If your code of construction references ASME Section IX for WPS qualification; refer to QW-200.4 "Combination of Welding Procedures".

There is a lot of discussion. Briefly: You are still limited in the range of thcknesses originally qualified (both base metal and filler metal deposited, for each process). The thicknesses may not be added to allow welding on a thcker base metal than either process originally allowed.

If you need the actual wording, list your email and I will send the appropriate pages. If your construction code is not ASME Section IX, someone else will have to answer.

Charles