JP3581931B2 - Electromagnetic ultrasonic inspection method using cross-correlation method - Google Patents

Electromagnetic ultrasonic inspection method using cross-correlation method Download PDF

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JP3581931B2
JP3581931B2 JP2002130996A JP2002130996A JP3581931B2 JP 3581931 B2 JP3581931 B2 JP 3581931B2 JP 2002130996 A JP2002130996 A JP 2002130996A JP 2002130996 A JP2002130996 A JP 2002130996A JP 3581931 B2 JP3581931 B2 JP 3581931B2
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wave
defect
electromagnetic ultrasonic
ultrasonic probe
surface wave
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捷宏 川島
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捷宏 川島
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【０００１】
【発明の属する技術分野】
本発明は、超音波の表面波あるいは板波を用いて材料の表面あるいは表面近くの内部の欠陥を探るための検査方法に関するものである。
【０００２】
【従来の技術】
従来、製鉄所でつくられる厚鋼板等の材料の表層部を検査するために超音波の表面波がよく用いられている。例えば特開平６−３３１６０３公報には可変角振動子を内部に備えたタイヤ探触子による表面欠陥検査法が開示されている。しかしこの方法ではタイヤ探触子中の可変角振動子から発せられる超音波を材料の表面に伝えるために、タイヤ探触子を水等の媒体液を介して材料表面に接触させ、タイヤ探触子と材料表面との音響的結合を確立させる必要がある。この場合に使用される水等の媒体液はタイヤ探触子周辺のみにとどまっているとは限らず、材料表面を流れて表面波の伝播路にまで広がることがあり、表面波はこの水等の媒体液を表面欠陥と区別できずに誤検出してしまうという問題があった。
【０００３】
また、薄鋼板等の材料の表層部を検査するために超音波の板波がよく用いられているがこれに用いるタイヤ探触子に関しても同じ問題があった。
【０００４】
このような問題点を解決する方法として水等の媒体液を使用する必要がなく材料に非接触で超音波を発受信できる電磁超音波法（ＥＭＡＴ）が発明され、特開平７−７７４６５公報や「超音波ハンドブック」（出版社：丸善、刊行年月：平成１１年８月）の第３章第４節に開示されている。しかしながら電磁超音波法は原理的に電気・音響エネルギー変換効率が低いために超音波を発受信する効率が悪く、これを補うために小さな超音波信号を増幅するための増幅率の大きな増幅器を使用する必要がある。増幅率の大きな増幅器は微小なランダムノイズも同時に増幅してしまうため、目的とする表面欠陥あるいは表面近くの内部欠陥から反射されてきた小さな超音波信号はランダムノイズに埋もれてしまう傾向があり誤検出の最大の原因となっていた。
【０００５】
【発明が解決しようとする課題】
本発明は、このような実情に鑑みてなされたもので、表面欠陥あるいは表面近くの内部欠陥から反射されてきたランダムノイズに埋もれた小さな超音波信号を抽出することのできる電磁超音波検査方法を提供することを課題とする。
【０００６】
【問題を解決する手段】
表面波による検査に関する前記課題を解決する手段は、表面波発信用の電磁超音波探触子と表面波受信用の電磁超音波探触子とを被検査材料の表面に短距離を隔てて設け、該表面波発信用の電磁超音波探触子により発信され該短距離を伝播してきた直達表面波と表面欠陥あるいは表面近くの内部欠陥から反射されてきた欠陥表面波の両方を該表面波受信用の電磁超音波探触子により受信し、増幅し、ＡＤ変換器によりディジタル化した後に該直達表面波と該欠陥表面波との相互相関関数を算出することによりランダムノイズに埋もれた欠陥表面波を抽出するものである。
【０００７】
板波による探傷に関する前記課題を解決する手段は、板波発信用の電磁超音波探触子と板波受信用の電磁超音波探触子とを被検査材料の表面に短距離を隔てて設け、該板波発信用の電磁超音波探触子により発信され該短距離を伝播してきた直達板波と表面欠陥あるいは表面近くの内部欠陥から反射されてきた欠陥板波の両方を板波受信用の電磁超音波探触子により受信し、増幅し、ＡＤ変換器によりディジタル化した後に該直達板波と該欠陥板波との相互相関関数を算出することによりランダムノイズに埋もれた欠陥板波を抽出するものである。
【０００８】
【発明の実施の形態】
発明の実施の形態を実施例にもとづき図面を参照して説明する。図１は発明の実施の１例である電磁超音波検査装置の概要を示す概要図である。図１において、１は被検査体である厚鋼板、２は表面欠陥、３はパルス送信器、４は表面波発信用の電磁超音波探触子、５は表面波発信用の電磁超音波探触子４から短い距離（８ｃｍ）に設けられた表面波受信用の電磁超音波探触子、６は増幅器、７はＡＤ変換器、８はデータ蓄積器、９は演算器、１０は出力装置である。データ蓄積器８はコンピューターのＩＣメモリで構成されるが、ＩＣメモリのかわりにコンピューターのハードディスクでもよい。
１１の波形矢印は表面波発信用の電磁超音波探触子４により発信された表面波が鋼材表面を伝播し、表面欠陥２に反射されてもどっていく様子を表している。図２（ａ）は表面波発信用の電磁超音波探触子４の下面図、図２（ｂ）は表面波発信用の電磁超音波探触子４と被検体である厚鋼板１との関係を示した図である。図３（ａ）は表面波受信用の電磁超音波探触子５の下面図、図３（ｂ）は表面波受信用の電磁超音波探触子５と被検体である厚鋼板１との関係を示した図である。１２、１４は永久磁石、１３、１５は往復する繰り返し線路を有するコイルである。図２、図３では永久磁石を使用しているが電磁石を使用してもよい。図２、図３からわかるように表面波発信用の電磁超音波探触子４と表面波受信用の電磁超音波探触子５とは全く同じ構造を有している。このような構造の電磁超音波探触子が表面波を発信し、また受信できることは特開平７−７７４６５公報の図９、図１０に開示されているように一般によく知られているが以下に簡単にその原理を説明する。図２の表面波発信用の電磁超音波探触子４のコイル１３にパルス送信器３より送信電流を流すと電磁誘導により厚鋼板１の表面に渦電流が流れる。この渦電流と永久磁石１２により発している磁界との間のローレンツ力や厚鋼板１の持つ磁歪効果によって表面波が発信される。図３の表面波受信用の電磁超音波探触子の直下を表面波が通過すると発信とは全く逆の物理的過程によりコイル１５に電気信号を発生し表面波が受信されることなる。
【０００９】
実施の他の例としては図２、図３に示す電磁超音波探触子のかわりに、「超音波便覧」（出版社：丸善、刊行年月：平成１１年８月）の第３章第４節図３．９．１ に開示されている材料表面に平行な磁界成分を有するマグネットを使用したタイプのＬａｍｂ波用の電磁超音波探触子と同じ構造のものを用いても表面波を発受信できるのでこれを使用してもよいし、特開２０００−１８７０２２公報の図１に開示されている表面にＳＨ波を発受信するタイプの電磁超音波探触子を使用してもよい。
【００１０】
パルス送信器３は周波数が１ＭＨｚ、波数が１０、繰り返し周波数が４００Ｈｚであるバースト波電流を表面波発信用の電磁超音波探触子４に送信する。すると上に述べた原理により厚鋼板１の表面に表面波が発信される。この表面波は図１において、まず右方へ伝播して表面波発信用の電磁超音波探触子４より８ｃｍの距離に設けられた表面波受信用の電磁超音波探触子５により直達表面波として受信され、さらに右方へ伝播して表面波発信用の電磁超音波探触子４より２８ｃｍの距離にある表面欠陥２により反射されて左方へ伝播し表面波受信用の電磁超音波探触子５により欠陥表面波として受信される。増幅器６は直達表面波、欠陥表面波を増幅する。
【００１１】
図４には表面欠陥２が十分大きい（長さ３．５ｃｍ、深さ１ｍｍ）場合に、こうして増幅されたままの、即ち相互相関関数を算出していない従来の方法による表面波信号の例を示している。横軸は時間、縦軸は表面波信号の大きさである。図４において１６は超音波発信のためのバースト波電流によって空間を隔てた電磁的誘導により発生した電気信号である。１７は直達表面波、１８は欠陥表面波、１９はランダムノイズである。この場合は表面欠陥２が十分大きい（長さ３．５ｃｍ、深さ１ｍｍ）ので欠陥表面波１８も大きく、図４に示すように明瞭に受信されるため問題はない。
【００１２】
図５には表面欠陥２が小さい（長さ１．５ｃｍ、深さ０．３ｍｍ）場合に、増幅されたままの、即ち相互相関関数を算出していない従来の方法による表面波信号の例を示している。図５において１６は超音波発信のためのバースト波電流によって空間を隔てた電磁的誘導により発生した電気信号である。１７は直達表面波、１９はランダムノイズである。この場合には直達表面波１７は明瞭に検出されているが欠陥表面波はランダムノイズ１９に埋もれてしまい識別することが不可能であることがわかる。すなわち図５によれば表面欠陥２が小さい（長さ１．５ｃｍ、深さ０．３ｍｍ）場合は受信された欠陥表面波も小さいためにランダムノイズに埋もれてしまい、欠陥表面波として識別することは不可能となることがわかる。
【００１３】
本発明の発明者は、まず直達表面波１７と表面欠陥から反射された欠陥表面波１８を拡大して詳しく調査した結果、両者は大きさは異なるが形は非常に似ていることを見出した。さらにこのことを利用し、直達表面波とランダムノイズに埋もれた欠陥表面波との相互相関関数を算出することにより欠陥表面波を明瞭に抽出されることを見出したわけである。すなわち図１において増幅器６により増幅された超音波信号をＡＤ変換器７によりディジタル化しこれをデータ蓄積器８に蓄積する。演算器８は蓄積されたデータから直達表面波と欠陥表面波との相互相関関数を次の式により算出する。

Figure 0003581931
ここでＡ（ｉ×Δｔ）は、直達表面波がΔｔの時間間隔でディジタル化されてできたｉ番目のディジタル値を、Ｂ（（ｉ−ｊ）×Δｔ）は欠陥表面波がΔｔの時間間隔でディジタル化されてできた（ｉ−ｊ）番目のディジタル値を表す。Ｃ（ｊ×Δｔ）は算出された相互相関関数のｊ番目のディジタル値である。こうして算出された相互相関関数を図６に示す。図６において２０は相互相関関数を算出した結果小さくなったランダムノイズであり、２１は相互相関関数を算出した結果明瞭に現れた欠陥表面波である。こうして、図５ではランダムノイズに埋もれ識別することのできなかった欠陥表面波が、相互相関関数を算出することにより図６に示すように欠陥表面波２１が明瞭に識別できるようになったことがわかる。
【００１４】
演算器８の演算速度が十分大きい場合には、繰り返し発信されるバースト波電流の合間に演算を完了できるので、その場合にはデータ蓄積器８を必要としない。また繰り返して受信される超音波信号の１回毎に相互相関関数を算出するかわりに、繰り返して受信される超音波信号の複数回の加算平均を算出して信号対雑音比を改善してから相互相関関数を算出すれば所要時間は長くはなるがさらに効果が大きくなることは言うまでもない。 対象となる欠陥は表面欠陥とは限らず表面近くの内部欠陥でもこの方法は適用できる。被検査材料は厚鋼板とは限らずアルミニウム合金、銅等の導電性材料ならどのような材料の検査にも適用できる。 また表面波用の電磁超音波探触子と同じ構造を有する板波（Ｌａｍｂ波およびＳＨ板波）用の電磁超音波探触子による板状の導電性材料の板波（Ｌａｍｂ波およびＳＨ板波）による検査にもこの方法は適用できる。
【００１５】
【発明の効果】
相互相関関数を算出することにより、表面欠陥あるいは表面近くの内部欠陥から反射されてきたランダムノイズに埋もれた小さな欠陥表面波信号あるいは欠陥板波信号を抽出することのできる電磁超音波検査方法を実現することができ、その結果欠陥の誤検出が皆無となり信頼性も飛躍的に向上する。従前の超音波検査のように接触媒質を使用する必要もなく、その結果検査コストの大幅な削減が可能となる。本発明はこのように優れた実用的効果を有するものである。
【図面の簡単な説明】
【図１】本発明の相互相関法を用いた電磁超音波検査方法を説明するための電磁超音波検査装置の概要図である。
【図２】表面波発信用の電磁超音波探触子を説明するための図である。
【図３】表面波受信用の電磁超音波探触子を説明するための図である。
【図４】従来の方法で大きな表面欠陥を有する厚鋼板を検査した結果を表す図である。
【図５】従来の方法で小さな表面欠陥を有する厚鋼板を検査した結果を表す図である。
【図６】本発明の相互相関法を用いた電磁超音波検査方法で小さな表面欠陥を有する厚鋼板を検査した結果を表す図である。
【符号の説明】
１ 厚鋼板
２ 表面欠陥
３ パルス送信器
４ 表面波発信用の電磁超音波探触子
５ 表面波受信用の電磁超音波探触子
６ 増幅器
７ ＡＤ変換器
８ データ蓄積器
９ 演算器
１０ 出力装置
１１ 表面波伝播の経路
１２ 永久磁石
１３ コイル
１４ 永久磁石
１５ コイル
１６ 空間を隔てた電磁的誘導による電気信号
１７ 直達表面波
１８ 欠陥表面波
１９ ランダムノイズ
２０ 相互相関関数を算出した結果小さくなったランダムノイズ
２１ 相互相関関数を算出した結果明瞭に現れた欠陥表面波[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inspection method for searching for a defect inside or near a surface of a material using a surface wave or a plate wave of an ultrasonic wave.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, ultrasonic surface waves are often used to inspect a surface layer of a material such as a thick steel plate made in an ironworks. For example, Japanese Patent Application Laid-Open No. 6-331603 discloses a surface defect inspection method using a tire probe having a variable angle vibrator therein. However, in this method, in order to transmit the ultrasonic waves emitted from the variable angle transducer in the tire probe to the surface of the material, the tire probe is brought into contact with the material surface via a medium liquid such as water, and the tire probe is performed. It is necessary to establish an acoustic coupling between the element and the material surface. The medium liquid such as water used in this case does not always remain only around the tire probe, and may flow on the material surface and spread to the propagation path of the surface wave. There is a problem that the medium liquid cannot be distinguished from the surface defect and is erroneously detected.
[0003]
Further, ultrasonic wave waves are often used to inspect the surface layer of a material such as a thin steel plate. However, the same problem also occurs with respect to a tire probe used therefor.
[0004]
As a method for solving such a problem, an electromagnetic ultrasonic method (EMAT) capable of transmitting and receiving ultrasonic waves without contacting a material without using a medium liquid such as water has been invented. It is disclosed in Chapter 3 Section 4 of "Ultrasonic Handbook" (publisher: Maruzen, date of publication: August 1999). However, in principle, the electromagnetic ultrasonic method has low efficiency in transmitting and receiving ultrasonic waves due to low efficiency of electric / acoustic energy conversion. To compensate for this, an amplifier with a large amplification factor is used to amplify small ultrasonic signals. There is a need to. Since an amplifier with a high amplification factor also amplifies minute random noise at the same time, small ultrasonic signals reflected from a target surface defect or an internal defect near the surface tend to be buried in random noise and are erroneously detected. Was the biggest cause.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and provides an electromagnetic ultrasonic inspection method capable of extracting a small ultrasonic signal buried in random noise reflected from a surface defect or an internal defect near the surface. The task is to provide.
[0006]
[Means to solve the problem]
Means for solving the above-mentioned problem related to inspection by surface waves is to provide an electromagnetic ultrasonic probe for transmitting surface waves and an electromagnetic ultrasonic probe for receiving surface waves at a short distance on the surface of the material to be inspected. Receiving both a direct surface wave transmitted by the electromagnetic ultrasonic probe for transmitting the surface wave and propagated over the short distance and a defect surface wave reflected from a surface defect or an internal defect near the surface. Defect surface wave buried in random noise by calculating the cross-correlation function between the direct surface wave and the defect surface wave after receiving and amplifying by the electromagnetic ultrasonic probe for use and digitizing by the AD converter Is extracted.
[0007]
Means for solving the above-mentioned problem relating to flaw detection by a plate wave is to provide an electromagnetic ultrasonic probe for transmitting a plate wave and an electromagnetic ultrasonic probe for receiving a plate wave at a short distance on the surface of a material to be inspected. Both a direct plate wave transmitted by the electromagnetic ultrasonic probe for transmitting the plate wave and propagated in the short distance and a defective plate wave reflected from a surface defect or an internal defect near the surface for receiving the plate wave. The defect plate wave buried in random noise is calculated by calculating the cross-correlation function between the direct plate wave and the defect plate wave after receiving by the electromagnetic ultrasonic probe, amplifying and digitizing by the AD converter. It is to extract.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a schematic diagram showing an outline of an electromagnetic ultrasonic inspection apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a steel plate to be inspected, 2 denotes a surface defect, 3 denotes a pulse transmitter, 4 denotes an electromagnetic ultrasonic probe for transmitting a surface wave, and 5 denotes an electromagnetic ultrasonic probe for transmitting a surface wave. Electromagnetic ultrasonic probe for receiving surface waves provided at a short distance (8 cm) from the probe 4, 6 is an amplifier, 7 is an AD converter, 8 is a data storage device, 9 is a calculator, 10 is an output device. It is. The data accumulator 8 is configured by a computer IC memory, but may be a computer hard disk instead of the IC memory.
The waveform arrow 11 indicates that the surface wave transmitted by the electromagnetic ultrasonic probe 4 for transmitting a surface wave propagates on the surface of the steel material and is reflected back by the surface defect 2. FIG. 2A is a bottom view of the electromagnetic ultrasonic probe 4 for transmitting a surface wave, and FIG. 2B is a diagram of the electromagnetic ultrasonic probe 4 for transmitting a surface wave and the thick steel plate 1 as an object. It is a figure showing a relation. FIG. 3A is a bottom view of the electromagnetic ultrasonic probe 5 for receiving a surface wave, and FIG. 3B is a diagram showing the electromagnetic ultrasonic probe 5 for receiving a surface wave and the thick steel plate 1 as an object. It is a figure showing a relation. Reference numerals 12 and 14 denote permanent magnets, and reference numerals 13 and 15 denote coils having reciprocating reciprocating lines. Although a permanent magnet is used in FIGS. 2 and 3, an electromagnet may be used. As can be seen from FIGS. 2 and 3, the electromagnetic ultrasonic probe 4 for transmitting a surface wave and the electromagnetic ultrasonic probe 5 for receiving a surface wave have exactly the same structure. It is generally well-known that an electromagnetic ultrasonic probe having such a structure can transmit and receive a surface wave, as disclosed in FIGS. 9 and 10 of JP-A-7-77465. The principle will be briefly described. When a transmission current is supplied from the pulse transmitter 3 to the coil 13 of the electromagnetic ultrasonic probe 4 for transmitting a surface wave shown in FIG. 2, an eddy current flows on the surface of the thick steel plate 1 by electromagnetic induction. A surface wave is transmitted by the Lorentz force between the eddy current and the magnetic field generated by the permanent magnet 12 and the magnetostrictive effect of the thick steel plate 1. When the surface wave passes directly below the surface acoustic wave receiving electromagnetic probe of FIG. 3, an electric signal is generated in the coil 15 by a physical process completely opposite to the transmission, and the surface wave is received.
[0009]
As another example of the implementation, instead of the electromagnetic ultrasonic probe shown in FIGS. 2 and 3, Chapter 3 of "Ultrasonic Handbook" (publisher: Maruzen, date of publication: August 1999) Section 4 The surface wave can be obtained even when using the same structure as the Lamb wave electromagnetic ultrasonic probe of the type using a magnet having a magnetic field component parallel to the material surface disclosed in Fig. 3.9.1. Since transmission and reception can be performed, this may be used, or an electromagnetic ultrasonic probe of a type that transmits and receives SH waves to the surface disclosed in FIG. 1 of JP-A-2000-187022 may be used.
[0010]
The pulse transmitter 3 transmits a burst wave current having a frequency of 1 MHz, a wave number of 10, and a repetition frequency of 400 Hz to the electromagnetic ultrasonic probe 4 for transmitting a surface wave. Then, a surface wave is transmitted to the surface of the thick steel plate 1 according to the principle described above. In FIG. 1, the surface wave first propagates rightward and reaches the direct surface by an electromagnetic ultrasonic probe 5 for receiving surface waves, which is provided at a distance of 8 cm from the electromagnetic ultrasonic probe 4 for transmitting surface waves. It is received as a wave, further propagates to the right, is reflected by a surface defect 2 at a distance of 28 cm from the electromagnetic ultrasonic probe 4 for transmitting a surface wave, propagates to the left, and propagates to the left. It is received by the probe 5 as a defect surface wave. The amplifier 6 amplifies the direct surface wave and the defective surface wave.
[0011]
FIG. 4 shows an example of a surface wave signal obtained by a conventional method in which a surface defect 2 is sufficiently amplified (3.5 cm in length and 1 mm in depth) and thus remains amplified, that is, a cross-correlation function is not calculated. Is shown. The horizontal axis represents time, and the vertical axis represents the magnitude of the surface wave signal. In FIG. 4, reference numeral 16 denotes an electric signal generated by electromagnetic induction across a space by a burst wave current for transmitting an ultrasonic wave. 17 is a direct surface wave, 18 is a defect surface wave, and 19 is a random noise. In this case, since the surface defect 2 is sufficiently large (3.5 cm in length and 1 mm in depth), the defect surface wave 18 is also large, and there is no problem because it is clearly received as shown in FIG.
[0012]
FIG. 5 shows an example of a surface wave signal according to a conventional method which is still amplified, that is, a cross-correlation function is not calculated when the surface defect 2 is small (length 1.5 cm, depth 0.3 mm). Is shown. In FIG. 5, reference numeral 16 denotes an electric signal generated by electromagnetic induction separated from a space by a burst wave current for transmitting an ultrasonic wave. 17 is a direct surface wave, and 19 is a random noise. In this case, the direct surface wave 17 is clearly detected, but the defective surface wave is buried in the random noise 19 and cannot be identified. That is, according to FIG. 5, when the surface defect 2 is small (length 1.5 cm, depth 0.3 mm), the received defect surface wave is also small and is buried in random noise, and is identified as a defect surface wave. Turns out to be impossible.
[0013]
The inventor of the present invention first enlarged and investigated the direct surface wave 17 and the defect surface wave 18 reflected from the surface defect, and found that both were different in size but very similar in shape. . Further, by utilizing this fact, it has been found that a defect surface wave can be clearly extracted by calculating a cross-correlation function between a direct surface wave and a defect surface wave buried in random noise. That is, in FIG. 1, the ultrasonic signal amplified by the amplifier 6 is digitized by the AD converter 7 and stored in the data storage 8. The arithmetic unit 8 calculates a cross-correlation function between the direct surface wave and the defect surface wave from the accumulated data according to the following equation.
Figure 0003581931
Here, A (i × Δt) is the i-th digital value obtained by digitizing the direct surface wave at the time interval of Δt, and B ((ij) × Δt) is the time when the defect surface wave is Δt. Represents the (ij) th digital value digitized at intervals. C (j × Δt) is the j-th digital value of the calculated cross-correlation function. FIG. 6 shows the cross-correlation function thus calculated. In FIG. 6, reference numeral 20 denotes a random noise reduced as a result of calculating the cross-correlation function, and reference numeral 21 denotes a defect surface wave which clearly appears as a result of calculating the cross-correlation function. In this manner, the defect surface wave buried in the random noise in FIG. 5 and cannot be identified can be clearly identified as shown in FIG. 6 by calculating the cross-correlation function. Understand.
[0014]
When the operation speed of the operation unit 8 is sufficiently high, the operation can be completed between the burst wave currents repeatedly transmitted, and in that case, the data accumulator 8 is not required. Also, instead of calculating the cross-correlation function for each of the repeatedly received ultrasonic signals, the signal-to-noise ratio is improved by calculating the averaging of the repeatedly received ultrasonic signals a plurality of times. If the cross-correlation function is calculated, the required time becomes longer, but it goes without saying that the effect is further increased. This method is applicable not only to the surface defect but also to an internal defect near the surface. The material to be inspected is not limited to a thick steel plate, but can be applied to inspection of any conductive material such as aluminum alloy and copper. Further, a plate wave (Lamb wave and SH plate) of a plate-shaped conductive material is formed by an electromagnetic ultrasonic probe for plate wave (Lamb wave and SH plate wave) having the same structure as the electromagnetic wave probe for surface wave. This method can also be applied to inspection by wave).
[0015]
【The invention's effect】
By calculating the cross-correlation function, an electromagnetic ultrasonic inspection method that can extract a small defect surface wave signal or defect plate wave signal buried in random noise reflected from surface defects or internal defects near the surface is realized. As a result, there is no erroneous detection of a defect, and the reliability is dramatically improved. It is not necessary to use a couplant as in the conventional ultrasonic inspection, and as a result, inspection costs can be greatly reduced. The present invention has such excellent practical effects.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an electromagnetic ultrasonic inspection apparatus for explaining an electromagnetic ultrasonic inspection method using a cross-correlation method of the present invention.
FIG. 2 is a diagram for explaining an electromagnetic ultrasonic probe for transmitting a surface wave.
FIG. 3 is a diagram for explaining an electromagnetic ultrasonic probe for receiving a surface wave.
FIG. 4 is a diagram showing a result of inspecting a thick steel plate having a large surface defect by a conventional method.
FIG. 5 is a diagram showing a result of inspecting a thick steel plate having a small surface defect by a conventional method.
FIG. 6 is a diagram showing a result of inspecting a thick steel plate having a small surface defect by the electromagnetic ultrasonic inspection method using the cross-correlation method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Thick steel plate 2 Surface defect 3 Pulse transmitter 4 Electromagnetic ultrasonic probe for transmitting surface waves 5 Electromagnetic ultrasonic probe 6 for receiving surface waves 6 Amplifier 7 A / D converter 8 Data accumulator 9 Computing unit 10 Output device Reference Signs List 11 Path of surface wave propagation 12 Permanent magnet 13 Coil 14 Permanent magnet 15 Coil 16 Electric signal by electromagnetic induction separated by space 17 Direct surface wave 18 Defect surface wave 19 Random noise 20 Calculated cross-correlation function reduced random Noise 21 Defect surface wave that clearly appears as a result of calculating the cross-correlation function

Claims (2)

表面波発信用の電磁超音波探触子と表面波受信用の電磁超音波探触子とを被検査材料の表面に短距離を隔てて設け、該表面波発信用の電磁超音波探触子により発信され該短距離を伝播してきた直達表面波と表面欠陥あるいは表面近くの内部欠陥から反射されてきた欠陥表面波の両方を該表面波受信用の電磁超音波探触子により受信し、増幅し、ＡＤ変換器によりディジタル化した後に該直達表面波と該欠陥表面波との相互相関関数を算出することによりランダムノイズに埋もれた欠陥表面波を抽出することを特徴とする電磁超音波検査方法An electromagnetic ultrasonic probe for transmitting a surface wave and an electromagnetic ultrasonic probe for receiving a surface wave are provided at a short distance on the surface of a material to be inspected, and the electromagnetic ultrasonic probe for transmitting a surface wave is provided. Receiving and amplifying both a direct surface wave transmitted by the short distance and a defect surface wave reflected from a surface defect or an internal defect near the surface by the electromagnetic ultrasonic probe for receiving the surface wave. And extracting a defect surface wave buried in random noise by calculating a cross-correlation function between the direct surface wave and the defect surface wave after digitization by an AD converter. 板波発信用の電磁超音波探触子と板波受信用の電磁超音波探触子とを被検査材料の表面に短距離を隔てて設け、該板波発信用の電磁超音波探触子により発信され該短距離を伝播してきた直達板波と表面欠陥あるいは表面近くの内部欠陥から反射されてきた欠陥板波の両方を板波受信用の電磁超音波探触子により受信し、増幅し、ＡＤ変換器によりディジタル化した後に該直達板波と該欠陥板波との相互相関関数を算出することによりランダムノイズに埋もれた欠陥板波を抽出することを特徴とする電磁超音波検査方法An electromagnetic ultrasonic probe for transmitting a plate wave and an electromagnetic ultrasonic probe for receiving a plate wave are provided at a short distance on the surface of the material to be inspected, and the electromagnetic ultrasonic probe for transmitting a plate wave Both the direct plate wave transmitted and transmitted by the short distance and the defective plate wave reflected from a surface defect or an internal defect near the surface are received and amplified by an electromagnetic ultrasonic probe for receiving a plate wave. Extracting a defective plate wave buried in random noise by calculating a cross-correlation function between the direct plate wave and the defective plate wave after digitizing by an AD converter.
JP2002130996A 2002-03-28 2002-03-28 Electromagnetic ultrasonic inspection method using cross-correlation method Expired - Fee Related JP3581931B2 (en)

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CN103134856A (en) * 2013-02-19 2013-06-05 重庆镪镔实业有限公司 Electromagnetic ultrasonic detecting device and method for surface defects of cold rolled ribbed steel bar
CN104007179B (en) * 2014-05-12 2017-01-11 北京化工大学 Determination apparatus for surface internal stress of polymer plane thin-plate product and implementation method thereof
JP2016027321A (en) * 2014-07-03 2016-02-18 Ｊｆｅエンジニアリング株式会社 Ultrasonic inspection method and probe installation fixture
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CN106363030A (en) * 2016-08-22 2017-02-01 重庆伟铭金属有限公司 Impedance measurement-based PC steel bar electric induction excitation frequency control apparatus and method
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