Linepack is the total volume of natural gas compressed and contained inside an operating pipeline network at standard conditions. Because gas is highly compressible, operators can increase pipeline pressure during off-peak hours (packing) and draw down pressure during morning and evening consumption peaks (drafting), utilizing the steel pipeline as an intraday storage gas-holder without surface tanks.

Because gas density decreases as it moves downstream, velocity accelerates and friction loss steepens parabolically toward the pipe outlet (dP/dx ∝ 1/P). Integrating this non-linear pressure profile yields Pavg = 2/3 [P1 + P2 - (P1*P2)/(P1+P2)]. The simple arithmetic average (P1+P2)/2 overpredicts true average pressure and overestimates available linepack storage by 8% to 15%.

At high transmission pressures (60 to 120 bar), intermolecular attraction causes natural gas to compress into a smaller volume than an ideal gas (Z < 1.0, typically 0.80 to 0.88). Because linepack volume is inversely proportional to Z (V = Vg * [P/Pb] * [Tb/T] * [1/Z]), accounting for real gas behavior per AGA-8 reveals up to 20% more stored gas mass than ideal gas equations predict.

Total linepack is all the gas mass inside the pipe. Draftable (usable) linepack is only the incremental gas that can be withdrawn while keeping downstream delivery pressure above the customer contract minimum (Pmin). The remaining volume below Pmin is permanent inactive cushion pack required to maintain physical transmission pressure.

The Panhandle B equation is an industry-standard empirical flow formula developed for large-diameter, high-pressure natural gas transmission lines operating at high Reynolds numbers (4 to 40 million). It incorporates a Reynolds number exponent of 0.0196 and pipeline efficiency factor (E ≈ 0.92 to 0.95) to predict throughput without requiring iterative Darcy-Weisbach Colebrook friction factor solutions.