1 FUNDAMENTALS OF CORIOLIS METERS AGA REPORT NO. 11 Stan Calame
Oil and Gas Business Development Manager Emerson Process
Management- Micro Motion, Inc. 7070 Winchester Circle Boulder,
CO80301 Introduction Sincetheearly1980s,Coriolismetershavegained
worldwideacceptanceingas,liquid,andslurry
applicationswithaninstalledbaseofmorethanone
millionunits.Throughsignificantdesign,enhancements
intheearly1990sCoriolismetershaverapidlygained
worldwideacceptanceingasphaseapplicationswith
over100,000metersinstalledworldwideandmost
notablythepublicationofthesecondeditionofAGA
ReportNumber11,MeasurementofNaturalGasby Coriolis Meter.
Havingtheabilitytobidirectionalmeasurealmostany
gasfrom-400to+660degreesFahrenheitwithlittleto noconcern
oferrorcausedby flow profile disturbances, pulsations, orflow
surges, Coriolismeters are becoming the meter of preference in many
applications. Coriolisisasmalltomediumline-sizetechnology;
currentlythelargestofferingfromanyvendorforgas applications is a
250mm (10) equivalent flow diameter.
ThepressuredropandflowrangeofaCoriolismeter
drawsadirectrelationshiptotheactualflowarea
throughthemeter.WhencomparingCoriolistoother metering technologies;
i.e. the flow area trough a turbine
meteristheareanotdisplacedbytheturbineinternals and rotor, the flow
area of an orificemeter is that of the
orificediameter.Becauseofthisrelationship,aCoriolis
meterwilltypicallybeonepipesizesmallerthana
turbinemeterandseveralsizessmallerthananorifice whilehaving similar
pressuredrops at flowing pressures in the 300 ANSI class and above.
200mm (8) Coriolis meter installed in 250mm (12) line
Beingatechnologywithoutwearingparts,Coriolis meters are immune to
flow factor shift as they age. Most
recently,resonantmodalanalysistechniques
incorporatedintosomeCoriolismeterdesignsallowing flow
accuracyverificationon-line,withoutdisruptionin flow, and without
visual inspection of the flow element.
Overall,Coriolismetersgreatlyreducemeasurement
uncertaintyandmaintenancecostsascomparedtoother gas flow
technologies. This paper will discuss the theory
ofoperation,application,maintenance,andprovide
examplesofCoriolismeterapplicationingas measurement. Theory of
Operation A Coriolismeteris comprisedof twomain components, a
sensor (primary element) and a transmitter (secondary).
Coriolismetersdirectlyinferthegasmassflowrateby
sensingtheCoriolisforceonavibratingtube(s).The conduit consists of
one or more tubes that vibrate at their
resonantfrequencybyaDriveCoil.Sensingpickoff
coilslocatedontheinletandoutletsectionsofthe
tube(s),oscillateinproportiontothesinusoidal vibration. 2 Coriolis
Sensor Components Duringflow,thevibratingtube(s)andgasmassflow
coupletogether,duetotheCoriolisforce,causing
twistingoftheflowtube(s),frominlettooutlet, producing a phase shift
between the signals generated by
thetwo-pickoffcoils.Thephaseshiftordifferencein time is directly
proportional to mass flow rate. Coriolis Sensing/Pickoff Signals
Notethatthevibrationfrequencyoftheflowtubesis
proportionaltotheflowingdensityofthefluid.Forgas
applications,theflowingorlivedensitymeasured by the Coriolis meter
is not used for gas measurement, as
itspotentialerrorinrelationtogasdensitiesisnot
acceptableforgasflowmeasurementpurposes.
Althoughthisisthecase,densitymeasurementingas
applicationscanbeusedasanindicatorofchangeina Meter Selection -
Temperature ThetypicaloperatingtemperaturerangeofCoriolis meters is
-400 to +400 degrees Fahrenheit (-240 to +200 degrees Celsius).
Some advanced designshave extended the high temperature operating
range up to +660 degrees Fahrenheit (+350 degrees Celsius).
Otherthantemperaturecompensationfortheeffectof
Youngsmodulus,flowingtemperaturemeasurementis not requiredfor
themeasurement ofmass, basevolume, or energy with Coriolis meters.
Meter Selection - Pressure Most Coriolis meters are designed to
operate at pressures upto1480psi(600ANSI),withmetersconstructedof
hastalloyandduplextubescapableofoperatingat pressures up to 3600
psi (1500 ANSI). Changesinoperatingpressurecanproduceabiasoften
referredtoastheflowpressureeffectthatcanbe compensated for. The
"flow pressure effect" of a Coriolis
meteriscausedbythestiffeningoftheCoriolisflow
tube(s)asthefluidpressureinthemincreases.This effect issimilar to
abicycle innertube as itsinternal air pressure is increased; the
inner tube ismore flexible at a lower pressure than at a higher
pressure. Highfluidpressurescausetheflowtubetobemore
resistanttothetwistingforceof theCoriolis Effectthan
theyareatlowpressures.Astheinternalflowtube(s)
pressureincreases,theCoriolisEffectortwistingofthe
flowtube(s)observedforagivenmassflowrate
decreases.Likewise,astheinternalpressuredecreases
theCoriolisEffectobservedforagivenmassflowrate increases. Every
Coriolis meter design and size has a different flow pressure effect
specification. To correct for flow pressure
effecttheflowpressureeffectcompensationfactor detailed below is
applied to the indicated mass flow rate. 1 Coriolis meters flow
factor and/or clean vs. dirty. Coriolis is a direct inferential
mass meter eliminating the Where: Fp = 1 + ((P Effect /100) * (P
Static P)) Cal requirementtoquantifygasvolumetricallyatflowing
conditions; i.e. the need to measure flowing temperature,
flowingpressure,andcalculateaflowing
compressibility.Equationsandmethodsforthe
conversionofmasstobasevolumearedocumentedin AGA Report Number 11,
Measurement of Natural Gas Fp PEffect PStatic PCal =Flow pressure
effect compensation factor = Pressure effect in percent psi =
Measurement fluid static pressure in psi = Calibration static
pressure in psi by Coriolis Meter and AGA Report Number 8,
Compressibility Factors for Natural Gas and Other Hydrocarbon
Gases. MostCoriolistransmittershaveprovisionsforapplying
anaverageflowpressureeffectcorrectionandthe
monitoringastaticpressuretransmittertofacilitatelive pressure
compensation. 3 Meter Selection - Compressibility, Density,
Viscosity, and Reynolds Number
Althoughchangeincompressibility,density,viscosity,
andReynoldsNumberareaconcernwithalmostall
meteringtechnologies,theinferredmassflowrateofa
curvedtubeCoriolismeterisinsensitivetoerrorcaused by these changes.
Meter Selection Rate of Change High rates-of-change in flow or flow
surges are the most commoncauseofdamageinflowmeterswithrotating
flowelements;e.g.Turbine,Rotary,Positive
Displacement,etc.Highratesofchangeinflowcause
thesemeterstoover-speedandaretypicallyinherentto engine, boiler,
and burner fuel gas applications. Duringaflowsurge,theinletflow
splitterofaCoriolis meter chokesflow to the diameter of theflow
tubes and theflowingdensitiesofnaturalgasmixturesdonot provide
enough inertialforce to be imparted on theflow
tubestodamagethem.Thiscoupledwiththeabilityof
advanceddesignstomeasureuptochokevelocities
removesanyrate-of-changeconcernintheuseof Coriolis. Meter Selection
- Over Range Overrangingoftencausesmechanicaldamageand/or loss of
measurement in the use of almost any flow meter. Some Coriolis
meter designs can measure gas flow up to sonic velocity or choke
point (approximately 1400 ft/sec with naturalgasmixturesfrom
atmosphericto 2220psi)
withoutlossofmeasurementordamage.Manufacturers
shouldbeconsultedonthemaximumvelocitylimitof their particular
Coriolis meter design. Pipingerosioncausedbyhighflowvelocitiesisa
commonconcerningasapplications.Althoughthis concern is valid for
carbon steel piping, it is not valid for
stainlesssteelpipingorCoriolismeters.Foragasto erode ametal,
themetalssurfacemustfirst oxidize and
thenhighgasvelocitieserodethesoftoxidelayer.In
mostgasapplications,moistureinthegascauses
oxidationofcarbonsteelpipingdrivingthevelocity
concernsofmanypipingengineers.ACoriolismeters
immunitytohighvelocitygaserosionissimilartothat of an orificeplate
or sonicnozzle, in that they aremade of stainless
steelorothernickelalloyswhicharehighly
immunetocorrosion/oxidationandthushighvelocity gas erosion. If
abrasive contaminants (sand, welding rods, rocks, etc.) are present
in the gas flow stream, erosionor damage of
thewettedmetercomponentscausedbythisdebris
travelingathighflowvelocitiesisofconcern.These
concernsareapplicationspecific,butwhenpresent, filtration should be
used to protect the meter. Meter Selection - Flow Pulsation The
pulsation of flow is typically ofhigh concernin the
useofeveryflowmeteringtechnology.Pulsatingflow
cancausemeasurementerror(e.g.fluidicoscillation,
orifice/differentialhead,rotary,turbine,andultrasonic
meters)andmechanicaldamageinmetering
technologieswithloadbearingsandgears(e.g.rotary,
andturbinemeters).Flowpulsationsaretypicallya
concernonfuelgaslinestoreciprocatingengines,the
inletandoutletcompressionlinesofreciprocating compressors, and the
inlet and outlet lines of regulators.
AdvancementsinCoriolisflowmeterdesignhave yielded designs that
maintain accuracy over a wide range
ofpulsatingflowconditions.AlthoughCoriolismeters,
forthemostpart,areimmunetoerrorcausedbyfluid pulsations, they are
sensitive to pulsations at the resonant frequency of themeters flow
tubes. In gas applications, Coriolismeters typically operate at
resonantfrequencies above100Hzor6000cyclesperaminute,wheregas
pulsations are typically not found. Meter Selection - Gas Quality
Shoulddebris(i.e.sand,gravel,weldingrods,welding slag) exist that
could erode, scar, or plug theflow tubes,
filtrationshouldbeutilizedinthemeteringsystem
designtoprotectthemeter.Althoughfinesoftparticles
likeironoxide,oils,anddustwillnotdamagetheflow
tubesofaCoriolismeter,build-upofthisdebriscan
causeanimbalanceintheflowtubesandoutof
specificationshiftinthemeterszero.Coriolismeters
havehigherrorimmunitytodirtyprocessesbecausean
outofspecificationzerocausedbydebrisbuildupwill induce detectable
errors only at the low end of ameters flow range and are typically
insignificant/undetectable at flows in the high end of the flow
range. Inmostapplications,gasvelocitiesthroughtheflow
tubesatthehighendoftheflowrangearetypically
sufficienttomaintainameterscleanliness.AZero
Checkperformedduringmaintenancewillidentifyif
debrisbuilduporcoatingisaffectingthemeters
measurementaccuracy.Ifanoutoftolerancecondition
exists,themeterszerocanberecalibratedtoregain accuracy. Meter
Selection - Bidirectional Coriolismeters are bidirectionalmeters,
duringflow the signal from the inlet pick-off coil lags the outlet
pick-off 4 coilsignal,bydeterminingwhichpickoffsignalis lagging
flow direction is determined. Meter Selection - Measurement
Accuracy Themeasurement accuracy of a Coriolismeter is design
andfluidspecific.MostbendingmodeCoriolismeters
canmeasuregasmixturesataccuraciesbetterthan1%.
SomeadvancedCoriolisdesignscanachieveaccuracies of +/- 0.35%. Meter
Selection Flow Range Theflow rangeof aCoriolismeteris
determinedonthe lowendbyminimumacceptableaccuracyandworst-
casedriftinameterszero,referredtoasZero
Stability.ZeroStabilityisthepotentialerrorinall
indicatedflowrates.Duetothisfact,aCoriolismeters
accuracynaturallyimprovesasmassflowrateincreases until amaximum
accuracy, dictated by meter design and measurement fluid,is
reached. ThehighendofaCoriolismetersflowrangeis
determinedbyflowvelocity.MostCoriolismeterscan
measuregasvelocitiesupto200ft/secandadvanced
designscanmeasuregasflowatvelocitiesuptosonic
velocityorchokepointwithoutlossofmeasurementor
damage.AlthoughsomeCoriolismeterdesignscan
measuregasflowsuptosonicvelocity,amaximum
allowablepressuredropdictatedbytheapplicationin
whichtheywillbeappliedtypicallydetermines
maximumflow.Thisisquitedifferentfromtraditional
flowtechnologieswheremaximumflowiswhere
measurementislostand/orflowdamageoccurstothe flow element.
Therefore,theappropriatesizeofCoriolismeterforan application is
determined by the following. -Allowable Pressure Drop @ Maximum
Flow -Minimum Acceptable Accuracy @ Minimum Flow Sinceflow
throughthemeterincreaseswithsquareroot of static pressure change
and the minimum flow through
themeterisconstantandrelativetotheminimum
acceptableaccuracy,applyingameterathigher
pressures,ineffect,increasesoperatingrangeand turndown. Coriolis
Turndown versus Operating Pressure
Insummarytheoperatingrangeforagivenpressure
dropcanbeincreasedbyinstallingaCoriolismeterat
high-pressurelocationsorupstream of regulationversus downstream.
Meter Selection Low Flow
Thefollowingequationisthemostutilizedmethodfor determining the
minimum flow rate of a Coriolis meter. MinFlow = ZeroStabilty
Accuracy% /100 Since Zero Stability can be expressed in standard
volume (scf)unitsforagivenrelativedensity,the minimum
standardvolumeflow rateatauserspecifiedacceptable
accuracyneverchangesregardlessofpressureor
temperatureforagivenmeterdesignandsize.Thisis differentfrom
othergasmeasurement technologieswere
theminimumflowratevarieswithpressureand temperature. Meter
Selection - Maximum flow
SomeCoriolismeterdesignscanmeasuregasflowsup
tochokepointoraflowvelocityequivalenttosonic
velocity(Mach1)ofthegasmixture(Approximately 1400 ft/secfornatural
gasmixtures from atmospheric to
2220psi).Althoughthisisthecase,Coriolisare
typicallysizedwithinanacceptablepressuredroplimit
dictatedbytheapplication.Utilizingasetofgas
referenceconditions,oftenfoundinthemanufacturers specifications,
thefollowing equation can be utilizedfor
calculatingtheflowratethroughameteratagiven pressure drop. 5 ( b vf
vb f f b vf vb f f f APAppGas f ( RefGa s ( Installation - Meter
Mounting APRe fGas Q RefGa s f Ap p Ga s Ap p Ga s f Ap p Ga s = Q
Ap p Ga s Considerationshouldbegiventothesupportofthe
sensorandthealigEnqm. e(6n.t3o) ftheinletandoutletpiping flanges
with the sensor. For field fabrication of piping, a spool piece
should be used in place of the meter to align Where: APAppGas RefGa
s APRe fGas Ap p Ga s Q RefGa s Ap p Ga s Q Ap p Ga s = Maximum
allowable pressure drop across the Coriolis meter with an
application gas density ( ) in psi Ap p Ga s = Density of reference
gas at flowing conditions in lb/cf = Reference differential
pressure across Coriolis meter with reference gas density ( ) in
psi RefGa s = Density of application gas at flowing conditions in
lb/cf = Volume flow rate of reference gas at flowing conditions
ofand RefGa s APRe fGasin cf/hr = Density of application gas at
base conditions in lb/cf = Volume flow rate of application gas at
base conditions in cf/hr or scf/hr
pipe-workpriortoweldingtheCoriolissensormating flanges; i.e. slip
fit is ideal. Pipingshouldfollowtypicalindustrypipingcodes.
Meterperformance,specificallymeterzero,canbe
affectedbyaxial,bending,andtorsionstresses.When
thesestressesexist,pressure,weight,andthermal
expansioneffectscanamplifythem.Althoughmost
Coriolismetersaredesignedtoberelativelyimmuneto
theseeffects,utilizingproperlyalignedpipe-workand
pipingsupportsinsurestheutmostperformanceofany
meterdesignandinmanycasesyieldsperformance better than the
manufacturers specifications. Installation - Meter Orientation
Coriolismetersareimmunetoorientationeffectswhen
measuringsingle-phasefluids,manyfluidsarerarely
alwaysinasinglephaseorfreefromsporadic
contaminatesintheoppositephase.Asaruleingas
measurement,theCoriolissensorshouldbeorientedin
suchawayastominimizethepossibilityofheavier
components,likecondensate,settlinginthesensorflow
tube(s).Solids,sediment,plugging,coatings,ortrapped
liquidscanaffectthemeterperformance,especially
whenpresentduringzeroingofthemeter.Allowable
sensororientationswilldependontheapplicationand Installation -
Electrical Classification
MostCoriolismetersaredesignedtomeetClass1,
Division1,andClass1,Division2hazardousarea classifications.
Installation Up and Downstream Piping
InstallationeffectstestingperformedbySouthwest
ResearchInstitute(SwRI)andsponsoredbytheGas
ResearchInstitute(GRI)in2002confirmedbenttube
Coriolismeterstobemostlyimmune,withinthe
uncertaintyoftheflowlab,toupstreaminstallation
effects.ThetestresultscanbefoundinGRITopical Report GRI-01/0222.
Perturbation testing including pulsation and regulator valves
placed in close proximity of a bent tube Coriolis meters has also
been conducted by other organizations and independent parties and
has shown flow conditioning or straight pipe up and downstream of a
Coriolis meter is not required.
thegeometryofthevibratingflowtube(s).Ingas
service,theidealorientationofthesensoriswiththe flow tubes in the
upright position. Installation Piping Configuration Curved or bent
tube Coriolis flow sensors are immune to
velocityprofiledistortionandswirleffects,thus
allowingthedesignerflexibilityrestrictedonlybygood
pipingsupportpracticestominimizestructuralstresses on the sensor
body. The piping configuration of a Coriolis installation should
consistofblockvalvesupanddownstreamofthe
Coriolismeterwithbleedvalvestofacilitatepurgingof
thepiping,zeroingofthemeter,andmaintenance
procedures.Abypassshouldbeinstalledaroundthe
meterifinterruptionofservicetothecustomerisan issue.
Althoughthepressureportforflowpressureeffect
compensationhasapreferredlocationupstreamofthe
Coriolissensor,itcanbelocatedupordownstreamof 6
theCoriolissensor.Atemperatureportforverification of theCoriolis
sensorsmeasuredtemperatureshould be located upstream of the sensor
due to the Joule Thomson effect at high differential pressures
across the sensor. Typical Coriolis Meter Installation Metrology -
Calibration Duetothevariabilityofmanufacturingprocesses,all
Coriolismetersrequireaflowcalibrationtoadjusttheir
performancetotheaccuracylimitsinherenttotheir
particulardesign.AsacommonpracticemostCoriolis
calibrationoverawatercalibrationonCoriolismeters
intendedforgasmeasurement.Althoughthisisthecase theusershouldreview
industry recommendedpractices,
standards,andregulatoryrequirementswhen establishing calibration
policy for Coriolis. Coriolismetersareanattractivetechnologywhenthe
availability,capability,oreconomicviabilityofgas calibrations is
limited. Highly accurate water calibrations
andconstructionofwatercalibrationfacilitiesare achieved at a
fraction the cost of their gas counterparts. Metrology Volume
Measurement ToaccuratelyquantifythemassoutputofaCoriolis
meterappliedatpressuresotherthancalibration
pressure,aflowpressureeffectcorrectionmustbe
applied.EveryCoriolismeterdesignandsizehasa
differentflowpressureeffectspecification.Inorderto correct
fortheflow pressureeffectin aCoriolismeters indicatedmassflow rate,
thefollowing correctionfactor should be applied to the indicated
mass output. 1 manufacturerscapitalizeontheeconomicsandhigh
stabilityofawatercalibrationtoperformthese
calibrations.SomeadvancedCoriolismeterdesignsare
immunetofluidphase,density,andviscosity;enabling water calibrations
to transferto all otherfluids; i.e.gas, Fp = 1 + ((P Effect Where:
/100) * (P Static P)) Cal liquid, and slurries.
TestingbynumerousEuropeanandNorthAmerican
flowlabshasconfirmedthetransferabilityofwater
calibrationdataonaCoriolismetertogasapplications.
MostnotablytestingsponsoredbytheGasResearch Fp PEffect PStatic PCal
=Flow pressure effect compensation factor = Pressure effect in
percent psi = Measurement fluid static pressure in psi =
Calibration static pressure in psi Institutein
2004anddocumentedinreportGRI-04/172,
whichcoverswatertogastransferabilityandwetgas
performanceofCoriolismeters.Conclusionsinthe report state, The
single fluid calibrationtests show that a water calibration of a
Coriolis mass flow meter can be
usedfornaturalgasapplicationswithoutlossof accuracy.
Forgasapplications,themeasurementaccuracyof
densitymeasuredbyaCoriolismeterisrelativetoa
liquiddensitometersaccuracy,thisdoesnotmeetthe
accuraciesrequiredforgasmeasurement.Thereforethe
on-linedensityfromthemeterisnotusedforflow measurement with gas;
rather the relative density or base
densityofthegasisenteredintoaflowcomputeras determinedfrom
eithersamplingmethods or on-linegas analysis. It should be noted
that the gas physical property
informationrequiredbyAGA8GrossMethod1,Gross Method 2, or Detail
Method and proceduralmethodsfor
applyingthisinformationintheuseofaCoriolismeter
areidenticaltothoserequiredbyvolumetricmeters;i.e.
Turbine,Orifice,Rotary,andUltrasonic.Coriolis
technologyusesthefollowingcalculationstooutputa highly accurate
standard or normal volumetric output. GRI 04/0172 Water, Air, and
Gas Transferability Data SCF (gas)= Mass(gas) F p b(Gas) Industry
testing has shown there is minimal benefit, from a calibration
uncertainty perspective, in performing a gas SCF= Mass(gas) F p 7
(gas) Grx (Gas)b( Air ) 8 = Pb x Mrb will affect a Coriolis meters
accuracy more at low flows than at high flows. If the buildup is
causing ashift in the meter zero, cleaning and re-zeroing will
bring the Where: Zb xR x Tb meters performance back to its original
specification. At anygivenlevelofcoating,ifthecoatingisstable,the
metercanbere-zeroed,withoutcleaning,andmeter
performancecanberestored.Ifcoatingofthesensor SCF( gas) =Gas volume
atTb andPb continues, the zero may continue to drift. Mass=Weight
of gas (Coriolis output) Inspection and Re-zeroing b = Density atTb
andPb Tb= Temperature at base conditions Pb= Pressure at base
conditions Zb= Compressibility at base conditions ( Tb
Toinspectorre-zeroaCoriolismeter,thermal equilibrium
ofthemetershouldbeestablished.Flowing at a flow rate above the
transitional flow rate can be used
toestablishthermalequilibrium.Oncethermal equilibrium is achieved
the meter is to be blocked in and themeters zero verified. Even
though thestream isnot and Pb ) flowing, theflow metermay indicate
a small amount of flow bias, either positive ornegative. Causesfora
bias Gr(Ga s)=Real Gravity atTb andPb in the zero are usually
related to the differences between previous and current zero flow
conditions, which R= Universal gas constant M r = Molar Weight Fp
=Flow pressure effect compensation factor Field Maintenance and
Meter Verification ThefieldmaintenanceofaCoriolismeterisan
inspection process consisting of the following 1)Transmitter
Verification 2)Sensor Verification 3)Sensor Temperature
Verification 4)Sensor Zero Verification AGA11 states the user
should use meter verification data
toguidethemontheneedtore-zerotheCoriolismeter and when to flow
test. Field Maintenance Zero Verification
Themeterzeroshouldbeverifiedperiodicallyand
recalibratedifitisnotwithinthemanufacturers
specification.Ataminimum,inspectionofthemeters
zeroshouldbeperformedseasonallyinthefirstyearof operation to
identify and installation or process condition issues.After
thefirstyear of operation, zero verification
intervalscanbeextendedbasedonthehistoric performance of the meters
zero for the application. Drift in Zero Reading
Productbuildup,erosion,orcorrosionwillaffectthe
meterzeroperformance.Productbuildup(coating)may
biasthemeterzero.Itshouldbenotedthatazeroshift include.
-Differences between thecalibrationmedia density and the gas
density -Differences in temperature Themetershouldreadamassflow
ratethatislessthan themanufacturer is zero stability
specificationunder the no-flow condition. If the zero iswithin
specification re-zeroing themeter is
unwarranted.Ifoutsideofspecificationthecurrentzero
valueandmetertemperatureshouldberecordedfor
futurereferenceandthezeroingprocedurespecifiedby the meter
manufacturer should be followed. Field Maintenance Diagnostics
DiagnosticLED(s)anddisplay aretypically providedto
indicatetheoperatingstatusofthesensorand
transmitter.ThediagnosticsoftheCoriolistransmitter
verifytheintegrityoftheCPUandinsureoperational
parametersarewithintolerance.Coriolissensor
diagnosticsverifythesensingcomponentsofthesensor
arenotdamagedandoperatingwithinnormallimits.
Sensordiagnosticsalsoprovideinsightintotheprocess
flowconditionsandpotentialmeasurementproblems with them.
SomeCoriolissensordesignsalsoprovideon-line
verificationoftheflowtube(s)structure.Theflowtube structure of a
Coriolis sensor dictates its flow calibration factor. This method
of verification measures flow tube(s)
stiffnesstoinferdensityandmasscalibrationfactoras unchanged.
Utilizing resonantmodal analysis techniques
thetransmitteractivelyteststheflowtube(s)stiffness 8
duringflowingconditionsanddeterminesifanoutof tolerance stiffness
change has occurred.
Coriolismeterverificationbyresonantmodalanalysis
methodisasignificantadvancementinCoriolis
technology.Thiscapabilityallowsforverificationa Coriolis meters
accuracy without interruption in flow or inspection of the meters
components for damage. CAPEX
CapitalExpenditures(CAPEX)toimplementCoriolis
measurementwillvarydependentuponmeterdesign,
size,pressureratings,materialsofconstruction,and
accuracy.Typicalcapitalexpendituresrequiredinthe
implementationofaCoriolismeteringsysteminclude the following.
-Coriolis Sensor -Flow Computer or Transmitter -Power System
-Installation and Startup
Coriolistechnologyreducesoreliminatesseveralofthe
capitalexpendituresrequiredintheapplicationofother
gasflowtechnologiesandtypicallyassociatedwith
naturalgasmetering.Typicalcapitalexpendituresthat are reduced or
eliminated are as follows.
-Pressuremeasurement-Typicallynotrequired
forflowmeasurementandifrequired,ahigh accuracy transmitter is
unwarranted -Temperature measurement- Integral to Coriolis sensor
design -Specialtyupstreamanddownstreampiping and/or flow
conditioning Not required -Gasflowcalibrationofsensor-Factorywater
flowcalibrationtransferstonaturalgas measurement -Installation and
startup OPEX OperatingExpenditures(OPEX)tomaintainCoriolis
measurementwillvarydependentuponmeterdesign,
powersystem,cleanlinessofprocess,andverification
proceduresrequiredbymeterdesign,adoptedbythe
usersorganization,ordictatedbyregulatory requirements. Typical
operating expenditures required in the use a Coriolis metering
system include the following.
-Routineverification/inspectionofsensorzero and meter diagnostics
-The replacement of battery backup power cells, if used, when their
efficiency has declined.
Coriolistechnologyreducesoreliminatesseveralofthe
operatingexpendituresassociatedwithgasflow
technologies.Typicaloperatingexpendituresthatare reduced or
eliminated are as follows. -PressurecalibrationAlthoughpressure
measurement,ifused,willrequireperiodic
verificationitsrecalibrationwithaprecision reference is typically
not required. -Temperaturemeasurement-Although
temperaturemeasurementwillrequireperiodic
verificationitsrecalibrationwithaprecision reference is typically
not required -Inspectionandcleaningofspecialtyupstream
anddownstreampipingand/orflow conditioning
-Validationofflowfactor-Coriolismeterscan
bevalidatedwithwaterflowreferences,which are typically more
economical than that of their natural gas counterparts. Some
Coriolis designs incorporatestructuralintegritydiagnosticsthat
verifythesensorsflowfactororidentifythe
requirementforrecalibration.Structural
diagnosticseliminateunnecessaryflow validations or recalibrations.
Application Examples Coriolismetersareappliedinawidevarietyof
applications,fromthewellheadtotheburnertip.
Coriolismetersareprimarilyasmallertomediumline
sizemeter,ideallysuitedtothefollowinggasmetering sweet spots: -Line
sizes 250mm (12) and smaller -300 ANSI through 900 ANSI -High
turndown requirements -Dirty,wet,orsourgaswheremaintenancecan be an
issue with other technologies -There is no room for long
straight-runs -Changing gas composition and density
-Suddenchangesingasflowvelocity(fueland production gas
applications) -Pulsatinggasflows(fuelgasandcompression gas in the
use of reciprocating compressors)
-Applicationswereabnormallyhighflowrates can occur.
Coriolismeterscanbesizedforverylow-pressuredrop
(100H2O),butcanalsobeinstalledupstreamofthe pressure regulator with
high-pressure drops for increased turndown without concern of
damage or malfunction due
toflownoise.Forinstance,inoneapplicationfor custody transfer of
nitrogen, a 50-psid drop (1390 H2O) 9
wasallowedacrosstheCoriolismeterandthepressure regulator adjusted
accordingly.This allowed the use of a
1Coriolismeterinsteadofa3meterdownstreamof
theregulatoranda40:1useableturndown(Betterthan
1%accuracyatminimumflowandanaverage0.35%
basevolumeaccuracyover95%oftheupperflow range).
Separatorgas:SaudiAramcousesanumberofCoriolis
metersonboththeliquidandgassideofseparators.
Thisapplicationisofparticularnotebecausethegas
streamiswet,withentrainedhydrocarboncondensates. Measurement of
this stream iswithin a few percent over
awiderangeofconditions,greatlyenhancingseparator
operationandaccuratelyquantifyingthevalueofthe liquid hydrocarbon
entrained stream. Coriolis Liquid and Gas Separator Measurement
Fuel Control: A major US vendor of gas turbines designs
ahigh-efficiency,lowemissionsoffering.Thisdesign
utilizesatrioofCoriolismeterstomeasurethenatural
gasburnedineachofthreecombustionzones.The combination of no damage
due to flow rate-of-change at start-up,highturndown,
highaccuracy,immunityto
vibrationinaveryhighvibrationenvironment,along
witheaseofinstallationduetonostraightpiperun requirement, makes
Coriolis the technology of choice. Coriolis Fuel Gas Measurement on
a Gas Turbine Natural Gas Fiscal Transfer: One specific example of
gas measurementcapabilityisatanaturalgasutilityin
WesternAustralia.Two3metersareusedinparallel
withathirdusedasahotspareformonthly verifications of the transfer
meters. The justification for using the Coriolis meters was based
oninstallationandcalibration/maintenancecost
improvementsoverthemoretraditionalgasmetering
systems.SinceCoriolismetersrequirenostraightruns or flow
conditioning the installed costswere reducedby
fivetimes,evenwiththeparallelmetersrequiredto handle the highest
flows. Additionally,periodicmaintenancecostswerereduced
duetotheintrinsicreliabilityofCoriolismeters(i.e.no
movingparts).Similarly,reliabilityimprovements reduced calibration
and proving costs. Internalchecksbythecustomerhaveshownagreement
tobetterthan0.1%onallgastransfersovera6-year period. Western
Australia: Previous installation using turbine meters for 50:1
turndown After installation since 1996, with two operating and one
hot spare meter for 80:1 turndown. 10 Natural Gas Storage: A
storage field in Hungary utilizes
27two-inchCoriolismetersfortheinjectionand
withdrawalmeasurementofnaturalgas.Thestorage
reservoirconsistsofamultilayersandstoneformation
withanaquiferflowingthroughit.Duetothe
complexityofmanagingthewaterlevelinasandstone formation on the
injection and withdrawal of natural gas, multiple smallwells are
required. Thewithdrawalgas is alsofully
saturated,containsH2S,andduringhighflow thewells producesand.In
this difficultapplicationonly
Coriolismeterscanprovidebidirectionalmeasurement,
long-termaccuracy,andachievethewideturndowns required for reservoir
management. Coriolis Natural Gas Storage Measurement in Hungary
Energy Metering:EnergyperSCFcanvary asmuch as
10timesthatofenergyperaunitweightfor Hydrocarbons. Ifthetotal
concentration ofCO2andN2
inthenaturalgasmixtureremainsconstantandmostof
thevariationincompositionisrelatedtohydrocarbon
concentrations,anaverageheatingvaluecanbeutilized
forenergymeasurementallowingCoriolistoachieve
totalenergyaccuraciesunparalleledbyvolumetric
metersutilizingthesameaveragevalue.ACoriolis
meterbyitselfoffersaveryaffordablemethodof inferring energy flow
rates on some natural gas streams.
Combustioncontroltoboilers:Inthisapplication,a Pulpmill in Quebec
sought amore reliableway tomeet
EPAemissionsrequirements.Combustioncontrolwas
easier,basedonthemassratiobetweenthenaturalgas
andcombustionair.Highturndownandconcernover
damagetothemeasurementelementduetoflowsurge when the boilers fired
drove the selection of Coriolis for this application. Combustion
control application to boilers Ethylene gas transfer: Ethylene is
commonly viewed as a difficult tomeasuregas, due to
itsnon-idealnature. In
thisapplication,Coriolismetersareusedforintra-plant transfers
attainingaccuraciesunattainablebyvolumetric meters,helping tomeet
both unitmass-balance goals, as well as reactor feed rate
requirements. Ethylene application, where ethylene is fed
continuously to a polymerization reactor Summary Although a
relatively new technology for the natural gas
industry,Coriolismetershavegainedworldwide
acceptanceastheidealmeterformeasurementofmany
fluidsinotherindustries.Withaworldwideinstalled
baseofoveronemillionunits,Coriolistechnologyis
seeingexpandeduseforbothliquidpetroleumand
naturalgas.Mostcountriesandmeasurement
organizationshaveapprovedorpublishedstandardsfor
theuseofthetechnology.MostnotablyisAGAand 11
APIwhohavejointlypublishedAGAReportNo.11/
APIMPMSChapter14.9,MeasurementofNaturalGas by Coriolis Meter.
Technologylimitationsofearlierdesignshavelargely
beenovercome,withhighaccuracymeasurementnow
possibleatlow-pressuredrop.Coriolissweetspots
arelinesizesof300mm(12)andsmaller,300to900
ANSI,wherehighturndownisneeded,flow
conditioningwithothertechnologiestomeetAGA
requirementsiscostly,flowsurgesoccur,pulsationsare present, energy
metering is required, and/or the gas is of dirty, sour, or changing
composition. Coriolistechnologymeritsseriousconsiderationasa
bonafidecontendertocomplementUltrasonicinlow
costofownershipmeteringfornaturalgasapplications.
Thesetwotechnologiesoverlapinthe100mm(4)to 300mm (12) line size
range. Parallel3 Coriolis and 16 ultrasonic in a fuel gas metering
installation. Third-partydatafromCEESI,Pigsar,SwRI,andothers
showlittleifanyeffectofflowprofileandthe
transferabilityofafactorywatercalibrationtonatural gas measurement
applications. CommonCoriolisgasapplicationsrangefromwellhead
separator,mediumtohigh-pressurefiscalmetering,and
fuelgastopowerturbines,reciprocatingengines,and
boilers.AsusersofgasmetersinvestigateCoriolisthey are finding it to
be the fiscally responsible choice for gas
measurementintodayscompetitivebusiness environment. References -AGA
Engineering Technical Note XQ0112, Coriolis Flow Measurement for
Natural Gas Applications, American Gas Association, 400 N. Capitol
Street, N.W., 4th Floor, Washington, DC 20001 -AGA Report No. 3,
Orifice Metering of Natural Gas and Other Related Hydrocarbon
Fluids, American Gas Association, 1515 Wilson Boulevard, Arlington,
VA22209 -AGA Report No. 7, Measurement of Gas by Turbine Meters,
American Gas Association, 1515 Wilson Boulevard, Arlington, VA22209
-AGA Report No. 8, Compressibility Factors of Natural Gas and Other
Related Hydrocarbon Gases, American Gas Association, 1515 Wilson
Boulevard, Arlington, VA22209 -AGA Report No. 9, Measurement of Gas
by Multipath Ultrasonic Meters, American Gas Association, 1515
Wilson Boulevard, Arlington, VA 22209 -AGA Report No.11,
Measurement of Natural Gas by Coriolis Meter, American Gas
Association, 1515 Wilson Boulevard, Arlington, VA22209 -ANSI B16.5,
Pipe Flanges and Flanged Fittings, American National Standards
Institute, 25 West 42nd Street, New York, NY 10036 -API Manual of
Petroleum Measurement Standards Chapter 21.1, September 1993, Flow
Measurement Using Electronic Metering Systems, American Petroleum
Institute, 1220 L Street NW, Washington, DC20005 -ASME MFC-11M,
2006, Measurement of Fluid Flow by Means of Coriolis Mass
Flowmeters, American Society of Mechanical Engineers, Three Park
Avenue, 23S2, New York, NY 10016-5990 -ISO 10790, 1999, Measurement
of fluid flow in closed conduits Coriolis meters, International
Organization for Standardization, Case Postale 56, CH-1211 Geneve
20, Switzerland -GTI Topical Report, GRI-01/0222, Coriolis mass
flow meter performance with natural gas, Gas Technology Institute,
1700 South Mount Prospect Road, Des Plaines, Illinois60018 -GRI
Topical Report, GRI-04/0172, Coriolis mass flow meter performance
with water, air, dry - gas, & wet gas, Gas Research Institute,
1700 South Mount Prospect Road, Des Plaines, Illinois 60018