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Quantity Conversion

Quantity conversions are calculations which convert a given bulk product quantity value to another quantity value, where the two quantities involved are different.


Converting a gross volume quantity value of crude oil to a net mass quantity value of crude oil:

An oil tank is measured via tank dipping to contain 10 640.6 barrels at 95 °F (gross observed volume – GOV) of crude oil. What is the net standard weight (NSW) and net standard mass (NSM) in long tons of the crude oil in the tank?

This is not a straightforward calculation:

To determine the net weight, we require the crude oil density (in air and in vacuum), potentially a sediment and water correction factor and a correction factor for the effect of temperature (and pressure) on the liquid product (CT(P)L) and unit conversion factors.

Quantity conversions of crude oil and products (including  LPG) thus require four distinct kinds of petroleum measurement standards:

  • Unit conversion standards
  • Standards that define the CT(P)L factors
  • Standards that define the mass-to-weight conversion
  • Standards that define the right sequence (and rounding) for the conversion calculation steps – the calculation model

For each of these four kinds of standards, a variety of measurement standards (including historical versions and national versions) is available, which, when combined, explain why quantity conversions are complex.

Natural gas and LNG quantity conversions do not require mass-to-weight conversions but an additional type of standard:

  • Standards defining calculations of densities and heating values from chemical composition of the natural gas including physical property data
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