ASTM D6897 Standard Test Method for Vapor Pressure of Liquefied Petroleum Gases (LPG) (Expansion Method)
1. Scope
1.1 This test method covers the use of automatic vapor pressure instruments to determine the vapor pressure of liquefied petroleum gas products at a temperature of 37.8 °C, vapor to liquid ratio of 0.5:1, and pressures from 200 kPa to 1550 kPa on a sample volume of 3.33 mL.
1.2 This test method is applicable to the determination of vapor pressures of liquefied petroleum gas products at temperatures from 37.8 °C to 70 °C, vapor to liquid ratios of 0.1:1 to 4:1, and pressures up to 3500 kPa; however, the precision of the test method (see Section 15) has only been determined for a vapor to liquid ratio of 0.5:1, at a temperature of 37.8 °C, and a pressure range from 300 kPa to 1500 kPa.
NOTE 1 - This test method is not intended to determine the true vapor pressure of LPG samples, but rather determine and report the vapor pressure of LPG at the 37.8 °C temperature and 0.5:1 vapor to liquid ratio as the Test Method D1267 method.
NOTE 2 - This test method is not a true vapor pressure method and will not measure the full contribution from any dissolved gases such as nitrogen or helium if they are present. The contribution of light gases to the measured vapor pressure is highly dependent on the test temperature, type of gas, and V/L ratio of the test.
1.3 The values stated in SI units are to be regarded as standard.
1.3.1 Exception - Non-SI units are included in parentheses for information only.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see Appendix X2.
2. Referenced Documents
2.1 ASTM Standards:
D1265 Practice for Sampling Liquefied Petroleum (LP) Gases, Manual Method
D1267 Test Method for Gage Vapor Pressure of Liquefied Petroleum (LP) Gases (LP-Gas Method)
D2892 Test Method for Distillation of Crude Petroleum (15-Theoretical Plate Column)
D3700 Practice for Obtaining LPG Samples Using a Floating Piston Cylinder
D5191 Test Method for Vapor Pressure of Petroleum Products (Mini Method)
D6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measurement System Performance
2.2 Energy Institute Standards:
IP 181 Sampling Petroleum Gases
3. Terminology
3.1 Definitions:
3.1.1 liquefied petroleum gases (LPG), n - narrow boiling range hydrocarbon mixtures, consisting mainly of propane or propylene, or both (Warning - Extremely flammable. Harmful if inhaled), butanes and butylenes, or both; in which the concentration of hydrocarbon compounds with boiling point greater than 0 °C is less than 5 % by liquid volume, and whose vapor pressure at 37.8 °C (100 °F) is not greater than 1550 kPa.
3.1.2 platinum resistance thermometer, n - temperature measuring device with platinum wire, whose electrical resistance changes in relation to temperature.
3.1.3 vapor-liquid ratio (V/L), n - of a liquid, the ratio of the vapor volume to the liquid volume of specimen, in equilibrium, under specified conditions.
3.2 Definitions ofTerms Specific to This Standard:
3.2.1 total vapor pressure (Ptot ), n - the absolute vapor pressure (relative to vacuum) exerted by the specimen at the specified temperature and vapor-liquid ratio.
3.2.2 true vapor pressure, n - the physical property of a given liquid which specifies the maximum pressure at which a vapor phase can coexist with the liquid phase at a given equilibrium temperature condition.
3.2.3 vapor pressure of LPG, n - the total pressure corrected relative to normal barometric pressure.
3.3 Abbreviations:
3.3.1 LPG - liquefied petroleum gas
3.3.2 V/L - vapor liquid ratio
