ASTM D2501 Test Method for Calculation of Viscosity-Gravity Constant (VGC) of Petroleum Oils
3. Summary of Test Method
3.1 The kinematic viscosity at 40°C (104°F) and the density at 15°C of the oil are determined. If the oil is extremely viscous, or if it is otherwise inconvenient to determine the viscosity at 40°C, the kinematic viscosity at 100°C (212°F) can be used. The viscosity-gravity constant is calculated from the measured physical properties using the appropriate equation.
4. Significance and Use
4.1 The viscosity-gravity constant (VGC) is a useful function for the approximate characterization of the viscous fractions of petroleum. It is relatively insensitive to molecular weight and is related to a fluids composition as expressed in terms of certain structural elements. Values of VGC near 0.800 indicate samples of paraffinic character, while values close to 1.00 indicate a preponderance of aromatic structures. Like other indicators of hydrocarbon composition, the VGC should not be indiscriminately applied to residual oils, asphaltic materials, or samples containing appreciable quantities of nonhydrocarbons.
