JP2008224495A - Eddy current inspection method, steel pipe inspected thereby and eddy current inspection device for executing the eddy current inspection method - Google Patents
Eddy current inspection method, steel pipe inspected thereby and eddy current inspection device for executing the eddy current inspection method Download PDFInfo
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Abstract
Description
本発明は、磁性を有する鋼管等の金属材料を渦流検査する方法、該渦流検査方法で検査した鋼管、及び該渦流検査方法を実施するための渦流検査装置に関する。特に、本発明は、金属材料に局部的に存在する高硬度部を確実に検出可能であると共に、高硬度部を除去するためにグラインダー研削等の手入れ処理を施した後に、該高硬度部が除去されているか否かを確実に確認することができる渦流検査方法、該渦流検査方法で検査した鋼管、及び該渦流検査方法を実施するための渦流検査装置に関する。 The present invention relates to a vortex inspection method for a metal material such as a steel pipe having magnetism, a steel pipe inspected by the eddy current inspection method, and an eddy current inspection apparatus for performing the eddy current inspection method. In particular, the present invention is capable of reliably detecting a high hardness portion locally present in a metal material, and after performing a maintenance process such as grinder grinding in order to remove the high hardness portion, the high hardness portion The present invention relates to an eddy current inspection method capable of reliably confirming whether or not it has been removed, a steel pipe inspected by the eddy current inspection method, and an eddy current inspection apparatus for carrying out the eddy current inspection method.
鋼管等の金属材料の製造過程では、熱処理時における浸炭、脱炭、脆化相の析出等の組織変化による金属材料の脆化や、搬送時における金属材料同士の衝突或いは金属材料と搬送設備との衝突や、冷間加工時における焼き付き等に起因した強加工などによって、金属材料の組織が局部的に変化し、変化しない部位と比べて場合によってはビッカース硬度で５０Ｈｖ以上高い局部的な高硬度部が発生することが知られている。金属材料にこのような局部的な高硬度部が発生すれば、該高硬度部での金属材料の脆化や耐食性の劣化による破損が懸念される。 In the manufacturing process of metal materials such as steel pipes, the embrittlement of metal materials due to structural changes such as carburization, decarburization, and precipitation of embrittlement phase during heat treatment, collision between metal materials during transportation, or metal materials and transportation equipment The structure of the metal material locally changes due to strong collisions caused by collisions or seizure during cold working, etc., and in some cases, the local high hardness is 50 Vv or more higher in Vickers hardness than the part that does not change Is known to occur. If such a local high hardness portion is generated in the metal material, there is a concern that the metal material becomes brittle or breaks due to deterioration of corrosion resistance in the high hardness portion.
このため、金属材料に存在する局部的な高硬度部を検出する必要があると共に、該高硬度部を除去するための手入れ処理（グラインダー研削等の処理）を施した後に、実際に高硬度部が除去されたか否かを確認する必要がある。 For this reason, it is necessary to detect a local high hardness portion existing in the metal material, and after performing a care process (such as grinder grinding) for removing the high hardness portion, It is necessary to confirm whether or not has been removed.
しかしながら、人手による目視や、金属材料に圧子を圧入して圧入の大きさや圧子の超音波共振周波数により硬度を測定する簡易硬度計を用いた高硬度部の検出や高硬度部除去の確認は、連続的な測定が困難であるために時間が掛かったり、判定にバラツキが生じるという問題がある。このため、局部的な高硬度部を非接触・非破壊的方法で検出すると共に、高硬度部を除去するための手入れ処理を施した後、実際に高硬度部が除去されていることを非接触・非破壊的方法で確認できれば、高硬度部の検出や高硬度部除去の確認の効率や確実性を高めることが可能である。 However, visual inspection by hand, detection of high hardness part using a simple hardness meter that measures the hardness by press-fitting the indenter into a metal material and the ultrasonic resonance frequency of the indenter, and confirmation of high-hardness part removal, Since continuous measurement is difficult, there are problems that it takes time and variations in determination occur. For this reason, a local high hardness part is detected by a non-contact / non-destructive method, and after performing a care process for removing the high hardness part, it is confirmed that the high hardness part is actually removed. If it can be confirmed by a contact / non-destructive method, it is possible to increase the efficiency and certainty of detection of a high hardness portion and confirmation of removal of a high hardness portion.
金属材料の硬度や硬度の変化部を非接触で非破壊的に検出する技術として、例えば、特許文献１には、鋼板が磁化されることにより変化した磁界（透過磁気）が鋼板の硬度と相関があることを利用した技術が開示されている。特許文献２には、鋼材の磁気特性(保持力、残留磁化、飽和磁化、透磁率、ヒステリシス損)と機械的性質（硬さ、焼き入れ深さ、強度、結晶粒度）には相関があることを利用した技術が開示されている。特許文献３には、検査コイル及び比較コイルを含むブリッジ回路を用いて鋼管の材質（硬度、炭素含有量）や性状の変化を検出する技術が開示されている。特許文献４には、鋼の複数の磁気的パラメータを測定することによって鋼の硬度を概算する技術が開示されている。 As a technique for non-destructively detecting the hardness of a metal material and a hardness change part, for example, Patent Document 1 discloses that a magnetic field (transmission magnetism) changed by magnetizing a steel sheet correlates with the hardness of the steel sheet. A technology that utilizes this is disclosed. In Patent Document 2, there is a correlation between the magnetic properties (retention force, remanent magnetization, saturation magnetization, magnetic permeability, hysteresis loss) and mechanical properties (hardness, quenching depth, strength, crystal grain size) of steel materials. A technique using the is disclosed. Patent Document 3 discloses a technique for detecting changes in material (hardness, carbon content) and properties of a steel pipe using a bridge circuit including an inspection coil and a comparison coil. Patent Document 4 discloses a technique for estimating the hardness of steel by measuring a plurality of magnetic parameters of the steel.
また、特許文献５には、鋼板の一部表面が浸炭し、結晶組織が微細化した異常組織欠陥部を磁気飽和型の渦流センサを用いて検出する技術が開示されている。特許文献６には、渦流検査装置を用いたステンレス鋼材のシグマ相検査方法が開示されている。 Patent Document 5 discloses a technique for detecting an abnormal structure defect portion in which a partial surface of a steel plate is carburized and the crystal structure is refined by using a magnetic saturation type eddy current sensor. Patent Document 6 discloses a sigma phase inspection method for a stainless steel material using an eddy current inspection device.
さらに、特許文献７には、熱処理によって生じる鋼管や丸棒鋼の表面脱炭層を除去する旋削の削り残し部を渦電流を利用して検出する方法が開示されている。 Furthermore, Patent Document 7 discloses a method for detecting an uncut portion of a turning that removes a surface decarburized layer of a steel pipe or a round bar steel generated by heat treatment using eddy current.
上記のように、渦流検査方法等によって金属材料の磁気特性の変化を測定することにより、該金属材料の硬度等の機械的性質の変化部を非破壊的に検出できることや、手入れ処理後に異常部が除去されているか否かを渦流検査方法によって確認する方法は既に知られている。従って、これら公知技術を適用し、金属材料に存在する局部的な高硬度部を渦流検査方法で検出すると共に、高硬度部を除去するための手入れ処理を施した後、実際に高硬度部が除去されていることを渦流検査方法で確認することが考えられる。 As described above, by measuring the change in the magnetic properties of the metal material by an eddy current inspection method or the like, it is possible to detect non-destructive changes in the mechanical properties such as hardness of the metal material, A method for confirming whether or not the water has been removed by an eddy current inspection method is already known. Therefore, after applying these known techniques, the local high hardness part existing in the metal material is detected by the eddy current inspection method, and after the care process for removing the high hardness part is performed, the high hardness part is actually It can be considered that the removal is confirmed by an eddy current inspection method.
しかしながら、金属材料が磁性材料である場合には、渦流検査を行った際に、局部的な高硬度部での検出信号に対して、金属材料固有の磁性変動（磁性ムラ）に起因した検出信号や、金属材料と検出コイルとの距離（リフトオフ）変動に起因した検出信号がノイズとして重畳されるため、正確な高硬度部の検出が困難となる場合がある。さらには、高硬度部をグラインダー研削等で除去した部分は、金属材料表面が削られてリフトオフ変動によるノイズ信号がより大きくなる。このため、局部的な高硬度部をより確実に検出可能な渦流検査方法が求められている。
本発明は、斯かる従来技術の問題点を解決するべくなされたものであり、磁性を有する金属材料に局部的に存在する高硬度部を確実に検出可能であると共に、高硬度部を除去するための手入れ処理を施した後に、該高硬度部が除去されているか否かを確実に確認することができる渦流検査方法、該渦流検査方法で検査した鋼管、及び該渦流検査方法を実施するための渦流検査装置を提供することを課題とする。 The present invention has been made to solve such problems of the prior art, and can reliably detect a high hardness portion locally present in a magnetic metal material and remove the high hardness portion. In order to carry out the eddy current inspection method, the steel pipe inspected by the eddy current inspection method, and the eddy current inspection method capable of reliably confirming whether or not the high-hardness portion has been removed It is an object of the present invention to provide an eddy current inspection apparatus.
前記課題を解決するべく、本発明の発明者らは鋭意検討した結果、以下の（１）〜（４）の知見を得た。
（１）一対の検出コイルを具備し、被検査材である金属材料に対向配置された各検出コイルでの検出信号の差を出力するように構成されたプローブコイル（いわゆる自己比較方式のプローブコイル）を用いて渦流検査することにより、金属材料固有の磁性変動に起因した検出信号（磁性変動信号）の振幅と、金属材料とプローブコイル（特に検出コイル）とのリフトオフ変動に起因した検出信号（リフトオフ信号）の振幅とが抑制され（ノイズが抑制され）、局部的な高硬度部の検出能（Ｓ／Ｎ比）が向上する。
（２）しかしながら、自己比較方式のプローブコイルを用いれば、上記（１）のように局部的な高硬度部の検出能が良好となるため、その有無を検知することはできるものの、その位置（特に最大深さを有する位置）を精度良く特定することが困難である。具体的には、局部的な高硬度部での自己比較方式のプローブコイルの検出信号（各検出コイルでの検出信号の差）は、高硬度部のエッジ部近傍で正負にそれぞれピークを有する信号となるが、高硬度部の最大深さを有する部位に自己比較方式のプローブコイルを構成する各検出コイルの中心を対向配置した場合、自己比較方式のプローブコイルの検出信号はゼロ近傍の値となり、ノイズに埋もれ易いため、最大深さを有する位置を精度良く特定することが困難である。また、自己比較方式のプローブコイルの検出信号にはハイパスフィルタを適用する場合が多く、ハイパスフィルタのカットオフ周波数に応じた速度で自己比較方式のプローブコイルを金属材料に対して相対移動させて初めて検出信号に基づく高硬度部の検知が可能となる（静止した状態では自己比較方式のプローブコイルの検出信号に基づく高硬度部の検知はできない）ため、最大深さを有する位置を精度良く特定することが困難である。このように、高硬度部の最大深さを有する位置を精度良く特定できなければ、手入れ処理を施す際に不都合が生じる。なお、自己比較方式のプローブコイルを用いて高硬度部の最大深さ位置を特定するために一対の検出コイルの間隔を高硬度部の幅よりも離せば、原理上、上記プローブコイルの検出信号（各検出コイルコイルでの検出信号の差）のピーク位置より高硬度部の最大深さを有する位置が特定可能となるが、上記（１）に記載した金属材料固有の磁性変動に起因した検出信号やプローブコイルとのリフトオフ変動に起因した検出信号の振幅が拡大され、局部的な高硬度部の検出能（Ｓ／Ｎ比）が大幅に低下するため、高硬度部の検出が困難となる。
（３）これに対し、被検査材である金属材料に対向配置された単一の検出コイルを具備するプローブコイルか、或いは、一対の検出コイルを具備し、一方の検出コイルを被検査材である金属材料に対向配置し、他方の検出コイルを標準となるものに対向配置して各検出コイルでの検出信号の差を出力するように構成されたプローブコイル（いわゆる標準比較方式のプローブコイル）を用いて渦流検査すれば、局部的な高硬度部の最大深さを有する位置を精度良く特定することが可能である。具体的には、局部的な高硬度部での標準比較方式のプローブコイルの検出信号（単一の検出コイルでの検出信号、或いは、金属材料に対向配置した検出コイルでの検出信号と標準となるものに対向配置した検出コイルでの検出信号との差）は、ハイパスフィルタを適用しないためにプローブコイルを静止させた状態や極低速走査した状態でも用いることができる上、局部的な高硬度部の断面形状と略相似形の信号となり、高硬度部の最大深さを有する部位に標準比較方式のプローブコイルを構成する検出コイルを対向配置した場合にピークを有するため、最大深さを有する位置を精度良く特定することが可能である。ただし、標準比較方式のプローブコイルのみを用いて渦流検査したのでは、金属材料固有の磁性変動に起因した検出信号（磁性変動信号）の振幅と、金属材料とプローブコイル（特に検出コイル）とのリフトオフ変動に起因した検出信号（リフトオフ信号）の振幅とが抑制されない（ノイズが抑制されない）ため、局部的な高硬度部の検出能（Ｓ／Ｎ比）が悪い。
（４）従って、高硬度部の検出能に優れた自己比較方式のプローブコイルを用いて渦流検査することにより高硬度部を検知した後、該検知した部位近傍を高硬度部の位置特定に優れた標準比較方式のプローブコイルで再度渦流検査すれば、高硬度部を確実に検出可能（高硬度部の有無を精度良く検知するのみならず、その位置（最大深さを有する位置）も精度良く特定可能）である。また、自己比較方式のプローブコイルを構成する一対の検出コイルの内、いずれか一方の検出コイルを標準比較方式のプローブコイルを構成する検出コイル（単一の検出コイル、或いは、一対の検出コイルの内、金属材料に対向配置する検出コイル）としても用いれば、金属材料に対して相対移動させるプローブコイルを一つにすることができるため、装置コストが低減すると共に、取り扱いが容易であるという利点が得られる。
As a result of intensive studies, the inventors of the present invention have obtained the following findings (1) to (4) in order to solve the above problems.
(1) A probe coil (a so-called self-comparison type probe coil) that includes a pair of detection coils and outputs a difference between detection signals at each of the detection coils arranged opposite to a metal material to be inspected. ) To detect the amplitude of the detection signal (magnetic fluctuation signal) due to the magnetic fluctuation inherent in the metal material, and the detection signal due to lift-off fluctuation between the metal material and the probe coil (especially the detection coil) The amplitude of the lift-off signal) is suppressed (noise is suppressed), and the local high hardness portion detectability (S / N ratio) is improved.
(2) However, if a self-comparison type probe coil is used, the local high hardness portion can be detected as in (1) above, so that the presence or absence can be detected, but the position ( In particular, it is difficult to accurately specify the position having the maximum depth. Specifically, the detection signal of the probe coil of the self-comparison method in the local high hardness part (difference of the detection signal in each detection coil) is a signal having positive and negative peaks in the vicinity of the edge part of the high hardness part. However, if the center of each detection coil that constitutes the self-comparison probe coil is placed opposite to the part having the maximum depth of the high hardness part, the detection signal of the self-comparison probe coil becomes a value near zero. Since it is easily buried in noise, it is difficult to accurately specify the position having the maximum depth. In addition, a high-pass filter is often applied to the detection signal of the self-comparison probe coil, and the self-comparison probe coil is moved relative to the metal material at a speed corresponding to the cutoff frequency of the high-pass filter. High hardness part can be detected based on the detection signal (high hardness part cannot be detected based on the detection signal of the self-comparison probe coil in the stationary state), so the position having the maximum depth can be specified with high accuracy. Is difficult. Thus, if the position having the maximum depth of the high-hardness portion cannot be specified with high accuracy, inconvenience occurs when performing the care process. In principle, if the distance between the pair of detection coils is separated from the width of the high hardness portion in order to identify the maximum depth position of the high hardness portion using a self-comparison probe coil, the detection signal of the probe coil in principle. Although the position having the maximum depth of the high hardness portion can be specified from the peak position (difference of detection signal in each detection coil), the detection caused by the magnetic fluctuation inherent in the metal material described in (1) above. The amplitude of the detection signal due to the signal and the lift-off fluctuation with the probe coil is enlarged, and the detection capability (S / N ratio) of the local high hardness portion is greatly reduced, so that it is difficult to detect the high hardness portion. .
(3) On the other hand, it is a probe coil having a single detection coil arranged opposite to a metal material which is an inspection object, or a pair of detection coils, and one detection coil is made of the inspection object. A probe coil (so-called standard comparison type probe coil) configured to be placed opposite to a certain metal material and the other detection coil to be placed opposite to a standard one to output a difference in detection signal between each detection coil If the eddy current inspection is performed using, the position having the maximum depth of the local high hardness portion can be accurately identified. Specifically, the detection signal of the standard comparison type probe coil in the local high hardness part (the detection signal in the single detection coil or the detection signal and the standard in the detection coil arranged opposite to the metal material) The difference from the detection signal at the detection coil arranged opposite to the object) can be used even when the probe coil is stationary or scanned at a very low speed because a high-pass filter is not applied. It has a maximum depth because it has a peak when the detection coil that constitutes the probe coil of the standard comparison method is placed opposite to the portion having the maximum depth of the high hardness portion. It is possible to specify the position with high accuracy. However, if the eddy current inspection was performed using only the standard comparison type probe coil, the amplitude of the detection signal (magnetic fluctuation signal) due to the magnetic fluctuation inherent in the metal material and the metal material and the probe coil (especially the detection coil) Since the amplitude of the detection signal (lift-off signal) resulting from the lift-off fluctuation is not suppressed (noise is not suppressed), the local high-hardness portion detection ability (S / N ratio) is poor.
(4) Therefore, after detecting a high hardness portion by eddy current inspection using a probe coil of a self-comparison method that is excellent in detectability of the high hardness portion, the vicinity of the detected portion is excellent in specifying the location of the high hardness portion. If the eddy current test is performed again with the standard comparison type probe coil, the hard part can be detected reliably (not only the presence or absence of the hard part is detected accurately, but the position (position with the maximum depth) is also accurate. Can be specified). In addition, one of the pair of detection coils constituting the self-comparison probe coil is a detection coil (single detection coil or pair of detection coils) constituting the standard comparison probe coil. Among them, if it is used as a detection coil facing a metal material, the probe coil moved relative to the metal material can be integrated into one, so that the cost of the apparatus is reduced and the handling is easy. Is obtained.
本発明は、上記発明者らの知見に基づき完成されたものである。すなわち、本発明は、磁性を有する金属材料に存在する局部的な高硬度部を検出する渦流検査方法であって、前記金属材料に対向配置した一対の検出コイルを具備するプローブコイルを前記金属材料に対して相対移動させながら、前記プローブコイルに交流電流を通電して前記金属材料に交流磁界を作用させると共に、前記交流磁界によって前記金属材料に誘起された渦電流を前記一対の検出コイルで検出して得られる差動信号に基づいて、前記局部的な高硬度部の有無を検知し、前記交流磁界によって前記金属材料に誘起された渦電流を前記一対の検出コイルの内のいずれか一方で検出して得られる絶対値信号に基づいて、前記検知した局部的な高硬度部の位置を特定することを特徴とする渦流検査方法を提供するものである。 The present invention has been completed based on the findings of the inventors. That is, the present invention is an eddy current inspection method for detecting a localized high hardness portion existing in a magnetic metal material, wherein the probe coil including a pair of detection coils arranged opposite to the metal material is the metal material. The probe coil is supplied with an alternating current to cause an alternating magnetic field to act on the metallic material, and an eddy current induced in the metallic material by the alternating magnetic field is detected by the pair of detection coils. Based on the differential signal obtained, the presence or absence of the local high hardness portion is detected, and the eddy current induced in the metal material by the AC magnetic field is detected by either one of the pair of detection coils. The eddy current inspection method is characterized in that the position of the detected local high hardness portion is specified based on an absolute value signal obtained by detection.
なお、本発明における「プローブコイル」には、検出コイルが交流磁界を作用させる励磁コイルの機能を兼ねる自己誘導型コイル、及び、検出コイルと励磁コイルとが別体とされた相互誘導型コイルの双方が含まれる。また、本発明における「差動信号」とは、プローブコイルを構成する一対の検出コイルでの検出信号の差を意味する。また、本発明における「絶対値信号」とは、プローブコイルを構成する一対の検出コイルの内、いずれか一方の検出コイル単体での検出信号、或いは、該検出コイルでの検出信号と、プローブコイルを構成しない他の検出コイル（標準となるものに対向配置する検出コイル）での検出信号との差を意味する。 The “probe coil” in the present invention includes a self-inductive coil in which the detection coil functions as an excitation coil for applying an alternating magnetic field, and a mutual induction coil in which the detection coil and the excitation coil are separated. Both are included. Further, the “differential signal” in the present invention means a difference between detection signals at a pair of detection coils constituting the probe coil. In the present invention, the “absolute value signal” refers to a detection signal in one of the pair of detection coils constituting the probe coil, or a detection signal in the detection coil and the probe coil. This means a difference from a detection signal in another detection coil (a detection coil arranged to be opposed to a standard one) that does not constitute.
ここで、局部的な高硬度部の有無をより一層精度良く検知するため、本発明の発明者らは鋭意検討した結果、以下の（５）〜（７）の知見を得た。
（５）プローブコイルに通電する交流電流の周波数（検査周波数）を調整することにより、磁性変動信号とリフトオフ信号との位相差を調整可能である。
（６）上記（５）の位相差を１３５°以上に調整すれば、局部的な高硬度部での差動信号の位相が、磁性変動信号の位相とリフトオフ変動信号の位相との間に確実に位置する（局部的な高硬度部での差動信号の位相と、磁性変動信号の位相と、リフトオフ信号の位相とを確実に識別可能である）。
（７）従って、金属材料に存在する局部的な高硬度部の有無を検知するための情報として、検査周波数調整後のプローブコイルから出力された差動信号の振幅のみならず位相も用いれば、高硬度部をより一層精度良く検知可能である。
Here, in order to detect the presence or absence of a local high hardness part with higher accuracy, the inventors of the present invention have made extensive studies and as a result, obtained the following findings (5) to (7).
(5) The phase difference between the magnetic fluctuation signal and the lift-off signal can be adjusted by adjusting the frequency (inspection frequency) of the alternating current that is passed through the probe coil.
(6) If the phase difference in (5) above is adjusted to 135 ° or more, the phase of the differential signal in the local high hardness portion is surely between the phase of the magnetic fluctuation signal and the phase of the lift-off fluctuation signal. (The phase of the differential signal, the phase of the magnetic fluctuation signal, and the phase of the lift-off signal can be reliably identified in the local high hardness portion).
(7) Therefore, if not only the amplitude of the differential signal output from the probe coil after adjusting the inspection frequency but also the phase is used as information for detecting the presence or absence of a local high hardness portion present in the metal material, High hardness parts can be detected with higher accuracy.
上記発明者らの知見によれば、本発明に係る渦流検査方法において、前記金属材料に誘起された渦電流を前記一対の検出コイルで検出して得られる差動信号の内、前記金属材料の磁性変動信号とリフトオフ信号との位相差が１３５°以上となるように、前記プローブコイルに通電する交流電流の周波数を設定し、前記差動信号の振幅及び位相に基づいて、前記金属材料に存在する局部的な高硬度部の有無を検知することが好ましい。 According to the knowledge of the above-mentioned inventors, in the eddy current inspection method according to the present invention, of the differential signals obtained by detecting the eddy current induced in the metal material by the pair of detection coils, The frequency of the alternating current applied to the probe coil is set so that the phase difference between the magnetic fluctuation signal and the lift-off signal is 135 ° or more, and it exists in the metal material based on the amplitude and phase of the differential signal. It is preferable to detect the presence or absence of a local high hardness portion.
なお、本発明における「磁性変動信号」とは、プローブコイルによって検出される差動信号の内、金属材料固有の磁性変動（磁性ムラ）に起因した差動信号を意味する。さらに、本発明における「リフトオフ信号」とは、プローブコイルによって検出される差動信号の内、金属材料と差動型コイル（特に検出コイル）との距離（リフトオフ）変動に起因した差動信号を意味する。 The “magnetic fluctuation signal” in the present invention means a differential signal caused by magnetic fluctuation (magnetic unevenness) unique to a metal material among differential signals detected by a probe coil. Further, the “lift-off signal” in the present invention refers to a differential signal caused by a variation (lift-off) between a metal material and a differential type coil (especially a detection coil) among differential signals detected by a probe coil. means.
上記の検出対象となる局部的な高硬度部は、例えば、前記金属材料の他の部位（局部的な高硬度部が存在しない健全部位）よりもビッカース硬度で５０Ｈｖ以上高い部位とされる。 The local high hardness part to be detected is, for example, a part having a Vickers hardness of 50 Hv or more higher than the other part of the metal material (a healthy part where no local high hardness part exists).
なお、手入れ処理によって高硬度部が除去されたか否かを確実に確認するには、金属材料に存在する局部的な高硬度部を除去するための手入れ処理を施した後、前記渦流検査方法で前記金属材料を検査することにより前記高硬度部が除去されているか否かを確認することが好ましい。 In order to confirm whether or not the high hardness part has been removed by the care process, after performing the care process for removing the local high hardness part existing in the metal material, the eddy current inspection method is used. It is preferable to check whether or not the high hardness portion has been removed by inspecting the metal material.
また、前記渦流検査方法で検出した金属材料に存在する局部的な高硬度部を除去するための手入れ処理を施した後、前記渦流検査方法で前記金属材料を再度検査することにより前記高硬度部が除去されているか否かを確認してもよい。 Further, after performing a care process for removing a localized high hardness portion existing in the metal material detected by the eddy current inspection method, the high hardness portion is inspected again by inspecting the metal material by the eddy current inspection method. It may be confirmed whether or not is removed.
また、本発明は、前記渦流検査方法によって、前記局部的な高硬度部が除去されていることを確認した鋼管としても提供される。 Moreover, this invention is provided also as a steel pipe which confirmed that the said local high hardness part was removed by the said eddy current test | inspection method.
さらに、本発明は、磁性を有する金属材料に存在する局部的な高硬度部を検出する渦流検査装置であって、前記金属材料に対向配置され、前記金属材料に交流磁界を作用させて渦電流を誘起すると共に、前記金属材料に誘起された渦電流を検出する一対の検出コイルを具備するプローブコイルと、前記プローブコイルに交流電流を通電すると共に、前記金属材料に誘起された渦電流を前記一対の検出コイルで検出して得られる差動信号に基づいて、前記局部的な高硬度部の有無を検知し、前記金属材料に誘起された渦電流を前記一対の検出コイルの内のいずれか一方で検出して得られる絶対値信号に基づいて、前記検知した局部的な高硬度部の位置を特定する信号処理部とを備えることを特徴とする渦流検査装置としても提供される。 Further, the present invention is an eddy current inspection device for detecting a localized high hardness portion existing in a magnetic metal material, and is arranged opposite to the metal material, and an eddy current is applied to the metal material by applying an AC magnetic field. And a probe coil comprising a pair of detection coils for detecting eddy currents induced in the metal material, and supplying an alternating current to the probe coil, and the eddy currents induced in the metal material Based on a differential signal obtained by detection with a pair of detection coils, the presence or absence of the local high-hardness portion is detected, and eddy currents induced in the metal material are detected from either of the pair of detection coils. On the other hand, the present invention is also provided as an eddy current inspection apparatus comprising a signal processing unit that identifies the position of the detected local high hardness portion based on an absolute value signal obtained by detection.
なお、本発明における「局部的な高硬度部の位置を特定する信号処理部」とは、信号処理部が局部的な高硬度部の位置を自動的に特定する構成の他、信号処理部自体は局部的な高硬度部の位置を特定するための情報を出力するに留まる構成（高硬度部の位置特定は、信号処理部から出力された情報に基づいて人間が行う）も含む意味である。 The “signal processing unit for specifying the position of the local high hardness portion” in the present invention is a signal processing unit itself in addition to the configuration in which the signal processing unit automatically specifies the position of the local high hardness portion. Means a configuration that only outputs information for specifying the position of the local high hardness portion (positioning of the high hardness portion is performed by a human based on information output from the signal processing unit). .
本発明によれば、磁性を有する金属材料に局部的に存在する高硬度部を確実に検出可能（高硬度部の有無を精度良く検知するのみならず、その位置（最大深さを有する位置）も精度良く特定可能）であると共に、高硬度部を除去するための手入れ処理を施した後に、該高硬度部が除去されているか否かを確実に確認することができる。 According to the present invention, it is possible to reliably detect a high-hardness portion locally present in a magnetic metal material (not only the presence or absence of a high-hardness portion is accurately detected, but also its position (position having the maximum depth). It is also possible to accurately specify whether or not the high-hardness portion has been removed after performing a care process for removing the high-hardness portion.
以下、添付図面を適宜参照しつつ、本発明の一実施形態について、被検査材である金属材料が磁性を有する鋼管（二相ステンレス鋼）である場合を例に挙げて説明する。 DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings, taking as an example the case where a metal material as a material to be inspected is a steel pipe having magnetism (duplex stainless steel).
＜渦流検査装置の構成＞
図１は、本発明の一実施形態に係る渦流検査装置の概略構成を示す模式図である。また、図２は、図１に示すプローブコイルから出力される信号を模式的に説明する図であり、図２（ａ）は差動信号を、図２（ｂ）は絶対値信号を示す。図１に示すように、本実施形態に係る渦流検査装置１００は、プローブコイル１と、信号処理部２とを備えている。
<Configuration of eddy current inspection device>
FIG. 1 is a schematic diagram showing a schematic configuration of an eddy current inspection apparatus according to an embodiment of the present invention. 2 schematically illustrates signals output from the probe coil shown in FIG. 1. FIG. 2A shows a differential signal and FIG. 2B shows an absolute value signal. As shown in FIG. 1, the eddy current inspection apparatus 100 according to the present embodiment includes a probe coil 1 and a signal processing unit 2.
プローブコイル１は、鋼管Ｐの外面に対向配置され、鋼管Ｐに交流磁界を作用させて渦電流を誘起すると共に、鋼管Ｐに誘起された渦電流を検出するように構成されている。具体的に説明すれば、本実施形態に係るプローブコイル１は、鋼管Ｐに交流磁界を作用させる励磁コイル（図示せず）と渦電流を検出するための検出コイルとが別体とされた相互誘導型コイルであると共に、一対の検出コイル１１ａ、１１ｂを具備し、各検出コイル１１ａ、１１ｂでの検出信号の差（差動信号）を出力するように構成された、いわゆる自己比較方式のコイルとして機能する。また、プローブコイル１は、上記の差動信号を出力すると同時に、一対の検出コイル１１ａ、１１ｂの内のいずれか一方（本実施形態では検出コイル１１ｂ）での検出信号と、標準となるものに対向配置された他の検出コイル１１ｃでの検出信号との差（絶対値信号）を出力するように構成された、いわゆる標準比較方式のプローブコイルとしても機能する。 The probe coil 1 is disposed opposite to the outer surface of the steel pipe P, and is configured to induce an eddy current by applying an AC magnetic field to the steel pipe P and to detect an eddy current induced in the steel pipe P. More specifically, the probe coil 1 according to the present embodiment is configured such that an excitation coil (not shown) for applying an AC magnetic field to the steel pipe P and a detection coil for detecting eddy current are separated. A so-called self-comparison coil that is an induction coil and includes a pair of detection coils 11a and 11b and is configured to output a difference (differential signal) between detection signals of the detection coils 11a and 11b. Function as. In addition, the probe coil 1 outputs the above-described differential signal, and at the same time, a detection signal from one of the pair of detection coils 11a and 11b (the detection coil 11b in the present embodiment) becomes a standard one. It also functions as a so-called standard comparison type probe coil that is configured to output a difference (absolute value signal) from a detection signal from another detection coil 11c arranged oppositely.
励磁コイルは、鋼管Ｐの外面に垂直な方向に交流磁界を作用させる一方、検出コイル１１ａ、１１ｂは、渦電流によって生じる鋼管Ｐの外面に垂直な方向の交流磁界の変化を検出する。各検出コイル１１ａ、１１ｂは鋼管Ｐの周方向に離間して配置されており、プローブコイル１を鋼管Ｐの周方向に相対移動させれば、プローブコイル１からは各検出コイル１１ａ、１１ｂに対向する鋼管Ｐの部位についての検出信号の差が差動信号として出力される。この磁性変動信号やリフトオフ信号の振幅が抑制された差動信号に基づいて検査することにより、局部的な高硬度部の検出能（Ｓ／Ｎ比）が高まり、精度良く高硬度部の有無を検知することが可能である。しかしながら、差動信号に基づいて検査したのでは、上記のように精度良く高硬度部の有無を検知することは可能であるものの、その位置（特に最大深さを有する位置）を精度良く特定することが困難である。すなわち、図２（ａ）に示すように、差動信号は、高硬度部ＰＨのエッジ部近傍で正負にそれぞれピークを有する信号となるが、高硬度部ＰＨの最大深さを有する部位にプローブコイル１を構成する各検出コイル１１ａ、１１ｂの中心を対向配置（図２（ａ）に示すＢの状態）した場合、差動信号はゼロ近傍の値となり、ノイズに埋もれ易いため、最大深さを有する位置を精度良く特定することが困難である。また、差動信号には後述のようにハイパスフィルタ２５Ａを適用するため、ハイパスフィルタ２５Ａのカットオフ周波数に応じた速度でプローブコイル１を鋼管Ｐに対して相対移動させて初めて差動信号に基づく高硬度部ＰＨの検知が可能となる（静止した状態では差動信号に基づく高硬度部ＰＨの検知はできない）ため、最大深さを有する位置を精度良く特定することが困難である。このように、高硬度部ＰＨの最大深さを有する位置を精度良く特定できなければ、手入れ処理を施す際に不都合が生じる。 The excitation coil applies an alternating magnetic field in a direction perpendicular to the outer surface of the steel pipe P, while the detection coils 11a and 11b detect a change in the alternating magnetic field in a direction perpendicular to the outer surface of the steel pipe P caused by an eddy current. The detection coils 11a and 11b are spaced apart from each other in the circumferential direction of the steel pipe P. When the probe coil 1 is relatively moved in the circumferential direction of the steel pipe P, the probe coil 1 faces the detection coils 11a and 11b. The difference of the detection signal about the part of the steel pipe P to be output is output as a differential signal. By inspecting based on the differential signal in which the amplitude of the magnetic fluctuation signal and the lift-off signal is suppressed, the detection capability (S / N ratio) of the local high hardness portion is increased, and the presence or absence of the high hardness portion is accurately determined. It is possible to detect. However, the inspection based on the differential signal can accurately detect the presence or absence of the high-hardness portion as described above, but the position (particularly the position having the maximum depth) is specified with high accuracy. Is difficult. That is, as shown in FIG. 2A, the differential signal is a signal having positive and negative peaks in the vicinity of the edge portion of the high hardness portion PH, but is probed at a portion having the maximum depth of the high hardness portion PH. When the centers of the detection coils 11a and 11b constituting the coil 1 are arranged opposite to each other (state B shown in FIG. 2A), the differential signal has a value near zero and is easily buried in noise. It is difficult to specify a position having a high accuracy. Since the high-pass filter 25A is applied to the differential signal as described later, the differential signal is based on the differential signal only after the probe coil 1 is moved relative to the steel pipe P at a speed corresponding to the cutoff frequency of the high-pass filter 25A. Since the high hardness portion PH can be detected (the high hardness portion PH cannot be detected based on the differential signal in a stationary state), it is difficult to accurately specify the position having the maximum depth. As described above, if the position having the maximum depth of the high hardness portion PH cannot be specified with high accuracy, inconvenience occurs when performing the maintenance process.
このため、前述のように、本実施形態に係るプローブコイル１からは検出コイル１１ｂに対向する鋼管Ｐの部位についての検出信号と標準となるものに対向配置された他の検出コイル１１ｃでの検出信号との差が絶対値信号として出力されるように構成されている。この絶対値信号は、ハイパスフィルタを適用しないためにプローブコイル１を静止させた状態や極低速走査した状態でも用いることができる上、図２（ｂ）に示すように、局部的な高硬度部ＰＨの断面形状と略相似形の信号となり、高硬度部ＰＨの最大深さを有する部位にプローブコイル１を構成する検出コイル１１ｂを対向配置（図２（ｂ）に示すＥの状態）した場合にピークを有するため、最大深さを有する位置を精度良く特定することが可能である。従って、プローブコイル１を鋼管Ｐに対して相対移動させ、差動信号を用いて高硬度部を検知した後、該検知した部位近傍でプローブコイル１を再度相対移動させ、絶対値信号を用いて高硬度部の位置を特定すれば、高硬度部の有無を精度良く検知するのみならず、その位置（最大深さを有する位置）も精度良く特定可能である。 For this reason, as described above, from the probe coil 1 according to the present embodiment, the detection signal for the part of the steel pipe P facing the detection coil 11b and the detection by the other detection coil 11c arranged opposite to the standard are detected. The difference from the signal is output as an absolute value signal. This absolute value signal can be used even when the probe coil 1 is stationary or scanned at an extremely low speed because no high-pass filter is applied. Further, as shown in FIG. When the signal is substantially similar to the cross-sectional shape of PH, and the detection coil 11b constituting the probe coil 1 is disposed opposite to the portion having the maximum depth of the high hardness portion PH (state E shown in FIG. 2B). Therefore, the position having the maximum depth can be specified with high accuracy. Accordingly, after the probe coil 1 is moved relative to the steel pipe P and the high hardness portion is detected using the differential signal, the probe coil 1 is moved relative again in the vicinity of the detected portion and the absolute value signal is used. If the position of the high hardness portion is specified, not only the presence or absence of the high hardness portion can be detected with high accuracy, but also the position (the position having the maximum depth) can be specified with high accuracy.
信号処理部２は、プローブコイル１に交流電流を通電すると共に、プローブコイル１から出力された差動信号に基づいて、鋼管Ｐに存在する局部的な高硬度部の有無を検知し、プローブコイル１から出力された絶対値信号に基づいて、前記検知した局部的な高硬度部の位置を特定するように構成されている。具体的には、本実施形態に係る信号処理部２は、発信器２１と、差動信号を処理するための増幅器２２Ａ、同期検波器２３Ａ、位相回転器２４Ａ、ハイパスフィルタ２５Ａ、Ａ／Ｄ変換器２６Ａ及び判定部２７Ａとを備える。また、本実施形態に係る信号処理部２は、絶対値信号を処理するための増幅器２２Ｂ、同期検波器２３Ｂ、位相回転器２４Ｂ、Ａ／Ｄ変換器２６Ｂ及び判定部２７Ｂを備える。 The signal processing unit 2 applies an alternating current to the probe coil 1 and detects the presence or absence of a local high-hardness portion existing in the steel pipe P based on the differential signal output from the probe coil 1. Based on the absolute value signal output from 1, the position of the detected local high hardness portion is specified. Specifically, the signal processing unit 2 according to the present embodiment includes a transmitter 21, an amplifier 22A for processing a differential signal, a synchronous detector 23A, a phase rotator 24A, a high-pass filter 25A, and A / D conversion. 26A and determination unit 27A. The signal processing unit 2 according to the present embodiment includes an amplifier 22B, a synchronous detector 23B, a phase rotator 24B, an A / D converter 26B, and a determination unit 27B for processing an absolute value signal.
発信器２１は、プローブコイル１（具体的には、プローブコイル１の励磁コイル）に所定周波数の交流電流を供給する。これにより、前述のように、プローブコイル１から鋼管Ｐの外面に向かう交流磁界が生じ、鋼管Ｐに渦電流が誘起される。なお、プローブコイル１に通電する交流電流の周波数（検査周波数）の設定方法については後述する。 The transmitter 21 supplies an alternating current having a predetermined frequency to the probe coil 1 (specifically, the exciting coil of the probe coil 1). Thereby, as described above, an alternating magnetic field from the probe coil 1 toward the outer surface of the steel pipe P is generated, and an eddy current is induced in the steel pipe P. In addition, the setting method of the frequency (inspection frequency) of the alternating current supplied to the probe coil 1 will be described later.
プローブコイル１から出力された差動信号は、増幅器２２Ａによって増幅された後、同期検波器２３Ａに出力される。なお、増幅器２２Ａは、一定の増幅率で差動信号を増幅する構成の他、ＡＧＣ（Auto Gain Control）機能を具備する構成とすることも可能である。 The differential signal output from the probe coil 1 is amplified by the amplifier 22A and then output to the synchronous detector 23A. The amplifier 22A may be configured to have an AGC (Auto Gain Control) function in addition to a configuration for amplifying a differential signal at a constant amplification factor.
同期検波器２３Ａは、発振器２１から出力される参照信号に基づき、増幅器２２Ａの出力信号を同期検波する。具体的に説明すれば、発振器２１から同期検波器２３Ａに向けて、プローブコイル１に供給する交流電流と同一の周波数で同一の位相を有する第１参照信号と、該第１参照信号の位相を９０°だけ移相した第２参照信号とが出力される。そして、同期検波器２３Ａは、増幅器２２Ａの出力信号から、第１参照信号の位相と同位相の信号成分（第１信号成分）及び第２参照信号の位相と同位相の信号成分（第２信号成分）を分離・抽出する。分離・抽出された第１信号成分及び第２信号成分は、それぞれ位相回転器２４Ａに出力される。 The synchronous detector 23A synchronously detects the output signal of the amplifier 22A based on the reference signal output from the oscillator 21. More specifically, the first reference signal having the same phase as the alternating current supplied to the probe coil 1 from the oscillator 21 toward the synchronous detector 23A and the phase of the first reference signal are set. A second reference signal shifted by 90 ° is output. Then, the synchronous detector 23A, from the output signal of the amplifier 22A, a signal component having the same phase as the phase of the first reference signal (first signal component) and a signal component having the same phase as the phase of the second reference signal (second signal) Ingredients) are separated and extracted. The separated and extracted first signal component and second signal component are each output to the phase rotator 24A.
位相回転器２４Ａは、同期検波器２３Ａから出力された第１信号成分及び第２信号成分の位相を互いに同一の所定量だけ回転（移相）し、例えば、第１信号成分をＸ信号、第２信号成分をＹ信号として、ハイパスフィルタ２５Ａに出力する。なお、位相回転器２４Ａから出力されるＸ信号及びＹ信号は、互いに直交する２軸（Ｘ軸、Ｙ軸）で表されるＸ−Ｙベクトル平面においていわゆるリサージュ波形と称される信号波形（すなわち、振幅をＺ、位相をθとして極座標（Ｚ、θ）で表したプローブコイル１の差動信号波形（正確には、増幅器２２Ａによって増幅した後の差動信号波形））を、Ｘ軸及びＹ軸にそれぞれ投影した成分に相当することになる。位相回転器２４Ａによる位相回転は、例えば、磁性変動信号がＸ−Ｙベクトル平面のＸ軸上に位置するように調整する目的でなされる。 The phase rotator 24A rotates (shifts) the phase of the first signal component and the second signal component output from the synchronous detector 23A by the same predetermined amount, for example, the first signal component is the X signal, The two signal components are output as a Y signal to the high pass filter 25A. Note that the X and Y signals output from the phase rotator 24A are signal waveforms called so-called Lissajous waveforms on the XY vector plane represented by two axes (X axis and Y axis) orthogonal to each other (that is, , The differential signal waveform of the probe coil 1 expressed in polar coordinates (Z, θ) with the amplitude Z and the phase θ (more precisely, the differential signal waveform after being amplified by the amplifier 22A), the X axis and the Y axis This corresponds to the component projected on each axis. The phase rotation by the phase rotator 24A is performed for the purpose of adjusting the magnetic fluctuation signal so as to be positioned on the X axis of the XY vector plane, for example.
ハイパスフィルタ２５Ａは、位相回転器２４Ａから出力されたＸ信号及びＹ信号から所定の低周波成分を除去し、Ａ／Ｄ変換器２６Ａに出力する。 The high pass filter 25A removes a predetermined low frequency component from the X signal and Y signal output from the phase rotator 24A, and outputs the result to the A / D converter 26A.
Ａ／Ｄ変換器２６Ａは、ハイパスフィルタ２５Ａの出力信号をＡ／Ｄ変換し、判定部２７Ａに出力する。 The A / D converter 26A performs A / D conversion on the output signal of the high-pass filter 25A and outputs it to the determination unit 27A.
判定部２７Ａは、例えば、後述の演算処理を行うためのプログラムがインストールされた汎用のパーソナルコンピュータ等から構成される。判定部２７Ａは、Ａ／Ｄ変換器２６Ａの出力データ（すなわち、ハイパスフィルタ２５Ａによって低周波成分が除去されたＸ信号及びＹ信号をＡ／Ｄ変換したデジタルデータ。以下、Ｘ信号データ及びＹ信号データという）に基づいて、鋼管Ｐに存在する局部的な高硬度部の有無を検知する。具体的に説明すれば、判定部２７Ａは、先ず最初に、入力されたＸ信号データ及びＹ信号データに基づき、プローブコイル１の差動信号（正確には、増幅器２２Ａによって増幅し、ハイパスフィルタ２５Ａによって低周波成分を除去した後の差動信号）の振幅Ｚ及び位相θを演算する。Ｘ信号データの値をＸ、Ｙ信号データの値をＹとすると、振幅Ｚ及び位相θは、それぞれ下記の式（１）及び（２）によって演算される。
Ｚ＝（Ｘ２＋Ｙ２）１／２ ・・・ （１）
θ＝ｔａｎ−１（Ｙ／Ｘ） ・・・ （２）
The determination unit 27A includes, for example, a general-purpose personal computer in which a program for performing arithmetic processing described later is installed. The determination unit 27A outputs digital data obtained by A / D converting the output data of the A / D converter 26A (that is, the X signal and Y signal from which the low-frequency component has been removed by the high pass filter 25A. Hereinafter, the X signal data and the Y signal The presence or absence of a local high hardness portion existing in the steel pipe P is detected based on the data). More specifically, the determination unit 27A firstly, based on the input X signal data and Y signal data, the differential signal of the probe coil 1 (more precisely, it is amplified by the amplifier 22A, and the high-pass filter 25A is amplified). To calculate the amplitude Z and phase θ of the differential signal after removing the low-frequency component. When the value of the X signal data is X and the value of the Y signal data is Y, the amplitude Z and the phase θ are calculated by the following equations (1) and (2), respectively.
Z = (X 2 + Y 2 ) 1/2 (1)
θ = tan −1 (Y / X) (2)
次に、判定部２７Ａは、前記演算した振幅Ｚが予め定めたしきい値よりも大きいか否かを判定する。振幅Ｚが予め定めたしきい値以下である場合、判定部２７Ａは、この振幅Ｚを有する差動信号は局部的な高硬度部での差動信号ではないと判定する。一方、振幅Ｚが予め定めたしきい値よりも大きい場合には、判定部２７Ａは、前記演算した位相θが予め定めた範囲内にあるか否かを判定する。位相θが予め定めた範囲内にある場合、判定部２７Ａは、この振幅Ｚ及び位相θを有する差動信号は鋼管Ｐに存在する局部的な高硬度部での差動信号（以下、適宜、「高硬度部信号」という）であると判定して、局部的な高硬度部を検知したことを知らせる所定のアラームを出力する。 Next, the determination unit 27A determines whether or not the calculated amplitude Z is greater than a predetermined threshold value. When the amplitude Z is equal to or smaller than a predetermined threshold value, the determination unit 27A determines that the differential signal having the amplitude Z is not a differential signal in a local high hardness portion. On the other hand, when the amplitude Z is larger than a predetermined threshold value, the determination unit 27A determines whether or not the calculated phase θ is within a predetermined range. When the phase θ is within a predetermined range, the determination unit 27A determines that the differential signal having the amplitude Z and the phase θ is a differential signal in a local high hardness portion existing in the steel pipe P (hereinafter, as appropriate, And a predetermined alarm informing that the local high hardness portion has been detected is output.
一方、プローブコイル１から出力された絶対値信号は、増幅器２２Ｂによって増幅された後、同期検波器２３Ｂで同期検波され、位相回転器２４Ｂで移相される。その後、Ａ／Ｄ変換器２６ＢでＡ／Ｄ変換された後、判定部２７Ｂに出力される。なお、絶対値信号の処理に用いられる増幅器２２Ｂ、同期検波器２３Ｂ、位相回転器２４Ｂ及びＡ／Ｄ変換器２６Ｂの構成及び機能は、差動信号の処理に用いられる増幅器２２Ａ、同期検波器２３Ａ、位相回転器２４Ａ及びＡ／Ｄ変換器２６Ａの構成及び機能と同様であるため、ここでは説明を省略する。 On the other hand, the absolute value signal output from the probe coil 1 is amplified by the amplifier 22B, then synchronously detected by the synchronous detector 23B, and phase-shifted by the phase rotator 24B. Then, after A / D conversion is performed by the A / D converter 26B, it is output to the determination unit 27B. The configurations and functions of the amplifier 22B, the synchronous detector 23B, the phase rotator 24B and the A / D converter 26B used for processing the absolute value signal are the same as those of the amplifier 22A and the synchronous detector 23A used for processing the differential signal. Since the configuration and function of the phase rotator 24A and the A / D converter 26A are the same, the description thereof is omitted here.
判定部２７Ｂでは、Ａ／Ｄ変換器２６Ｂから出力された絶対値信号についてのＸ信号データ及びＹ信号データ（位相回転器２４Ｂから出力された絶対値信号の信号成分であるＸ信号及びＹ信号をＡ／Ｄ変換したデジタルデータ）に基づき、上記の式（１）によってプローブコイル１の絶対値信号（正確には、増幅器２２Ｂによって増幅した後の絶対値信号）の振幅Ｚを演算する。そして、プローブコイル１を相対移動させている最中に最大の振幅Ｚが得られた場合には、この振幅Ｚを有する絶対値信号は鋼管Ｐに存在する局部的な高硬度部の最大深さを有する位置での絶対値信号であると判定し、必要に応じて、局部的な高硬度部の位置を特定したことを知らせる所定のアラームを出力する。なお、演算した振幅Ｚが最大であることの判定及び最大の振幅Ｚが得られたときのプローブコイル１の位置の特定（すなわち、高硬度部の最大深さを有する位置の特定）は、例えば、判定部２７Ｂが、プローブコイル１を相対移動させている最中に、所定の基準位置からのプローブコイル１の変位と各変位で演算した振幅Ｚとを紐付けて逐次記憶するように構成し、該記憶した振幅Ｚの中から最大の振幅Ｚを検出すると共に、該最大の振幅Ｚが得られたときのプローブコイル１の変位を検出するように構成することで実現可能である。ただし、本発明は、上記のような判定部２７Ｂによる自動的な高硬度部の位置特定に限るものではなく、例えば、判定部２７Ｂが、プローブコイル１を相対移動することに伴う振幅Ｚの変動をモニタ表示するように構成し、オペレータが手動でプローブコイル１を相対移動させながら前記モニタ表示を目視することにより、振幅Ｚが最大となったことを判定すると共に、最大の振幅Ｚが得られたときのプローブコイル１の位置を特定することも可能である。或いは、判定部２７Ｂが、判定部２７Ａと同様に、絶対値信号の位相θも演算して、振幅Ｚ及び位相θによって算出されるリサージュ波形をモニタ表示するように構成し、オペレータが手動でプローブコイル１を相対移動させながら前記モニタ表示を目視することにより、振幅Ｚが最大となったことを判定すると共に、最大の振幅Ｚが得られたときのプローブコイル１の位置を特定してもよい。すなわち、判定部２７Ｂ自体は局部的な高硬度部の位置を特定するための情報（振幅、リサージュ波形等）を出力するに留まり、高硬度部の位置特定は、判定部２７Ｂから出力された情報に基づいてオペレータが行う構成を採用することも可能である。また、信号処理部２に判定部２７Ｂを設けることなく、位相回転器２４Ｂから出力されるＸ信号及びＹ信号をオシロスコープ等に入力することにより表示される絶対値信号のリサージュ波形を目視することによって、オペレータが振幅Ｚが最大となったことを判定すると共に、最大の振幅Ｚが得られたときのプローブコイル１の位置を特定することも可能である。 In the determination unit 27B, the X signal data and the Y signal data (the X signal and the Y signal that are signal components of the absolute value signal output from the phase rotator 24B) about the absolute value signal output from the A / D converter 26B. Based on (A / D converted digital data), the amplitude Z of the absolute value signal of the probe coil 1 (more precisely, the absolute value signal after being amplified by the amplifier 22B) is calculated by the above equation (1). When the maximum amplitude Z is obtained during the relative movement of the probe coil 1, the absolute value signal having this amplitude Z is the maximum depth of the local high-hardness portion existing in the steel pipe P. It is determined that the signal is an absolute value signal at a position having, and if necessary, a predetermined alarm informing that the position of the local high hardness portion has been specified is output. The determination that the calculated amplitude Z is the maximum and the specification of the position of the probe coil 1 when the maximum amplitude Z is obtained (that is, the specification of the position having the maximum depth of the high hardness portion) are, for example, The determination unit 27B is configured to sequentially store the displacement of the probe coil 1 from a predetermined reference position and the amplitude Z calculated by each displacement while the probe coil 1 is relatively moved. This can be realized by detecting the maximum amplitude Z from the stored amplitude Z and detecting the displacement of the probe coil 1 when the maximum amplitude Z is obtained. However, the present invention is not limited to the automatic identification of the position of the high hardness portion by the determination unit 27B as described above. For example, the variation of the amplitude Z caused by the determination unit 27B relatively moving the probe coil 1. Is displayed on the monitor, and the operator can visually determine the monitor display while moving the probe coil 1 relative to it to determine that the amplitude Z is maximized, and the maximum amplitude Z is obtained. It is also possible to specify the position of the probe coil 1 at this time. Alternatively, similarly to the determination unit 27A, the determination unit 27B calculates the phase θ of the absolute value signal and monitors and displays the Lissajous waveform calculated by the amplitude Z and the phase θ. By visually observing the monitor display while relatively moving the coil 1, it may be determined that the amplitude Z is maximized, and the position of the probe coil 1 when the maximum amplitude Z is obtained may be specified. . That is, the determination unit 27B itself outputs only information (amplitude, Lissajous waveform, etc.) for specifying the position of the local high hardness portion, and the position specification of the high hardness portion is information output from the determination unit 27B. It is also possible to adopt a configuration performed by the operator based on the above. Further, without providing the determination unit 27B in the signal processing unit 2, by visually observing the Lissajous waveform of the absolute value signal displayed by inputting the X signal and Y signal output from the phase rotator 24B to an oscilloscope or the like. It is also possible for the operator to determine that the amplitude Z is maximized and to specify the position of the probe coil 1 when the maximum amplitude Z is obtained.
図３は、図１に示すプローブコイルから出力される差動信号及び絶対値信号のリサージュ波形の一例を示す図である。図３（ａ）は差動信号のリサージュ波形（正確には、ハイパスフィルタ２５Ａから出力される低周波成分が除去されたＸ信号及びＹ信号をオシロスコープ等に入力することにより表示される差動信号のリサージュ波形）を、図３（ｂ）は絶対値信号のリサージュ波形（正確には、位相回転器２４Ｂから出力されるＸ信号及びＹ信号をオシロスコープ等に入力することにより表示される絶対値信号のリサージュ波形）を示す。図３（ａ）に示すように、差動信号の振幅Ｚが予め定めたしきい値よりも大きく、且つ、位相θが予め定めた範囲内にある場合、判定部２７Ａは、この振幅Ｚ及び位相θを有する差動信号は高硬度部信号であると判定して、局部的な高硬度部を検知したことを知らせる所定のアラームを出力する。そして、検知した部位近傍でプローブコイル１を再度相対移動させ、図３（ｂ）に示すように、絶対値信号の振幅Ｚが最大となるプローブコイル１の位置を特定（自動又は目視での特定）すれば、高硬度部の有無を精度良く検知するのみならず、その位置（最大深さを有する位置）も精度良く特定可能である。 FIG. 3 is a diagram illustrating an example of a Lissajous waveform of a differential signal and an absolute value signal output from the probe coil illustrated in FIG. FIG. 3A shows a Lissajous waveform of a differential signal (more precisely, a differential signal displayed by inputting an X signal and a Y signal from which a low-frequency component output from the high-pass filter 25A is removed to an oscilloscope or the like. 3 (b) shows the absolute value signal Lissajous waveform (more precisely, the absolute value signal displayed by inputting the X signal and Y signal output from the phase rotator 24B to an oscilloscope or the like). Lissajous waveform). As shown in FIG. 3A, when the amplitude Z of the differential signal is larger than a predetermined threshold value and the phase θ is within a predetermined range, the determination unit 27A determines the amplitude Z and The differential signal having the phase θ is determined to be a high hardness part signal, and a predetermined alarm is output to notify that a local high hardness part has been detected. Then, the probe coil 1 is relatively moved again in the vicinity of the detected part, and as shown in FIG. 3B, the position of the probe coil 1 at which the amplitude Z of the absolute value signal is maximum is specified (automatically or visually specified). ), It is possible not only to accurately detect the presence / absence of the high hardness portion, but also to accurately identify the position (the position having the maximum depth).
＜検査周波数の設定方法＞
以上に説明した構成を有する渦流検査装置１００において、信号処理部２（発振器２１）からプローブコイル１に通電する交流電流の周波数（検査周波数）は、プローブコイル１によって検出した差動信号の内、鋼管Ｐの磁性変動信号とリフトオフ信号との位相差が１３５°以上となるように設定される。具体的には、検査周波数を適宜変更して、鋼管Ｐの健全部位（局部的な高硬度部が存在しない部位）を検査し、判定部２７Ａによって演算される鋼管Ｐの磁性変動信号の位相（検出した磁性変動信号のうち最大の振幅を有する磁性変動信号の位相）と、リフトオフ信号の位相（検出したリフトオフ信号のうち最大の振幅を有するリフトオフ信号の位相）との差が１３５°以上となる検査周波数を設定値として選択すればよい。
<Inspection frequency setting method>
In the eddy current inspection apparatus 100 having the configuration described above, the frequency (inspection frequency) of the alternating current supplied from the signal processing unit 2 (oscillator 21) to the probe coil 1 is the differential signal detected by the probe coil 1. The phase difference between the magnetic fluctuation signal of the steel pipe P and the lift-off signal is set to be 135 ° or more. Specifically, the inspection frequency is appropriately changed to inspect a healthy part of the steel pipe P (part where no local high hardness part exists), and the phase of the magnetic fluctuation signal of the steel pipe P calculated by the determination part 27A ( The difference between the phase of the magnetic variation signal having the maximum amplitude among the detected magnetic variation signals and the phase of the lift-off signal (phase of the lift-off signal having the maximum amplitude among the detected lift-off signals) is 135 ° or more. The inspection frequency may be selected as the set value.
以下、鋼管Ｐの磁性変動信号とリフトオフ信号との位相差が１３５°以上となるように検査周波数を設定する理由について具体的に説明する。
本発明の発明者らによる検査試験の結果、高硬度部信号の位相は、磁性変動信号の位相とリフトオフ信号の位相との間に位置する傾向のあることが分かった。しかしながら、高硬度部信号の位相が高硬度部の組織状態等によって変動する上、磁性変動信号やリフトオフ信号の位相も変動するため、磁性変動信号とリフトオフ信号との位相差が小さいと、高硬度部信号に磁性変動信号及びリフトオフ信号がノイズとして重畳される場合（高硬度部信号の位相と、磁性変動信号又はリフトオフ信号の位相とが同程度となる場合）があることも分かった。このため、振幅のみならず位相も情報として用いて、高硬度部信号を確実に検出するには、磁性変動信号とリフトオフ信号との位相差をできるだけ大きくする必要があることに想到した。
Hereinafter, the reason why the inspection frequency is set so that the phase difference between the magnetic fluctuation signal of the steel pipe P and the lift-off signal is 135 ° or more will be specifically described.
As a result of the inspection test by the inventors of the present invention, it has been found that the phase of the high hardness portion signal tends to be located between the phase of the magnetic fluctuation signal and the phase of the lift-off signal. However, since the phase of the high hardness part signal varies depending on the structure of the high hardness part and the phase of the magnetic fluctuation signal and lift-off signal also fluctuates, if the phase difference between the magnetic fluctuation signal and the lift-off signal is small, high hardness It has also been found that the magnetic fluctuation signal and the lift-off signal are superimposed as noise on the part signal (the phase of the high hardness part signal and the phase of the magnetic fluctuation signal or the lift-off signal are comparable). For this reason, it was conceived that the phase difference between the magnetic fluctuation signal and the lift-off signal needs to be as large as possible in order to reliably detect the high hardness portion signal using not only the amplitude but also the phase as information.
図４は、検査周波数を変更した場合において、プローブコイル１によって検出される鋼管Ｐの磁性変動信号とリフトオフ信号との位相差の変化を示すグラフである。本発明の発明者らによる検査試験の結果、図４に示すように、検査周波数を高めれば高めるほど、磁性変動信号とリフトオフ信号との位相差が大きくなることが分かった。そして、磁性変動信号とリフトオフ信号との位相差が１３５°以上となるように検査周波数を設定（本実施形態では、検査周波数を６４ｋＨｚに設定）すれば、高硬度部信号の位相が、磁性変動信号の位相とリフトオフ変動信号の位相との間に確実に位置すること（高硬度部信号の位相と、磁性変動信号の位相と、リフトオフ信号の位相とを確実に識別可能であること）が分かった。 FIG. 4 is a graph showing changes in the phase difference between the magnetic fluctuation signal of the steel pipe P and the lift-off signal detected by the probe coil 1 when the inspection frequency is changed. As a result of the inspection test by the inventors of the present invention, as shown in FIG. 4, it was found that the higher the inspection frequency, the larger the phase difference between the magnetic fluctuation signal and the lift-off signal. Then, if the inspection frequency is set so that the phase difference between the magnetic fluctuation signal and the lift-off signal is 135 ° or more (in this embodiment, the inspection frequency is set to 64 kHz), the phase of the high hardness portion signal becomes magnetic fluctuation. It is known that it is reliably positioned between the phase of the signal and the phase of the lift-off fluctuation signal (the phase of the high hardness part signal, the phase of the magnetic fluctuation signal, and the phase of the lift-off signal can be reliably identified). It was.
図５は、プローブコイル１によって検出される各差動信号（高硬度部信号、磁性変動信号、リフトオフ信号）の位相関係を模式的に示す図であり、具体的には、検査周波数を６４ｋＨｚとした場合に、位相回転器２４Ａから出力されるＸ信号及びＹ信号に基づいて算出される各差動信号に対応するリサージュ波形の延びる方向を模式的に示す図である。図５に示すように、検査周波数を６４ｋＨｚとし、Ｘ軸上（位相１８０°の位置）に鋼管Ｐの磁性変動信号が位置するように位相回転器２４Ａの回転量（移相量）を調整すれば、リフトオフ信号の位相は４５°よりも小さくなり（すなわち、磁性変動信号とリフトオフ信号との位相差が１３５°以上となり）、高硬度部信号の位相は、磁性変動信号の位相とリフトオフ信号の位相との間（具体的には、位相７０°から１３５°の間）で検出されることが分かった。このように、磁性変動信号とリフトオフ信号との位相差が１３５°以上となるように検査周波数を設定すれば、高硬度部信号の位相と磁性変動信号又はリフトオフ信号の位相とが同程度となることなく、位相の差異によって高硬度部信号を正確に検出することが可能である。 FIG. 5 is a diagram schematically showing the phase relationship of each differential signal (high hardness portion signal, magnetic fluctuation signal, lift-off signal) detected by the probe coil 1, and specifically, the inspection frequency is 64 kHz. FIG. 6 is a diagram schematically showing the direction in which the Lissajous waveform corresponding to each differential signal calculated based on the X signal and the Y signal output from the phase rotator 24A is extended. As shown in FIG. 5, the inspection frequency is 64 kHz, and the rotation amount (phase shift amount) of the phase rotator 24A is adjusted so that the magnetic fluctuation signal of the steel pipe P is located on the X axis (position of 180 ° phase). For example, the phase of the lift-off signal is smaller than 45 ° (that is, the phase difference between the magnetic fluctuation signal and the lift-off signal is 135 ° or more), and the phase of the high hardness portion signal is the same as that of the magnetic fluctuation signal and the lift-off signal. It was found to be detected between the phases (specifically, between the phases of 70 ° and 135 °). As described above, if the inspection frequency is set so that the phase difference between the magnetic fluctuation signal and the lift-off signal is 135 ° or more, the phase of the high hardness portion signal and the phase of the magnetic fluctuation signal or the lift-off signal become approximately the same. Without this, it is possible to accurately detect the high hardness portion signal by the difference in phase.
以上に説明した理由により、前述のように、信号処理部２では、鋼管Ｐの磁性変動信号とリフトオフ信号との位相差が１３５°以上となるように検査周波数を設定している。ただし、検査周波数を変更することによって渦電流の浸透深さが変化する（検査周波数を高くすれば、渦電流の浸透深さは小さくなる）ため、検査周波数を高くすればするほど良いということではなく、検出対象とする高硬度部の鋼管Ｐ表面からの深さも考慮して検査周波数を設定することが好ましい。また、検査周波数を過度に高周波に設定すると、渦電流の浸透深さが小さくなりすぎ、鋼管Ｐ表面の凹凸に過敏になってノイズ信号が大きくなったり、高硬度部の深さ情報が失われる等の不具合が生じるため、これらの点も考慮して検査周波数を設定することが好ましい。 For the reasons described above, as described above, the signal processing unit 2 sets the inspection frequency so that the phase difference between the magnetic fluctuation signal of the steel pipe P and the lift-off signal is 135 ° or more. However, since the penetration depth of eddy current changes by changing the inspection frequency (if the inspection frequency is increased, the penetration depth of eddy current is reduced), the higher the inspection frequency, the better However, it is preferable to set the inspection frequency in consideration of the depth from the surface of the steel pipe P of the high hardness portion to be detected. If the inspection frequency is set to an excessively high frequency, the penetration depth of eddy current becomes too small, and the noise signal becomes large due to the unevenness on the surface of the steel pipe P, or the depth information of the high hardness portion is lost. Therefore, it is preferable to set the inspection frequency in consideration of these points.
図６は、検査周波数を１６ｋＨｚ、３２ｋＨｚ、６４ｋＨｚと変更した場合に得られる、局部的な高硬度部の硬度（ビッカース硬度）と、判定部２７Ａによって演算された高硬度部信号の振幅との関係の一例を示すグラフである。なお、図６の横軸の硬度は、鋼管Ｐの表面から深さ０．１ｍｍでの硬度を意味する。また、図６に示すノイズレベルは、磁性変動信号又はリフトオフ信号の最大の振幅を意味する。図６に示すように、検査周波数を６４ｋＨｚに設定することにより、検査周波数を１６ｋＨｚに設定した場合に比べて渦電流が鋼管Ｐの表面近傍に集中するため、高硬度部信号の振幅が大きくなり、健全部位の硬度（約３５０Ｈｖ）よりも５０Ｈｖ以上高い（従って、硬度が約４００Ｈｖ以上の）高硬度部であれば、ノイズレベルよりも大きな高硬度部信号の振幅（すなわち、高硬度部のＳ／Ｎ比＞１）を得ることができる。本実施形態では、前述のように、検査周波数を６４ｋＨｚに設定しているため、ノイズレベルよりも大きな高硬度部信号の振幅を得ることができると共に、磁性変動信号とリフトオフ信号との位相差を１３５°以上にする（高硬度部信号の位相と、磁性変動信号の位相と、リフトオフ信号の位相とを確実に識別可能）ことができる。従って、前述のように、判定部２７Ａが、演算した振幅Ｚが予め定めたしきい値（例えばノイズレベル）よりも大きいか否かを判定し、振幅Ｚが予め定めたしきい値よりも大きい場合には、演算した位相θが予め定めた範囲内（例えば、位相７０°から１３５°の間）にあるか否かを判定することにより、金属材料に局部的に存在する高硬度部を確実に検出可能である。 FIG. 6 shows the relationship between the local high hardness part hardness (Vickers hardness) obtained when the inspection frequency is changed to 16 kHz, 32 kHz, and 64 kHz and the amplitude of the high hardness part signal calculated by the determination unit 27A. It is a graph which shows an example. The hardness on the horizontal axis in FIG. 6 means the hardness at a depth of 0.1 mm from the surface of the steel pipe P. Further, the noise level shown in FIG. 6 means the maximum amplitude of the magnetic fluctuation signal or the lift-off signal. As shown in FIG. 6, by setting the inspection frequency to 64 kHz, the eddy current is concentrated near the surface of the steel pipe P as compared with the case where the inspection frequency is set to 16 kHz. In the case of a high hardness part that is 50 Hv or more higher than the hardness (about 350 Hv) of the healthy part (and hence the hardness is about 400 Hv or more), the amplitude of the high hardness part signal that is larger than the noise level (that is, S of the high hardness part) / N ratio> 1). In the present embodiment, as described above, since the inspection frequency is set to 64 kHz, the amplitude of the high hardness portion signal larger than the noise level can be obtained, and the phase difference between the magnetic fluctuation signal and the lift-off signal can be obtained. It can be set to 135 ° or more (the phase of the high hardness portion signal, the phase of the magnetic fluctuation signal, and the phase of the lift-off signal can be reliably identified). Therefore, as described above, the determination unit 27A determines whether or not the calculated amplitude Z is larger than a predetermined threshold (for example, noise level), and the amplitude Z is larger than the predetermined threshold. In this case, it is possible to reliably determine the high hardness portion that exists locally in the metal material by determining whether or not the calculated phase θ is within a predetermined range (for example, between 70 ° and 135 °). Can be detected.
１・・・プローブコイル
２・・・信号処理部
１１ａ、１１ｂ、１１ｃ・・・検出コイル
２１・・・発信器
２２Ａ、２２Ｂ・・・増幅器
２３Ａ、２３Ｂ・・・同期検波器
２４Ａ、２４Ｂ・・・位相回転器
２５Ａ・・・ハイパスフィルタ
２６Ａ、２６Ｂ・・・Ａ／Ｄ変換器
２７Ａ、２７Ｂ・・・判定部
１００・・・渦流検査装置
Ｐ・・・鋼管
DESCRIPTION OF SYMBOLS 1 ... Probe coil 2 ... Signal processing part 11a, 11b, 11c ... Detection coil 21 ... Transmitter 22A, 22B ... Amplifier 23A, 23B ... Synchronous detector 24A, 24B ... -Phase rotator 25A ... high-pass filters 26A, 26B ... A / D converters 27A, 27B ... determination unit 100 ... eddy current inspection device P ... steel pipe
Claims (7)
前記金属材料に対向配置した一対の検出コイルを具備するプローブコイルを前記金属材料に対して相対移動させながら、前記プローブコイルに交流電流を通電して前記金属材料に交流磁界を作用させると共に、
前記交流磁界によって前記金属材料に誘起された渦電流を前記一対の検出コイルで検出して得られる差動信号に基づいて、前記局部的な高硬度部の有無を検知し、
前記交流磁界によって前記金属材料に誘起された渦電流を前記一対の検出コイルの内のいずれか一方で検出して得られる絶対値信号に基づいて、前記検知した局部的な高硬度部の位置を特定することを特徴とする渦流検査方法。 An eddy current inspection method for detecting a local high hardness portion existing in a metal material having magnetism,
While moving a probe coil having a pair of detection coils opposed to the metal material relative to the metal material, an AC current is applied to the probe coil to cause an AC magnetic field to act on the metal material,
Based on the differential signal obtained by detecting the eddy current induced in the metal material by the alternating magnetic field with the pair of detection coils, the presence or absence of the local high hardness portion is detected,
Based on an absolute value signal obtained by detecting an eddy current induced in the metal material by the alternating magnetic field in one of the pair of detection coils, the position of the detected local high hardness portion is determined. An eddy current inspection method characterized by specifying.
前記金属材料に対向配置され、前記金属材料に交流磁界を作用させて渦電流を誘起すると共に、前記金属材料に誘起された渦電流を検出する一対の検出コイルを具備するプローブコイルと、
前記プローブコイルに交流電流を通電すると共に、前記金属材料に誘起された渦電流を前記一対の検出コイルで検出して得られる差動信号に基づいて、前記局部的な高硬度部の有無を検知し、前記金属材料に誘起された渦電流を前記一対の検出コイルの内のいずれか一方で検出して得られる絶対値信号に基づいて、前記検知した局部的な高硬度部の位置を特定する信号処理部とを備えることを特徴とする渦流検査装置。 An eddy current inspection device for detecting a localized high hardness portion existing in a magnetic metal material,
A probe coil provided with a pair of detection coils disposed opposite to the metal material and inducing an eddy current by applying an alternating magnetic field to the metal material and detecting the eddy current induced in the metal material;
The probe coil is supplied with an alternating current, and the presence or absence of the local high hardness portion is detected based on a differential signal obtained by detecting the eddy current induced in the metal material by the pair of detection coils. Then, based on an absolute value signal obtained by detecting an eddy current induced in the metal material by one of the pair of detection coils, the position of the detected local high hardness portion is specified. An eddy current inspection apparatus comprising a signal processing unit.
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