text: Most countries have legislation or pressure vessel codes which requires vessels to be regularly tested, for example every two years (with a visual inspection annually) for high pressure gas cylinders and every five or ten years for lower pressure ones such as used in fire extinguishers.  Gas cylinders which fail are normally destroyed as part of the testing protocol to avoid the dangers inherent in them being subsequently used.
  These common US standard gas cylinders have the following requirements:
  * DOT-3AL gas cylinders must be tested every 5 years and have an unlimited life.
  * DOT-3HT gas cylinders must be tested every 3 years and have a 24-year life.
  * DOT-3AA gas cylinders must be tested every 5 years and have an unlimited life. (Unless stamped with a star (*) in which case the cylinder meets certain specifications and can have a 10-year hydrostatic test life).
  Typically organizations such as DOT PHMSA, ISO, ASTM and ASME specify the guidelines for the different types of pressure vessels.