Tiêu chuẩn iso tr 15377 2007

Microsoft Word C040029e doc Reference number ISO/TR 15377 2007(E) © ISO 2007 TECHNICAL REPORT ISO/TR 15377 Second edition 2007 02 01 Measurement of fluid flow by means of pressure differential devices[.]

Drain holes through the upstream face of the square-edged orifice plate or nozzle

Square-edged orifice plates and nozzles with drain holes may be used, installed and manufactured in accordance with the following guidelines

When drilling a drain hole through an orifice plate, the coefficient values in ISO 5167-2 are only applicable if specific conditions are met: the diameter $D$ must exceed 100 mm, the drain hole diameter should not surpass $0.1d$, and it must be positioned outside a concentric circle with a diameter of $D - 0.2d$ Additionally, the drain hole should be as close to the pipe wall as possible, deburred, and have a sharp upstream edge Single pressure tappings must be oriented between 90° and 180° relative to the drain hole, and the measured orifice diameter $d_m$ should be adjusted to account for the extra area introduced by the drain hole of diameter $d_k$.

NOTE This equation is based on the assumption that the value for Cε(1 − β 4 ) −0,5 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:

When drilling a drain hole through the nozzle's upstream face, the coefficient values from ISO 5167-3 are only applicable if specific conditions are met: the value of β must be less than 0.625, the drain hole diameter should not exceed 0.1d and must be positioned outside a concentric circle with a diameter of (D - 0.2d), the length of the drain hole must not exceed 0.1D, and the hole should be deburred with a sharp upstream edge.

Copyright International Organization for Standardization

Provided by IHS under license with ISO

According to ISO/TR 15377:2007(E), single pressure tappings must be positioned at an angle between 90° and 180° relative to the drain hole Additionally, the measured diameter, denoted as \$d_m\$, should be adjusted to account for the extra throat area indicated by the drain hole's diameter, \$d_k\$, as specified in the relevant equation.

NOTE This equation is based on the assumption that the value for Cε(1 − β 4 ) −0,5 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:

Drain holes through these primary elements should not be used.

Square-edged orifice plates installed in pipes of diameter 25 mm u D < 50 mm

Orifice plates should be installed and manufactured in accordance with ISO 5167-2

When installing square-edged orifice plates in pipes with a bore of 25 mm to 50 mm, it is essential to ensure that the pipes have high-quality internal surfaces, such as drawn copper, brass tubes, glass, plastic pipes, or fine-machined stainless steel tubes for corrosive fluids like water, adhering to ISO 5167-2:2003 standards for roughness Additionally, corner tappings should preferably be of the carrier ring type as specified in ISO 5167-2:2003, Figure 4 a) Furthermore, the diameter ratio, β, must be maintained within the range of 0.5 to 0.7.

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

The Reader-Harris/Gallagher equation, as specified in section 5.3.2.1 of ISO 5167-2:2003, is essential for calculating discharge coefficients for corner tappings This equation is applicable when the pipe Reynolds numbers fall within the specified limits outlined in section 5.3.1 of the same standard.

An additional uncertainty of 0,5 % should be added arithmetically to the uncertainty derived from 5.3.3.1 of ISO 5167-2:2003

No upstream or downstream pipeline

This clause is applicable when there is no pipeline present on either the upstream or downstream side of the device, or on both sides It pertains to the flow from a large space into a pipe or the reverse, as well as 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

For optimal performance, the upstream space of the device must be sufficiently large, defined by three key criteria: first, there should be no wall within 4d of the device's axis or the upstream face of the orifice or nozzle; second, the fluid velocity at any point more than 4d from the device must be less than 3% of the velocity at the orifice or throat; and third, the downstream pipeline diameter should be at least 2d.

To ensure optimal flow conditions, an upstream pipeline with a diameter exceeding 8d (where β < 0.125) is classified as a large space Additionally, to prevent disturbances from draughts, swirl, and jet effects, the fluid must enter the space uniformly across an area at least 33 times larger than the orifice or throat For instance, when flow is driven by a liquid level drop in a tank, the surface area of the liquid must be no less than 33 times the area of the discharge orifice or throat.

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

For optimal performance, the upstream tapping should be positioned in a wall that is perpendicular to the orifice plane and within a distance of 0.5d from it Alternatively, the tapping can be placed in open space; however, in large areas such as rooms, it is essential to shield the tapping from draughts.

Downstream tappings must be positioned according to the corner tapping specifications outlined in ISO 5167-2 In cases where the downstream side features a large space, the tapping should mirror the upstream tapping placement, with the exception of Venturi nozzles, which require the use of throat tappings.

When the upstream and downstream tappings are positioned at varying horizontal levels, it is essential to account for the difference in hydrostatic head This is typically achieved by measuring the differential-pressure transmitter without fluid flow and applying the necessary 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:

⎯ downstream there is either a large space or a pipeline whose diameter is not less than 2d;

NOTE 1 It is possible to have 12,5 mm > d > 6 mm, but the uncertainty increases significantly if d < 12,5 mm

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 d W 3 500 with an uncertainty on the value of the discharge coefficient, C, of 1 % (if Re D < 5 000)

5.3.2.2.3 The discharge coefficient, C, is given by

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 2 /p 1 > 0,75:

When ∆p/p 1 and κ are assumed to be known without error, the relative uncertainty of the value of e is equal to

Test results for determining the isentropic exponent (ε) are available for air, steam, and natural gas Nonetheless, there is no known objection to applying the same formula to other gases and vapors with a known isentropic exponent.

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:

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 2 /p 1 W 0,75:

The relative uncertainty of the value of ε is equal to 2∆p/p 1 %

5.3.2.4.1 Venturi nozzles should be manufactured in accordance with 5.3 of ISO 5167-3:2003

5.3.2.4.2 The limits of use for Venturi nozzles where there is flow from a large space should be as follows:

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 2 /p 1 W 0,75:

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)

For optimal performance, the downstream area of the device is deemed sufficiently spacious if no wall is located within a distance of 4d from the device's axis or the downstream side 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

For optimal performance, the downstream tapping should be positioned in a wall that is perpendicular to the orifice plane and within a distance of 0.5d from it While the tapping can be placed in open space, it is essential to shield it from draughts, especially in large areas like rooms.

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

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 u1 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

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

The coefficients and uncertainties specified in sections 5.1.6.2, 5.1.6.3, and 5.1.7, as well as in sections 5.3.4.2, 5.3.4.3, and 5.3.5 of ISO 5167-3:2003, should be utilized However, for an ISA 1932 nozzle, an additional uncertainty of 0.4% must be added arithmetically to the uncertainty derived from section 5.1.7.1 of ISO 5167-3:2003.

6 Orifice plates (except square-edged)

Conical entrance orifice plates

A conical entrance orifice plate maintains a constant discharge coefficient even at low Reynolds numbers, making it ideal for measuring the flow rate of viscous fluids like oil Unlike other orifice plates, its discharge coefficient remains consistent across various diameter ratios as 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

The limits of use for conical entrance orifice plates should be as follows:

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:

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

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

6.1.3.1.1 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

X carrier ring with annular slot

The individual tappings are defined by the thickness of the slot $ f $, the length of the upstream ring $ c $, and the length of the downstream ring $ c' $ Additionally, $ a $ represents the width of the annular slot or the diameter of a single tapping, while $ g $ and $ h $ denote the dimensions of the annular chamber.

Figure 1 — Conical entrance orifice plate

Table 2 — Minimum internal diameter of upstream pipe for conical entrance orifice plates

Minimum internal diameter Material Condition mm

Brass, copper, lead, glass, plastics, steel smooth, without sediments 25 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

When designing and installing the orifice plate, it is crucial to prevent plastic buckling and elastic deformation caused by differential pressure or other stresses This ensures that the slope of the straight line defined in section 6.1.3.2.1 remains within 1% during flowing conditions.

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

To ensure accurate measurements, the flatness of the orifice plate can be assessed when it is removed from the pipe, provided that the mounting method does not cause distortion The plate is deemed flat if the maximum gap between its upstream face and a straight edge of length D is less than \$0.005(D - d - 2e_1)/2\$, indicating a slope of less than 0.5% This evaluation should be conducted before the plate is inserted into the meter line, particularly focusing on the critical area near the orifice bore Compliance with uncertainty requirements for this measurement can be achieved using feeler gauges, as referenced in ISO 5167-2:2003, Figure 2.

6.1.3.2.2 The upstream face of the orifice plate should have a roughness criterion R a u 10 −4 d within a circle whose diameter is not less than 1,5d and which is concentric with the orifice

To ensure proper installation of the orifice plate, it is essential to include a visible distinctive mark that indicates the upstream face, aligning it correctly with the flow direction.

The downstream face should be flat and parallel with the upstream face

It is not essential to achieve the same surface finish quality on the downstream face as on the upstream face The flatness and surface condition of the downstream face can be assessed through simple visual inspection.

6.1.3.4.1 The thickness, e 1 , of the conical entrance should be 0,084d ± 0,003d

6.1.3.4.2 The thickness, E 1 , of the orifice plate for a distance of not less than 1,0d from the centreline axis should not exceed 0,105d

The orifice plate thickness, denoted as E, can exceed 0.105d at a distance greater than 1.0d from the centerline axis, but it must not surpass 0.1D Any additional thickness should be applied to the downstream face of the plate.

For a diameter (D) of 200 mm or greater, the variation in E1 values measured at any point on the plate must not exceed 0.001D Conversely, if the diameter is less than 200 mm, the difference in E1 values should not surpass 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

The upstream edge of the orifice should be bevelled at an angle of 45° ± 1°

6.1.3.6.1 The bore of the orifice should be parallel within ± 0,5° to the centreline

6.1.3.6.2 The axial length, e, of the parallel bore should be 0,021d ± 0,003d

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

The orifice diameter, denoted as $d$, should be determined by calculating the mean value from multiple measurements taken in axial planes, ensuring that the measurements are evenly spaced at approximately equal angles.

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

6.1.3.8.2 The parallel bore of the orifice should be cylindrical and perpendicular to the upstream face

Corner tappings as specified in 5.2.3 of ISO 5167-2:2003 should be used with conical entrance orifice plates Both the upstream and downstream tappings should be the same

6.1.5.1 The discharge coefficient, C, is equal to 0,734 The uncertainty on the value of C is 2 %

The expansibility factor $ e $ for conical entrance orifice plates should be considered as the arithmetic mean of the values for square-edged orifice plates and ISA 1932 nozzles, as outlined in section 5.3.2.2.

ISO 5167-2: 2003 and 5.1.6.3 of ISO 5167-3:2003, respectively

The values used should be calculated under the same conditions The uncertainty on the expansibility factor, in percent, is given by 33(1 − ε)

6.1.5.3 The uncertainties on other quantities should be determined in accordance with Clause 8 of

Quarter-circle orifice plates

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 the measurement of the flowrate of viscous fluids such as oil

Quarter-circle orifice plates should be used and installed in accordance with Clause 6 of ISO 5167-1:2003 and

The limits of use for quarter-circle orifice plates should be as follows:

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 such that:

The lower limit of the Reynolds number, Re D , is given by the following equation:

For convenience, values of Re D (min.) are given in Table 4

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

Minimum internal diameter Material Condition mm

Brass, copper, lead, glass, plastics smooth, without sediments 25

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

The axial plane cross-section of the orifice plate is shown in Figure 2

NOTE The letters shown in Figure 2 are for reference purposes in 6.2.3.2 to 6.2.3.7 only

6.2.3.1.1 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

Figure 2 — Quarter-circle orifice plate

To ensure accurate measurements of flatness, it is essential to demonstrate that the mounting method does not distort the plate When the plate is detached from the pipe, it can be assessed for flatness The plate is deemed flat if the maximum gap between its upstream face and a straight edge of length D, placed across any diameter, is below specified values.

The slope is below 0.5% when the orifice plate is inspected before being placed into the meter line, as illustrated in Figure 2 of ISO 5167-2:2003 The critical area is located near the orifice bore, which contributes to the overall uncertainty.

6.2.3.2.2 The upstream face of the orifice plate should have a roughness criterion R a u 10 −4 d within a circle whose diameter is not less than 1,5d and which is concentric with the orifice

To ensure proper installation of the orifice plate in relation to the flow direction, it is beneficial to include a visible distinctive mark on the upstream face of the plate.

It is not essential to achieve the same surface finish quality on the downstream face as on the upstream face The flatness and surface condition of the downstream face can be assessed through simple visual inspection.

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

When the radius, r, of the profile is greater than 0.1D, specifically when β exceeds 0.571, it is necessary to reduce the plate thickness from r to 0.1D by removing metal from the upstream face.

When the orifice plate thickness, E, surpasses the radius, r, it is essential to reduce the plate thickness to match the radius This can be achieved by removing metal from the downstream face, creating a new downstream face with a recess of diameter 1.5d and beveling the edge to 45°.

If the diameter $ D $ is 200 mm or greater, the variation in the measured values of $ e $ at any point on the plate should not exceed $ 0.001D $ Conversely, if $ D $ is less than 200 mm, the difference in the measured values of $ e $ should not be greater than 0.2 mm.

6.2.3.5.1 The profile of the upstream edge should be circular and of radius r with its centre on the downstream face of the plate

NOTE The profile might not be a full quarter circle owing to the limit recommended in 6.2.3.4.2

6.2.3.5.2 The radius, r, of the profile should be determined from the following equation: r/d = 3,17 × 10 −6 e 16,8 β + 0,055 4e 1,016 β + 0,029 (10) to within ±0,05r

For convenience, values of r/d are given in Table 4

The radius of the profile should be the same for all sections to within ±0,01r

NOTE The permitted variation in profile radius allows an orifice plate designed for a given D to be used in pipes of 0,95D to 1,05D

6.2.3.5.3 The tangent to the profile at the downstream edge should be perpendicular to the upstream face of the plate to within ±1°

6.2.3.5.4 The profile surface should not have wire edges, burrs or any peculiarities visible to the naked eye

The downstream edge of the orifice should be square and should not have wire edges, burrs or any peculiarities visible to the naked eye

The orifice diameter, denoted as $d$, should be determined by averaging multiple measurements taken in axial planes, ensuring they are spaced at approximately equal angles It is essential to conduct at least four diameter measurements for accuracy.

For pipes with a diameter of up to 40 mm, it is recommended to use corner tappings in accordance with section 5.2.3 of ISO 5167-2:2003, along with quarter-circle orifice plates For pipes that are 40 mm or larger, alternative corner tappings can be utilized.

5.2.3 of ISO 5167-2:2003 or flange tappings as specified in 5.2.2 of ISO 5167-2:2003 should be used with quarter-circle orifice plates

The discharge coefficient, C, is given by the following equation:

The uncertainty on the value of C is 2 % when β > 0,316 and 2,5 % when βu 0,316

For convenience, Table 4 gives values of C as a function of β

For the two tapping arrangements, the empirical formula for computing the expansibility (expansion) factor, ε, is as follows and is only applicable if p 2 /p 1 W 0,75:

This formula is applicable only within the range of the limits of use given in 6.2.2

Test results for the determination of the isentropic exponent (ε) are available for air, steam, and natural gas Nonetheless, there are no known objections to applying the same formula to other gases and vapors with a known isentropic exponent.

When β, ∆p/p 1 and κ are assumed to be known without error, the relative uncertainty of the value of ε is equal to

Table 4 — Discharge coefficients for quarter-circle orifice plates β C r/d Re D (min.)

Eccentric orifice plates

The eccentric orifice plate is engineered to allow unobstructed flow of gas, liquid, and sediments in a fluid, while also being easy to manufacture and install It is essential to use eccentric orifice plates in compliance with Clause 6 of ISO 5167-1:2003 and to follow the installation guidelines outlined in the same clause.

The limits of use for eccentric orifice plates should be as follows:

The eccentric orifice plate is shown in Figure 3

NOTE The letters shown in Figure 3 are for reference purposes in 6.3.3.2 to 6.3.3.9 only

The plate section within the pipe must be circular, with the orifice tangentially aligned to the pipe's interior Additionally, the surfaces of the plate should be flat and parallel.

6.3.3.1.2 Unless otherwise stated, the recommendations of 6.3.3.1.3 and of 6.3.3.2 to 6.3.3.9 apply only to that part of the plate located within the pipe

To ensure accurate measurements of flatness, it is essential to demonstrate that the mounting method does not distort the plate When the plate is detached from the pipe, it can be assessed for flatness The plate is deemed flat if the maximum gap between its upstream face and a straight edge of length D, placed across any diameter, is less than 0.005(D − d)/2, indicating a slope of less than approximately 0.005.

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

The upstream face of the orifice plate must meet a roughness criterion of \$R_{a} \leq 10^{-4} d\$ within a circular area with a diameter of at least \$1.5d\$, centered on the orifice, excluding the section beyond diameter \$D\$ (refer to section 6.3.3.1.2).

NOTE It is useful to provide a distinctive mark, which is visible even when the orifice plate is installed, to show that

It is not essential to maintain the same surface finish quality for the downstream face as for the upstream face, as the flatness and surface condition of the downstream face can be assessed through visual inspection.

4 outside diameter of the plate

6.3.3.4.1 The thickness, e, of the orifice should be between 0,005D and 0,02D

6.3.3.4.2 The values of e measured at any point on the orifice should not differ from each other by more than 0,001D

6.3.3.4.3 The thickness, E, of the orifice plate should be between e and 0,05D

For a diameter (D) of 200 mm or greater, the variation in the measured values of E at any point on the plate should not exceed 0.001D Conversely, if the diameter is less than 200 mm, the difference in the measured values of E should be limited to a maximum of 0.2 mm.

6.3.3.5.1 If the thickness, E, of the plate exceeds the thickness, e, of the orifice, the plate should be bevelled on the downstream side and the bevelled surface should be well finished

6.3.3.5.2 The angle of bevel, f, should be 45° ± 15°

6.3.3.5.3 The plate should not be bevelled if its thickness, E, is less than or equal to 0,02D

To prevent potential entrapment of debris in the downstream bevel, it is advisable to limit the thickness, E, of the plate to match the orifice thickness, e, thereby eliminating the need for a bevel.

6.3.3.6.1 The upstream edge G and the downstream edges H and I should not have wire edges, burrs or any peculiarities visible to the naked eye

6.3.3.6.2 The upstream edge G should be considered sharp if the edge radius is not greater than 0,000 4d

If the diameter $d$ is 125 mm, a simple visual inspection can confirm compliance with this recommendation, ensuring that the edge does not reflect light when observed with the naked eye.

If the diameter is less than 125 mm, a visual inspection alone is inadequate; however, this requirement can be deemed met if the upstream face of the orifice plate features a finely finished radial cut extending from the center outward.

However, if there is any doubt as to whether this recommendation is satisfied, the edge radius should actually be measured

The orifice diameter, denoted as $d$, should be determined by calculating the mean value from multiple measurements taken in axial planes, ensuring that the measurements are distributed at approximately equal angles between each adjacent measurement.

At least four measurements of the diameter should be made

6.3.3.7.2 The parallel bore of the orifice should be cylindrical and perpendicular to the upstream face

6.3.3.7.3 The diameter, d, should be between 0,46D and 0,84D

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

For accurate measurement of reverse flows using an orifice plate, it is essential that the plate remains unbeveled and that both faces adhere to the specifications outlined for the upstream face in section 6.3.3.2.

The thickness of the plate, denoted as E, must match the thickness of the orifice, referred to as e, as outlined in section 6.3.3.4.1 Additionally, the specifications for the two edges of the orifice should align with those provided for the upstream edge in section 6.3.3.6.2.

Eccentric orifice plates should be used with a single pair of corner tappings as specified in ISO 5167-2:2003,

5.2.3, except that the pressure-tapping hole diameter, a, should be within the limits 3 mm u a u 10 mm

NOTE In an eccentric orifice plate, the orifice is not concentric with the pipe bore and, consequently, the pressure difference depends on the angular position of the pressure tappings

For optimal accuracy, pressure tappings should be positioned directly opposite the point where the orifice meets the pipe wall This Technical Report's discharge coefficient values are derived from this specific arrangement.

However, rotating the tappings by only 90° from the ideal position would result in an error of not more than

Positioning pressure tappings directly opposite each other at the top or bottom of a pipe can lead to issues like air entrainment or dirt blockage To mitigate these problems, it is acceptable to rotate the tappings by 30° from the vertical centerline, ensuring minimal impact on flow metering accuracy.

6.3.4.1 The discharge coefficient, C, is given by the following equation:

For convenience, Table 5 gives values of C as a function of β

When β, D, Re D and k/D are assumed to be known without error, the uncertainty of the value of C is 1 % when βu 0,75

General

Reducing the convergent angle of Venturi tubes in high-pressure gas applications offers notable advantages, including a decrease in the increase of the discharge coefficient with Reynolds number and a reduction in calibration curve humps This approach allows for the development of a discharge coefficient equation that aligns more closely with a physical model than those established for Venturi tubes as outlined in ISO 5167-4:2003.

Description

Venturi tubes featuring a machined convergent angle of 10.5° are consistent with the specifications outlined in sections 5.1 to 5.4 of ISO 5167-4:2003 Notably, both Figure 1 and section 5.2.3 of ISO 5167-4:2004 indicate that the conical convergent section B has an included angle of 10.5° ± 1° Consequently, the overall length of the convergent B, measured parallel to the centerline of the Venturi tube, is approximately 5.4 times the difference between the diameters D and d.

Limits of use

Venturi tubes with machined convergent of angle 10,5° can be used over the range

R a is the arithmetical mean deviation of the roughness profile of the Venturi tube;

Re* is a type of throat-tapping Reynolds number (based on the tapping diameter and the throat velocity) obtained from

= d (15) d tap is the diameter of the pressure tappings

The limits for using Venturi tubes to determine the discharge coefficient are based on the specifications outlined in section 7.4 It is acceptable to use diameters greater than 160 mm as long as the Reynolds number limits for both $Re_D$ and $Re^*$ are satisfied However, altering the diameter of the pressure tappings can lead to increased uncertainty in the discharge coefficient Additionally, the sharpness of the pressure tappings, especially in the throat area, plays a crucial role in the accuracy of the measurements.

Discharge coefficient

The discharge coefficient is a function of the relative roughness of the Venturi tube, of the throat Reynolds number and of the throat-tapping Reynolds number It is given by

The friction factor, denoted as \$\lambda\$, in the throat is represented by the equation \$C = -\lambda\$, where \$\lambda_{sp}\$ is the value that would be expected if the throat were a long straight pipe with roughness \$R_a\$ This value is derived from the Colebrook-White Equation.

The relative uncertainty of the discharge coefficient is equal to 1 %

NOTE The equation given here is based on work described in References [2] to [4] A total of eight Venturi tubes were used.

Expansibility [expansion] factor

The expansibility [expansion] factor and its uncertainty are as given in 5.6 and 5.8 of ISO 5167-4:2003.

Pressure loss

Pressure loss measurements across Venturi tubes with a convergent angle of 10.5° have not been conducted However, the guidelines outlined in section 5.9 of ISO 5167-4:2003 are applicable, and Annex C of the same standard provides useful guidance.

Installation requirements

The installation requirements for Venturi tubes with a machined convergent angle of 10.5° align with those specified in Clause 6 of ISO 5167-4:2003 However, it is important to note that in Table 1, the specifications for "Single 90° bend" in columns 2 and 3 differ.

“Two or more 90° bends in the same plane or different planes” are replaced by the appropriate columns in

NOTE 1 Lengths are not shown in Table 7 for fittings where no data have been obtained for Venturi tubes with machined convergent of angle 10,5° (see Reference [5])

NOTE 2 The text below Table 1 of ISO 5167-4:2003 applies and, for example, includes footnotes a to d

Table 7 — Required straight lengths for Venturi tubes with machined convergent of angle 10,5°

Single 90° bend a Two or more 90° bends in the same plane or different planes a

The orifice plate discharge coefficient equation, as outlined in ISO 5167-1, is discussed in detail by Reader-Harris and Sattary in their paper presented at the 14th North Sea Flow Measurement Workshop This research, published by the National Engineering Laboratory in October 1996, provides essential insights into flow measurement techniques.

[2] R EADER -H ARRIS , M.J., B RUNTON , W.C., G IBSON , J.J., H ODGES , D and N ICHOLSON , I.G Discharge coefficients of Venturi tubes with standard and non-standard convergent angles Flow Measurement and Instrumentation, 12, No 2, pp 135-145, April 2001

[3] READER-HARRIS, M.J., BRUNTON, W.C., HODGES, D and NICHOLSON, I.G Venturi tubes: improved shape Proc of 20th North Sea Flow Measurement Workshop, St Andrews, Scotland National

Engineering Laboratory, East Kilbride, Glasgow, October 2002

[4] READER-HARRIS, M.J., GIBSON, J.J., HODGES, D., NICHOLSON, I.G and RUSHWORTH, R Venturi tubes with a 10,5° convergent angle: development of a discharge coefficient equation Proc of FLOMEKO

2005, Peebles, Scotland National Engineering Laboratory, East Kilbride, Glasgow, June 2005

The study by Reader-Harris, Rushworth, and Gibson, presented at the 22nd North Sea Flow Measurement Workshop in St Andrews, Scotland, investigates the installation effects on Venturi tubes with a convergent angle of 10.5° The research was conducted by the National Engineering Laboratory in East Kilbride, Glasgow, and was published in October 2004.

[6] ISO 5167-2:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full — Part 2: Orifice plates

[7] ISO 5167-3:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full — Part 3: Nozzles and Venturi nozzles

[8] ISO 5167-4:2003, Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running full — Part 4: Venturi tubes

Tiêu đề	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
Trường học	International Organization for Standardization
Chuyên ngành	Measurement of Fluid Flow
Thể loại	technical report
Năm xuất bản	2007
Thành phố	Geneva

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