SIST EN ISO 23251:2007
(Main)Petroleum, petrochemical and natural gas industries - Pressure-relieving and depressuring systems (ISO 23251:2006)
Petroleum, petrochemical and natural gas industries - Pressure-relieving and depressuring systems (ISO 23251:2006)
This European Standard 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 International Standard is intended to supplement the practices set forth in ISO 4126 or API RP 520-I for establishing a basis of design. This International Standard specifies requirements and gives guidelines for examining the principal causes of overpressure; and determining individual relieving rates; and selecting and designing disposal systems, including such component parts as piping, vessels, flares, and vent stacks. This International Standard does not apply to direct-fired steam boilers. Piping information pertinent to pressure-relieving systems is presented in 7.3.1.
Erdöl-, petrochemische und Erdgasindustrie - Druckentlastungs- und Druckausgleichssysteme (ISO 23251:2006)
Industries du pétrole, de la pétrochimie et du gaz naturel - Systemes de dépressurisation et de protection contre les surpressions (ISO 23251:2006)
L'ISO 23251:2006 est applicable aux systèmes de protection contre les surpressions et de dépressurisation des phases gazeuses. Bien qu'elle soit principalement destinée à être utilisée dans les raffineries de pétrole, elle est également applicable aux installations pétrochimiques, aux usines de traitement de gaz, aux installations pour gaz naturel liquéfié (GNL) et aux installations de production de pétrole et de gaz. Les informations fournies sont conçues pour faciliter le choix du système le plus approprié, compte tenu des risques et des circonstances associés à diverses installations. L'ISO 23251:2006 a pour objet de compléter les pratiques énoncées dans l'ISO 4126 ou l'API RP 520-I en vue d'établir une base de conception.
L'ISO 23251:2006 spécifie les exigences et donne des lignes directrices pour étudier les principales causes de surpression, déterminer les débits de décharge individuels et sélectionner et concevoir des systèmes d'évacuation, y compris des composants tels que tuyauteries, récipients, torches et colonnes d'évent.
L'ISO 23251:2006 ne s'applique pas aux chaudières à vapeur à flamme directe.
Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina - Sistemi za sproščanje in izravnavanje tlaka (ISO 23251:2006)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 23251:2007
01-oktober-2007
3HWURNHPLþQDLQGXVWULMDWHULQGXVWULMD]DSUHGHODYRQDIWHLQ]HPHOMVNHJDSOLQD
6LVWHPL]DVSURãþDQMHLQL]UDYQDYDQMHWODND ,62
Petroleum, petrochemical and natural gas industries - Pressure-relieving and
depressuring systems (ISO 23251:2006)
Erdöl-, petrochemische und Erdgasindustrie - Druckentlastungs- und
Druckausgleichssysteme (ISO 23251:2006)
Industries du pétrole, de la pétrochimie et du gaz naturel - Systemes de dépressurisation
et de protection contre les surpressions (ISO 23251:2006)
Ta slovenski standard je istoveten z: EN ISO 23251:2007
ICS:
75.180.20 Predelovalna oprema Processing equipment
SIST EN ISO 23251:2007 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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EUROPEAN STANDARD
EN ISO 23251
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2007
ICS 75.180.20
English Version
Petroleum, petrochemical and natural gas industries - Pressure-
relieving and depressuring systems (ISO 23251:2006)
Industries du pétrole, de la pétrochimie et du gaz naturel - Erdöl-, petrochemische und Erdgasindustrie -
Systèmes de dépressurisation et de protection contre les Druckentlastungs- und Druckausgleichssysteme (ISO
surpressions (ISO 23251:2006) 23251:2006)
This European Standard was approved by CEN on 12 July 2007.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, 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
© 2007 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 23251:2007: E
worldwide for CEN national Members.
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EN ISO 23251:2007 (E)
Foreword
The text of ISO 23251:2006 has been prepared by Technical Committee ISO/TC 67 "Materials,
equipment and offshore structures for petroleum and natural gas industries” of the International
Organization for Standardization (ISO) and has been taken over as EN ISO 23251:2007 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 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 January 2008, and conflicting national
standards shall be withdrawn at the latest by January 2008.
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, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United
Kingdom.
Endorsement notice
The text of ISO 23251:2006 has been approved by CEN as EN ISO 23251:2007 without any
modifications.
2
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INTERNATIONAL ISO
STANDARD 23251
First edition
2006-08-15
Corrected version
2006-10-01
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 23251:2006(E)
©
ISO 2006
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ISO 23251:2006(E)
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ii © ISO 2006 – All rights reserved
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ISO 23251:2006(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Causes of overpressure. 10
4.1 General. 10
4.2 Overpressure protection philosophy. 10
4.3 Potentials for overpressure . 11
4.4 Recommended minimum relief system design content . 17
4.5 List of items required in flare-header calculation documentation . 20
4.6 Guidance on vacuum relief. 20
5 Determination of individual relieving rates. 22
5.1 Principal sources of overpressure. 22
5.2 Sources of overpressure . 24
5.3 Effects of pressure, temperature, and composition . 24
5.4 Effect of operator response. 24
5.5 Closed outlets . 24
5.6 Cooling or reflux failure . 25
5.7 Absorbent flow failure. 26
5.8 Accumulation of non-condensables. 26
5.9 Entrance of volatile material into the system . 26
5.10 Failure of process stream automatic controls. 27
5.11 Abnormal process heat input . 29
5.12 Internal explosion (excluding detonation) .30
5.13 Chemical reaction. 30
5.14 Hydraulic expansion. 31
5.15 External pool fires. 36
5.16 Jet fires . 51
5.17 Opening manual valves. 51
5.18 Electric power failure. 51
5.19 Heat-transfer equipment failure . 52
5.20 Vapour depressuring. 55
5.21 Special considerations for individual pressure-relief devices . 63
5.22 Dynamic simulation. 64
6 Selection of disposal systems . 65
6.1 General. 65
6.2 Fluid properties that influence design. 65
6.3 Atmospheric discharge. 66
6.4 Disposal by flaring. 76
6.5 Disposal to a lower-pressure system . 95
6.6 Disposal of liquids and condensable vapours . 96
7 Disposal systems. 97
7.1 Definition of system design load . 97
7.2 System arrangement . 100
7.3 Design of disposal system components. 102
7.4 Flare gas recovery systems. 137
© ISO 2006 – All rights reserved iii
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ISO 23251:2006(E)
Annex A (informative) Determination of fire relief requirements. 142
Annex B (informative) Special system design considerations . 146
Annex C (informative) Sample calculations for sizing a subsonic flare stack. 149
Annex D (informative) Typical details and sketches. 166
Annex E (informative) High integrity protection systems (HIPS) . 169
Bibliography . 176
iv © ISO 2006 – All rights reserved
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ISO 23251:2006(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 23251 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 corrected version of ISO 23251:2006 incorporates corrections to Table 4, column 2, second row under
the header, and the five rows of data in column 3.
© ISO 2006 – All rights reserved v
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ISO 23251:2006(E)
Introduction
This International Standard is based on the draft 5th edition of API RP 521, with the intent that the 6th edition
of API RP 521 will be identical to this International Standard.
The portions of this International Standard dealing with flares and flare systems are an adjunct to
[10]
API Std 537 , which addresses mechanical design, operation and maintenance of flare equipment. It is
important for all parties involved in the design and use of a flare system to have an effective means of
communicating and preserving design information about the flare system. To this end, API has developed a
set of flare data sheets, which can be found in of API Std 537, Appendix A. The use of these data sheets is
both recommended and encouraged as a concise, uniform means of recording and communicating design
information.
vi © ISO 2006 – All rights reserved
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INTERNATIONAL STANDARD ISO 23251:2006(E)
Petroleum, petrochemical and natural gas industries —
Pressure-relieving and depressuring systems
1 Scope
This International Standard 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 International Standard is intended to supplement the practices set forth in ISO 4126 or
API RP 520-I for establishing a basis of design.
This International Standard specifies requirements and gives guidelines for examining the principal causes of
overpressure; and determining individual relieving rates; and selecting and designing disposal systems,
including such component parts as piping, vessels, flares, and vent stacks. This International Standard does
not apply to direct-fired steam boilers.
Piping information pertinent to pressure-relieving systems is presented in 7.3.1.
2 Normative references
The following referenced documents are indispensable for the application 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 (all parts), Safety devices for protection against excessive pressure
API RP 520-I:2000, Sizing, Selection and Installation of Pressure-Relieving Devices in Refineries — Part I:
1)
Sizing and Selection
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
accumulation
pressure increase over the maximum allowable working pressure of the vessel allowed during discharge
through the pressure-relief device
NOTE Accumulation is expressed in units of pressure or as a percentage of MAWP or design pressure. Maximum
allowable accumulations are established by pressure-design codes for emergency operating and fire contingencies.
1) American Petroleum Institute, 1220 L Street, N.W., Washington, D.C., 20005-4070, USA.
© ISO 2006 – All rights reserved 1
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ISO 23251:2006(E)
3.2
administrative controls
procedures intended to ensure that personnel actions do not compromise the overpressure protection of the
equipment
3.3
assist gas
combustible gas that is added to relief gas prior to the flare burner or at the point of combustion in order to
raise the heating value
3.4
atmospheric discharge
release of vapours and gases from pressure-relieving and depressuring devices to the atmosphere
3.5
back pressure
pressure that exists at the outlet of a pressure-relief device as a result of the pressure in the discharge system
NOTE The back pressure is the sum of the superimposed and built-up back pressures.
3.6
balanced pressure-relief valve
spring-loaded pressure-relief valve that incorporates a bellows or other means for minimizing the effect of
back pressure on the operational characteristics of the valve
3.7
blowdown
depressurization of a plant or part of a plant, and equipment
NOTE Not to be confused with the difference between the set pressure and the closing pressure of a pressure-relief
valve.
3.8
blow-off
loss of a stable flame where the flame is lifted above the burner, occurring if the fuel velocity exceeds the
flame velocity
3.9
breaking-pin device
pressure-relief device actuated by static differential or static inlet pressure and designed to function by the
breakage of a load-carrying section of a pin that supports a pressure-containing member
3.10
buckling pin device
pressure-relief device actuated by static differential or static inlet pressure and designed to function by the
buckling of an axially-loaded compressive pin that supports a pressure-containing member
3.11
built-up back pressure
increase in pressure at the outlet of a pressure-relief device that develops as a result of flow after the
pressure-relief device opens
3.12
buoyancy seal
dry vapour seal that minimizes the amount of purge gas needed to protect against air infiltration
NOTE The buoyancy seal functions by trapping a volume of light gas in an internal inverted compartment; this
prevents air from displacing buoyant light gas in the flare.
2 © ISO 2006 – All rights reserved
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ISO 23251:2006(E)
3.13
burnback
internal burning within the flare tip
NOTE Burnback can result from air backing down the flare burner at purge or low flaring rates.
3.14
burning velocity
flame velocity
speed at which a flame front travels into an unburned combustible mixture
3.15
burn-pit flare
open excavation, normally equipped with a horizontal flare burner that can handle liquid as well as vapour
hydrocarbons
3.16
burst pressure
value of the upstream static pressure minus the value of the downstream static pressure just before a rupture
disk bursts
NOTE If the downstream pressure is atmospheric, the burst pressure is the upstream static gauge pressure.
3.17
closed disposal system
disposal system capable of containing pressures that are different from atmospheric pressure
3.18
cold differential test pressure
CDTP
pressure at which a pressure-relief valve is adjusted to open on the test stand
NOTE The cold differential test pressure includes corrections for the service conditions of back pressure or
temperature or both.
3.19
combustion air
air required to combust the flare gases
3.20
conventional pressure-relief valve
spring-loaded pressure-relief valve whose operational characteristics are directly affected by changes in the
back pressure
3.21
corrected hydrotest pressure
hydrostatic test pressure multiplied by the ratio of stress value at design temperature to the stress value at test
temperature
NOTE See 4.3.2.
3.22
deflagration
explosion in which the flame-front of a combustible medium is advancing at less than the speed of sound
cf. detonation (3.25)
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ISO 23251:2006(E)
3.23
design pressure
pressure, together with the design temperature, used to determine the minimum permissible thickness or
physical characteristic of each component, as determined by the design rules of the pressure-design code
NOTE The design pressure is selected by the user to provide a suitable margin above the most severe pressure
expected during normal operation at a coincident temperature, and it is the pressure specified on the purchase order. The
design pressure is equal to or less than the MAWP (the design pressure can be used as the MAWP in cases where the
MAWP has not been established).
3.24
destruction efficiency
mass fraction of the fluid vapour that can be oxidized or partially oxidized
NOTE For a hydrocarbon, this is the mass fraction of carbon in the fluid vapour that oxidizes to CO or CO .
2
3.25
detonation
explosion in which the flame-front of a combustible medium is advancing at or above the speed of sound
cf. deflagration (3.22)
3.26
dispersion
dilution of a vent stream or products of combustion as the fluids move through the atmosphere
3.27
elevated flare
flare where the burner is raised high above ground level to reduce radiation intensity and to aid in dispersion
3.28
enclosed flare
enclosure with one or more burners arranged in such a manner that the flame is not directly visible
3.29
enrichment
process of adding assist gas to the relief gas
3.30
flame-retention device
device used to prevent flame blow off from a flare burner
3.31
flare
device or system used to safely dispose of relief gases in an environmentally compliant manner through the
use of combustion
3.32
flare burner
flare tip
part of the flare where fuel and air are mixed at the velocities, turbulence and concentration required to
establish and maintain proper ignition and stable combustion
3.33
flare header
piping system that collects and delivers the relief gases to the flare
4 © ISO 2006 – All rights reserved
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ISO 23251:2006(E)
3.34
flashback
phenomenon occurring in a flammable mixture of air and gas when the local velocity of the combustible
mixture becomes less than the flame velocity, causing the flame to travel back to the point of mixture
3.35
ground flare
non-elevated flare
NOTE A ground flare is normally an enclosed flare but can also be a ground multi-burner flare or a burnpit.
3.36
heat release
total heat liberated by combustion of the relief gases based on the lower heating value
3.37
huddling chamber
annular chamber located downstream of the seat of a pressure-relief valve, which assists the valve to lift
3.38
hydrate
solid, crystalline compound of water and a low-boiling-point gas (e.g. methane and propane), in which the
water combines with the gas molecule to form a solid
3.39
jet fire
fire created when a leak from a pressurized system ignites and forms a burning jet
NOTE A jet fire can impinge on other equipment, causing damage.
3.40
knockout drum
vessel in the effluent handling system designed to remove and store liquids
3.41
lateral
section of pipe from outlet flange(s) of single-source relief device(s) downstream of a header connection
where relief devices from other sources are tied in
NOTE The relief flow in a lateral is always from a single source, whereas the relief flow in a header can be from
either single or multiple sources simultaneously.
3.42
lift
actual travel of the disc from the closed position when a valve is relieving
3.43
liquid seal
water seal
device that directs the flow of relief gases through a liquid (normally water) on the path to the flare burner,
used to protect the flare header from air infiltration or flashback, to divert flow, or to create back pressure for
the flare header
3.44
Mach number
ratio of a fluid’s velocity, measured relative to some obstacle or geometric figure, divided by the speed at
which sound waves propagate through the fluid
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ISO 23251:2006(E)
3.45
manifold
piping system for the collection and/or distribution of a fluid to or from multiple flow paths
3.46
marked burst pressure
rated burst pressure
〈rupture disk〉 burst pressure, established by tests for the specified temperature and marked on the disk tag by
the manufacturer
NOTE The marked burst pressure can be any pressure within the manufacturing design range unless otherwise
specified by the customer. The marked burst pressure is applied to all of the rupture disks of the same lot.
3.47
maximum allowable working pressure
MAWP
maximum gauge pressure permissible at the top of a completed vessel in its normal operating position at the
designated coincident temperature specified for that pressure
cf. design pressure (3.23)
NOTE The MAWP is the least of the values for the internal or external pressure as determined by the vessel design
rules for each element of the vessel using actual nominal thickness, exclusive of additional metal thickness allowed for
corrosion and loadings other than pressure. The MAWP is the basis for the pressure setting of the pressure-relief devices
that protect the vessel.
3.48
non-condensable gas
gas or vapour that remains in the gaseous state at the temperature and pressure expected
3.49
operating pressure
pressure the process system experiences during normal operation, including normal variations
3.50
overpressure
〈general〉 condition where the MAWP, or other specified pressure, is exceeded
〈relieving device〉 pressure increase over the set pressure of a relieving device
NOTE In the latter context, overpressure is the same as accumulation (3.1) only when the relieving device is set to
open at the MAWP of the vessel.
3.51
pilot burner
small, continuously operating burner that provides ignition energy to light the flared gases
3.52
pilot-operated pressure-relief valve
pressure-relief valve in which the major relieving device or main valve is combined with and controlled by a
self-actuated auxiliary pressure-relief valve (pilot)
3.53
pin device
non-reclosing pressure-relief device actuated by static pressure and designed to function by buckling or
breaking a pin that holds a piston or a plug in place; upon buckling or breaking of the pin, the piston or plug
instantly moves to the fully open position
6 © ISO 2006 – All rights reserved
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ISO 23251:2006(E)
3.54
pool fire
burning pool of liquid
3.55
pressure-design code
standard to which the equipment is designed and constructed
[20]
EXAMPLE ASME Section VIII, Division 1 .
3.56
pressure-relief valve
valve designed to op
...
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