EN ISO 5167-2:2022

SLOVENSKI STANDARD
01-september-2022
Nadomešča:
SIST EN ISO 5167-2:2004
Merjenje pretoka fluida na osnovi tlačne razlike, povzročene z napravo, vstavljeno
v polno zapolnjen vod s krožnim prerezom - 2. del: Zaslonke (ISO 5167-2:2022)
Measurement of fluid flow by means of pressure differential devices inserted in circular
cross-section conduits running full - Part 2: Orifice plates (ISO 5167-2:2022)
Durchflussmessung von Fluiden mit Drosselgeräten in voll durchströmten Leitungen mit
Kreisquerschnitt - Teil 2: Blenden (ISO 5167-2:2022)
Mesurage de débit des fluides au moyen d'appareils déprimogènes insérés dans des
conduites en charge de section circulaire - Partie 2: Diaphragmes (ISO 5167-2:2022)
Ta slovenski standard je istoveten z: EN ISO 5167-2:2022
ICS:
17.120.10 Pretok v zaprtih vodih Flow in closed conduits
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 5167-2
EUROPEAN STANDARD
NORME EUROPÉENNE
June 2022
EUROPÄISCHE NORM
ICS 17.120.10 Supersedes EN ISO 5167-2:2003
English Version
Measurement of fluid flow by means of pressure
differential devices inserted in circular cross-section
conduits running full - Part 2: Orifice plates (ISO 5167-
2:2022)
Mesurage de débit des fluides au moyen d'appareils Durchflussmessung von Fluiden mit Drosselgeräten in
déprimogènes insérés dans des conduites en charge de voll durchströmten Leitungen mit Kreisquerschnitt -
section circulaire - Partie 2: Diaphragmes (ISO 5167- Teil 2: Blenden (ISO 5167-2:2022)
2:2022)
This European Standard was approved by CEN on 17 June 2022.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 5167-2:2022 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 5167-2:2022) has been prepared by Technical Committee ISO/TC 30
"Measurement of fluid flow in closed conduits" in collaboration with CCMC.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by December 2022, and conflicting national standards
shall be withdrawn at the latest by December 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 5167-2:2003.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 5167-2:2022 has been approved by CEN as EN ISO 5167-2:2022 without any
modification.
INTERNATIONAL ISO
STANDARD 5167-2
Second edition
2022-06
Measurement of fluid flow by means of
pressure differential devices inserted
in circular cross-section conduits
running full —
Part 2:
Orifice plates
Mesurage de débit des fluides au moyen d'appareils déprimogènes
insérés dans des conduites en charge de section circulaire —
Partie 2: Diaphragmes
Reference number
ISO 5167-2:2022(E)
ISO 5167-2:2022(E)
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 5167-2:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
4 Principles of the method of measurement and computation . 2
5 Orifice plates . 2
5.1 Description . 2
5.1.1 General . 2
5.1.2 General shape . 2
5.1.3 Upstream face A . 3
5.1.4 Downstream face B . 4
5.1.5 Thicknesses E and e . 4
5.1.6 Angle of bevel, α . 5
5.1.7 Edges G, H and I . 5
5.1.8 Diameter of orifice, d . 5
5.1.9 Bidirectional plates . 6
5.1.10 Material and manufacture . 6
5.2 Pressure tappings . 6
5.2.1 General . 6
5.2.2 Orifice plate with D and D/2 tappings or flange tappings . 6
5.2.3 Orifice plate with corner tappings . 8
5.3 Coefficients and corresponding uncertainties of orifice plates . 11
5.3.1 Limits of use . 11
5.3.2 Coefficients .12
5.3.3 Uncertainties .13
5.4 Pressure loss, Δϖ . 14
6 Installation requirements .15
6.1 General . 15
6.2 Minimum upstream and downstream straight lengths for installation between
various fittings and the orifice plate . 16
6.3 Flow conditioners . 21
6.3.1 General . 21
6.3.2 19-tube bundle flow straightener (1998) . 21
6.3.3 The Zanker flow conditioner plate . 27
6.4 Circularity and cylindricality of the pipe .28
6.5 Location of orifice plate and carrier rings .29
6.6 Method of fixing and gaskets . 30
7 Flow calibration of orifice meters .30
7.1 General .30
7.2 Test facility . 31
7.3 Meter installation . . 31
7.4 Design of the test programme . 31
7.5 Reporting the calibration results . 31
7.6 Uncertainty analysis of the calibration . 32
7.6.1 General . 32
7.6.2 Uncertainty of the test facility . 32
7.6.3 Uncertainty of the orifice meter . 32
Annex A (informative) Tables of discharge coefficients and expansibility [expansion]
factors .33
Annex B (informative) Flow conditioners .47
iii
ISO 5167-2:2022(E)
Bibliography .52
iv
ISO 5167-2:2022(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 of 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
www.iso.org/iso/foreword.html.
ISO 5167-2 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed conduits,
Subcommittee SC 2, Pressure differential devices, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/SS F05, Measuring instruments, in accordance with
the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition of ISO 5167-2 cancels and replaces the first edition (ISO 5167-2:2003), which has
been technically revised.
The main changes are as follows:
— a revised maximum orifice edge thickness is given for β < 0,2;
— a correction has been made to the required spacing between two 45° bends for which the straight
length upstream of an orifice plate is stated;
— a clearer specification has been given for the tee for which the straight length upstream of an orifice
plate is stated;
— flow calibration of orifice plates is included;
— there is improved wording of the rules for spacing of multiple fittings but no change in actual
requirements.
A list of all parts in the ISO 5167 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
ISO 5167-2:2022(E)
Introduction
ISO 5167, consisting of six parts, covers the geometry and method of use (installation and operating
conditions) of orifice plates, nozzles, Venturi tubes, cone meters and wedge meters when they are
inserted in a conduit running full to determine the flow rate of the fluid flowing in the conduit. It also
gives necessary information for calculating the flow rate and its associated uncertainty.
ISO 5167 (all parts) is applicable only to pressure differential devices in which the flow remains
subsonic throughout the measuring section and where the fluid can be considered as single-phase, but
is not applicable to the measurement of pulsating flow. Furthermore, each of these devices can only be
used uncalibrated in accordance with this standard within specified limits of pipe size and Reynolds
number, or alternatively they can be used across their calibrated range.
ISO 5167 (all parts) deals with devices for which direct calibration experiments have been made,
sufficient in number, spread and quality to enable coherent systems of application to be based on
their results and coefficients to be given with certain predictable limits of uncertainty. ISO 5167 also
provides methodology for bespoke calibration of differential pressure meters.
The devices introduced into the pipe are called primary devices. The term primary device also includes
the pressure tappings. All other instruments or devices required to facilitate the instrument readings
are known as secondary devices, and the flow computer that receives these readings and performs
the algorithms is known as a tertiary device. ISO 5167 (all parts) covers primary devices; secondary

devices (see ISO 2186) and tertiary devices will be mentioned only occasionally.
Aspects of safety are not dealt with in ISO 5167-1 to ISO 5167-6. It is the responsibility of the user to
ensure that the system meets applicable safety regulations.
vi
INTERNATIONAL STANDARD ISO 5167-2:2022(E)
Measurement of fluid flow by means of pressure
differential devices inserted in circular cross-section
conduits running full —
Part 2:
Orifice plates
1 Scope
This document specifies the geometry and method of use (installation and operating conditions) of
orifice plates when they are inserted in a conduit running full to determine the flow rate of the fluid
flowing in the conduit.
This document also provides background information for calculating the flow rate and is applicable in
conjunction with the requirements given in ISO 5167-1.
This document is applicable to primary devices having an orifice plate used with flange pressure
tappings, or with corner pressure tappings, or with D and D/2 pressure tappings. Other pressure
tappings such as “vena contracta” and pipe tappings are not covered by this document. This document
is applicable only to a flow which remains subsonic throughout the measuring section and where the
[1]
fluid can be considered as single phase. It is not applicable to the measurement of pulsating flow . It
does not cover the use of orifice plates in pipe sizes less than 50 mm or more than 1 000 mm, or where
the pipe Reynolds numbers are below 5 000.
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 5167-1, Measurement of fluid flow by means of pressure differential devices inserted in circular-cross
section conduits running full — Part 1: General principles and requirements
ISO 5168, Measurement of fluid flow — Procedures for the evaluation of uncertainties
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM: 1995)
3 Terms, definitions and symbols
For the purposes of this document, the terms, definitions and symbols given in ISO 4006 and ISO 5167-1
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
ISO 5167-2:2022(E)
4 Principles of the method of measurement and computation
The principle of the method of measurement is based on the installation of an orifice meter into
a pipeline in which a fluid is running full. The presence of the orifice plate causes a static pressure
difference between the upstream and downstream sides of the plate. The mass flow rate, q , can be
m
determined using Formula (1):
C π
q = ερdp2Δ (1)
m 1
4 4
1−β
The uncertainty limits can be calculated using the procedure given in ISO 5167-1:2022, Clause 8.
Computation of the mass flow rate, which is an arithmetic process, can be performed by replacing the
different terms on the right-hand side of the basic Formula (1) by their numerical values.
Similarly, the value of volume flow rate, q , is calculated from Formula (2):
V
q
m
q = (2)
V
ρ
where ρ is the fluid density at the temperature and pressure for which the volume is stated.
As will be seen later in this document, the discharge coefficient, C, is dependent on the Reynolds number,
Re, (see ISO 5167-1:2022, 3.3.2), which is itself dependent on q , and has to be obtained by iteration
m
(see ISO 5167-1:2022, Annex A, for guidance regarding the choice of the iteration procedure and initial
estimates).
The diameters d and D used in Formula (1) (since D is required to calculate β) are the values of the
diameters at working conditions. Measurements taken at any other conditions should be corrected
for any possible expansion or contraction of the orifice plate and the pipe due to the values of the
temperature and pressure of the fluid during the measurement.
It is necessary to know the density and the viscosity of the fluid at the working conditions. In the case
of a compressible fluid, it is also necessary to know the isentropic exponent of the fluid at working
conditions.
5 Orifice plates
5.1 Description
5.1.1 General
The various types of standard orifice meter designs are similar and therefore only a single description
is needed. Each type of standard orifice meter design is characterized by the arrangement of the
pressure tappings.
‘Orifice plate’ can refer just to the plate or to the whole meter; where it is important to be clear that the
plate and pipework are meant, ‘orifice meter’ can be used.
NOTE Limits of use are given in 5.3.1.
The axial plane cross-section of a standard orifice plate is shown in Figure 1.
The letters given in the following text refer to the corresponding references in Figure 1.
5.1.2 General shape
5.1.2.1 The part of the plate inside the pipe shall be circular and concentric with the pipe centreline.
The faces of the plate shall always be flat and parallel.
ISO 5167-2:2022(E)
5.1.2.2 Unless otherwise stated, the following requirements apply only to that part of the plate
located within the pipe.
5.1.2.3 Care shall be taken in the design of the orifice plate and its installation to ensure that plastic
buckling and elastic deformation of the plate, due to the magnitude of the differential pressure or of any
other stress, do not cause the slope of the straight line specified in 5.1.3.1 to exceed 1 % under working
conditions.
Traditionally, many differential pressure systems had a maximum differential pressure limit of 50 kPa
(500 mbar). With modern digital differential pressure instrumentation, a higher maximum differential
pressure is possible, provided that the plate material, plate thickness, and method of support are
sufficient to prevent bending or buckling.
NOTE Further information is given in ISO/TR 9464:2008, 5.2.5.1.2.3.
Key
1 upstream face A
2 downstream face B
a
Direction of flow.
Figure 1 — Standard orifice plate
5.1.3 Upstream face A
5.1.3.1 The upstream face A of the plate shall be flat when the plate is installed in the pipe with zero
differential pressure across it. Provided that it can be shown that the method of mounting does not
distort the plate, this flatness may be measured with the plate removed from the pipe. Under these
circumstances, the plate may be considered to be flat when the maximum gap between the plate and a
straight edge of length D laid across any diameter of the plate (see Figure 2) is less than 0,005(D – d)/2,
ISO 5167-2:2022(E)
i.e. the slope is less than 0,5 % when the orifice plate is examined prior to insertion into the meter line.
As can be seen from Figure 2, the critical area is in the vicinity of the orifice bore. The uncertainty
requirements for this dimension can be met using feeler gauges.
Key
1 orifice plate outside diameter
2 pipe inside diameter, D
3 straight edge
4 orifice
5 departure from flatness (measured at edge of orifice)
Figure 2 — Orifice plate-flatness measurement
−4
5.1.3.2 The upstream face of the orifice plate shall have a roughness criterion Ra < 10 d within a
circle of diameter not less than D and which is concentric with the orifice. In all cases, the roughness of
the upstream face of the orifice plate shall not be such that it affects the edge sharpness measurement.
If, under working conditions, the plate does not fulfil the specified conditions, it shall be repolished or
cleaned to a diameter of at least D.
5.1.3.3 Where possible, it is useful to provide a distinctive mark which is visible even when the orifice
plate is installed to show that the upstream face of the orifice plate is correctly installed relative to the
direction of flow.
5.1.4 Downstream face B
5.1.4.1 The downstream face B shall be flat and parallel with the upstream face (see also 5.1.5.4).
5.1.4.2 Although it may be convenient to manufacture the orifice plate with the same surface finish
on each face, it is unnecessary to provide the same high-quality finish for the downstream face as for
the upstream face (see Reference [5]; but also see 5.1.9).
5.1.4.3 The flatness and surface condition of the downstream face may be judged by visual inspection.
5.1.5 Thicknesses E and e
5.1.5.1 The thickness e of the orifice shall be between 0,005D and 0,02D and shall always be less than
0,1d.
5.1.5.2 The difference between the values of e measured at any point on the orifice shall not be
greater than 0,001D.
ISO 5167-2:2022(E)
5.1.5.3 The thickness E of the plate shall be between e and 0,05D.
However, when 50 mm ≤ D ≤ 64 mm, a thickness E up to 3,2 mm is acceptable.
It shall also meet the requirements of 5.1.2.3.
5.1.5.4 If D ≥ 200 mm, the difference between the values of E measured at any point of the plate shall
not be greater than 0,001D. If D < 200 mm, the difference between the values of E measured at any point
of the plate shall not be greater than 0,2 mm.
5.1.6 Angle of bevel, α
5.1.6.1 If the thickness, E, of the plate exceeds the thickness e of the orifice, the plate shall be bevelled
on the downstream side. The bevelled surface shall be well finished.
5.1.6.2 The angle of bevel, α, shall be 45° ± 15°.
5.1.7 Edges G, H and I
5.1.7.1 The upstream edge G shall not have wire-edges or burrs.
NOTE A burr is a small sharp piece of metal typically left behind after a manufacturing process. A wire-edge
is a burr which extends along a significant part of an edge.
5.1.7.2 The upstream edge G shall be sharp. It is considered so if the edge radius is not greater than
0,000 4d.
If d ≥ 25 mm, this requirement can generally be considered as satisfied by visual inspection, by checking
that the edge does not reflect a beam of light when viewed with the naked eye.
If d < 25 mm, visual inspection is insufficient. Alternatively, a flow calibration can be performed, in
accordance with Clause 7.
If there is any doubt as to whether this requirement is met, the edge radius shall be measured.
5.1.7.3 The upstream edge shall be square; it is considered to be so when the angle between the
orifice bore and the upstream face of the orifice plate is 90° ± 0,3°. The orifice bore is the region of the
orifice plate between edges G and H.
5.1.7.4 The downstream edges H and I are within the separated flow region and hence the
requirements for their quality are less stringent than those for edge G. This being the case, small defects
(for example, a single nick) are acceptable.
5.1.7.5 Various small non-conformities to the sharp inlet edge G, such as a small nick or partial wear
on a small segment of the orifice circumference, do not necessarily produce significant flow prediction
biases (see Reference [5]). However, as it is not possible to quantify the effect of all possible non-
conformities that may be encountered in service, a plate that is out of specification should be evaluated,
and if necessary, changed.
5.1.8 Diameter of orifice, d
5.1.8.1 The diameter d shall in all cases be greater than or equal to 12,5 mm. The diameter ratio,
β = d/D, shall be always greater than or equal to 0,10 and less than or equal to 0,75.
Within these limits, the value of β may be chosen by the user.
ISO 5167-2:2022(E)
5.1.8.2 The value d of the diameter of the orifice shall be taken as the mean of the measurements of at
least four diameters at approximately equal angles to each other. Care shall be taken that the edge and
bore are not damaged when making these measurements.
5.1.8.3 The orifice shall be cylindrical.
No diameter shall differ by more than 0,05 % from the value of the mean diameter. This requirement
is deemed to be satisfied when the difference in the length of any of the measured diameters complies
with the said requirement in respect of the mean of the measured diameters. In all cases, the roughness
of the orifice bore cylindrical section shall not be such that it affects the edge sharpness measurement.
5.1.9 Bidirectional plates
5.1.9.1 If the orifice plate is intended to be used for measuring reverse flows, the following
requirements shall be fulfilled:
a) the plate shall not be bevelled;
b) the two faces shall comply with the specifications for the upstream face given in 5.1.3;
c) the thickness, E, of the plate shall be equal to the thickness e of the orifice specified in 5.1.5;
consequently, it may be necessary to limit the differential pressure to prevent plate distortion
(see 5.1.2.3);
d) the two edges of the orifice shall comply with the specifications for the upstream edge specified in
5.1.7.
5.1.9.2 Furthermore, for orifice plates with D and D/2 tappings (see 5.2), two sets of upstream and
downstream pressure tappings shall be provided and used according to the direction of the flow.
5.1.10 Material and manufacture
The plate may be manufactured from any material and in any way, provided that it is and remains in
accordance with the foregoing description during the flow measurements.
5.2 Pressure tappings
5.2.1 General
For each orifice plate, at least one upstream pressure tapping and one downstream pressure tapping
shall be installed in one or other of the standard locations, i.e. as D and D/2, flange or corner tappings.
A single orifice plate may be used with several sets of pressure tappings suitable for different types
of standard orifice meters, but to avoid mutual interference, several tappings on the same side of the
orifice plate shall be offset by at least 30°.
The location of the pressure tappings characterizes the type of standard orifice meter.
5.2.2 Orifice plate with D and D/2 tappings or flange tappings
5.2.2.1 The spacing l of a pressure tapping is the distance between the centreline of the pressure
tapping and the plane of a specified face of the orifice plate. When installing the pressure tappings, due
account shall be taken of the thickness of the gaskets and/or sealing material.
ISO 5167-2:2022(E)
5.2.2.2 For orifice plates with D and D/2 tappings (see Figure 3), the spacing, l , of the upstream
pressure tapping is nominally equal to D, but may be between 0,9D and 1,1D without altering the
discharge coefficient.
The spacing, l , of the downstream pressure tapping is nominally equal to 0,5D but may be between the
following values without altering the discharge coefficient:
— between 0,48D and 0,52D when β ≤ 0,6;
— between 0,49D and 0,51D when β > 0,6.
Both l and l spacings are measured from the upstream face of the orifice plate.
1 2
5.2.2.3 For orifice plates with flange tappings (see Figure 3), the spacing l of the upstream pressure
tapping is nominally 25,4 mm and is measured from the upstream face of the orifice plate.
'
The spacing l of the downstream pressure tapping is nominally 25,4 mm and is measured from the
downstream face of the orifice plate.
'
These upstream and downstream spacings l and l may be within the following ranges without
1 2
altering the discharge coefficient:
— 25,4 mm ± 0,5 mm when β > 0,6 and D < 150 mm;
— 25,4 mm ± 1 mm in all other cases, i.e. β ≤ 0,6, or β > 0,6, but 150 mm ≤ D ≤ 1 000 mm.
5.2.2.4 The centreline of the tapping shall meet the pipe centreline at an angle as near to 90° as
possible, but in every case within 3° of the perpendicular.
5.2.2.5 At the point of break-through, the hole shall be circular. The edges shall be flush with the
internal surface of the pipe wall and as sharp as possible. To ensure the elimination of all burrs or wire
edges at the inner edge, rounding is permitted but shall be kept as small as possible and, where it can be
measured, its radius shall be less than one-tenth of the pressure tapping diameter. No irregularity shall
appear inside the connecting hole, on the edges of the hole drilled in the pipe wall or on the pipe wall
close to the pressure tapping.
5.2.2.6 Conformity of the pressure tappings with the requirements specified in 5.2.2.4 and 5.2.2.5
may be judged by visual inspection.
5.2.2.7 The diameter of pressure tappings shall be less than 0,13D and less than 13 mm.
No restriction is placed on the minimum diameter, which is determined in practice by the need
to prevent accidental blockage and to give satisfactory dynamic performance. The upstream and
downstream tappings shall have the same diameter.
5.2.2.8 The pressure tappings shall be circular and cylindrical over a length of at least 2,5 times the
internal diameter of the tapping, measured from the inner wall of the pipeline.
5.2.2.9 The centrelines of the pressure tappings may be located in any axial plane of the pipeline.
ISO 5167-2:2022(E)
5.2.2.10 The axis of the upstream tapping and that of the downstream tapping may be located in
different axial planes, but are normally located in the same axial plane.
Key
1 D and D/2 pressure tappings
2 flange tappings
a
Direction of flow.
b
l = D ± 0,1D
c
l = 0,5D ± 0,02D for β ≤ 0,6
0,5D ± 0,01D for β > 0,6
d
'
l = l = (25,4 ± 0,5) mm for β > 0,6 and D < 150 mm
1 2
(25,4 ± 1) mm for β ≤ 0,6
(25,4 ± 1) mm for β > 0,6 and 150 mm ≤ D ≤ 1 000 mm
Figure 3 — Spacing of pressure tappings for orifice plates with D and D/2 tappings or flange
tappings
5.2.3 Orifice plate with corner tappings
5.2.3.1 The spacing between the centrelines of the tappings (see Figure 4) and the respective faces
of the plate is equal to half the diameter or to half the width of the tappings themselves, so that the
tapping holes break through the wall flush with the faces of the plate (see also 5.2.3.5).
ISO 5167-2:2022(E)
5.2.3.2 The pressure tappings may be either single tappings or annular slots. Both types of tappings
may be located either in the pipe or in its flanges or in carrier rings as shown in Figure 4.
Key
1 carrier ring with annular slot f thickness of the slot
2 individual tappings c length of the upstream ring
3 pressure tappings c' length of the downstream ring
4 carrier ring b diameter of the carrier ring
5 orifice plate a width of annular slot or diameter of single tapping
s distance from upstream step to carrier ring
a
Direction of flow. g, h dimensions of the annular chamber
j chamber tapping diameter
Figure 4 — Corner tappings
ISO 5167-2:2022(E)
5.2.3.3 The diameter a of a single tapping and the width a of annular slots are specified below. The
minimum diameter is determined in practice by the need to prevent accidental blockage and to give
satisfactory dynamic performance.
For clean fluids and vapours:
— for β ≤ 0,65: 0,005D ≤ a ≤ 0,03D;
— for β > 0,65: 0,01D ≤ a ≤ 0,02D.
If D < 100 mm, a value of a up to 2 mm is acceptable for any β.
For any values of β
— for clean fluids: 1 mm ≤ a ≤ 10 mm;
— for vapours, in the case of annular chambers: 1 mm ≤ a ≤ 10 mm;
— for vapours and for liquefied gases, in the case of single tappings: 4 mm ≤ a ≤ 10 mm.
NOTE The requirements on size as a fraction of pipe diameter are based on geometrical similarity to the
original orifice runs on which the discharge coefficient is based. For vapours and for liquefied gases, there
are pipe diameters for which it is not possible to manufacture a system using single corner tappings that is in
conformity with this document.
5.2.3.4 The annular slots usually break through the pipe over the entire perimeter, with no break
in continuity. If not, each annular chamber shall connect with the inside of the pipe by at least four
openings, the axes of which are at equal angles to one another and the individual opening area of which
is at least 12 mm .
5.2.3.5 If individual pressure tappings, as shown in Figure 4, are used, the centreline of the tappings
shall meet the centreline of the pipe at an angle as near to 90° as possible.
If there are several individual pressure tappings in the same upstream or downstream plane, their
centrelines shall form equal angles with each other. The diameters of individual pressure tappings are
specified in 5.2.3.3.
The pressure tappings shall be circular and cylindrical over a length of at least 2,5 times the internal
diameter of the tappings measured from the inner wall of the pipeline.
The upstream and downstream pressure tappings shall have the same diameter.
5.2.3.6 The internal diameter b of the carrier rings shall be greater than or equal to the diameter D
of the pipe, to ensure that they do not protrude into the pipe, but shall be less than or equal to 1,04D.
Moreover, the condition in Formula (3) shall be met:
bD− c 01,
××100< (3)
D D
01,,+23β
The lengths c and c' of the upstream and downstream rings (see Figure 4) shall not be greater than
0,5D.
The thickness, f, of the slot shall be greater than or equal to twice the width a of the annular slot. The
area of the cross-section of the annular chamber, gh, shall be greater than or equal to half the total area
of the opening connecting this chamber to the inside of the pipe.
5.2.3.7 All surfaces of the ring that are in contact with the measured fluid shall be clean and shall
have a well-machined finish. The surface finish shall meet the pipe roughness requirements (see 5.3.1).
ISO 5167-2:2022(E)
5.2.3.8 The pressure tappings connecting the annular chambers to the secondary devices are pipe-
wall tappings, circular at the point of break-through and with a diameter j between 4 mm and 10 mm
(see 5.2.2.5).
5.2.3.9 The upstream and downstream carrier rings need not necessarily be symmetrical in relation
to each other, but they shall both conform with the preceding requirements.
5.2.3.10 The diameter of the pipe shall be measured as specified in 6.4.2, the carrier ring being
regarded as part of the primary device. This also applies to the distance requirement given in 6.4.4 so
that s shall be measured from the upstream edge of the recess formed by the carrier ring.
5.3 Coefficients and corresponding uncertainties of orifice plates
5.3.1 Limits o
...