Masahiro Miki

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...

Approximate Evaluation of Acoustical Focal Beams by Phased Array Probes for Austenitic Weld Inspections

Phased array techniques are capable of the sensitive detection and precise sizing of flaws or cracks in components of nuclear power plants by using arbitrary focal beams with various depths, positions and angles. Aquantitative investigation of these focal beams is essential for the optimization of array probes, especially for austenitic weld inspection, in order to improve the detectability, sizing accuracy, and signal‐to‐noise ratio using these beams. In the present work, focal beams generated by phased array probes are calculated based on the Fresnel‐Kirchhoff diffraction integral (FKDI) method, and an approximation formula between the actual focal depth and optical focal depth is proposed as an extension of the theory for conventional spherically focusing probes. The validity of the approximation formula for the array probes is confirmed by a comparison with simulation data using the FKDI method, and the experimental data.

Experimental Study on Acoustic Energy Absorbers to Suppress Acoustic Resonance in Tube Bundles of Boiler Plants

The present paper deals with acoustic resonance in tube bundles which occurred in actual boiler plants. A practical method to suppress the resonant noise is proposed based on scale model tests. In those experiments, besides the transverse modes which are relatively well-known, longitudinal modes which are known to be difficult to suppress, were realized. The relation of both kinds of acoustic modes to vortex shedding frequency was clarified. In the following step, a design method of the acoustic energy absorbers is proposed based on the feedback system stability theory. According to this theory, acoustic energy absorbers were equipped in the duct of the test model, and remarkable increase of the critical flow velocity was confirmed for both types of resonant mode. Based on these results, this method was applied to the actual boiler plants and it was confirmed that the proposed method is the effective countermeasure for both types of acoustic resonant modes.Copyright

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.