Formula & Engineering Reference
Pstd = 101.325 kPa abs, Tstd = 15°C (AGA/GPSA reference conditions). The pipe's internal volume is also the actual gas volume — the gas fills the pipe at line conditions; the standard-volume correction is what makes that number comparable across pressures.
What this means: line pack is the gas inventory the pipeline itself is holding right now — a buffer that can be drawn down or built up without immediately changing what's flowing in at the upstream end.
Why it matters: operators use line pack to ride out short demand swings and to plan controlled pressure changes; a transmission system's flexibility during a cold-weather demand spike often comes more from line pack than from added supply.
Common mistakes: using Z=1 at high transmission pressures (overstates standard volume), and confusing actual volume (at line conditions) with standard volume (the commercially meaningful number) when reporting inventory.
Practical field notes: always source Z from an actual correlation (AGA8, Standing-Katz chart, or a flow computer) for the gas composition and pressure in question — a generic 0.9 estimate is fine for screening but not for billing-grade inventory.
The gas stored inside a pipeline at its operating pressure and temperature — a short-term buffer for demand swings.
It gives a common basis comparable across pipeline segments at different pressures — the same basis used for commercial gas metering.
Real gas deviates from ideal behavior at high pressure — ignoring Z (using 1.0) can overstate standard volume by 10% or more.
Standard volume times the gas's gross heating value per standard cubic metre — the same basis used for commercial billing.