Mayur,
Its not more than 13 mm. (QW-452.1b) Its 13 mm or greater, but you are partially correct. It would be limited by process, i.e. If you weld with the GTAW process on a 13 mm coupon then the welder has "Maximum to be welded (or as interpreted, unlimited qualifications) with that process. That would hold true for his/her performance qualification, but the welder, even if they have an unlimited performance qualification can be limited by the WPS on how much material can be deposited into any given joint. A good rule to remember is, basically, ASME Sec. IX is broken into two parts. Welding procedure qualification and welder performance qualification.