1、Manual of PetroleumMeasurement StandardsChapter 5MeteringSection 2Measurement of Liquid Hydrocarbons by Displacement MetersTHIRD EDITION, SEPTEMBER 2005REAFFIRMED, JULY 2015Manual of PetroleumMeasurement StandardsChapter 5MeteringSection 2Measurement of Liquid Hydrocarbons by Displacement MetersMeas
2、urement CoordinationTHIRD EDITION, SEPTEMBER 2005REAFFIRMED, JULY 2015SPECIAL NOTESAPI publications necessarily address problems of a general nature. With respect to partic-ular circumstances, local, state, and federal laws and regulations should be reviewed.Neither API nor any of APIs employees, su
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10、nstituteFOREWORDChapter 5 of the API Manual of Petroleum Measurement Standards (API MPMS) pro-vides recommendations, based on best industry practice, for the custody transfer metering ofliquid hydrocarbons. The various sections of this Chapter are intended to be used in con-junction with API MPMS Ch
11、apter 6 to provide design criteria for custody transfer meteringencountered in most aircraft, marine, pipeline, and terminal applications. The informationcontained in this chapter may also be applied to non-custody transfer metering.The chapter deals with the principal types of meters currently in u
12、se: displacement meters,turbine meters and Coriolis meters. If other types of meters gain wide acceptance for themeasurement of liquid hydrocarbon custody transfers, they will be included in subsequentsections of this chapter.Nothing contained in any API publication is to be construed as granting an
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16、Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least everyfive years. A one-time extension of up to two years may be added to this review cycle. Statusof the publication can be ascertained from the API Standards Department, telephone (202)682-8000. A catalog of API pu
17、blications and materials is published annually and updatedquarterly by API, 1220 L Street, N.W., Washington, D.C. 20005.Suggested revisions are invited and should be submitted to the Standards and PublicationsDepartment, API, 1220 L Street, NW, Washington, DC 20005, standardsapi.org.iiiCONTENTSPage5
18、.2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.2 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15.2.3 FIELD OF APPLICATION . . . . . . .
19、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15.2.4 REFERENCED PUBLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15.2.5 METER PERFORMANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20、. .15.2.5.1 Meter Readout Adjustment Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15.2.5.2 Causes of Variations in Meter Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2v1Manual of Petroleum Measurement StandardsChapter 5MeteringSection 2Measurement of Li
21、quid Hydrocarbons by Displacement Meters5.2.1 IntroductionAPI MPMS Chapter 5.2, together with the general consid-erations for measurement by meters found in API MPMSChapter 5.1, describes methods for obtaining accurate quan-tity measurement with displacement meters in liquid hydro-carbon service.A d
22、isplacement meter is a volume measuring device whichseparates a flowing liquid stream into discrete volumes andcounts the separated volumes. The meter carries through itsmeasuring element a theoretical swept volume of liquid, plusthe slippage for each stroke, revolution, or cycle of the mov-ing part
23、s. The indicated volume of the displacement metermust be compared with a known volume that has been deter-mined by proving, as discussed in MPMS Chapter 4.It is recognized that meters other than the types describedin this chapter are used to meter liquid hydrocarbons. Thispublication does not endors
24、e or advocate the preferential useof displacement meters, nor does it intend to restrict thedevelopment of other types of meters.5.2.2 ScopeThis section of API MPMS Chapter 5 covers the uniqueperformance characteristics of displacement meters in liquidhydrocarbon service5.2.3 Field of ApplicationThe
25、 field of application of this section is all segments ofthe petroleum industry in which dynamic measurement of liq-uid hydrocarbons is required. This section does not apply tothe measurement of two-phase fluids.5.2.4 Referenced PublicationsThe current editions of the following API MPMS Stan-dards co
26、ntain information applicable to this chapter:API Manual of Petroleum Measurement StandardsChapter 4 “Proving Systems”Chapter 4.2 “Pipe Provers” Chapter 5.1 “General Considerations for Measurementby Meters”Chapter 5.4 “Accessory Equipment for Liquid Meters”Chapter 7 “Temperature”Chapter 8 “Sampling”C
27、hapter 11.1 “Volume Correction Factors” (ASTM1 D1250, ISO2 91.1)Chapter 12 “Calculation of Petroleum Quantities”Chapter 13 “Statistical Aspects of Measuring andSampling”5.2.5 Meter PerformanceMeter performance is defined by how well a metering sys-tem produces, or can be made to produce, accurate me
28、asure-ments. See 5.1 for additional details.5.2.5.1 METER READOUT ADJUSTMENT METHODSEither of two methods of meter readout adjustment may beused, depending on the meters intended application andanticipated operating conditions.5.2.5.1.1 Direct Volume Readout MethodWith the first method the readout i
29、s adjusted until thechange in meter reading during a proving equals or nearlyequals the volume measured in the prover. It is then sealed toprovide security against unauthorized adjustment. Adjustedmeters are most frequently used on retail delivery trucks andon truck and rail-car loading racks, where
30、 it is desirable to havea direct quantity readout without having to apply mathematicalcorrections. An adjusted or direct-reading meter is correct onlyfor the liquid and flow conditions at which it was proved.5.2.5.1.2 Meter Factor MethodWith the second method of meter readout adjustment, themeter re
31、adout is not adjusted, and a meter factor is calculated.The meter factor is a number obtained by dividing the actualvolume of liquid passed through the meter during proving bythe volume indicated by the meter. For subsequent meteringoperations, the actual throughput or measured volume isdetermined b
32、y multiplying the volume indicated by the meterby the meter factor (see Chapter 4 and Chapter 12.2).2CHAPTER 5METERINGWhen direct quantity readout is not required, the use of ameter factor is preferred for several reasons: a. It is difficult or impossible to adjust a meter calibratormechanism to reg
33、ister with the same resolution that isachieved when a meter factor is determined. b. Adjustment generally requires one or more reprovings toconfirm the accuracy of the adjustment. c. In applications where the meter is to be used with severaldifferent liquids or under several different sets of operat
34、ingconditions, a different meter factor can be determined foreach liquid and for each set of operating conditions.For most pipelines, terminals, and marine loading andunloading facilities, meters are initially adjusted to be correctat average conditions, and the mechanisms are sealed at thatsetting.
35、 Meter factors are then determined for each petroleumliquid and for each set of operating conditions at which themeters are used. This method provides flexibility and main-tains maximum accuracy.5.2.5.2 CAUSES OF VARIATIONS IN METER FACTORThere are many factors which can change the performanceof a d
36、isplacement meter. Some factors, such as the entranceof foreign matter into the meter, can be remedied only byeliminating the cause of the problem. Other factors depend onthe properties of the liquid being measured; these must beovercome by properly designing and operating the meteringsystem.The var
37、iables which have the greatest effect on the meterfactor are flow rate, viscosity, temperature, and foreign matter(for example, paraffin in the liquid). If a meter is proved andoperated on liquids with inherently identical properties, underthe same conditions as in service, the highest level of accu
38、-racy may be expected. If there are changes in one or more ofthe liquid properties or in the operating conditions betweenthe proving and the operating cycles, then a change in meterfactor may result, and a new meter factor must be determined. 5.2.5.2.1 Flow Rate ChangesMeter factor varies with flow
39、rate. At the lower end of therange of flow rates, the meter-factor curve may become lessreliable and less consistent than it is at the middle and higherrates. If a plot of meter factor versus flow rate has been devel-oped for a given set of operating conditions, it is possible toselect a meter facto
40、r from the curve; however, if a provingsystem is permanently installed, it is preferable to reprove themeter and apply the value determined by the reproving. If achange in total flow rate occurs in a bank of two, three, ormore displacement meters installed in parallel, the usual pro-cedure is to avo
41、id overranging or underranging an individualmeter by varying the number of meters in use, thereby distrib-uting the total flow among a suitable number of parallel dis-placement meters.5.2.5.2.2 Viscosity ChangesThe meter factor of a displacement meter is affected bychanges in viscosity which results
42、 in variable “slippage”.Slippage is a term used to describe the small flow ratethrough the meter clearances which bypasses the measuringchamber. The meter factor accounts for the rate of slippageonly if the slippage rate is constant. Viscosity may vary as aresult of changes in the liquids to be meas
43、ured or as a resultof changes in temperature that occur without any change inthe liquid. It is therefore important to take into account theparameters that have changed before a meter factor isselected from a plot of meter factor versus viscosity. It ispreferable to reprove the meter if the liquid ch
44、anges or if asignificant viscosity change occurs.5.2.5.2.3 Temperature ChangesIn addition to affecting the viscosity of the liquid, changesin the temperature of the liquid have other important effectson meter performance, as reflected in the meter factor. Forexample, the volume displaced by a cycle
45、of movements ofthe measuring chambers is affected by temperature. Themechanical clearances of the displacement meter may also beaffected by temperature. Higher temperatures may partiallyvaporize the liquid, causing two-phase flow, which willseverely impair measurement performance.Either an automatic
46、 temperature compensator, or a calcu-lated temperature correction based on the volume weightedaverage temperature of the delivery, may be used to correctindicated volume to a volume at a base or reference tempera-ture.5.2.5.2.4 Pressure ChangesIf the pressure of a liquid when it is metered varies fr
47、omthe pressure that existed during proving, the relative volumeof the liquid will change as a result of its compressibility. Thepotential for error increases in proportion to the magnitude ofthe difference between the proving and operating conditions.For greatest accuracy, the meter should be proved
48、 at the oper-ating conditions (see Chapter 4 and Chapter 12).The physical dimensions of the meter measuring chamberwill also vary as a result of changes in the expansion of itshousing with varying pressures. The use of double-casemeters prevents this from occurring. Volumetric corrections for pressu
49、re effects on liquids thathave vapor pressures above atmospheric pressure are refer-enced to the equilibrium vapor pressure of the liquid at a stan-dard temperature, 60F, 15C, or 20C, rather than toatmospheric pressure, which is the typical reference for liq-uids with measurement-temperature vapor pressures belowSECTION 2MEASUJREMENT OF LIQUID HYDROCARBONS BY DISPLACEMENT METERS 3atmospheric pressure. Both the volume of the liquid in theprover and the indicated metered volume are corrected fromthe measurement pressure to the equivalent volumes at theequilibrium vapor pressure
