JP5306919B2 - Ultrasonic flaw detection method and apparatus - Google Patents
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Description
本発明は、超音波探傷法及び装置に関する。更に詳述すると、本発明は、斜角探触子と垂直探触子を用いて傷先端に超音波を入射することによって発生する縦波回折波を最短径路で受信する超音波探傷法(短経路回折波法(Short Path of Diffraction:本明細書ではSPOD法と呼ぶ))の改良に関する。 The present invention relates to an ultrasonic flaw detection method and apparatus. More specifically, the present invention relates to an ultrasonic flaw detection method (short method) in which a longitudinal wave diffracted wave generated by incidence of ultrasonic waves on the wound tip using a bevel probe and a vertical probe is received on the shortest path. The present invention relates to an improvement in the path diffracted wave method (Short Path of Diffraction).
本発明者等は、先に、超音波探傷試験におけるき裂深さ測定法として、垂直および斜角探触子を送受信に用いる簡便・高精度なSPOD法を開発し、反欠陥側および欠陥側探傷において、高精度にき裂深さを測定できることを確認した(特許文献1参照)。 The present inventors have previously developed a simple and highly accurate SPOD method using vertical and oblique probes for transmission and reception as a crack depth measurement method in an ultrasonic flaw detection test. In flaw detection, it was confirmed that the crack depth can be measured with high accuracy (see Patent Document 1).
このSPOD法は、検査対象物に斜角探触子によって斜めから超音波を入射し、傷の端部において発生する縦波回折波を傷の真上の垂直探触子で受信する方法であり、傷の端部から直接垂直探触子へ向かう回折波と底面に一旦向かって反射してくる回折波との到達時間差から傷高さを求めるものである。このSPOD法によると、超音波ビームのパスが短いため、結晶粒が大きく超音波の減衰が大きいステンレス鋼やインコネル(Special Metals Corporationの登録商標)などに対しても使えるし、それらの溶接部の傷の高さを簡単かつ高精度に測定可能とする。しかも、傷の端部において発生する回折波の直接波と間接波との到達時間差だけできず端部の高さ位置惹いてはきず高さを簡便に算出することができ、検査員に相当の経験と技量がなくとも、精度良く測定できるなどのさまざまの利点を有することから、期待されている探傷法である。 This SPOD method is a method in which an ultrasonic wave is incident on an inspection object obliquely by an oblique probe, and a longitudinal wave diffracted wave generated at the edge of the wound is received by a vertical probe directly above the wound. The flaw height is obtained from the arrival time difference between the diffracted wave directly from the edge of the flaw toward the vertical probe and the diffracted wave once reflected toward the bottom surface. According to this SPOD method, since the path of the ultrasonic beam is short, it can be used for stainless steel and Inconel (registered trademark of Special Metals Corporation) with large crystal grains and large ultrasonic attenuation. The height of the flaw can be measured easily and with high accuracy. Moreover, not only the arrival time difference between the direct wave and the indirect wave of the diffracted wave generated at the edge of the scratch, but the height of the edge can be easily calculated and the height of the scratch can be calculated easily. This is a promising flaw detection method because it has various advantages such as accurate measurement without experience and skill.
しかしながら、従前のSPOD法によると、斜角探触子のビーム中心軸と垂直探触子のビーム中心軸とが交わる点(本明細書においては交軸点と呼ぶ)において感度が良いものであるが、その交点から反射体・傷などが外れるに従って反射体・傷などに対応するエコーの強度が低下するという問題を有している。例えば、裏面開口部周辺に焦点を合わせた場合、浅いスリットには感度が良いが、深いスリットにはエコー強度が大きく減衰し感度が悪くなるという問題が生ずる。このため、厚肉の検査対象物における全厚の体積検査で検出すべきき裂先端を、厚さ方向の位置によっては見逃す可能性がある。したがって、実機へ適用するためには、検査対象物の厚さ方向において、検出感度があまり変化しないこと即ち検出感度が低下しないことが望ましい。 However, according to the conventional SPOD method, the sensitivity is good at a point where the beam center axis of the oblique angle probe and the beam center axis of the vertical probe intersect (referred to as an intersection point in this specification). However, there is a problem that the intensity of the echo corresponding to the reflector / scratch decreases as the reflector / scratch deviates from the intersection. For example, when focusing on the periphery of the back opening, the sensitivity is good for a shallow slit, but the deep slit has a problem that the echo intensity is greatly attenuated and the sensitivity is deteriorated. For this reason, the crack tip to be detected in the full-thickness volume inspection in the thick inspection object may be missed depending on the position in the thickness direction. Therefore, in order to apply to an actual machine, it is desirable that the detection sensitivity does not change so much in the thickness direction of the inspection object, that is, the detection sensitivity does not decrease.
一方、超音波探傷法を全厚の体積検査へ適用するには、検査対象物の厚さ方向のき裂先端位置に関わらず先端を検出する必要がある。このため、従来のSPOD法を全厚の体積検査へ適用する場合には、交軸点が反射位置(傷の位置・反射体の位置)に合致するように、かなりの量の探触子の組み替えが必要となることから、探触子間隔および屈折角を変えた複数回の機械走査が要求されるが、このような検査要領は実機の非破壊検査では非現実的である。このため、SPOD法で得られるエコー強度はきずの深さに大きく依存しており、きずが深くなるほど大幅にエコー強度が低下していた。そうすると、どこにどの位の深さの傷があるか不明の場合に従来のSPOD法を適用することは難しい。また、垂直探傷では垂直な疲労亀裂の先端のきずは検出することができない。 On the other hand, in order to apply the ultrasonic flaw detection method to a full-thickness volume inspection, it is necessary to detect the tip regardless of the crack tip position in the thickness direction of the inspection object. For this reason, when the conventional SPOD method is applied to the full-thickness volume inspection, a considerable amount of the probe is required so that the intersection point coincides with the reflection position (scratch position / reflector position). Since recombination is required, a plurality of mechanical scans with different probe intervals and refraction angles are required, but such inspection procedures are impractical for nondestructive inspection of actual machines. For this reason, the echo intensity obtained by the SPOD method greatly depends on the depth of the flaw, and the echo intensity greatly decreases as the flaw becomes deeper. Then, it is difficult to apply the conventional SPOD method when it is unclear where and how deep there is a flaw. In addition, vertical flaw detection cannot detect a flaw at the tip of a vertical fatigue crack.
また、実機の主要配管において発生した開口き裂または内部き裂は、配管内面に対して必ずしも垂直に進展するとは限らず、き裂の傾斜によってき裂深さ測定に必要な端部エコーの強度は大きく変化する。例えば、本発明者等の実験によると、従来の斜角探傷法によって傾斜したき裂の深さ測定を行う場合、傾斜角が50°の傾斜き裂のように、き裂の反射面と超音波のビーム中心軸のなす角が90°に近づくと、き裂面での鏡面反射が顕著になり、端部エコーと開口部エコーとを分離できなくなるという問題がある。さらには、この種のき裂深さ測定には超音波周波数が与える影響もあると考えられる。しかしながら、従来、傾斜したき裂の深さ測定にSPOD法を適用することが可能か、さらには他の測定法よりも優位性が有るのか否かについては明らかとされておらず、内部き裂の状況が不明な状態においてはSPOD法を適用することの判断が難しいものであった。 In addition, the opening crack or internal crack generated in the main pipe of the actual machine does not necessarily propagate perpendicularly to the inner surface of the pipe, but the strength of the end echo required for crack depth measurement due to the crack inclination. Changes greatly. For example, according to the experiments by the present inventors, when measuring the depth of a crack tilted by the conventional oblique flaw detection method, the surface of the crack reflected from the surface of the crack as a tilt crack with a tilt angle of 50 °. When the angle formed by the central axis of the sound wave approaches 90 °, there is a problem that specular reflection at the crack surface becomes remarkable and the end echo and the opening echo cannot be separated. Furthermore, it is considered that this kind of crack depth measurement also has an influence of ultrasonic frequency. However, conventionally, it has not been clarified whether the SPOD method can be applied to the measurement of the depth of an inclined crack, and whether it has an advantage over other measurement methods. It was difficult to determine whether to apply the SPOD method in a state in which the situation was unknown.
本発明は、SPOD法において検査対象物の厚さ方向の検出感度差を抑制する方法、即ち厚さ方向の感度低下をできるだけ低減し深さが変わってもほぼ同じ感度で検出できるようにする方法を提供することを目的とする。また、本発明は、SPOD法において、周波数の大きさや傷の傾斜の有無にかかわらず、き裂先端に対応するエコーを確実に検出できる方法を提供することを目的とする。 The present invention is a method for suppressing a difference in detection sensitivity in the thickness direction of an inspection object in the SPOD method, that is, a method for reducing sensitivity reduction in the thickness direction as much as possible and enabling detection with substantially the same sensitivity even when the depth changes. The purpose is to provide. Another object of the present invention is to provide a method that can reliably detect an echo corresponding to a crack tip in the SPOD method regardless of the magnitude of the frequency and the presence or absence of a crack inclination.
かかる目的を達成するため、請求項1記載の発明にかかる超音波探傷法は、フェーズドアレイを用い、前記フェーズドアレイの一部の振動素子で垂直送信を行うと共に一部の振動素子群で斜角受信を行い、前記フェースドアレイが設置された範囲で試験体の画像化する範囲をメッシュ状に区画して少なくとも垂直送信の超音波ビームの範囲内の各区画毎に複数の前記振動素子で斜角受信したAスコープ波形信号を加算する開口合成処理を前記送受信用振動素子の間隔を一定に保った電子走査を行うことにより前記画像化範囲の全域に亘って行い、前記開口合成処理により合成された各区画の位置における前記Aスコープ波形の振幅値を輝度値に変換する輝度変調処理を施して画像表示手段の対応する画素に表示することにより検査対象の任意断面のBスコープ画像を構築するようにしている。 In order to achieve this object, the ultrasonic flaw detection method according to the first aspect of the present invention uses a phased array, performs vertical transmission with some vibration elements of the phased array, and performs oblique transmission with some vibration element groups. The range in which the facet array is installed is divided into a mesh shape within the range where the faced array is installed, and at least in each of the sections within the range of the ultrasonic beam for vertical transmission, the plurality of vibration elements are oblique. Aperture synthesis processing for adding the A-scope waveform signal received at the angle is performed over the entire imaging range by performing electronic scanning with the interval between the transmitting and receiving vibration elements kept constant, and synthesized by the aperture synthesis processing. An arbitrary object to be inspected can be obtained by performing luminance modulation processing for converting the amplitude value of the A scope waveform at the position of each section into a luminance value and displaying it on the corresponding pixel of the image display means. And so as to construct a B-scope image of the surface.
また、請求項2記載の発明は、請求項1記載の超音波探傷法において、垂直送信を行う送信用振動素子を挟んで両側に斜角受信を行う受信用振動素子群を配置するようにしている。 According to a second aspect of the present invention, in the ultrasonic flaw detection method according to the first aspect, a receiving vibration element group that performs oblique reception is disposed on both sides of a transmitting vibration element that performs vertical transmission. Yes.
さらに、送信用振動素子と受信用振動素子群とは、隣接しても良いし、場合によっては送信用振動素子は受信用振動子の一部に含まれても良いが、送信用振動素子と受信用振動素子群との間には少なくも1素子分のギャップが配置されていることが好ましい。 Further, the transmission vibration element and the reception vibration element group may be adjacent to each other, and in some cases, the transmission vibration element may be included in a part of the reception vibrator. It is preferable that a gap of at least one element is disposed between the receiving vibration element group.
さらに、請求項4記載の発明にかかる超音波探傷装置は、複数の小さな振動素子を一列に配置したフェーズドアレイと、前記フェーズドアレイの一部の振動素子に垂直送信を行わせると共に一部の振動素子群に斜角受信を行わせ、かつ前記フェースドアレイが設置された範囲で試験体の画像化する範囲をメッシュ状に区画して少なくとも垂直送信の超音波ビームの範囲内の各区画毎に複数の前記振動素子でAスコープ波形信号を斜角受信させると共に前記送受信用振動素子の間隔を一定に保って前記画像化範囲の全域に亘って電子走査を行う制御装置と、各区画の位置毎に複数の前記振動素子で斜角受信した前記Aスコープ波形信号を波形が重なるように加算する開口合成処理を行い、前記開口合成処理により合成された各区画の位置における前記Aスコープ波形の振幅値を輝度値に変換する輝度変調処理を施して画像表示手段の対応する画素に表示することにより検査対象の任意断面のBスコープ画像を構築する画像化処理装置とを備えるようにしている。 Furthermore, an ultrasonic flaw detection apparatus according to a fourth aspect of the invention includes a phased array in which a plurality of small vibration elements are arranged in a line, and a part of vibration elements of the phased array performs vertical transmission and a part of vibration. The element group performs oblique angle reception, and the range in which the specimen is imaged is divided into a mesh shape within the range where the faced array is installed, and at least for each division within the range of the ultrasonic beam for vertical transmission A control device for receiving an A scope waveform signal at an oblique angle by a plurality of the vibration elements and performing electronic scanning over the entire imaging range with a constant interval between the transmission / reception vibration elements, and for each position of each section An aperture synthesis process is performed in which the A scope waveform signals received at an oblique angle by a plurality of the vibration elements are added so that the waveforms overlap each other, and at the position of each section synthesized by the aperture synthesis process. An imaging processing apparatus for constructing a B-scope image of an arbitrary cross section to be inspected by performing luminance modulation processing for converting the amplitude value of the A-scope waveform into a luminance value and displaying it on a corresponding pixel of the image display means; I am doing so.
また、請求項5記載の発明は、請求項4記載の超音波探傷装置において、垂直送信を行う送信振動素子を挟んで両側に斜角受信を行う受信振動素子群を配置するようにしたものである。 According to a fifth aspect of the present invention, in the ultrasonic flaw detector according to the fourth aspect of the present invention, reception vibration element groups that perform oblique reception are arranged on both sides of a transmission vibration element that performs vertical transmission. is there.
さらに、本発明の超音波探傷装置において、送信用振動素子と受信用振動素子群とは、隣接しても良いし、場合によっては送信用振動素子は受信用振動子の一部に含まれても良いが、送信用振動素子と受信用振動素子群との間には少なくも1素子分のギャップが配置されていることが好ましい。。 Furthermore, in the ultrasonic flaw detector of the present invention, the transmitting vibration element and the receiving vibration element group may be adjacent to each other, and in some cases, the transmitting vibration element is included in a part of the receiving vibrator. However, it is preferable that a gap of at least one element is disposed between the transmitting vibration element and the receiving vibration element group. .
請求項1並びに4記載の超音波探傷法並びに超音波探傷装置によると、少なくとも垂直送信の超音波ビームの範囲内で試験体深さ方向に斜角受信ビームの焦点の位置を変化させながら電子走査することによりSPOD法と同じ波形を得ると共にこの波形への開口合成処理により距離振幅特性を修正することで、断面像構築領域の各画素の輝度を取得してSPOD法のBスコープ画像を構築するようにしているので、探傷範囲のBスコープ画像をSPOD法により効率良く構築できると共にエコー強度がスリット深さにあまり依存せずに強く受信でき、図5に示したように従来のSPOD法よりも検査対象物の厚さ方向の検出感度差を抑制して厚さ方向の感度低下を低減することができる。しかも、効率的に少ない受信波形の信号処理で見つけ難いき裂の先端を見つけられる。したがって、厚肉構造物の全厚の体積検査に適用でき、かつ従来SPOD法よりも高感度な検査が可能となる。ここで、探傷対象となるきずや欠陥などは、試験体の探触子を設置する面とは反対側の裏面側(あるいは内側の面)に開口する亀裂などの傷や、閉じている傷のBスコープ画像を得る場合に限られず、開口傷(探触子を配置する面側に開口して、裏面側に向けて進展している亀裂)の先端を求めこともできることはいうまでもなく、更には表層近くの閉じたきずなども鮮明にBスコープ画像として画像化できる。 According to the ultrasonic flaw detection method and the ultrasonic flaw detection apparatus according to claim 1 and 4, electronic scanning is performed while changing the focal position of the oblique reception beam in the depth direction of the specimen at least within the range of the ultrasonic beam for vertical transmission. As a result, the same waveform as the SPOD method is obtained, and the distance amplitude characteristic is corrected by aperture synthesis processing to this waveform, thereby acquiring the luminance of each pixel in the cross-sectional image construction region and constructing the B scope image of the SPOD method. As a result, the B scope image in the flaw detection range can be efficiently constructed by the SPOD method, and the echo intensity can be received strongly without depending on the slit depth. As shown in FIG. A difference in detection sensitivity in the thickness direction of the inspection object can be suppressed, and a decrease in sensitivity in the thickness direction can be reduced. In addition, it is possible to find the tip of a crack that is difficult to find with efficient signal processing of the received waveform. Therefore, it can be applied to the volume inspection of the total thickness of the thick structure and can be inspected with higher sensitivity than the conventional SPOD method. Here, flaws and defects to be inspected are scratches such as cracks opening on the back surface (or inner surface) opposite to the surface on which the probe of the specimen is installed, or closed scratches. Needless to say, it is not limited to obtaining a B-scope image, and it is also possible to obtain the tip of an opening scratch (a crack that opens toward the surface side where the probe is placed and progresses toward the back surface side). Furthermore, closed flaws near the surface layer can be clearly imaged as B-scope images.
また、垂直送信の少なくとも超音波ビームの範囲内で試験体の深さ方向に複数の振動素子で斜角受信しながら送受信素子の間隔を一定に保って電子走査するので、きず検出の条件に合致した超音波ビームが入射され、きずを見逃す恐れがない。そこで、どこにどの位の深さの傷があるのか不明の検査対象物・試験体にも本発明のSPOD法を適用することができる。 In addition, it meets the flaw detection conditions because electronic scanning is performed with a constant interval between the transmitting and receiving elements while receiving oblique angles with multiple vibrating elements in the depth direction of the specimen within at least the ultrasonic beam range of vertical transmission. The incident ultrasonic beam is incident and there is no fear of missing a flaw. Therefore, the SPOD method of the present invention can be applied to an inspection object / test body in which it is unknown where and how deep there is a flaw.
また、本発明者等の実験により、傾斜したき裂の深さ測定においては斜角探傷法による場合よりも優位性があることが判明した。そして、周波数の大きさや傷の傾斜の有無にかかわらず、き裂先端に対応するエコーを確実に検出できることが確認できた。 Further, the inventors' experiments have revealed that the measurement of the depth of an inclined crack has an advantage over the case of the oblique flaw detection method. It was confirmed that the echo corresponding to the crack tip could be reliably detected regardless of the magnitude of the frequency and the presence or absence of the crack slope.
また、請求項2並びに5記載の超音波探傷法及び装置によると、受信素子を送信素子の両脇に設けているので、左右対称な指示の重なりが生じてノイズがキャンセルされて端部エコーのS/N比が向上させられると共に、斜角受信のために本来斜めに出現する指示が重なり合ってその重なり部分が位相が合うので指示が左右対称となり、垂直探傷でないにもかかわらず、垂直探傷と同様の、実際の反射体により近い像が得られる。 Further, according to the ultrasonic flaw detection method and apparatus according to claims 2 and 5, since the receiving element is provided on both sides of the transmitting element, a symmetrical instruction overlap occurs, noise is canceled, and the end echo is Since the S / N ratio is improved and the instructions that appear obliquely for the reception of the oblique angle overlap and the overlapping portions are in phase, the instructions are symmetric, and although the vertical inspection is not vertical inspection, A similar image closer to the actual reflector can be obtained.
さらに、請求項3並びに6記載の超音波探傷法及び装置によると、送信素子と受信素子との間にギャップ・不動作振動素子が存在するために、幾何学的に垂直と斜角が効果的に成立する。この送信用振動素子と受信用振動素子との間隔・不動作振動素子の数が適切であればSPOD法の効果があがる。 Furthermore, according to the ultrasonic flaw detection method and apparatus according to claims 3 and 6, since there is a gap / non-operating vibration element between the transmitting element and the receiving element, geometrically vertical and oblique angles are effective. Is established. If the distance between the transmitting vibrating element and the receiving vibrating element and the number of non-operating vibrating elements are appropriate, the SPOD method is effective.
以下、本発明の構成を図面に示す実施形態に基づいて詳細に説明する。 Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.
図1および図2に本発明にかかる超音波探傷法の実施の一形態を示す。この超音波探傷法は、フェーズドアレイ1を用い、フェーズドアレイ1の一部の振動素子で垂直送信を行うと共に一部の振動素子群で斜角受信を行い、フェースドアレイ1が設置された範囲で試験体の画像化する範囲20をメッシュ状に区画して少なくとも垂直送信の超音波ビーム3tの範囲内の各区画2毎に複数の振動素子1rで斜角受信したエコー3r即ちAスコープ波形信号を加算する開口合成処理を送受信用振動素子1t,1rの間隔を一定に保った電子走査を行うことにより画像化範囲20の全域に亘ってくまなく重複して行い、開口合成処理により合成された各区画2の位置におけるAスコープ波形の振幅値を輝度値に変換する輝度変調処理を施して画像表示手段の対応する画素に表示することにより検査対象の任意断面のBスコープ画像を構築するようにしている。つまり、Bスコープ画像の各画素の輝度を開口合成処理により取得している。尚、明細書中においては、送信用の振動子を送信用振動素子1t、受信用の振動子を受信用振動素子1rと呼ぶ。また、非アクティブな振動素子1gは送受信用振動素子1t,1rの間のギャップを構成する。 1 and 2 show an embodiment of an ultrasonic flaw detection method according to the present invention. This ultrasonic flaw detection method uses a phased array 1, performs vertical transmission with some vibration elements of the phased array 1 and receives oblique angles with some vibration element groups, and a range in which the faced array 1 is installed Then, an echo 3r, that is, an A scope waveform signal received at an oblique angle by a plurality of vibration elements 1r for each of the sections 2 within the range of the ultrasonic beam 3t for vertical transmission at least in the range 20 to be imaged of the specimen. The aperture synthesis process for adding is performed electronically with the interval between the transmitting and receiving vibration elements 1t and 1r being kept constant, so that the entire area of the imaging range 20 is overlapped and synthesized by the aperture synthesis process. A luminance modulation process for converting the amplitude value of the A scope waveform at the position of each section 2 into a luminance value is performed and displayed on the corresponding pixel of the image display means, whereby the B cross section of an arbitrary cross section to be inspected is displayed. So that to construct the-loop image. That is, the luminance of each pixel of the B scope image is acquired by the aperture synthesis process. In the specification, the transmission vibrator is referred to as a transmission vibration element 1t, and the reception vibrator is referred to as a reception vibration element 1r. The inactive vibrating element 1g forms a gap between the transmitting / receiving vibrating elements 1t and 1r.
図3に上述の超音波探傷法を実施する装置の一実施形態を示す。この超音波探傷装置は、複数の小さな振動素子(以下、単に素子と呼ぶこともある)を一列に配置したフェーズドアレイ1と、フェーズドアレイ1の一部の振動素子に垂直送信を行わせると共に一部の振動素子群に斜角受信を行わせ、かつフェースドアレイ1が設置された範囲で試験体の画像化する範囲をメッシュ状に区画して少なくとも垂直送信の超音波ビームの範囲内の各区画毎に複数の振動素子でAスコープ波形信号を斜角受信させると共に送受信用振動素子の間隔を一定に保って画像化範囲の全域に亘って電子走査を行う制御装置4と、各区画の位置毎に複数の振動素子で斜角受信したAスコープ波形信号を波形が重なるように加算する開口合成処理を行い、開口合成処理により合成された各区画の位置におけるAスコープ波形の振幅値を輝度値に変換する輝度変調処理を施して画像表示手段7の対応する画素に表示することにより検査対象の任意断面のBスコープ画像を構築する画像化処理装置5とを備え、相反性と電子走査を利用して斜角探触子の屈折角や入射点間距離を変えて試験体深さ方向に垂直送信ビームと斜角受信ビームとの交点(焦点)位置を変化させながらSPOD法と同じ波形を得ると共にこの波形への開口合成処理により距離振幅特性を修正することで、断面像構築領域の各画素の輝度を取得してBスコープ画像を構築するようにしている。 FIG. 3 shows an embodiment of an apparatus for performing the above-described ultrasonic flaw detection method. This ultrasonic flaw detector has a phased array 1 in which a plurality of small vibration elements (hereinafter, simply referred to as elements) are arranged in a line, and causes a part of the vibration elements of the phased array 1 to perform vertical transmission and perform vertical transmission. The range in which the test piece is imaged within the range where the faced array 1 is installed is divided into a mesh shape within at least the range of the ultrasonic beam for vertical transmission. A control device 4 that receives an A-scope waveform signal at an oblique angle with a plurality of vibration elements for each section and performs electronic scanning over the entire imaging range while maintaining a constant interval between the transmission and reception vibration elements, and the position of each section Aperture synthesis processing is performed in which the A scope waveform signals received at an oblique angle by a plurality of vibration elements are added so that the waveforms overlap each other, and the A scope waveform at each position synthesized by aperture synthesis processing is modulated. An imaging processing device 5 for constructing a B-scope image of an arbitrary cross section to be inspected by performing luminance modulation processing for converting a value into a luminance value and displaying it on a corresponding pixel of the image display means 7, and having reciprocity SPOD method while changing the intersection (focal point) position of the vertical transmission beam and the oblique reception beam in the depth direction of the specimen by changing the refraction angle of the oblique probe and the distance between the incident points using electronic scanning By obtaining the same waveform and correcting the distance amplitude characteristics by aperture synthesis processing to this waveform, the brightness of each pixel in the cross-sectional image construction region is acquired and a B scope image is constructed.
超音波探傷器10は、例えばフェーズドアレイ1とコネクタ9を介して接続される制御装置(送受信回路)4と、複数の受信用振動子1rで斜角受信したAスコープ波形信号に対して開口合成処理を施してからBスコープ画像を生成する画像合成処理を行う画像化処理装置5と、これらに所定の処理を実行させるシステムソフトとUIソフトなどの必要なソフトをROMやその他の記憶手段に格納して制御する中央演算処理部6及びタッチパネルディスプレイ7などから構成される。送受信回路たる制御装置4は、送受信切替回路11と、送信回路12、受信アンプ14及び送受信制御回路13とを有し、送受信制御回路13によって送受信切替回路11と送信回路12と受信アンプ14とが制御されている。そして、メッシュ状に区画されて座標付けされた試験体の画像化範囲20の各区画2の位置において、各受信素子1rで受信されたAスコープ信号は画像化処理装置5のA/D変換回路15を経て並列演算回路16に入力され、開口合成処理を施してからBスコープ画像を生成する画像合成処理を行う。尚、図中の符号8はバスである。 The ultrasonic flaw detector 10, for example, performs aperture synthesis on a control device (transmission / reception circuit) 4 connected to the phased array 1 via a connector 9 and an A scope waveform signal received at an oblique angle by a plurality of receiving transducers 1 r. The image processing apparatus 5 that performs the image composition processing for generating the B scope image after performing the processing, and the necessary software such as system software and UI software for executing the predetermined processing are stored in the ROM or other storage means. The central processing unit 6 and the touch panel display 7 are controlled. The control device 4 serving as a transmission / reception circuit includes a transmission / reception switching circuit 11, a transmission circuit 12, a reception amplifier 14, and a transmission / reception control circuit 13. The transmission / reception control circuit 13 causes the transmission / reception switching circuit 11, the transmission circuit 12, and the reception amplifier 14 to be connected. It is controlled. The A scope signal received by each receiving element 1r at the position of each section 2 of the imaging range 20 of the test body partitioned and coordinated in a mesh shape is an A / D conversion circuit of the imaging processing device 5. 15 is input to the parallel arithmetic circuit 16, and after performing aperture synthesis processing, image synthesis processing for generating a B scope image is performed. Reference numeral 8 in the figure denotes a bus.
ここで、制御装置4は、フェーズドアレイ1の各振動素子に与えるパルス電圧の遅延時間を個別に制御して超音波ビームの集束や偏向を容易に制御可能にすると共に、フェーズドアレイ1の一部の素子1tに垂直送信を行わせ、一部の素子1r群で斜角受信を行わせることによって、少なくとも垂直送信の超音波ビーム3tの範囲内の各区画2毎に複数の振動素子1rでエコー3r(Aスコープ波形信号)を斜角受信させると共に送受信用振動素子1t,1rの間隔を一定に保って画像化範囲の全域に亘って電子走査を行うように制御する。これにより、垂直送信の超音波ビーム3tの重なりが生じて同じ区画2に対し垂直送信と斜角受信が繰り返される。通常、制御装置4の送受信制御回路13は、予め求められた遅延時間のパターンに従ってフェーズドアレイ1の複数の受信用振動素子1rの群に対して斜角受信位置を任意の区画2に焦点が一致するように制御する。例えば、フェースドアレイ1を試験体の上に設置して、置いた範囲で探傷範囲20をメッシュ状に区画して座標を設定し、各座標(各区画)と各斜角受信用振動素子1rとの幾何学的位置関係から各区画に焦点を合わせるための遅延時間のパターンが求められて記憶される。つまり、各区画2の点の座標が定まれば、上述の幾何学的関係は定まる。また、フェーズドアレイ1の位置はエンコーダ(図示省略)によって同時に記録されているので、前述の各区画2の座標は1つの座標軸上のものとして認識できる。このため、フェーズドアレイ1の設置位置を機械走査させることによって探傷範囲20を移動させても、各区画2の座標を一致させることができる。そこで、垂直ビーム3tの広がりの範囲内の各区画2の位置、即ちBスコープ画像を構成する画素に相当する位置で複数の受信用振動素子1rにより全厚方向に斜角受信をくまなく行うこと(換言すれば開口合成すること)を、アクティブな振動素子1t,1rをそれらの間隔を保って1素子分だけ走査方向(フェースドアレイの長さ方向)へずらす毎に繰り返すことによって、探傷範囲の各区画2毎にAスコープ波形を重複取得する。各受信用振動素子1rで受信されたAスコープ波形信号は、画像化処理装置5に入力されて同装置のA/D回路15においてデジタル信号に変換されてから各区画2毎に図示しないメモリなどの記憶手段に順次格納される。 Here, the control device 4 individually controls the delay time of the pulse voltage applied to each oscillating element of the phased array 1 so as to easily control focusing and deflection of the ultrasonic beam, and a part of the phased array 1. By transmitting a plurality of vibration elements 1r at least for each section 2 within the range of the ultrasonic beam 3t for vertical transmission. Control is performed so that 3r (A scope waveform signal) is received at an oblique angle and electronic scanning is performed over the entire imaging range with the interval between the transmitting and receiving vibration elements 1t and 1r being kept constant. As a result, overlapping of the ultrasonic beams 3t for vertical transmission occurs, and vertical transmission and oblique angle reception are repeated for the same section 2. In general, the transmission / reception control circuit 13 of the control device 4 has the focal point coincident with the arbitrary section 2 with respect to the group of the plurality of receiving vibration elements 1r of the phased array 1 according to the delay time pattern obtained in advance. Control to do. For example, the faced array 1 is placed on a specimen, the flaw detection range 20 is divided into a mesh shape within the set range, and coordinates are set. Each coordinate (each section) and each oblique angle receiving vibration element 1r are set. The delay time pattern for focusing on each section is obtained and stored from the geometrical positional relationship with. That is, if the coordinates of the points of each section 2 are determined, the above-described geometric relationship is determined. In addition, since the position of the phased array 1 is recorded simultaneously by an encoder (not shown), the coordinates of each of the sections 2 can be recognized as being on one coordinate axis. For this reason, even if the flaw detection range 20 is moved by mechanically scanning the installation position of the phased array 1, the coordinates of the respective sections 2 can be matched. Therefore, oblique angle reception is performed in all thickness directions by the plurality of receiving vibration elements 1r at the position of each section 2 within the range of the spread of the vertical beam 3t, that is, the position corresponding to the pixels constituting the B scope image. (In other words, aperture synthesis) is repeated each time the active vibration elements 1t and 1r are shifted by one element in the scanning direction (length direction of the faced array) while maintaining the distance therebetween. The A scope waveform is redundantly acquired for each of the sections 2. The A scope waveform signal received by each receiving vibration element 1r is input to the imaging processing device 5 and converted into a digital signal by the A / D circuit 15 of the device, and then a memory (not shown) for each section 2 or the like. Are sequentially stored in the storage means.
尚、斜角受信ひいては開口合成処理はエネルギーが存在しない領域即ち垂直送信の超音波ビーム3tの範囲の外の区画2について行っても開口合成の効果はなく、処理時間の無駄である。そこで、音の広がり(指向性)を考慮して垂直送信ビームの範囲内の区画2に焦点を合わせて斜角受信並びに開口合成を行う。振動子の寸法、周波数などでビームの広がり方(指向性)は容易に予測できることから、ビームの想定される広がり方を考慮して開口合成を施す範囲を定めることができる。尚、本発明では、フェーズドアレイ1の素子群の一部の素子を使って垂直送信を行う一方、一部の素子群を使って斜角受信を行うようにしているが、測定系が線形であれば、相反性により、傷先端に超音波を入射することによって発生する縦波回折波を最短径路で受信する短経路回折波法(SPOD法)と同じ波形が得られる。 Note that even if the oblique angle reception and thus the aperture synthesis process is performed on a region 2 where there is no energy, that is, the section 2 outside the range of the ultrasonic beam 3t for vertical transmission, there is no effect of aperture synthesis, and processing time is wasted. Therefore, in consideration of the spread of sound (directivity), oblique angle reception and aperture synthesis are performed focusing on the section 2 within the range of the vertical transmission beam. Since how the beam spreads (directivity) can be easily predicted based on the size and frequency of the vibrator, the range in which aperture synthesis is performed can be determined in consideration of the expected beam spreading method. In the present invention, while vertical transmission is performed using some elements of the element group of the phased array 1, oblique reception is performed using some elements, but the measurement system is linear. If present, due to reciprocity, the same waveform as the short path diffracted wave method (SPOD method) in which a longitudinal wave diffracted wave generated by incident ultrasonic waves on the wound tip is received through the shortest path can be obtained.
本実施形態のフェーズドアレイの場合、送信用振動素子1tと受信用振動素子1rとの間には、動作していない振動素子1gを設けて送信用振動素子1tと受信用振動素子1rとの間に一定の間隔(不動作領域)を空けている。この場合には、探傷領域の深い地点でも送信用振動素子1tに対して受信用振動素子1rが離れていることにより、容易かつ確実に斜角探傷を実現できる。幾何学的に垂直送信、斜角受信となるためには送信用振動素子1tと受信用振動素子1rとの間にギャップとなる不動作領域を設けることが簡単かつ効果的であり、送信用振動素子1tと受信用振動素子1rとの間隔が開いているほどSPOD法の効果を高める上で好ましい。ここで、送信用振動素子1tの数を増やすこと即ち送信用振動子1tの寸法を大きくすることは、疲労き裂の先端の指示のような微弱な指示を識別できるようにS/N比を向上させる手段として有効な手段の一つである。例えば、従来のフェーズドアレイ探触子を用いた垂直探傷で観測できなかった疲労き裂の先端の指示を送信用振動素子1tの数を増やすことによって識別できるようになる。尚、不動作領域の振動素子1gの数は試験体の肉厚に依存するものであり、適宜素子数が設定される。本実施形態の場合、使用するフェーズドアレイ探触子の素子数を64とした場合、例えば図2に示すように、受信用振動素子1r群を10素子、送信用振動素子1t数を1〜9、不動作領域の素子数を1〜5として、送信用振動素子1tの両脇に不動作領域を介在させて受信用振動素子1r群をそれぞれ10素子ずつ配置するようにしている。もっとも、送信用振動素子1tと受信用振動素子1rとの間の不動作領域は必ずしも設けなくとも良く、送信用振動素子1tと受信用振動素子1rの群とが隣接しても良いし、場合によっては送信用振動素子1tは受信用振動子1rの群に重なって含まれても良い。 In the case of the phased array of the present embodiment, a non-operating vibration element 1g is provided between the transmission vibration element 1t and the reception vibration element 1r, and the transmission vibration element 1t and the reception vibration element 1r are provided. A certain interval (non-operating area) is provided. In this case, the oblique flaw detection can be realized easily and reliably because the receiving vibration element 1r is separated from the transmission vibration element 1t even at a deep point in the flaw detection area. In order to achieve geometrical vertical transmission and oblique angle reception, it is simple and effective to provide a non-operating region that becomes a gap between the transmitting vibration element 1t and the receiving vibration element 1r. The larger the distance between the element 1t and the receiving vibration element 1r, the better the effect of the SPOD method. Here, increasing the number of transmitting vibration elements 1t, that is, increasing the size of the transmitting vibrator 1t increases the S / N ratio so that a weak instruction such as an instruction of the tip of a fatigue crack can be identified. This is one of the effective means for improving. For example, an indication of the tip of a fatigue crack that could not be observed by vertical flaw detection using a conventional phased array probe can be identified by increasing the number of transmitting vibration elements 1t. Note that the number of vibration elements 1g in the non-operating region depends on the thickness of the specimen, and the number of elements is appropriately set. In the case of this embodiment, when the number of elements of the phased array probe to be used is 64, for example, as shown in FIG. 2, the receiving vibration element 1r group has 10 elements and the transmission vibration element 1t has 1 to 9 vibration elements. The number of elements in the non-operating area is set to 1 to 5, and the receiving vibration element 1r group is arranged for each 10 elements with the non-operating area interposed on both sides of the transmitting vibration element 1t. However, the non-operating region between the transmitting vibration element 1t and the receiving vibration element 1r is not necessarily provided, and the group of the transmitting vibration element 1t and the receiving vibration element 1r may be adjacent to each other. Depending on the case, the transmitting vibration element 1t may be included so as to overlap the group of the receiving vibrator 1r.
また、垂直送信を行う送信用振動素子1tを挟んで両側に斜角受信を行う受信用振動素子1r群を配置することが好ましい。この場合には、端部エコーL1のS/N比を向上させると共に、図4の(B)に示すように左右対称の指示の重なりが生じて点に近づいた指示が得られる。しかしながら、場合によっては、片側にのみ受信用振動素子1r群を配置した受信としても良い。この場合には、左右対称の指示の重なりが生じないので、図4の(A)に示すように、指示に斜めの線が含まれて表れるが、それでも傷の存在並びに位置の検出ができないものではない。 In addition, it is preferable to arrange a group of receiving vibration elements 1r that perform oblique reception on both sides of the transmitting vibration element 1t that performs vertical transmission. In this case, the S / N ratio of the end echo L1 is improved, and as shown in FIG. 4B, an instruction that is close to a point is obtained due to the overlapping of symmetrical instructions. However, in some cases, reception may be performed in which the receiving vibration element 1r group is disposed only on one side. In this case, since there is no overlapping of symmetrical instructions, as shown in FIG. 4 (A), the instruction includes an oblique line, but it still cannot detect the presence and position of a flaw. is not.
画像化処理装置5は、各区画2の位置毎に複数の振動素子1rで斜角受信したAスコープ波形信号を波形が重なるように加算する開口合成処理を行い、開口合成処理により合成された各区画2の位置におけるAスコープ波形の振幅値を輝度値に変換する輝度変調処理を施して画像表示手段の対応する画素に表示することにより検査対象の任意断面のBスコープ画像を構築するものである。 The imaging processing device 5 performs aperture synthesis processing for adding the A scope waveform signals received at an oblique angle by the plurality of vibration elements 1r for each position of each section 2 so that the waveforms overlap each other, and each synthesized by aperture synthesis processing A B-scope image of an arbitrary cross section to be inspected is constructed by performing luminance modulation processing for converting the amplitude value of the A scope waveform at the position of the section 2 into a luminance value and displaying it on the corresponding pixel of the image display means. .
開口合成処理は、並列演算回路16で、各受信用振動素子1r毎の波形データから、各ビーム路程でのフライトタイムの振幅値を取り出し探傷範囲の区画2に対応する画像メモリーに加算し、引き続き、他の受信用振動素子1rで得られた波形データについても同様の処理を施して多数の反射波形のピーク値を同位相で加算することにより、信号強度を相対的に増加させるものである。これにより、その区画2に傷が存在すれば波形が足し合わされて波形の振幅値が大きくなり、傷が存在しなければ波形が足し合わされないので振幅が変わらない。つまり、欠陥からの多数の反射波形のピーク値が同位相で加算され、さらに輝度変調処理により鮮明な欠陥画像・画素が得られる。きずの存在しないバックグランド画像では、加算される波形が存在しないため波形値の増幅は起こらず相対的にバックグランドレベルが低減されることとなる。依って、これら処理を画像化処理領域の全てのメッシュに対して行うことにより、鮮明なBスコープ画像が合成される。 In the aperture synthesis process, the parallel arithmetic circuit 16 extracts the amplitude value of the flight time in each beam path from the waveform data for each receiving vibration element 1r, and adds it to the image memory corresponding to the section 2 of the flaw detection range. The same processing is applied to the waveform data obtained by the other receiving vibration element 1r, and the peak values of many reflected waveforms are added in the same phase, thereby relatively increasing the signal intensity. As a result, if there is a flaw in the section 2, the waveforms are added to increase the amplitude value of the waveform, and if there is no flaw, the waveforms are not added, so the amplitude does not change. That is, the peak values of a large number of reflected waveforms from the defect are added in the same phase, and a clear defect image / pixel is obtained by luminance modulation processing. In the background image in which no flaw exists, since the waveform to be added does not exist, the amplification of the waveform value does not occur, and the background level is relatively reduced. Therefore, a clear B-scope image is synthesized by performing these processes on all meshes in the imaging process area.
ここで、送信用振動素子1tを出た波は試験体の中を広がって伝播して行くので、超音波ビームの中心軸から外れる程にエネルギーは弱くなる。したがって、傷・反射体の位置が送受信用振動素子1rの直下から離れたところに存在する程に受信信号の遅れとエネルギー強度の減衰とが顕著となる。しかし、電子走査により垂直送信の位置を1素子分ずつずらしながら垂直送信の超音波ビーム3tの範囲内を試験体深さ方向にくまなく斜角受信することを繰り返すため、同じ区画2に対する開口合成処理の繰り返しによって波形のある受信信号がさらに増幅されるのに対し波形のない(きずの存在しないバックグランド画像)受信信号は変化しないため、相対的にバックグランドレベルが低減されてきずを示すエコー強度を明瞭なものとする。このことは、厚肉の検査対象物における深い位置にあるきずなどの検出の際に効果的である。小さな振動子を用いる場合、垂直送信の超音波ビームの広がりはより大きくなり、底部側においてはエネルギーの減衰が大きくなると共にエコーの減衰も大きくなり、感度が悪くなる。しかし、超音波ビーム3tの広がりが大きくなる底部側ほど、同じ区画2に対する開口合成処理の繰り返しが多くなって波形のある受信信号を増幅して相対的なバックグランドレベルの低減によりエコー強度の減衰を補って明瞭なものとすることができる。しかも、この開口合成処理により超音波の拡散による指示の広がりに対しても補正される効果を有している。他方、超音波ビーム3tの広がりが少ない試験体の表面側においては元々強い信号が得られるので、開口合成を重ねる必要はない。勿論、振動子の寸法を大きくして垂直送信の超音波ビームのエネルギを大きくする場合には、ビームの指向性が高いためビームの広がりは少なくなるが、送信用振動素子1tの直下(垂直送信の超音波ビームの中心軸上)にきずやき裂などの反射体が存在する場合には、強い受信信号・Aスコープ波形信号が取得されることから、底部側にあるきずからのエコーが減衰されたとしても大きく信号強度を損ねることはない。 Here, since the wave exiting the transmitting vibration element 1t spreads and propagates in the test body, the energy becomes weaker as it deviates from the central axis of the ultrasonic beam. Therefore, the delay of the received signal and the attenuation of the energy intensity become more prominent as the position of the scratch / reflector is located far from the position directly below the transmitting / receiving vibration element 1r. However, since the vertical transmission position is shifted by one element by electronic scanning and the oblique transmission is repeated throughout the range of the ultrasonic transmission beam 3t in the vertical direction, the aperture synthesis for the same section 2 is repeated. Repetition of the process further amplifies the received signal with the waveform, while the received signal without the waveform (background image without flaws) does not change, so the echo indicating that the background level has not been reduced relatively Make the strength clear. This is effective when detecting a flaw or the like at a deep position in a thick inspection object. When a small transducer is used, the spread of the ultrasonic beam for vertical transmission becomes larger, and at the bottom side, the attenuation of energy increases and the attenuation of echoes also increases, resulting in poor sensitivity. However, the bottom side where the spread of the ultrasonic beam 3t becomes larger, the repetition of the aperture synthesis process for the same section 2 increases, and the received signal having a waveform is amplified, and the echo intensity is attenuated by reducing the relative background level. Can be made clear. In addition, the aperture synthesis process has an effect of correcting the spread of instructions due to the diffusion of ultrasonic waves. On the other hand, since a strong signal is originally obtained on the surface side of the test body where the spread of the ultrasonic beam 3t is small, it is not necessary to repeat aperture synthesis. Of course, when enlarging the size of the transducer and increasing the energy of the ultrasonic beam for vertical transmission, the beam spread is reduced due to the high directivity of the beam, but directly under the transmitting vibration element 1t (vertical transmission). If a reflector such as a flaw or crack exists on the center axis of the ultrasonic beam, a strong received signal and A scope waveform signal are acquired, so the echo from the flaw on the bottom side is attenuated. Even if it does not, the signal strength is not greatly impaired.
B(brighthess)スコープ画像は、反射波の振幅を時間軸上に明るさの強弱に変換する輝度変調を行い、さらにプローブを走査して、プローブの位置情報と時間−輝度信号を2次元に描画し、検査対象の任意断面の断層像を表示するものものである。具体的には、開口合成処理により合成された波形上でその点のビーム路程に相当する値を画素値、即ち各収録点における輝度を示すものとしてメモリに記憶される。そして、この各画素での輝度に基づいて、Bスコープ画像が作成され、表示装置に表示される。この処理をBスコープ画像内の各データ収録点(画素に相当)について行う(各画素の輝度を開口合成処理により取得)。尚、本実施形態では、Bスコープ画像上のある点の影響を受けるAスコープ波形を探触子の指向性の半値幅に基づき抽出することとしている。
即ち、断面像構築領域の各画素の輝度を取得してBスコープ画像を構築する。
The B (brighthess) scope image performs luminance modulation that converts the amplitude of the reflected wave into brightness intensity on the time axis, and further scans the probe to draw the probe position information and the time-luminance signal in two dimensions. Then, a tomographic image of an arbitrary cross section to be inspected is displayed. Specifically, a value corresponding to the beam path of the point on the waveform synthesized by the aperture synthesis process is stored in the memory as a pixel value, that is, a luminance at each recording point. Based on the luminance at each pixel, a B scope image is created and displayed on the display device. This process is performed for each data recording point (corresponding to a pixel) in the B scope image (the luminance of each pixel is acquired by the aperture synthesis process). In this embodiment, the A scope waveform affected by a certain point on the B scope image is extracted based on the half-value width of the directivity of the probe.
That is, the B scope image is constructed by acquiring the luminance of each pixel in the cross-sectional image construction region.
なお、上述の実施形態は本発明の好適な実施の一例ではあるがこれに限定されるものではなく、本発明の要旨を逸脱しない範囲において種々変形実施可能である。例えば、本実施形態では、探触子を設置する面とは反対側の裏面側(あるいは内側の面)に開口する亀裂などの傷や、閉じている傷のBスコープ画像を得る場合について主に説明したが、開口傷(探触子を配置する面側に開口して、裏面側に向けて進展している亀裂)の先端を求め場合にも適用できることはいうまでもなく、更には表層近くの閉じたきずなども鮮明にBスコープ画像として画像化できる。また、垂直送信振動素子1tと斜角受信振動素子1rとの間に、不動作素子1gの領域を設けるようにしているが、場合によっては不動作領域を設けなくても良い。 The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the case of obtaining a B-scope image of a crack such as a crack opened on the back surface (or the inner surface) opposite to the surface on which the probe is installed or a closed wound is mainly obtained. Although explained, it is needless to say that it can also be applied to the case of finding the tip of an opening flaw (a crack that opens on the surface side where the probe is placed and progresses toward the back surface side). Close flaws can be clearly imaged as B-scope images. In addition, although the region of the non-operating element 1g is provided between the vertical transmission vibration element 1t and the oblique reception vibration element 1r, the non-operational area may not be provided depending on circumstances.
さらに、本実施形態では、垂直送信の超音波ビーム3tの範囲内の各区画2に対して斜角受信を行いかつ開口合成処理を施すようにしているが、場合によっては垂直送信の超音波ビーム3tの中心軸と斜角受信の超音波ビーム3rの中心軸との交点(交軸点)がメッシュ状に区画された各区画上となるように電子制御を行うことにより、走査するようにしても良い。この場合にも、垂直送信用の振動素子1tの直下にきずなどの反射体が存在する場合には、斜角受信の信号が強くなるので、厚肉検査物に適用しても底部側でのエコー強度の低減に対する抑制効果は上述の実施形態と遜色ないものが得られる。 Furthermore, in this embodiment, the oblique angle reception and the aperture synthesis processing are performed on each section 2 within the range of the vertical transmission ultrasonic beam 3t. Scanning is performed by performing electronic control so that the intersection (intersection axis point) between the central axis of 3t and the central axis of the oblique angle receiving ultrasonic beam 3r is on each section partitioned in a mesh shape. Also good. Also in this case, if there is a reflector such as a flaw directly under the vertical transmission vibrating element 1t, the oblique reception signal becomes strong. The effect of suppressing the echo intensity reduction is comparable to that of the above-described embodiment.
以上のように構成された本発明のSPOD法による超音波探傷装置並びに探傷法において、検査対象物の厚さ方向の検出感度差が抑制されること、即ち厚さ方向の感度低下を低減させたことをシミュレーションによって確認した。また、本発明のSPOD法において、周波数の大きさや傷の傾斜の有無にかかわらず、き裂先端に対応するエコーを確実に検出できることを確認した。 In the ultrasonic flaw detection apparatus and flaw detection method according to the SPOD method of the present invention configured as described above, the difference in detection sensitivity in the thickness direction of the inspection object is suppressed, that is, the decrease in sensitivity in the thickness direction is reduced. This was confirmed by simulation. Moreover, it was confirmed that the echo corresponding to the crack tip can be reliably detected in the SPOD method of the present invention regardless of the magnitude of the frequency and the presence or absence of the inclination of the scratch.
まず、シミュレーション手法について説明する。探触子から放射される超音波は、探傷面を透過するときの屈折、き裂面及び試験体底面での反射、き裂先端での回折により、振幅と伝搬方向が変化する。また、それぞれの過程でモード変換が発生するため、その伝搬経路は無数に存在する。 First, the simulation method will be described. The amplitude and propagation direction of the ultrasonic waves radiated from the probe change due to refraction when passing through the flaw detection surface, reflection at the crack surface and the bottom of the specimen, and diffraction at the crack tip. In addition, since mode conversion occurs in each process, there are an infinite number of propagation paths.
ここで、SPOD法は、斜角探触子を用いて、超音波をき裂へ斜めに入射することにより発生する縦波回折波をき裂真上で受信する方法である。したがって、無数の伝搬経路のうち、SPOD法の受信波形に寄与する伝搬経路は、図7に示す6通りに限られる。図中の実線は縦波を、破線は横波を示す。一例として、L2’は試験体に入射された縦波がき裂状欠陥の先端で横波にモード変換した後に、底面で縦波にモード変換し受信される伝搬経路を表す。尚、伝搬経路は、フェルマーの原理に従って決定した。いま、図8に示すように媒質1の点0と、媒質2の点Fの2点間の伝搬経路を決定する場合を考えると、幾何学的に次の数式1が成り立つ。
次いで、受信波形の算出方法について述べる。本実験では、試験体が平板で、斜角探触子の遠距離音場内にき裂状欠陥を模擬したスリットが存在する場合を想定して、幾何光学的回折理論(電磁波や光などの波動の伝播を光線と波面により幾何学的に取り扱う幾何光学に、き裂状欠陥の先端などでの回折理論を組み合わせて、より一般的に応用できるようにした近似理論,Geometrical Theory of Diffraction, GTD)に基づく受信波形の算出方法について述べる。
まず、境界面での屈折および反射の繰り返しによる超音波の振幅と位相の変化を求める式について述べる。つぎに、斜角探触子の遠距離音場を示し、また、固体内部のスリット先端での回折についても示す。最終的に、これらの関係を用いて、受信波形を求める計算式を導出する。
Next, a method for calculating the received waveform will be described. In this experiment, assuming that the specimen is a flat plate and there is a slit simulating a crack-like defect in the far field of the oblique probe, geometrical optical diffraction theory (waves such as electromagnetic waves and light) are assumed. Geometrical Theory of Diffraction (GTD) that can be applied more generally by combining geometrical optics that handles the propagation of light geometrically with rays and wavefronts, and diffraction theory at the tip of crack-like defects, etc. A method of calculating a received waveform based on the above will be described.
First, an equation for obtaining changes in the amplitude and phase of ultrasonic waves due to repeated refraction and reflection at the boundary surface will be described. Next, the far field of the oblique probe is shown, and the diffraction at the slit tip inside the solid is also shown. Finally, a calculation formula for obtaining the received waveform is derived using these relationships.
(屈折および反射による振幅・位相の変化)
試験体の材質に起因した減衰がないときには、点音源から放射された超音波の振幅は、エネルギー保存則により距離に反比例して減衰する。図9は、点音源を起点に試験体内に入射し、試験体の上下境界面でn回反射を繰り返して伝搬する超音波の音線を示す。この場合の振幅と位相の変化は次の数式3で表せる。
When there is no attenuation due to the material of the specimen, the amplitude of the ultrasonic wave radiated from the point sound source is attenuated in inverse proportion to the distance according to the energy conservation law. FIG. 9 shows an acoustic ray of an ultrasonic wave that is incident on the test body starting from a point sound source and propagates by being repeatedly reflected n times on the upper and lower boundary surfaces of the test body. The change in amplitude and phase in this case can be expressed by the following Equation 3.
(斜角探触子の遠距離音場)
斜角探触子により生成される音場は、相反定理を利用して斜角探触子を用いたときの信号を計算するための間野の式(間野浩太郎,固体の内部の超音波伝搬理論と超音波探傷への応用,鉄道技術研究報告,第276号,1962。)を用いて計算した。振動子である圧電セラミックスに比べ、樹脂で作られたウェッジの音響インピーダンスは小さいので、振動子面は、送信時には剛体のようなピストン運動を行い、受信時には静止に近い状態で入射波をほとんど反射すると考えてよい。よって、振動子表面の変位速度は次の数式6で表せる。
送信過程と受信過程を図10に示す。点Fnは試験体中の任意の点である。送信過程では、振動子がピストン運動し、超音波が試験体に放射され、数回の反射を経て点Fnに入射する。一方、受信過程では、点Fnが仮想的な点音源となり、数回の反射を経て超音波がウェッジ内に放射される。この2つの過程に相反関係が成り立つことから、上述の数式6を利用すると、斜角探触子から放射された点Fnにおける超音波の変位速度の振幅unは次の数式7で求められる。
The sound field generated by the oblique probe uses the Reciprocity Theorem to calculate the signal when using the oblique probe (Kotaro Mano, theory of ultrasonic propagation inside a solid) And application to ultrasonic flaw detection, Railway Technology Research Report, No. 276, 1962.). The acoustic impedance of the wedge made of resin is small compared to the piezoelectric ceramic that is the vibrator, so the vibrator surface performs a piston motion like a rigid body at the time of transmission, and almost reflects the incident wave in a state of being stationary at the time of reception. You can think of it. Therefore, the displacement speed of the vibrator surface can be expressed by the following formula 6.
A transmission process and a reception process are shown in FIG. Point Fn is an arbitrary point in the specimen. In the transmission process, the vibrator moves as a piston, and ultrasonic waves are radiated to the test body and enter the point Fn after being reflected several times. On the other hand, in the reception process, the point Fn becomes a virtual point sound source, and ultrasonic waves are radiated into the wedge through several reflections. Since a reciprocal relationship is established between these two processes, the amplitude un of the ultrasonic displacement speed at the point Fn radiated from the oblique probe can be obtained by the following formula 7 using the above formula 6.
(スリット先端からの回折)
図11に示すように、振幅uinの平面波がスリットの先端に入射したときの回折波は次の数式9で表せる。
As shown in FIG. 11, a diffracted wave when a plane wave having an amplitude uin is incident on the tip of the slit can be expressed by the following Equation 9.
(受信波形の算出)
図12に示すように、スリット先端周囲に境界面SFを考え、この境界面と受信探触子の振動子面SPとに相反関係を用いる。送信波がスリット先端で回折して受信されるまでの経路をRで表し、受信探触子から送信された超音波が経路Rと同じ経路を逆に伝搬してスリット先端に入射する仮想的な経路をVで表す。このとき、二つの境界面SFとSPに関して次の数式12の相反関係が成り立つ。
As shown in FIG. 12, a boundary surface SF is considered around the slit tip, and a reciprocal relationship is used between this boundary surface and the transducer surface SP of the receiving probe. The path until the transmitted wave is diffracted at the slit tip and received is represented by R, and the ultrasonic wave transmitted from the receiving probe propagates in the same path as the path R and enters the slit tip. The route is represented by V. At this time, the reciprocal relationship of the following formula 12 holds for the two boundary surfaces SF and SP.
以上述べたとおり、受信波形の算出方法については定式化できた。そこで、定式化した上記計算手法を、本発明者等が既に開発しているシミュレーションツール(一振動子の探触子による探傷結果をノートパソコンでも高速に予測できるシミュレーションツール(林山,山田尚雄,福冨広幸,緒方隆志,超音波探傷試験の高精度化・高効率化に活用するシミュレーションツールの開発(第1報),電力中央研究所発行の電中研報告書Q07004,2008.参照))に組み込み、SPOD法をはじめ、TOFD法などの2探触子法のシミュレーションを可能とした。このシミュレーションツールにより得られた予測結果は実際の探傷結果と良く一致したことから、その妥当性を確認できた(図4(A)(B)参照)。 As described above, the calculation method of the received waveform has been formulated. Therefore, the above-described calculation method is a simulation tool that has been developed by the present inventors (a simulation tool that can predict the flaw detection result of a single transducer probe at high speed even on a laptop computer (Hayashiyama, Naohio Yamada, Hiroyuki, Takashi Ogata, Development of simulation tools for improving the accuracy and efficiency of ultrasonic flaw detection tests (1st report), incorporated in the Chuo Electric Power Research Institute report Q07004, 2008.)) SPOD The simulation of the two-probe method such as the TOFD method was enabled. Since the prediction result obtained by this simulation tool was in good agreement with the actual flaw detection result, its validity could be confirmed (see FIGS. 4A and 4B).
次いで、上述のシミュレーション手法について検証した。
(実験方法)
まず、開発したシミュレーション手法を検証するため、深さが2mm〜15mmのスリットを有する試験体と深さ5mmで傾斜角が50°〜90°のスリットを有する試験体を用いて実験を行った。試験体の材質はステンレス鋼(SUS316)であり、試験体およびスリットの形状および配置は図13(A),(B)に示す通りである。同一の公称中心周波数(以下、単に周波数と記す)の探触子を送受信に用い、図14に示すように試験体中央で一次元走査して反欠陥側探傷を行った。なお、傾斜角が異なるスリットの試験体に関してはA側からB側へ、B側からA側への2方向で探触子を走査した。周波数の違いによる影響を調べるために、一般的な周波数2MHzおよび5MHzの探触子を用いた。振動子径はともに10mmである。ウェッジのSTB縦波屈折角は45°であり、材質はアクリル製である。また、SPOD法と比較するための斜角探傷では周波数5MHz、振動子寸法10mm×10mm、縦波屈折角45°の斜角探触子も用いた。探触子走査時の位置計測にはリニアスケールエンコーダ(MTL社製)を用い、0.5mm間隔でAスコープ波形を取得してBスコープ画像を描画した。探傷データ取得には市販の超音波探傷装置(TOMOSCAN III)を、接触媒質にはグリセリンペーストを使用した。
Next, the simulation method described above was verified.
(experimental method)
First, in order to verify the developed simulation method, an experiment was performed using a test body having a slit having a depth of 2 mm to 15 mm and a test body having a slit having a depth of 5 mm and an inclination angle of 50 ° to 90 °. The material of the test body is stainless steel (SUS316), and the shape and arrangement of the test body and the slit are as shown in FIGS. 13 (A) and 13 (B). Probes having the same nominal center frequency (hereinafter simply referred to as frequency) were used for transmission and reception, and as shown in FIG. For the test specimens with slits having different inclination angles, the probe was scanned in two directions from the A side to the B side and from the B side to the A side. In order to investigate the influence of the difference in frequency, probes having general frequencies of 2 MHz and 5 MHz were used. Both vibrator diameters are 10 mm. The wedge has a STB longitudinal wave refraction angle of 45 ° and is made of acrylic. In the oblique flaw detection for comparison with the SPOD method, an oblique probe having a frequency of 5 MHz, a transducer size of 10 mm × 10 mm, and a longitudinal wave refraction angle of 45 ° was also used. A linear scale encoder (manufactured by MTL) was used for position measurement during probe scanning, and A scope waveforms were acquired at intervals of 0.5 mm to draw B scope images. A commercially available ultrasonic flaw detector (TOMOSCAN III) was used for flaw detection data acquisition, and glycerin paste was used for the contact medium.
(結果と考察)
(周波数による影響)
深さが異なるスリットを有する試験体に対して送受信に2MHzの探触子を用いた場合と5MHzを用いた場合に得られるBスコープ画像の実験結果を図15(A),(B)に示す。ここでは、垂直および斜角探触子の交軸点が底面(FP=0mm)および試験体厚さ方向に底面から10mm(FP=10mm)に位置するように探触子間隔を設定した。同図から2MHzと5MHzの場合を比較すると、5MHzのほうが明瞭なL1およびL2エコーが得られ、2MHzでは両エコーと比較して底面エコー(図中のBW)が強くなっている。これは探触子の指向性に起因している。よって、散乱減衰による影響が少ない場合には5MHzの探触子が望ましい。散乱減衰の影響があり、低い周波数の探触子を用いる場合には、S/N比と時間分解能の低下に加えL1およびL2エコーと底面エコーの強度比が大きく変化することを留意する必要がある。交軸位置については交軸点と近い位置に先端があるスリットのL1エコーが最も強く、図15(B)の5MHzの場合のL1エコーの強度をFP=0mmとFP=10mmの場合の最大値で規格化した数値を図16に示す。参考のために記載した縦波斜角探触子による値(図中のLA45)とは異なり、交軸点から離れるとL1エコーが検出し難くなる。
(Results and discussion)
(Effect of frequency)
FIGS. 15 (A) and 15 (B) show experimental results of B scope images obtained when a 2 MHz probe is used for transmission and reception and 5 MHz is used for a specimen having slits with different depths. . Here, the probe interval was set so that the intersecting point of the vertical and oblique probes was located 10 mm (FP = 10 mm) from the bottom surface (FP = 0 mm) and the thickness direction of the specimen. Comparing the cases of 2 MHz and 5 MHz from the figure, clearer L1 and L2 echoes are obtained at 5 MHz, and the bottom echo (BW in the figure) is stronger at 2 MHz than both echoes. This is due to the directivity of the probe. Therefore, a 5 MHz probe is desirable when the influence of scattering attenuation is small. When using a low-frequency probe due to the influence of scattering attenuation, it is necessary to note that the intensity ratio of the L1 and L2 echoes to the bottom echo greatly changes in addition to the decrease in S / N ratio and temporal resolution. is there. As for the cross axis position, the L1 echo of the slit with the tip close to the cross axis point is the strongest, and the intensity of the L1 echo at 5 MHz in FIG. 15B is the maximum value when FP = 0 mm and FP = 10 mm. The numerical values normalized by Fig. 16 are shown in FIG. Unlike the value by the longitudinal wave oblique angle probe described for reference (LA45 in the figure), it becomes difficult to detect the L1 echo away from the intersection point.
上記の実験結果に対応する計算結果を図17および18に示す。1つのスリットに対するBスコープ画像の計算時間はクロック周波数3.06GHzのXeon(マイクロソフト社の登録商標)を搭載したパソコンで5秒程度であった。なお、受信波形の算出方法についての定式化では音場の計算の簡単さから振動子を方形として定式化したのに対し、実験では円形振動子を用いた。円形振動子の中心軸上の近距離音場を除くと、パルス音場への振動子の形状による影響は少ない。よって、同図のシミュレーションでは振動子寸法を10mm×10mmとした。シミュレーションによるL1およびL2エコーのビーム路程差は実験結果と良好に一致し、図15に見るようにL1およびL2エコーと底面エコーの強度の大小関係が周波数の違いにより大きく変化する傾向は図17からも見て取れる。計算結果は実験結果と定性的に一致することから、他の探傷方法と異なるSPOD法の特徴の把握や測定条件の検討などに、開発したシミュレーションツールは十分活用できると考えられる。 The calculation results corresponding to the above experimental results are shown in FIGS. The calculation time of the B scope image for one slit was about 5 seconds on a personal computer equipped with Xeon (registered trademark of Microsoft Corporation) with a clock frequency of 3.06 GHz. In the formulation of the calculation method of the received waveform, the transducer was formulated as a square for simplicity of calculation of the sound field, whereas in the experiment, a circular transducer was used. Except for the near field on the central axis of the circular vibrator, the influence of the shape of the vibrator on the pulse sound field is small. Therefore, in the simulation of the same figure, the vibrator size was set to 10 mm × 10 mm. The difference in the beam path length of the L1 and L2 echoes from the simulation agrees well with the experimental results, and as shown in FIG. 15, the tendency of the magnitude relationship between the L1 and L2 echoes and the bottom echo to change greatly depending on the frequency is shown in FIG. You can also see. Since the calculation results are qualitatively consistent with the experimental results, the developed simulation tool can be fully utilized for grasping the features of the SPOD method different from other flaw detection methods and examining the measurement conditions.
(傾斜したき裂のエコー)
き裂の傾斜度合いが探傷結果に与える影響を調査した。まず、参考のため傾斜角の異なるスリットを有する試験体を縦波斜角探傷した結果を図19に示す。この図から傾斜角が50°のスリットのようにスリット面と超音波の中心ビームのなす角が90°に近づくとスリット面での鏡面反射波が顕著になり、端部エコーと開口部エコーを分離できなくなる。一方、FP=10mmとしたときのSPOD法の探傷結果は図20の通りである。なお、図19および20は周波数5MHzの探触子を用いた場合の結果である。SPOD法の場合、スリット面への入射角は上記の斜角探傷の場合と同じにも関わらず、受信経路の違いからL1およびL2エコーを分離できることを同図から確認できる。図20に対応した計算結果を図21に示す。両図から、鏡面反射の条件に近づくにつれてL1エコーの指示が強くなっている。傾斜したスリットの傾斜角によるエコーの分離性やエコー強度において計算結果は実験結果と良く一致している。実験および計算結果から、SPOD法は従来の斜角探傷と比べ傾斜したき裂の深さ測定において優位性があることを確認できた。斜角探触子の屈折角を30度とし、スリット先端付近に交軸点を設定した場合の計算結果を図22に示す。この結果からも両エコーの分離が確認され、屈折角の違いにより両者の大小関係が変化していることが判る。
(Echo of inclined crack)
The effect of crack inclination on flaw detection results was investigated. First, for reference, FIG. 19 shows the result of longitudinal wave oblique angle flaw detection on a specimen having slits with different inclination angles. As shown in this figure, when the angle between the slit surface and the ultrasonic central beam approaches 90 °, as in the case of a slit with an inclination angle of 50 °, the specular reflection at the slit surface becomes prominent. It becomes impossible to separate. On the other hand, the flaw detection result of the SPOD method when FP = 10 mm is as shown in FIG. 19 and 20 show the results when a probe having a frequency of 5 MHz is used. In the case of the SPOD method, it can be confirmed from the figure that the L1 and L2 echoes can be separated from the difference in the reception path, although the incident angle to the slit surface is the same as that in the case of the oblique flaw detection. FIG. 21 shows the calculation result corresponding to FIG. From both figures, the indication of the L1 echo becomes stronger as the specular reflection condition is approached. The calculated results are in good agreement with the experimental results in the separability of echoes and the echo intensity depending on the tilt angle of the inclined slit. From the experiment and calculation results, it was confirmed that the SPOD method has an advantage in measuring the depth of an inclined crack compared to the conventional oblique flaw detection. FIG. 22 shows the calculation result when the refraction angle of the oblique angle probe is 30 degrees and the intersection point is set near the slit tip. From this result, separation of both echoes is confirmed, and it can be seen that the magnitude relationship between the two echoes changes due to the difference in refraction angle.
以上のことから、製作したシミュレーションツールは、傾斜したき裂に対するSPOD法の探傷結果の予測や探傷条件の検討に十分有効であることが確認された。即ち、試験周波数やき裂状欠陥の傾斜が検査結果へ与える影響に関する評価へ十分適用できることを確認した。 From the above, it was confirmed that the manufactured simulation tool was sufficiently effective for prediction of the flaw detection result of the SPOD method for the inclined crack and examination of flaw detection conditions. That is, it was confirmed that the method can be sufficiently applied to the evaluation of the influence of the test frequency and the inclination of the crack-like defect on the inspection result.
次に、上述したシミュレーション手法によって、本発明の超音波探傷法並びに装置の有用性について確認をした。 Next, the usefulness of the ultrasonic flaw detection method and apparatus of the present invention was confirmed by the simulation method described above.
(フェーズドアレイ技術を利用した開口合成処理)
まず、シミュレーションによる性能予測を行った。なお、SPOD法では送信に斜角探触子を、受信に垂直探触子を用いた場合と、それらを入れ替えた場合とでは、測定系が線形であれば相反性により同じ波形が得られる。また、フェーズドアレイを電子走査することによって効率的にデータ取得できるようになる。相反性および電子走査を利用して、距離振幅特性を修正することをシミュレーションツールを活用し検討した。図26に示す計算モデルは、前述のシミュレーション手法の検証において、異なる深さのスリットを有する試験体での実験を参考として設定した。周波数5MHzのフェーズドアレイ探触子の素子の幅を1mmとし、深さ2、5、10および15mmのスリットを有する試験体の厚さを25mmとした。送信には1個の素子を、受信には11個の素子を用い、これらの間に9個の素子を設けた。受信用振動素子1r群で得られた素子ごとのAスコープ波形を焦点が各スリット先端となるように開口合成処理した。
(Aperture synthesis processing using phased array technology)
First, performance prediction was performed by simulation. In the SPOD method, the same waveform is obtained due to reciprocity when the oblique probe is used for transmission and the vertical probe is used for reception, and when the probe is replaced, if the measurement system is linear. Further, data can be efficiently acquired by electronic scanning of the phased array. Using reciprocity and electronic scanning, we studied the modification of distance amplitude characteristics using a simulation tool. The calculation model shown in FIG. 26 was set with reference to experiments with test specimens having slits with different depths in the verification of the simulation method described above. The width of the element of the phased array probe with a frequency of 5 MHz was 1 mm, and the thickness of the test body having slits with depths of 2, 5, 10, and 15 mm was 25 mm. One element was used for transmission and eleven elements were used for reception, and nine elements were provided between them. The A scope waveform for each element obtained in the group of receiving vibration elements 1r was subjected to aperture synthesis processing so that the focal point would be the tip of each slit.
上記のモデルにより電子走査した場合のL1エコーの最大値と、フェーズドアレイ探触子の代わりに縦波斜角探触子(周波数5MHz、振動子寸法10mm×10mm)を用いて一探触子法により機械走査した場合の端部エコーの最大値をシミュレーションによって求めた。これらの最大値を比較して図27に示す。同図には比較のため縦波斜角探触子の結果に対して開口合成処理を実施した場合の端部エコーの最大値を記載している。同図から、単にSPOD法の探傷結果を処理した図25のような場合に比べ、距離振幅特性が修正されることがシュミレーションにより確認された。 One probe method using the maximum value of L1 echo when electronically scanned with the above model and a longitudinal wave oblique angle probe (frequency 5 MHz, transducer size 10 mm × 10 mm) instead of a phased array probe The maximum value of the end echo in the case of mechanical scanning was obtained by simulation. These maximum values are compared and shown in FIG. For comparison, the figure shows the maximum value of the end echo when aperture synthesis processing is performed on the result of the longitudinal wave oblique angle probe. From the figure, it was confirmed by simulation that the distance amplitude characteristic is corrected as compared with the case of FIG. 25 in which the flaw detection result of the SPOD method is simply processed.
(実験方法)
上記のシミュレーション結果を検証するため、前述のシミュレーション手法の検証において用いた深さの異なるスリットを有する試験体および図28に示す機械試験によって付与した疲労き裂を有する厚さ38mmのステンレス鋼(SUS316)製試験体2体を用いて実験を行った。なお、4本の疲労き裂の最大深さは7mmから15mmである。フェーズドアレイ探触子の周波数は5MHzである。また、素子数は64 であり、各素子の開口面積は0.8mm×10mm、ピッチは1mmである。探触子には高さが30mmのポリスチレン製の垂直探傷用ウェッジを装着した。スキャナーを用いて試験体中央で一次元機械走査し、L1エコーが確認された位置でBスコープ画像データを記録した。探傷データ取得には開口合成処理機能を有する超音波フェーズドアレイ探傷装置((株)東芝製商品名Matrixeye EX)のほかに、SPOD法と従来のパルスエコー法を比較するために一般的な超音波フェーズドアレイ探傷装置(商品名OmniscanMX)も使用した。接触媒質には水を使用した。図1及び図2に示すように本発明の超音波探傷法の性能予測を行ったシミュレーション結果と探傷装置と探触子の仕様を勘案し、送受信パターン1(図2(A))および2(図2(B))を決定した。その結果、送信に1または9個の素子1tを、受信には送信用振動素子1tの両側に合計20個の素子1rを用いた。送信用振動素子1tと受信用振動素子1r群の間の素子数は5または1とした。受信用振動素子1r群を両側に配置した理由は、L1エコーのS/N比を向上させる狙いと左右対称な指示を得るためである。なお、図26の計算モデルと実験条件は異なるが、この条件でも期待される効果が得られることをシミュレーションにより確認している。Matrixeyeでは各素子で受信されたAスコープ波形からBスコープ画像内の画素の値を内蔵された並列演算回路と4つのA/Dコンバータにより高速に開口合成処理し、リアルタイムでBスコープ画像を表示可能である(唐沢博一,磯部英夫,浜島隆之,3次元開口合成(3D-SAFT)アレイと適用事9例,非破壊検査,Vol.56,No.10,520-524,2007)。本測定で設定した画素数は垂直および水平方向にそれぞれ512および64であり、空間分解能は垂直および水平方向に0.07mmおよび1mmである。
(experimental method)
In order to verify the simulation results described above, the specimen having slits with different depths used in the verification of the above-described simulation technique and the 38 mm thick stainless steel (SUS316 having a fatigue crack provided by the mechanical test shown in FIG. ) Experiments were conducted using two test specimens. The maximum depth of the four fatigue cracks is 7 mm to 15 mm. The frequency of the phased array probe is 5 MHz. The number of elements is 64, the opening area of each element is 0.8 mm × 10 mm, and the pitch is 1 mm. The probe was equipped with a 30 mm-high polystyrene flaw detection wedge. One-dimensional mechanical scanning was performed at the center of the specimen using a scanner, and B-scope image data was recorded at the position where the L1 echo was confirmed. In addition to an ultrasonic phased array flaw detector (trade name: Matrixeye EX manufactured by Toshiba Corporation) that has an aperture synthesis processing function for acquiring flaw detection data, general ultrasonic waves are used to compare the SPOD method with the conventional pulse echo method. A phased array flaw detector (trade name OmniscanMX) was also used. Water was used as the contact medium. As shown in FIG. 1 and FIG. 2, the transmission / reception pattern 1 (FIG. 2 (A)) and 2 ( FIG. 2 (B)) was determined. As a result, 1 or 9 elements 1t were used for transmission, and a total of 20 elements 1r were used on both sides of the transmitting vibration element 1t for reception. The number of elements between the transmitting vibration element 1t and the receiving vibration element 1r group was set to 5 or 1. The reason why the receiving vibration element 1r group is arranged on both sides is to obtain an instruction symmetrical to the aim of improving the S / N ratio of the L1 echo. Although the calculation model of FIG. 26 and the experimental conditions are different, it has been confirmed by simulation that the expected effect can be obtained even under these conditions. Matrixeye can display the B scope image in real time by performing aperture synthesis processing at high speed using the parallel arithmetic circuit and four A / D converters that incorporate the pixel values in the B scope image from the A scope waveform received by each element. (Haraichi Karasawa, Hideo Isobe, Takayuki Hamajima, 3D Aperture Synthesis (3D-SAFT) Array and 9 Cases, Nondestructive Inspection, Vol.56, No.10, 520-524, 2007). The number of pixels set in this measurement is 512 and 64 in the vertical and horizontal directions, respectively, and the spatial resolution is 0.07 mm and 1 mm in the vertical and horizontal directions.
(実験結果)
スリット入り試験体に対して送受信パターン1で得られたBスコープ画像を図29に示す。L1およびL2エコーが観測され、送信用振動素子1tの両側に受信用振動素子1rを対称に配置したことにより、両エコーの指示が対称に現れている。各スリットのL1エコーの最大振幅を図30に示す。図24(A),(B)では開口合成処理したにも関わらず、距離振幅特性が修正されなかったのに対し、本発明の超音波探傷法を用いることによって最大値に対して4割の範囲内に修正できることが確認できた。よって、本発明にかかる探傷法の活用により、SPOD法のBスコープ画像が構成できるといった効率改善が図られるだけでなく、距離振幅特性も修正できることを確認できた。また、従来の斜角探傷では端部エコーと開口部エコーが分離できない傾斜したき裂状欠陥に対してもL1およびL2エコーは分離することを確認できた。
(Experimental result)
FIG. 29 shows a B-scope image obtained with the transmission / reception pattern 1 for the test specimen with slits. L1 and L2 echoes are observed, and the receiving vibration elements 1r are arranged symmetrically on both sides of the transmitting vibration element 1t, so that the instructions of both echoes appear symmetrically. FIG. 30 shows the maximum amplitude of the L1 echo of each slit. In FIGS. 24 (A) and 24 (B), the distance amplitude characteristic was not corrected despite the aperture synthesis processing, but 40% of the maximum value was obtained by using the ultrasonic flaw detection method of the present invention. It was confirmed that it could be corrected within the range. Therefore, it was confirmed that by utilizing the flaw detection method according to the present invention, not only the efficiency improvement that a B-scope image of the SPOD method can be constructed but also the distance amplitude characteristic can be corrected. In addition, it was confirmed that the L1 and L2 echoes were separated even for the inclined crack-like defect in which the edge echo and the opening echo could not be separated by the conventional oblique flaw detection.
次に、疲労き裂入り試験体に対して探傷を実施した。SPOD法による測定に先立ち、Omniscanを用いてパルスエコー法による垂直探傷を実施した。
電子走査はリニアスキャンとし、同時送受信用振動素子1rの数を16素子まで増やしたが、いずれの疲労き裂の先端も捉えることができなかった。一方、送受信パターン1で疲労き裂をSPOD法により探傷したときのBスコープ画像を図31に示す。疲労き裂4本中3本は図31(A)の破線で囲まれた領域のようにき裂先端を容易に捉えることができたが、1本は図31(B)に示すように明瞭な先端の指示が得られなかった。これは他の3本に比べ、先端が閉じているためと考えられる。そこで、送信用振動素子1t数を増やし図2の送受信パターン2で探傷を行った。このBスコープ画像を図31(C)に示す。図31(B)と比較して判るように明瞭なき裂先端の指示を確認できる。つまり、従来のフェーズドアレイ探触子を用いた垂直探傷で観測できなかった疲労き裂の先端の指示を送信用振動素子1t数を増やすことによって識別できるようになった。疲労き裂の先端の指示のような微弱な指示のS/N比を向上させる手段として、超音波の送受信の開口面積を増やすこと、例えば、送信用振動素子1t数を増やすことは有効な手段の一つであることが判明した。
Next, flaw detection was carried out on the fatigue cracked specimen. Prior to measurement by SPOD method, vertical flaw detection by pulse echo method was performed using Omniscan.
The electronic scan was a linear scan, and the number of simultaneous transmitting / receiving vibration elements 1r was increased to 16. However, the tip of any fatigue crack could not be captured. On the other hand, FIG. 31 shows a B-scope image when a fatigue crack is detected by the SPOD method in the transmission / reception pattern 1. Three of the four fatigue cracks could easily grasp the crack tip as shown in the area surrounded by the broken line in FIG. 31 (A), but one was clearly as shown in FIG. 31 (B). I couldn't get the correct tip instructions. This is probably because the tip is closed compared to the other three. Therefore, flaw detection was performed with the transmission / reception pattern 2 of FIG. This B scope image is shown in FIG. As can be seen in comparison with FIG. 31 (B), a clear indication of the crack tip can be confirmed. That is, the indication of the tip of the fatigue crack that could not be observed by vertical flaw detection using a conventional phased array probe can be identified by increasing the number of transmitting vibration elements 1t. As means for improving the S / N ratio of a weak instruction such as an instruction at the tip of a fatigue crack, it is effective to increase the opening area of ultrasonic transmission / reception, for example, increase the number of transmitting vibration elements 1t. Turned out to be one of.
以上の実験の結果から、本発明が検査対象物の厚さ方向の検出感度差を抑制することについて、実証実験によりその有効性が確認された。 From the results of the above experiments, the effectiveness of the present invention in confirming the difference in detection sensitivity in the thickness direction of the inspection object was confirmed by a demonstration experiment.
1 フェーズドアレイ
1t 送信用振動素子
1r 受信用振動素子
1g 不動作振動素子
2 試験体の画像化する範囲をメッシュ状に区画した点
3t 垂直送信の超音波ビーム
3r 斜角受信したエコー
4 制御装置
5 画像化処理装置
20 試験体の画像化する範囲
DESCRIPTION OF SYMBOLS 1 Phased array 1t Transmission vibration element 1r Reception vibration element 1g Non-operation vibration element 2 The point which imaged the range to image the test body in the shape of a mesh 3t Ultrasonic beam of vertical transmission 3r Echo received obliquely 4 Control device 5 Imaging processor 20 Range of specimen image
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