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Lab Methods

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Api Gravity, Density, and Specific Gravity

  • Method ASTM D4052
  • Repeatability 0.0001
  • Reproducibility 0.0005
  • Blending linear
  • Additive Correction No

The purpose of this test is to determine the Density and Api of liquid petroleum products. It can be used for Distillates and if heated Residual Fuel Oils. When running crude the same technology (Density Meter) is used but the method is D5002.

Density is expressed in units of mass per volume at a specific temperature. For example: Density @ 60°F = 0.7536 g/cm3. This basically means that at 60°F 0.7536 grams of the sample will occupy 1 cubic centimeter of space. This measurement can be converted into any units used to measure weight and volume per customer request.

API gravity is another expression of this measurement that uses the Density/Specific gravity for its conversion. The higher the api the less dense the sample is. For example at 60°F: an api of 10.0 is equal to 1.0000 g/cm3. While an api of 80.0 is equal to 0.6684 g/cm3.

Temperature is very important in relation to api and density. As petroleum products are heated they expand and become less dense. The inverse is true when the product is cooled, it becomes denser. For this reason standard organizations have reached agreements on what temperature to confirm quantities and volumes when measuring product levels. Here in the United States a temperature of 60°F is the standard. Overseas many places use 15°C or 20°C.

Api and density also play important roles in the identification of products and distillate cuts. See below for a breakdown of typical api gravities.
Bunker Fuel (6 Oil) – 11-12 deg
Heavy Crude – 19 deg
Vgo - 28 deg
Reformate – 30-40 deg
Diesel Fuel (2 Oil) – 30-40 deg
Kerosene/Jet Fuel - 40 deg
Gasoline – 50-60 deg
Natrual Gas – 70 - 80 deg

The lower api products are usually very high in carbon content, high in viscosity (very thick), High in sulfur, and tend to be darker in nature. The higher the api the inverse is true. The method operates by using a U shaped tube that oscillates at a specific frequency. When product is injected into the unit this vibration is changed depending upon how heavy or light the product is. This frequency shift is used to calculate the api and density of the product.