報告書番号

Q05006

タイトル（和文）

先進的な超音波方法を用いた配管の減肉測定法の開発 -第1報：ガイド波及び電磁超音波探触子を用いた測定システムの開発-

タイトル（英文）

Development of Measuring Method of Pipe Wall Thinning Using Advanced Ultrasonic TechniquesPart 1: Development of Measurement Systems Based on Guided Waves and Electromagnetic Acoustic Transducers

概要 （図表や脚注は「報告書全文」に掲載しております）

ガイド波による広域測定方法に用いる周波数0.35MHzの斜角探触子を設計・製作し，局部減肉を模擬した欠陥を有する厚さ10mmの試験体におけるガイド波の送受信を行った．実験結果から，1) A0モードのガイドは励起され，1m以上の距離を伝搬することができること，2)深さが試験体厚さの20％以上の減肉を検出でき，2%以内の誤差で減肉の位置を推定できること，3)反射波の振幅比は，減肉深さに応じて変化すること, 4)波が伝搬する方向の欠陥寸法がその振幅比に影響を及ぼすことが明らかになった．同時に減肉深さを高精度に測定できる接触媒質を不要する電磁超音波探触子（EMAT）を開発した．ステンレス，アルミ及び低合金鋼の試験体によって検証した結果，1)電気ノイズを遮蔽することにより，EMATのSN比は遮蔽のない場合に比べてSN比を0.8から7.2へと大幅に改善することができた．2)EMATによる試験体の厚さはRMS誤差が0.09であり，圧電型の探触子での測定値及び実測値と良く一致することが判った．3)試験体に対して1mmのリフトオフがあっても試験体の肉厚測定に影響しないことが明らかになった．

概要 （英文）

It is strongly expected to develop a method which can measure pipe wall thinning efficiently. In this report, one measurement system is developed based on guided waves, which can measure wall thinning over a wide area from once measurement at a position. A broad band variable oblique transducer with a peak frequency of 0.35 MHz is developed to generate guided waves. This system is verified by a stainless steel specimen with a thickness of 10 mm in which 5 artificial defects with various depths are introduced to model wall thinning. Experimental results show 1) A0 mode guided wave is excited as a prediction and it can propagate more than 1m, 2) it is probable to detect defects whose depth is not less than 20% of wall thickness and deduce its location with an error of less than of 2% by reflected waves from defects, and 3) the amplitude ratio of reflected waves from defects to that from specimen end rises with the increase of defect depth. However it is difficult to determine defect depth accurately just from the amplitude ratio, because it is also related to defect length. Therefore another measure system is developed based on electromagnetic acoustic transducers (EMAT), which can measure defect depth accurately and efficiently because it is couplant-free. An EMAT prototype is fabricated, whose SN ratio rises from 0.8 to 7.2 by means of electrical noise shield. Its performance is verified by stainless steel, aluminum and low-alloy steel specimens. The verification shows that the measured thicknesses of various specimens by EMAT are in good agreement with actual ones with a RMS of 0.09. And EMAT has almost the same accuracy with piezoelectric transducers. Moreover, back wall echoes can be detected by EMAT even with a lift off of 1mm, which means that it is possible to measure wall thickness with a scale oxide or coal ash slag whose thickness is less than 1mm.

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