ISO/TR 15377:2007
(Main)Measurement of fluid flow by means of pressure-differential devices — Guidelines for the specification of orifice plates, nozzles and Venturi tubes beyond the scope of ISO 5167
Measurement of fluid flow by means of pressure-differential devices — Guidelines for the specification of orifice plates, nozzles and Venturi tubes beyond the scope of ISO 5167
ISO/TR 15377:2007 describes the geometry and method of use for conical-entrance orifice plates, quarter-circle orifice plates, eccentric orifice plates and Venturi tubes with 10,5 degree convergent angles. Recommendations are also given for square-edged orifice plates and nozzles under conditions outside the scope of ISO 5167.
Mesurage du débit des fluides au moyen d'appareils déprimogènes — Lignes directrices pour la spécification des diaphragmes, des tuyères et des tubes Venturi non couverts par l'ISO 5167
General Information
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Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 15377
Second edition
2007-02-01
Measurement of fluid flow by means of
pressure-differential devices —
Guidelines for the specification of orifice
plates, nozzles and Venturi tubes beyond
the scope of ISO 5167
Mesurage du débit des fluides au moyen d'appareils déprimogènes —
Lignes directrices pour la spécification des diaphragmes, des tuyères et
des tubes Venturi non couverts par l'ISO 5167
Reference number
ISO/TR 15377:2007(E)
©
ISO 2007
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ISO/TR 15377:2007(E)
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ii © ISO 2007 – All rights reserved
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ISO/TR 15377:2007(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Symbols . 1
5 Square-edged orifice plates and nozzles: With drain holes, in pipes below 50 mm
diameter, and as inlet and outlet devices . 3
5.1 Drain holes through the upstream face of the square-edged orifice plate or nozzle . 3
5.2 Square-edged orifice plates installed in pipes of diameter 25 mm u D < 50 mm . 4
5.3 No upstream or downstream pipeline . 5
6 Orifice plates (except square-edged). 8
6.1 Conical entrance orifice plates. 8
6.2 Quarter-circle orifice plates . 12
6.3 Eccentric orifice plates. 18
7 Venturi tubes with machined convergent of angle 10,5°. 23
7.1 General. 23
7.2 Description . 23
7.3 Limits of use. 23
7.4 Discharge coefficient. 24
7.5 Expansibility [expansion] factor . 24
7.6 Pressure loss . 24
7.7 Installation requirements . 24
Bibliography . 26
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ISO/TR 15377:2007(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, 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), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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.
ISO/TR 15377 was prepared by Technical Committee ISO/TC 30, Measurement of fluid flow in closed
conduits, Subcommittee SC 2, Pressure differential devices.
This second edition cancels and replaces the first edition (ISO/TR 15377:1998), which has been technically
revised. It incorporates Technical Corrigendum ISO/TR 15377:1998/Cor.1:1999.
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TECHNICAL REPORT ISO/TR 15377:2007(E)
Measurement of fluid flow by means of pressure-differential
devices — Guidelines for the specification of orifice plates,
nozzles and Venturi tubes beyond the scope of ISO 5167
1 Scope
This Technical Report describes the geometry and method of use for conical-entrance orifice plates, quarter-
circle orifice plates, eccentric orifice plates and Venturi tubes with 10,5° convergent angles.
Recommendations are also given for square-edged orifice plates and nozzles under conditions outside the
scope of ISO 5167.
NOTE The data on which this report is based are old or incomplete in some cases.
2 Normative references
The following referenced documents are indispensable for the application 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 5167-1:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular
cross-section conduits running full — Part 1: General principles and requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4006 and ISO 5167-1 apply.
4 Symbols
For the purposes of this document, the symbols given in Table 1 apply.
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ISO/TR 15377:2007(E)
Table 1 — Symbols
Dimensions
M: mass
Symbols Represented quantity SI unit
L: length
T: time
a Pressure-tapping hole diameter L m
C Discharge coefficient dimensionless
Diameter of orifice or throat of primary device at
d L m
operating conditions
Upstream internal pipe diameter at operating
D L m
conditions
d Diameter of pressure tappings L m
tap
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 flowrate MT kg/s
m
r Radius of profile L m
Arithmetical mean deviation of the (roughness)
R L m
a
profile
Re Reynolds number dimensionless
Re , Re Reynolds number referred to D or d dimensionless
D d
Re* Throat-tapping Reynolds number (= d Re /d) dimensionless
tap d
d
β Diameter ratio, β = dimensionless
D
−1 −2
∆p Differential pressure ML T Pa
ε Expansibility (expansion) factor dimensionless
κ Isentropic exponent dimensionless
λ Friction factor 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 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.
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ISO/TR 15377:2007(E)
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.
5.1.2 Square-edged orifice plates
If a drain hole is drilled through the orifice plate, the coefficient values specified in ISO 5167-2 should not be
used unless the following conditions are observed.
a) D 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 – 0,2d). The outer edge of the drain hole should be as close to
the pipe wall as practicable.
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
m
represented by the drain hole of diameter d , as shown in the following equation:
k
2
⎧⎫
⎛⎞d
⎪⎪
k
dd=+10,55 (1)
⎨⎬⎜⎟
m
d
⎪⎪⎝⎠m
⎩⎭
4−0,5
NOTE This equation is based on the assumption that the value for Cε(1 − β ) for flow through the drain hole is
10 % greater than the value for flow through the orifice.
When estimating the overall uncertainty of the flow measurement, the following additional percentage
uncertainty should be added arithmetically to the discharge coefficient percentage uncertainty:
2
⎛⎞d
k
55 (2)
⎜⎟
d
⎝⎠m
5.1.3 ISA 1932 nozzles
If a drain hole is drilled through the nozzle upstream face, the coefficient values specified in ISO 5167-3
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 0,1d and no part of the hole should lie within a circle,
concentric with the throat, of diameter (D – 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.
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ISO/TR 15377:2007(E)
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
m
drain hole of diameter d , as shown in the following equation:
k
2
⎧⎫
⎛⎞
d
⎪⎪
k
dd=+10,40 (3)
⎨⎬⎜⎟
m
d
⎝⎠m
⎪⎪
⎩⎭
4−0,5
NOTE This equation is based on the assumption that the value for Cε(1 − β ) for flow through the drain hole is
20 % less than the value for flow through the throat of the nozzle.
When estimating the overall uncertainty of the flow measurement, the following additional percentage
uncertainty should be added arithmetically to the discharge coefficient percentage uncertainty:
2
⎛⎞
d
k
40 (4)
⎜⎟
d
⎝⎠m
5.1.4 Long radius nozzles
Drain holes through these primary elements should not be used.
5.2 Square-edged orifice plates installed in pipes of diameter 25 mm u D < 50 mm
5.2.1 General
Orifice plates should be installed and manufactured in accordance with ISO 5167-2.
5.2.2 Limits of use
When square-edged orifice plates are installed in pipes of bore 25 mm 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
plastic 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 roughness should be in accordance with ISO 5167-2:2003, 5.3.1.
b) Corner tappings should be used, preferably of the carrier ring type detailed in ISO 5167-2:2003,
Figure 4 a).
c) The diameter ratio, β, should be within the range 0,5 u β u0,7.
NOTE It is possible to have 0,23 u β < 0,5, but the uncertainty increases significantly if d < 12,5 mm.
5.2.3 Discharge coefficients and corresponding uncertainties
[1]
The Reader-Harris/Gallagher equation for corner tappings given in 5.3.2.1 of ISO 5167-2:2003 should be
used for deriving the discharge coefficients, provided the pipe Reynolds numbers are within the limits given in
ISO 5167-2:2003, 5.3.1.
An additional uncertainty of 0,5 % should be added arithmetically to the uncertainty derived from 5.3.3.1 of
ISO 5167-2:2003.
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ISO/TR 15377:2007(E)
5.3 No upstream or downstream pipeline
5.3.1 General
This clause should apply where there is no pipeline on either the upstream or the downstream side of the
device or on both the upstream and the 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, and
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) can 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 has to be not less than 33 times the area of the orifice or throat through which the tank is discharged.
The distance of the upstream tapping (i.e. the tapping in the large space) from the orifice or nozzle centreline
should be greater than 4d.
The upstream 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.
The downstream tapping should be located as specified for corner tappings in ISO 5167-2. 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 tapping should be used.
NOTE 2 When the upstream and downstream tappings are at different horizontal levels, it may be necessary to make
allowance for the difference in hydrostatic head. This is usually done by reading the differential-pressure transmitter with
no fluid flow and making an appropriate correction.
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 5 of ISO 5167-2:2003.
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 W 12,5 mm;
⎯ downstream there is either a large space or a pipeline whose diameter is not less than 2d;
⎯ Re W 3 500.
d
NOTE 1 It is possible to have 12,5 mm > d > 6 mm, but the uncertainty increases significantly if d < 12,5 mm.
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ISO/TR 15377:2007(E)
NOTE 2 Provided that β u 0,2 and d W 12,5 mm, the Reader-Harris/Gallagher (1998) equation given in 5.3.2.1 of
ISO 5167-2:2003 can be used in a pipeline for Re W 3 500 with an uncertainty on the value of the discharge coefficient, C,
d
of 1 % (if Re < 5 000).
D
5.3.2.2.3 The discharge coefficient, C, is given by
0,7
6
⎛⎞
10
C=+0,596 1 0,000 521⎜⎟ (5)
⎜⎟
Re
d
⎝⎠
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:
2 1
1/κ
⎡⎤
⎛⎞p
2
⎢⎥
ε=−1 0,351 1− (6)
⎜⎟
⎢⎥
p
⎝⎠1
⎣⎦
When ∆p/p and κ are assumed to be known without error, the relative uncertainty of the value of e is equal to
1
∆p
3,5 %.
κ p
1
Test results for the determination of ε 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 whose isentropic exponent is known.
5.3.2.3 ISA 1932 nozzles
5.3.2.3.1 ISA 1932 nozzles should be manufactured in accordance with 5.1 of ISO 5167-3:2003.
5.3.2.3.2 The limits of use for ISA 1932 nozzles where there is flow from a large space should be as
follows:
⎯ d W 11,5 mm;
⎯ downstream there is either a large space or a pipeline whose diameter is not less than 2d;
⎯ Re W 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 expected to be
no better than 1 %.
5.3.2.3.4 The expansibility factor, ε, is given by the following equation and is only applicable if p /p W 0,75:
2 1
0,5
2
⎧⎫
⎛⎞
()κκ-1/
κ⎛⎞
κτ 1−τ
⎪⎪
⎜⎟
ε= ⎜⎟ (7)
⎨⎬
⎜⎟
⎜⎟
κτ−−11
⎜⎟
⎪⎪
⎝⎠
⎝⎠
⎩⎭
The relative uncertainty of the value of ε is equal to 2∆p/p %.
1
5.3.2.4 Venturi nozzle
5.3.2.4.1 Venturi nozzles should be manufactured in accordance with 5.3 of ISO 5167-3:2003.
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ISO/TR 15377:2007(E)
5.3.2.4.2 The limits of use for Venturi nozzles where there is flow from a large space should be as follows:
⎯ d W 50 mm;
⎯ downstream there is either a large space or a pipeline whose diameter is not less than 2d;
5 6
⎯ 3 × 10 u Re u 3 × 10 .
d
5.3.2.4.3 The discharge coefficient, C, is equal to 0,985 8. The uncertainty in the value of C is expected to
be no better than 1,5 %.
5.3.2.4.4 The expansibility factor, ε, is given by the following equation and is only applicable if p /p W 0,75:
2 1
0,5
2
⎧⎫
⎛⎞
()κκ-1/
κ⎛⎞
κτ 1−τ
⎪⎪
⎜⎟
ε= (8)
⎜⎟
⎨⎬
⎜⎟
⎜⎟
κτ−−11
⎜⎟
⎪⎪
⎝⎠
⎝⎠
⎩⎭
The relative uncertainty of the value of ε is equal to 4 ∆p/p %.
1
5.3.3 Flow into a large space (no downstream pipeline)
5.3.3.1 General
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 upstream tapping should be located as specified for corner tappings in ISO 5167-2 and in ISO 5167-3 for
orifice plates and nozzles respectively.
The distance of the downstream tapping (i.e. the tapping in the large space) from the orifice or nozzle
centreline should be greater than 4d.
For Venturi nozzles, the throat tapping should be used.
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 Where the upstream and downstream tappings are at different horizontal levels, it may be necessary to make
allowance for the difference in hydrostatic head.
5.3.3.2 Square-edged orifice plates with corner tappings
5.3.3.2.1 Square-edged orifice plates with corner tappings should be manufactured in accordance with
Clause 5 of ISO 5167-2:2003.
5.3.3.2.2 Where 25 mm u D < 50 mm, the limits given in 5.2.2 and 5.2.3 should apply.
Where 50 mm u D u 1 000 mm, the limits given in 5.3.1 of ISO 5167-2:2003 should apply.
5.3.3.2.3 Where 25 mm u D < 50 mm, the coefficients and uncertainties given in 5.2.3 should apply.
Where 50 mm u D u 1 000 mm, the coefficients and uncertainties given in 5.3.2 and 5.3.3 of
ISO 5167-2:2003 should apply, except that an additional uncertainty of 0,4 % is to be added arithmetically to
the uncertainty derived from 5.3.3.1 of ISO 5167-2:2003.
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ISO/TR 15377:2007(E)
5.3.3.3 ISA 1932 nozzles and Venturi nozzles
5.3.3.3.1 ISA 1932 nozzles and Venturi nozzles should be manufactured in accordance with 5.1 or 5.3 of
ISO 5167-3:2003.
5.3.3.3.2 The limits given in 5.1.6.1 or 5.3.4.1 of ISO 5167-3:2003 should apply.
5.3.3.3.3 The coefficients and uncertainties given in 5.1.6.2, 5.1.6.3 and 5.1.7 or in 5.3.4.2, 5.3.4.3 and
5.3.5 of ISO 5167-3:2003 should apply, except that in the case of an ISA 1932 nozzle an additional
uncertainty of 0,4 % should be added arithmetically to the uncertainty derived from 5.1.7.1 of ISO 5167-3:2003.
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 the 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 Clause 6 of ISO 5167-1:2003
and Clause 6 of ISO 5167-2:2003.
6.1.2 Limits of use
The limits of use for conical entrance orifice plates should be as follows:
⎯ d > 6 mm;
⎯ D u 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 u β u 0,316
5
⎯ 80 u Re u 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
The axial plane cross-section of the orifice plate is shown in Figure 1.
NOTE The letters shown in Figure 1 are for reference purposes in 6.1.3.2 to 6.1.3.8 and 6.1.4 only; 6.1.4 refers to
5.2.3 of ISO 5167-2:2003.
6.1.3.1 General shape
6.1.3.1.1 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.
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ISO/TR 15377:2007(E)
Key
1 annular slots G downstream edge
2 carrier ring H, I upstream edges
3 upstream face A X carrier ring with annular slot
4 downstream face B Y individual tappings
5 axial centreline f is the thickness of the slot
6 direction of flow c is the length of upstream ring
7 pressure tappings c′ is the length of the downstream ring
8 orifice plate a is the width of annular slot or diameter of single tapping
g, h are the dimensions of the annular chamber
Figure 1 — Conical entrance orifice plate
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ISO/TR 15377:2007(E)
Table 2 — Minimum internal diameter of upstream pipe for conical entrance orifice plates
Minimum internal diameter
Material Condition
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, do 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.
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
when the maximum gap between the flat portion of the upstream face of the plate and a straight edge of
length D, laid across any diameter of the plate, is less than 0,005(D − d − 2e )/2; i.e. the slope is less than
1
0,5 % when the orifice plate is examined prior to insertion into the meter line (see also ISO 5167-2:2003,
Figure 2). The critical area is in the vicinity of the orifice bore. The uncertainty requirements for this dimension
may be met using feeler gauges.
−4
6.1.3.2.2 The upstream face of the orifice plate should have a roughness criterion R u 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.
6.1.3.3 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.
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ISO/TR 15377:2007(E)
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
1
should not exceed 0,105d.
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 If D W 200 mm, the difference between the values of E measured at any point of the plate should
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not be greater than 0,001D. If D < 200 mm, the difference between the values of E measured at any point of
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the plate should not be greater than 0,2 mm.
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
6.1.3.6.1 The bore of the orifice should be parallel within ± 0,5° to the ce
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