EN ISO 15156-2:2009

SLOVENSKI STANDARD
01-januar-2010
1DGRPHãþD
SIST EN ISO 15156-2:2004
SIST EN ISO 15156-2:2004/AC:2007
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 15156-2:2009)
Petroleum and natural gas industries - Materials for use in H2Scontaining environments
in oil and gas production - Part 2: Cracking-resistant carbon and low-alloy steels, and the
use of cast irons (ISO 15156-2:2009)
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 15156-2:2009)
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 15156-2:2009)
Ta slovenski standard je istoveten z: EN ISO 15156-2:2009
ICS:
75.180.10 Oprema za raziskovanje in Exploratory and extraction
odkopavanje equipment
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 15156-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2009
ICS 75.180.01 Supersedes EN ISO 15156-2:2003
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 15156-2:2009)
Industries du pétrole et du gaz naturel - Matériaux pour Erdöl- und Erdgasindustrie - Werkstoffe für den Einsatz in
utilisation dans des environnements contenant de H2S-haltiger Umgebung bei der Öl- und Gasgewinnung -
l'hydrogène sulfuré (H2S) dans la production de pétrole et Teil 2: Gegen Rissbildung beständige unlegierte und
de gaz - Partie 2: Aciers au carbone et aciers faiblement niedriglegierte Stähle und Gusseisen (ISO 15156-2:2009)
alliés résistants à la fissuration, et utilisation de fontes (ISO
15156-2:2009)
This European Standard was approved by CEN on 29 September 2009.

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: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 15156-2:2009: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 15156-2:2009) 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 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 April 2010, and conflicting national standards shall be withdrawn at the
latest by April 2010.
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.
This document supersedes EN ISO 15156-2:2003.
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 the United Kingdom.
Endorsement notice
The text of ISO 15156-2:2009 has been approved by CEN as a EN ISO 15156-2:2009 without any
modification.
INTERNATIONAL ISO
STANDARD 15156-2
Second edition
2009-10-15
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 15156-2:2009(E)
©
ISO 2009
ISO 15156-2:2009(E)
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ii © ISO 2009 – All rights reserved

ISO 15156-2:2009(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
8 Evaluation of carbon and low alloy steels for their resistance to HIC/SWC .17
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 .35
Annex D (informative) Recommendations for determining pH .37
Annex E (informative) Information that should be supplied for material purchasing .42
Bibliography.44

ISO 15156-2:2009(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 15156-2 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries.
This second edition cancels and replaces the first edition (ISO 15156-2:2003), of which it constitutes a minor
revision, specifically by the following:
⎯ inclusion of the requirements for welding-procedure qualification for overlay welding;
⎯ inclusion of changes to the limitations that apply to Table A.1 on weld hardness;
⎯ inclusion of the ISO equivalents of ASTM hardness standards;
⎯ inclusion of a small number of other technical changes;
⎯ inclusion of changes to make the intent of the text clearer and to correct editorial errors.
ISO 15156 consists of the following parts, under the general title 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
⎯ Part 2: Cracking-resistant carbon and low-alloy steels, and the use of cast irons
⎯ Part 3: Cracking-resistant CRAs (corrosion-resistant alloys) and other alloys
iv © ISO 2009 – All rights reserved

ISO 15156-2:2009(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 three parts of ISO 15156 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 part of ISO 15156 involves a consolidation of all changes agreed and published in the
Technical Corrigendum 1, ISO 15156-2:2003/Cor.1:2005 and by the Technical Circular 1,
ISO 15156-2:2001/Cir.1:2007(E), published by the ISO 15156 maintenance agency secretariat at DIN, Berlin.
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
maintenance website www.iso.org/iso15156maintenance.
When found necessary by oil and gas production industry experts, future interim changes to this part of
ISO 15156 will be processed in the same way and will lead to interim updates to this part of ISO 15156 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 part of ISO 15156.
The ISO 15156 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/WG 7, and the process for approval of amendments. It is available
from the ISO 15156 maintenance website and from the ISO/TC 67 Secretariat. The website also provides
access to related documents that provide more detail of ISO 15156 maintenance activities.

INTERNATIONAL STANDARD ISO 15156-2:2009(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 part of ISO 15156 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 part of ISO 15156 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 part of ISO 15156 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 part of ISO 15156 also addresses the resistance of these steels to hydrogen-induced cracking (HIC) and
its possible development into stepwise cracking (SWC).
This part of ISO 15156 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 part of ISO 15156 is applicable, including
permitted exclusions.
This part of ISO 15156 applies to the qualification and selection of materials for equipment designed and
constructed using conventional elastic design criteria. For designs utilizing plastic criteria (e.g. strain-based
and limit-state designs), see ISO 15156-1:2009, 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 part of ISO 15156 is not necessarily suitable for application to equipment used in refining or downstream
processes and equipment.
ISO 15156-2:2009(E)
Table 1 — List of equipment
ISO 15156 is applicable to materials used
Permitted exclusions
for the following equipment
Drilling, well construction and well-servicing equipment Equipment exposed only to drilling fluids of controlled
a
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 equipment, Sucker rod pumps and sucker rods
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 total

processing plants
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 multiphase Lines handling gas prepared for general commercial and
fluids 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 permitted exclusions.
d
For sucker rod pumps and sucker rods, reference can be made to NACE MR0176.
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 6506-1, Metallic materials — Brinell hardness test — Part 1: Test method
ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method
ISO 6508-1, Metallic materials — Rockwell hardness test — Part 1: Test method (scales A, B, C, D, E, F, G, H,
K, N, T)
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 15156-1:2009, 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 15156-3:2009, 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 2009 – All rights reserved

ISO 15156-2:2009(E)
1)
NACE TM0177-05 , 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
2)
EFC Publications Number 16 , Guidelines on materials requirements for carbon and low alloy steels for
H S-containing environments in oil and gas production
3)
SAE AMS-2430P , Shot Peening, Automatic
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 15156-1 and the following apply.
3.1
Brinell hardness
HBW
hardness value, measured in accordance with ISO 6506-1, normally using a 10 mm diameter tungsten ball
and a force of 29,42 kN
NOTE For the purposes of this provision, 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
See Clause C.2.
3.3
burnish
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) NACE International, P.O. Box 2183140, Houston, Texas 77218-8340, USA.
2) European Federation of Corrosion, available from The Institute of Materials, 1 Carlton House Terrace, London SW1Y
5DB, UK [ISBN 0-901716-95-2].
3) Society of Automotive Engineers (SAE), 400 Commonwealth Drive, Warrendale, PA 15096-0001 USA.
ISO 15156-2:2009(E)
3.5.3
malleable cast iron
white cast iron that is thermally treated to convert most or all of the cementite to graphite (temper carbon)
3.5.4
ductile cast 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 working
cold deforming
cold forging
cold forming
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)
EXAMPLES Liquid nitriding, gas nitriding, ion nitriding and plasma nitriding.
3.12
normalizing
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 parts
those parts whose failure to function as intended results in a release of retained fluid to the atmosphere
EXAMPLES Valve bodies, bonnets and stems.
4 © ISO 2009 – All rights reserved

ISO 15156-2:2009(E)
3.15
quenched and tempered
quench hardened and then tempered
3.16
Rockwell C hardness
HRC
hardness value, measured in accordance with ISO 6508, obtained using a diamond cone indenter and a force
of 1 471 N
NOTE For the purposes of this provision, 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 relieving
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
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, measured in accordance with ISO 6507-1, obtained using a diamond pyramid indenter and
one of a variety of possible applied loads
NOTE For the purposes of this provision, ASTM E92 is equivalent to ISO 6507-1.
3.24
weldment
that portion of a component on which welding has been performed, including the weld metal, the heat-affected
zone (HAZ), and the adjacent parent metal
ISO 15156-2:2009(E)
3.25
weld metal
that portion of a weldment that has been molten during welding
3.26
wrought metal
metal in the solid condition that is formed to a desired shape by working (rolling, extruding, forging, etc.),
usually at an elevated temperature
4 Symbols and abbreviated terms
For the purposes of this document, the abbreviated terms given in ISO 15156-1 and the following apply.
AYS actual yield strength
CLR crack length ratio
CR c-ring (test)
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
HV Vickers hardness
OCTG oil country tubular goods, i.e. casing, tubing and drill pipe
p partial pressure of H S
H S 2
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 2009 – All rights reserved

ISO 15156-2:2009(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 complies with ISO 15156-1 and this part of ISO 15156.
5.2 The following information shall be provided:
⎯ preferred material types and/or grades (if known);
⎯ equipment type (if known);
⎯ reference to this part of ISO 15156;
⎯ 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, 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;
ISO 15156-2:2009(E)
f) exposure to non-production fluids;
g) exposure temperature;
h) total tensile stress (applied plus residual);
i) exposure time.
These factors shall be considered when using this part of ISO 15156 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 Clause A.2
7.1.1 For p < 0,3 kPa (0,05 psi)
H S
The selection of materials for SSC resistance for p below 0,3 kPa (0,05 psi) is not considered in detail in
H S
this part of ISO 15156. 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 W 0,3 kPa (0,05 psi)
H S
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 Clause A.2.
NOTE 1 The steels described or listed in Clause 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, refer to 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.
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 2009 – All rights reserved

ISO 15156-2:2009(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 H S) and the steel’s performance outside
2 2
these limits (for both low and high H S).
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 15156-2:2009(E)
7.2.1.3 Region 0 — For p < 0,3 kPa (0,05 psi)
H S
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.
⎯ A 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 Clause A.2, A.3 or A.4; steels for region 2 may be selected using Clause A.2 or A.3; and steels for
region 3 may be selected using Clause 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.
Clause 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 part of ISO 15156 may be considered acceptable if the average of several readings taken within close
proximity does not exceed the value permitted by this part of ISO 15156 and no individual reading is greater
than 2 HRC above the specified value. Equivalent requirements shall apply to other methods of hardness
measurement when specified in this part of ISO 15156 or referenced in a manufacturing specification.
NOTE The number and location of hardness tests on parent metal are not specified in ISO 15156.
10 © ISO 2009 – All rights reserved

ISO 15156-2:2009(E)
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 compliance 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 E92 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 used for the qualification of alternative weld-
hardness acceptance criteria as permitted in 7.3.3.4.
7.3.3.3 Hardness surveys for welding procedure qualification
Vickers hardness surveys shall be in accordance with Figure 2 for butt welds, Figure 3 for fillet welds and
Figure 4 for repair and partial penetration welds. HRC surveys of butt welds shall be in accordance with
Figure 5. Survey requirements for other joint configurations shall be developed from these figures.
Hardness surveys for qualification of overlay welding procedures shall be in accordance with Figure 6.
ISO 15156-2:2009(E)
Dimensions in millimetres
Key
A weld heat-affected zone (visible after etching)
B lines of survey
C hardness impressions: Impressions 2, 3, 6, 7, 10, 11, 14, 15, 17 and 19 should be entirely within the heat-affected
zone and located as close as possible to the fusion boundary between the weld metal and the heat-affected zone.
The top line of survey should be positioned so that impressions 2 and 6 coincide with the heat-affected zone of the final
run or change of profile of the fusion line associated with the final run.
Figure 2 — Butt-weld survey method for Vickers hardness measurement
12 © ISO 2009 – All rights reserved

ISO 15156-2:2009(E)
Dimensions in millimetres
Key
A weld heat-affected zone (visible after etching)
B line of survey
C line of survey, parallel to line B and passing through the fusion boundary between the weld metal and the heat-
affected zone at the throat
D hardness impressions: Impressions 3, 6, 10 and 12 should be entirely within the heat-affected zone and located as
close as possible to the fusion boundary between the weld metal and the heat-affected zone.
Figure 3 — Fillet weld
ISO 15156-2:2009(E)
Dimensions in millimetres
Key
A original weld heat-affected zone
B repair-weld heat-affected zone
C parallel lines of survey
D hardness impressions: Impressions in the heat-affected zone should be located as close as possible to the fusion
boundary.
The top line of survey should be positioned so that the heat-affected zone impressions coincide with the heat-affected
zone of the final run or change in profile of the cap of fusion line associated with the final run.
Figure 4 — Repair and partial penetration welds
14 © ISO 2009 – All rights reserved

ISO 15156-2:2009(E)
Dimensions
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