CO2 Tank Certification, Hydro Testing Date, and DOT Stamp 

All CO2 and Nitrogen tanks have some information permanently stamped on them near the top of the tank. First is the certifying agency, like DOT, second is the tank pressure (USA is PSI), then the serial number of the tank, then the tank hydro certification date (good for 5 years on CO2), then the tear weight of the tank (empty weight).
Nitrogen tanks are generally good for 10 years.
coldbreak.sjv....
-----
Coldbreak Customer Service
support@coldbreakusa.com
@coldbreakusa
(616) 591-0200
M-F 9:00am-4:00pm (eastern time)