oSIST prEN ISO 15156-2:2026

SLOVENSKI STANDARD
01-marec-2026
Naftna in plinska industrija, vključno z nizkoogljično energijo - Materiali za
uporabo v okoljih s H2S v proizvodnji olja in plina - 2. del: Ocena okolja storitev in
izbira materialov (ISO/DIS 15156-2:2025)
Oil and gas industries including lower carbon energy - Materials for use in H2S-
containing environments in oil and gas production - Part 2: Service environment
assessment and material selection (ISO/DIS 15156-2:2025)
Öl- und Gasindustrie einschließlich kohlenstoffarmer Energieträger - Werkstoffe für den
Einsatz in H₂S-haltiger Umgebung bei der Öl- und Gasgewinnung - Teil 2:
Bewertung der Betrie bsumgebung und Werkstoffauswahl (ISO/DIS 15156-2:2025)
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: Évaluation de l'environnement de service et choix des matériaux
(ISO/DIS 15156-2:2025)
Ta slovenski standard je istoveten z: prEN ISO 15156-2
ICS:
75.180.01 Oprema za industrijo nafte in Equipment for petroleum and
zemeljskega plina na splošno natural gas industries in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 15156-2
ISO/TC 67
Oil and gas industries including
Secretariat: NEN
lower carbon energy — Materials
Voting begins on:
for use in H2S-containing
2025-12-19
environments in oil and gas
Voting terminates on:
production —
2026-03-13
Part 2:
Service environment assessment
and material selection
ICS: 75.180.01
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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Reference number
ISO/DIS 15156-2:2025(en)
DRAFT
ISO/DIS 15156-2:2025(en)
International
Standard
ISO/DIS 15156-2
ISO/TC 67
Oil and gas industries including
Secretariat: NEN
lower carbon energy — Materials
Voting begins on:
for use in H2S-containing
environments in oil and gas
Voting terminates on:
production —
Part 2:
Service environment assessment
and material selection
ICS: 75.180.01
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland Reference number
ISO/DIS 15156-2:2025(en)
ii
ISO/DIS 15156-2:2025(en)
Contents Page
Foreword .iv
Introduction .vi
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 3
4 Symbols and abbreviated terms. 5
5 General principles . 6
6 H S-service assessment . 8
6.1 Analysis of the environment and application severity .8
6.1.1 General .8
6.1.2 Environmental parameters .9
6.1.3 Influence of equipment design and application . 12
6.2 Analysis of applicable damage mechanisms .14
6.2.1 General .14
6.2.2 Carbon and low alloy steels . 15
6.2.3 Cast irons .18
6.2.4 Corrosion-resistant and other alloys .18
7 Materials selection . 19
7.1 General .19
7.2 Guidance on specific equipment .19
7.2.1 Wellhead and tree components .19
7.2.2 Other equipment and components . 20
8 Specification, qualification and verification .21
8.1 General .21
8.1.1 Material selected using Annex A or Annex B .21
8.1.2 Verification .21
8.1.3 Qualification .21
8.2 Carbon and low alloy steels. 22
8.3 Cast irons . 22
8.4 CRA and other alloys . 22
8.5 Weldments . 22
8.5.1 General . 22
8.5.2 Weldments in carbon and low alloy steels . 23
8.5.3 Weldments in CRA and other alloys . 23
8.5.4 Dissimilar welds .24
8.6 Weld overlayed, clad, metallic lined and hard-faced components .24
8.7 Wear-resistant alloys used for sintered, cast, or wrought components .24
8.8 Coated, plated or polymeric lined components .24
8.9 Surface treatments . 25
8.10 Additively manufactured equipment and components . 25
9 Report on the method of selection .25
Annex A (normative) SSC-resistant cast irons, carbon and low alloy steels .26
Annex B (normative) Environmental cracking-resistant CRAs and other alloys .34
Annex C (informative) Determination of HS partial pressure, fugacity, activity and
concentration in the aqueous phase .58
Annex D (informative) Assessment of pH . 61
Annex E (informative) Fundamental mechanistic aspects of H S cracking .62
Bibliography .64

iii
ISO/DIS 15156-2:2025(en)
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, Oil and gas industries including lower carbon
energy, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/
TC 12, Oil and gas industries including lower carbon energy, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
This fifth edition cancels and replaces the fourth edition (ISO 15156-2:2020) which has been technically
revised. The main changes compared to the previous edition are as follows:
— ISO 15156 series has been rewritten and the content reorganized into three new parts as follows:
— Part 1: Materials and materials processing requirements;
— Part 2: Service environment assessment and material selection;
— Part 3: Verification, qualification and balloting requirements.
— greater detail is given in assessing H S-containing environments in Clause 6, including:
— the definition of a new region of SSC environmental severity (Region 4) that has been defined for the
most severe environments;
— clearer guidance on when and how to apply parameters other than p in the definition of
H2S
environmental severity (e.g. f , aH S and cH S).
H2S 2 2
— cast iron, and carbon and low alloy steel material selection requirements are detailed for the new SSC
environmental severity Region 4 in Annex A;
— CRA materials selection tables in Annex B have been rationalised and updated according to the latest
industry experiences;
— many equipment-specific CRA entries in ISO 15156-3:2020 with few or no environmental limits have
been moved to Clause B.3, providing better guidance on why this was historically acceptable and the
potential limits of its applicability;
— guidance has been added to increase clarity with respect to API 6A wellhead and tree material classes.

iv
ISO/DIS 15156-2:2025(en)
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.

v
ISO/DIS 15156-2:2025(en)
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 ANSI/NACE MR0175, which
was published in 1975 by the National Association of Corrosion Engineers, now known as AMPP (Association
for Materials Protection and Performance). Collaboration with the European Federation of Corrosion (EFC)
resulted in the first joint publication of the ISO 15156 series in 2003.
The fifth edition of the ISO 15156 series makes substantive changes to the structure of the standard and is
organized as follows:
— Part 1: Materials and materials processing requirements;
— Part 2: Service environment assessment and material selection;
— Part 3: Verification, qualification, and balloting requirements.
Material specification requirements are given in ISO 15156-1. This includes requirements that are generic to
a material class and those that are specific to a material listed in ISO 15156-2. In some instances, specifically
for those grades whose performance in H S-containing environments is most susceptible to materials
processing variation, ISO 15156-1 also specifies materials processing or qualification requirements for a
listed material.
Acceptable materials selections for a given combination of equipment and service environment are stated
in ISO 15156-2: it lists environmental limits for materials that have been accepted through the development
and maintenance of the ISO 15156 series, and stipulates the path to acceptance for materials and/or
environmental conditions not listed.
The processes and procedures for qualification and verification by H S-testing (including where required
by ISO 15156-1 and ISO 15156-2) are given in ISO 15156-3. Processes and procedures for balloting new
materials, material conditions, environmental limits, and/or product specifications for incorporation into
the ISO 15156 series are also described in ISO 15156-3.
Conformance with the ISO 15156 series can require conformance with more than one document in the
ISO 15156 series. Paths for conformance with the ISO 15156 series are given in Figure 1.

vi
ISO/DIS 15156-2:2025(en)
a
See exclusions in ISO 15156-2:202x, Table 1.
b
There is an option to ballot for inclusion in the ISO 15156 series.
Figure 1 — Path for conformance with the ISO 15156 series
The ISO 15156 series were developed and approved by representative groups from within the oil and gas
production industry, following the applicable ISO and ANSI/AMPP rules.
Future changes to the ISO 15156 series may be published as interim updates to this document in the form of
ISO Technical Circulars. Document users should check for applicable ISO Technical Circulars when applying
the ISO 15156 series.
ISO 15156-3 describes the requirements for balloting changes based on test data and/or field experience
(e.g. new materials, alternative requirements or alternative limits).
The joint ISO 15156 and ANSI/NACE MR0175/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
makeup of the agency, which includes experts from AMPP and ISO/TC 67, and the process for approval of
ISO Technical Circulars. 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 on ISO 15156
series maintenance activities.
In this document, the following verbal forms are used:
— “shall” indicates a requirement;
— “should” indicates a recommendation;
— “may” indicates a permission;
— “can” indicates a possibility or a capability.

vii
DRAFT International Standard ISO/DIS 15156-2:2025(en)
Oil and gas industries including lower carbon energy —
Materials for use in H2S-containing environments in oil and
gas production —
Part 2:
Service environment assessment and material selection
WARNING — It is the equipment user’s responsibility to ensure that the equipment is suitable for
the intended application with consideration of all H S-related damage mechanisms (not just those
considered in this document) and that the materials are specified appropriately.
1 Scope
This document specifies requirements and gives recommendations for assessment of the service
environment, and the selection of metallic materials used in oil and gas production in H S-containing
environments, where the failure can pose a risk to the functionality of the equipment, to the health and
safety of the public and personnel or to the environment.
This document is not intended for application to equipment for carbon capture, utilisation and/or storage
(CCUS, CCS) or downstream oil and gas (for downstream applications see ISO 17945/NACE MR0103), but the
guidance and principles can be applied by the equipment user for these applications.
This document addresses the selection of carbon and low alloy steels, cast irons, corrosion-resistant
alloys and other alloys for resistance to damage mechanisms that are a consequence of H S, or which are
exacerbated by H S. This includes sulphide stress cracking, hydrogen-induced cracking, stepwise cracking,
stress-oriented hydrogen-induced cracking, soft-zone cracking, galvanically induced hydrogen stress
cracking and stress corrosion cracking. Some of these mechanisms can also occur in environments that do
not contain H S, but these are not included in the scope of this document. These are not included in the scope
of this document. Materials with established service limits, or which have a successful history of application
are listed. A path for qualifying and accepting materials that are not listed is described in ISO 15156-3.
NOTE H S can also influence degradation mechanisms other than cracking, including general and localized
corrosion.
This document is intended primarily for equipment users and other parties that select and accept materials
and equipment for service in H S-containing environments. It stipulates when materials need to be specified
to be in conformance with ISO 15156-1 or qualified in conformance with ISO 15156-3.
All oil and gas production equipment categories handling H S-containing fluids are within the scope of this
document, including but not limited to:
a) drilling, well construction, and well-servicing equipment;
b) wells including subsurface equipment, gas lift equipment, wellheads, and tree equipment;
c) flow-lines, gathering lines, field facilities, and field processing plants;
d) water-handling, injection and disposal equipment;
e) gas-handling and injection equipment including those used for CO enhanced oil recovery;
f) natural gas treatment plants (for gas sweeting plants see also API RP 945);
g) transportation pipelines for liquids, gases, and multi-phase fluids.

ISO/DIS 15156-2:2025(en)
Exclusions to the scope of this document are given in Table 1.
Table 1 — List of exclusions to this document
Equipment category Exclusions within the equipment category
Drilling, well construction, and well-servicing Drilling riser systems
equipment (see NOTE 1 and NOTE 2)
Work strings
c
Surface and intermediate casing
a
Wireline and wireline equipment
Drill bits
Temporary service tools that are not a barrier element,
including but not limited to fishing tools, wellbore clean-
up tools, casing exits, and through-tubing intervention
equipment
b
Wells, including subsurface equipment, gas lift Sucker rod pumps and sucker rods
equipment, wellheads, and tree equipment
Electric submersible pumps
Other artificial lift equipment
Slips
Transportation pipelines for liquids, gases, and Lines handling gas prepared for general commercial
multi-phase fluids (see NOTE 3) and domestic use
For all equipment categories Components that are not exposed to H S-containing
environments
Components loaded in compression and which experi-
ence principal stresses that are compressive at surfaces
exposed to H S-containing fluids
NOTE 1 Previous editions of the ISO 15156 series listed “equipment exposed only to drilling fluids of controlled composition” as
an exemption. This document gives requirements for the controlled environment that permits use of materials that are neither
listed in this document, nor qualified in accordance with ISO 15156-3. See A.4.3.3 for more information.
NOTE 2 Previous editions of the ISO 15156 series listed blowout preventor (BOP shear blades) as an exemption. This document
gives guidance for the acceptance of BOP shear blades materials that are neither listed in this document, nor qualified in
accordance with ISO 15156-3. See A.4.3.2 for more information.
NOTE 3 Previous editions of the ISO 15156 series listed stabilized crude pipelines as an exemption with certain provisos. This
exemption remains and conditions for the exemption are detailed in A.8.1.
a
Wireline lubricators and lubricator connecting devices are not permitted exemptions.
b
For sucker rod pumps and sucker rods, see NACE MR0176.
c
Intermediate casing that is a barrier element, for example in some gas lift wells, is within the scope of this document.
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 11960, Petroleum and natural gas industries — Steel pipes for use as casing or tubing for wells
ISO 15156-1:202x, Oil and gas industries including lower carbon energy — Materials for use in H S-containing
environments in oil and gas production — Part 1: Materials and materials processing requirements
ISO 15156-3:202x, Oil and gas industries including lower carbon energy — Materials for use in H S-containing
environments in oil and gas production — Part 3: Verification, qualification and balloting requirements
1)
API 5CT , Casing and Tubing
2)
SAE— ASTM, Metals and alloys in the Unified Numbering System, ISBN 0-7680-04074
1) www .api .org
2) www .sae .org
ISO/DIS 15156-2:2025(en)
3 Terms and definitions
For the purposes of this document, the following 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 https:// www .electropedia .org/
3.1
barrier element
equipment that is part of the primary or secondary pressure containing envelope preventing the release of
the fluids that it contains, as specified by the governing code, standard or specification for that equipment
and application
3.2
chemical activity
unit-less ratio of actual fugacity (of a gas species) divided by its fugacity at a conveniently defined reference state
Note 1 to entry: In this document, the term chemical activity is primarily used as a property of species in the liquid or
aqueous phase, a “pseudo mole fraction”, see Annex C.
3.3
environmental severity
aggressiveness of the service environment with respect to the cracking mechanisms of relevance to the
ISO 15156 series
3.4
galvanically-induced hydrogen stress cracking
GHSC
cracking that results from hydrogen absorbed by the cathode of a galvanic couple in the presence of tensile
stress (residual and/or applied)
Note 1 to entry: This mostly affects CRA in a carbon/low alloy steel to CRA couple.
3.5
H S fugacity
effective pressure of H S under ideal gas conditions, which has the same chemical potential (partial Gibbs
free energy) as the H S under real gas conditions
Note 1 to entry: In this document, the term H S fugacity is primarily used as a property of H S in the gas phase, an
2 2
“effective partial pressure”, but for all liquid systems it is the H S fugacity of H S vapor that would be in equilibrium
2 2
with the concentration present in the liquid, see Annex C.
3.6
H S content
general description of the amount of H S in a system, which could be based upon classical (partial pressure or
dissolved concentration) and/or thermodynamic considerations (H S fugacity (3.5), chemical activity (3.2))
3.7
H S service assessment
assessment of the environment and credible cracking mechanisms that can influence a materials selection
3.8
maximum sustained tensile stress
greatest principal stress that can be experienced by the material in the H S-containing environment for a
defined period, determined for the purposes of comparison with threshold stress (3.15 ) limits for H S service
ISO/DIS 15156-2:2025(en)
3.9
pH
in situ pH of the H S-containing aqueous phase at the temperature(s) and pressure(s) of interest
3.10
production environment
oil and gas production fluids without contamination from oxygen or chemicals that will temporarily or
continuously reduce pH
3.11
qualification
demonstration of the resistance of the material to the cracking modes of relevance to this document,
typically involving H S-testing of sufficient material to establish confidence in performance
Note 1 to entry: The result of the qualification is effectively a validation statement similar to the desired outcome from
ISO/IEC 17029:2019 regarding the specific material and environment combination examined.
Note 2 to entry: Examples of qualification are:
EXAMPLE 1 qualification to permit use of a material in a service environment outside of the temperature, pH, p
H2S
and/or chloride limits given in Annex A or Annex B;
EXAMPLE 2 Qualification of a material produced by a defined manufacturing route to validate application within
the limits given in Annex A or Annex B (e.g. OCTG and martensitic stainless steel bar stock);
EXAMPLE 3 Qualification of a material not listed in Annex A or Annex B, or with materials properties that differ
from the specification referenced in this document (including ISO 15156-1, where applicable).
3.12
specific service
conditions of application for the materials/products for which H S-testing is defined to match the user’s
requirements
Note 1 to entry: Fitness-for-purpose has also been historically used to define these same requirements but also
extends to evaluation steps related to in-service issues, assessment of damage etc.
3.13
stabilized crude
processed hydrocarbon liquids that have a vapor pressure below 101 kPa at 25 °C per ASTM D6377 at 4:1
liquid/gas volume ratio, and that are dehydrated to ≤ 0,5 vol% water with a pH typically ≥ 5,6
Note 1 to entry: Processing includes that achieved by separation or heater treaters, reducing water content and
removing free gas phase(s).
3.14
soft-zone cracking
SZC
form of SSC that can occur when a steel contains a local “soft zone” of low-yield-strength material
Note 1 to entry: Under service loads, soft zones can yield and accumulate plastic strain locally, increasing the SSC
susceptibility to cracking of an otherwise SSC-resistant material. Such soft zones are typically associated with welds
in carbon steels.
3.15
threshold stress
maximum stress permitted for some materials for application within their defined environmental limits

ISO/DIS 15156-2:2025(en)
4 Symbols and abbreviated terms
AM additive manufacturing
AYS actual yield strength
BOP blowout preventer
CRA corrosion-resistant alloy
CCS carbon capture and storage
CCUS carbon capture, utilisation and storage
CS carbon steel
EAC environmentally-assisted cracking
ER equivalent round
ERW electric resistance welded
f H S fugacity
H2S 2
F pitting-resistance equivalent number
PREN
GHSC galvanically induced hydrogen stress cracking
HAZ heat-affected zone
HFI high frequency induction (welded)
HFW high frequency welding
HIC hydrogen-induced cracking
HRC Rockwell C hardness (scale C)
HV Vickers hardness
LAS low alloy steel
NDS No data submitted
OCTG oil country tubular goods, i.e. casing, tubing and drill pipe
p partial pressure of CO
CO2 2
p bubble-point pressure
B
p partial pressure of H S
H2S 2
Q&T quenched and tempered
R 0,2 % proof stress in accordance with ISO 6892-1 and ASTM A370/E8
p0,2
SCC stress-corrosion cracking
SI International System of Units
SOHIC stress-oriented hydrogen-induced cracking

ISO/DIS 15156-2:2025(en)
SMYS specified minimum yield strength
SSC sulfide stress-cracking
SWC step-wise cracking
SZC soft-zone cracking
S elemental sulfur
T temperature
TDS total dissolved solids
TMCP thermo-mechanically controlled process
UNS unified (alloy) numbering system
WAAM wire arc additive manufacturing
X mole fraction of H S in the gas
H2S 2
5 General principles
The material manufacturer shall ensure that material specified for service in H S-containing environments
is manufactured in conformance with ISO 15156-1. Where required by this document, the material
manufacturer can also be responsible for qualification of the manufacturing route in accordance with
ISO 15156-3.
The material supplier shall ensure that all material supplied within the scope of the ISO 15156 series have
been specified and documented in conformance with ISO 15156-1.
The equipment manufacturer shall ensure that equipment specified for service in H S-containing
environments is manufactured in conformance with the ISO 15156 series (including manufacturing
requirements specific to an ISO 15156-3 qualification, where applicable).
The equipment supplier shall ensure that all equipment within the scope of the ISO 15156 series have been
specified and documented in conformance with the ISO 15156 series.
The equipment user shall ensure that the material selection is suitable for the intended service environment.
NOTE 1 A single party can have one or more of the above roles. For example, it is common for a manufacturer to also
be a supplier. In such instances, the party concerned has responsibilities encompassing all the roles that they fulfil.
NOTE 2 Materials processing requirements are given in ISO 15156-1 for most materials listed in Annex A and
Annex B. For some materials listed in these Annexes, ISO 15156-1 has no additional requirements other than meeting
the listed materials specification given in Annex A or Annex B. For materials not listed in Annex A or Annex B, the
materials requirements would be defined as part of a qualification defined in ISO 15156-3.
This document shall be applied by those selecting materials or determining if a material is acceptable for
service in an H S-containing environment. This may include equipment users, equipment manufacturers
and those acting on behalf of these parties. A simplified flow chart illustrating the use of this document and
its relationship with ISO 15156-1 and ISO 15156-3 is shown in Figure 2.

ISO/DIS 15156-2:2025(en)
Figure 2 — Simplified flowchart illustrating the use of this document and its relationship with
ISO 15156-1 and ISO 15156-3
Equipment users shall conduct an H S service assessment to demonstrate that materials selections have
been made in conformance with this document. This assessment shall define and evaluate all H S-containing
service conditions to which equipment can be exposed.
NOTE 3 If such assessments are performed by other parties, the equipment user remains responsible for ensuring
that they are in conformance.
The equipment user may accept environmental assessments conducted to previous editions of the ISO 15156
series, if conducted prior to the release of this edition, as valid H S service assessments. In this instance,
an H S service assessment per Clause 6, should be conducted if the environmental conditions change from
ISO/DIS 15156-2:2025(en)
those assessed previously. Equipment users should also perform an H S service assessment per Clause 6 if
the equipment is to operate in SSC Region 4, per Figure 3.
The H S service assessment shall:
a) determine if a material can be selected using Annex A or Annex B;
b) determine the qualification requirements for materials not selected using Annex A or Annex B;
NOTE 4 This includes materials listed in Annex A or Annex B, which are to be used in a condition not
in conformance with ISO 15156-1, or which are to be used in environments that are more severe than the
environmental limits given by these Annexes for the material.
c) determine if additional material requirements are necessary. These could be in addition or different
to those specified in ISO 15156-1, for materials selected using Annex A or Annex B, or to ensure that a
material qualified in accordance ISO 15156-3 is adequately verified.
The H S service assessment should include analysis of:
— the environment (see 6.1.2);
— application and equipment design (see 6.1.3);
— damage mechanisms applicable to the proposed material selection (see 6.2).
Materials may be selected using Clause 7 (in accordance with Annex A or Annex B), where the listed
environmental limits of these materials are adequate for all expected service conditions. Materials
(including their manufacturing process and condition) selected per Clause 7 from Annex A or Annex B shall
be specified in accordance with ISO 15156-1.
Materials (including their manufacturing process and/or condition) that are not listed in this document,
or which are used outside of the limits given in Annex A or Annex B, may be selected provided these are
qualified in accordance with ISO 15156-3.
The use of this document often requires an exchange of information between the equipment user and the
supply chain.
6 H S-service assessment
6.1 Analysis of the environment and application severity
6.1.1 General
The focus of the assessments in this document is for service in production fluids. Reference is also made to
other relevant service environments, e.g. packer and completion fluids, but only guidance is given for their
assessment in this document.
The behaviour of materials in H S-containing environments is affected by complex interactions of factors,
including the following:
a) metallurgical aspects, including:
i. chemical composition;
ii. method of manufacture;
iii. product form;
iv. strength and other mechanical properties;
v. hardness and its local variations;

ISO/DIS 15156-2:2025(en)
vi. amount of cold work;
vii. heat-treatment condition;
viii. microstructure and its uniformity, including grain size and cleanliness.
b) H S content (see 6.1.2.2);
c) chloride concentration in the water phase (see 6.1.2.4);
d) acidity (pH) of the water phase (see 6.1.2.1);
e) presence of oxygen (see 6.1.2.6), sulfur (see 6.1.2.5) or other oxidants in the service environment;
f) exposure to non-production fluid service environments;
g) temperature (see 6.1.2.3);
h) stress (applied plus residual), (see 6.1.3.1);
i) galvanic coupling of materials (see 6.1.3.4)
Each factor, when applicable, should be part of the H S service assessment undertaken by the equipment
user. Different service instances (for example through life scenarios for a souring production reservoir
subject to pressure depletion) can result in various combinations of these factors. Different equipment in the
same production system can also see different combinations of parameters (for example, due to adiabatic
heating).
Damage mechanisms to be addressed include SSC, SCC, HIC, SOHIC and GHSC. A mechanistic description of
these cracking mechanisms is given in Annex E.
For each damage mechanism, service conditions may be evaluated:
— separately (i.e. evaluating multiple conditions, with different specific environmental parameters);
— aggregated (i.e. evaluating a single condition, comprising the most severe combination of environmental
parameters selected from the different service conditions).
NOTE Guidance on what constitutes a more severe environment for each environmental parameter is given in 6.2.
For materials listed in this document, relevant controls on the metallurgical aspects listed in 6.1.1 a) are
given in ISO 15156-1.
6.1.2 Environmental parameters
6.1.2.1 pH
The pH is necessary for the selection of most materials per this document and the minimum estimated in
situ pH shall be included in the H S service assessment.
When pH is calculated by third parties, the method shall be agreed with the equipment user.
NOTE While in situ pH can be directly measured for systems operating at or near atmospheric pressure, direct
measurement is challenging in most oil and gas production environments. Accurate calculation of the equilibrium
in situ pH requires speciation of the aqueous (water/brine) phase in equilibrium with the non-aqueous phases,
necessitating the use of proprietary software. Further information on the essential parameters for pH calculation is
given in Annex D.
6.1.2.2 H S
The maximum H S content expected during the life of the equipment shall be included in the H S service
2 2
assessment.
ISO/DIS 15156-2:2025(en)
The H S content shall be defined in terms of the maximum H S partial pressure in the gas phase (see Annex C
2 2
for determination of p in the absence of a separate gas phase). Alternatively, the equipment user may
H2S
define the H S content as H S fugacity, a
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