ISO/TR 15377:1998
(Main)Measurement of fluid flow by means of pressure-differential devices — Guidelines for the specification of nozzles and orifice plates beyond the scope of ISO 5167-1
Measurement of fluid flow by means of pressure-differential devices — Guidelines for the specification of nozzles and orifice plates beyond the scope of ISO 5167-1
Mesurage du débit des fluides au moyen d'appareils déprimogènes — Lignes directrices pour les spécifications des tuyères et diaphragmes non couverts par l'ISO 5167-1
General Information
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Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 15377
First edition
1998-05-15
Measurement of fluid flow by means of
pressure-differential devices — Guidelines
for specification of nozzles and orifice
plates beyond the scope of ISO 5167-1
Mesurage du débit des fluides au moyen d'appareils déprimogènes —
Lignes directrices pour les spécifications des tuyères et diaphragmes non
couverts par l'ISO 5167-1
A
Reference number
ISO/TR 15377:1998(E)
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ISO/TR 15377:1998(E)
Contents
1 Scope .1
2 Reference.1
3 Symbols.1
4 Principle of the method of measurement and computation.1
5 Square-edged orifice plates and nozzles with drain holes, in pipes below 50 mm diameter and as inlet and
outlet devices.1
6 Orifice plates (except square-edged).7
© ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
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Internet central@iso.ch
X.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
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ISO ISO/TR 15377:1998(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 main task of technical committees is to prepare International Standards, but in exceptional circumstances a
technical committee may propose the publication of a Technical Report of one of the following types:
– type 1, when the required support cannot be obtained for the publication of an International Standard, despite
repeated efforts;
– type 2, when the subject is still under technical development or where for any other reason there is the future
but not immediate possibility of an agreement on an International Standard;
– type 3, when a technical committee has collected data of a different kind from that which is normally published
as an International Standard (“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they
can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until data they provide are considered to be no longer valid or useful.
ISO/TR 15377, which is a Technical Report of type 3, was prepared by Technical Committee ISO/TC 30,
Measurement of fluid flow in closed conduits, Subcommittee SC 2, Differential pressure methods.
iii
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TECHNICAL REPORT ISO ISO/TR 15377:1998(E)
Measurement of fluid flow by means of pressure-differential
devices — Guidelines for specification of nozzles and orifice plates
beyond the scope of ISO 5167-1
1 Scope
This Technical Report describes the geometry and method of use for conical-entrance orifice plates, quarter-circle
orifice plates and eccentric orifice plates. Recommendations are also given for square-edged orifice plates and
nozzles under conditions outside the scope of ISO 5167-1.
2 Reference
ISO 5167-1:1991, Measurement of fluid flow by means of pressure differential devices — Part 1 : Orifice plates,
nozzles and Venturi tubes inserted in circular cross-section conduits running full.
3 Symbols
The symbols used in this Technical Report are given in table 1.
4 Principle of the method of measurement and computation
The principle of the method of measurement and computation is as specified in clause 5 of ISO 5167-1:1991.
5 Square-edged orifice plates and nozzles with drain holes, in pipes below 50 mm
diameter and as inlet and outlet devices
5.1 Drain holes through the upstream face of the square-edged orifice plate or nozzle
5.1.1 General
Square-edged orifice plates and nozzles with drain holes may be used, installed, and manufactured in accordance
with the following guidelines.
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ISO/TR 15377:1998(E) ISO
Table 1 — Symbols
Symbols Represented quantity Dimensions SI unit
M: mass
L: length
T: time
a Pressure tapping hole diameter L m
C Discharge coefficient dimensionless
d Diameter of orifice or throat of primary device Lm
at operating conditions
D Upstream internal pipe diameter at operating Lm
conditions
e Thickness of bore L m
E, E Thickness of orifice plate L m
1
F Correction factor dimensionless
E
k Uniform equivalent roughness L m
-1 -2
p Static pressure of the fluid ML T Pa
-1
q Mass rate of flow MT kg/s
m
Radius of profile L m
r
R Roughness criterion L m
a
Re Reynolds number dimensionless
Re Re Reynolds number referred to D or d dimensionless
D d
d
β dimensionless
Diameter ratio, β =
D
-1 -2
Δp Differential pressure ML T Pa
e Expansibility (expansion) factor dimensionless
κ Isentropic exponent dimensionless
-3 3
ρ Mass density of the fluid ML kg/m
p
2
Pressure ratio, τ =
τ dimensionless
p
1
NOTE 1 Other symbols used in this Technical Report are defined at their place of use.
NOTE 2 Some of the symbols used in this Technical Report are different from those used in
ISO 5167-1.
NOTE 3 Subscript 1 refers to the cross-section at the plane of the upstream pressure tapping.
Subscript 2 refers to the cross-section at the plane of the downstream pressure tapping.
5.1.2 Square-edged orifice plates
If a drain hole is drilled through the orifice plate, the coefficient values specified in ISO 5167-1: 1991 should not be
used unless the following conditions are observed.
a) The pipe diameter should be larger than 100 mm.
b) The diameter of the drain hole should not exceed 0,1d and no part of the hole should lie within a circle,
concentric with the orifice, of diameter (D 2 0,2d). The outer edge of the drain hole should be as close to the
pipe wall as practicable.
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ISO ISO/TR 15377:1998(E)
c) The drain hole should be deburred and the upstream edge should be sharp.
d) Single pressure tappings should be orientated so that they are between 90° and 180° to the position of the
drain hole.
e) The measured orifice diameter, d , should be corrected to allow for the additional orifice area represented by
m
the drain hole of diameter d as shown in the following equations.
k
2
d
k
dd≈+10,55
m
d
m
2
d
k
dd≈−10,55
m
d
4 -0,5
NOTE These equations are based on the assumption that the value for Cε(1 2 β ) for flow through the drain hole is
10 % greater than the value for flow through the orifice.
An additional uncertainty equivalent to 100 % of the drain hole correction should be added arithmetically to the
discharge coefficient uncertainty when estimating the overall uncertainty of the flow measurement.
5.1.3 ISA 1932 nozzles
If a drain hole is drilled through the nozzle upstream face, the coefficient values specified in ISO 5167-1:1991
should not be used unless the following conditions are observed.
a) The value of β should be less than 0,625.
b) The diameter of the drain hole should not exceed 0,1 d and no part of the hole should lie within a circle,
concentric with the throat, of diameter (D 2 0,2d).
c) The length of the drain hole should not exceed 0,1D.
d) The drain hole should be deburred and the upstream edge should be sharp.
e) Single pressure tappings should be orientated so that they are between 90° and 180° to the position of the
drain hole.
f) The measured diameter, d , should be corrected to allow for the additional throat area represented by the drain
m
hole of diameter d as shown in the following equations.
k
2
d
k
dd≈+10,40
m
d
m
2
d
k
dd≈−10,40
m
d
4 -0,5
NOTE These equations are based on the assumption that the value for Cε(1 2 β ) for flow through the drain hole is
10 % greater than the value for flow through the throat of the nozzle.
An additional uncertainty equivalent to 100 % of the drain hole correction should be added arithmetically to the
discharge coefficient uncertainty when estimating the overall uncertainty of the flow measurement.
5.1.4 Long radius nozzles
Drain holes through these primary elements should not be used.
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5.2 Square-edged orifice plates installed in pipes of diameter 25 mm ≤ D < 50 mm
5.2.1 General
Orifice plates should be installed and manufactured in accordance with ISO 5167-1.
5.2.2 Limits of use
When square-edged orifice plates are installed in pipes of bore 25 mm up to 50 mm the following conditions should
be strictly observed.
a) The pipes should have high quality internal surfaces such as drawn copper or brass tubes, glass or plastics
pipes or drawn or fine-machined steel tubes. The steel tubes should be of stainless steel for use with corrosive
fluids such as water. The uniform equivalent roughness, k, should be < 0,03 mm for all diameter ratios. If the
pipe is machined, the surface finish should be better than 0,3 μm.
b) Corner taps should be used, preferably of the carrier ring type detailed in figure 6 a) of ISO 5167-1: 1991.
2 4 -0,5
c) The diameter ratio, β, should be within the range 0,23 ≤ β ≤ 0,7 where 0,032 ≤ β (1 2 β ) ≤ 0,350.
C
5.2.3 Discharge coefficients and corresponding uncertainties
The Stolz equation for corner tappings given in 8.3.2.1 of ISO 5167-1: 1991 should be used for deriving the
discharge coefficients provided the minimum pipe Reynolds numbers are above the following values.
2
Re ≥ 40 000 β for 0,23 ≤ β ≤ 0,5
D
Re ≥ 10 000 for 0,5 ≤ β ≤ 0,7
D
An additional uncertainty of 1,0 % should be added arithmetically to the uncertainty derived from 8.3.3 of
ISO 5167-1:1991.
5.3 No upstream or downstream pipeline
5.3.1 General
This clause should apply where there is no pipeline on either or both the upstream or downstream sides of the
device, that is for flow from a large space into a pipe or vice versa, or flow through a device installed in the partition
wall between two large spaces.
5.3.2 Flow from a large space (no upstream pipeline) into a pipeline or another large space
5.3.2.1 Upstream and downstream tappings
The space on the upstream side of the device should be considered large if:
a) there is no wall closer than 4d to the axis of the device or to the plane of the upstream face of the orifice or
nozzle,
b) the velocity of the fluid at any point more than 4d from the device is less than 3 % of the velocity in the orifice or
throat,
c) the diameter of the downstream pipeline is not less than 2d.
NOTE 1 The first condition implies, for example, that an upstream pipeline of diameter greater than 8d (that is where β <
0,125) may be regarded as a large space. The second condition, which excludes upstream disturbances due to draughts, swirl
and jet effects, implies that the fluid is to enter the space uniformly over an area of not less than 33 times the area of the orifice
or throat. For example, if the flow is provided by a fall in level of a liquid in a tank, the area of the liquid surface is not to be less
than 33 times the area of the orifice or throat through which the tank is discharged.
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The distance of the upstream tapping (i.e. the tapping in the large space) from the orifice or nozzle centreline should
be greater than 5 d.
NOTE 2 The upstream tapping should preferably be located in a wall perpendicular to the plane of the orifice and be within a
distance of 0,5 d from that plane. The tapping does not necessarily have to be located in any wall; it can be in the open space.
If the space is very large, for example a room, the tapping should be shielded from draughts.
The downstream tapping should be located as specified for corner tappings in ISO 5167-1: 1991. If the downstream
side also consists of a large space, the tapping should be located as for the upstream tapping, except for Venturi
nozzles where the throat tap should be used.
NOTE 3 When the upstream and downstream tappings are at different horizontal levels, it may be necessary to make
allowance for the difference in hydrostatic head.
5.3.2.2 Square-edged orifice plates with corner tappings
5.3.2.2.1 Square-edged orifice plates with corner tappings should be manufactured in accordance with clause 8 of
ISO 5167-1: 1991.
5.3.2.2.2 The limits of use for square-edged orifice plates with corner tappings where there is a flow from a large
space should be as follows:
d > 6 mm
upstream: β ≤ 0,125
pipeline downstream: 0,2 ≤ β ≤ 0,5
large space downstream: β ≤ 0,125
2 4 -0,5
(1 ) 0,009
C β 2 β ≤
50 000
Re ≥
d
5.3.2.2.3 The discharge coefficient, C, is equal to 0,596. The uncertainty on the value of C is 1 %.
5.3.2.2.4 The expansibility factor, e, is given by the following equation and is only applicable if p /p > 0,75:
1 2
Dp
4
eb=−10(),,41+035
kp
1
When β, Δp/p and κ are assumed to be known without error, the percentage uncertainty of the value of e is equal to
1
4Δp/p .
1
Test results for the determination of e are known for air, steam and natural gas only. However, there is no known
objection to using the same formula for other gases and vapours the isentropic exponent of which is known.
5.3.2.3 ISA nozzle and Venturi nozzle
5.3.2.3.1 ISA nozzles and Venturi nozzles should be manufactured in accordance with clause 9 or 10.2 of
ISO 5167-1:1991.
5.3.2.3.2 The limits of use for ISA and Venturi nozzles where there is flow from a large space should be as follows:
d ≥ 11,5 mm
upstream: β ≤ 0,125
pipeline downstream: 0,2 ≤ β ≤ 0,5
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ISO/TR 15377:1998(E) ISO
large space downstream: β ≤ 0,125
2 4 -0,5
Cβ (1 - β ) ≤ 0,015
Re ≥ 100 000
d
5.3.2.3.3 The discharge coefficient, C, is equal to 0,99. The uncertainty in the value of C is 1 %.
5.3.2.3.4 The expansibility factor, e, is given by the following equation and is only applicable if p /p ≥ 0,75:
2 1
05,
2
()κκ-1/
κ
κτ 1− τ
e =
κ − 1 1− τ
The uncertainty on the expansibility factor, in percent, is equal to 2 Δp/p
1.
5.3.3 Flow into a large space (no downstream pipeline)
5.3.3.1 The space on the downstream side of the device should be considered large if there is no wall closer than
4d to the axis of the device or to the downstream face of the orifice plate or nozzle.
The diameter of the upstream pipeline should be greater than 2,5 (that is, < 0,4).
d β
The upstream tapping should be located as specified for corner tappings in ISO 5167-1:1991.
The distance of the downstream tapping (i.e. the tapping in the large space) from the orifice or nozzle centreline
should be greater than 5d.
For Venturi nozzles, the throat tap should be used.
NOTE 1 The downstream tapping should preferably be located in a wall perpendicular to the plane of the orifice and be
within a distance of 0,5d from that plane. The tapping does not necessarily have to be located in any wall; it can be in the open
space. If the space is very large, for example a room, the tapping should be shielded from draughts.
NOTE 2 Where the upstream and downstream tappings are at different horizontal levels, it may be necessary to make
allowance for the difference in hydrostatic head.
5.3.3.1 Square-edged orifice plates with corner tappings
5.3.3.1.1 Square-edged orifice plates with corner tappings should be manufactured in accordance with clause 8 of
ISO 5167-1: 1991.
5.3.3.1 Where 25 mm ≤ D < 50 mm, the limits given in 5.1.2 should apply except that:
0,4 ≤ β ≤ 0,7
2 4 -0,5
0,1 ≤ Cβ (1 2 β ) ≤ 0,35
Where 50 mm ≤ D ≤ 1000 mm, the limits given in 8.3.1 of ISO 5167-1: 1991 should apply except that:
0,4 ≤ β ≤ 0,8
2 4 -0,5
0,1 ≤ Cβ (1 2 β ) ≤ 0,50
5.3.3.1.1 Where 25 mm ≤ D < 50 mm, the coefficients and uncertainties given in 5.1.3 should apply.
Where 50 mm ≤ D ≤ 1000 mm, the coefficients and uncertainties given in 8.3.2 and 8.3.3 of ISO 5167-1:1991
should apply.
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5.3.3.2 ISA nozzle and Venturi nozzle
5.3.3.2.1 ISA nozzles and Venturi nozzles should be manufactured in accordance with clause 9 or 10.2 of ISO
5167-1: 1991.
5.3.3.2.2 The limits given in 9.1.6.1 of ISO 5167-1: 1991 should apply except that:
0,4 ≤ β ≤ 0,8
2 4 -0,5
0,16 (1 2 β ) 0,75
≤ Cβ ≤
5.3.3.2.3 The coefficients and uncertainties given in 9.1.6.2, 9.1.6.3 and 9.1.7 of ISO 5167-1:1991 should apply.
6 Orifice plates (except square-edged)
6.1 Conical entrance orifice plates
6.1.1 General
NOTE A conical entrance orifice plate has the characteristic that its discharge coefficient remains constant down to a low
Reynolds number, thus making it suitable for the measurement of flowrate of viscous fluids such as oil. Conical entrance orifice
plates are further distinguished from other types of orifice plates in that their discharge coefficient is the same for any diameter
ratio within the limits specified in this Technical Report.
Conical entrance orifice plates should be used and installed in accordance with clauses 6 and 7 of
ISO 5167-1:1991.
6.1.2 Limits of use
The limits of use for conical entrance orifice plates should be as follows:
d > 6 mm
D ≤ 500 mm
The lower limit of pipe diameter, D, depends on the internal roughness of the upstream pipeline and should be in
accordance with table 2 and within the following limits:
0,1 ≤ β ≤ 0,316
2 4 -0,5
0,007 ≤ Cβ (1 2 β ) ≤ 0,074
5
80 ≤ Re ≤ 2 × 10 β
D
NOTE Within these limits, the value of β is chosen by the user taking into consideration parameters such as required
differential pressure, uncertainty, acceptable pressure loss and available static pressure.
6.1.3 Description
NOTE The axial plane cross-section of the orifice plate is shown in figure 1.
The letters shown in figure 1 are for reference purposes in 6.1.3.2 to 6.1.3.8 only.
6.1.3.1 General shape
The part of the plate inside the pipe should be circular and concentric with the pipe centreline. The faces
6.1.3.1.1
of this plate should always be flat and parallel.
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Key
1 Annular slots
2 Carrier ring
3 Upstream face A
4 Downstream face B
5 Axial centreline
6 Direction of flow
7 Pressure tappings
8 Orifice plate
X Carrier ring with annular slot
Y Individual tappings
Figure 1 — Conical entrance orifice plate
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Table 2 — Minimum internal diameter of upsteam pipe for conical entrance orifice plates
Material Condition Minimum internal diameter
mm
brass, copper, lead, glass, smooth, without sediments 25
plastics, steel
new, cold drawn 25
new, seamless 25
new, welded 25
slightly rusty 25
rusty 50
slightly encrusted 200
bituminized, new or used 25
galvanized 25
cast iron bituminized 25
not rusty 50
rusty 200
6.1.3.1.2 Unless otherwise stated, the recommendations of 6.1.3.1.3 and 6.1.3.2 to 6.1.3.8 should apply only to
that part of the plate located within the pipe.
6.1.3.1.3 Care should be taken in the design of the orifice plate and its installation to ensure that the plastic
buckling and elastic deformation of the plate, due to the magnitude of the differential pressure or of any other stress,
does not cause the slope of the straight line defined in 6.1.3.2.1 to exceed 1 % under flowing conditions.
6.1.3.2 Upstream face A
6.1.3.2.1 The upstream face of the plate A should be flat when the plate is installed in the pipe with zero differential
pressure across it.
NOTE Provided 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 flat if the slope of a straight line
connecting any two points of its surface in relation to a plane perpendicular to the centreline is less than 0,5 %, ignoring the
inevitable local defects of the surface which are invisible to the naked eye.
-4
6.1.3.2.2 The upstream face of the orifice plate should have a roughness criterion R ≤ 10 d within a circle whose
a
diameter is not less than 1,5d and which is concentric with the orifice.
NOTE 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.
6.1.3.3 Downstream face B
The downstream face should be flat and parallel with the upstream face.
NOTE It is unnecessary to provide the same quality of surface finish for the downstream face as for the upstream face.
The flatness and surface condition of the downstream face can be judged by mere visual inspection.
6.1.3.4 Thicknesses e , E and E
1 1
6.1.3.4.1 The thickness, e , of the conical entrance should be 0,084d ± 0,003d.
1
6.1.3.4.2 The thickness, E , of the orifice plate for a distance of not less than 1,0d from the centreline axis should
1
not exceed 0,105d.
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6.1.3.4.3 The thickness, E, of the orifice plate at a distance greater than 1,0d from the centreline axis may exceed
0,105d but should not exceed 0,1D and the extra thickness if any should be on the downstream face.
6.1.3.4.4 The values of E measured at any point on the plate should not differ from each other by more than
1
0,001D.
6.1.3.4.5 The values of E measured at any point on the plate should not differ from each other by more than
0,005D.
6.1.3.5 Conical entrance
The upstream edge of the orifice should be bevelled at an angle of 45° ± 1°.
6.1.3.6 Parallel bore
The bore of the orifice should be parallel within ± 0,5° to the centreline.
6.1.3.6.1
The axial length, , of the parallel bore should be 0,021 0,003
6.1.3.6.2 e d ± d.
6.1.3.7 Edges H, I and G
6.1.3.7.1 The upstream edge H formed by the intersection of the conical entrance and the upstream face should
not be rounded.
6.1.3.7.2 The upstream edge I formed by the intersection of the parallel bore and the conical entrance should not
be rounded.
6.1.3.7.3 The upstream edges H and I and the downstream edge G should not have wire-edges, burrs, or any
peculiarities visible to the naked eye.
6.1.3.8 Diameter of orifice
6.1.3.8.1 The diameter of the orifice, d, should be taken as the mean value of a number of measurements of the
diameter distributed in axial planes and at approximately equal angles between adjacent measurements. At least
four measurements of the diameter should be made.
No diameter should differ by more than 0,05 % from the value of the mean diameter.
The parallel bore of the orifice should be cylindrical and perpendicular to the upstream face.
6.1.3.8.2
6.1.4 Pressure tappings
Corner tappings as specified in 8.2.2 of ISO 5167-1:1991 should be used with conical entrance orifice plates. Both
the upstream and downstream tappings should be the same.
6.1.5 Coefficients and corresponding uncertainties
6.1.5.1 The discharge coefficient, C, is equal to 0,734. The uncertainty on the value of C is 2 %.
6.1.5.2 The value of the expansibility factor, e, for the conical entrance orifice plates should be taken as the mean
of that for square-edged orifice plates and that for ISA 1932 nozzles specified in 8.3.2.2 and 9.1.6.3 of
ISO 5167-1:1991 respectively.
The values used should be calculated at the same conditions. The uncertainty on the expansibility factor, in percent,
is given by 33(1 2 e).
6.1.5.3 The uncertainties on other quantities should be determined in accordance with clause 11 of
ISO 5167-1:1991.
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6.2 Quarter-circle orifice plates
6.2.1 General
NOTE A quarter-circle orifice plate has the characteristic that its discharge coefficient remains constant down to a low
Reynolds number, thus making it suitable for measurement of flowrate of viscous fluids such as oil.
Quarter-circle orifice plates should be used and installed in accordance with clauses 6 and 7 of ISO 5167-1:1991.
6.2.2 Limits of use
The limits of use for quarter-circle orifice plates should be as follows:
d ≥ 15 mm
D ≤ 500 mm
The lower limit of pipe diameter, D, depends on the internal roughness of the upstream pipeline and should be in
accordance with table 3 and within the following limits:
0,245 ≤ β ≤ 0,6
2 4 -0,5
0,046 ≤ Cβ (1 2 β ) ≤ 0,326
5
Re ≤ 10 β
D
The lower limit of the Reynolds number, Re , is given by the following equation:
D
6 8
Re (min.) = 1000β + 9,4 × 10 (β 2 0,24)
D
For convenience, values of Re (min.) are given in table 4.
D
NOTE Within these limits, the value of β is chosen by the user taking into consideration parameters such as required
differential pressure, uncertainty, acceptable pressure loss and available static pressure.
Table 3 — Minimum internal diameter of upstream pipe for quarter-circle orifice plates
Material Condition Minimum internal diameter
mm
Brass, copper, lead, smooth, without sediments 25
glass, plastics
Steel new, cold drawn 25
new, seamless 25
new, welded 25
slightly rusty 50
rusty 100
slightly encrusted 200
bituminized, new 25
bituminized, used 75
galvanized 50
Cast iron bituminized 25
not rusty 50
rusty 200
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6.2.3 Description
NOTE The axial plane cross-section of the orifice plate is shown in figure 2.
The letters shown in figure 2 are for reference purposes in 6.2.3.2 to 6.2.3.7 only.
6.2.3.1 General shape
6.2.3.1.1 The part of the plate inside the pipe should be circular and concentric with the pipe centreline. The faces
of this plate should always be flat and parallel.
6.2.3.1.2 Unless otherwise stated, the recommendations of 6.2.3.1.3 and of 6.2.3.2 to 6.2.3.7 should apply only to
that part of the plate located within the pipe.
6.2.3.1.3 Care should be taken in the design of the orifice plate and its installation to ensure that the plastic
buckling and elastic deformation of the plate, due to the magnitude of the differential pressure or of any other stress,
does not cause the slope of the straight line defined in 6.2.3.2.1 to exceed 1 % under flowing conditions.
Key
1 Upstream face A
2 Upstream face B
3 Direction of flow
Figure 2 — Quarter-circle orifice plate
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6.2.3.2 Upstream face A
6.2.3.2.1 The upstream face of the plate A should be flat when the plate is installed in the pipe with zero differential
pressure across it.
NOTE Provided 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 flat if the slope of a straight line
connecting any two points of its surface in relation to a plane perpendicular to the centreline is less than 0,5 %, ignoring the
inevitable local defects of the surface which are invisible to the naked eye.
-4
6.2.3.2.2 The upstream face of the orifice plate should have a roughness criterion (R ≤ 10 d) within a circle
a
whose diameter is not less than 1,5d and which is concentric with the orifice.
NOTE 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.
6.2.3.3 Downstream face B
The downstream face should be flat and parallel with the upstream face.
NOTE It is unnecessary to provide the same quality of surface finish for the downstream face as for the upstream face.
The flatness and surface condition of the downstream face can be judged by mere visual inspection.
6.2.3.4 Thicknesses e and E
6.2.3.4.1 The thickness, e, of the bore section should be not less than 2,5 mm and should not exceed 0,1D.
Where the radius, , of the profile exceeds 0,1 , which is the case when β exceeds 0,571, the thickness
6.2.3.4.2 r D
of the plate should be reduced from r to 0,1D by removing metal from the upstream face.
6.2.3.4.3 When the thickness, E, of the orifice plate exceeds the radius, r, then the thickness of the plate should be
reduced to equal this radius by removing metal from the downstream face to form a new downstream face in a
recess of diameter 1,5 with its edge bevelled to 45 .
d °
6.2.3.4.4 The values of e measured at any point on
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