SIST EN ISO 4126-3:2006

SLOVENSKI STANDARD
SIST EN ISO 4126-3:2006
01-maj-2006
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Safety devices for protection against excessive pressure - Part 3: Safety valves and
bursting disc safety devices in combination (ISO 4126-3:2006)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 3: Sicherheitsventile und
Berstscheibeneinrichtungen in Kombination (ISO 4126-3:2006)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 3:
Dispositifs de sureté combinant soupapes de sureté et disques de rupture (ISO 4126-
3:2006)
Ta slovenski standard je istoveten z: EN ISO 4126-3:2006
ICS:
13.240
SIST EN ISO 4126-3:2006 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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EUROPEAN STANDARD
EN ISO 4126-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2006
ICS 13.240

English Version
Safety devices for protection against excessive pressure - Part
3: Safety valves and bursting disc safety devices in combination
(ISO 4126-3:2006)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 3: Dispositifs de sûreté combinant Teil 3: Sicherheitsventile und Berstscheibeneinrichtungen
soupapes de sûreté et disques de rupture (ISO 4126- in Kombination (ISO 4126-3:2006)
3:2006)
This European Standard was approved by CEN on 27 February 2006.
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, Romania,
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
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-3:2006: E
worldwide for CEN national Members.

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EN ISO 4126-3:2006 (E)


Foreword

This document (EN ISO 4126-3:2006) 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 September 2006, and conflicting
national standards shall be withdrawn at the latest by September 2006.

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(s).

For relationship with EU Directive(s), 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, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

2

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EN ISO 4126-3:2006 (E)

Annex ZA
(informative)
Relationship between this International Standard and the
Essential Requirements of EU Directive 97/23/EC (PED)

This European Standard has been prepared under a mandate given to CEN by the European
Commission and the European Free Trade Association to provide one means of conforming
to Essential Requirements of the New Approach Directive 97/23/EC, Pressure Equipment
Directive (PED).

Once this standard is cited in the Official Journal of the European Communities under that
Directive and has been implemented as a national standard in at least one Member State,
compliance with the normative clauses of this standard given in Table ZA.1 confers, within the
limits of the scope of this standard, a presumption of conformity with the corresponding
Essential Requirements of that Directive and associated EFTA regulations.

Table ZA.1 — Correspondence between this International Standard and Directive
97/23/EC (PED)
Sub-clauses of this EN Essential Requirements of Directive 97/23/EC (PED)
Essential Requirements Annex I of PED
5, 6, 7, 8, 9, 11 and 12 Safety accessories 2.11.1 and 2.11.2
5, 9 and 12 General design 2.1
5 Design for adequate strength 2.2
5, 6 and 7 Safe operation 2.3
8.1, 8.4, 8.5 and 8.6 Performance testing 2.2.4
13 Marking and labelling 3.3

WARNING — Other requirements and other EU Directives may be applicable to the
products falling within the scope of this standard.

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INTERNATIONAL ISO
STANDARD 4126-3
First edition
2006-03-01

Safety devices for protection against
excessive pressure —
Part 3:
Safety valves and bursting disc safety
devices in combination
Dispositifs de sécurité pour protection contre les pressions
excessives —
Partie 3: Soupapes de sûreté et dispositifs de sûreté à disque de
rupture en combinaison




Reference number
ISO 4126-3:2006(E)
©
ISO 2006

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ISO 4126-3:2006(E)
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ii © ISO 2006 – All rights reserved

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ISO 4126-3:2006(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 2
4 Symbols . 4
5 Design of combination . 5
6 Installation of combination . 5
7 Combination performance . 6
8 Determination of combination discharge capacity factor, F , by testing. 6
d
9 Derivation of combination discharge capacity factor, F . 9
d
10 Alternative to testing for F . 9
d
11 Certification of combination discharge capacity factor, F . 10
d
12 Application and use of the certified combination discharge capacity factor, F . 10
d
13 Marking and identification of combination devices . 10
14 Certification . 11
15 Preparation for storage and transport. 11

© ISO 2006 – All rights reserved iii

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ISO 4126-3:2006(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.
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 4126-3 was prepared by the European Committee for Standardization (CEN) Technical Committee
CEN/TC 69, Industrial valves, ISO/TC 185, Safety devices for protection against excessive pressure, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This first edition of ISO 4126-3 cancels and replaces ISO 6718:1991, of which it constitutes a technical
revision.
ISO 4126 consists of the following parts, under the general title Safety devices for protection against
excessive pressure:
⎯ 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 9: Application and installation of safety devices excluding stand-alone bursting disc safety devices
Part 7 contains data which is common to more than one of the parts of this standard to avoid unnecessary
repetition.
iv © ISO 2006 – All rights reserved

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ISO 4126-3:2006(E)
Introduction
Bursting disc safety devices can be used in conjunction with safety valves in following cases:
a) to protect the safety valve against corrosion, fouling or operating conditions which could affect the safety
valve performance;
b) to prevent leakage;
c) to prevent total loss of contents from the protected equipment following the bursting of the bursting disc.
The term combination is used to describe the close-coupled (i.e. within 5 pipe diameters) assembly of a
bursting disc safety device with a safety valve or CSPRS, as defined by this part of ISO 4126. In some cases,
the bursting disc safety device and the safety valve or CSPRS are connected together to form the combination
by a short length of pipe or a spool piece.
© ISO 2006 – All rights reserved v

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INTERNATIONAL STANDARD ISO 4126-3:2006(E)

Safety devices for protection against excessive pressure —
Part 3:
Safety valves and bursting disc safety devices in combination
1 Scope
This part of ISO 4126 specifies the requirements for a product assembled from the in-series combination of
safety valves or CSPRS (controlled safety pressure relief systems) according to ISO 4126-1, ISO 4126-4 and
ISO 4126-5, and bursting disc safety devices according to ISO 4126-2 installed within no more than five pipe
diameters from the valve inlet. It specifies the design, application and marking requirements for such products,
which are used to protect pressure vessels, piping or other enclosures from excessive pressure, and which
comprise the bursting disc safety device, a safety valve or CSPRS and, where applicable, a short length of
connecting pipe or spool piece. In addition, it gives a method for establishing the combination discharge factor
used in sizing combinations.
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 4126-1:2004, Safety devices for protection against excessive pressure — Part 1: Safety valves
ISO 4126-2:2003, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety
devices
ISO 4126-4:2004, Safety devices for protection against excessive pressure — Part 4: Pilot-operated safety
valves
ISO 4126-5:2004, Safety devices for protection against excessive pressure — Part 5: Controlled safety
pressure relief systems (CSPRS)
ISO 4126-6:2003, Safety devices for protection against excessive pressure — Part 6: Application, selection
and installation of bursting disc safety devices
EN 764-7:2002, Pressure equipment — Part 7: Safety systems for unfired pressure equipment
EN 13480-1:2002, Metallic industrial piping — Part 1: General
EN 13480-2:2002, Metallic industrial piping — Part 2: Materials
EN 13480-3:2002, Metallic industrial piping — Part 3: Design and calculation
EN 13480-4:2002, Metallic industrial piping — Part 4: Fabrication and installation
EN 13480-5:2002, Metallic industrial piping — Part 5: Inspection and testing
EN 13480-6:2002, Metallic industrial piping — Part 6: Additional requirements for buried piping
CEN/TR 13480-7:2002, Metallic industrial piping — Part 7: Guidance on the use of conformity assessment
procedures
© ISO 2006 – All rights reserved 1

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ISO 4126-3:2006(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
combination
installation which comprises a bursting disc safety device installed within five pipe diameters (from outlet of
bursting disc holder to inlet of valve) before the inlet of a safety valve or a CSPRS
See Figure 1.

Key
1 safety valve or CSPRS
2 bursting disc safety device
3 safety valve or CSPRS inlet
4 bursting disc safety device outlet
NOTE Other bursting disc safety device configurations used in conjunction with safety valves or CSPRS are specified
in ISO 4126-6.
Figure 1 — Diagram of combination showing relative distance
3.2
combination discharge capacity factor
F
d
factor used to determine the discharge capacity of a safety valve or CSPRS when the safety valve or CSPRS
is used in combination with a bursting disc safety device installed upstream of the safety valve or CSPRS
3.3
flow resistance factor
K
r
factor which determines the resistance to flow in a pipe work system caused by the presence therein of a
burst bursting disc, forming part of a bursting disc safety device, installed in the system
NOTE Its symbol, K , is a dimensionless factor expressed as the velocity head loss.
r
3.4
bursting disc safety device
non-reclosing pressure relief device actuated by differential pressure and designed to function by the bursting
of the bursting disc(s)
NOTE It is the complete assembly of installed components including, where appropriate, the bursting disc holder.
2 © ISO 2006 – All rights reserved

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ISO 4126-3:2006(E)
3.5
bursting disc assembly
complete assembly of the components installed in the bursting disc holder to perform the desired function
3.6
bursting disc
pressure-containing and pressure-sensitive component of a bursting disc safety device
3.7
bursting disc holder
part of a bursting disc safety device that retains the bursting disc assembly in position
3.8
specified bursting pressure
bursting pressure quoted with a coincident temperature when defining the bursting disc requirements
NOTE It is used in conjunction with a performance tolerance (3.11).
3.9
specified maximum bursting pressure
maximum bursting pressure quoted with the coincident temperature when defining the bursting disc
requirements
NOTE It is used in conjunction with a specified minimum bursting pressure (3.10).
3.10
specified minimum bursting pressure
minimum bursting pressure quoted with the coincident temperature when defining the bursting disc
requirements
NOTE It is used in conjunction with a specified maximum bursting pressure (3.9).
3.11
performance tolerance
range of pressure between the specified minimum bursting pressure and the specified maximum bursting
pressure or the range of pressure in positive and negative percentages or quantities which is related to the
specified bursting pressure
3.12
operating pressure
pressure existing at normal operating conditions within the system being protected
3.13
relieving pressure
maximum pressure under discharge conditions in the pressurized system
NOTE It may differ from the bursting pressure of the bursting disc.
3.14
bursting disc safety device discharge area
minimum cross-sectional flow area of the bursting disc safety device, taking into consideration the possible
reduction of the cross-section by, for example, back pressure supports, catching devices or parts of the
bursting disc which remain after bursting
3.15
batch
quantity of bursting discs or bursting disc safety devices made as a single group of the same type, size,
materials and specified bursting pressure requirements, and where the bursting discs are manufactured from
the same lot of material
© ISO 2006 – All rights reserved 3

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ISO 4126-3:2006(E)
3.16
bursting pressure
value of the differential pressure between the upstream side and the downstream side of the bursting disc
when it bursts
3.17
bursting disc safety device discharge capacity
rate at which a bursting disc safety device can discharge fluid after bursting of the bursting disc
3.18
replacement period
time period beginning at the installation of a bursting disc assembly and ending with its replacement
3.19
pressure relief system
system intended for the safe relief of fluids from pressure equipment for prevention of excessive pressure
NOTE It can consist of equipment nozzle
...