Feasibility study of applying phased array ultrasonic method to weld inspection of mercury target vessel for spallation neutron source

Wakui, Takashi  ; Wakai, Eiichi  ; Naoe, Takashi   ; Kogawa, Hiroyuki  ; Haga, Katsuhiro  ; Zhou, Y.*; Kobayashi, Akihiko*

A mercury target vessel has been used for the spallation neutron source at J-PARC. It has a complicated multi-layered structure composed of a mercury target and surrounding double-walled water shroud, which is assembled with thin plates (minimum thickness of 3 mm) by welding. Thus, welding inspection during the manufacturing process is important. We investigated the applicability of new ultrasonic inspection, named as phased array ultrasonic method, to improve the accuracy of welding inspection for the mercury target vessel. Experiments and simulations of the phased array ultrasonic method were conducted using3-mm-thick specimen with a fatigue crack. In the case of short crack, the ultrasonic test overestimates the crack length. The difference was small by using sensor with a high frequency, suggesting a possibility of further improvement.