DENSITY, RELATIVE DENSITY AND API GRAVITY BY THERMOHYDROMETER METHOD: ASTM D6822
EXPLANATION
Density and API gravity are used in custody transfer quantity calculations and to satisfy transportation, storage, and regulatory requirements. These are also the factors that indicate the quality of crude petroleum. Crude petroleum prices are often posted against values in kg/ m3 or in degrees API. However, this property of petroleum is an uncertain indication of its quality unless correlated with other properties.
Because the thermohydrometer incorporates both the hydrometer and thermometer in one device, it is more applicable in field operations for determining density or API gravity of crude petroleum and other liquid petroleum products with Reid vapor pressures of 101.325 kPa or less. This test method is suitable for analyzing low viscosity transparent or opaque liquids, or both. When used for opaque liquids, it requires the use of a meniscus correction.
TEST SUMMARY
The density or API gravity, after temperature equilibrium has been reached, is read by observing the freely floating thermo-hydrometer and noting the graduation nearest to the apparent intersection of the horizontal plane surface of the liquid with the vertical scale of the hydrometer after temperature equilibrium has been reached. The observed thermo-hydrometer reading is reduced to the reference temperature value by means of the Petroleum Measurement Tables, and observed temperature from the enclosed thermometer.
TEST PRECISION
Repeatability: 0.6 kg/m3 or 0.2° API
Reproducibility: 1.5 kg/m3 or 0.5° API
Bias of this method has not been determined.
