Manual of Petroleum Measurement Standards Chapter 4—Proving Systems

Section 2—Displacement Provers

THIRD EDITION, SEPTEMBER 2003 REAFFIRMED, MARCH 2011

ADDENDUM, FEBRUARY 2015

Manual of Petroleum Measurement Standards Chapter 4—Proving Systems

Section 2—Displacement Provers

Measurement Coordination

THIRD EDITION, SEPTEMBER 2003 REAFFIRMED, MARCH 2011

ADDENDUM, FEBRUARY 2015

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   Copyright © 2003 American Petroleum Institute

   
   

   FOREWORD

   
   

   Chapter 4 of the Manual of Petroleum Measurement Standards was prepared as a guide for the design, installation, calibration, and operation of meter proving systems used by the majority of petroleum operators. The devices and practices covered in this chapter may not be applicable to all liquid hydrocarbons under all operating conditions. Other types of prov- ing devices that are not covered in this chapter may be appropriate for use if agreed upon by the parties involved.

   The information contained in this edition of Chapter 4 supersedes the information con- tained in the previous edition (First Edition, May 1978), which is no longer in print. It also supersedes the information on proving systems contained in API Standard 1101 Measure- ment of Petroleum Liquid Hydrocarbons by Positive Displacement Meter (First Edition, 1960); API Standard 2531 Mechanical Displacement Meter Provers; API Standard 2533 Metering Viscous Hydrocarbons; and API Standard 2534 Measurement of Liquid Hydrocar- bons by Turbine-meter Systems, which are no longer in print.

   This publication is primarily intended for use in the United States and is related to the standards, specifications, and procedures of the National Institute of Standards and Technol- ogy (NIST). When the information provided herein is used in other countries, the specifica- tions and procedures of the appropriate national standards organizations may apply. Where appropriate, other test codes and procedures for checking pressure and electrical equipment may be used.

   For the purposes of business transactions, limits on error or measurement tolerance are usually set by law, regulation, or mutual agreement between contracting parties. This publi- cation is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved.

   Chapter 4 now contains the following sections:

   Section 1, “Introduction”

   Section 2, “Displacement Provers” Section 4, “Tank Provers”

   Section 5, “Master-meter Provers” Section 6, “Pulse Interpolation”

   Section 7, “Field-standard Test Measures” Section 8, “Operation of Proving Systems” Section 9, “Calibration of Provers”

   API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict.

   Suggested revisions are invited and should be submitted to API, Standards department, 1220 L Street, NW, Washington, DC 20005.

   
   

   iii

   
   

   CONTENTS

   
   

   Page

   1. INTRODUCTION 1

      1. Scope 1

      2. Displacement Prover Systems 1

      3. Definition of Terms 1

      4. Referenced Publications 2

   2. GENERAL PERFORMANCE CONSIDERATIONS 2

      1. Repeatability and Accuracy 2

      2. Base Prover Volume 2

      3. Valve Seating 2

      4. Flow Stability 2

      5. Freedom from Hydraulic Shock 2

      6. Temperature Stability 2

      7. Pressure Drop Across the Prover 3

      8. Meter Pulse Train 3

      9. Detectors 3

   3. GENERAL EQUIPMENT CONSIDERATIONS 3

      1. Materials and Fabrication 3

      2. Internal and External Coatings 3

      3. Temperature Measurement 3

      4. Pressure Measurement 3

      5. Displacing Devices 4

      6. Valves 5

      7. Connections 5

      8. Detectors 5

      9. Peripheral Equipment 6

      10. Unidirectional Sphere Provers 6

      11. Unidirectional Piston Provers 8

      12. Bidirectional Sphere Provers 9

      13. Bidirectional Piston Provers 9

   4. DESIGN OF DISPLACEMENT PROVERS 11

      1. Initial Considerations 11

      2. Design Accuracy Requirements 12

      3. Dimensions of a Displacement Prover 13

   5. INSTALLATION 18

      1. General Considerations 18

      2. Prover Location 19

APPENDIX A ANALYSIS OF SPHERE POSITION REPEATABILITY 21

APPENDIX B EXAMPLES OF PROVER SIZING 27

APPENDIX C A PROCEDURE FOR CALCULATING MEASUREMENT

SYSTEM UNCERTAINTY 35

APPENDIX D TYPICAL DISPLACEMENT PROVER DESIGN CHECK LIST 39

APPENDIX E EVALUATION OF METER PULSE VARIATIONS 45

APPENDIX F PROVER SPHERE SIZING 47

v

Page

Figures

1. Typical Unidirectional Return-type Prover System 7

2. Piston Type Prover with Shaft and Optical Switches 8

3. Typical Bidirectional U-type Sphere Prover System 10

4. Typical Bidirectional Straight-type Piston Prover System 11

5. Pulse Train Types 13

1. Diagram Showing the Relationship Between Sphere Position Repeatability

   and Mechanical Detector Actuation Repeatability 21

2. Sphere versus Detector Relationship at Various Insertion Depths for a 12 in.

   Prover with a 0.75 in. Diameter Detector Ball 25

3. Prover Length versus Detector Repeatability at Various Insertion Depths for a

12 in. Unidirectional Prover with a 0.75 in. Diameter Detector Ball. 25

Tables

1. Range to Standard Deviation Conversion Factors 35

2. Student t Distribution Factors for Individual Measurements 36

3. Estimated Measurement Uncertainty of the System at the 95% Confidence

Level for Data that Agree within a Range of 0.05% 36

Chapter 4—Proving Systems

Section 2—Displacement Provers

1. Introduction

   This document, including figures, graphs and appendices addresses displacement provers. It includes provers that were commonly referred to as either “conventional” pipe provers or “small volume” provers. “Conventional” pipe provers were those with sufficient volume to accumulate a minimum of 10,000 whole meter pulses between detector switches for each pass of the displacer. “Small volume” provers were those with insufficient volume to accumulate a minimum of 10,000 whole meter pulses between detector switches for each pass of the displacer.

   Displacement provers may be straight or folded in the form of a loop. Both mobile and stationary provers may be con- structed in accordance with the principles described in this chapter. Displacement provers are also used for pipelines in which a calibrated portion of the pipeline (straight, U-shaped, or folded) serves as the reference volume. Some provers are arranged so that liquid can be displaced in either direction.

   When using a displacement prover the flow of liquid is not interrupted during proving. This uninterrupted flow permits the meter to be proved under specific operating conditions and at a uniform rate of flow without having to start and stop.

   The reference volume (the volume between detectors) required of a displacement prover depends on such factors as the discrimination of the proving counter, the repeatability of the detectors, and the repeatability required of the proving system as a whole. At least 10,000 whole meter pulses are required for Meter Factors (MFs) derived to a resolution of 0.0001. The relationship between the flow range of the meter and the reference volume must also be taken into account. For provers that do not accumulate a minimum of 10,000 whole meter pulses between detectors for each pass of the displacer, meter pulse discrimination using pulse interpolation tech- niques is required (see API MPMS Chapter 4.6).

   
   

   1. SCOPE

      This chapter outlines the essential elements of provers that do, and also do not, accumulate a minimum of 10,000 whole meter pulses between detector switches, and provides design and installation details for the types of displacement provers that are currently in use. The provers discussed in this chapter are designed for proving measurement devices under dynamic operating conditions with single-phase liquid hydrocarbons. These provers consist of a pipe section through which a dis- placer travels and activates detection devices before stopping at the end of the run as the stream is diverted or bypassed.

      1

      
      

   2. DISPLACEMENT PROVER SYSTEMS

      All types of displacement prover systems operate on the principle of the repeatable displacement of a known volume of liquid from a calibrated section of pipe between two detec- tors. Displacement of the volume of liquid is achieved by an oversized sphere or a piston traveling through the pipe. A cor- responding volume of liquid is simultaneously measured by a meter installed in series with the prover.

      A meter that is being proved on a continuous-flow basis must be connected at the time of proof to a proving counter. The counter is started and stopped when the displacing device actuates the two detectors at the ends of the calibrated section. The two types of continuous-flow displacement provers are unidirectional and bidirectional. The unidirectional prover allows the displacer to travel in only one direction through the proving section and has an arrangement for returning the dis- placer to its starting position. The bidirectional prover allows the displacer to travel first in one direction and then in the

      other by reversing the flow through the displacement prover. Both unidirectional and bidirectional provers must be con-

      structed so that the full flow of the stream through a meter being proved will pass through the prover. Displacement provers may be manually or automatically operated.

      
      

   3. DEFINITION OF TERMS

Terms used in this chapter are defined below.

A prover pass is one movement of the displacer between the detectors in a prover.

A prover round trip refers to the forward and reverse passes in a bidirectional prover.

A prover run is equivalent to a prover pass in a unidirec- tional prover, a round trip in a bidirectional prover, or a group of multiple passes.

A meter proof refers to the multiple prover runs for pur- poses of determining a MF.

Interpulse deviations refer to random variations between meter pulses when the meter is operated at a con- stant flow rate.

Interpulse spacing refers to the meter pulse width or space when the meter is operated at a constant flow rate.

Pulse rate modulation refers to a consistent variation in meter pulse spacing when the meter is operated at a constant flow rate.

Pulse stability (Ps) refers to the variations of time between meter pulses.

A proving counter is a device that counts the pulses from the meter during a proving run.