Line Pack Overview
The CygNet Line Pack application performs a simple volumetric estimation for the following commodities using pipeline segments of a monitored pipeline at any given time:
- the volume of natural gas
- the mass of supercritical carbon dioxide (CO2)
- the volume of petroleum liquids
Line Pack calculations are performed on distinct pipeline segments called Pack Segments. These pack segments are configured in the Line Pack device in the Device Definition Service (DDS) with a number of different inputs, which can be either hard-coded values or points within the CygNet system. Once the calculation for a pack segment is performed, output values are stored in points with the facility of the pack segment and configurable UDCs. Once all the pack segments in a pipeline have been calculated and set, the results are combined and rolled up a preconfigured hierarchy.
Calculated line pack values are not associated with the Line Pack device facility. Rather, a calculated line pack value (for example, current line pack volume (Pack: Current)) is assigned to a point whose facility represents a "pipeline segment." The "pipeline segment" is usually defined as all pipes (possibly represented by sub-segment facilities) running between two measurement stations.
The Line Pack driver configuration provides settings for identifying pack segment and pack sub-segment facilities in your system and then individual input readings (for example, pressures, temperature, GQ values) are configured per identified segment facility. The individual segment line pack values are then summed together and associated with other grouping facilities that make sense for your enterprise's pipeline such as "area", "division" or just a top-level "pipeline" segment facility. The Line Pack device facility will have the auto-generated statistics points assigned to it, which record various state information of Line Pack EIE.
See the following subsections for more information:
Pack Segment Configuration
When configuring a pipeline for Line Pack analysis, each Pack Segment should describe the shortest amount of pipe between sensors with telemetry. Further, a pack segment may contain any number of pack sub-segments. Pack Sub-Segments are used to further break down the values for any pack segment, so that the volume of any individual section of pipe can be specified, and so that individual sections can be taken offline as necessary. Pack sub-segments would typically span between two valves in a pipeline.
The Line Pack driver uses facility types and hierarchy relationships to determine the facilities upon which to perform a calculation. Only two facility elements are required for Line Pack: pack segments and pack sub-segments. The default facility types are PACK_SEG and PACK_SUB, although others can be configured. The hierarchy structure of the pack segments and pack sub-segments is stored in facility attributes. Pack sub-segments are always the children of pack segments and each pack segment can have zero or more child pack sub-segments.
Pack segment facility types, pack sub-segment facility types, and the hierarchical structure are configured on the Settings page of the device editor and the hierarchical tree of pack segments is displayed on the Line Pack page of the device editor.
Note: Volumetric input must be specified for all pack sub-segments and for any pack segment with no child pack sub-segments. See Configuring Line Pack Calculation Rules for more information.
Line Pack Calculations
The type of Line Pack calculation is selected on the Calculations page.
Natural Gas
The CygNet Line Pack application calculates natural gas volume for pipeline segments for any selected time period. A supercompressibility factor is applied to correct the calculated volumes, using AGA 8 - Gross Method 2, NX19 - Legacy, or NX19.
The CygNet Line Pack application complies with the American Petroleum Institute’s (API) standards for gas measurement as published in Chapter 21.1. The Line Pack calculations accommodate NX19 for natural gas. NX19 support is the NX19 Gravity/Carbon/Nitrogen (GCN) Method 1962, which includes two calculation options based on gravity:
- NX19 Legacy — which uses the NX19 GCN formula for gravities less than or equal to 0.75. (Earlier Line Pack calculations used custom NX19 calculations without Methane as an input. This option is included for backward compatibility of Line Pack calculations.)
- NX19 GCN — this formula is for gravities greater than 0.75.
See Natural Gas Volume (Estimated) and Supercompressibility Factor for more information.
Supercritical CO2
The CygNet Line Pack application calculates supercritical CO2 mass for pipeline segments for any selected time period. The input CO2 density value can be derived from two sources:
- Measured density — a density sensor in the pipeline provides a measured density value.
- Calculated density — a density value is derived from a lookup table of density values (based on input temperature and pressure) calculated by REFPROP, a program developed by the National Institute of Standards and Technology (NIST) for calculating the thermodynamic and transport properties of industrially important fluids and their mixtures. For CO2 density values that fall between a given temperature and pressure range, CygNet will interpolate the closest value. The CO2 density table is based on absolute pressure (psia). The Line Pack driver makes the conversion to absolute pressure before doing the density lookup.
See Supercritical CO2 Mass (Estimated) for more information.
Petroleum Liquids
The CygNet Line Pack application calculates petroleum liquids volume for pipeline segments for any selected time period.
The liquids calculations performed in this application conform to the calculations outlined in the API publication: Manual of Petroleum Measurement Standards, Chapter 11 — Physical Properties Data, Section 1 — Temperature and Pressure Volume Correction Factors for Generalized Crude Oils, Refined Products, and Lubricating Oils. Adjunct to: ASTM D 1250-04 and IP 200/04. Measurement Coordination October 2002. May 2004. Addendum 1, September 2007.
See Petroleum Liquids Volume (Estimated) for more information.
MAOP
In addition to the primary pack calculation, a secondary calculation may be optionally performed to calculate the pack at the Maximum Allowable Operating Pressure (MAOP) for any pipeline content type. The result of this calculation is stored in the same manner as the primary pack.
See MAOP formula for more information.
Calculation Inputs
Inputs to the Line Pack calculation for any segment can be sourced from one of three places:
- Custom calculation rules for any pack segment — configured on the Adjusted inputs section of the Calculations Rules dialog box off the Rules page.
- Base input rules for any pack segment — configured on the Base Inputs dialog box off the Rules page.
- Global Inputs — configured on the Global Inputs page of the device editor.
Depending on changing conditions in the field, it may be appropriate to use different input values for the same calculation. See Configuring Custom Calculation Rules for information about configuring custom rules and setting their precedence order.
The UDC mappings for the required and optional inputs are configured on the UDC Map page of the device editor.
Sample Results
A Line Pack calculation can be tested locally using all the current rules and inputs configured for the selected pack segment from the Line Pack page of the device editor. Additionally you can manipulate the inputs as necessary in a testing mode to achieve the appropriate results.
Mass Balance
The Line Pack application supports a Mass Balance calculation, which can be used to detect pipeline leakage. Mass Balance calculations are available for all types of Line Pack calculations: natural gas, supercritical CO2, and petroleum liquids. See Configuring Mass Balance for more information.
Scheduling Calculations
A Line Pack calculation is executed by sending a UIS command of the type CALCULATE or VCALCULATE to the Line Pack driver. These commands can be scheduled via the MSS or executed directly on the Device page of the device editor.
Execution time of the Line Pack calculation can be measured in seconds, which allows for a high frequency of calculations. A throttle can be applied to pause the calculation to conserve CPU processing, if desired.
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