ISO 18735:2026

International
Standard
ISO 18735
First edition
Ships and marine technology —
2026-03
High-manganese austenitic steel —
Specification for high-manganese
austenitic steel castings for
cryogenic temperature
Navires et technologie maritime — Acier austénitique à haute
teneur en manganèse — Spécification pour les pièces moulées
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 . 4
5.1 Health and safety requirements .4
5.2 Quality requirements .4
6 Material designation . . 4
7 Manufacture . 5
7.1 Steel making practice .5
7.2 Moulding .5
8 Chemical composition . 5
9 Heat treatment . 6
9.1 Temperature uniformity survey (TUS) for heat treatment furnace .6
9.2 Heat treatment.7
10 Mechanical properties . 7
10.1 Preparation of test specimens .7
10.2 Extent of testing .8
10.3 Mechanical properties .8
10.3.1 General .8
10.3.2 Tensile testing .8
10.3.3 Impact testing .9
10.3.4 Bend testing .9
10.4 Retesting .9
11 Inspection . 10
11.1 General requirements .10
11.2 Visual inspection .10
11.3 Liquid penetrant inspection .10
11.4 Radiographic inspection .10
11.5 Ultrasonic inspection.11
11.6 Hydrostatic testing .11
12 Repairs .12
13 Dimension inspection .13
14 Traceability, handling and packing .13
15 Documentation .13
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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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 document should be noted. This document was drafted in accordance with the editorial rules of the
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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 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 18735:2026(en)
Ships and marine technology — High-manganese austenitic
steel — Specification for high-manganese austenitic steel
castings for cryogenic temperature
1 Scope
This document specifies minimum requirements for high-manganese austenitic steel castings for valves,
flanges and other pressure-containing components used at cryogenic temperature.
This document 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 4990, Steel castings — General technical delivery requirements
ISO 5173, Destructive tests on welds in metallic materials — Bend tests
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 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 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
ASME B31.3, Process Piping
ASME Boiler and Pressure Vessel Code, Section V, Non-Destructive Testing
ASME Boiler and Pressure Vessel Code, Section VIII, Rules for Construction of Pressure Vessels Division 1
ASTM A991/991M, Standard Test Method for Conducting Temperature Uniformity Surveys of Furnaces Used to
Heat Treat Steel Products
ANSI/MSS SP-55, Quality Standard for Steel Castings for Valves, Flanges, and Fittings and Other Components -
visual method for evaluation of surface irregularities

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
chaplet
metallic support to maintain the space between a core and the mould
3.2
cryogenic service
service environment in which the minimum design temperature (3.4) is lower than −104 °C
3.3
DN
diameter nominal
alphanumeric designation of size that is common for components used in piping system, used for reference
purposes, comprising the letters “DN” followed by a dimensionless number indirectly related to the physical
size of the bore or outside diameter of the end connection as appropriate
Note 1 to entry: The dimensionless number following “DN” does not represent a measurable value and is not for
[3]
calculation purpose except where specified in ASME B16.34.
3.4
design temperature
minimum temperature for selection of materials at which cargo or fuel can be loaded or transported in the
cargo or fuel tanks
3.5
heat
molten metal poured from a single melting furnace or the molten metal from two or more furnaces poured
into a single ladle
3.6
high-manganese austenitic steel
steel with a high amount of manganese to retain austenitic as its primary phase at atmospheric and service
temperature
3.7
internal chill
metallic device placed in a mould cavity to promote directional solidification by increasing the rate of heat
extraction at a specific location
3.8
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.

3.9
lot
two or more products having the same chemical composition (i.e. from the same melt), subjected to the
same heat treatment in the same furnace cycle, with the same product type and thickness within ±20 % of
the maximum thickness in the lot
3.10
manufacturer
organization, including subcontractors, which carries out operations (e.g. casting, heat treatment) that
affect the material properties of the finished product
3.11
NPS
nominal pipe size
alphanumeric designation of size that is common for components used in piping system, used for reference
purposes, comprising the letters “NPS” followed by a dimensionless number indirectly related to the physical
size of the bore or outside diameter of the end connection as appropriate
Note 1 to entry: The dimensionless size identification number following “NPS” does not represent a measurable value
and is not for calculation purpose except where specified in ASME B16.34. Prefix NPS usage is applicable to valves
bearing class designations.
3.12
pilot casting
casting made and tested as part of the initiation and development of the production method
EXAMPLE The first casting from a new or modified pattern, which is produced using identical foundry practices
as the production castings it is intended to represent.
3.13
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 castings
3.14
set temperature
target-holding temperature for heat treatment
3.15
test coupon
part from which the test specimens (3.16) are extracted
3.16
test specimen
part that is subject to mechanical testing
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

DN Diameter Nominal
NDT non-destructive testing
NPS nominal pipe size
PT penetrant testing
RT radiographic testing
SMYS specified minimum yield strength
WPS welding procedure specification
5 Health, safety and quality requirements
5.1 Health and safety requirements
Each manufacturer is expected to operate according to 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:
— ventilation and extraction facilities for welding-related activities or work in a confined space;
— personal protective equipment including eye, breathing and hearing protection;
— access/scaffolding/working platforms and fall-arrest protective equipment for working at height;
— access and secure temporary formwork for working below product;
— 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 foundry is responsible for carrying out effective quality, process and production controls, according to
the manufacturer's specifications.
[4]
NOTE For information on quality management systems, see ISO 9001.
The manufacturer shall prepare and document procedures for critical manufacturing processes, including
but not limited to melting, alloying, casting, heat treatment, welding, machining and non-destructive testing.
This document specifies the requirements for high-manganese austenitic steel castings, including chemical
composition and mechanical properties. See Clause 8 for chemical composition and Clause 10 for mechanical
properties.
6 Material designation
The high-manganese steel casting for cryogenic temperature is designated as follows:

“HMC xxx” which denotes High-manganese steel castings with SMYS xxx N/mm
where
HM is high-manganese steel
C is castings
XXX is the SMYS, expressed in N/mm
7 Manufacture
7.1 Steel making practice
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.
Molten metal shall be killed by de-oxidation practice.
7.2 Moulding
The foundry shall prepare a relevant moulding procedure.
The mould design, including gating, risers, and mould making, shall follow documented internal procedures
that are based on established industry standards or proven foundry engineering practices.
Unless otherwise agreed between the purchaser and the manufacturer, the dimension of test coupon shall
conform to those specified in ISO 4990.
ASTM A1067/A1067M may be used as an alternative standard for specifying test coupon dimensions when
explicitly agreed upon between the manufacturer and the purchaser.
A separated test coupon can be used upon agreement with the purchaser, but the thickness of the test
...