Need: This manual is based on the findings of PAR Research Project NX-19 initiated by the Pipeline Research Committee in 1956 upon the recommendation of the Gas Measurement Committee. The initial purpose was to extend the range of the A.G.A. Supercompressibility Factor Tables published in 1955, 1956. However, a significant out-come of the project was that in addition to providing the basic data for extending the range, a base equation for calculation of supercompressibility factors was developed.
Benefit: The methods, tables, and equations presented in this manual provide extended ranges of coverage, simplification of use, and broadening of the applicability of the procedures published in A.G.A. Gas Measurement Committee Report No. 3. "Orifice Metering of Natural Gas." To determine a supercompressibility factor for natural gas, the A.G.A. Method uses pseudo-critical pressures and temperatures to obtain pressure and temperature correction factors. These correction factors adjust the flowing gas pressure and temperature to correspond to the chosen standard 0.600 specific gravity hydrocarbon gas. With the adjusted temperatures and pressures, supercompressibility factors can be determined directly from Fpv tables or by applying a definitive equation.
Result: The most practical method of determining pressure and temperature adjusting factors for normal mixtures of natural gas is by application of the specific gravity relationship. Consequently, the specific gravity method is presented as the standard method. For less common natural gas mixtures up to 1.000 specific gravity alternate methods employing other relationships of natural gas are offered in the appendix.
