ISO 18741:2026

International
Standard
ISO 18741
First edition
Ship and marine technology —
2026-02
High-manganese austenitic steel —
Specification for high-manganese
austenitic steel forgings for
cryogenic temperature
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 . 1
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
7.1 Steel making .4
7.2 Forging .4
8 Chemical composition . 4
9 Heat treatment . 5
10 Mechanical properties . 6
10.1 Preparation of test specimens .6
10.2 Extent of testing .6
10.3 Mechanical properties .7
10.3.1 General .7
10.3.2 Tensile testing .7
10.3.3 Impact testing .7
10.4 Retesting .8
11 Inspection . 8
11.1 General requirements .8
11.2 Visual inspection .8
11.3 Liquid penetrant inspection .9
11.4 Ultrasonic inspection.9
11.5 Hydrostatic testing .9
12 Repairs . 10
13 Dimension . 10
14 Traceability, handling and packing .10
15 Documentation . 10
Bibliography .12

iii
Foreword
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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 system for liquefied
hydrogen.
This document provides a standard specification of high-manganese austenitic steel castings for material
suppliers, ship owners, ship yards, manufacturers and shipping companies with regard to producing,
purchasing and using such materials.

v
International Standard ISO 18741:2026(en)
Ship and marine technology — High-manganese austenitic
steel — Specification for high-manganese austenitic steel
forgings for cryogenic temperature
1 Scope
This document specifies minimum requirements for high-manganese austenitic steel forgings for valves,
flanges, fittings and other pressure-containing components used at cryogenic temperature.
The specification of high-manganese austenitic steel forgings can be applicable to all pressure retaining
components and any non-pressure retaining component.
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 5208, Industrial valves — Pressure testing of metallic valves
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 10474, Steel and steel products — Inspection documents
ASME B31.3, Process Piping
ASME Boiler and Pressure Vessel Code, Section VIII, Rules for Construction of Pressure Vessels Division 1
ASTM A370, Standard test methods and definitions for mechanical testing of steel products
ASTM A388, Standard Practice for Ultrasonic Examination of Heavy Steel Forgings
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
end user
entity responsible for the operation of an installation/facility and its component
3.4
heat
molten metal poured from a single melting furnace or all the molten metal from two or more furnaces
poured into a single ladle
3.5
high-manganese austenitic steel
steel with a high amount of manganese to retain austenitic as its primary phase at atmospheric and service
temperature
3.6
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.
3.7
lot
two or more products with the same chemical composition (same melt of material), same heat treated in a
same heat treatment furnace, same thickness (within ±20 %, maximum thickness base), and same product
type
3.8
manufacturer
organization, including subcontractors, which carries out operations (e.g. forging, heat treatment) that
affect the material properties of the finished product
3.9
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 forging
3.10
set temperature
target holding temperature for heat treatment
3.11
test coupon
part from which the test specimens (3.12) will be extracted
3.12
test specimen
part that is subject to mechanical testing
3.13
starting material
material used as the initial input for the forging operation, such as a billet, bloom, or cast preform

3.14
calibration notch
artificial notch used to calibrate ultrasonic testing equipment
4 Abbreviated terms
For the purposes of this document, the following abbreviated terms are used.
ACCP ASNT Central Certification Program
AOD Argon oxygen decarburization
ASNT American Society for Non-destructive Testing
BPVC Boiler and pressure vessel code
NDT Non-destructive testing
PT Penetrant testing
QMS Quality management system
RT Radiographic testing
SMYS Specified minimum yield strength
UT Ultrasonic 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 carrying out effective quality, process and production controls
according to the manufacturing specifications.
The manufacturer shall establish and maintain documented procedures for all critical manufacturing
processes.
High-manganese austenitic steel forgings shall meet the chemical composition requirements specified in
Clause 8 and the mechanical property requirements specified in Clause 10.

6 Material designation
The high-manganese steel forgings for cryogenic temperature are desi
...