ISO 12764:2017

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

General Information

• Status: Published
• Publication Date: 15-Aug-2017
• ICS: 17.120.10 - Flow in closed conduits
• Technical Committee: ISO/TC 30/SC 5 - Velocity and mass methods
• Drafting Committee: ISO/TC 30/SC 5 - Velocity and mass methods
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 12-Jan-2023

Relations

• Revises: ISO/TR 12764:1997 - Measurement of fluid flow in closed conduits — Flowrate measurement by means of vortex shedding flowmeters inserted in circular cross-section conduits running full
• Effective Date: 20-Jul-2013

Standards Content (Sample)

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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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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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
...