All propane tanks require certification, and a date stamped on the collar of the tank tells the user if the tank's certification is valid. Federal law dictates that all propane tanks must be re-certified within a specified time period of manufacture, depending on the type of inspection performed.
If there is no letter following the most recent date stamp, then the certification is good for 12 years from that date. If the date stamp is followed by the letter "S," it must be re-certified every seven years, and if it has the letter "E," it is good for five years. It is the owner of the tank that is responsible for compliance to proper inspection schedules.