46 CFR §147.66

1. (a)Inert gas cylinders forming part of a clean agent fixed fire extinguishing system must be retested every 12 years.
2. (b)An inert gas cylinder must be removed from service if it:
   1. (1)Leaks;
   2. (2)Is dented, bulging, severely corroded, or otherwise weakened;
   3. (3)Has lost more than 5 percent of its tare weight; or
   4. (4)Has been involved in a fire.
3. (c)Flexible connections between cylinders and discharge piping for fixed inert gas fire extinguishing systems must be renewed or retested in accordance with section 7.3 of NFPA 2001 (incorporated by reference, see § 147.7), except that this renewal or retesting must occur when the cylinders are retested.