ASTM D6377 for determination of vapor pressure of crude oil
ASTM D6377 standard test method for determination of vapor pressure of crude oil: VPCR(X) (Expansion method)
13. Report
13.1 Report the results to the nearest 0.1 kPa (0.02 psi), and specify the test temperature and V/L.
VPCRx (Tm°C) = ##.# kPa or ##.## psi
where:
X = vapor-liquid ratio, and
Tm = measuring temperature.
14. Precision and Bias
14.1 Precision - The precision of this test method as determined by the statistical examination of interlaboratory test results is as follows:
NOTE 12 - The following precision data are provisional and further data are to be developed in an interlaboratory cooperative test program before the five year reapproval required by the society.
14.1.1 Repeatability - The difference between successive test results obtained by the same operator with 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 values calculated as per the following equations only in one case in twenty:
V/L = 4 and 37.8°C: repeatability = 0.015 VPCR4 (37.8°C)
V/L = 0.1 and 37.8°C: repeatability = 0.055 VPCR0.1 (37.8°C)
V/L = 0.2 and 37.8°C: repeatability = 0.065 VPCR0.02 (37.8°C)
NOTE 13 - The listed repeatability data were derived on more than 30 different crude oil samples in three different laboratories. The vapor pressure ranges were from 2.8 to 16.6 kPa at V/L of 4:1, and vapor pressures up to 240 kPa at a V/L of 0.02:1. Further data are to be developed in an interlaboratory cooperative test program before the five year reapproval required by the society.
14.1.2 Reproducibility - The reproducibility of this test method is being determined and will be available within five years.
14.2 Bias - Since there is no accepted reference material suitable for determining the bias for the procedures in this test method, a bias cannot be determined.
14.3 Relative Bias to Test Method D323 for Crude Oil - A statistically significant relative bias was observed for crude oil in a limited interlaboratory test program between VPCR4(37.8°C) obtained using this test method and the vapor pressure obtained using Test Method D323 (see Appendix X1).
15. Keywords
15.1 crude oil; mini method; Reid vapor pressure; vapor pressure
