ISO 19723-2:2018

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 in accordance with the ISO 15403 series. It is not applicable to the following: original-production and converted vehicles. This document is only applicable on the components in the "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 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: 16-Jul-2018
• 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/WG 7 - General safety requirements for gaseous fuelled vehicles and terminology
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 12-Dec-2025
• Completion Date: 27-Dec-2025

Relations

• Revised: ISO 19723-2:2025 - Road vehicles - Liquefied natural gas (LNG) fuel systems - Part 2: Test methods
• Effective Date: 08-Mar-2023

Overview

ISO 19723-2:2018 - 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 motor vehicles (as defined in ISO 3833). It applies to mono‑fuel, bi‑fuel and dual‑fuel vehicle systems using LNG per the ISO 15403 series and covers the LNG system components up to and including the vaporizer. Downstream components are treated as CNG components (ISO 15501). All pressure references are gauge pressures.

Key topics and requirements

This part of ISO 19723 specifies practical laboratory and on‑vehicle tests and acceptance criteria for LNG system components. Major test areas include:

• Tank mounting strength tests
  • Inertia test: vehicle/tank mounted on test trolley with deceleration measurements (ISO 6487) and liquid nitrogen load simulation.
  • Static test: applied traction force based on tank mass and LNG equivalent load; hold and release procedure and acceptance (no detachment or interference with seats).
• Leak test
  • System pressurization to 90% working pressure; bubble test (no bubbles for 3 min or leakage < 20 Ncm3/h) with procedures for detected leaks.
• Functional LNG/CNG automatic valve test
  • Verify valve closes when ignition is off, engine stalls, cranking occurs on non‑LNG fuel, or engine not running on LNG.
• Receptacle tests
  • Compliance with ISO 12617; cap protection; clearance and mounting strength (670 N axial pull, 200 N·m moment) and subsequent leak check.
• Hold time test
  • Verifies tank can maintain hydrostatic pressure stability for a minimum of 120 hours with specified fill and ambient conditions; tank must remain bubble‑tight.
• Venting and accumulation system checks
  • Vent routing, protection from fouling/ice, sizing to avoid pressure drops, and safe discharge locations.
• Additional checks
  • Bonfire test, marking requirements and engineering guidance for tank mounting (Annex A).

Applications and who uses it

ISO 19723-2 is essential for:

• Vehicle OEMs and after‑market converters designing or installing LNG systems (except original‑production and converted vehicles as noted).
• Component manufacturers (tanks, valves, fittings, receptacles) validating product performance.
• Test labs, certification bodies and compliance engineers performing type‑approval or in‑service testing.
• Fleet operators and integrators specifying safe LNG fuel systems and refuelling interfaces.

Practical benefits: ensures consistent test procedures, improves safety and interoperability of LNG components, and supports regulatory compliance and type‑approval processes.

Related standards

• ISO 19723-1:2018 - Safety requirements (companion document)
• ISO 12991 - On‑board LNG storage tanks
• ISO 12617 - LNG refuelling connector (3.1 MPa)
• ISO 15403 series - Natural gas fuel quality
• ISO 15501 - CNG system components (downstream of vaporizer)

Keywords: ISO 19723-2, LNG fuel systems, test methods, tank mounting, leak test, hold time, venting system, road vehicles, LNG standard.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 19723-2
First edition
2018-07
Road vehicles — Liquefied natural 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 2018
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii © ISO 2018 – All rights reserved

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 strenght 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
4.2 Leak test . 3
4.3 Functional LNG/CNG 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
4.6 Acceptable test results . 5
4.7 Venting system check . 5
4.8 LNG accumulation system check . 5
4.9 Bonfire test . 5
5 Marking . 5
Annex A (informative) Engineering experience for the mounting of LNG tanks .7
Bibliography .11
Foreword
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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
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URL: www .iso .org/iso/foreword .html.
This document was prepared by ISO/TC 22, Road vehicles, Subcommittee SC 41, Specific aspects for
gaseous fuels.
A list of all the parts in the ISO 19723 series, can be found on the ISO website.
iv © ISO 2018 – All rights reserved

Introduction
For the purposes of this document, all fuel system components in contact with liquid natural gas have
been considered 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.
INTERNATIONAL STANDARD ISO 19723-2:2018(E)
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
in accordance with the ISO 15403 series. It is not applicable to the following: original-production and
converted vehicles.
This document is only applicable on the components in the "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 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/
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 19723-1:2018, 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 terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Test methods
4.1 Tank mounting strenght 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 tank can be tested individually.
When performing these tests, accessories and piping shall not contribute to reinforcing the tank
mounting.
The requirements of ISO 19723-1:2018, 4.4.3, shall be verified by the test specified in 4.1.1, 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 equivalent full weight of liquid nitrogen saturated to one-half the
working pressure.
b) Measure the trolley deceleration with data channels of channel frequency class (CFC) 60
corresponding to the characteristics given in ISO 6487.
c) Maintain the value of the deceleration as defined in ISO 19723-1:2018, 4.4.3, for at least 30 ms.
4.1.3 Static test
This test may be carried out on a vehicle body or on a part of a vehicle body.
The tank or group of ta
...