VAPOR PRESSURE OF CRUDE OIL: ASTM D6377
EXPLANATION
Vapor pressure of crude oil at various vapor-liquid ratios is an important physical property for shipping and storage. This test method covers the use of automated vapor pressure instruments to determine the vapor pressure of crude oils at temperatures between 5 and 80° C for vapor-liquid ratios from 4:1 to 0.02:1 and pressures from 7 to 500 kPa. This test method allows the determination of VPCRx samples having pour points above 0 ° C.
The vapor pressure determined by this test method at a V/L of 4:1 of crude oil at 37.8° C can be related to the vapor pressure value determined on the same material when tested by the Test Method ASTM D323.
TEST SUMMARY
Employing a measuring chamber with a built-in piston, a sample of known volume is drawn from a pressurized sampling system (floating piston cylinder) into the temperature controlled chamber at 20° C or higher. After sealing the chamber, the volume is expanded by moving the piston until the final volume produces the desired vapor-liquid ratio value. The temperature of the measuring chamber is then regulated to the measuring temperature. After temperature and pressure equilibrium, the measured pressure is recorded as the VPCRx of the sample. The test specimen is mixed during the measuring procedure by shaking the measuring chamber to achieve pressure equilibrium in a reasonable time between 5 and 30 min.
TEST PRECISION
Repeatability:
V/L = 4 and 37.8° C: repeatability = 0.15 VPCR4 (37.8° C)
V/L = 0.1 and 37.8° C: repeatability = 0.055 VPCR 0.1 (37.8° C)
V/L = 0.2 and 37.8° C: repeatability = 0.065 VPCR0.02 (37.8° C)
Reproducibility is being determined. Bias is not known.
