Manual of Petroleum Measurement Standards Chapter 5—Metering

Section 3—Measurement of Liquid

Hydrocarbons by Turbine Meters

FIFTH EDITION, SEPTEMBER 2005 REAFFIRMED: AUGUST 2014

Manual of Petroleum Measurement Standards Chapter 5—Metering

Section 3—Measurement of Liquid

Hydrocarbons by Turbine Meters

Measurement Coordination Department

FIFTH EDITION, SEPTEMBER 2005 REAFFIRMED: AUGUST 2014

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Copyright © 2005 American Petroleum Institute

FOREWORD

Chapter 5 of the API Manual of Petroleum Measurement Standards (API MPMS) pro- vides recommendations, based on best industry practice, for the custody transfer metering of liquid hydrocarbons. The various sections of this Chapter are intended to be used in conjunc- tion with API MPMS Chapter 6 to provide design criteria for custody transfer metering encountered in most aircraft, marine, pipeline, and terminal applications. The information contained in this chapter may also be applied to non-custody transfer metering.

The chapter deals with the principal types of meters currently in use: displacement meters, turbine meters and Coriolis meters. If other types of meters gain wide acceptance for the measurement of liquid hydrocarbon custody transfers, they will be included in subsequent sections of this chapter.

Nothing contained in any API publication is to be construed as granting any right, by impli- cation or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API stan- dard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually and updated quarterly by API, 1220 L Street, N.W., Washington, D.C. 20005.

Suggested revisions are invited and should be submitted to the Standards and Publications Department, API, 1220 L Street, NW, Washington, DC 20005, standards@api.org.

iii

CONTENTS

Page

1. INTRODUCTION. 1

2. SCOPE 1

3. FIELD OF APPLICATION 2

4. REFERENCED PUBLICATIONS 2

5. FLOW CONDITIONING 2

6. MINIMUM BACK PRESSURE TO PREVENT CAVITATION 2

7. METER PERFORMANCE 3

   1. Meter Factor 3

   2. Causes of Variations in Meter Factor 3

APPENDIX A FLOW CONDITIONING TECHNOLOGY WITHOUT STRAIGHTENING ELEMENTS 7

APPENDIX B SIGNAL GENERATION. 11

APPENDIX C RECOMMENDED PRACTICE FOR PROVING TURBINE

METERS AT MANUFACTURERS’ FACILITIES 13

Figures

1. Names of Typical Turbine Meter Parts 1

2. Example of Flow Conditioning Assembly with Tube Type

   Straightening Element 3

3. Effects of Cavitation on Rotor Speed 4

4. Turbine Meter Performance Characteristics 5

1. Piping Configuration in Which a Concentric Reducer Precedes

   the Meter Run (Ks = 0.75) 7

2. Piping Configuration in Which a Sweeping Elbow Precedes the

   Meter Run (Ks = 1.0) 8

3. Piping Configuration in Which Two Sweeping Elbows Precede the

   Meter Run (Ks = 1.25) 8

4. Piping Configuration in Which Two Sweeping Elbows at Right Angles

   Precede the Meter Run (Ks = unknown) 9

5. Piping Configuration in Which a Valve Precedes the Meter Run (Ks = 2.50) 9

Table

A-1 Values for L and L/D for Figures A-1 Through A-5 8

v

Chapter 5—Metering

Section 3—Measurement of Liquid Hydrocarbons by Turbine Meters

1. Introduction

   API MPMS Chapter 5.3, together with general consider- ations for measurement by meters in API MPMS Chapter 5.1, is intended to describe methods of obtaining accurate quan- tity measurements with turbine meters in liquid hydrocarbon service.

   A turbine meter is a flow-measuring device with a rotor that senses the velocity of flowing liquid in a closed conduit (see Figure 1). The flowing liquid causes the rotor to move with a tangential velocity proportional to the average stream velocity (which is true if the drag on the rotor—mechanical and viscous—is negligible). The average stream velocity is assumed to be proportional to the volumetric flow rate (which is true if the cross-sectional flow area through the rotor remains constant). The movement of the rotor can be detected

   mechanically, optically, or electrically and is registered. The volume that passes through the meter is determined by prov- ing against a known volume, as discussed in API MPMS Chapter 4.

   It is recognized that meters other than the types described in Chapter 5.3 are used to meter liquid hydrocarbons. This publication does not endorse or advocate the preferential use of turbine meters, nor does it intend to restrict the develop- ment of other types of meters. Those who use other types of meters may find sections of this chapter useful.

   
   

2. Scope

   This section of API MPMS Chapter 5 covers the unique installation requirements and performance characteristics of turbine meters in liquid-hydrocarbon service.

   
   

   
   

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   1

   2 CHAPTER 5—METERING

   
   

   
   

3. Field of Application

   The field of application of this section is all segments of the petroleum industry in which dynamic measurement of liq- uid hydrocarbons is required. This section does not apply to the measurement of two-phase fluids.

   
   

4. Referenced Publications

   The current editions of the following API MPMS Stan- dards contain information applicable to this chapter:

   API

   Manual of Petroleum Measurement Standards

   Chapter 4, “Proving Systems”

   Chapter 5.1, “General Considerations for Measurement by Meters”

   Chapter 5.4, “Accessory Equipment for Liquid Meters” Chapter 5.5, “Fidelity and Security of Flow Measurement

   Pulsed-Data Transmission Systems” Chapter 7, “Temperature”

   Chapter 8, “Sampling”

   Chapter 11, “Physical Properties Data”

   Chapter 12, “Calculation of Petroleum Quantities” Chapter 13, “Statistical Aspects of Measuring and

   Sampling”

   
   

5. Flow Conditioning

   1. The performance of turbine meters may be affected by swirl and non-uniform velocity profiles that are induced by upstream and downstream piping configurations, valves, pumps, fittings, joint misalignment, protruding gaskets, weld- ing projections, or other obstructions. Flow conditioning shall be used to overcome the adverse effects of swirl and non-uni- form velocity profiles on turbine meter performance.

   2. Flow conditioning requires the use of sufficient lengths of straight pipe or a combination of straight pipe and flow conditioning elements that are inserted in the meter run upstream (and downstream, if flow through the meter is bidi- rectional) of the turbine meter (see Figure 2).

   3. When only straight pipe is used, the liquid shear, or internal friction between the liquid and the pipe wall, shall be sufficient to accomplish the required flow conditioning. Appendix A should be referred to for guidance in applying the technique. Experience has shown that in many installa- tions (e.g., downstream of a simple elbow or Tee) a straight pipe length of 20 meter-bore diameters upstream of the meter and 5 meter-bore diameters downstream of the meter often provides effective flow conditioning.

   4. For severe swirl, such as generated by two close coupled elbows out-of-plane (i.e., non-symmetrical swirl) or by a header (i.e., dual symmetrical swirl), a straightening ele- ment (i.e., swirl breaker) type of flow conditioner is required. These types of swirl are slow to dissipate in straight pipe, often existing after 100+ diameters of straight pipe.

   5. A straightening element or swirl-breaker type of flow conditioner usually consists of a cluster of tubes, vanes, or equivalent devices that are inserted longitudinally in a sec- tion of straight pipe (see Figure 2). Straightening elements effectively assist flow conditioning by eliminating swirl. Straightening elements may also consist of a series of perfo- rated plates or wire-mesh screens, but these forms normally cause a larger pressure drop than do tubes or vanes.

   6. Proper design and construction of the straightening element is important to ensure that swirl is not generated by the straightening element since swirl negates the function of the flow conditioner. The following guidelines are recom- mended to avoid the generation of swirl:

      1. The cross-section should be as uniform and symmetrical as possible.

      2. The design and construction should be rugged enough to resist distortion or movement at high flow rates.

      3. The general internal construction should be clean and free from welding protrusions and other obstructions.

   7. Isolating type flow conditioners, which produce a swirl-free, uniform velocity profile, independent of upstream piping configurations, are typically more sophisti- cated, expensive and higher pressure drop than simple straightening element type flow conditioners. However, in certain installations, they provide a performance advantage and should be considered.

   8. Flanges and gaskets shall be internally aligned, and gaskets shall not protrude into the liquid stream. Meters and the adjoining straightening section shall be concentrically aligned.

5.3.6 Minimum Back Pressure to Prevent Cavitation

In the absence of a manufacturer’s recommendation, the numerical value of the minimum back pressure at the outlet of the meter may be calculated with the following expression, which has been commonly used. The calculated back pres- sure has proven to be adequate in most applications, and it may be conservative for some situations.

Pb = 2p + 1.25pe