The primary purpose of this test method is to characterize the carbon-type composition of an oil. It is also applicable in observing the effect on oil constitution, of various refining processes such as hydrotreating, solvent extraction, and so forth. It has secondary application in relating the chemical nature of an oil to other phenomena that have been demonstrated to be related to oil composition.

Results obtained by this method are similar to, but not identical with, results obtained from Test Method D 3238. The relationship between the two methods and the equations used in deriving Fig. 1 are discussed in the literature.⁵

Although this test method tends to give consistent results, it may not compare with direct measurement test methods such as Test Method D 2007.

1.1 This test method may be used to determine the carbon-type composition of mineral insulating oils by correlation with basic physical properties. For routine analytical purposes it eliminates the necessity for complex fractional separation and purification procedures. The test method is applicable to oils having average molecular weights from 200 to above 600, and 0 to 50 aromatic carbon atoms.

1.2 Carbon-type composition is expressed as percentage of aromatic carbons, percentage of naphthenic carbons, and percentage of paraffinic carbons. These values can be obtained from the correlation chart, Fig. 1, if both the viscosity-gravity constant (VGC) and refractivity intercept (r_I) of the oil are known. Viscosity, density and specific gravity, and refractive index are the only experimental data required for use of this test method.

1.3 This test method is useful for determining the carbon-type composition of electrical insulating oils of the types commonly used in electric power transformers and transmission cables. It is primarily intended for use with new oils, either inhibited or uninhibited.

1.4 This standard does not purport to address all of the safety concerns, 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.