ISO 18742:2026

International
Standard
ISO 18742
First edition
Ship and marine technology —
2026-02
High-manganese austenitic steel —
Specification for high-manganese
austenitic steel welded fittings for
cryogenic temperature
Navires et technologie maritime — Acier austénitique à haute
teneur en manganèse — Spécification pour les raccords soudés
en acier austénitique à haute teneur en manganèse pour
température cryogénique
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Abbreviated terms . 3
5 Health, safety and quality requirements . 3
5.1 Health and safety requirements .3
5.2 Quality requirements .3
6 Material designation . . 4
7 Manufacture . 4
8 Chemical composition . 4
9 Forming and welding . 5
10 Heat treatment . 6
11 Mechanical properties . 7
11.1 Preparation of test specimens and extent of testing .7
11.2 Mechanical properties .7
11.2.1 General .7
11.2.2 Tensile testing .8
11.2.3 Impact testing .8
11.2.4 Bend testing .8
11.2.5 Hardness testing.9
11.3 Retesting .9
12 Inspection . 9
12.1 General requirements .9
12.2 Visual inspection .9
12.3 RT and UT .10
12.4 PT . .10
12.5 Hydrostatic testing .11
13 Repairs .11
14 Dimension inspection .12
15 Traceability, handling and packing .12
16 Documentation .12
Annex A (normative) Hardness of Hi-Mn steel welded fittings . 14
Bibliography .15

iii
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
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This document was prepared by Technical Committee TC 8, Ships and marine technology, Subcommittee SC
4, Outfitting and deck machinery.
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
Introduction
The aim of this document is to provide a set of common requirements for metallic materials used in cryogenic
[1] [2]
applications, in alignment with the IGC Code and IGF Code adopted by the International Maritime
Organization (IMO).
The newly developed, high-manganese austenitic steel is expected to possess mechanical properties
including Charpy impact energy values comparable to those materials for cryogenic service listed in both the
IGC Code and IGF Code. Consequently, high-manganese steel is intended to satisfy the strength requirements
of the structure of cargo tanks, fuel tanks and piping systems.
In addition, upon agreement with a purchaser, this document can be applied to piping systems for liquefied
hydrogen.
This document provides a standard specification of high-manganese austenitic steel welded fittings
for material suppliers, ship owners, ship yards, manufacturers and shipping companies with regard to
producing, purchasing and using such materials.

v
International Standard ISO 18742:2026(en)
Ship and marine technology — High-manganese austenitic
steel — Specification for high-manganese austenitic steel
welded fittings for cryogenic temperature
1 Scope
This document provides requirements for wrought high-manganese austenitic steel welded fittings used for
pressure piping at cryogenic temperature.
The specification of high-manganese austenitic steel welded fittings is applicable to all pressure retaining
components and any non-pressure retaining components used in hull systems for marine technology and in
onshore projects.
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 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 2566-1, Steel — Conversion of elongation values — Part 1: Carbon and low-alloy steels
ISO 2566-2, Steel — Conversion of elongation values — Part 2: Austenitic steels
ISO 3452-1, Non-destructive testing — Penetrant testing — Part 1: General principles
ISO 4136, Destructive tests on welds in metallic materials — Transverse tensile test
ISO 5173, Destructive tests on welds in metallic materials — Bend tests
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10474, Steel and steel products — Inspection documents
ISO 15609-1, Specification and qualification of welding procedures for metallic materials — Welding procedure
specification — Part 1: Arc welding
ISO 15614-1, Specification and qualification of welding procedures for metallic materials — Welding procedure
test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys
ISO 18265, Metallic materials — Conversion of hardness values
ASME B16.28, Wrought Steel Butt-Welding Short Radius Elbows and Returns
ASME B16.9, Factory-Made Wrought Buttwelding Fittings
ASME B31.3, Process Piping
ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, 2023, Rules for Construction of Pressure Vessels
ASTM A960/960M, Standard Specification for Common Requirements for Wrought Steel Piping Fittings

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology 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
cryogenic service
service environment in which the minimum design temperature (3.2) is lower than −104 °C
3.2
design temperature
minimum temperature for selection of materials at which cargo or fuel can be loaded or transported in the
cargo or fuel tanks
3.3
heat
molten metal poured from a single melting furnace or all the molten metal from two or more furnaces
poured into a single ladle
3.4
high-manganese austenitic steel
steel with high amount of manganese to retain austenitic as its primary phase at atmospheric and service
temperature
3.5
leak testing
hydrostatic leak test
pneumatic leak test
application of a pressure load, greater than the design load, to demonstrate the integrity of a pressure
system to safely withstand the design load
Note 1 to entry: ASME B31.3 uses the terms hydrostatic leak test, pneumatic leak test, or a combination of both methods,
such as a hydro-pneumatic test.
3.6
lot
fitting which is manufactured by the same manufacturer process, same heat number (same chemical
composition), same heat treatment and same welding procedure specification
3.7
manufacturer
organization, including subcontractors, which carries out operations (e.g. forming, heat treatment) that
affect the material properties of the finished product
3.8
purchaser
owner or another party acting on their behalf, who is responsible for procuring materials, components or
services intended for the design, construction or modification of fittings
3.9
test specimen
part that is subject to mechanical testing
3.10
starting material
material used as the initial input for the forging operation, such as a billet, bloom, or cast preform

3.11
under match
condition where the tensile strength of the weld metal is lower than that of the base metal
4 Abbreviated terms
For the purposes of this document, the following abbreviated terms are used.
ACCP ASNT Central Certification Program
AOD Argon oxygen decarburization
API American Petroleum Institute
ASNT American Society for Non-destructive Testing
BPVC Boiler and Pressure Vessel Code
HAZ Heat-affected zone
NDT Non-destructive testing
PT Penetrant testing
RT Radiographic testing
SMAW Shielded-metal arc welding
SMYS Specified minimum yield strength
UT Ultrasonic testing
VT Visual testing
5 Health, safety and quality requirements
5.1 Health and safety requirements
Each manufacturer is expected to operate in accordance with all relevant statutory health and safety
legislation pertaining to the location where manufacturing, testing and inspection take place.
At least, the following safety equipment and systems shall be provided:
a) ventilation and extraction facilities for welding-related activities or work in a confined space;
b) personal protective equipment including eye, breathing and hearing protection;
c) access/scaffolding/working platforms and fall-arrest protective equipment for working at height;
d) access and secure temporary formwork for working below product;
e) protective systems to prevent electric shock and build-up, or discharge, of static electricity.
Each manufacturer shall manage all work undertaken during manufacturing, including cleaning, flushing,
and leak testing activities.
5.2 Quality requirements
The manufacturer is responsible for implementing effective quality, process, production controls according
to manufacturing specifications.

The manufacturer shall prepare documented procedures for all critical manufacturing processes, including
but not limited to forging, heat treatment, machining and non-destructive testing.
The document specifies the requirements for high-manganese austenitic steel welded fittings, including
chemical composition (see Clause 8) and mechanical properties (see Clause 10) as specified in this
specification.
6 Material designation
The high-manganese steel welded fittings for cryogenic temperature is designated as follows:
2”
“HMW XXX” which denotes “High-Manganese Steel Welded fittings with SMYS XXX N/mm
where
HM is High-manganese steel
W is Welded fittings
XXX is the SMYS, expressed in N/mm
7 Manufacture
High-manganese steel shall be manufactured by electric furnace, open hearth or by other processes, with or
without separate refining such as argon-oxygen-decarburization (AOD), unless otherwise specified by the
purchaser.
Steel metal shall be killed by de-oxidation practice.
8 Chemical composition
An analysis of each heat (i.e. each batch of molten steel) shall be carried out by the manufacturer to determine
the mass fractions of each element specified in Table 1.
The ladle analysis shall be carried out from a test sample which is taken during the pouring of the molten
metal into the mould.
When more than one ladle is poured into a single mould, the molten metal in each ladle shall be analysed in
accordance with Table 1.
When performing chemical analysis for elements that are not specified in Table 1, the manufacturer may
add elements or modify upon agreement with the purchaser. Residual elements such as Sn, Pb, Sb, As shall
not be added intentionally.
Table 1 — Chemical requirements
Dimensions in per cent (%) (mass fraction)
C Mn Si P S Cr Cu B N
22,50 to max.
0,35 to 0,55 0,10 to 0,50 max. 0,030 max. 0,010 3,00 to 4,00 0,30 to 0,70 max. 0,050
25,50 0,005 0
NOTE 1 These requirements apply to both heat and product analyses.
NOTE 2 Total aluminium is considered when the aluminium content is 0,03 % or higher, or acid soluble aluminium is 0,025 % or
higher.
Product analysis is not required for production, but a product analysis may be carried out upon agreement
between the manufacturer and the purchaser.

For product analysis, specimens shall be obtained from a finished product, or from production material that
is in the same condition of working, or from broken tensile test specimens after mechanical testing.
The product analysis result shall conform to the requirements in Table 2.
Table 2 — Product analysis tolerance
Dimensions in per cent (%) (mass fraction)
Elements Permissible variations
C ±0,02
Mn ±0,06
Si ±0,1
P ±0,010
S ±0,005
Cr ±0,10
Cu ±0,05
B ±0,000 5
N ±0,01
When a manufacturer adds elements which are not specified in Table 2, additional limitations may be
established upon agreement between the purchaser and manufacturer.
9 Forming and welding
Forming operations shall be performed by pressing, bending or machining, or by a combination of two
or more of these operations. The forming process shall be performed carefully so as to prevent injurious
defects, dents, distortions, scratches, etc. in the fittings.
For preparation of the forming process, tack welding may be used.
All welding shall be carried out by one of fusion-welding process in accordance with the following.
a) A welding procedure specifica
...