Reliability and Installation Effects of Ultrasonic Custody Transfer Gas Flow Meters Under Special Conditions

8/13/2019 Reliability and Installation Effects of Ultrasonic Custody Transfer Gas Flow Meters Under Special Conditions

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Paper 7.1

RELIABILITY AND INSTALLATION EFFECTS OFULTRASONIC CUSTODY TRANSFER GAS FLOW

METERS UNDER SPECIAL CONDITIONS

Volker HerrmannSICK|MAIHAK

Toralf Dietz

SICK|MAIHAK

Matthias Wehmeier

SICK|MAIHAK

Index


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4thInternational South East Asia Hydrocarbon Flow Measurement Workshop

9 - 11 March 2005

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RELIABILITY AND INSTALLATION EFFECTS OF ULTRASONICCUSTODY TRANSFER GAS FLOW METERS UNDER SPECIAL

CONDITIONS

Volker Herrmann, Toralf Dietz and Matthias Wehmeier, SICK|MAIHAK

1 INTRODUCTION

Ultrasonic gas flow meters have been available commercially since the 1980s for a range ofmeasuring tasks. Numerous developments have seen their application range increaseenormously. Modern gas flow meters are more and more used in custody transferapplications.

Even after more than 20 years of development, new advances are being made for ultrasonicgas flow meters and there is still room for improvement. Optimising the meter concept andanalysing all the potential sources of errors are aimed at eliminating or minimising as many

uncertainty factors as possible. Factors that result in significant measurement uncertaintymust be identified and appropriate manufacturing technologies, procedures, and teststrategies developed.

A discussion on the uncertainty budget of the meter itself was presented in [2]. Taking intoaccount the conclusions of this study, a reliable meter concept was developed, which ensuresa high degree of accuracy and reproducibility.

The typical field installation differs significantly from the test lab, leading to deviations andadditional uncertainties for the ultrasonic gas flow meters. As is emphasised in a recent study[1] this is valid for different meter sizes and designs. The reason for this behaviour is basedon the nature of the flowing fluid the fluid dynamics itself and the response of the meter onthis special situation. A detailed knowledge of the velocity profiles in typical field installation

and an improved understanding of the meter physics can help to further optimise the meterbehaviour.

This paper follows the recent study on uncertainty budget and manufacturing accuracy [2]. Amodern measurement technique the particle image velocimetry (PIV) - is presented, whichallows to measure the velocity profiles in the pipe independently, resulting in a completerepresentation of flow velocity pattern at each point of the pipe. The results of the PIV-methods where compared with the responses of an ultrasonic meter. Different installationconfigurations where tested with the PIV method. Using a modern disturbance plate [4] toproduce the disturbed flow profiles was a time and effort saving fact.

The results of these tests where implemented into the measurement algorithm of the flowmeter FLOWSIC 600, leading to the fact, that the meter can detect and compensate

installation effects to some certain extent. The practical meaning of this algorithm waschecked on standard test procedures during the type approval at ambient conditions and onthe high pressure test lab of Ruhrgas AG in Lintorf (Germany) with typical practical installationconditions. Inlet disturbances with only 5 D straight pipe where chosen as a worst casescenario, which is neither practical nor recommended by the manufacturer of the meter, butshows the response of the algorithm to unexpected and unusual flow disturbances.

The benefit the user will gain from this (and future) investigations is mainly certainty: Certaintythat the meter will behave like specified and that the number of unexpected installationeffects will decrease. Another benefit is that it will be possible to gain a few points of apercent accuracy which counts to relevant numbers.


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2 FLOW PROFILE INDUCED MEASURING UNCERTAINTY OF ULTRASONIC GASFLOW METERS

Gas flow meters rarely work under conditions comparable with those ideal situations in acalibration facility. To identify the sensitivity of the gas meter to flow profile conditions, testshave been carried out within pattern approvals for the gas meters. The deviation of thebaseline under disturbed conditions should be within the allowable error range.

Ultrasonic gas flow meters for custody transfer (fiscal applications) are before installationcalibrated in a national recognised test facility. In the final result at least the averagedeviation over the measured range will be corrected by an adjust factor. The design of testfacilities guarantees stable and approved flow profiles over the full measuring range.

In practice the ultrasonic gas flow meter should possibly operate to a great extentindependently of deviations from the calibration conditions. In order to respond as little aspossible, on the flow profile conditions, the gas flow meter should be as tolerant as possibleagainst deviations in the flow profile.

2.1 Flow Profiles And Standard Test Configurations

The flow profiles inside a pipe are influenced by many constructive piping elements (e.g.bends, double bends, T-pieces, reducers and expanders). The most common practicalinstallations are simple 90 degree bends (elbows) and double bends (double elbows) either inor out of plane. Such elements create asymmetry of the axial velocity pattern and/or swirlmovements, depending on the nature of the construction element.

The gas flow meter should be tolerant against such disturbances of the profile. Therefor, itsreaction on this is tested during pattern approval. These test configurations should produceswirl affected, asymmetric flow profiles and should represent extreme installation conditions.To ensure compatibility of the results a standard procedure is used. The InternationalOrganisation of Legal Metrology OIML defined therefore standard pipe configurations toperform perturbation tests within pattern approvals. Figure 1 shows the defined standard

configurations for testing the disturbance sensitivity as described in OIML RecommendationR32 [5]. A double bend out of plane in a nominal pipe size smaller than the meter size isfollowed by a expander. This is the low level perturbation test configuration, but the flowprofile distortion is heavier than just with a double-bend out of plane. For high levelperturbation a half moon plate is installed between the two bends; this increases again theflow profile distortion. Both configurations create asymmetry and swirl in different degrees.As a result of these tests, a deviation from base line under undisturbed conditions ismeasured, which should mark the maximum of the expected deviations in practice and shoulddefine also the minimum length of the necessary undisturbed inlet and outlet lengths.

Fig. 1 Standard OIML test configurations


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For transmitting and receiving of the ultrasonicsignals, the FLOWSIC 600 utilises new small size,high frequency transducers (figure 4). Thesetransducers cause only negligible perturbations forthe flow profile close to the wall of the meter body.Therefore the influence of the transducers can be

neglected in this study.

Fig. 4 Ultrasonic transducers

A special problem of all ultrasonic gas flow meters is their sensitivity to the orientation of theasymmetry in a disturbed flow profile. All path layouts are not symmetrically in amathematical sense. Hence, a meter may show different results with a certain disturbance atdifferent inlet lengths. The reason for this phenomenon is the length depending change of theasymmetry position in the grid of the paths and the resulting changes in path velocity

pattern. These changes can be easily simulated in experiments by rotation of theperturbation plate instead of installing different pipe length. On the other hand, theindependently determined path velocities offer the possibility to compensate for influences ofswirl and asymmetry. Algorithms that determine the degree of asymmetry and the swirlstrength using the path velocities can compensate for the measurement deviations producedby the disturbances. The implementation of such algorithms needs a full understanding of thelocal gas velocity distributions. To gain these information from the flowing gas a twodimensional velocity measurement method is necessary. A suitable method was found withthe Particle Image Velocimetry (PIV).

3 PARTICLE IMAGE VELOCIMETRY (PIV)

3.1 BasicsThe Particle Image Velocimetry is a non intrusive method for the measurement ofsimultaneous two-dimensional velocity fields in one plane. The method is based on thetracing of particles that are transported with the movement of the flow, with algorithms ofimage processing. With a particle generator an adapted tracer is added to the flow andilluminated by a double pulse laser through light sheet optics. A special CCD cameraprovides two images of the measuring plane in a defined time distance, which will be dividedin smaller portions for further processing, the so-called interrogation spots. For every spot adisplacement of the particles from two successive images is calculated with help of cross-

correlation as shown in figure 5.This displacement, together withthe time difference between thetwo exposures, results in the

velocity components. Theresults of single spots arecombined to a vector field for thewhole measuring plane, whichcan be further processeddepending on the purpose of theexperiment.

Fig. 5 - Example for interrogationspots taken from a double image

with resulting spatial correlation


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3.2 PIV - Measurements On The Perturbation Plate Generated Flow Profile

In connection with these test programs PIV measurements were carried out in air underambient pressure 10D after the perturbation plate for the above-referenced path levels of afour-path FLOWSIC 600 with size DN200 (8-inch). Two perturbation plates were used withclockwise and counter-clockwise swirl. To test the response of the meter relative to thedisturbed flow profile, the plates were rotated in 30 degrees steps. The PIV layout issketched in figure 6.

Tracerparticels

Measuring section

CCD-Camera

Laser

pipe

Gas flow

Fig. 6 - Picture of PIV test setup

The essential advantage of the PIV-method is that, because of the two-dimensional nature,the axial and tangential velocity (the latter one does not contribute to the total flow) can be

determined directly. From the measuring values of the ultrasonic gas flow meter these singlecomponents can generally not be derived, since they are connected by the path angle. ThisPIV measurement can help to better understand how swirl and asymmetry are projected inthe path velocities. With this knowledge an algorithm should be developed, which allows for acorrection of the measuring deviations caused by the disturbed flow using only the pathvelocities.

As an example for a PIV result in figure 7 average fields of axial and tangential velocity for thepath level 2 are presented as grey scale diagrams. Drawn is here the trace of the acousticmeasuring path, along which in a further step of processing the path velocities are integrated.The integration of the local velocities is performed in the virtual region, which is the directconnection between the two transducer membranes (between the two dotted lines).

Fig. 7 - Average velocity patterns 10D after disturber plate 2, orientation 60

transducerposition


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Figure 9 represents examples for this, with especially extreme behaviour, as block diagrams.First of all it is clear that the two perturbation plates at same orientation show similar profiledeformation (vax), but opposed swirl (vtan). The tangential contribution from thesedisturbances can reach until 15% of the axial velocities on the outer paths. But is alsonoticeable at the inner paths. The distribution of the tangential velocities on the single pathsshows asymmetry. Furthermore it is striking that the path velocities differ considerably from

the axial components, which determine the flow. Here lies the essential reason for themeasurement deviations of ultrasonic gas flow meters in disturbed flow profiles.

From the complete data set, collected with the perturbation plates, an optimal correctionalgorithm was developed based only on the path velocities. The operation of this algorithmwas tested, as described in the following sections, with the OIML standard disturbances aswell as with more practically relevant installation conditions.

4 PRACTICAL TEST WITH DISTURBED FLOW PROFILES

4.1 Verification With OIML Standard Configurations At Ambient Test Conditions

Without a priori knowledge of the present disturbed flow situations device characteristics wereobtained for the following situations:

- ideal flow condition (20D straight upstream pipe)- OIML Low-level disturbance, 10D upstream- OIML High-Level disturbance, 10D upstream- Single bend (90), 10D upstream, in two positions (12 oclock and 9 oclock)

The test of the characteristics in a disturbed configuration was carried out according to theOIML directive at relative flow values of 10%, 25%, 40%, 70% and 100% of Q max. For betterunderstanding the following results are represented based on the initial characteristics (idealflow condition). The presented deviation was calculated as follows:

ibaseidisturbedi EEDev

,, =

Figure 11 shows the response of the FLOWSIC 600 on the disturbances according toOIML R32 at ambient test conditions. The algorithm shows the general ability tocompensate for the swirl and asymmetry induced flow measurement deviations. Forthe Low-level disturbance the deviations can be kept in a bandwidth of less than

0.35%.


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-1,0

-0,5

0,0

0,5

1,0

0 20 40 60 80 100 120Q / Qmax[%]

Deviation[%]

Low-level left Low-level right

air @ pamb, Tamb

Fig. 11 Test result FLOWSIC 600 (DN 200, Qmax2500 m/h), OIML standard configurations

10D upstream at ambient conditions

The results of the high-level disturbance tests have left the error band of 0.5%. For suchheavy distorted situations it is recommended to condition the disturbed flow with a flowconditioner. Therefore additional test series with an upstream installed flow conditioner weredone. The flow conditioner was placed at 2D upstream of the meter. If using a preferred flowconditioner, the necessary upstream pipe length could be reduced to 5D upstream of thedisturbance. In this configuration also the very heavy distorted flow situations of the high-level

disturbance, which is caused by the half moon plate, can be kept in a bandwidth of 0.35%.Furthermore, the use of a flow conditioner flattened also the error curves.

-1,0

-0,5

0,0

0,5

1,0

0 20 40 60 80 100 120

Q / Qmax[%]

Devia

tion[%]

Low-level left Low-level right

High-level left High-level right

air @ pamb, Tamb

Fig. 12 Test result FLOWSIC 600 (DN 200, Qmax2500 m/h), OIML standard configurations5D upstream at ambient conditions


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A single 90-bend was used to test the algorithm in a more common situation. The bend wasrotated by 90 to check this flow situation in two different relations for the path layout.

-1,0

-0,5

0,0

0,5

1,0

0 20 40 60 80 100 120

Q / Qmax[%]

Deviation[%]

single elbow 9 o'clock

single elbow 12 o'clock

air @ pamb, Tamb

Fig. 13 Test result FLOWSIC 600 (DN 200, Qmax2500 m/h), single 90-bend in two

orientations 10D upstream at ambient conditions

The FWME of the meter deviations during the different tests was calculated and issummarised for a general overview as shown in the next picture.

-1,0

-0,5

0,0

0,5

1,0

Low- leve l r igh t Low- level le ft H igh- leve l l ef t H igh -l evel ri gh t

avg.

deviation[%]

10D

5D with FC

-1,0

-0,5

0,0

0,5

1,0

single elbow 9 o'clock single elbow 12 o'clock

avg.

deviation[%]

10D

Fig. 14 FWME presentation of all tested configurations at ambient conditions

4.2 Verification With Typical Installation Elements At High Pressure Conditions

Because the OIML standard pipe configuration does normally not exist in real worldapplications, the question arises of course how well the compensation works for other,practically relevant installation elements, like single bends, u-bends and double bends. Alsountil now all measurements were carried out with atmospheric air, on one meter size. Howwill the compensation relate in another Reynolds-domain, determined by high pressurenatural gas as test medium and different meter diameter? For this purpose extensive testseries will be reported from the test rig of Ruhrgas AG in Lintorf, Germany. These results willbe presented in the following section.

The used meter size was a DN 300 (12 inch), four-path meter FLOWSIC 600. The tests werecarried out with high pressure natural gas at 10 bar. Figure 15 and Figure 16 show two of thetested configurations. The U-bend was build from two 90-bends. The double bend out ofplane has used the same elements. For every test a Zanker-type flow conditioner was


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-1,0

-0,5

0,0

0,5

1,0

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000flow rate [m/h]

deviation[%]

0 90

180 270

0 03/2004

natural gas

10bar(g)

Fig. 18 - Test results FLOWSIC 600, DN 300 (12 inch), double bend out of plane 5D upstream

at high pressure gas, HDV Lintorf, Germany

Also under these more severe situation the deviation remains in a error band of 0.5%. Finallyalso the test results are shown for a single bend at 20, 10 and 5 diameter distances and for a u-bend at 10 and 5 diameter distances.

-1,0

-0,5

0,0

0,5

1,0

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

flow rate [m/h]

deviation[%]

90-bend 5D 90-bend 10D 90-bend 20D

U-bend 5D U-bend 10D

natural gas

10bar(g)

Fig. 19 - Test results FLOWSIC 600, DN 300 (12 inch), single bend and u-bend on different

upstream distances, at high pressure gas, HDV Lintorf, Germany


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To summarise all test results, again the flow weighted mean errors (FWME) of the tests arecalculated and shown together in the next picture.

FWME of meter deviation, test double bend out of plane

-1,0

-0,5

0,0

0,5

1,0

0 90 180 270

meter orientation

avg.

deviation[%]

5D

10D

FWME of the 90-bend and U-bend tests

-1,0

-0,5

0,0

0,5

1,0

90-bend

5D

90-bend

5D90

turn

90-bend

10D

90-bend

20D

U-bend

5D

U-bend

10D

avg.

deviation[%

]

Fig. 20 - FWME presentation of all tested configurations, HDV Lintorf Germany

5 CONCLUSION

The investigations show that it is possible to gain a better understanding of the fluid dynamicsand the resulting meter behaviour. The FLOWSIC 600 has the ability to work well in typical fieldconfiguration, if taking into account the installation recommendations. Furthermore, if using thepreferred flow conditioner, only 5D upstream inlet length can be used.

The fact, that ultrasonic gas flow meters have become really mature over the last years doesnot mean that there is no room for improvements left. Substantial efforts in research willimprove quality standards for the future even more and most important will reduce theoverall uncertainty picture of ultrasonic meters.

6 NOTATION

Dev resulting deviation of the meter

idisturbedE

, error in disturbed flow situation

ibaseE

, error in ideal flow condition

i test flow rate 10, 25, 40, 70, 100% Q/Qmax

tanv tangential velocity component

axv axial velocity component

7 REFERENCES

[1] Delenne, Mouton, Pritchard, Huppertz, Ciok, van den Heuvel, Folkestad, Vieth, Lezuan,Marini, Evaluation of Flow Conditioners Ultrasonic Gas flow meters combinations,North Sea Flow Measurement Workshop, October, 2004

[2] Herrmann, Ehrlich, Dietz, MANUFACTURING ACCURACY A KEY FACTOR FOROVERALL PERFORMANCE ON AN ULTRASONIC GAS FLOW METER, 3

rd

International SE Asia Hydrocarbon Flow Measurement Workshop, March 2004

[3] Pereira, Mickan, Kramer, Dopheide, von Lavante, INVESTIGATION OF FLOWCONDITIONING IN PIPES, FLOWMEKO 2002

[4] Dr. Rainer Kramer, Physikalisch-Technische Bundesanstalt, Braunschweig, Specialaspects concerning the type approval of ultrasonic gas flow meters used for legalmetrology applications, Gas Berlin 2003,

[5] OIML Recommendation R32, Rotary piston gas flow meters and turbine gas meters,

Annex A, 1989

Documents

Reliability and Installation Effects of Ultrasonic Custody Transfer Gas Flow Meters Under Special Conditions