ISO 12991:2012

Overview

ISO 12991:2012 - "Liquefied natural gas (LNG) - Tanks for on‑board storage as a fuel for automotive vehicles" defines construction and testing requirements for refillable LNG fuel tanks permanently attached to land vehicles. The standard aims to ensure a reasonable level of protection against loss of life and property from fire, explosion and cryogenic hazards. It covers design, materials, insulation, manufacturing, type tests and routine inspection for on‑board cryogenic storage systems.

Key topics and technical requirements

• Scope and application: Applicable to fuel tanks permanently mounted on land vehicles; can be used as guidance for other transport modes.
• Terminology: Defines critical terms such as inner tank, outer jacket, MAWP (maximum allowable working pressure) and holding time (insulation performance metric).
• Mechanical requirements:
  • Inner and outer pressure design and test levels (inner tank designed for pressures related to MAWP; outer jacket to resist 1 bar outer pressure).
  • Dynamic loads and crash/acceleration criteria by vehicle category (e.g., M1/N1: 20 g forward, 8 g lateral; M2/N2: 10 g forward, 5 g lateral; M3/N3: 6.6 g forward, 5 g lateral).
• Thermal requirements:
  • Design temperature baseline 20 °C; ambient design range −40 °C to 85 °C (or 120 °C for engine compartments if applicable).
  • Components in contact with LNG must tolerate cryogenic temperatures (down to −196 °C).
• Materials:
  • Compatibility with LNG and common vehicle fluids (coolant, brake fluid, battery acid).
  • Cryogenic toughness per ISO 21028‑1 for low‑temperature materials; outer jackets typically austenitic stainless steel to preserve insulation integrity.
• Design and insulation:
  • Requirements for insulation performance measured by holding time, and design rules for fittings, supports and accessories (pressure relief valves, level gauges).
• Testing and inspection:
  • Type tests: burst pressure, holding time, maximum fuelling level and accessory tests.
  • Routine tests: pressure, leak checks, dimensional verification, destructive/non‑destructive weld tests, visual inspection.
• Marking and labelling: Mandatory markings for inner tank, outer jacket and temporary markings for first fuelling.

Applications and users

ISO 12991:2012 is essential for:

• Vehicle OEMs (cars, buses, trucks) integrating LNG fuel tanks
• Cryogenic tank designers and fabricators
• Component suppliers (pressure‑relief devices, valves, sensors)
• Testing laboratories, certification bodies and regulatory authorities
• Fleet operators converting vehicles to LNG

Practical uses include tank design validation, supplier specifications, type approval, factory inspection protocols and safety case documentation.

Related standards (if applicable)

• ISO 21028‑1 (toughness at cryogenic temperatures)
• ISO 21014 (insulation performance)
• ISO 21013‑3 (pressure‑relief accessory sizing)
• ISO 23208 (cleanliness for cryogenic service)
• ISO 12617 (fuelling system interface - under preparation)

Keywords: ISO 12991:2012, LNG tanks, on‑board storage, vehicle fuel tanks, cryogenic vessels, MAWP, holding time, pressure testing, insulation performance.