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    • .. MPMS 4 - 1 - 8 8 I 0732290 0054861 fir Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 3-Small Volume Provers FIRST EDITION, JULY 1988 American Petroleum Institute 1220 L Street, Northwest rT> Washington, D.C. 20005COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • Manual of Petroleum Measurement Standards Chapter 4-Proving Systems Section 3-Small Volume Provers Measurement Coordination Department FIRST EDITION, JULY 1988 American Petroleum InstituteCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • MPMS 4.3-88 0732270 O054864 3 r FOREWORD Chapter 4 of the Manual of Petroleum Measurement Standards was prepared as a guide for the design, installation, calibration, and operation of meter proving systems commonly used by the majority of petroleum operators. The devices and practices covered in this chapter may not be applicable to all liquid hydrocarbons under all operating conditions. Other types of proving devices that are not covered in this chapter may be appropriate for use if agreed upon by the parties involved. The information contained in this edition of Chapter 4 supersedes the informa- tion contained in theprevious edition (First Edition, May 1978), which is longer no in print. It also supersedes the information on proving systems contained i A P T n Standard 1101, Measurement of Petroleum Liquid Hydrocarbons by Positive Dis- placement Meter (First Edition, 1960); API Standard 2531, Mechanical Displace- ment Meter Provers;API Standard 2533, Metering ViscousHydrocarbons; and API Standard 2534, Measurement of Liquid Hydrocarbons by Turbine-Meter Systems, which are no longer in print. This publication is primarilyintended for use in the United States and is related to the standards, specifications, and procedures of the National Bureau of Stan- dards (NBS). When the information provided herein is used in other countries, the specifications and procedures of the appropriate national standards organizations may apply. Where appropriate, other test codes and procedures for checking pres- sure and electrical equipment may be used. For the purposes of business transactions, limits on error or measurement toler- ance are usually set by law, regulation, or mutual agreement between contracting parties. This publication is not intended to set tolerances for such purposes; it is intended only to describe methods by which acceptable approaches to any desired accuracy can be achieved. Chapter 4 now contains the following sections: Section 1, “Introduction” Section 2, “Conventional Pipe Provers” Section 3, “Small Volume Provers” Section 4, “Tank Provers” Section 5 , “Master-Meter Provers” Section 6, “Pulse Interpolation” Section 7, “Field-Standard Test Measures” API publications may be used by anyone desiringto do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted to the director of the Measurement Coordination Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. iii ._COPYRIGHT American Petroleum Institute ..-Licensed by Information Handling Services
    • MPMS 4-3-88 0732270 0054865 5r CONTENTS SECTION 3 4 M A L L VOLUME PROVERS Page 4.3.1 Introduction ................................................. 1 Scope .................................................. 1 Definition of Terms ...................................... 1 Referenced Publications .................................. 1 4.3.2 Small Volume Prover Systems .................................. 2 4.3.3 Equipment .................................................. 2 Materials and Fabrication ................................. 2 Temperature Stability .................................... 2 TemperatureMeasurement ............................... 2 Pressure Measurement ................................... 2 ...................................... 2 Valves .................................................. 7 Connections ............................................ 7 Detectors ............................................... 7- Meter Pulse Generator ................................... 7 Pulse-Interpolation System .............................. 7 Controller ............................................. 7 4.3.4 Design of Small Volume Provers ......;........................ 7 Initial Considerations .................................... 7 Pressure Drop Across the Prover .......................... 8 ....................................... 8 Volume ................................................ 8 Parts ............................................ 8 Counters ............................................... 8 Meter ProvingGuidelines ................................ 8 4.3.5 Sample Calculations for the Design of Small Volume Provers ...... 8 Problem ................................................ 9 Solution ................................................ 9. Summary of Prover Design Calculations .................... 11 Other Considerations .................................... 11 4.3.6 Installation .................................................. 11 4.3.7 Calibration .................................................. 12 General Considerations .................................. 12 Waterdraw Method ...................................... 12 .......................... 12 Calibrating Unidirectional Provers ......................... 14 Repeatability ........................................... 14 Certificate of Calibration ................................. 14 4.3.8 Operation ................................................... 15 4.3.9NonuniformPulses ........................................... 15 APPENDIX A-EVALUATION OF DISPLACEMENT METER PULSEVARIATIONS .............................. 17 APPENDIX B-"ETER FACTOR DETERMINATION WITH SMALL VOLUME PROVERS ....................... 23 Figures l-Generalized SystemOverview ................................. 3 2"SystemOverview. Internal Valve .............................. 4 VCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • M y s t e m Overview.InternalBypassPorting With External Valve. .. 5 M y s t e m Overview.Pass-ThroughDisplacerWithExternalValve ... 6 %SystemOverviewforWaterdraw Calibration. ................... 13 A-1-PulseVariationGraph/Direct ................................. 19 A-2-PulseVariation’GrapWGeared ................................ 20 A-3-Pulse VariationGrapW4-Percent Adjustment ................... 21COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services vi
    • MPMS 4-3-84 0732290 O054867 7 r Chapter &Proving Systems SECTION %SMALL VOLUME PROVERS 4.3.1 Introduction Interpuke spacing refers to variations in the meter pulse width or space, normally expressed in per- The use of smallvolume provers has been made cent. possible by the availabili€y of high-precision displacer- position detectors used in conjunction with pulse- Meter proof refers to the multiple passes or interpolation techniques (see Chapter 4.6). The small round trips of the displacer in a prover for purposes of volume prover normally has a smaller base volume than determining a meter factor. that of conventional pipe provers (see Chapter 4.2) and A meterprover is an open or closed vesselof is usually capable of fast proving passes over a wide known volume utilized as a volumetric reference stan- range of flow rates. dard for the calibration of meters in liquid petroleum Small volumeprovers have a volume between detec- service.Such provers are designed, fabricated, and tors that does not permit a minimum accumulation of operated within the recommendations of Chapter 4. 10,000 direct (unaltered) pulses from the meter. Small volume provers require meter pulse discrimination us- A prover pass is one movement of the dis- ing a pulse-interpolation counter or another technique placer between the detectors in a prover. that increases the resolution (see Chapter 4.6). This A prover round trip is the result of the for- may include using provers with both large and small ward and reverse passes in a bidirectional prover. base volumes, depending on the pulse rates of the me- ters to be proved. A proving timerlcounter is a high-speed The smallvolumeprovermay be usedinmany counter used in double chronometry to measure time applications in which pipe provers or tank provers are with a pulsed signal of known frequency. commonly used. Smallvolume provers may be sta- tionary or portable. The volume required of a small volume prover can be REFERENCED PUBLICATIONS less than that of a conventional pipe prover when high- The current editions of the following standards, precision detectors are used in conjunction with pulse- codes, and specifications are cited in this chapter: interpolation techniques. Pulse-interpolation methods of counting a series of pulses to fractional parts of a API pulse are used to achieve high resolution without count- Manual of Petroleum Measurement Standards ing 10,000 whole meter pulses for a single pass of the Chapter 4,“Proving Systems,” Section 2, “Con- displacer between detectors (see Chapter 4.6.) ventional Pipe Provers,” Section 6, “Pulse Inter- To achievethe required proving accuracy and repeat- polation,” and Section 7, “Field-Standard Test ability, the minimum volume between detector switches Measures’’ depends on the discrimination of a combination of Chapter 5 , “Metering,” Section 2, “Measure- pulse-interpolation electronics, detectors, and uniform ment of Liquid Hydrocarbons by Displacement meter pulses, as well as flow rate, pressure, tempera- Meters,” Section 3, “Measurement of Liquid ture, and meter characteristics. Hydrocarbons by Turbine Meters,” and Section 4, “Accessory Equipment for Liquid Meters” SCOPE Chapter 7.2, “Dynamic Temperature Deter- This chapter outlines the essential elements of a small mination” volume prover and provides descriptions of and oper- Chapter 12.2, “Calculation of Liquid Petroleum ating details for the various types of small volumepro- Quantities Measured by Turbine or Displace- vers that meet acceptable standards of repeatability and ment Meters” accuracy. NFPA’ 70 National Electrical Code Terms used in this chapter are defined in National Fire Protection Association, Batterymarch Park, Quincy, through Massachusetts 02269. 1 . .. ’,*.9 . .. _. .iCOPYRIGHT American Petroleum Institute r : iLicensed by Information Handling Services
    • 2 PROVING SYSTEMS CHAPTER 4.3.2SmallVolumeProverSystems The small volume prover available in several differ- is The calibrated volume-measurement section of the prover, located between the displacer-position sensors, a must be designedto exclude anyappurtenances such as ent configurations that allow a continuous and uniform vents or drains. rate of flow. All types operate on the common principle Flanges or other provisions should be included for of the repeatable displacement of a known volume of access to the inside surfaces of the calibrated and prerun liquid in the calibrated section of a pipe or tube. A sections. Care should be exercised to ensure and main- displacer travels through a calibrated section with its tain proper alignment and concentricity of pipe joints. limits defined by one or more highly repeatable de- Internally coating the prover section with a coating or tectors. The corresponding metered volume simulta- plating material thatwill provide a hard, smooth, long- neously passes.through the meter, the whole num- and lasting finishwill reduce corrosion and prolong the life ber of pulses is counted. Precise calculations are made of the displacer or displacer seals and the prover. using a pulse-interpolation technique (see Chapter 4.6). The two types of continuous-flow small volume pro- TEMPERATURE STABlLlTY vers are unidirectional and bidirectional. The uni- directional prover allows the displacer to traveland Temperature stability is necessary to achieve accept- measure in only one direction through the proving sec- able proving results. Temperature stabilization is nor- tion and has a means of returning the displacer to its mally achieved by continuously circulating liquid starting position, The bidirectional prover allows the through the prover section, with or without insulation. displacer to travel and measure first inone direction and When provers are installed aboveground, the applica- then in the other and is capable of reversing the flow tion of thermal insulation will contribute to better tem- through the prover section. perature stabilization. Both unidirectional and bidirectional small volume provers must be constructed so that the full flow of the TEMPERATURE MEASUREMENT stream passing through the meter being proved will pass Temperature-measurement sensors should be of suit- through the prover. able range and accuracy and should be graduated by temperature discrimination in fractional degrees to at 4.3.3 Equipment least 0.5"F(0.25"C). See Chapters 7.2 and 12.2. The small volume prover must be suitable for the Temperature-measurement devices shall be installed at intended fluids, pressures, temperatures, and type of appropriate locations to measure temperature at the installation. The materials usedmustbe compatible meter and the prover. Caution must be exercised to with the fluid stream and the location where the prover ensure that the temperature sensors are located in a will be installed. position in which they will not be shut off from the A small volume prover will normally consist of the liquid path. following elements: PRESSURE MEASUREMENT a. A precision cylinder.. b. A displacer piston, spheroid,other or fluid- Pressure-measurement devices of suitable range and separation device. accuracy, calibrated to an accuracy of 2 percent full c. A means of positioning and launching the displacer scale or better, shall be installed at appropriate loca- upstream of the calibrated section. tions to measure pressure at the meter and the prover. d. A displacer detector or detectors. (See Figures 1-4 and Chapter 12.2 for further informa- e. A valve arrangement thatallows fluid flow while the tion). displacer is traveling from one position to the opposite position, DISPLACING DEVICES f. Pressure-measurement devices. g. Temperature-measurement devices. One type of displacer is a piston, with seals, con- nected to a centralshaft. A second type of displacer is h. Instrumentation with timers, counters, and pulse- interpolation capability. a freepiston that uses seals between the precision cylin- 1 der and the piston. A third type is the elastomer sphere filled with liquid under pressure. To provide a seal with- out excessive friction,thesphere is expanded toa di- @. i The materials selected for a prover shall-conform to ameter greater than theprover pipes inside diameter, applicable codes, pressure ratings, corrosion resistance, which is normally percent. Insufficient expansion of 2-4 and area classifications. the sphere can lead to leakage past the sphere and ICOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • N P N S 4.3-88 ~~ 0732290 0 0 5 4 8 6 7 2 r SECTION " s VOLUME 3 ~ ~ PROVERS 3 a âj c C 3 8 5 2 I(i(iCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 4 SYSTEMS CHAPTER &PROVING V L LCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • . MPMS 4.3-88 1 07322q0 0054873 or PROVERS VOLUME SECTION +SMALL 5 r Y- OCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 6 ~~ &PROVING SYSTEMS CHAPTER . I- O tCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • MPMS 4-3-88 0732270 0054873 4r SECTIONSMALL VOLUME PROVERS 7 consequently €omeasurement error. Excessive expan- sion of the sphere may not improve sealing ability and A meter pulse generator shall be provided for trans- will generally cause the sphere to wear more rapidly and mitting flow data. Thegenerator must provide electrical move erratically. Care must be exercised to ensure that pulses that have satisfactory characteristics for the type no air remains inside the sphere. Theelastomer should ~ ~ of electronic instrumentation employed. ~. be impervious to the operating liquids. ~ A means for inspecting or monitoring displacer-seal integrity must be included in the design and operation PULSE-INTERPOLATION SYSTEM of allsmallvolume provers. Displacer-seal integrity may be either statically or dynamically verified under The prover timer/counter for small volume provers is conditions of low-pressure differential that are consis- an electronic device that utilizes pulse interpolation and tent with normal operations. double chronometry (see Chapter 4.6). Other types of displacers will be acceptable if they provide accuracy and repeatability that is equal to or CONTROLLER better than the three types described above. The controller is used to process all signals both to and from the prover. It receives the startkop signals VALVES from the detector or detectors that gate the timers, All valves used in small volume prover systems that receives the pulses generated by the test meter, per- can provide or contribute to a bypass of liquid around forms the calculations, and displays all data. The prov- the prover or meter or to leakage between the prover ing controller may be equipped to provide remote and meter shall be of the block-and-bleed type. operation, alarms, printing, logic sequences, and other Full positioning of the flow-reversing valve or valves desired functions. in a bidirectional prover or the interchange valve in a unidirectional prover must be established before the .~ displacer is allowed to actuate the first detector. This 4.3.4 Design of Small Volume Provers ~ . design ensures that no liquid is allowed to bypass the INITIAL CONSIDERATIONS prover during the displacer’s travel through the cali- brated volume. The distance before the first detector, Before a small volume prover is designedor selected, commonly called prerun, depends on valve operation it is necessary to establish the type of prover required time and the velocity of the displacer. Methods used to for the application and the manner in which it will be shorten this prerun, such as faster operation of the valve connected to the meter piping. The followingitems or delay of the displacer launching, require that caution should be established from a study of the application, be exercised in the design so that hydraulic shock or intended use, and space limitations of the prover: additional undesired pressure drop is not introduced. a. Whether the prover will be stationary or mobile. 1. Whether a stationary prover will be dedicated CONNECTIONS (on line) or used as part of a central system. 2. Whether a stationary and dedicated prover will Vent and drain lines shall be provided on the prover be kept in service continuously or isolated from the or the connecting piping and musthave a means of metered stream when it is not being used to prove a checking for leaks. Provisions should be made to allow meter. field waterdraw calibration of the small volume prover. b. The temperature and pressure ranges that will be encountered. c. The expected maximum and minimum flow rates DETECTORS and the flow-rate stability. Detectors must indicate the position of the displacer d. The maximum pressure drop allowable across the within +0.01 percent. The repeatability with which a prover. prover’s detector can signal position of the displacer the e. The physical properties of the fluids to be handled. (which is one of the governing factors in determining f. The degree of automation to be incorporated into the length of the calibrated prover section) must be the proving operation. ascertained asaccurately as possible. Care must be g. The availability of electric power and other utilities. taken to correct detector positions that are subject to h. The size and types of meters to be proved. temperature changes throughout the proving operation. i, The applicable codes.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 0 CHAPTER &PROVING SYSTEMS f. The uniformity of the meter signal, or pulse, relative THE PROVER to time (interpulse spacing). g. The meter’s displaced volume per revolution. In determining the size ofthe piping andthe openings to be used in the manifolding and the prover, the pres- CRITICAL PARTS sure loss through the prover system should be com- When a detector’s worn or damaged parts are re- patible with the pressure loss considered tolerable in the metering installation. Flow rate should not vary signifi- placed, care must be taken to ensure that neither the cantly during movement of the displacer. detector’s actuating depth norits electrical switch com- ponents are altered the extent that the to prover volume DISPLACER VELOCITY is changed. This is especially important in the case of in unidirectional provers because changes detector actu- The velocity of the displacer can be determined by ation are not compensated for by round trip sphere the diameter of the prover cylinder and the maximum travel, as they are in bidirectional provers. When uni- and minimum flowrates of the meters to be proved. A directional provers are used, recalibration is needed as practical limit to the maximum velocity of a displacer soon as practical. must be established to prevent damage to thedisplacer and the detectors. COUNTERS Typical maximum displacer velocities close to but are The small volumeprover requires using a meter not limited to 5 feet per second (1.5 meters per second). pulse-interpolation-type system (see Chapter 4.6) to The developing state of the art advises againstsetting a provide a resolution of at least one partin 10,000 of the firm limiton displacer velocity as criterion for design. a indicated meter volume for each pass of the displacer Demonstrated results are better to use as a criterion. between the detectors. The results are manifested in repeatability, accuracy, and reproducibility of meter factors using the prover in . METER PROVING GUIDELINES question, Different types of meters produce pulse trains that Establishing guidelinesfor minimum velocities is dif- have different characteristics. ficult because of the many factors that must be consid- At a steady flow, the rotation of a turbine meter and ered, such as the following: its pulse train is uniform. Under comparable flow, the a. The smoothness of the cylinder’s internal surface. rotation of some displacement-meter elements is also b. The type of displacer used. uniform; however,mechanical gears, couplings, ad- c. The displacer’s launching capability. justors, counters, temperature-correction devices, d. The lubricity of the liquid being measured. and other accessories reduce the uniformity of the displacement-meter pulses. Piston-type displacers can generallyoperate at lower Demonstrations have shownthat thecloser the pulse velocities than can sphere types. generator is to the meter rotor, the more uniform the The intention of this standard is not to limit the pulse train will be. The further the pulse is moved from velocity of the displacer. Provided that acceptable the meter rotor, the more erratic the pulse train be- performance is guaranteed, there is no arbitrary limit comes (see Appendix A). imposed on velocity. For example, a displacement meter that has a close- coupled pulser will require only a minimal number of VOLUME prover passes performed by a relatively-low-volume In determining the volume of a prover between de- prover to establish a meter factor. (See Figure A-2 for tectors, thedesigner must consider following items: the pulse train characteristics.) A displacement meter with a full assortment of accessories willusually require a. The overall repeatability required of the proving more passes or the use of a larger prover to establish a system. meter factor. (See Figure A-3 for pulse train character- b. The repeatability of the detectors. istics.) c. The ability of the electronic counter to indicate whole pulses, unless pulse interpolation is employed. d. The resolution of the meter pulse generator (the 4.3.5 Sample Calculations for the number of pulses per unit volume). Design of Small Volume Provers e.The maximum and minimum flow rates of the A typical approach to the design and application of system. small volumeprovers is provided in and American Petroleum InstituteLicensed by Information Handling Services
    • MPMS 4 - 3 - 8 8 0732290 0054875 8 SMALL VOLUME SECTION PROVERS 9 Note: Test-run observation indicates that the calculation method used The number of clock pulses accumulated during a in should provide a minimum volume for proving prover pass is calculated as follows: a meter with a uniform pulse train (for example, a turbine meter or a displacement meter that has a uniform pulse output). A proving method that consists of íïve prover passes, or round trips, with a N, = Tz F, (2) repeatability range of 0.05 percent is achievable. Proving methods for Where: use on nonuniform pulse oufput meters are discussed in Appendix B. The examples used in this section are not intended to imply that the Tz = clock operating time during a prover pass, in meter and prover data will be appropriate for all equipment or that seconds. other methods of prover design analysis are inappropriate. F = clock frequency, in hertz. , PROBLEM The clock operating time during a prover pass is cal- The maximum flowrate of the meter to be proved is culated as follows: 1715 barrels per hour (1200 gallons per minute, 272.66 Tz = N,/ F, (3) cubic meters per hour). The minimum flow rate is 343 Where: barrels per hour (240 gallons per minute, 54.49 cubic meters per hour). N, = number of meter pulses during a prover pass, in The meter is a 6-inch displacement meter with a pulse pulses. rate of 8400 pulses per barrel (52,834.4 pulsesper cubic F = meter pulse frequency, in hertz. , meter). The maximum interpulse spacing is equal to a10 percent of the average. The meter pulse output is Equations 1,2, and 3 can be combined to express the error of the timers in terms of meter output and timer approximately uniform with the rotation of the meter frequency: element. The pulse interpolation is performed by the double- Ut= k2F,/N,FC (4) chronometry method using one clock with a frequency The meter pulse frequency is calculated as follows: of 100,000 hertz. The prover displacer-position detectors have a re- F = Q, P, 13600 , peatability range of 0.001 inch (0.0254 millimeter) and Where: a position stability range of 0.001 inch (0.0254 milli- meter). Q, flow rate, in barrels per hour (cubic = meter The meter output resolution at the start and end of meters per hour). one prover pass is kO.01 percent (+0.0001 percent of P, = meter pulse rate, in pulses per barrel (pulses the average). The prover displacer-position error at the per cubic meter). start and end of a prover pass has an uncertainty of 3600 = number of seconds per hour. kO.01 percent. The maximum displacer velocity is3.5 In this example the maximum pulse frequency is cal- feet per second (1.067 meters per second). The mini- mum displacer velocity is 1.2 inches per second (3.048 culated asfollows: - centimeters per second). F,(mxl (1715)(8400) 13600 = The required design data is the minimum volume, = 4002 hertz minimum diameter, and minimum length of the prover. In SIunits, SOLUTION F,(,ax) (272.66)(56,834.4) I3600 = The potential error due to the resolution of double- = 4002 hertz chronometry timers during a prover pass can be calcu- The potential error of the double-chronometry time lated as follows: can be calculated from Equation 4 as follows: U t = k2lNc (1) Ut = (+ 2)(4002) I (N,)(lOO,OOO) Where: = k0.08O1Nm U, potential error in time accumulated by two tim- = The error due to nonuniform meter interpulse spac- ers (one that times meter pulse output and one ing at the startand end of a prover pass iscalculated as that times prover displacement), expressed as a follows: pluslminus fraction of a pulse. 2 = number of timers. U, = (2)( 2PS) IN, (5) Where: N,= number of clock pulses accumulated during a prover pass. U, = potential error due tononuniform meter inter- aCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • IO SYSTEMS +PROVING CHAPTER .pulse spacingduring a prover pass, expressed as a plus /minus fraction. Qm= meter flow rate, in cubic inches (cubic centimeters per second), per second a 2 = number of displacer detections during a prover vd = displacer velocity, in inches per second (centi- pass. meters per second). P, = meter interpulse spacing expressedas a In this examplethe minimum proverdiameter for the plus/minus fraction of a pulse. velocity limit is calculated as follows: In this example the error due to nonuniform meter interpulse spacing is as follows: D,(-) {4620/ [(0.7854)(42)]}0*5 = = 11.83 inches U, = 2(k0.10)/Nm In SI units, = +O.20/Nm D,,, = {75,708.2/[(0.7854)(106.68)]}0.5 The combined meter output errorat the startand end = 30.06 centimeters of a prover pass can be estimated by combining Equa- tions 4 and 5 as follows: The velocity of the displacer at the minimum flow rate, with the inside diameter given above, is calculated U, + U,,,= k2Fm N,F, / + (2) (fPS)/N, (6) as follows: Note: Equation 6 sums the errors U, and U instead of taking the root , of mean square, the usual method calculation. This approach results Vqmi.l= Q,/ [0.7854(0:)] in a slightly Iarger prover than might otherwise be calculated. = 924/.[(0.7854)(11.832)] In this example the combined meter pulse uncer- = 8.4 inches per second tainty during a prover pass is as follows: = 0.7 foot per second U, + U, = ( 0,080 + k0.20) /N,,, f In SI units, = k 0.280 /Nm Vd(&) = &m/ [(30-05)(D2)] The maximum meter output error at the start end of a prover pass is limited to the following: U, + U, = kO.O001(~0.01 percent) and = 15,141.6/[(0.7854)(30.052)] = 21.35 centimeters per second = 0,213 meter per second a Since the minimum calculated displacer velocity of In this example the minimum number of meter pulses 0.7 foot per second (0,213 meter per second) is more that limits meter error to fO.0001 is as follows: than the design limitof 0.1 foot per second (0.03 meter k0.28Ö/Nm= +0.0001 per second), the diameter of 11.83 inches (30.05 centi- meters) is satisfactory. Therefore, The prover’s calibrated section is calculated as fol- N,,,= 2800 meter pulses lows: The minimum provervolume is calculated as follows: L, = V,/ [ö.7854(0:)] V,(-) =N m/ P r In this example the minimum proverlength, based on = 2800 / 8400 the minimum volume and diameter of the prover sec- = 0.33333 barrel (0.05299 cubic meter) tion, is as follows: = 14.000 gallons (52.996 liters) Lp(~,,) = 3234/[(0.7854)(11.832)] = 3234.0 cubicinches (52,996 cubic centimeters) = 29,42 inches The minimum diameter of a prover’s calibrated In SI units, chamber at themaximum flow rate is calculated as fol- lows: L,,,) = 52,9961 [(0.7854)(30.052)] = 74.72 centimeters D,= [Qm/(0.7854vd)]o.5 The error in the displacer’s position during a prover In SI units, pass can be estimated as follows: D, = [Qm/(0.7854&)]0.5 U d = [2(Ud + S) / L , d] Where: Where: D,= internal diameter of the prover’s calibrated üd range of error in the displacer’s positionduring = chamber, in inches (centimeters). a prover pass, expressed as a fraction.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • SECTION PROVERS *SMALL VOLUME 11 2 = number of displacer positions during a prover accordance with sound engineeringprinciples. Ade- pass. quate provisions should made for expansion and con- be rd = range of repeatability of the displacer detector traction, vibration, reaction to pressure surges, and or detectorsj in inches (centimeters). other conditions. s d = range of stability in the mounting position of the Suitable valves shallbe installed to isolate the prover displacer detector or detectors, in inches (centi- unit from line pressure during maintenance, removal meters). of the displacer, replacement of seals, cleaning, and recalibration. Likewise, connectionson the prover or in In this example the minimum length of the prover’s the lines should be considered for subsequent re- calibrated section for a maximum error range of 0.0002 calibrations. (0.02 percent) in displacer positions during a prover All units shall be equipped with vent and drain con- pass would be as follows: nections, and provision should be made the disposal for = 2(rd + sd) 1Ud of liquids or vapors that aredrained or vented from the + = [2(0.001 O.OOl)] /0.0002 small volumeprover section. This may be accomplished = 20 inches by pumping liquids vapors backinto thesystem or by or diverting them to a collecting point. In SI units, Temperature and pressure devices shall be installed = 2(rd + sd) / Ud in suitable locations near the meter and the prover so + = [2(0.00254 0.00254)]/0.0002 that they canb e used to determine the temperature and = 50.8 centimeters pressure of each. Blinded valves or valve connections should probably Since the minimum prover length corresponding to be provided on either side of a bubbletight block valve the minimum diameter [29.42 inches (74.72centi- in the carrier stream to serve asa permanent connection meters)] is longer thanthe minimumproverlength for proving portable meters. based on displacer detector error [20 inches (50.8 centi- Installations in hazardous locations must be recog- meters)], the former prover length is satisfactory. nized as such, and all wiringand controls in these loca- tions shallconform to the requirements of NFPA 70 and OF PROVERDESIGN any other applicableelectrical standards. Provisions CALCULATIONS shall be made for proper grounding and electrical instal- The minimum volume equals 14.000 gallons (52.996 lation o€portable small volume provers. liters). The minimum diameter equals 11.83 inches Components shall come from the class and group that (30.05 centimeters). The minimum length equals 29.42 are most appropriate for the location and operation. All inches (74.72 centimeters). electrical controIs and components should be placed in a location that is convenient for operation and mainte- OTHER CONSIDERATIONS nance. Manufacturers’ instructions should be strictly followed during the installation and grounding o€ such When operating at its maximum design flow rate, the items as electronic counters, pulse-interpolation equip- small volumeprover shall allowthe displacer to come to ment, and signal cables (see Chapter 5.4). rest safely without shock at the end of its travel. Pressure reliefvalves and leak-detection facilities When the prover is operating at its maximum flow shall be installed with discharge piping to control ther- rate with liquids for which it was designed, there shall mal expansion of the liquid in the small volume prover be no sign of cavitation in the prover, the valves, or any while it is isolated from the main stream. other apparatus within the specified temperature and Power controls and remote controls should be suit- pressure ranges. ably protected with lockout switches between remote and adjacent panel locations to prevent accidental re- 4.3.6 Installation mote operation while a unit is beingcontrolled locally. All installation components of the small volumepro- Suitable safety devices and locks should be installed to ver, including connecting piping, valves, manifolds, and prevent inadvertent operation of or unauthorized so forth, shall be in accordance with the applicable pip- tampering with equipment. ing codes. Once the prover is onstream, it becomes a Automated or power-operated meter proving sys- part of the pressure system. tems may be equipped with emergency manual oper- If the proving section and related components are ators for use during a power failure. installed aboveground, they shall havesuitable hangers Small volume provers may require straining or fil- and supports prescribed by the applicable codes and in tering equipment. SCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 12 CHAPTER &PROVING SYSTEMS 4.3.7 Calibration ing the prover, field standards, and test liquid ina stable temperature environment shaded from direct sunshine GENERAL CONSIDERATIONS to allow the equipment and liquid to reach an equi- A small volume prover must calibrated before it be is librium temperature. placed in service determineits base volume (the cali- to Water is the ideal calibrating medium because of its brated volume corrected to standard conditions). Pe- high heat capacity, low compressibility, and low coeffi- riodic recalibration of the prover is also required. Chap- cient of thermal expansion compared to petroleum ter 12.2 gives details for determining all the correction liquids. The use of any other medium inthese measures factors and calculating the base volume. Some of the changes the surface tension; consequently, the measure differences in calculating the base volume of a small is no longer calibrated. To prevent contamination of the volumeprover are discussedin the following para- water, the prover and fill lines must be voidof foreign graphs. materials. The accuracy of the base volume (documented on a The displacers should be moved through the small calibration certificate), as determined, cannot better be volume prover enough times to flush the prover and than the accuracy of the field standard used in deter- eliminate air that may have been caught in parts of the mining it (see Chapter 12.2). small volume prover system and to allow both the metal It should be clearly understood that the base volume and liquid of the prover system to reach a common and of a unidirectional prover is the calibrated volume cor- steady temperature. Uninsulated small volume provers rected to standard conditions and displaced between that are calibrated outdoors under hot or cold condi- detectors for a single pass. The base volume of a bi- tions should be temporarily insulated and sheltered to directional prover is the sum of the volumes displaced reduce variations in temperature. In addition to stabi- between detectors fora round trip of the displacer and lizing the prover, is necessary verify that thevalves, it to corrected to standard conditions. seals, and displacer are secure and that thereis no leak- Some unidirectional small volume provers have one age from or around the prover. or more shafts attached the displacer, The shaft may to The temperature and pressure of the water at the be continuous or may be on only one side of the dis- prover, between the displacer and the standard mea- placer. If the shaft is continuous and uniform, the effec- sures, shall then be observed and recorded as the tem- tive upstream volume may be equal to the effective perature and pressure in the prover at the startof cali- downstream volume; however, if the shaft is on only bration. one side of the displacer, the effective upstream volume Test measures for the calibration of smallvolume will differ from the effective downstream volume. For provers shallcomplywith the requirements givenin further clarification, if the shaft is on the upstream side Chapter 4.7. High-sensitivityfield standards with a of the displacer, the effective volume when a meter is resolution of 0.02 percent or better are recommended proved upstream of the prover will be less than the for use in calibrating small volume provers. Only sin- a effective volume when meter proved downstreamof a is gle field standard or as few field standards as possible the prover. Conversely, if the shaft is on the down- should be used during a waterdraw calibration of a small stream side of the displacer, the effective volume when volume prover. a meter proved upstream of the prover will be greater is The prover may be calibrated using small-diameter than the effective volume whenmeter is proved down- a water lines and temporary valves. Automated fast- stream of the prover. The difference involumesis responding valves actuated by the detector switches, equivalent to the volume displaced by the shaft. Both commonly called solenoid valves, shall be used. (See volumes shall therefore be stated on calibration cer- the Figure 5 . ) Provisions shall be made to ensure that no tificate. If only one volume is determined, the certifi- water bypasses the field standard. The data recording cate shall clearly state and identify the side of the prover sheets should be checked and signed by all parties that that is calibrated to ensure that it is the side used to witness the calibration. prove a meter, The methods of calibrating a small volume prover CALIBRATING BIDIRECTIONAL include the waterdraw method, the gravimetric method, PROVERS and the master-meter method. The waterdraw method, After completion of the preparatory steps for flush- described in, is by far the most common. ing air out of the prover and stabilizing the temperature, at least one trial calibration run should be made to WATERDRAWMETHOD determine theapproximate volume of the small volume The calibration of small volume provers by the water- prover between its detectors so that the appropriate draw method may be simplified where possible by plac- number and sizesoffield standardscan beestimated. ACOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • I " rCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 14 &PROVING SYSTEMS CHAPTER minimum number of field standards should be used (see one detector switch point to a second detector switch Chapter 4.7). point. The described one-way trip procedureshould be Bidirectional calibration runs should now be started, repeated until satisfactory repeatability is achieved, The The displacer should be driven pastone of the switches average value for a minimum of two such one-way cor- into the space just outside the calibrated volume at rected volumes is considered the base volume for the either end of the smallvolume prover. The valves prover at standard conditions. should be reversed so that the displacer travels toward This publication does not restrict the determination the section to be calibrated while wasting the effluent of the base volume to two consecutive runs. More runs water, Before reaching the detector, the water should may be used if agreed to by the parties involved. be wastedslowly through a fast-acting automated valve. The procedurefor calibrating a unidirectional prover The waste should be stopped by using the fast-acting by the waterdraw method is substantially the same as automated valve at the instant the switch indication the proceduredescribed for a single one-waytrip of the shows “ON.” The temperature and pressure of the displacer ina bidirectional prover. The results of two or water in the prover should be recorded.Next, all addi- more consecutive runs (as agreed upon by the inter- tional effluent water should be directed into the se- ested parties) shall agree within 0.02 percent (kO.01 lected field standards. The withdrawals should be con- percent of the average) or better to determine base the tinued until the last field standard is being filled, The volume, For waterdrawcalibration of the upstream sec- withdrawal should be reduced to a controllable slow- in tion with the displacer moving the opposite direction, bleed rate through the fast-acting automated valve until the procedures are exactly the same except that care the “ON” switch indication is observed at the second must be taken to use the same edge of the detector detector point; the withdrawal should be stopped at the trigger that is used in calibrating the downstream sec- instant the switch shows “ON.” The total of the field- tion, and the displacer and valve seals must be con- standard volumes indicates the observed displaced vol- firmed in this direction. In effect, the difference be- ume betweendetectors in that direction of travel under tween upstream and downstream volumesis equivalent conditions of pressure and temperature thatexist at-the to the area of the shaft or shafts times the length be- start of calibration. The fill condition of the drain hose tween detector trigger points. and other withdrawal equipment shall be the same at the end of the withdrawal as it was at the start. REPEATABILITY , A similar displacer trip should now be made in the Repeatability is only one component of calibration opposite direction, repeating the procedure. These two accuracy. By filling the same field standards with the trips do not necessarily have to agree in observed dis- test runs made at an equal rate, an operator can com- placed volume because the action of the detectors may plete a series of erroneous calibrations as the result of be different for each direction of travel, a consistent leak. This hazard can be reduced or elimi- The calibrating procedure should be repeated until nated by making an additional run at a rate change of satisfactory repeatability is achieved. The average of at at least 25 percent. With a changed flowrate, adifferent least twoconsecutive round trip corrected volumes volume (after correction) that is outside 0.02 percent within 0.02 percent (rtO.01 percent of the average) is (kO.01 percent of the average) of the initial runs (after required.The corrected volume forthe consecutive correction) indicates the possibility of a leak in the trips in any given direction shall also agree within 0.02 proving circuit, which must be corrected before cali- percent (kO.01 percent of the average). bration can be achieved.All corrected volumes at both The base volume is the average of two or more con- flow rates shall fall within 0,02 percent (kO.01 percent secutive round trips of the displacer within the toler- of the average). This is true of both unidirectional and ances after correcting to the standard temperature and bidirectional provers. pressure. Failure to repeatmay be caused by leaking valves,air in the system, varying pressure, improper condition of OF CALIBRATION the displacer or detectors, or poor calibration tech- After a small volume prover is calibrated, the data nique. sheets shall be used to prepare a certification of cali- bration.The certificate shall state the calibration CALIBRATING UNIDIRECTIONAL method used, the base volume or volumes, the refer- PROVERS ence conditions, the serial numbers, and the date. The base volume of a unidirectional prover is the For unidirectional small volume provers that have a volume that is displaced as the displacer moves from shaft attached to the piston, thecertificate shall clearlyCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • MPMS 4.3-88 I 0732270 0054881 g- state and identlfy the side of the prover that is calibrated Pulse-interpolation or other types of counters used in to ensure that it isthe side used to prove a meter. conjunction with small volumeprovers shall be verified for correct operation before proof runs are conducted. 4.3.8 Operation (See Chapter 4.6 for descriptions of calibration tests and functional checks.) Proving with small volume provers requires the same Automated smallvolumeprovers that incorporate good practices commonly associated with provers. pipe microprocessor computer sequence control, pulse inter- All valves in the flow path between the meter and the polation, data acquisition, and data reduction shall be small volume prover must be positioned so that fluid tested for functional operation before meter proofs are cannot be diverted from or added to the stream. All- conducted. Such systems should contain self-test fea- valves associated with the proving system must include tures to verify the operation of computer software and a method for detecting leaks and must be free from hardware. Manufacturers’ procedures and recommen- leaks. dations should be followed in accordance with the ap- The proving system shallinclude at least one tempera- propriate sections of the Manual of Petroleum Mea- ture indicator in the flow lineadjacent to the meter and - surement Standards. at least one indicator adjacent tothe prover (see In unidirectional small volume provers, proving run a consists of one trip of the displacer through the cali- Pressure indicators shall be installed at appropriate brated section. locations to measure pressure at the meter and the Note: Care must be exercised during the use of displacers that incor- prover (see porate a rod or rods,since the volumes upstream and downstreamof Venting should be performed on the small volume the displacer will be different. prover and at other appropriate locations to ensure that In bidirectional small volume provers, a proving run air or gas is not trapped in the flowsystem before consists of a round tripof the displacer (that is, the sum proving. Steady flow should be established in the system to of two consecutive trips in opposite directions through ensure stable temperature and pressure before proving. the calibrated section). The need for maintaining backpressure on the meter/ prover system depends on various factors such as fluid 4.3.9 NonuniformPulses velocity, fluid vapor pressure, and operating pressure Caution isrecommendedwhen gear-driven pulse and temperature. (See Chapters 5.2 and 5.3 for recom- generators are used on displacement meters to ensure mendations.) that backlash, drive-shaft torsion, and cyclic effects do Meter pulse output should b e checked to ensure pulse not cause irregular pulse generation. If these problems integrity. Mechanical or electrical meter register tests occur, an evaluation of the gearing and pulse- should be conducted before proving. generation systemsshould bemadeto ensure that The displacer seals of small volume provers should be proper equipment is selected to provide optimum checked for sealingintegrity in accordancewith the performance. Problems should be referred to the manufacturer’s recommended procedure. manufacturer of the meter and the small volume prover.COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • APPENDIX A-EVALUATION OF DISPLACEMENT METER PULSE VARIATIONS A.1 General with a chart speed of 50 millimeters per second was used to display the pulse trains generated by the meters. During the development of Chapter 4.3, a question was raised about the magnitude of the pulse variations A.3 Analysis of Results in conventional displacement meter systems. No experi- ence or data were known, and two manufacturers vol- The chart records of the test were analyzed manually unteered to test several meters to define the range of to quantify the pulse variations. The following method pulse variations that could reasonably be expected. was used: Some of the terms used to describe pulse variations a. Pulses generated by several rotations of the meter include interpulse linearity and pulse interspace vari- system were recorded. ations. In fact, theconcern is with pulse frequency vari- b. The number of pulses representing 0.25 gallon of ations within one cycle or rotation of a meter-measuring liquidpassing through the meter was counted and element or the gear train that provides the output mo- marked. This resulted in 25- and 50-pulse segments for tion for the proving pickup or counter. Gear systems, the meter outputs that were tested. universal joints, and clutch-type adjustment devices are c. The length of chart represented by the pulses from known to impart accelerations within a single revolution 0.25 gallon was measured and recorded. of a meter. The same variations may occur in gear- d. The series of chart lengths was plotted in bar-graph driven turbine-meter outputs and turbine-meter rotors style. where the magnetic plugs are not uniformly spaced on e. The maximum chart length (that is, the lowest fre- the perimeter of the rotor. These are probably minor quency segment) and the minimum chart length (that is, variations compared with those that would be expected the highest frequency segment) within a meter rotation from displacement meters. No tests were performed on were identified. turbine meters. g. The pulse variation was calculated as follows: Forty-four tests consisting of 10-25 provings with a small volumeprover and 1 tests consisting of five pass 1 Percent pulse range = provings with a 54-barrel unidirectional displacement (maximum chart length - minimum chart length) X 100 f prover were completed and recorded. The results are 2 x mean chart length summarized in A.2 through A.4. A.2 Equipment A.4 Results A.2.1 METERSANDPROVERS A.4.1 GENERAL The displacement meters were connected in series in Figures A-1, A-2, and A-3 illustrate the typical bar- flowing-liquid test loops with nominal 15-gallon small graph analysis and results. The plots represent typical volume provers for the tests. A conventional 54-barrel results obtained for the threemeter sizes andthe acces- displacement prover was in the loop in one series of sory equipment noted on the respective figures. The tests. graphs are typical and cannot be considered specific for The meters were new production units available at anygiven manufacturer’s equipment. The charts do, the manufacturer’s test facility. Each had limited pre- however, illustrate the quality of the pulse output for test operation. various accessory arrangements and indicate the trend The pulses were generated in the conventional man- in pulse quality that may be expected from more or less ner from commercial displacement meters. Two 3-inch equipment on a meter stack. meters, two 4-inch meters, and one 6-inch meter were used. In addition, a 3-inch and a 6-inch meter were A.4.2 EXPLANATION OF BARCHART equipped with special close-coupled pickup arrange- A displacement meter equipped with a pulse gener- ments to monitor the performance of the measuring ator produces a series of electrical pulses separated by element only, without the influence of gears and shafts. spaces. For simplification, a pulse should be considered to have a length of $4 inch, which is then followed by a A.2.2 RECORDER space of 34 inch. This is termed a 50-percent-on/ A precisionhigh-frequency recording system was 50-percent-off pulse train. This is predicated on the used for the tests at both locations. The 8-pen recorder meter operating at a constant flow rate. 17COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 18 &PROVING SYSTEMS CHAPTER Even though the meter may be running at a constant between the pulses counted on the horizontalaxis. flow rate, irregularities in the meter’s drive mechanism Thus, on Figure A-1 the first six pulses/spaces account may cause the pulse train to be alternately compressed for 15.9 inches, whereas the second six pulses and ac- and expanded. companyingspacesaccountfor16.0inches, and so Each of the bar charts has a horizontal and vertical forth. The shortest and the longest lengths in the bar- axis, The horizontal axis represents the-total number of chart group are 15.85 and 16.1 inches,respectively. pulses accumulated over a given period ö time, andthe f Thus, 16.1minus 15.85 divided the mean lengthof 16 by numbers shown represent pulses counted on a linear inches is equal to 1.5 percent interspace variation. chart. The vertical axisrepresents the number of inches ,COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • SECTIONSMALL VOLUMEPROVERS 19 c .- O v .- SCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • 20 CHAPTER &PROVING SYSTEMSCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • MPMS 4 - 1 - 8 8 1 0732290 0054886 Z r *SMALL SECTION VOLUME PROVERS 21 a,COPYRIGHT American Petroleum InstituteLicensed by Information Handling Services
    • APPENDIX B-METER FACTOR DETERMINATION WITH SMALL VOLUME .PROVERS B.l General 8.3 Method 2 The contributors to the initial Chapter 4.3 perceived Meters that have a nonuniform pulse output (that is, a need to provide guidance for the development of ac- turbine and displacement meters with gear trains, shaft ceptable meter factors with small volume provers. The couplings, and shaft-driven accessories) maybe proved methods described in the following paragraphs have by increasing the number of passes or prover round been demonstrated to yield meter factors either com- trips or by increasing the repeatability tolerance. For parable to those obtained from conventional displace- example, ment provers or considered to beaccurate within usual 10 passes or prover round trips that repeat within tolerances by virtue of the repeatability of individual 0.10 percent (f0.05 percent of the average). passes or prover round trips or groups of passes or prover round trips from properly operated systems. The average of the prover-pass results becomes the Calculation details shall be in accordance with the usual meter factor to be used in subsequent operations. practices and as documented in Chapter 12.2. Additional passes or prover round trips may be added The meter factors obtained from two separate pro- as required toaccommodate meters that repeat beyond vers for a specific meter and operating condition will 0.10 percent (f 0.05 percent of the average) because of rarely agree exactly because of the differences in the the nonuniform pulse characteristics. For example, 15 equipment, base-volume calibration tolerances, meter prover passes or prover round trips that repeat within repeatability, and other factors. Agreement within 0.04 0.15 percent (k0.075 percent of the average) would be percent (f0.02 percent of the average) is generally con- the next level of consideration. sidered acceptable for normal industry practice if no The rationale for this procedure is that as the number other agreement has been defined. of passes or prover round trips is increased, the repeat- The following methods, based on observations and ability performance of the meter usually increases and experience, were compiled by the working group before at the same time the quality of the average improves. 1986. The methods are for guidance only; they are not a final recommendation, nor are they all-inclusive. Other methods,some of which were arrived at by vari- 8.4 Method 3 ous statistical techniques, exist but have not been suf- A meter that more severe nonuniform pulse out- has ficiently demonstrated to be listed here. The methods put or a prover that is minimal in size may necessitate will ultimately be replaced by mature techniques to be using the following method. The concept is to accumu- documented in a future section of Chapter 4 that will late individual prover passes or prover round trips to address operational aspects of proving and will super- form groups and thento average each group.The sede this appendix. ranges of these groups should fall withintolerances that are consistent with the first and second methods. The B.2 Method 1 average of the group averages then becomes the meter factor to be used in subsequent operations. Turbine meters anddisplacement meters whose pulse Increasing the number of passes or prover round trips generation is directly from, or very close the to, measur- in each group will improve the quality of the.intergroup ing elements can be proved with the same methods used repeatability. Twenty passes or prover round trips per for conventional displacement provers. This normally group is considered a practical limit; more will not im- consists of five consecutive passes or round trips that prove the quality. If an acceptable repeatability is not repeat within 0.05 percent (f 0.025 percent of the aver- obtained in 20or fewer passesor prover round trips, the age). The average of the results from these passes or meter manufacturer should be consulted. prover round trips then becomes the meterfactor to be used in subsequent operations. 23 GCOPYRIGHT American Petroleum InstituteLicensed by Information Handling Services