Code of Federal Regulations Title 49. Transportation § 49.179.400–3 Type

(1) Consist of an inner tank of circular cross section supported essentially concentric within an outer jacket of circular cross section, with the out of roundness of both the inner tank and outer jacket limited in accordance with Paragraph UG–80 in Section VIII of the ASME Code (IBR, see § 171.7 of this subchapter);

(2) Have the annular space evacuated after filling the annular space with an approved insulating material;

(3) Have the inner tank heads designed concave to pressure;  and

(4) Have the outer jacket heads designed convex to pressure.