Manual of Petroleum Measurement Standards Chapter 14—Natural Gas Fluid Measurement

Section 12—Measurement of Gas by Vortex Meters

FIRST EDITION, MARCH 2017

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Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, Symbols, and Abbreviations 2

   1. Terms and Definitions 2

   2. Symbols 4

   3. Acronyms 6

4. Field of Application 6

   1. General Characteristics of the Vortex Flow Measurement Technology 7

   2. Principle of Measurement 7

5. Flowmeter Description 9

   1. Physical Components 9

   2. Transmitter 11

6. Design and Installation Requirements 14

   1. Meter Selection 14

   2. Installation 15

7. Operation and Performance 18

   1. Process Influences 18

   2. Operation 19

   3. Effect of Process Fluid Changes 19

   4. Mechanical Characteristics 19

   5. Performance Characteristics 20

   6. Quantity Computations 20

8. Proving, Calibration, and Performance Verification 21

   1. Factory Calibration 21

   2. Field Calibration/Verification 21

9. Uncertainty Calculation—Vortex Meter Flow Measurement Uncertainty Analysis Procedure 22

10. Auditing and Reporting Requirements 24

Annex A (normative) Factory Calibration 25

Annex B (informative) Proving Form for Meter Output (Numerical Example in the US Customary Units) . . . 26 Annex C (informative) System Uncertainty 27

Annex D (informative) Special Considerations for Steam 31

Annex E (informative) Period Jitter and Its Effect on Calibration 32

Annex F (informative) Experimental Data Showing Pressure Tap Location Effect on K-factor 34

Figures

1. Vortex Formation 8

2. Vortex Shedder Cross Sections 10

3. Example of Vortex Sensor 10

4. The 4–20mA and Pulse Outputs 11

5. Raw Pulse Output 12

6. Schematic Showing Recommended Pressure and Temperature Tap Locations 17

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   Contents

   Page

7. Example of a K-factor Curve 20

C.1 An Example of Calibration Data Plot of a Vortex Meter 29

D.1 Improper Installation for Saturated Steam 31

1. K vs Velocity Using Inlet Pressure 34

2. K vs Velocity Using Downstream Pressure 34

3. Error in K-factor Using Inlet Pressure 35

4. Error in K-factor Using Downstream Pressure 35

Tables

1 Symbols and Dimensions 4

E.1 Time (sec), a, Needed for a Flow Rate Uncertainty of 0.25 % 33

Introduction

This document describes the design, installation and operation of vortex shedding flowmeters for the measurement of hydrocarbon gases and steam flows.

Vortex shedding is a flow phenomenon that occurs when a bluff body is placed in flowing fluid and depending on the size and shape of a bluff body, under certain flowing conditions, alternating vortices are created on the downstream side of the body and detach periodically from either side of the body. The fluid flow past the object, often referred to as the vortex shedder, creates alternating low-pressure vortices on the downstream side of the object.

The vortex shedding frequency, with a few exceptions, is proportional to flow rate. Hence, by monitoring the shedding frequency and through numerical computational techniques, the fluid velocity and flow rate at the actual flowing conditions can be determined.

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Chapter 14—Natural Gas Fluid Measurement Section 12—Measurement of Gas by Vortex Meters

1. Scope

   This Standard addresses the following:

   
   

   1. provides generic information on full-bore vortex shedding flowmeters, including glossary, and sets of engineering equations useful in specifying performance;

      
      

   2. describes vortex shedding flowmeters in which alternating vortices are shed from one or more bluff bodies installed in a closed conduit;

      
      

   3. describes how the vortex shedding frequency is used to determine the velocity to infer the volume, mass, and/or energy flow rate and the total gas flow through the meter over a specific time interval;

      
      

   4. applies only to single phase gas flows in closed conduit that are steady or vary slowly in time. For fiscal measurement, the output of the flow rate shall be within the acceptable limits of steady state flow rate;

      
      

   5. describes the physical components of vortex shedding flowmeters and identifies need for inspection, certification, and material traceability;

      
      

   6. addresses the effect of gas properties, installation, and process conditions that may affect the measurement uncertainty and describes guidelines for reducing or eliminating their influences;

      
      

   7. defines the method for calculating uncertainty of the flow rate measurement;

      
      

   8. defines the meter output requirements and necessary information pertaining to the meter output for the purpose of fiscal measurement of gas; and

      
      

   9. provides calibration and/or performance verification guidance for the field application.

   
   

2. Normative References

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 Chapter 4.5, Master Meter Provers, 2011

API MPMS Chapter 4.2, Displacement Provers, Reaffirmed 2011

API MPMS Chapter 14.2, AGA Report No. 8/GPA 8185, Compressibility Factors of Natural Gas and other Related Hydrocarbon Gases, Reaffirmed 2012

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