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  • 1. Manual of Petroleum Measurement Standards Chapter 3-Tank Gauging Section 1B-Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by Automatic Tank Gauging SECOND EDITION, JUNE 2001 American Petroleum Institute Helping You Get The Job Done Right?COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 2. COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 3. Manual of Petroleum Measurement Standards Chapter 3-Tank Gauging Section 1B-Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by AutomaticTank Gauging Measurement Coordination Department SECOND EDITION, JUNE 2001 American Petroleum Institute Helping You Get The Job Done Right?COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 4. SPECIAL NOTES A P I publications necessarily address problems a general nature. With respect to partic- of ular circumstances, local, state, and federal laws and regulations be reviewed. should A P I is not undertaking to meet the duties of employers, manufacturers, or suppliers to warn and properly t a n and equip their employees, and others exposed, concerning health ri and safety risks and precautions, nor undertaking their obligations under local, state, or fed- eral laws. Information concerning safety and health risks and proper precautions with respect to par- ticular materials and conditions should be obtained from the employer, the manufacturer or supplier of that material, or the material safety data sheet. Nothing contained in any A P I publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, of any method, apparatus, or prod- or use uct covered by letters patent. Neither should anything contained in the publication be con- strued as insuring anyone against liability for infringement of letters patent. Generally,A P I standards are reviewed and revised,e a f h e d , or withdrawn at least every r five years. Sometimesa one-time extension up to two years will be added to review of this cycle. This publication will no longer be effect five years after its publication date as an in operative A P I standard or, where an extension has been granted, upon republication. Status of the publication can ascertained from the P I Measurement Coordination Department be A [telephone (202) 682-8000].A catalog of A P I publications and materials is published annu- ally and updated quarterly by 1220 L Street, N.W., Washington, D.C.20005. API, This document was produced underP I standardization procedures that ensure appropri- A ate notification and participation in the developmental process and is designated asPan A I standard. Questions concerning the interpretation of the content of this standard or com- ments and questions concerning the procedures under which this standard was developed should be directed in writing to the standardization manager, 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 gen- eral manager. A P I standards are published to facilitate the broad availabilityproven, sound engineer- of ing and operating practices. These standards not intended to obviate the need for apply- are ingsoundengineeringjudgmentregardingwhenandwherethesestandardsshould be utilized. The formulation and publication of A P I standards is not intended in any way to inhibit anyone from using other practices. any Any manufacturer marking equipment or materials in conformance with the marking requirements of anA P I standard is solely responsible for complying with all the applicable requirements of that standard.A P I does not represent, warrant, or guarantee that such prod- ucts do in fact conform to the applicable A P I standard. All rights reserved. No part o this work may be reproduced, stored in a f retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, otherwise, or without prior written permission fiom the publisher. Contact the Publisher, API Publishing Services, 1220 L Street, N.W, Washington,D.C. 20005. Copyright O 2001 American Petroleum InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 5. FOREWORD do so. API publications may be used by anyone desiring to Every effort has been made by the Institute to assure the accuracy and reliability data contained them; however, the of the in Institute makes no representation, warranty, or guaranteein connection withthis publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting this from its use or for the violation of any federal, state, or municipal regulation with which publication may conflict. Suggested revisions are invited and should be submitted to the standardization manager, American Petroleum Institute,1220L Street, N.W., Washington, D.C. 20005. ... 111COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 6. COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 7. CONTENTS Page 3.1B.1 SCOPE ........................................................... 1 3.1B.2REFERENCEDPUBLICATIONS ..................................... 1 3.1B.3 DEFINITIONS ..................................................... 1 3.1B.4 GENERAL ........................................................ 2 3.1B.4.1 Safety Precautions .............................................. 2 3.1B.4.2GeneralPrecautions ............................................ 2 3.1B.4.3Accuracy ..................................................... 3 3.1B.4.4 Use of ATGs For Custody Transfer or Inventory Control............... 3 3.1B.4.5 Installation ofATGs ............................................ 4 3.1B.4.6RemoteReadout ............................................... 9 3.1B.5 GENERAL PROCEDURES FOR INITIAL SETTING AND INITIAL THE FIELD ............................. VERIFICATION OF ATGs IN 9 3.1B.5.1InitialRequirements ............................................ 9 3.1B.5.2 Reference Manual Level Measurement Procedure .................... 9 3.1B.5.3 Reference Measurement Tape and Weight Certification................ 9 3.1B.5.4 Effect of Weather .............................................. 9 3.1B.5.5 ATG Technology- Specific Considerations ......................... 9 3.1B.5.6 Application-Specific Considerations .............................. 9 3.1B.6 INITIAL SETTING OF ATGs IN FIELD .......................... THE 10 3.1B.6.1 Ullage-Based ATGs ............................................ 10 3.1B.6.2Innage-BasedATGs ........................................... 10 3.1B.7 INITIALVERIFICATION .......................................... 10 3.1B.7.1Introduction .................................................. 10 3.1B.7.2 Verification Conditions ......................................... 11 3.1B.7.3 Initial Verification Procedures .................................... 11 3.1B.8RECORDKEEPING ............................................... 12 3.1B.9 SUBSEQUENT VERIFICATION OF ATGs FOR CUSTODY TRANSFER OR INVENTORY CONTROL....................................... 12 3.1B.9.1General ..................................................... 12 3.1B.9.2 Frequency of Subsequent Verification ............................. 12 3.1B.9.3 Procedure for Subsequent Verification............................. 13 3.1B.9.4 Tolerance for Subsequent Verification............................. 13 3.1B.10 DATA COMMUNICATION AND RECEIVING ........................ 13 VCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 8. Page APPENDIXA SAFETY PRECAUTIONS:PHYSICALCHARACTERISTICS AND FIRE CONSIDERATIONS ............................. 15 APPENDIXBACCURACY REQUIREMENTS FORATGs ................... 17 Figures 1 Example of an ATG (Contact or Non-contact) Mounted on aStill Pipe SupportedbyTankBottom ............................................ 5 2 Example of an ATG (Contact or Non-contact) Supported by a Bracket Hinged to the Lower Tank Shell Plate ................................... 6 3 Example Installationof Top-Mounted ATGs on Fixed Roof Tanks Without Still Pipe ................................................... 7 4 Example Installationof Top-Mounted Innage-ATG on Fixed Roof or Floating Roof Tanks Without Still .................................. Pipe 8 viCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 9. Manual of Petroleum Measurement Standards Chapter 3-Tank Gauging Section 1B-Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by Automatic Tank Gauging 3.1B.l Scope Chapter 3.6 “MeasurementofLiquidHydrocarbons by Hybrid Tank Measurement Systems” This standard covers level measurement of liquid hydro- carbonsstationary, in aboveground, atmosphericstorage Chapter 7 “Temperature Determination” tanks using automatictank gauges (ATGs). The standard dis- cusses automatic tank gauging in general, accuracy, installa- Chapter 8.1 “Manual Sampling of Petroleumand tion,commissioning,calibrationandverificationofATGs Petroleum Products” that measure either innage or ullage. It covers both intrusive and non-intrusive ATGs used for either custody transfer or Chapter 8.2 “Automatic Sampling of Petroleum and inventory control. The standard also covers the requirements Petroleum Products” for data collection, transmission and receiving. Chapter 9.1 “HydrometerTestMethod forDensity, This standard does not cover the following: RelativeDensity(SpecificGravity),or a.Hydrocarbonshaving aReidvaporpressureabove 15 APIGravityofCrudePetroleumand pounds per square inch absolute kPa). (100 Liquid Petroleum Products” b. Measurement of weight or mass with ATG equipment. This is covered in Chapter and Chapter 16.2 of the Man- 3.6 Chapter 12.1 “Calculation of Static Petroleum Quanti- ual o Petroleum Measurement Standards. f ties,Part 1, UprightCylindricalTanks c. Measurement of level in underground tanks or in pressur- and Marine Vessels” ized tanks storing liquid hydrocarbons. Chapter 16.2 “Mass Measurement of Liquid Hydro- This is covered d. Conversion of tank level to liquid volume. carbons in Vertical Cylindrical Storage in Chapter 12.1 of the Manual o Petroleum Measurement f Tanks by Hydrostatic Tank Gauging” Standards. e. Measurement of temperature, sampling, density and sedi- Chapter 19.2 “Evaporative on Loss Floating roof (S ment and water &W), which are discussed in Chapters 7- tanks” 10 of the Manual o Petroleum Measurement Standards. f RP 500 Recommended Practice for ClassiJication o f Safety and material compatibility precautions should be Locations for Electrical Installationsat Petro- taken when using ATG equipment. Manufacturers’ recom- leum Facilities mendationsontheuseandinstallationoftheequipment should be followed. Users should comply with applicable dl RP 2003 ProtectionAgainst Ignition Arising Out of codes and regulations, API Standards and NFPA National 70 State, Lightning and Stray Currents Electric Code. International Organization for Standardization 3.1B.2 Referenced Publications IS0 4266 PetroleumLiquid and Petroleum Prod- API ucts-Measurement o Temperature f and by Level in Storage Tanks Automatic Meth- (MPMS) Manual o Petroleum Measurement Standards f ods. Part 1: Measurement o Level f in Atmospheric Tanks Chapter 1 “Vocabulary” Chapter 2 “Tank Calibration” 3.1B.3 Definitions Chapter 3.1A “Standard Practice for Manual Gauging Refer to MPMS, Chapter 1, “Vocabulary”, which lists dl of Petroleum and Petroleum Products in of the terms and definitions relating to measurement used in Stationary Tanks” API standards on petroleum products and lubricants. 1COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 10. 2 API MANUALOF PETROLEUM MEASUREMENT STANDARDS, CHAPTER 3 " T A N K GAUGING 3.1B.4 General 3.1B.4.1.5Sealing This section applies to all types ATGs. of All ATGs shall be sealed to withstand the vapor pressure of liquid in thetank. (SI) This standard presents both Metric units and US Cus- tomary units and may be implemented in either system of 3.1B.4.1.6ManualGauging units. The presentation of both units are for convenience of the user and are not necessarily exact conversions. The units Manual tank gauging can be associated with exposure to of implementation are typically determined by contract, regu- immediately dangerous chemicals. When an is checked ATG latory requirement, the manufacturer or the users calibration or calibrated by manual gauging, the manual gauging should program. Once a systemof units is chosen for a given appli- be done in accordance with MPMS Chapter 3.1A. cation, it is not the intent this standard to allow arbitrarily of this changing units within standard. 3.1B.4.1.7 Speed of Response Safety precautions are listed separately from general pre- ATGs should have sufficient dynamic response to track cautions that affect accuracy or performance. the liquid level during maximum rates oftankfilling or emptying. Note: The following precautions are given addition to any existing in federal, state, orlocalregulations(forexample,theOccupational Safety and Health Administration) that govern practices described in 3.1B.4.2GENERALPRECAUTIONS this standard. Users of standard should be familiar with appli- this all The following general measurement precautions affect the cable safety and health regulations. accuracy and performance of all types of ATGs. They should be observed where they are applicable. 3.1B.4.1SAFETYPRECAUTIONS This These safety precautions represent good practice. list 3.1B.4.2.1 TankTemperatures is not necessarily complete or comprehensive. Refer also to Tank temperature should be measured at the same time the the safety precautions described in API Recommended Prac- tank level is measured. The temperature should be repre- tank tice 2003. sentative of the tank contents in accordance with MPMS Chapter 7. 3.1B.4.1. I Tank Entry 3.1B.4.2.2RecordingLevels Before a t n that once contained hydrocarbon liquids, ak Level measurements should be recorded as soon as they tank vapors or toxic material is entered, all lines to the shall are taken, unless the remote readout equipmentof the ATG be disconnected or blinded anda gas-free certificate shall be system automatically records the levels periodically. obtained. 3.1B.4.2.3 Opening and Closing Gauges 3.1B.4.1.2HazardousAreas The same procedures should be used to measure a tank All regulations covering entry into hazardous areas shall be level before the product transfer (opening gauge) and after the observed. Electric equipment for use in electrically classified product transfer (closing gauge). areas shall meet the area classification. Refer to the following API Recommended Practices s ) : W 3.1B.4.2.4Compatibility a. RP500. All parts of the ATG in contact with the product or its vapor should be compatible with the product to avoid both b. RP 2003. product contamination andATG corrosion. TheATG should be designed to meet the operating conditions. 3.1B.4.1.3Maintenance 3.1B.4.2.5 Settling Time All ATG equipment shall be maintained in safe operating condition and manufacturers instructions shall be complied Refer to MPMS Chapter for guidance settling time 3.1A on with. before tank levels are measured. 3.1B.4.2.6 ATG Security 3.1B.4.1.4Environment ATGs shouldprovidesecuritytopreventunauthorized All ATGs shall be capable of withstanding the pressure, adjustmentortampering. ATGs usedincustodytransfer temperature and other environmental conditions likely to be applications should provide facilities to allow sealing for cali- encountered in service. bration adjustment.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 11. SECTION 1B-LEVEL MEASUREMENT LIQUIDHYDROCARBONS STATIONARY TANKS AUTOMATIC OF IN BY TANKGAUGING 3 3.1B.4.3ACCURACY ual tank gauging measurements. It is imperative that the user understand these limitations, which are addressed in more 3.1B.4.3.1 Intrinsic Accuracy of ATGs detail inMPMS Chapter 3.1.A, butare listed here for conve- The level measurement accuracyall ATGs is affected by of nience. Other limitations uniqueATGs are also listed. to the intrinsic accuracy of the ATG, i.e., the accuracy of the ATG when tested under controlled conditions as specified by 3.1B.4.3.5.1 Accuracy limitations Inherent to both the manufacturers. ManualTank Measurement and ATGs a.Accuracyof tank capacity table, including the effect of 3.1B.4.3.2 Calibration Prior to Installation (Factory tank tilt and hydrostatic pressure. Calibration) b. Bottom movement. The reading of an ATG to be used for custody transfer application should agree with a certified measurement instru-c.Incrustation. ment within *1 mm or (k1/16 inch) over the entire range of d. Movement of the manual gauging reference point or the the ATG. The certified measurement instrument should be tank ATG reference point during transfers or because ther-of traceable to the national standards and should be provided mal expansion. Both affect ullage gauging. with a calibration correction table. The uncertainty ref- of the erence should not exceed mm or (l/32 inch), with the cali- e. The accuracy of measurements using innage-based ATGs 0.5 bration correction applied. is affected by vertical movement of the datum plate used to The reading an ATG to be usedfor inventory application of calibrate the ATG or vertical movement of the reference ATG should agree with a certified measurement instrument within point during tank transfers. *3 mm (k1/8 inch) over the entire range the ATG. The cer- of f. Random and system errors in level, density, and tempera- tifiedmeasurementinstrumentshouldbetraceabletothe ture measurement. national standards and should be provided with a calibration correction table. g. Expansion of the tank diameter due to temperature. ATGs installed prior to the effective date of this document h. Operational procedures usedin the transfer. may not have factory calibration documentation. These ATGs are not required for re-test at the factory, but the installed i. Minimum difference between opening and closing levels accuracy of these ATGs shouldmeettherequirements in (parcel size). 3.1B.7.3.3 for their intended application. j. Errors in measured level caused by sticking and/or cock- ing of floating roofs. 3.1B.4.3.3 Error Caused by Installation and Operating Conditions 3.1B.4.3.5.2 Accuracy Limitations Unique to ATG Thetotalerror of an ATG incustodytransferservice Systems should not be affected by more thanmm (k1/8 inch) due to *3 a. Errors caused by the improper installation ATG. of the installation, to variation operating conditions (refer to Sec- of tion 3.1B.4.3.5) or variationof physical and electrical proper- b. Errors in transmitting thetank level and temperature infor- ties of the liquid and/or vapor, provided that these conditions mation to the remote readout. are within the limits specified. c. Errors in tank capacity table, physical property and other 3.1B.4.3.4 Overall Accuracy of the InstalledATG tank data input into the gauging system computer. The overall accuracy the installed of ATG includes both the 3.1B.4.4 USE OF ATGs FOR CUSTODYTRANSFER intrinsic accuracy of theATG, as verified by factory calibra- OR INVENTORY CONTROL tion, and those effects caused by installation and operating The overall accuracy of level measurement by ATGs, as conditions. The overall accuracy of an in custody trans- ATG installed(“installedaccuracy”),islimitedbytheintrinsic fer service should be within mm (*3/16 inch). The overall *4 error of theATG equipment, the effect installation methods of accuracy of an ATG in Inventory control service should be and the effect of changes in the operating conditions. within *25 mm (*l inch). Depending on the overall accuracy of ATG, as installed, the ATGs may be used either for custody transfer or for inventory 3.1B.4.3.5 Accuracy Limitations of Tank control purposes. The use of ATGs for custody transfer nor- Measurement mallyrequiresmutualcontractualagreementbetweenthe ATGs (and measurements derived therefrom, e.g., volume) buyer and the seller and may be subject to federal, state and are affected by the same inherent accuracy limitation as man- local regulations.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 12. 4 API MANUALOF PETROLEUM MEASUREMENT STANDARDS, CHAPTER 3 ” T A N K GAUGING The use of ATGs in custody transfer application requires 3.1B.4.5.2.1 Top Mounting With a Slotted Still Pipe high accuracy. The use of ATGs for inventory control pur- Figure 1 shows an ullage-ATG mounted on a slotted still poses often permits a lower degree of accuracy. pipe supported by tank bottom. Figure 2 shows an ullage- ATG mounted ona slottedstill pipe supported by bracket. a 3.1B.4.4.1 Use of ATGs for Custody Transfer Ullage-ATGs mounted on properly supported slotted still Purposes pipes, as illustrated in Figures1 and 2, deliver higher accu- 3.1B.4.4.1. I The ATG should meet the factory calibration racy because the slotted still pipe is supported on a stable tolerances prior to installation (refer to Section 3.1B.4.3.2). location and ATG movement is minimized when the tank is filled or emptied. 3.1B.4.4.1.2 The ATG shouldmeetthefieldverification tolerance for custody transfer (refer to Section 3.1B.7.3.3), 3.1B.4.5.2.2 Top Mounting Without a Slotted Still including the effects of installation methods and changes in Pipe operating conditions (refer to Section 3.1B.4.3.3). Alternatively, an ullage-ATG may be supported on the roof 3.1B.4.4.2 Use of ATGs for Inventory Control of a fixed-roof tank or on a “gallows” on a k e d or floating Purposes roof tank, as illustrated in Figure 3. This kind of mounting may cause the tank ATG to move vertically when the is filled 3.1B.4.4.2.1 The ATG should meet the factory calibration or emptied. Ullage-ATGs mounted without slotted still pipes tolerances prior to installation (refer to Section 3.1B.4.3.2). can be used for custody transfer or inventory control the if 3.1B.4.4.2.2 The ATG shouldmeetthefieldverification ATG as installed, can be verified to meet the requirements set tolerance for inventory control (refer to Section3.1B.7.3.3), forth in Section 3.1B.4.3.4. including the effects of installation methods and changes in operating conditions. 3.1B.4.5.2.3 Mounting Without a Slotted Still Pipe for Small Tanks 3.1B.4.4.3 Remote Readout Custody Transfer For small (less than 5000 barrels) tanks, an ullage-ATG may be mounted without a slotted still pipe. The Reference The remote readout, used, should meet the requirements if Height variation should be measured with the tank full and of this standard (refer to Section 3.1B.4.6). empty. 3.1B.4.5 INSTALLATION OF ATGs 3.1B.4.5.3 Mounting Location of Innage-ATGs 3.1B.4.5.1Manufacturer’sRequirements The gauge head of an innage-ATG may be mounted in any The ATG and the associated electronics should be installed suitable location. The mounting locationof the ATG should and wired in accordance with the manufacturers’ instructions, be such that the ATG may be easily verified by manual gaug- NFPA National Electrical Code andor local standards. ing from the official gauge hatch. The point the zero of measuring element should be 3.1B.4.5.2 Mounting Location of Ullage-ATGs mounted at a stable location ontank bottom that has mini- the malverticalmovementwithrespecttothebottomcorner The mounting location of an ATG may affectits accuracy (which is the joint where the tank shell and bottom meet). after installation. The mounting locationof the ATG should be such that the ATG may be easily verified by manual gaug- 3.1B.4.5.3.1MountingInnage-ATGs ing from the official gauge hatch. For custody transfer accuracy, is essential that the mount- Innage-ATGs it usually not do require pipes. still If an ing location should be stable, with minimal vertical move- innage-ATG is mounted on a still pipe, it should be slotted. ment with respect to the reference (which is typically the Innage-ATGsshouldbemountedinaccordancewiththe tank joint where the tank shell and bottom meet). If the datum manufacturer’s instructions. Refer to Figure 4. plate is found to stable,it may be used to verify the stabil- be ity of ATG mounting. 3.1B.4.5.4 Avoiding Turbulence The stability of the mounting location is affected by the If the measuring element is subjected to excessive turbu- changes in liquid head, vapor pressureor loadingof the roof lence, certain typesof ATGs may be thrown out of calibra- or gauging platform. tion. TheATG should be located away fromtank inlets, tank For best accuracy, an ullage-ATG should be mounted on a outlets and tank mixers. When this cannot be done, the level still properly supported, slotted (or perforated) pipe, as illus- detecting element should protected by means of a slotted be trated in Figures 1 and 2. still pipe to minimize the effectturbulence and swirl. ofCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 13. SECTION 1B-LEVEL MEASUREMENT LIQUIDHYDROCARBONS STATIONARY TANKS AUTOMATIC OF IN BY TANKGAUGING 5 See Note 1 r Slotted still pipe - Slotted still pipe (see Note 1 and 4) (see Note 1 and 3) r Pontoon Level sensor (see Note 2) / t -Datum plate (see Note 4) (a) Installation of top-mounted ATGs on fixed roof (b) Installation of top-mounted ATGs on external floating tanks with still pipe. roof tanks or on internal floating roof tanks. Notes: 1.Separate slotted still pipe@) for manual gauging and temperature measurement may be installed adjacent to theATG slotted still pipe. 2.Non-contact, top-mountedATGs can be installed in a similar way. 3.Use of slotted still pipes ATG, manual gauging, and temperature measurement open floating for on tanks may be subjectto environmental regulations. SeeMPMS Chapter 19.2. 4.Datum plate should mounted on t n bottom, below the slotted still pipe located 100 to 150 be ak or mm (4 to 6 inches) below the slotted still pipe shown). (as Figure I-Example of an ATG (Contact or Non-contact) Mounted on a Still Pipe Supported by Tank BottomCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 14. 6 API MANUAL PETROLEUM MEASUREMENT OF STANDARDS, CHAPTER 3"TANK GAUGING Automatic tank gauge (ATG) attached to top of still pipe See Note E 5 Sliding guide I 01 I 1 r S l o t t e d still pipe (see Note 1 and 3) Slotted still pipe (see Note 1 and 4) L7 /Pontoon Datum plate (see Note 4) (a) Installation of top-mountedATGs on fixed roof (b) Installation of top-mountedATGs on external floating tanks with still pipe. roof tanksor oninternal floating roof tanks. Notes:O 1.meparate slotted still pipe(s) for manual gauging and temperature measurement may be installed adjacent to the slotted still pipe.0 ATG 2.[Non-contact, top-mountedATGs can be installed in a similar way.0 ATG, on 3.UJse of slotted still pipes for manual gauging, and temperature measurementopen floating tanksmay be subject to environmental regulations.e e MPMS Chapter 19.2.0 S on 4.Ulatum plate should be mounted tank bottom, below the slotted still pipe or located to 100 150 mm (4 to 6 inches) below the slotted still pipe (as shown).O 5.mhe bottom bracket shouldbe mounted approximately 250 mm (10 inches) from the bottom. Figure 2-Example of an ATG (Contact or Non-contact) Supported by a Bracket Hinged to the Lower Tank Shell PlateCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 15. SECTION 1B-LEVEL MEASUREMENT LIQUIDHYDROCARBONSSTATIONARY TANKSBY AUTOMATIC OF IN TANKGAUGING 7 Automatic tank gauge (ATG) mounted on a bracket Bracket welded to upper to Flexible seal prevent emission ring segment of tank from vapor of tank (see Note 2) Level sensor (see Note 1) Notes:O 1 .mhisfigure shows an intrusive ullage-ATG. Non-contact, top-mounted ATGs can be installed in a similar way. Mounting an ullage-ATG without a slotted still pipe may affect the accuracy.0 2.mhe use of a flexible seal fixed rooftanks may be subject to environmental regulations. on Figure 3-Example Installation of Top-Mounted ATGs on Fixed Roof Tanks Without Still Pipe (This installation may not be suitable for Custody Transfer) 3.1B.4.5.5 Proximity to the Gauging Hatch The still pipe may be supported on the bottom of thetank (Figure 1) or by a non-rigid trunnion or hinged bracket con- Wherenotsubjecttoturbulence,the ATG should be nected to the bottom course of the shell (Figure 2). located near the gauging hatchso that its accuracy caneas- be ily checked by manual gauging. The upper end of the slotted still pipe and the sliding guide should be designed to allow vertical expansion of the still 3.1B.4.5.6MultipleGaugingHatches pipe when the tank shell bulges or moves vertically. The con- still struction of the slotted pipe and the top guide should not If the tank has more than one gauging hatch, the gaug- restrict vertical roof movement. inghatchanddatumplateused for manualreference innage gauging for calibration and verification should be 3.1B.4.5.7.2 Location of the Slotted Still Pipe the "official" gauging hatch used for referencing the tank strapping table. The slotted still pipe may be supported on the bottom of the tank, as shown Figures 1 and 2, if the tank bottom does 3.1B.4.5.7 Slotted Still Pipe Design not move in relation to the joint where the shell and bottom meet. 3.1B.4.5.7.1 Support for the Slotted Still Pipe When a tank is filled, the bottom of the tank may be The bottom corner of the tank, where the shell plate is deflected upward by the angular deflection of the shell in the welded to the bottom plate, is the stable point to which the area immediately adjacent to the bottom joint. Further from datum plate is referred. theshell,thebottomisusuallydeflecteddownward.TheCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 16. 8 API MANUAL PETROLEUM MEASUREMENT OF STANDARDS, CHAPTER 3"TANK GAUGING Automatic tank gauge (ATG) Automatic tank gauge (ATG) mounted mounted on a bracket (see Note 1) l- n on a bracket (see Notes 1 and 3) Mounting support bracket (see Note 3) - Level sensor/point Level sensor/point of measurement of measurement Perforated still pipe Notes:O 1 .W still pipeis often not required for innage-ATGs, especially in small tanks. Where a still pipe is provided for protection, for stability mounting, and tominimize turbulence, it should be of slotted (refer to this standard for more information slotted still pipes).O on 2.Wchor weight or other means to secure and support the innage-ATG at the bottom should be provided.0 3.Uf an innage-ATGis mounted on the fixed roof, mounting the ATG should not be rigidly of connected to the roof. The installation the ATG should minimize or eliminate the of effect of roof movement due to tank shell bulging, whicha resultof liquid head stress. is Figure 4-Example Installation of Top-Mounted Innage-ATG on Fixed Roof or Floating Roof Tanks Without Still Pipe (This installation may not be suitable for Custody Transfer) amount of deflection depends on the soil conditions and the to accommodate larger level sensing elements for some types foundation design. In most cases, the bulging of the shell of ATGs. ceases to cause bottom movement approximately 450-600 tank mm (1 8-24 inches) from the shell. For construction con- 3.1B.4.5.7.4Depth siderations, the centerline of the slotted still pipe should be The slotted still pipe should extend within 300 mm (12 located between450 to 800 mm (18 and 30 inches) from the inches) of the bottom of the tank.The top of the slotted still shell of the tank as shown in Figuresand 2. 1 pipe should be above the maximum liquid level. After the tank has been hydrostatically tested, the slotted still pipe should remain vertical 3.1B.4.5.7.5 Slotted Still Pipes 3.1B.4.5.7.3NominalDiameter The slotted still pipe should have one or two rowsslots of or holes of about mm (1 inch) width, on opposite sides and 25 The recommended minimum slotted still pipe diameter is continuingabovethemaximumliquidlevel.Thespacing 200 mm (8 inches). Smaller diameter still pipes may be used between the slots or holes should be less than 150 mm (6 dependingonthetypeanddesignofthe ATGs used. If inches), or as recommended by the manufacturer of the ATG. smaller diameter slotted still pipes are used, the design and The still pipe should be straight with internal burrs and welds construction should be checked for mechanical rigidity and removed. Evaporation losses will be reduced the slots face if strength. Larger diameter slotted still pipes may be required tank parallel to the shell.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 17. SECTION 1B-LEVEL MEASUREMENT LIQUIDHYDROCARBONS STATIONARY TANKS AUTOMATIC OF IN BY TANKGAUGING 9 In certain locations, still pipes without slots (“solid” or tank the liquid to come to rest. The should be run through at “non-perforated”) have been used to comply with local air leastoneoperationalcycle,fillingandemptyingthe tank pollutionregulations.Solidstillpipescanleadtoserious within normal working limits of filling and discharge rate. errors in level and temperature measurementsmay cause and For electrostatic charge relaxation, refer to API Recom- tank overfills.Theyshouldnotbeusedformeasurement. mended Practice 2003. Alternatives to solid still pipes which meet air pollution regu- lations are available. ReferMPMS Chapter 19.2. to 3.1B.5.2 REFERENCE MANUAL LEVEL MEASUREMENTPROCEDURE 3.1B.4.5.7.6DatumPlates When an ATG is set to level or verified by comparison tank Refer to MPMS Chapter 3.1A on manual gauging for with reference manual level measurement, the manual mea- details on installationof the datum plate. surements shouldbe performed in accordance withMPMS Chapter 3.1A. Reference manual measurements should be 3.1B.4.5.8 Mounting of ATGs performed by skilled operators. The ATG should be mounted securely to have minimal ver- 3.1B.5.3REFERENCEMEASUREMENTTAPEAND tical movement with respect to the tank reference, which is WEIGHT CERTIFICATION the bottom corner or joint. The mounting should comply with manufacturer’s instructions. The measurement tape and weight usedATG setting or for verification should be a reference master tape/weight (bob) 3.1B.4.6REMOTEREADOUT combination certified by an accredited calibration laboratory and traceable toa national measurement standard, or a work- 3.1B.4.6.1 General ingtape/weight(bob)combinationthathasbeenrecently compared with a certified reference tape and weight meeting The manufacturers ATGs also make associated electron- of the maximum permissible error limits specified in MPMS ics that convert the level information into an analog or digital Chapter 3.1A. The calibration corrections for the tape/weight electronic signal. The level resolution the transmitted sig- of combination should be applied. nal is typically1 mm for Metric (SI) units l/16 inch forUS or Customary units. 3.1B 5 4 EFFECT OF WEATHER Provisions for signal security and transient and surge pro- tection are set forth in Section 3.1B 10. High winds, heavyrain, snow or severe storms may cause movements of the tank shell, the ATG mounting and/or the 3.1B.5 General Procedures for Initial liquid surface. These movements can influence both manual and ATG readings. The effect on manual gauging may be dif- Setting and Initial Verification of ferent from thaton the ATG. Setting and verification should ATGs in the Field not be carried out during high winds or severe storms. The initial setting is the procedure by which the ATG read- tank ing is set equal to the average level determined by refer- 3.1B.5.5 ATGTECHNOLOGY-SPECIFIC ence manual level measurement (at a single level). The initial CONSIDERATIONS verification is the procedure that verifies or confirms that the There be may additionaltechnology-specificconsider- installed accuracy the ATG is appropriate for the intended ations which can affect verification. Specific, additional of ATG service. It is performed by comparing the ATG against refer- steps may be needed to prepare the ATG prior to the initial ence manual level measurements with the liquid at three dif- setting. Technology-specific considerations include, for ferent levels. The differences between the manual and the example, the effect of physical and electrical properties of the ATG readings should be evaluated. liquid and vapor in the the need of checking free-move- tank, ment of the level sensor and other considerations. Refer to the 3.1B.5.1 INITIAL REQUIREMENTS ATG manufacturer’s documentation. Prior to initial setting or initial verification of a new or 3.1B.5.6APPLICATION-SPECIFIC repaired ATG, thetank should be allowed to stand at a con- CONSIDERATIONS stant level long enough for air or vapor to be released from tank the liquid and for the bottom to reach a stable position as In tanks storing heavy or viscous liquids (i.e., asphalt), it recommended in MPMS Chapter 2, “Tank Calibration.” New may be difficult to measure or verify the Reference Height. tanks should be filled and allowed to stand to minimize the The procedures for measuringthe Reference Height errors caused by initial bottom settlement. The tank mixer describedinSection3.1B.6maynotbeapplicableunder should be turned off long enough before adjustment to allow these circumstances.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 18. 10 API MANUALOF PETROLEUM MEASUREMENT STANDARDS, CHAPTER 3 " T A N K GAUGING 3.1B.6 Initial Setting of ATGs in the Field ments. Check whether the presence of the gauger ontank the top affects the ATG reading. If the ATG reading varies by 3.1B.6.1 ULLAGE-BASED ATGS more than 1 mm (l/16 inch), investigate the cause and evalu- a. With the tank contents static at a level between one third ate the impact before proceeding. and two thirds full, record the stable ATG reading before the b. Determine the level the tank contents by reference man- of gaugerarrivesatthe tank. Also recordthe ATG reading innage ualmeasurements u t l three ni consecutive immediately before making the manual reference measure- measurements agree within a range of 1 mm (l/16 inch) or ments. Check whether the presence of the gauger ontank the 4 mm five consecutive measurements agree within a range of top affects the ATG reading. If the ATG reading varies by (3/16 inch). more than 1 mm (l/16 inch), investigate the cause and evalu- ate the impact before proceeding. c. Calculate the arithmetic average value of the innage mea- surement (i.e., the average of the consecutive measurements b. Measure thetank Reference Height at the official gauging obtained in Step b. access position until three consecutive measurements agree within a range of 1 mm (l/16 inch) or five consecutive mea- d.Recordthe ATG reading immediately after making the surements agree within a range 3 mm (l/8 inch). Calculate of manual reference innage measurements and confirm that no the arithmetic average value for Reference Height (i.e., the If change has occurred during the manual gauging. the ATG average of the consecutive measurements) and compare with reading has changed from that recorded during Stepcheck a, the calibration Reference Height. measured and calibra- If the that there has been no transfer either to or fromtank and the tion Reference Heights differ by more thanmm (l/8 inch), 2 that the tank valves are closed. Repeat the procedure from then difficulties may be experienced with the initial verifica- Step a. tion procedure. Investigate the cause before proceeding. e. Compare the ATG reading with the average manual refer- Note: This is not an inconsistency with otherparagraphs, but is nec- ence innage measurement. the two do not agree (within the If essary to stay within the permissible tolerance. resolution of theATG), set theATG so that it reads the same c. Determine the reference manual ullage measurement of as the average manual reference innage measurement. the tank contents from the same gauging access point (using the same measurement tape and weight) until three consecu- 3.1B.7 Initial Verification tive measurements agree within a range of 1 mm (l/16 inch) or five consecutive measurements agree within a range 4 of 3.1B.7.1 INTRODUCTION mm (3/16 inch). Calculate the arithmetic average value the of Ullage-based ATGs are designed to measure the distance ullagemeasurement(i.e.,theaverageoftheconsecutive from the ATG reference point to the liquid surface. Some measurements). types of ullage-based ATG may be able to compensate for d.Determinetheequivalentinnagemeasurementbysub- tank reference datum movement (where such movement has tracting the average manual ullage measurement from the been quantified and found to be repeatable), but most tradi- average measured tank Reference Height. tionaltypes of ullagebased ATG cannotcompensatefor many of the accuracy limitations of tank level measurement e.Recordthe ATG reading immediately after making the described in Section 3.1B.4.3 of this standard. manual reference measurements and confirm that no change Innage-based ATGs are designedtomeasuretheliquid If has occurred during the manual gauging. the ATG reading tank innage directly. They should be less prone to some of the has changed from that recorded during Step a, check that stability problems that can cause level measurement errors there has been no transfer either to or from tank and that the with ullage-based ATGs, but they require the tank innage the tank valves are closed. Repeat the procedure from Step a. datum to be stable. f. Compare the ATG reading with the calculated equivalent Apart from the effect the stability of the of ATG reference innage measurement. the two do not agree (within the reso- point and the manual gauging reference point on the accuracy If ATG so that it reads the same as the of ATG and manual level measurements, several other factors lution of the ATG), set the equivalent innage measurement. may result in level measurement errors and should be consid- ered during ATG verification. These include: 3.1B.6.2 INNAGE-BASED ATGS Tank installation errors. a. With the tank contents static at a level between one third Changes in operating conditions. and two thirds full, record the stable ATG reading before the gaugerarrivesatthe tank. Also recordthe ATG reading Changesinphysicalpropertiesoftheliquid andor immediately before making the manual reference measure- vapor.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 19. SECTION 1B-LEVEL MEASUREMENT LIQUIDHYDROCARBONS STATIONARY TANKS AUTOMATIC OF IN BY TANKGAUGING 11 Changesinelectricalproperties of theliquid andor the arithmetic average value for the tank Reference Height vapor. (i.e., the average of the qualified, consecutive measurements which agree within the specified tolerance) without rounding Changes in local ambient conditions. and compare with the calibration Reference Height. If the Manualgaugingerrors. measured and calibration Reference Heights differ by more than 3 mm (l/8 inch),theninvestigatethecausebefore Errors inherent in theATG. proceeding. Following the initial setting of the ATG, its overall accu- d. Determine the reference manual ullage measurement of racy is verified by: the tank contents from the same gauging access point (using Comparingthe ATG againstmanualreferencelevel the same measurement tape and weight) until five consecutive measurement at three different levels and evaluating the measurements within a range4 mm (3/16 inch). of differences between the ATG readings and the manual Note: A failure to achieve manual measurements within these toler- reference measurements. ances may be due to adverse weather conditions, movement of the liquid surface, or inconsistencies in the measurement technique. The Measuringthe tank ReferenceHeightateachofthe verification procedure should be repeated corrective action has after three levels and evaluating any change in tank Refer- been taken. ence Height. e. Calculate the arithmetic average value of the ullage (i.e., Depending on the results, the tank and ATG combination the average the qualified, consecutive measurements which of shouldbeconsideredsuitable forcustodytransferorfor agree within the specified tolerance). Do not round this result. inventory control purposes,if the applicable calibratiordveri- fication tolerances set forth in this standard are met. f. Determinetheequivalentinnagemeasurementbysub- tracting average the manual from average ullage the 3.1B.7.2VERIFICATIONCONDITIONS measured tank Reference Height. Do not round this result. The initial verification ofan ATG requires measurement g. Record the ATG reading immediately after making the comparisonstobemadewiththeliquidlevelwithinthe manual reference measurements confirm no and that regions of the tank corresponding to the upper, middle and change has occurred during the manual gauging. If the ATG lower thirdsof the tank‘s working capacity. The middle level readinghaschangedfromthatrecordedduringStepb, measurement may be the same one used during the initial set- check that there has been no transfer either to or from the ting procedure (Section 3.1B.6) or it may be repeated. tank and that the tank valves are closed. Repeat the proce- dure from Step b. Verification comparisons should only be carried out under static conditions with no liquid being transferred to or from h. Compare the ATG reading with the calculated equivalent the tank. innage measurement. The difference between these two mea- The time interval between the verification measurement at surements is referred to as the “Test Difference.” the three different levels should be kept as short as practical. tank so i. Arrange for another transfer to or from the that the liquid level is within the other third of the tank‘s working 3.1B.7.3 INITIAL VERIFICATION PROCEDURES capacity and repeat Steps b through h to determine the Test 3.1B.7.3.1Ullage-Based ATGs Difference at this level. a. After the initial setting of the ATG (Section 3.1B.6), a 3.1B.7.3.2Innage-Based ATGs transfer should be made either to or fromtank so that the the level is within either the upper or lower third of the tank a. After the initial setting of the ATG (Section 3.1B.6), a working capacity (Section 3.1B.7.2). transfer should be made either to or fromtank so that the the level is within either the upper or lower third of the tanks b. Record the stableATG reading before the gauger arrives at working capacity (Section 3.1B.7.2). the tank. Also record the ATG reading immediately before making the manual reference measurements. Check whether b. Record the stableATG reading before the gauger arrives at the presence of the gauger on the tank top affects the ATG the tank. Also record the ATG reading immediately before reading. If the ATG reading varies by more than 1 mm (l/16 making the manual reference measurements. Check whether inch), then investigate the cause before proceeding. the presence of the gauger on the tank top affects the ATG reading. If the ATG reading varies by more than 1 mm (l/16 c. Measure the tank Reference Height at the official gauging inch), investigate the cause before proceeding. access position until three consecutive measurements agree within a range of 1 mm (l/16 inch) or five consecutive mea- c. Determine the reference manual innage measurement of surements agree within a range 3 mm (l/8 inch). Calculate of the tank contents from the same gauging access point (usingCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 20. 12 API MANUALOF PETROLEUM MEASUREMENT STANDARDS, CHAPTER 3 ” T A N K GAUGING the same measurement tape and weight) until three consecu- 3.1B.7.3.3.2 Tolerance for ATGs in Custody tive measurements agree within a range of 1 mm (l/16 inch) Transfer Application or five consecutive measurements agree within a range 4 of If the Test Difference is not greater4 than(3/16 inch) at mm mm (3/16 inch). any of the three test levels, the ATG should be considered to Note: A failure to achieve manual measurements within these toler- be suitable for custody transfer. ances may be due to adverse weather conditions, movement of the liquid surface or inconsistencies in the measurement technique. The 3.1B.7.3.3.3 Tolerance for ATGs in Inventory verification procedure should be repeated corrective action has after Control Application been taken. 25 mm (1 inch) at If the Test Difference is not greater than d. Calculate the arithmetic average value of the innage mea- any of the three test levels, the ATG should be considered to surement the (i.e., average the of qualified, consecutive be suitable for inventory control. measurements which agree within the specified tolerance). Do not round this result. 3.1B.7.3.3.4 ATGs Found Out of Tolerance e. Record the ATG reading immediately after making the If the test difference exceeds the limits for the proposed manualreference measurements confirm no and that application at any of the three test levels, check the stabil- for change has occurred during the manual gauging. If the ATG ity of the manual gauging reference point and for possible readinghaschangedfromthatrecordedduringStepb, problems with the installation. ATG check that there has been no transfer either to or from the tank and that the tank valves are closed. Repeat the proce- 3.1B.8 Record Keeping dure from Step b. Full records should be keptthe initial setting, initial ver- of f. Compare the ATG reading with the average manual innage ification,andsubsequentverification of each ATG used. measurement. The difference between these two measure- Records of maintenance work should kept. be ments is referred to as the “Test Difference.” 3.1B.9 Subsequent Verification of ATGs g. Arrange for another transfer to or from theso that the tank liquid level is within the other third of the tank‘s working for Custody Transfer or Inventory capacity and repeat Steps b through f to determine the Test Control Difference at this level. 3.1B.9.1 GENERAL 3.1B.7.3.3 Verification Tolerance forATGs in A verification program should be established for ATGs Custody Transfer or Inventory Control Ue s used for custody transfer or inventory control.of statisti- cal quality control methods to monitor the performance of 3.1B.7.3.3.1 General ATGs arerecommended,especiallyforATGsinCustody Transfer applications. The purpose the custody transfer verification is to ensure of that theATG, asinstalled, can sense and indicate level over 3.1B.9.2FREQUENCYOFSUBSEQUENT its measuring range as accurately as properly performed refer- VERIFICATION ence manual a k level measurement. tn ATGs used for either custody transfer or inventory control The purpose of the inventory control verification is to should be verified on a regular basis. The liquid level where ensure that the ATG, as installed, can sense and indicate the ATG is verified should be randomly chosen and should be level over its measuring range to a somewhat lower accu- within the normal opening and closing gauge readings of the racy than properly performed reference manual tank level tank. measurement. Inventory control has less rigorous accuracy requirements 3.1B.9.2.1 ATGs in Custody Transfer Application than custody transfer. Since inventory control is largely for internal use, the user can substitute more or less rigorous ATGs used in custody transfer service should inspected be requirements. and its accuracy verified at a single level at least once per Whereloss-controlor inventory accountingbalances month. require it, themaximuminventorycontrolATGtolerance 3.1B.9.2.2 ATGs in Inventory Control Application 25 should be reduced to less than mm (1 inch). The final max- imum accuracy should be established by the user to meet his ATGs usedin inventory control service should be inspected internal requirements. and its accuracy verified at a single level at least once perCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 21. SECTION 1B-LEVEL MEASUREMENT LIQUIDHYDROCARBONS STATIONARY TANKS AUTOMATIC OF IN BY TANKGAUGING 13 quarter. If operating experience confirms stable performance For ATGs used in inventory control service, Test Differ- ence described in Section within the verification tolerance, the verification schedule can 3.1B.7.3.3,25 mm (1 inch) should be extended to once a year. be used as the tolerance. If this tolerance is met, the ATG shouldbeconsideredwithincalibrationandsuitablefor 3.1B.9.3PROCEDUREFORSUBSEQUENT inventory control. VERIFICATION 3.1B.9.3.1 ATGs in Custody Transfer Application 3.1B.10 DataCommunicationand Receiving For ATGs used custody transfer service, the initial verifi- in cationproceduresinSection 3.1B.7 shouldbefollowed, The following clauses provides recommendations for the except that the ATG accuracy is verified at a randomly chosen specification of the communication between level transmit- single level close to normal opening and closing gauge read- ter@) and receiver(s) and vice versa. The measurement data ing (i.e., liquid level). provided by an ATG may include other information. The ATG system should be designed and installed such 3.1B.9.3.2 ATGs in Inventory Control Application that the data transmission and receiving unit should: For ATGs used in inventory control service, the initial a.notcompromisetheaccuracyofthemeasurement.The verification procedure Section 3.1B.7 should be followed, in difference between the level readings displayed by the remote except that theATG accuracy is verified at a randomly cho- receiving unit and the level readings displayed (or measured) sen single level close to normal opening and closing gauge by the ATG at t n should not exceed mm (l/16 inch); the a k *1 reading. b. not compromise the resolution of the measurement output 3.1B.9.4TOLERANCEFORSUBSEQUENT signal; VERIFICATION c. provide proper security and protection of the measured For ATGs usedin custody transfer service, the Test Differ- data to ensure its integrity; ence described in Section 3.1B.7.3.3,4mm (3/16 inch) should d. provide adequate speed to meet the update time required be used as the tolerance. If this tolerance is met, the ATG for the receiving unit; should be considered within calibration and suitable for cus- tody transfer. e. be electromagnetically immune.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 22. COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 23. APPENDIX A-SAFETY PRECAUTIONS: PHYSICAL CHARACTERISTICS AND FIRE CONSIDERATIONS Personnel involved with handling petroleum-related substances and other chemical mate- rials should be familiar with the materials’ physical and chemical characteristics, including potential for fire, explosion, and reactivity and appropriate emergency procedures. These personnel should comply with safe operating practices of the individual company and local, state and federal regulations, including of proper protective clothing and equipment. Per- use sonnel should be alert to potential sources of ignition and should keep containers of materi- als closed when not in use. Note: Information regarding particular materials and conditions shouldbe obtained from the employer, manufacturer, or supplier of that material, or the material safety data sheet. 15COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 24. COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 25. APPENDIX B-ACCURACY REQUIREMENTS FOR ATGS (See Note) Inventory Custody Transfer Requirement Factory calibration 1 mm (116 inch) 3 mm (/S inch) Effect of installation 3 mm (/S inch) na. Initial verification 4 mm (3/16 inch) 25 mm (1 inch) Subsequent verification 4 mm (3/16 inch) 25 mm (1 inch) Frequency of verification quarterly monthly Note: This table is for reference only. Please refer to the entire document. 17COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
  • 26. COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
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