Yoshiaki Nagashima

Fundamental study of molten pool depth measurement method using an ultrasonic phased array system

The molten pool depth measurement method using an ultrasonic phased array system has been developed. The molten pool depth distribution is evaluated by comparing the times taken by the ultrasonic wave to propagate through a molten pool and a solid-phase and through only the solid-phase near the molten pool. Maximum molten pool depths on a flat type-304 stainless-steel plate, formed with a gas tungsten arc welding machine for different welding currents from 70 to 150 A, were derived within an error of ±0.5 mm.

EVALUATION FOR DEFECT DETECTION OVER BENDING ZONE IN PIPING BY GUIDED WAVE

Guided wave inspection technique is effective as detecting defects like corrosion in piping. Effectiveness to the straight parts in piping by the guided wave inspection has been clarified by many researches. The inspection performance using guided wave decreases due to the unwanted wave when there is a bend part in the inspection area. On above motivation, the inspection performance could be improved if the guided wave was transmitted from many circumferentially‐set sensors based on the same principle as for phased‐array methods. Then, the validity of phased array methods using the guided wave technique was confirmed by the following experiments using a piping with bend. The delayed pulse by phased‐array methods was set from the reflected wave which was transmitted from a local defect, and it was calculated based on time reversal theory. This transmission wave was confirmed by one experiment using the guided wave focused over the bend zone. Thus, the unwanted wave caused in the bend zone could be suppress...

DEFECT SIZING METHOD USING ULTRASONIC GUIDED WAVES IN PIPES

This paper presents a defect‐sizing method using swept‐frequency guided waves. In this technique, reflection coefficients of multiple frequencies were measured, and the coefficients were compared with the 3‐D analysis result that was calculated by integration of reflection waves from divided calculation‐regions that had different characteristic acoustical impedances. The effectiveness of the method was evaluated experimentally using torsional mode guided waves that propagated in pipe specimens. The experimental results were in good agreement with analysis results.