46 CFR §58.50-15

Materials other than those specifically listed in table 1 to § 58.50-5(a)(2) and in table 1 to § 58.50-10(a)(2) may be used for fuel tank construction only if the tank design meets material and testing requirements approved by the Commandant (CG-ENG). Approved testing may be accomplished by any acceptable laboratory, or may be done by the fabricator if witnessed by a marine inspector.