Jerry:
I'll take part of your question. When you back gouge, you back gouge to clean weld metal on the other side. This provides your backing for your full penetration weld. You are still welding with backing.

Look at the standard WPS you say can be open root and see what it says about backing. If it is a two process WPS, GTAW/SMAW for example the GTAW will provide the backing for the SMAW. Not to forget that the GTAW will be able to weld out to a maximum thickness.

Regards, Donnie Mann

Check 3.13.3 of D1.1. CJP welds made from one side without backing, regardless of process, are not considered prequalified. These joints can be used, and commonly are, but the WPS must be qualified in accordance with Section 4.
Look also at 4.1.1 and 4.1.1.2 of D1.1. WPSs qualified in accordance with B2.1 are not automatically in compliance with D1.1. WPSs qualified in accordance with B2.1 must be approved by the Engineer.
Mankenberg

Standard WPS's are NOT the same as a prequalified WPS. The prequalified WPS's mentioned in D1.1 have to fall within the requirements set forth in that code and if that range of variables is met, a WPS can be writtenn which does NOT have to be proven by testing.

A Standard WPS has been qualified by testing to meet the requirements of B2.1 (I believe). The STandard WPS's is allowed to be used by some other codes with some provisions made. Some testing is required for ASME use.

Hope this helps.

Gerald Austin
Iuka, MS