JP2014211398A - Tubular structure defect inspection method and device - Google Patents
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Abstract
Description
本発明は超音波探傷法に関する。さらに詳述すると、本発明は、管状構造物の腐食や傷、割れ等の欠陥を超音波探傷で検査する欠陥検査方法及び装置に関する。 The present invention relates to an ultrasonic flaw detection method. More specifically, the present invention relates to a defect inspection method and apparatus for inspecting a tubular structure for defects such as corrosion, scratches and cracks by ultrasonic flaw detection.
鋼管などの管状構造物、例えば架空送電設備の鋼管鉄塔において腐食の有無を検査することが必要とされる場合がある。架空送電設備の一部である鋼管鉄塔では腐食による劣化現象が顕在化しており、鋼管鉄塔では腹材や水平材の鋼管内面に不めっきによる局所的な腐食が確認されている。そこで、現状では、鋼管鉄塔の内面の腐食に対しては、外面からの点検では打撃点検、カメラ点検および超音波厚さ測定が実施されている（非特許文献１）。 It may be necessary to inspect for the presence or absence of corrosion in tubular structures such as steel pipes, for example, steel pipe towers of overhead power transmission facilities. In steel pipe towers that are part of overhead power transmission facilities, deterioration due to corrosion has become obvious, and in steel pipe towers, local corrosion due to non-plating has been confirmed on the inner surface of steel pipes of abdominal materials and horizontal materials. Therefore, at present, for the corrosion of the inner surface of the steel pipe tower, a hit inspection, a camera inspection, and an ultrasonic thickness measurement are performed in the inspection from the outer surface (Non-Patent Document 1).
また、管状構造物の腐食等の非破壊検査手法としては、超音波を利用したものもある。例えば、超音波探傷にガイド波を用いることにより広い範囲における非破壊検査を行うことが提案されている（特許文献１，２）。例えば、特許文献１記載の発明の場合、検査対象物に対してバースト波形のガイド波を入射し、ガイド波を受信して透過法により検査を行うものである。また、特許文献２記載の発明では、欠陥を検査しようとする円筒部材の周方向に伝播するガイド波のうち波長の最も短いガイド波の波長未満の間隔で複数の超音波探触子を円筒部材の周方向の一部に配列して成る第１超音波探触子列及び第２超音波探触子列との２つの超音波探触子列を、円筒部材の軸方向に間隔をあけて配置し、第１超音波探触子列と第２超音波探触子列からガイド波が送信される時刻が円筒部材の軸方向における第１超音波探触子列と第２超音波探触子列の距離をガイド波が伝播するために要する時間だけずれるように制御することにより、周方向ガイド波の振幅を軸方向ガイド波の振幅の約１０００分の１に達するまで低減することを可能とし、受信信号の中に含まれる周方向ガイド波に起因するノイズを低減してより小さな欠陥を認識することができるようにしている。この２つの超音波探触子列の円筒部材の外表面に設置する箇所を円筒部材の周方向に沿って順次変更することによって、円筒部材の全周における欠陥位置を確認するようにするものである。 Further, as a nondestructive inspection method such as corrosion of a tubular structure, there is a method using ultrasonic waves. For example, it has been proposed to perform nondestructive inspection over a wide range by using a guide wave for ultrasonic flaw detection (Patent Documents 1 and 2). For example, in the case of the invention described in Patent Document 1, a guide wave having a burst waveform is incident on an inspection object, the guide wave is received, and inspection is performed by a transmission method. In the invention described in Patent Document 2, a plurality of ultrasonic probes are arranged at intervals less than the wavelength of the shortest guide wave among the guide waves propagating in the circumferential direction of the cylindrical member to be inspected for defects. The two ultrasonic probe rows of the first ultrasonic probe row and the second ultrasonic probe row arranged in a part in the circumferential direction are spaced apart in the axial direction of the cylindrical member. The time at which the guide waves are transmitted from the first ultrasonic probe array and the second ultrasonic probe array is the first ultrasonic probe array and the second ultrasonic probe in the axial direction of the cylindrical member. It is possible to reduce the amplitude of the circumferential guide wave until it reaches about 1/1000 of the amplitude of the axial guide wave by controlling the distance of the child row so as to shift by the time required for the guide wave to propagate. And reduce the noise caused by the circumferential guide wave included in the received signal. So that it is possible to recognize the defects of the. By sequentially changing the locations of the two ultrasonic probe rows installed on the outer surface of the cylindrical member along the circumferential direction of the cylindrical member, the defect position on the entire circumference of the cylindrical member is confirmed. is there.
しかしながら、打撃点検は腐食による減肉が相当進行した状況で検知できるようになるものであり、しかも周囲の環境及び点検員の個人差の影響を受けるため、客観的な基準を設けることが困難である。また、カメラ点検では腐食の有無は判るものの、その進行具合は不明である。一方、超音波厚さ測定法は現場環境で実施できる最も高精度な厚さ測定法ではあるが、超音波厚み計は、検査範囲が狭いため、長尺の配管に対する検査には膨大な手間がかかり長い時間を要するし、現状での一般的な測定では、相当数の箇所を測定したとしても局所的な腐食を見逃す可能性がある。しかも、鋼管鉄塔のような管状構造物の場合、厚み測定計によるスポット的な厚み測定や打音検査を周方向に行おうとしても、周辺の管状構造物やその他の支持構造物が邪魔して作業が妨げられることがある。つまり、これらの検査方法においては、局所的な腐食の見逃しの虞があり、作業効率が低いといった問題がある。 However, it is difficult to set an objective standard for the impact inspection because it can be detected in a situation where thinning due to corrosion has progressed considerably, and it is affected by the surrounding environment and individual differences of the inspector. is there. Moreover, although the presence or absence of corrosion is known by camera inspection, the progress is unknown. On the other hand, the ultrasonic thickness measurement method is the most accurate thickness measurement method that can be performed in the field environment, but the ultrasonic thickness gauge has a narrow inspection range, so it takes a lot of labor to inspect long pipes. It takes a long time, and in the current general measurement, there is a possibility that local corrosion may be missed even if a considerable number of points are measured. In addition, in the case of a tubular structure such as a steel pipe tower, the surrounding tubular structure and other supporting structures are obstructing even if spot thickness measurement by a thickness meter and sounding inspection are performed in the circumferential direction. Work may be hindered. That is, in these inspection methods, there is a possibility that local corrosion may be overlooked, and there is a problem that work efficiency is low.
また、特許文献１及び２の非破壊検査手法の場合、０．６ＭＨｚ〜０．７５ＭＨｚあるいは０．０４ＭＨｚの比較的低周波の超音波から長距離伝播特性に優れるガイド波を励起させるようにしているため、ガイド波の波長が長いため、液滴エロージョン等に起因する局所減肉を検出することが困難である。即ち、管状構造物の広範囲をスクリーニングすることにより局所的な腐食の見逃しリスクを低減させることが困難である。 In the case of the non-destructive inspection methods disclosed in Patent Documents 1 and 2, a guide wave having excellent long-range propagation characteristics is excited from a relatively low frequency ultrasonic wave of 0.6 MHz to 0.75 MHz or 0.04 MHz. Therefore, since the wavelength of the guide wave is long, it is difficult to detect local thinning due to droplet erosion or the like. That is, it is difficult to reduce the risk of missing local corrosion by screening a wide range of tubular structures.
さらに、特許文献１及び２の非破壊検査手法の場合、管構造物の軸方向にガイド波を伝播させるため、管状構造物の一端が完全に露出し送信部が周方向に走査可能な状況にない場合、例えば周辺に他の支持構造物が存在したり、保温材などが巻かれていたり部分的に埋設されたりしている場合には、これらが邪魔して検査作業が妨げられることがある。 Furthermore, in the case of the non-destructive inspection methods of Patent Documents 1 and 2, since the guide wave is propagated in the axial direction of the tube structure, one end of the tubular structure is completely exposed and the transmitter can be scanned in the circumferential direction. If not, for example, if there are other support structures in the vicinity, or a heat insulating material is wound or partially embedded, these may interfere with the inspection work. .
本発明は、局所減肉の見逃し防止のためのスクリーニングに有効な管状構造物の欠陥検査方法を提供することを目的とする。具体的には、本発明は、ガイド波を周方向に伝播させながら探触子を被検査管状構造物の軸方向に機械走査させることにより管状構造物全体の検査を行うことを可能とする管状構造物の欠陥検査方法を提供することを目的とする。 An object of this invention is to provide the defect inspection method of a tubular structure effective in the screening for prevention of oversight of local thinning. Specifically, the present invention provides a tubular structure that can inspect the entire tubular structure by mechanically scanning the probe in the axial direction of the tubular structure to be inspected while propagating a guide wave in the circumferential direction. An object of the present invention is to provide a defect inspection method for a structure.
かかる目的を達成するために請求項１記載の管状構造物の欠陥検査方法は、検査対象となる管状構造物の外表面の円周方向に互いに超音波出射方向が向き合うように内向きに２つの斜角探触子を隣接させて配置し、波列が短く速度分散性が弱くなるガイド波を管状構造物内で生成するための入射角でかつ横波の波長が板厚未満となる周波数の体積波をいずれか一方の探触子から送信させると共に他方の探触子で周方向に伝播する透過波を受信させ、２つの探触子の入射点の間のガイド波に変換される前の体積波の透過波と、２つの探触子の入射点の外の領域で多重反射させられた体積波が複数のモードを含むガイド波に変換されて周方向に１周回以上伝播されたガイド波の透過波との２経路の透過波を他方の探触子で受信させ、透過法による２経路の透過波から管状構造物の周方向全周の欠陥を検出するようにしている。 In order to achieve such an object, a defect inspection method for a tubular structure according to claim 1 is characterized in that two inwardly directed ultrasonic wave emission directions face each other in the circumferential direction of the outer surface of the tubular structure to be inspected. An oblique angle probe is placed adjacent to each other, and the volume of the incident angle for generating a guide wave in the tubular structure, in which the wave train is short and the velocity dispersion is weak, and the frequency of the transverse wave is less than the plate thickness. A volume before a wave is transmitted from one of the probes and a transmitted wave propagating in the circumferential direction is received by the other probe and converted into a guide wave between the incident points of the two probes The transmitted wave of the wave and the volume wave that is multiple-reflected in the region outside the incident point of the two probes are converted into a guide wave including a plurality of modes and propagated more than once in the circumferential direction. The transmitted wave of two paths with the transmitted wave is received by the other probe, and the transmission method is used. And to detect the entire circumference of the defects of the tubular structure from the transmitted wave path.
また、本発明の管状構造物の欠陥検査方法は、さらに、２つの探触子のいずれか一方の探触子から、波列が短く速度分散性が弱くなるガイド波を管状構造物内で生成するための入射角でかつ横波の波長が板厚未満となる周波数の体積波を送信させ、多重反射によりガイド波に変えて周方向に伝播させ、同探触子で欠陥からの反射ガイド波を検出し、伝播時間から周方向の欠陥の位置を求めるようにしている。 In addition, the defect inspection method for a tubular structure according to the present invention further generates a guide wave in one of the two probes in which the wave train is short and the velocity dispersion is weak in the tubular structure. The volume wave of the incident wave angle and the frequency of the transverse wave is less than the plate thickness is transmitted, and it is propagated in the circumferential direction instead of the guide wave by multiple reflection, and the reflected wave from the defect is transmitted by the probe. The position of the defect in the circumferential direction is detected from the propagation time.
また、本発明の管状構造物の欠陥検査方法は、さらに、２つの探触子のいずれか一方の探触子から、波列が短く速度分散性が弱くなるガイド波を管状構造物内で生成するための入射角でかつ横波の波長が板厚未満となる周波数の体積波を送信させ、多重反射によりガイド波に変えて周方向に伝播させ、同探触子で欠陥からの反射ガイド波を検出する一方、他方の探触子から逆方向に波列が短く速度分散性が弱くなるガイド波を管状構造物内で生成するための入射角でかつ横波の波長が板厚未満となる周波数の体積波を送信させ、多重反射によりガイド波に変えて周方向に伝播させ、同探触子で欠陥からの反射ガイド波を検出し、互いに逆方向に伝播する反射ガイド波の伝播時間から周方向の前記欠陥の位置を求めるようにしている。 In addition, the defect inspection method for a tubular structure according to the present invention further generates a guide wave in one of the two probes in which the wave train is short and the velocity dispersion is weak in the tubular structure. The volume wave of the incident wave angle and the frequency of the transverse wave is less than the plate thickness is transmitted, and it is propagated in the circumferential direction instead of the guide wave by multiple reflection, and the reflected wave from the defect is transmitted by the probe. While detecting, the incident angle for generating a guide wave in the tubular structure whose wave train is short in the reverse direction from the other probe and the velocity dispersion is weak, and the frequency of the transverse wave is less than the plate thickness. A volume wave is transmitted, converted into a guide wave by multiple reflections and propagated in the circumferential direction, and the reflected guide wave from the defect is detected by the probe, and the propagation direction of the reflected guide wave propagating in the opposite direction from the circumferential direction. The position of the defect is determined.
また、請求項４記載の発明は、２つの探触子を検査対象物の管軸方向に走査させながら周方向における体積波の送信と体積波の多重反射した波動の透過波並びにガイド波の透過波との受信を連続的に行うことにより管状構造物全体の検査を行うようにしている。 Further, the invention described in claim 4 is that the two probes are scanned in the direction of the tube axis of the object to be inspected while transmitting the volume wave in the circumferential direction, the transmitted wave of the reflected wave of the volume wave, and the transmission of the guide wave. The entire tubular structure is inspected by continuously receiving waves.
また、請求項５記載の発明は、２つの探触子の一方の探触子から他方の探触子への経路のエコー強度若しくはそれとウエッジ内エコー強度との比を求め、このエコー強度若しくは強度比で検出値をゲイン調整することにより一定レベルを維持するように補正するようにしている。 In the invention according to claim 5, the echo intensity of the path from one probe of the two probes to the other probe or the ratio of the echo intensity in the wedge to the echo intensity in the wedge is obtained. Correction is performed so that a constant level is maintained by adjusting the gain of the detection value with the ratio.
また、本発明の管状構造物の欠陥検査装置は、検査対象となる管状構造物の外表面に互いに向き合うように円周方向に内向きに隣接させて配置される２つの斜角探触子と、超音波探傷器とから成り、超音波探傷器はいずれか一方の探触子から波列が短く速度分散性が少なくなるガイド波を管状構造物内で生成するための入射角で横波の波長が板厚未満となる周波数の体積波を送信させる一方、他方の探触子で２つの探触子の入射点の間のガイド波に変換される前の体積波の透過波と、２つの探触子の入射点の外の領域で多重反射させられた体積波が複数のモードを含むガイド波に変換されて周方向に１周回以上伝播されたガイド波の透過波との２経路の透過波を受信させる制御部と、体積波の送信と同期させた時間経過軸上に受信した透過体積波並びに透過ガイド波の受信パルスを画像表示する表示部とを備えるようにしている。 Further, the tubular structure defect inspection apparatus of the present invention includes two oblique angle probes arranged adjacently inward in the circumferential direction so as to face each other on the outer surface of the tubular structure to be inspected. The ultrasonic flaw detector is composed of an ultrasonic flaw detector, and the ultrasonic flaw detector emits a guide wave in which the wave train is short and the speed dispersibility is low from either one of the probes. Transmits a volume wave having a frequency less than the plate thickness, while the other probe transmits a volume wave transmission wave before being converted into a guide wave between the incident points of the two probes and the two probes. A two-path transmitted wave, which is a guided wave transmitted in one or more rounds in the circumferential direction, is converted into a guided wave including a plurality of modes by a volume wave that has been multiple-reflected in a region outside the incidence point of the transducer A control unit that receives the signal and a transmission body that is received on the time lapse axis synchronized with the transmission of the volume wave It has a received pulse waves and transmitted guided wave to a display unit for displaying images.
また、本発明にかかる管状構造物の欠陥検査装置は、制御部が、２つの探触子の少なくともいずれか一方の探触子から、波列が短く速度分散性が少なくなるガイド波を管状構造物内で生成するための入射角で横波の波長が板厚未満となる周波数の体積波を送信させ、同探触子で欠陥からの反射ガイド波を受信して、反射ガイド波の伝播時間から周方向の前記欠陥の位置を求める一探触子法をさらに実行するものであることを特徴とする。 Further, in the tubular structure defect inspection apparatus according to the present invention, the control unit generates a guide wave from the probe of at least one of the two probes so that the wave train is short and the speed dispersion is small. From the propagation angle of the reflected guide wave, the volume wave of the transverse wave whose wavelength is less than the plate thickness is transmitted at the incident angle to generate in the object, and the reflected guide wave from the defect is received by the probe. One probe method for obtaining the position of the defect in the circumferential direction is further executed.
また、本発明にかかる管状構造物の欠陥検査装置は、制御部が、２つの探触子のいずれか一方の探触子から、波列が短く速度分散性が少なくなるガイド波を管状構造物内で生成するための入射角で横波の波長が板厚未満となる周波数の体積波を送信すると共に同探触子で欠陥からの反射ガイド波を受信させる一方、他方の探触子から逆方向に波列が短く速度分散性が少なくなるガイド波を管状構造物内で生成するための入射角で横波の波長が板厚未満となる周波数の体積波を送信すると共に同探触子で欠陥からの反射ガイド波を受信させ、互いに逆方向に伝播する反射ガイド波の伝播時間から周方向の欠陥の位置を求める一探触子法をさらに実行するものであることを特徴とする。 Further, in the tubular structure defect inspection apparatus according to the present invention, the control unit transmits a guide wave from one of the two probes, which has a short wave train and less velocity dispersion, to the tubular structure. While transmitting the volume wave of the frequency where the wavelength of the transverse wave is less than the plate thickness at the incident angle for generating in the same direction and receiving the reflected guide wave from the defect with the same probe, the other probe is in the reverse direction In addition, a volume wave having a frequency at which the transverse wave wavelength is less than the plate thickness is transmitted at an incident angle to generate a guide wave in the tubular structure with a short wave train and a reduced velocity dispersion. The one-probe method is further executed to obtain the position of the defect in the circumferential direction from the propagation time of the reflected guide waves propagating in opposite directions.
また、本発明にかかる管状構造物の欠陥検査装置は、制御部が、２つの探触子の一方の探触子から他方の探触子への経路のエコー強度若しくはそれとウエッジ内エコー強度との比を求め、このエコー強度若しくは強度比で検出値をゲイン調整する補正機能を有するようにしている。 Moreover, in the defect inspection apparatus for a tubular structure according to the present invention, the controller is configured to calculate the echo intensity of the path from one probe of the two probes to the other probe or the echo intensity in the wedge. A correction function for obtaining the ratio and gain-adjusting the detected value by this echo intensity or intensity ratio is provided.
さらに、本発明にかかる管状構造物の欠陥検査装置は、２つの斜角探触子を検査対象となる管状構造物の外表面に互いに向き合うように円周方向に内向きに隣接させた状態を保持して、周方向における超音波の送受信を行いながら探触子を管状構造物の軸方向に機械走査させる走査機構を備えるようにしている。 Furthermore, the defect inspection apparatus for a tubular structure according to the present invention has a state in which two oblique probes are adjacent inward in the circumferential direction so as to face each other on the outer surface of the tubular structure to be inspected. A scanning mechanism is provided that allows the probe to mechanically scan in the axial direction of the tubular structure while transmitting and receiving ultrasonic waves in the circumferential direction.
本発明にかかる管状構造物の欠陥検査方法及び装置によれば、管状構造物の外表面に互いに内向きに配置された２つの斜角探触子のうちのいずれか一方を送信子、他方を受信子とする二探触子法により、２つの斜角探触子の入射点の間では通常の超音波探傷と同様にピッチ・キャッチ（pitch-catch technique）による欠陥の検出ができ、２つの斜角探触子の入射点の外の領域では多重反射によりモード変換して生成された高周波ガイド波の透過性を利用して欠陥が検出される。即ち、一方の探触子から他方の探触子の間の最短経路ではガイド波に成りきれていない体積波の多重反射した波動の透過性を利用し、一方の探触子から他方の探触子を通過して周方向に１周回以上伝播されてから再び他方の探触子に至る周回経路ではガイド波の透過性を利用して、２経路の透過波から管状構造物の周方向全周の欠陥を透過法により検出することができる。 According to the defect inspection method and apparatus for a tubular structure according to the present invention, either one of two oblique probes arranged inwardly on the outer surface of the tubular structure is a transmitter, and the other is the other. By using the two-probe method as a receiver, it is possible to detect defects by the pitch-catch technique between the incident points of two oblique angle probes as in the case of normal ultrasonic flaw detection. In a region outside the incident point of the oblique angle probe, a defect is detected using the transmission of a high-frequency guide wave generated by mode conversion by multiple reflection. In other words, in the shortest path between one probe and the other probe, the transmissivity of the multiple reflected waves of the volume wave that cannot be a guide wave is used, and the probe from one probe to the other probe is used. In the circular path that passes through the child and propagates more than once in the circumferential direction and then reaches the other probe again, the entire circumference of the tubular structure is transmitted from the transmitted wave of the two paths using the transmission of the guide wave. Can be detected by the transmission method.
しかも、管状構造物の周方向に入射させた体積波の多重反射を繰り返させることにより高周波ガイド波を生成して周方向に伝播させるため、透過法を利用して欠陥を検出することができると共に、被検査物の肉厚よりも長い波長の超音波を用いる低周波ガイド波に比べて検出性能が高く、局所減肉を検出することができる。依って、高周波ガイド波により広範囲をスクリーニングすることにより局所的な腐食の見逃しリスクを低減することにより、外面から効率的に内面の腐食状況を把握できる。 In addition, since the high-frequency guide wave is generated and propagated in the circumferential direction by repeating multiple reflection of the volume wave incident in the circumferential direction of the tubular structure, a defect can be detected using a transmission method. The detection performance is higher than that of a low-frequency guide wave using ultrasonic waves having a wavelength longer than the thickness of the object to be inspected, and local thinning can be detected. Therefore, it is possible to efficiently grasp the corrosion state of the inner surface from the outer surface by reducing the risk of overlooking the local corrosion by screening a wide area with a high-frequency guided wave.
また、一探触法によるパルス反射法の併用により、欠陥からの反射ガイド波の伝播時間から欠陥の周方向位置を求めることができる。特に、管状構造物の外表面に互いに内向きに配置された２つの斜角探触子からそれぞれ互いに逆方向に高周波ガイド波を伝播させる場合には、欠陥に近い側の探触子で受信する反射ガイド波は管状構造物のおおよそ半周以内の距離となることから、反射ガイド波の減衰を抑えて感度低下を少なくできるので、周方向の欠陥の位置をより求め易くなる。 Further, by using the pulse reflection method by one probe method, the circumferential position of the defect can be obtained from the propagation time of the reflected guide wave from the defect. In particular, when high-frequency guide waves are propagated in opposite directions from two oblique angle probes arranged inward from each other on the outer surface of the tubular structure, they are received by the probe closer to the defect. Since the reflected guide wave is within a distance of approximately half a circumference of the tubular structure, it is possible to suppress the attenuation of the reflected guide wave and reduce the decrease in sensitivity, thereby making it easier to obtain the position of the defect in the circumferential direction.
また、２つの探触子を検査対象物の管軸方向に走査させるだけで、管状構造物全体の検査を簡単に行うことができる。このことは、管状構造物の局所減肉の見逃し防止のためのスクリーニングに有効である。 In addition, the entire tubular structure can be easily inspected by simply scanning the two probes in the tube axis direction of the inspection object. This is effective for screening for preventing oversight of local thinning of the tubular structure.
また、２つの探触子の一方の探触子から他方の探触子への経路のエコー強度若しくはそれとウエッジ内エコー強度との比を求め、このエコー強度若しくは強度比で検出値をゲイン調整することにより補正する場合には、高周波ガイド波のエコーレベルを維持することができるので、管状構造物の表面が粗かったり、ペンキ層の塗布状況が悪く凹凸が生じたり、ペンキ層が厚いことによる高周波ガイド波の減衰が大きい場合にも、高周波ガイド波の検出感度の低下を防ぐことができる。 Also, the echo intensity of the path from one probe of the two probes to the other probe or the ratio of the echo intensity in the wedge to the echo intensity in the wedge is obtained, and the detection value is gain-adjusted by the echo intensity or the intensity ratio. In this case, the echo level of the high-frequency guide wave can be maintained, so that the surface of the tubular structure is rough, the coating layer is not coated properly, unevenness occurs, or the paint layer is thick. Even when the attenuation of the high frequency guide wave is large, it is possible to prevent the detection sensitivity of the high frequency guide wave from being lowered.
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に本発明の管状構造物の欠陥検査方法の実施の一形態を原理図で示す。 FIG. 1 is a principle view showing an embodiment of a defect inspection method for a tubular structure according to the present invention.
検査対象構造物の肉厚全体を振動させ伝播するガイド波は、長距離伝播特性を有する振動モードであり、境界面を長手方向（管状構造物に適用する場合には軸方向）に伝播する超音波モードとして非破壊評価技術分野では広く知られている。そして、このガイド波を励起させるためには、超音波の波長は構造物の厚さ以上にすることが必要と考えられていた。構造物の厚さよりも短い波長の超音波では構造物内にガイド波を励起させられないと考えられていた。このため、厚肉の構造物にガイド波を適用する場合には、低周波超音波を用いなければならない。例えば厚み１４ｍｍ程度であれば、０．３ＭＨｚ〜０．７５ＭＨｚ程度の低周波の使用が一般的である（特許文献１参照）。しかし、構造物の厚さ以上の波長の超音波により生成されるガイド波（本明細書では説明の便宜上、これを低周波ガイド波と呼ぶ）では、波長が長いため、液滴衝撃エロージョン等に起因する局所減肉を検出することが困難である。 The guided wave that vibrates and propagates through the entire thickness of the structure to be inspected is a vibration mode with long-distance propagation characteristics, and is a supersonic wave that propagates along the boundary surface in the longitudinal direction (axial direction when applied to a tubular structure). The sound wave mode is widely known in the non-destructive evaluation technology field. And in order to excite this guide wave, it was thought that the wavelength of an ultrasonic wave needed to be more than the thickness of a structure. It has been considered that an ultrasonic wave having a wavelength shorter than the thickness of the structure cannot excite a guide wave in the structure. For this reason, when applying a guide wave to a thick structure, low-frequency ultrasonic waves must be used. For example, if the thickness is about 14 mm, use of a low frequency of about 0.3 MHz to 0.75 MHz is common (see Patent Document 1). However, a guide wave generated by ultrasonic waves having a wavelength equal to or greater than the thickness of the structure (in this specification, for convenience of explanation, this is called a low frequency guide wave) has a long wavelength. It is difficult to detect the resulting local thinning.
これに対し、横波の波長が検査対象である構造物の板厚未満となる周波数の超音波（体積波）を検査対象構造物内で多重反射させることによりガイド波（本明細書では説明の便宜上、これを高周波ガイド波と呼ぶ）を生成する、本発明者等が開発した手法によれば、上述の低周波ガイド波に比べて有効測定範囲が短いものの、検出性能が高い。また、管状構造物の周方向に高周波ガイド波を伝播させれば、長手方向となる軸方向に比べて短距離である上に、透過法を利用して欠陥を検出することができる。そこで、本発明の管状構造物の欠陥検査方法並びに装置においては、横波音速に対する波長が管状構造物の肉厚未満、好ましくは半分以下程度となる周波数の超音波（体積波）を用い、縦波および横波を多重反射させることで発生した、複数のモード（ＡモードやＳモード）が混在する高周波ガイド波を波列が短く速度分散が軽微な条件で利用するようにしている。 On the other hand, a guide wave (in this specification, for convenience of explanation) is obtained by multiple reflection of ultrasonic waves (volume waves) having a frequency in which the wavelength of the transverse wave is less than the plate thickness of the structure to be inspected. According to the technique developed by the present inventors that generates a high-frequency guide wave), the effective measurement range is shorter than that of the above-described low-frequency guide wave, but the detection performance is high. In addition, if a high-frequency guide wave is propagated in the circumferential direction of the tubular structure, the distance is shorter than the axial direction, which is the longitudinal direction, and defects can be detected using the transmission method. Therefore, in the tubular structure defect inspection method and apparatus of the present invention, ultrasonic waves (volume waves) having a frequency with which the wavelength with respect to the transverse wave velocity is less than the thickness of the tubular structure, preferably about half or less, are used. In addition, a high-frequency guide wave in which a plurality of modes (A mode and S mode) are mixed and generated by multiple reflection of transverse waves is used under the condition that the wave train is short and the speed dispersion is slight.
即ち、この管状構造物の欠陥検査方法は、図１に示すように、検査対象となる管状構造物１の外表面の円周方向に互いに超音波出射方向が向き合うように、内向きに２つの斜角探触子２，３を隣接させて配置し、管状構造物１内でガイド波を生成するための入射角と周波数の体積波をいずれか一方の探触子から送信させると共に、他方の探触子で周方向に伝播する透過波を受信させ、２つの探触子の入射点の間のガイド波に変換される前の体積波の透過波と、２つの探触子の入射点の外の領域で多重反射させられた体積波が複数のモードを含むガイド波に変換されて周方向に１周回以上伝播されたガイド波の透過波との２経路の透過波を他方の探触子で受信させ、透過法による２経路の透過波から管状構造物の周方向全周の欠陥を検出するようにしている。 In other words, as shown in FIG. 1, this tubular structure defect inspection method has two inward directions so that the ultrasonic emission directions face each other in the circumferential direction of the outer surface of the tubular structure 1 to be inspected. The oblique angle probes 2 and 3 are arranged adjacent to each other, and a volume wave having an incident angle and a frequency for generating a guide wave in the tubular structure 1 is transmitted from one of the probes, and the other The transmitted wave propagating in the circumferential direction is received by the probe, and the transmitted wave of the volume wave before being converted into the guide wave between the incident points of the two probes and the incident point of the two probes The other probe is used to transmit the two-way transmitted wave, which is a guide wave transmitted in one or more rounds in the circumferential direction, by converting the volume wave multi-reflected in the outer region into a guide wave including a plurality of modes. And detect defects in the entire circumference of the tubular structure from the two transmitted waves by the transmission method. It has to.
検査に際しては、管状構造物１の板厚に応じて横波の波長が少なくとも板厚未満、好ましくは板厚半分程度またはそれ以下になるように周波数を決める。また、管の曲率に応じて、波列が短く速度分散性が少ないガイド波が発生するような屈折角となるように入射角を設定する。ここで、被検査構造物内で体積波（通常の超音波）が多重反射を起こし、生成されるガイド波の波列が短く（時間分解能が高く）速度分散性が少なくなるような横波屈折角は、具体的には、例えば鋼管の外径および肉厚が約１０１．６mmおよび３．０mmの送電鉄塔の腹材に適用する場合、５０〜７０°程度の範囲であり、最適には６０°である。これは単に幾何学的なものではなく、ガイド波の特性から求められるものである。 In the inspection, the frequency is determined according to the plate thickness of the tubular structure 1 so that the wavelength of the transverse wave is at least less than the plate thickness, preferably about half the plate thickness or less. Further, the incident angle is set so as to have a refraction angle that generates a guide wave having a short wave train and low velocity dispersion according to the curvature of the tube. Here, the transverse wave refraction angle is such that the volume wave (normal ultrasonic wave) causes multiple reflections in the structure to be inspected, and the wave train of the generated guide wave is short (high time resolution) and the velocity dispersibility is low. Specifically, for example, when applied to the abdominal material of a transmission tower having an outer diameter and a wall thickness of about 101.6 mm and 3.0 mm, the range is about 50 to 70 °, and optimally 60 °. It is. This is not simply geometrical, but is obtained from the characteristics of the guide wave.
そして、検査対象となる管状構造物１の外表面に互いに向き合うように円周方向に内向きに隣接させて配置される２つの斜角探触子２，３のいずれか一方の探触子から、管状構造物の周方向に超音波を送信する。 From one of the two oblique angle probes 2 and 3 arranged adjacent to each other inward in the circumferential direction so as to face each other on the outer surface of the tubular structure 1 to be inspected The ultrasonic wave is transmitted in the circumferential direction of the tubular structure.
管状構造物の外表面に互いに内向きに配置された２つの斜角探触子のうちのいずれか一方を送信子、他方を受信子とする二探触子法によれば、２つの斜角探触子の入射点の間では通常の超音波探傷と同様に、ピッチ・キャッチ（pitch-catch technique）による欠陥が検出ができ、２つの斜角探触子の入射点の外の領域では多重反射によりモード変換して生成された高周波ガイド波の透過性を利用して欠陥が検出されることとなる。即ち、一方の探触子から他方の探触子の間の最短経路では高周波ガイド波に成りきれていない体積波の多重反射した波動の透過性を利用し、一方の探触子から他方の探触子を通過して周方向に１周回以上伝播されてから再び他方の探触子に至る周回経路では高周波ガイド波の透過性を利用して、２経路の透過波から管状構造物の周方向全周の欠陥を検出する透過法により周方向の欠陥の検出を可能とする。 According to the two-probe method in which one of two oblique angle probes arranged inward on the outer surface of the tubular structure is a transmitter and the other is a receiver, two oblique angles As with normal ultrasonic flaw detection, defects due to the pitch-catch technique can be detected between the incident points of the probe, and multiple areas outside the incident points of the two oblique angle probes can be detected. Defects are detected by utilizing the transparency of the high-frequency guide wave generated by mode conversion by reflection. That is, the shortest path between one probe and the other probe uses the transmissivity of the multiple reflected waves of the volume wave that cannot be formed as a high-frequency guide wave. In the circular path that passes through the transducer and propagates in the circumferential direction one or more times and then reaches the other probe again, the circumferential direction of the tubular structure is changed from the transmitted wave of the two paths to the other probe by using the permeability of the high-frequency guide wave. It is possible to detect defects in the circumferential direction by a transmission method that detects defects around the entire circumference.
一方、この二探触子法による透過法では、受信する高周波ガイド波の透過波が極端に弱くなることによって欠陥ありと判断できるが、周方向の位置の依存性がないので、周方向の欠陥の位置を測定することができない。そこで、２つの探触子のいずれか一方の探触子あるいは双方の探触子を用いて、１探触子法によるパルス反射法を実施して周方向の欠陥の位置を伝播時間から求めることが好ましい。２つの探触子のいずれか一方の探触子から、横波音速に対する波長が管状構造物の肉厚以下、好ましくは半分以下程度となる周波数の超音波（体積波）を所定の横波屈折角となるように送信し、縦波および横波を多重反射させることで発生した、複数のモードが混在する高周波ガイド波を波列が短く速度分散が軽微な条件で周方向に伝播させ、同じ探触子で欠陥からの反射ガイド波を受信して、反射ガイド波の伝播時間から周方向の欠陥の位置を求める。 On the other hand, in the transmission method by the two-probe method, it can be determined that there is a defect because the transmitted wave of the received high-frequency guide wave becomes extremely weak, but since there is no dependency on the position in the circumferential direction, there is no circumferential defect. The position of cannot be measured. Therefore, using one or both of the two probes, the pulse reflection method using the single probe method is performed, and the position of the defect in the circumferential direction is obtained from the propagation time. Is preferred. From one of the two probes, an ultrasonic wave (volume wave) having a frequency with which the wavelength with respect to the transverse wave velocity is less than the thickness of the tubular structure, preferably about half or less, is set as a predetermined transverse wave refraction angle. The same probe is used to propagate a high-frequency guide wave with multiple modes generated by multiple reflections of longitudinal and transverse waves in the circumferential direction under conditions where the wave train is short and the speed dispersion is slight. Then, the reflected guide wave from the defect is received, and the position of the defect in the circumferential direction is obtained from the propagation time of the reflected guide wave.
このとき、１探触子法によるパルス反射法で欠陥を検出には、１つの斜角探触子から一方向に超音波を入射して得られる反射エコーだけから欠陥の有無とその位置を求めるようにしても良いが、一方の斜角探触子に管の半周分を、他方の斜角探触子に管の反対側の半周分をそれぞれ担当させることが感度を良好にする上で好ましい。例えば、超音波探傷器４の送信器と受信器への各探触子の接続ハードウェアを電子的に切り替えることにより、２つの探触子のうちの一方の探触子を用いてパルス反射法により欠陥を検出する一探触子法を右回り、左回りに実施して、欠陥の位置を補足的に検出する。この場合、欠陥に近い側の探触子で受信する反射ガイド波は管状構造物のおおよそ半周以内の距離となることから、減衰による感度低下が少なくなる。 At this time, in order to detect the defect by the pulse reflection method by the single probe method, the presence / absence of the defect and its position are obtained only from the reflection echo obtained by entering the ultrasonic wave in one direction from one oblique angle probe. However, in order to improve sensitivity, it is preferable that one bevel probe is responsible for the half circumference of the tube and the other bevel angle probe is responsible for the half circumference on the opposite side of the tube. . For example, the pulse reflection method using one of the two probes by electronically switching the connection hardware of each probe to the transmitter and receiver of the ultrasonic flaw detector 4 One probe method for detecting a defect is performed clockwise and counterclockwise to detect the position of the defect supplementarily. In this case, the reflected guide wave received by the probe closer to the defect becomes a distance within about a half circumference of the tubular structure, so that a decrease in sensitivity due to attenuation is reduced.
ここで、高周波ガイド波の感度は、探触子が接触する被検査物の表面、即ち管状構造物の外表面の状況に影響を受け易い。そこで、２つの探触子の第１の探触子から第２の探触子への経路のエコー強度若しくはそれとウエッジ内エコー強度との比を求め、このエコー強度若しくは強度比で検出値を一定レベルに維持するようにゲイン調整することにより補正することが好ましい。例えば、ピッチ・キャッチ（pitch-catch technique）の信号レベルを使って高周波ガイド波の信号レベルを持ち上げるように調整することで、高周波ガイド波のＳ／Ｎ比を改善する。即ち、健全部で得られるピッチ・キャッチの信号レベルに対して高周波ガイド波の信号レベルが何％程度落ちたのかを評価し、その低下分だけ高周波ガイド波の信号レベルを補正する。 Here, the sensitivity of the high-frequency guide wave is easily affected by the condition of the surface of the inspection object with which the probe contacts, that is, the outer surface of the tubular structure. Therefore, the echo intensity of the path from the first probe to the second probe of the two probes or the ratio between it and the echo intensity in the wedge is obtained, and the detected value is constant by this echo intensity or intensity ratio. Correction is preferably performed by adjusting the gain so as to maintain the level. For example, the S / N ratio of the high-frequency guide wave is improved by adjusting the signal level of the high-frequency guide wave using the signal level of the pitch-catch technique. That is, it is evaluated how much the signal level of the high-frequency guide wave has dropped with respect to the signal level of the pitch catch obtained at the sound part, and the signal level of the high-frequency guide wave is corrected by that amount.
以上のようにして二探触子法あるいはこの二探触子法と一探触子法との併用による周方向の欠陥検査を、検査対象物の管軸方向に２つの探触子を走査させながら連続的に行うことにより、管状構造物全体のスクリーニング検査を簡単に行うことができる。 As described above, the two-probe method or the two-probe method and the combined use of the one-probe method are used to scan the two probes in the tube axis direction of the inspection object. However, the screening inspection of the entire tubular structure can be easily performed by performing continuously.
本発明にかかる管状構造物の欠陥検査方法は、例えば、図１に示すような、検査対象となる管状構造物１の外表面に互いに向き合うように円周方向に内向きに隣接させて配置される２つの斜角探触子２，３と、超音波探傷器４とで実施される。 The tubular structure defect inspection method according to the present invention is arranged, for example, as shown in FIG. 1, adjacent to the outer surface of the tubular structure 1 to be inspected so as to face each other inward in the circumferential direction. The two oblique angle probes 2 and 3 and the ultrasonic flaw detector 4 are used.
超音波探傷器４は、フェーズドアレイから成る２つの斜角探触子２，３のいずれか一方の探触子から波列が短く速度分散性が少ない高周波ガイド波を管状構造物１内で生成する入射角でかつ横波の波長が板厚未満となる周波数の体積波を送信させると共に、他方の探触子で２つの探触子の入射点の間のガイド波に変換される前の体積波の透過波と、２つの探触子の入射点の外の領域で体積波が多重反射により複数のモードを含む高周波ガイド波に変換されて周方向に１周回以上伝播された透過波との２経路の透過波を受信させる制御部５と、体積波の送信と同期させた時間経過軸上に受信した透過体積波並びに透過ガイド波の受信パルスを画像表示する表示部９とを少なくとも備える。 The ultrasonic flaw detector 4 generates in the tubular structure 1 a high-frequency guide wave with a short wave train and low velocity dispersion from either one of the two oblique angle probes 2 and 3 formed of a phased array. Volume wave having an incident angle and a frequency at which the wavelength of the transverse wave is less than the plate thickness, and being converted into a guide wave between the incident points of the two probes by the other probe 2 and a transmitted wave that is converted into a high-frequency guided wave including a plurality of modes by multiple reflection in a region outside the incident point of the two probes and propagated more than once in the circumferential direction. It includes at least a control unit 5 that receives the transmitted wave of the path, and a display unit 9 that displays an image of the received volumetric wave and the received guided wave received on the time lapse axis synchronized with the transmission of the volume wave.
そして、制御部５は、パルサー（送信器）とレシーバー（受信器）とを含み、同期部６を介して時間軸部７と同期され、体積波の送信と同期させた時間経過軸上に受信した透過体積波並びに透過ガイド波の受信パルスを表示部９で画像表示すると共にメモリ部８に受信データを格納するようにしている。二探触子法あるいはこの二探触子法と一探触子法との併用による周方向の欠陥検査は、所定の信号処理の後、例えばサイドビュー画像などで、ビーム路程軸上に欠陥が画像表示され、一探触子法で得られる欠陥の周方向位置がビーム路程から求められる。 The control unit 5 includes a pulsar (transmitter) and a receiver (receiver), is synchronized with the time axis unit 7 via the synchronization unit 6, and is received on the time lapse axis synchronized with the transmission of the volume wave. The received volumetric wave and the transmitted guided wave are displayed on the display unit 9 and the received data is stored in the memory unit 8. In the circumferential defect inspection using the two-probe method or a combination of the two-probe method and the one-probe method, after predetermined signal processing, for example, a side view image has a defect on the beam path axis. An image is displayed and the circumferential position of the defect obtained by the single probe method is obtained from the beam path.
また、超音波探傷器４は、２つの斜角探触子２，３の検査対象となる管状構造物１の外表面での配置関係を変更せずに、超音波探傷器４の制御部５による電子的切り替えで、透過法で管状構造物１内の欠陥１０を検出しようとする２探触子法と、パルス反射法で管状構造物１内の欠陥の位置を検出しようとする１探触子法とを実施可能とされる。二探触子法と一探触子法とは、いずれを先に実施しても良いが、本実施形態の場合には、２探触子法による体積波と高周波ガイド波との透過波を利用した周方向の欠陥検出を行った後に、ハードウェアを電子的に切り替えて１探触子法を補足的に行なうようにしている。 Further, the ultrasonic flaw detector 4 does not change the positional relationship on the outer surface of the tubular structure 1 to be inspected by the two oblique angle probes 2 and 3, and controls the control unit 5 of the ultrasonic flaw detector 4. The two-probe method for detecting the defect 10 in the tubular structure 1 by the transmission method and the one probe for detecting the position of the defect in the tubular structure 1 by the pulse reflection method. The child law can be implemented. Either the two-probe method or the one-probe method may be performed first, but in the case of this embodiment, transmitted waves of the volume wave and the high-frequency guide wave by the two-probe method are used. After performing the circumferential defect detection, the hardware is electronically switched to supplement the one-probe method.
ここで、二探触子法・透過法による欠陥の検出は、表示部９に受信する高周波ガイド波の透過波が極端に弱くなるという画像表示によって表されるが、２つの探触子のうちの一方を用いた一探触子法・パルス反射法による欠陥の検出は、サイドビュー画像などでビーム路程軸上に欠陥を示す画像が表示されることで現れされる。つまり、一探触子法によると、反射エコーの伝播時間から周方向の欠陥の位置が画像表示されるが、演算などにより欠陥位置を求めて出力するようにしても良い。 Here, the detection of the defect by the two-probe method / transmission method is represented by an image display in which the transmitted wave of the high-frequency guide wave received on the display unit 9 becomes extremely weak. Of the two probes, The defect detection by the one-probe method or the pulse reflection method using one of the above is shown by displaying an image showing the defect on the beam path axis in a side view image or the like. That is, according to the one-probe method, the position of the defect in the circumferential direction is displayed as an image from the propagation time of the reflected echo, but the defect position may be obtained and output by calculation or the like.
尚、斜角探触子２，３としては、本実施形態ではフェーズドアレイが使用されて、波列の短い高周波ガイド波を発生できる屈折角の範囲で超音波を検査対象となる構造物に入射できるように設定されている。しかし、後述の実験では、管状構造物の周方向に超音波を送信したときに体積波に多重反射を起こさせるに適した屈折角度となるように入射角度をフェーズアレイで選んだ後に、その角度の固定角のプローブを使っている。即ち、斜角探触子はフェーズドアレイでも、固定角探触子でも良い。 In this embodiment, a phased array is used as the oblique angle probes 2 and 3, and an ultrasonic wave is incident on a structure to be inspected within a refraction angle range in which a high-frequency guide wave with a short wave train can be generated. It is set to be possible. However, in the experiment described later, after selecting the incident angle with the phase array so that the refraction angle is suitable for causing multiple reflection in the volume wave when ultrasonic waves are transmitted in the circumferential direction of the tubular structure, the angle is selected. A fixed angle probe is used. That is, the oblique angle probe may be a phased array or a fixed angle probe.
また、２つの斜角探触子２，３の配置は、２つの探触子の入射点の間で体積波の多重反射した波動の透過性によりその間の欠陥を検出できる間隔内であれば離して設置可能であるが、好ましくは接近限界まで間隔を狭めて隣接させることである。そして、振動子径は実施可能な範囲で可能な限り大きいほうが良く、ビームは収束させないことが好ましい。 Also, the two oblique angle probes 2 and 3 are arranged so long as they are within an interval in which a defect can be detected between them by the transparency of the wave reflected by the volume wave between the incident points of the two probes. However, it is preferable to reduce the distance to the approach limit and make them adjacent. The vibrator diameter should be as large as possible within the feasible range, and the beam is preferably not converged.
また、制御部５は、２つの探触子２，３の一方の探触子から他方の探触子への経路のエコー強度若しくはそれとウエッジ内エコー強度との比を求め、このエコー強度若しくは強度比で検出値をゲイン調整する補正部を有することが好ましい。 The control unit 5 obtains the echo intensity of the path from one probe of the two probes 2 and 3 to the other probe or the ratio of the echo intensity within the wedge and the echo intensity or intensity. It is preferable to have a correction unit that adjusts the gain of the detection value by the ratio.
さらに、２つの斜角探触子２，３は、検査対象となる管状構造物１の外表面に互いに向き合うように円周方向に内向きに隣接させた状態を保持して、手動により管軸方向に走査させるようにしても良いが、機械走査させる走査機構（図示省略）を備えることが好ましい。さらにこの走査機構にはエンコーダ１１が搭載され、軸方向移動距離と周方向の検出結果が関連づけられて記憶装置に記憶されることが好ましい。 Further, the two oblique angle probes 2 and 3 are held in a state where they are adjacent to each other inward in the circumferential direction so as to face each other on the outer surface of the tubular structure 1 to be inspected. Although scanning may be performed in the direction, it is preferable to include a scanning mechanism (not shown) for mechanical scanning. Further, it is preferable that the scanning mechanism is equipped with an encoder 11 and the axial movement distance and the circumferential detection result are associated with each other and stored in the storage device.
なお、上述の形態は本発明の好適な形態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。 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 scope of the present invention.
以下、内面に局所的な腐食部を有する実際の送電鉄塔の腹材（外径101.6mm，厚さ3.0mm）を用い、鋼管鉄塔における内面の局所的な腐食に対する外面からの点検技術の高精度および高効率化を目的に、本発明の腐食測定方法のスクリーニングへの適用の有効性について検討した結果について説明する。尚、試験では、２つの斜角探触子の配置を本発明とは逆に、検査対象管状構造物の外表面の円周方向に互いに超音波出射方向が逆向きとなるように外向きに隣接させて配置し、管状構造物内で高周波ガイド波が生成されること、並びに欠陥を検出できることについてのみ確認した。 The following is a high-precision inspection technique from the outside for local corrosion of the inner surface of a steel pipe tower, using an abdominal material (outer diameter 101.6 mm, thickness 3.0 mm) of an actual transmission tower with a locally corroded part on the inner surface. For the purpose of improving the efficiency, the results of studying the effectiveness of applying the corrosion measurement method of the present invention to screening will be described. In the test, the arrangement of the two bevel probes is opposite to that of the present invention, so that the ultrasonic emission directions are opposite to each other in the circumferential direction of the outer surface of the tubular structure to be inspected. They were placed adjacent to each other and confirmed only that high-frequency guided waves were generated in the tubular structure and that defects could be detected.
［試験体および機材］
［試験体］
高周波ガイド波法について検討するため、内面腐食による局所的な減肉を模擬した欠陥（模擬減肉）を有する平板および鋼管試験体、不めっき領域を有する鋼管試験体を製作した。試験体の寸法は腹材を参考にして決定しており、試験体寸法、欠陥付与位置、欠陥および不めっきの概要を図３に示す。平板および鋼管試験体の母材はそれぞれSPCCおよびSTK400である。模擬減肉は放電加工により付与し、その後に溶融亜鉛めっきを施工した。平板試験体では単に防食を目的としめっき厚の設計値を0.01mmに、鋼管試験体では実機を想定して0.1mmとした。鋼管試験体の端部を切断調査した結果、めっき厚は内面で概ね0.085mm〜0.11mmおよび外面で0.095mm〜0.11mmであった。内面の断面SEM像の一例を図４に示す。
[Test specimens and equipment]
[Specimen]
In order to study the high-frequency guided wave method, flat plate and steel pipe test specimens having defects (simulated thinning) simulating local thinning due to internal corrosion, and steel pipe test specimens having non-plated regions were manufactured. The dimensions of the test specimen are determined with reference to the abdominal material. FIG. 3 shows an outline of the specimen dimensions, defect application positions, defects, and non-plating. The base materials for the flat plate and steel pipe specimens are SPCC and STK400, respectively. Simulated thinning was applied by electrical discharge machining, followed by hot dip galvanization. For the flat plate specimen, the design value of the plating thickness was set to 0.01 mm for the purpose of corrosion protection, and the steel pipe specimen was set to 0.1 mm assuming the actual machine. As a result of cutting investigation of the ends of the steel pipe specimens, the plating thickness was approximately 0.085 mm to 0.11 mm on the inner surface and 0.095 mm to 0.11 mm on the outer surface. An example of a cross-sectional SEM image of the inner surface is shown in FIG.
人工的に不めっきとなる領域を設けた鋼管試験体において、同領域の付与方法は以下の通りである。まず、不めっきの処理を実施する範囲に一般的なさび止め塗料を塗布し、亜鉛めっき施工後に残存するさび止め塗料をスクレーパーおよびワイヤブラシにより除去した。 In a steel pipe test body provided with an artificially non-plated region, the method for applying the region is as follows. First, a general rust preventive paint was applied in a range where the non-plating treatment was performed, and the rust preventive paint remaining after the galvanization was removed with a scraper and a wire brush.
上記の試験体を用いて検討した結果を検証するため、廃却材で内面腐食を有する部分を切り出した。鋼管の外径および肉厚は約101.6mmおよび3.0mmであった。内面腐食部を触診した結果、腐食生成物による凹凸が確認された。 In order to verify the results of the examination using the above test specimen, a portion having internal corrosion was cut out from the discarded material. The outer diameter and wall thickness of the steel pipe were about 101.6mm and 3.0mm. As a result of palpating the internally corroded part, irregularities due to corrosion products were confirmed.
［機材］
本実験で使用した探触子および測定装置について説明する。使用した探触子の用途と主な仕様を表１に示す。リニアアレイおよび一振動子探触子はポリスチレン製ウェッジおよび検査技術研究所製の適合型ウェッジを装着して使用した。適合型ウェッジを用いた定点での厚さ測定には接触媒質を用いず、探触子を機械走査する場合にはポリスチレン製ウェッジの場合と同様に接触媒質に水を使用した。測定装置として、リニアアレイおよび一振動子探触子を使用する測定には小型超音波フェーズドアレイ探傷器（Zetec社製、商品名OMNISCAN）を、EMAT を使用する測定には電磁超音波厚さ計（Acoustic control Systems社製、商品名A1270）を使用した。
The probe and measurement apparatus used in this experiment will be described. Table 1 shows the usage and main specifications of the probe used. The linear array and the single transducer probe were used with a polystyrene wedge and a compatible wedge made by the laboratory. When measuring the thickness at a fixed point using an adaptive wedge, the contact medium was not used. When the probe was mechanically scanned, water was used as the contact medium as in the case of the polystyrene wedge. A small ultrasonic phased array flaw detector (Zetec, trade name OMNISCAN) is used for measurement using a linear array and a single transducer probe, and an electromagnetic ultrasonic thickness gauge is used for measurement using EMAT. (Trade name A1270, manufactured by Acoustic Control Systems) was used.
［スクリーニング］
［平板試験体を用いた基礎検討］
周波数、送受信方式、屈折角に関する基礎検討のため、横波屈折角45°のポリスチレン製ウェッジを装着した１MHz、２MHz、５MHzのリニアアレイ探触子を用い、図５に示すように一探触子法および二探触子法により平板試験体を測定した。試験体端面から入射点までの距離を２０mm探触子を配置した。なお、横波屈折角を単に屈折角(θr)と記す。
[screening]
[Fundamental study using flat plate specimen]
For basic studies on frequency, transmission / reception method, and refraction angle, a 1MHz, 2MHz, and 5MHz linear array probe equipped with a polystyrene wedge with a transverse wave refraction angle of 45 ° is used as shown in Fig. 5. And flat plate specimens were measured by the two probe method. A 20 mm probe was placed at a distance from the end face of the specimen to the incident point. The transverse wave refraction angle is simply referred to as a refraction angle (θr).
間隔を2.5°とした。各探触子において図６中の破線で示した波列の短い高周波ガイド波を発生できる屈折角のA スコープ波形を比較して図７に示す。同図では、反射エコー強度を80％となるように調整した。背景雑音に対するS/N 比の観点において、2MHzの結果が優位と判断した。よって、以下の検討には2MHzの探触子を用いることとした。 The interval was 2.5 °. FIG. 7 shows a comparison of A-scope waveforms having a refraction angle that can generate a high-frequency guide wave having a short wave train indicated by a broken line in FIG. 6 in each probe. In the figure, the reflected echo intensity was adjusted to 80%. From the viewpoint of S / N ratio against background noise, the result of 2MHz was judged to be superior. Therefore, we decided to use a 2MHz probe for the following study.
模擬減肉の検出性を比較するために、探触子走査により得られた、異なる屈折角のサイドビュー画像を図８に示す。屈折角20°では試験体端面からの反射エコーの波列は長いが、図中の破線に囲まれた３つの模擬減肉によるエコーを認識できる。一方、屈折角50°以上の場合では、波列は短いものの、模擬減肉のエコーを認識できず、図中の一点鎖線で囲まれた、探傷面に直径５mm程度の小滴のソニコートを垂らした位置からのエコーが確認された。よって、屈折角が小さい場合、探触子と反対の面にエネルギーは集中し、大きい場合には探触子側の面に集中することが考えられる。また、同図において、模擬減肉の位置ではガイド波のエネルギーの一部しか透過しないことから、試験体端面からのエコーが消失していることが観測できる。このことから、模擬減肉からの反射エコーではなく、透過エコーに着目することとした。 In order to compare the detection of simulated thinning, side view images with different refraction angles obtained by probe scanning are shown in FIG. When the refraction angle is 20 °, the wave train of the reflected echo from the end face of the specimen is long, but the echoes due to the three simulated thinnings surrounded by the broken line in the figure can be recognized. On the other hand, when the refraction angle is 50 ° or more, the wave train is short, but the echo of simulated thinning cannot be recognized, and a small sonicoat with a diameter of about 5 mm is hung on the flaw detection surface surrounded by a dashed line in the figure. An echo from the specified position was confirmed. Therefore, it is conceivable that when the refraction angle is small, the energy is concentrated on the surface opposite to the probe, and when it is large, the energy is concentrated on the surface on the probe side. Further, in the same figure, since only a part of the energy of the guide wave is transmitted at the position of the simulated thinning, it can be observed that the echo from the end face of the specimen has disappeared. For this reason, we decided to focus on transmitted echoes, not reflected echoes from simulated thinning.
同仕様のリニアアレイ探触子を用い、図５(b)に示す二探触子法による測定を実施した。模擬減肉の影響を受けない位置でのセクター画像を図９に示す。屈折角の範囲は横波で２０°から７０°とし、間隔を１°とした。同図から波列の短い高周波ガイド波が発生する屈折角の範囲は５０°から７０°と図８の場合と比べて広いことが判る。図１０には波列が短い試験体端面からの反射エコーが得られる屈折角６０°の場合のサイドビュー画像を示しており、模擬減肉部では透過エコーが消失していることを確認できる。なお、この場合の高周波ガイド波の群音速は2,500m/s 程度であった。よって、今後の高周波ガイド波法による測定においては、この結果に基づき、周波数はS/N 比が高かった２MHz、屈折角に関しては破列が短い高周波ガイド波を発生できた６０°を用いることとした。 Using the linear array probe of the same specification, measurement was performed by the two probe method shown in FIG. 5 (b). FIG. 9 shows a sector image at a position not affected by simulated thinning. The range of the refraction angle was 20 ° to 70 ° in the transverse wave, and the interval was 1 °. From this figure, it can be seen that the range of the refraction angle at which a high-frequency guide wave with a short wave train is generated is 50 ° to 70 ° as compared with the case of FIG. FIG. 10 shows a side view image in the case of a refraction angle of 60 ° from which a reflection echo from the end face of the test object having a short wave train is obtained, and it can be confirmed that the transmission echo disappears in the simulated thinning portion. In this case, the group sound velocity of the high-frequency guided wave was about 2,500 m / s. Therefore, in the future measurement by the high-frequency guided wave method, based on this result, the frequency is 2 MHz, which has a high S / N ratio, and the refraction angle is 60 °, which can generate a high-frequency guided wave with a short break. did.
波列が短い高周波ガイド波を発生させるためには屈折角の選定が極めて重要である。そこで、亜鉛めっきによる屈折角への影響について考察する。図１１に示すようにウェッジ（媒体１）から鋼（媒体２）へ直に超音波を入射したケース１と亜鉛めっき（媒体３）を介して鋼に入射したケース２を考えると、それぞれの入射角と屈折角の関係はスネルの法則により In order to generate a high-frequency guide wave with a short wave train, the selection of the refraction angle is extremely important. Therefore, the effect of galvanization on the refraction angle will be considered. As shown in FIG. 11, considering the case 1 in which the ultrasonic wave is directly incident on the steel (medium 2) from the wedge (medium 1) and the case 2 in which the ultrasonic wave is incident on the steel via the galvanizing (medium 3), The relationship between the angle and the refraction angle depends on Snell's law
［ケース１］
sinθｉ/sinθｒ=ｃ1/ｃ2 （式１）
［ケース２］
sinθｉ/sinφ=ｃ1/ｃ３ （式２）
sinφ/sinθ’ ｒ=ｃ３/ｃ2 （式３）
となる。ここで、ｃ1、ｃ2 およびｃ３は各媒体の音速であり、θｉ、θｒ、θ’ ｒおよびφは同図に示すように入射角、屈折角である。(２)および(３)式から
sinθｉ/sinθ’ ｒ=ｃ1/ｃ2 （式４）
が得られ、ある入射角に対して両ケースにおける鋼への屈折角は等しくなる。さらに、亜鉛めっきの上にペンキが塗装されている場合も同様である。また、鋼管における多重反射時の反射角に関しても亜鉛めっきおよびペンキによる影響はない。
[Case 1]
sinθ i / sinθ r = c 1 / c 2 (Formula 1)
[Case 2]
sinθ i / sinφ = c 1 / c 3 (Formula 2)
sinφ / sinθ 'r = c 3 / c 2 ( Equation 3)
It becomes. Here, c 1 , c 2 and c 3 are sound speeds of the respective media, and θ i , θ r , θ ′ r and φ are an incident angle and a refraction angle, as shown in FIG. From equations (2) and (3)
sinθ i / sinθ ′ r = c 1 / c 2 (Formula 4)
And the refraction angle to the steel in both cases is equal for a given incident angle. Further, the same applies when the paint is painted on the galvanizing. Moreover, there is no influence by galvanization and paint also about the reflection angle at the time of the multiple reflection in a steel pipe.
［鋼管への適用性］
鋼管に対して上記の高周波ガイド波法を適用する際、ガイド波を伝播させる方向によって多重反射時の反射角およびガイド波の減衰が異なり、さらに、作業性などが変わる。具体的には、送信および受信用探触子を隣接して配置する方が作業性は良い。減衰に関しては軸方向の方が小さい。反射角に関しては、軸方向に伝播した場合、屈折角および外面と内面における反射角は一致する。しかしながら、周方向に伝播させた場合、外面の反射角は屈折角と一致するが、内面の反射角は屈折角より大きくなる。送電鉄塔の鋼管において作業性を優先する場合、近接した探触子配置の状態でガイド波を周方向に伝播させて減肉を検知できるかを確認する必要がある。
[Applicability to steel pipes]
When the above-described high-frequency guide wave method is applied to a steel pipe, the reflection angle at the time of multiple reflection and the attenuation of the guide wave differ depending on the direction in which the guide wave propagates, and workability and the like change. Specifically, the workability is better if the transmission and reception probes are arranged adjacent to each other. The attenuation is smaller in the axial direction. Regarding the reflection angle, when propagating in the axial direction, the refraction angle and the reflection angles on the outer surface and the inner surface are the same. However, when propagated in the circumferential direction, the reflection angle of the outer surface coincides with the refraction angle, but the reflection angle of the inner surface becomes larger than the refraction angle. When priority is given to workability in the steel pipe of a power transmission tower, it is necessary to confirm whether thinning can be detected by propagating a guide wave in the circumferential direction in a state of close probe arrangement.
ポリスチレン製ウェッジおよび適合型ウェッジを装着した一振動子探触子を用い、周方向模擬減肉を有する鋼管試験体に対し、図１２に示す探触子配置で測定を実施した。得られたサイドビュー画像を図１３に示す。屈折角６０°の場合の内面の反射角は67.52°となり、図９に示した波列の短い高周波ガイド波を発生できる屈折角の範囲に収まっている。両探触子の入射点間隔は３５mmであり、模擬減肉と両探触子の中間点との方位角θを９０°、１８０°および２７０°とした。適合型ウェッジの使用の際には、機械走査のため探傷面側に厚さ0.05mm のポリプロピレンテープを貼付した。図１３からθおよびウェッジの材質に依らず、模擬減肉による透過エコーの消失が観測できる。それぞれの結果を数値的に比較するため、Ａスコープ波形ｄを超音波の伝播方向に積分した量Ｄを求め、以下の規格化および閾値処理を行った。 Using a single transducer probe equipped with a polystyrene wedge and an adaptive wedge, measurement was carried out with the probe arrangement shown in FIG. The obtained side view image is shown in FIG. When the refraction angle is 60 °, the reflection angle of the inner surface is 67.52 °, which is within the range of the refraction angle that can generate a high-frequency guide wave with a short wave train shown in FIG. The distance between the incident points of both probes was 35 mm, and the azimuth angle θ between the simulated thinning and the intermediate point of both probes was 90 °, 180 ° and 270 °. When using a compatible wedge, a 0.05 mm thick polypropylene tape was applied to the flaw detection side for mechanical scanning. From FIG. 13, disappearance of the transmitted echo due to simulated thinning can be observed regardless of the material of θ and the wedge. In order to numerically compare the results, an amount D obtained by integrating the A scope waveform d in the ultrasonic wave propagation direction was obtained, and the following normalization and threshold processing were performed.
［正規化］
Ｅ１（ｘ）＝Ｄ（ｘ）／ｍａｘ（Ｄ（ｘ）） （式６）
[Normalization]
E 1 (x) = D (x) / max (D (x)) (Formula 6)
［閾値処理］
Ｅ２（ｘ）＝ｔ−Ｅ１（ｘ） Ｅ１（ｘ）≧ｔ
＝０ Ｅ１（ｘ）＜ｔ （式７）
[Threshold processing]
E 2 (x) = t−E 1 (x) E 1 (x) ≧ t
= 0 E 1 (x) <t (Expression 7)
ここで、
であり、ｘは探触子位置、ｔは閾値、ｌはビーム路程を表す。図１３のデータに対するＥ１ およびＥ２を図１４に示す。図中のP はポリスチレン製ウェッジを、Ｃは適合型ウェッジを表す。同図の模擬減肉以外の領域でＥ１に０．６〜１．０の変動があったため、ｔを０．６としてＥ２を算出した。この図からも測定結果は探触子と模擬減肉の相対位置やウェッジの材質にほとんど影響されないと考えられる。なお、送信および受信用探触子のいずれかによる一探触子法により検出できる減肉に限り探触子と減肉の相対位置を推定できると考える。
here,
Where x is the probe position, t is the threshold value, and l is the beam path length. E 1 and E 2 for the data of FIG. 13 are shown in FIG. In the figure, P represents a polystyrene wedge, and C represents a conforming wedge. Since there was a variation of E 1 to 0.6-1.0 in a region other than the simulated thinning in the figure was calculated E 2 t for 0.6. From this figure, it is considered that the measurement results are hardly affected by the relative position of the probe and simulated thinning and the material of the wedge. Note that the relative position between the probe and the thinning can be estimated only by the thinning that can be detected by the single probe method using either the transmission or reception probe.
模擬不めっきを有する鋼管試験体を用い、不めっき部検知への適用性について調査した。ポリスチレン製ウェッジを装着した一振動子探触子を用いて得られたサイドビュー画像を図１５に示す。模擬不めっきと両探触子の中間点とのθを１８０°とした。めっき部と不めっき部で受信されるエコー強度について顕著な差はないが、めっき部と不めっき部の境界においてエコー強度の低下が確認できる。 Using steel pipe specimens with simulated non-plating, the applicability to unplated part detection was investigated. FIG. 15 shows a side view image obtained using a single transducer probe equipped with a polystyrene wedge. The θ between the simulated non-plating and the midpoint of both probes was 180 °. Although there is no significant difference in echo intensity received between the plated part and the non-plated part, a decrease in echo intensity can be confirmed at the boundary between the plated part and the non-plated part.
（廃却材への適用）
最初に、廃却材に対して、ポリスチレン製ウェッジを装着した一振動子探触子を用い、図１２に示す体系で高周波ガイド波によるスクリーニングを実施した。得られたサイドビュー画像とそれによる(７)式のＥ２を図１６に示す。腐食部と両探触子の中間点とのθを１８０°程度とした。軸方向に対して３５mm程度の範囲に亘り顕著な透過エコーの強度変化が観測された。
(Application to waste materials)
First, screening with a high-frequency guided wave was carried out on the discarded material using a single transducer probe equipped with a polystyrene wedge with the system shown in FIG. FIG. 16 shows the obtained side view image and E 2 in the equation (7). The θ between the corroded portion and the midpoint between the two probes was about 180 °. A remarkable change in transmitted echo intensity was observed over a range of about 35 mm with respect to the axial direction.
高周波ガイド波によるスクリーニングで透過エコーの強度変化が観測された領域周辺に対して、適合型ウェッジを装着したリニアアレイ探触子による厚さ測定に先立ち、10MHz の一振動子探触子による測定を行った。廃却材外面において探触子を小型自動スキャナにより二次元走査することにより得られた投影像、断面像を図１７に示す。同画像においては底面エコーの強度をカラー表示しており、断面像は投影像の破線部に対応している。投影像の色の変化および断面像の底面エコーが消失していることから腐食１および２による減肉を検知できる。 Prior to the thickness measurement with a linear array probe equipped with an adaptive wedge, the area around the area where the intensity change of the transmitted echo was observed by screening with a high-frequency guided wave was measured with a 10 MHz single transducer probe. went. FIG. 17 shows a projected image and a cross-sectional image obtained by two-dimensionally scanning the probe with a small automatic scanner on the outer surface of the discarded material. In this image, the intensity of the bottom echo is displayed in color, and the cross-sectional image corresponds to the broken line portion of the projected image. Since the change in the color of the projected image and the bottom echo of the cross-sectional image have disappeared, thinning due to corrosion 1 and 2 can be detected.
以上、内面に局所的な腐食部を有する実際の送電鉄塔の腹材（外径101.6mm，厚さ3.0mm）を用い、高周波ガイド波法の適用性を評価した結果、腹材に対して超音波の周波数を2MHz、横波屈折角を６０°とした条件下で、時間分解能が高い高周波ガイド波を発生させることに成功した。そして、この条件でガイド波を周方向に伝播させながら探触子を腹材の軸方向に機械走査した結果、腐食している個所を検知できた（図１２,図１６）。このことから、腐食による局所的な減肉に対する高周波ガイド波法が有効であり、かつスクリーニングが可能であることが判明した。 As a result of evaluating the applicability of the high-frequency guided wave method using an abdominal material (outer diameter 101.6 mm, thickness 3.0 mm) of an actual power transmission tower that has a locally corroded part on the inner surface, Succeeded in generating a high-frequency guide wave with high temporal resolution under the conditions of a sound wave frequency of 2 MHz and a transverse wave refraction angle of 60 °. As a result of mechanical scanning of the probe in the axial direction of the abdomen while propagating the guide wave in the circumferential direction under these conditions, the corroded portion was detected (FIGS. 12 and 16). From this, it was found that the high-frequency guided wave method for local thinning due to corrosion is effective and screening is possible.
１ 被検査物である管状構造物
２ 斜角探触子
３ 斜角探触子
４ 超音波探傷器
５ 制御部
９ 表示部
１０ 欠陥
DESCRIPTION OF SYMBOLS 1 Tubular structure which is to-be-inspected object 2 Oblique probe 3 Oblique probe 4 Ultrasonic flaw detector 5 Control part 9 Display part 10 Defect
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110118824A (en) * | 2019-05-16 | 2019-08-13 | 武汉中科创新技术股份有限公司 | A kind of oblique shortcoming detection system of pipeline and method |
| CN112305073A (en) * | 2020-10-26 | 2021-02-02 | 西安热工研究院有限公司 | Ultrasonic detection method for crack of sliding pair weld toe of boiler heated surface pipe |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110118824A (en) * | 2019-05-16 | 2019-08-13 | 武汉中科创新技术股份有限公司 | A kind of oblique shortcoming detection system of pipeline and method |
| CN112305073A (en) * | 2020-10-26 | 2021-02-02 | 西安热工研究院有限公司 | Ultrasonic detection method for crack of sliding pair weld toe of boiler heated surface pipe |
| CN112305073B (en) * | 2020-10-26 | 2024-01-19 | 西安热工研究院有限公司 | Ultrasonic detection method for weld toe cracks of sliding pair of boiler heating surface pipe |
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