flowguide op 99-30287
TRANSCRIPT
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OG-Registered DocumentREPORT OP 99-30287
31/05/99
FLOW MEASUREMENTS
BEST PRACTICES GUIDE FOR THE SELECTION
OF FLOW DEVICES
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Document History
DATE REASON FOR CHANGE
AUTHOR
Name
Ref. indicator
APPROVED
Name
Ref. Indicator
Signature
May 31, 1999 Original D.C. Bruinzeel
(TAIE/145), SNR Pernis,
the Netherlands
A.J. de Visser (TAIE/1x1),SNR Pernis, the
Netherlands
Yuen Heng Seng
SIOP-OGBH/6
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Table of Contents
1. PURPOSE AND BACKGROUND......................................................................................14
2. PREFACE..........................................................................................................................15
2.1 Introduction.......................................................................................................................15
2.2 Velocity head devices ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ 15
2.3 Turbine and positive displacement flow meters ........ ........ ........ ........ ........ ......... ........ ........ .... 15
2.4 Abbreviations and Terms ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ...15
3. CALIBRATION METHODS..............................................................................................16
3.1 Introduction.......................................................................................................................16
3.2 In-line calibration method....................................................................................................16
3.3 Off-line calibration method..................................................................................................16
3.4 Factors to be considered .....................................................................................................17
4. VELOCITY PROFILES ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ .... 18
4.1 Velocity profile dependent flow meters.................................................................................18
4.2 Velocity profile independent flow meters........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 18
4.3 Fully Developed Velocity Profile..........................................................................................18
4.4 Asymmetric velocity profile.................................................................................................19
4 4 1 General 19
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6. CALIBRATED METER RUNS........ ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ . 27
6.1 Purpose.............................................................................................................................27
6.2 Introduction.......................................................................................................................27
6.3 Possible construction types ......... ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ....... 27
6.3.1 Option 1.........................................................................................................................27
6.3.2 Option 2.........................................................................................................................28
6.3.3 Option 3.........................................................................................................................28
6.3.4 Option 4.........................................................................................................................28
7. GENERAL INSTALLATION REQUIREMENTS... ........ ........ ........ ........ ......... ........ ........ ... 30
7.1 General .............................................................................................................................30
7.2 Liquid service ....................................................................................................................30
7.3 Gas service........................................................................................................................30
7.4 Vibration ........................................................................................................................... 30
7.5 Flange alignment tolerances.................................................................................................307.6 Type of gasket................................................................................................................... 31
7.7 Pressure tapping/thermowell................................................................................................31
7.8 Heat insulated/traced pipes..................................................................................................31
8. STRAIGHT LENGTH REQUIREMENTS IN GENERAL ........ ........ ........ ........ ........ ........ .. 32
8.1 General .............................................................................................................................32
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10. PIPE LINE versus FLOW METER VELOCITY........ ......... ........ ........ ........ ........ ........ ....... 39
10.1 Liquid service...................................................................................................................39
10.2 Gas service ......................................................................................................................39
11. VORTEX SHEDDING FLOW METER....... ........ ........ ........ ........ ........ ........ ........ ........ ...... 40
11.1 Introduction.....................................................................................................................40
11.1.1 General.........................................................................................................................40
11.1.2 Flow variations (oscillating flow) ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ .... 40
11.1.3 Mechanical vibration......................................................................................................4011.1.4 Pressure drop................................................................................................................41
11.2 Principle of operation........................................................................................................41
11.3 Meter characteristics.........................................................................................................42
11.3.1 General.........................................................................................................................42
11.3.2 Calibration ....................................................................................................................42
11.3.3 Principles of frequency sensing.......................................................................................4311.3.3.1 Differential pressure sensors ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ....... 43
11.3.3.2 Thermistor sensors......................................................................................................44
11.3.3.3 Piezo-electrical sensors................................................................................................44
11.3.3.4 Variable capacitance sensors ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ....... 44
11.4 Electronic part..................................................................................................................44
11 5 P l d id f it ti 44
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11.10 Make-specific comments.................................................................................................51
11.10.1 Make: Yokogawa (YEWFLO Style E)...........................................................................51
11.10.1.1 General....................................................................................................................51
11.10.1.2 Shedder bar..............................................................................................................51
11.10.1.3 Sensors....................................................................................................................52
11.10.1.4 Electric noise abatement features................................................................................52
11.10.1.4.1 Noise balance 52
11.10.1.4.2 Noise detection circuit 52
11.10.1.4.3 High frequency noise filter 52
11.10.1.5 Combination of control and instrumented protective functions...... .... .... .... .... .... .... .... .... . 52
11.10.1.6 Back flow ................................................................................................................53
11.10.1.7 Remote vortex meter flow converter...........................................................................53
11.10.1.8 Electric power supply ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ....... 53
11.10.1.9 Re-number correction................................................................................................53
11.10.1.10 ‘K’ factor curve fitting.............................................................................................53
11.10.2 Other Makes ...............................................................................................................53
12. SWIRL FLOW METER ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ .. 54
12.1 Introduction.....................................................................................................................54
12.1.1 General......................................................................................................................... 54
12.1.2 Flow variation (oscillating flow) ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ..... 54
12 1 3 M h i l ib ti 54
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12.8.2 Pressure and temperature based density compensation........ ........ ........ ........ ........ ........ ...... 59
12.8.3 Fluid oscillations........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ...59
12.8.4 Pipe vibration................................................................................................................59
12.8.5 Instrumented Protective Functions (IPFs) ........ ........ ......... ........ ........ ........ ........ ........ ....... 59
12.9 Installation notes...............................................................................................................59
12.9.1 General.........................................................................................................................59
12.9.2 Fouling service ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ .... 59
12.9.3 Pipe vibration................................................................................................................60
12.10 Make-specific comments.................................................................................................60
12.10.1 Make: Elsaq Bailey Hartmann & Braun (formerly Fisher & Porter)..................................60
12.10.1.1 General....................................................................................................................60
12.10.1.2 Pressure take off for pressure compensation................................................................60
12.10.1.3 Re-number dependability ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ......... .60
12.10.1.4 Straight length requirements ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ...... 61
12.10.2 Other Makes ...............................................................................................................61
13. ULTRASONIC TRANSIT-TIME FLOW METER.............. ........ ........ ........ ........ ........ ....... 62
13.1 Introduction.....................................................................................................................62
13.1.1 General.........................................................................................................................62
13.1.2 Clamp-on meters ...........................................................................................................63
13.1.3 In-line meters ................................................................................................................63
13 1 3 1 G l 63
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13.3.3.1 Laminar/turbulent region ....... ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ..... 71
13.3.3.2 Asymmetrical velocity profile.......................................................................................72
13.3.3.3 Swirl.......................................................................................................................... 72
13.3.3.3.1 Parallel paths at mid radius 73
13.3.3.3.2 Cross over paths at mid radius 73
13.4 Electronic part..................................................................................................................73
13.5 Pressure drop/loss ............................................................................................................74
13.6 Pressure and temperature correction ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ . 74
13.6.1 Pressure correction........................................................................................................74
13.6.2 Temperature correction..................................................................................................74
13.6.2.1 Cross-sectional error ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ .. 74
13.6.2.2 Path length error......................................................................................................... 75
13.6.2.3 Transit-time error .......................................................................................................75
13.7 Application notes..............................................................................................................76
13.7.1 Clamp-on ultrasonic meters ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ... 76
13.7.2 In-line ultrasonic meters ......... ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ....... 76
13.7.2.1 Multiple traverse.........................................................................................................76
13.7.2.2 Acoustic crosstalk ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ...... 76
13.7.2.3 Acoustic shortcut........................................................................................................77
13.7.2.4 Ultrasound beam scattering/dispersion ......... ........ ........ ........ ........ ........ ........ ........ ........ . 77
13.7.2.5 Ultrasound beam deflection ....... ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ . 78
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13.8.7 Instrumented Protective Functions ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... .83
13.9 Installation notes...............................................................................................................83
13.9.1 General.........................................................................................................................83
13.9.2 Nozzle orientation..........................................................................................................83
13.9.3 Flanged transducers ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ...... 83
13.9.4 Extended buffer rods......................................................................................................84
13.9.5 Split delivery of parts ........ ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ .... 84
13.10 Make-specific comments.................................................................................................85
13.10.1 Make: Panametrics.......................................................................................................85
13.10.1.1 General....................................................................................................................85
13.10.1.2 Spool piece configurations..........................................................................................85
13.10.1.3 Flow profile factor ( K re).............................................................................................85
13.10.1.4 Transducers..............................................................................................................86
13.10.1.5 Electronics................................................................................................................86
13.10.1.6 Software features ......................................................................................................86
13.10.1.7 Split delivery.............................................................................................................86
13.10.2 Make: Krohne .............................................................................................................86
13.10.2.1 General....................................................................................................................86
13.10.2.2 Electronics................................................................................................................86
13.11 Application note on MW calculation for refinery fuel gas....................................................87
13.11.1 Nomenclature..............................................................................................................87
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14.3.2 Calibration ....................................................................................................................95
14.4 Electronic part..................................................................................................................95
14.5 Pressure loss and avoidance of cavitation ........ ........ ........ ......... ........ ........ ........ ........ ........ .. 96
14.6 Pressure and temperature correction ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ . 96
14.6.1 Pressure correction........................................................................................................96
14.6.2 Temperature correction..................................................................................................96
14.6.2.1 Cross-sectional error ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ .. 96
14.6.2.2 Electrode spacing error................................................................................................96
14.7 Application notes..............................................................................................................97
14.7.1 General......................................................................................................................... 97
14.7.2 Corrosion/erosion aspects...............................................................................................97
14.7.2.1 Liner ......................................................................................................................... 97
14.7.2.2 Edge protectors ..........................................................................................................98
14.7.2.3 Electrodes ..................................................................................................................98
14.7.3 Fouling service ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ..... 98
14.7.4 Multiple phase flow ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ...... 99
14.7.4.1 Bubble flow ...............................................................................................................99
14.7.4.2 Stratified flow.............................................................................................................99
14.8 Engineering notes ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ... 99
14.8.1 General......................................................................................................................... 99
14.8.2 Sizing........................................................................................................................... 99
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15.1.4 Pressure drop.............................................................................................................. 103
15.2 Principle of operation....... ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ...... 103
15.3 Meter characteristics.. ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ .... 105
15.3.1 General....................................................................................................................... 105
15.3.2 Calibration ..................................................................................................................105
15.3.3 Uncertainty in reading......... ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ........ 106
15.4 Electronic part................................................................................................................106
15.5 Pressure loss and avoidance of cavitation.............. ........ ........ ........ ........ ........ ........ ........ .... 106
15.6 Pressure and temperature correction............... ........ ......... ........ ........ ........ ........ ........ ........ . 106
15.6.1 Pressure correction ...................................................................................................... 106
15.6.2 Temperature correction......... ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ...... 106
15.7 Application notes.. ........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ . 107
15.7.1 General....................................................................................................................... 107
15.7.2 Tube arrangement............... ........ ......... ........ ........ ........ ........ ........ ........ ........ ........ ........ 107
15.7.2.1 Fouling service........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ . 107
15.7.2.1.1 Homogeneous fouling 107
15.7.2.1.2 Non homogeneous fouling 107
15.7.2.2 Plugging...................................................................................................................107
15.7.3 Corrosion and erosion aspects........ ........ ........ ........ ........ ........ ........ ......... ........ ........ ...... 108
15.7.4 Fluid oscillations........ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ . 108
15.7.5 Mechanical vibration ......... ........ ........ ........ ........ ........ ........ ........ ........ ......... ........ ........ .. 108
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16. THERMAL DISPERSION MASS FLOW METER ........ ......... ........ ........ ........ ........ ........ 114
16.1 Introduction................................................................................................................... 114
16.1.1 General....................................................................................................................... 114
16.1.2 Flow variations (oscillating flow)....... ......... ........ ........ ........ ........ ........ ........ ........ ........ ... 114
16.1.3 Mechanical vibration.... ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ ........ ....... 114
16.1.4 Pressure drop.............................................................................................................. 114
16.2 Principle of operation (CTA method) ....... ......... ........ ........ ........ ........ ........ ........ ........ ....... 115
16.2.1 Introduction ................................................................................................................ 115
16.2.2 Sources of systematic errors.... ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ .... 117
16.2.2.1 General.................................................................................................................... 117
16.2.2.2 Heat conductivity coefficient (λ) of gas....................................................................... 117
16.2.2.3 Viscosity of gas (µ) ................................................................................................... 117
16.2.2.4 Differential temperature (t s - t a).................................................................................. 117
16.2.2.5 Probe orientation ...................................................................................................... 117
16.3 Meter characteristics.......... ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ .... 118
16.3.1 General....................................................................................................................... 118
16.3.2 Calibration .................................................................................................................. 118
16.4 Electronic part........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ ........ ....... 118
16.5 Pressure drop/loss .......................................................................................................... 119
16.6 Pressure and temperature correction ........ ......... ........ ........ ........ ........ ........ ........ ........ ....... 119
16 6 1 P i 119
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16.10.1 Kurz Instruments Inc. ................................................................................................ 121
16.10.1.1 Electronics............ ........ ........ ........ ........ ........ ......... ........ ........ ........ ........ ........ ........ . 121
16.10.1.2 Response time ........................................................................................................121
16.10.2 Other Makes .............................................................................................................121
Original distribution............................................................................................................122
APPENDICES
1. LINER AND ELECTRODE MATERIAL SELECTION TABLE FOR ELECTRIC MAGNETIC
FLOW METERS.
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2. PREFACE
2.1 Introduction
As compared with the previous release (issue April 1992), this release describes in more detail the
operating principles of the meters dealt with, since it is of major importance to know what they can
and cannot do to arrive at the optimum choice for a particular application.
Furthermore, this release has been extended with common factors to be considered in relation to the
selection of flow devices (Sections 3 through 8 and 10). Application and engineering notes have been
enhanced with the facts from ‘Lessons Learned PER+ project’.
2.2 Velocity head devices
For the selection of orifice and venturi type flow meters the reader is referred to the ‘Shell flow meter
engineering handbook’, 2nd Edition 1985, Shell Internationale Petroleum Maatschappij B.V.
2.3 Turbine and positive displacement flow meters
The use of these kinds of meters in process lines is not advocated. Due to their rotating internals they
are susceptible to wear and tear, which adversely affects their calibration. Hence they require
regularly re-calibration. On top of that they require in-line filters to avoid mechanical damage of their
internals.
2.4 Abbreviations and Terms
CPA C t t P A t
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3. CALIBRATION METHODS
3.1 Introduction
Normally, flow meters have to be calibrated to establish the flow versus output relationship.
There are a few exceptions where direct calibration is not carried out. In most of their applications,
orifice meters such as square edge orifice plate, venturi tubes and the like, the relationship between
flow and differential pressure generated is calculated from a general set of data obtained by laboratory
experiments under reference conditions.
Another example is the ‘clamp-on’ ultrasonic flow meter, which is often applied as a non-calibratedflow device. Most other flow devices such as vortex, ultrasonic (other than clamp-on), turbine,
magnetic inductance and Coriolis mass flow meters, will require calibration by means of a calibration
method (volumetric/gravimetric).
Calibration methods can be distinguished into in-line and off-line methods. In-line calibration is rarely
used. Off-line calibration will be normally carried out.
3.2 In-line calibration method
With the in-line calibration method, sometimes referred to as the ‘in-situ’ method, the flow meter
concerned is calibrated under operation conditions, i.e. calibrated in its actual position (‘in-situ’),
exposed to the process fluid under actual pressure and temperature conditions.
This method is very expensive and time consuming and will be applied for very high accuracy
measurements, where actual circumstances (flow profile, viscosity, density etc.) play a significant role
and where the uncertainty in meter reading should be very low indeed.
NOTE S ti it ill b ibl d di th t l l t f th l t t th t hi h i b
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If a too large unpredictable error is introduced by deviating too much from the reference conditions at
the off-line flow rig, one could make use of a calibrated meter-run, instead of calibrating the meter
alone.
NOTE: For velocity profile dependent meters it will be of major interest to know the velocity profile the meter was exposedto at the time of calibration. Especially for large rigs it is common usage to adapt the size of the rig to the size of
the meter by using concentric reducers/enlargers. By doing so, the velocity profile is not fully developed but plug
type (see Section 4: ‘Velocity profiles’).
3.4 Factors to be considered
The following factors, amongst others, may be of concern in connection with the use of flow meters:
• single/multiple phase flow;
• velocity profile;• turbulence intensity (Re-number);• friction coefficient of pipe wall;• pressure;• temperature;• viscosity;• density;• Velocity Of Sound (VOS);• mechanical vibration;• response/sample time;• average molecular weight (especially for gases).
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4. VELOCITY PROFILES
Depending on the measuring principle, most flow meters will be more or less dependent on thevelocity profile they will be exposed to. Velocity profile dependent meters require certain straight
lengths at their upstream and downstream side.
Normally, they require a so-called Fully Developed Velocity Profile to avoid systematic errors.
Depending on their measuring principle and upstream pipe configuration, the required length of
straight pipe is expressed in a number of inner pipe diameters (D). Since the downstream pipe
configuration will influence the upstream velocity profile by retroaction, straight length requirements
for the downstream piece (expressed in D) are given as well and should be adhered to.
4.1 Velocity profile dependent flow meters
The following flow meters are dependent on the velocity profile they are exposed to:
• Orifice/venturi devices;• Turbine meters;• Vortex meters;• Ultrasonic meters;
• Electric Magnetic meters;• Thermal mass flow meters;• Swirl meters (less dependent).
4.2 Velocity profile independent flow meters
The following flow meters are independent of the velocity profile they are exposed to:
• Positive displacement meters;
C i li fl
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NOTE: The length of the de-swirl device, often referred to as ‘flow straightener’, depends on the pitch of the swirl. A high
pitch swirl (slow swirl) requires at least a length of 6D to eliminate the swirl (refer to Section 8: ‘Straight Length
Requirements in General’).
Recapitulation:
Firstly:
A concentric reducer with sufficient constriction appeared to have a strong remedial effect as far as
asymmetry and uniformity of the velocity profile is concerned, irrespective of the velocity profile
upstream of the concentric reducer.
Secondly:
A concentric reducer has no remedial effect in respect of swirls, introduced e.g. by ‘space-bends’.
Remark:It must be stressed that the improving effect on the velocity profile holds good only for concentric
reducers. Use of eccentric reducers will result in substantial deviations of velocity profiles.
Concentric eccentric
FIGURE4.1: R EDUCERS
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5. EFFECT OF VELOCITY PROFILES ON FLOW
METERS
5.1 Vortex meters
5.1.1 Introduction
Vortex meters demand certain straight lengths, since their reading uncertainty is dependent on the
velocity profile.
5.1.2 Additional test results
Four makes of vortex meters (see reference 2, Section 5.3.4) were subjected to various tests in
respect of installation conditions. In one test, the effect of two consecutive bends in the same plane
was investigated on two different makes of meters. The results at installation locations downstream of
the last bend at 2D, 5D, 10D and 20D were compared with the readings at the location of 30D. For
the 10D-location, errors were reported ranging from minus 0.5% up to plus 0.7% of reading. At the
location of 20D, errors were reported to be within +/- 0.1% of reading.
Although not mentioned in reference 2 of Section 5.3.4, the effect of a reducer has also been
investigated at the same premises, as we received written information of such a test from Yokogawa.
Tests were carried out at 5D, 10D, 20D, 30D, 42D and 55D downstream of the reducer. Readings
were compared with the installation at 100D (FDVP). Tests were carried out with water at
Re-numbers of 300,000 and 600,000. At 5D, the errors were reported to be 0.00% and 0.4% of
reading at the respective Re-numbers. At 10D, the errors were reported to be minus 0.1% and plus
0.1% of reading respectively.
NOTE: Within SNR’s instrument department similar behaviour was observed at 5D and 10D downstream of a concentric
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5.2.2 Additional information
The experience of Shell Pernis’ instrument department with respect to dual beam (at ½ radius of
centre line) ultrasonic meters is that the additional uncertainty in reading for meters, installed at 5D to10D downstream of a concentric reducer, can be expected to be in the same order as that of vortex
meters (within +/- 0.1% of reading).
5.2.3 Recap
What holds good for a vortex meter (Section 5.1.3), holds good for a dual beam (at ½ radius of
centre line) as well.
So, as indicated under Section 5.2.2, by using a concentric reducer with sufficient constriction, i.e.
Ddownstr. /Dupstr . ≤ 0.7, only a minor additional uncertainty can be expected, smaller than +/-0.1% of reading, providing the meter is installed at a location of 5D up to 10D downstream of the reducer.
Hence, by using a concentric reducer as indicated, the upstream straight length can be reduced to a
distance of 5D downstream of the reducer.
NOTE: For downstream straight length requirements, refer to Section 8.3 ( ‘Straight Length Requirements in General’,
‘reduced size meters’).
5.3 Electric Magnetic (Magnetic inductance) meters
5.3.1 Introduction
Depending on their design, Electric Magnetic (EM) meters, are more or less vulnerable to the velocity
profile they are exposed to. In general, they are less susceptible to an asymmetric velocity profile than
vortex meters and ultrasonic meters are.
Meters provided with a built-in conical entrance and outlet piece (e.g. make Krohne, series IFS 5000)
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5.3.4 References
Reference 1. Hand-out ‘Nieuwe inzichten flowmeterinstallatie’ as presented by Ir. J. Teijema
of Delfts Hydraulics, at the seminar; ‘FLOWMETING; NU EN MORGEN’, onOctober 31, 1990 at Delft, Holland.
Reference 2. VDI Berichte 768, with respect to the 5th . International IMEKO conference on
flow measurements ‘FLOMEKO’, held on October 9-10, 1989 at Duesseldorf,
Germany.
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U
Uav
= 1.2C L
C L
FULLY DEVELOPED VELOCITY PROFILE (FDVP)
FIGURE 5.1
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REDUCER 5D DOWNSTREAM OF BEND CHANGES AN
ASYMMETRIC VELOCITY PROFILE INTO A SYMMETRIC
PLUG PROFILE
FDVP
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C L
D
FOR A < 10D, A SPACE BEND WILL CREATE A SWIRL
A
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6. CALIBRATED METER RUNS
6.1 Purpose
Meter run configuration to be such that the velocity profile to which the meter is exposed in the plant
is practically equal to the velocity profile during calibration on the rig.
To be used for instruments employed in custody transfer applications. For lower grade applications, a
calibrated meter run is to be considered depending upon required accuracy and/or location of meter.
6.2 IntroductionMeter runs consist of :
• Upstream pipe piece.• Meter.• Downstream pipe piece.
Remark:
All pressure retaining parts of the run (incl. meter) must meet the mechanical specificationassociated with the pipe class concerned.
Construction details (e.g. castings, welds, welding procedure, acceptance criteria, NACE
requirements etc.) are subject to the written approval of the Mechanical/Piping department
prior to the release of construction of meter and run.
De-swirl device (flow straightener) and concentric reducer/enlarger (to match the meter size with the
pipe size) shall be an integral part of the meter run. If a meter and control valve are installed in series,
the downstream enlarger can usually be omitted since the control valve will have the same nominal
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2. In-situ removal/replacement of meter internals (shedder bar of vortex meter or wetted parts of buffer rods of
ultrasonic meter) will be required during line flushing/cleaning to remove debris/line junk after new
construction/revamp activities. Furthermore, this is required to allow inspection of the shedder bar/buffer rods
in connection with possible damage after a lengthy period of operation(fouling, erosion, corrosion, mechanical
damage). During line flushing, the holes of shedder bar in body (vortex meter) or transducer nozzles (ultrasonic
meter) to be blinded off with a blind flange. If special flanges are required to blind off hole(s), blindflanges/gaskets to be ordered with meter.
If flanges for the hydraulic test at the factory are required, factory testing to be waived. Instead,
meter run to be hydraulically tested as part of the on site hydraulic test of the pipe work.
NOTE: Replacing the hydraulic test at the factory by in-situ testing during test of pipe work is to be discussed and agreed
upon prior to ordering with Mechanical department and with meter run and meter Supplier.
6.3.2 Option 2
Meter provided with flanged ends, meter run pipe pieces provided with butt welded ends. If option 1
cannot be chosen (e.g. shedder cannot be removed/replaced in-situ) or if meter body and flanges are
cast/forged in one piece, next preference will be option 2.
NOTE: During line flushing/cleaning, meter to be replaced by spool piece. Alternatively, depending on the flushing
operation meter body to be removed and flushing loop to start/end at meter body counter flanges. In the latter case
no spool piece will be required.
6.3.3 Option 3
Both meter and meter run pipe pieces provided with flanged ends. This allows the replacement of the
meter by a spool piece during line flush/cleaning operations. Furthermore, meter and meter run pipe
pieces can be hydraulically tested in advance at the factory. If meter run pipe pieces and meter are
not delivered by the same Manufacturer, the mating flanges shall avoid flow pattern disturbance.
NOTE: If the flushing loop starts/ends at meter body counter flanges no spool piece will be required.
6.3.4 Option 4
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METER Downstreampiping
Upstreampiping
L1 L2
BEVELLED TO ANSI B16.25 AT BOTH ENDS
(TYPICAL)
OPTION 1
OPTION 2
L TO BE MACHINED OUT BEFORE WELDING
TOGETHERL 4(T2-T1)
T 1
T 2
TRANSITION AT WELDED JOINT FOR
UNEQUAL THICKNESS
DETAIL 'A'
(TYPICAL)
TO BE MADE SMOOTH
C L
CONSTRUCTION TYPES
APPENDIX 6.1: CALIBRATED METER RUNS
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7. GENERAL INSTALLATION REQUIREMENTS
7.1 General
Installation of meters in vertical pipe lines is preferred to installation in horizontal lines.
7.2 Liquid service
In vertical lines flow must be upward.
NOTE: With downward flow in liquid service (at low flow rates) the pipe may not be completely filled with liquid, hence
creating two phase (liquid/gas) flow.
Meters not to be installed in horizontal lines at a high point in the piping (e.g. thermal expansion
loops) where (non condensable) gases are likely to collect and be hard to remove.
NOTES: 1. For batch operations pipe should remain full at nil flow to provide for a stable zero point. If this is not possible
and the line will purged by gas for one reason or another, ultrasonic and magnetic inductance meters to be
provided with an empty pipe detection facility.
2. During start-up of all or part of a liquid pipe system non condensable gas (air/nitrogen) could be present if the
system is not properly filled with liquid and vented. If this cannot be avoided an automatic vent system
(upstream of meter) to be installed to get rid of non condensable gas.
7.3 Gas service
Meters not to be installed in horizontal lines at a low point in the piping, where in case of unexpected
wet gas, liquid will collect and be hard to remove.
For wet gas applications (gas with entrained liquid) or gas containing particles, flow direction to be
downward.
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7.6 Type of gasket
Type of gasket to be such that it will be centred by its outer ring. An inner ring should prevent (soft)
material from protruding into the line during tensioning, causing flow pattern disturbance.
7.7 Pressure tapping/thermowell
Pressure measurement should be placed at one pipe diameter (1D) upstream and temperature should
be measured at least 5D downstream of the flow meter.
NOTE: In case of bi-directional flow measurements skin type TC or RTD to be used.
7.8 Heat insulated/traced pipes
Only the body or pipe spool of the meter to be provided with heat insulation/tracing. Extensions
meant to keep the electronics and transducers at a lower temperature (near ambient) must not be heat
insulated/traced.
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8. STRAIGHT LENGTH REQUIREMENTS IN
GENERAL
8.1 General
The minimum straight length requirements as given in the following tables are based upon velocity
profiles. They shall be adhered to in order to avoid too much deviation from the Fully Developed
Velocity Profile (FDVP) or Plug Type Velocity Profile (PTVP) for line size meters or reduced size
meters respectively.
For line size meters the upstream straight length requirements depend on the upstream pipe work configuration, i.e. bends (90°), consecutive bends (90°), T-pieces, on/off valves and the like. For reduced size meters (see Section 4: ‘Velocity profiles’), a concentric reducer with a sufficient
constriction factor will shorten the upstream straight length requirements to 5D.
To eliminate the effect of downstream devices on the velocity profile (retroaction), 5D of straight
downstream length is required for both line and reduced size meters.
NOTE: To determine the straight length, the diameter (D) to be taken as the inner diameter immediately
upstream/downstream of the meter. Hence in the case of a reduced size meter the straight length is the number
times 'D' of the reduced pipe.
8.2 Control valves
For downstream control valves a minimum downstream straight length requirement of
5D + concentric reducer or 7D straight pipe without a concentric reducer has proven to be successful
for control valves operating under non-critical operating conditions (no cavitation and no flashing in
liquid service, no sonic velocity in gas service).
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8.6 Interference of fluid oscillations/vibration
8.6.1 Audible frequency range (FR < 20 kHz)Apart from the velocity profile effect, the possible interference of fluid oscillations/vibration on the
primary sensing elements, introduced by e.g. control valves operating under critical conditions, has to
be taken into account for flow devices equipped with piezo-electric/inductive/capacitive sensors
working in the audible frequency range, i.e. vortex, swirl and Coriolis flow meters.
NOTE: Frequency range of vortex, swirl and Coriolis meters will not exceed 2 kHz.
Control valves operating under critical conditions (cavitation, flashing, critical pressure ratio in gas
service) shall be equipped with proper trims to avoid excessive vibration.NOTES: 1. Such trims are, apart from avoiding interference with flow meters, required to obtain a reasonable life time of
the valve with its internals and accessories.
2. Valves subject to cavitation require a special anti-cavitation trim, or in the worse case two control valves in
series with an anti-cavitation trim. Valves in flashing service should have an increased outlet size (reduced
trim). Valves exposed to a critical pressure ratio (gas service) require proper Lo-dB trims, which will reduce the
sound generated and thus vibration. Moreover, they will shift the dominant frequencies outside the audible
range (>20 kHz).
By using proper trims to abate the vibration under critical operating conditions the minimum
downstream straight length requirement of 7D will be normally sufficient, as experienced in practice.
NOTES: 1. To eliminate possible interference of frequencies outside the working frequency range, the high frequency filter
to be set active.
2. The above does not mean that control valves may not be located further downstream of the flow meter in order
to be confident that interference of vibration is ruled out. The additional downstream length of pipe (above 5D or
7D) need not be straight since only distance plays a role.
8.6.2 Ultrasonic frequency range (20 kHz < FR < 100 kHz)
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LEGEND: 'D' = ACTUAL DIAMETER OF PIPE OR DUCT NOTES: 1) STRAIGHT LENGTHS ONLY APPLICABLE FOR
TURBULENT FLOW
2) FOR CERAMIC SPOOL OR LINER ONLY
CB
'A'
CB
'A'
CB
'A'
1 0 D
Table 8.1: REDUCED SIZE METERS Dmeter
/D pipe
=< 0.7
5D 5D5D
SPACEBEND
DEVICE
'A'
VORTEX 1)
SWIRL
MAGNETIC 1)
THERMAL 1)
ULTRA SONIC 1)
CORIOLIS
STRAIGHT LENGTHS IN 'D'
B C
5
MOUNTING
ALW AYSSUPPORT
REQ'D
V ER T. L IN E H OR Z. L IN E
5
5
5
5
5
5
13
5 NO
NO
NO YESYES
YES YES
YESYES
YESYES
NO
YESYESYES 2)
YESYES
YESNOT APPLICABLE
Additional length in 'D'
for downstream control
valves
25
25
30
refer to note
not applicable
not applicable
X
'A'
CV
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MAGNETIC 1)
1 0 D
CE
'A'
CD
'A'
CB
'A'
1 0 D
SPACE
BEND
1) STRAIGHT LENGTHS ONLY APPLICABLE FOR
TURBULENT FLOW
2) FOR CERAMIC SPOOL OR LINER ONLY
TABLE 8.2: LINE SIZE METERS Dmeter
/D pipe
= 1
'D' = ACTUAL DIAMETER OF PIPE OR DUCT NOTES:
DEVICE
'A'
VORTEX 1)
SWIRL
THERMAL 1)
ULTRA SONIC 1)
CORIOLIS
STRAIGHT LENGTHS IN 'D'
B HGEDC
10
MOUNTING
3
20
5
20
10
3
10
5
10
10
10
20
20
13
5
10
20
20
15
20
20
3
15
10
20
20
3
10 NO
NO
NO YESYES
YES YES
YESYES
YESYES
NO
YESYESYES 2)
YESYES
YES NOT APPLICABLE
Additional length in
'D' for downstream
control valves
L
5
20
15
30
30
X
25
25
not applicable
not applicable
refer to note
30
ALWAYSSUPPORT
REQ'DVER T. L IN E H OR Z. L IN E
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< 1 0 D
'A'
'A'
TABLE 8.3: DE-SWIRL DEVICES TO ELIMATE SWIRL OWING TO TOO CLOSE A SPACE BEND
NOTES:
DEVICE
'A'
VORTEX 1)
SWIRL
MAGNETIC 1)
THERMAL 1)
ULTRA SONIC 1)
CORIOLIS
STRAIGHT LENGTHS IN 'D'
C
MOUNTING
5
5
5
5 NO
NO
NO YESYES
YES YES
YESYES
YESYES
NO
YESYESYES 2)
YESYES
YESNOT APPLICABLE
NOT APPLICABLE
C
1) STRAIGHT LENGTHS ONLY APPLICABLE FOR
TURBULENT FLOW
LEGEND: 'D' = ACTUAL DIAMETER OF PIPE OR DUCT
C
5 D
6 D
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9. MULTIPLE PHASE FLOW
9.1 Introduction
Flow regimes can be single phase or multiple phase. Single phase means that the fluid will be either in
the gas or liquid phase. Multiple phase flow means that gas and liquid phase will be present
continuously or alternately.
Basically flow meters can only handle a single phase flow, i.e. gas or liquid flow. Depending on the
multiple phase flow they are exposed to, the effect can range from a systematic error in the reading to
severe mechanical damage.
NOTE: Because the cross-section of the pipe is not fully filled with a single phase fluid (gas or liquid) a cross-sectional
related error will be introduced. Note that this has a quadratic impact, causing the meter to produce too high a
reading in liquid service and too low a reading in gas service.
For liquids, the actual density under reference conditions as compared with the reference density used for
correlation to mass flow will be too low, which will work out as too high a reading on a mass flow basis. For gas
service it will be the other way around.
9.2 Multiple phase flow regimes
In literature one often finds the following descriptions:
• Bubble flow.Gas phase is divided into bubbles and liquid; the bubbles have the velocity of the liquid.
• Plug and Slug flow.When the amount of gas increases, the bubbles unite forming bullet shaped plugs and slugs
(alternating passing of gas slugs and liquid bullets).
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9.2.2 Plug & Slug and Churn flow
No meter can handle these flow regimes.
Intrusive meters like vortex meters and ultrasonic meters with wetted sensors protruding in the pipecould become severely damaged by the impact of the liquids slugs (water hammer effect). Coriolis
meters having bent pipes will be damaged by the water hammer effect.
NOTE: Plug & slug flow may occur in liquid service during start-up of a pipe line system that is not properly vented. The
same will happen in gas/steam systems unless condensed liquids are properly drained from the line before
start-up.
9.2.3 Annular flow
Vortex meters in gas service will survive and produce a reading. Swirl meters will handle the annular flow better than vortex meters. Ultrasonic meters with wetted sensors flush with the wall will
‘presumably’ not, since the liquid film will absorb/disperse the sound beam.
NOTES 1. ‘Presumably’ means that no data is available at the present time to support or to dispute this statement.
2. Ultrasonic meters with protruding wetted sensors will possibly survive.
The effect on Coriolis mass flow meters is unknown.
NOTE: For Coriolis meters having bent measuring tubes, the annular flow will probably not be maintained due to
centrifugal forces, resulting in erratic behaviour of the meter.
9.2.4 Stratified flow
With a small gas gap, vortex meters in liquid service will give a reading. As long as their electrodes are
submerged in the liquid phase the magnetic inductance meter will give a reading.
NOTE: Meters for partially filled pipes are commercially available; refer to Electric Magnetic flow meters.
The same holds good for ultrasonic meters as long as there is one interrogation path through the
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10. PIPE LINE versus FLOW METER VELOCITY
10.1 Liquid service
Process designers will normally design pipe lines for liquids so that the average velocity at normal
design flow rate will be typically between 1 and 5 m/s. The target velocity will be around 1.5 m/s. In
large pipe lines, velocities above the target value of 1.5 m/s may be chosen (depending on pressure
loss) to reduce size and thus cost and weight of pipes.
The above mechanical design constraints are in conflict with the typical velocity range as required for
most flow meters, as reflected in the picture below.
6 80 2 4 m/s10
vortex
electric-magnetic
ultrasonic
12 14
LlQUID SERVICE
piping constraints
target value
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11. VORTEX SHEDDING FLOW METER
11.1 Introduction
11.1.1 General
Vortex meters can be used on a wide range of fluids, i.e. liquids, gases and steam. They are to be
seen as a first choice, subject to verification, to cover the requirements of a particular application.
Vortex meters are essentially frequency meters, since they measure the frequency of the vortices
generated by a fixed obstruction indicated as ‘bluff body’ or ‘shedder bar’. Vortices will only occur
from a certain velocity (Re-number) onwards, consequently vortex meters will have an elevated zero
referred to as the ‘cut off’ point. Before the velocity becomes nil, the meter output will be cut to
zero.
NOTE: The low cut off point is of particular relevance for meters used in (closed) control loops and will introduce instability
(hunting) at the cut off point. As its measured value becomes nil and its set point will not, the controller will
response to its error signal by increasing the flow rate. As soon as its measured value is above its set point, the
controller will reduce the flow (below the cut off point) and hunting will be the result.
It goes without saying that in such a case a meter size shall be chosen that gives the lowest possible cut off point.
The cut off point value is to be discussed with and approved by the Process Control engineer.
As a last resort, if the cut off point of the already installed vortex meter appears to be too high, the control valvecould be used as ‘a flow rate estimator’ to avoid the hunting problem at the low flow region below the cut off point.
Vortex meters are uni-directional velocity profile dependent flow meters.
NOTE: At a certain back-flow (above cut off point) some vortex meters could produce an output signal, which could lead to
a false interpretation.
Vortex meters are actual volume flow meters (like orifice meters). Since actual volume flow is not
generally relevant for plant operating purposes, their output is correlated to mass flow assuming a
fixed actual density (reference density) under operating conditions. Deviations in actual density will
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11.1.4 Pressure drop
Vortex meters, being intrusive meters like orifice meters, will cause the pressure to drop (pressure
gradient) as the flow is increased, resulting in a permanent pressure loss. Consequently, liquids near
their boiling point, could introduce cavitation as the pressure across the meter drops below the vapour
pressure of the liquid (forming of vapour bubbles). As soon as the pressure recovers above the
vapour pressure the bubbles will implode. Cavitation causes the meter to malfunction and should be
avoided at all times.
11.2 Principle of operation
A fluid flowing with a certain velocity and passing a fixed obstruction generates vortices. The vortices
are generated alternately on opposite flanks of the obstruction, grow in size and are subsequently
shed from the obstructive element. As they flow along with the fluid as it moves downstream (refer
to figure 11.1 below), they will grow in size, culminate and then subside.
x
w
x x
V
FIGURE11.1: GENERATION OF VORTICES(K ARMAN’S VORTEX STREET)
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where:
f = Vortex frequency : Hz
St = Strouhal’s number or shape factor : without dimension
V = Fluid velocity at the shedder bar : m/s
D = Inner diameter of the pipe : m
c = Constant (ratio d/D) : without dimension
d = Face width of shedder bar : m
NOTES: 1. For most vortex meters, the d/D ratio will vary between 0.22 to 0.26. Consequently, the vortex frequency (at
the same fluid velocity) will be dependent on the size of meter: The larger the size, the lower the frequency.
2. For vortex meters of make Yokogawa, the frequency (Hz) per unity of velocity (m/s) will range from 62.7
(Hz/m/s) for size DN 15 (1/2 inch) to 3.37 (Hz/m/s) for size DN 300 (12 inch).
The maximum diameter of a vortex meter is restricted, as at lower frequencies the resolution of themeter could become a problem for control purposes. To overcome this problem use can be made of
on-board digital multipliers, which will multiply the vortex frequency (unscaled frequency) without an
additional error (phase locked digital multipliers).
11.3 Meter characteristics
11.3.1 General
Vortex meters are unaffected by the fluid as long as it is in single phase. Below a certain minimum
Re-number they cease to operate.
11.3.2 Calibration
The calibration factor (‘K’ factor) of a vortex meter defines the relationship between input (actual
volumetric flow) and output (frequency) and is expressed as the number of pulses per unit of actual
volume (e.g. pulses per litre). When the ‘K’ factor is measured for a given meter at various flow rates
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NOTE: 1. The ‘K’ factor, determined for a vortex meter on a test rig with water, is valid for hydrocarbon fluids as well as
for gas/steam service.
2. The pipe Reynolds number (Re) is expressed as:
Re = ∗∗
1000
V D D
υ
where:
Re = Reynolds number (without dimension)
V D = Mean pipe velocity (m/s)
D = Inner pipe diameter (mm)
υ = Kinematic viscosity (cSt)
The minimum flow which can be measured is determined by one of the following factors:
• The Reynolds number at which the vortex shedding phenomenon ceases.
• The point at which the sensors can no longer distinguish between the frequency signal and the background noise (signal/noise ratio too low).
• Note by the SIOP editor:In addition to the two factors mentioned above, a minimum velocity is required. Especially for
larger meter sizes this may become the decisive factor. The Manufacturer should be consulted for
minimum velocity requirements.
Example: Manufacturer Emco has specified a minimum velocity of 0.3 m/sec for a certain
DN 150 meter, corresponding to a Re-number of 50,000 in water service.
NOTE: Below a Re-number of 40,000, the ‘K’ factor starts to deviate in the ‘plus’ direction. According to Yokogawa, the
additional error will be independent of the fluid and could be corrected by using some type of curve fitting. In their
vortex meter, model YF100, the microprocessor has a look-up table on board with correction factors versus
Re-numbers. Use of these correction factors will adversely affect the accuracy. The larger the correction, the larger
the effect on accuracy. This facility is to be employed with caution.
The upper limit is restricted by the maximum velocity of the fluid (dynamic forces) or, in the case of
liquids, by cavitation resulting from too high a pressure differential across the meter. Also, the
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11.3.3.2 Thermistor sensors
Another method is to make use of a pair of thermistors placed in the shedder bar. These cool quickly
if the fluid velocity is high and less quickly if the velocity is low resulting in an alternating change of
electrical resistance, so creating a pulse train with a frequency linearly proportional to the velocity of the fluid.
11.3.3.3 Piezo-electrical sensors
A pair of piezo-electrical crystals is built into the shedder bar. As the shedder bar will be subject to
alternating forces caused by the shedding frequency, so will the piezo crystals.
11.3.3.4 Variable capacitance sensors
A pair of variable capacitance sensors is built into the shedder bar. As the shedder bar will be subjectto alternating micro movements caused by forces as a result of the shedding frequency, the capacitors
will change their capacitance accordingly.
11.4 Electronic part
The electronic part can be an integral part of the vortex meter or a separate part (remote type) to be
mounted at a distance (e.g. for hot applications).
Depending on the make the electronics of a vortex meter will contain in general the following parts:
• pick-up elements;
• AC-pre-amplifiers;
• AC-amplifier with filters;
• noise abatement features;
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where:
∆P = Permanent pressure loss in bar.
Qlps = Liquid flow rate at flowing conditions in m3/h.
QNCMH = Gas flow rate at base conditions of 15 °C and 1.013 bar (abs) in standard m3/h.
QKPH = Steam flow rate in kg/h.
ρ f = Density at f lowing conditions in kg/m3.
ρb = Density of gas at base conditions of 15 °C and 1.013 bar (abs) in kg/m3.
D = Flow meter bore diameter in mm.
The pressure loss gradient across the vortex meter will have a similar shape to that of an orifice
meter. The lowest point in pressure will be at the shedder bar or closely downstream of it
(comparable with the ‘vena contracta’ for orifice meters). Downstream of this point the pressure will
recover gradually, finally resulting in the permanent pressure loss. To avoid cavitation, the pressure
loss at the ‘vena contracta’ is of interest.
2 1 0 1 2 3 4 5
3 . 2
*
P
P
P m i n
= 3 . 2
* P + 1 . 2
5 * P
v
4 . 2
* P
1.25 * PvP
v
P r e s s u r e i n B a r a
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11.6 Pressure and temperature correction
11.6.1 Pressure correction
The influence of pressure on the increase of the cross-section is negligible in normal applications.
11.6.2 Temperature correction
Thermal expansion creates an increase in area for a given cross-section. This results in a lower
average velocity, thus a lower frequency and hence reduces the ‘K’ factor.
The following formula is to be used to correct the ‘K’ factor. Manufacturer to recalculate and
confirm this correction.
( ) K o K r
t o t r =
+ −*
*
1
1 α
where:
K o = ‘K’ factor at operation temperature; t o = operating temperature;
K r = ‘K’ factor at reference temperature; t r = reference temperature;
α = area expansion coefficient.
NOTE: The cross-sectional area at an operating temperature (t o) can be found by following formula:
( ) At o At r a t o t r = ∗ + ∗ −
1 (1)
where:
At o= cross-sectional area at operating temperature (t o);
At r = cross-sectional area at reference temperature (t r );
t r = reference temperature;
t o = operating temperature;
α = area expansion coefficient.
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Making the termV avr
V avo
explicit yields:V avr
V avo
At o
At r
= (13)
Since the average velocity is directly proportional to the frequency, equation (13) can be written as:
f r f o
At o At r
= (14)
Substituting equation (14) into equation (8) yields: K o K r At r At o
=
* (15)
Substituting for ( At o
) equation (1) into equation (15) yields:
( ) ( ) K o K r
At r
At r t o t r
K r t o t r
=+ −
=+ −
** *
**1
1
1α α(16)
The following area expansion coefficients are to be used:
Carbon steel : 3.42 x 10-5.
Stainless steel 304/316 : 4.88 x 10-5.
Stainless steel AISI 410 : 4.15 x 10-5.Monel : 3.76 x 10-5.
Hastelloy C : 3.17 x 10-5.
Inconel : 3.42 x 10-5.
Attention has to be paid to the fact that the area expansion coefficient may differ, if different
materials are used for shedder bar and body. Manufacturer has to advise.
Example:
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From extensive experiments, it has been established that the performance of vortex meters can be
significantly influenced by:
• Change in shedder bar geometry owing to erosion;• Change in shedder bar geometry owing to deposits, such as wax layers;• Corrosion of upstream piping;• Change in position of the shedder bar owing to not properly secured position;• Hydraulic noise.NOTES: 1. D.C. Bruinzeel reports in Paper S201 (6th Shell Instrument Engineering Meeting, 1986) a deviation, owing to
simulated erosion (rounding off of sharp edges) of the shedder bar, of 7% of actual reading.
2. For fouling (wax layer of 2 - 5 mm on the upstream edge of the shedder bar ) a deviation of 3% or more of
actual reading is stated in Paper S201.
Vortex meters are to be regarded as the ‘workhorse’ in flow applications, just as the orifice meter used to be in the past.
One aspect which should not be overlooked is viscosity in liquid applications. During not ‘normal
operation’ (start-up, shut down, off-spec situations) the viscosity for some liquids (e.g. DIPA, oil) will
be drastically increased owing to a lower temperature (logarithmic relationship!), resulting in lower
Re-numbers, which in turn may raise the cut off point drastically, even beyond a low trip setting, thus
causing a nuisance trip.
11.7.2 Flow oscillations/mechanical vibrationCare should be taken with fluids transported by positive displacement pumps without suction and
discharge dampers, especially in liquid applications.
With the use of centrifugal pumps, dominant oscillating flow/pipe vibration could occur at a
frequency equal to the revolving speed of the rotor.
11.7.3 Two meters in series
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Be reluctant to deviate from the optimum choice. If you have to, do not ignore the following
engineering rules, which are to be considered as minimum requirements:
• Re-number at minimum flow preferably not to be lower than 40,000 and definitely not lower than
20,000.
• Addition by SIOP editor: the minimum velocity requirements, as specified by the Manufacturer,should be met.
• Maximum flow to be accommodated should not be less than 35% of the range of size chosen.
• Trigger adjustment should be taken as ‘worst’, i.e. at its highest value.
• Low alarm/trip functions should be equal to or larger than 10% of Meter’s Available Range
(MAR), given by the minimum flow (trigger adjustment = highest) and maximum flow capable to be handled by the meter size.
• High alarm/trip functions should not exceed 95% of the maximum flow capable of being handled by the meter size.
0
flow cut off
max flow of meter
meter's available range (MAR)
min. flow setting:
10% of MAR
max. flow setting:
95% of max flow
of meter
min. adj range: 35% of
max. flow of meter 100%
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11.8.3 Fluid oscillations
For pumped systems, check whether the dominant oscillating fluid frequency falls into the frequency
working range of the meter. Try to avoid this by using a different size. As the size is reduced the
working frequency will increase.
11.8.4 Pipe vibration
As for fluid oscillations, check whether the dominant vibration frequency falls into the frequency
working range of the meter. Try to avoid this by using a different size. As the size is reduced the
working frequency will increase.
NOTE: For positive displacement pumps, the ripple frequency of the fluid at the discharge will be the principal factor in
fluid oscillations. For mechanical vibration, the revolving speed of the crankshaft will be relevant. For centrifugalpumps the frequency at the revolving speed of the rotor will be relevant and to a lesser extent the frequency
obtained by multiplying the number of rotor blades by the revolving speed of the rotor. This information could be
obtained from the Rotating Equipment Engineer.
11.8.5 Instrumented Protective Functions (IPFs)
For combined control functions and IPFs, two (2) independent, fully segregated output signals have
to be generated. Only the shedder bar may be used as a shared element, as is the case with an orifice
meter using separate impulse lines and differential pressure transmitters for the control function and
IPF.
NOTE: If no corresponding flow measurement for indication, recording or control is available, the vortex meter serving the
IPF shall be designed as described above to allow for automatic Measurement Validation and Comparison (MVC).
11.9 Installation notes
11.9.1 General
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11.10 Make-specific comments
11.10.1 Make: Yokogawa (YEWFLO Style E)Specific comments of this Section apply to the following models:
• Model YF100 vortex flow meter (integral and remote type).
• Model YFA11 vortex flow converter (remote type).
11.10.1.1 General
For the PER+ project, Yokogawa had been awarded an umbrella agreement for vortex meters.
Meters have proven to operate successfully in all plants (SGHP, HCU, PSU, PGP and SARU).
11.10.1.2 Shedder bar
The shedder bar is removable from the body. It is flange-mounted at the top. At its bottom the
shedder bar rests on a spine which is welded into the body.
NOTES: 1. The spine is placed slightly out of centre (eccentric) to ensure a good reproducible and fixed contact with the
shedder bar.
2. With the above eccentric placement of the shedder bar, it is said that the susceptibility to fouling at the bottom
part of the shedder bar will be negligible. Nevertheless for the PER+ project all vortex meters in horizontal lineswere placed with their shedder bar in horizontal position or, in case of lack of space, moved away from the
lowest position as much as possible.
The required torque for the flange bolts as given by the Manufacturer shall be strictly adhered to,
since it will determine the required tension force of the shedder bar on the spine.
NOTE: If the tension of shedder bar is too low, it will start to move, soon resulting in a worn out spine. A worn out spine
can only be cured by replacing the total body.
Removal and replacement of a shedder bar will slightly affect the accuracy, but not by more than
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If this clearance is filled up by hard deposits obstructing movement of the shedder bar, substantial
misreading will be the result.
NOTE: The clearance may get filled up with very fine powder/crystals as experienced by Shell Chemicals - Pernis,
resulting in erroneous readings.
11.10.1.3 Sensors
Yokogawa uses non wetted piezo-electric crystals embedded into the shedder bar to sense the
frequency. The shedder bar is equipped with an additional set of piezo crystals to eliminate as much
pipe vibration as possible by adjusting the noise balance.
If the shedder bar or its sensors are damaged, it shall be replaced by a new shedder bar.
Consequently, to replace the shedder bar the line has to be taken out of service, de-pressurised,
cooled down and cleaned, if necessary.NOTE: At the time of the engineering of the PER+ project (4thQ,1993), Yokogawa quoted a mean time between failure
(MTBF) of 228 years based upon failed shedder bars returned to their factory. Post mortem analysis learned that
they had suffered from fatigue resulting in cracks in the shedder bar at the transient area shedder bar/connection
flange. As a result the component was redesigned to avoid too high a stress in that region. For their electronics
they quoted a MTBF figure of 76 years. So, the total MTBF was derived as 72 years.
11.10.1.4 Electric noise abatement features
The following aspects are of particular interest as they have to be adjusted for each particular
application.11.10.1.4.1 Noise balance
Can be adjusted to eliminate (to a certain extent) pipe vibration.
NOTE: To adjust the noise balance the use of an oscilloscope is mandatory to observe the frequency signal and the effect
of the adjustment. Be careful: too rigorous an adjustment will cause the signal to be over-suppressed, leading to
errors.
11.10.1.4.2 Noise detection circuit
Will judge whether the signal originates from vortices or is to be regarded as noise.
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11.10.1.6 Back flow
At a certain back flow (above cut off point), an output signal will be produced, which could lead to
wrong interpretation.
NOTES: 1. For the PER+ project, in order to measure bi-directional flows in steam balancing lines, two vortex meters
were used in series in opposite flow direction. Signal selection by using a high selector between the two
output signals failed since the vortex meter exposed to back flow does not always produce a lower signal than
the vortex meter used in its normal flow direction. As a remedial action, after start-up, a differential pressure
measurement across both vortex meters had to be installed to select the correct output signal.
2. In steam (balancing) lines (bi-) directional ultrasonic flow meters are to be used.
11.10.1.7 Remote vortex meter flow converter
The electronic head of the vortex meter shall be properly grounded to the electronic earth of the
remotely placed converter using a separate ground lead (insulated from the protective ground) in between.
NOTE: Normally, the electronic ground, i.e. the cable shielding, is not connected to the transmitter but taped back to
avoid ground loops. However, if this is done with a remote converter the electronic head of the vortex meter is not
connected to the electronic ground, resulting in erratic behaviour.
11.10.1.8 Electric power supply
Transmitter is powered (24 VDC) via its signal output. It requires a relatively high voltage at its
terminals to function properly.NOTE: Power loss over cable length to be calculated. For the PER+ project an external dual power supply (make Delta)
had to be used.
11.10.1.9 Re-number correction
The microprocessors in YF100 vortex meters have a look-up table on board with correction factors
for Re-numbers below 40,000 (Re-numbers 5,500 - 20,000). Use of these correction factors will
adversely affect the accuracy. The larger the correction, the larger the effect on accuracy. This
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12. SWIRL FLOW METER
12.1 Introduction
12.1.1 General
Swirl meters can be used on a wide range of fluids (gas, liquid and steam). Although they generate
vortices like vortex meters do, their operating principle is entirely different.
NOTE: As far as known, only Elsaq Bailey Hartmann & Braun (formerly Fisher & Porter) have a swirl meter in their
production line.
Swirl meters are uni-directional flow meters. Their dependency on the velocity profile is far less than
for other meters as given in Section 8 (‘Straight Length Requirements in General’).
NOTE: An upstream length of 3D and a downstream length of 1D will be sufficient.
12.1.2 Flow variation (oscillating flow)
Like vortex meters, swirl meters are susceptible to continuous flow variations (oscillating flow).
12.1.3 Mechanical vibrationSwirl meters, equipped with piezo-electric crystals sensors are susceptible to mechanical vibration.
Swirl meters equipped with thermistors are in principle not vulnerable to mechanical vibration
NOTE: Swirl meters delivered by Elsaq Bailey Hartmann & Braun are no longer equipped with thermistors.
Swirl meters, being intrusive meters, will cause the pressure to drop (pressure gradient) as the flow is
increased, resulting in a permanent pressure loss.
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Basically it consists of a fixed vane wheel (swirler) and acceleration section, extension pipe (nozzle),
enlarger (destabilisation section) and de-swirler (straightener), as shown in the picture below.
swirler andacceleration
section nozzle straightener
DESWIRL
DIFFUSER
SENSOR
SWIRLER
destabilisation
section
FIGURE12.1: PRINCIPLE OF SWIRL METER
(PICTURE TAKEN FROM REFERENCE 2)
In the swirler, the fluid is forced to rotate and since it contracts as well the fluid will be accelerated.
Consequently, in the nozzle a symmetric swirl is present. At the enlarger (destabiliser) the swirl starts
swinging round, i.e. it will have in addition a secondary rotation, called the precession rotation. Finally
in the de-swirler (straightener) the swirl and the swing round are killed.
As a result of the precession rotation the vortex core is forced into the direction of the wall.
Consequently, there will be a back flow to fill up the area of lower pressure in the middle.
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The precession rotation speed is picked up by the sensor as a frequency, which is linear with the
precession rotation speed as depicted below:
SENSOR SENSOR SENSOR SENSOR
precession rotation speedω
FIGURE12.3: PRECESSION ROTATION
In the effective area the forward flow (V A) is linearly proportional to the precession rotation speed ω.
Hence, the actual flow through the meter is: Qact = Aeff * V A or Qact = Aeff *ω *C
where:
Qact = actual volumetric flow (m3/s).
Aeff = effective area for forward flow (m2).
V A = forward flow in effective area (m/s).
ω = precession rotation speed (m/s).C = constant.
If a sensor is placed at the pipe wall of the enlarger section, it will measure the number of revolutions
of the precession rotation per time unit, i.e. frequency. Hence the precession swirl can be considered
as an imaginary rotor of a turbine meter, which will rotate faster as the fluid velocity increases and
vice versa.
As for turbine meters, the actual volume per rotation will be constant, i.e. independent of the