ISO 15501-2:2016

Overview

ISO 15501-2:2016 specifies test methods for verifying the minimum safety requirements for compressed natural gas (CNG) fuel systems in road vehicles (as defined in ISO 3833). It is the Part 2 companion to ISO 15501‑1 (safety requirements) and focuses on practical tests for system functionality after installation, covering cylinder mounting strength, leak tightness, functional operation and receptacle mounting.

Key topics and technical requirements

• Cylinder mounting strength tests
  • Inertia (dynamic) test: cylinders mounted to vehicle/body or body part; cylinders filled to at least 90% of 20 MPa (200 bar) capacity (density 0.2 kg/l); trolley deceleration measured with channel frequency class CFC 60 (ISO 6487); deceleration maintained for ≥30 ms.
  • Static test: applies a traction force F = (M + 0.9 ρ V) a to the cylinder centre of gravity; force applied within 0.2 s, held ≥0.2 s.
  • Alternative methods: compliant crash tests or approved calculation methods may be accepted.
  • Acceptance: cylinders must remain attached and not interfere with seat structure; calculations require authority approval.
• Leak test
  • Per-vehicle test after installation at ambient temperature.
  • System upstream of the first-stage regulator pressurized at 1 MPa (10 bar) ±0.1 MPa and then 20 MPa (200 bar) ±1 MPa; inspect connections with gas detector or foam; no bubbles for 3 minutes or leak rate < 20 cm3/h.
• Functional tests
  • Main shut-off valve: must close when ignition is off, when engine stalls, when cranking on non‑CNG fuel, or when engine not running on CNG.
  • Receptacle clearance: verify free space conforms to ISO 15501‑1.
• Receptacle mounting tests
  • With service pressure applied, nozzle attached: apply 670 N axial pull and 200 N·m moment; gas tightness must be maintained.
• Annex A: engineering guidance for steel (Type 1) cylinder mountings, fastener/property recommendations and typical acceptable/ unacceptable arrangements.

Applications and users

ISO 15501-2 is used by:

• Vehicle OEMs and aftermarket converters for design validation and retrofit verification
• Test laboratories, notified bodies and regulatory authorities for certification and conformity assessment
• Installation engineers and fleet managers to ensure safe CNG cylinder anchoring, leak tightness and fuelling interface integrity
• Safety and compliance teams integrating CNG systems into passenger and commercial vehicles

Related standards

• ISO 15501-1 - Safety requirements for CNG fuel systems
• ISO 15500 series - CNG fuel system components
• ISO 11439 - High-pressure cylinders for on-board NG storage
• ISO 14469 - CNG refuelling connector
• ISO 6487 - Instrumentation for impact tests

Keywords: ISO 15501-2, CNG test methods, compressed natural gas fuel systems, cylinder mounting test, leak test, receptacle mounting, vehicle CNG safety.