Some industries use UT for pipe welds routinely. One area is in power plants for inservice inspection. Especially Nuclear Plants.
Another area where UT is widely being used lately is pipelines where mechanized welding is used. Particulary if a narrow weld groove is used with GMAW welding. The steep angle of the weld prep makes it difficult if not impossible to detect much of the lack of sidewall fusion. Whereas, Automated UT (AUT) or compterized UT, using an array of search units focused for various zones in the weld will detect these flaws. Each zone is intended to represent 1 fill. They use a combination of pitch catch, pulse echo, and TOFD search units.
It really depends on your customers requirements. If they decide to go with UT then so be it. Some regions, such as Canada, I believe, use both AUT and x-ray for pipelines.
If you are interested in learning more about this, go to www.ndt.net.
My old UT instructer had several different tranducer shoes that were radiused to fit the od of various pipe sizes. He had them special made in a machine shop from lexan. If I remeber right, he also had a different calibration procedure for each of them.
He was alot better at UT than I'll ever be...
Tim