EN ISO 4126-6:2014

SLOVENSKI STANDARD
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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.

Contents Page
Foreword .3
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.
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
ISO 4126-6:2014(E)
© 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
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2014 – All rights reserved

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 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
iv © ISO 2014 – All rights reserved

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 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.
vi © ISO 2014 – All rights reserved

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
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

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 .
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
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
4 © ISO 2014 – All rights reserved

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
A Required minimum cross-sectional flow area mm
o
A Cross-sectional area of upstream piping mm
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 —
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.
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 —
p Test system pipe inlet pressure bar abs.
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
v Specific volume at actual relieving pressure and temperature m /kg
o
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 —
Z Compressibility factor at actual relieving pressure and temperature —
o
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

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
result in the total loss of pressure/contents from the protected equipment.
5.4 For all applications the pressure relief system shall be such that following the bursting of the
bursting disc assembly any fragmentation or release of material does not:
a) cause an unacceptable flow restriction within the pressure relief system;
b) impair the proper functioning of any other safety device;
c) affect the certified (discharge) capacity of any other safety device.
5.5 Bursting disc safety devices may be used in association with safety valves, pilot operated safety
valves or CSPRS (according to ISO 4126-1, ISO 4126-4 and ISO 4126-5 respectively) as permitted by the
relevant standard. The application of the bursting disc safety devices shall not result in excessive pressure
in the protected equipment.
5.5.1 Bursting disc safety devices in conjunction with safety valve(s) may be used in the following
cases:
a) in series, to protect the safety valve against corrosion, fouling or operating conditions which may
affect the safety valve performance;
b) in series, to prevent leakage;
c) in series, to prevent total loss of contents from the protected equipment following the bursting of
the bursting disc;
d) in parallel, as an additional safeguard.
5.5.2 Where a bursting disc safety device is to be installed upstream of a safety valve the following
requirements shall be met:
a) the space between the bursting disc safety device and the safety valve shall be provided with an
appropriate means to prevent or detect an unacceptable build up in pressure;
b) the bursting disc safety device shall be a non-fragmenting design;
c) the nominal pipe size of the bursting disc safety device shall be not less than the nominal size of the
inlet of the safety valve;
d) where the bursting disc safety device is within 5 pipe diameters, see ISO 4126-3.
e) where the bursting disc safety device is beyond 5 pipe diameters of the safety valve consult the
manufacturer for application guidance.
NOTE Bursting discs, being pressure differential devices, will require a higher pressure in the protected
equipment to burst the bursting disc if pressure builds up in the space between the bursting disc and the safety
valve which will occur should leakage develop in the bursting disc due to corrosion, or due to back pressure in the
discharge piping or other cause.
ISO 4126-6:2014(E)
5.5.3 where a bursting disc safety device is to be installed downstream of the safety valve, the following
requirements shall be met:
a) the bursting disc safety device and discharge piping shall be so designed as not to impair the
operating characteristics of the safety valve;
b) the space between the bursting disc safety device and the safety valve shall be provided with an
appropriate means to prevent or detect an unacceptable build up in pressure;
c) the space between the bursting disc and safety valve shall be large enough to ensure the correct
functioning of the bursting disc.
NOTE A spring-loaded safety valve, which is not balanced, cannot open at its set pressure if back pressure
builds up in the space between the safety valve and the bursting disc safety device. A particular design of
safety valve can be required.
d) the maximum limit of bursting pressure of the bursting disc at the coincident temperature plus any
pressure in the discharge piping shall not exceed the:
1) back pressure limitations of the safety valve;
2) design pressure of any pipe or fitting between the safety valve and the bursting disc safety
device;
3) pressure permitted by the relevant standard.
5.5.4 A bursting disc safety device may be installed both upstream and downstream of a safety valve
provided that the requirements of 5.5.2 and 5.5.3 are met.
5.5.5 A bursting disc safety device fitted in parallel with a safety valve as an additional safeguard (e.g.
to protect equipment against the consequence of a rapid rise in pressure) shall be specified to burst at a
pressure not exceeding the relevant requirements of the protected equipment.
5.6 Where a bursting disc safety device is fitted in series with a second bursting disc safety device, the
following requirements shall be met:
a) a space between the two bursting discs shall be large enough to ensure the correct functioning of
the bursting discs;
b) the space between the bursting disc shall be provided with a means for preventing unacceptable
build up in pressure.
NOTE Bursting discs, being pressure differential devices, will require a higher pressure in the protected
equipment to burst the bursting disc if pressure builds up in the space between the bursting discs which will
occur should leakage develop in the bursting disc due to corrosion or other causes.
6 Selection
6.1 Selection of bursting disc safety devices
6.1.1 The manufacturer’s advice should be sought when selecting a bursting disc safety device for a
particular application.
6.1.2 Bursting disc safety devices are differential pressure devices and therefore the pressure on both
the upstream and the downstream side of the bursting disc shall be taken into consideration.
8 © ISO 2014 – All rights reserved

ISO 4126-6:2014(E)
6.1.3 Consideration needs to be given to the replacement period of the bursting disc assembly. This
period depends upon the type and material of the bursting disc assembly, operating conditions and many
other factors.
Guidelines for determining the replacement period of a bursting disc are given in Annex B.
6.1.4 Bursting disc safety devices are frequently required to work in corrosive environments where
corrosion may cause premature failure of the bursting disc. Materials likely to be affected by corrosion
may be protected by coating, plating or lining which shall be supplied only by the manufacturer.
6.1.5 Selection of the appropriate bursting disc material depends upon the chemical and physical
conditions that will exist on both the upstream side and the downstream side of the bursting disc safety
device when it is in service.
6.1.6 Where there is the possibility of deposition of sublimates or other solids on the upstream side
of the bursting disc safety device, consideration shall be given to selecting a type of bursting disc safety
device suitable for such conditions.
6.1.7 When selecting the size of bursting disc safety devices, area restricting features shall be taken into
account when determining the vent area.
6.1.8 The bursting pressure of a bursting disc according to its material and type may vary with its
temperature.
NOTE Data regarding the expected variation of bursting pressure according to the temperature for a batch
of bursting discs should be requested from the manufacturer. Generally, in the temperature range 15 °C to 30 °C
inclusive, there is no significant variation in the bursting pressure. However, below or above this range a bursting
disc may have respectively a higher or lower bursting pressure than that within the range. When a bursting disc
safety device is specified with a bursting pressure at a coincident temperature to protect equipment, the bursting
disc may not give the necessary protection with regard to the bursting pressure of the bursting disc over the
whole temperature range of the protected equipment. The coincident temperature may not be the same as the
temperature of the fluid.
The coincident temperature may be determined by the direct measurement or by the calculation using
established heat transfer methods.
6.1.9 Bursting discs can be protected from excessive temperature by suitable location, temperature
shields or other means. When it is necessary to protect a bursting disc from excessive temperature, the
influence of the protection shall be considered when establishing the coincident temperature.
The use of temperature shields shall be evaluated by the manufacturer of the bursting disc safety device.
6.1.10 The type of bursting disc holder and its inlet and outlet connections shall be appropriate to the
method of installing the bursting disc safety device and the requirements for the safe discharge of the
fluid.
6.1.11 Where a bursting disc safety device is to be installed upstream of a safety valve, so as to form a
combination device, the selection shall take into consideration the requirements of ISO 4126-3.
6.1.12 Where a bursting disc safety device is to be selected for installation upstream and/or downstream
of a safety valve, both the bursting disc safety device manufacturer and the safety valve manufacturer
shall be consulted. In the case of downstream application the effects on the set pressure of the safety valve
due to potential leakage across the safety valve seat and/or from the downstream side of the bursting disc
safety device need to be considered.
ISO 4126-6:2014(E)
6.2 Selection of the performance tolerance
The performance tolerance is dependent upon a number of factors, including the following:
a) type of bursting disc;
b) material of the bursting disc;
c) method of manufacture.
In selecting the performance tolerance for a particular application, consideration shall be given to
the above factors and the process conditions. The performance tolerance shall be specified by the
manufacturer after consultation with the purchaser using one of the two alternative methods according
to ISO 4126-2:2003, Clause 12. Typical performance tolerances are given in Table F.1.
The maximum bursting pressure at the coincident temperature shall never exceed 1,1 times PS and
provisions shall be made to ensure that the operating pressure will not permanently exceed PS.
The minimum limit of bursting pressure shall be selected to ensure that there is a suitable margin between
it and the operating pressure. Due consideration shall be given to the operating ratio appropriate to the
material and type of bursting disc and the process conditions. Typical maximum operating ratios are
given in Table F.2.
10 © ISO 2014 – All rights reserved

ISO 4126-6:2014(E)
a) Specified maximum bursting pressure and specified minimum bursting pressure with a
coincident temperature
b) Specified bursting pressure and performance tolerance with a coincident temperature
Figure 1 — Methods for specifying bursting discs
ISO 4126-6:2014(E)
7 Installation
7.1 General
The requirements for the location of bursting disc safety devices within the system which they protect,
are specified in 7.2. General requirements for the safe installation of bursting disc safety devices are
given in 7.3.
7.2 Location of bursting disc safety devices
7.2.1 A bursting disc safety device shall be placed as close as practicable to the protected equipment,
taking into account pressure pulsations, temperature, and other service conditions.
7.2.2 The pressure relief system shall be properly sized, as straight and as short as practicable,
terminating in such a way as to avoid dangerous or damaging conditions arising on venting.
7.2.3 The pressure relief system piping shall be properly designed, so that any thermal movement of
the protected equipment and the pressure relief system piping does not cause excessive forces on the
bursting disc safety device that may lead to incorrect functioning or failure.
7.2.4 Bursting disc safety devices shall be mounted so that they are accessible for replacement and
protected from accidental damage.
7.2.5 Provision shall be made to absorb the effect of reaction forces on the protected equipment, which
will arise during relieving conditions.
A baffle plate may be fitted downstream of a bursting disc safety device to redirect the discharge fluid
and/or reduce recoil providing that it does not reduce the required discharge capacity of the pressure
relief system.
7.2.6 In the case of the discharge of a hazardous fluid, the potential danger shall be considered and
appropriate measures taken to minimize the risk.
7.2.7 Precautions shall be taken to prevent deposition on the upstream side of the bursting disc safety
device and in the part leading to it, of sublimates or other solids that could affect the safe operation of the
bursting disc.
Liquid or foreign matter shall be prevented from accumulating within the discharge piping and/or on
the downstream side of the bursting disc.
7.2.8 In the case of graphite monobloc bursting discs which are recessed on the inlet side (see ISO 4126-
2:2003, Figure 4) the internal diameter of the discharge pipe adjacent to the downstream side of the
bursting disc shall be larger than the inside diameter of the recess.
7.2.9 Where plug/screw bursting disc holders are to be installed in a pressure relief system, an
additional connection may be required to facilitate the assembly and replacement of the bursting disc
assembly.
7.3 Installation of bursting disc safety devices
7.3.1 The bursting disc safety device shall be assembled and installed in accordance with the
manufacturer’s assembly and installation instructions.
NOTE If the components of a bursting disc safety device are handled, assembled or installed incorrectly, the
bursting disc can burst at a pressure higher or lower than the required burst pressure.
12 © ISO 2014 – All rights reserved

ISO 4126-6:2014(E)
7.3.2 The bursting disc safety device or any of its components as supplied shall not be modified in any
way except with the approval of the manufacturer.
The application of an additional protective film or coating to a bursting disc is not allowed, except when
approved by the manufacturer since this may considerably affect the bursting pressure of the bursting
disc.
7.3.3 The bursting disc safety device shall be checked for freedom from visible defects immediately
before installation and care taken during installation to avoid damage.
7.3.4 Prior to assembly, the bursting disc holder reference, marked on the bursting disc/bursting disc
assembly, shall be checked to ensure that it coincides with that marked on the bursting disc holder.
7.3.5 When assembling the bursting disc safety device components the fitting of any back pressure
support shall be checked to ensure that it is correct.
7.3.6 Any directional arrow, bolting torque instructions and reference to the use of gaskets shall be
complied with during installation.
7.3.7 The type, material and dimensions of the gaskets used between the bursting disc safety device and
the flanges between which it is to be installed
...