2001 PROCEEDINGS PAGE 161AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

GTI METERING RESEARCH FACILITY UPDATEEdgar B. Bowles, Jr.

Manager, GTI Metering Research Facility ProgramSouthwest Research Institute

6220 Culebra RoadSan Antonio, TX 78238-5166 USA

recommended the development of an independent,qualified flow test facility that would be operated underthe sponsorship of the gas industry. This facility had tobe capable of providing performance data on a broadspectrum of meter types and sizes over a wide range offlow conditions. In response to this recommendation,GTI initiated the MRF program with Southwest ResearchInstitute in 1987.

To cover the wide range of flow conditions necessaryfor the research and testing needs of the natural gasindustry, development of the MRF1 included three primarycomponents: a High Pressure Loop (HPL), Low PressureLoop (LPL), and Distribution Meter Test Stand (DTS).Table 1 lists the operational ranges for all three systems.The HPL and LPL are re-circulating flow loops, while theDTS is a “blow-down” type system. Each system canflow either natural gas or nitrogen.

Parameter HPL LPL DTSMax. Rate (MSCFH) 7,084 610 2.5Max. Rate (ACFH) 84,000 43,600 2,500Pressure (psig) 150 - 1,200 20 - 210 0 - 40Gas Temp. (˚F) 40 - 120 40 - 120 AmbientPipe Size (inches) 2 - 20 1 - 8 up to 2Specific Gravity 0.55 - 0.97 0.55 - 0.97 0.55 - 1.0

TABLE 1. Metering Research Facility Operational Ranges

An on-line, laboratory-grade gas chromatograph is usedfor detailed analysis of the test gas.

Flow measurement accuracy on the order of 0.1 to 0.25%is achieved in the HPL, LPL, and DTS through the use ofindividual gravimetric primary calibration systems. Sonicnozzles, gas turbine meters, and laminar flow elementsare also used as secondary transfer standards. Thegravimetric calibration system for the High Pressure Loopis shown on Figure 2.

An example of the performance of the MRF is illustratedby Figure 3, which plots orifice meter dischargecoefficients (Cd) from the HPL against similar data fromother international flow calibration laboratories.

In addition to serving as a test bed for GTI-sponsoredresearch, the MRF is available to any other interestedparties for test and calibration services. The MRFtechnical staff also provide assistance with meter stationdesign and help troubleshoot metering problems in thefield. In addition, the MRF offers training courses on meterstation design and operation.

INTRODUCTION

The Gas Technology Institute (formerly the Gas ResearchInstitute) sponsors a comprehensive flow measurementresearch, development, and commercialization (RD&C)program aimed at improving natural gas meteringperformance in the field. This paper summarizes someof the recent accomplishments of the research programat the Gas Technology Institute (GTI) Metering ResearchFacility (MRF), a high-accuracy natural gas flowcalibration laboratory capable of simulating a wide rangeof operating conditions for the industry’s research,calibration, and testing needs. The MRF, located atSouthwest Research Institute (SwRI) in San Antonio,Texas, supports a variety of GTI-sponsored research andthird-party test and calibration activities. Major researchinitiatives currently being funded by GTI includeultrasonic, turbine, and Coriolis flow meter research; gassampling methods research; and development of a newenergy flow rate meter concept. Through its portfolio ofprojects addressing priority research needs, the GTInatural gas measurement program provides significantbenefits to the natural gas industry.

FIGURE 1. GTI Metering Research Facility

METERING FACILITY DEVELOPMENT

The Metering Research Facility program was initiatedby GTI in the late 1980s in direct response to a growingneed within the natural gas industry for improvement inthe state-of-the-art of gas flow measurement. Theconcept of a natural gas industry metering research andcalibration facility was first proposed in the Gas IndustryMeasurement Plan prepared by the Operating Sectionof the American Gas Association (AGA). This plan

PAGE 162 2001 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

FIGURE 2. GTI MRF High Pressure Loop Weigh Tank

FIGURE 3. GTI MRF High Pressure Loop 10-inchDiameter Orifice Discharge Coefficient Data

ORIFICE FLOW METER RESEARCH

Recently, three separate orifice meter operational effectswere studied experimentally at the MRF. One cause ofmeasurement bias in the orifice discharge coefficient,Cd, examined in the study was the backward installationof orifice plates, which is known to cause under-measurement of the flow rate. Another set of experimentsdetermined biases in Cd due to pressure fluctuations andmeasurement uncertainties at low differential pressuresbelow 20 inches of water column (20” H2O), a lower limitoften found in natural gas applications. The thirdinvestigation evaluated meter tubes with surfaceroughnesses beyond the limits specified in AGA ReportNo. 3, Part 2, the resulting biases in Cd, and theusefulness of isolating flow conditioners in such cases.In connection with the experiments on backwards orificeplates, Computational Fluid Dynamics (CFD) studieswere performed at Texas A&M University to correlateorifice meter dimensions to trends in the under-measurement bias.

The key findings from these studies are as follows.Measurement errors caused by an orifice plateinadvertently installed backwards in the field may becharacterized as a function of the orifice β ratio, the ratioof orifice bore thickness to plate thickness, e/E, and theratio of orifice plate thickness to meter tube diameter, E/D. The error can range from about -10% to -20%. Thetest results suggest that an alternative to the currentindustry procedure for adjusting such measurementerrors is possible, although this new approach is not yetpractical due to the amount of data required.

MRF test results also indicate that orifice flowmeasurements involving pressure differentials of lessthan about 6” H2O should generally be avoided, becausemost data taken below this differential pressure have anexcessive amount of scatter, high measurementuncertainties, or both. Error analyses and observedpressure fluctuations suggest the following, morerestrictive, lower limits for particular β ratios: 22” H2O forβ = 0.75, 17” H2O for β = 0.67, and 19” H2O for β = 0.50.

MRF experiments with artificially roughened lengths ofmeter pipe suggest that honing or cleaning a roughenedmeter tube to AGA Report No. 3, Part 2 specifications 10pipe diameters upstream of the orifice meter may allowthe flow to reach a new equilibrium distribution and bringthe discharge coefficient into agreement with the Reader-Harris-Gallagher discharge coefficient equation. Flowconditioners placed between the roughened and honedsections of meter tube did not have adverse effects onorifice meter accuracy in the cases tested. However, theflow conditioners did not produce flow profiles that couldovercome the effects of excessive surface roughnessdownstream of the flow conditioners.

The results of these investigations are documented in aGTI Topical Report2 and a technical paper3 that waspresented at the AGA Operations Conference held inDallas, Texas in May 2001.

ULTRASONIC FLOW METER RESEARCH

In June 1998, the AGA Transmission MeasurementCommittee (TMC) published its Report No. 9, entitledMeasurement of Gas by Multipath Ultrasonic Meters.4

This document represents the first industry guidelineson the use of ultrasonic flow meters for natural gasapplications. Report No. 9 is fundamentally different frommost other gas flow meter standards in that it isperformance-based and does not include dimensionaland other mechanical specifications associated with themeter installation. Instead, the report states that the flowmeter must perform within specified measurement errorlimits when installed per the meter manufacturer’srecommended installation configuration.

Since the publication of Report No. 9, the AGATransmission Measurement Committee has proposedthat a flow performance verification test be included inthe next revision of the report to help ensure that meters

Pipe Reynolds

10 5 10 6 10 7

Orifice C

d

0.59

0.59

0.59

0.59

0.59

0.60

0.60

0.60

0.60

0.60 β =

250 mm Orifice Meter Tube

NISCEA

NEDH

Ruhr

British Gasuni

AGA - 3 (RG) equation for flange tapped orifice

GRI MRF

95% confidence interval for RG

Water Natural gas

2001 PROCEEDINGS PAGE 163AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

perform within the specified measurement error limits.This verification test would allow a manufacturer tovalidate recommended installation configurations andallow meter users to compare meter performance andinstallation requirements under a common set of pipingconfigurations. The AGA TMC has also proposed thatthe next revision of Report No. 9 include recommendedinstallation configurations.

An MRF research program that addresses both thedevelopment of a meter verification test protocol andthe identification of acceptable piping installationconfigurations has been ongoing since the publicationof AGA Report No. 9. Commercially-available multipathultrasonic gas flow meters from Daniel Flow Products,FMC/Kongsberg, and Instromet Ultrasonic have beentested during the course of this project. Meterinstallations both with and without flow conditioners havebeen evaluated. The test flow conditioners are picturedin Figure 4.

FIGURE 4. Flow Conditioners Used During MRF Ultrasonic FlowMeter Tests

The test installation piping configurations evaluated inthe MRF test program have been based onrecommendations from the flow meter and flowconditioner manufacturers and previous MRF research.5,6

The test results have demonstrated that each flow meter/flow conditioner combination produces uniqueoperational characteristics. This is because each meteruses a unique calculation method to determine flow ratefrom the measured path velocities. Thus, each meter hasa unique response to velocity profile shape changes. Theability of a meter to compensate for the velocity profiledistortion determines the amount of bias there will be inthe meter error.

Space limitations for this paper prohibit the presentationof all of the MRF test results. The reader is referred tothe paper by Grimley7 for a detailed summary of the testresults. In general, the MRF test data suggest that withthe use of an effective flow conditioner, commerciallyavailable multipath ultrasonic meters can attain the AGAReport No. 9 accuracy specification with 20 diameters

or less of straight upstream piping. Furthermore, theoptimum location for the flow conditioner will vary withthe brand of meter and flow conditioner selected. Tominimize the measurement bias associated with the flowconditioner/flow meter “package,” flow calibration of thepackage is recommended.

The new MRF test data are sufficient to allow specificinstallation configuration recommendations to beincluded in the next revision of Report No. 9. Furthermore,sufficient test data are available to allow a verificationtest protocol to be recommended in the next revision ofReport No. 9.

At present, additional MRF test work is underway toquantify the effect on meter performance of a mismatchbetween the meter body diameter and meter tubediameter. Later this year, the effect of gas temperaturemeasurement error will be assessed. The effect ofthermally-driven flows on low flow rate performance willalso be investigated. The effect of line pressure variationwill also be studied in greater detail.

NATURAL GAS SAMPLING RESEARCH

Natural gas sampling is a process critical to themeasurement of gas heating value. Improper samplingcan distort the composition of natural gas, whichindirectly affects flow rate measurement through gasproperties, such as density, and directly impacts heatingvalue measurement. Because of the importance ofaccurate sampling of the natural gas flowing through apipeline, GTI, API, and the U.S. Minerals ManagementService (MMS) initiated a consortium research projectto document the causes of gas sample distortion and toimplement procedures that produce accurate sampleresults. Much of the consortium research work has beencarried out at the MRF. A GTI Topical Report8 has beenpublished summarizing work completed through 1999and two other GTI reports on the subject will becompleted in 2001.

The research results have lead to a revision of the industrystandard for gas sampling methods, i.e., API MPMS,Chapter 14.1 - Collecting and Handling of Natural GasSamples for Custody Transfer9.

This comprehensive research program has looked at allaspects of natural gas sampling methodology. Twelvespot sampling methods, four composite samplingmethods, and two on-line analysis methods have beenstudied. Many causes of gas sample (composition)distortion have been identified during the course of thework. Such effects as thermodynamic phase changes,molecular adsorption (adsorption is a process ofattraction between gas molecules and the surfaces ofsolids or liquids), sample probe location, filtering of thesample gas, cleanliness of the gas sampling equipment,and sampling methodology have been studied.

PAGE 164 2001 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

Although the revision of API MPMS Chapter 14.1 hasbeen completed, several unmet research needs havebeen identified by the API Working Group responsiblefor the revision of Chapter 14.1. Additional MRF researchfunded by GTI and MMS is currently underway to addressthe research needs identified by the API Working Group.

In year 2001, gas sampling research at the MRF isfocusing on (1) development of an accurate database ofhydrocarbon mixture phase behavior, (2) assessment ofthe accuracy of currently-available equation-of-statemodels, (3) assessment of the accuracy of the chilledmirror method for determining hydrocarbon dew point,(4) evaluation of the fill-and-empty gas sampling methodwhen the equipment temperature is below thehydrocarbon dew point (i.e., the self-heating method),(5) development of a performance verification test fornew gas sampling methods, and (6) evaluation of theperformance of cold sample cylinders used with heatedcomposite sampling systems.

CORIOLIS FLOW METER RESEARCH

The AGA Transmission Measurement Committee recentlypublished an Engineering Technical Note10 on Coriolisflow meters used in high-pressure natural gasapplications. After completing this Tech Note, the AGATMC concluded that Coriolis meter technology showsenough promise for custody transfer applications thatan effort has been initiated to produce an AGA report(i.e., industry standard). GTI has provided funding for anMRF research program to support the AGA effort.

The MRF research program for 2001 includes thefollowing elements: (1) ‘baseline’ performance testing offive commercially-available meters in 2-inch to 4-inchdiameter line sizes and (2) installation and operationaleffects. Results of the MRF research will be reported ina GTI Topical Report that is scheduled to be publishedin September 2001.

TURBINE FLOW METER RESEARCH

The AGA Transmission Measurement Committee hasembarked on an effort to revise AGA Report No. 7 –Measurement of Gas by Turbine Meters.11 In support ofthis effort, GTI is funding a research program at the MRF.The 2001 research plans call for testing of nominal6-inch diameter meters with priority testing of 30º rotor(or “extended-capacity”) turbine designs and, whenpossible, testing of dual-rotor meters. The measurementperformance of the meter installation configurationsreferenced in AGA Report No. 7 (i.e., the ‘recommended,’‘short-coupled,’ and ‘close-coupled’ configurations) willbe evaluated in MRF tests. An International StandardsOrganization (ISO) 9951 ‘high-perturbation’ pipingconfiguration will be placed upstream of the meter runsin these evaluation tests. The performance of the variousmeter tube piping configurations will be evaluated withand without a flow conditioner installed upstream of thetest meter. The effect of line pressure variation on meteraccuracy will also be assessed.

FIGURE 5. Coriolis Flow Meter Under Test at the MRF

The results of the MRF research will be documented in aGTI Topical Report that is tentatively scheduled to bepublished in the fourth quarter of 2001.

OTHER GTI-FUNDED RESEARCH

In addition to the ongoing work described above, theGTI MRF program is sponsoring other flow measurementresearch. For example, a prototype energy flow ratemeter is under development at the MRF. This work isbeing co-funded by GTI and the U.S. Department ofEnergy. The device is designed to measure a smallnumber of process variables (e.g., gas sound speed,diluent concentrations, pressure, temperature, andvolumetric or mass flow rate) to determine energy flowrate in real time, and at normal pipeline operatingconditions. This new device is expected to be a morecost effective approach to determining energy flow ratethan the conventional approach of combiningmeasurements from a volumetric flow meter and gaschromatograph. Prototype testing is currently in progressat the MRF and gas transmission pipeline field sites inthe U.S. Two preliminary reports on this device areavailable from GTI.12,13

GTI is also funding an inter-laboratory test comparisonof the MRF, the Colorado Engineering Experiment Stationflow calibration lab in Ventura, Iowa, and theTransCanada Calibrations test facility in Winnipeg,Manitoba. These are the three high-volume natural gas

2001 PROCEEDINGS PAGE 165AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

flow meter test facilities in North America. This marksthe first time that these three test labs have undergone adirect performance comparison. This project has federalgovernment participation from the U.S. National Instituteof Standards and Technology and Measurement Canada.Test results should be available by the end of 2001.

CONCLUSIONS

GTI’s applied flow measurement research programcontinues to address the priority needs of the naturalgas industry. This paper summarizes some of the recentmeasurement research activities at the GTI MRF. Acomplete listing of all MRF research reports and technicalpapers is available from GTI or the MRF website (http://www.grimrf.org).

REFERENCES

1. Johnson, J. E., et al., “Metering Research FacilityDesign,” GRI Topical Report No. GRI-91/0251, GRI,Chicago, IL, March 1992.

2. George, D. L. and T. B. Morrow “Orifice MeterOperational Effects: Orifice Meter Flow Measurementat Low Differential Pressures,” GRI Topical ReportNo. GRI-00/0216, GRI Contract No. 5097-270-3937,GRI, Chicago, IL, February 2001.

3. George, D. L., P. J. LaNasa, G. L. Morrison, and T. B.Morrow, “Effects of Orifice Plates InstalledBackwards and Meter Tube Roughness on DischargeCoefficients,” Proceedings of the American GasAssociation Operations Conference, Dallas, Texas,April 29-May 2, 2001.

4. Measurement of Gas by Multipath Ultrasonic Meters,American Gas Association TransmissionMeasurement Committee Report No. 9, AmericanGas Association, Arlington, VA, June 1998.

5. Grimley, T. A., “Performance Testing of UltrasonicFlow Meters,” 15th North Sea Flow MeasurementWorkshop, Kristiansand, Norway, October 1997.

6. Grimley, T. A., “The Influence of Velocity Profile onUltrasonic Flow Meter Performance,” Proceedingsof the American Gas Association OperationsConference, Seattle, WA, May 1998.

7. Grimley, T. A., “Ultrasonic Meter InstallationConfiguration Testing,” Proceedings of the AmericanGas Association Operations Conference, Denver,CO, May 8-10, 2000.

8. Behring, K. A. and E. Kelner, “Metering ResearchProgram: Natural Gas Sample Collection andHandling-Phase I,” GRI Topical Report No. GRI-99/0194, GRI, Chicago, IL, August 1999.

9. Collecting and Handling of Natural Gas Samples forCustody Transfer, Manual of Petroleum MeasurementStandards, Chapter 14.1, 4th Edition, AmericanPetroleum Institute, Washington, D.C., August 1993.

10. Coriolis Flow Measurement for Natural GasApplications, American Gas AssociationTransmission Measurement Committee EngineeringTechnical Note, American Gas Association,Washington, D.C., July 2001.

11. Measurement of Gas by Turbine Meters, AmericanGas Association Transmission MeasurementCommittee Report No. 7, American Gas Association,Arlington, VA, June 1996.

12. Behring II, K. A., E. Kelner, A. Minachi, C. R. Sparks,T. B. Morrow, and S. J. Svedeman, “A TechnologyAssessment and Feasibility Evaluation of Natural GasEnergy Flow Measurement Alternatives,” FinalReport, Tasks A and B, Southwest Research Institutefor the U.S. Department of Energy, MorgantownEnergy Technology Center, Morgantown, WV, May1999.

13. Morrow, Thomas B., E. Kelner, and A. Minachi,“Development of a Low Cost Inferential Natural GasEnergy Flow Rate Prototype Retrofit Module,” TopicalReport to GRI Contract No. 5097-270-3937, DOECooperative Agreement No. DE-FC21-96M33033,October 2000.

Edgar B. Bowles, Jr.