Looks like a very generalized WPS.  If it's fillet welded, it's prequalified as long as the base metals being welded are prequalified, and they are being welded with a prequalified process.  If it's groove welded, it's prequalified as long as a prequalified groove joint detail is used, as long as the base metals being welded are prequalified, and they are being welded with a prequalified process.  Pipe diameter becomes an issue with welder qualifications because there are limitations with regard to groove welded pipes of less that 24" in diameter.

3.9.2 on Page 59, 3.12.4 and 3.13.3 on Page 60 of D1.1:2006 all read that you can do tubular joints without qualification in a prequalified WPS. I would assume that the 2" limitation comes from what their welder's are qualified for.

Realize that this is for structural welding and not pressure piping.  In D1.1, pipe is a product form only and could be used for tubular structures, penetration sleeves in concrete pours, handrails, etc.  D1.1 is not intended for pressurized piping welds.