JP3729044B2 - Ultrasonic flaw detection method and ultrasonic flaw detection apparatus - Google Patents

Description

【００３７】
表１より、本発明のアレイ探触子４を用いた場合、通常の斜角探傷よりも内外面スリットきずの感度差が少ないことが判る。これは下記の理由による。
図６は、屈折角度２０°〜８０°の範囲において、屈折角度と相対エコー強度の相関関係を示したグラフである。
通常の斜角探傷では屈折角度は同一にし、きずからの距離を変えて内外面きずを検出するので、内外面スリットそれぞれの感度（相対エコー強度）は図６の点Ａ、点Ｂとなる。
一方、実施例１に係る探傷では、きずからの距離は一定にし、屈折角を変えることにより内外面スリットを検出するので、内外面スリットそれぞれの感度は点Ａ、点Ｃとなる。図６より、点ＡＢ間の感度差に比べ、点ＡＣ間の感度差が小さいことが判る。
従って、本発明においては、内外面きずの感度差が小さい探傷を行うことが可能となり、同一寸法のきずであれば、内外面のどちらに存在していても同一のエコー強度で検出することができる。
【００３８】
また、順次選択振動子群を切り替えて走査を行うときに、各選択振動子群で送受信する超音波ビームは、くさび３と鋼管１との接触面上の、長さ２０ｍｍ×くさび３の幅程度の部分を通過することが実験により確認されているので、この部分の接触状態を安定させることにより、再現性のよい探傷を実施することができる。以上のように、本発明を適用することにより、ＳＡＷ鋼管等のオンライン探傷を行う場合に探触子４の数を大幅に削減することが可能となった。
【００３９】
［実施例２］
次に、実施例２に係る超音波探傷方法について説明する。この方法においては、実施の形態１に係る超音波探傷装置を用い、グループとして選択された各振動子４ａの送受信の遅延時間を探傷位置に合わせて変更する。
実施例２では、内面きず探傷の場合は、選択振動子群で送受信される超音波が溶接部２の内面に集束するような遅延時間を与え、外面きず探傷の場合は、溶接部２の外面でビームが集束するような遅延時間を与え、探傷の深さに合わせて送受信遅延時間を変更する。
【００４０】
図７は、実施例２と、前記斜角探傷の２つ方法により、図３の人工きずを探傷した場合のＳＮ比を示すグラフである。きずの深さに対応させて超音波ビームの集束位置を変えることによりＳＮ比が向上しており、実施例１に係る方法による図５の場合と比較して微小なきずまで検出可能になったことが判る。
被検査材の板厚によって、内外面、及び被検査材の板厚中央部までのビーム路程が変わるので、実施例２では被検査材の板厚及び探傷深さに対応させて送受信の遅延時間を変更する必要性があるが、この方法は微小きずまで検出する必要がある場合には極めて有効な探傷方法である。
【００４１】
［実施例３］
実施の形態２に係る超音波探傷装置を用い、送受信遅延を与えずに、超音波探傷を実施した。
図８は、実施例３に係る方法と、前記斜角探傷の２つ方法により、図３の人工きずを探傷した場合のＳＮ比を示すグラフである。図８より、実施例２の結果（図７参照）よりは若干劣るが、実施例１の結果（図５参照）、及び通常の斜角探傷に比肩するＳＮ比が得られており、十分にオンライン探傷に適用可能なことが判る。
【００４２】
図９は、深さ１０〜８０ｍｍに加工したφ３．２ｍｍ横穴から得られるきずエコー強度（相対エコー強度）の深さ依存性を示すグラフである。図９より、実施例２の方法によりきず深さに依存しない相対エコー強度が得られており、実施例１及び実施例３の場合、従来の斜角探傷方法と比較して、エコー強度の深さ依存性が減じていることがわかる。
【００４３】
以上のように、本発明は鋼管１の溶接部２に存在するきずを超音波探傷する方法において、溶接部２の片側から１つの探触子（溶接部両側から２個）を用いて、溶接部２から探触子４までの距離を一定に保ちながら、溶接線方向に直線走査するだけで、溶接部２の全断面を高精度に探傷することができる。
また、比較的小さな送受信遅延を与えるだけで肉厚方向の各深さで超音波ビームを集束することができ、溶接部２の全断面で微小きずの検出が可能となる。
そして、くさび３の形状を、集束位置が溶接部２内部の所定位置（例えば中央部）になるような形状にすることにより、送受信遅延処理をしなくても（またはごくわずかの遅延量を与えるのみで）集束点近傍の微小きずを検出することができる。
【００４４】
なお、前記実施の形態においては、ＳＡＷ鋼材溶接部探傷における縦方向きず検出（溶接線に垂直に超音波ビーム入射）につき説明しているが、これに限定されるものではなく、溶接線に対し斜めにビームを入射する横方向きず検出にも適用することが可能である。
さらに、本発明は、鋼管１の溶接部２の探傷に限定されるものではなく、鋼板の突き合わせ溶接部等の超音波探傷に適用することも可能である。
【００４５】
【発明の効果】
以上、詳述したように、第１発明及び第４発明による場合は、アレイ探触子との接触面を曲面状になした音響媒質体を用いるので、超音波送受信に関わる超音波振動子のグループを順次切り替えることにより、被検査部分への超音波入射点から探触子までの距離を一定に保ちながら、セクター走査同様の屈折角度変更を行うことができ、被検査部分の全断面を高精度に探傷することが可能になる。特に厚肉の溶接部を自動探傷し、内在きずを精度良く検出する溶接部の超音波探傷方法として有益である。
そして、各超音波振動子群で送受信する超音波ビームが音響媒質体と鋼管との接触部において、ほぼ同一の場所を通過するようになり、音響媒質体の長さの短縮を実現することができる。
また、選択振動子群を切り替えるだけで屈折角度の変更が可能であるので、各超音波振動子に送受信遅延を与えずに探傷することができる。
【００４６】
第２及び第５発明による場合は、少なくとも１回の鋼管内面での反射を利用して、鋼管の肉厚方向のビーム走査を行うようにしたので、鋼管の全断面に漏れなく超音波ビームを走査させることができる。
第６発明による場合は、屈折角度制御器が走査する屈折角度範囲を５５°〜７０°とするようにしたので、鋼管の全断面に漏れなく超音波ビームを走査させることができる。
第３及び第７発明による場合は、送受信遅延を与えるので、超音波ビームが鋼管中で拡散するのが防止される。また、遅延時間を小さく、波形歪みを極小化することができ、サイドローブによる虚像の発生を防止することができる。そして、選択振動子群毎に最大２００ｎｓｅｃ程度の比較的小さな送受信遅延を与えるだけで肉厚方向の各深さで超音波ビームを集束することができ、被検査部分の全断面で微小きず検出が可能となる。
【００４７】
第８発明による場合は、音響媒質体が、集束位置が鋼管内部の所定位置（例えば溶接部の中央部）になるような形状を有しているので、送受信遅延処理をしなくても（またはごくわずかの遅延量を与えるのみで）集束点近傍の微小きずを検出することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１に係る超音波探傷装置を示す模式図である。
【図２】本発明の実施の形態２に係る超音波探傷装置を示す模式図である。
【図３】肉厚４０ｍｍの鋼板に人工きずを設けた状態を示す図であり、（ａ）は側面図、（ｂ）は平面図である。
【図４】実施例１の方法により前記鋼板の人口きずを調べた場合を示す波形図である。
【図５】実施例１と、斜角探傷の２つの方法できずを探傷した場合のＳＮ比を示すグラフである。
【図６】屈折角度２０°〜８０°の範囲において、屈折角度と相対エコー強度の相関関係を示したグラフである。
【図７】実施例２と、斜角探傷の２つ方法により、図３の人工きずを探傷した場合のＳＮ比を示すグラフである。
【図８】実施例３に係る方法と、斜角探傷の２つ方法により、図３の人工きずを探傷した場合のＳＮ比を示すグラフである。
【図９】きず深さと相対エコーとの相関関係を示したグラフである。
【図１０】従来の管軸方向きず検査用探触子の配置及び超音波伝搬挙動を示す模式図である。
【図１１】従来の管軸方向きず検査用探触子の配置及び超音波伝搬挙動を示す模式図である。
【符号の説明】
１ 鋼管
２ 溶接部
３ くさび
４ アレイ探触子
４ａ 超音波振動子
５ パルサ
６ 送信用遅延素子
７ レシーバ
８ 受信用遅延素子
９ 屈折角度制御器
１２ きず評価器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flaw detection method and an ultrasonic flaw detection device that detect flaws inherent in a welded portion and the like, and more particularly to an ultrasonic flaw detection method and an ultrasonic flaw detection device for flaw detection of the entire cross section of a thick welded portion.
[0002]
[Prior art and problems to be solved by the invention]
Various flaws occur in a welded portion such as a welded steel pipe depending on the welding method and conditions, which causes a deterioration in the quality of the welded portion. For this reason, nondestructive inspection using X-rays and ultrasonic waves is performed. X-rays can easily detect point-like flaws such as pinholes and slag entrainment, and have many inspection results, but have problems such as low efficiency and high equipment costs.
[0003]
For this reason, in submerged arc welding (SAW) steel pipes, ultrasonic flaw detection is performed, and X-ray inspection is performed only on the part determined to have a flaw and both pipe ends.
Ultrasonic flaw detection is a method suitable for detecting cracks and surface defects such as poor fusion, and is superior to X-ray inspection in terms of inspection efficiency and equipment cost. In charge of inspection of the entire welded area.
[0004]
As an example, the outline of the on-line automatic flaw detection method in the SAW steel pipe manufacturing process is described in 4 of Reference 1 (“Ultrasonic flaw detection method of welded steel pipe”, edited by the Steel Association Quality Control Subcommittee (NDI section), published on February 22, 1999). 4.1-4.4.3 (pp60-62). This technology is equipped with a plurality of probes for detecting flaws on the inner surface and flaws on the inner and outer flaws in each of the vertical and horizontal flaws so that they can be detected without missing various flaws that occur in the weld. .
[0005]
In on-line flaw detection, the above-mentioned probe group is always conveyed at a predetermined position from the welded portion by using a vortex type or optical seam detector and a seam tracking mechanism, and the steel pipe is conveyed in a straight line so that the entire surface of the welded portion is covered. We are inspecting. In this case, in order not to miss a flaw, the ultrasonic beam transmitted and received by the probe group at each position in the longitudinal direction of the tube needs to cover the entire cross section of the weld.
[0006]
The ultrasonic beam transmitted / received by the ultrasonic probe propagates through the material while diffusing at a directivity angle defined by the flaw detection frequency and the vibrator diameter.
FIG. 10 is a schematic diagram showing the arrangement of the probe for flaw inspection in the tube axis direction and the ultrasonic propagation behavior, in which 1 is a steel pipe.
The steel pipe 1 has a welded portion 2. On the outer surface of the steel pipe 1, an inner surface flaw probe 23 is positioned 0.5 skip from the welded portion 2, and an outer surface flaw probe 24. It is arranged at the 0 skip position.
When the inner surface flaw probe 23 and the outer surface flaw probe 24 are used, the intensity of the ultrasonic beam at the center of the welded portion 2 is weakened, and the flaw detection capability is lowered. That is, as shown in FIG. 10, a flaw detection sensitivity deficient area A occurs in the center of the welded portion 2. This tendency becomes more prominent with thicker materials.
[0007]
Therefore, as described in the probe setting example in the steel pipe flaw detection (Reference 1: Table 4.11, p65) in the technique described in Reference 1, the thick material has a skip of 1.0 skip or more from the weld 2. It is recommended to have two probes at a distance.
FIG. 11 is a schematic diagram showing the arrangement and ultrasonic propagation behavior of the probe for flaw inspection in the tube axis direction arranged at the recommended position, in which 1 is a steel pipe.
The steel pipe 1 has a welded portion 2. On the outer surface of the steel pipe 1, an inner surface flaw probe 23 is positioned 1.0 skip from the welded portion 2, and an outer surface flaw probe 24. It is arranged at a position of 5 skips. In FIG. 11, the flaw detection sensitivity insufficient region does not occur.
This is based on the fact that the ultrasonic beam diffuses as the propagation distance increases, but the ultrasonic beam intensity per unit area decreases in proportion to the increase in the propagation distance. The reflection echo intensity from the light also decreases, and the flaw echo may be buried in the noise signal.
[0008]
In order to solve the above-mentioned problem, a probe for a center flaw is added to a probe (for example, an outer surface flaw and an inner surface flaw) at a position where the ultrasonic propagation distance to the welded portion 2 is short. 3) are desirable.
However, increasing the number of probes not only increases the number of flaw detectors, but also requires the addition of the seam detector and the seam tracking mechanism, resulting in a huge equipment cost. .
[0009]
In order to solve the above problem, a flaw detection technique using an array probe has been proposed in recent years.
For example, linear scanning of an oblique array probe described in Reference 2 (Non-destructive inspection Vol. 47 No. 1 (1998) pp 45-52 “Development of linear array type ultrasonic flaw detection technology applied to gas conduit”) This corresponds to the sector scanning method of the oblique angle array probe described in JP-A-11-183446. That is, the idea is to secure two or more flaw detection areas described in FIGS. 10 and 11 with one array probe. However, these technologies have the following problems.
[0010]
In the technique described in the above-mentioned document 2, an acoustic medium body made of synthetic resin for placing the array probe inclined at a predetermined angle with respect to the flaw detection surface, called a wedge, becomes large, and the entire welded part having a wall thickness of 19 mm is formed. It has been reported that the length of the contact portion between the wedge and the material to be inspected needs to be about 150 mm (width 20 mm) in order to cover the cross section. In order to carry out highly accurate and stable flaw detection, a contact medium such as water is necessary for the contact portion between the wedge and the material to be inspected. It is difficult to keep supplying the contact medium. This becomes even more remarkable when the surface of the material to be inspected such as a SAW steel pipe has a curvature.
[0011]
In the technique disclosed in Japanese Patent Laid-Open No. 11-183446, the problem is relatively small. However, in order to deflect the ultrasonic beam with respect to the refraction angle determined by the wedge shape and change the refraction angle, a large transmission / reception delay time is required.
For example, an array probe composed of 16 transducers with a pitch of 1 mm (wedge material is acrylic: longitudinal wave speed of 2700 m / s), and the wedge set refraction angle is 60 ° (incident angle 46 °), about ± 8 °. In order to change the refraction angle, a delay time of about 620 ns is required between the vibrators at both ends (= 16 vibrators × sin (6 °) / 2700 m / s). .
An analog delay line is usually used as a means for giving a delay to the received signal in each transducer, but there are drawbacks that the amount of delay is increased, the received waveform is distorted, and the vibration duration is increased. Therefore, when performing sector scanning, there is a problem that phase matching on the receiving side is difficult, and it is difficult to perform flaw detection with high accuracy and high resolution.
In addition, when performing sector scanning, there is a problem that a virtual image due to side lobes is likely to occur.
[0012]
The present invention has been made in view of such circumstances, and an acoustic medium having a curved contact surface with the array probe is used, and a plurality of ultrasonic transducers of the array probe are grouped into one group. An ultrasonic beam is transmitted and received by the transducer group, and this group is sequentially switched, and flaw detection is performed by changing the refraction angle of the ultrasonic beam. An object of the present invention is to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus for carrying out this method.
[0013]
  Further, the present invention provides a delay time for transmission / reception of each ultrasonic transducer of the group every time the group is switched,Steel pipeIt is an object of the present invention to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus that can focus an ultrasonic beam at each depth in the thickness direction and detect minute flaws in the entire cross section of the weld.
[0014]
  Furthermore, according to the present invention, the shape of the acoustic medium body is changed so that the ultrasonic beam transmitted from the ultrasonic transducer isSteel pipeIt is an object of the present invention to provide an ultrasonic flaw detector capable of detecting minute flaws without performing transmission / reception delay processing by forming a shape that is focused inside.
[0015]
[Means for Solving the Problems]
  In the ultrasonic flaw detection method according to the first invention, an acoustic medium body is disposed on a surface of a steel pipe, an array probe including a plurality of ultrasonic transducers is disposed on the acoustic medium body, In the ultrasonic flaw detection method for flaw-detecting the steel pipe by transmitting and receiving an ultrasonic beam by a group of transducers having a plurality of groups,eachThe passing position of the ultrasonic beam transmitted and received by the transducer group isBetween each transducer groupA group of transducers in which an acoustic medium body having a curved contact surface with the array probe is arranged so as to be substantially the same at a contact portion between the acoustic medium body and the steel pipe, and the group is the group The ultrasonic beam is transmitted / received by changing the refraction angle of the ultrasonic beam by sequentially switching the groups, and the ultrasonic beam is scanned in the thickness direction of the steel pipe.
[0016]
  The ultrasonic flaw detection method of the second invention is the first invention,The beam scanning in the thickness direction is performed using at least one reflection on the inner surface of the steel pipe.It is characterized by that.
  The ultrasonic flaw detection method according to a third aspect of the present invention is the ultrasonic inspection method according to the first or second aspect, wherein each time the group is switched, a delay time is given to transmission / reception of each ultrasonic transducer of the group, and an ultrasonic beam is given to the predetermined steel pipe It is characterized by focusing at a position.
[0017]
  An ultrasonic flaw detector according to a fourth aspect of the present invention is an oscillation circuit in which an array probe including a plurality of ultrasonic transducers is disposed on the surface of a steel pipe via an acoustic medium body, and is connected to the ultrasonic transducer separately. In the ultrasonic flaw detection apparatus that drives each ultrasonic vibrator to transmit an ultrasonic beam, takes in an echo signal received by the ultrasonic vibrator into a signal processing circuit, and flaws the steel pipe,eachThe passing position of the ultrasonic beam transmitted and received by the transducer group isBetween each transducer groupThe acoustic medium body having a curved contact surface with the array probe is disposed so as to be substantially the same at the contact portion between the acoustic medium body and the steel pipe, A refraction angle controller having a circuit for selecting the ultrasonic transducers as one group, a circuit for sequentially switching the groups, and a circuit for giving timings for driving the ultrasonic transducers of the groups to the oscillation circuits.The refraction angle of the ultrasonic beam is changed by sequentially switching the groups, and the ultrasonic beam is scanned in the thickness direction of the steel pipe.It is characterized by that.
[0018]
  An ultrasonic flaw detector according to a fifth aspect of the present invention is characterized in that, in the fourth aspect, the refraction angle controller scans a refraction angle within an angle range in which the ultrasonic beam is reflected on the inner surface of the steel pipe at least once.
  The ultrasonic flaw detector according to a sixth aspect of the present invention is the ultrasonic inspection apparatus according to the fifth aspect, wherein the refraction angle range scanned by the refraction angle controller is55 ° -70 °It is characterized by being.
  An ultrasonic flaw detector according to a seventh aspect of the present invention is the ultrasonic flaw detector according to any one of the fourth to sixth aspects, wherein the transmission delay element provides each oscillation circuit with a timing obtained by adding the delay time controlled by the refraction angle controller to the timing. And a reception delay element for adding the delay time controlled by the refraction angle controller to the timing at which the ultrasonic transducer receives the echo signal and supplying the echo signal to the signal processing circuit. And
[0019]
  Eighth inventionUltrasonic flaw detectorAny of the fourth to seventh inventionsIn this case, the acoustic medium body transmits the ultrasonic beam transmitted from the ultrasonic transducer.Steel pipeIt is characterized by having a shape for focusing inside.
[0020]
  1st invention andFourth inventionSince an acoustic medium body having a curved contact surface with the array probe is used, the ultrasonic incident point on the part to be inspected can be changed by sequentially switching the group of ultrasonic transducers related to ultrasonic transmission / reception. While keeping the distance from the probe to the probe constant, the refraction angle can be changed in the same manner as the sector scanning, and the entire cross section of the inspected portion can be detected with high accuracy. In particular, it is useful as an ultrasonic flaw detection method for a welded part that automatically detects a thick welded part and accurately detects an internal defect.
  Then, the ultrasonic beam transmitted and received by each ultrasonic transducer group is connected to the acoustic medium body.Steel pipeIn the contact portion, the sound medium passes through substantially the same place, so that the length of the acoustic medium body can be shortened.
  Further, since the refraction angle can be changed by simply switching the selected transducer group, flaw detection can be performed without giving a transmission / reception delay to each ultrasonic transducer.
[0021]
  In the second and fifth aspects of the invention, the beam is scanned in the thickness direction of the steel pipe by utilizing at least one reflection on the inner surface of the steel pipe, so that the ultrasonic beam is scanned over the entire cross section of the steel pipe without leakage.
  In the sixth invention, the refraction angle range scanned by the refraction angle controller is set.55 ° -70 °By doing so, the ultrasonic beam is scanned without leakage over the entire cross section of the steel pipe.
  In the third and seventh inventions, since transmission and reception delay is given, the ultrasonic beam isSteel pipeSpreading in is prevented. In addition, the delay time can be reduced, waveform distortion can be minimized, and generation of virtual images due to side lobes can be prevented. In addition, the ultrasonic beam can be focused at each depth in the thickness direction by giving a relatively small transmission / reception delay of about 200 nsec at the maximum for each selected transducer group. It becomes.
[0022]
  The ultrasonic beam transmitted / received from the transducer group arranged on the curved surface is focused at a position determined by the curved surface shape.Eighth inventionIn the case of the acoustic medium body, the focusing position isSteel pipeBecause it has a shape that becomes a predetermined position inside (for example, the center of the weld), even if it does not perform transmission / reception delay processing (or only by giving a very small delay amount) Can be detected.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 1 of the present invention, in which 1 is a steel pipe.
The steel pipe 1 has a welded portion 2. On the outer surface of the steel pipe 1, a wedge-shaped wedge 3 (curvature 50 mm × width 15 mm cylinder 1/4) made of a resin such as acrylic is disposed. An array probe 4 composed of a plurality of ultrasonic transducers 4a (length: 1 mm × width: 10 mm) is disposed on the outer peripheral surface of 3. In this embodiment, the array probe 4 is made up of 32CH, the apex side is the first CH, and the 90 ° side is the 32nd CH.
[0024]
A pulser 5, a transmission delay element 6, a receiver 7, and a reception delay element 8 are connected to each of the vibrators 4a. In this embodiment, an analog delay line is used as the reception delay element 8.
The vibrator 4a is driven by the corresponding pulser 5, and the operation timing of each pulser 5 is determined by the transmission delay element 6.
[0025]
Each transmission delay element 6 is connected to a refraction angle controller 9. The refraction angle controller 9 includes a circuit for selecting a group of transducers having a predetermined number of transducers 4a as one group, a circuit for switching the group, and a timing for driving each transducer 4a in the group. A circuit for providing the pulser 5 and a circuit for providing a delay time to the transmission delay element 6 and the reception delay element 8 are provided.
The refraction angle controller 9 selects a transducer group, and the refraction angle controller 9 controls the selected transducer 4a at the timing at which each transducer 4a is driven by the corresponding transmission delay element 6. The timing obtained by adding the delayed times is given to each pulser 5. By applying a transmission voltage by the pulser 5 at the timing, an ultrasonic beam is transmitted from the vibrator 4 a into the steel pipe 1.
[0026]
Reception of scratch echo etc. is performed as follows.
A signal received by each transducer 4 a of the selected transducer group is input to the receiver 7. The signal input to the receiver 7 is output to the adder 10 after the receiving delay element 8 is given a delay time controlled by the refraction angle controller 9.
The received signal is synthesized by the adder 10 and amplified by the amplifier 11 to a signal level necessary for evaluation. The amplified signal value is compared with a predetermined threshold value by the flaw evaluator 12 to evaluate the presence or absence of flaws.
In the ultrasonic flaw detector according to this embodiment, the angle of refraction incident on the steel pipe 1 is changed by sequentially switching, for example, 16 selected transducer groups that contribute to ultrasonic beam formation at predetermined intervals. Thus, the entire cross section of the welded portion 2 can be detected.
[0027]
FIG. 1 shows the state of a beam in which flaw detection is performed on the inner surface side with 0.5 skip and flaw detection is performed on the outer surface side (array probe 4 installation side) with 1.0 skip. It is preferable to change the beam irradiation position in multiple stages to detect the entire cross section of the welded portion 2. As will be described later, in addition to the flaw detection on the inner and outer surfaces, the inventors of the present application are also conducting a test for flaw detection at the central thickness portion (0.75 skip).
[0028]
In this embodiment, the following delay is given. Note that the unit of the delay time is ns.
CH1: 170, CH2: 130,
CH3: 90, CH4: 60,
CH5: 35, CH6: 20,
CH7: 5, CH8: 0,
CH9: 0, CH10: 5,
CH11: 20, CH12: 35,
CH13: 60, CH14: 90,
CH15: 130, CH16: 170
These transmission / reception delay times are given in the same pattern even when the selected transducer group is sequentially switched. That is, a delay of about 170 ns is always given to the vibrator 4a at both ends as compared with the vibrator 4a at the center.
[0029]
Embodiment 2. FIG.
In the ultrasonic flaw detector according to the first embodiment, since a 1/4 cylinder is used as the wedge 3, when no transmission / reception delay time is given, the ultrasonic beam transmitted / received by each selected transducer group is the wedge 3 and the steel pipe 1. It converges on the boundary surface between them and propagates while diffusing inside the steel pipe 1, so that the flaw detection ability decreases.
For this reason, in Embodiment 1, the transmission / reception delay corresponding to the distance to the welding part 2 is given, and an ultrasonic beam is focused. However, in order to give the transmission / reception delay time, the transmission delay element 6 group and the reception delay element 8 group are necessary, and the electronic circuit is complicated and expensive. Further, the delay time given in the first embodiment is about 200 nsec at the maximum, but problems such as waveform distortion and increase in duration remain as described above.
[0030]
Accordingly, the inventors of the present application have developed an ultrasonic flaw detector that does not require transmission / reception delay time by examining the shape of the wedge 3 on which the array probe 4 is disposed.
FIG. 2 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 2 of the present invention, in which the same parts as those in FIG. 1 are denoted by the same reference numerals.
In the second embodiment, the shape of the wedge 3 is such that a part of a cylinder having a curvature of 200 mmR is cut out, and the end surface on the welded part 2 side (ultrasonic beam traveling side) is formed from the opposite end surface. It is enlarged. As a result, the beam is focused to a position of about 45 mm along the beam path in the steel pipe 1 without giving a transmission / reception delay time.
[0031]
On the end surface of the wedge 3 on the welded part 2 side, a sound absorbing material 13 for suppressing an irregular reflection signal inside the wedge 3 is attached. In addition, the contact surface between the wedge 3 and the steel pipe 1 is stable contact except for an area (length 50 mm × width of the wedge 3) necessary and sufficient for an ultrasonic beam transmitted and received by each selected transducer group to pass. And a notch for preventing irregular reflection of sound waves in the wedge 3 is provided.
In this embodiment, since no transmission / reception delay is required, the transmission delay element group 6 and the reception delay element group 8 are not required, the electronic circuit is simplified, can be manufactured at low cost, and the ultrasonic flaw detection apparatus is inexpensive. It is possible to provide.
[0032]
【Example】
Hereinafter, the first and second embodiments will be described in more detail with reference to examples.
[Example 1]
In Example 1, the ultrasonic flaw detection apparatus according to Embodiment 1 was used, and flaw detection was performed by switching the selected transducer group without giving a transmission / reception delay time. By switching the transducer group, the refraction angle is changed and the ultrasonic beam incident on the steel pipe 1 is deflected.
FIG. 3 is a view showing a state in which an artificial flaw is provided on a steel plate having a thickness of 40 mm, FIG. 3 (a) is a side view, and FIG. 3 (b) is a plan view.
FIG. 4 is a waveform diagram showing a case where the flaws of the steel sheet are examined by the method of Example 1 using the ultrasonic flaw detector according to Embodiment 1, and FIG. 4 (a) is a sheet thickness center of the steel sheet. (B) shows the case where the outer surface slit is detected, and (c) shows the case where the inner surface slit is detected. The arrow in the figure indicates the flaw waveform position.
[0033]
FIG. 6 shows the result of detecting the inner and outer surface slits and the lateral hole at the center of the plate thickness by sequentially switching the selected transducer group while keeping the distance from the processing position of the flaw on the array probe 4 constant. The refraction angles at the time of detecting each part are as follows.
-Refraction angle when detecting internal slit: approx. 70 °
-Refraction angle when detecting outer slit: approx. 55 °
-Refraction angle when detecting the center side hole: approx. 63 °
[0034]
At the same time, a normal oblique inspection test was conducted. In this flaw detection test, the angle of refraction was fixed at 55 °, the position of the probe was changed according to the flaw depth in the plate thickness direction of the steel sheet, and flaw detection was performed at the position with the best SN ratio. The separation distance from the flaws was generally set to flaws on the inner surface: 0.5 skip, flaws on the outer surface: 1.0 skip, and central lateral hole: 0.75 skip.
[0035]
FIG. 5 is a graph showing the SN ratio when the flaw detection is performed in the first example and the two methods of the oblique angle flaw detection. In Example 1, although the distance from the flaw processing position to the array probe 4 is kept constant, flaw detection is performed while changing the refraction angle, so that the normal oblique distance in which the distance to the flaw is optimally adjusted is detected. It can be seen that an S / N ratio comparable to that of angular flaw detection is obtained. That is, one array probe 4 covers the flaw detection range of three normal oblique angle probes.
Table 1 shows the difference in sensitivity when the above-mentioned inner and outer surface slit flaws are flaw-detected by a normal probe and the array probe 4 of the present invention.
[0036]
[Table 1]

[0037]
From Table 1, it can be seen that when the array probe 4 of the present invention is used, the sensitivity difference between the inner and outer surface slit flaws is smaller than that of the normal oblique flaw detection. This is due to the following reasons.
FIG. 6 is a graph showing the correlation between the refraction angle and the relative echo intensity in the refraction angle range of 20 ° to 80 °.
In normal oblique angle flaw detection, since the refraction angle is the same and the distance from the flaw is changed to detect flaws on the inner and outer surfaces, the sensitivity (relative echo intensity) of the inner and outer surface slits is point A and point B in FIG.
On the other hand, in the flaw detection according to the first embodiment, the inner and outer surface slits are detected by keeping the distance from the flaw constant and changing the refraction angle, so the sensitivity of the inner and outer surface slits is point A and point C, respectively. FIG. 6 shows that the sensitivity difference between the points AC is smaller than the sensitivity difference between the points AB.
Therefore, in the present invention, it is possible to perform a flaw detection with a small sensitivity difference between the inner and outer surface flaws, and if the flaw has the same size, it can be detected with the same echo intensity regardless of whether the flaw is present on the inner or outer surface. it can.
[0038]
In addition, when scanning is performed by sequentially switching the selected transducer group, the ultrasonic beam transmitted and received by each selected transducer group is approximately 20 mm in length × wedge 3 on the contact surface between the wedge 3 and the steel pipe 1. Since it has been confirmed by experiments that this portion passes, it is possible to carry out flaw detection with good reproducibility by stabilizing the contact state of this portion. As described above, by applying the present invention, it is possible to greatly reduce the number of probes 4 when performing online flaw detection on a SAW steel pipe or the like.
[0039]
[Example 2]
Next, an ultrasonic flaw detection method according to Example 2 will be described. In this method, the ultrasonic flaw detection apparatus according to Embodiment 1 is used, and the transmission / reception delay time of each transducer 4a selected as a group is changed in accordance with the flaw detection position.
In the second embodiment, in the case of an inner surface flaw detection, a delay time is given so that the ultrasonic waves transmitted and received by the selected transducer group are focused on the inner surface of the welded portion 2, and in the case of an outer surface flaw detection, the outer surface of the welded portion 2 is given. Gives a delay time to focus the beam, and changes the transmission / reception delay time according to the depth of flaw detection.
[0040]
FIG. 7 is a graph showing the SN ratio when the artificial flaw of FIG. 3 is detected by the two methods of Example 2 and the oblique angle flaw detection. The S / N ratio is improved by changing the focal position of the ultrasonic beam in accordance with the depth of the flaw, and it is possible to detect even a fine flaw as compared with the case of FIG. 5 by the method according to the first embodiment. I understand that.
Depending on the thickness of the material to be inspected, the beam path to the inner and outer surfaces and the center of the thickness of the material to be inspected changes. However, this method is a very effective flaw detection method when it is necessary to detect even a minute flaw.
[0041]
[Example 3]
Using the ultrasonic flaw detector according to Embodiment 2, ultrasonic flaw detection was performed without giving a transmission / reception delay.
FIG. 8 is a graph showing the S / N ratio when the artificial flaw of FIG. 3 is flawed by the method according to the third embodiment and the oblique flaw flaw detection method. From FIG. 8, although slightly inferior to the result of Example 2 (see FIG. 7), the result of Example 1 (see FIG. 5) and the SN ratio comparable to that of normal oblique flaw detection are obtained. Applicable to online flaw detection.
[0042]
FIG. 9 is a graph showing the depth dependence of the flaw echo intensity (relative echo intensity) obtained from a φ3.2 mm side hole processed to a depth of 10 to 80 mm. From FIG. 9, the relative echo intensity independent of the flaw depth is obtained by the method of Example 2, and in the case of Example 1 and Example 3, the depth of echo intensity is compared with the conventional oblique flaw detection method. It can be seen that the dependence is reduced.
[0043]
As described above, in the method for ultrasonic flaw detection of flaws existing in the welded portion 2 of the steel pipe 1, the present invention uses one probe from one side of the welded portion 2 (two from both sides of the welded portion) to perform welding. The entire cross section of the welded portion 2 can be detected with high accuracy by only performing a linear scan in the weld line direction while keeping the distance from the portion 2 to the probe 4 constant.
Further, it is possible to focus the ultrasonic beam at each depth in the thickness direction only by giving a relatively small transmission / reception delay, and it is possible to detect minute flaws in the entire cross section of the welded portion 2.
Then, by making the shape of the wedge 3 such that the converging position is a predetermined position (for example, the central portion) inside the welded portion 2, the transmission / reception delay processing is not performed (or a very slight delay amount is given). Only) can detect minute flaws near the focal point.
[0044]
In the above-described embodiment, the detection of longitudinal flaws (ultrasonic beam incidence perpendicular to the weld line) in the SAW steel material flaw detection has been described. However, the present invention is not limited to this. It can also be applied to detection of lateral flaws in which a beam is incident obliquely.
Furthermore, the present invention is not limited to the flaw detection of the welded portion 2 of the steel pipe 1, but can be applied to ultrasonic flaw detection such as a butt weld portion of a steel plate.
[0045]
【The invention's effect】
  As described above in detail, the first invention andFourth inventionIn this case, since an acoustic medium body with a curved contact surface with the array probe is used, ultrasonic waves are incident on the part to be inspected by sequentially switching the group of ultrasonic transducers related to ultrasonic transmission / reception. While keeping the distance from the point to the probe constant, the refraction angle can be changed in the same manner as the sector scanning, and the entire cross section of the part to be inspected can be detected with high accuracy. In particular, it is useful as an ultrasonic flaw detection method for a welded portion in which a thick welded portion is automatically flawed and an internal defect is accurately detected.
  Then, the ultrasonic beam transmitted and received by each ultrasonic transducer group is connected to the acoustic medium body.Steel pipeIn the contact portion, the sound passes through substantially the same place, and the length of the acoustic medium body can be shortened.
  Further, since the refraction angle can be changed by simply switching the selected transducer group, flaw detection can be performed without giving a transmission / reception delay to each ultrasonic transducer.
[0046]
  In the case of the second and fifth inventions, the beam scan in the thickness direction of the steel pipe is performed by utilizing at least one reflection on the inner surface of the steel pipe. Can be scanned.
  In the case of the sixth invention, the refraction angle range scanned by the refraction angle controller is set.55 ° -70 °Therefore, the ultrasonic beam can be scanned without leaking over the entire cross section of the steel pipe.
  In the case of the third and seventh inventions, transmission / reception delay is given, so that the ultrasonic beam is prevented from diffusing in the steel pipe. In addition, the delay time can be reduced, waveform distortion can be minimized, and generation of virtual images due to side lobes can be prevented. Then, the ultrasonic beam can be focused at each depth in the thickness direction only by giving a relatively small transmission / reception delay of about 200 nsec at the maximum for each selected transducer group, and minute flaws can be detected in the entire cross section of the part to be inspected. It becomes possible.
[0047]
  Eighth inventionIf the acoustic medium body isSteel pipeSince it has a shape that becomes a predetermined internal position (for example, the center of the welded portion), even if it does not perform transmission / reception delay processing (or only gives a very small amount of delay), a small flaw near the focal point Can be detected.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 1 of the present invention.
FIG. 2 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 2 of the present invention.
FIG. 3 is a view showing a state in which an artificial flaw is provided on a steel plate having a thickness of 40 mm, (a) is a side view, and (b) is a plan view.
4 is a waveform diagram showing the case where the artificial flaw of the steel sheet is examined by the method of Example 1. FIG.
FIG. 5 is a graph showing the SN ratio when flaw detection is carried out for Example 1 and two methods of oblique flaw detection.
FIG. 6 is a graph showing a correlation between a refraction angle and a relative echo intensity in a refraction angle range of 20 ° to 80 °.
7 is a graph showing the SN ratio when the artificial flaw shown in FIG. 3 is detected by two methods of Example 2 and oblique angle flaw detection.
8 is a graph showing the SN ratio when the artificial flaw of FIG. 3 is detected by the method according to Example 3 and the two methods of oblique angle flaw detection.
FIG. 9 is a graph showing a correlation between a flaw depth and a relative echo.
FIG. 10 is a schematic diagram showing the arrangement and ultrasonic propagation behavior of a conventional tube axis direction flaw inspection probe.
FIG. 11 is a schematic diagram showing the arrangement and ultrasonic propagation behavior of a conventional tube axis direction flaw inspection probe.
[Explanation of symbols]
1 Steel pipe
2 Welded part
3 Wedge
4 Array probe
4a Ultrasonic vibrator
5 Pulsa
6 Delay element for transmission
7 Receiver
8 Receiving delay element
9 Refraction angle controller
12 Scratch Evaluator

Claims (8)

A transducer group in which an acoustic medium body is disposed on a surface of a steel pipe, an array probe including a plurality of ultrasonic transducers is disposed on the acoustic medium body, and a plurality of the ultrasonic transducers are grouped into one group. by the ultrasonic flaw detection method for flaw detection of the steel pipe by transmitting and receiving an ultrasonic beam, the said acoustic medium material between the passage position of the ultrasonic beams transmitted and received by each transducer group are the respective transducer groups and the steel pipe The acoustic medium body having a curved contact surface with the array probe is disposed so as to be substantially the same in the contact portion of
The ultrasonic beam is transmitted and received by the group of transducers as the group, the refraction angle of the ultrasonic beam is changed by sequentially switching the group, and the ultrasonic beam is scanned in the thickness direction of the steel pipe. Ultrasonic flaw detection method.   The ultrasonic flaw detection method according to claim 1, wherein the beam scanning in the thickness direction is performed using at least one reflection on the inner surface of the steel pipe.   The ultrasonic flaw detection method according to claim 1 or 2, wherein a delay time is given to transmission / reception of each ultrasonic transducer of the group every time the group is switched, and the ultrasonic beam is focused at a predetermined position of the steel pipe. An array probe including a plurality of ultrasonic transducers is arranged on the surface of the steel pipe via an acoustic medium body, and each ultrasonic transducer is driven by an oscillation circuit connected to each ultrasonic transducer. In an ultrasonic flaw detector that transmits an ultrasonic beam and takes an echo signal received by the ultrasonic transducer into a signal processing circuit to detect the steel pipe,
Wherein as the passing position of the ultrasonic beams transmitted and received by each transducer group is substantially the same In the contact portion between the acoustic medium body and the steel pipe between the respective transducer groups, and the array probe The acoustic medium body having a curved contact surface is disposed,
A circuit for selecting a plurality of the ultrasonic transducers as one group;
A circuit for sequentially switching the groups;
And a refraction angle controller having a circuit that gives each oscillation circuit a timing for driving each ultrasonic transducer of the group ,
An ultrasonic flaw detector which scans the ultrasonic beam in the thickness direction of the steel pipe by changing the refraction angle of the ultrasonic beam by sequentially switching the groups .   5. The ultrasonic flaw detector according to claim 4, wherein the refraction angle controller scans a refraction angle within an angle range in which an ultrasonic beam is reflected on the inner surface of the steel pipe at least once. The ultrasonic flaw detection apparatus according to claim 5, wherein a refraction angle range scanned by the refraction angle controller is 55 ° to 70 ° . A transmission delay element that gives each oscillation circuit a timing obtained by adding a delay time controlled by the refraction angle controller to the timing;
5. A reception delay element that adds a delay time controlled by the refraction angle controller to a timing at which the ultrasonic transducer receives an echo signal, and gives the echo signal to the signal processing circuit. 6. The ultrasonic flaw detector according to any one of items 6.   The ultrasonic flaw detector according to any one of claims 4 to 7, wherein the acoustic medium body has a shape for focusing an ultrasonic beam transmitted from the ultrasonic transducer inside the steel pipe.

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