Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids— Concentric, Square-edged Orifice Meters

Part 3: Natural Gas Applications

AGA Report No. 3 Part 3

Manual of Petroleum Measurement Standards Chapter 14.3.3

American Gas Association 400 North Captiol Street, NW Washington, DC 20001

American Petroleum Institute 1220 L Street, NW Washington, DC 20005

FOURTH EDITION, NOVEMBER 2013

An American National Standard

ANSI/API MPMS Ch. 14.3.3/AGA Report No. 3, Part 3

Special Notes

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Foreword

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iii

1. Scope 1

   1. General 1

   2. Definition of Natural Gas 1

   3. Basis for Equations 1

   4. Expansion Factor Application 1

2. Normative References 1

3. Symbols, Units, and Terminology 2

   1. General 2

   2. Symbols and Units 2

   3. Terminology 4

4. Flow Measurement Equations 5

   1. General 5

   2. Equations for Mass Flow of Natural Gas 5

   3. Equations for Volume Flow of Natural Gas 6

   4. Volume Conversion from Reference Base to Base Conditions 8

5. Flow Equation Components Requiring Additional Computation 9

   1. General 9

   2. Diameter Ratio (β) 9

   3. Coefficient of Discharge for Flange-tapped Orifice Meter [Cd (FT)] 9

   4. Velocity of Approach Factor (Ev) 11

   5. Reynolds Number (ReD) 12

   6. Expansion Factor (Y) 13

6. Gas Properties 16

   1. General 16

   2. Physical Properties 16

   3. Compressibility 16

   4. Relative Density 18

   5. Density of Fluid at Flowing Conditions 20

Annex A (informative) Adjustments for Instrument Calibration 24

Annex B (informative) Factors Approach 30

Annex C (informative) Flow Calculation Examples 33

Annex D (informative) Pipe Tap Orifice Metering 41

Annex E (informative) SI Conversions 42

Annex F (informative) Development of Constants for Flow Equations 44

Annex G (informative) Buckingham and Bean Empirical Expansion Factor (Y) for

Flange-tapped Orifice Meters 50

Bibliography 54

Tables

1 Linear Coefficient of Thermal Expansion 10

A.1 Water Density Based on Patterson and Morris Equation 28

1. Volume Reference Conditions for Custody Transfer Operations: Natural Gas Volume 42

2. Energy Reference Conditions 42

3. Heating Value Reference Conditions 43

G.1 Comparison Between Equation (35) and Equation (G.3). 53

Introduction

API MPMS Chapter 14.3.3/AGA Report No. 3, Part 3 is organized as follows: Symbols and units are first defined, the basic flow equation is presented, then key equation components are defined, and finally the gas properties applicable to orifice metering of natural gas are developed. Factors to compensate for meter calibration and location are included in Annex A. The factor approach to orifice measurement is included in Annex B. Annex F covers derivation of constants. The user is cautioned that the symbols may be different from those used in previous orifice metering standards.

Orifice Metering of Natural Gas and Other Related Hydrocarbon Fluids— Concentric, Square-edged Orifice Meters

Part 3: Natural Gas Applications

1. Scope

   1. General

      
      

      This part of API MPMS Ch. 14.3/AGA Report No. 3 has been developed as an application guide for the calculation of natural gas flow through a flange-tapped, concentric orifice meter, using the U.S. customary (USC) inch-pound system of units.

      
      

      For applications involving international system (SI) of units, a conversion factor can be applied to the results (Qm, Qv, or Qb) determined from the equations in 4.3. Intermediate conversion of units will not necessarily produce consistent results. As an alternative, the more universal approach specified in API MPMS Ch. 14.3.1/AGA Report No. 3, Part 1 can be used. The meter has to be constructed and installed in accordance with API MPMS Ch. 14.3.2/AGA Report No. 3, Part 2.

      
      

   2. Definition of Natural Gas

      
      

      As used in this document, 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 Table 1 of API MPMS Ch. 14.2/AGA Report No. 8. For other hydrocarbon mixtures, the more universal approach specified in API MPMS Ch. 14.3.1/AGA Report No. 3, Part 1 may be more applicable. Diluents or mixtures other than those stipulated in API MPMS Ch. 14.2/AGA Report No. 8 may increase the flow measurement uncertainty.

      
      

   3. Basis for Equations

      
      

      The computation methods used in this document are consistent with those developed in API MPMS Ch. 14.3.1/AGA Report No. 3, Part 1 and include the Reader-Harris/Gallagher (RG) equation for flange-tapped orifice meter discharge coefficient. The equation has been modified to reflect the more common units of the USC inch-pound system.

      
      

   4. Expansion Factor Application

      
      

      For all existing installations, the decision as to which expansion factor equation to use is at the discretion of the parties involved. However, the parties should be cognizant of the following:

      
      

      1. If the calculated difference between previous revision (1990) Buckingham and Bean expansion factor equation (refer to Annex G) and the new revised expansion factor equation (refer to 5.6) is less than or equal to 0.25 %, then the expansion factor values produced by either expansion factor equation will be within the uncertainty of the new expansion factor database and the existence of any flow bias is uncertain.

         
         

      2. However, if the calculated difference between expansion factor equations exceeds 0.25 %, then a variable flow

         1

         bias, which is a function of diameter ratio (β), isentropic exponent (, and ΔP  Pf

         unless the new expansion factor equation is utilized.

         
         

2. Normative References

ratio (x1), will be experienced

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

API MPMS Ch. 14.2/AGA Report No. 8, Compressibility Factors of Natural Gas and Other Related Hydrocarbon Gases

1