報告書番号

Q10011

タイトル（和文）

超音波を用いた先進的な配管減肉測定法の開発 ー第4報：高周波ガイド波法による局所減肉の検出限界の解明ー

タイトル（英文）

Development of Measuring Method of Pipe Wall Thinning Using Advanced Ultrasonic Techniques Part 4:Clarification of Detectability of Local Wall Thinning by Guided Waves with High Frequency

概要 （図表や脚注は「報告書全文」に掲載しております）

周波数0.5MHz, 1MHz及び2MHzの探触子を用いて平板試験体，小口径試験体及びエルボ試験体に付与した，減肉を模擬した人工欠陥を計測した．その結果，1）平板試験体の場合，深さが肉厚20%の減肉が検出限界であること，（2）小口径配管試験体の外面に付与した減肉の場合，深さ20%以上の減肉を測定距離3m以上でも容易に検出できたこと，及び（3）エルボ配管試験体の背側付近の内面に付与した減肉の場合，深さが肉厚22%の減肉が検出限界であることを明らかにした．また，周波数2MHzのフェーズドアレイ探触子を利用して，平板試験体の深さの異なる減肉を計測した．その結果，減肉深さの変化に従って，屈折角に対する減肉エコーの強さの依存性も変化することに着眼し，探触子の接触状態によらず減肉深さを推定可能な方法を考案した．

概要 （英文）

The detectability of guided waves with high frequency for local wall thinning has been investigated. Variable angle beam probes with different frequencies were used to detect artificial defects modeling local wall thinning in plate, small size pipe and elbow specimens. For plate and elbow specimens, defects are introduced in inner surfaces, but outer surfaces for small size pipe specimens. Measurement results show (1) it is difficult to detect a defect whose depth is smaller than 20% of wall thickness in plate specimens, (2) it is possible to detect a defect whose depth is larger than 20% of wall thickness with a measurement distance of 3.5 m in small size pipe specimens, and (3) it is difficult to detect a defect whose depth is smaller than 23% of wall thickness for elbow specimens. After a defect has been detected in plate specimen, a method is proposed to determine defect depth by means of the dependence of defect echo on refraction angle. In order to improve measurement efficiency, phased array technique is more favorable. Measurement results show that it is possible to determine defect depth using the dependency of defect echo on refraction angle. In particular, the center of defect echo over refraction angle increases with the increase of defect depth.

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