Page 65 - Petroleum and Gas Field Processing

quality of crude oil stocks. The tests included in the following list are
primarily physical (except sulfur determination):
1. Distillation
2. Density, specific gravity, and API (American Petroleum Indus-
try) gravity
3. Viscosity
4. Vapor pressure
5. Flash and fire points
6. Cloud and pour points
7. Color
8. Sulfur content
9. Basic sediments and water (B.S.&W.)
10. Aniline point
11. Carbon residue
The details of some of these tests are described next.

API Gravity
Earlier, density was the principal specification for petroleum products.
However, the derived relationships between the density and its fractional
composition were only valid if they were applied to a certain type of
petroleum. Density is defined as the mass of a unit volume of material at a
specified temperature. It has the dimensions of grams per cubic centimeter.
Another general property, which is more widely, is the specific
gravity. It is the ratio of the density of oil to the density of water and is
dependent on two temperatures, those at which the densities of the oil

sample and the water are measured. When the water temperature is 4 C
(39 F), the specific gravity is equal to the density in the cgs system,

because the volume of 1 g of water at that temperature is, by definition,
1 mL. Thus, the density of water, for example, varies with temperature,
whereas its specific gravity is always unity at equal temperatures. The
standard temperatures for specific gravity in the petroleum industry in

North America are 60/60 F and 15.6/15.6 C.
Although density and specific gravity are used extensively in the oil
industry, the API gravity is considered the preferred property. It is
expressed by the following relationship:
141:5

API ¼ 131:5

where
is the oil specific gravity at 60 F. Thus, in this system, a liquid
with a specific gravity of 1.00 will have an API of 10 deg. A higher API

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.