Unlike ASME construction codes, AWS welding codes do not specify anything other than visual examination for the majority of the work. The need to incorporate other NDT, such as UT or RT, is at the discression of the engineer or owner. When additional NDT is needed, it should be included in the project specification and on the drawings.
If NDT is imposed after the project has been awarded, both the cost of NDT, additional preparation, handling, and repairs are born by the owner (not the contractor) unless a case for gross nonconformance can be proven.
There is a paragraph that permits the use of UT in lieu of RT for tubular joints (which must be examined) that are welded from one side without backing.
Best regards - Al