The viscosity-gravity constant (VGC) is a useful function for the approximate characterization of the viscous fractions of petroleum.² 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.

1.1 This test method covers the calculation of the viscosity-gravity constant (VGC) of petroleum oils having viscosities in excess of 4 cSt. = 4 X 10-6 m-2/s at 40°C (104°F).

1.2 Annex A1 describes a method for calculating the VGC from Saybolt (SUS) viscosity and relative density.

1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.>

1.4 The values stated in either acceptable SI units or in other units shall be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system must be used independently of the other, without combining values in any way.