Section 64.17 - Minimum tank thickness(a) Except as allowed in paragraph (b) of this section, a tank with a diameter of- (1) 6 feet or less must have a shell and head of 3/16 inch thickness or more; or(2) More than 6 feet must have a shell and head of 1/4 inch thickness or more.(b) If the tank has additional framework to guard against accidental puncturing of the tank, the shell and head thickness must be 1/8 inch or more.