scope:

APPLICATION

General

This part of Chapter 14, Section 3, has been developed as an application guide for the calculation of natural gas flow through a flange-tapped, concentric orifice meter, using the inch-pound system of units. For applications involving SI units, a conversion factor may be applied to the results (Qm, Qv, or Qb) determined from the equations in 3.3. Intermediate conversion of units will not necessarily produce consistent results. As an alternative, the more universal approach specified in Chapter 14, Section 3, Part 1, should be used. The meter must be constructed and installed in accordance with Chapter 14, Section 3, Part 2.

Definition of Natural Gas

As used in this part, the term natural gas applies to fluids that for all practical purposes are considered to include both pipeline- and production-quality gas with single-phase flow and mole percentage ranges of components as given in American Gas Association (A.G.A.) Transmission Measurement Committee Report No. 8, "Compressibility and Supercompressibility for Natural Gas and Other Hydrocarbon Gases." For other hydrocarbon mixtures, the more universal approach specified in Part 1 may be more applicable. Diluents or mixtures other than those stipulated in A.G.A. Transmission Measurement Committee Report No.8 may increase the flow measurement uncertainty.

BASIS FOR EQUATIONS

The computation methods used in this part are consistent with those developed in Part 1 and include the Reader-Harris/Gallagher equation for flange-tapped orifice meter discharge coefficient. The equation has been modified to reflect the more common units of the inch-pound system. Since the new coefficient of discharge equation does not address pipe tap meters, the pipe tap methodology of the 1985 edition of ANSI/API 2530 has been retained for reference in Appendix 3-D.

ORGANIZATION OF PART 3

Chapter 14, Section 3, Part 3, is organized as follows: Symbols and units are defined in 3.2, the basic flow equation is presented in 3.3, the key equation components are defined in 3.4, and the gas properties applicable to orifice metering of natural gas are developed in 3.5. All values are assumed to be absolute. Factors to compensate for meter calibration and location are included in Appendix 3-A. The factor approach to orifice measurement is included in Appendix 3-B. Appendix 3-C covers examples to assist the user in interpreting this part. Appendix 3-D covers pipe tap meters. Appendix 3-E covers SI conversions, Appendix 3-F covers heating value calculation, and Appendix 3-G covers derivation of constants. The user is cautioned that the symbols as defined in 3.2 may be different from those used in previous orifice metering standards.