-7 Tank heads.

(a)Tank heads of the inner tank and outer jacket must be flanged and dished, or ellipsoidal.#

(b)Flanged and dished heads must have—#

(1)A main inside dish radius not greater than the outside diameter of the straight flange;#

(2)An inside knuckle radius of not less than 6 percent of the outside diameter of the straight flange; and#

(3)An inside knuckle radius of at least three times the head thickness.#