179.400-7 Tank heads.§ 179.400-7 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.