ISO 18735:2026

Ships and marine technology — High-manganese austenitic steel — Specification for high-manganese austenitic steel castings for cryogenic temperature

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.

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

General Information

• Status: Published
• Publication Date: 01-Mar-2026
• ICS: 47.020.05 - Materials and components for shipbuilding
• Technical Committee: ISO/TC 8/SC 4 - Outfitting and deck machinery
• Drafting Committee: ISO/TC 8/SC 4 - Outfitting and deck machinery
• Current Stage: 6060 - International Standard published
• Start Date: 02-Mar-2026
• Due Date: 15-Dec-2025
• Completion Date: 02-Mar-2026

Overview

ISO 18735:2026 sets the international foundation for specifying minimum requirements for high-manganese austenitic steel castings intended for use in cryogenic temperatures-notably for pressure-containing components like valves and flanges, as well as non-pressure retaining parts in ships and marine technology. Developed by the International Organization for Standardization (ISO), this standard aims to align with relevant codes adopted by the International Maritime Organization (IMO), including the IGC and IGF Codes, ensuring robust performance for metallic materials under extremely low temperatures.

High-manganese austenitic steel castings are favored in marine and cryogenic applications due to their superior mechanical properties and consistent performance at ultra-low temperatures, fulfilling stringent strength and safety requirements for ships’ cargo tanks, fuel tanks, and piping systems.

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Key Topics

• Material Designation and Composition
  • Defines the designation “HMC xxx” for high-manganese steel castings, where “xxx” denotes the specified minimum yield strength (SMYS).
  • Specifies required chemical compositions and tolerances for elements like manganese (Mn), silicon (Si), chromium (Cr), and boron (B).
• Manufacturing and Heat Treatment
  • Outlines acceptable manufacturing processes, including electric furnace or open hearth, with precise guidelines for moulding, casting, and test coupon preparation.
  • Details heat treatment requirements, including temperature uniformity surveys and controlled cooling, ensuring uniform mechanical properties.
• Mechanical Properties and Testing
  • Requires extensive mechanical property testing, including tensile tests, Charpy impact tests, and bend tests, with clear minimum criteria for acceptance.
  • Addresses preparation, extent of testing, alternative testing standards, and retesting procedures in case of non-compliance.
• Inspection and Quality Assurance
  • Emphasizes rigorous inspection requirements: visual, liquid penetrant, radiographic, and ultrasonic testing, based on international and industry-recognized standards.
  • Mandates thorough traceability, documentation, and quality management processes in line with ISO 9001 principles.
• Health and Safety
  • Requires manufacturers to comply with statutory health and safety legislation, providing protective equipment and monitoring.

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Applications

ISO 18735:2026 is critical for stakeholders involved in the specification, manufacture, and procurement of steel castings used in:

• Marine Engineering and Shipbuilding
  • Valves, flanges, and pressure-retaining components for gas carriers, LNG/LPG fuel systems, and other vessels operating at cryogenic temperatures.
  • Piping systems, including those processing liquefied hydrogen, when agreed upon by the purchaser.
• Pressure Systems
  • Any pressure-containing system, such as storage tanks and piping, requiring steels with verified performance at low temperatures to ensure operational safety and regulatory compliance.
• Manufacturing, Testing, and Certification
  • Provides foundries, ship owners, manufacturers, and certifying bodies with a unified, consistent standard for high-manganese austenitic steel casting production, testing, and inspection.

By standardizing materials and processes, ISO 18735:2026 enhances the reliability and global interoperability of marine and cryogenic equipment, supporting marine safety and efficiency.

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Related Standards

For comprehensive implementation, users of ISO 18735:2026 should also be familiar with the following standards and codes:

• ISO 148-1: Charpy pendulum impact test - Methodology for impact testing of metallic materials.
• ISO 2566-1/2: Conversion tables for elongation values of steel.
• ISO 4990: General delivery requirements for steel castings.
• ISO 6892-1: Tensile testing methods for metallic materials.
• ISO 5173: Destructive bend tests for welds in metals.
• ISO 5208: Pressure testing of metallic valves.
• ISO 9606-1 / ISO 9712: Qualification testing of welders and NDT personnel respectively.
• ISO 10474: Inspection documentation for steel products.
• ASME B31.3 / BPVC: American Society of Mechanical Engineers codes for process piping and pressure vessel construction.
• API 598 / ASME B16.5: Alternative pressure testing and mechanical property standards.

Aligning with these documents ensures comprehensive compliance and safety for all stakeholders in the marine and cryogenic sectors.

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By implementing ISO 18735:2026, companies across the supply chain can assure consistent product quality, safety, and performance-meeting both regulatory and operational demands for high-manganese austenitic steel castings in cryogenic and marine environments.

Standards Content (Sample)

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
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
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
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 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
...