SIST EN ISO 4126-1:2004

SLOVENSKI STANDARD
SIST EN ISO 4126-1:2004
01-september-2004
Naprave za varovanje pred visokim tlakom - 1. del: Varnostni ventili (ISO 4126-
1:2004)
Safety devices for protection against excessive pressure - Part 1: Safety valves (ISO
4126-1:2004)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 1: Sicherheitsventile (ISO
4126-1:2004)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 1 :
Soupapes de sureté (ISO 4126-1:2004)
Ta slovenski standard je istoveten z: EN ISO 4126-1:2004
ICS:
13.240
SIST EN ISO 4126-1:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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EUROPEAN STANDARD
EN ISO 4126-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
February 2004
ICS 13.240
English version
Safety devices for protection against excessive pressure - Part
1: Safety valves (ISO 4126-1:2004)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 1 : Soupapes de sûreté (ISO 4126- Teil 1: Sicherheitsventile (ISO 4126-1:2004)
1:2004)
This European Standard was approved by CEN on 16 May 2003.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-1:2004: E
worldwide for CEN national Members.

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EN ISO 4126-1:2004 (E)
Contents
Page
1 Scope .4
2 Normative references .4
3 Terms and definitions.5
4 Symbols and units .8
5 Design .8
5.1 General.8
5.2 End connections .9
5.3 Minimum requirements for springs.11
5.4 Materials.11
6 Production testing .11
6.1 Purpose.11
6.2 General.11
6.3 Hydrostatic testing .12
6.4 Pneumatic testing .13
6.5 Adjustment of cold differential test pressure .14
6.6 Seat leakage test.14
7 Type testing.14
7.1 General.14
7.2 Tests to determine operating characteristics.15
7.3 Tests to determine flow characteristics .17
7.4 Determination of the coefficient of discharge .18
7.5 Certification of coefficient of discharge .19
8 Determination of safety valve performance.19
8.1 Determination of coefficient of discharge.19
8.2 Critical and subcritical flow .19
8.3 Discharge capacity at critical flow .19
8.4 Discharge capacity for any gas at subcritical flow .20
8.5 Discharge capacity for non-flashing liquid as the test medium in the turbulent zone where the
R
Reynolds number is equal to or greater than 80 000 .20
e
9 Sizing of safety valves.20
9.1 General.20
9.2 Valves for gas or vapour relief .21
9.3 Calculation of capacity.21
10 Marking and sealing .22
10.1 Marking on the shell of a safety valve .22
10.2 Marking on an identification plate.22
10.3 Sealing of a safety valve .22
Annex A (informative) Examples of sizing calculations for various fluids.23
A.1 Capacity calculations for gaseous media at critical flow (see 9.3.3.1) .23
A.2 Capacity calculations for gaseous media at subcritical flow (see 9.3.3.2) .25
A.3 Capacity calculations for liquids (see 9.3.4) .27
Annex ZA (informative) Relationship between this European Standard and the Essential Requirements
of EU Directive 97/23/EC (PED).28
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EN ISO 4126-1:2004 (E)
Foreword
This document (EN ISO 4126-1:2004) has been prepared by Technical Committee CEN/TC 69 “Industrial valves”,
the secretariat of which is held by AFNOR, in collaboration with Technical Committee ISO/TC 185 “Safety devices
for protection against excessive pressure”.
This European Standard shall be given the status of a national standard, either by publication of an identical text or
by endorsement, at the latest by August 2004, and conflicting national standards shall be withdrawn at the latest by
August 2004 .
This document has been prepared under a mandate given to CEN by the European Commission and the European
Free Trade Association, and supports essential requirements of EU Directive.
For relationship with EU Directive, see informative annex ZA, which is an integral part of this document.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark,
Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
This standard for safety devices for protection against excessive pressure consists of seven parts of which this is
Part 1. The various parts are:
 Part 1 : Safety valves
 Part 2 : Bursting disc safety devices
 Part 3 : Safety valves and bursting disc safety devices in combination
 Part 4 : Pilot operated safety valves
 Part 5 : Controlled safety pressure relief systems (CSPRS)
 Part 6 : Application, selection and installation of bursting disc safety devices
 Part 7 : Common data
Part 7 contains data that is common to more than one of the parts of this standard to avoid unnecessary repetition.
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EN ISO 4126-1:2004 (E)
1 Scope
This part of this European Standard specifies general requirements for safety valves irrespective of the fluid for
which they are designed.
It is applicable to safety valves having a flow diameter of 6 mm and above which are for use at set pressures
of 0,1 bar gauge and above. No limitation is placed on temperature.
This is a product standard and is not concerned with applications for safety valves.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references, subsequent amendments to or revisions of any of these publications apply to this European
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies (including amendments).
EN 1092-1, Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories PN designated –
Part 1: Steel flanges.
EN 1092-2, Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories PN designated –
Part 2: Cast iron flanges.
EN 1092-3 , Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories PN designated –
Part 3: Copper alloy flanges.
prEN 1759-1, Flanges and their joints - Circular flanges for pipes, valves, fittings and accessories, Class
designated - Part 1: Steel flanges NPS 1/2 to 24.
EN 12516-3, Valves – Shell design strength – Part 3: Experimental method.
EN 12627, Industrial Valves – Butt welding ends for steel valves.
EN 12760, Valves – Socket welding ends for steel valves.
EN ISO 6708, Pipework components – Definition and selection of DN (nominal size) (ISO 6708:1995).
ISO 7-1, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances and
designation.
ANSI B1.20.1, NPT threads.
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EN ISO 4126-1:2004 (E)
3 Terms and definitions
For the purposes of this European Standard, the following terms and definitions apply.
3.1
safety valve
valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a
quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to
re-close and prevent further flow of fluid after normal pressure conditions of service have been restored
NOTE The valve can be characterised either by pop action (rapid opening) or by opening in proportion (not necessarily
linear) to the increase in pressure over the set pressure.
3.1.1
types of safety valve
3.1.1.1
direct loaded safety valve
safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by a direct
mechanical loading device such as a weight, lever and weight, or a spring
3.1.1.2
assisted safety valve
safety valve which, by means of a powered assistance mechanism, may additionally be lifted at a pressure lower
than the set pressure and will, even in the event of failure of the assistance mechanism, comply with all the
requirements for safety valves given in this standard
3.1.1.3
supplementary loaded safety valve
safety valve which has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional
force which increases the sealing force
NOTE 1 This additional force (supplementary load), which may be provided by means of an extraneous power source, is
reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary
loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge
capacity at a pressure not greater than 1,1 times the maximum allowable pressure of the equipment to be protected.
NOTE 2 Other types of supplementary loaded safety devices are dealt with in Part 5 of this standard.
3.1.1.4
pilot operated safety valve
safety valve, the operation of which is initiated and controlled by the fluid discharged from a pilot valve which is
itself a direct loaded safety valve subject to the requirement of this standard
NOTE Other types of pilot operated safety valves with flowing, non-flowing and modulating pilots are in Part 4 of this
standard.
3.2
pressure
5
pressure unit used in this standard is the bar (1 bar = 10 Pa), quoted as gauge (relative to atmospheric pressure)
or absolute as appropriate
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EN ISO 4126-1:2004 (E)
3.2.1
set pressure
predetermined pressure at which a safety valve under operating conditions commences to open
NOTE It is the gauge pressure measured at the valve inlet at which the pressure forces tending to open the valve for the
specific service conditions are in equilibrium with the forces retaining the valve disc on its seat.
3.2.2
maximum allowable pressure, PS
maximum pressure for which the equipment is designed as specified by the manufacturer
3.2.3
overpressure
pressure increase over the set pressure, at which the safety valve attains the lift specified by the manufacturer,
usually expressed as a percentage of the set pressure
NOTE This is the overpressure used to certify the safety valve.
3.2.4
reseating pressure
value of the inlet static pressure at which the disc re-establishes contact with the seat or at which the lift becomes
zero
3.2.5
cold differential test pressure
inlet static pressure at which a safety valve is set to commence to open on the test bench
NOTE This test pressure includes corrections for service conditions, e.g. back pressure and/or temperature.
3.2.6
relieving pressure
pressure used for the sizing of a safety valve which is greater than or equal to the set pressure plus overpressure
3.2.7
built-up back pressure
pressure existing at the outlet of a safety valve caused by flow through the valve and the discharge system
3.2.8
superimposed back pressure
pressure existing at the outlet of a safety valve at the time when the device is required to operate
NOTE It is the result of pressure in the discharge system from other sources.
3.2.9
balanced bellows
bellows device which minimises the effect of superimposed back pressure on the set pressure of a safety valve
3.2.10
blowdown
difference between set and reseating pressures, normally stated as a percentage of set pressure except for
pressures of less than 3 bar when the blowdown is expressed in bar
3.3
lift
actual travel of the valve disc away from the closed position
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EN ISO 4126-1:2004 (E)
3.4
flow area
minimum cross-sectional flow area (but not the curtain area) between inlet and seat which is used to calculate the
theoretical flow capacity, with no deduction for any obstruction
NOTE The symbol is A.
3.5
flow diameter
diameter corresponding to the flow area
3.6
discharge capacity
3.6.1
theoretical discharge capacity
calculated capacity expressed in mass or volumetric units of a theoretically perfect nozzle having a cross-sectional
flow area equal to the flow area of a safety valve
3.6.2
coefficient of discharge
value of actual flowing capacity (from tests) divided by the theoretical flowing capacity (from calculation)
3.6.3
certified (discharge) capacity
that portion of the measured capacity permitted to be used as a basis for the application of a safety valve
NOTE It may, for example, equal the :
a) measured capacity times the derating factor ; or
b) theoretical capacity times the coefficient of discharge times the derating factor ; or
c) theoretical capacity times the certified derated coefficient of discharge.
3.7
DN (nominal size)
see EN ISO 6708
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EN ISO 4126-1:2004 (E)
4 Symbols and units
Table 1 — Symbols and their descriptions
Symbol Description Unit
2
A Flow area of a safety valve (not curtain area)
mm
Function of the isentropic exponent –
C
K Theoretical capacity correction factor for subcritical flow –
b
a
Coefficient of discharge –
K
d
a
–
K Certified derated coefficient of discharge (K · 0,9)
dr
d
K Viscosity correction factor –
v
Isentropic exponent –
k
Molar mass kg/kmol
M
n Number of tests –
p Relieving pressure bar (abs.)
o
Back pressure bar (abs.)
p
b
Critical pressure bar (abs.)
p
c
Q Mass flow rate kg/h
m
2
q Theoretical specific discharge capacity
m
kg/(h⋅mm )
2
q’ Specific discharge capacity determined by tests
m
kg/(h⋅mm )
R Universal gas constant –
Relieving temperature K
T
o
Critical temperature K
T
c
Dynamic viscosity Pa·sm
3
v Specific volume at actual relieving pressure and temperature
m /kg
x Dryness fraction of wet steam at the valve inlet at actual relieving pressure –
b
and temperature
Compressibility factor at actual relieving pressure and temperature –
Z
a
K and K are expressed as 0,xxx.
dr
d
b
x is expressed as 0,xx.
5 Design
5.1 General
5.1.1 The design shall incorporate guiding arrangements necessary to ensure consistent operation and seat
tightness.
5.1.2 The seat of a safety valve, other than when it is an integral part of the valve shell, shall be fastened
securely to prevent the seat becoming loose in service.
5.1.3 In the case of valves where the lift can be reduced to conform to the required discharge capacity, restriction
of the lift shall not interfere with the operation of the valve. The lift restricting device shall be designed so that, if
adjustable, the adjustable feature can be mechanically locked and access sealed. The lift restricting device shall be
installed and sealed by the valve manufacturer.
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EN ISO 4126-1:2004 (E)
Valve lift shall not be restricted to a value less than 30 % of unrestricted lift or 1 mm whichever is the greater.
5.1.4 Means shall be provided to lock and/or to seal all external adjustments in such a manner so as to prevent
or reveal unauthorised adjustments of the safety valve.
5.1.5 Safety valves for toxic or flammable fluids shall be of the closed bonnet type to prevent leakage to
atmosphere or if vented it shall be disposed of to a safe place.
5.1.6 Provision shall be made to prevent liquid collecting on the discharge side of the safety valve shell.
5.1.7 The design stress of load carrying parts shall not exceed that specified in the appropriate European
Standard e.g. EN 12516-3.
5.1.8 In the case of failure of a balanced bellows, if any, the safety valve shall discharge its certified capacity at
not more than 1,1 times the maximum allowable pressure of the equipment being protected.
5.1.9 The materials for adjacent sliding surfaces such as guide(s) and disc/disc holder/spindle shall be selected
to ensure corrosion resistance and to minimise wear and avoid galling.
5.1.10 Sealing elements, which may adversely affect the operating characteristics by frictional forces, are not
permitted.
5.1.11 Easing gear shall be provided when specified.
5.1.12 Safety valves shall be so constructed that breakage of any part, or failure of any device, will not obstruct
free and full discharge through the valve.
5.2 End connections
5.2.1 Types
The types of end connections shall be as follows:
Butt welding EN 12627 ;
Socket welding EN 12760 ;
Flanged EN 1092-1 ;
EN 1092-2 ;
EN 1092-3 ;
prEN 1759-1;
Threaded ISO 7-1 or ANSI B1.20.1.
Other types of end connections are possible by agreement between the manufacturer and purchaser.
5.2.2 Design of valve end connections
The design of valve end connections, whatever their type, shall be such that the internal area of the external
pipe or stub connection at the safety valve inlet is at least equal to that of the valve inlet connection (see
Figure 1 a).
The internal area of the external pipe connection at the safety valve outlet shall be at least equal to that of the
valve outlet, except those valves with female threaded outlet connections (see Figure 1 b).
NOTE See clause 7 regarding type testing.
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EN ISO 4126-1:2004 (E)
Key
1Valve
2 Satisfactory
3 Unsatisfactory
4 Required internal diameter of the safety valve for the valve to function properly
Figure 1 a) — Inlet
Key
1Valve
2 The nominal diameter of the pipe to be equal to the nominal diameter of the valve outlet
With this construction at the valve outlet, a suitable pipe shall be fitted during testing as specified in 7.1.5
Figure 1 b) — Outlet
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EN ISO 4126-1:2004 (E)
Key
1Valve
With this construction at the valve outlet, no pipe is required during testing as specified in 7.1.5
Figure 1 c) — Outlet
Figure 1 — Design of end connections
5.3 Minimum requirements for springs
Springs shall be in accordance with Part 7 of this standard.
5.4 Materials
The materials for pressure retaining shells shall be in accordance with Part 7 of this standard.
6 Production testing
6.1 Purpose
The purpose of these tests is to ensure that all safety valves meet the requirements for which they have been
designed without exhibiting any form of leakage from pressure retaining components or joints.
6.2 General
It is permissible to adopt an alternative test of equal validity (e.g. proof of design tests associated with statistical
sampling) to the hydrostatic test for valve shells with:
 threaded ends ; and
 a maximum inlet diameter of 32 mm ; and
 a ratio of bursting pressure to design pressure of at least 8 ; and
 a design pressure equal to or less than 40 bar ; and
 for use with non-hazardous fluids ;
and also for valves as above but with :
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EN ISO 4126-1:2004 (E)
 a design pressure greater than 40 bar ; and
 a ratio of bursting pressure to design pressure of at least 10 ; and
 material which is either wrought or forged.
All temporary pipes and connections and blanking devices shall be adequate to safely withstand the test pressure.
Any temporary welded-on attachments shall be carefully removed and the resulting weld scars shall be ground
flush with the parent material. After grinding, all such scars shall be inspected by using magnetic particle or fluid
penetrant techniques.
6.3 Hydrostatic testing
6.3.1 Application
The portion of the valve from the inlet to the seat shall be tested to a pressure 1,5 times the manufacturer’s stated
maximum pressure for which the safety valve is designed.
The shell on the discharge side of the seat shall be tested to 1,5 times the manufacturer’s stated maximum back
pressure for which the valve is designed.
6.3.2 Duration
The test pressure shall be applied and maintained at the required magnitude for a sufficient length of time to permit
a visual examination to be made of all surfaces and joints, but in any case for not less than the times given in
Table 2. For tests on the discharge side of the seat, the testing time shall be based on the pressure specified
in 6.3.1 and the discharge size.
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EN ISO 4126-1:2004 (E)
Table 2 — Minimum duration of hydrostatic test
Nominal size Pressure rating
Up to 40 bar Greater than 40 bar (4 MPa) up Greater than 63 bar
DN
(4 MPa) to 63 bar (6,3 MPa) (6,3 MPa)
Minimum duration in minutes
  DN£  50 22 3
 50 < DN£  65 22 4
23 4
 65 < DN£  80
24 5
 80 < DN£ 100
24 6
100 < DN£ 125
25 7
125 < DN£ 150
35 9
150 < DN£ 200
36 11
200 < DN£ 250
47 13
250 < DN£ 300
48 15
300 < DN£ 350
49 17
350 < DN£ 400
49 19
400 < DN£ 450
510 22
450 < DN£ 500
512 24
500 < DN£ 600
6.3.3 Acceptance criteria
No leakage from the tested parts as defined in 6.3.1 is accepted.
6.3.4 Safety requirements
Water shall normally be used as the test medium. Where other liquids are used, additional precautions may be
necessary. Valve bodies shall be properly vented to remove entrapped air.
If materials which are liable to failure by brittle fracture are incorporated in that part of the safety valve which is to
be hydrostatically tested, then both the safety valve, or part thereof, and the testing medium shall be at a sufficient
temperature to prevent the possibility of such failure.
No valve or part thereof undergoing pressure testing shall be subjected to any form of shock loading, for example
hammer testing.
6.4 Pneumatic testing
6.4.1 Application and duration of test
Pressure testing with air or other suitable gas may be carried out in place of the standard shell hydrostatic test
with the agreement of all parties involved in the following cases:
a) valves of such design and construction that it is not practicable for them to be filled with liquid ; and/or
b) valves that are to be used in service where even small traces of water cannot be tolerated.
The test pressure and duration of application shall be as specified in 6.3.
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EN ISO 4126-1:2004 (E)
6.4.2 Safety requirements
The hazards involved in pneumatic pressure testing shall be considered and adequate precautions taken.
Particular attention is drawn to some relevant factors as follows:
a) if a major rupture of the valve should occur at some stage during application of pressure, considerable energy
will be released; hence no personnel should be in the immediate vicinity during pressure raising (for example a
given volume of air contains 200 times the amount of energy that a similar volume of water contains, when
both are at the same pressure) ;
b) the risk of brittle failure under test conditions shall have been critically assessed at the design stage and the
choice of materials for valves that are to be pneumatically tested shall be such as to avoid the risk of brittle
failure during test. This necessitates provision of an adequate margin between the transition temperature of all
parts and the metal temperature during testing ;
c) attention is drawn to the fact that if there is a reduction in gas pressure between the high pressure storage and
the valve under test, the temperature will decrease.
6.5 Adjustment of cold differential test pressure
Before adjusting a safety valve to the cold differential test pressure using air or other gas as the test medium, it
shall previously be subjected to a hydrostatic test (see 6.3).
6.6 Seat leakage test
The seat leakage test of a safety valve shall be carried out. The test procedure and leakage rate shall be agreed
between the manufacturer and the purchaser.
7 Type testing
7.1 General
7.1.1 Introduction
The operating and flow characteristics of safety valves shall be determined by type tests in conformity with this
clause.
7.1.2 Application
This subclause applies to the types of safety devices defined in 3.1.1. For other types see:
 part 4 of this standard for other types of pilot operated safety valves ;
 part 5 of this standard for controlled safety pressure
...