EN ISO 15156-2:2020

SLOVENSKI STANDARD
01-januar-2021
Nadomešča:
SIST EN ISO 15156-2:2015
Industrija za predelavo nafte in zemeljskega plina - Materiali za uporabo v okoljih s
H2S v proizvodnji olja in plina - 2. del: Proti razpokam odporna ogljikova in
malolegirana jekla ter uporaba litega železa (ISO 15156-2:2020)
Petroleum and natural gas industries - Materials for use in H2S-containing environments
in oil and gas production - Part 2: Cracking-resistant carbon and low-alloy steels, and the
use of cast irons (ISO 15156-2:2020)
Erdöl- und Erdgasindustrie - Werkstoffe für den Einsatz in H2S-haltiger Umgebung bei
der Öl- und Gasgewinnung - Teil 2: Gegen Rissbildung beständige unlegierte und
niedriglegierte Stähle und Gusseisen (ISO 15156-2:2020)
Industries du pétrole et du gaz naturel - Matériaux pour utilisation dans des
environnements contenant de l'hydrogène sulfuré (H2S) dans la production de pétrole et
de gaz - Partie 2: Aciers au carbone et aciers faiblement alliés résistants à la fissuration,
et utilisation de fontes (ISO 15156-2:2020)
Ta slovenski standard je istoveten z: EN ISO 15156-2:2020
ICS:
75.180.10 Oprema za raziskovanje, Exploratory, drilling and
vrtanje in odkopavanje extraction equipment
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 15156-2
EUROPEAN STANDARD
NORME EUROPÉENNE
November 2020
EUROPÄISCHE NORM
ICS 75.180.01 Supersedes EN ISO 15156-2:2015
English Version
Petroleum and natural gas industries - Materials for use in
H2S-containing environments in oil and gas production -
Part 2: Cracking-resistant carbon and low-alloy steels, and
the use of cast irons (ISO 15156-2:2020)
Industries du pétrole et du gaz naturel - Matériaux Erdöl- und Erdgasindustrie - Werkstoffe für den
pour utilisation dans des environnements contenant de Einsatz in H2S-haltiger Umgebung bei der Öl- und
l'hydrogène sulfuré (H2S) dans la production de Gasgewinnung - Teil 2: Gegen Rissbildung beständige
pétrole et de gaz - Partie 2: Aciers au carbone et aciers unlegierte und niedriglegierte Stähle und Gusseisen
faiblement alliés résistants à la fissuration, et (ISO 15156-2:2020)
utilisation de fontes (ISO 15156-2:2020)
This European Standard was approved by CEN on 12 October 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 15156-2:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 15156-2:2020) 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 May 2021, and conflicting national standards shall be
withdrawn at the latest by May 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 15156-2:2015.
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 15156-2:2020 has been approved by CEN as EN ISO 15156-2:2020 without any
modification.
INTERNATIONAL ISO
STANDARD 15156-2
Fourth edition
2020-11
Petroleum and natural gas
industries — Materials for use in H S-
containing environments in oil and
gas production —
Part 2:
Cracking-resistant carbon and low-
alloy steels, and the use of cast irons
Industries du pétrole et du gaz naturel — Matériaux pour utilisation
dans des environnements contenant de l'hydrogène sulfuré (H S) dans
la production de pétrole et de gaz —
Partie 2: Aciers au carbone et aciers faiblement alliés résistants à la
fissuration, et utilisation de fontes
Reference number
ISO 15156-2:2020(E)
©
ISO 2020
ISO 15156-2:2020(E)
© 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
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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

ISO 15156-2:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 3
4 Symbols and abbreviated terms . 6
5 Purchasing information . 7
6 Factors affecting the behaviour of carbon and low alloy steels in H S-containing
environments . 7
7 Qualification and selection of carbon and low-alloy steels with resistance to SSC,
SOHIC and SZC . 8
7.1 Option 1 — Selection of SSC-resistant steels (and cast irons) using A.2 . 8
7.1.1 For p < 0,3 kPa (0,05 psi) . 8
HS
7.1.2 For p ≥ 0,3 kPa (0,05 psi) . 8
HS
7.2 Option 2 — Selection of steels for specific sour-service applications or for ranges
of sour service . 8
7.2.1 Sulfide stress cracking . 8
7.2.2 SOHIC and SZC .10
7.3 Hardness requirements .10
7.3.1 General.10
7.3.2 Parent metals .10
7.3.3 Welds .11
7.4 Other fabrication methods .16
8 Evaluation of carbon and low alloy steels for their resistance to HIC/SWC .16
9 Marking, labelling, and documentation .17
Annex A (normative) SSC-resistant carbon and low alloy steels (and requirements and
recommendations for the use of cast irons) .18
Annex B (normative) Qualification of carbon and low-alloy steels for H S service by
laboratory testing .27
Annex C (informative) Determination of H S partial pressure and use of alternative parameters .35
Annex D (informative) Recommendations for determining pH .40
Annex E (informative) Information that should be supplied for material purchasing .45
Bibliography .47
ISO 15156-2:2020(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 67, Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 12, Materials, equipment and
offshore structures for petroleum, petrochemical and natural gas industries, in accordance with the
Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 15156-2:2015), which has been
technically revised. The main changes compared to the previous edition are as follows:
— corrections of temperature conversion for welding (see A.2.1.4), vold deformation and stress relief
(see A.2.1.6), identification stamping (see A.2.1.9), tubulars and tubular components (see A.2.2.3.4),
compressor impellers (see A.2.3.3.2);
— title change from Shear rams to Rams in A.2.3.2.2;
— addition of C110 and changes the designation of C95 to R95 in Table A.3;
— reference change to NACE TM0316 in Table B.1;
— addition of reference to BS 8701 in B.4.3;
— changes and additions to Table B.3;
— modification of Annex C to include alternative parameters and expanded explanation for the use of
chemical activity and fugacity, and to provide some general guidance for the use of thermodynamic
modeling for the determination of environmental severity.
A list of all parts in the ISO 15156 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

ISO 15156-2:2020(E)
Introduction
The consequences of sudden failures of metallic oil and gas field components, associated with their
exposure to H S-containing production fluids, led to the preparation of the first edition of NACE MR0175,
which was published in 1975 by the National Association of Corrosion Engineers, now known as NACE
International.
The original and subsequent editions of NACE MR0175 established limits of H S partial pressure above
which precautions against sulfide stress cracking (SSC) were always considered necessary. They
also provided guidance for the selection and specification of SSC-resistant materials when the H S
thresholds were exceeded. In more recent editions, NACE MR0175 has also provided application limits
for some corrosion-resistant alloys, in terms of environmental composition and pH, temperature and
H S partial pressures.
In separate developments, the European Federation of Corrosion issued EFC Publication 16 in 1995 and
EFC Publication 17 in 1996. These documents are generally complementary to those of NACE though
they differed in scope and detail.
In 2003, the publication of the ISO 15156-series and NACE MR0175/ISO 15156 was completed for the
first time. These technically identical documents utilized the above sources to provide requirements
and recommendations for materials qualification and selection for application in environments
containing wet H S in oil and gas production systems. They are complemented by NACE TM0177 and
NACE TM0284 test methods.
The revision of this document, i.e. ISO 15156-2,involves a consolidation of all changes agreed
and published in the Technical Circular 1, ISO 15156-2:2015/Cir.1:2017, the Technical Circular 2,
ISO 15156-2:2015/Cir.2:2018 and the Technical Circular 3, ISO 15156-2:2015/Cir.3:2019, published by
the ISO 15156 series Maintenance Agency secretariat at DIN.
The changes were developed by and approved by the ballot of, representative groups from within
the oil and gas production industry. The great majority of these changes stem from issues raised by
document users. A description of the process by which these changes were approved can be found at
the ISO 15156 series maintenance website: www .iso .org/ iso15156maintenance.
When found necessary by oil and gas production industry experts, future interim changes to this
document will be processed in the same way and will lead to interim updates to this document in
the form of Technical Corrigenda or Technical Circulars. Document users should be aware that such
documents can exist and can impact the validity of the dated references in this document.
The ISO 15156 series Maintenance Agency at DIN was set up after approval by the ISO Technical
Management Board given in document 34/2007. This document describes the make up of the agency,
which includes experts from NACE, EFC and ISO/TC 67, and the process for approval of amendments.
It is available from the ISO 15156 series maintenance website and from the ISO/TC 67 Secretariat. The
website also provides access to related documents that provide more detail of the ISO 15156 series
maintenance activities.
INTERNATIONAL STANDARD ISO 15156-2:2020(E)
Petroleum and natural gas industries — Materials
for use in H S-containing environments in oil and gas
production —
Part 2:
Cracking-resistant carbon and low-alloy steels, and the use
of cast irons
WARNING — Carbon and low-alloy steels and cast irons selected using this document are
resistant to cracking in defined H S-containing environments in oil and gas production but
not necessarily immune to cracking under all service conditions. It is the equipment user's
responsibility to select the carbon and low alloy steels and cast irons suitable for the intended
service.
1 Scope
This document gives requirements and recommendations for the selection and qualification of carbon
and low-alloy steels for service in equipment used in oil and natural gas production and natural gas
treatment plants in H S-containing environments, whose failure can pose a risk to the health and safety
of the public and personnel or to the environment. It can be applied to help to avoid costly corrosion
damage to the equipment itself. It supplements, but does not replace, the materials requirements of the
appropriate design codes, standards or regulations.
This document addresses the resistance of these steels to damage that can be caused by sulfide stress
cracking (SSC) and the related phenomena of stress-oriented hydrogen-induced cracking (SOHIC) and
soft-zone cracking (SZC).
This document also addresses the resistance of these steels to hydrogen-induced cracking (HIC) and its
possible development into stepwise cracking (SWC).
This document is concerned only with cracking. Loss of material by general (mass loss) or localized
corrosion is not addressed.
Table 1 provides a non-exhaustive list of equipment to which this document is applicable, including
exclusions.
This document applies to the qualification and selection of materials for equipment designed and
constructed using load controlled design methods. For design utilizing strain-based design methods,
see ISO 15156-1:2020, Clause 5.
Annex A lists SSC-resistant carbon and low alloy steels, and A.2.4 includes requirements for the use of
cast irons.
This document is not necessarily suitable for application to equipment used in refining or downstream
processes and equipment.
ISO 15156-2:2020(E)
Table 1 — List of equipment
This document is applicable to materials used
Exclusions
for the following equipment
Drilling, well construction and well-servicing Equipment exposed only to drilling fluids of controlled
a
equipment composition
Drill bits
b
Blowout preventer (BOP) shear blades
Drilling riser systems
Work strings
c
Wireline and wireline equipment
Surface and intermediate casing
d
Wells, including subsurface equipment, gas lift Sucker rod pumps and sucker rods
equipment, wellheads and christmas trees
Electric submersible pumps
Other artificial lift equipment
Slips
Flow-lines, gathering lines, field facilities and field Crude oil storage and handling facilities operating at a
processing plants total absolute pressure below 0,45 MPa (65 psi)
Water-handling equipment Water-handling facilities operating at a total absolute
pressure below 0,45 MPa (65 psi)
Water injection and water disposal equipment
Natural gas treatment plants —
Transportation pipelines for liquids, gases and Lines handling gas prepared for general commercial
multiphase fluids and domestic use
For all equipment above Components loaded only in compression
a
See A.2.3.2.3 for more information.
b
See A.2.3.2.1 for more information.
c
Wireline lubricators and lubricator connecting devices are not excluded.
d
For sucker rod pumps and sucker rods, reference can be made to NACE MR0176.
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 6506 (all parts), Metallic materials — Brinell hardness test
ISO 6507 (all parts), Metallic materials — Vickers hardness test
ISO 6508 (all parts), Metallic materials — Rockwell hardness test
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 10423, Petroleum and natural gas industries — Drilling and production equipment — Wellhead and
christmas tree equipment
ISO 15156-1:2020, Petroleum and natural gas industries — Materials for use in H S-containing
environments in oil and gas production — Part 1: General principles for selection of cracking-resistant
materials
ISO 15156-3, Petroleum and natural gas industries — Materials for use in H S-containing environments in
oil and gas production — Part 3: Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys
2 © ISO 2020 – All rights reserved

ISO 15156-2:2020(E)
1)
NACE TM0177 , Laboratory testing of metals for resistance to sulfide stress cracking and stress corrosion
cracking in H S environments
NACE TM0284, Evaluation of pipeline and pressure vessel steels for resistance to hydrogen-induced cracking
NACE TM0316, Four-point bend testing of materials for oil and gas applications
2)
SAE AMS-2430 , Shot Peening
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 15156-1 and the following 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/
3.1
Brinell hardness
HBW
hardness value of a material measured normally using a 10 mm diameter tungsten carbide ball indenter
with a force of 29,42 kN
Note 1 to entry: The measurement shall be in accordance with the ISO 6506 series. Here, ASTM E10 is equivalent
to ISO 6506-1.
3.2
bubble-point pressure
p
B
pressure under which gas bubbles form in a liquid at a particular operating temperature
Note 1 to entry: See C.2.
3.3
burnishing
process of smoothing surfaces using frictional contact between the material and some other hard
pieces of material, such as hardened steel balls
3.4
casting
metal that is obtained at or near its finished shape by the solidification of molten metal in a mould
3.5
cast iron
iron-carbon alloy containing approximately 2 % to 4 % mass fraction carbon
3.5.1
grey cast iron
cast iron that displays a grey fracture surface due to the presence of flake graphite
3.5.2
white cast iron
cast iron that displays a white fracture surface due to the presence of cementite
1) www .nace .org
2)  www .sae .org
ISO 15156-2:2020(E)
3.5.3
malleable iron
white cast iron that is thermally treated to convert most or all of the cementite to graphite (temper carbon)
3.5.4
ductile iron
nodular cast iron
cast iron that has been treated while molten with an element (usually magnesium or cerium) that
spheroidizes the graphite
3.6
cementite
microstructural constituent of steels composed principally of iron carbide (Fe C)
3.7
cold deforming
cold forging
cold forming
cold working
deforming metal plastically under conditions of temperature and strain rate that induce strain-
hardening, usually, but not necessarily, conducted at room temperature
3.8
fitness-for-purpose
suitability for use under the expected service conditions
3.9
free-machining steel
steel to which elements such as sulfur, selenium and lead have been added intentionally to improve
machineability
3.10
lower critical temperature
temperature of a ferrous metal at which austenite begins to form during heating or at which the
transformation of austenite is completed during cooling
3.11
nitriding
case-hardening process in which nitrogen is introduced into the surface of metallic materials (most
commonly ferrous alloys)
EXAMPLE Liquid nitriding, gas nitriding, ion nitriding and plasma nitriding.
3.12
normalize
heating a ferrous metal to a suitable temperature above the transformation range (austenitizing),
holding at temperature for a suitable time and then cooling in still air (or protective atmosphere) to a
temperature substantially below the transformation range
3.13
plastically deformed
permanently deformed by stressing beyond the limit of elasticity, i.e. the limit of proportionality of
stress to strain
3.14
pressure-containing part
part whose failure to function as intended results in a release of retained fluid to the atmosphere
EXAMPLE Valve bodies, bonnets and stems.
4 © ISO 2020 – All rights reserved

ISO 15156-2:2020(E)
3.15
quenched and tempered
quench hardened and then tempered
3.16
Rockwell C hardness
HRC
hardness value of a material measured using a Rockwell C diamond cone indenter with a force of 1 471 N
Note 1 to entry: The measurement shall be in accordance with the ISO 6508 series. Here, ASTM E18 is equivalent
to ISO 6508-1.
3.17
shot-peening
inducing compressive stresses in the surface layer of a material by bombarding it with a selected
medium (usually round steel shot) under controlled conditions
3.18
stress relief
heating a metal to a suitable temperature, holding at that temperature long enough to reduce residual
stresses, and then cooling slowly enough to minimize the development of new residual stresses
3.19
tempering
heat treatment by heating to a temperature below the lower critical temperature, for the purpose
of decreasing the hardness and increasing the toughness of hardened steel, hardened cast iron and,
sometimes, normalized steel
3.20
tensile strength
ultimate strength
ratio of maximum load to original cross-sectional area
Note 1 to entry: See ISO 6892-1.
3.21
test batch
group of items representing a production batch whose conformity with a specified requirement can be
determined by testing representative samples in accordance with a defined procedure
3.22
tubular component
cylindrical component (pipe) having a longitudinal hole, used in drilling/production operations for
conveying fluids
3.23
Vickers hardness
HV
hardness value of a material using a diamond pyramid indenter and one of a variety of possible
applied loads
Note 1 to entry: The measurement shall be in accordance with the ISO 6507 series. Here, ASTM E384 is equivalent
to ISO 6507-1.
3.24
weldment
portion of a component on which welding has been performed, including the weld metal, the heat-
affected zone, and the adjacent parent metal
ISO 15156-2:2020(E)
3.25
weld metal
portion of a weldment that has been molten during welding
3.26
wrought
formed to a desired shape by working (rolling, extruding, forging, etc.), usually at an elevated
temperature
4 Symbols and abbreviated terms
AYS actual yield strength
CLR crack length ratio
CSR crack surface ratio
CTR crack thickness ratio
DCB double cantilever beam (test)
FPB four-point bend (test)
HBW Brinell hardness
HIC hydrogen-induced cracking
HRC Rockwell hardness (scale C)
HSC hydrogen stress cracking
OCTG oil country tubular goods, i.e. casing, tubing and drill pipe
p partial pressure of H S
HS
p partial pressure of CO
CO
R 0,2 % proof stress in accordance with ISO 6892-1
p0,2
SMYS specified minimum yield strength
SOHIC stress-oriented hydrogen-induced cracking
SSC sulfide stress cracking
SWC stepwise cracking
SZC soft-zone cracking
T temperature
UNS Unified Numbering System (from SAE-ASTM, Metals and alloys in the Unified Numbering System)
UT uniaxial tensile (test)
6 © ISO 2020 – All rights reserved

ISO 15156-2:2020(E)
5 Purchasing information
5.1 The preparation of material purchasing specifications can require co-operation and exchange of
data between the equipment user, the equipment supplier and the material manufacturer to ensure that
the material purchased conforms with ISO 15156-1 and this document.
5.2 The following information shall be provided:
— preferred material types and/or grades (if known);
— equipment type (if known);
— reference to this document;
— acceptable bases for selection of materials for SSC resistance (see Clause 7);
— requirements for HIC resistance (see Clause 8).
5.3 The equipment user and the equipment supplier/material manufacturer may agree that carbon or
low-alloy steels other than those described and/or listed in Annex A may be selected subject to suitable
qualification testing in accordance with Annex B and ISO 15156-1. The qualification requirements may
be extended to include resistance to SOHIC and SZC.
If the purchaser intends to make use of such agreements, extensions and qualifications, the appropriate
additional information shall be clearly indicated in the materials purchasing specification. This
information may include
— requirements for SSC testing (see 7.1 and 7.2),
— service conditions for specific sour-service application, and
— other special requirements.
5.4 Annex C describes how to calculate the H S partial pressure and Annex D gives guidance on how to
determine the pH-value of a fluid.
5.5 The information required for material purchasing shall be entered on suitable data sheets.
Suggested formats are given in Annex E.
6 Factors affecting the behaviour of carbon and low alloy steels in H S-
containing environments
The behaviour of carbon and low-alloy steels in H S-containing environments is affected by complex
interactions of parameters, including the following:
a) chemical composition, method of manufacture, product form, strength, hardness of the material
and its local variations, amount of cold work, heat-treatment condition, microstructure,
microstructural uniformity, grain size and cleanliness of the material;
b) H S partial pressure or equivalent concentration in the water phase;
c) chloride ion concentration in the water phase;
d) acidity (pH) of the water phase;
e) presence of sulfur or other oxidants;
f) exposure to non-production fluids;
ISO 15156-2:2020(E)
g) exposure temperature;
h) total tensile stress (applied plus residual);
i) exposure time.
These factors shall be considered when using this document for the selection of materials suitable for
environments containing H S in oil and gas production systems.
7 Qualification and selection of carbon and low-alloy steels with resistance to
SSC, SOHIC and SZC
7.1 Option 1 — Selection of SSC-resistant steels (and cast irons) using A.2
7.1.1 For p < 0,3 kPa (0,05 psi)
HS
The selection of materials for SSC resistance for p below 0,3 kPa (0,05 psi) is not considered in detail
HS
in this document. Normally, no special precautions are required for the selection of steels for use under
these conditions, nevertheless, highly susceptible steels can crack. Additional information on factors
affecting susceptibility of steels and attack by cracking mechanisms other than SSC is given in 7.2.1.
7.1.2 For p ≥ 0,3 kPa (0,05 psi)
HS
If the partial pressure of H S in the gas is equal to or greater than 0,3 kPa (0,05 psi), SSC-resistant steels
shall be selected using A.2.
NOTE 1 The steels described or listed in A.2 are considered resistant to SSC in oil and natural-gas production
and natural-gas treatment plants.
NOTE 2 Users concerned with the occurrence of SOHIC and/or SZC can refer to Option 2 (see 7.2.2).
NOTE 3 For HIC and SWC, see Clause 8.
7.2 Option 2 — Selection of steels for specific sour-service applications or for ranges of
sour service
7.2.1 Sulfide stress cracking
7.2.1.1 General
Option 2 allows the user to qualify and select materials for sulfide stress cracking (SSC) resistance for
specific sour-service applications or for ranges of sour service.
For a given material, the limits of environmental and metallurgical variables defined for specific sour
service or for a range of sour service by qualification in accordance with Option 2 may replace any
limits of environmental and metallurgical variables listed for that material in A.2 (Option 1).
The use of option 2 can require knowledge of both the in situ pH and the H S partial pressure and their
variations with time; see ISO 15156-1.
Option 2 facilitates the purchase of bulk materials, such as OCTG or line pipe, where the economic
incentive to use materials not described nor listed in Annex A outweighs the additional qualification
and other costs that can be incurred. Steels for other equipment may also be qualified. In some cases,
this requires an agreement between the supplier and the equipment user with respect to test and
acceptance requirements. Such agreements shall be documented.
Option 2 can also facilitate fitness-for-purpose evaluations of existing carbon or low-alloy steel
equipment exposed to sour-service conditions more severe than assumed in the current design.
8 © ISO 2020 – All rights reserved

ISO 15156-2:2020(E)
7.2.1.2 SSC regions of environmental severity
The severity of the sour environment, determined in accordance with ISO 15156-1, with respect to the
SSC of a carbon or low-alloy steel shall be assessed using Figure 1. In defining the severity of the H S-
containing environment, the possibility of exposure to unbuffered, condensed aqueous phases of low
pH during upset operating conditions or downtime, or to acids used for well stimulation and/or the
backflow of stimulation acid after reaction should be considered.
Key
X H S partial pressure, expressed in kilopascals
Y in situ pH
0 region 0
1 SSC region 1
2 SSC region 2
3 SSC region 3
NOTE 1 The discontinuities in the figure below 0,3 kPa (0,05 psi) and above 1 MPa (150 psi) partial pressure
H S reflect uncertainty with respect to the measurement of H S partial pressure (low p ) and the steel’s
2 2
HS
performance outside these limits (for both low and high p ).
HS
NOTE 2 Guidance on the calculation of H S partial pressure is given in Annex C.
NOTE 3 Guidance on the calculation of pH is given in Annex D.
Figure 1 — Regions of environmental severity with respect to the SSC of carbon and low-
alloy steels
ISO 15156-2:2020(E)
7.2.1.3 Region 0 — For p < 0,3 kPa (0,05 psi)
HS
Normally, no precautions are required for the selection of steels for use under these conditions.
Nevertheless, a number of factors, as follows, that can affect a steel's performance in this region should
be considered.
— Steels that are highly susceptible to SSC and HSC can crack.
— Steel's physical and metallurgical properties affect its inherent resistance to SSC and HSC;
see Clause 6.
— Very high-strength steels can suffer HSC in aqueous environments without H S. Above about
965 MPa (140 ksi) yield strength, attention should be given to steel composition and processing to
ensure that these steels do not exhibit SSC or HSC in region 0 environments.
— Stress concentrations increase the risk of cracking.
7.2.1.4 SSC regions 1, 2 and 3
Referring to the regions of severity of the exposure as defined in Figure 1, steels for region 1 may be
selected using A.2, A.3 or A.4; steels for region 2 may be selected using A.2 or A.3; and steels for region 3
may be selected using A.2.
In the absence of suitable choices from Annex A, carbon and low-alloy steels may be tested and qualified
for use under specific sour-service conditions or for use throughout a given SSC region. Testing and
qualification shall be in accordance with ISO 15156-1 and Annex B.
Documented field experience may also be used as the basis for material selection for a specific sour-
service application; see ISO 15156-1.
7.2.2 SOHIC and SZC
The user should consider SOHIC and SZC, as defined in ISO 15156-1, when evaluating carbon steels in
plate form and their welded products for sour service in H S-containing environments.
B.4 provides guidance on test methods and acceptance criteria to evaluate resistance to SOHIC and SZC.
NOTE The occurrence of these phenomena is rare and they are not well understood. They have caused
sudden failures in parent steels (SOHIC) and in the HAZ of welds (SOHIC and SZC). Their occurrence is thought to
be restricted to carbon steels. The presence of sulfur or oxygen in the service environment is thought to increase
the probability of damage by these mechanisms.
7.3 Hardness requirements
7.3.1 General
The hardness of parent materials and of welds and their heat-affected zones play important roles in
determining the SSC resistance of carbon and low alloy steels. Hardness control can be an acceptable
means of obtaining SSC resistance.
7.3.2 Parent metals
If hardness measurements on parent metal are specified, sufficient hardness tests shall be made to
establish the actual hardness of the steel being examined. Individual HRC readings exceeding the
value permitted by this document may be considered acceptable if the average of several readings
taken within close proximity does not exceed the value permitted by this document and no individual
reading is greater than 2 HRC above the specified value. Equivalent requirements shall apply to other
10 © ISO 2020 – All rights reserved

ISO 15156-2:2020(E)
methods of hardness measurement when specified in this document or referenced in a manufacturing
specification.
NOTE The number and location of hardness tests on parent metal are not specified in the ISO 15156 series.
[38]
For ferritic steels, EFC Publication 16 shows graphs for the conversion of hardness readings, from
Vickers (HV) to Rockwell (HRC) and from Vickers (HV) to Brinell (HBW), derived from the tables of
ASTM E140 and ISO 18265. Other conversion tables also exist. Users may establish correlations for
individual materials.
7.3.3 Welds
7.3.3.1 General
The metallurgical changes that occur on welding carbon and low-alloy steels affect their susceptibility
to SSC, SOHIC and SZC.
Processes and consumables should be selected in accordance with good practice and to achieve the
required cracking resistance.
Welding shall be carried out in conformance with appropriate codes and standards as agreed between
the supplier and the purchaser. Welding procedure specifications (WPSs) and procedure qualification
records (PQRs) shall be available for inspection by the equipment user.
The qualification of welding procedures for sour service shall include hardness testing in accordance
with 7.3.3.2, 7.3.3.3 and 7.3.3.4.
7.3.3.2 Hardness testing methods for welding procedure qualification
Hardness testing for welding procedure qualification shall normally be carried out using the Vickers
HV 10 or HV 5 method in accordance with ISO 6507-1, or the Rockwell method in accordance with
ISO 6508-1 using the 15N scale.
NOTE For the purposes of this provision, ASTM E384 is equivalent to ISO 6507-1 and ASTM E18 is equivalent
to ISO 6508-1.
The HRC method may be used for welding procedure qualification if the design stress does not exceed
two-thirds of SMYS and the welding procedure specification includes post-weld heat treatment. The use
of the HRC method for welding procedure qualification in all other cases shall require the agreement of
the equipment user.
NOTE Hardness surveys using the Vickers or Rockwell 15N testing method produce a more detailed picture
of weld hardness and its variations. Hardness surveys using the HRC testing method might not detect small zones
in welds or HAZs where the hardness exceeds the acceptance criteria for the Vickers or Rockwell 15N testing
method. The significance of such small hard zones is not well understood.
The use of other hardness testing methods shall require the agreement of the equipment user.
The Vickers or Rockwell 15N hardness testing method shall be
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