A new non-destructive examination technique using phased-array ultrasonics can detect flaws in dissimilar metal welds such as those on PWR vessel head penetrations, according to Frank Ammirato, senior technical manager of NDE Technology at the Electric Power Research Institute (EPRI).
Ammirato said that the phased-array ultrasonic testing technique, adapted from medical imaging, would reduce the time needed to inspect welds on a PWR main coolant pipe from an entire shift to "five minutes or less." The phased-array technique involves packaging a number of very small probe elements - a typical package contains 16 elements - and timing the excitation sequence of the transducers to send ultrasonic signals into the material at very short intervals. The techniques developed by the medical industry involve timing beams in milliseconds rather than seconds.
Tests with the new technique have shown that a phased-array UT probe, because of its highly focused beam, can scan dissimilar metal welds with a single pass, even in places with difficult access, such as reactor pressure vessel head penetration welds.