EN ISO 17349:2016

Petroleum and natural gas industries - Offshore platforms handling streams with high content of CO2 at high pressures (ISO 17349:2016)

ISO 17349:2016 contains provisions for design of topside facilities for offshore plants handling CO2-rich streams at high pressures; i.e. CO2 molar concentration above 10 %. The surface systems include usual offshore process unit operations, as shown in Figure 1.
ISO 17349:2016 is applicable only to topside facilities of fixed and floating oil and gas production offshore units up to the last barrier, such as an ESDV. Subsea production systems and Cryogenic CO2 separation are not covered.

Erdöl- und Erdgasindustrie - Offshore Plattformen, von denen Ströme mit hohem CO2-Gehalt bei hohen Drücken zu handhaben sind (ISO 17349:2016)

Industries du pétrole et du gaz naturel - Plates-formes en mer traitant des fluides à forte teneur en CO2 à haute pression (ISO 17349:2016)

L'ISO 17349:2016 contient des dispositions relatives à la conception des installations de surface d'installations de production en mer qui traitent des fluides riches en CO2 à haute pression, c'est-à-dire des fluides dont la concentration molaire en CO2 est supérieure à 10 %. Les installations de surface concernent les opérations ordinaires des unités de traitement en mer, comme illustré à la Figure 1.
L'ISO 17349:2016 s'applique uniquement aux installations de surface des unités fixes et flottantes de production de pétrole et de gaz en mer jusqu'au dernier dispositif de sécurité, tel qu'une vanne d'arrêt d'urgence. Les systèmes de production immergés et la séparation cryogénique du CO2 ne sont pas traités.

Industrija za predelavo nafte in zemeljskega plina - Ploščadi na morju z oskrbo s paro z visoko vsebnostjo CO2 pri visokem tlaku (ISO 17349:2016)

Ta mednarodni standard vključuje določila za načrtovanje opreme na palubah naftnih ploščadi, prek katerih teče CO2 pri visokem tlaku, tj. pri molarni koncentraciji CO2, večji od 10 %. Površinski sistemi vključujejo običajne dejavnosti proizvodne enote na ploščadi, kot je prikazano na sliki 1.
Ta mednarodni standard se uporablja samo za opremo na palubi nepremičnih in plavajočih ploščadi za pridobivanje nafte in plina do zadnje pregrade, kot je ESDV. Podmorski proizvodni sistemi in kriogensko ločevanje CO2 niso obravnavani.

General Information

• Status: Published
• Publication Date: 01-Mar-2016
• Withdrawal Date: 29-Sep-2016
• ICS: 75.020 - Extraction and processing of petroleum and natural gas
• Technical Committee: CEN/TC 12 - Materials, equipment and offshore structures for petroleum and natural gas industries
• Drafting Committee: CEN/TC 12 - Materials, equipment and offshore structures for petroleum and natural gas industries
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 02-Mar-2016
• Due Date: 02-Jan-2015
• Completion Date: 02-Mar-2016
• Ref Project: SIST EN ISO 17349:2016 - Petroleum and natural gas industries - Offshore platforms handling streams with high content of CO2 at high pressures (ISO 17349:2016)

Overview

EN ISO 17349:2016 (ISO 17349:2016) provides design and safety provisions for topside facilities on offshore platforms that handle CO2‑rich streams at high pressures (CO2 molar concentration above 10%). Prepared under CEN/ISO, the standard applies to fixed and floating oil & gas production units and covers process systems up to the last barrier (for example an Emergency Shutdown Valve, ESDV). Subsea production systems and cryogenic CO2 separation are explicitly excluded.

Keywords: EN ISO 17349:2016, ISO 17349:2016, CO2‑rich streams, offshore platforms, topside facilities, high pressure CO2.

Key topics

The standard addresses technical and safety aspects specific to high‑CO2, high‑pressure service on topside process equipment:

• Behavior of CO2‑rich streams: hydrate and CO solid formation, flow metering considerations.
• Depressuring and relieving: blowdown strategies, depressuring methodology and design of relief systems.
• Flare and vent systems: selection and configuration of flares and vents suited for CO2‑rich streams.
• Materials and corrosion: internal corrosion control, corrosion‑resistant alloys (CRAs), non‑metallic materials and seals, brittle/delayed ductile fracture considerations.
• Safety and risk management: hazard identification, consequence analysis (CO2 dispersion, cold jet effects), toxicology and detection strategies.
• Special scenarios: BLEVE (Boiling Liquid Expanding Vapour Explosion) guidance, cold‑jet effects, and running ductile fracture evaluation.

The published standard also includes informative annexes on evaluation of EOS for CO2, hydrate formation, water‑content specification, depressuring, and material guidance.

Applications

EN ISO 17349:2016 is used to:

• Design and specify topside process equipment (separators, compressors, piping, valves) for high‑CO2 service.
• Size and configure flare, vent and depressuring systems to manage CO2 relief safely.
• Select materials, seals and lubricants resistant to CO2‑induced corrosion, low‑temperature embrittlement and solid CO2 formation.
• Perform hazard and consequence analyses for CO2 releases, and define CO2 detection and emergency response strategies.
• Develop operating procedures for dehydration, flow metering and mitigation of hydrates in topside process systems.

Who should use this standard

• Offshore process and design engineers
• Safety, risk and HAZID/HAZOP teams
• Materials and corrosion specialists
• Facilities/operators planning CO2 injection or handling
• Regulatory bodies and project approvers working on high‑CO2 offshore developments

Related standards

EN ISO 17349:2016 complements other oil & gas offshore standards developed by ISO/TC 67 and CEN technical committees covering process safety, pressure systems and materials selection. Users should reference relevant ISO/CEN documents for detailed pressure‑equipment and environmental requirements.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2016
,QGXVWULMD]DSUHGHODYRQDIWHLQ]HPHOMVNHJDSOLQD3ORãþDGLQDPRUMX]RVNUERV
SDUR]YLVRNRYVHEQRVWMR&2SULYLVRNHPWODNX,62
Petroleum and natural gas industries - Offshore platforms handling streams with high
content of CO2 at high pressures (ISO 17349:2016)
Erdöl-, petrochemische und Erdgasindustrie - Dampf mit hohem CO2 Gehalt bei hohen
Drücken und hohen Durchflussraten - Richtlinien (ISO 17349:2016)
Industries du pétrole et du gaz naturel - Plates-formes en mer traitant des courants à fort
teneur en CO2 à haute pression (ISO 17349:2016)
Ta slovenski standard je istoveten z: EN ISO 17349:2016
ICS:
75.180.10 Oprema za raziskovanje in Exploratory and extraction
odkopavanje equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 17349
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2016
EUROPÄISCHE NORM
ICS 75.020
English Version
Petroleum and natural gas industries - Offshore platforms
handling streams with high content of CO at high
pressures (ISO 17349:2016)
Industries du pétrole et du gaz naturel - Plates-formes Erdöl-, petrochemische und Erdgasindustrie - Dampf
en mer traitant des courants à fort teneur en CO2 à mit hohem CO2 Gehalt bei hohen Drücken und hohen
haute pression (ISO 17349:2016) Durchflussraten - Richtlinien (ISO 17349:2016)
This European Standard was approved by CEN on 10 January 2016.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATIO N

EUROPÄISCHES KOMITEE FÜR NORMUN G

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17349:2016 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
European foreword
This document (EN ISO 17349:2016) has been prepared by Technical Committee ISO/TC 67 "Materials,
equipment and offshore structures for petroleum, petrochemical and natural gas industries" in
collaboration with 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 September 2016, and conflicting national standards
shall be withdrawn at the latest by September 2016.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands,
Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 17349:2016 has been approved by CEN as EN ISO 17349:2016 without any modification.
INTERNATIONAL ISO
STANDARD 17349
First edition
2016-02-15
Petroleum and natural gas
industries — Offshore platforms
handling streams with high content of
CO at high pressures
Industries du pétrole et du gaz naturel — Plates-formes en mer
traitant des courants à fort teneur en CO à haute pression
Reference number
ISO 17349:2016(E)
©
ISO 2016
ISO 17349:2016(E)
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2016 – All rights reserved

ISO 17349:2016(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Abbreviated terms . 4
5 Overview of CO -rich streams behaviour . 5
5.1 General . 5
5.2 Hydrate formation . 5
5.3 CO solid formation. 6
5.4 Flow metering . 6
6 Blow down, depressuring and relieving of plant and equipment .6
7 Flare and vent system configuration . 7
7.1 General . 7
7.2 System selection . 7
7.3 System configuration . 8
7.3.1 Flare . 8
7.3.2 Vent . 9
8 Materials . 9
8.1 Corrosion . 9
8.1.1 General. 9
8.1.2 Internal corrosion control by dehydration. 9
8.1.3 CRAs .10
8.1.4 Internal corrosion protecting chemicals .10
8.1.5 Internal organic coatings .10
8.2 Brittle fracture .10
8.3 Ductile fracture .10
8.4 Lubricants .10
8.5 Non-metallic seals for CO service .11
9 Safety .11
9.1 General .11
9.2 Impacts of the loss of containment of CO -rich streams .11
9.2.1 General.11
9.2.2 Respiratory physiological parameters .12
9.2.3 Low temperature impact .12
9.2.4 CO -rich stream BLEVE .12
9.3 Hazard identification and risk assessment and management .12
9.3.1 General.12
9.3.2 Hazard identification.13
9.3.3 Risk assessment and management .13
9.4 Consequence analysis .14
9.4.1 General.14
9.4.2 CO dispersion .14
9.4.3 Effects of cold CO jet .14
9.5 CO detection .14
9.6 Strategies.15
Annex A (informative) Evaluation of EOS for CO -rich streams .16
Annex B (informative) Hydrate formation .22
Annex C (informative) Water content specification .26
ISO 17349:2016(E)
Annex D (informative) Depressuring of CO -rich streams .33
Annex E (informative) Configuration of flare and vent systems .37
Annex F (informative) Boiling liquid expanding vapour explosion (BLEVE) .40
Annex G (informative) Methodology for evaluation of running ductile fracture .42
Annex H (informative) Non-metallic materials for use in CO service .44
Annex I (informative) CO toxicology information .45
Bibliography .48
iv © ISO 2016 – All rights reserved

ISO 17349:2016(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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries.
ISO 17349:2016(E)
Introduction
In recent years, the oil industry has been facing challenges in developing and operating high-CO
content offshore fields. The CO -rich streams, separated from the produced natural gas, can be injected
to enhance oil recovery from the reservoirs. Even in cases where the oil recovery increase is not so
significant, operators have to consider the CO -rich stream compression and injection, in order to avoid
its venting to the atmosphere.
Main concerns comprise surface safety system and material selection areas, which lack specific
standards and regulations for this scenario. The commercial tools available, for instance, to model the
dispersion of gases, need to be validated for CO and CO /hydrocarbon mixtures, which have distinctive
2 2
thermodynamic behaviour. This will affect the choice of materials and plant design.
This International Standard addresses concepts and criteria for processing CO -rich streams, as a
supplement to existing standards for offshore installations.
vi © ISO 2016 – All rights reserved

INTERNATIONAL STANDARD ISO 17349:2016(E)
Petroleum and natural gas industries — Offshore
platforms handling streams with high content of CO at
high pressures
1 Scope
This International Standard contains provisions for design of topside facilities for offshore plants
handling CO -rich streams at high pressures; i.e. CO molar concentration above 10 %. The surface
2 2
systems include usual offshore process unit operations, as shown in Figure 1.
This International Standard is applicable only to topside facilities of fixed and floating oil and gas
production offshore units up to the last barrier, such as an ESDV. Subsea production systems and
Cryogenic CO separation are not covered.
NOTE This example is within the scope of this International Standard.
Figure 1 — Example of a Process Flow Diagram (in grey zone)
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 13702, Petroleum and natural gas industries — Control and mitigation of fires and explosions on
offshore production installations — Requirements and guidelines
ISO 17349:2016(E)
ISO 15156 (all parts), Petroleum and natural gas industries — Materials for use in H S-containing
environments in oil and gas production
ISO 21457, Petroleum, petrochemical and natural gas industries — Materials selection and corrosion
control for oil and gas production systems
ISO 23936-1, Petroleum, petrochemical and natural gas industries — Non-metallic materials in contact
with media related to oil and gas production — Part 1: Thermoplastics
ISO 23936-2:2011, Petroleum, petrochemical and natural gas industries — Non-metallic materials in
contact with media related to oil and gas production — Part 2: Elastomers
API STD 521, Pressure-relieving and Depressuring Systems, API Standard, January 2014
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
compressibility factor
Z
thermodynamic property for modifying the ideal gas law to account for the real gas behaviour
3.2
corrosion resistant alloy
CRA
alloy intended to be resistant to general and localized corrosion by oil field environments that are
corrosive to carbon steels
[SOURCE: ISO 15156-1:2015, 3.6]
3.3
dense phase
fluid state (supercritical or liquid) above critical pressure
3.4
equation of state
EOS
thermodynamic equation describing the state of matter under a given set of physical conditions
3.5
free water
water not dissolved in the CO -rich stream
Note 1 to entry: This can be pure water, water with dissolved salts, water wet salts, water glycol mixtures or
other mixtures containing water.
3.6
gas-assisted flare
flare with gas assistance system in order to increase gas net heating value
3.7
high-velocity tip flare
flare with gas exit velocities higher than 122 m/s
3.8
high-velocity vent
vent with gas exit velocities higher than 150 m/s
2 © ISO 2016 – All rights reserved

ISO 17349:2016(E)
3.9
hydrate
solid, crystalline compound of water and light hydrocarbons or CO , in which the water molecules
combine with the gas molecules to form a solid
3.10
CRA clad
metallic coating of CRA in which the bond between the parent metal and liner is metallurgical
3.11
low-velocity tip flare
flare with gas exit velocities lower than 122 m/s
3.12
low-velocity vent
vent with gas exit velocities lower than 150 m/s
3.13
minimum design temperature
minimum temperature below which the application limits for the materials involved are exceeded
3.14
platform
complete assembly, including structure, topsides, foundations and stationkeeping systems
[SOURCE: ISO 19900:2013, 3.35]
3.15
rapid gas decompression
RGD
depressurization
explosive decompression
rapid pressure-drop in a high pressure gas-containing system which disrupts the equilibrium between
external gas pressure and the concentration of gas dissolved inside any polymer, with the result that
excess gas tries to escape from the solution at points throughout the material, causing expansion
[SOURCE: ISO 23936-2:2011, 3.1.10]
3.16
supercritical phase
fluid state above critical pressure and temperature
3.17
topsides
structures and equipment placed on a supporting structure (fixed or floating) to provide some or all of
a platform’s functions
Note 1 to entry: For a ship-shaped floating structure, the deck is not part of the topsides.
Note 2 to entry: For a jack-up, the hull is not part of the topsides.
Note 3 to entry: A separate fabricated deck or module support frame is part of the topsides.
[SOURCE: ISO 19900:2013, 3.52]
3.18
triple point
temperature and pressure where CO exists as a gas, liquid and solid simultaneously
ISO 17349:2016(E)
4 Abbreviated terms
AIV acoustically induced vibration
BLEVE boiling liquid expanding vapour explosion
BDV blow down valve
CH methane
CO carbon dioxide
CCR central control room
CRA corrosion resistant alloy
EERS evacuation, escape and rescue strategy
EOS equation of state
ESD emergency shut down
FES fire and explosion strategy
GDU gas dehydration unit
H S hydrogen sulfide
HC hydrocarbon
HP high pressure
HSE health, safety and environment
IDLH immediately dangerous to life or health
LP low pressure
MMSCF million standard cubic feet gas (60 °F and 1 atm)
NHV net heating value
NIOSH National Institute for Occupational Safety and Health
NIST National Institute of Standards and Technology
OSHA Occupational Safety and Health Administration
Pa ambient pressure
Pc critical pressure
PEL permissible exposure limit
PHA Preliminary Hazard Analysis
ppmv parts per million, volumetric basis
PR Peng-Robinson EOS
PR-HV Peng-Robinson EOS modified by using mixing rule of Huron-Vidal and Peneloux factor
4 © ISO 2016 – All rights reserved

ISO 17349:2016(E)
PR-SV Peng-Robinson-Stryjek-Vera EOS
PSV pressure safety valve
RGD rapid gas decompression
RO restriction orifice
SCF standard cubic feet
SVLE solid-liquid-vapour equilibrium
STEL short-term exposure limit
SRK Soave-Redlich-Kwong EOS
Tc critical temperature
TWA time weighted average
v maximum permitted velocity, expressed in m/s
max
Z compressibility factor
5 Overview of CO -rich streams behaviour
5.1 General
In an offshore plant design, CO -rich streams can be handled close to or above its critical pressure (dense
[8]
phase) or above its critical pressure and temperature (supercritical phase). In the latter, some of its
properties are similar to that of a liquid (e.g. density) and other similar to that of a gas (e.g. viscosity).
The physical and thermodynamic properties of the CO -rich streams will have an impact on issues like
hydrate formation and depressuring.
The design of a plant handling CO -rich streams at high pressures should be conducted using an
EOS supported by experimental data in the range of operations. Examples of this approach are shown
in Annex A. If experimental data are not available, data from thermodynamic based models, including
readily available EOS, should be used taking into account any related uncertainties therefore allowing
for sufficient safety margins.
Particular attention should be given when performing simulations near the critical point due to strong
variation on stream properties and uncertainty on the description of the existing phases. For that
reason, equipment normal operation envelope should avoid critical point region.
5.2 Hydrate formation
CO -rich streams can present a potential risk for hydrate formation similar to sweet natural gas, if
water is present (as free water or in gas phase).
For high pressures, CO has an inhibitor effect on hydrate formation, since an increase on the
CO concentration shifts the hydrate equilibrium curve towards low temperatures, as it can be
seen in Annex B.
Dehydration unit design should take into account all operational conditions, including low temperatures
that might occur in process systems and pipeline segments downstream from the offshore plant. Special
attention should be given to the fact that CO tends to increase water-holding capacity at higher pressures.
ISO 17349:2016(E)
For that reason, depending on CO content in the stream, it is not safe to set a water dew point
specification based on higher pressure requirements only, since water condensation can occur at lower
pressures (see Figure B.1).
As a first approach, a margin of 10 °C on water dew point or a reduction down to 50 % of the water
saturation content should be considered.
An example of moisture content specification for Dehydration Unit is presented in Annex C.
5.3 CO solid formation
Solid formation can be observed in a CO -rich stream depending on temperature and pressure. Low
temperatures that lead to solid formation can be achieved during planned and unplanned depressuring
operations, for equipment maintenance purposes and emergency conditions as well. Annex D presents
phase diagram for CO -rich streams and discusses solid formation based on experimental and
theoretical calculations.
The influence of methane content in solid formation temperature can be found in Reference [9].
The frost point is presented for a CO -CH mixture in a wide range of concentrations, showing that
2 4
increasing CH content shifts the frost point curve toward lower temperatures, as shown in Annex D.
According to References [9] and [10], there is an indication that solid formed from a CO -rich stream
in low temperature operations may be considered as composed of pure CO . Therefore, in the absence
of experimental data and specific phase diagrams for mixtures with the solid region represented,
available phase diagrams for pure CO may be used as conservative approach, in order to predict the
low temperatures in which solid formation is expected in an offshore plant design.
Process plant design should take into account the predicted low temperatures with additional design
margin in order to specify suitable mitigation measures to avoid or deal with solid formation. More
details are presented in Clause 6.
5.4 Flow metering
Design of metering systems shall take into account the peculiarities of behaviour of CO -rich streams.
Preferably, metering systems should be located in plant sections where physical and transport
properties are stable and predictable, i.e. far from critical point or phase transitions. Depending on the
[11]
process, this means some meters may be designed for gas phase, while others for liquid phase.
Flow computers with input for composition as well as temperature and pressure online measurements
using the AGA-8 method, commonly used for natural gas, may be extended to CO -rich streams as long
[12]
as conditions guarantee gas phase. AGA-8 method also shows good predictability of supercritical
phase as shown in Annex A.
Differential pressure flow meters such as orifice plates, Venturi or V-Cone are well suitable and robust,
especially when working at very high pressures. Coriolis meters, being mass flow meters, are less
susceptible to the variation of fluid properties or phase changes as long as no solids are formed but can
be limited to operational pressures due to meter body construction.
Special care should be taken regarding changes in the CO -rich stream properties and potential
flashing, so meter sizing and location should be properly selected.
6 Blow down, depressuring and relieving of plant and equipment
Temperature decrease observed in CO -rich streams during depressuring depends upon the initial and
final pressures, initial temperature and stream composition.
In order to avoid brittle fracture, minimum temperatures achieved during an isenthalpic depressuring
should be considered for material selection of let-down pressure devices (PSVs, BDVs, ROs) and for the
6 © ISO 2016 – All rights reserved

ISO 17349:2016(E)
entire low pressure system. Piping sections upstream the let-down pressure device can also be subjected
to low temperatures and should be designed for co-incident high pressure at minimum temperature.
Apart from low temperature effects, designing relief systems of process plants (equipment or piping)
should consider solid CO formation, hydrate formation, adhesion and two-phase flow analysis.
Plant design should avoid operational conditions that lead to the triple point and solid formation in
order to prevent plugging, piping erosion and vibration. Annex D presents examples of depressuring
route in a phase diagram for CO -rich streams.
Designer should evaluate the following:
— control of blow down rate (such as manual assisted operations, restriction orifice or automatic
control in steps);
— selection of backpressure of the blow down relief header higher than triple point and frost line. In this
case proper transient studies should be carried out for a better evaluation of the whole relief system;
— avoiding pockets and minimizing bends in pipe segments downstream relief device up to main flare
or vent header;
— main flare or vent header configuration to avoid potential plugging;
— use of heat tracing;
— application the full upstream pressure rating to the blow down systems in the event of risk of plugging.
For depressuring criteria, designer shall comply with API STD 521 requirements even in cases of non-
flammable CO -rich streams.
ESD system design should consider proper installation of shutdown/isolation valves in order to limit
inventory and thereby minimize trapped fluid amount and potential for incident escalation.
The risk of Rapid Gas Decompression (RGD) damages to non-metallic materials can impose limitations
on the depressuring rate. This scenario should be included in the consequence analysis.
7 Flare and vent system configuration
7.1 General
Flare and Vent system design shall comply with API STD 521.
Design of CO -rich streams flare and vent systems shall consider the following aspects, as a minimum:
— CO -rich streams composition and respective minimum net heating values (NHVs);
— combustibility (flare);
— safe gas dispersion (vent);
— CO solid formation (see Clause 5);
— temperature profile during depressuring (see Clause 6 and Clause 8);
— selection of metallic and non-metallic materials (see Clause 8).
7.2 System selection
Possible flare and vent system configurations are described in Table E.1.
In case of H S present in CO -rich streams, flaring should be preferred instead of venting. For flare
2 2
systems, design should comply with H S destruction temperature, as low NHV streams have lower
ISO 17349:2016(E)
flame temperature. For vent systems, design shall warrant proper H S dispersion due to hazard and
safety aspects.
Flaring gases with low NHV influences ignition stability and can cause flame extinction. Header and
disposal segregation between low and high NHV releases may be considered as an option.
For streams with NHV lower than 7,5 MJ/Sm (200 BTU/SCF), which corresponds approximately to
a 75 % (molar) CO mixture with methane, vent or gas-assisted low-velocity tip flare should be used.
Minimum NHV shall be ensured in flare systems to allow flammability and combustion efficiency at the
flare tip, by mixing assistance fuel gas from a reliable source to CO -rich streams being relieved. The
capacity of assistance fuel gas should be designed for the worst-case scenario.
3 3
For streams with NHV higher than 7,5 MJ/Sm (200 BTU/SCF) and lower than 28,1 MJ/Sm
(800 BTU/SCF), high-velocity tip flares are not recommended. The use of such tip compared with low
velocity one shall be carefully evaluated. Manufacturer guarantee is required in case the high-velocity
tip will be used.
For high-velocity tip flares, a typical minimum NHV gas mixture to be burned is 28,1 MJ/Sm
(800 BTU/SCF). This corresponds approximately to a 25 % (molar) CO mixture with methane.
7.3 System configuration
7.3.1 Flare
For units dealing with CO -rich streams, alternative flare system for low NHV and/or low temperature
may be considered in additional to typical HP and LP systems.
The ignition of CO -rich streams requires a high energy ignition source. Such condition can be achieved
by increasing the number of pilot burners in relation to minimum requirements of pilot manufacturers’
recommendations as detailed in ISO 25457.
To ensure combustion, special attention shall be given to flare tip velocities. It is important to take into
account the following considerations: Low-velocity flares are those designed for and operated with an
exit tip velocity lower than the maximum permitted velocity, v , as determined by the Formula (1),
max
limited to 122 m/s (400 ft/s).
log v =+()NHVK12/K (1)
()
10 max
where
v is the maximum permitted velocity, expressed in m/s;
max
K1 is the constant equal to 28,8;
K2 is the constant equal to 31,7;
.
NHV is the net heating value, expressed in MJ/Sm
The method to determine the maximum permitted velocity v is shown in Reference [13].
max
As a rule, maximum permitted velocity calculated from Formula (1) will dictate flare tip area equivalent
diameter. Effects of low temperature on flame stability can be countered by lowering velocity or adding
assistance gas. Flare tip design will be dictated by flare tip suppliers and experimental evidence
should be required for all critical relief scenarios and/or unproven solutions. Interaction with flare tip
suppliers is recommended from the early phases of design.
Designer should evaluate noise and acoustically induced vibration (AIV) aspects.
Flare thermal design shall comply with API STD 521, following recommendations about admissible
total radiation fluxes over the working areas, without the need of any heat shield in the unit.
8 © ISO 2016 – All rights reserved

ISO 17349:2016(E)
Dispersion simulations are necessary for defining the following designing aspects: flare length, height,
position and orientation due to dominant wind directions. The snuffed flare scenario should be one
of those covered by dispersion studies, especially considering that low temperature releases are less
likely to ignite.
7.3.2 Vent
Vent tip location shall be assessed based on dispersion studies, practical safety zones, noise, acoustically
induced vibration (AIV) and thermal radiation in case of accidental ignition scenario.
Dispersion simulations, including evaluation of the CO plume, are necessary for defining the following
designing aspects: vent length, height, position and orientation due to dominant wind directions. The
final location of the outlet orifices shall ensure that the low flow discharges be adequately dispersed.
As a general recommendation, the vent tip should be pointing 45° from the horizontal plane in the
direction away from working areas. Some protection against rain may be provided.
When designing the vent system, consideration should be given to the formation of solid CO due to
low temperatures downstream of blow down/relief valves. If solid CO formation is possible, the vent
design should minimize the potential for blockage.
High-velocity vents are recommended whenever possible, in order to reduce potential CO or hydrate
plugging, solid adhesion and improve gas dispersion.
8 Materials
8.1 Corrosion
8.1.1 General
Internal corrosion can be a significant risk to the carbon steel piping and equipment integrity dealing
with CO -rich streams in presence of free water. Free water combined with high CO partial pressure is
2 2
likely to lead to high corrosion rates. As discussed is Annexes B and C, water can be less likely to drop
out from vapour phase CO -rich streams when compared to natural gas.
The presence of H S in combination with free water will have a significant effect on the corrosion
rate. The possibility of oxidizing species ingress in the presence of H S can induce elemental sulfur
deposition leading to higher corrosion rates.
Materials selection shall comply with ISO 21457. Physicochemical and corrosion models used for internal
corrosion evaluation should take into account considering high CO contents and high pressures.
Piping, fittings and equipment with fluids containing H S shall be evaluated according to ISO 15156 (all
parts).
Pipe segments and other parts of the system that can have stagnant conditions (pockets) should be
evaluated carefully for internal corrosion.
8.1.2 Internal corrosion control by dehydration
In general, for carbon steel piping and equipment no internal corrosion protection is required providing
that free water in the CO -rich streams be avoided through a strict water content control procedure.
This consideration should be used downstream of the dehydration system. Moisture content monitoring
should be considered as part of piping and equipment design and operation.
Upset conditions and downtimes shall be taken into account. This can include dehydration system failure
and dehydration off-spec when specifying critical systems where significant failure cannot be tolerated.
ISO 17349:2016(E)
8.1.3 CRAs
Most of CRAs are suitable for wet CO -rich streams applications. The use of solid CRA or CRA clad for
corrosion prevention should be considered for the dehydration system itself and the upstream facilities.
Some guidelines for selecting CRAs are indicated in ISO 21457.
8.1.4 Internal corrosion protecting chemicals
Reliance on pH stabilization and injection of corrosion inhibitors can be an effective way to control CO -
rich streams corrosion rates where free water is present. If this approach is to be adopted a qualification
program is required, in order to ensure the effectiveness of this solution.
8.1.5 Internal organic coatings
Internal coating for corrosion protection is not recommended where there is a risk of damage such as
detachment from the base pipe material due to RGD, erosion, installation and work-overs. Extensive
[14]
corrosion rates are likely to result in sections with coating damages.
8.2 Brittle fracture
If a CO -rich stream experiences depressuring, it can cool down rapidly because of the Joule-Thomson
effect. Selected materials shall be suitable for the minimum design temperature. This applies to both
parent metal and welded joints.
These materials with guaranteed low-temperature properties shall be applied to vessels, pipes, valves
and fittings, including body and internals of pressure relief devices. In addition, the low temperature
upstream pressure let down device in piping sections should be considered (refer to Clause 5).
8.3 Ductile fracture
Piping systems handling CO -rich streams are more susceptible to running ductile fractures than
those for natural gas service. When a fracture initiates in a pipe with dense phase CO -rich stream
and vapour starts to form, the decompression speed drops rapidly, keeping the pipe subjected to a
high loading state. The selected piping material should resist this high loading state and thus prevent
fracture propagation.
Likelihood of fracture propagation depends on piping material and thickness, on operation temperature
[15]
and pressure and on the physical properties of the CO -rich stream. A methodology for evaluating
ductile fracture propagation is described in Annex G.
8.4 Lubricants
Petroleum based greases and many synthetic types of greases, used in components such as valves
and pumps, can be deteriorated by CO -r
...