http://www.generalaviationnews.com/2001/01/flying-versus-driving/

Oxygen cylinder expiration dates - yes there is a regulation for that too!

Recently I spent some time looking into oxygen usage for general aviation. I was looking into the various portable oxygen systems and their details. Several clubs let members check out portable oxygen tanks including San Carlos Flight Center and West Valley Flying Club. When I looked at the WVFC oxygen tank I was told that the next time it needed to be refilled it had to be certified. Huh? Certified? What’s up with that? This got my searching. What I found were the regulations governing recertification of the cylinders that are used for the oxygen tanks. All the cylinders I have seen are aluminum and are of type 3AL. The regulation is in 49 CFR 180.209. It states that the cylinders need to be hydrostatically tested every five (5) years. There is actually a stamp that is imprinted on the cylinder when it is manufactured and also stamped when it is tested. In the picture you can see this cylinder has a "06 * 99" stamp indicating it was originally tested in June of 1999. It has another stamp of "05 * 07" when it was recertified in May of 2007. It turns out that it is not legal to refill a tank that is not current like the one pictured. So it is a good idea to know when a tank needs to be recertified. There are a couple of places that can perform the required test and stamp the cylinder. Near SQL, Alliance Gas Products will do it but it does take them a couple of weeks.