Ultrasonic imaging of stress corrosion crack formed in high temperature pressurized water using subharmonic phased array

Evaluation of Closed Stress Corrosion Cracks in Ni-Based Alloy Weld Metal Using Subharmonic Phased Array

“…The present method has further applications. Although the NBAWM was investigated in this study, SCCs have been generated in other materials such as stainless steel 1,22,32) and low alloy steel 34,35) in nuclear power plants. This method can also be applied to these materials.…”

“…SCCs have been generated at various positions depending on the types of alloys used. In the weld metal of AISI 304 1) and 316L 2) stainless steel, it is well known that SCCs are generated in the heat-affected zone. On the other hand, in Ni-based alloy weld metal (NBAWM), SCCs are generated in the weld metal.…”

“…However, subharmonic waves have a higher signal-to-noise ratio than superharmonic ones because the attenuation of subharmonic waves with half frequency of the input wave is much lower than that of the superharmonic ones. Thus far, we have developed a novel imaging method, namely, the subharmonic phased array for crack evaluation (SPACE), 1,[17][18][19][20][21][22] on the basis of subharmonic waves and a phased array algorithm with frequency filtering. We demonstrated its performance in closed fatigue cracks [17][18][19][20] made of aluminum alloy and stainless steel and SCCs 1,18,21,22) made of stainless steel.…”

“…Thus far, we have developed a novel imaging method, namely, the subharmonic phased array for crack evaluation (SPACE), 1,[17][18][19][20][21][22] on the basis of subharmonic waves and a phased array algorithm with frequency filtering. We demonstrated its performance in closed fatigue cracks [17][18][19][20] made of aluminum alloy and stainless steel and SCCs 1,18,21,22) made of stainless steel. In the normal SPACE, we used a LiNbO 3 single-crystal transmitter for generating large short-burst waves and an array transducer as a receiver for focusing on reception.…”

“…Recently, we have developed a single-array SPACE using an array transducer for emission and reception, and verified the single-array SPACE in a realistic closed SCC in a weld. 22) For the application of new inspection methods to actual plants and training/educating of inspection engineers, realistic closed SCCs similar to those in actual nuclear power plants are required. General SCC formation methods are shown in Table I.…”