in the 20th edition of the 1104 and go to chapter 9 Acceptance Standards for Nondestructive Testing has all the answers you are looking for hope this helps
This related to your design.
I do not thnk that you could find in API 1104 the perecentages of NDT.
in normal practice in all pipelines all joints will inspected with 100 X or gamma ray and for further inspection mabe UT is used