SH/T 0604-2000 Determination of density of crude petroleum and petroleum products (U-shaped oscillating tube method)

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

• Standard number: SH/T 0604-2000
• Chinese title: Determination of density of crude petroleum and petroleum products (U-shaped oscillating tube method)
• English title: Crude petroleum and petroleum products — Determination of density — Oscillating U-tube method
• Replacement relationship: replaces SH/T 0604-1994 "Determination of density and relative density of liquids (digital density meter method)"
• Adoption relationship: equivalent adoption of ISO 12185:1996
• Approval/implementation: approved by the State Bureau of Petroleum and Chemical Industry 2000-09-11, implemented on 2001-01-01
• Main differences from ISO 12185:1996: ① the definition of "wax precipitation temperature" and related content are not adopted; ② the content of ISO 12185:1996 Annex A is changed to the main body of the standard; ③ the British Petroleum Institute (IP) "Standards for Analysis and Testing Methods for Petroleum and Related Products" (1999) Annex G water density table, Annex H air density table) are used as Annex A and Annex B of this standard
• Revisions to SH/T 0604-1994: ① the standard title is changed; ② content related to determining crude oil density with a digital density meter is added; ③ content related to relative density is deleted
• Annex A and Annex B are both annexes of the standard

2. Scope of application and non-applicability

• Applicable to crude petroleum and petroleum products (1.1) that can be handled as a single-phase liquid at the test temperature and pressure, with a density range of 600～1100 kg/m³.
• Can be used for liquids of any vapor pressure, but appropriate measures must be taken to ensure that the sample remains single-phase during handling and density determination, with no loss of light components and no change in composition or density (1.1).
• Note: If petroleum measurement tables are used to convert the measured density to density at standard temperature, the temperature at which density is measured should be as close as possible to the standard temperature to reduce the uncertainty introduced by the general tables (1.1 Note).
• Not applicable: This method cannot be used for calibration of online density meters (1.1).
• Safety note: Use of this standard may involve hazardous materials, operations and equipment; it is the user's responsibility to establish appropriate safety and health measures and regulations before operation (1.2).

3. Method principle

A small amount of sample (generally less than 1 mL) is injected into a temperature-controlled sample tube, the vibration frequency or period is recorded, and the sample density is calculated using the sample tube constant obtained in advance. The sample tube constant is determined from the vibration frequency when the sample tube is filled with a calibration liquid of known density (Chapter 4).

4. Reagents and materials (purity / preparation)

• Unless otherwise specified, only analytical grade reagents may be used (Chapter 6).
• 6.1 Washing solvent: any solvent may be used, provided that a clean and dry sample tube can be obtained.
• 6.2 Ammonium persulfate: prepare a 8 g/L sulfuric acid solution. Warning: ammonium persulfate is a strong oxidant. (The source text reads "ammonium persulfate money"; requires confirmation against the source standard (source-text extraction))
• 6.3 Calibration liquids: at least two calibration liquids are required to calibrate the sample tube; the selected density range should be within the density range of the test samples, and the density of the calibration liquids should be traceable to national standards or use internationally recognized values. When water and air are used, they should comply with 6.3.1 and 6.3.2.
  • 6.3.1 Water: should comply with grade two or higher requirements of GB/T 6682; before use, filter through a 0.45 μm filter, boil to remove dissolved air and cool; once air has been removed, handle carefully to minimize re-dissolution of air; water density values at different temperatures are given in Annex A. (The source clause number shows "5.3.1"; requires confirmation against the source standard (source-text extraction))
  • 6.3.2 Air: the air density values used are given in Annex B. (The source clause number shows "3.3.2"; requires confirmation against the source standard (source-text extraction))
• 6.4 Water: for washing use, should comply with grade three requirements in GB/T 6682. (The source clause number shows "3.4"; requires confirmation against the source standard (source-text extraction))

5. Apparatus and equipment

• 5.1 Density meter: calibrated, with density resolution of ±0.1 kg/m³ or higher.
  • Note 1: The density meter generally displays two kinds of digital results, one being the density value and the other being the vibration period for calculating the density value.
  • Note 2: The deviation of the density meter due to viscosity effects can be as large as 1 kg/m³; the user may use the GB/T 13377 method to check whether viscosity correction is needed, and may also use calibration standards with chemical properties and viscosity similar to the sample to minimize the viscosity effect.
  • Note 3: When the temperature of the density meter sample tube is lower than the dew point temperature of the ambient air, water vapor will condense on the sample tube sensor and electronic components, so the surrounding air must be kept dry.
• 5.2 Circulating constant-temperature bath: if a constant-temperature bath is required, it must be able to maintain the temperature of the circulating liquid within ±0.05℃ of the required temperature.
• 5.3 Calibrated temperature sensor: capable of measuring the sample tube temperature to an accuracy of at least ±0.1℃. The rate of energy transfer through the sample tube is very low; care should be taken to use a sensor with very thin wires so as to minimize heat transfer into and out of the sample tube along the wires.
• 5.4 Homogenizer: suitable for the sample and sample container, capable of making the sample uniform; a high-speed shear mixer, static mixer or other suitable form may be used.

6. Recommended operating conditions

• 9.1.1 The sample density should be measured at the standard temperature whenever possible; if this is not possible, a temperature should be selected that is above the cloud point by 3℃ or above the pour point by 20℃ and below the temperature at which gas appears in the sample.
• 9.1.2 If the density meter sample tube itself has a thermostat, set the sample tube temperature according to the manufacturer's instructions; otherwise, connect a separate constant-temperature bath to maintain temperature equilibrium. The temperature and pressure of the density meter sample tube should not exceed the manufacturer's specified operating range. When using a constant-temperature bath, keep the circulating liquid clean.
• 11.6 When the density reading displayed by the density meter stabilizes at 0.1 kg/m³ or the vibration period reaches five significant figures, record the displayed number and the sample tube temperature accurate to 0.1℃.
• Standard temperature: may be 20℃ or 15℃ (3.2 Note).

7. Sampling and sample preparation

• Sampling (Chapter 7): Unless otherwise specified, samples should be taken in accordance with GB/T 4756. Special care must be taken to prevent loss of any volatile components in the sample; sample withdrawal, transfer and storage should be carried out in the same container whenever possible. Automatic sampling techniques are not recommended for volatile liquids unless a variable-volume container is used to collect and transfer the sample to the laboratory; using a fixed-volume container (pressure-resistant or non-pressure-resistant) may cause loss of light components during sampling and affect density determination. When using a variable-volume container for sampling, the sample pressure and temperature should be recorded on the container label. Ensure that the test portion represents the entire sample; usually mix the sample before sampling to ensure uniformity.
• Sample preparation (Chapter 8):
  • 8.1 General requirements: Samples should be handled in the following manner: a) minimize loss of light components; b) the sample temperature must not be lower than one of the following values: 1) the cloud point of the sample determined in accordance with GB/T 6986; 2) or 20℃ above the pour point of the sample determined in accordance with GB/T 3535. Note: When homogenizing or heating volatile crude petroleum and petroleum products containing sediment, water or insoluble wax, loss of light components is inevitable and may cause errors in density determination.
  • 8.2 Petroleum products that are free of water or sediment and have sufficient fluidity: mix by gentle shaking.
  • 8.3 Crude petroleum or petroleum products containing water or sediment: mix the sample in the original container, taking all measures to minimize loss of light components. Note: Mixing volatile crude petroleum and petroleum products in an open container will cause loss of light components and is not recommended.
  • 8.4 Waxy crude petroleum: before mixing, heat the sample to 20℃ above its pour point, taking all measures to minimize loss of light components.
  • 8.5 Waxy distillates: before mixing, heat the sample to 3℃ above its cloud point.
  • 8.6 Fuel oils: before mixing, heat the sample to a fluid state.

8. Analytical procedure

• Instrument preparation (Chapter 9):
  • 9.2 Sample tube cleaning: clean and dry the sample tube with washing solvent; if water must be used (6.4)), rinse with a washing solvent miscible with water, then blow dry with clean dry air. After testing crude petroleum containing dissolved salts, rinse with washing solvent, then clean the sample tube with water (6.4)). If organic deposits appear in the sample tube, inject ammonium persulfate solution into the sample tube for cleaning; after removing the ammonium persulfate solution, clean with water (6.4)), then clean with a washing solvent miscible with water, and then blow dry with clean dry air.
• Instrument calibration (Chapter 10):
  • 10.1 The density meter should be calibrated upon first installation, when the test temperature changes, after repair, or after the system has been disturbed. If more than 7 days have passed since the last calibration, recalibrate before use.
  • 10.2 If air is used as a calibration substance, fill the sample tube with ambient air, record the density reading or vibration period, and 10.3 may be omitted.
  • 10.3 Inject the first calibration liquid (6.3)) into the sample tube, allow it to reach temperature equilibrium with the sample tube, record the vibration period or density reading and the sample tube temperature, and clean and dry the sample tube in accordance with 9.2.
  • 10.4 Inject the second calibration liquid into the sample tube, allow it to reach temperature equilibrium with the sample tube, and record the vibration period or density reading and the sample tube temperature.
  • 10.5 Calculate the sample tube constant in accordance with the manufacturer's instructions.
  • 10.6 After calibration, clean and dry the sample tube in accordance with the procedure given in 9.2.
• Test procedure (Chapter 11):
  • 11.1 When the sample tube is filled with ambient air, check the density meter reading and compare it with the standard value reached during calibration; it should be within the range of its least significant digit ±1. If not, clean and dry the sample tube again and check again; if the reading is still out of tolerance, recalibrate the density meter.
  • 11.2 Inject the sample into the sample tube with a suitable syringe or automatic sampler, filling the sample tube as required by the instructions. When testing waxy distillates, waxy crude petroleum or residual fuel oils, the syringe or automatic sampler should be heated during the test to 3℃ above the sample cloud point or 20℃ above the pour point.
  • 11.3 When using an automatic sampler, double injection or a sample check method should be used in order to check for errors caused by air bubbles and to monitor system performance.
  • 11.4 At no stage may the sample be siphoned, because this can cause loss of light components. The sample should be poured into the syringe and then injected into the sample tube, or forced into the instrument under pressure by an automatic sampler.
  • 11.5 When injecting the sample manually, turn on the sample tube illumination lamp before injection, and while injecting according to the manufacturer's instructions, check whether there are bubbles in the sample tube; if bubbles are found, empty the sample tube, inject the sample again, and recheck for bubbles. Immediately turn off the illumination lamp after checking the sample tube, because the heat generated by the lamp affects the sample tube temperature.
  • 11.6 When the density reading displayed by the density meter stabilizes at 0.1 kg/m³ or the oscillation period reaches five significant figures, record the displayed number and the sample tube temperature accurate to 0.1℃. Note: If the oscillation period or density reading keeps drifting, it indicates that the sample tube temperature has not yet reached equilibrium; random changes in the reading generally indicate the presence of air or bubbles in the sample tube, and the sample should be reinjected; if the reading changes due to bubbles, the test must be carried out at a lower temperature to ensure that the sample remains single-phase. If the sample contains large water droplets before injection due to insufficient mixing, the indicated density value and oscillation period will both be unstable.
  • 11.7 When measuring the density of viscous liquids, stable readings are sometimes obtained even when air or bubbles are present. For these liquids, slightly pressurize the sample tube and remeasure the density. If the liquid is single-phase, the density drift caused by pressurization will be very small; on the other hand, due to the presence of gas or air bubbles, when they are compressed, a large drift in the density value will be observed; in this case, reinject the sample.
  • 11.8 If the sample contains very fine suspended water droplets, observe the density immediately after thermal equilibrium is reached.
  • 11.9 If the sample contains very fine suspended water droplets, and if the sample remains in the sample tube for a long time, the water droplets will slowly coalesce and migrate to the lowest point of the sample tube, causing a significant change in density.
  • Clean and dry the sample tube according to the procedure given in 9.2.

9. Qualitative and Quantitative and Calculation Formulas

• 12.1 If the density meter displays the oscillation period, calculate the sample density from the observed sample tube oscillation period according to the manufacturer's instructions.
• 12.2 If the density at the standard temperature is required rather than the density at the test temperature, first make the glass density meter expansion coefficient correction [see formula (1), formula (2)], then use GB/T 1885 to convert the density to the density at the standard temperature.
  • Note: Because GB/T 1885 "Petroleum Measurement Tables" is based on soda-lime glass density meters, when the density is not determined with a soda-lime glass density meter or by the pycnometer method calibrated at the standard temperature, before citing GB/T 1885, consider the influence of the density meter glass expansion correction already included in the tables.
  • Standard temperature is 20℃: coefficient = 1 − 0.000023(t − 20) − 0.00000002(t − 20)² …………(1), where t is the test temperature (℃). The corrected density is obtained by multiplying the observed density by the reciprocal of this coefficient.
  • Standard temperature is 15℃: coefficient = 1 − 0.000023(t − 15) − 0.00000002(t − 15)² …………(2), where t is the test temperature (℃). The corrected density is obtained by multiplying the observed density by the reciprocal of this coefficient.
• 12.3 Example of applying this correction to crude oil:
  • Observed density = 875.5 kg/m³ (measured by a non-glass density meter)
  • Test temperature = 50℃
  • Find the density of crude oil at 20℃
    • a) Calculate the glass expansion correction coefficient according to formula (1) in 12.2: 1 − 0.000023(50 − 20) − 0.00000002(50 − 20)² = 0.999292
    • b) The corrected density is obtained by multiplying the reciprocal of the glass expansion correction coefficient by the observed density: 875.5 × 1/0.999292 = 876.12 (rounded)
    • c) Using the corrected observed density at 50℃, look up the crude oil table in GB/T 1885 "Petroleum Measurement Tables" to obtain the density at 20℃ as 896.1 kg/m³

10. Precision

Judge the reliability of the results according to the following provisions (95% confidence level) (Chapter 14).

• 14.1 Repeatability: The difference between two consecutive determination results obtained by the same operator using the same instrument under constant test conditions on the same test substance, operated according to normal and correct experimental methods, shall not exceed the following values:
  • Transparent middle distillates: 0.2 kg/m³
  • Crude oil and other petroleum products: 0.4 kg/m³
• 14.2 Reproducibility: The difference between two separate results obtained by different operators in different laboratories on the same test substance, operated according to normal and correct experimental methods, shall not exceed the following values:
  • Transparent middle distillates: 0.5 kg/m³
  • Crude oil and other petroleum products: 1.5 kg/m³

11. Report

Report the final density result to 0.1 kg/m³ or 0.0001 g/cm³ (Chapter 13).

12. Normative References

• GB/T 1885 Petroleum Measurement Tables
• GB/T 3535 Determination of Pour Point of Petroleum Products
• GB/T 4756 Manual Sampling of Petroleum Liquids
• GB/T 6682 Specifications and Test Methods for Water for Analytical Laboratory Use
• GB/T 6986 Determination of Cloud Point of Petroleum Products
• GB/T 13377 Determination of Density or Relative Density of Crude Petroleum and Liquid or Solid Petroleum Products (Capillary-Stoppered Pycnometer and Graduated Double-Capillary Pycnometer Methods)
• Citation principle: The provisions contained in the following standards, by reference in this standard, constitute part of this standard. Unless otherwise expressly specified in the standard, the following referenced standards shall all be currently effective standards (Chapter 2).

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