ASTM D6378 Determination of Vapor Pressure of Petroleum Products
ASTM D6378 Standard Test Method for Determination of Vapor Pressure (VPX) of Petroleum Products, Hydrocarbons, and Hydrocarbon-Oxygenate Mixtures (Triple Expansion Method)
14. Report
14.1 Report the results to the nearest 0.1 kPa (0.02 psi), and specify the test temperature and vapor-liquid ratio.
VPX(Tm°C) = ##.# kPa or ##.## psi
Pair(Tm°C) = ##.# kPa or ##.## psi
where:
X = vapor-liquid ratio,
Pair = partial pressure of the dissolved air, and
TM = measuring temperature.
14.2 If a haze was observed in 8.4, state on the report document that the test sample was hazy. Examples of acceptable reporting statements are a result of xx.xH or the statement Sample Hazy - Yes.
15. Precision and Bias
15.1 Precision - The precision of this test method as determined by the statistical examination of interlaboratory test results is as follows:
15.1.1 Repeatability - The difference between successive test results obtained by the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following value only in one case in twenty:
repeatability = 0.50 kPa (0.07 psi)
NOTE 14 - The listed repeatability value was derived with 208 measurements on four different gasoline samples. The vapor pressure ranges were from 58 to 75 kPa at a vapor to liquid ratio of 4:1. Further data are to be developed in an interlaboratory cooperative test program before the five year reapproval required by the society.
15.1.2 Reproducibility - The difference between two single and independent test results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following value only in one case in twenty:
reproducibility = 1.63 kPa (0.22 psi)
NOTE 15 - These precision data were developed in a 1995 interlaboratory cooperative test program from SHELL, CARB, and EPA over a time period of two years. Samples were sent and analyzed weekly. Participants analyzed sample sets comprised by hydrocarbons and hydrocarbon-oxygenate blends. The vapor pressure ranged from 46 to 100 kPa (6.5 to 13.9 psi) nominal. A total of 50 laboratories including EPA and CARB participated. Comparison was performed against Test Method D5191.
15.2 Relative Bias to Test Method D5191 - A statistically significant relative bias was observed using this test method for VP4 at 37.8°C (vapor-liquid ratio of 4 to 1) and the DVPE obtained by using Test Method D5191. This bias can be corrected by applying the correlation Eq 7:
DVPE = VP4(37.8°C) - Relative bias
where:
Relative bias = 1.027 kPa (0.15 psi).
NOTE 16 - The precision and bias statements may not be applicable to gasolines observed hazy in 8.4.
NOTE 17 - Different correlation formulas have been developed for Test Method D5191 by various agencies to correlate either to Test Method D4953, Procedure B, or to Test Method D323. The relative bias for the VPX calculated by these different formulas are as follows:
Correlation formula for Test Method D4953, Procedure B, used by the EPA.
EPA: DVPE = (0.956 Ptot) - 2.39in kPa
DVPE = (0.956 Ptot) - 0.347 in psi
Relative bias = 0.137 kPa (0.02 psi)
Correlation formula for Test Method D323, used by CARB
CARB: RVPE = (0.972 Ptot) - 4.93in kPa
RVPE = (0.972 Ptot) - 0.715 in psi
Relative bias = 1.575 kPa (0.23 psi)
16. Keywords
16.1 dry vapor pressure; gasoline; hydrocarbon-oxygenate blends; mini method; petroleum products; vapor pressure; variable volume method
