Dear Mauricio:
As you can see in the table 4.1 of AWS D1.1-98, the qualification test on plate using complete penetration joints in grooves also qualifies production pipe welding for circunferential welds in nominal outer diameters equal to or greater than 24" (you have 30"), as you can write in the note 2; however you must to do qualification tests in 2G, 3G and 4G for make welds on pipes without rotate it. The qualification thickness on plate, pipe or tube, as Mr Neal says, is 2T where T is the thickness of your qualification coupon, I mean T=16mm for you, then you may weld thicknesses up to 32mm (Table 4.2 of the code).
I hope this help you.
Jorge Giraldo
Medellín, Colombia