I'm hoping some of the other UT folks will chime in here, I'm not familiar with the process, but have seen video of pipe at the pipe mfg being scanned by UT which consisted of several probes around the perimeter with water squirters to serve as the coupling and this arrangement is fixed while the pipe is being flown through at a high rate of speed. The system actually has spray paint that paints the rejectable spots that have signals strong enough to break the gates set up by the UT operator or what ever parameters that were required.
John Wright
PS, Is there a way to buy your pipe from a mfg that already has the UT done prior to you purchasing it? They could furnish the UT reports to maintain in your files.
edit: added a couple links :
http://www.unicorn-automation.co.uk/Theory.htm
http://www.usultratek.com/products/mtscan.htm