FC-0710-FD.2:Layout 1 6/24/10 12:47 PM Page 14 flow update ... › articles › PDF_Files › 2010 › July 2010.… · FC-0710-FD.2:Layout 1 6/24/10 12:47 PM Page 14. 16 July 2010

flow update

Accuracy MattersThe Where & Why of Flowmeter Calibration

by Jesse Yoder, Ph.D.

Almost anyone who owns a flowmeter has dealt with thetopic of flowmeter calibration at one time or another.Even though a flowmeter performs well “out of thebox,” it is an electronic and mechanical device, and as such,it is subject to performance variations over time. Like a carthat needs a periodic tuneup, flowmeters need to be calibrat-ed periodically to make sure that they are performing at a satisfactory optimal level.

Calibrations can take many forms. For some calibrations,the performance of a flowmeter is compared to that of a“master meter.” A master meter is a highly accurate flowme-ter whose performance has been checked against a referencestandard. When a calibration is performed, the performanceof the flowmeter being calibrated is compared to that of themaster meter. If there is a variation between the two, anadjustment is made to the calibrated flowmeter to correct itsperformance.

Another calibration method uses a weigh scale to measureliquid volume. This method, called proving, is an especiallyaccurate method of calibration. This volumetric methodrequires accurate timing. As is the case with the master metermethod, the performance of the meter being calibrated iscompared to that of the prover. The flowmeter being calibrat-

ed is adjusted to bring its performance in line with that of theprover. This is often done with a meter factor.

Why Flowmeter Performance Changes Over TimeThere are many reasons why flowmeter performance variesover time. Deposits on the inside wall of a flowmeter canhave an impact on performance. Water contamination in fuelor hydrocarbon-based liquids can cause corrosion and com-ponent wear. Flowmeters with moving parts, such as turbinemeters, are subject to wear, and performance can degradeover time. In some cases, bearings may need to be replaced.

Changes in the type of fluid being measured can affect theperformance of a flowmeter. A flowmeter that is calibrated onone type of fluid can perform differently when a different typeof fluid is being measured. In many cases, corrections can bemade to compensate for the fluid change. Another factor isimproper installation. This involves factors such as theamount of upstream or downstream piping, the proper posi-tion of a sensing element, or allowing protrusions in the line.

Other factors that affect flowmeter performance includeoutside influences such as variations in pressure or tempera-ture, vibration, and electromagnetic interference. Pressureand temperature are especially important when gas flow is

being measured. For steam flow, steam flowquality has an important impact on correct flowmeasurement.

Some Options for CalibrationMany flowmeters today have expanded diagnosticcapability. While self-diagnostics are not a substi-tute for calibration, they can serve to identifyflowmeter parameters that have shifted over time.Often the self-diagnostics compare current meas-urement parameters with those made at the fac-tory to identify any changes. Expanded diagnosticcapabilities are an important step towards main-taining the integrity of flowmeters in the field.

One option that companies have for flowmetercalibration is to have the calibration done on-site.Equipment is available, both in the form of master meters and flowmeter provers, to perform on-site calibration. There are companies that offeron-site calibration as a service, and some compa-nies may choose to buy this equipment to have itavailable so they can perform on-site calibrationson their own.

Another option for calibration is to have theflowmeter sent to an outside flowmeter laboratory.There are a number of excellent facilities available,

Table 1: Reasons for Calibrating New-Technology Flowmeters

Flowmeter Type Technology Reasons for Calibrating

Coriolis Fluid passes through a vibratingtube. The degree of twistingmotion is directly proportionalto mass flow

Coating and wear of the flowtubes; electronic failure

Magnetic The voltage generated by electrically conductive fluidpassing through a pipe ismeasured to compute flowrate.

Liner damage; electrode coating; electronic failure

Ultrasonic An ultrasonic signal is sentacross a pipe and back. Thedifference between the twotransit times in either directionis proportional to flowrate.

Changes in the sonic proper-ties of the fluid; transducerfailure; lack of contactbetween transducer and pipewall; electronic failure

Vortex A bluff body in the flowstreamgenerates vortices. Flowrate isproportional to the frequencyof the vortices.

Flowmeter mounted improperlyin pipe; vibration; sensor failure; shedder wear

Thermal Heat is introduced into the flow-stream. The amount of heat thatdissipates is measured usingtemperature sensors. This valueis used in calculating mass flow.

Sensor wear; sensor failure;contamination of thermallyconductive surfaces; electronic failure

14 July 2010 Flow Control

FC-0710-FD.2:Layout 1 6/24/10 12:47 PM Page 14


although most of them are located in the UnitedStates, Canada, and Europe. While these are rela-tively convenient for end-users in those regions,they are less convenient for end-users in theMiddle East, Africa, and Asia.

There are a number of issues to be consideredin selecting a flow laboratory. To send a flowme-ter to an outside laboratory, it has to be pulledout of service and shipped to the calibration facility. So one issue to consider is how long theend-user will be without the use of the meter.Some companies have spare flowmeters they can put into service while a flowmeter is beingcalibrated. Having a spare meter is a good idea,but it can be expensive, depending on the cost ofthe meter. Some companies run two flowmetersin series as a check so that while one meter isout for calibration, the company can make dowith a single meter. This is sometimes the casefor custody-transfer applications.

A second issue is the cost of shipping theflowmeter to the calibration facility and back.Here, there is a choice between ground and airmethods, depending on the location. The decisionabout the mode of transportation and cost isdetermined in part by the location of the calibra-

Table 2: Reasons for Calibrating Traditional Technology Flowmeters

Flowmeter Type Technology Reasons for Calibrating

Differential Pressure A constriction called a primaryelement is placed in the flow-stream. The difference inupstream vs. downstreampressure is used to computeflowrate.

Orifice plates, nozzles, andVenturis are subject to wear;Orifice place get knocked outof position; Pitot tubesbecome clogged; transmitterfailure

Positive Displacement Fluid is captured in a containerof known volume andreleased. Flowrate is determined based on howmany times this is done.

Dirty liquids, corrosion, andabrasion change the volume;bearing wear degrades accura-cy; gear service affects calibra-tion; solids can cause plugging

Turbine Fluid passes over a spinningrotor. Flowrate is proportionalto the speed of the rotor.

Bearings affected by chemi-cals or dirty; bearing serviceaffects calibration; rotorswear; electronic failure

Open Channel Some use liquid levels at weirsor flumes; others computeflow from velocity, level, depth,and/or diameter data.

Level transmitter calibration;accumulation of debris; electronic failure of transmitter

Variable Area Fluid passes through a taperedtube containing a float.Flowrate is indicated by theheight of the float in the tube.

Material buildup; plugging;meter tube failure

flow update �

Circle 12 or Request Info Instantly at www.FlowControlNetwork.com


tion facility and the importance of a quick turnaround.It is important to consider the capabilities of the flowmeter

laboratory when deciding where to send a meter for calibra-tion. Some flowmeters, such as multi-path ultrasonic flowme-ters for custody-transfer applications, have to be tested underhigh-pressure conditions. Not all calibration facilities havethis capability. Other facilities specialize more in measuringliquid rather than gas flows. It is also important to be surethat the calibration facility is properly certified and meetsindustry standards for testing.

Some Calibration OptionsThere are a number of calibration facilities to choose from.Several of them are described here.

CEESI: The origins of Colorado Engineering ExperimentStation Inc. (CEESI, www.ceesi.com) go back to 1951, whenit was a program for the College of Engineering at theUniversity of Colorado at Boulder for the research and testingof small rockets. In 1966, the program separated from theuniversity and moved to its current location, a surplus Atlasmissile site near Nunn, Colorado. At that time, the facilitywas non-profit. It remained non-profit until 1986, when itwas purchased by Steve Caldwell and Walt Seidl.

CEESI can calibrate a wide range of flowmeter types,including orifice meters, Venturis, turbine meters, ultrasonic,vortex, and many other types. In addition to its facilities nearNunn, Colorado, CEESI maintains a High Flow Natural GasCalibration Facility in Garner, Iowa. This facility is used to calibrate and test ultrasonic and turbine flowmeters for custody transfer of natural gas.

Trans Canada Calibrations: TransCanada Calibrations(www.tccalibrations.com) is located along TransCanada

pipelines near Winnipeg in Manitoba, Canada. TransCanadaspecializes in calibration of turbine and ultrasonic flowmetersfor custody transfer of natural gas. The facility began opera-tion in 1999, and performed its first calibrations of ultrasonicand turbine flowmeters in 2001. TransCanada offers door-to-door service, including transportation management, as sup-port for its calibration services. In addition to its calibrationservices, the facility offers flowmeter repair, technical services,and training.

GL Noble Denton: GL Noble Denton (www.gl-nobledenton.com),based in London, is a technical service provider for the oil &gas industry. The company designs, builds, and operates oil andgas assets, such as pipelines, subsea systems, import termi-nals, and drilling units. In 2007, Germanischer Lloyd (GL) andAdvantica combined their operations. Advantica was a flowme-ter calibration facility in the United Kingdom. In 2009, Advanticachanged its name to GL Industrial Services. In January 2010,GL’s oil & gas division combined with Noble Denton to form GL

flow update


A Daniel ultrasonic natural gas flowmeter mounted inline for calibration at Southwest Research Institute in San Antonio, Texas.

A 42-inch natural gas supply pipeline at CEESI’s natural gas custodytransfer station in Iowa.

Some of the turbine flowmeters that serve as the transfer standardat CEESI Iowa.


Noble Denton. GL’s Flow Centre performsa wide variety of calibrations, includingcalibrations of ultrasonic, turbine, andVenturi flowmeters. The Centre canundertake natural gas calibrations ofwhole metering packages. Most of theflowmeters tested and calibrated arebetween two inches and 24 inches.

Netherlands Metrology Institute (NMi):NMi (www.nmi.nl) is based inDordrecht, the Netherlands, but hasagencies in Belgium, Turkey andJapan. It also has additional officeselsewhere in the Netherlands, Italy andthe United Kingdom. NMi can calibrateboth liquid and gas flowmeters. It iscurrently working on a new facility inRotterdam, the Netherlands, calledEuroloop. NMi calls Euroloop “theworld’s largest test site for flow andquantity measurement of natural gasand petroleum.” Euroloop is beingdeveloped together with KROHNE, amajor flowmeter supplier with officesin Dordrecht.

Other FacilitiesWhile the above are some of the maincalibration facilities globally, other laboratories are available. One is the Metering Research Facility atSouthwest Research Institute(www.mrf.swri.org) in San Antonio,Texas. The Metering Research Facilityhas both a high-pressure loop and a low-pressure loop for handingflowmeters of different sizes and pressures. Other calibration facilitiesare Alden Research Laboratory(www.aldenlab.com) in Holden, Mass.,and Flow Dynamics (www.flow-dynamics.com) in Scottsdale, Arizona.Many flowmeter technology suppliersalso offer calibration services, not onlyfor their own flowmeters, but also for arange of flowmeter types and manufac-tures. At some point, some facilitiesfigure to come online that are moreconvenient for end-users in the MiddleEast, Africa and Asia.

Jesse Yoder, Ph.D., is president ofFlow Research, Inc. in Wakefield, Mass.,a company he founded in 1998. He has22 years of experience as an analyst

and writer in process control. Yoder specializes in flowmeters and other fielddevices, including pressure and tempera-ture products. He has written over 100market research studies in industrialautomation and process control and haspublished more than 110 journal articleson instrumentation topics. Dr. Yoder canbe reached at [email protected] 781 245-3200.

www.flowresearch.com

EDITOR’S NOTE: To expand upon thetopic of Flow Calibration, Flow Controlmagazine will be publishing a two-partseries on flowmeter calibration bestpractices for liquid and gas applica-tions. Look for the first part of thisseries to appear in the August issue.

FC

�

FLEXIMHIGH ACCURACY FLOW METERS

For Extreme Temperatures & Pressures

– non-intrusive ultrasonic clamp-on technology

– for temperatures from –276 °F to 750 °F

– independent of process pressure

– multi-beam for high accuracy

– wide turn down

– installation without process shut down

– no maintenance

– no pressure loss

– standard volume calculation

– portable and permanent models available

TYPICAL APPLICATIONS:

HEAT TRANSFER OILS | BITUMEN | PITCH/TAR | COKER FEED | CRUDE OILS/SYNTHETIC CRUDE | GAS OILS | REFINED PETROLEUM PRODUCTS | HOT OR TOXIC CHEMICALS | WATER | SLUDGES | MOLTEN SALT | LNG | CRYOGENIC LIQUIDS

www.flexim.com [email protected]

FLEXIM AMERICAS

Corporation

Phone: (631) 492-2300

Toll Free: 1-888-852-7473

www.FlowControlNetwork.com July 2010 19Circle 14 or Request Info Instantly at www.FlowControlNetwork.com

FC-0710-FD.2:Layout 1 6/29/10 7:31 AM Page 19

014_FC0710.pdf016_FC0710.pdf018_FC0710.pdf019_FC0710_LR.pdf

/ColorImageDict > /JPEG2000ColorACSImageDict > /JPEG2000ColorImageDict > /AntiAliasGrayImages false /CropGrayImages false /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict > /GrayImageDict > /JPEG2000GrayACSImageDict > /JPEG2000GrayImageDict > /AntiAliasMonoImages false /CropMonoImages false /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages false /MonoImageDownsampleType /Average /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict > /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False

/Description > /Namespace [ (Adobe) (Common) (1.0) ] /OtherNamespaces [ > /FormElements false /GenerateStructure false /IncludeBookmarks false /IncludeHyperlinks false /IncludeInteractive false /IncludeLayers false /IncludeProfiles true /MarksOffset 12 /MarksWeight 0.250000 /MultimediaHandling /UseObjectSettings /Namespace [ (Adobe) (CreativeSuite) (2.0) ] /PDFXOutputIntentProfileSelector /NA /PageMarksFile /RomanDefault /PreserveEditing true /UntaggedCMYKHandling /LeaveUntagged /UntaggedRGBHandling /LeaveUntagged /UseDocumentBleed false >> > ]>> setdistillerparams> setpagedevice







Documents

FC-0710-FD.2:Layout 1 6/24/10 12:47 PM Page 14 flow update ... › articles › PDF_Files › 2010 › July 2010.… · FC-0710-FD.2:Layout 1 6/24/10 12:47 PM Page 14. 16 July 2010