ISO 19723-2:2025

Road vehicles - Liquefied natural gas (LNG) fuel systems - Part 2: Test methods

This document specifies performance and general test methods for liquefied natural gas fuel system components intended for use on the types of motor vehicles defined in ISO 3833. This document is applicable to vehicles (mono-fuel, bi-fuel or dual-fuel applications) using liquefied gas according to the ISO 15403 series. It is applicable to original-production and converted vehicles. This document is only applicable on the components in the "liquefied natural gas (LNG) system" meaning an assembly of components (tanks, valves, flexible fuel lines, etc.) and connecting parts (fuel lines, fittings, etc.) fitted on motor vehicles using LNG in their propulsion system and related components up to and including the vaporizer. Other parts downstream from the vaporizer are considered as compressed natural gas (CNG) components covered by ISO 15501. NOTE All references to pressures, given in megapascals and bar (1 bar = 0,1 MPa = 105 Pa; 1 MPa = 1 N/mm2) are considered gauge pressures, unless otherwise specified.

Véhicules routiers — Systèmes à carburant gaz naturel liquéfié (GNL) — Partie 2: Méthodes de test

General Information

• Status: Published
• Publication Date: 11-Dec-2025
• ICS: 43.060.40 - Fuel systems
• Technical Committee: ISO/TC 22/SC 41 - Specific aspects for gaseous fuels
• Drafting Committee: ISO/TC 22/SC 41 - Specific aspects for gaseous fuels
• Current Stage: 6060 - International Standard published
• Start Date: 12-Dec-2025
• Due Date: 07-Mar-2026
• Completion Date: 12-Dec-2025

Relations

• Revises: ISO 19723-2:2018 - Road vehicles - Liquefied natural gas (LNG) fuel systems - Part 2: Test methods
• Effective Date: 08-Mar-2023

Overview

ISO 19723-2:2025, "Road vehicles - Liquefied natural gas (LNG) fuel systems - Part 2: Test methods," defines performance and general test methods for LNG fuel system components fitted to road vehicles (as defined in ISO 3833). It applies to mono‑fuel, bi‑fuel and dual‑fuel vehicles using liquefied gas per the ISO 15403 series, for both original-production and converted vehicles. The standard covers the LNG system up to and including the vaporizer; downstream components fall under CNG standards (ISO 15501).

Key topics and technical requirements

The standard specifies practical tests and acceptance criteria for LNG system safety and integrity. Key topics include:

• Tank mounting strength tests

  • Inertia and static tests to verify tank anchorages remain secure under defined accelerations/forces.
  • Use of equivalent test media (e.g., liquid nitrogen) to simulate fill mass and pressure conditions.
  • Acceptance: tanks must remain attached and not interfere with seating structures.

• Leak test

  • System pressurization and inspection (including bubble-testing) after installation.
  • Tests performed at ambient temperature, typically at a high percentage of working pressure; detected leaks must be rectified and re-tested.

• Functional automatic valve test

  • Verifies LNG/CNG automatic valves close in defined conditions (ignition off, engine stall, cranking on another fuel, or engine not running on LNG).

• Receptacle and coupling tests

  • Receptacle compliance with ISO 12617, protection against contamination, clearance checks, and mounting tests (e.g., 670 N axial pull and 200 N·m moment) with subsequent leak checks.

• Hold time test

  • Confirms tanks maintain acceptable hydrostatic pressure stability for a minimum hold time (120 hours) under specified temperature conditions.

• Venting, accumulation system checks and bonfire test

  • Procedures to validate safe venting and emergency behaviour are defined.

• Marking and documentation

  • Requirements for component identification and traceability.

Practical applications and users

ISO 19723-2:2025 is intended for:

• Automotive OEMs and component manufacturers designing or validating LNG tanks, valves, fittings and receptacles.
• After‑market converters and retrofitters of LNG propulsion systems.
• Test laboratories and certification bodies performing conformity and safety testing.
• Fleet operators and integrators seeking documented proof of LNG system performance and safety.

By following these test methods, stakeholders can demonstrate compliance with internationally recognized procedures for LNG fuel system safety, reliability and interchangeability.

Related standards

• ISO 19723-1:2025 (Safety requirements)
• ISO 12991 (On‑board LNG tanks)
• ISO 12617 (LNG refuelling connector)
• ISO 15501 (CNG components downstream of vaporizer)
• ISO 15403 series (Liquefied gas specifications)
• ISO 3833 (Vehicle categories)
• ISO 6487, ISO 898-1 (test instrumentation and fasteners)

Keywords: ISO 19723-2:2025, LNG fuel system test methods, road vehicles, tank mounting strength, leak test, hold time test, receptacle test, LNG safety standard.

Standards Content (Sample)

International
Standard
ISO 19723-2
Second edition
Road vehicles — Liquefied natural
2025-12
gas (LNG) fuel systems —
Part 2:
Test methods
Véhicules routiers — Systèmes à carburant gaz naturel
liquéfié (GNL) —
Partie 2: Méthodes de test
Reference number
© ISO 2025
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 . 1
4 Test methods . 2
4.1 Tank mounting strength tests .2
4.1.1 General .2
4.1.2 Inertia test . .2
4.1.3 Static test .2
4.1.4 Acceptance criteria .3
4.1.5 Best practice examples (for reference only) by engineering experience .3
4.2 Leak test .3
4.3 Functional liquefied natural gas/compressed natural gas automatic valve test .4
4.4 Receptacle .4
4.4.1 General .4
4.4.2 Receptacle clearance test .4
4.4.3 Receptacle mounting tests .4
4.5 Hold time test.4
4.5.1 General .4
4.5.2 Procedure .4
4.5.3 Acceptable test results .5
4.6 Venting system check .5
4.7 LNG accumulation system check .5
4.8 Bonfire test .5
5 Marking . . 5
Annex A (informative) Engineering experience for the mounting of LNG tanks . 7
Bibliography .11

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 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).
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)
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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 ISO/TC 22, Road vehicles, Subcommittee SC 41, Specific
aspects for gaseous fuels.
This second edition cancels and replaces the first edition (ISO 19723-2:2018), which has been technically
revised.
The main changes are as follows:
— generally updated wording and update of some requirements.
A list of all parts in the ISO 19723 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.

iv
Introduction
All fuel system components in contact with liquid natural gas are suitable for natural gas as defined in the
ISO 15403 series.
When applying this document, it is understood that a safety device to prevent overfilling the vehicle's fuel
system is part of the refueling station. The pressure gauge has not been considered as a safety component.
When necessary, technical solutions regarding functional requirements are given in Annex A.

v
International Standard ISO 19723-2:2025(en)
Road vehicles — Liquefied natural gas (LNG) fuel systems —
Part 2:
Test methods
1 Scope
This document specifies performance and general test methods for liquefied natural gas fuel system
components intended for use on the types of motor vehicles defined in ISO 3833.
This document is applicable to vehicles (mono-fuel, bi-fuel or dual-fuel applications) using liquefied gas
according to the ISO 15403 series. It is applicable to original-production and converted vehicles.
This document is only applicable on the components in the "liquefied natural gas (LNG) system" meaning an
assembly of components (tanks, valves, flexible fuel lines, etc.) and connecting parts (fuel lines, fittings, etc.)
fitted on motor vehicles using LNG in their propulsion system and related components up to and including
the vaporizer. Other parts downstream from the vaporizer are considered as compressed natural gas (CNG)
components covered by ISO 15501.
5 2
NOTE All references to pressures, given in megapascals and bar (1 bar = 0,1 MPa = 10 Pa; 1 MPa = 1 N/mm ) are
considered gauge pressures, unless otherwise specified.
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 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and
studs with specified property classes — Coarse thread and fine pitch thread
ISO 6487, Road vehicles — Measurement techniques in impact tests — Instrumentation
ISO 12617, Road vehicles — Liquefied natural gas (LNG) refuelling connector — 3,1 MPa connector
ISO 12991:2012, Liquefied natural gas (LNG) — Tanks for on-board storage as a fuel for automotive vehicles
ISO 19723-1:2025, Road vehicles — Liquefied natural gas (LNG) fuel systems — Part 1: Safety requirements
3 Terms and definitions
No terms and definitions are listed in this document.
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/

4 Test methods
4.1 Tank mounting strength tests
4.1.1 General
When a vehicle is equipped with several tanks, they should be tested as a unit.
When a tank or groups of tanks are installed on a vehicle such that they are separately anchored to the
original structure of the vehicle, then each tank or separate group of tanks can be tested individually.
When performing these tests, accessories and piping shall not contribute to reinforcing the tank mounting.
The general design requirements of ISO 19723-1 shall be verified by the tests specified in 4.1.2 or 4.1.3.
4.1.2 Inertia test
The tank or group of tanks to be tested shall be mounted on the vehicle body or a part of the vehicle body,
according to the specifications of the original equipment manufacturer (OEM) or after-market converter.
The vehicle body or part of the vehicle body shall be firmly anchored to the test trolley. The method used for
anchoring the vehicle body to the test trolley shall not result in reinforcement of the tank anchorages or the
part of the vehicle structure participating in anchoring the tank or tanks. Testing performed with a trolley
shall geometrically match original vehicle conditions.
The test shall be carried out using the following procedure.
a) Fill the tank or tanks with an
...