Custody orifice plate calculations for gases (pressure and temperature compensated) are based on the Reader-Harris Gallagher equation for the orifice coefficient found in the Third Edition of the Manual of Petroleum Measurements Standards, Chapter 14 - Natural Gas Fluids Measurements, Section 3 - Concentric Square-Edged Orifice Meters, Part 3 - Natural Gas Applications.
Flow is corrected back to a base (or contract) flowrate by compensation for base temperature, base pressure and base compressibility. Correction is also made for thermal expansion of the orifice plate and the pipe from a base temperature of 20°C (or 68°F). Note that when solving for orifice bore the calculations may not converge for a beta ratio greater than 0.8.
Copyrighted 2001, 2003