I don't understand what you are asking. I don't have a 04 D1-1 but the question seems a little unclear. Is this something that is a recent code change you are asking about?

There are provisions in D1.1 to certify to weld tubular products.

Gerald

The only restriction I can think of for the joint designation you mentioned is that the WPS can not be prequalified without backing or backgouging. If there is a WPQR for an open root 6G pipe test there should not be a problem. As for the API or ASME if you use the right processes the WPQR should full fill their requirement also.

Figure 4.4 of D1.1 shows- positions of test pipe or tubing for Groove Welds
View D Show the 6G position "Fixed"
The only question is are you welding T, K or Y joints? These usually require a restriction ring on the coupon for testing. Called 6GR.
.120 or schedule 120 isn't really considered heavy wall. When you get over 3/8" wall thickness your gettin there.

Figure 4.8 Detail B shows where the bend specimens are to be removed

6G qualifies you for all positions
The diameter and thickness qualifications are discussed in Table 4.9