49 CFR § 178.920 - Standards for metal Large Packagings.
(1) 50A steel
(2) 50B aluminum
(3) 50N metal (other than steel or aluminum)
(b) Each Large Packaging must be made of suitable ductile metal materials. Welds must be made so as to maintain design type integrity of the receptacle under conditions normally incident to transportation. Low-temperature performance must be taken into account when appropriate.
(c) The use of dissimilar metals must not result in deterioration that could affect the integrity of the Large Packaging.
(d) Metal Large Packagings may not have a volumetric capacity greater than 3,000 L (793 gallons) and not less than 450 L (119 gallons).