Re: Radiographic Examination of Weld in Pipes
The surface you describe is (or used to be!) called a counterbore. It has lots of benefits and few drawbacks, except for the machining costs...
1. Machining an identical counterbore on both joining pipes should prevent root-misalignment. This is leads to a more easily welded root-run, with less likelhood of root defects.
2. The counterbore provides uniform geometry on each side of the root so that radiography (and ultrasonic) inspection can more readily differentiate real defects from false geometric indications.
3. The counterbore reduces the included-angle at each root edge, and also distributes stresses adjacent to the root over a larger area thus minimising the risk of cracking and/or stress corrosion in this critical area.
Hope this helps.