All depends upon which code your job is to.
'ASSUMING' you are dealing with D1.1, look in Clause 6 under the subclauses concerning UT as well as Clause 5 for Fabrication. You should be able to find what you are looking for within those clauses.
Brent
It depends on a few things. And then it depends on a few other things. You didn't mention which AWS code you're working to so the following references are from AWS D1.1-2015. The answers may differ from the likes of D1.5 or D1.8, et al.
If you're probing the extent (depth, as defined by 5.14.5) of a lamination open to a cut surface, acceptance criteria may be found in Table 5.4.
If you've discovered a lamination that interferes with angle beam of a weld, see 6.25.5. There really is no criteria in this case, the goal of the straight beam is simply to ensure 100% of the weld be examined. Determine extent and report location, size, depth.
There may be other considerations depending on the circumstances.