SIST EN ISO 4126-6:2014

Safety devices for protection against excessive pressure - Part 6: Application, selection and installation of bursting disc safety devices (ISO 4126-6:2014)

EN ISO 4126-6 gives guidance on the application, selection and installation of bursting disc safety devices used to protect pressure equipment from excessive pressure and/or excessive vacuum. Annex A provides a checklist for the information to be supplied by the purchaser to the manufacturer. Annex B gives guidance on the replacement period of a bursting disc and annex C guidance on determining the mass flow rate, for single phase fluids, of a pressure relief system that contains a bursting disc safety device Annex E is a non-mandatory procedure for establishing the flow resistance of a burst bursting disc assembly. Annex F non-mandatory procedure for type testing of bursting disc safety devices Annex G provides typical performance characteristics for various bursting disc safety device types. The requirements for the manufacture, inspection, testing, marking, certification and packaging of bursting disc safety devices are given in ISO 4126-2.

Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 6: Berstscheibeneinrichtungen; Anwendung, Auswahl und Einbau (ISO 4126-6:2014)

Diese Norm enthält Leitlinien für die Anwendung, die Auswahl und den Einbau von Berstscheiben-einrichtungen, die zum Schutz von Druckgeräten gegen unzulässigen Über- und/oder Unterdruck eingesetzt werden.
Anhang A enthält eine Checkliste mit den Angaben, die der Käufer dem Hersteller zur Verfügung stellen muss.
Anhang B enthält Leitlinien zur Bestimmung des Zeitraums bis zum Austausch einer Berstscheibe, Anhang C enthält Leitlinien zur Bestimmung des Ausflussmassenstroms einer Druckentlastungs¬einrichtung, die eine Berstscheibeneinrichtung enthält (bei einphasigen Medien (Fluiden)).
Anhang E ist ein nicht verbindlich vorgeschriebenes Verfahren zur Bestimmung des Strömungswiderstandes einer Berstscheibeneinheit.
Anhang F ist ein nicht verbindlich vorgeschriebenes Verfahren für die Bauartprüfung von Berstscheiben-einrichtungen.
Anhang G enthält typische Leistungsmerkmale für verschiedene Bauarten von Berstscheibeneinrichtungen.
Die Anforderungen an die Herstellung, Überwachung, Prüfung, Kennzeichnung, Zertifizierung und Verpackung von Berstscheibeneinrichtungen sind in Teil 2 von EN ISO 4126 enthalten.

Dispositifs de sécurité pour protection contre les pressions excessives - Partie 6: Application, sélection et installation des dispositifs de sûreté à disque de rupture (ISO 4126-6:2014)

L'ISO 4126-6:2014 donne des lignes directrices pour l'application, la sélection et l'installation de dispositifs de sûreté à disque de rupture utilisés pour protéger les équipements sous pression contre des pressions excessives et/ou des dépressions excessives.

Naprave za varovanje pred visokim tlakom - 6. del: Uporaba, izbira in vgradnja razpočnih membran (ISO 4126-6:2014)

Standard EN ISO 4126-6 podaja smernice za uporabo, izbiro in vgradnjo varnostnih naprav z razpočnimi membranami, ki se uporabljajo za zaščito tlačne opreme pred visokim tlakom in/ali prekomernim vakuumom. Priloga A vsebuje kontrolni seznam informacij, ki jih mora kupec izročiti proizvajalcu. Priloga B podaja smernice o časovnem obdobju, v katerem je treba zamenjati razpočno membrano, Priloga C pa smernice za določitev masnega pretoka enofaznih tekočin v sistemu za razbremenitev tlaka, ki vsebuje varnostno napravo z razpočno membrano. Postopek v prilogi E ni obvezen za vzpostavitev pretočnega upora sestava z razpočno membrano. Postopek v prilogi F ni obvezen za preskus tipa varnostnih naprav z razpočno membrano. Priloga G ponuja tipične značilnosti delovanja za različne tipe varnostnih naprav z razpočnimi membranami. Zahteve za proizvodnjo, pregled, preskušanje, označevanje, certificiranje in pakiranje varnostnih naprav z razpočnimi membranami so podane v standardu ISO 4126-2.

General Information

• Status: Published
• Public Enquiry End Date: 14-Apr-2014
• Publication Date: 10-Jul-2014
• ICS: 13.240 - Protection against excessive pressure
• Technical Committee: IHPV - Hydraulics and pneumatics
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 19-Jun-2014
• Due Date: 24-Aug-2014
• Completion Date: 11-Jul-2014
• Directive: 97/23/EC - Directive 97/23/EC of the European Parliament and of the Council of 29 May 1997 on the approximation of the laws of the Member States concerning pressure equipment
• Mandate: M/071 - Mandate to CEN for standardization in the field of Pressure equipment
• Ref Project: EN ISO 4126-6:2014 - Safety devices for protection against excessive pressure - Part 6: Application, selection and installation of bursting disc safety devices (ISO 4126-6:2014)

Relations

• Replaces: SIST EN ISO 4126-6:2004 - Safety devices for protection against excessive pressure - Part 6: Application, selection and installation of bursting disc safety devices (ISO 4126-6:2003)
• Effective Date: 01-Sep-2014
• Replaces: SIST EN ISO 4126-6:2004/AC:2007 - Safety devices for protection against excessive pressure - Part 6: Application, selection and installation of bursting disc safety devices (ISO 4126-6:2003)
• Effective Date: 01-Sep-2014

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 4126-6:2014
01-september-2014
1DGRPHãþD
SIST EN ISO 4126-6:2004
SIST EN ISO 4126-6:2004/AC:2007
1DSUDYH]DYDURYDQMHSUHGYLVRNLPWODNRPGHO8SRUDEDL]ELUDLQYJUDGQMD
UD]SRþQLKPHPEUDQ,62
Safety devices for protection against excessive pressure - Part 6: Application, selection
and installation of bursting disc safety devices (ISO 4126-6:2014)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 6:
Berstscheibeneinrichtungen; Anwendung, Auswahl und Einbau (ISO 4126-6:2014)
Dispositifs de sécurité pour protection contre les pressions excessives - Partie 6:
Application, sélection et installation des dispositifs de sûreté à disque de rupture (ISO
4126-6:2014)
Ta slovenski standard je istoveten z: EN ISO 4126-6:2014
ICS:
13.240 Varstvo pred previsokim Protection against excessive
tlakom pressure
SIST EN ISO 4126-6:2014 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 4126-6:2014

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SIST EN ISO 4126-6:2014

EUROPEAN STANDARD
EN ISO 4126-6

NORME EUROPÉENNE

EUROPÄISCHE NORM
June 2014
ICS 13.240 Supersedes EN ISO 4126-6:2003
English Version
Safety devices for protection against excessive pressure - Part
6: Application, selection and installation of bursting disc safety
devices (ISO 4126-6:2014)
Dispositifs de sécurité pour protection contre les pressions Sicherheitseinrichtungen gegen unzulässigen Überdruck -
excessives - Partie 6: Application, sélection et installation Teil 6: Berstscheibeneinrichtungen; Anwendung, Auswahl
des dispositifs de sûreté à disque de rupture (ISO 4126- und Einbau (ISO 4126-6:2014)
6:2014)
This European Standard was approved by CEN on 22 May 2014.

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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2014 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-6:2014 E
worldwide for CEN national Members.

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SIST EN ISO 4126-6:2014
EN ISO 4126-6:2014 (E)
Contents Page
Foreword .3
2

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SIST EN ISO 4126-6:2014
EN ISO 4126-6:2014 (E)
Foreword
This document (EN ISO 4126-6:2014) has been prepared by Technical Committee ISO/TC 185 “Safety
devices for protection against excessive pressure” in collaboration with Technical Committee CEN/TC 69
“Industrial valves” the secretariat of which is held by AFNOR.
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 December 2014, and conflicting national standards shall be withdrawn
at the latest by December 2014.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4126-6:2003.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 4126-6:2014 has been approved by CEN as EN ISO 4126-6:2014 without any modification.
3

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SIST EN ISO 4126-6:2014

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SIST EN ISO 4126-6:2014
INTERNATIONAL ISO
STANDARD 4126-6
Second edition
2014-06-15
Safety devices for protection against
excessive pressure —
Part 6:
Application, selection and installation
of bursting disc safety devices
Dispositifs de sécurité pour protection contre les pressions
excessives —
Partie 6: Application, sélection et installation des dispositifs de sûreté
à disque de rupture
Reference number
ISO 4126-6:2014(E)
©
ISO 2014

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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2014
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved

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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

Contents Page
Foreword .iv
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 5
5 Application . 6
6 Selection . 8
6.1 Selection of bursting disc safety devices . 8
6.2 Selection of the performance tolerance.10
7 Installation .12
7.1 General .12
7.2 Location of bursting disc safety devices .12
7.3 Installation of bursting disc safety devices .12
Annex A (informative) Information to be supplied by the purchaser .14
Annex B (informative) Guidelines for determining the replacement period of a bursting disc .16
Annex C (informative) Pressure relief system discharge capacity .18
Annex D (informative) Flow testing of bursting disc safety devices .21
Annex E (informative) Type testing of non-reclosing bursting disc safety devices .35
Annex F (informative) Performance characteristics of bursting disc safety devices .37
Bibliography .39
© ISO 2014 – All rights reserved iii

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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directives
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. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received. www.iso.org/patents
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT), see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 185, Safety devices for protection against excessive
pressure.
This second edition cancels and replaces the first edition (ISO 4126-6:2003), which has been technically
revised.
The main technical modifications are:
a) Revision to Annex C to refer to Part 7 for capacity calculations;
b) Annex D was deleted as this information is found in Part 7;
c) Annex E was revised to include methodology for establishing flow resistance values for bursting
discs opened in incompressible fluid;
d) Annex F was added to include existing and additional guidelines for type testing;
e) Annex G was added to provide a place for informative information relative to bursting disc tolerances
and operating parameters.
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
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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

— Part 7: Common data
— Part 9: Application and installation of safety devices excluding stand-alone bursting disc safety devices
— Part 10: Sizing of safety valves for gas/liquid two-phase flow
1)
— Part 11: Performance testing
Part 7 contains data, which is common to more than one of the parts of ISO 4126 to avoid unnecessary
repetition.
1) In development.
© ISO 2014 – All rights reserved v

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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

Introduction
Safety devices for the protection of pressure equipment against excessive pressure include pressure relief
devices such as safety valves and bursting disc safety devices which, dependent upon the application,
may be used either as the sole pressure relieving devices or in conjunction with each other.
Operating problems frequently arise due to the use of pressure relieving devices not having been
properly selected for the intended service or properly selected but whose performance is adversely
affected by improper handling, wrong installation or lack of maintenance, any of which may affect the
safety of the pressure equipment being protected.
It is important to consider not only the pressure relief devices but also the whole of the pressure relief
system so as not to reduce the relieving capacity below that required or adversely affect the proper
operation of the pressure relieving devices.
A bursting disc safety device is a non-reclosing pressure relief device which typically comprises a
bursting disc, which is a pressure-containing and pressure-sensitive part designed to open by bursting
at a predetermined pressure, and a bursting disc holder. There are many different types of bursting disc
safety devices manufactured in corrosion resistant materials, both metallic and non-metallic, to cover
a wide range of nominal sizes, burst pressures and temperatures. They are used to protect pressure
equipment such as vessels, piping, gas cylinders or other enclosures from excessive pressure and/or
excessive vacuum.
This standard covers the important considerations necessary in the application, selection and
installation of bursting disc safety devices to give the required protection against excessive pressure
and/or excessive vacuum.
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SIST EN ISO 4126-6:2014
INTERNATIONAL STANDARD ISO 4126-6:2014(E)
Safety devices for protection against excessive pressure —
Part 6:
Application, selection and installation of bursting disc
safety devices
1 Scope
This International standard gives guidance on the application, selection and installation of bursting disc
safety devices used to protect pressure equipment from excessive pressure and/or excessive vacuum.
Annex A provides a checklist for the information to be supplied by the purchaser to the manufacturer.
Annex B gives guidance on the replacement period of a bursting disc.
Annex C provides guidance for determining the discharge capacity, for single phase fluids, of a pressure
relief system that contains a bursting disc safety device.
Annex D is a non-mandatory procedure for establishing the flow resistance of a burst bursting disc
assembly.
Annex E is a non-mandatory procedure for type testing of bursting disc safety devices.
Annex F provides typical performance characteristics for various bursting disc safety device types.
The requirements for the manufacture, inspection, testing, marking, certification and packaging of
bursting disc safety devices are given in ISO 4126-2.
2 Normative references
The following referenced documents, in whole or in part, are normatively referenced in this document
and are indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 4126-2, Safety devices for protection against excessive pressure — Part 2: Bursting disc safety devices
ISO 4126-3, Safety devices for protection against excessive pressure — Part 3: Safety valves and bursting
disc safety devices in combination
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4126-2 and the following apply.
3.1
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), and which is the complete assembly of installed components including,
where appropriate, the bursting disc holder
3.2
bursting disc assembly
complete assembly of components, which are installed in the bursting disc holder to perform the desired
function
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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

3.3
bursting disc
pressure-containing and pressure-sensitive component of a bursting disc safety device
3.4
bursting disc holder
that part of a bursting disc safety device, which retains the bursting disc assembly in position
3.5
conventional domed bursting disc (also referred to as, forward acting)
bursting disc which is domed in the direction of the bursting pressure (i.e. where the bursting pressure
is applied to the concave side of the bursting disc
Note 1 to entry: See ISO 4126-2:2003, Figure 1).
3.6
slotted lined bursting disc
bursting disc made up of two or more layers, at least one of which is slit or slotted to control the bursting
pressure of the bursting disc
3.7
reverse domed bursting disc (also referred to as, reverse acting)
bursting disc which is domed against the direction of the bursting pressure (i.e. where the bursting
pressure is applied to the convex side of the bursting disc
Note 1 to entry: See ISO 4126-2:2003, Figure 2).
3.8
flat bursting disc
bursting disc having one or more layers which is flat when installed. It may be made of a ductile or brittle
material
3.9
graphite bursting disc
bursting disc manufactured from graphite, impregnated graphite, flexible graphite or graphite composite
and designed to burst due to bending or shearing forces
3.10
specified bursting pressure
bursting pressure quoted with a coincident temperature when defining the bursting disc requirements
(used in conjunction with a performance tolerance, see 3.14)
3.11
specified maximum bursting pressure
maximum bursting pressure quoted with the coincident temperature when defining the bursting disc
requirements (used in conjunction with specified minimum bursting pressure, see 3.12)
3.12
specified minimum bursting pressure
minimum bursting pressure quoted with the coincident temperature when defining the bursting disc
requirements (used in conjunction with specified maximum bursting pressure, see 3.11)
3.13
coincident temperature
temperature of the bursting disc associated with a bursting pressure (see 3.10, 3.11 and 3.12) and which
is the expected temperature of the bursting disc when it is required to burst
2 © ISO 2014 – All rights reserved

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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

3.14
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
3.15
operating pressure
pressure existing at normal operating conditions within the system being protected
3.16
relieving pressure
maximum pressure under discharge conditions in the pressurized system
Note 1 to entry: It can differ from the bursting pressure of the bursting disc.
3.17
relieving temperature
temperature under discharge conditions in the pressurized system
Note 1 to entry: It can differ from the coincident temperature specified for the bursting disc.
3.18
differential back pressure
differential pressure across a bursting disc in the opposite direction to the direction of the bursting
pressure, which is the result of pressure in the discharge system from other sources and/or a result of
vacuum on the upstream side of the bursting disc
3.19
vent area
cross-section area available for discharge of fluid as calculated by the manufacturer
Note 1 to entry: The calculated vent area should not exceed the cross-sectional area of the upstream piping, A .
1
3.20
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 where the bursting discs are manufactured
from the same lot of material
3.21
bursting pressure
value of the differential pressure between the upstream side and the downstream side of the bursting
disc when it bursts
3.22
stiffening ring
component of a bursting disc assembly used primarily for reinforcing bursting discs
3.23
back pressure support
component of a bursting disc safety device, which prevents damage to the bursting disc due to differential
back pressure
Note 1 to entry: A back pressure support, which is intended to prevent damage to the bursting disc when the
system pressure falls below atmospheric pressure, is sometimes referred to as a vacuum support.
3.24
coating
layer of metallic or non-metallic material applied to components of a bursting disc safety device by a
coating process
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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

3.25
lining
additional sheet or sheets of metallic or non-metallic material forming part of a bursting disc assembly
or bursting disc holder
3.26
plating
metal layer applied to a bursting disc or bursting disc holder by a plating process
3.27
temperature shield
device which protects a bursting disc from excessive temperature
3.28
operating ratio
ratio between the operating pressure and the minimum limit of bursting pressure
Note 1 to entry: See Figure 1.
Note 2 to entry: In the case of a pressure system with an operating pressure expressed in bar gauge and
atmospheric pressure on the downstream side of the bursting disc:
operating pressure (bar)
Operating ratio =
minimum limit of bursting pressure (bar)
Note 3 to entry: In the case of a pressure system with a back pressure on the downstream side of the bursting
disc, the operating ratio is the value of the differential pressure between the upstream side and the downstream
side of the bursting disc divided by the minimum limit of bursting pressure expressed as a differential pressure.
3.29
bursting disc safety device discharge capacity
rate at which a bursting disc safety device can discharge fluid after bursting of the bursting disc
3.30
replacement period
time period beginning at the installation of a bursting disc assembly and ending at replacement
3.31
pressure relief system
system intended for the safe relief of fluids from pressure equipment for prevention of excessive pressure
Note 1 to entry: It can consist of equipment nozzle, inlet piping, pressure relief device(s) and discharge piping to
atmosphere/collecting vessel/header.
3.32
discharge coefficient
coefficient which determines reduction of theoretical discharge capacity of a pressure relief system by
the simplified approach (see C.2) which incorporates a burst bursting disc, forming part of a bursting
disc safety device
Note 1 to entry: It is denoted by the symbol α.
3.33
flow resistance factor
K
R
dimensionless expression of the velocity head loss attributed to the presence of a bursting disc safety
device in a piping system
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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

3.33.1
flow resistance factor
K
RG
flow resistance of a bursting disc safety device when burst with compressible fluid in contact with the
upstream side of the bursting disc
3.33.2
flow resistance factor
K
RL
flow resistance of a bursting disc safety device when burst with incompressible fluid in contact with the
upstream side of the bursting disc
3.33.3
flow resistance factor
K
RGL
flow resistance of a bursting disc safety device when burst with either compressible or incompressible
fluid in contact with the upstream side of the bursting disc
3.34
base pressure
pressure recorded at the pipe inlet of the bursting disc flow test system
3.35
base temperature
temperature recorded at the pipe inlet of the bursting disc flow test system
3.36
maximum allowable pressure
p
S
maximum pressure for which the equipment is designed, as specified by the manufacturer
3.37
non-fragmenting bursting disc safety device
bursting disc safety device that is designed to retain the petals produced during activation
4 Symbols and units
Table 1 — Symbols and their descriptions
Symbol Description Units
2
A Required minimum cross-sectional flow area mm
o
2
A Cross-sectional area of upstream piping mm
1
2
A Bursting disc safety device vent area mm
B
C Function of the isentropic exponent —
C Sonic velocity at pressure tap m/s
tap
D Test system pipework inside diameter mm
f Fanning friction for system, pipe —
2
G Mass velocity kg/(m ·h)
k Isentropic exponent —
K Theoretical capacity correction factor for subcritical flow —
b
K Viscosity correction factor —
v
K Flow resistance factor —
R
a
x is expressed as 0,xx.
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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

Table 1 (continued)
Symbol Description Units
K Total resistance factor from pipe inlet of test system to pressure tap —
tap
M Molecular mass kg/kmol
Ma Mach number at pressure tap —
tap
Ma Mach number at pipe inlet of test system —
1
p Test system pipe inlet pressure bar abs.
1
p Base pressure bar abs.
B
p Back pressure bar abs.
b
p Critical pressure bar abs.
c
p Relieving pressure bar abs.
o
p Pressure at pressure tap bar abs.
tap
p Reduced pressure —
r
Q Mass flow rate kg/h
m
−1 −1
R Universal gas constant 8 314 J∙kmol ∙K
Re Reynolds Number —
T Base temperature K
B
T Relieving temperature K
o
T Temperature recorded at pressure tap K
tap
T Test system pipe inlet temperature K
1
3
v Specific volume at actual relieving pressure and temperature m /kg
o
3
v Specific volume at pressure tap m /kg
tap
a
x Dryness of wet steam —
Y Expansion factor at pressure tap —
tap
Y Expansion factor at pipe inlet of test system —
1
Z Compressibility factor at actual relieving pressure and temperature —
o
3
ρ Density kg/m
µ Dynamic viscosity Pa·s
Δp Differential pressure on venting across bursting disc safety device bar abs.
α Discharge coefficient (see C.2) —
a
x is expressed as 0,xx.
5 Application
5.1 Subject to the requirements of the relevant standard covering the equipment to be protected,
bursting disc safety devices may be used either as the sole pressure relieving device, in conjunction with
safety valves or as part of a combination device.
5.2 The discharge capacity of a system including a bursting disc safety device and its maximum limit of
bursting pressure (see Figure 1) at the coincident temperature shall be such that the maximum relieving
pressure does not exceed the requirements of the protected equipment. Annex C gives methods for
determining discharge capacity of pressure relief systems incorporating bursting disc safety devices.
5.3 The use of a bursting disc safety device as the sole pressure relieving device may be preferred in the
following cases where:
6 © ISO 2014 – All rights reserved

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SIST EN ISO 4126-6:2014
ISO 4126-6:2014(E)

a) the rate of increase in pressure may be such that the rate of response of a safety valve would make
it unsuitable;
b) leakage of the fluid cannot be tolerated under operating conditions;
c) operating conditions may involve deposition, which would make a safety valve inoperative;
d) the effect of low temperature would prevent a safety valve from operating;
e) large discharge areas are required.
NOTE A bursting disc safety device is a non-reclosing pressure relieving device, which after bursting could
res
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