SH/T 0794-2007 Determination of vapor pressure of petroleum products — Micro method

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Card type: Test method

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

• Standard number: SH/T 0794—2007
• Chinese title: Determination of vapor pressure of petroleum products — Micro method
• English title: Standard test method for vapor pressure of petroleum products (mini method)
• Replacement relationship: not provided in the available source (the foreword only states modified adoption of ASTM D5191-04a, and does not mention replacement of an old version of the standard)
• Adoption relationship: modified adoption of ASTM D5191-04a "Determination of vapor pressure of petroleum products (Micro method)", redrafted according to ASTM D5191-04a
• Main differences from ASTM D5191-04a: some referenced standards were changed to the corresponding national standards of our country; references were added
• Editorial modifications: the wording of repeatability and reproducibility was modified according to the practice of our country; the keywords of Chapter 16 were deleted
• Proposing organization: China Petrochemical Corporation
• Administering organization: Sinopec Research Institute of Petroleum Processing
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafters: Zhang Cuijun, Gong Dongmei
• Publication/implementation: published on 2007-08-01, implemented on 2008-01-01
• Publishing organization: National Development and Reform Commission of the People's Republic of China

2. Scope of application and non-applicability

• 1.1 specifies a method for determining the total vapor pressure of volatile liquid petroleum products containing air under reduced pressure using an automatic vapor pressure tester.
• Applicable to: liquid petroleum products with a boiling point higher than 0℃ and a vapor pressure of 7 kPa~130 kPa under the conditions of 37.8℃ and a vapor-to-liquid ratio of 4:1.
• Sample amount: 1 mL~10 mL.
• Dissolved water in the sample is not considered.
• Note 1: The sample may also be tested under other vapor-to-liquid ratios, temperatures, and pressure conditions, but the precision and bias of this standard may not apply.
• Note 2: When the precision of this standard was determined by laboratory study, crude oil samples were not included; ASTM D6377 and IP 481 are suitable for determining the vapor pressure of crude oil.
• 1.1.1 Some oxygenated blended gasoline samples become cloudy when cooled to 0℃~1℃; if the cloudiness described in clause 8.5 is observed, it should be noted when reporting the results. The precision and bias for cloudy samples have not been determined (see clause 14.2, note 1).
• 1.2 is suitable for calculating the dry vapor pressure equivalent (DVPE) of gasoline and oxygenated blended gasoline using the correlation equation (see clause 13.2); the calculated DVPE is very close to the results measured by the ASTM D4953 method.
• 1.3 uses SI (International System of Units) units; units in parentheses are for reference only.
• 1.4 may involve hazardous materials, operations, and equipment in use; this standard does not provide recommendations for all safety issues, and users are responsible for establishing safety and protection measures and clarifying the restricted scope of application.

3. Method principle

• 4.1 A known volume of air-saturated sample is cooled and introduced into a thermostatted vacuum test chamber, where the volume of the test chamber is 5 times the volume of the added sample. After the sample is injected into the test chamber, thermal equilibrium is reached (at this point in the source, source-text extraction contains noise, and the temperature expression is "Liao 8C", requires confirmation against the source standard (source-text extraction)). The increase in pressure in the test chamber is measured and displayed by a pressure sensor and indicator. Although some instruments can also measure the absolute pressure of the sample, this method only determines the total pressure (the sum of the sample partial pressure and the dissolved air partial pressure).
• 4.2 The total pressure of the sample measured is converted to the dry vapor pressure equivalent (DVPE) using the correlation equation (clause 13.2).
• Terms and definitions:
  • 3.1 Absolute pressure: the pressure of a sample containing no air; the result obtained after subtracting the dissolved air partial pressure from the total pressure of the sample.
  • 3.2 Dry vapor pressure equivalent (DVPE): calculated from the total pressure by the correlation equation (see clause 13.2); equivalent to the value measured by the A method in ASTM D4953.
  • 3.3 Total pressure: the observed pressure measured in the test, that is, the sum of the sample partial pressure and the dissolved air partial pressure.

4. Reagents and materials (purity / preparation)

• 7.1 Reagent purity: the purity of compounds used for quality control checks shall be at least 99% (see Chapter 10). Unless otherwise specified, all reagents shall be of analytical grade. Note: The compounds listed in this chapter are used in the quality control check procedure (see Chapter 11), not for calibration of the instrument.
• 7.2 Cyclohexane. Warning: cyclohexane is flammable and harmful to health.
• 7.3 Cyclopentane.
• 7.4 2,2- dimethylbutane. Warning: 2,2- dimethylbutane is flammable and harmful to health.
• 7.5 2,3- dimethylbutane. Warning: 2,3- dimethylbutane is flammable and harmful to health.
• 7.6 2- methylpentane. Warning: 2- methylpentane is flammable and harmful to health.
• 7.7 Toluene. Warning: toluene is flammable and harmful to health.
• 11.2 Acceptable reagents and their corresponding vapor pressures (which can be found in ASTM DS4B "Physical Constants of Hydrocarbon and Non-Hydrocarbon Compounds"): cyclopentane 68.3 kPa; 2,2- dimethylbutane 68.0 kPa; 2,3- dimethylbutane 51.1 kPa; 2- methylpentane 46.7 kPa; toluene 7.1 kPa.

5. Apparatus and equipment

• 6.1 Automatic instrument: an instrument suitable for this test method, having a small-volume test chamber with a pressure sensor, and auxiliary facilities for controlling the test chamber temperature and evacuating before sample introduction.
• 6.1.1 The test chamber shall be designed to contain 5 mL–50 mL of liquid and gas, so as to ensure a vapor-to-liquid ratio between 3.95:1.00–4.06:1.00. Note 1: The precision and bias of this standard were determined using test chambers made of stainless steel or aluminum. Note 2: A test chamber with a capacity exceeding 15 mL may be used, but precision and bias are not provided (see Chapter 15).
• 6.1.2 Pressure sensor: minimum operating range 0 kPa~177 kPa (in the source, source-text extraction is "gkPac T77kPa", requires confirmation against the source standard (source-text extraction)), minimum resolution 0.1 kPa, minimum accuracy ±0.1 kPa (in the source, source-text extraction is "tu 0", requires confirmation against the source standard (source-text extraction)). The pressure measurement system shall include auxiliary electronic equipment and a readout device to display pressure readings.
• 6.1.3 Temperature-controlled heater: used to maintain the test chamber at 37.8℃±0.1℃ during the vapor pressure determination.
• 6.1.4 The test chamber temperature is measured with a platinum resistance thermometer. The minimum temperature measurement range of the instrument is from room temperature to 75℃, the minimum resolution is 0.1℃ (in the source, source-text extraction is "0.", requires confirmation against the source standard (source-text extraction)), and the minimum accuracy is 0.1℃.
• 6.1.5 The vapor pressure tester shall have equipment for injecting the test sample into the vacuum test chamber and for cleaning or purging for the next test.
• 6.2 Vacuum source: capable of reducing the absolute pressure of the test chamber to below 0.01 kPa.
• 6.3 Syringe (instrument selected according to the injection method): airtight, volume 1 mL~20 mL, accuracy ±1% or better, precision ±1% (in the source, source-text extraction is "precision is ±1", requires confirmation against the source standard (source-text extraction)). The syringe capacity shall not exceed 2 times the added test sample.
• 6.4 Ice-water bath: cool the sample and syringe to 0℃~1℃.
• 6.5 Pressure measuring device: used to determine the local pressure at the same altitude as the laboratory where the instrument is located, with an accuracy not lower than 0.20 kPa. 6.5.1 When the pressure measuring device used is not a mercury manometer, the pressure measuring device shall be calibrated periodically (using a traceable standard pressure measuring device) to ensure that the accuracy meets the requirements of clause 6.5.
• 6.6 McLeod gauge or vacuum measuring instrument: range at least between 80 kPa–0.1 kPa (0.1 mmHg–5 mmHg) (in the source, source-text extraction is "8O1kPa~0.g/kPa", requires confirmation against the source standard (source-text extraction)). Calibration of the electronic vacuum measuring instrument is carried out according to the standard operation of the vacuum gauge in Appendix C of GB/T 9168.

6. Recommended operating conditions

• Test temperature: 37.8℃±0.1℃ (see 6.1.3).
• Vapor-to-liquid ratio: 4:1 (the test chamber volume is 5 times the sample volume, see 4.1, 6.1.1).
• Sample amount: 1 mL~10 mL (see 1.1).
• Sample cooling temperature: 0℃~1℃ (see 6.4, 8.2).
• Syringe cooling temperature: 0℃~4.5℃ (see 9.3).
• Other vapor-to-liquid ratios, temperatures, and pressure conditions: may be tested, but precision and bias may not apply (see 1.1 note 1).

7. Sampling and sample preparation

• 8.1 Vapor pressure determination is extremely sensitive to evaporation loss of the sample and changes in composition, and sampling and handling of the sample require very careful precautions. Sample and prepare the test specimen according to the requirements of GB/T 4756, place the sample in a suitable container, and fill the sample to 70%~80% of its volume. The sample container used when the precision of the standard was determined was 1 L. However, containers that meet the sample filling requirements as specified in the GB/T 4756 method may also be used, but precision will be affected. For arbitration tests, the sample container of 1 L must be used.
• 8.1.x The first 1 test specimen drawn from the sample container shall be used for vapor pressure determination. The remaining test specimen in that sample container shall not be used for a second vapor pressure determination. If a second determination is required, resample.
• To prevent the sample from becoming too warm before testing, the sample may be stored in a suitable ice bath or refrigerator.
• Samples stored in leaking containers shall not be tested. If a container is found to be leaking, discard the sample and resample.
• 8.2 Sample handling temperature: Before opening the sample container, first cool the sample container and the sample in the container in a cold bath or refrigerator to 0℃~1℃. Allow sufficient time for the sample to cool to this temperature. The sample temperature is obtained by directly measuring a similar liquid in a similar container placed in the cold bath or refrigerator at the same time as the sample.
• 8.3 Check the capacity of the sample container: When the sample has cooled to 0℃~1℃, remove the sample container and dry it with a highly absorbent material. If the sample container is opaque, open the lid and use a suitable measuring gauge to determine the sample volume, to ensure that the sample amount is 70%~80% of the container volume (see note to clause 8.3.3). If the sample container is transparent, use a suitable method to verify that it fills 70%~80% of the container (see note to clause 8.3.3).
  • 8.3.1 If the sample volume is less than 70% of the sample container volume, discard the sample.
  • 8.3.2 If the sample volume exceeds 80% of the sample container volume, pour out part of the sample so that the sample amount is 70%~80%. The poured-out sample must not be returned to the container.
  • 8.3.3 If necessary, replace the sample container and return it to the cold bath or refrigerator. Note: For opaque containers, a dipstick marked with the positions of container volumes 70%~80% may be used to check the sample volume. The material of the dipstick should not contaminate the sample after being immersed in and removed from the sample. The inspection method is to insert the dipstick vertically to the bottom of the sample container, then remove it. For transparent containers, a ruler may be used for measurement, or comparison may be made with an identical container having the same 70%~80% volume marking.
• 8.4 Air saturation of the sample in the sample container:
  • 8.4.1 Refers only to transparent containers: Since clause 8.3 does not require opening transparent sample containers to check sample capacity, in order to treat samples in transparent containers in the same way as samples in opaque containers, samples in transparent containers are also required to be opened and then resealed.
  • 8.4.2 Remove the container containing the 0℃~1℃ sample from the cold bath or refrigerator, dry it with a highly absorbent material, open the lid, being careful not to introduce water, reseal and shake vigorously. Return to the cold bath or refrigerator for at least 2 min.
  • 8.4.3 Repeat clause 8.4.2 at least 2 times, return the sample to the cold bath or refrigerator, and wait for testing.
• 8.5 Inspection of single-phase sample: After sampling and injection into the analytical instrument, check the phase separation of the retained sample. If the sample is contained in a transparent container, it may be checked before sampling. If the sample is contained in an opaque container, after thoroughly mixing the sample, immediately pour some into a clean glass container to observe its phase separation. Carefully distinguish between phase separation and turbidity. Turbidity must not be used as a reason for rejecting fuel. If phase separation is observed, abandon the test and the sample. Turbid samples may be analyzed (see Chapter 14).

8. Analytical Procedure

• 9 Instrument preparation:
  • 9.1 Prepare the instrument according to the instructions provided by the instrument manufacturer.
  • 9.2 Clean and dry the test chamber as required to avoid contaminating the test specimen. Inject the test specimen only when the test chamber pressure displayed by the instrument is stable and the pressure change does not exceed 0.1 kPa. When the test chamber pressure is unstable or exceeds this value, check the removal of residual volatile substances from the previous sample in the test chamber, or calibrate the sensor.
  • 9.3 If a syringe is used to inject the sample, before sampling, the syringe should be placed in a refrigerator or cold bath and cooled to 0℃~4.5℃. To prevent water from contaminating the syringe barrel, the syringe outlet should be sealed during cooling.
• 10 Calibration:
  • 10.1 Pressure sensor:
    • 10.1.1 The sensor shall be calibrated at least every six months, or at shorter intervals based on quality control checks (see Chapter 11). The sensor is calibrated using pressures at two reference points, namely 0 pressure (<0.1 kPa) and ambient atmospheric pressure.
    • 10.1.2 Connect a McLeod gauge or a calibrated electronic vacuum measuring instrument (see note) to the vacuum line of the test chamber, and evacuate. When the pressure reading of the vacuum measuring instrument is lower than 0.1 kPa (0.8 mmHg), adjust the display pressure to zero, or according to the instrument design or manufacturer's instructions, adjust to the actual reading of the vacuum measuring instrument. Note: For calibration reference of the vacuum measuring instrument, see Appendix C of GB/T 9168 for standard operation of vacuum gauges.
    • 10.1.3 Open the test chamber, restore to atmospheric pressure, and observe the corresponding pressure change of the sensor. The instrument display should be set to total pressure, not a calculated or corrected value. When comparing pressures, use the value of the pressure measuring instrument as the reference standard and compare it with the pressure value of the sensor. The pressure measured by the pressure measuring instrument should be the local atmospheric pressure at the same altitude as the laboratory where the instrument is located. Warning: Do not read from aneroid barometers such as those used in meteorological stations and airports, because the readings of these barometers are pre-corrected for atmospheric pressure.
      • 10.1.3.1 When a mercury barometer is used as the pressure measuring instrument, the atmospheric pressure reading should be corrected from the operating temperature to 0℃ based on the density change of mercury, and then converted to the same pressure unit as the vapor pressure instrument. After density correction, the mercury column height at 0℃ is converted to kPa according to the following formula: at 0℃, 25 mmHg = 3.3865 kPa.
    • 10.1.4 Repeat the steps of 10.1.2 and 10.1.3 until the zero pressure and atmospheric pressure readings can be read accurately.
  • 10.2 Thermometer: The platinum resistance thermometer used to monitor the test chamber temperature shall be verified at least every six months in accordance with the requirements for traceable thermometers.
• 11 Quality control check:
  • 11.1 When the instrument is in use, calibrate the instrument daily with a determined liquid of known volatility. For pure compound samples (see clause 7.1) that have been air-saturated according to the procedure of clause 8.4, multiple test specimens may be taken from the same container at different times. However, used test specimens must not be reused. Record DVPE and compare with the statistical values of the control sample used in this laboratory. If the discrimination exceeds the control limit, check the instrument and calibrate it.
  • 11.2 Some acceptable reagents and their corresponding vapor pressures are given in Section 4 (Reagents and Materials).
  • Note: It is recommended that at least one representative fuel routinely tested by the laboratory be used as the control sample used in clause 11.1. Using a pre-prepared sample from one batch taken according to the procedure specified in 8.1.2, periodically verify the total saturated vapor pressure determination process (including the operator's technique) by this test method. The sample should be stored in a suitable environment that will not degrade during long-term storage. The test results of these quality control samples may be analyzed by control chart methods.
• 12 Test procedure:
  • 12.1 Remove the sample from the cold bath or refrigerator, dry the outside of the container with absorbent material, open the lid, and insert the cooled transfer tube or syringe (see clause 9.3). Withdraw a portion of bubble-free test specimen using a sealed syringe or transfer tube, and deliver the test specimen into the test chamber as quickly as possible. The time from opening the cooled sample container to inserting and/or securing the syringe in the sealed test chamber shall not exceed 1 min.
  • 12.2 Inject the test specimen into the test chamber according to the instructions provided by the instrument manufacturer, then operate the instrument to determine the total vapor pressure of the test specimen.
  • 12.3 Set the instrument readout to total vapor pressure. If the instrument can calculate DVPE, ensure that only the parameters in clause 13.2 are used.

9. Qualitative and Quantitative and Calculation Formulas

• 13.1 Record the total vapor pressure reading on the instrument, accurate to 0.1 kPa. For instruments that cannot automatically record a stable pressure value, manually record the pressure reading every minute, accurate to 0.1 kPa. When three consecutive readings change by no more than 0.1 kPa, record that reading as the result, accurate to 0.1 kPa.
• 13.2 Calculate the dry vapor pressure equivalent value DVPE using formula (1). Ensure that the instrument reading used in the formula is total pressure and has not been corrected by an automatic program correction factor.
  • DVPE = (0.965X) − A …(1)
  • Where: DVPE—— dry vapor pressure equivalent value, kPa; X—— total vapor pressure, kPa; A——3.78 kPa.
  • Note: The correlation formula is derived from the results of the American Society for Testing and Materials 1988 cooperative project, and was verified in laboratory research in 1991.
• 13.3 The calculation of formula (1) may be performed automatically by the instrument. If equipped with this function, the user need not perform the correction.

10. Precision

• 15 Precision and bias: Judge the reliability of test results according to the following rules (95% confidence level).
• 15.1 Precision: The precision of this test method is determined by statistical analysis of interlaboratory test results.
  • Note: The following precision data were generated by the 1991 interlaboratory cooperative test program. Participants analyzed a batch of samples, which were duplicate blind samples composed of 14 type hydrocarbons and oxygenated blending hydrocarbons. The nominal volume of oxygenated compounds (MTBE, ethanol, and methanol) was 0–15, and the nominal pressure was 14 kPa–100 kPa. A total of 60 laboratories participated. Some laboratories used more than one test method, and the samples used for each method were separate. 26 group of samples was determined by ASTM D5190 method, and 27 group of samples was determined by this method. In addition, 6 group of samples was determined by modified ASTM D5190, and 13 group of samples was determined by modified this method.
  • 15.1.1 Repeatability (r): The difference between two results obtained by the same operator, in the same laboratory, using the same instrument, following the procedure specified in the method, on the same sample for repeated determinations shall not exceed the requirement of formula (2):
    • r = 0.00807(DVPE + B) …(2)
    • Where: DVPE—— dry vapor pressure equivalent value; B——124 kPa (the original source-text extraction is "-124kPa", requires confirmation against the source standard (source-text extraction)).
  • 15.1.2 Reproducibility (R): The difference between two independent test results obtained by different operators, using different instruments, following the procedure specified in the method, on the same sample shall not exceed the requirement of formula (3):
    • R = 0.0161(DVPE + B) …(3)
    • Where: DVPE—— dry vapor pressure equivalent value; B——124 kPa (the original source-text extraction is "-124k7a", requires confirmation against the source standard (source-text extraction)).
• 15.2 Deviation: the source text source-text extraction is severely incomplete ("[severely incomplete bias statement]"), requires confirmation against the source standard (source-text extraction).
• 15.3 The source text source-text extraction is severely incomplete ("[garbled comparison wording] ASTM D4953 method A…[garbled pressure/correction wording] DVpE…clause 2)"), requires confirmation against the source standard (source-text extraction). Identifiable key points: between the total pressure measured by this test method and the ASTM D4953 method A there is a relatively large statistically significant deviation, which is corrected by observing the total pressure and calculating DVPE (see clause 13.2).

11. Report

• 14.1 Report DVPE, precise to 0.1 kPa, no need to indicate temperature.
• 14.2 If the turbidity described in clause 8.5 is visible in the sample, still report the result in accordance with clause 14.1, but append the letter H.
  • Note 1: The precision and bias of turbid samples have not been determined, because this type of sample was not evaluated as part of an interlaboratory study.
  • Note 2: The letter H in clause 14.2 is used to remind the data recipient that turbidity occurred in the sample. If the laboratory's computer system cannot report alphanumeric results as required by clause 14.2, then that laboratory is permitted, when reporting the results obtained in accordance with clause 14.1, to attach a formal statement or annotation clearly informing the data recipient that the analyzed sample exhibited turbidity.

12. Normative references

• GB/T 4756 Petroleum liquids — Manual sampling (GB/T 4756-1998, eqv ISO 3170:1988)
• GB/T 9168 Determination of petroleum products by vacuum distillation (its annex C Standard practice for vacuum gauges)
• ASTM D4953 Determination of vapor pressure of gasoline and oxygenated blend gasoline (dry method)
• ASTM D5190 Determination of vapor pressure of petroleum products (automatic method)
• ASTM D5191-04a Determination of vapor pressure of petroleum products (micro method) (modified adoption of the source standard)
• ASTM DS4B Physical constants of hydrocarbon and non-hydrocarbon compounds (used to look up reagent vapor pressures)
• ASTM D6377 and IP 481 (applicable to determination of crude oil vapor pressure, see 1.1 Note 2)
• References (the foreword mentions that this standard adds references; the specific entries are not provided in the available source)

13. Source and verification

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14. Quick Q&A reference