JP3653785B2 - C-scan ultrasonic flaw detection method and apparatus - Google Patents

C-scan ultrasonic flaw detection method and apparatus Download PDF

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JP3653785B2
JP3653785B2 JP10500595A JP10500595A JP3653785B2 JP 3653785 B2 JP3653785 B2 JP 3653785B2 JP 10500595 A JP10500595 A JP 10500595A JP 10500595 A JP10500595 A JP 10500595A JP 3653785 B2 JP3653785 B2 JP 3653785B2
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ultrasonic
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JPH08304352A (en
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一 高田
文彦 市川
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JFE Steel Corp
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JFE Steel Corp
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Description

【0001】
【産業上の利用分野】
本発明は、Cスキャン超音波探傷方法および装置に係り、特に圧延金属板の切出しサンプルのなかの10〜 100μm 程度の内部欠陥の検出に用いるのに好適なCスキャン超音波探傷方法および装置に関するものである。
【0002】
【従来の技術】
近年、自動車、缶などの素材となる薄鋼板は、軽量化、素材コスト削減のため、薄肉化が進むと共に、部品点数を削減して製作コストを低減するため、プレス、絞り等の加工において素材の著しい変形を伴う強い加工が施されるようになっている。鋼板に強い加工を施すとき、変形の著しい部分に非金属介在物等からなる内部欠陥が存在すると割れが発生するが、鋼板の肉厚が薄いほど内部欠陥による割れの発生は顕著となり、かつ、割れの原因となる内部欠陥のサイズも微小化する。また欠陥の形態と割れの発生にも関係があり、欠陥形態として球状の単体、一方向に伸延した単体、微小球状欠陥の集合体などがあるが、それぞれによって割れの発生しやすさには違いがみられる。また、サワーガス用のラインパイプに用いられる厚鋼板など使用条件の厳しい製品も増加し、10μm 程度の大きさの微小介在物でも水素誘起割れの原因となり有害とされ、欠陥形態によっても水素誘起割れの発生しやすさは相違する。このようなことから、前記した鋼板では内部欠陥を極力少なくすること、欠陥形態を割れの発生しにくいものとすることが要求され、製品の内部欠陥の発生レベルおよびその形態を微小欠陥まで含め評価することが必要になっている。
【0003】
このような鋼板の内部欠陥検出およびその形態の評価手段として、製品の一部をサンプルとして切出し、このサンプルのなかの内部欠陥をCスキャン超音波探傷装置と称される装置を用いて探傷することが広く用いられてきた。図9に従来のCスキャン超音波探傷装置による探傷法を示す。
すなわち、溶媒液中に浸漬された被検査板101 の上方の点集束型超音波送受信子102 は、コントローラ114 の信号によって移動する走査装置104 によって走査され、かつ電気パルス発生器116 から一定時間間隔で送信される電気パルスを超音波に変換し、被検査板101 に向けて略垂直に超音波ビーム103 を送信するとともに、被検査板101 の内部欠陥および表面からの反射波を受信し、電気信号に変換する。受信された信号は受信増幅器111 で増幅され、ゲート回路112 で欠陥からの反射波が抽出される。抽出された信号はピーク値検出回路113 に送られ、ここで欠陥反射波の振幅が検出され、コントローラ114 に送信される。コントローラ114 は前記欠陥反射波の振幅と前記走査装置104 の位置信号とを表示器115 に出力し、表示器115 は内部欠陥の2次元分布図を表示し、このようにして内部欠陥を検出する。
【0004】
このような1つの点集束型超音波送受信子102 で被検査板101 に略垂直に超音波を送信し、被検査板101 からの反射波を受信して欠陥を検出する方法では、超音波ビームが表面に入射したとき、大振幅であり、かつ、残響がしばらく持続する表面エコーが発生するため、表面近傍の欠陥反射波が前記表面エコーあるいはその残響と重なって存在が識別できなくなり、表面近傍の欠陥を検出することができないという問題があった。
【0005】
また、Cスキャン超音波探傷方法あるいは装置に関する従来技術としては、高周波の超音波を用いる特開昭59−17153 号公報や特開平5−333000号公報などが挙げられる。前者は30〜100MHz、後者は15〜50MHz の何れも高周波の超音波を用いビーム径を小さくすることにより、分解能を向上させ、内部欠陥の検出能を向上させたものである。また、後者は、超音波周波数、焦点距離および被検査板と焦点位置との関係を最適化することにより、表面近傍に存在する微小欠陥の検出を確実にし、探傷結果の定量的評価を可能としたものである。
【0006】
【発明が解決しようとする課題】
しかし、特開昭59−17153 号や特開平5−333000号に記載のように、高周波の超音波を用い焦点のビーム径を小さくすると、一方では、焦点深度が低下することが一般に知られている(例えば、R.Saglio et al "THE USE OF FOCUSED PROBES FOR DETECTION, IMAGING, AND SIZING OF FLAWS", in Proc. First Intrenational Symposium on Ultrasonic Materials Characterization-Gaithersburg Md.(1978)参照)。
【0007】
なお、焦点深度とは、例えば、送受信する超音波ビームの中心軸上での音圧が、焦点位置の音圧に比べ−6dB以内である範囲の長さのことであり、焦点深度が大きいほど被検査板の板厚の方向に広い範囲にわたって内部欠陥を検出することが可能である。前記文献によれば、超音波の周波数をf、速度をC、超音波送受信子に内蔵されている振動子の径をD、焦点距離をFとしたとき、焦点位置での超音波ビーム径dおよび焦点深度Lはそれぞれ(1) ,(2) 式のように表される。
【0008】
d=(C/f)×(F/D) …………………(1)
L=(C/f)×(F/D)2 …………………(2)
(1) 式から、焦点位置での超音波ビーム径dを小さくするために、周波数fを高くすると、(2) 式より焦点深度Lが小さくなることがわかる。このため、高周波超音波を用いた探傷では、被検査板の板厚方向の全断面を均一な感度で探傷することが難しく、焦点位置以外の深さに存在する欠陥の検出能は大きく低下し、検出洩れが多発する欠点がある。このため欠陥を板厚方向にわたり洩れなく検出するためには、焦点位置を変更して、必要回数探傷を実施し直す必要があり、探傷に時間がかかる欠点があった。
【0009】
また、前出特開平5−333000号では、表面直下の不感帯が低減されているとはいえ、皆無とは言えず、垂直探傷法によるCスキャン超音波探傷には依然として表面近傍に存在する微小欠陥が検出できないという問題が残されている。
ところで、本発明者らは、上記問題点を解消すべく、既に特願平6−7176号において、被検査板を挟んでラインフォーカス型超音波送信センサと1次元アレー型超音波センサとを対向配置し、該送信センサから帯状超音波ビームを被検査板に向けてほぼ垂直に送信し、被検査板に入射した超音波によって生起された内部欠陥からの反射波を前記1次元アレー型超音波受信センサによって受信し、受信された超音波を増幅し、反射波のみを抽出した後に所定の振幅に達した反射波の有無を検出することを特徴とする超音波探傷方法および装置を提案し、これによって表面直下での不感帯なしに、全厚にわたり一度に一定幅の線状の領域を探傷することが可能になった。
【0010】
しかしながら、この方法では、微小な欠陥までその有無は明瞭にわかるものの、送受信する超音波が2次元的に集束していないため、幅方向の分解能が低く、欠陥の形態までは判別できない問題があった。
この発明は、前記従来技術の問題点を解消すべくなされたもので、Cスキャン超音波探傷において、被検査板の表面近くでの不感帯がなく、1回の走査で板厚方向全断面の探傷ができ、微細な内部欠陥の形態まで検出することが可能なCスキャン超音波探傷方法および装置を提供することを目的とする。
【0011】
【課題を解決するための手段】
本発明は、液中に浸漬された被検査板を挟んで、点集束型の超音波送信子と点集束型の超音波受信子とを対向配置して走査するとともに、前記超音波送信子から点集束した超音波を被検査板内に略垂直に入射し、前記超音波が内部欠陥の上側で反射して被検査板の表面に向かい、表面で反射して、裏面から液中に伝播し受信される反射波と、前記超音波が最初に被検査板の裏面で反射し、内部欠陥に向かい、内部欠陥の下側で反射した後、裏面から液中に伝播し受信される反射波の両方を前記超音波受信子で受信し、該受信信号を増幅した信号から前記内部欠陥からの両方の反射波の信号を抽出し、該抽出された信号に基づいて被検査板の内部欠陥を検出することを特徴とするCスキャン超音波探傷方法である。
【0012】
なお、前記内部欠陥からの反射波の信号を、超音波の透過波が前記超音波受信子に到達する時刻をτ0 とし、直接透過波の到達から該透過波の残響が終了するまでの時間をτ D とし、該超音波が被検査板の厚さ方向に伝播するのに要する時間をτ1 したとき、時刻(τ0 τ D )以後で、かつ(τ0 +2×τ1 )以前の受信信号から抽出するのがよい。
【0013】
さらに、前記超音波送信子と前記超音波受信子の焦点距離を比較し、該焦点距離が異なる場合は大きい方の焦点距離をFL とし、または前記焦点距離が等しい場合はその焦点距離をFL とし、被検査板の板厚をtとしたとき、前記超音波送信子と前記超音波受信子との間の距離LS が下記式を満足するように両者を配置するのがよい。
【0014】
S ≦FL −{(CM /CL )−1}×t+FL ×5/38
ただし、CM ;被検査材中での超音波の伝播速度、CL ;液中での超音波の伝播速度。
また、本発明は、被検査板の表面に超音波を略垂直に送信する点集束型の超音波送信子と、被検査板を挟んで前記点集束型超音波送信子と対向する位置に配置し、前記超音波が内部欠陥の上側で反射して被検査板の表面に向かい、表面で反射して、裏面から液中に伝播し受信される反射波と、前記超音波が最初に被検査板の裏面で反射し、内部欠陥に向かい、内部欠陥の下側で反射した後、裏面から液中に伝播し受信される反射波の両方を受信する点集束型の超音波受信子と、前記超音波送信子と前記超音波受信子とを被検査板を挟んで支持する支持アームと、該支持アームを走査する走査装置と、前記超音波送信子に内蔵された圧電振動子に送信する電気パルスを発生する電気パルス発生装置と、受信信号を増幅する増幅装置と、増幅された信号から内部欠陥からの両方の反射波の信号を抽出するゲート手段と、を備えたことを特徴とするCスキャン超音波探傷装置である。
なお、前記ゲート手段は、前記内部欠陥からの反射波の信号を、超音波の透過波が前記超音波受信子に到達する時刻をτ0 とし、直接透過波の到達から該透過波の残響が終了するまでの時間をτ D とし、該超音波が被検査板の厚さ方向に伝播するのに要する時間をτ1 したとき、時刻(τ0 τ D )以後で、かつ(τ0 +2×τ1 )以前の受信信号から抽出するように設定され、前記超音波送信子と前記超音波受信子との間の距離LS は、前記超音波送信子と前記超音波受信子の焦点距離を比較して、該焦点距離が異なる場合は大きい方の焦点距離をFL とし、または前記焦点距離が等しい場合はその焦点距離をFL とし、被検査板の板厚をtとして、下記式を満足するように両者を配置するのがよい。
S ≦FL −{(CM /CL )−1}×t+FL ×5/38
ただし、CM ;被検査材中での超音波の伝播速度、CL ;液中での超音波の伝播速度。
【0015】
【作用】
本発明によれば、液中に浸漬された被検査板を挟んで、点集束型の超音波送信子と点集束型の超音波受信子とを対向配置して走査するとともに、前記超音波送信子から点集束した超音波を被検査板内に略垂直に入射し、前記超音波の透過波と、前記超音波によって生起された内部欠陥からの反射波とを前記超音波受信子で受信し、該受信信号を増幅した信号から前記内部欠陥からの反射波の信号を抽出し、該抽出された信号に基づいて被検査板の内部欠陥を検出するようにしたので、被検査板表裏面近傍での内部欠陥であっても不感帯なく、全断面にわたり均一な感度で検出することが可能である。
【0016】
【実施例】
以下、本発明の実施例を図を用いて詳細に説明する。図1は本発明の一実施例の構成を示す一部斜視図を含むブロック線図である。
図1において、11は点集束型超音波送信子(以下、単に超音波送信子という)、12は点集束型超音波受信子(以下、単に超音波受信子という)で、被検査板13を挟んで対向配置される。14は超音波送信子11、超音波受信子12を支持するコの字状の支持アームである。なお、超音波送信子11および超音波受信子12と被検査板13との間には、超音波伝播媒質として好適に使用される水が介在されている。15は支持アーム14を走査する走査装置である。
【0017】
16は内蔵したクロック回路(図示せず)から、一定の時間間隔で電気パルスを超音波送信子11に内蔵した圧電振動子(図示せず)に送信する電気パルス発生器である。17は超音波受信子12からの信号を受信する受信増幅器、18はゲート回路、19はピーク値検出回路、20はコントローラ、21は表示器である。
超音波送信子11は、電気パルス発生器16から一定の時間間隔で送信された電気パルスを超音波に変換し、水を介して被検査板13に略垂直に超音波送信ビーム11Aを送信する。超音波受信子12は、被検査板13に入射した超音波によって生起された内部欠陥からの反射波を含む超音波受信ビーム12Aを水を介して受信する。そして、支持アーム14はコントローラ20からの信号で駆動される走査装置15によって走査され、これによって対向配置された超音波送信子11と超音波受信子12を被検査板13の面を方形走査し、その内部欠陥を探傷する。
【0018】
受信増幅器17で増幅された受信信号はゲート回路18で、内部欠陥からの反射波を前記受信信号から抽出する。この抽出された信号はピーク値検出回路19に送信され、ピーク値検出回路19では前記反射波の振幅を検出して、アナログ量またはデイジタル量としてコントローラ20に出力する。コントローラ20は前記反射波の振幅と走査装置15の位置信号とを表示器21に出力し、内部欠陥の2次元分布図を作成する。
【0019】
ここで、ゲート回路18の機能について、図2を用いて詳しく説明する。
まず、被検査板13の厚みをtとし、内部欠陥22が被検査板13の表面13aの近く、すなわち表面13aからの距離dがt/2以下に存在する場合を例にすると、超音波送信子11から送信された超音波送信ビーム11Aは、液中を伝播して被検査板13の表面13aに達すると、被検査板13の内部に入射してその内部に伝播する。
【0020】
このとき、被検査板13の内部に伝播した超音波はその一部が直進し、直接透過波30として超音波受信子12で受信される。また、内部欠陥22が超音波の伝播経路に存在すると、最初にこの内部欠陥22の上側で1回反射して表面13aに向かい、表面13aで反射して、被検査板13の厚さt内を 0.5往復伝播し、裏面13bから液中に伝播し受信される反射波31と、最初に被検査板の厚さt内を 0.5往復伝播し裏面13bで反射し、内部欠陥22に向かい、内部欠陥22の下側で1回反射した後、裏面13bから液中に伝播し受信される反射波32とが生起される。
【0021】
なお、これらの反射波31および32は、さらに裏面13bで1回以上反射し、被検査板13の厚さt内を1往復以上して、超音波受信子12に受信される反射波が生起されるが、ここでは図示を省略した。このように、本発明は受信し増幅した信号から、前記した内部欠陥からの反射波の信号を抽出して、それに基づき内部欠陥を検出する。内部欠陥22が被検査板13の表面13aからの距離dがt/2以下に存在する場合は、反射波32が反射波31よりも遅れて超音波受信子12に到達する。
【0022】
さらに、超音波受信子12で受信される信号の時間的推移を図3で説明する。この図において、τ0 は被検査板13の厚さt内を 0.5往復伝播した直接透過波30が超音波受信子12に到達した時刻、τ1 は超音波が被検査板13の厚さt内を 0.5往復伝播するのに要する時間である。なお、33は被検査板13の厚さt内を0.5 往復伝播し、さらに被検査板13を1往復した透過波の信号である。
【0023】
このように、反射波32の伝播距離が反射波31の伝播距離よりも大きいために、反射波32が反射波31よりも遅れて受信される。この図より、内部欠陥22による反射波32は、被検査板13の厚さt内を 0.5往復伝播した前記直接透過波30が超音波受信子12に到達した時刻τ0 から超音波が被検査板13の厚さt内を0.5 往復伝播するのに要する時間τ1 経過した以後であって、直接透過波30による不感帯領域から外れたところに現れ、かつ時刻τ0 から(2×τ1 )経過以前であって、透過波33よりも早い時間に現れる。また、内部欠陥22の位置が表面13aに近くなるほどτ2 (τ2 は超音波が被検査板13中の内部欠陥22までの距離dを1往復する、すなわち距離2dだけ伝播するのに要する時間)が小さくなるが、透過波33よりも早い時間に現れる。そのため、内部欠陥22が表面13aの直下に存在しても、内部欠陥22による反射波32を明瞭に識別して抽出できるので、これを抽出して内部欠陥22を検出するのが好ましい。
【0024】
内部欠陥22による反射波32の現れる時間τは下記式(3) で表される。
(τ0 +τ1 )≦τ≦(τ0 +2×τ1 ) ………………(3)
なお、直接透過波30の到達から該透過波の残響が終了するまでの時間をτD (図3参照)としたとき、時刻(τ0 +τD )以後で、かつ、(τ0 +2×τ1 )以前に受信した信号を抽出するようにすれば、反射波31および32の両方を検出することが可能である。
【0025】
以上の説明は、内部欠陥が表面の近くに存在する場合についてであるが、次に裏面13bの近く、すなわち、表面13aからの距離dがt/2以上の位置に存在する場合について説明する。この場合、図2と異なり内部欠陥22による反射波31の伝播距離が反射波32の伝播距離よりも大きくなるので、反射波31が遅れて受信される。この反射波31が前述したと同様に、直接透過波30による不感帯領域から外れたところに現れ、また、透過波33よりも早い時間に現れる。そのため、内部欠陥22が裏面13bの直下に存在しても、内部欠陥22による反射波31を明瞭に識別して抽出できるので、内部欠陥22が検出できて好ましい。
【0026】
これまで説明したように、被検査板13を 0.5往復伝播した直接透過波30と、さらに被検査板13を1往復伝播した透過波33との間に現れる伝播距離が長い方の内部欠陥からの反射波を抽出するのが、ノイズとなる雑エコー成分が小さいのでより好ましいが、超音波が被検査板13を 0.5往復伝播し、さらに被検査板13を1往復以上の整数回往復伝播した透過波と該透過波よりもさらに被検査板13を1往復伝播した透過波との間に現れる伝播距離が長い方の内部欠陥からの反射波を抽出するようにしてもよい。
【0027】
本発明では2次元的に集束した点集束型の超音波送信子と点集束型の超音波受信子を用い、超音波送信子と超音波受信子を被検査板に対して相対的に走査しているので、幅方向の分解能が高く、内部欠陥の形態を検出することが可能となった。
さらに、本発明は図4に示すように、超音波送信子11からの超音波送信ビーム11Aが超音波受信子12の表面で焦点Fを結ぶようにし、かつ、超音波受信子12の超音波受信ビーム12Aの焦点Gは超音波送信子11の表面となるようにするとよい。このようにすると、超音波送信子11から送信される超音波送信ビーム11Aの強度は、被検査板13の表面に近いほど低くなるので、そこに存在する内部欠陥からの反射波の強度は小さくなるが、一方、超音波受信子12の受信効率は焦点Fに近い方が大きいので、被検査板13の表面に近いほど大きくなる。そのため、超音波受信子12で受信された内部欠陥からの反射波の強度は両者の効果が相殺して、内部欠陥の存在する位置が変化してもほぼ一定とすることができ、厚さ方向にわたって均一な感度とすることができるからである。
【0028】
図5は、本発明法と従来法で人工欠陥を検出した結果を示したものである。すなわち、本発明法は前出図4に示したような焦点F,Gが結ぶように配置した周波数25MHz 、水中焦点距離38mmの超音波送信子11および超音波受信子12を用いて測定したものであり、また従来法は前出図9に示したように、一方向から一つの点集束型の周波数25MHz 、水中焦点距離38mmの超音波送受信子で超音波を送信し、受信する方法で測定したものである。なお、人工欠陥は板厚5.5mm の被検査板13に、表面からの距離を変化させて、厚さ方向と直角に0.2 mmφの横ドリル孔を開けて製作したものである。
【0029】
この図から、本発明法は、従来法に比較して反射波の振幅が欠陥の表面からの距離に依らず一定であり、格段に優れた焦点深さを有し、厚さ方向にわたって均一な感度で検出できることがわかる。
次に、点集束型の超音波送信子11、点集束型の超音波受信子12および被検査板13の位置関係について、実験データに基づいて詳細に説明する。すなわち、図6は、前出図4に示したように焦点F,Gが結ぶように超音波送信子11と超音波受信子12を配置し、そのときの超音波送信子11と超音波受信子12間の距離をLS とし、厚さtが4.5mm である被検査板13を超音波送信子11と超音波受信子12の間で移動して超音波受信子12と被検査板13の間の距離L2 を変化させたときの、被検査板13の内部欠陥からの反射波の振幅およびS/Nを測定したものである。用いた超音波送信子11および超音波受信子12は周波数25MHz 、水中焦点距離38mmである。これより、被検査板13は超音波送信子11と超音波受信子12間のどの位置においても、内部欠陥による反射波の振幅およびS/Nはほとんど変化がない。すなわち、被検査板13は超音波送信子11と超音波受信子12間のどの位置においてもよいことがわかる。
【0030】
いま、超音波送信子11と超音波受信子12の焦点距離が等しい場合、すなわち、前出図4に示したように、超音波送信ビーム11Aの焦点Fが超音波受信子12の表面に一致し、超音波受信ビーム12Aの焦点Gが超音波送信子11の表面と一致するように超音波送信子11と超音波受信子12を配置したとき、超音波送信子11と超音波受信子12との間の距離をLS0とすると、この距離LS0は下記(4) 式のように表される。
【0031】
S0=FL −{(CM /CL )−1}×t ………………(4)
ただし、FL ;点集束型の超音波送信子11の焦点距離、または点集束型の超音波受信子12の焦点距離、t;被検査板の板厚、CM ;被検査材中での超音波の伝播速度、CL ;液中での超音波の伝播速度である。
図7はこのように超音波送信子11と超音波受信子12の焦点距離が等しい場合、距離LS0を基準距離として、水中で超音波送信子11と超音波受信子12との間の距離を変化させ、被検査板の内部欠陥からの反射波の振幅を測定したものである。用いた超音波送信子11および超音波受信子12は周波数;25MHz 、水中焦点距離;38mmであり、被検査板は板厚tが4.5 mmの薄鋼板を用いた。距離LS が基準距離LS0よりも小さいときには反射波の振幅は若干大きいが、距離LS が基準距離LS0よりも大きくなると反射波の振幅は急激に低下することがわかる。反射波の振幅が基準距離LS0の場合よりも3dB以上低下することは、欠陥検出におけるS/Nの低下につながり、好ましくないので、超音波送信子11と超音波受信子12との間の距離LS (mm)は下記(5) 式を満足することが必要である。
【0032】
S ≦LS0+FL ×5/38 ………………(5)
すなわち、
S ≦FL −{(CM /CL )−1}×t+FL ×5/38 …………(6)
として表される。
なお、(6) 式のFL の係数5/38は超音波送信子11および超音波受信子12の焦点距離が38mm以外の場合も考えて、一般化を図ったものである。
【0033】
次に、超音波送信子11の焦点距離と超音波受信子12の焦点距離が等しくないときにも、次のように配置することにより、前出図5および図6に示したものと同様の効果を得ることができる。例えば、超音波送信子11の焦点距離が超音波受信子12の焦点距離よりも大きいときには、超音波送信ビーム11Aの焦点Fが超音波受信子12の表面に一致するように超音波送信子11と超音波受信子12を配置する。このとき、被検査板13を超音波受信ビーム12Aの焦点Gよりも超音波受信子12に近い位置におけば、前出図4を用いて説明したものと同様のことが成立する。また、超音波受信子12の焦点距離が超音波送信子11の焦点距離よりも大きいときには、超音波受信ビーム12Aの焦点Gが超音波送信子11の表面と一致するように超音波送信子11と超音波受信子12を配置する。このとき、被検査板13を超音波送信ビーム11Aの焦点Fよりも超音波送信子11に近い位置におけば、前出図4を用いて説明したものと同様のことが成立する。
【0034】
また、超音波送信子11の焦点距離と超音波受信子12の焦点距離が等しくないときの両者の間隔LS について実験データに基づいて詳細に説明する。いま、超音波送信子11の焦点距離が超音波受信子12の焦点距離よりも大きい場合を例にとって説明する。このとき、大きい方の焦点距離をFL とする。
そこで、超音波送信ビーム11Aの焦点Fが超音波受信子12の表面に一致するように超音波送信子11と超音波受信子12とを配置したとき、超音波送信子11と超音波受信子12との間の距離をLS0とすると、この距離LS0は下記(7) 式のように表される。
【0035】
S0=FL −{(CM /CL )−1}×t ………………(7)
図8はこの距離LS0を基準距離として、水中で超音波送信子11と超音波受信子12との間の距離を変化させ、被検査板の内部欠陥からの反射波の振幅を測定したものである。用いた超音波送信子11は周波数;25MHz 、水中焦点距離;38mmであり、超音波受信子12は周波数;25MHz 、水中焦点距離;25mmである。被検査板は板厚tが4.5 mmの薄鋼板を用いた。
【0036】
前出図7と同様に、距離LS が基準距離LS0よりも小さいときには反射波の振幅は若干大きいが、距離LS が基準距離LS0よりも大きくなると反射波の振幅は急激に低下することがわかる。反射波の振幅が基準距離LS0の場合よりも3dB以上低下することは、欠陥検出におけるS/Nの低下につながり、好ましくないと判断されるため、超音波送信子11と超音波受信子12との間の距離LS (mm)は下記(8) 式を満足することが必要である。
【0037】
S ≦LS0+FL ×5/38 ………………(8)
すなわち、
S ≦FL −{(CM /CL )−1}×t+FL ×5/38 …………(9)
として表される。
なお、(9) 式のFL の係数5/38は超音波送信子11および超音波受信子12の焦点距離が38mm以外の場合も考えて、一般化を図ったものである。
【0038】
次に、超音波受信子12の焦点距離が超音波送信子11の焦点距離が大きい場合について、超音波送信子11として周波数;25MHz 、水中焦点距離;25mmであり、超音波受信子12として周波数;25MHz 、水中焦点距離;38mmのものを用いて実験を行ったところ、図示は省略するが、図8とほぼ同等の結果を得ることができた。したがって、超音波送信子11の焦点距離と超音波受信子12の焦点距離が等しくないときには、大きい方をFL とし、超音波送信子11と超音波受信子12との間の距離LS が前出(9) 式となるように、超音波送信子11と超音波受信子12とを配置すればよい。
【0039】
被検査板13として厚さ1.2 〜5.5 mmの薄鋼板の欠陥探傷を行う際に、本発明法を適用した。このとき用いた超音波送信子11としては周波数25MHz 、水中焦点距離38mmのものを用いて、25MHz の周波数の超音波を送信し、また超音波受信子12としては周波数25MHz 、水中焦点距離38mmのものを用いて探傷した。その結果、欠陥の厚さ方向の位置によらずに、10μm φの超微小欠陥を検出することができた。
【0040】
なお、上記した本実施例においては、超音波送信子11と超音波受信子12を支持アーム14で保持することにより被検査板に対して対向配置された前記超音波送信子と前記超音波受信子を走査するようにしたが、本発明はこれに限るものではなく、逆に被検査板側を走査するように構成してもよいことは、言うまでもない。
【0041】
【発明の効果】
本発明によれば、圧延金属板等の微細な介在物などの内部欠陥を表面の不感帯をなくして、全断面にわたり均一な感度で検出することができ、これによって製品の品質管理および品質そのものの向上に寄与することが可能である。
【図面の簡単な説明】
【図1】本発明の一実施例の構成を示す一部斜視図を含むブロック線図である。
【図2】欠陥からの反射波の伝播経路と位置関係を示す説明図である。
【図3】受信される超音波信号と時間の関係を示す説明図である。
【図4】送信子と受信子の超音波ビームの焦点を示す説明図である。
【図5】欠陥の表面からの距離と反射波の振幅の関係を示す特性図である。
【図6】内部欠陥からの反射波の振幅およびS/Nを示す特性図である。
【図7】内部欠陥からの反射波の振幅を示す特性図である。
【図8】内部欠陥からの反射波の振幅を示す特性図である。
【図9】従来例の構成を示す一部斜視図を含むブロック線図である。
【符号の説明】
11 超音波送信子(点集束型超音波送信子)
11A 超音波送信ビーム
12 超音波受信子(点集束型超音波受信子)
12A 超音波受信ビーム
13 被検査板
13a 表面
13b 裏面
14 支持アーム
15 走査装置
16 電気パルス発生器
17 受信増幅器
18 ゲート回路
19 ピーク値検出回路
20 コントローラ
21 表示器
22 内部欠陥
30 直接透過波
31, 32 反射波
33 透過波
[0001]
[Industrial application fields]
The present invention relates to a C-scan ultrasonic flaw detection method and apparatus, and more particularly to a C-scan ultrasonic flaw detection method and apparatus suitable for use in detecting an internal defect of about 10 to 100 μm in a cut sample of a rolled metal sheet. It is.
[0002]
[Prior art]
In recent years, thin steel sheets used as materials for automobiles, cans, etc. have been made thinner in order to reduce weight and reduce material costs, and to reduce production costs by reducing the number of parts and materials used in processing such as pressing and drawing. Strong processing with significant deformation of the material is applied. When performing strong processing on the steel sheet, cracks occur if there are internal defects consisting of non-metallic inclusions, etc., in the part where the deformation is significant, but the occurrence of cracks due to internal defects becomes more pronounced as the thickness of the steel sheet is thin, and The size of internal defects that cause cracking is also reduced. There is also a relationship between the form of defects and the occurrence of cracks. Defect forms include spherical single bodies, single bodies that extend in one direction, and aggregates of microspherical defects. Is seen. In addition, products with severe usage conditions such as thick steel plates used in sour gas line pipes are increasing, and even small inclusions with a size of about 10 μm are considered to be harmful and cause hydrogen-induced cracking. Ease of occurrence is different. For this reason, it is required that the above-described steel sheet has as few internal defects as possible, and that the defect form is less likely to be cracked. It is necessary to do.
[0003]
As a means for detecting the internal defect of such a steel sheet and evaluating its form, a part of the product is cut out as a sample, and the internal defect in this sample is detected using a device called a C-scan ultrasonic flaw detector. Has been widely used. FIG. 9 shows a flaw detection method using a conventional C-scan ultrasonic flaw detector.
That is, the point-focusing type ultrasonic transceiver 102 above the inspection plate 101 immersed in the solvent liquid is scanned by the scanning device 104 that is moved by the signal of the controller 114 and is spaced from the electric pulse generator 116 at a constant time interval. The electrical pulse transmitted in step 1 is converted into an ultrasonic wave, and the ultrasonic beam 103 is transmitted substantially vertically toward the inspected plate 101, and the internal defect of the inspected plate 101 and the reflected wave from the surface are received. Convert to signal. The received signal is amplified by the receiving amplifier 111, and the reflected wave from the defect is extracted by the gate circuit 112. The extracted signal is sent to the peak value detection circuit 113, where the amplitude of the defect reflected wave is detected and transmitted to the controller 114. The controller 114 outputs the amplitude of the defect reflected wave and the position signal of the scanning device 104 to the display 115, and the display 115 displays a two-dimensional distribution map of the internal defects, thus detecting the internal defects. .
[0004]
In such a method in which ultrasonic waves are transmitted substantially perpendicularly to the inspected plate 101 by one point-focusing type ultrasonic transmitter / receiver 102 and a reflected wave from the inspected plate 101 is received to detect a defect, an ultrasonic beam is used. When a surface is incident on the surface, a surface echo having a large amplitude and reverberation is generated for a while, so that a defect reflected wave in the vicinity of the surface overlaps the surface echo or the reverberation, and the presence cannot be identified. There was a problem that it was not possible to detect defects.
[0005]
Further, as conventional techniques relating to a C-scan ultrasonic flaw detection method or apparatus, there are JP-A-59-17153 and JP-A-5-333000 which use high-frequency ultrasonic waves. The former is 30 to 100 MHz, and the latter is 15 to 50 MHz, both using high frequency ultrasonic waves and reducing the beam diameter, thereby improving resolution and improving internal defect detection ability. The latter also optimizes the ultrasonic frequency, focal length, and the relationship between the inspected plate and the focal position, thereby ensuring the detection of minute defects existing near the surface and enabling quantitative evaluation of flaw detection results. It is a thing.
[0006]
[Problems to be solved by the invention]
However, as described in JP-A-59-17153 and JP-A-5-333000, it is generally known that when the focal beam diameter is reduced using high-frequency ultrasonic waves, the depth of focus decreases. (See, for example, R. Saglio et al "THE USE OF FOCUSED PROBES FOR DETECTION, IMAGING, AND SIZING OF FLAWS", in Proc. First Intrenational Symposium on Ultrasonic Materials Characterization-Gaithersburg Md. (1978)).
[0007]
The depth of focus is, for example, the length of the range in which the sound pressure on the central axis of the ultrasonic beam to be transmitted and received is within −6 dB compared to the sound pressure at the focus position, and the greater the depth of focus, the greater the depth of focus. It is possible to detect internal defects over a wide range in the direction of the plate thickness of the plate to be inspected. According to the above document, when the frequency of ultrasonic waves is f, the velocity is C, the diameter of the transducer built in the ultrasonic transceiver is D, and the focal length is F, the ultrasonic beam diameter d at the focal position is as follows. And the focal depth L are expressed by the equations (1) and (2), respectively.
[0008]
d = (C / f) × (F / D) (1)
L = (C / f) × (F / D)2                  ………………… (2)
From the equation (1), it can be seen that when the frequency f is increased in order to reduce the ultrasonic beam diameter d at the focal position, the focal depth L is reduced from the equation (2). For this reason, in flaw detection using high-frequency ultrasonic waves, it is difficult to detect the entire cross section in the plate thickness direction of the inspected plate with uniform sensitivity, and the ability to detect defects existing at depths other than the focal position is greatly reduced. There is a drawback in that detection omissions occur frequently. For this reason, in order to detect a defect without omission in the thickness direction, it is necessary to change the focal position and perform the flaw detection as many times as necessary.
[0009]
In the above-mentioned Japanese Patent Application Laid-Open No. 5-333000, although the dead zone directly under the surface is reduced, it cannot be said that there is none, and the fine defect still exists in the vicinity of the surface in the C-scan ultrasonic flaw detection by the vertical flaw detection method. The problem remains that cannot be detected.
By the way, in order to solve the above-mentioned problems, the present inventors have already faced the line focus type ultrasonic transmission sensor and the one-dimensional array type ultrasonic sensor with Japanese Patent Application No. 6-7176 across the board to be inspected. And transmitting a band-like ultrasonic beam from the transmitting sensor toward the inspection plate substantially perpendicularly, and reflecting a reflected wave from an internal defect caused by the ultrasonic wave incident on the inspection plate to the one-dimensional array type ultrasonic wave. Proposing an ultrasonic flaw detection method and apparatus characterized by detecting the presence or absence of a reflected wave that has reached a predetermined amplitude after amplifying the received ultrasonic wave received by a receiving sensor and extracting only the reflected wave, As a result, it became possible to detect a linear region having a constant width all over the thickness without a dead zone immediately below the surface.
[0010]
However, with this method, the presence or absence of a minute defect can be clearly seen, but since the ultrasonic waves to be transmitted and received are not two-dimensionally focused, the resolution in the width direction is low, and there is a problem that the form of the defect cannot be identified. It was.
The present invention has been made to solve the problems of the prior art, and in C-scan ultrasonic flaw detection, there is no dead band near the surface of the plate to be inspected, and flaw detection in the entire cross section in the plate thickness direction in one scan. It is an object of the present invention to provide a C-scan ultrasonic flaw detection method and apparatus capable of detecting even fine internal defect forms.
[0011]
[Means for Solving the Problems]
  The present invention scans a point-focusing type ultrasonic transmitter and a point-focusing type ultrasonic wave receiver facing each other with a test plate immersed in a liquid interposed between the ultrasonic transmitter and the ultrasonic transmitter. Point-focused ultrasonic waves are incident almost perpendicularly into the inspected plate, and the ultrasonic waves are reflected on the upper side of the internal defect and directed to the surface of the inspected plate, reflected on the surface, and propagated from the back surface into the liquid. The reflected wave to be received and the reflected wave that is first reflected on the back surface of the inspection plate, directed to the internal defect, reflected on the lower side of the internal defect, and then propagated into the liquid from the back surface and received.BothFrom the internal defect from the amplified signal.BothA C-scan ultrasonic flaw detection method characterized in that a reflected wave signal is extracted and an internal defect of a plate to be inspected is detected based on the extracted signal.
[0012]
  The signal of the reflected wave from the internal defect is expressed as τ when the transmitted wave of the ultrasonic wave reaches the ultrasonic receiver.0age,The time from the arrival of the directly transmitted wave to the end of the reverberation of the transmitted wave is expressed as τ D age,The time required for the ultrasonic wave to propagate in the thickness direction of the plate to be inspected is τ1WhendidWhenTimes of Day0+τ D ) And after (τ0+ 2 × τ1) It is better to extract from the previous received signal.
[0013]
Further, the focal lengths of the ultrasonic transmitter and the ultrasonic receiver are compared. If the focal lengths are different, the larger focal length is set to F.LOr if the focal lengths are equal, the focal length is FLAnd the distance L between the ultrasonic transmitter and the ultrasonic receiver, where t is the thickness of the plate to be inspectedSAre preferably arranged so that the following equation is satisfied.
[0014]
    LS≦ FL-{(CM/ CL) -1} × t + FL× 5/38
  However, CM; Ultrasonic wave propagation speed in the material to be inspected, CLThe propagation speed of ultrasonic waves in the liquid.
  The present invention also provides a point-focusing ultrasonic transmitter that transmits ultrasonic waves substantially vertically to the surface of the board to be inspected, and a position facing the point-focusing ultrasonic transmitter across the board to be inspected. Then, the ultrasonic wave is reflected on the upper side of the internal defect and directed to the surface of the inspected plate, reflected on the surface, propagated from the back surface into the liquid and received, and the ultrasonic wave is first inspected. Reflected wave that reflects on the back side of the plate, faces the internal defect, reflects on the lower side of the internal defect, then propagates into the liquid from the back side and is receivedBothA point-focusing type ultrasonic receiver, a support arm that supports the ultrasonic transmitter and the ultrasonic receiver with an inspection plate interposed therebetween, a scanning device that scans the support arm, and the ultrasonic An electric pulse generator for generating an electric pulse to be transmitted to a piezoelectric vibrator incorporated in the acoustic wave transmitter, an amplifying device for amplifying a received signal, and an amplified signal from an internal defectBothReflected waveSignalAnd a C-scan ultrasonic flaw detector characterized by comprising:
  The gate means uses the reflected wave signal from the internal defect as a time τ when the transmitted ultrasonic wave reaches the ultrasonic receiver.0age,The time from the arrival of the directly transmitted wave to the end of the reverberation of the transmitted wave is expressed as τ D age,The time required for the ultrasonic wave to propagate in the thickness direction of the plate to be inspected is τ1WhendidWhenTimes of Day0+τ D ) And after (τ0+ 2 × τ1) A distance L between the ultrasonic transmitter and the ultrasonic receiver that is set to extract from the previous received signal.SCompares the focal lengths of the ultrasonic transmitter and the ultrasonic receiver, and if the focal lengths are different, the larger focal length is FLOr if the focal lengths are equal, the focal length is FLAnd the thickness of the board to be inspected is t, and both should be arranged so as to satisfy the following formula.
    LS≦ FL-{(CM/ CL) -1} × t + FL× 5/38
  However, CM; Ultrasonic wave propagation speed in the material to be inspected, CLThe propagation speed of ultrasonic waves in the liquid.
[0015]
[Action]
According to the present invention, a point-focusing type ultrasonic transmitter and a point-focusing type ultrasonic receiver are arranged to face each other with a test plate immersed in a liquid interposed therebetween, and the ultrasonic transmission is performed. Ultrasound that has been point-focused from the child is incident substantially perpendicularly into the inspected plate, and the ultrasonic wave transmitted by the ultrasonic wave and the reflected wave from the internal defect generated by the ultrasonic wave are received by the ultrasonic wave receiver. Since the signal of the reflected wave from the internal defect is extracted from the amplified signal, and the internal defect of the inspection board is detected based on the extracted signal, the vicinity of the front and back surfaces of the inspection board It is possible to detect even an internal defect with a uniform sensitivity over the entire cross section without a dead zone.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram including a partial perspective view showing the configuration of an embodiment of the present invention.
In FIG. 1, 11 is a point-focusing ultrasonic transmitter (hereinafter simply referred to as an ultrasonic transmitter), 12 is a point-focusing ultrasonic receiver (hereinafter simply referred to as an ultrasonic receiver), Oppositely arranged with a sandwich. Reference numeral 14 denotes a U-shaped support arm that supports the ultrasonic transmitter 11 and the ultrasonic receiver 12. Note that water that is suitably used as an ultrasonic propagation medium is interposed between the ultrasonic transmitter 11 and the ultrasonic receiver 12 and the board 13 to be inspected. A scanning device 15 scans the support arm 14.
[0017]
Reference numeral 16 denotes an electric pulse generator that transmits electric pulses from a built-in clock circuit (not shown) to a piezoelectric vibrator (not shown) built in the ultrasonic transmitter 11 at regular time intervals. Reference numeral 17 denotes a receiving amplifier that receives a signal from the ultrasonic receiver 12, 18 denotes a gate circuit, 19 denotes a peak value detection circuit, 20 denotes a controller, and 21 denotes a display.
The ultrasonic transmitter 11 converts the electric pulse transmitted from the electric pulse generator 16 at a predetermined time interval into an ultrasonic wave, and transmits the ultrasonic transmission beam 11A substantially perpendicularly to the inspected plate 13 through water. . The ultrasonic receiver 12 receives an ultrasonic reception beam 12A including a reflected wave from an internal defect caused by the ultrasonic wave incident on the inspection plate 13 through water. Then, the support arm 14 is scanned by the scanning device 15 driven by a signal from the controller 20, and the ultrasonic transmitter 11 and the ultrasonic receiver 12 which are arranged to face each other are squarely scanned on the surface of the inspected plate 13. Investigate its internal defects.
[0018]
The received signal amplified by the receiving amplifier 17 is extracted by the gate circuit 18 from the received signal. The extracted signal is transmitted to the peak value detection circuit 19, and the peak value detection circuit 19 detects the amplitude of the reflected wave and outputs it to the controller 20 as an analog amount or a digital amount. The controller 20 outputs the amplitude of the reflected wave and the position signal of the scanning device 15 to the display 21 to create a two-dimensional distribution map of internal defects.
[0019]
Here, the function of the gate circuit 18 will be described in detail with reference to FIG.
First, when the thickness of the inspected plate 13 is t and the internal defect 22 is near the surface 13a of the inspected plate 13, that is, the distance d from the surface 13a is equal to or less than t / 2, ultrasonic transmission is taken as an example. When the ultrasonic transmission beam 11A transmitted from the child 11 propagates in the liquid and reaches the surface 13a of the inspected plate 13, it enters the inspected plate 13 and propagates therein.
[0020]
At this time, a part of the ultrasonic wave propagated inside the board to be inspected 13 travels straight and is received by the ultrasonic receiver 12 as a direct transmitted wave 30. Further, when the internal defect 22 exists in the ultrasonic wave propagation path, first, it is reflected once on the upper side of the internal defect 22, directed to the surface 13 a, reflected by the surface 13 a, and within the thickness t of the inspected plate 13. 0.5 reciprocally propagates, and the reflected wave 31 propagates from the back surface 13b into the liquid and is received, and first propagates 0.5 reciprocally within the thickness t of the plate to be inspected and is reflected by the back surface 13b toward the internal defect 22, After being reflected once under the defect 22, a reflected wave 32 is generated which propagates from the back surface 13 b into the liquid and is received.
[0021]
The reflected waves 31 and 32 are further reflected once or more on the back surface 13b, and the reflected wave received by the ultrasonic receiver 12 is generated one or more times within the thickness t of the board 13 to be inspected. However, illustration is omitted here. As described above, the present invention extracts the reflected wave signal from the internal defect from the received and amplified signal, and detects the internal defect based on the extracted signal. When the internal defect 22 has a distance d from the surface 13a of the inspection plate 13 of t / 2 or less, the reflected wave 32 reaches the ultrasonic receiver 12 later than the reflected wave 31.
[0022]
Further, the temporal transition of the signal received by the ultrasonic receiver 12 will be described with reference to FIG. In this figure, τ0Is the time when the directly transmitted wave 30 that has propagated 0.5 reciprocating times within the thickness t of the inspected plate 13 reaches the ultrasonic receiver 12, τ1Is the time required for the ultrasonic wave to propagate 0.5 reciprocating times within the thickness t of the plate 13 to be inspected. Reference numeral 33 denotes a transmitted wave signal that travels 0.5 reciprocatingly within the thickness t of the inspected plate 13 and then reciprocates once through the inspected plate 13.
[0023]
Thus, since the propagation distance of the reflected wave 32 is larger than the propagation distance of the reflected wave 31, the reflected wave 32 is received later than the reflected wave 31. From this figure, the reflected wave 32 due to the internal defect 22 is the time τ when the directly transmitted wave 30 that has propagated 0.5 reciprocatingly within the thickness t of the inspected plate 13 reaches the ultrasonic receiver 12.0From the time τ required for the ultrasonic wave to propagate 0.5 times in the thickness t of the plate to be inspected τ1After a lapse of time and appearing outside the dead zone region due to the direct transmitted wave 30, and at time τ0To (2 × τ1) Appears before the passage and earlier than the transmitted wave 33. Further, the closer the position of the internal defect 22 is to the surface 13a, the τ22Is smaller than the distance d required to propagate the distance d to the internal defect 22 in the inspected plate 13 (that is, the time required for propagation by the distance 2d), but appears earlier than the transmitted wave 33. Therefore, even if the internal defect 22 exists directly under the surface 13a, the reflected wave 32 caused by the internal defect 22 can be clearly identified and extracted. Therefore, it is preferable to extract this and detect the internal defect 22.
[0024]
The time τ when the reflected wave 32 appears due to the internal defect 22 is expressed by the following formula (3).
0+ Τ1) ≦ τ ≦ (τ0+ 2 × τ1) ……………… (3)
The time from the arrival of the direct transmitted wave 30 to the end of the reverberation of the transmitted wave is expressed as τD(See FIG. 3), the time (τ0+ ΤD) And after (τ0+ 2 × τ1) If the previously received signal is extracted, it is possible to detect both the reflected waves 31 and 32.
[0025]
The above description is about the case where the internal defect exists near the front surface. Next, the case where the distance d from the front surface 13a is located near the rear surface 13b, that is, at a position where the distance d is t / 2 or more will be described. In this case, unlike FIG. 2, the propagation distance of the reflected wave 31 due to the internal defect 22 is longer than the propagation distance of the reflected wave 32, so that the reflected wave 31 is received with a delay. As described above, the reflected wave 31 appears outside the dead zone region due to the direct transmitted wave 30 and appears earlier than the transmitted wave 33. Therefore, even if the internal defect 22 exists directly under the back surface 13b, the reflected wave 31 due to the internal defect 22 can be clearly identified and extracted, so that the internal defect 22 can be detected and is preferable.
[0026]
As explained so far, the direct propagation wave 30 that has propagated 0.5 reciprocatingly through the plate 13 to be inspected and the transmitted wave 33 that has propagated 1 reciprocating propagation through the substrate 13 to be inspected from the internal defect with the longer propagation distance. It is more preferable to extract the reflected wave because the noise component that makes noise is small. However, the ultrasonic wave propagates 0.5 times reciprocatingly through the board 13 to be inspected, and further propagates through the board 13 to be reciprocated an integer number of times. A reflected wave from an internal defect having a longer propagation distance appearing between the wave and the transmitted wave that has propagated one reciprocating propagation through the inspection target plate 13 may be extracted.
[0027]
In the present invention, a two-dimensionally focused point-focusing ultrasonic transmitter and a point-focusing ultrasonic receiver are used, and the ultrasonic transmitter and the ultrasonic receiver are scanned relative to the inspected plate. Therefore, the resolution in the width direction is high, and the form of internal defects can be detected.
Further, in the present invention, as shown in FIG. 4, the ultrasonic transmission beam 11A from the ultrasonic transmitter 11 is focused on the surface of the ultrasonic receiver 12, and the ultrasonic wave of the ultrasonic receiver 12 is set. The focal point G of the reception beam 12A may be the surface of the ultrasonic transmitter 11. In this way, the intensity of the ultrasonic transmission beam 11A transmitted from the ultrasonic transmitter 11 becomes lower as it approaches the surface of the inspected plate 13, so the intensity of the reflected wave from the internal defect existing there is small. On the other hand, since the reception efficiency of the ultrasonic receiver 12 is larger near the focal point F, it becomes larger as it is closer to the surface of the inspected plate 13. Therefore, the intensity of the reflected wave from the internal defect received by the ultrasonic receiver 12 can be made almost constant even if the position where the internal defect exists is changed by canceling the effect of both, and the thickness direction This is because the sensitivity can be uniform over the entire area.
[0028]
FIG. 5 shows the result of detecting an artificial defect by the method of the present invention and the conventional method. That is, the method of the present invention was measured using an ultrasonic transmitter 11 and an ultrasonic receiver 12 having a frequency of 25 MHz and an underwater focal length of 38 mm arranged so that the focal points F and G are connected as shown in FIG. In the conventional method, as shown in FIG. 9, the measurement is performed by transmitting and receiving ultrasonic waves from one direction to one point focusing type with a frequency of 25 MHz and an underwater focal length of 38 mm. It is what. The artificial defect was manufactured by changing the distance from the surface of the inspected plate 13 having a thickness of 5.5 mm and making a 0.2 mmφ horizontal drill hole perpendicular to the thickness direction.
[0029]
From this figure, compared with the conventional method, the method of the present invention has a constant amplitude of the reflected wave regardless of the distance from the surface of the defect, has a remarkably excellent focal depth, and is uniform over the thickness direction. It can be seen that it can be detected with sensitivity.
Next, the positional relationship among the point-focusing type ultrasonic transmitter 11, the point-focusing type ultrasonic receiver 12, and the inspected plate 13 will be described in detail based on experimental data. That is, in FIG. 6, the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so that the focal points F and G are connected as shown in FIG. 4, and the ultrasonic transmitter 11 and the ultrasonic receiver at that time are arranged. The distance between the children 12 is LSAnd a distance L between the ultrasonic receiver 12 and the inspection plate 13 by moving the inspection plate 13 having a thickness t of 4.5 mm between the ultrasonic transmitter 11 and the ultrasonic receiver 12.2The amplitude and S / N of the reflected wave from the internal defect of the inspected plate 13 are measured. The used ultrasonic transmitter 11 and ultrasonic receiver 12 have a frequency of 25 MHz and an underwater focal length of 38 mm. As a result, the amplitude and S / N of the reflected wave due to the internal defect hardly change at any position between the ultrasonic transmitter 11 and the ultrasonic receiver 12 in the inspection target plate 13. That is, it can be seen that the inspected plate 13 may be at any position between the ultrasonic transmitter 11 and the ultrasonic receiver 12.
[0030]
Now, when the focal lengths of the ultrasonic transmitter 11 and the ultrasonic receiver 12 are equal, that is, as shown in FIG. 4, the focal point F of the ultrasonic transmission beam 11 </ b> A is on the surface of the ultrasonic receiver 12. When the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so that the focal point G of the ultrasonic reception beam 12A coincides with the surface of the ultrasonic transmitter 11, the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged. The distance between andS0Then, this distance LS0Is expressed by the following equation (4).
[0031]
LS0= FL-{(CM/ CL) -1} × t (4)
However, FLThe focal length of the point-focusing type ultrasonic transmitter 11 or the focal length of the point-focusing type ultrasonic receiver 12, t; the thickness of the plate to be inspected, CM; Ultrasonic wave propagation speed in the material to be inspected, CLThe propagation speed of ultrasonic waves in the liquid.
FIG. 7 shows the distance L when the ultrasonic transmitter 11 and the ultrasonic receiver 12 have the same focal length.S0Is the reference distance, the distance between the ultrasonic transmitter 11 and the ultrasonic receiver 12 is changed in water, and the amplitude of the reflected wave from the internal defect of the inspection board is measured. The ultrasonic transmitter 11 and the ultrasonic receiver 12 used had a frequency of 25 MHz, an underwater focal length of 38 mm, and a thin steel plate having a thickness t of 4.5 mm was used as the inspected plate. Distance LSIs the reference distance LS0Is smaller than the amplitude of the reflected wave, the distance LSIs the reference distance LS0It can be seen that the amplitude of the reflected wave suddenly decreases as the value becomes larger. The amplitude of the reflected wave is the reference distance LS0Since a reduction of 3 dB or more than in the case of (3) leads to a decrease in S / N in defect detection, which is not preferable, the distance L between the ultrasonic transmitter 11 and the ultrasonic receiver 12 is not preferable.S(mm) must satisfy the following formula (5).
[0032]
LS≦ LS0+ FL× 5/38 ……………… (5)
That is,
LS≦ FL-{(CM/ CL) -1} × t + FL× 5/38 ………… (6)
Represented as:
Note that F in equation (6)LThe coefficient 5/38 is generalized in consideration of the case where the focal lengths of the ultrasonic transmitter 11 and the ultrasonic receiver 12 are other than 38 mm.
[0033]
Next, even when the focal length of the ultrasonic transmitter 11 and the focal length of the ultrasonic receiver 12 are not equal, the same arrangement as shown in FIGS. An effect can be obtained. For example, when the focal length of the ultrasonic transmitter 11 is larger than the focal length of the ultrasonic receiver 12, the ultrasonic transmitter 11 so that the focal point F of the ultrasonic transmission beam 11 A coincides with the surface of the ultrasonic receiver 12. And an ultrasonic receiver 12 are arranged. At this time, if the inspected plate 13 is positioned closer to the ultrasonic receiver 12 than the focal point G of the ultrasonic reception beam 12A, the same thing as that described with reference to FIG. Further, when the focal length of the ultrasonic receiver 12 is larger than the focal length of the ultrasonic transmitter 11, the ultrasonic transmitter 11 so that the focal point G of the ultrasonic reception beam 12A coincides with the surface of the ultrasonic transmitter 11. And an ultrasonic receiver 12 are arranged. At this time, if the inspected plate 13 is positioned closer to the ultrasonic transmitter 11 than the focal point F of the ultrasonic transmission beam 11A, the same thing as that described with reference to FIG.
[0034]
The distance L between the focal length of the ultrasonic transmitter 11 and the focal length of the ultrasonic receiver 12 is not equal.SWill be described in detail based on experimental data. Now, a case where the focal length of the ultrasonic transmitter 11 is larger than the focal length of the ultrasonic receiver 12 will be described as an example. At this time, the larger focal length is set to FLAnd
Therefore, when the ultrasonic transmitter 11 and the ultrasonic receiver 12 are arranged so that the focal point F of the ultrasonic transmission beam 11A coincides with the surface of the ultrasonic receiver 12, the ultrasonic transmitter 11 and the ultrasonic receiver The distance between 12 and LS0Then, this distance LS0Is expressed by the following equation (7).
[0035]
LS0= FL-{(CM/ CL) -1} × t (7)
FIG. 8 shows this distance LS0Is the reference distance, the distance between the ultrasonic transmitter 11 and the ultrasonic receiver 12 is changed in water, and the amplitude of the reflected wave from the internal defect of the inspection board is measured. The ultrasonic transmitter 11 used has a frequency of 25 MHz and an underwater focal length of 38 mm, and the ultrasonic receiver 12 has a frequency of 25 MHz and an underwater focal length of 25 mm. A thin steel plate having a thickness t of 4.5 mm was used as the inspected plate.
[0036]
Similar to FIG. 7, the distance LSIs the reference distance LS0Is smaller than the amplitude of the reflected wave, the distance LSIs the reference distance LS0It can be seen that the amplitude of the reflected wave suddenly decreases as the value becomes larger. The amplitude of the reflected wave is the reference distance LS0Since a decrease of 3 dB or more than in the case of the above leads to a decrease in S / N in defect detection and is judged to be undesirable, the distance L between the ultrasonic transmitter 11 and the ultrasonic receiver 12S(mm) must satisfy the following formula (8).
[0037]
LS≦ LS0+ FL× 5/38 ……………… (8)
That is,
LS≦ FL-{(CM/ CL) -1} × t + FL× 5/38 ………… (9)
Represented as:
Note that F in equation (9)LThe coefficient 5/38 is generalized in consideration of the case where the focal lengths of the ultrasonic transmitter 11 and the ultrasonic receiver 12 are other than 38 mm.
[0038]
Next, when the focal length of the ultrasonic receiver 12 is large, the ultrasonic transmitter 11 has a large focal length; the ultrasonic transmitter 11 has a frequency of 25 MHz, an underwater focal length of 25 mm, and the ultrasonic receiver 12 has a frequency. An experiment was carried out using 25 MHz and an underwater focal length of 38 mm, and although the illustration was omitted, a result almost equivalent to FIG. 8 could be obtained. Therefore, when the focal length of the ultrasonic transmitter 11 and the focal length of the ultrasonic receiver 12 are not equal, the larger one is F.LAnd the distance L between the ultrasonic transmitter 11 and the ultrasonic receiver 12STherefore, the ultrasonic transmitter 11 and the ultrasonic receiver 12 may be arranged so that the above equation (9) is satisfied.
[0039]
The present invention method was applied when defect inspection was performed on a thin steel plate having a thickness of 1.2 to 5.5 mm as the inspected plate 13. As the ultrasonic transmitter 11 used at this time, an ultrasonic wave having a frequency of 25 MHz and an underwater focal length of 38 mm was used to transmit an ultrasonic wave having a frequency of 25 MHz, and as the ultrasonic receiver 12, a frequency of 25 MHz and an underwater focal length of 38 mm was used. We used a thing to detect flaws. As a result, it was possible to detect an ultra-fine defect of 10 μm φ regardless of the position in the thickness direction of the defect.
[0040]
Note that, in the above-described embodiment, the ultrasonic transmitter 11 and the ultrasonic receiver 12 that are disposed to face the board to be inspected by holding the ultrasonic transmitter 11 and the ultrasonic receiver 12 with the support arm 14. Although the child is scanned, the present invention is not limited to this, and it goes without saying that it may be configured to scan the inspected plate side.
[0041]
【The invention's effect】
According to the present invention, internal defects such as fine inclusions such as rolled metal sheets can be detected with uniform sensitivity over the entire cross section, eliminating the dead zone on the surface. It is possible to contribute to improvement.
[Brief description of the drawings]
FIG. 1 is a block diagram including a partial perspective view showing a configuration of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a propagation path and a positional relationship of a reflected wave from a defect.
FIG. 3 is an explanatory diagram showing a relationship between a received ultrasonic signal and time.
FIG. 4 is an explanatory diagram showing focal points of ultrasonic beams of a transmitter and a receiver.
FIG. 5 is a characteristic diagram showing the relationship between the distance from the surface of the defect and the amplitude of the reflected wave.
FIG. 6 is a characteristic diagram showing amplitude and S / N of a reflected wave from an internal defect.
FIG. 7 is a characteristic diagram showing the amplitude of a reflected wave from an internal defect.
FIG. 8 is a characteristic diagram showing the amplitude of a reflected wave from an internal defect.
FIG. 9 is a block diagram including a partial perspective view showing a configuration of a conventional example.
[Explanation of symbols]
11 Ultrasonic Transmitter (Point Focusing Ultrasonic Transmitter)
11A Ultrasonic transmission beam
12 Ultrasonic receiver (Point-focusing type ultrasonic receiver)
12A Ultrasonic receiving beam
13 Board to be inspected
  13a surface
  13b reverse side
  14 Support arm
  15 Scanning device
16 Electric pulse generator
  17 Receiver amplifier
  18 Gate circuit
  19 Peak value detection circuit
  20 Controller
  21 Display
22 Internal defects
  30 Direct transmitted wave
31, 32 Reflected wave
33 Transmitted wave

Claims (5)

液中に浸漬された被検査板を挟んで、点集束型の超音波送信子と点集束型の超音波受信子とを対向配置して走査するとともに、
前記超音波送信子から点集束した超音波を被検査板内に略垂直に入射し、
前記超音波が内部欠陥の上側で反射して被検査板の表面に向かい、表面で反射して、裏面から液中に伝播し受信される反射波と、前記超音波が最初に被検査板の裏面で反射し、内部欠陥に向かい、内部欠陥の下側で反射した後、裏面から液中に伝播し受信される反射波の両方を前記超音波受信子で受信し、
該受信信号を増幅した信号から前記内部欠陥からの両方の反射波の信号を抽出し、
該抽出された信号に基づいて被検査板の内部欠陥を検出することを特徴とするCスキャン超音波探傷方法。
While interposing the inspection plate immersed in the liquid, scanning with the point-focusing type ultrasonic transmitter and the point-focusing type ultrasonic wave receiver facing each other,
Ultrasound that is point-focused from the ultrasonic transmitter is incident on the inspected plate substantially perpendicularly,
The ultrasonic wave is reflected on the upper side of the internal defect and is directed to the surface of the inspected plate, reflected by the surface, propagated from the back surface into the liquid and received, and the ultrasonic wave is first reflected on the inspected plate. Reflected on the back surface, directed to the internal defect, reflected on the lower side of the internal defect, and then received by the ultrasonic receiver both reflected waves propagated and received from the back surface into the liquid,
Extracting both reflected wave signals from the internal defect from the amplified signal
A C-scan ultrasonic flaw detection method comprising detecting an internal defect of a plate to be inspected based on the extracted signal.
前記内部欠陥からの反射波の信号を、超音波の透過波が前記超音波受信子に到達する時刻をτ0 とし、直接透過波の到達から該透過波の残響が終了するまでの時間をτ D とし、該超音波が被検査板の厚さ方向に伝播するのに要する時間をτ1 したとき、時刻(τ0 τ D )以後で、かつ(τ0 +2×τ1 )以前の受信信号から抽出することを特徴とする請求項1記載のCスキャン超音波探傷方法。The signal of the reflected wave from the internal defect is defined as τ 0 when the transmitted ultrasonic wave reaches the ultrasonic receiver, and τ is the time from the arrival of the transmitted wave to the end of the reverberation of the transmitted wave. is D, when the ultrasonic is the tau 1 the time required to propagate in the thickness direction of the test plate, the time in 0 + τ D) after, and (τ 0 + 2 × τ 1 ) previous 2. The C-scan ultrasonic flaw detection method according to claim 1, wherein the method is extracted from a received signal. 前記超音波送信子と前記超音波受信子の焦点距離を比較し、該焦点距離が異なる場合は大きい方の焦点距離をFL とし、または前記焦点距離が等しい場合はその焦点距離をFL とし、被検査板の板厚をtとしたとき、前記超音波送信子と前記超音波受信子との間の距離LS が下記式を満足するように両者を配置することを特徴とする請求項1または2記載のCスキャン超音波探傷方法。
S ≦FL −{(CM /CL )−1}×t+FL ×5/38
ただし、CM ;被検査材中での超音波の伝播速度、CL ;液中での超音波の伝播速度。
Wherein comparing the focal length of the ultrasonic receiver and ultrasonic transmitter element, the focal length of the person when the distance focal point is different from large as F L, or if the focal length is equal to the focal length F L The both are arranged so that a distance L S between the ultrasonic transmitter and the ultrasonic receiver satisfies the following expression, where t is the thickness of the plate to be inspected. 3. The C-scan ultrasonic flaw detection method according to 1 or 2.
L S ≦ F L − {(C M / C L ) −1} × t + F L × 5/38
Where C M is the ultrasonic wave propagation speed in the material to be inspected, and C L is the ultrasonic wave propagation speed in the liquid.
被検査板の表面に超音波を略垂直に送信する点集束型の超音波送信子と、
被検査板を挟んで前記点集束型超音波送信子と対向する位置に配置し、前記超音波が内部欠陥の上側で反射して被検査板の表面に向かい、表面で反射して、裏面から液中に伝播し受信される反射波と、前記超音波が最初に被検査板の裏面で反射し、内部欠陥に向かい、内部欠陥の下側で反射した後、裏面から液中に伝播し受信される反射波の両方を受信する点集束型の超音波受信子と、
前記超音波送信子と前記超音波受信子とを被検査板を挟んで支持する支持アームと、
該支持アームを走査する走査装置と、
前記超音波送信子に内蔵された圧電振動子に送信する電気パルスを発生する電気パルス発生装置と、
受信信号を増幅する増幅装置と、
増幅された信号から内部欠陥からの両方の反射波の信号を抽出するゲート手段と、
を備えたことを特徴とするCスキャン超音波探傷装置。
A point-focusing type ultrasonic transmitter that transmits ultrasonic waves substantially vertically to the surface of the inspection plate;
Arranged at a position facing the point-focusing ultrasonic transmitter across the board to be inspected, the ultrasonic wave is reflected on the upper side of the internal defect and directed to the surface of the board to be inspected, reflected on the surface, and from the back surface The reflected wave that is propagated and received in the liquid and the ultrasonic wave are first reflected on the back surface of the board to be inspected, directed to the internal defect, reflected on the lower side of the internal defect, and then propagated into the liquid from the back surface and received. A point-focusing ultrasonic receiver that receives both reflected waves , and
A support arm that supports the ultrasonic transmitter and the ultrasonic receiver with an inspection plate interposed therebetween;
A scanning device for scanning the support arm;
An electric pulse generator for generating an electric pulse to be transmitted to a piezoelectric vibrator incorporated in the ultrasonic transmitter;
An amplifying device for amplifying the received signal;
Gate means for extracting signals of both reflected waves from internal defects from the amplified signal ;
A C-scan ultrasonic flaw detector characterized by comprising:
前記ゲート手段は、前記内部欠陥からの反射波の信号を、超音波の透過波が前記超音波受信子に到達する時刻をτ0 とし、直接透過波の到達から該透過波の残響が終了するまでの時間をτ D とし、該超音波が被検査板の厚さ方向に伝播するのに要する時間をτ1 したとき、時刻(τ0 τ D )以後で、かつ(τ0 +2×τ1 )以前の受信信号から抽出するように設定され、
前記超音波送信子と前記超音波受信子との間の距離LS は、前記超音波送信子と前記超音波受信子の焦点距離を比較して、該焦点距離が異なる場合は大きい方の焦点距離をFL とし、または前記焦点距離が等しい場合はその焦点距離をFL とし、被検査板の板厚をtとして、下記式を満足するように両者を配置することを特徴とする請求項4記載のCスキャン超音波探傷装置。
S ≦FL −{(CM /CL )−1}×t+FL ×5/38
ただし、CM ;被検査材中での超音波の伝播速度、CL ;液中での超音波の伝播速度。
The gate means sets the reflected wave signal from the internal defect to τ 0 when the ultrasonic transmitted wave reaches the ultrasonic receiver, and the reverberation of the transmitted wave ends from the arrival of the direct transmitted wave. and the time until the tau D, when the time for ultrasound takes to propagate in the thickness direction of the test plate was tau 1, at time 0 + τ D) after, and (τ 0 + 2 × τ 1 ) set to extract from previous received signal,
The distance L S between the ultrasonic transmitter and the ultrasonic receiver is compared with the focal length of the ultrasonic transmitter and the ultrasonic receiver. distance and F L, or if the focal length is equal to the focal length F L, claims, characterized in that to place the plate thickness of the test plate as t, the two so as to satisfy the following formula 4. The C-scan ultrasonic flaw detector according to 4.
L S ≦ F L − {(C M / C L ) −1} × t + F L × 5/38
Where C M is the ultrasonic wave propagation speed in the material to be inspected, and C L is the ultrasonic wave propagation speed in the liquid.
JP10500595A 1995-04-28 1995-04-28 C-scan ultrasonic flaw detection method and apparatus Expired - Fee Related JP3653785B2 (en)

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