Zhao Zhongfu, Liu Wen, Liu Jiliang
• Previous versions: GB/T 6533—1986

Main technical changes compared with GB/T 6533—1986 (according to the foreword):

• Changed "water determination must use GB/T 260..." to "water determination should use GB/T 8929" (see Chapter 1)
• Added "Normative references" (see Chapter 2)
• Added the calculation formula for relative centrifugal force (see 4.1.6)
• Added content on calibrating the centrifuge tube graduations (see 4.2)
• Added "For highly viscous or high-wax crude oil, the temperature needs to be controlled at 71 ℃±3 ℃ so that the wax crystals in the crude oil dissolve." (see 4.3)
• Added the method for adding viscous crude oil samples to the centrifuge tube (see 7.2)
• Added "Quality assurance and control" (see Chapter 10)
• Added "Test report" (see Chapter 11)
• Changed the title of Figure A.1 from "Solubility of toluene in water" to "Solubility of water in toluene"

Technical differences compared with ASTM D4007-08 (according to the foreword):

• Use GB/T 4756 instead of ASTM D4057 (see Chapter 6)
• Use GB/T 6531 instead of ASTM D473 (see Chapter 1)
• Use GB/T 8929 instead of ASTM D4006 (see Chapter 1)
• Use SY/T 5317 instead of ASTM D4177 (see Chapter 6)
• Editorial modification: deleted the informative appendix X1 of ASTM D4007-08

2. Scope of application and non-applicability

• This standard specifies a method for determining the water and sediment content in crude oil by centrifugal separation.
• This standard applies to crude oil.
• The water content in crude oil determined by this standard is generally lower than the actual water content. When higher measurement precision is required, the sediment determination should use GB/T 6531, and the water determination should use GB/T 8929.
• Warning: Personnel using this standard should have practical experience in regular laboratory work. This standard does not point out all possible safety issues. Users are responsible for taking appropriate safety and health measures and ensuring compliance with the conditions specified in relevant national laws and regulations.

3. Method principle

Equal volumes of crude oil and water-saturated toluene are placed in a conical centrifuge tube. After centrifugal separation, the volume of water and sediment at the bottom of the tube is read. (See Chapter 3 Method summary)

4. Reagents and materials (purity / preparation)

• 5.1 Toluene: purity greater than 99.5%. Warning: toluene is flammable and toxic.
• 5.2 Water-saturated toluene solution: toluene should be prepared into a saturated toluene solution with water in a 60 ℃±3 ℃ constant-temperature bath (see 4.3), but there must be no suspended water. The preparation method is according to Appendix A.
• 5.3 Demulsifier solution: demulsifier can accelerate the separation of water from oil and prevent water from adhering to the centrifuge tube wall. The demulsifier solution is recommended to be prepared with toluene into a 25% (mass fraction) demulsifier solution. For certain crude oils, the ratio of demulsifier to toluene may be changed as needed. The amount of demulsifier solution used is not counted in the measured volume of water and sediment. The demulsifier solution should be stored in a dark bottle and sealed.

Appendix A Preparation method of water-saturated toluene solution (normative appendix):

• A.1 Scope: specific content not provided in the available source (source-text extraction only the title is present)
• A.2 Significance: This method is used to prepare the water-saturated toluene solution used in the determination of water and sediment in crude oil (centrifuge method). Figure A.1 shows the solubility of water in toluene. The percentage of water dissolved in toluene increases with increasing temperature; at 21 ℃ it is about 0.03%, while at 70 ℃ it is 0.17%. Since generally supplied toluene is relatively "anhydrous", if used directly, it may dissolve part or even all of the water present in the crude oil sample, which will significantly reduce the measured value of water and sediment in the crude oil. In order for the centrifuge method to accurately determine water and sediment in crude oil, toluene should be pre-saturated at the temperature of the centrifuge test.
• A.3 Reagents: A.3.1 Toluene: purity greater than 99.5%; A.3.2 distilled water or tap water.
• A.4 Apparatus: A.4.1 Liquid constant-temperature bath: capable of immersing at least a 1 L container, with temperature controllable at 60 ℃±3 ℃ (see 4.3); A.4.2 Glass bottle with stopper: 1 L.
• A.5 Test procedure:
  • A.5.1 Adjust the temperature of the constant-temperature bath to the temperature required for the centrifuge experiment, and maintain the temperature of the constant-temperature bath at ±3 ℃.
  • A.5.2 Place 700 mL~800 mL toluene into a glass bottle with stopper, add a sufficient amount of water (at least 2 mL, but not exceeding 25 mL), and maintain the presence of free water in the bottle. Tighten the stopper and shake vigorously for 30 s.
  • A.5.3 Loosen the stopper, place the glass bottle in the constant-temperature bath, keep at constant temperature for 30 min, remove the bottle, tighten the stopper, and shake carefully for 30 s.
  • A.5.4 Repeat A.5.3 test procedure 3 times. Note: The vapor pressure of toluene at 60 ℃ is about twice that at 38 ℃.
  • A.5.5 Place the bottle containing water and toluene in the constant-temperature bath for 48 h to ensure complete equilibrium between toluene and free water and complete saturation at the required temperature. If the water-saturated toluene solution needs to be used before equilibrium at 48 h, the toluene solution should be injected into a centrifuge tube and centrifuged in the same centrifuge at the centrifugal force and temperature required for the centrifuge test, then carefully pipette the toluene out of the centrifuge tube without disturbing the free water settled at the bottom of the tube.
  • A.5.6 Water saturation of toluene depends on time and temperature. It is recommended that the water-saturated toluene solution always be stored at the test temperature so that a water-saturated toluene solution can be obtained at any time for testing.

5. Apparatus and equipment

• 4.1 Centrifuge
  • 4.1.1 The centrifuge can rotate two or more conical centrifuge tubes of about 203 mm filled with sample, and the speed can be controlled so that the relative centrifugal force (rcf) at the end of the centrifuge tube is at least 600 (see 4.1.6).
  • 4.1.2 The rotating head, centrifuge cups, and centrifuge rings, including cushion pads, should be well constructed to withstand the maximum centrifugal force from the power source. During centrifugation, the bottom gasket and upper pad of the centrifuge cup should firmly support the centrifuge tube. The centrifuge should be enclosed by a sufficiently sturdy metal guard to prevent danger if the centrifuge tube breaks.
  • 4.1.3 The centrifuge should have a heating function and be able to stably control temperature to avoid unsafe situations. The temperature is controlled at 60 ℃±3 ℃ throughout the centrifugation period. The temperature control of the centrifuge can control the temperature within the required range, and safe operation must be noted in a flammable environment.
  • 4.1.4 The centrifuge, motor, and heater should all comply with relevant laboratory safety regulations.
  • 4.1.5 The centrifuge speed is calculated according to formula (1) (the original formula source-text extraction is unclear in the source text, requires confirmation against the source standard (source-text extraction)).
  • 4.1.6 The relative centrifugal force is calculated from the centrifuge speed according to formula (2) (the original formula source-text extraction is unclear in the source text, requires confirmation against the source standard (source-text extraction)).
• 4.2 Centrifuge tube: each conical tube has a length of 203 mm, dimensions conforming to the requirements of Figure 1, and the centrifuge tube should be fully annealed. The graduation numbers are as shown in Figure 1 and should be clear and distinct; the mouth of the centrifuge tube can be tightly closed with a stopper. The allowable tolerance of graduations and the minimum graduation between marks are listed in Table 1. Calibration can be performed with freshly boiled 20 ℃ distilled water, reading the volume at the lower edge of the meniscus. Before use, the accuracy of the graduations of the centrifuge tube must be verified volumetrically. The verification includes every graduation up to the 0.25 mL mark (as shown in Figure 2), and also includes the graduations at 0.5 mL, 1.0 mL, 2.0 mL, 50.0 mL, and 100 mL. If the error of the centrifuge tube graduations exceeds the allowable range shown in Table 1, the centrifuge tube cannot be used.
  • Figure 1 Centrifuge tube dimensions (source-text extraction excerpt): inner diameter 17 mm±1 mm; outer diameter 36.00 mm–37.75 mm; length 195 mm–203 mm; at the bottom 10 mL at 82 mm~90 mm; the side of the tube body must be straight; inner bottom line; volume allowable error see Table 1.
• 4.3 Constant-temperature bath: a liquid bath or metal block bath capable of vertically immersing the centrifuge tube to the 100 mL mark, and capable of controlling temperature at 60 ℃±3 ℃. For highly viscous or high-wax crude oil, the temperature needs to be controlled at 71 ℃±3 ℃ so that crystals in the crude oil dissolve.
• 4.4 Pipette: 50 mL pipette or equivalent volumetric adapter.

Table 1 Allowable error of 203 mm type centrifuge tubes (unit: milliliters):

6. Recommended Operating Conditions

• Centrifugation temperature: during the entire centrifugation period, the temperature shall be controlled at 60 ℃±3 ℃ (see 4.1.3, 7.6).
• Highly viscous or high-wax crude oil: the temperature shall be controlled at 71 ℃±3 ℃ so that the wax crystals in the crude oil dissolve (see 4.3).
• Relative centrifugal force: at least 600 (see 4.1.1).
• Centrifugation time: 10 min, repeat centrifugation until two consecutive readings remain unchanged (see 7.4, 7.5).
• Residence in constant-temperature bath: at least 15 min (see 7.3).
• Preparation temperature of water-saturated toluene solution: 60 ℃±3 ℃ (see 5.2, A.4.1).

7. Sampling and Test Sample Preparation

• Obtain a representative sample in accordance with GB/T 4756 or SY/T 5317, and preserve it sealed. (See Chapter 6.)
• 7.1 Add the test sample directly from the container to the 50 mL mark of two centrifuge tubes. Using a pipette or an equivalent volumetric adapter, add to each of the two centrifuge tubes 50 mL of toluene solution that has been water-saturated in a 60 ℃±3 ℃ or 71 ℃±3 ℃ constant-temperature bath (see 5.2). Read the volumes of 50 mL and 100 mL at the upper edge of the meniscus. Using a pipette or an automatic burette, add to each centrifuge tube 0.2 mL demulsifier solution (see 5.3). Stopper tightly, and invert 10 times to ensure that the test sample and toluene solution are mixed uniformly.
• 7.2 If a very viscous crude oil is encountered, mixing the test sample and solvent will be relatively difficult; the solvent may first be added to the centrifuge tube, and then the test sample added, which facilitates mixing. However, care should be taken that the test sample does not exceed the 100 mL mark.

8. Analytical Procedure

• 7.3 Loosen the stopper gently, place the centrifuge tube in a 60 ℃±3 ℃ constant-temperature bath, immerse to the 100 mL mark, and allow to remain for at least 15 min; stopper tightly and invert up and down 10 times to ensure that the test sample and toluene solution are mixed uniformly. Note: At 60 ℃, the vapor pressure of toluene is about twice that at 40 ℃; the pressure in the tube is relatively high, and care should be taken when opening the cap.
• 7.4 Place the centrifuge tubes into opposite centrifuge cups in the centrifuge to maintain balance (if the placed centrifuge tubes cannot maintain balance, add an equal amount of water to the opposite centrifuge cups to maintain balance). Stopper tightly again, calculate according to formula (1) or formula (2) the centrifuge speed under the condition that the minimum relative centrifugal force is 600, and rotate the centrifuge under this condition for 10 min.
• 7.5 After rotation stops, immediately read and record the volume of water and sediment at the bottom of each tube. When the water and sediment are 0.1 mL~1 mL, read accurately to 0.05 mL; when above 1 mL, read accurately to 0.1 mL; when less than 0.1 mL, estimate to 0.025 mL (refer to Figure 2). Without agitating the centrifuge tube, place it back in the original position in the centrifuge, rotate at the same speed for 10 min, read the readings, until the volume of water and sediment remains unchanged in two consecutive readings.
• 7.6 During the entire centrifugation test process, the temperature of the test sample shall be maintained at 60 ℃±3 ℃.
• 7.7 To avoid breakage of the centrifuge tube in the centrifuge cup, care should be taken to place the centrifuge tube on the bottom gasket, and no part of the tube should contact the edge of the centrifuge cup.

9. Qualitative and Quantitative Determination and Calculation Formulas

• 8.1 Record the final volume of water and sediment in each centrifuge tube. If the difference between the two readings is greater than one graduation on the centrifuge tube (see Table 1), or if the final volume of water and sediment is not greater than 0.1 mL and the difference between the two readings is greater than 0.025 mL, the test results shall not be used and the determination shall be repeated.
• 8.2 Take the sum of the two usable readings as the volume fraction of water and sediment in the test sample (%), and report the test results as shown in Table 2.

Table 2 Expression of results:

(Note: Table 2 source-text extraction layout is garbled, and the correspondence of some rows requires confirmation against the source standard (source-text extraction))

• For the relative centrifugal force calculation formula, see 4.1.5 formula (1), 4.1.6 formula (2) (the original formula source-text extraction is unclear in the source text, requires confirmation against the source standard (source-text extraction)).

10. Precision

• 9.1 Repeatability: For determination of the same test sample by the same operator using the same instrument, the difference between two repeat determination results shall not exceed the following values (95% confidence level):
  • When the determination result is between 0.0%~0.3%, see Figure 3;
  • When the determination result is between 0.3%~1.0%, not greater than 0.12%.
• 9.2 Reproducibility: For determination of the same test sample by different operators in different laboratories, the difference between two single and independent results shall not exceed the following values (95% confidence level):
  • When the determination result is between 0.0%~0.3%, see Figure 3;
  • When the determination result is between 0.3%~1.0%, not greater than 0.28%.
• Figure 3 Precision of water and sediment (the original is a figure, values are represented graphically, and the specific curve values are not provided in the available source).

11. Report

The test report shall at least provide the following aspects (see Chapter 11):

• a) All information required to identify the sample tested;
• b) The standard used (including the year of publication);
• c) Test results;
• d) Differences from the specified analytical procedure;
• e) Abnormal phenomena observed during the test;
• f) Test date.

12. Referenced Documents

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 6531 Determination of sediment in crude petroleum and fuel oils—Extraction method (GB/T 6531—1986 (91), eqv ISO 3735:1983)
• GB/T 8929 Determination of water in crude petroleum—Distillation method (GB/T 8929—2006, ISO 9029:1990, MOD)
• SY/T 5317 Petroleum liquids—Automatic pipeline sampling (SY/T 5317—2006, ISO 3171:1988, IDT)

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