The Weymouth Equation for High Pressure Gas Flow

This Excel spreadsheet helps you calculate pressures and flowrates using the the Weymouth Equation, a relationship usually used in long-distance natural gas pipelines.

The Weymouth Equation gives more conservative results than the Panhandle equations, and is hence more frequently used.  It is valid for steady-state adiabatic (isothermal) flow.  The version of the Weymouth equation used in this spreadsheet also accounts for elevation differences between the pipe entrance and exit.

In Imperial units, the Weymouth equation is

• Tsc and Psc are the temperature and pressure at standard conditions, in absolute Fahrenheit
• Tm is the average temperature of the gas line, in absolute Fahrenheit
• P1 and P2 are the pressures at the pipe entrance and exit, in absolute psi
• L is the length of the pipe, in miles
• G is the relative gas density with respect to air
• Z is the gas compressibility
• E is the pipeline efficiency
• Le is the effective length of the pipeline
• Δz is the elevation of the pipe exit with respect to the entrance in feet
• Q is the flowrate, in standard cubic feet per day

The gas compressibility Z and density are calculated at an average pressure and temperature, defined below.

The equations given above use several empirical factors, and normally the input parameters would need to be specified in specific units.  However, I've programmed the spreadsheet to handle the unit conversions for you.  You simply specify the input units using drop-down menus.

For dry gas fields, the pipeline efficiency is generally around 0.92, casing-head gas would have a pieline efficiency of 0.77, while gas and condensate pipes have an efficiency of 0.66

Download Weymouth Equation Calculator for Excel