Linepack calculation method for API

Linepack refers to the volume a pipe can hold at specified conditions of pressure and temperature. Linefill refers to the volume of fluid contained within a pipe. In AVEVA Pipeline Operations for Liquids, it is assumed that linefill is equal to linepack. Batch Tracking converts linefill to a net value (via API corrections).

Batch Tracking determines net linefill on a pipe segment basis. Within the pipe segment, the calculations operate on fragments, from the upstream to downstream end. Properties of batch fragments in the pipe segment are derived from the Batch Tracking application in order to calculate linepack. They are:

• Average temperature, which is interpolated using the temperature value at the upstream end of the segment and the temperature value at the downstream end of the segment. A search algorithm is used to determine these values. For more information, refer to Determine temperature and pressure values for a segment.

• Average pressure, which is interpolated using the pressure value at the upstream end of the segment and the pressure value at the downstream end of the segment. A search algorithm is used to determine these values. For more information, refer to Determine temperature and pressure values for a segment.

• Density, or Product density, from the Prodtype table is used.

• Thermal coefficient is inherited from the Prodtype table.

• Temperature Correction Factor (CTL) is applied using the API method. Fragment temperature, density, and in certain cases, thermal coefficient is used to calculate the CTL.

• Pressure Correction Factor (CPL) is applied using the API method. Fragment temperature, pressure and density are used to calculate the CPL.

• Correction for temperature on steel (CTS) is applied using the API method, which relies on temperature and CTL.

• Correction for pressure on steel (CPS) is applied using the API method, which relies on the following information:

  • Pressure

  • CPL

  • Internal diameter of pipe segment

  • Wall thickness of pipe segment

The fragment component of the linepack is calculated for each fragment in the pipe segment as follows:

1. Calculate what the corrected volume in the pipe segment would be if the fragment filled the entire segment. This is the capacity of the segment corrected using CTL, CPL, CTS, and CPS of the fragment applied using the API defined netting algorithm.

2. Factor this corrected volume by the proportion of the fragment to the total linepack. Divide the size of the fragment as measured in from the meter or previous segment by the sum of the fragment volumes in the segment from the previous calculation and multiply the result by the segment volume corrected from capacity.

The linepack of the pipe segment is the sum of each fragment component as calculated above.

Actual linepack saved is adjusted by a configurable filter factor as follows, where a factor of one is no adjustment:

It is assumed that no slack line exists when linepack is calculated. Linepacks will be inaccurate if slack line is present.