Place compressor stations along a gas pipeline and size their horsepower, per GPSA and ASME B31.8.
Each station raises the gas to its discharge pressure, which cannot exceed the pipeline MAOP. The gas then loses pressure to friction and elevation until it reaches the minimum suction pressure of the next station. The distance between those two pressures is the station spacing. This calculator walks the line in short steps using the GPSA flow equations and places each station where the suction limit is reached.
Once the gas has enough pressure to coast to the delivery point, full discharge pressure is no longer needed. The calculator marches backward from the delivery point to find the pressure required at every milepost and sizes the final station to that value, so horsepower is not overstated.
A column of gas has weight, so an uphill run costs pressure and a downhill run returns some. Because gas density rises with pressure, the effect is larger at high pressure: about 21 psi per 1,000 ft of rise at 900 psia for 0.6 gravity gas, and about 4 psi at 200 psia. The calculator applies the correction in pressure squared form at the average line pressure, as GPSA describes.
Horsepower follows the polytropic method in GPSA Section 13: polytropic head from suction temperature, average compressibility and compression ratio (Eq 13-34b), gas horsepower from mass flow and polytropic efficiency (Eq 13-35), and brake horsepower after mechanical losses (Eqs 13-38 and 13-39). Suction is taken at the flowing gas temperature, assuming the gas is cooled after each station.
GPSA describes the Weymouth equation as agreeing more closely with metered rates on short pipelines and gathering systems. Panhandle A approximates partially turbulent flow and Panhandle B approximates fully turbulent flow, which is typical of large transmission lines. The AGA fully turbulent equation uses the pipe roughness directly. Efficiency factors are best calibrated against field data.