Safety devices for protection against excessive pressure - Part 3: Safety valves and bursting disc safety devices in combination (ISO 4126-3:2020)

This document specifies only the requirements for a product assembled from the in-series combination
of safety valves or CSPRS (controlled safety pressure relief systems) according to ISO 4126-1, ISO 4126-4
and ISO 4126-5, and bursting disc safety devices, according to ISO 4126-2, installed upstream of the
valve within five pipe diameters of the valve inlet. It specifies the design, application and marking
requirements for such products, composed of the bursting disc safety device, a safety valve or CSPRS
and, where applicable, a connecting pipe or spool piece. In addition, it gives a method for establishing
the combination discharge factor used in sizing combinations.

Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 3: Sicherheitsventile und Berstscheibeneinrichtungen in Kombination (ISO 4126-3:2020)

Dieses Dokument legt nur die Anforderungen fest an ein Produkt, bestehend aus einer in Reihe geschalteten Kombination von Sicherheitseinrichtungen bzw. gesteuerten Sicherheitsventilen (CSPRS) nach ISO 4126 1, ISO 4126 4 und ISO 4126 5 und Berstscheibeneinrichtungen nach ISO 4126 2, bei der die Berstscheibeneinrichtung in einem Abstand von höchstens 5 Rohrdurchmesser vor der Ventileintrittsseite eingebaut ist. Es legt die Anforderungen für Konstruktion, Anwendung und Kennzeichnung von Produkten fest, die eine Berstscheibeneinrichtung, ein Sicherheitsventil oder ein gesteuertes Sicherheitsventil (CSPRS) und ggf. ein Anschlussrohr- oder Leitungsstück umfassen. Zusätzlich wird ein Verfahren festgelegt, nach dem die bei der Bemessung der Kombination eingesetzte Ausflussziffer bestimmt wird.

Dispositifs de sécurité pour protection contre les pressions excessives - Partie 3: Soupapes de sûreté et dispositifs de sûreté à disque de rupture en combinaison (ISO 4126-3:2020)

Le présent document spécifie seulement les exigences applicables aux combinaisons en série de soupapes de sûreté ou de DSDCS (dispositifs de sécurité à décharge contrôlés contre les surpressions), conformément à l'ISO 4126‑1, à l'ISO 4126‑4 et à l'ISO 4126‑5, et de dispositifs de sûreté à disque de rupture conformément à l'ISO 4126‑2 installés en amont de la soupape à une distance de l'orifice d'entrée de la soupape au plus égale à cinq diamètres de tuyauterie. Il spécifie les exigences de conception, d'application et de marquage de tels produits, composés du dispositif de sûreté à disque de rupture, une soupape de sûreté ou un DSDCS et, le cas échéant, la tuyauterie ou manchette de raccordement. Il donne, en outre, la méthode permettant d'établir le coefficient de débit de la combinaison utilisé pour le dimensionnement des combinaisons.

Naprave za varovanje pred visokim tlakom - 3. del: Varnostni ventili in razpočne plošče v kombinaciji (ISO/FDIS 4126-3:2020)

General Information

Status
Published
Public Enquiry End Date
19-Oct-2019
Publication Date
12-Oct-2020
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
08-Oct-2020
Due Date
13-Dec-2020
Completion Date
13-Oct-2020

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SLOVENSKI STANDARD
SIST EN ISO 4126-3:2020
01-november-2020
Nadomešča:
SIST EN ISO 4126-3:2006
Naprave za varovanje pred visokim tlakom - 3. del: Varnostni ventili in razpočne
plošče v kombinaciji (ISO/FDIS 4126-3:2020)

Safety devices for protection against excessive pressure - Part 3: Safety valves and

bursting disc safety devices in combination (ISO 4126-3:2020)

Sicherheitseinrichtungen gegen unzulässigen Überdruck - Teil 3: Sicherheitsventile und

Berstscheibeneinrichtungen in Kombination (ISO 4126-3:2020)

Dispositifs de sécurité pour protection contre les pressions excessives - Partie 3:

Soupapes de sûreté et dispositifs de sûreté à disque de rupture en combinaison (ISO

4126-3:2020)
Ta slovenski standard je istoveten z: EN ISO 4126-3:2020
ICS:
13.240 Varstvo pred previsokim Protection against excessive
tlakom pressure
SIST EN ISO 4126-3:2020 en

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

---------------------- Page: 1 ----------------------
SIST EN ISO 4126-3:2020
---------------------- Page: 2 ----------------------
SIST EN ISO 4126-3:2020
EN ISO 4126-3
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2020
EUROPÄISCHE NORM
ICS 13.240 Supersedes EN ISO 4126-3:2006
English Version
Safety devices for protection against excessive pressure -
Part 3: Safety valves and bursting disc safety devices in
combination (ISO 4126-3:2020)

Dispositifs de sécurité pour protection contre les Sicherheitseinrichtungen gegen unzulässigen

pressions excessives - Partie 3: Soupapes de sûreté et Überdruck - Teil 3: Sicherheitsventile und

dispositifs de sûreté à disque de rupture en Berstscheibeneinrichtungen in Kombination (ISO

combinaison (ISO 4126-3:2020) 4126-3:2020)
This European Standard was approved by CEN on 11 July 2020.

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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, 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: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4126-3:2020 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 4126-3:2020
EN ISO 4126-3:2020 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

Annex ZA (informative) Relationship between this European Standard and the Essential

Requirements of EU Directive 2014/68/EU (PED) aimed to be covered .................................... 4

---------------------- Page: 4 ----------------------
SIST EN ISO 4126-3:2020
EN ISO 4126-3:2020 (E)
European foreword

This document (EN ISO 4126-3:2020) 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 March 2021, and conflicting national standards shall

be withdrawn at the latest by March 2021.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 4126-3:2006.

This document has been prepared under a mandate given to CEN by the European Commission and the

European Free Trade Association, and supports essential requirements of EU Directive(s).

For the relationship with EU Directive(s) see informative Annex ZA, which is an integral part of this

document.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 4126-3:2020 has been approved by CEN as EN ISO 4126-3:2020 without any

modification.
---------------------- Page: 5 ----------------------
SIST EN ISO 4126-3:2020
EN ISO 4126-3:2020 (E)
Annex ZA
(informative)
Relationship between this European Standard and the Essential
Requirements of EU Directive 2014/68/EU (PED) aimed to be covered

This European Standard has been prepared under a Commission’s standardization request to provide

one voluntary means of conforming to Essential Requirements of New Approach Directive 2014/68/EU,

Pressure Equipment Directive (PED).

Once this document is cited in the Official Journal of the European Union under that Directive,

compliance with the normative clauses of this document given in Table ZA.1 confers, within the limits of

the scope of this document, a presumption of conformity with the corresponding essential

requirements of that Directive and associated EFTA regulations.

Table ZA.1 — Correspondence between this European Standard and Annex I of the Directive

2014/68/EU
Essential Requirements of Clause(s)/sub-clause(s) Remarks/Notes
Directive 2014/68/EU of this EN
Clause 2.1 5, 7, 9 and 12 General design
Clause 2.11.1 and 2.11.2 5, 6, 7, 8, 9, 11 and 12 Safety accessories
Clause 3.4 a), 1st indent 6 Installation instructions

WARNING 1 — Presumption of conformity stays valid only as long as a reference to this European

Standard is maintained in the list published in the Official Journal of the European Union. Users of this

document should consult frequently the latest list published in the Official Journal of the European

Union.

WARNING 2 — Other Union legislation may be applicable to the product(s) falling within the scope of

this document.
---------------------- Page: 6 ----------------------
SIST EN ISO 4126-3:2020
INTERNATIONAL ISO
STANDARD 4126-3
Second edition
2020-09
Safety devices for protection against
excessive pressure —
Part 3:
Safety valves and bursting disc safety
devices in combination
Dispositifs de sécurité pour protection contre les pressions
excessives —
Partie 3: Soupapes de sûreté et dispositifs de sûreté à disque de
rupture en combinaison
Reference number
ISO 4126-3:2020(E)
ISO 2020
---------------------- Page: 7 ----------------------
SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Symbols .......................................................................................................................................................................................................................... 4

5 Design of combination .................................................................................................................................................................................... 4

6 Installation of combination ....................................................................................................................................................................... 5

7 Combination performance ......................................................................................................................................................................... 5

8 Determination of combination discharge capacity factor, F , by testing....................................................6

8.1 General ........................................................................................................................................................................................................... 6

8.2 Test requirements ................................................................................................................................................................................ 6

8.3 Test rig ............................................................................................................................................................................................................ 6

8.4 Test method ............................................................................................................................................................................................... 7

8.5 Test procedure ......................................................................................................................................................................................... 7

8.6 Acceptance criteria of the tests ................................................................................................................................................. 7

8.6.1 General...................................................................................................................................................................................... 7

8.6.2 Conditions applicable to the safety valve ................................................................................................... 8

8.6.3 Conditions applicable to the bursting disc safety device .............................................................. 8

8.6.4 Conditions applicable to combination .......................................................................................................... 8

9 Derivation of combination discharge capacity factor, F ........................................................................................... 9

10 Alternative to testing for F ...................................................................................................................................................................... 9

11 Certification of combination discharge capacity factor, F ...................................................................................... 9

12 Application and use of the certified combination discharge capacity factor, F ...............................9

13 Marking and identification of combination devices ........................................................................................................ 9

13.1 Bursting disc safety device ........................................................................................................................................................... 9

13.2 Safety valve ..............................................................................................................................................................................................10

13.3 Combination ...........................................................................................................................................................................................10

14 Documentation ....................................................................................................................................................................................................10

15 Preparation for storage and transport .......................................................................................................................................11

© ISO 2020 – All rights reserved iii
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SIST EN ISO 4126-3:2020
ISO 4126-3:2020(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 (see 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 (see 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 of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 185, Safety devices for protection against

excessive pressure, in collaboration with the European Committee for Standardization (CEN) Technical

Committee CEN/TC 69, Industrial valves, in accordance with the Agreement on technical cooperation

between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 4126-3:2006), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— Eliminated unnecessary references and definitions throughout the document.

— Clause 5: Inlet line and pressure drop requirements from prior 6.2 were moved to Clause 5 and a

reference to ISO 4126-9 was also added.

— Clause 7: Deleted specific references to specific EN standards to refer to the applicable pressure

vessel standard to reflect the global nature of this document.
— Clause 9: The restrictions for F values less than 0,97 were eliminated.

— Clause 12: Clarified the applicable minimum bursting pressure for which the F value can be used

for sizes larger than those flow tested.

— Clause 14: Added a requirement for the supplier to provide a test certificate if the F being used is a

certified combination discharge coefficient.
A list of all parts in the ISO 4126 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
---------------------- Page: 10 ----------------------
SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)
Introduction

Bursting disc safety devices can be used upstream of safety valves in the following cases:

a) to protect the safety valve against corrosion, fouling or operating conditions which could affect the

safety valve performance;
b) to prevent leakage;

c) to prevent total loss of contents from the protected equipment following the bursting of the

bursting disc.

The term combination is used to describe the close-coupled (i.e. within 5 pipe diameters) assembly of

a bursting disc safety device upstream of a safety valve or controlled safety pressure relief systems

(CSPRS), as defined by this document. Requirements for other installation arrangements of bursting

discs with safety valves or CSPRS are defined in ISO 4126-9.
© ISO 2020 – All rights reserved v
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SIST EN ISO 4126-3:2020
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SIST EN ISO 4126-3:2020
INTERNATIONAL STANDARD ISO 4126-3:2020(E)
Safety devices for protection against excessive pressure —
Part 3:
Safety valves and bursting disc safety devices in
combination
1 Scope

This document specifies only the requirements for a product assembled from the in-series combination

of safety valves or CSPRS (controlled safety pressure relief systems) according to ISO 4126-1, ISO 4126-4

and ISO 4126-5, and bursting disc safety devices, according to ISO 4126-2, installed upstream of the

valve within five pipe diameters of the valve inlet. It specifies the design, application and marking

requirements for such products, composed of the bursting disc safety device, a safety valve or CSPRS

and, where applicable, a connecting pipe or spool piece. In addition, it gives a method for establishing

the combination discharge factor used in sizing combinations.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 4126-1:2013, Safety devices for protection against excessive pressure — Part 1: Safety valves

ISO 4126-2:2018, Safety devices for protection against excessive pressure — Part 2: Bursting disc

safety devices

ISO 4126-4:2013, Safety devices for protection against excessive pressure — Part 4: Pilot operated

safety valves

ISO 4126-5:2013, Safety devices for protection against excessive pressure — Part 5: Controlled safety

pressure relief systems (CSPRS)

ISO 4126-6:2014, Safety devices for protection against excessive pressure — Part 6: Application, selection

and installation of bursting disc safety devices

ISO 4126-9:2008, Safety devices for protection against excessive pressure — Part 9: Application and

installation of safety devices excluding stand-alone bursting disc safety devices

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO 2020 – All rights reserved 1
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SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)
3.1
combination

installation which comprises a bursting disc safety device (3.3) installed within five pipe diameters

(from outlet of bursting disc holder (3.6) to inlet of valve) before the inlet of a safety valve or a CSPRS

Note 1 to entry: See Figure 1.
Key
1 safety valve or CSPRS
2 bursting disc safety device
3 safety valve or CSPRS inlet
4 bursting disc safety device outlet

NOTE Other bursting disc safety device configurations used in conjunction with safety valves or CSPRS are

specified in ISO 4126-6.
Figure 1 — Diagram of combination showing relative distance
3.2
combination discharge capacity factor

factor used to determine the discharge capacity of a safety valve or CSPRS when the safety valve or

CSPRS is used in combination with a bursting disc safety device (3.3) installed upstream of the safety

valve or CSPRS
3.3
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) (3.5)

Note 1 to entry: It is the complete assembly of installed components including, where appropriate, the bursting

disc holder (3.6).
3.4
bursting disc assembly

complete assembly of the components installed in the bursting disc holder (3.6) to perform the desired

function
3.5
bursting disc

pressure-sensitive component(s) of a bursting disc safety device (3.3) designed to open by bursting at a

specified bursting pressure (3.7)
3.6
bursting disc holder

part of a bursting disc safety device (3.3) which retains the bursting disc assembly (3.4) in position

2 © ISO 2020 – All rights reserved
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SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)
3.7
specified bursting pressure

bursting pressure (3.13) quoted with a coincident temperature when defining the bursting disc (3.5)

requirements
Note 1 to entry: It is used in conjunction with a performance tolerance (3.10).
3.8
specified maximum bursting pressure

maximum bursting pressure (3.13) quoted with the coincident temperature when defining the bursting

disc (3.5) requirements

Note 1 to entry: It is used in conjunction with a specified minimum bursting pressure (3.9).

3.9
specified minimum bursting pressure

minimum bursting pressure (3.13) quoted with the coincident temperature when defining the bursting

disc (3.5) requirements

Note 1 to entry: It is used in conjunction with a specified maximum bursting pressure (3.8).

3.10
performance tolerance

range of pressure between the specified minimum bursting pressure (3.9) and the specified maximum

bursting pressure (3.8) or the range of pressure in positive and negative percentages or quantities which

is related to the specified bursting pressure (3.7)
3.11
relieving pressure
maximum pressure under discharge conditions in the pressurised system

Note 1 to entry: It may differ from the bursting pressure of the bursting disc (3.5).

3.12
batch

quantity of bursting discs or bursting disc safety devices (3.3) made as a single group of the same type,

size, materials and specified bursting pressure (3.7) requirements, and where the bursting discs (3.5) are

manufactured from the same lot of material
3.13
bursting pressure

value of the differential pressure between the upstream side and the downstream side of the bursting

disc (3.5) when it bursts
3.14
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.
3.15
certified derated coefficient of discharge
adjusted coefficient of discharge (3.16) for the safety valve or CSPRS
Note 1 to entry: See ISO 4126-1, ISO 4126-4, or ISO 4126-5 as applicable.
© ISO 2020 – All rights reserved 3
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SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)
3.16
coefficient of discharge

value of actual discharge capacity (from tests) divided by the theoretical discharge capacity (from

calculation) of the safety valve or CSPRS.
Note 1 to entry: See ISO 4126-1, ISO 4126-4, or ISO 4126-5 as applicable.
3.17
combination coefficient of discharge

tested value of actual discharge capacity of the combination (3.1) divided by the theoretical discharge

capacity of the safety valve or CSPRS
3.18
set pressure
set

predetermined pressure at which a safety valve or CSPRS under operating conditions commences to open

Note 1 to entry: It is the gauge pressure measured at the valve inlet at which the pressure forces tending to open

the valve for the specific service conditions are in equilibrium with the forces retaining the valve disc on its seat.

4 Symbols
A flow area of a safety valve (not curtain area), in square millimetres
F combination discharge capacity factor
K coefficient of discharge of the safety valve or CSPRS
K combination coefficient of discharge
K certified derated coefficient of discharge for safety valve or CSPRS
P set pressure of safety valve or CSPRS
set
5 Design of combination
Bursting disc safety devices shall comply with ISO 4126-2.

Application and selection of bursting disc safety devices shall be in accordance with ISO 4126-6.

Safety valves shall comply with ISO 4126-1 or ISO 4126-4.
CSPRS shall comply with ISO 4126-5.

Where additional components are used to combine the bursting disc safety device and the safety valve

or CSPRS into a combination (e.g. spool piece), these shall comply with the applicable design standard.

The connection from the protected equipment to the safety valve inlet shall be as short as practicable

and designed so that the total pressure drop to the safety valve or CSPRS inlet, including the effect of

the bursting disc safety device, shall meet the requirements for the inlet line as described in ISO 4126-9.

Calculate the total inlet pressure drop (difference of stagnation pressures, i.e. non-recoverable losses)

using the actual flowing capacity, which is the capacity of the safety device calculated using the certified

coefficient of discharge, divided by the derating factor 0,9 and multiplied by the certified combination

discharge capacity factor F or a value of F = 1,0 if a certified value is not available. Please be aware of

d d
4 © ISO 2020 – All rights reserved
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SIST EN ISO 4126-3:2020
ISO 4126-3:2020(E)

national codes or regulations regarding the total inlet pressure drop. The pressure drop shall include

the effects of isolating valves, fittings and bursting disc safety devices.

NOTE 1 This guidance is not intended to cause a redesign of existing systems that have demonstrated stable

operation during valve discharge.

The space between the bursting disc safety device and the safety valve or CSPRS shall be provided with

a connection to prevent or detect an unacceptable build up in pressure.

NOTE 2 Bursting discs, being pressure-differential devices, 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 or the CSPRS. This occurs when leakage develops through the bursting disc due to corrosion, due to back

pressure in the discharge piping or other cause.

After bursting, the bursting disc petals shall not protrude into the valve inlet unless the influence of the

petals on the capacity and performance of the safety valve or CSPRS have been assessed and proven to

meet the requirements of Clause 7.

The design of the bursting disc safety device shall be such that on bursting, release of bursting disc

material shall not impair the performance of the safety valve or the CSPRS.

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 or CSPRS.
6 Installation of combination

The discharge of the combination shall be disposed of safely and be prevented from unintentional

flowing into other equipment to create a hazard (for example, into equipment out of service or

undergoing maintenance). The discharge pipe, between the outlet of the combination and the

atmosphere or venting system, shall always be adequately drained to prevent accumulation of liquids.

Provisions shall be made to absorb the reaction forces expected during the discharge of material.

The supplier of the combination shall provide a
...

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