Crude oil composition is not identical and its characteristics may vary significantly from one crude oil reservoir to another source. A crude oil assay test helps to estimate the crude oil feed stock yields of fractions at various boiling rangers. TBP, the True Boiling Point test data available from the laboratory on specific crude batches relates the refiners to decide the commercial value as well as for the detailed refinery engineering.

Assay test of crude oil can be limited to know the various fractions yield or extensive by the characterization of the whole crude and its fractions. The various fractions expected from a normal stabilized crude oil are LPG, Light Naphtha, Heavy Naphtha, Kerosene, Gasoil and Residual Fuel oil.

ASTM D 2892 is the standard method for the TBP distillation. Potstill distillation by ASTM D 5236 is subsequently conducting on the TBP distillation residue at 0.1 mm Hg absolute pressure to determine the further yields boiling ranges.

The maximum atmospheric equivalent vapor temperature achievable by TBP distillation is 400° celcius whereas in the Potstill distillation it is 565° celcius.




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