Scope: This Guideline provides a method to properly determine crude oil/ product density at temperatures between 15 °C and 35 °C with vapor pressure below 600 mm per ASTM D5002: Test Method for Density and Relative Density of Crude Oil by Digital Density Meter.
Frequency As needed:
DIGITAL DENSITY METER CALIBRATION PROCEDURE AND VERIFICATION
PREPARATIONS:
A volume (about 0.7 mL) of liquid is introduced into an oscillating tube and
the change in frequency caused by the change in mass of the tube in
respect to calibration data determines the density of the sample.
CALIBRATION EQUIPMENT:
A. Digital Density Analyzer, Anton Paar DMA 58.
B. Syringes 5 mL in volume with a luerlock adapter.
C. Dry Air for calibration.
D. Cooled, freshly boiled deionized water for calibration.
E. Pentane, 99% pure, [109-66-0] for flush between diesel and gasoline samples.
F. Toluene [108-88-3] for Check Standard.
G. Acetone [67-64-1] to flush and dry tube after water calibration.
PROCEDURE:
a) Flush the 5 mL syringe with the sample at least twice before taking the actual sample to be injected into the tube. Pass at least 3 ml of sample through the tube and continue injecting sample until no more bubbles are observed in the tube.
b) Initial calibration of the digital density meter is performed at a temperature of 15 °F; 15.56 °F and 20 °F before use. After that, conduct a monthly calibration of each of these three temperatures. If any other temperature is requested, a calibration must also be performed at that temperature.
c) Calibration necessitates calculation of the values of A and B by the instrument for internal calculations from the period of oscillation (T) when the sample cell contains dry air and then cooled freshly boiled water. The instrument uses these constants to calculate density.
d) With dry air in the tube, press “F” and 100, then the “Enter” key. Allow the air in the tube to come to thermal equilibrium with the test temperature and record the T-value for air.
e) Press “F” and 101, then the “Enter” key. Inject a volume of cooled freshly boiled water into the sample tube using a 5 mL syringe. The sample in the tube must be free of the smallest gas bubbles. Allow the display to reach a steady reading and record the T-value for water.
f) In the record book, record the Dev.B, which the Densitometer automatically calculates. The Dev.B value must be within ±0.001 g per cm3 of the previous calibration. If it is not within this tolerance, check the instrument and re-run the.
g) Flush the 5 mL syringe with the sample at least twice before taking the actual sample to be injected into the tube. Turn on the light and pass at least 3 ml through the tube and continue until no bubbles are observed in the tube.
h) Turn the light off immediately after sample introduction, because heat generated by the light can affect the measurement.
i) The results automatically print out after the optical period stabilizes.
j) Calculating Densitometer: The recorded value is the final result.
k) Constants A and B comprise the spring constant of the oscillator, the mass of the empty tube and the volume of the sample involved in the oscillation. Constants A and B are therefore device constants for each individual oscillator and are calculated by the instrument for its internal use.
l) Specific Gravity is the ratio of the density of the material at a stated temperature to the density of water at that temperature and is unit-less.
m) API gravity is density at 60 °F and is equal to (141 / specific gravity) – 131.5 and is expressed in degrees as API°.
n) The calculated results are printed by the Densitometer.
o) The set temperature and the actual temperature must be within ±0.01 °C.
p) The actual temperature can be adjusted to set temperature by pressing “F” then 390 and the “Enter” key.
q) An error of 0.1 °C can result in a change of one ten thousandth in the density value.
r) Toluene must be run before the first analysis of the day and the Density must be 0.8708 ±0.0001 g/mL @ 15.56 °C. The results are recorded into the instrument log.
s) Control fluid must be run at 15.56 °C once a week. If the density differs more than ±0.001 g/mL from the previous values, the tube must be cleaned with warm micro-90 solution and the density of air re-measured. If the density of air is not the same as it was on the last calibration, a new calibration must be run. The results are recorded into the instrument log.
DENSITY METER PROVING BY PYCNOMETER
Scope: This Guideline provides a method to properly determine product density by pycnometer.
Frequency As needed
Procedure Refer to API MPMS Chapter 6 for the instructions of preparing, installing, filling and calculation of density for a double wall vacuum sphere pycnometer.