"Tanks" are not the same as "cylinders". The portable things on travel trailers & grills are correctly called "cylinders." They must be tested 12 yrs after the date of manufacture. The date of manufacture is stamped on the top outer ring. Subsequent re-testing depends on the first re-test method---it is either 5, 7, or 12 years.
Cylinders are regulated by DOT, because they are transported by commercial carriers while filled.
DOT requirements for propane cylinder testingPermanently installed propane containers are correctly called "tanks." They are not regulated by DOT because they are filled in place, and thus are not transported by commercial carriers while filled. They are built to standards set by ASME (American Society of Mechanical Engineers). There is no re-testing required for tanks.
You should ALWAYS take a good look at your cylinders or tanks, plus connecting hoses, at least annually. Inspect the cylinders, tanks, and fittings for any obvious damage. Leak check the hoses and connections. Replace any thing that you think might have been damaged.
Propane is nothing to fool around with, for sure.
