Linepack calculation method for NIST REFPROP

The linepack calculation that is supplied by the National Institute of Standards and Technology’s (NIST) Reference Fluid Thermodynamic and Transport Properties (REFPROP) database for use with Highly Volatile Liquid (HVL) products is different from the linepack calculation used for crudes, products, and NGLs that is offered by the American Petroleum Institute’s Manual of Petroleum Measurement Standards (API MPMS).

The API linepack calculation is as follows:

Where:

• fragVol — Volume of the fragment

• CTL — Temperature correction factor, calculated using the API library.

• CPL — Pressure correction factor, calculated using the API library.

• CTS — Correction factor for temperature on steel.

• CPS — Correction factor for pressure on steel.

This gives the linepack of a fragment. It is summed up for every fragment in a segment to get the segment’s linepack.

When using the REFPROP library for HVL products is used, linepack is calculated in the following manner:

Where:

• fragVol — Volume of the fragment.

• baseDensity — Base density of the product, as defined on the Product Type (prodtype) record.

• correctedDensity — Density of the product at the temperature and pressure conditions of the associated fragment, calculated by the REFPROP library.

• CTS — Correction factor for temperature on steel.

• CPS — Correction factor for pressure on steel.

The corrected density calculated by the REFPROP library takes temperature and absolute pressure as inputs. However, the pressure that AVEVA Pipeline Operations for Liquids reads by default is considered to be gauged.Therefore, it must be corrected by applying an atmospheric pressure offset to the reading (which then makes it an absolute pressure). This offset is 14.7 PSI.

In both of these cases, the correction factors are unit-less. The densities in the REFPROP calculation are converted so that they all share the same units. As a result, the linepack units are always whatever units of volume are on the pipe_segment, as defined in the unit profile.

It is also possible to use the REFPROP library to calculate a linepack in pounds (lbs). The following formula is used in those situations:

Where:

• fragVol — Volume of the fragment.

• correctedDensity — Density of the product at temperature and pressure conditions of the fragment, calculated by the REFPROP library.

• CTS — Correction factor for temperature on steel.

• CPS — Correction factor for pressure on steel.

• conversionFactor — Used to convert the density and volume into pounds.

Again, as mentioned above, the pressure reading used to calculate corrected density has a pressure offset of 14.7 PSI applied to it to make it into an absolute pressure.

In order for a consistent, simple conversion, the units for the fragment volume and corrected density are converted to US barrels (bbls) and pounds per foot cubed (lbs/ft3) before this calculation.

The conversion factor is simply the number of cubed feet in a US barrel (5.61458333). This will result in a linepack that is calculated in pounds.