ISO 11439 faq

  • What is ISO 11439?
    • ISO 11439 is the required standard for "Gas cylinders. High pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles"
  • Why is ISO 11439 important?
    • It is an international standard which is generally accepted by most countries.
  • What are the cyliners with ISO 11439 approval used for?
    • Generally ISO 11439 approved cylinders are used for Natural Gas Vehicles (generally called CNG Cylinder) and Hydrogen cylinders are also using this standard for Hydrogen powered vehicles as these gas must be compressed to high pressure before storing as the gas content is generally very thin.
  • What are cylinder categories covered by this standard?
    • ISO 11439 clearly defines 4 categories of cylinders
    • CNG-1 Metal
    • CNG-2 Metal liner reinforced with resin impregnated continuous filament (composite hoop wrapped)
    • CNG-3 Metal liner reinforced with resin impregnated continuous filament (fully wrapped composite cylinder)
    • CNG-4 Resin impregnated continuous filament with a non-metallic liner (all composite)
    (information from ISO 11439 paper)
  • What are minimum burst pressure for each type of cylinder?
    • ISO 11439 defines different burst pressure for each type of cylinder based on the raw material used
    • CNG-1 Metal:2.25
    • CNG-2 Type of fiber: Glass:2.75 Aramid:2.35 Carbon:2.35
    • CNG-3 Type of fiber: Glass:3.65 Aramid:3.1 Carbon:2.35
    • CNG-4 Type of fiber: Glass:3.65 Aramid:3.1 Carbon:2.35
    • These factors define the minimum burst pressure in ratio to working pressure. E.g. A 200bar working pressure cylinder of type 3 is made with metallic liner and wrapped with Carbon fiber. This means the cylinder should not be filled over 200bar of content gas and will have to be able to withstand minimum pressure of 470bar (The cylinder may burst above this pressure).
  • What is filament winding and what does it have todo with resin impregnated continuous filament?
    • Filament winding is a process to lay-up fiber rovings on to a liner. Generally this method includes wetting the fiber with resin before the lay-up.
  • What are the major differences in using each of the 4 categories of cylinders?
    • With the same volume content, CNG-1 would be the heaviest in terms of weight, followed by CNG-2 and CNG-3 while CNG-4 would be the lightest. However, the market price of CNG-1 is generally the lowest followed by CNG-2 and CNG-3, while CNG-4 is generally the most expensive.
      In terms of safety, as long as they are ISO 11439 approved, there should not be any difference.

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