Let me add to what Shane pointed out in AWS D1.1 Clause 5.10.2...Full length backing:
Steel backing shall be made continuous for the full length of the weld.
...kinda hard to get around the splice in the backing ring, IMHO.
edit: I know you are working to D1.1, but I was looking through D1.5 a few minutes ago, and they spell it out very clear about the continuous backing and how it must pass UT or RT "before" you are allowed to use the backing.