standard bs 1042 part 1 1964 - baixardoc.com

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ONLYNOT TO BE REMOVED

ME"1'~ODhI

FOR THE

MEASUREMENT OF

FLUID FLOW IN PIPES

Part 1 . Orifice Plates, Nozzles

and Venturi Tubes

LIBRARY


METHODS FOR THE

MEASUREMENT OF

FLUID FLOW IN PIPES

Part 1. Orifice Plates, Nozzles

and . Venturi Tubes

B.S. 1042 : Part 1 : 1964

Incorporating amendments issued September, 1965 .(PD 5636) and December 1968 (AMD 149)

Gr 9

A

BRITISH STANDARDS INSTITUTION

Incorporated by Royal Charter

British Standards House, 2 Park St ., London, W1Y 4AA

Telegrams: Standards London Wi Telephone : 01-629 9000

UDC 532 .54 .0E


B .S . 1042 : Part I : 1964

Tatra Bsmsat STANDARD, having been approved by the

Instrument Industry Standards Committee and endorsed by

the Chairman of the Engineering Divisional Council, was

published under the authority of the General Council on

25th September, 1964.

First published, February, 1943 .First revision, September, 1964 .

The Institution desires to call attention to the fact that this

British Standard does not purport to include all the necessary

provisions of a contract .

In order to keep abreast of progress in the industries

concerned, British Standards are subject to periodical review .

Suggestions for improvements will be recorded and in due

course brought to the notice of the committees charged with

the revision of the standards to which they refer .

A complete list of British Standards, numbering over 5000 .

fully indexed and with a note of the contents of each, will be

found in the British Standards Yearbook. The

B.S. Yearbook may be consulted in many public libraries

and similar institutions .

This standard makes reference to the following BritishStandards :

B.S. 188. Methods for the determination of the viscosity of

liquids in c.g.s. units.B.S. 733 . Density bottles .

B.S. 1041 . Code for temperature measurement.

B .S. 1339. Humidity of the air. Definitions, formulae andconstants.

British Standards are revised, when necessary, by the lame either

of amendment slips or of revised editions. It is important that

users of British Standards should ascertain that they are In

possession of the latest amendments or editions .

The following B.S.I. references relate to the work on this standard :

Committee reference INE/3, INW/3/ 1

Draft for comment CX(INE)9141

0508Li1012

B.S. 1042 : Part I : 1964

CO-OPERATING ORGANIZATIONS

The Instrument Industry Standards Committee, under whosesupervision this British Standard was prepared, consists ofrepresentatives from the following Government departmentsand scientific and industrial organizations :

Association of Scientific Worker sBritish Clock and Watch Manufacturers' Association

'British Electrical and Allied Manufacturers' Association'British Industrial Measuring and Control Apparatus

Manufacturers' Association'British Iron and Steel FederationBritish Nautical Instrument Trade AssociationBritish Railways BoardBritish Scientific Instrument Research AssociationCouncil of British Manufacturers of Petroleum EquipmentElectrical Research AssociationElectricity Council, the Generating Board and the Area Boards

in England and WalesElectronic Engineering AssociationEngineering Equipment Users' AssociationGauge and Tool Makers' AssociationInstitution of Chemical EngineersInstitution of Electrical EngineersInstitution of Heating and Ventilating Engineers

'Institution of Mechanical Engineers

'Iron and Steel Institute

Meteorological Office

'Ministry of Defence, Army Department

Ministry of Health

Ministry of Housing and Local GovernmentNational Coal Board

'National Physical Laboratory (D .S.I.R.)'Oil Companies Materials AssociationScientific Instrument Manufacturers' AssociationSociety of Instrument TechnologyWater-tube Boilermakers' Association

The Government departments and scientific and industrialorganizations marked with an asterisk in the above list,together with the following, were directly represented on thecommittee entrusted with the preparation of this standard ;British Cast Iron Research AssociationBritish Coal Utilisation Research Association

British Compressed Air Society

D.S .LL-Hydraulic Research Station

DS.I.R .-National Engineering Laboratory

Institute of Petroleu m

Institution of Gas EngineersMinistry of PowerSociety of Chemical IndustrySociety of Glass TechnologyIndividual manufactures and consultants

3


B.S. 1042 : Part l : 1964 B .S . 1042 : Part 1 : 1964

CONTENTS CONTENTS--(continued)

Page

anizations 3Co-o eratin orTABLES

p g g

Foreword 9Page

l ti fi t lA f1Scope 10

cu a on oma e caccuracy o approx.

Section One Method 12orifice diameter 28

Section Two Calculations 22 2. Critical pressure ratios 30

Section Three Measurements 33 3. Density (in lb/ft') of distilled water 37

Section Four Accuracy 67

Section Five General arrangement of devices 76 i

Section Six Conditions for use 96

4. Physical properties of selected gases 4 1

5 . Density (in 1b/ft') of saturated and

Section Seven Orifice plate with cornersuperheated steam 43-46

tappings 107 6. Saturation pressure (fn Ibf/in') of water vapour 48

Section Eight Orifice plate with D and D/27. Minimum internal diameter of upstrea m

tappings 117

Section Nine Orifice plate with flangepipeline 99

tappings 123 8 . Minimum lengths of straight pipeline upstream

Section Ten Conical-entrance orifice plate 130 of device 100-101

Section Eleven Quarter-circle orifice plate 134 9 . Determination of pipe size correction factorSection Twelve Nozzle 139 for orifice plate with corner tappings orSection Thirteen Venturi nozzle 149 with D and D/2 tappings 115

Section Fourteen : Venturi tube 15210 . Percentage variation from nominal pip e

A.

APPENDICES

Conversion factors 159

diameter within which interpolation of Z

values given in Figs. 41b-j is not necessary 129

11 . Determination of pipe size correction factor

B . Summary of calculations 164 for nozzles or venturi nozzles 143

C. Values of gas law deviation coefficients at 12 . Determination of pipe size correction factor

D.

E .

high pressures 174

Estimation of tolerances 194

Damping of pulsating flow 200

for venturi tubes 155

13 . Conversion factors and numerical constants 162

F. Damping of swirling motion 204 14 . Conversion of volume rates of flow expressed

G. Summary of equations 205 at various reference conditions 16 3

H. Cross-reference to principal figures and tables 206 15 . Tolerance on gas law deviation coefficient K 175

J.

K .

Chart to obtain E from dJD, and to obtain

dJD from mE 207

List of principal symbols 213

16 . Lower limit of Hodgson number for sine

wave pulsations at the source giving an

Index 215 error of I per cent 203

4 5

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H .S . 10421 Part 1 : 1964 E.S. 1042 : Part I : 1964

CONTENTS-{continued)

FIGURES

CONTENTS-(continued)

FIGURES (continued)

Page

1 . Section of orifice plate, nozzle and venturi tube 24 . Examples of constructional arrangement of

Page

showing general pattern of flow lines

2. Section of square-edged orifice plate showing

13 an orifice plate with flange tappings

25 . Examples of constructional arrangement of

78

variation of pressure along the pipe wal l

3 . Values of m plotted against CmE (for use only

16 a conical-entrance orifice plate

26. Example of constructional arrangement of

79

in calculation of orifice or throat diameter)

4. Net pressure loss as a percentage of pressure27 a quarter-circle orifice plate

27. Examples of constructional arrangement of

80

difference (see also Fig. 62)

5 . Multiplying factors for thermal expansion32 a nozzle

34 28. Examples of constructional arrangement of

8 1

6 . Values of K for air

7. Values of K for ammonia

50 a venturi nozzle

51 29. Examples of constructional arrangement of

82

8. Values of K for carbon monoxide

9. Values of K for carbon dioxide

a venturi tub e5 1

52 30. Piezometer ring tapping (for an orifice plate

83

with D and D/2 tappings) 8910. Values of K for hydrogen 52

31 . Layout of pressure pipe connections 9311 . Values of K for methane 53

32. Location and types of condensation chamber12. Values of K for nitrogen

53 for steam and vapours 9413 . Values of K for oxygen

54 33. Layout of sealing chambers 9514. Values of K for propane

54 34. Orifice plate with comer tappings 10 815. Viscosity of water at I atm

16. Viscosity of water from 212 to 750°F at57 35. Data for orifice plate with comer tappings

36 . Expansibility factor for orifice plate with

11 3

saturation pressure58 comer tappings 11 4

17. Viscosity of selected gases at 1 atm 59 37. Orifice plate with D and D/2 tappings 11 718 . Multiplying factors for viscosity of gases at

38 . Data for orifice plate with D and D/2 tappings 12 1high pressures 61

39. Expansibility factor for orifice plate with D19. Viscosity of steam

62 and D/2 tappings or with flange tappings 12220. Coefficients for the calculation of the viscosity 40. Orifice plate with flange tappings 124

of gas mixtures 6441 . Data for orifice plate with flange tappings 126-128

21 . Specific heat ratios of selected gases 66

22. Examples of constructional arrangement of an42. Conical-entrance orifice plate 13 1

43 Quarter-circle orifice late 13 5orifice plate with corner tappings . p76

23 . Example of constructional arrangement of 44 . Values of rid for quarter-circle orifice plate 136

an orifice plate with D and D/2 tappings 77 45. Data for quarter-circle orifice plate 138

6 7

z5c~l~~o~


B.S. 1042 : Part 1 : 1964

CONTENTS-(continued)

FIGURES (continued)

Page

46 . Nozzle profile 14 1

47 . Data for nozzle 145

48. Expansibility factor for nozzle, venturi

nozzle or venturi tube 146

49 . Critical flow factor for nozzle 147

50 . Venturi nozzle 15 1

51 . Venturi tube 153

52 . Data for venturi tube 157

53 . Values of K for air at high pressures 177

54 . Values of K for ammonia at high pressures 179

55 . Values of K for carbon monoxide at high

pressures 18 1

56 . Values of K for carbon dioxide at high

pressures 18 3

57 . Values of K for hydrogen at high pressures 18 5

58 . Values of K for methane at high pressures 18 7

59 . Values of K for nitrogen at high pressures 18 9

60 . Values of K for oxygen at high pressures 19 1

61 . Values of K for propane at high pressures 19 3

62 . Net pressure loss of pressure difference

devices, expressed in number of pip e

velocity heads 202

8

i

i

B.S. 1042 : Part 1 : 1964

BRITISH STANDARD

METHODS FOR THE MEASUREMENT

OF FLUID FLOW IN PIPES

Part 1 . Orifice Plates, Nozzles and Venturi Tube s

FOREWORD

This British Standard was first published in 1943 under the title' Flow Measure-

ment' and contained information on orifice plates, nozzles, venturi tubes and

picot tubes . In the present revision, the standard is restricted to the measurement

of fluid flow in circular pipes by orifice plates, nozzles and venturi tubes .

Information on pitot tubes will be published as B .S. 1042: Part 2 . Further stan-

dards are at present being prepared on methods of flow measurement in open

channels .

The information in this standard is not intended to replace the methods

specified in the following British Standards, which refer to specific applications .

B .S . 353 . Methods of testing water turbine efficiency.

B .S . 599 . Pump tests.

B .S . 722. Borehole and well pump tests .

B .S . 723. Sewage pump tests.

B .S . 724 . Vaporizing liquid pump tests .

B .S . 726. Measurement of air flow for compressors and exhausters.

B .S . 848 . Testing of fans for general purposes (excluding mine fans) .

There are many differences between this revision and the 1943 edition of the

standard. Included among these are amended values for some dimensions of

the devices, for some coefficients and correction factors and for minimum

upstream straight pipe lengths. The latter have been based on a review of the

latest information on this subject, but further research is planned to improve

this data since tests have shown that shorter lengths can on occasions-be used .

The numerical values of the tolerances are also different in consequence of a

revised method of presentation of the errors of flow measurement . In order to

take account of some recent tests which gave values of the discharge coefficientoutside the predicted limits given in the previous edition, the tolerances for the

coefficients for orifice plates with D and D/2 tappings have been increased for

the higher area ratios although the coefficients themselves are unchanged . In

accordance with draft ISO Recommendation No . 532 'Measurement of fluid

flow by means of orifice plates and nozzles', all equations in this edition are

based on mass rate of flow units and correspondingly on mass density . If,

9

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B .S . 1042 : Part 1 : 1964

however, consistent units are used in this standard, as with the previous edition,

no conversion factors are required .

The committee charged with the revision has been guided in the problem of

the effects of upstream pipe roughness by information contained in the draft

ISO Recommendation No . 532 . Whilst the conclusion given in that document

that the influence of pipe size and Reynolds number are not interdependent

appears sound, the evidence for presenting an accurate unified approach is still

considered insufficient . In this present edition of the standard, therefore, tables

are included which, while retaining the simplified concept of separate influences

of pipe size and Reynolds number, give limiting pipe sizes for various degrees of

internal roughness. The selection of these limiting pipe sizes has been based on

broad categorizations of relative roughness figures from the ISO document .For example, for orifice plates with corner tappings, three groups were adopted

for small, medium and large relative roughness values which give the specified

ranges of pipe size when particular surfaces, e .g. slightly rusty steel, occurs ; thecorrection factors to the basic coefficients then increase with increasing rough-

ness. It is realised that while this approach is an improvement on that used in

the previous edition, it is only an interim solution, and the committee will

continue to study the problem.

This present edition includes information on orifice plates with flange

tappings and also on conical-entrance and quarter-circle orifice plates which

are suitable for measurements at low Reynolds numbers, for example with

highly viscous fluids.

It is only when a flow metering installation complies with all the requirements

set out in this standard that the errors will lie within the ranges quoted herein .If, however, from one cause or another, standard conditions are not or cannot

be obtained then the corresponding accuracies may not be achieved . It has

therefore been decided to issue separately, as Part 3* of this standard, informa-

tion on the effects of deviating from the requirements of the standard .

SCOPE

1 . This British Standard specifies the geometrical shape, relative dimensions,

constructional requirements and accuracy of manufacture of the following

types of pressure difference device :

Square-edged orifice plate with :

(i) corner pressure tappings.

(ii) D and D/2 pressure tappings,

(iii) flange pressure tappings.

• B .S . 1042, ' Methods for the measurement of fluid flow in pipes,' Part 3, 'Guide to theeffects of departure from the methods in Part t ' .

10

B .S. 1042 : Part I : 196 4

Conical-entrance orifice plate.

Quarter-circle orifice plate' .

Nozzle (having International Standards Association (LS.A) 1932

profile).

Venturi nozzle (a nozzle having a divergent outlet) .Venturi tube (conical or classical venturi) .

The standard gives the information required for calculating the rate of flow

of any homogeneous fluid flowing in a pipe of circular cross-section of internal

diameter not less than one inch, from a measurement of the pressure difference

across the device .

The method may also be applied for the calculation of the rate of flow of a

fluid through a device installed in a partition wall between two large spaces, or

through a device fitted at the outlet or inlet of a pipe discharging into or from

a large space.

The information given in the standard may be used conversely to calculate

the dimensions of a device suitable for metering a given rate of flow .

The range of application and conditions for use for each type of device are

specified. The conditions for use include the provision of a sufficient length of

straight pipeline upstream of the device.

The method is applicable to both compressible and incompressible fluids, to

the flow of viscous liquids at low Reynolds numbers and to flow at high pressure

differences (critical flow). It is not applicable to fluids exhibiting non-Newtonian

behaviour, to suspensions of solids in liquids or gases, to non-steady or pulsating

flow or to flow in partially filled pipelines.

The standard does not specify methods of measuring the pressure difference,

or of determining the density, viscosity, pressure and temperature of the fluid .Advice is, however, given on making these and other ancillary measurements

required for the calculation of the rate of flow . The physical properties of water

and of selected gases are given .

A method is given for calculating approximately the reliability of a rate of

flow determined in accordance with the standard. The overall error may be

computed from the individual errors, or tolerances, of the various quantities

entering into the calculation of the rate of flow. Numerical values are given for

the tolerances of those quantities that are determined by the requirements of the

standard . The tolerances of those other quantities, such as pressure difference,

which are not detailed in the standard are to be estimated for each particular

case ; the overall error cannot therefore be given within the standard but only

the method of determining it.

• Referred to in some publications as a quadrant-edged orifice plate .

1 1

I%SQSL I 10 1


B .S . 1042 : Part 1 : 1964

SECTION ONE : METHOD

INTRODUCTION

2. A pressure difference device for the purpose of this standard consists of an

annular obstruction having an axial hole smaller than the bore of the pipe inwhich it is installed . The rate of flow through the device is calculated from a

measurement of the difference between the pressures on the wall of the pipe at

specified distances upstream and downstream of the obstruction . The pressuredifference is measured by a manometer connected to pressure tapping holes

communicating with the fluid through the wall of the pipe . The numericalrelationship between rate of flow and pressure difference depends on the shape

of the obstruction and the positions of the pressure tappings as well as on the

physical properties of the fluid. This relationship has been established, partly

from theoretical considerations and partly on the basis of calibration tests, for a

number of types of device installed in pipelines having a long straight approachlength. This information permits the rate of flow to be obtained without

calibration from the manometer reading for pressure difference devices con-structed and installed in accordance with the standard. The manometer may begraduated in rate of flow units instead of pressure difference .

The method gives the instantaneous rate of flow at the moment of measuring

the pressure difference. Changes in rate of flow may be recorded, for exampleby a pen-and-chart recorder incorporated in the manometer . The total flow may

be obtained by the use of a suitable integrating mechanism in the recorder.

PRESSURE DIFFERENCE DEVICES

3. The three main classes of device are shown in Fig. 1 . They are described andcompared in more detail in Clauses 37, 38 and 39, where advice is given also on

the selection of the device most suitable for a particular application .

a . Orifice plates . An orifice plate is simply a thin, flat plate having a centralhole . Orifice plates are distinguished as (a) square- (or sharp-) edged,

(b) conical-entrance or (c) quarter-circle, according to the shape of the upstreamedge of the orifice. The downstream edge of a square-edged orifice plate is

bevelled unless the plate is thin, whilst the downstream edges of conical-entrance

and quarter-circle plates are square.

The square-edged orifice plate is further distinguished as an orifice plate(i) with corner tappings, (ii) with D and D/2 tappings or (iii) with flange tappings,according to the positions of the pressure tappings .

b. Nozzles. A nozzle has a bell-mouth shaped convergent entry followed bya short cylindrical throat which projects into the downstream pipe . A venturinozzle (not shown in Fig. 1) consists of a nozzle followed by a divergent outlet ;it has features in common with both nozzles and venturi tubes .

c. Venturi tubes. A venturi tube has a conical convergent entry followed by acylindrical throat and a conical divergent outlet .

12

B.S . 1042 : Part 1 : 1964

Corner, pressure tapping s

a. Orifice plate.

Plane of VenaJ Contract a

Pressure tapping s

b. Nozzle.

Pressure tapping s

c. Venturi tube .

Fig. 1. Section of orifice plate, nozzle and ♦enturi tube, showing general

pattern of flow lines

1 3

SSO'LL101


il

LI

B . S . 1042 ; Part 1 : 1964

PRINCIPLE OF THE METHOD

4 . When a fluid flows through a pressure difference device, the flow follows

approximately the streamlines illustrated in Fig. 1 . In the case of a venturitube (and also a venturi nozzle) the flowing stream fills the whole cross-sectional

area of the device throughout its length . In the case of a nozzle it fills

the convergent entry and the throat but then issues as a cylindrical jet into thefluid filling the downstream pipe ; the jet is slowed down by eddying and mixing

with the non-moving fluid and gradually diverges to fill the cross-section of thedownstream pipe. In the case of an orifice plate the flowing stream issues from

the orifice as a convergent jet which continues to contract for a short distance

downstream of the orifice plate before it diverges to fill the pipe ; the minimumcross-section, or neck, of the jet is known as the vena contracta. The area andposition of the ve a contracta depends on the rate of flow, on the size of the

orifice relative to the pipe and on the pressure difference if the fluid is com-pressible . It is also sensitive to the shape of the upstream edge of the plate

and is smaller for square-edged than for conical-entrance or quarter-circleorifice plates .

The velocity of the flowing stream increases as it passes into the constriction

and reaches a maximum in the plane of the minimum cross-section of theflowing stream (4t the vena contracta for an orifice plate and at the throat for

a nozzle or venturi tube) . The kinetic energy of the stream, which is related

to the squares of the local velocity, increases correspondingly . The consequentdecrease in potential energy is manifested as a decrease in the pressure of the

fluid on the wall of the pipe or device (that is, at right angles to the direction ofthe flow lines).

This is illustrated in Fig, 2 in which is shown the variation of the pressure

on the pipe wall as the fluid passes through an orifice plate . The behaviour issimilar for nozzles and venturi tubes . As the fluid flows through the upstreampipe towards the device, the pressure on the pipe wall decreases very slowly

owing to dissipation of energy as heat in frictional losses ; this is shown in thefigure on a grossly exaggerated scale . In the absence of the device the pressurewould continue to fall as shown by the dotted line . Immediately in front of theconstriction there is a small increase in pressure on the pipe wall ; it occurs with

orifice plates, and to a lesser extent with nozzles, because a part of the impactpressure on the plate is conveyed to the pipe wall . There is a very slight increase

for venturi tubes, similarly arising from the curvature of the flowlines into theconstriction . When the fluid enters the orifice, its velocity increases very rapidly

and the pressure on the pipe wall falls abruptly as shown in Fig. 2, The pressuredecreases to a minimum at the vena contracta where the velocity is a maximum.In the case of nozzles and venturi tubes, the fluid is accelerated steadily as it

flows from the upstream pipe into the throat and the pressure on the pipe wall

decreases smoothly to a minimum at the throat .

1 4

9cos ttot

B .S. 1042 : Part 1 : 1964

Downstream of the vena contracts or the throat, the pressure on the pipe

wall increases as the area of the flowing stream increases and as the fluid velocity

of the fluid falls to its initial value. The pressure does not however reach quite

the value that it would have had in the absence of the device . The difference is

known as the net pressure loss. (see Fig. 2) and is due to dissipation of energy

as heat in the damping of turbulent eddies by internal friction . It is appreciable

for orifices and nozzles where the fluid issues from the orifice or throat as a jet,

but is much smaller for venturi nozzles and venturi tubes where the deceleration

of the fluid is controlled by the slowly diverging outlet .

From the preceding discussion it will be apparent that the pressure difference

across the device depends on :

the type of device : its geometrical shape and proportions,

the positions of the upstream and downstream pressure tappings (three pairs

of tappings are shown in Fig. 2 : corner tappings, D and D/2 tappings andflange tappings),

the change in the fluid velocity, or kinetic energy, between the planes of the

upstream and downstream tappings, which depends in turn on the rate of

flow and the dimensions of the device .

It is this last fact that permits the calculation of the rate of flow from the

pressure difference across the device.

THEORETICAL EQUATION FOR IDEAL FLUID S

S. A theoretical equation relating the change in kinetic energy, and hence the

rate of flow, to the pressure difference between an upstream and downstream

pressure tapping may be derived for the flow of an ideal, frictionless fluid through

a convergent (or convergent-divergent) tube . It is applicable to a compressible,

as well as an incompressible fluid provided the fluid is a perfect gas and that its

expansion during flow between the planes of the two pressure tappings is isen-

tropic (frictionless and adiabatic) . The theoretical equation for the mass rate o f

flow M (lb/a) is given by

M=EeaV(2g,p4P)lb/s

where E is l Jv/(l -m'), and is known as the velocity of approach factor,

m is the non-dimensional area ratio a/A,

(1 )

a is the cross-sectional area (ft') of the flowing stream at the down-

stream pressure tapping,

A is the cross-sectional area (ft) of the stream at the upstream pressure

tapping,

c is a non-dimensional quantity known as the expansibility factor (seebelow),

15


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