ASTM D6378-22

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Designation: D6378 − 20 D6378 − 22
Standard Test Method for
Determination of Vapor Pressure (VP ) of Petroleum
X
Products, Hydrocarbons, and Hydrocarbon-Oxygenate
Mixtures (Triple Expansion Method)
This standard is issued under the fixed designation D6378; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers the use of automated vapor pressure instruments to determine the vapor pressure exerted in vacuum
by volatile, liquid petroleum products, hydrocarbons, and hydrocarbon-oxygenate mixtures including ethanol blends up to 85 %
(volume fraction). This test method is suitable for testing samples with boiling points above 0 °C (32 °F) that exert a vapor pressure
between 7 kPa and 150 kPa (1.0 psi and 21 psi) at 37.8 °C (100 °F) at a vapor-to-liquid ratio of 4:1. The liquid sample volume size
required for analysis is dependent upon the vapor-to-liquid ratio chosen (see Note 1) and the measuring chamber volume capacity
of the instrument (see 6.1.1 and Note 5).
NOTE 1—The test method is suitable for the determination of the vapor pressure of volatile, liquid petroleum products at temperatures from 0 °C to 100 °C
at vapor to liquid ratios of 4:1 to 1:1 (X = 4 to 1) and pressures up to 500 kPa (70 psi), but the precision statement (see Section 16) may not be applicable.
NOTE 2—The precision (see Section 16) using 1 L containers was determined in a 2003 interlaboratory study (ILS); the precision using 250 mL containers
was determined in a 2016 ILS.
1.2 This test method also covers the use of automated vapor pressure instruments to determine the vapor pressure exerted in
vacuum by aviation turbine fuels. This test method is suitable for testing aviation turbine fuel samples with boiling points above
0 °C (32 °F) that exert a vapor pressure between 0 kPa and 110 kPa (0 psi and 15.5 psi) at a vapor-to-liquid ratio of 4:1, in the
temperature range from 25 °C to 100 °C (77 °F to 212 °F).
NOTE 3—The precision (see Section 16) for aviation turbine fuels using 100 mL containers was determined in a 2007 ILS.
1.3 The vapor pressure (VP ) determined by this test method at a vapor-liquid ratio of 4:1 (X = 4) of gasoline and
X
gasoline-oxygenate blends at 37.8 °C can be correlated to the dry vapor pressure equivalent (DVPE) value determined by Test
Method D5191 (see 16.3). This condition does not apply when the sample is aviation turbine fuel.
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.08 on Volatility.
Current edition approved May 1, 2020July 1, 2022. Published May 2020August 2022. Originally approved in 1999. Last previous edition approved in 20182020 as
D6378 – 18a.D6378 – 20. DOI: 10.1520/D6378-20.10.1520/D6378-22.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1619. Contact ASTM Customer
Service at service@astm.org.
Research Report IP 394 (EN 130161) and IP 619 (EN 130163) 2016, available from the Energy Institute, 61 New Cavendish Street, London W1G 7AR, UK , email:
ILS@energyinst.org.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D02-1651. Contact ASTM Customer
Service at service@astm.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6378 − 22
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for
information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. For specific warning statements, see 7.2 – 7.8.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D323 Test Method for Vapor Pressure of Petroleum Products (Reid Method)
D2892 Test Method for Distillation of Crude Petroleum (15-Theoretical Plate Column)
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4306 Practice for Aviation Fuel Sample Containers for Tests Affected by Trace Contamination
D4953 Test Method for Vapor Pressure of Gasoline and Gasoline-Oxygenate Blends (Dry Method)
D5191 Test Method for Vapor Pressure of Petroleum Products and Liquid Fuels (Mini Method)
D5842 Practice for Sampling and Handling of Fuels for Volatility Measurement
D5854 Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-
ment System Performance
D6300 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products, Liquid Fuels, and
Lubricants
D6708 Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport
to Measure the Same Property of a Material
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 dry vapor pressure equivalent (DVPE), n—a value calculated by a correlation equation from the total pressure (Test Method
D5191), which is equivalent to the value obtained on the sample by Test Method D4953, Procedure A.
3.1.2 partial pressure from dissolved air (PPA), n—the pressure exerted in vacuum from dissolved air that escapes from the liquid
phase into the vapor phase.
3.1.3 Reid vapor pressure equivalent (RVPE), n—a value calculated by a correlation equation from the TP , which is equivalent
X
to the value obtained on the sample by Test Method D323.
3.1.4 total pressure (TP ),n—the pressure exerted in vacuum by air- and gas-containing petroleum products, components and
X
feedstocks, and other liquids, in the absence of undissolved water at a vapor-liquid ratio of X:1.
3.1.5 vapor pressure (VP ),n—the total pressure minus the PPA in the liquid at a vapor-liquid ratio of X:1.
X
VP 5 TP 2 PPA (1)
X X
4. Summary of Test Method
4.1 Employing a measuring chamber with a built-in piston, a sample of known volume is drawn into the temperature controlled
chamber at 20 °C or higher. After sealing the chamber, the temperature of the chamber is increased to a specified value
simultaneously with the first expansion. Two further expansions are performed to a final volume of (X + 1) times that of the test
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volume information, refer to the standard’s Document Summary page on the ASTM website.
D6378 − 22
specimen. After each expansion, the TP is determined. The PPA and the solubility of air in the specimen are calculated from the
X
three resulting pressures. The (VP ) is calculated by subtracting the PPA in the liquid from TP .
X X
NOTE 4—For liquids containing very low levels of high vapor pressure contaminants, which behave like a gas, this test method of determination of the
PPA and gases may lead to wrong results since the partial pressure of the contaminants will be included in the PPA. This effect is shown when the value
of the PPA and gases exceeds the average maximum limit of 7 kPa (1 psi).
5. Significance and Use
5.1 Vapor pressure is a very important physical property of volatile liquids for shipping and storage.
5.2 The vapor pressure of gasoline and gasoline-oxygenate blends is regulated by various government agencies.
5.3 Specifications for volatile petroleum products generally include vapor pressure limits to ensure products of suitable volatility
performance.
5.4 In this test method, an air saturation procedure prior to the measurement is not required, thus eliminating losses of high volatile
compounds during this step. This test method is faster and minimizes potential errors from improper air saturation. This test method
permits VP determinations in the field.
X
5.5 This test method can be applied in online applications in which an air saturation procedure prior to the measurement cannot
be performed.
6. Apparatus
6.1 The apparatus suitable for this test method employs a small volume, cylindrically shaped measuring chamber with associated
equipment to control the chamber temperature within the range from 0 °C to 100 °C. The measuring chamber shall contain a
movable piston with a maximum dead volume of less than 1 % of the total volume at the lowest position to allow sample
introduction into the measuring chamber and expansion to the desired vapor-liquid ratio. A static pressure transducer shall be
incorporated in the piston. The measuring chamber shall contain an inlet/outlet valve combination for sample introduction and
expulsion. The piston and the valve combination shall be at the same temperature as the measuring chamber to avoid any
condensation or excessive evaporation.
6.1.1 The measuring chamber shall be designed to contain between 5 mL and 15 mL of liquid and vapor and be capable of
maintaining a vapor-liquid ratio of 4:1 to 1:1. The accuracy of the adjusted vapor-liquid ratio shall be within 0.05.
NOTE 5—The measuring chamber employed by the instruments used in generating the precision and bias statements were constructed of nickel plated
aluminum and stainless steel with a total volume of 5 mL. Measuring chambers exceeding a 5 mL capacity can be used, but the precision and bias
statements (see Section 16) are not known to apply.
6.1.2 The pressure transducer shall have a minimum operational range from 0 kPa to 200 kPa (0 psi to 29 psi) with a minimum
resolution of 0.1 kPa (0.01 psi) and a minimum accuracy of 60.2 kPa (60.03 psi). The pressure measurement system shall include
associated electronics and readout devices to display the resulting pressure reading.
6.1.3 Electronic temperature control shall be used to maintain the measuring chamber at the prescribed temperature within
60.1 °C for the duration of the vapor pressure measurement.
6.1.4 A platinum resistance thermometer shall be used for measuring the temperature of the measuring chamber. The minimum
temperature range of the measuring device shall be from 0 °C to 100 °C with a resolution of 0.1 °C and an accuracy of 60.1 °C.
6.1.5 The vapor pressure apparatus shall have provisions for rinsing the measuring chamber with a solvent of low vapor pressure
or with the next sample to be tested.
6.2 Vacuum Pump for Calibration, capable of reducing the pressure in the measuring chamber to less than 0.01 kPa (0.001 psi)
absolute.
6.3 McLeod Vacuum Gauge or Calibrated Electronic Vacuum Measuring Device for Calibration, to cover at least the range from
D6378 − 22
TABLE 1 Accepted Reference Value (ARV) and Acceptable Testing Range for Reference Fluids (Note 17)
Recommended Instrument Acceptable Testing Range for
ARV [VP (37.8 °C)] ± Uncertainty,
Reference Fluid Manufacturer Tolerance, Reference Fuel [VP (37.8 °C)],
(kPa)
(kPa) (kPa)
Pentane 107.9 ± 0.2 ±1.0 107.9 ± 1.2 (106.7 to 109.1)
2,2 Dimethylbutane 68.8 ± 0.2 ±1.0 68.8 ± 1.2 (67.6 to 70.0)
2,3 Dimethylbutane 51.7 ± 0.2 ±1.0 51.7 ± 1.2 (50.5 to 52.9)
Recommended Instrument Acceptable Testing Range for
ARV [VP (37.8 °C)] ± Uncertainty,
Reference Fluid Manufacturer Tolerance, Reference Fuel [VP (37.8 °C)],
(psi)
(psi) (psi)
Pentane 15.65 ± 0.03 ±0.14 15.65 ± 0.17 (15.48 to 15.82)
2,2 Dimethylbutane 9.98 ± 0.03 ±0.14 9.98 ± 0.17 (9.81 to 10.15)
2,3 Dimethylbutane 7.50 ± 0.03 ±0.14 7.50 ± 0.17 (7.33 to 7.67)
0.01 kPa to 0.67 kPa (0.1 mm to 5 mm Hg). The calibration of the electronic vacuum measuring device shall be regularly verified
in accordance with Annex A6.3 on Vacuum Sensors in Test Method D2892.
6.4 Pressure Measuring Device for Calibration, capable of measuring local station pressure with an accuracy and a resolution of
0.1 kPa (1 mm Hg), or better, at the same elevation relative to sea level as the apparatus in the laboratory.
NOTE 6—This test method does not give full details of instruments suitable for carrying out this test. Details on the installation, operation, and maintenance
of each instrument may be found in the manufacturer’s manual.
7. Reagents and Materials
7.1 Purity of Reagents—Use chemicals of at least 99 % purity for verification of instrument performance (see Section 11). Unless
otherwise indicated, it is intended that all reagents conform to the specifications of the Committee of Analytical Reagents of the
American Chemical Society where such specifications are available. Lower purities can be used, provided it is first ascertained
that the reagent is of sufficient purity to permit its use without lessening the accuracy of the determination.
7.1.1 The chemicals in 7.3, 7.4, and 7.7 are suggested for verification of instrument performance (see Section 11), based on the
reference fuels analyzed in the 2003 interlaboratory study (ILS) (see 16.1, Table 1, and Note 17). Such reference fuels are not to
be used for instrument calibration. Table 1 identifies the accepted reference value (ARV) and uncertainty limits, as well as the
acceptable testing range for each of the reference fuels listed.
NOTE 7—Verification fluids reported by 12 of the D6378 data set participants in the 2003 ILS (see 16.1) included the following (with number of data sets
identified in parentheses): 2,2-dimethylbutane (11), and 2,3-dimethylbutane (1).
7.2 Cyclopentane, (Warning—Cyclopentane is flammable and a health hazard).
7.3 2,2-Dimethylbutane, (Warning—2,2-dimethylbutane is flammable and a health hazard).
7.4 2,3-Dimethylbutane, (Warning—2,3-dimethylbutane is flammable and a health hazard).
7.5 Methanol, (Warning—Methanol is flammable and a health hazard).
7.6 2-Methylpentane, (Warning—2-methylpentane is flammable and a health hazard).
7.7 Pentane, (Warning—Pentane is flammable and a health hazard).
7.8 Toluene, (Warning—Toluene is flammable and a health hazard).
7.9 Cyclopentane, 98.0 minimum purity (Warning—Cyclopentane is flammable and a health hazard).
ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference Materials, American Chemical Society, Washington, DC. For
suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and
the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D6378 − 22
8. Sampling and Sample Introduction
8.1 General Requirements:
8.1.1 The extreme sensitivity of vapor pressure measurements to losses through evaporation and the resulting changes in
composition is such as to require the utmost precaution and the most meticulous care in the drawing and handling of samples.
8.1.2 Obtain a sample and test specimen in accordance with Practice D4057, D4177, D4306, D5842, or D5854 when appropriate,
except do not use the Sampling by Water Displacement section for fuels containing oxygenates.
8.1.2.1 For gasolines and gasoline-oxygenate blends, use either a 250 mL or 1 L (1 qt) sized container filled between 70 % and
80 % with sample. Samples in containers of other sizes, as prescribed in 8.1.2, may be used with the same ullage requirements,
but precision can be affected.
NOTE 8—Relative bias information when testing gasoline and gasoline-oxygenate blends using 250 mL or 1 L containers is given in Section 16.
8.1.2.2 For aviation turbine fuel, use a 100 mL size container filled to a minimum of 80 % with sample. However, samples in
containers of other sizes as prescribed in 8.1.2 may be used, with the same ullage requirement, but the precision can be affected.
8.1.3 Perform the VP determination, including the rinsing (see 9.3), on the first test specimen withdrawn from a sample container.
X
Do not use the remaining sample in the container for a second VP determination. If a second determination is necessary, obtain
X
a new sample. This condition does not apply when the sample is aviation turbine fuel.
NOTE 9—For gasoline and gasoline-oxygenate blends, the effect of taking more than one test specimen from the same sample container was evaluated
as part of the 2003 ILS (see 16.1). A precision effect was observed between the first and second replicates taken from the containers evaluated. The current
precision statements were derived using the first test specimen withdrawn from 250 mL and 1 L containers.
NOTE 10—For aviation turbine fuels the effect of taking more than one test specimen from the same sample container was evaluated as part of the 2007
ILS (see 16.1). No precision effect was observed between the first and second replicates taken from the 100 mL containers evaluated.
8.1.4 Protect samples from excessive temperatures prior to testing. This can be accomplished by storage in an appropriate ice bath
or refrigerator.
8.1.5 Do not test samples stored in leaky containers. Discard and obtain a new sample if leaks are detected.
8.2 Sampling Handling—This test method does not require pre-chilling of the sample and air saturation at ambient barometric
pressure in order to limit the variability in the dissolved gas content of the sample prior to measurement. This test method measures
the total sample vapor pressure at three V/L ratios (triple expansion) in order to estimate the partial pressure of dissolved gas and
hydrocarbon partial pressure using ideal gas calculations. This has been shown to be acceptable up to at least 5 bar (about 5
atmospheres) of gas saturation.
8.2.1 Samples may be introduced to the instrument over a wide variation of temperatures and pressures, provided the test specimen
remains as a single phase (that is, no separated liquid or gaseous phase). Experiments with temperatures between –10 °C to +50 °C
and ambient pressures up to 300 kPa have been found suitable with certain gasoline samples.
8.2.2 For gasoline and gasoline-oxygenate blends, the precision statement is based on sample introduction at ambient temperature
and pressure from either 250 mL or 1 L containers. For aviation turbine fuels, the precision is based on sample introduction at
ambient temperature and pressure from 100 mL containers. Precision may be affected with sample introduction under different
conditions, but such information has not been determined.
8.2.3 Sample pre-chilling or air saturation, or both, are not required, but sample chilling, air saturation, or degassing, or a
combination thereof, is acceptable, as it will have no significant effect on the result. This allows vapor pressure and distillation tests
to be conducted on the same sample.
8.2.4 Degassing and some hydrocarbon loss occurs during the air saturation step when the sample is supersaturated with dissolved
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D6378 − 22
gas relative to ambient barometric pressure. Hydrocarbon loss increases as saturation gas pressure increases. Sealed sample
systems are recommended for gas saturations greater than about 2 bar gas pressure (about 2 atmospheres or 30 psia).
8.2.5 For bottle samples, insert the sample introduction tube as close to the sample bottle bottom as practical.
8.2.6 Pressurized samples from a sealed sample system, pressurized floating pressure cylinders or equivalent may be used within
the pressure and temperature limits specified by the manufacturer for the instrument being used. Excessive extremes of pressure
and temperature may result in precision different than that measured under the conditions of ambient pressure and temperature used
to prepare the precision statement. The temperature and pressure of the sample system should be controlled so that only a single
phase liquid is in the sealed sample system during sample introduction.
8.2.6.1 Excessive cooling of samples that contain alcohols could result in phase separation (see 8.4), extraction of alcohol, and
a lower vapor pressure value being determined, unless the sample remains well mixed during sample introduction (that is,
introduction of a test specimen is representative of the composition once heated to test temperature). This can be prevented by not
cooling samples containing alcohols, prior to the vapor pressure determination.
8.2.6.2 Excessive cooling of samples may result in formation of ice or hydrates that may impair proper operation of the sample
system.
8.2.6.3 Excessive heating of samples may result in vapor formation, resulting in a higher or lower measured vapor pressure,
depending if vapor or remaining liquid phase is introduced, respectively.
8.3 Verification of Sample Container Filling—If the sample is contained in a transparent container, verify that the container is 70 %
to 80 % full by suitable means, such as by using a marked ruler or by comparing it to a like container that has the 70 % and 80 %
levels clearly marked. If the container is not transparent, unseal it and, using a suitable gauge, confirm that the sample volume
equals 70 % to 80 % of the container capacity (see Note 11). When the sample is aviation turbine fuel, verify that the container
is at least 80 % full prior to removal of the first specimen.
NOTE 11—For non-transparent containers, one way to confirm that the sample volume equals 70 % to 80 % of the container capacity is to use a dipstick
that has been pre-marked to indicate the 70 % and 80 % container capacities. The dipstick should be of such material that it shows wetting after being
immersed and withdrawn from the sample. To confirm the sample volume, insert the dipstick into the sample container so that it touches the bottom of
the container at a perpendicular angle before removing the dipstick.
8.3.1 Discard the sample if the container is filled to less than 70 %, by volume, of the container capacity.
8.3.2 If the container is more than 80 % by volume full, pour out enough sample to bring the container contents within the 70 %
to 80 % by volume range. Do not return any sample to the container once it has been withdrawn.
8.3.3 Reseal the container, if opened.
8.4 Verification of Single Phase Sample—After drawing the test specimens and transferring them into the instrument for analysis,
check the remaining sample for phase separation. If the sample is contained in a transparent container, this observation can be made
prior to sample transfer. If the sample is contained in a non-transparent container, shake the sample thoroughly and immediately
pour a portion of the remaining sample into a glass container and observe for evidence of phase separation. A hazy appearance
is to be carefully distinguished from separation into distinct phases. If the sample separates into two distinct phases with a
discernible common boundary, then discard the test and the sample. If the sample has a hazy appearance, but does not have two
distinct phases, then phase separation has not occurred. The test is valid, but the precision and bias in Section 16 may not apply
(see 15.2). This verification procedure does not apply when the sample is aviation turbine fuel.
9. Preparation of Apparatus
9.1 Prepare the instrument for operation in accordance with the manufacturer’s instructions.
9.2 Rinse the measuring chamber, if necessary, with a solvent. Acetone has a sufficiently low vapor pressure and can be used
successfully. Rinsing is performed by drawing the solvent into the chamber by the piston and expelling the solvent into the waste
container.
D6378 − 22
9.3 To avoid contamination of the test specimen with the previous sample or the solvent, rinse the measuring chamber a minimum
of three times with the sample to be tested. Fill the measuring chamber with sample to at least half the total volume of the chamber
for each rinse. This rinsing procedure shall always be carried out immediately before the measuring procedure (see 13.4).
9.4 If a syringe is used for introduction of the test specimen, ensure the syringe is at the same temperature conditions as the sample.
Avoid water contamination of the syringe reservoir by suitably sealing the syringe during the cooling process.
10. Calibration
10.1 Pressure Transducer:
10.1.1 Check the calibration of the transducer as indicated from the verification of instrument performance (see Section 11) and
quality control checks (see Section 12). The calibration of the transducer is checked using two reference points: zero pressure
(<0.1 kPa) and the ambient barometric pressure.
NOTE 12—Calibration frequency of the pressure transducer may vary with instrument type and frequency of use. A calibration check of the pressure
transducer at least once every six months is recommended.
10.1.2 Connect a McLeod gauge or a calibrated electronic vacuum measuring device to the vacuum source in line with the
measuring chamber (see Note 13). Apply vacuum to the measuring chamber. When the vacuum measuring device registers a
pressure less than 0.1 kPa (0.8 mm Hg), adjust the transducer control to zero or to the actual reading on the vacuum measuring
device as dictated by the instrument design or manufacturer’s instructions.
NOTE 13—Refer to Annex A6.3 on Vacuum Sensors in Test Method D2892 for further details concerning the calibration of electronic vacuum measuring
devices and proper maintenance of McLeod gauges.
10.1.3 Open the measuring chamber of the apparatus to atmospheric pressure and observe the corresponding pressure value of the
transducer. Ensure that the apparatus is set to display the TP and not a calculated or corrected value. Compare this pressure value
X
with the pressure obtained from a mercury barometer, or equivalent, as the pressure reference standard. The pressure measuring
device shall measure the local station pressure at the same elevation as the apparatus in the laboratory at the time of pressure
comparison.
NOTE 14—Many aneroid barometers, such as those used at weather stations and airports, are precorrected to give sea level readings. These shall not be
used for calibration of the apparatus.
10.1.4 Repeat 10.1.2 and 10.1.3 until the zero and barometric pressures read correctly without further adjustments.
10.2 Temperature Sensor—Verify the calibration of the platinum resistance thermometer used to monitor the measuring chamber
temperature at least every six months against a nationally traceable thermometer, such as one that is traceable to National Institute
of Standards and Technology (NIST) or to na
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