Please advise weather the welder shall be qualified on the whole pipe circumferential or just the half pipe could be enough or cover welding of the whole circumferential, since we performed a  welder performance qualification test on 8" test coupon 12.7mm thickness as 2 welders have welded 2 circumferential halves  and were qualified on the same pipe.   taking into your account that as per Structural Welding Code - Steel  AWS D1.1 2006 item 4.30.3.1 RT  Test Procedure and Technique which reveal that "Welded test pipe or tubing 4in. (100mm) in diameter or larger shall be examined for a minimum of one half of the weld perimeter selected to include a sample of all positions welded. (For example, a test pipe or tube welded in the 5G, 6G or 6GR position shall be radiographed from the top centerline to the bottom centerline on either side). Welded test pipe or tubing less than 4in. (100mm) in diameter shall require 100% RT"
Consequently, welding half circumference of the pipe decrease the welder opportunity to pass the examination when his half would be radiographed which also will restrict his performance during qualification and encourage him to do his best in his half. (Only the welder with high skill would pass the radiographic examination)
Furthermore, in the performance qualification welding half circumferential of the pipe already covers all welding positions for 6G which means that half pipe contains flat, vertical and overhead positions which will be repeated if the welder would weld the other half of the same pipe.
Moreover, there is no essential variable, instruction or restriction during performance qualification in Structural Welding Code - Steel AWS D1.1 2006 to stipulate that the welder shall weld the whole pipe circumferential.   

Thanks & Best Reagrds.