JP2023008510A

JP2023008510A - Ultrasonic flaw detection method

Info

Publication number: JP2023008510A
Application number: JP2021112130A
Authority: JP
Inventors: 大輔森; Daisuke Mori; 武森永; Takeshi Morinaga
Original assignee: Daido Steel Co Ltd
Current assignee: Daido Steel Co Ltd
Priority date: 2021-07-06
Filing date: 2021-07-06
Publication date: 2023-01-19

Abstract

To provide an ultrasonic flaw detection method that never decreases in an SN ratio of defect detection even when a clear reception signal cannot be obtained from some vibrators of a phased array probe.SOLUTION: There is provided an ultrasonic flaw detection method comprising: providing a plurality of vibrators 11 adjacently; transmitting ultrasonic waves from those vibrators 11 to an analyte 2; receiving reflected waves by the respective vibrators 11; and calculating an addition average of flaw signal parts Sd of respective reception signals Sr1 to Sr5 obtained by the respective vibrators 11 to obtain a composite flaw signal part CSd. The ultrasonic flaw detection method further comprises: detecting signal levels of the flaw signal parts Sd of the respective reception signals Sr1 to Sr5; and then excluding from the addition average a flaw signal part Sd whose signal level is equal to or less than a predetermined threshold value Th.SELECTED DRAWING: Figure 1

Description

本発明は超音波探傷方法に関し、特にフェーズドアレイプローブを使用した超音波探傷方法においてその探傷精度の向上を図ったものである。 The present invention relates to an ultrasonic flaw detection method, and in particular, is intended to improve the flaw detection accuracy in an ultrasonic flaw detection method using a phased array probe.

フェーズドアレイプローブは複数の振動子を備えて、各振動子を所定の遅れ時間で励振することによって、出力される入射超音波の合成波面を一定の角度方向へ向けたり、所望の焦点位置へ収束させたりして、被検体の欠陥で反射された反射超音波を再び複数の振動子で受信し、各受信信号を適宜時間シフトさせて重ね合わせることによって高精度な欠陥検出を可能としたものである。 A phased array probe has multiple transducers, and by exciting each transducer with a predetermined delay time, the synthesized wavefront of the output incident ultrasonic waves can be directed in a certain angular direction or converged to a desired focal position. Then, the reflected ultrasonic waves reflected by the defect of the object are received again by a plurality of transducers, and the received signals are superimposed with an appropriate time shift to enable highly accurate defect detection. be.

ここで、特許文献1にはフェーズドアレイプローブを使用した超音波探傷において、最初の探傷によって欠陥の存在する領域を特定し、２回目には特定された領域内のみを再度探傷することによって高精度な欠陥検出を短時間で行えるようにした方法が提案されている。 Here, in Patent Document 1, in ultrasonic flaw detection using a phased array probe, the area where the defect exists is identified by the first flaw detection, and the second flaw detection is performed again only in the identified area to achieve high accuracy. A method has been proposed in which such defects can be detected in a short period of time.

特開２０１１－２３６０JP 2011-2360

ところで、フェーズドアレイプローブでは前述したように複数の振動子で受信した信号を重ね合わせて欠陥検出を行っているが、故障等により一部の振動子の感度が低下したり、被検体の結晶粒が粗大な場合や被検体の表面に部分的に気泡が生じる等によって被検体の表面状態が劣悪な場合に、一部の振動子から明瞭な受信信号が得られないことがある。このような場合に常に所定数の全ての振動子の受信信号を重ね合わせて欠陥検出を行うとそのＳＮ比が大きく低下してしまうおそれがある。 By the way, in the phased array probe, as described above, the signals received by multiple transducers are superimposed to detect defects. If the surface condition of the object is poor due to a large surface area, air bubbles on the surface of the object, etc., clear reception signals may not be obtained from some of the transducers. In such a case, if the received signals of all the transducers of a predetermined number are always superimposed for defect detection, the SN ratio may be greatly reduced.

そこで、本発明はこのような課題を解決するもので、フェーズドアレイプローブの一部の振動子から明瞭な受信信号が得られない場合にも欠陥検出のＳＮ比を向上させることができる超音波探傷方法を提供することを目的とする。 Therefore, the present invention solves such problems, and is capable of improving the SN ratio of defect detection even when clear reception signals cannot be obtained from some transducers of a phased array probe. The purpose is to provide a method.

上記目的を達成するために、本第１発明では、複数の振動子（１１）を隣接して設けてこれら振動子（１１）より被検体（２）に超音波を発信するとともに各振動子（１１）で反射波を受信し、各振動子（１１）で得られる各受信信号（Ｓr1～Ｓr5）中の疵信号部（Ｓd）を加算平均して合成疵信号部（ＣＳd）を得る超音波探傷方法において、前記各受信信号（Ｓr1～Ｓr5）の疵信号部（Ｓd）の信号レベルを検出して、当該信号レベルが所定の閾値（Ｔh）以下の疵信号部（Ｓd）を上記加算平均から排除することを特徴とする。 In order to achieve the above object, in the first invention, a plurality of transducers (11) are provided adjacently, ultrasonic waves are transmitted from these transducers (11) to the subject (2), and each transducer ( 11) receives the reflected wave, and adds and averages the flaw signal part (Sd) in each reception signal (Sr1 to Sr5) obtained by each transducer (11) to obtain a composite flaw signal part (CSd) Ultrasonic wave In the flaw detection method, the signal level of the flaw signal portion (Sd) of each of the received signals (Sr1 to Sr5) is detected, and the flaw signal portion (Sd) whose signal level is equal to or lower than a predetermined threshold value (Th) is added and averaged. characterized by excluding from

本第１発明においては、信号レベルが所定の閾値以下の疵信号部を加算平均から排除しているから、加算平均して得られる合成疵信号部の大きさが、信号レベルの低い疵信号部の影響を受けることが無く、これによって欠陥検出のＳＮ比の低下が避けられる。 In the first invention, since the flaw signal portion whose signal level is equal to or lower than the predetermined threshold value is excluded from the averaging, the size of the synthetic flaw signal portion obtained by averaging is the flaw signal portion with the low signal level. , thereby avoiding degradation of the signal-to-noise ratio of defect detection.

本第２発明では、前記閾値（Ｔh）を、前記各受信信号（Ｓr1～Ｓr5）の疵信号部（Ｓd）の最大値からその５～５０％減じた値に設定する。なお、前記閾値（Ｔh）は最大値からその５～２０％減じた値に設定するのがより好ましく、さらに好ましくは５～１０％減じた値に設定するのが良い。 In the second invention, the threshold (Th) is set to a value obtained by subtracting 5 to 50% from the maximum value of the defect signal portion (Sd) of each of the received signals (Sr1 to Sr5). The threshold value (Th) is preferably set to a value that is 5 to 20% less than the maximum value, and more preferably to a value that is 5 to 10% less.

上記カッコ内の符号は、後述する実施形態に記載の具体的手段との対応関係を参考的に示すものである。 The symbols in parentheses above refer to the corresponding relationship with specific means described in the embodiments described later.

以上のように、本発明の超音波探傷方法によれば、フェーズドアレイプローブの一部の振動子から明瞭な受信信号が得られない場合にも欠陥検出のＳＮ比を向上させることができる。 As described above, according to the ultrasonic flaw detection method of the present invention, it is possible to improve the SN ratio of flaw detection even when clear reception signals cannot be obtained from some transducers of the phased array probe.

超音波探傷方法を説明する断面図である。It is a sectional view explaining an ultrasonic testing method. 各振動子で得られた受信信号の模式的波形図である。4 is a schematic waveform diagram of received signals obtained by each transducer; FIG. 全ての受信信号を加算平均した合成信号の模式的波形図である。FIG. 4 is a schematic waveform diagram of a synthesized signal obtained by averaging all received signals; 不明瞭な受信信号を除いて加算平均した合成信号の模式的波形図である。FIG. 4 is a schematic waveform diagram of a composite signal obtained by averaging excluding unclear received signals; 正常な受信信号の波形図である。FIG. 4 is a waveform diagram of a normal received signal; 不明瞭な受信信号の波形図である。FIG. 4 is a waveform diagram of an ambiguous received signal; 全ての受信信号を加算平均した合成信号の波形図である。FIG. 4 is a waveform diagram of a composite signal obtained by averaging all received signals; 不明瞭な受信信号を除いて加算平均した合成信号の波形図である。FIG. 4 is a waveform diagram of a composite signal obtained by averaging excluding unclear received signals;

なお、以下に説明する実施形態はあくまで一例であり、本発明の要旨を逸脱しない範囲で当業者が行う種々の設計的改良も本発明の範囲に含まれる。 The embodiments described below are merely examples, and various design improvements made by those skilled in the art are also included in the scope of the present invention without departing from the gist of the present invention.

図１にはフェーズドアレイプローブ１を使用した探傷方法の一例を示す。図1において、厚肉板状の被検物２には底面近くに欠陥３があり、これを被検物２の表面に近接して設けたフェーズドアレイプローブ１によって検出する。フェーズドアレイプローブ１には、被検物２の表面に沿って等間隔で隣接する複数の超音波振動子１１が設けられている。そして、探傷装置４から出力される励振信号によって各振動子１１の励振が所定の遅れ時間で行われて、各振動子１１から入射されるパルス状探傷超音波Ｐｓの合成波面Ｃｗが欠陥３の頂面でフォーカスされる。 FIG. 1 shows an example of a flaw detection method using a phased array probe 1. As shown in FIG. In FIG. 1, a thick plate-shaped test object 2 has a defect 3 near the bottom, which is detected by a phased array probe 1 provided close to the surface of the test object 2 . The phased array probe 1 is provided with a plurality of ultrasonic transducers 11 adjacent to each other at equal intervals along the surface of the test object 2 . Then, each transducer 11 is excited with a predetermined delay time by an excitation signal output from the flaw detection device 4, and the synthesized wavefront Cw of the pulsed flaw detection ultrasonic waves Ps incident from each transducer 11 is the defect 3. Focused on the top surface.

各探傷超音波Ｐｓは欠陥３で反射されて各振動子１１に戻り、受信される。各振動子１１で得られた受信信号はその疵信号部が同期するように探傷装置４内で適宜時間シフトさせられて、互いに重ね合わされる。探傷装置４では重ね合わせた受信信号をその信号数で除して（加算平均）、合成信号を得る。そして合成信号中の疵信号部を合成疵信号部として、その大きさで被検体２中の疵の有無を判定する。 Each flaw detection ultrasonic wave Ps is reflected by the defect 3, returns to each transducer 11, and is received. The received signals obtained by the vibrators 11 are appropriately time-shifted in the flaw detector 4 so that the flaw signal portions thereof are synchronized, and superimposed on each other. The flaw detector 4 divides the superimposed received signals by the number of signals (additional averaging) to obtain a combined signal. Then, the presence or absence of a flaw in the subject 2 is determined based on the size of the flaw signal portion in the composite signal, which is used as the composite flaw signal portion.

ところで、故障等によって複数の振動子１１のうちいくつかの感度が低下し、あるいは被検体２の結晶粒が局所的に粗大な場合や被検体２の表面状態が局部的に劣悪な場合等には、一部の振動子１１で十分に大きな受信信号が得られないことがある。これを図２で説明する。図２は５つの振動子１１からそれぞれ受信信号Ｓr1～Ｓr5が得られた状態を示しており、各受信信号Ｓr1～Ｓr5の疵信号部Ｓdは同期させられている。そして、５つの振動子１１からの受信信号Ｓr1～Ｓr5のうち信号Ｓr4では十分な大きさの疵信号部Ｓdが得られていない。受信信号Ｓr1～Ｓr5の疵信号部Ｓdが十分な大きさであるか否かの閾値は例えば信号検出フルスケールの４０％に設定される。 By the way, when the sensitivity of some of the plurality of transducers 11 is lowered due to a failure or the like, or when the crystal grains of the subject 2 are locally coarse, or when the surface condition of the subject 2 is locally poor, etc. , some transducers 11 may not be able to obtain a sufficiently large received signal. This is explained in FIG. FIG. 2 shows the state in which the reception signals Sr1 to Sr5 are respectively obtained from the five transducers 11, and the defect signal portions Sd of the reception signals Sr1 to Sr5 are synchronized. Of the signals Sr1 to Sr5 received from the five vibrators 11, the signal Sr4 does not provide a sufficiently large defect signal portion Sd. A threshold for determining whether the flaw signal portion Sd of the received signals Sr1 to Sr5 is sufficiently large is set to, for example, 40% of the signal detection full scale.

全ての受信信号Ｓr1～Ｓr5を重ね合わせて信号数で除する加算平均で得られた合成信号ＣＳr1を図３に示し、一方、図４には、疵信号部Ｓdの大きさが不十分な受信信号Ｓr4を除いて、残る受信信号Ｓr1～Ｓr3，Ｓr5を重ね合わせて信号数で除して得られた合成信号ＣＳr2を示す。図３と図４を比較すれば明らかなように、疵信号部Ｓdの大きさが不十分な受信信号Ｓr4を除いて残る受信信号Ｓr1～Ｓr3，Ｓr5を重ね合わせて得られた合成信号ＣＳr2（図４）では、疵信号部Ｓdの大きさが不十分な受信信号Ｓr4を含めてすべての受信信号Ｓr1～Ｓr5を重ね合わせて得られた合成信号ＣＳr1（図３）に比して、合成疵信号部ＣＳdが十分な大きさで現れてＳ／Ｎ比が向上する。 FIG. 3 shows the combined signal CSr1 obtained by averaging all the received signals Sr1 to Sr5 and dividing them by the number of signals. On the other hand, FIG. A combined signal CSr2 obtained by superimposing the remaining received signals Sr1 to Sr3 and Sr5 except for the signal Sr4 and dividing by the number of signals is shown. As is clear from a comparison of FIGS. 3 and 4, a composite signal CSr2 ( In FIG. 4), compared to the synthesized signal CSr1 (FIG. 3) obtained by superimposing all the received signals Sr1 to Sr5 including the received signal Sr4 with an insufficient flaw signal portion Sd, the synthesized flaw The signal portion CSd appears with a sufficient size to improve the S/N ratio.

この方法で、例えば３２ｃｈ（振動子１１が３２個）のフェーズドアレイプローブ１（図１参照）を使用し、上記と同形の被検体２内でフォーカス位置５０ｍｍのところにある直径１ｍｍの平底穴欠陥について探傷を行った結果を以下に示す。 In this method, for example, a 32ch (32 transducers 11) phased array probe 1 (see FIG. 1) is used, and a flat-bottomed hole defect with a diameter of 1mm at a focus position of 50mm is detected in a subject 2 having the same shape as the above. The results of flaw detection for are shown below.

図５は通常状態の振動子１１で得られた受信信号Ｓr6である。受信信号Ｓr6には、被検体２の表面と底面からの反射波による表面反射部Ｓurと底面反射部Ｓbrの間に、疵信号部Ｓdが上記閾値Ｔh以上の十分な大きさで現れている。これに対して、被検体２の表面状態が一部劣悪な場合にはこの部分に設置された振動子１１から得られる受信信号Ｓr7（図６）の疵信号部Ｓdは上記閾値Ｔh以下で十分な大きさとはならない。 FIG. 5 shows the received signal Sr6 obtained by the vibrator 11 in the normal state. In the received signal Sr6, between the surface reflection portion Sur and the bottom reflection portion Sbr due to the reflected waves from the surface and bottom surface of the subject 2, a flaw signal portion Sd appears with a sufficient size equal to or larger than the threshold value Th. On the other hand, when the surface condition of the subject 2 is partially deteriorated, the defect signal part Sd of the received signal Sr7 (FIG. 6) obtained from the transducer 11 installed in this part is sufficiently below the threshold value Th. not as large as

ここにおいて、探傷装置４において、全ての受信信号Ｓrを重ね合わせて信号数で除する加算平均で得られた合成信号ＣＳr3（図７）では、その合成疵信号部ＣＳdのＳ／Ｎ比は８．７であった。これに対して、疵信号部Ｓdが不十分な大きさの受信信号Ｓrを除いて残る受信信号Ｓrを重ね合わせ、これを信号数で除して得られた合成信号ＣＳr4（図８）では、合成疵信号部ＣＳdのＳ／Ｎ比は９．７と向上した。 Here, in the composite signal CSr3 (FIG. 7) obtained by adding and averaging all the received signals Sr in the flaw detector 4 and dividing by the number of signals, the S/N ratio of the composite flaw signal portion CSd is 8. .7. On the other hand, in the synthesized signal CSr4 (FIG. 8) obtained by superimposing the remaining received signals Sr after removing the received signals Sr with insufficient magnitude of the flaw signal part Sd and dividing this by the number of signals, The S/N ratio of the composite flaw signal portion CSd was improved to 9.7.

なお、上記実施形態では受信信号全体を加算平均したが、疵信号部のみを加算平均しても良い。 In the above-described embodiment, the overall received signal is averaged, but only the flaw signal portion may be averaged.

１…フェーズドアレイプローブ、１１…振動子、２…被検体、Ｓr1～Ｓr5…受信信号、ＣＳd…合成疵信号部、Ｓd…疵信号部、Ｔh…閾値。 Reference Signs List 1 Phased array probe 11 Vibrator 2 Subject Sr1 to Sr5 Received signal CSd Synthetic flaw signal part Sd Flaw signal part Th Threshold.

Claims

複数の振動子を隣接して設けてこれら振動子より被検体に超音波を発信するとともに各振動子で反射波を受信し、各振動子で得られる各受信信号中の疵信号部を加算平均して合成疵信号部を得る超音波探傷方法において、前記各受信信号の疵信号部の信号レベルを検出して、当該信号レベルが所定の閾値以下の疵信号部を上記加算平均から排除することを特徴とする超音波探傷方法。 A plurality of transducers are provided adjacent to each other, ultrasonic waves are transmitted from these transducers to the subject, and reflected waves are received by each transducer, and the flaw signal part in each received signal obtained by each transducer is added and averaged. In the ultrasonic flaw detection method for obtaining a composite flaw signal portion by detecting the signal level of the flaw signal portion of each of the received signals, the flaw signal portion whose signal level is equal to or lower than a predetermined threshold is excluded from the above average. An ultrasonic flaw detection method characterized by:

前記閾値を前記各受信信号の疵信号部の最大値からその５～５０％減じた値に設定した請求項１に記載の超音波探傷方法。 2. The ultrasonic flaw detection method according to claim 1, wherein the threshold value is set to a value obtained by subtracting 5 to 50% from the maximum value of the flaw signal portion of each of the received signals.