As LM says the geometry of sat-on weldolets precludes rigorous NDT examination by RT or UT. In common UT parlance (just about)anything can be UT'ed but a comprehensive scan plan will reveal the test limitations.
The quality of either RT or UT examination of weldolets will be greatly dependent on the quality of the NDT service company or department utilised, but only so much can be done to overcome "difficult" geometries.
Careful process control to an approved welding procedure combined with stage penetrant or magnetic particle inspection including final inspection should be sufficient to ensure weld quality.
