Everything within quotation marks in my long post are directly from A3.0 or A2.4...
5)"backing. A material or device placed on the backside of a joint adjacent to the joint root" What's the problem understanding this?
Do you understand the meaning of the word "adjacent" when used in the previous part of a sentence? Heck, I even made a comment regarding that very same sentence in parentheses! I personally did not depict anything other than what is written verbatim in A3.0...

"Instead of the groove face or land, I see it as distance apart or offset between two members. Thank you."  Maybe this will clarify your understanding of what a "joint root" is depicting from the definition below...

If you have A3.0 handy, then go to page 22, right column, third definition down from the top...
"Joint Root. that portion of a joint to be welded where the members approach closest to each other. In cross section, the joint root may be either a point, a line, or an area. See figure 4."

I strongly suggest that get in your possession a copy of both A3.0 and A2.4 if you don't have them available for reference to use when working to AWS D1.1.

Lawrence, I have no problem with the fabricator doing as you suggest. Now assuming the project specifies the welding to meet AWS D1.1, the Owner has retained the services of an Engineer as per the requirements of D1.1, assuming there are drawings that have been approved by the Engineer bearing his stamp, and assuming I am the Third Party Inspector (Verification Inspector per D1.1), I would allow you to change the joint detail as long as the approved drawing is changed to reflect the change from a single V-groove to a single U-groove and with the proviso that the change be approved by the Engineer that represents the Owner.

You have changed the groove detail completely from what is specified. The B-U2 is a single V-groove that utilizes a back gouge operation and a back weld. You are changing the detail to a single U-groove that must comply with a prequalified U-groove (unless you have qualified an alternate U-groove detail per clause 4) that employs a backing weld. Very few similarities between the specified detail, i.e., B-U2, and what you have proposed. What you have proposed, i.e., a backing weld with a back gouge operation from the opposite side must comply with clause 5.22.5.

If the Engineer wanted to grant the fabricator unfettered latitude, CJP in the tail of the reference line would have been sufficient. That isn't the case when the welding symbol specifies a specific prequalified groove detail.

Best regards - Al

Let's revisit some of the terminology that has or appears to have originated by our friends at Lincoln Electric;

Weldor: one who welds.
Welder: the power supply providing current and voltage suitable for welding.
Land: the root face.
Seal weld: you seemed to have found evidence of the definition in the Welding Procedure Handbook published by J. F. Lincoln Foundation.

However, in all cases the examples are not considered "standard" terminology. Most welding standards and codes include a reference to AWS A3.0 for the approved and required welding terms and definitions. The use of standard terminology simply makes communication more efficient.

Al

A big thanks to all who had contributed to this post. I greatly appreciate your comments,participations and suggestions. I will confront the client as suggested diplomatically but firm and will let you all know the outcome in the future. Thanks alot.
Sincerely,
Delawgee

Conflict on the fabrication floor is fairly common. The TPI is trying to ensure the fabricator is meeting the requirements of the project specification, approved drawings, and the code. Meanwhile the contractor is trying to change the approved drawings on the fly, twisting the code by intermingling "the way we have always done it for the last twenty years",  and trying to incorporate requirements for other codes that are not applicable on the current project.

Just a bad is the Third Party Inspector that doesn't know the requirements of the applicable code, doesn't have a copy of the applicable code, and remembers "how it was done on the last big job."

I try to accommodate the fabricator when possible, but the only requirements that apply are those contained in the project specifications, the applicable code, and those specifically approved in writing by the Engineer. I really don't care how the fabricator "usually does it" or "that is the way they have done it for the last twenty years" unless it complies with the approved drawings. If the fabricator wants to change the approved joint detail from what is shown on the approved drawings, my position is knock yourself out, but get the Engineer's approval first.

When a fabricator wants to change the joint detail I think back to the Hyatt Regency walkway collapse. The change was just a "minor" change that made it easier for the erector, but cost the lives of many innocent people. The change was never approved in writing.

I also think back to the first Hartford Civic Center that collapsed after a basketball game with several thousand people in attendance. The projections were that six thousand plus people would have been killed had it collapsed several hours earlier. The fabricator did not build what was "fed into the computer." The rigid plate connections that required CJP groove welds were changed to thin plates with fillet weld. None of the welds measured after the collapse were full sized fillet welds. Of course there are many factors that came into play, but protocols were not followed and warning signs were not recognized. Why didn't the parapet steel fit correctly? Why did the roof sag several inches before the roof decking was installed and the roof lifted off the false work?

Le'Ambiance  collapsed killing 28 workers. Why wasn't the details for the rebar around the column openings checked and approved by the Engineer before the contractor changed the layout? Why were leaking pumps not repaired before being pressed into service?

The third party inspector is on the job to serve as the engineer’s eyes and ears. The TPI is responsible to inform the Engineer of all nonconforming work. All noncompliant work, even when the contractor corrects the faulty work immediately, is reported to the Engineer. The TPI is not on the job to be the contractor’s consultant. Nor is the inspector on the job to be the welder’s buddy. The TPI does not have the authority to approve noncompliant work, to approve repair procedures, or changes in the design, or the extent of inspection, or invoke additional NDE.

The Engineer is the individual that has the authority to accept noncompliant “as built” work or to require corrective action. The Engineer has the authority to review and accept repair procedures. The Engineer has the authority to review and approve design changes. When the situation warrants additional NDE, it is the Engineer that has the authority to invoke additional NDE. 

When the fabricator changes the approved details, i.e., a groove detail is changed or a material substitution is made, the Engineer must be informed and must approve or deny the change. The Engineer may not know of the change unless the TPI does his job.

Best regards -Al