Have your tank hydrostatically tested
“Hydro testing” is process that tests the strength of a pressure cylinder by filling it to 5/3 (166%) of it’s rated service pressure. As the scuba tank is over filled, the metal begins to stretch and the tank swells. The amount of expansion is measured during the test and if it’s within acceptable guidelines, the tank is deemed safe for service until the next test is due. Typically a hydrostatic test must be repeated every five years, but it’s best to consult your local regulations to see if your tanks must be tested on a different interval. The month and year of the last hydro test is stamped into the neck of the cylinder so it’s easy to find.
Simply being ‘in-hydro’ isn’t enough to guarantee that a cylinder won’t fail, unfortunately. As I mentioned earlier, my friend’s tank had been hydro tested less than five years ago.