2008paper production and upstream flow measurement workshop

8/7/2019 2008paper Production and Upstream Flow Measurement Workshop

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Production and Upstream Flow Measurement Workshop12-14 February 2008

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PETROLEUM MEASUREMENT AND DIAGNOSTICS OFULTRASONIC FLOW METERS IN HIGH FLOWRATES AND

VISCOSITIES

Josaphat Dias da Mata, PETROBRAS

Thiago B. Vidal Oliveira, PETROBRASJos Alberto Pinheiro S. Filho, PETROBRAS

Jos Jorge T. Churro, consultantAlcir F. Orlando, PUC-Rio

Luiz Gustavo do Val , PUC-Rio

1 INTRODUCTION

A ll the petroleum production in the MarlimA sset, Campos Basin, after treatment, is stored in theproduction platform tanks for some days, until is offloaded. During this period, the residual water is partially stratified, resulting in petroleum layers near the bottom of the tank with higher water content, more than what is allowed. In order to meet the specifications of the National A gency of Petroleum, Natural Gas and Biofuels (A NP), refineries or even international export marketrequirements, the high water content petroleum is removed from the treated oil tanks, beingdirected to another treatment process, and, therefore, being misaccounted for the second time inthe petroleum fiscal metering before tank storage.

In order to overcome this problem, all the fiscal metering of the petroleum production in theMarlimA sset, Campos Basin, is made in the offloading lines of P-32, P-33, P-35, P-37 and P-47FPSOs, thus eliminating any interference, either present or future, of the petroleum treatmentand retreatment systems over the oil production measured volumes.

The objective of this paper is to show the feasibility of the exposed concept, so that themeasuring system be considered as fiscal, according to the Technical Regulation of Measurement, issued jointly by A NP and INMETRO (National Institute of Metrology and

Industrial Quality). Ultrasonic flowmeters were placed in the FPSO offloading lines to accomplishthe objectives. Metrological certification of the flowmeters required tests with high viscosity oils(up to 330 cP) in an international laboratory and analysis of the Netherlands MeasurementInstitute (NMI). This fact is unique in the world, being considered as a technological barrier in thearea of petroleum flowrate measurement.

2 LEGISLATION

The Joint Decree n 1 A NP/INMETRO, June 19, 2000, establishes the conditions and minimumrequirements for petroleum and natural gas measuring systems, aiming to assure accurate and complete results.

The 2705/98 Law, A ugust 3, 1998, establishes the values of the Governamental Royalties to bepaid by authorized companies for exploration and production of petroleum and natural gas to theNational A gency of Petroleum, Natural Gas and Biofuels (A NP), according to the measuredvalues in each field.

A ccording to n 9478 Law, A rt.47, the Royalties are paid monthly, in Brazilian currency, since thebeginning of the commercial production of each field, at a rate of 10% of the correspondingvalue of the petroleum or natural gas production.


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The Governmental Royalties are calculated from the knowledge of the measured values of petroleum and natural gas volumes in the so-called fiscal metering points, where the productownership is transferred from Government, represented by A NP, to the authorized company.

The Technical Regulation of Measurement, issued jointly byA NP and INMETRO, establishes theconditions for design, installation, operation, test and maintenance of different volumetric

measuring systems, mainly the fiscal ones, which this paper is concerned with.The fiscal metering points must be submitted to the analysis of the metrological control of INMETRO, if adequate, in order to demonstrate their traceability to measurement standards, andthen be approved by A NP.

Positive displacement, turbine or mass (Coriolis) types of online fluid measurement systems canbe used in the fiscal metering points. Other types of systems must be submitted to the analysisand approval by A NP.

The petroleum fiscal metering systems must be designed, installed and operated in accordancewith OIML R117A ccuracy Class 0.3 measurement requirements. The n 64 INMETRO Decree,A pril 11, 2003, approved the Technical Regulation of Measurement, which establishes thetechnical and metrological requirements for fluid meters in petroleum measurement systems,following OIML recommendations.

Online fiscal metering systems of the petroleum production must be calibrated every sixty (60)days at most. Larger calibration intervals may be approved by A NP on the basis of historicalrecords.

The calibration of online fiscal metering systems must be made with the same measurementfluid and flow conditions, within a maximum allowed deviation of 2% in specific mass andviscosity, 5C in temperature, 10% in pressure, and 10% in flowrate. Provers, tanks,measurement standards or other previously authorized system by A NP can be use in thecalibration as the reference meter.

3 VERIFICATION/CALIBRATION OF ALTOSONIC V ULTRASONIC METER

Calibration is defined as an operation establishing the relation between quantity values providedby measurement standards and the corresponding indications of a measuring system, carried outunder specified conditions and including evaluation of measurement uncertainty.

Verification is defined as the confirmation through examination of a given item and provision of objective evidence that fullfils specified requirements.

In Germany, the A LTOSONIC V ultrasonic meter must be verified every two (2) years for fiscalmetering purposes.

A ccording to a document issued by NMI in 04/05/2000, if the following measuring parametersremain the same during a certain period, the performance of the A LTOSONIC V ultrasonic meter

also remains the same.y The meter is used to measure clean refined fluid, without solid particles.y Meter cross section is the same.y The ultrasonic transmitter-receiver transducer is operated correctly.y The electronic data base of the data processing hardware remains the same.

Based on this evidence, on the principle of operation of the meter and on experimental data, NMIsuggests a four (4) year time interval between two successive calibrations. In Brazil, based onstudies [4], A NP approved a two (2) year time interval between two successive calibrations of the


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A LTOSONIC V meter for fiscal metering purposes (A ccuracy Class 0.3) and typical operatingconditions of PETROBRA S in the field where the meter is placed.

Table 1 presents a comparison between typical operating conditions of PETROBRA S andavailable test for the meter in laboratories around the world.

Table 1 - Comparison between typical operating conditions of PETROBRA S and test.

Parameter Unit PETROBRAS

TEST

Typical Cond.Diameter mm 200 - 250 150 - 300Flowrate m/h 500 - 780 60 - 2500Velocity m/s 2.7 6.7 1 - 10Specific Mass kg/m 870 - 940 740 - 960Viscosity mPa.s 9.12 44.5 0.4 - 125Reynolds Number 10 14 - 140 2.8 - 3580Pressure bar 0.2 2.9 3 6.1Temperature C 53 - 58 10 - 35

The available calibration data for the A LTOSONIC V meter were analyzed in this study [4],showing that the performance of the meter meets the OIML R117 specifications in the testedrange, and that for at least two (2) years it remained the same. In this paper the tested range wasenlarged to cover the operating conditions of the Marlim A sset, as presented in Table 2, bytesting the meter in a French laboratory. This paper also shows a new concept of fiscal meteringwithout using an online standard meter for calibrating the fiscal meter, which was demonstratedby its long term stability.

Table 2 - Comparison between typical operating conditions of MA RLIM and test.

Parameter Unit PETROBRAS

TEST

Typical Cond.Diameter mm 600 600Flow rate m/h 550 - 5500 253 - 5917Velocity m/s 0.5 5.4 0.25 5.8Specific Mass kg/m 905 - 933 859 - 1000Viscosity mPa.s 22 - 140 1 - 258Reynolds Number 10 2.2 135.1 0.6 - 3500Pressure bar 10 0.6 5.1Temperature C 27 - 55 12 - 26

4 PRINCIPLES OF ULTRASONIC MEASUREMENT

The ISO/TR 12765 standard [2] presents the fundamentals of fluid flowrate measurement inpipes with ultrasonic meters using the transit time method. Figure 1 shows the ultrasonic beammaking an angle J with the flow direction in the pipe, with internal diameter D . The beamemitter 1 and the beam receiver 2 are placed on the surface of a pipe, and are separated by adistance Lp along the direction of the flow . The average flow velocity (u ) is related to transittimes t12 and t21 by Eq. (1).

A five (5) beam ultrasonic meter was installed in Marlim for fiscal flow measurement purposes.Two of them are placed symmetrically in the middle distance, approximately, between the center


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line and the wall, measuring the average velocities along the beam paths 2u and 4u . Two of them are placed symmetrically near the wall, measuring the average velocities along the beampaths 1u and 5u . Finally, the last one is placed along the center line, measuring the averagevelocity along the beam path 3u .

Fig. 1 - Schematics of ultrasonic meter using the transit time method

pL

ut t

J cos..211

1221

! (1)

Orlando & Do Val [5] showed that the average velocity along the beam path, as measured by themeter, and the fluid velocity at a point of the cross section equally distant from the center linethan the beam path, are approximately the same. Therefore, the flow profile can be defined byfive (5) points. The average flow velocity at the cross section, which is related to the flowrate,can be calculated by means of the Gauss method, using Legendre polynomials, as shown by Eq.(2)

!

!!5

1

34251

2.568888,0

2)(

.478828,02

)(.236926,0.

21

i

ii

uuuuuuwu (2)

Orlando & Do Val [5] also showed that the velocity profile is only a function of the Reynoldsnumber (Re), defined in terms of the average flow velocity u , diameter D, and kinematicviscosity Y :

Y

Du .Re ! (3)

Before delivering the instrument to the client, the manufacturer calibrates the meter as a functionof the Reynolds number, thus characterizing its performance in an operation called fingerprint. During this operation, flowrate and viscosity are varied in such a way that all the Reynoldsnumber range can be covered. In fact there is no need of calibrating the meter at the same

J

L P

D

u t 12

t 21

1

2


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measuring flowrate and viscosity, provided the Reynolds numbers during calibration andoperation are the same.

The calibration provides a correction factor to the value calculated in Eq. (2), as a function of Reynolds number, so that the average flow velocity, and thus the flowrate, can be estimatedfrom the measured velocities along all five beam paths.

The purpose of the performance verification is to determine if the difference between the initialvalues and the measured values of the flowrate is still smaller than what is specified by OIMLR117.

Orlando & Do Val [6] analyzed the calibration certificates of the meter and showed that itsperformance meets the OIML R117 requirements for a large range of Reynolds number

5 CALIBRATION AND VERIFICATION OF THE ULTRASONIC METER

Orlando & Do Val [5] showed that the velocity profile of fully developed turbulent flows in pipesdepend only on Reynolds number, based on the cross section average velocity. Furthermore, if uncertainties smaller than 0.2% are to be achieved, each meter has to be individually calibrated,since the literature provides data for average conditions only. The initial calibration of the meter,made by the manufacturer, is called fingerprint. The Meter Factor, defined as the ratio betweenthe indicated values by the measurement standard and the meter during calibration, is calculatedfor a large number of Reynolds number values, so that during measurement an interpolationprocedure can result in reliable values of the flowrate, according to OIML R117A ccuracy Class0.3.

The acceptance of the meter for fiscal metering purpose is done through the so-calledperformance verification procedure of the meter, where at least six (6) nominal flowrate valuesare chosen along the whole range. The Meter Factor for each flowrate value is calculated at leastthree (3) times, so that the repeatability, defined as the difference between the larger and smaller values, can be estimated and expressed percentage wise.

The n 64 INMETRO Decree and OIML R117, specify that the meter can be approved if all theMeter Factor errors are less that 0.2%. Moreover, the MF repeatability , for each flowrate, mustbe smaller than 0,12%.

In this study, several calibration certificates were analyzed for the 150 mm, 300 mm and 600 mmdiameter meters, aiming their approval for accuracy class 0.3. The calibration procedure adoptedby the manufacturer is validated if the meter is approved over the whole Reynolds number range.

This study also shows that, besides meeting the OIML R117 requirements, the meter performance is only a function of Reynolds number, and not separately on diameter, flowrate andviscosity. Seven (7) 600 mm diameter meters were sent to SPSE Laboratory in France, which isaccredited by COFRA C, after being calibrated with water as a working fluid in the manufacturer

laboratory, which is accredited by NMI. Several graphs were built, showing theMeter Factor as afunction of Reynolds number, for each diameter, flowrate and viscosity values. The followingcalibration fluids, with viscosity measured at 20 C, were used : Fuel (186 cSt), Heavy Fuel (271cSt), Condensat (37-77 cSt), Oural (9,3 cSt) and water (1 cSt).

Furthermore, the data bank used by the statistical analysis procedure was complemented withthe calibration certificate data of the 150 mm and 300 mm diameter meters, as supplies bySPSE and TR A PIL in France, which are accredited by COFRA C, and including data supplied bythe manufacturer accredited laboratory. The dispersion is defined as twice the standard deviation(2. ) of theMeter Factor in each analyzed condition.


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In this study, the metrological quality of the meter is characterized by how close the Meter Factor is to 1, and its dispersion (2. ).

Tables 3, 4, 5 and 6 show that the metrological quality of the meter is approximately the samefor the 600 mm diameter meter, when calibration fluid, viscosity, flowrate and Reynolds number

vary. One can conclude that both manufacturing and calibration procedures of the meter arerepetitive. Finally, the metrological quality does not depend on the meter diameter.

Table 3 - Metrological quality as a function of calibration fluid and viscosity, 600 mm diameter meter

FLUID METER FA CTOR DISPERSION(2. )

HEA VY FUEL 1,0002 0,0018FUEL 1,0000 0,0014

CONDENSA T 1,0001 0,0015OURA L 1,0001 0,0018WA TER 0,9999 0,0016

A

VERA

GE 1,0001 0,0016Table 4 - Metrological quality as a function of Reynolds number, 600 mm diameter meter.

REYNOLDS METER FA CTOR DISPERSION(2. )

200 a 2000 1,0002 0,00182000 a 10000 1,0001 0,001510000 a 30000 1,0002 0,0014

30000 a 100000 0,9998 0,0016100000 a 1000000 1,0005 0,00061000000 a 3500000 0,9995 0,0012

A VERA GE 1,0001 0,0016

Table 5 - Metrological quality as a function of flowrate, 600 mm diameter meter.

FLOWRA TE METER FA CTOR DISPERSION(m3/h) (2. )

200 a 500 1,0001 0,0016500 a 1000 1,0002 0,00181000 a 1500 1,0001 0,00191500 a 2000 1,0000 0,00112000 a 2500 1,0002 0,00172500 a 3000 1,0001 0,00123000 a 6000 0,9998 0,0017A VERA GE 1,0001 0,0016

Tabela 6 - Manufacturing and calibration repeatability of the 600 mm diameter meter

METER METER FA CTOR DISPERSION(2. )

232575-1001 1,0002 0,0017232575-3001 1,0000 0,0014232575-3002 0,9999 0,0018232575-5001 1,0002 0,0015


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232575-7001 1,0002 0,0015232575-9001 1,0000 0,0019232575-9002 1,0000 0,0014

A VERA GE 1,0001 0,0016

A bout 600 data points were used for approving seven (7) 600 mm diameter meters, according to

OIML R117, varying calibration fluid, viscosity and flowrate over a wide Reynolds number range.The Meter Factor uncertainty is almost the same as the calculated average dispersion (2. ) of 0,0016. Considering that the Meter Factor error limit is 0.20 %, the probability of having avalue outside this range is 1,24 %, following the Gaussian probability distribution. Only 3 out of 600 points were outside the range, or 0,5 %.

The calibration certificates of the 150 mm and 600 mm diameter meters were analyzed [6], andthe conclusion is that the metrological quality is independent of the meter diameter, as seen inTable 7.

Table 7 - Metrological quality as a function of meter diameter.

DIA METER METER FA CTOR DISPERSION

mm (2. )150 1,0000 0,0016300 1,0000 0,0015600 1,0001 0,0016

A VERA GE 1,0000 0,0016

Therefore, one can conclude that the meter calibration and measurement procedures, as afunction of Reynolds number, as suggested by the theory, are reliable, resulting in meeting theOIML R117A ccuracy Class 0.3.

5 .1 Calibration of the ultrasonic meter

The calibration of the ultrasonic meters for the MarlimA

sset was made by varying both flowrateand viscosity in such a way the calibration and measuring Reynolds numbers are the same, thusavoiding the need of calibrating the meter at the specified operating conditions.

Water can be used to calibrate the meter, provided the resulting Reynolds number be the sameas the measuring value. The Reynolds number range of the Marlim A sset flow is 2,000 to150,000. Considering the minimum measuring flow velocity of the ultrasonic meter (0.2 m/s),Table 8 presents the range of Reynolds number to be covered by different diameter meters,when water is the calibrating fluid.

Table 8 - Reynolds number range for calibrating ultrasonic meter with water for MarlimA sset

Diameter Reynolds Number mm Minimum Maximum150 30000 150000300 60000 15000600 120000 15000

Table 8 shows that a large Reynolds number range can be covered with water, when smalldiameter meters are used. However, when large diameter meters are used, only a small rangecan be covered. Therefore, there is a need of having more viscous fluids to calibrate the meter at the lower end of Reynolds number range.


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Fig. 2 presents a scheme to be used for calibrating the meter with different calibrating fluids inorder to cover the whole Reynolds number range.


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ondensat - 40 c&

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B eynolds de trabalhodo Ativo Marlim

C

aD o de trabalho do Ativo Marlim

Fig. 2 - Calibration of the meter with different fluids

Fig. 2 presents for different fluids (viscosities) the relationship between flowrates and Reynoldsnumbers. The lower and upper flowrate limits for a 600 mm meter are 200 (0.2 m/s) and 10000(10 m/s) m/h, respectively. Inside these limits it is possible to have the plot of Reynolds number as function of the flowrate for different fluids or viscosities, thus setting up the lower and upper Reynolds number limits for different fluids.A lso it is presented the operational Reynolds range of Marlim asset (2200 to 135100) and its flowrate range, represented by the blue rectangle. A s itcan be observed, the calibration with water does not cover the whole Reynolds range of theMarlimA sset, needing three fluids at least: Oural, Condensat and Fuel. A nother important issueis the fact that the maximum flowrate (3000 m/h) at the SPSE laboratory is sufficient to calibrate

the 600 mm ultrasonic flowmeters, since with different fluids it is possible to achieve theoperational Reynolds of the MarlimA sset with flowrates lower than 3000 m/h.

It is possible to conclude that, with the procedure shown above, the ultrasonic flowmeter does notneed to be calibrated over the full operational flowrate range of the MarlimA sset (550 a 5500m/h) for one specific fluid or even for different fluids, once the flowmeter works as a function of the actual Reynolds number. Therefore the calibration procedure using different fluids at SPSElaboratory complies with the operational specifications of the MarlimA sset, i.e., all 600 mmflowmeters were calibrated over the full Reynolds range.

5 .2 Periodic verification of the ultrasonic flowmeter performance

The periodic verification differs from the calibration due to the fact that the initial adjustmentscarried out during the Fingerprint are kept. The flowmeter shall be periodically verified in order toassure its reproducibility. Once it is not possible to be verified at its operational location, theflowmeter shall be sent to an accredited laboratory for its verification. In this case, the zeroingprocedure and acoustic paths are verified. Following this stage, the flowmeter can be verified atthe full Reynolds number (operational), keeping the maximum errors and repeatability below thefigures specified by OIML R117 (Class 0.3). Otherwise the flowmeter shall be calibrated at anaccredited laboratory.


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A s demonstrated in this study, the flowmeter verification can be done using only water, once theReynolds number range found in the operation (duty) is reproduced. The bigger the flowmeter diameter, the lower the Reynolds number range that can be covered by the water verification.

Nevertheless, when the full operational Reynolds number range for a specific flowmeter cannotbe verified with water, it is still valid to carry out one verification with this fluid over a range of Reynolds covered by the initial verification. A s the flowmeter performance has the samemetrological quality over the full Reynolds number range, the periodic verification can be donewith water for only a part of the Reynolds number range established by the initial verification. If there is any drift at the performance figures, with errors greater than the errors set up by theOIML limits, so a calibration job has to be done at an accredited laboratory.

5 .3 Ultrasonic flowmeter performance diagnosis

A s demonstrated, the flowmeter calibration cannot be done with water only, thus needing other more viscous fluids so as to cover the full Reynolds number range. The bigger the flowmeter diameter, the lower the Reynolds number range that can be covered by the water verification. Itwas confirmed that the flowmeter performance has the same metrological quality over the fullReynolds number range. The metrological quality in this study is characterized by the averagevalue of the Meter Factor and by its dispersion (2. ) among all runs carried out with the purposeof comparison.

So, a periodic verification can be done over a part of the operational Reynolds number rangeonly, or other one part that is practicably feasible. If there is any drift at the performance figures,a calibration job needs to be done with water or other more viscous fluids.

Besides this verification, it is important that a more frequently monitorating of the flowmeter health and flow behavior is carried out. The monitoring can be done through the diagnostics toolspresent at the A LTOSONIC V meter itself. Then it was proposed a monthly procedure in order toenable the metrological monitoring of the diagnosis data from a typical liquid ultrasonic meteringsystem (oil), thus evaluating the time evolution of the indexes (drift) which could identify thequality of the measurement work done. The periodicity for the diagnosis data acquisition wouldbe: every single oil transfer (offloading), in cases of fiscal metering or custody transfer meteringfrom one FPSO to any other FPSO or to any relief ship; every month, in the other cases of fiscalor custody transfer; shorter periods, in case there is characterized the need of a more accuratemonitoring. The following information can be acquired instantaneously, namely:

A xial velocity of the fluid at each ultrasonic path (m/s); Speed of sound (SOS) at each ultrasonic path (m/s); Swirl Number (which characterizes the flow rotation inside the pipe); Temperature of the f lowmeter body (C); Temperature of the fluid (C).A larms can also be generated from the flowmeter, meaning that problems exist at the meter itself, at the installation or in the flow. The velocity profile can also be monitored online, as per

the screen shown in Fig. 3.


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Fig. 3. Velocity Profile

Other indexes and correlations can also be established for the monitoring of the ultrasonicflowmeter, like:

Symmetry (X1): the meter compares the flow pattern at the upper section to the lower section of the pipe. Ideally this value is close to the unity (1). A ny variation out of therange of 0.02 can indicate that the flow conditioner or straightening vane is blocked or that the velocity profile is varying.

54

211

uu

uuX ! (4)

Cross Flow (X2): the meter compares the velocities at two right angle planes, twovelocities for each plane. Ideally this value is close to the unity (1).A ny variation out of the range of 0.02 can indicate a block in the pipe or incrustation.

52

412

uu

uuE ! (5)

Swirl (X3): the meter compares the internal acoustic paths to the external ones as anindicator of the flow rotation inside the pipe. Ideally this value is close to 1.17. If there isa flow conditioner or straightening vane installed, a variation up to 2% can be expected.Greater values might indicate blockage.

51

423

uu

uuF ! (6)

Roughness: the meter can detect any increase on the roughness by its effect at thevelocity profile. If the profile does not vary more than 2%, probably the roughness mustbe remained as constant.

Flow stratification: the stratification leads to different values for the speed of sound(SOS) at each path. Flow velocities smaller than 0.1 m/s cause a stratification of the flowdue to the presence of natural convection currents, thus increasing the measurement


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uncertainty. The NMi pattern approval of the A LTOSONIC V indicates a recommendedminimum value of 0.2 m/s.

Turbulence: the meter calculates the turbulence intensity by the root mean squarevalue of the velocity fluctuations. This value can be compared to the expected, enablingthe diagnosis on the distortion at the velocity profile. For paths close to the pipe wall, avalue of 4% is considered as normal. For internal paths, it would be 2%. Variations from1 to 2% above or below are permitted.

Thus, through the meter diagnostics, one can conclude that there is either a flow change or thereis a meter drift. The flow change can be shown if, by verifying with water calibration, there is nometer calibration change. If there is drift, a calibration with more viscous fluids should be done,in order to cover all the Reynolds number range.

Pipe or meter incrustations can be minimized cleaning them with water just after an offloading,as it is usually done at PETROBRA S.

Considering that the meter performance is uniform within its operation range, the water verification, corresponding to a given Reynolds number range, may be an indication that there isno need to calibrate with more viscous fluids.

5 .4 Meter long-term stabilit drift

A study was made to determine, via calibration certificate analysis, the minimum necessaryperiod for a significant drift on the ultrasonic meter calibration to take place, requiring itsrecalibration, so that the measurement errors and repeatability are less than the maximumvalues permitted by standards for its acceptance as a fiscal meter (accuracy class 0.3). This timeinterval between successive calibrations is compared with the calibration frequency demandedby the Joint Decree n 1 A NP/INMETRO, issued on June 19, 2000, which establishes 60 days.Being bigger, one can demand a longer calibration periodicity.

To reach this goal, a single meter should be calibrated several times within a period, varying theinterval between calibrations. However, the available calibration data belong to four 6-inchmeters of the same model. It was shown that the measurement procedures and the calibration of the 7 Marlim A sset meters are reliable and result in errors compatible with the 0.3 Classspecified by OIML R117. It was considered that this set of data could represent the performanceof a class of meter of the same pattern (model), in time. In addition, a single 12-inch meter wasrecalibrated with fluids with a broad viscosity range.

The data analysis of the calibration certificate of meter n 600052, Fig. 4 and 5, with a 150-mm(6-inch) diameter, issued by TRA PIL Laboratory, accredited by COFRA C, according to OIMLproving criteria, allows one to conclude that the meter did not show any drift after almost 23months of time interval betweens calibrations, keeping the error and the repeatability of themeter factor within the range of the standards. The inclusion of the manufacturers data for thesame meter allowed us to increase this interval to 26 months.

Likewise, meter n 1101391001, with a 150-mm diameter, did not show any drift after almost 9months of time interval betweens calibrations, keeping the error and the repeatability of themeter factor within the range of the standards. Meter n 1101391002, with a 150-mm diameter,did not show any drift after almost 20 months of time interval betweens calibrations, keeping theerror and the repeatability of the meter factor within the range of the standards. Meter n11910871, with a 300-mm diameter, did not show any drift after almost 8 months of time intervalbetween calibrations, for a broad range of viscosity and Reynolds number.


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Fig.4 - Error of meter 600052 as a function of Reynolds number

Fig. - 5 : Repeatibility of meter 600052 as a function of Reynolds number

These results are valid for a broad range of viscosity and Reynolds number, for 150-mm and300-mm meters. Since the Reynolds number range, in the typical operational conditions of Marlim, is covered by the certificate data issued by TRA PILl, reinforced by the manufacturerscertificates and those obtained in TRA PIL and SPSE, one can conclude that these results maybe also applied to the 600-mm (24-inch) Marlim meter.

To confirm this hypothesis, calibration data of a 600-mm ultrasonic meter (Fig. 6 and 7), issuedby SPSE laboratory, accredited by COFRA C, were used. They lead to the conclusion that themeter did not drift after almost 46 months of interval between calibrations, for a large range of viscosity and Reynolds number.

Fig.6 - Error of the meter 12526902 as a function of Reynolds number


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Fig.7 - Repeatibility of meter 12526902 as a function of Reynolds number

One can conclude, then, based on these results, that an interval of aproximately 4 years betweencalibrations can be used, so that the drift may be considered negligible, based on the OIML R117approval criteria for fiscal meters.

6 CONCLUSION

Fluid mechanics shows that the velocity profile of a fully developed flow in pipes is only afunction of the Reynolds number and the internal surface roughness of these pipes. In this paper,this fact is demonstrated from the analyses of the certificates of calibrations, made ininternational laboratories, of ultrasonic meters with 5 types of fluids (and, thus, differentviscosities), different flowrates and 150-mm, 300-mm and 600-mm diameters.

It was shown that the metrological quality of the meters, based on the Meter Factor average andits dispersion, is the same for all ranges of viscosity, flowrate, Reynolds number and diameter,allowing the calibration of the meter with any fluid, chosing an appropriate combination of flowrate and viscosity, so that the Reynolds number existing in the operation conditions isreproduced. Thus, different fluids and flowrates may be chosen for calibration. Therefore,calibration does not need to be done in the same operation conditions, turning it much easier.Moreover, it was shown that the meter manufacturing and calibration process is repetitive,resulting in a similar performance for all the 7 meters tested of MarlimA sset, in Campos Basin,Brazil.

The performance verification of the meter can be done with water, using the same Reynoldsnumber range of the operation, partially or totally. If there is a drift, the meter should be sent toan accredited laboratory for a calibration in the whole Reynolds number range.

A s the meter is very sensitive to velocity profile distortions, it is necessary to have a continuousmonitoring, using the available meter diagnostics. Thus, the performance diagnostics, besidesthe water periodic verification, present an important tool in order to guarantee the measurementaccuracy for a long term period.

A long term comparison among ultrasonic meter calibrations showed that during 4 years they did

not present calibration drifts, thus suggesting that this may be a minimum interval betweencalibrations.

In conclusion, the study shows that oil flow measurement procedure and the calibration of theultrasonic meters installed in Marlim A sset are reliable and result in errors compatible toA ccuracy Class 0.3, specified by OIML R117.


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7 NOTATION

D Meter internal diameter, mmLp Distance between emitter and receiver in axial direction, mRe Reynolds number t12 transit time, beam departing emitter 1 and reaching receiver 2, s

t21 transit time, beam departing emitter 2 and reaching receiver 1, su A verage flow velocity, m/siu A verage velocity measured by ultra-sonic meter at path i

wi Weighting function for pathi X1 Symmetry parameter X2 Cross flow parameter X3 Swirl parameter J A ngle between ultra-sonic beam and flow directionY Kinematic viscosity, cSt

8 REFERENCES

[1] FILHO, J.A .P.S., FITA RELLI, C.J., FERREIRA , J.A .P.G., ORLA NDO, A .F. & DO VA L,L.G., Medi o fiscal noA tivo Marlim utilizando-se medidores do tipo ultra-snico comleo pesado no offloading, PETROBRA S, 2006.

[2] ISO/TR, Measurement of fluid flow in closed conduits Methods using transit time ultra-sonic flowmeters, ISO/TR 12765:1998(E), 1998.

[3] NMI, Test certificate TC3586, revision 0, Project number 600112, NMI, 2006.[4] ORLA NDO, A .F. & DO VA L, L.G., Calibra o de medidor padr o de vaz o KROHNE

A LTOSONIC V para finalidades fiscais, PETROBRA S, 2004.[5] ORLA NDO, A .F. & DO VA L, L.G., Calibra o de medidor padr o de vaz o KROHNE

A LTOSONIC V Offloading Marlim, Relatrio 1: Embasamento terico, PETROBRA S,2006.

[6] ORLA NDO, A .F. & DO VA L, L.G., Calibra o de medidor padr o de vaz o KROHNEA LTOSONIC V Offloading Marlim, Relatrio 2: Extens o da faixa e calibra o comgua, PETROBRA S, 2006.

[7] ORLA NDO, A .F. & DO VA L, L.G., Calibra o de medidor padr o de vaz o KROHNEA LTOSONIC V Offloading Marlim, Relatrio 3: Estabilidade em longo prazo do medidor (deriva), PETROBRA S, 2006.

2008paper production and upstream flow measurement workshop

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