If you are speaking of a Prequalified WPS see table 3.7 in the 98 edition. This indicates a "Maximum Root Pass Thickness" for SMAW, GMAW, and FCAW.
For a WPS qualified by testing a change in the number of passes by more than 25% for a given groove area would also require requalification.
I don't have my 2002 D1.1 handy so this may all be different now.
Hope that helps
Gerald Austin
http://www.weldinginspectionsvcs.com