SH/T 0221-1992 Determination of density or relative density of liquefied petroleum gas (pressure density meter method)

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Card type: Test method

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

• Standard number: SH/T 0221-92
• Full name: Determination of density or relative density of liquefied petroleum gas (pressure density meter method)
• English name: not provided in the available source
• Replacement relationship: replaces ZB E46 001-86
• Equivalent adoption: ISO 3993—1984 "Determination of density or relative density of liquefied petroleum gas and light hydrocarbons (pressure density meter method)"
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20

2. Scope of application and non-applicability

• Applicable to liquefied petroleum gas and light hydrocarbons.
• Not applicable: for samples whose vapor pressure (gauge pressure) at the test temperature is higher than 1.4 MPa, the apparatus specified in this standard shall not be used.
• Note: The legal unit of measurement for pressure is Pa, 1 MPa = 10⁶ Pa = 10.1972 kgf/cm² (original text as such, requires confirmation against the source standard (source-text extraction)).

3. Method principle

Before filling the sample, first rinse the apparatus with a portion of the sample, then fill the pressure cylinder with the sample to a liquid level at which the density meter sealed inside the cylinder can float freely, and record the reading of the density meter and the sample temperature.

4. Reagents and materials (purity / preparation)

• 5 Reference liquids: if a density meter with a calibration certificate cannot be purchased, the following reference liquids are required to calibrate the density meter.
  • 5.1 Pure propane: with calibrated density or relative density. Density 15°C is 507.6 kg/m³ (0.5076 g/mL), 20°C is 500.0 kg/m³ (0.5000 g/mL); or 15.6/15.6°C relative density is 0.5073.
  • 5.2 Pure butane: with calibrated density or relative density. Density 15°C is 584.5 kg/m³ (0.5845 g/mL), 20°C is 578.8 kg/m³ (0.5788 g/mL); or 15.6/15.6°C relative density 0.5844.
• Cleaning solvents: it has been proven by testing that ethane, ethylene, butane, isobutane, n-butene, isobutene, n-pentane and isopentane do not attack the plastic; butadiene can also meet the expected requirement of not attacking the plastic. Be sure not to clean with ketones or alcohols, because they attack and reduce the strength of the plastic; aromatic hydrocarbons should likewise not be used for cleaning, because they also tend to attack the plastic surface.

5. Apparatus and equipment

• 4.1 Density meter: made of glass, graduated in density or relative density, with measuring range and dimensions conforming to Table 1.
  • Measuring range: 500–580 kg/m³ (0.500–0.580 g/mL); 570–650 kg/m³ (0.570–0.650 g/mL)
  • Scale division: 1 kg/m³ (0.001 g/mL)
  • Numerical interval: 5 or 10 kg/m³ (0.005 or 0.010 g/mL)
  • Overall length: maximum 330 mm
  • Body diameter: 18~20 mm
  • Body wall thickness: 0.4~0.6 mm
  • Stem tube diameter: 8~9 mm
  • Stem tube wall thickness: 0.3~0.35 mm
  • Scale length: 110~130 mm
  • Note ①: A differential-temperature density meter as described in Appendix A may also be used.
  • Note ②: A density meter with a measuring range of 0.500~0.650 g/mL may also be used.
  • For a density meter with a calibration certificate or calibrated according to Chapter 7, if the indication difference exceeds 0.5 scale divisions, a correction value shall be used.
• 4.2 Thermometer: sensitivity at least 2.7 mm/°C, calibrated for total immersion, of a size suitable for mounting on the inner side of the density meter cylinder, measuring range −15~45°C, minimum scale division 0.2°C.
• 4.3 Density meter cylinder: made of glass or transparent plastic (acrylic or equivalent material), conforming to the design dimensions in the figure, with both ends sealed by metal end plates and neoprene gaskets.
  • The operating pressure of the cylinder shall not exceed 1.4 MPa (gauge pressure).
  • The liquid inlet valve and outlet valve are connected to a bottom plate that has a common passage and drilled holes with the cylinder, and the vapor vent valve is connected to the top plate; all are 6 mm valves or equivalent needle valves.
  • Caution: A protective shield shall be placed around the cylinder; when the cylinder is found to have fog spots, cracks, fractures or corrosion marks, it shall be replaced.
• 4.4 Water bath: equipped with a thermostat or using other means to maintain a constant temperature to 15±0.2°C or 20±0.2°C, and of a size that allows the density meter cylinder to be completely immersed.

6. Recommended operating conditions

• Standard temperature: 20°C, but 15°C may also be used as the standard temperature.
• Water bath constant temperature: 15±0.2°C or 20±0.2°C.
• The operating pressure of the cylinder shall not exceed 1.4 MPa (gauge pressure).
• The density meter reading shall be estimated accurately to one fifth of a scale division.
• The temperature reading shall be accurate to 0.2°C; if the temperature difference is greater than 0.4°C, the measurement shall be repeated.

7. Sampling and sample preparation

For both instrument calibration and subsequent tests, sampling shall be carried out according to the following procedure:

• 6.1 Carefully clean and dry the density meter, thermometer and the inner wall of the pressure cylinder, place the density meter into the pressure cylinder, suspend the thermometer properly, and cover the end plate.
• 6.2 Connect a suitable adapter to the inlet valve and the sample supply source so as to introduce the sample into the cylinder. It shall be verified that the connection does not leak. Open the outlet valve and slightly open the inlet valve, allowing the sample to flow through the outlet valve at the bottom of the cylinder to rinse the sampling connection.
• 6.3 After rinsing the connection, close the outlet valve and the vent valve, open the inlet valve, and let the liquid enter the cylinder until it is full. If necessary, the vent valve may be opened slightly to completely fill the cylinder, and then closed immediately; the gauge pressure in the cylinder shall never be allowed to rise above 1.4 MPa.
• 6.4 When the cylinder is full of sample, close the inlet valve and open the outlet valve, allow all the contents of the cylinder to drain out, and reduce the pressure in the cylinder to atmospheric pressure.
• 6.5 Close the outlet valve and open the inlet valve, and fill the cylinder to a liquid level at which the density meter enclosed in the cylinder can float freely. If necessary, this filling may be accomplished by venting vapor through the vent valve. If the cylinder is repeatedly rinsed and sufficiently cooled before filling, venting is not necessary.
• 6.6 Close all valves and check the apparatus for leakage; if leakage is found, the sample is invalid. After reducing to atmospheric pressure, repair the leak point and repeat the above sampling procedure.

8. Analytical procedure

• 8.1 Instrument preparation and sampling shall be carried out according to Chapter 6.
• 8.2 Disconnect the cylinder from the sample supply source and place it in the water bath, maintaining 15±0.2°C, or 20±0.2°C until thermal equilibrium is obtained. To accelerate thermal adjustment, the cylinder may be removed from the water bath and slowly rotated for several minutes to ensure mixing, then returned to the water bath; care shall be taken to prevent damage to the density meter and thermometer. To prevent the thermometer inside the cylinder from being affected by pressure, a thermometer outside the cylinder is used to measure the water bath temperature; this thermometer is used to ensure that the sample inside the cylinder reaches a constant temperature, so that the sample temperature does not change too much during the measurement.
• 8.3 Remove the cylinder from the water bath (Note), stand it on a stable platform, and as soon as the density meter floats freely, read it as follows as quickly as possible.
  • Note: If the density meter reading can be seen clearly according to this clause, the cylinder may remain in the water bath.
  • When reading, first position the eye slightly below the liquid surface, then gradually raise the eye until the ellipse is seen as a straight line; the point where this line intersects a scale line of the density meter is the instrument reading. Fixing a white card behind the cylinder, just below the liquid level, will improve the clarity of observing the liquid surface. The density meter reading shall be estimated accurately to one fifth of a scale division. Before and after reading the density meter, the temperature inside the cylinder shall be read, accurate to 0.2°C; if the temperature difference is greater than 0.4°C, the measurement shall be repeated.
• 8.4 After each measurement, immediately drain the liquid from the cylinder and release the pressure to atmospheric pressure. The sample must not be left in the apparatus, because at higher ambient temperatures volatile liquids can generate sufficient pressure to burst the cylinder.
• 8.5 This standard may be used for on-site measurement at ambient temperature, but the precision of the results is lower. The precision data specified in Chapter 9 do not apply to it.
  • Caution: If during use the cylinder pressure rises above a gauge pressure of 1.4 MPa, the test shall be stopped and venting must be carried out.
• 8.6 If the density meter has a correction value, the measurement result shall be corrected; if the measurement is not made at the standard temperature, the result shall also be converted according to the density conversion tables listed in this standard.
  • Note: To convert the measurement result at the observed temperature to 15°C density, use Table B1 in Appendix B. To convert the measurement result at the observed temperature to 20°C density, use Table B2. To convert between 15°C and 20°C density, use Table B3.

9. Qualitative and quantitative determination and calculation formulas

• 2.1 Density: the mass of a liquid divided by its volume; the result shall state the density unit and temperature, for example, at t°C, kg/m³ or g/mL. The standard temperature is 20°C, but 15°C may also be used as the standard temperature.
  • Note: The legal unit of measurement for density is kg/m³, but g/mL is customarily used.
• 2.2 Relative density (commonly called "specific gravity"): the ratio of the mass of a certain volume of liquid at temperature t₁ to the mass of the same volume of pure water at temperature t₂, that is, the ratio of the density of the liquid at temperature t₁ to the density of pure water at temperature t₂. When reporting the result, the temperatures t₁ and t₂ shall be stated. For example, relative density 15/4°C. The standard temperature is 20°C, but 15°C may also be used.
• Calculation formula: not provided in the available source (only definitions and conversion tables are given).

10. Precision

Use the following data to judge the reliability of the measurement results (95% confidence level).

• 9.1 Repeatability: for two test results obtained by the same operator, using the same apparatus, on the same sample, under the same conditions, the difference between the two results shall not exceed the following values:
  • Density: 1 kg/m³ or 0.001 g/mL
  • Relative density: 0.001
• 9.2 Reproducibility: for two results obtained by different laboratories, different operators, on the same sample, the difference between the two results shall not exceed the following values:
  • Density: 3 kg/m³ or 0.003 g/mL
  • Relative density: 0.003

11. Report

The report shall state:

1. converted reading value, accurate to 1 kg/m³ or 0.001 g/mL;
2. state whether it is density or relative density;
3. for density, specify the unit and temperature;
4. for relative density, specify temperature t₁ and t₂;
5. the method used for hydrometer calibration (see Chapter 7).

12. Referenced Documents

• ISO 3993—1984 "Determination of Density or Relative Density of Liquefied Petroleum Gases and Light Hydrocarbons (Pressure Hydrometer Method)" (equivalent adoption)
• ZB E46 001-86 (superseded)
• Appendix A Use of Differential-Temperature Hydrometers (supplementary document)
• Appendix B (supplementary document): Table B1 Apparent density conversion to 15°C density table; Table B2 Apparent density conversion to 20°C density table; Table B3 20°C density and 15°C density conversion table

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