SIST EN ISO 23251:2020

Petroleum, petrochemical and natural gas industries - Pressure-relieving and depressuring systems (ISO 23251:2019)

This document is applicable to pressure-relieving and vapour depressuring systems. Although intended for use primarily in oil refineries, it is also applicable to petrochemical facilities, gas plants, Liquefied Natural Gas (LNG) facilities and oil and gas production facilities. The information provided is designed to aid in the selection of the system that is most appropriate for the risks and circumstances involved in various installations.
This document supplements API Std 521, 6th edition (2014), the requirements of which are applicable with the exceptions specified in this document.

Erdöl-, petrochemische und Erdgasindustrie - Druckentlastungs- und Druckausgleichssysteme (ISO 23251:2019)

Industries du pétrole, de la pétrochimie et du gaz naturel - Systèmes de dépressurisation et de protection contre les surpressions (ISO 23251:2019)

Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina - Sistemi za sproščanje in izravnavanje tlaka (ISO 23251:2019)

General Information

• Status: Published
• Public Enquiry End Date: 17-Jun-2020
• Publication Date: 09-Sep-2020
• ICS: 75.180.20 - Processing equipment
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 10-Sep-2020
• Due Date: 15-Nov-2020
• Completion Date: 10-Sep-2020
• Ref Project: EN ISO 23251:2020 - Petroleum, petrochemical and natural gas industries - Pressure-relieving and depressuring systems (ISO 23251:2019)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 23251:2020
01-november-2020
Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina -
Sistemi za sproščanje in izravnavanje tlaka (ISO 23251:2019)
Petroleum, petrochemical and natural gas industries - Pressure-relieving and
depressuring systems (ISO 23251:2019)
Erdöl-, petrochemische und Erdgasindustrie - Druckentlastungs- und
Druckausgleichssysteme (ISO 23251:2019)
Industries du pétrole, de la pétrochimie et du gaz naturel - Systèmes de dépressurisation
et de protection contre les surpressions (ISO 23251:2019)
Ta slovenski standard je istoveten z: EN ISO 23251:2020
ICS:
75.180.20 Predelovalna oprema Processing equipment
SIST EN ISO 23251:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 23251:2020

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SIST EN ISO 23251:2020


EN ISO 23251
EUROPEAN STANDARD

NORME EUROPÉENNE

September 2020
EUROPÄISCHE NORM
ICS 75.180.20
English Version

Petroleum, petrochemical and natural gas industries -
Pressure-relieving and depressuring systems (ISO
23251:2019)
Industries du pétrole, de la pétrochimie et du gaz Erdöl-, petrochemische und Erdgasindustrie -
naturel - Systèmes de dépressurisation et de protection Druckentlastungs- und Druckausgleichssysteme (ISO
contre les surpressions (ISO 23251:2019) 23251:2019)
This European Standard was approved by CEN on 19 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 23251:2020 E
worldwide for CEN national Members.

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SIST EN ISO 23251:2020
EN ISO 23251:2020 (E)
Contents Page
European foreword . 3

2

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SIST EN ISO 23251:2020
EN ISO 23251:2020 (E)
European foreword
The text of ISO 23251:2019 has been prepared by Technical Committee ISO/TC 67 "Materials,
equipment and offshore structures for petroleum, petrochemical and natural gas industries” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 23251:2020 by
Technical Committee CEN/TC 12 “Materials, equipment and offshore structures for petroleum,
petrochemical and natural gas industries” the secretariat of which is held by NEN.
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.
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 23251:2019 has been approved by CEN as EN ISO 23251:2020 without any modification.


3

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SIST EN ISO 23251:2020

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SIST EN ISO 23251:2020
INTERNATIONAL ISO
STANDARD 23251
Second edition
2019-03
Petroleum, petrochemical and natural
gas industries — Pressure-relieving
and depressuring systems
Industries du pétrole, de la pétrochimie et du gaz naturel — Systèmes
de dépressurisation et de protection contre les surpressions
Reference number
ISO 23251:2019(E)
©
ISO 2019

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SIST EN ISO 23251:2020
ISO 23251:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

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SIST EN ISO 23251:2020
ISO 23251:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Supplements to API Std 521, 6th edition (2014). 2
4.1 General requirements . 2
4.2 Chemical reaction . 2
4.3 Fires . 2
4.4 Causes for vacuum . 3
4.5 Considerations for individual PRDs . 3
4.5.1 General. 3
4.5.2 Multiple PRDs . 3
4.6 Piping . 3
4.6.1 General. 3
4.6.2 Backpressure . 3
4.6.3 Line sizing . 3
4.6.4 Multiple relief scenarios . 3
4.6.5 Reaction forces . 3
4.7 Disposal to flare . 4
4.7.1 General. 4
4.7.2 Combustion properties . 4
4.7.3 Combustion methods . 4
4.7.4 Flare systems designs . 4
4.7.5 Sizing . 4
4.7.6 Ignition of flare gases . 4
4.7.7 Liquid seal drum drums . 4
4.8 Single PRD protecting several components in a process system . 4
Bibliography . 5
© ISO 2019 – All rights reserved iii

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SIST EN ISO 23251:2020
ISO 23251:2019(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
...

SLOVENSKI STANDARD
oSIST prEN ISO 23251:2020
01-junij-2020
Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina -
Sistemi za sproščanje in izravnavanje tlaka (ISO 23251:2019)
Petroleum, petrochemical and natural gas industries - Pressure-relieving and
depressuring systems (ISO 23251:2019)
Erdöl-, petrochemische und Erdgasindustrie - Druckentlastungs- und
Druckausgleichssysteme (ISO 23251:2019)
Industries du pétrole, de la pétrochimie et du gaz naturel - Systèmes de dépressurisation
et de protection contre les surpressions (ISO 23251:2019)
Ta slovenski standard je istoveten z: prEN ISO 23251
ICS:
75.180.20 Predelovalna oprema Processing equipment
oSIST prEN ISO 23251:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 23251:2020

---------------------- Page: 2 ----------------------
oSIST prEN ISO 23251:2020
INTERNATIONAL ISO
STANDARD 23251
Second edition
2019-03
Petroleum, petrochemical and natural
gas industries — Pressure-relieving
and depressuring systems
Industries du pétrole, de la pétrochimie et du gaz naturel — Systèmes
de dépressurisation et de protection contre les surpressions
Reference number
ISO 23251:2019(E)
©
ISO 2019

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oSIST prEN ISO 23251:2020
ISO 23251:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 4 ----------------------
oSIST prEN ISO 23251:2020
ISO 23251:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Supplements to API Std 521, 6th edition (2014). 2
4.1 General requirements . 2
4.2 Chemical reaction . 2
4.3 Fires . 2
4.4 Causes for vacuum . 3
4.5 Considerations for individual PRDs . 3
4.5.1 General. 3
4.5.2 Multiple PRDs . 3
4.6 Piping . 3
4.6.1 General. 3
4.6.2 Backpressure . 3
4.6.3 Line sizing . 3
4.6.4 Multiple relief scenarios . 3
4.6.5 Reaction forces . 3
4.7 Disposal to flare . 4
4.7.1 General. 4
4.7.2 Combustion properties . 4
4.7.3 Combustion methods . 4
4.7.4 Flare systems designs . 4
4.7.5 Sizing . 4
4.7.6 Ignition of flare gases . 4
4.7.7 Liquid seal drum drums . 4
4.8 Single PRD protecting several components in a process system . 4
Bibliography . 5
© ISO 2019 – All rights reserved iii

---------------------- Page: 5 ----------------------
oSIST prEN ISO 23251:2020
ISO 23251:2019(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 67, Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 6, Processing
equipment and systems.
This second edition cancels and replaces the first edition (ISO 23251:2006), which has been technically
revised. It also incorporates the Technical Corrigendum ISO 23251:2006/Cor.1:2007 and the Amendment
ISO 23251:2006/Amd.1:2008.
This document supplements API Std 521, 6th edition (2014).
The technical requirements of this document and API Std 521 used to be identical. In the meantime
API Std 521 has been technically revised as API Std 521, 6th edition (2014). The purpose of this document
is to bring it up to date, by referencing the current edition of API Std 521 and adding supplementary
content.
The main changes compared to the previous edition are as follows:
— Permission to use administrative controls such as car-sealing or chain-locking valves to prevent an
over-pressure only if the corrected hydrotest pressures are not exceeded;
— Addition of requirements to cover choke valve failures and acoustic fatigue;
— Strengthening of the requireme
...