SIST EN ISO 4126-6:2004

SLOVENSKI STANDARD
SIST EN ISO 4126-6:2004
01-junij-2004
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Safety devices for protection against excessive pressure - Part 6: Application, selection
and installation of bursting disc safety devices (ISO 4126-6:2003)
Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 6:
Berstscheibeneinrichtung; Anwendung, Auswahl und Einbau (ISO 4126-6:2003)
Dispositifs de sécurité contre les pressions excessives - Partie 6: Application, sélection
et installation des dispositifs de sureté a disque de rupture (ISO 4126-6:2003)
Ta slovenski standard je istoveten z: EN ISO 4126-6:2003
ICS:
13.240 Varstvo pred previsokim Protection against excessive
tlakom pressure
SIST EN ISO 4126-6:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 4126-6:2004

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SIST EN ISO 4126-6:2004
EUROPEAN STANDARD
EN ISO 4126-6
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2003
ICS 13.240
English version
Safety devices for protection against excessive pressure - Part
6: Application, selection and installation of bursting disc safety
devices (ISO 4126-6:2003)
Dispositifs de sécurité contre les pressions excessives - Sicherheitseinrichtungen gegen unzulässigen Überdruck -
Partie 6: Application, sélection et installation des dispositifs Teil 6: Berstscheibeneinrichtung; Anwendung, Auswahl und
de sûreté à disque de rupture (ISO 4126-6:2003) Einbau (ISO 4126-6:2003)
This European Standard was approved by CEN on 27 December 2002.
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 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 Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, 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
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-6:2003 E
worldwide for CEN national Members.

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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
Contents
Foreword.3
Introduction .4
1 Scope .5
2 Normative references .5
3 Terms and definitions.5
4 Symbols and units .9
5 Application.10
6 Selection .11
6.1 Selection of bursting disc safety devices .11
6.2 Selection of the performance tolerance .12
7 Installation .15
7.1 General.15
7.2 Location of bursting disc safety devices .15
7.3 Installation of bursting disc safety devices .16
Annex A (informative) Information to be supplied by the purchaser.17
A.1 General.17
A.2 Application details .17
A.3 Bursting disc safety device operating details .17
A.4 Installation details.17
A.5 Special details .18
A.6 Language .18
A.7 Replacement bursting discs.18
Annex B (informative) Guidelines for determining the replacement period of a bursting disc .19
B.1 Introduction .19
B.2 Bursting disc safety devices .19
B.3 Replacement period.19
B.4 Methods of determining the replacement period .20
Annex C (informative) Pressure relief system discharge capacity .21
C.1 General.21
C.2 Simplified approach.21
C.3 Comprehensive approach.25
Annex D (informative) Derivation of compressibility factor Z .27
Annex E (informative) Flow testing of bursting disc safety devices.28
E.1 Scope .28
E.2 Test requirements.28
E.3 Method of testing.31
E.4 Test procedure .32
E.5 Determination of flow resistance factor K .33
R
E.6 Application of flow resistance factor K .36
R
Bibliography .37
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
Foreword
This document (EN ISO 4126-6:2003) 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 April 2004 and conflicting national standards shall be withdrawn at the latest by
April 2004.
This standard for safety devices for protection against excessive pressure consists of seven parts of which this is
Part 6. 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, which is common to more than one of the parts of this standard to avoid unnecessary
repetition.
Annexes A to E are informative.
This document includes a Bibliography.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,
Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (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 4126-6:2004
EN ISO 4126-6:2003 (E)
1 Scope
This 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 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.
The requirements for the manufacture, inspection, testing, marking, certification and packaging of bursting disc
safety devices are given in Part 2 of EN ISO 4126.
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 ISO 4126-1:2003, Safety devices for protection against excessive pressure — Part 1 : Safety valves (ISO 4126-
1:2003).
EN ISO 4126-2:2003, Safety devices for protection against excessive pressure — Part 2 : Bursting disc safety
devices (ISO 4126-2:2003).
EN ISO 4126-4, Safety devices for protection against excessive pressure — Part 4 : Pilot operated safety valves
(ISO 4126-4:2003).
EN ISO 4126-5, Safety devices for protection against excessive pressure — Part 5 : Controlled safety pressure
relief systems (CSPRS) (ISO 4126-5:2003).
EN ISO 4126-7:2003, Safety devices for protection against excessive pressure — Part 7 : Common data (ISO
4126-7:2003).
3 Terms and definitions
For the purposes of this European Standard, the terms and definitions given in EN ISO 4126-1:2003 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)
NOTE It 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
3.3
bursting disc
pressure-containing and pressure-sensitive component of a bursting disc safety device
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
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 (see Figure 1 of EN ISO 4126-2:2003)
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, see Figure 2 of EN ISO 4126-2:2003)
3.8
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
NOTE The following definitions apply :
a) graphite : a crystalline form of the element carbon ;
b) impregnated graphite : graphite in which the open porosity is impregnated with a filler material ;
c) flexible graphite : a graphite structure formed by the compression of thermally exfoliated graphite intercalation
compounds ;
d) graphite composite : made up of two or more distinct materials and having different properties to those of the separate
materials and in which the proportion of graphite is over 50 per cent by weight.
3.9
specified bursting pressure
bursting pressure quoted with a coincident temperature when defining the bursting disc requirements (used in
conjunction with a performance tolerance, see 3.13)
3.10
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 3.11)
3.11
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 3.10)
3.12
coincident temperature
temperature of the bursting disc associated with a bursting pressure (see 3.9, 3.10 and 3.11) and which is the
expected temperature of the bursting disc when it is required to burst
3.13
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
3.14
operating pressure
pressure existing at normal operating conditions within the system being protected
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
3.15
relieving pressure
maximum pressure under discharge conditions in the pressurised system
NOTE It can differ from the bursting pressure of the bursting disc.
3.16
relieving temperature
temperature under discharge conditions in the pressurised system
NOTE It can differ from the coincident temperature specified for the bursting disc.
3.17
differential back pressure
differential pressure across a bursting disc opposed to the direction of the bursting pressure
NOTE This can be 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.
3.18
bursting disc safety device discharge area
area which is the minimum cross-sectional flow area of the bursting disc safety device taking into consideration the
possible reduction of the cross-section, e.g. by back pressure supports, catching devices or parts of the bursting
disc which remain after bursting
3.19
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
3.20
bursting pressure
value of the differential pressure between the upstream side and the downstream side of the bursting disc when it
bursts
3.21
back pressure support
component of a bursting disc safety device, which prevents damage to the bursting disc due to differential back
pressure
NOTE 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.
3.22
coating
layer of metallic or non-metallic material applied to components of a bursting disc safety device by a coating
process
3.23
lining
additional sheet or sheets of metallic or non-metallic material forming part of a bursting disc assembly or bursting
disc holder
3.24
plating
metal layer applied to a bursting disc or bursting disc holder by a plating process
3.25
temperature shield
device which protects a bursting disc from excessive temperature
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
3.26
operating ratio
ratio between the operating pressure and the minimum limit of bursting pressure (see Figure 1)
NOTE 1 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 2 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.
3.27
bursting disc safety device discharge capacity
rate at which a bursting disc safety device can discharge fluid after bursting of the bursting disc
3.28
replacement period
time period beginning at the installation of a bursting disc assembly and ending at replacement
3.29
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, inlet piping, pressure relief device(s) and discharge piping to
atmosphere/collecting vessel/header.
3.30
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 It is denoted by the symbol
.
3.31
flow resistance factor
factor which determines the resistance to flow in a pipework system caused by the presence therein of a bursting
disc, forming part of a bursting disc safety device, installed in the system
NOTE It is denoted by the symbol K , a dimensionless factor expressed as the velocity head loss.
R
3.32
base pressure
pressure recorded at the pipe inlet of the bursting disc flow test system
3.33
base temperature
temperature recorded at the pipe inlet of the bursting disc flow test system
3.34
maximum allowable pressure, PS
maximum pressure for which the equipment is designed, as specified by the manufacturer
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
4 Symbols and units
Table 1 — Symbols and their descriptions
Symbol Description Units
A 2
Required minimum cross-sectional flow area
o mm
2
A
Cross-sectional area of upstream piping
mm
1
2
A
Bursting disc safety device discharge 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
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 bar abs.
r
Q
Mass flow rate kg/h
m
R Universal gas constant 8314 J/mol/K
R
Reynolds Number -
e
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
Dryness of wet steam -
x
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
3rDensity
kg/m
μ Dynamic viscosity Pa·s
Dp Differential pressure on venting across bursting disc safety device bar abs.

Discharge coefficient (see C.2.) -
a
x is expressed as 0,xx.
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
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. Annexes C, D and E give 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 :
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.
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.
5.4 Bursting disc safety devices may be used in association with pilot operated safety valves or CSPRS
(according to EN ISO 4126-4 and EN 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.
5.4.1 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.
5.4.2 Where a bursting disc safety device is to be installed upstream of a safety valve the following requirements
shall be met :
a) the specified bursting requirements of the bursting disc safety device shall comply with the relevant
requirements of the protected equipment ;
b) for those applications where the bursting disc safety device forms part of a combination device, the
requirements shall comply with the standard(s) applicable to such devices;
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SIST EN ISO 4126-6:2004
EN ISO 4126-6:2003 (E)
c) the space between the bursting disc and the safety valve 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 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.
5.4.3 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 and the safety valve shall be provided with a means for preventing
unacceptable build up in pressure ;
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.
c) 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.
5.4.4 A bursting disc safety device may be installed both upstream and downstream of a safety valve provided
that the requirements of 5.4.2 and 5.4.3 are met.
5.4.5 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
excee
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