Here is the 2010 edition:
5.3.3.1 Qualified Thickness Range
(1)A test weld with a base metal thickness of t shall qualify welds with a thickness range of 0.67t to 4t, except that when the test weld thickness is equal to or greater than 1 in [25 mm], the qualification range is 0.67t to unlimited. Two test welds shall qualify welds with all intermediate thicknesses.
(2)Qualification for sheet or tube fillet welds in material 0.063 in [1.6 mm] thickness (sheet or tube wall) or less requires a fillet weld test. A groove weld test cannot be used to qualify fillet welds in this thickness range.
NOTE: Tube fillet weld qualifications are based on tube thickness only, not mating sheet thickness.
(3)Qualification for tube welding on tubes of 1 in [25 mm] OD or less requires qualification of a tube weld. The tube weld qualification is for any tube size equal to or larger than the OD of the tested tube weld.
NOTE: Qualification for tube welding on tube one inch [25mm] or greater may be qualified using sheet.