Hmmm. The PQR is a procedure qualification record. Refer to QW 203, QW 250 (your specific process) and QW 451. I believe you'll find that the PQR itself can be welded on a flat plate. However, specific position restrictions as found in QW 250-265 may require a pipe. Without any such restrictions a plate is allowed for the PQR. Even with some restrictions such change in technique wsuch as vertical up vs down for SMAW a plate could technically be welded. The QW 300 series is for Welder Qualification, and has a different set of rules as they are not qualifying the process but rather the welder.

By PQR, do you mean "Procedure Qualification Record" or are you refering to the welder's "Performance Qualification Record"?  I'm assuming you are referring to the procedure.  For procedures, QW-200.2(b) requires the actual values of all essential variables for the welding process that was used must be recorded on the PQR form.  Base metal thickness is essential for all of the processes, but not pipe diameter.  However, it is a good practice to list both pipe diameter and wall thickness when identifying the base metal used for qualification.

If you were talking about welder qualification, pipe diameter is definitely an essential variable for manual welding and must be listed on the welder's performance qualification record.  For automatic or machine welding operator qualifications diameter is not an essential variable.

Check this out- I've have not validated the accuracy of this but it looks to be valid

http://www.gowelding.com/wp/calc3.htm