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.