INSTITUTE OF PETROLEUM

PETROLEUM MEASUREMENT MANUAL

PART XMeter Proving

Section 1

Field Guide to Proving MetersWith a Pipe Prover

INSTITUTE OF PETROLEUMPETROLEUM MEASUREMENT MANUAL

PART XMeter Proving

SECTION IFIELD GUIDE TO PROVING METERS WITH A

PIPE PROVER

This volume supersedes the Tentative edition published bythe Institute of Petroleum in 1979

FEBRUARY 1989

Published on behalf of

THE INSTITUTE OF PETROLEUM, LONDON

by

JOHN WILEY & SONS

Chichester • New York - Brisbane - Toronto • Singapore

Copyright ;C; 1989 by The Institute of Petroleum, London

All rights reserved .

No part of this book may be reproduced by any means, ortransmitted, or translated into a machine languagewithout the written permission of the copyright holder .

Library of Congress Cataloging in Publication Data :(Revised for pt . 10, sec . 1)

Petroleum measurement manual .

Includes various editions of same vol .1 . Petroleum-Tables . 2. Gaging. 1. Institute of

Petroleum (Great Britain)TP691.P446 1983

665.5'0212

83-10492

ISBN 0 471 92313 3

British Library Cataloguing in Publication Data :

Petroleum measurement manual .Pt . 10 : Meter provingSection 1 : Field guide to proving meters with a pipeprover .1 . Petroleum products. Measurement, StandardsI . Institute of Petroleum665 .5'38'0287

ISBN 0 471 92313 3

Printed in Great Britain by Galliard (Printers) Ltd, Great Yarmouth

CONTENTS

v

Foreword

Acknowledgements

List of Symbols .

Glossary of Terms .

.

vii

viii

ix

x

11 Introduction

2 Basic Principles . . 2

2 .1 Ways of expressing a meter's performance 2

2.2 How meter performance varies . 3

2.3 Correction factors 4

3 Meters and Provers . 63 .1 Pulse-generating meters

. 6

3.2 Sources of error in operating meters . 6

3 .3 Pulse interpolation

. 7

3.4 Conventional pipe provers . 8

3 .5 Compact pipe provers . 10

3 .6 Sources of error in operating pipe provers 11

3.7 Metering installations 12

4 Safety Requirements . 13

4 .1 General procedures 13

4.2 Permits . 13

4 .3 Mechanical safety 134.4 Electrical safety . 154.5 Fire precautions . . 16

4 .6 Miscellaneous safety precautions . 16

4.7 Safety records .

. 17

5 Operating a Pipe Prover 18

5 .1 Setting up a mobile prover 185.2 Warming up dedicated and mobile provers 18

5.3 Periodical checks of factors affecting accuracy 19

5.4 The actual proving operation . . 19

5 .5 Preliminary assessment of the results . 19

5 .6 Fault finding . 20

vi CONTENTS

6 Calculating and Reporting the Results of Proving 21

6 .1 Guidelines for rounding off figures in calculations 21

6.2 Method of calculating corrected volume of prover . 21

6.3 Method of calculating K-factor or one-pulse volume when pressure and temperature differ 21

6.4 Specimen calculation for a conventional unidirectional prover 22

6.5 Method of calculating K-factor or one-pulse volume when pressure and temperature

differences are negligible .

. 23

6.6 The pressure-compensated K-factor

. 23

6.7 Reporting the results of proving

. 23

6.8 Meter performance curves and control charts 23

7 Calculating Meter Throughput 25

7.1 Method based on K-factor or one-pulse volume 25

7.2 Specimen calculation, using Equation 14 . 26

7.3 Method based on meter factor . 26

7.4 Specimen calculation, using Equations 16 and 17 26

7.5 Mass throughput 26

Figures 28

Appendix A The operation of pipe provers fitted with twin detectors . 38

Appendix B Methods of pulse interpolation 41

Appendix C Trouble-shooting guide for pipe prover operators 46

Appendix D Specimen meter proving certificate 48

Appendix E Summary of proving and throughput equations 49

Appendix F Current practice concerning the number of passes in a run 51

Measurement accuracy is essential in the sale, purchase and handling of petroleum products . It avoids disputesbetween buyer and seller and provides control over losses . Accurate measurement involves the use of standardequipment and procedures .

The Petroleum Measurement Committee of the Institute of Petroleum is responsible for the production andmaintenance of standards and guides covering the various aspects of static and dynamic measurement of petroleum .These are issued as separate Parts and Sections of the Institute's Petroleum Measurement Manual, which was firstpublished in 1952 .

Membership of the IP working panels includes experts from the oil industry, equipment manufacturers, cargosurveyors and government authorities. Liaison is maintained where appropriate with parallel working groups of theCommittee on Petroleum Measurement of the American Petroleum Institute, and is extended as necessary toembrace other organizations concerned with quantitative measurement in other countries and in other industries .

Users are invited to send comments, suggestions, or details of experience with this issue to :

The Secretary, Petroleum Measurement Committee,Institute of Petroleum,61 New Cavendish Street,London W1M 8AR,United Kingdom .

The Petroleum Measurement Manual is widely used by the petroleum industry and has received recognition inmany countries by consumers and the authorities . In order to promote their wide adoption internationally, it is thepolicy to submit selected standards through the British Standards Institution to Technical Committee 28Petroleum Products and Lubricants of the International Organization for Standardization (ISO) as potentialInternational Standards .

A full List of Parts and Sections of the Petroleum Measurement Manual (PMM) is available on request from theInstitute of Petroleum .

Note

The IP Petroleum Measurement Manual is recommended for general adoption, but must be read and interpretedin conjunction with weights and measures, safety and other regulations in force in a particular country in which it isto be applied. Such regulatory requirements shall have precedence over corresponding clauses in the Manual . TheInstitute disclaims responsibility for any personal injury, or loss or damage to property howsoever caused, arisingfrom the use or abuse of any Part or Section of the Manual .

Attention is also drawn to the fact that some of the equipment mentioned in the Manual is protected by patentsthroughout the world. The mention of any proprietary information in this Guide does not imply its endorsement bythe IP for any particular application ; neither does omission imply rejection .

FOREWORD

vii

ACKNOWLEDGEMENTS

The following members of the IP Petroleum Measurement Committee and its Sub-Committees have beenassociated with this part of the Petroleum Measurement Manual .

W. M. CarterK. ElderfieldR. C. GoldA. T . J . HaywardH. HepworthG. InglisP. A. M . JelffsF. JordanF. KellyR. MaurerJ. E. MillerT. M. NobleP. D. O'ConnellG. Paul-ClarkR. J . PetersM . PughW. C. PursleyK. StothardS. A. VijayJ. M . Waring

Caleb Brett Laboratories LtdFMA Group of CompaniesConsultantMoore, Barrett & Redwood LtdShell UK ExproICE Petrochemical Engineering LtdMoore, Barrett & Redwood LtdHM Customs & ExciseShell Research LtdFlow Calibration Services LtdConsultantBrooks InstrumentInstitute of PetroleumDepartment of EnergyDaniel Industries LtdBritish Pipeline Agency LtdNational Engineering LaboratoryJordan Kent Metering Systems LtdDepartment of EnergyICI plc

viii

LIST OF SYMBOLS

Cp ,

Correction factor for effect of pressure change on liquidCp , p

Cp, at pressure of proverCp , m

Cp , at pressure of meterCp ,

Correction factor for effect of pressure change on steelCp , p

Correction factor for expansion of prover steel due to pressureCt.

Correction factor for thermal expansion of liquidClip

Cl , at temperature of proverCt ,r

C„ at temperature of meterC1 ,

Correction factor for thermal expansion of steelCts ,

Correction factor for thermal expansion of steel of prover•

Internal diameter of prover•

Elastic modulus of prover barrelF

Meter factor•

K-factor of meter•

Nominal K-factorKp

Pressure-compensated K-factorM

Mass throughput during a delivery•

Number of pulses collected during a deliveryn

Number of pulses collected during a proving passn12 Number of pulses collected between Detectors 1 and 2 in a bidirectional provern21 Number of pulses collected between Detectors 2 and 1 in a bidirectional proverp

Either gauge pressure or the excess of pressure above 1 .013 25 bar (these two quantities are slightly different,but the effect of the difference between them on the volume of a liquid is negligible)

q

One-pulse volumeq„

Nominal one-pulse volumeR

Pulse interpolation divisor•

Standard deviationt

Temperature•

Observed volume, i .e. volume of oil at actual pressure and temperature of meter•

Base volume of prover at reference conditions, usually 15°C and 0 bar gauge•

Corrected volume of prover at its actual pressure and temperature•

Volume indicated by the meterV,

Standard volume, i .e. volume of oil reduced to standard reference conditionsV12

Volume between Detectors 1 and 2 in a bidirectional proverV21

Volume between Detectors 2 and 1 in a bidirectional proverw

Wall thickness of provera

Linear coefficient of thermal expansion (used here of steel)fi

Compressibility factor (used here of liquids)p

Density at actual pressure and temperature of meterp,

Standard density, i .e . density at standard reference conditions

ix

GLOSSARY OF TERMS

Base Volume-The calibrated volume of a pipe prover,proving tank or volumetric measure at standardconditions of temperature and pressure .

Batch-The set of consecutive proving runs that isdeemed to be necessary to derive both (1) a mean valueof meter factor or K-factor suitable for subsequent useand (2) a range of individual values that can be used asan indication of the repeatability of the measurements .

Block-and-Bleed Valve-A high-integrity valve withdouble seals and provision for detecting leakage pasteither seal . (Also known as a Double-Block-and-BleedValve .)

Calibrated Volume-The volume at a stated tempera-ture and pressure between the detectors in a pipeprover, or the volume of a proving tank betweenspecified `empty' and `full' levels. The calibratedvolume of a bidirectional prover is the sum of the twovolumes swept out between detectors during a roundtrip .

Cavitation-The release of vapour and/or dissolvedgas from a flowing liquid caused by a sudden drop inpressure, for example as a result of local high velocityat a constriction, or at the trailing edges of rotatingmeter blades .

Cyclic Distortion-Any periodic variation in the pulsefrequency generated by a meter . This may be caused bymechanical asymmetry within the meter or by theaddition of accessories such as temperature com-pensators. (See also Intra-rotational Linearity .)

Detectors-Sensing devices set at each end of thecalibrated volume of a pipe prover, and which aredirectly or indirectly actuated by the displacer .

Discrimination- The ability of a measuring instru-ment to respond to small changes in the value of theinput.

Displacement Meter A meter which operates bydividing the flowing liquid into discrete quantities andtotalizing them .

x

Displacer A generic term which can be applied eitherto a sphere or to a piston when it is used to sweep outthe calibrated volume of a pipe prover .

Flashing-A serious form of cavitation occurringwhen the local pressure at a point within the liquidcontained in a closed pipe falls below the saturatedvapour pressure of the liquid at the operatingtemperature .

Flying-Start-and-Stop-A proving technique in whichthe flow through the meter and the proving devicecontinues at the same flowrate throughout the provingprocess. (Compare Standing-Start-and-Stop .)

Four-way Valve-A high-integrity flow-reversingvalve used with most bidirectional provers .

Gating-- The initiation and cessation of pulse totaliz-ation in a counter, e.g. by prover detectors .

Intra-rotational Linearity--A quantitative measure ofthe degree of regularity of spacing between the pulsesduring one revolution of a meter, generally expressedas the range of variation of pulse spacing about themean, at the 95 per cent confidence level .

K-factor-The number of pulses generated by a meterwhile a unit of volume is passing through .

Launch/Receive Chamber An enlarged section at theends of the pipe prover in which the displacer restsbetween proving passes .

Meter Factor The ratio of the actual volume of liquidpassed through a meter to the volume indicated by it .

Oval-wheel Meter A displacement meter in which thedisplaced volumes are segregated by enmeshing ovalgears .

Pass-A single movement of a displacer between thetwo detectors .

Primary Measure-A portable volumetric standardwhich is directly calibrated against national standards .

Proving Tank A volumetric standard usually consist-ing of a cylindrical central portion with conical top andbottom, and a cylindrical neck graduated either inunits of volume or in steps corresponding to fractionsof a percentage of the tank volume .

Pulse Density A qualitative expression used todescribe the number of pulses generated by a meter fora given volume of throughput .

Pulse Interpolation-An electronic technique forenhancing the resolution of a gated pulse count .

Pulse Interpolation Divisor The ratio of the enhancedpulse frequency to the frequency of the pulsesgenerated by the meter, used in the phase-locked-loopsystem of pulse interpolation .

Resolution-A quantitative expression of the abilityof an indicating device to distinguish meaningfullybetween closely adjacent values of the quantityindicated .

Run-The set of consecutive passes that is, in anyparticular case, deemed to be necessary to derive asingle value of meter factor or K-factor suitable forreporting. (The meter factors and K-factors derivedfrom individual passes within a multi-pass run are notreportable .)

Sour liquid-A liquid, particularly crude oil, con-taining high proportions of sulphur compounds.

Spade-A plate inserted between pipe flanges for thepurpose of isolating a section of a pipework system .

Standard Reference Conditions-Conditions of tem-perature and pressure to which measurements arereferred for standardization . In the United Kingdom,these are 15°C and 1 .013 25 bar .

Standing-Start-and-Stop-A proving technique inwhich the flow through the meter and the provingdevice is started at the beginning and stopped at theend of the proving process . (Compare Flying-Start-and-Stop .)

Temperature Compensator-A mechanism attached toa meter to correct for the effect of temperature on the

GLOSSARY OF TERMS

xi

measured volume, or an electronic device serving thesame purpose .

Thermowell-A protective metal pocket which pro-trudes through the wall of a pipe or tank and holds thesensing element of a thermometer .

Totalizer A mechanical or electronic device forintegrating and displaying the volumetric throughputof a flowmeter.

Traceability The property of a measuring instrumentenabling the measurements made by it to be related tosome primary standard, generally a national orinternational standard, through an unbroken chain ofcomparative measurements involving secondary stan-dards, tertiary standards, etc.

Turbine Meter A meter which provides a pulsedoutput at a frequency proportional to the angularvelocity of a bladed rotor (which occupies virtually thefull bore of the pipe), which is itself proportional to thevolumetric flowrate of the liquid passing through themeter .

Volume Correction Factor-A factor, dependentupon the oil density, which corrects oil volumesto a standard reference temperature . (Note : Forcrude oil and most petroleum products such factorscan be obtained from the API-ASTM-IP PetroleumMeasurement Tables, Tables 54A and 54B, or thecorresponding computer sub-routines .)

Vortex-Shedding Meter A pulsed output flowmeter,having an internal bluff body, designed to generate anddetect vortices which are produced at a rate propor-tional to the flowrate passing through it .

Water Draw The term applied to the technique ofcalibrating a pipe prover by the displacement of liquid,normally water, from the prover into a volumetric orgravimetric tank .

Wetted Area-A term commonly applied to thatportion of the internal surface of a volumetric tank,which is in contact with the liquid at some stage duringa proving operation .

In the petroleum industry the term `proving' is used torefer to the calibration of flowmeters for crude oil andpetroleum products . All measuring instruments thathave to meet a reasonable standard of accuracy needcalibration--that is to say, a test or a series of tests hasto be performed in which readings obtained from theinstrument are compared with independent measure-ments of high accuracy. Petroleum meters are noexception : nearly all those used for the purpose ofselling or assessing taxes need proving at intervals, andwhen there is a large amount of money at stake they arelikely to be proved frequently .

The most usual way to prove a flowmeter is to pass aquantity of liquid through it into an accurate device formeasuring volume, known as a prover . With very smallmeters the proving device may be nothing more than asmall container whose volume is known accurately .There are, for instance, standard measuring vesselsthat can be used to prove the meters incorporated ingasoline pumps at roadside filling stations . If the pumpdial registers 10 .2 litres when enough gasoline has beendelivered to fill a ten-litre vessel, it is evident that themeter is over-reading by 2 per cent .

In a large metering installation, where a single metermay be passing tens or hundreds of litres per second,the situation is very much more complicated . Themeters themselves generally do not have dialsgraduated in units of volume like a gasoline pump, butinstead they may be designed to emit a series ofelectrical pulses. With meters of this type the purposeof proving is to determine the relationship between thenumber of pulses emitted and the volume passedthrough the metera relationship which varies frommeter to meter and depends upon flowrate, viscosityand temperature .

Another difficulty is that the flow through theselarge meters usually cannot be stopped and started atwill. Consequently, both the meters and their proverhave to be capable of being read simultaneously and, on the fly', that is, while liquid is passing through themat full flowrate . The position is complicated still furtherby the effect of thermal expansion and compressibilityon the oil volume, and that of thermal expansion and

1

INTRODUCTION

1

elastic distortion under pressure on the steel bodies ofthe prover and the meter .

This Guide is concerned with only one kind ofprover, the pipe prover, which is used widely wherelarge meters for crude oil and petroleum products haveto be proved to the highest possible standard ofaccuracy. In principle a pipe prover is simply a lengthof pipe whose internal volume has been determinedvery accurately, and having a well-fitted piston (or atightly fitting sphere acting like a piston) inside it, sothat the volume swept out by the piston or sphere canbe compared with the meter readout while a steadyflow of liquid is passing from the meter into the prover .In practice, however, many accessories have to beadded to the simple pipe-and-piston arrangement toproduce a prover that will work effectively andaccurately.

In this Guide, Chapter 2 deals with the principlesunderlying the subject, and explains the various factorswhich are used to express the results of proving ameter. If a newcomer to the subject should find parts ofChapter 2 difficult, this will only be because the subjectmatter is unfamiliar . His best course will be to readChapter 2 fairly quickly, then pass onto Chapters 3, 4and 5, and afterwards return to Chapter 2 for a secondreading before attempting Chapters 6 and 7 .

Chapter 3 is concerned with hardware . It brieflydescribes the two main types of meter that have to beproved, and then describes in more detail the mostusual types of pipe prover. Because it can be dangerousto use any equipment carelessly, in the petroleumindustry there are official safety regulations whichoperators are obliged to study and follow, and Chapter4 sets out some of the most widely adopted safety rulesaffecting pipe provers. Then Chapter 5 explains how tooperate a pipe prover. Finally, Chapters 6 and 7 dealwith the processing of data Chapter 6 with provingdata and Chapter 7 with the calculation of throughput .

Additional information is provided in a series ofappendices .

The design, installation and calibration of pipeprovers are covered in the PMM, Part X, MeterProving, Section 3 .