# ISO 12764:2017

(Main)## Measurement of fluid flow in closed conduits — Flowrate measurement by means of vortex shedding flowmeters inserted in circular cross-section conduits running full

## Measurement of fluid flow in closed conduits — Flowrate measurement by means of vortex shedding flowmeters inserted in circular cross-section conduits running full

ISO 12764:2017 a) describes the use of vortex shedding flow meters for liquids, gases, and steam, including a glossary and a set of engineering equations used for specifying performance, b) provides technical information to assist the user in selecting, specifying and applying vortex shedding flowmeters, including influence effects, c) describes typical construction and provides recommendations for inspection, certification, and material traceability, d) describes availability of diagnostics associated with vortex shedding flowmeters, e) provides calibration guidance, f) does not apply to insertion type vortex shedding flowmeters, g) applies only to closed conduits running full, h) applies only to fluid flow that is steady or varies only slowly with time, and i) applies to fluids considered to be single-phase.

## Mesurage du débit de fluide dans les conduites fermées — Mesurage du débit par débitmètres à effet vortex insérés dans les conduites de section circulaire remplies au droit

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INTERNATIONAL ISO

STANDARD 12764

First edition

2017-08

Measurement of fluid flow in closed

conduits — Flowrate measurement by

means of vortex shedding flowmeters

inserted in circular cross-section

conduits running full

Mesurage du débit de fluide dans les conduites fermées — Mesurage

du débit par débitmètres à effet vortex insérés dans les conduites de

section circulaire remplies au droit

Reference number

ISO 12764:2017(E)

©

ISO 2017

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ISO 12764:2017(E)

COPYRIGHT PROTECTED DOCUMENT

© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

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copyright@iso.org

www.iso.org

ii © ISO 2017 – All rights reserved

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ISO 12764:2017(E)

Contents Page

Foreword .v

Introduction .vi

1 Scope . 1

2 Normative references . 1

3 Terms and definitions . 1

3.1 Definitions specific to this vortex flowmeter standard . 2

3.2 Definitions related to measurement of fluid flow in closed conduits . 3

3.3 Definitions related to the vocabulary used in metrology . 4

4 Symbols and subscripts . 4

4.1 Symbols . 4

4.2 Subscripts . 5

5 Principle . 5

5.1 Bluff body . 5

5.2 Shedding vortices detection/sensors . 6

5.3 Strouhal number. 6

6 Flowmeter description . 7

6.1 Physical components . 7

6.1.1 Flow tube . 8

6.1.2 System output . 8

6.2 Marking . 9

6.3 Safety issues . 9

6.3.1 Pressure and fluid-wetted parts . 9

6.3.2 In-line instrumentation, testing . 9

6.3.3 Materials . 9

7 Application . 9

7.1 Sizing . 9

7.2 Pressure loss and cavitation .10

7.3 Swirl and undeveloped profile .10

7.4 Flow stability .11

7.5 Vibration .11

8 Installation .11

8.1 General .11

8.2 Installation location .11

8.3 Piping .11

8.3.1 Straight sections .11

8.3.2 Mating pipe .12

8.3.3 Position of valves .12

8.3.4 Dual phase flow .12

8.3.5 Bypass .12

8.3.6 Additional process measurements for compensation .12

8.3.7 Installation orientation, electronics .13

8.3.8 Bluff body orientation .13

8.3.9 Full pipe condition .13

8.3.10 Condensable gas .13

8.3.11 Extreme conditions . .13

8.3.12 New installations .14

9 Operation .14

9.1 Operating limits .14

9.2 Start-up procedure .14

9.3 Shift of calibration .14

9.4 Maintenance .14

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ISO 12764:2017(E)

10 Performance characteristics .14

10.1 Reynolds number range .14

10.2 P-T conditions.14

10.3 Performance disturbing influences .14

11 Calibration (K-factor determination) .15

11.1 Mean K-factor .15

11.2 In situ calibration .15

Annex A (informative) Period jitter and its effects on calibration .16

Annex B (informative) Special considerations for steam .18

Bibliography .22

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ISO 12764:2017(E)

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed

conduits, Subcommittee SC 5, Velocity and mass methods.

This first edition of ISO 12764 cancels and replaces ISO/TR 12764:1997. In general this document

reflects the current state of vortex shedding flow meter methodology, with advancements that have

occurred since the original TR was published. In particular:

— the terms “systematic measurement error” and “measurement uncertainty” are more clearly

defined;

— the terms “rangeability”, “lowest local pressure”, “response time” and “fade” have been removed;

— 6.1.1.4 and 6.1.2 have been added;

— Clause 8 and Clause 9 have been revised;

— Annex A has been revised;

— a new Annex B has replaced the previous version;

— Annex C has been incorporated into 7.2 and updated.

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ISO 12764:2017(E)

Introduction

This document is one of the series of International Standards and Technical Reports covering a variety

of devices that measure the flow of fluids in closed conduits.

The term “vortex shedding flowmeter”, commonly referred to as a “vortex meter”, covers a large family

of devices with varying proprietary designs. These devices have in common the shedding of vortices

from an obstruction (called a bluff body) which has been deliberately placed in the flow path in the

meter. The natural laws of physics relate the shedding frequency of the vortices ( f ) to the fluid velocity

and hence the volumetric flowrate (q ) of the fluid in the conduit. The vortices can be counted over a

V

given period of time to obtain total flow.

The vortex shedding phenomenon has become an accepted basis for fluid flow measurement. Meters

are available for measuring the flow of fluids from cryogenic liquids to steam and high pressure gases.

Many vortex shedding flowmeter designs are proprietary and, therefore, their design details cannot be

covered in this document.

Insufficient data have been collected and analysed to be able to state, in this document, an expected

uncertainty band for this type of vortex-shedding flowmeter.

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INTERNATIONAL STANDARD ISO 12764:2017(E)

Measurement of fluid flow in closed conduits — Flowrate

measurement by means of vortex shedding flowmeters

inserted in circular cross-section conduits running full

1 Scope

This document

a) describes the use of vortex shedding flow meters for liquids, gases, and steam, including a glossary

and a set of engineering equations used for specifying performance,

b) provides technical information to assist the user in selecting, specifying and applying vortex

shedding flowmeters, including influence effects,

c) describes typical construction and provides recommendations for inspection, certification, and

material traceability,

d) describes availability of diagnostics associated with vortex shedding flowmeters,

e) provides calibration guidance,

f) does not apply to insertion type vortex shedding flowmeters,

g) applies only to closed conduits running full,

h) applies only to fluid flow that is steady or varies only slowly with time, and

i) applies to fluids considered to be single-phase.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 4006, Measurement of fluid flow in closed conduits — Vocabulary and symbols

ISO/IEC Guide 99:2007 (JCGM 200:2012), International vocabulary of metrology — Basic and general

concepts and associated terms (VIM)

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4006 and ISO/IEC Guide 99:2007

(JCGM 200:2012) and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at http://www.iso.org/obp

— IEC Electropedia: available at http://www.electropedia.org/

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ISO 12764:2017(E)

3.1 Definitions specific to this vortex flowmeter standard

3.1.1

K-factor

ratio of the meter output in number of pulses to the corresponding total volume of fluid passing through

the meter during a measured period

Note 1 to entry: The variations in the K-factor can be presented as a function of either the pipe Reynolds number

or flowrate at a specific set of thermodynamic conditions. The mean K-factor is commonly used and is defined by

the following formula:

KK+

maxmin

K =

mean

2

where

K is the maximum K-factor over a designated range;

max

K is the minimum K-factor over the same range.

min

Alternatively, the average of several values of K-factor taken over the whole flow range of a meter can be

calculated. The K-factor can change with pressure and thermal effects on the body of the meter; see Clause 11.

The manufacturer of the meter should be consulted concerning the difference, if any, of the K-factor between

liquid and gas and due to differences between pipe schedules of the adjacent pipe.

Note 2 to entry: It is expressed in pulses per unit volume.

Note 3 to entry: See Figure 1.

Key

1 K-factor

2 pipe Reynolds number

3 designated linear range

4 linearity (%)

Figure 1 — Typical shape of a K-factor curve

3.1.2

linearity

constancy of the K-factor (3.1.1) over a specified range defined either by the pipe Reynolds number or

flowrate

Note 1 to entry: The upper and lower limits of the linear range are specified by the manufacturer.

Note 2 to entry: See Figure 1.

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ISO 12764:2017(E)

3.1.3

cavitation

phenomenon following flashing, in which the pressure recovers above the vapour pressure and the

vapour bubble collapses (implodes)

Note 1 to entry: Cavitation can result in measurement error as well as mechanical damage to the meter.

3.1.4

flashing

formation of vapour bubbles

Note 1 to entry: Flashing occurs when the pressure falls below the vapour pressure of the liquid.

3.2 Definitions related to measurement of fluid flow in closed conduits

3.2.1

pressure loss

irrecoverable pressure loss caused by the presence of a primary device in the conduit

3.2.2

Strouhal number

dimensionless parameter relating the vortex shedding frequency, f, generated by a characteristic

dimension, l, to the fluid velocity, v, given by the following formula:

fl⋅

Sr =

v

where

f is vortex shedding frequency;

l is a characteristic length of the system in which the flow occurs;

v is the fluid velocity.

3.2.3

Reynolds number

dimensionless parameter expressing the ratio between the inertia and viscous forces given by the

following formula:

Ul⋅

Re =

v

where

U is the mean axial fluid velocity across a defined area;

l is a characteristic length of the system in which the flow occurs;

v nu (Greek alphabet) is the kinematic viscosity of the fluid.

Note 1 to entry: For pipe flows and closed pipe flow measurement, Reynolds number is usually based on the

diameter of the pipe.

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ISO 12764:2017(E)

3.3 Definitions related to the vocabulary used in metrology

3.3.1

systematic measurement error

systematic error of measurement

systematic error

component of measurement error that, in replicate measurements, remains constant or varies in a

predictable manner

Note 1 to entry: A reference quantity value for a systematic measurement error is a true quantity value, or a

measured quantity value of a measurement standard of negligible measurement uncertainty, or a conventional

quantity value.

Note 2 to entry: Systematic measurement error, and its causes, can be known or unknown. A correction can be

applied to compensate for a known systematic measurement error.

Note 3 to entry: Systematic measurement error equals measurement error minus random measurement error.

3.3.2

measurement uncertainty

uncertainty of measurement

uncertainty

non-negative parameter characterizing the dispersion of the quantity values being attributed to a

measurand, based on the information used

Note 1 to entry: Measurement uncertainty includes components arising from systematic effects, such as

components associated with corrections and the assigned quantity values of measurement standards, as well

as the definitional uncertainty. Sometimes estimated systematic effects are not corrected for but, instead,

associated measurement uncertainty components are incorporated.

Note 2 to entry: The parameter can be, for example, a standard deviation called standard measurement

uncertainty (or a specified multiple of it), or the half-width of an interval, having a stated coverage probability.

Note 3 to entry: Measurement uncertainty comprises, in general, many components. Some of these can be

evaluated by Type A evaluation of measurement uncertainty from the statistical distribution of the quantity

values from a series of measurements and can be characterized by standard deviations. The other components,

which can be evaluated by Type B evaluation of measurement uncertainty, can also be characterized by standard

deviations, evaluated from probability density functions based on experience or other information.

Note 4 to entry: In general, for a given set of information, it is understood that the measurement uncertainty is

associated with a stated quantity value attributed to the measurand. A modification of this value results in a

modification of the associated uncertainty.

4 Symbols and subscripts

4.1 Symbols

Symbol Quantity Dimensions SI units

2 2

A effective area L m

2 2

A manufacturer supplied constant L m

p

c ,c empirical constant dimensionless

1 2

D diameter of meter bore L m

−1

f frequency of vortex shedding T Hz

−3 −3

K K-factor, meter factor = 1/K L m

l characteristic length L m

N number of pulses dimensionless

NOTE Fundamental dimensions: M = mass, L = length, T = time, θ = temperature

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ISO 12764:2017(E)

Symbol Quantity Dimensions SI units

n number of period measurements dimensionless

−1 −2

p pressure ML T Pa

−1 −2

p minimum downstream pressure limit ML T Pa

d,min

−1 −2

p permanent pressure loss ML T Pa

p

−1 −2

Δp overall pressure drop ML T Pa

−1 −2

p liquid vapour pressure at the flowing temperature ML T Pa

vap

3 3

totalized volume flow at actual flowing conditions L m

Q

V

Q totalized mass M kg

m

3 −1 3

q volume flowrate at actual flowing conditions L T m /s

V

−1

q mass flowrate MT kg/s

m

Re Reynolds number dimensionless

Sr Strouhal number dimensionless

T temperature θ K

t two-tailed Student's at 95 % confidence dimensionless

−1

U average fluid velocity in meter bore LT m/s

−1

v fluid velocity LT m/s

−1 −1

α coefficient of linear expansion of material θ K

δ % error in the average period dimensionless

−1 −1

μ absolute viscosity (dynamic) ML T Pa · s

2 2

ν (nu) kinematic viscosity M /s m /s

−3 3

ρ fluid density ML kg/m

σ estimate of standard deviation of the average period T s

τ average period of vortex shedding T s

NOTE Fundamental dimensions: M = mass, L = length, T = time, θ = temperature

4.2 Subscripts

Subscript Description

b base conditions

m mass unit

V volume units, flowing conditions

mean average of extreme values

max maximum value

min minimum value

th

i the i measurement

d downstream

5 Principle

5.1 Bluff body

When a bluff body, sometimes referred to as shedder bar, is placed in a pipe in which fluid is flowing,

a boundary layer forms and grows along the surface of the bluff body. Due to insufficient momentum

and an adverse pressure gradient, separation occurs and an inherently unstable shear layer is formed.

Eventually, this shear layer rolls up into vortices that shed alternately from the sides of the body and

propagate downstream. This series of vortices is called a Von Karman-like vortex street (See Figure 2).

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ISO 12764:2017(E)

The frequency at which pairs of vortices are shed is directly proportional to the fluid velocity. Since the

shedding process is repeatable, it can be used to measure the flow.

Key

1 bluff body

2 conduit

a

Flow.

b

Vortex.

Figure 2 — Principle of Von Karman-like vortex street

5.2 Shedding vortices detection/sensors

Sensors are used to detect shedding vortices, i.e. to convert the pressure or velocity variations

associated with the vortices to electrical signals. Vortex shedding sensor technology varies and is

typically based on force, pressure, or velocity.

5.3 Strouhal number

The Strouhal number, Sr, relates the frequency, f, of generated vortices, the bluff body characteristic

dimension, l, and the fluid velocity, U, as shown in Formula (1).

fl⋅

Sr = (1)

U

remains essentially constant within a large range of Reynolds number. This means that the Strouhal

number is independent of density, pressure, viscosity and other physical parameters. Given this

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ISO 12764:2017(E)

situation, the flow velocity is directly proportional to the frequency at which the vortices are being

shed, i.e. the vortex pulse rate [see Formula (2)].

Uf=ξ ⋅ (2)

where ξ is a constant equal to l/Sr and q the volumetric flowrate at flowing conditions, i.e. the volume

V,

flowrate, is given by Formula (3):

()Al⋅

qA==⋅U ⋅ f (3)

V

Sr

where A is defined by the effective area of attack for the flow of the considered pipe/flowmeter

configuration. The K-factor for a vortex shedding flowmeter is defined by Formulae (4) and (5)

Sr f

K == (4)

()Al⋅ q

V

hence,

f

q = (5)

V

K

To obtain a mass flowrate [see Formula (6)] or volumetric flowrate at base conditions [see Formula (7)],

i.e. standard volume flowrate, the density at flowing temperature and pressure is needed.

f

q =ρ⋅ (6)

m

K

ρ f

q = ⋅ (7)

V ,b

ρ K

b

The total amount of fluid that has flowed through a meter over a specified time interval is given by

Formulae (8), (9), and (10).

N

Q = (8)

V

K

N

Q =ρ⋅ (9)

m

K

ρ N

Q = ⋅ (10)

V ,b

ρ K

b

where

N is the total number of vortices shed, i.e. total number of vortex pulses, over that time interval.

6 Flowmeter description

6.1 Physical components

The vortex shedding flowmeter consists of two elements: th

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