Download pdf - ORIFICE PLATE flow meters - · PDF file... , quarter-circle and square orifice plate, etc.. ... quadrant edge radius flange rating, orifice ... Each assembly consists of one orifice

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ORIFICEPLATEflowmeters1DifferentialpressureandpressurelossWhen a throttle element is interposed in a closed passage of fluid in piping, a difference is producedbetweenthepressureupstreamanddownstreamthethrottleelementasillustratedinfig1.Thisdifference(h=p1-p2) is called differential pressure. The fluid passing through the section 2 gradually regains itspressureas it flowsdownstream,butthedownstreampressurecannotberecovereduptotheupstreampressure,partofthepressurebeinglost.Thislossiscalledpressureloss(permanentpressureloss=p1-p3).The extent of this pressure loss depends on the type of throttle elemnts and their open area ratio, asshowninfig2.Therelationbetweentheflowrateandthedifferentialpressureisgivenby:

From the above, the relation between the flow rate and the differential pressurewhere the density istconstantbuttheflowisrateisvariableisaslistedinTable1.Inotherwords,theflowrateisobtainablebymeasuring the differential pressure.When the density is variable (when pressure and temperature arevariable),thetrueflowratecanbegivenbycompensatingthevarateofthedensitybytheaboveequations(this,however,isnotapplicablewhenthedensityvariestoagreatextent).


2Orificeplate2.1DescriptionOrificeplateshaveadisadvantageofpermittingagreaterpressurelossthanotherthrottleelements(flownozzles, venturi tubes, etc.) but are most popularly used because of their simpler shape, easiermanufacturability,lowercostandhigherreliability.Thetypesoforificeplatesincludeconcentric,eccentric,segmental,quarter-circleandsquareorificeplate,etc..2.2Specificationorificeboretype:

concentricsquareedgedorifices quadrantedgedorifices eccentricorifices

segmentalorificesminimumquadrantedgedorificediameter4.5mm

flowcalculationstandards: concentricsquareedgedorifices:ISO-5167-2003;ASME-19.5 1D-1/2D(radius)tap 2.5D-8D(pipe)tapeareper“ASMEFluidMeters,TheirTheoryandApplication, 5thEdition,1959” eccentricorifices/segmentalorifices:bs1042flangeratings: ASME,300,600,900,1500,2500lbs(RF,RTJ) (ASMEB16.36–ASMEB16.47AandB API2000,3000,5000,1000015000(API6A)


pressuretaps: flangetap

cornertap1Dand1/2D(Radius)tap–

platethickness: 3,6,9,12mm,etc.

tabhandle:

weldedtoorificeplatematerials:plate

ASTM304,316SS,Duplex,exoticmaterialdrainandventhole:

perISA-RP3.2recommendations.Notdrilledfororificeboresmallerthan25.4mm

markings:Upstreamsideoftabhandlestamped“+”boretypesize,linesize,TAGno.,quadrantedgeradiusflangerating,orificematerialserialnumber.

Specialmarkings:

specialmarkingmaybefurnishedtomeetspecificrequirements2.3Typesconcentric

This has special features such as simple structure, high accuracy, easymountinganddismounting.Theorificeplatesarecorrectly finishedto thedimensions, surface roughness and flatness to the applicable standard.Differentialpressureismeasuredthroughflange,venacontracta,radiusorcornertaps.

Eccentric

Forliquidscontainingsolidparticlesthatarelikelytosedimentorforvaporslikelyto deposit water condensate, this orifice plate is used with its eccentricbore bottom flush with the bottom of the piping surface so that thesedimentationofsuchinclusionsisavoided.Likewise,forgasesorvapors,itmaybeinstalledwithitseccentricboretopflushwithwiththeboretopofthepipingtoavoidthestayofgasorvaporinitsvicinty.Flangetapsorvenacontractatapsareusedfortheorificeplate.

Segmental


Theboreoftheorificeplateisasemicircletoperformthesamefunctionastheeccentricorificeplate.Thisisusedforsimilarpurposes.Flangetapsorvenacontractatapsareemployedtotakeoutfluidpressures.

Quarterant

Theinletedgeoftheboreofthisorificeplateisroundedtoaquartercircle.This orifice plate is principally used for measuring flow rates of lowReynoldsnumbers.Flangetapsorcornertapsareused.


3Orificeplatewithring3.1DescriptionOrifice ring assemblies are used for flow measurement of smaller or medium sized pipes at lowerpressures.Eachassemblyconsistsofoneorificeplateandtwoorificerings.Differentialpressuresaretakenoutinacornertapsystem.Orificeblocks,whichareofaunit-constructiontypeandprovidehigherpressureratingsthantheorificeringassemblies,alsoareavailable.Differentialpressuresaretakenoutinacornertapsystem.3.2Specificationorificeboretype:

concentricsquareedgedorificesquadrantedgedorificesminimumquadrantedgedorificediameter4.5mmminimumquadrantedgeradius0.5mm

flowcalculationstandards:

concentricsquareedgedorifices:ISO-5167-ASME19.51D-1/2D(radius)tap2.5D-8D (pipe) tape are per “ASME Fluid Meters, Their Theory andApplication,

flangeratings: ASME, 300, 600, 900, 1500, 2500 lbs (RF, RTJ) (ASMEB16.36–ASMEB16.47AandB API2000,3000,5000,1000015000(API6A)pressuretaps:

cornertapplatethickness:

3,6,9,12mm,etc.tabhandle:

weldedtoorificeplatepressuretaphandle:

15mm (½”) Sch80 length 150mm tap connections½”-NPT-male, socketweld,buttweld,flange(Flangeratingtobethesameastheoftheprocesspipeline.)

materials:

ringandpressuretapnipple:carbonsteel,ASTM304SS,316SS;DIN1.4571,etc.plate:ASTM304,316SS,duplex,superduplex,exoticmaterialtabhandle:ASTM304,316SS,

drainandventhole:


perISA-RP3.2recommendations.Notdrilledfororificeboresmallerthan25.4mm

markings: Upstreamsideoftabhandlestamped“+”

boretypesize,linesize,TAGno.,quadrantedgeradiusflangerating,orificematerialandserialnumber.

Specialmarkings:

specialmarkingmaybefurnishedtomeetspecificrequirementsGasket:

non-asbestoswith1.5mmthickness

4Orificeplatewithholdingring(RTJ)4.1DescriptionTheholdingringassemblyisacombinationofaholdingringandanorificeplatedesignedforring-type-joint(RTJ)flangesofANSIorJPIspecifications.Theholderringhasafunctionofholdingtheorificeplateandalsoafunctionasagaskettopreventleakageoftheprocessfluid.Thismetallicsealingsystemisapplicabletoafluid of high temperature and high pressure. The pressure tapping system normally is of the flange taptype.4.2Specificationsorificeboretype:

concentricsquareedgedorificesquadrantedgedorifices-

flowcalculationstandards:concentric square edged orifices: ISO-5167-1991; ASME-1991; JIS Z 8762-1988Note:ASME-1991,JISZ8762-1988flowdatausedtocalculateorificeboreisidenticaltothatofISO-5167-1991

flangeratings: ASME, 300, 600, 900, 1500, 2500 lbs (RF, RTJ) (ASMEB16.36–ASMEB16.47AandB API2000,3000,5000,1000015000(API6A)pressuretaps: flangetapsplatethickness:

3,6,9,12mmetc.tabhandle:

weldedtoring


holdingring:

rivetedtoplate,octagonalorovaldrainandventhole:

perASMErecommendations.Nodrillfororificeboressmallerthan25.4mm

materials:plate: ASTM304SS,316SS;duplex,superduplex,exoticmaterialholdingring: ARMCO,softiron,StainlessSteelwithhardnessaccordingtoASMEB16.20markings: Upstreamsideoftabhandlestamped“+”

withboretypelinesize,TAGno.,quadrantedgeradiusflangerating,orificematerialserialnumber.

Specialmarkings:

specialmarkingmaybefurnishedtomeetspecificrequirements.

sheetgaskets1.5mmspiralwoundedgasket4.5mm–

pipingconnectionmethod:

ANSI:buttweldingtype(weldedneck)