Manual of PetroleumMeasurement StandardsChapter 6—Metering Assemblies

Section 1—Lease Automatic Custody Transfer (LACT) Systems

SECOND EDITION, MAY 1991

REAFFIRMED, MAY 2012

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

Manual of PetroleumMeasurement StandardsChapter 6—Metering Assemblies

Section 1—Lease Automatic Custody Transfer(LACT) Systems

Measurement Coordination

SECOND EDITION, MAY 1991

REAFFIRMED, MAY 2012

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

SPECIAL NOTES

1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERALNATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE,AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED.

2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS,MANUFACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN ANDEQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTHAND SAFETY RISKS AND PRECAUTIONS NOR UNDERTAKING THEIR OBLIGA­TIONS UNDER LOCAL, STATE, OR FEDERAL LAWS.

3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPERPRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI­TIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTUREROR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

4. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED ASGRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THEMANUFACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCTCOVERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINEDIN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINSTLIABILITY FOR INFRINGEMENT OF LETTERS PATENT.

5. GENERALLY, API STANDARDS ARE REVIEWED AND REVISED, REAF­FIRMED, OR WITHDRAWN AT LEAST EVERY FIVE. YEARS. SOMETIMES AONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THISREVIEW CYCLE. THIS PUBLICATION WILL NO LONGER BE IN EFFECT AS ANOPERATIVE API STANDARD FIVE YEARS AFTER ITS PUBLICATION DATE OR,WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. THESTATUS OF THE PUBLICATION CAN BE ASCERTAINED FROM THE APIAUTHORING DEPARTMENT (TELEPHONE 202 682-8000). A CATALOG OF APIPUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATEDQUARTERLY BY API, 1220 L STREET, N.W., WASHINGTON, D.C. 20005.

Copyright© 1991 American Petroleum Institute

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

FOREWORD

This publication covers the design, installation, calibration~ and operation of leaseautomatic custody transfer (LACT) systems.

API publications may be used by anyone desiring to do so. Every effort has been madeby 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 thispublication and hereby expressly disclaims any liability or responsibility for loss or damageresulting from its use or for the violation of any federal, state, or municipal regulation withwhich this publication may conflict.

Suggested revisions are invited and should be submitted to the director of the Measure­ment Coordination Department, American Petroleum Institute, 1220 L Street, N.W.,Washington, D.C. 20005.

iii

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

CONTENTS

Page

SECTION I-LEASE AUTOMATIC CUSTODY TRANSFER(LACT) SYSTEMS

6.1.1 Introduction 16.1.1.1 Compliance 16.1.1.2 Future Developments ,' 1

6.1.2 Scope ~ _" 16.1.3 Field of Application " , .. 16.1.4 Referenced Publications 16.1.5 Requirements for All LACT Systems 1

6.1.5.1 Sampling _ : : 26.1.5.2 Maintaining Allowables 26.1.5.3 Monitoring Quality 3

6.1.6 Displacement and Turbine Meter LACT Systems .36.1.6.1 Installation .36.1.6.2 Specific Requirements .36.1.6.3 Facilities and Procedures for Proving Displacement

and Turbine Meters .36.1.6.4 Displacement and Turbine Meter System Operation 56.1.6.5 Nonmerchantable Oil Interruption 5

FigureI-Typical Displacement or Turbine Meter

LACT Unit Schematic Diagram .4

v

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

Chapter 6-Metering Assemblies

SECTION 1-LEASE AUTOMATIC CUSTODY TRANSFER (LACT) SYSTEMS

6.1.1 Introduction

This publication has been prepared as a guide for thedesign, installation, calibration, and operation ofa lease auto­matic custody transfer (LACT) system.

A LACT system is an arrangement of equipment designedfor the unattended custody transfer of liquid hydrocarbonsfrom producing leases to the transporting carrier. The systemmust determine net volume and quality, provide for fail-safeand tamperproof operation, and meet requirements of ac­curacy and dependability as agreed to by mutually concernedparties, such as the producer, the transporter, the royaltyowner, and federal, state, and municipal regulatorybodies.

6.1.1.1 COMPLIANCE

Compliance with the provisions ofthis standard may resultin an approach to accuracy or may establish safeguards thatare not necessary under all conditions. When not required,those portions ofthis standard not considered applicable maybe disregarded with the mutual agreement of all parties con­cerned. The compulsory verb form «shall," while not neces­sarily binding for all conditions, has been used when adeviation from the standard is likely to adversely affect thesatisfactory operation of a system that is designed for op­timum operation under typical producing conditions.

6.1.1.2 FUTURE DEVELOPMENTS

Although this standard presents the concurrence of theindustry on system requirements for lease automatic custodytransfer, it is not intended in any way to restrict futuredevelopments. Equipment now exists in the design or field­proving stages that may further improve the art of leaseautomatic custody transfer. The industry encourages suchdevelopments, and when concerned parties mutually agreeto use such systems or components, every effort should bemade to expedite their use and standardization.

6.1.2 Scope

This publication describes the metering function of aLACT unit and is intended to complement API SpecificationII N,Specificationfor Lease Automatic Custody Transfer(LACT) Equipment. LACT equipment includes a meter(either displacement or turbine), a proving system (eitherfixed or portable), devices for determining temperatureand pressure and for sampling the liquid, and a meansof determining nonmerchantable oil. Many of the aspects

of the metering function of a LACT unit are considered atlength in other parts of this manual and are referencedin 6.1.4.

6.1.3 Field of Application

The field of application of this publication is the unat­tended and automatic measurement by meter of hydrocarbonliquids produced in the field and transferred to a pipeline ineither a scheduled or a nonscheduled operation.

Note: The information contained in Chapter 6.7 should also be con­sidered when measuring viscous fluids by meter.

6.1.4 Referenced Publications

Many ofthe aspects of the metering function are discussedat length in other parts of this manual. Please refer to thefollowing chapters for more information.

APIManual of Petroleum Measurement Standards

Chapter 4-"Proving Systems"Chapter 5.1, "General Considerations forMeasurement by Meters"Chapter 5.2, "Measurement of LiquidHydrocarbons by Displacement Meters"Chapter 5.3, "Measurement of LiquidHydrocarbons by Turbine Meters"Chapter 6.7, "Metering Viscous Hydrocar­bons"Chapter 7-"Temperature Determination"Chapter 8-"Sampling"Chapter 8.2, "Automatic Sampling ofPetroleum and Petroleum Products"Chapter 9-"Density Determination"Chapter 1O-"Sediment and Water"Chapter 12.2, "Calculation of LiquidPetroleum Quantities Measured by Turbineor Displacement Meters"

Spec lIN Specification for Lease Automatic CustodyTransfer (LACT) Equipment

6.1.5 ReqUirements for All LACTSystems

The requirements for all LACT systems are as follows:

a. When hydrocarbon liquids are measured and trans­ferred, the fluid should be stable to permit subsequentstorage during transportation without abnormal evapora­tion losses.

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

2 CHAPTER 6-METERING ASSEMBLIES

b. During custody transfer, provisions shall be made fordetermining net standard volume. (See Chapter 12.2.)c. Temperature measurements, recordings, or correctionsapplicable to volumetric measurement shall be made in ac­cordance with Chapter 7.d. Temperature and pressure measurements (either recordedor indicated) shall be taken, and corrections applicable tovolumetric measurements shall be made in accordance withChapter 12.2. The method of performing temperature com­pensation is a matter of negotiation but should beaccomplished by use of volume-weighted temperature­averaging devices or temperature compensators for op­timum accuracy.e. A representative sample of transferred oil for determiningdensity (API gravity), sediment and water content, and anyother physical properties required shall be obtained. (SeeChapter 8, Chapter 9, and Chapter 10.)f. The merchantability of hydrocarbon liquids should beestablished when they are transferred; that is, when theliquids are within a specified density (API gravity) range,do not contain more than a specified sediment and waterpercentage, are at an acceptable temperature, and are ofan acceptable Reid vapor pressure. A means shall beprovided to stop the flow of oil to the carriers system andto the sampling system if the oil becomes unmerchant­able.g. A means should be provided to control flow rates, periodsof flow, and net quantities of oil delivered into the carrierssystem.h. A means shall be provided to stop the flow of oil into thecarriers system at or before completion of delivery of theleases assigned allowable capacity.i. The control and recording system shall include fail-safecomponents to prevent mismeasurement or hazardous operat­ing conditions in the event of a power or system functionalfailure of any of the system's components required for theLACT.j. All components of the system that require periodiccalibration and/or inspection should be accessible forinspection by all parties involved in the custody transfertransaction. Adjustment, repair, or replacement will beperformed by those responsible for the operation of thesystem. The design of the system shall provide a meansfor readily detecting leakage throughout the system, forexample, double-block and bleed-type valves, sightdrains, or pressure instruments.k. The piping system shall not have connections or bypassesthat would permit liquids to be transferred without measure­ment and shall be designed or equipped so that a reverse flowof liquid through the measuring device cannot occur.1. A means shall be provided to lock or seal components thataffect control or indicate measurement of quantity or quality.Unless this requirement has been specifically waived, such

components shall be unlocked or unsealed only after priornotice to and consent of the parties concerned.m. System malfunctions shall be anticipated, anddeliveries that could occur during such periods shall beestimated. This requirement may be met by independentgross fluid delivery-recording systems, that is, by usinga dual-head meter and temperature recorder, by using ameter in series, or by recording temperature or pressureor other instruments that indicate periods of flow. Ininstallations where such apparatus is not used, prioragreement should be established for calculating or es­timating procedures that will be followed in instances ofmeasurement system malfunction.n. Sediment and water content and density (API gravity)measurements shall be made from composite samples ob­tained by automatic samplers of acceptable design. Samplersshall be installed in accordance with Chapter 8.2.

6.1.5.1 SAMPLING

In most cases, accounting for a crude oil run is determinedon the basis of net standaFd volume, which includes correc­tions for meter factor, temperature, pressure, and sedimentand water content. Therefore, the composite sample accumu­lated in a run period and any portion used for the determina­tion of density (API gravity) and sediment and water contentmust represent all crude oil delivered during that run period.When density (API gravity) and sediment and water contentare based on a sample from the composite sample of the run,the procedures used must ensure that this secondary sampleis representative of the composite sample. (See Chapter 8 foradditional details.) The sampling should be proportioned tothe flow rate through the meter.

6.1.5.2 MAINTAINING ALLOWABLES

When regulatory agencies apply production allowables,runs from the LACT system shall conform to but shall notexceed these allowances. Automatic means shall be used toaccomplish this requirement. The system must be fail-safe,tamperproof, and sealed so that neither the producer nor thecarrier can change the arrangement without the consentand/or knowledge of the other party.

System devices must be capable ofbeing pre-set and verifiedfor a predetermined volume that will approach but not exceedthe lease allowable. When the predetermined volume hasbeen reached, the arrangement used mllst prevent anyfurther movement of oil from the lease until it is manuallyreset. The arrangement must be adjustable so that chan­ges in production allowables are accommodated.Registers and counters should be readily visible so thatoil deliveries can be checked at any time.

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

SECTION 1-LEASE AUTOMATIC CUSTODY TRANSFER (LACT) SYSTEMS 3

6.1.5.3 MONITORING QUALITY

Means shall be provided to prevent water-contaminatedoil or slugs of water from entering a carrier's system. Theparties shall agree on the maximum permissible sedimentand water content of the crude oil. One such satisfactoryautomatic device which detects water is an instrument thatmeasures capacitance (dielectric constant of the liquidstream). This device should be installed in a vertical riserin the piping before the meter and should be used to actuatecontrols so that water-contaminated oil is not delivered tothe pipeline. A time-delay element may be incorporatedinto the monitor system.

6.1.6 Displacement and Turbine MeterLACT Systems

Practical methods for obtaining accurate measurements oflease oil runs, using either a displacement or a turbine meter,with equipment arranged to meet the requirements defined inthis chapter are outlined in 6.1.6.1 through 6.1.6.5. (SeeChapters 5.1, 5.2, and 5.3 for details on meter selection.)

6.1.6.1 INSTALLATION

LACT systems that use meters shall be designed in accord­ance with applicable industry codes or standards. Each itemessential to quantity and quality control shall be located sothat it will consistently perform its function.

Figure 1is a schematic flow diagram showing the principalcomponents ofa meter-equippedLACTunit. All items shownmay be used in an installation, but if certain components arenot required for the integrity of quantity and quality control,they may be omitted.

6.1.6.2 SPECIFIC REQUIREMENTS

The design and function of a LACT system are matters ofnegotiation. These negotiations determine which of the re­quirements are applicable. However, when the quantity orquality measurement or control depends on compliance withthe requirement, the specific conditions detailed in 6.1.1.1shall apply.

LACT systems that use meters shall maintain fluid pres­sure throughout the measurement system in excess of theproduct bubble-point pressure by an amount sufficient toprevent the formation ofvapor. Ifvapor is introduced into themeasurement system, the measurement will be inaccurate.When vapor removers are specified, they shall be sized forreleasing vapor to the atmosphere or to a suitable vaporrecovery system at rates equal to or greater than the normalflow rates ofthe liquid. Vapor outlet lines from removers shallcomply with safety standards. When the design of storagefacilities ensures fluid-packed line conditions leading to themeter, vapor removers may not be required. Either the

producer or the carrier may require the installation of adielectric or capacitance instrument, more commonlyreferred to as a water monitor. This monitor will automat­ically stop or divert flow before liquid is delivered to themeter when the carrier's specifications are not met. The watermonitor shall be located upstream from the meter and shallbe in operation at all times during delivery. The carrier shallspecify the maximum water setting of the instrument.

Meters shall be operated within the manufacturer's recom­mended flow rates and at a rate as near as possible to the rateat the time of the meter proving when the meter factor wasobtained. A back-pressure control valve is necessary to main­tain a constant flow rate and pressure independent ofdownstream conditions. Meters shall not be subjected topressure pulsations, flow rate surges and shall not be sub­jected to shock pressures caused by quick-closing valves.When temperature compensators with density selectors areused, they shall be adjusted for the density (API gravity) ofthe metered liquids. When temperature variations result inmismeasurement, temperature stabilization and monitoringmay be required. The carrier may require that a pressure surgeandlor suction tank be installed upstream from the LACTsystem to ensure that fluid-packed line conditions lead to themeter and to protect the meter from flow rate surges."Weathering" the crude oil, expansion chambers, and othersuch requirements may be required by the carrier to preventunstable metering conditions.

When system pressure requires the use of the oil compres­sibility factor and pressure may not remain constant, flowweighted pressure-averaging devices or pressure recordersmay be required. (See Chapter 12.2 for computing Cpl.)When required by operating conditions that change suffi­ciently to alter the meter factor beyond acceptable limits,such as temperature variations and the associat.ed viscositychanges, the oil temperature shall be maintained reasonab­ly constant and shall be approximately the same as theproving temperature.

6.1.6.3 FACILITIES AND PROCEDURES FORPROVING DISPLACEMENT ANDTURBINE METERS

Proving procedures for each LACT location should beagreed to by the parties concerned. (See Chapter 4.) Copiesof the agreement should be furnished to both the operatingpersonnel and proving personnel. Such procedures shouldinclude:

a. A step-by-step method to be followed at the location.b. A procedure for checking valves for leakage before andduring the proving operation.c. A preliminary inspection or operation of the provingequipment.d. The locations and specifications of seals to be inspectedat time of proving.

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

4 CHAPTER 6-METERING ASSEMBLIES

~Deliverytank

Topipeline

1015

Proversystem

To wet oilstorage ordehydrationfacility

4, 4A, 48

e~16

.., '1:7, -J(

J .. ~TI

I

I

I

I

I

I

I13 lit-------------------~~

1. Charging pump and motor2. Sampler3. Sample container and circulation pump4. Strainer

a. Integral air/gas eliminator (optional)b. Separate air/gas eliminator (optional)

5. Water monitor probeNote: The monitor chassis may be mountedwith the electrical control systemor directly on the monitor probe.

6. Diverter valve7. Wet oil back-pressure valve (optional)8. Custody transfer meter and accessories9. Block valve

10. Back-pressure valveNote: Locate the back-pressure valve upstream ofthe prover loop for tank provers.

11. Power panel12. Control equipment (for example, water monitor,

allowable counter, and shutdown system)13. Recirculation pump (optional)14. Check valve15. Double-block and bleed-valve16. Pressure measurement device17. Temperature measurement device18. Level control-start19. Level control-stop20. Low level control (optional)

Note: This simplified diagram indicates primary components necessary for typical LACT units but is not in­tended to indicate preferred locations.

Figure 1-Typical Displacement or Turbine Meter LACT Unit Schematic Diagram

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

SECTION 1-LEASE AUTOMATIC CUSTODY TRANSFER (LACT) SYSTEMS 5

e. The notification and witnessing required when seals, arebroken for maintenance purposes.f. The location, type, scale division, and methods for readingthe thermometers used in the proving process.g. The location, type, scale division, and methods of readingpressure instruments used in proving.h. The specifications of a proving run, such as:

1. The number of times the prover tank should be filled.2. Specifying the number of runs for a pipe prover.3. Defining a minimum time and/or volume if themaster-meter method is used.

i. The repeatability criteria for runs to be used and thenumber of runs to be averaged to obtain a new meter factor.j. The normal period between required meter provings. Theperiod between provings may be established either on athroughput or on an elapsed-time basis. This period may beamended based on individual location meter performancerecords.k. The normal date and time of provings or the notice to begiven to witnessing parties when a proving schedule is estab­lished.1. The witnessing required for provings.m. The standard of consistency desired between meter fac­tors obtained from consecutive provings.n. The procedure to be followed when the desired consisten­cy is not obtained, either in the results of consecutive runsduring an attempted proving or in meter factors obtained fromconsecutive provings.o. The frequency of inspection or the frequency and methodofrecalibration or calibration verification ofthe basic provingdevice.p. The content for the forms to be used to record meter-prov­ing data, complete with sample calculations and references totables used for correction factors and conversions.

The proving record for each meter shall be kept on file forat least the same period as the meter tickets to which it appliesor for a period mutually agreed to by the parties concerned.At least one copy of each official proving record should besupplied to each party concerned.

6.1.6.4 DISPLACEMENT AND TURBINE METERSYSTEM OPERATION

The operation of a meter system will vary depending onthe characteristics of the liquid, the design of the installation,the type of pipeline facility connection, and the operatingschedule of the pipeline. To be successful, a system mustsatisfy the requirements of the producer and the carrier.Before an installation is completed, operating sequencesshould be checked to ensure that the requirements of allinterested parties have been met. The following cases aretypical, and the items to be checked are suggested as guidesfor system studies.

6.1.6.4.1 Case A-Normal Delivery toa GravityFlow Pipeline in NonscheduledOperation

a. When the liquid level in the delivery tank reaches thenormal high working level, the charge pump starts and thecontrol valve opens to the pipeline, admitting flow throughthe meter.b. When the valve reaches its open-to-pipeline position, theautomatic samplerbegins sampling as soon as the meter startsturning.,c. Under nonnal conditions, delivery to the pipeline con­tinues until the liquid level reaches the normal low-levelposition.d. The baCk-pressure valve then closes the pipeline outlet;the charge pump stops, and the automatic sampler stopssampling when the meter stops turning.

6.1.6.4.2 Case B-Normal Delivery to a Pres­surized Pipeline in NonscheduledOperation

a. When the liquid level in the delivery tank reaches thenonnal high working level, the charge pump starts and thecontrol valve opens to the pipeline, admitting flow throughthe meter.b. When the valve reaches its open-to-pipeline position, thepipeline shipping pump starts and the automatic samplerbegins sampling as soon as the meter starts turning.c. Under normal conditions, delivery to the pipeline con­tinues until the liquid level reaches the normal low-levelposition.d. The charge pump stops, the back-pressure valve closes thepipeline outlet, and the pipeline shipping pump is shut down.

6.1.6.4.3 Case e-Normal Delivery to a Pipelinein Scheduled Operation

Some pipeline systems are operated on a schedulewhereby it is desirable to admit oil only during a certaininterval. For this arrangement, the operation sequence shallbe the same as for nonscheduled delivery (6.1.6.4.1 and6.1.6.4.2) except that a time-interval controller shall be addedto the circuit that overrides the normal high working levelcontrol.

6.1.6.5 NONMERCHANTABLE OIL INTERRUPTION

In each of the three cases, the following procedures shallbe followed:

a. After delivery to the pipeline has begun, if nonmerchant­able oil flows continuously past the water monitor for apredetermined time interval, the charge pump is automat­ically stopped unless the pump is required to circulate oil fortreatment.

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

6 CHAPTER 6--METERING ASSEMBLIES

b. The valve closes, stopping flow to the pipeline.

c. The automatic sampler remains energized in case of inad­vertent flow through the meter.

d. The controls lock out the transfer ofoil to the pipeline untilthe nonmerchantable oil has been treated to meet specifica­tions. The LACT unit can be designed to restart automaticallyafter a period of recirculation.

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

1-170Q--5/91-8.5C (1E) U1-<:l1102-9/94-2C (3E) U

PO-<:l12Q(}-11/96-1C (3E) UPO-012Q(}-12197-1C (4E)

For Com

mittee U

se O

nly - D

o Not

Distrib

ute

Additional copies available from API Publications and Distribution:(202) 682-8375

Information about API Publications, Programs and Servicesis available on the World Wide Web at: http://www.apLorg

AmericanPetroleumInstitute

1220 L Street, Northwest

Washington, D.C. 20005-4070

202-682-8000 Order No. H30121

For Com

mittee U

se O

nly - D

o Not

Distrib

ute