JP2013002961A - Ultrasonic flaw detection method and device for round-bar steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve flaw detection over the whole circumference with simple and inexpensive device constitution including a small number of vibrators and to achieve easy maintenance.SOLUTION: For internal defect detection of round-bar steel 30 through water immersion ultrasonic flaw detection, an array probe 1 is used which has a plurality of excitation elements arrayed on a probe surface having a substantially circumferential probe surface facing the round-bar steel and having its center at the center axis of the round-bar steel, and is arranged so that the probe surface and a surface of the round-bar steel are at a predetermined water distance. The array probe and round-bar steel are changed in relative position in round-bar steel length directions while flaw detection of an internal defect is carried out by forming a converged ultrasonic beam by transmitting an ultrasonic wave from the array probe into the round-bar steel and receiving it, and flaw detection results are saved by round-bar steel length directions. Flaw detection in the round-bar steel length directions are carried out a plurality of times while the array probe and round-bar steel are changed in relative position in a circumferential direction so that the converged ultrasonic beam is formed in the round-bar steel at different positions.

Description

  The present invention relates to an ultrasonic flaw detection method and apparatus. In particular, ultrasonic waves of round bar steel suitable for flaw detection using electronic scanning array probe of fine (<φ100 μm) inclusions of high cleanliness round bar steel that requires rolling fatigue life such as bearing steel The present invention relates to a flaw detection method and apparatus.

  In recent years, with the improvement in performance of various mechanical devices, the use environment of machine parts and devices using bearing steel, etc. that require a rolling fatigue life has become extremely severe, and there is a strong demand for improved life and improved reliability. Yes. In response to such demands, as countermeasures from the steel material side, optimization of steel components and reduction of impurity elements are carried out to improve the life and reliability.

  According to Patent Document 1, it is said that non-metallic inclusions of about 20 μm or more affect the rolling fatigue life, and therefore defect inspection of the same size as these inclusions is required. Here, the generation of non-metallic inclusions exceeding 20 μm is extremely rare especially in steels with excellent rolling fatigue life. Therefore, in order to detect this, it is necessary to detect the entire region of a large volume, for example, a constant depth. There is.

  On the other hand, in the defect inspection of round bar steel, an electronic scanning ultrasonic array probe (hereinafter referred to as an array probe) is used in Patent Document 2 as a method of detecting a whole area at a constant depth at high speed. A water immersion ultrasonic flaw detection method has been proposed.

  Further, as an improvement in detection capability for detecting a minimum inclusion of about 20 μm, focusing of an ultrasonic beam as in Patent Document 3 and Patent Document 4 is effective.

Here, the sound pressure of the point focused beam will be described as an example. In this case, according to Non-Patent Document 1, page 47, if the sound pressure emitted from the vibrator is P ₀ and the sound pressure at the focal point is P, the following equation (see Non-Patent Document 1, page 47 (2.108)) ) Holds.

P / P ₀ = π · J (1)
Here, J is a focusing coefficient, and is defined by the following equation (see non-patent document 1, page 47 (2.109)).
J = D ² / (4 · λ · f _OP ) (2)
(D: transducer width, λ: wavelength of ultrasonic wave, f _OP : focal length)

  That is, in this case, the sound pressure P at the focal point can be increased in proportion to the focusing coefficient J (see FIG. 2.50 on page 48 of Non-Patent Document 1), thereby improving the defect detection ability at the focal point. .

  Although the above discussion is about transmission, according to Non-Patent Document 2, page 45, section 1.4.4, it is known that generally the same discussion can be made for transmission and reception of ultrasonic propagation. Regarding reception, it is known that the defect detection capability at the focal point increases in proportion to the focusing factor J.

  The focusing of the ultrasonic beam can be performed by electronic focusing using an array probe as described in Patent Document 2 and Patent Document 4, and therefore, by using an array probe and a focused beam. Small inclusions can be inspected over a large volume.

JP 2008-121035 A JP 2010-133856 A JP 2005-84036 A JP 2007-170871 A

Japan Nondestructive Inspection Association Ultrasonic Flaw Test III 2001, pp. 47-48 Nikkan Kogyo Shimbun, Ltd. Ultrasonic Technology Handbook (1980), p. 45

  However, the combination of the array probe and the focused beam as described above has the following problems in configuring the flaw detector.

According to Non-Patent Document 1, in the beam focusing described by Expressions (1) and (2), the beam thickness d _W at the focal point can be described as follows (page 48 (2.111) of Non-Patent Document 1). See formula).

d _W = (f _OP · λ) / D (3)

  Therefore, the following relationship is obtained from the equations (2) and (3).

J = D / (4 · d _W ) (4)

That is, if the focusing coefficient J is increased to improve the detection capability, it is necessary to reduce the beam thickness d _W.

  Here, in order to perform flaw detection without gaps, it is necessary to make the beam pitch equal to or less than the beam thickness.

  Further, in flaw detection using an array probe, a beam is generally formed at the same pitch as the transducer pitch, that is, the transducer pitch must be equal to or less than the beam thickness.

  Therefore, in order to perform a single flaw detection immediately below the surface of the entire circumference of the round bar test piece having a diameter W, the number n of transducers of the array probe needs to satisfy the following equation.

n ≧ (π · W) / d _W (5)

As an example, if D = 10 mm, λ = 0.074 mm (corresponding to a frequency of 20 MHz (underwater)), f _OP = 20 mm, and W = 30 mm with reference to Patent Document 2, d _W = 0.15 mm, n ≧ Therefore, an array probe composed of 628 or more transducers is necessary.

  However, since the cost of the array probe is approximately proportional to the number of transducers, an array probe is composed of a general array probe (in paragraph 0019 of Patent Document 2, 128 transducers). ) Has a problem that the cost is high.

  In addition, since the flaw detection is performed from the entire circumferential direction, the array probe has a shape that covers the entire circumferential direction of the subject, which makes it difficult to perform maintenance.

  The present invention has been made to solve the above-mentioned conventional problems, and it is possible to perform flaw detection on the entire circumference with a simple and inexpensive apparatus configuration with a small number of vibrators and to facilitate maintenance. And

  The present invention is a method for flaw detection of a round bar steel by water immersion ultrasonic flaw detection, wherein a plurality of probe surfaces having a substantially circumferential surface centering on the central axis of the round bar steel are opposed to the round bar steel. Using an array probe in which excitation elements are aligned and the probe surface and the surface of the round steel bar have a predetermined water distance, ultrasonic waves are generated from the array probe to the inside of the round steel bar. Is sent and received to form a focused ultrasonic beam, and the flaw detection results for each length of the round bar steel by changing the relative position in the length direction of the round bar steel between the array probe and the round bar steel while conducting the inspection of internal defects. And the relative position of the array probe and the round bar steel in the circumferential direction is changed so that the position where the focused ultrasonic beam is formed inside the round bar steel is different. The above-described problem is solved by performing the process a plurality of times.

  The present invention is also an internal defect inspection device for round bar steel by water immersion ultrasonic flaw detection, which is opposed to the round bar steel for transmitting and receiving ultrasonic waves into the round bar steel to form a focused ultrasonic beam. A plurality of excitation elements are aligned on a substantially circumferential probe surface centered on the central axis of the round steel bar, and the probe surface and the round steel bar surface have a predetermined water distance. A round bar steel length by changing the relative position in the length direction of the round bar steel between the array probe and the round bar steel while performing the inspection of internal defects using the array probe. Means for storing the flaw detection results for each length direction, and flaw detection in the length direction, so that the position where the focused ultrasonic beam is formed inside the round steel bar is different from each other. Means for performing multiple times while changing the relative position of the direction, and That is to provide an ultrasonic flaw detector round bar steel.

  Here, the focused ultrasonic beam is formed at intervals of a beam radius or less with respect to a circumferential surface around the central axis of the round bar steel, and the length of the plurality of times is within the round bar steel. As a result of directional flaw detection, a beam can be formed at least once at any point on the circumferential surface.

  Moreover, the defect distribution about the full length of a round bar steel and a perimeter can be displayed by synthesize | combining the flaw detection result of the said multiple times of length directions.

  Further, in the synthesis of the flaw detection results, the end portions in the length direction of the round steel bar specimen can be detected in each flaw detection result, and the flaw detection results can be synthesized by aligning the positions of the end portions as a reference.

  In addition, the focusing depth of the focused ultrasonic beam inside the round bar steel can be changed.

  The present invention uses an array probe capable of flaw detection on a part of the circumference of a round bar steel (also referred to as a subject), and rotates the round bar steel and the array probe relative to each other for each flaw detection. By doing so, the entire circumference is detected, so that the entire circumference can be detected with a simple and inexpensive apparatus configuration with a small number of vibrators. Also, since the array probe is only installed at a partial angle on the circumference, maintenance such as probe replacement and adjustment is easy.

The figure which shows the outline | summary of this invention (A) cross-sectional view and (b) plan view showing the configuration of an embodiment of the present invention Figure showing the outline of the technology that also changes the focusing depth Figure showing details in the same way Explanatory diagram showing the same way of thinking Similarly, an explanatory diagram showing the operation of the signal synthesis unit The flowchart which shows the process sequence of the said embodiment. The figure which shows the outline of 1 area flaw detection data similarly Figure showing the outline of flaw detection data combination Also a schematic diagram of beam formation The top view which shows the flaw detection result by the Example Schematic diagram of beam forming in the prior art

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a conceptual diagram of the present invention. In the present invention, using the array probe 1 having a small number of transducers capable of flaw detection on a part of the circumference of the subject 30, a part of the subject 30 in the circumferential direction is flawed by one flaw detection. . Here, the beam pitch in the circumferential direction is set to be less than half of the beam thickness so that no flaw detection is lost in the flaw detection area. In FIG. 1, it is assumed that all areas are detected from the surface to the center of the subject 30, but the present invention is not limited to this, and only a certain depth area may be detected. However, if beam focusing can be performed at different depths using, for example, the method described in Patent Document 4, flaw detection can be performed with a high detection capability in a wider depth region. If a single flaw detection area is set to about 1/4 or less in the circumferential direction, the number of transducers of the array probe can be reduced due to the configuration, and the covering angle becomes small. Etc. are advantageous. There is no particular limitation on the lower limit of the flaw detection area, but it is not desirable because the number of flaw detection increases if it is too narrow. Select the number of transducers that are readily available and easy to handle even when connected to the flaw detector (eg 96), and determine the same transducer pitch from the required beam pitch determined by the size of the defect you want to detect. The flaw detection area is automatically determined.

  FIG. 2 shows a schematic diagram of an example of a device configuration used in the embodiment of the present invention. As shown in the cross-sectional view of FIG. 2A, the subject 30 and the array probe 1 are both immersed in a water tank 32 filled with water as a contact medium. There is a subject moving mechanism 34 for moving the subject 30 in the water tank 32, and the subject 30 moves linearly from the start position on the right side in the figure to the end position on the left side in the figure. Thereby, the entire length direction can be detected by the array probe 1. In FIG. 2, the subject 30 is moved, but the present invention is not limited to this, and the array probe 1 is moved or both the subject 30 and the array probe 1 are moved. Also good. The flaw detector 36 transmits and receives ultrasonic signals to and from the array probe 1 and acquires a signal from the object moving mechanism 34 to acquire the position in the length direction of the object 30.

  On the other hand, with respect to the depth direction, as schematically shown in FIG. 3, ultrasonic waves are transmitted from some or all of the ultrasonic transducers of the array probe 1 and are generated by the transmitted ultrasonic waves. The reflected wave is received using a part or all of the ultrasonic transducers of the array probe 1, and the received signal is converted into a digital waveform signal. Based on the distance between each transducer of an ultrasound transducer group composed of a plurality of ultrasound transducers selected from n and n (n ≧ 2) receiving focal points formed inside the subject 30. From the digitized received signal of each transducer, for each of the n focal points, extract a signal that contributes to the formation of the focal point, and by adding and synthesizing the signals extracted for each of the n focal points, It enables flaw detection in a wide depth range by changing the focusing depth.

  3 to 5, for the sake of simplicity, the array probes 1 are linearly arranged, but in actuality they are arranged in an arc shape.

  Here, a case will be described in which the total number of elements (ultrasonic transducers) is 96 and the number of elements in one set used to form a received focused beam is 24. In the present embodiment, 24 receiving elements are used to form one receiving beam (hereinafter referred to as a needle beam) having a small beam diameter below the arrangement, and 24 elements that can be selected from all 96 elements. An example is shown in which a receiving needle beam curtain in which receiving needle beams are closely arranged below the array probe 1 is formed by simultaneously forming a receiving needle beam below the arrangement of the element groups. In this embodiment, in order to form the receiving needle beam, each element is arranged so that the beam is focused at eight positions (n = 8) having different distances from the array probe 1 to be in focus. By extracting the signal only in the vicinity of the focal point (predetermined region centered on the beam focal point position) from the received signal, and adding and synthesizing them, the receiving by the receiving needle beam is realized. Yes.

As shown in FIG. 3 (simplified view) and FIG. 4 (overall view), in this embodiment, ultrasonic waves are transmitted from the array probe 1 and the elements 1 ₁ to 1 _{96 of the} array probe 1. to order, reception amplifier 3 ₁ to 3 for the pulser 2 ₁ to 2 _96, the elements 1 ₁ to 1 ₉₆ amplifies the ultrasonic signal received by that apply electric pulses to elements 1 ₁ to 1 _{96 96} , A / D converters 4 ₁ to 4 ₉₆ for converting the signal of the received ultrasonic wave after amplification into a digital signal, a signal for extracting only the received signal of the received beam focus from the digitized received signal Extraction units 7 _{1 to} 7 ₉₆ , waveform memories 8 ₁ to 8 ₉₆ for storing the extracted signals, and the received signals that are synthesized by adding and synthesizing the stored extracted signals and converging to one point (also referred to as a received beam focus) And an addition synthesis processing unit 9 for generating a reception synthesis signal equivalent to reception by the addition synthesis processing unit 9 By joining the al signal temporally, the signal synthesizing unit for generating an equivalent received signal and for reception by a single needle beam is formed under between the elements 1 _i and 1 _{i + 1} 10 That is, in this embodiment, each element of the array probe ₁ 1 to 1 _96, pulsers 2 ₁ to 2 _96, reception amplifier 3 ₁ to 3 _96, A / D converter 41 _{to 96,} the signal extracting section 7 _{1 to} 7 ₉₆ and waveform memories 8 ₁ to 8 ₉₆ are provided. However, pulsers 2 _{1 to} 2 ₉₆ , receiving amplifiers 3 _{1 to} 3 ₉₆ , A / D converters 4 ₁ to 4 ₉₆ , signal extraction units 7 _{1 to} 7 ₉₆ , waveform memories 8 ₁ to 8 ₉₆ , addition synthesis processing unit Of the components 9 _{1 to} 9 ₉₆ and the signal synthesizers 10 ₁ to 10 ₉₆ , illustration of components that are not used for explanation of the operation is omitted. In the following drawings, illustration of components that are not used in the description of the operation is omitted.

FIG. 5 shows the concept of receiving needle beam formation in this embodiment. Ultrasonic waves are transmitted from all the elements 1 ₁ to 1 _{96 of the} array probe 1. Ultrasonic reflected signals from the subject 30 (echoes) are received using all of the elements 1 ₁ to 1 ₉₆ of the array probe 1. Signal by ultrasonic wave reception by the elements 1 ₁ to 1 ₉₆ is amplified by the reception amplifier 3 ₁ to 3 ₉₆ shown in FIG. 3, respectively, digital by the A / D converter 41 _{to 96} Converted to a signal. After performing phase alignment of these digitized signals, addition reception synthesis can be performed to form a received focused beam as shown in FIG. In the present embodiment, attention is paid to the fact that in order to inspect the cross section of the subject 30 with high resolution, it is only necessary to extract the reflected signal from the portion indicated by the dotted circle in FIG. Specifically, from the received digital signals converted by the A / D converters 4 ₁ to 4 ₉₆ , each element 1 _i-12 to 1 _{i + 11} and the circular shape are obtained using the signal extraction units 7 _{1 to} 7 _96. What is necessary is just to extract only the signal received in the time range corresponding to the distance with an area | region, and to perform addition composition. The signal extraction unit 7 is set with extraction condition parameters based on information such as the distance between each element 1 _i-12 to 1 _{i + 11} and the circular area input from the setting unit 20 and the speed of sound in the medium. The On the one-dot chain line in FIG. 5, a plurality of regions indicated by broken-line circles are taken, and circular regions as shown in FIG. 3 are arranged without breaks (a plurality of focal lengths so that regions are arranged without breaks). F _R is set), and only signals received from the plurality of regions are extracted and added and synthesized, so that signals from only the vicinity of the one-dot chain line can be received. At this time, it can be said that the received beam formed is a needle beam localized in a narrow region corresponding to the focused beam diameter centered on the one-dot chain line.

FIG. 3 shows a simplified configuration in which one receiving needle beam localized in a thin region centered on the one-dot chain line is formed. Eight regions (indicated by solid lines) where the receiving beam is focused so that the receiving needle beam can be formed between the elements 1 _i-12 to 1 _{i + 11 of the} array probe 1 and the distances F _{RS to} F _RE (Circular area) is set. The specific operation is as follows. Ultrasonic waves are transmitted from all the elements 1 ₁ to 1 _{96 of the} array probe 1. Ultrasonic reflected signals from the object (echo) are received using all of the elements 1 ₁ to 1 ₉₆ of the array probe 1. The ultrasonic signals received by the respective elements 1 _i-12 to 1 _{i + 11} are amplified by the receiving amplifiers 3 _{i-12 to} 3 _{i + 11} , respectively, and then A / D converter 4 _i-12. ~ 4 _{i + 11} is converted to a digital signal. Since the signal extraction units 7 _{i-12 to} 7 _{i + 11} form reception beams focused at the centers of the eight regions, the signal extraction units 7 _{i-12 to} 7 _{i + 11} extract the signals received from the respective regions and perform waveform memory 8 _i−. It is sent to _{12 ~8 i + 11.} The waveform memories 8 _i-12 to 8 _{i + 11} are divided into eight areas (displayed using eight kinds of patterns in FIG. 3), and store signals received from the eight areas, respectively. It has become. The signals recorded in the waveform memories 8 _i−12 to 8 _{i + 11} are sent to the addition / synthesis processing unit 9 to be added / synthesized. In FIG. 3, the waveform memory having the same pattern is connected to the same pattern portion of the addition / combination processing unit 9 using a single line. The signal received from the same region is supplied to the addition / combination processing unit 9. It shows that it is guiding. In addition, in addition synthesis processing, the signals stored in the waveform memories 8 _i-12 to 8 _{i + 11} are weighted according to the positional relationship between the elements 1 _i-12 to 1 _{i + 11} and the focal point. May be added and synthesized. In this way, the received signals by the received beams focused on the eight regions obtained by the addition synthesis processing are sent to the signal synthesis unit 10 and combined into one received signal.

Next, the operation of the signal synthesis unit 10 will be described with reference to FIG. When each of the eight regions is displayed and identified as a region k (k = 1, 2, 3,..., 8), the signal obtained by the received beam focused on each region k is, for example, in FIG. The signal has a time width corresponding to the size of the extracted region as shown in k = 1 to k = 8. Since the distance between the array probe 1 and each region is different, signals received by the array probe 1 from each region appear at different timings. The signal synthesizer 10 adds these signals to generate one received signal. In this way, a signal received by the receiving needle beam formed between the distances F _{RS to} F _RE is obtained.

FIG. 4 shows a configuration in which a receiving needle beam curtain is formed by simultaneously arranging a receiving needle beam below the elements of the array probe 1. In this configuration, a total of 73 receiving needle beams are arranged below the elements 1 _j to 1 _{j + 1} (j = 12, 13, 14,..., 82, 83, 84) of the array probe 1. It is formed. In FIG. 4, three positions of elements 1 _i-13 to 1 _{i + 10} , elements 1 _i-12 to 1 _{i + 11} , and elements 1 _i-11 to 1 _{i + 12} are shown in order to avoid complication of the drawing. A state in which a receiving needle beam is formed under each of them is shown. The receiving needle beam formed by the elements 1 _i-13 to 1 _{i + 10} is NB _i-1 , the receiving needle beam formed by the elements 1 _i-12 to 1 _{i + 11} is NB _i , and the element 1 _i- NB _{i + 1} is a receiving needle beam formed by ₁₁ to 1 _{i + 12} . The operations of the array probe 1, the pulser 2, the receiving amplifier 3, and the A / D converter 4 are the same as those already described with reference to FIG. Since one element of the array probe 1 is used to form 24 receiving needle beams at 24 positions simultaneously, signals from a total of 24 × 8 receiving beam focal points are connected to each element. Need to be stored in the waveform memory. For this reason, the waveform memories 8 ₁ to ₈₉₆ are divided into 24 × 8 areas. The signal extraction unit 7 for sending the received signal to the waveform memory 8 extracts 24 × 8 signals from the received signal according to the distance between each element and the region where the 24 × 8 received beams are focused. It is sent to the waveform memory 8. In order to obtain, for example, a received signal from the received needle beam NB _i-1 from the received signal recorded in the waveform memory 8, the received signals recorded in the waveform memories 8 _i-13 to 8 _{i + 10} are obtained. From among the eight receiving beam focal points (focal positions) set below elements 1 _i-13 to 1 _{i + 10} (specifically, below the middle point between elements 1 _i-2 and 1 _i-1 ) A signal from a predetermined area) is sent to the addition / synthesis processing unit 9. These signals are added and synthesized in the addition and synthesis processing unit 9. The signals obtained by the received beams focused on the eight regions thus obtained are sent to the signal synthesis unit 10 and combined into one received signal. In this way, a signal received by the receiving needle beam NB _i-1 formed between the distances F _{RS to} F _RE is obtained. Signals received by other receiving needle beams can be obtained using a similar process.

  In the present embodiment, in order to avoid complication of explanation, a configuration is shown in which reception by the receiving needle beam is performed in one type of medium. Needless to say, when there are two or more types of media such as a water immersion flaw detection of a metal material, the refraction of ultrasonic waves is taken into consideration in the above-described distance calculation.

  In the present embodiment, a method of forming a receiving needle beam by setting eight receiving beam focal points under 24 elements has been described. This is an example, and any number of elements used for beam forming may be used as long as it is four or more. Also, the number of received beam focal points to be set can be freely changed according to the thickness of the subject and the required resolution and detection capability.

  Furthermore, in the present embodiment, the focal points of the received beam are set to be constant at substantially equal intervals. This is also an example, and the distances between the focal points of the received beam to be set can be set at unequal intervals. In general, the focusing range in the transmission direction of the received beam becomes larger according to the distance between the focal point and the array probe. Therefore, the distance between the received beam focal points should be determined accordingly.

The ultrasonic beam thickness d _W at the focal position is approximately expressed by the following equation.

d _W = (λ · f _OP ) / D ′ (6)
Where λ: wavelength of ultrasonic wave, f _OP : focal length of focused beam, D ′: width of grouped transducers (corresponding to element pitch × number of elements)

Accordingly, if the focal length f _OP is increased while the transducer width D ′ is kept constant, the beam thickness d _W increases, so that the transducer width D so as to obtain a desired beam diameter according to the focal length f _OP. A configuration in which 'is changed is also possible. Specifically, the number of elements used for forming the receiving needle beam may be changed according to the focal length f _OP .

  FIG. 7 shows an exemplary procedure for flaw detection in the present invention.

  First, in step 100, angle marking (see FIG. 1) is performed on the subject 30 (only when necessary). This is necessary when manually setting the angle of the subject 30, and the angle setting for each number of times of flaw detection is marked.

  Next, in step 110, the subject 30 is placed and set at the predetermined start position illustrated in FIG. 2B (including angle setting). This arrangement / setting may be manual or automatic. Automation can simplify and speed up work. On the other hand, if it is performed manually, the movement of the subject moving mechanism 34 can be only the linear movement of the subject 30 and / or the array probe 1, and the apparatus can be simplified.

  Next, in step 120, the subject 30 or / and the array probe 1 are moved to scan the entire length of the subject 30.

  Next, steps 110 and 120 are performed until flaw detection on the entire circumference of the subject 30 is completed.

  If the flaw detection data for the entire circumference can be acquired, the data are combined in step 140 (only when necessary). The data combination may be performed after the data acquisition for each angle or may be performed simultaneously with the data acquisition for each angle.

  Here, when performing flaw detection repeatedly, the flaw detection direction may be reciprocated, or flaw detection may be performed only in one direction.

  Next, an example of the data combination method in step 140 will be described in detail with reference to FIGS.

  FIG. 8 shows a planar display of one area data obtained by one scan. This display is obtained by extracting and displaying the height of the defect echo for each length position and circumferential position (angle) of the subject (determined by the transducer used by the array probe). The defect echo detection gate is set based on, for example, a surface echo. In FIG. 8, the end of the subject is detected by the presence or absence of surface echo. That is, there is no surface echo in FIG. 8A where there is no subject, and only the surface echo exists in FIG. 8B where there is no defect in the subject, and there is a defect in the subject. In (c), there are surface echoes and defect echoes.

  FIG. 9 is an outline of a method for combining data for each region. By combining the data for each region in the circumferential direction, a plan view of flaw detection data for the entire circumference can be obtained. At this time, in FIG. 9, data alignment (parallel movement + expansion / contraction) is performed with reference to the subject end. Thereby, even if there is a deviation in the position in the length direction for each region, the data can be correctly combined. Therefore, even if there is a deviation in the subject scan start position in FIG. 2, the data can be correctly combined. .

  Note that the data combination in step 140 is not essential and may be evaluated separately for each area data. Also, in the length direction, the entire length may not be detected depending on the application.

  FIG. 10 shows a schematic diagram of beam forming in one embodiment of the present invention. FIG. 11 shows flaw detection results for the full length and half circumference of the subject acquired by the above example.

  The array probe used in this example has a frequency of 50 MHz, φ58 mm, 0.29 mm pitch, and 96 transducers. Using the method shown in FIGS. 3 to 6, 65 reception beams from 32 transducers are formed toward the center of the subject. The beam pitch is expressed as an angle of 0.57 °, and the circumferential flaw detection area in one flaw detection is 37.2 °. The object is a round bar steel test piece of φ32 mm × 1000 mm, and a plurality of flat bottom hole artificial defects of φ0.3 mm, φ0.5 mm, and φ1.0 mm are produced.

  In this embodiment, the circumferential direction is divided into 10 parts as in FIG. 1, flaw detection is performed for each region, and the results are combined. The pitch of the combined data is 0.062 mm in the length direction and 0.57 ° in the circumferential direction, and the number of data points is 16501 points in the length direction (including outside the end of the subject) × 650 points in the circumferential direction (circumference) Direction region 37.2 °> includes overlap by 36 °).

  The gate was set to a depth of 2 mm (excluding the surface dead zone) to 16 mm from the surface. In this case, the circumferential data pitch at a depth of 2 mm is 0.14 mm.

  In FIG. 11, the reason why some defect instructions spread in the circumferential direction is that the artificial defect is close to the center and is detected at any angle. The reason why the circumferential flaw detection is set to a half circle is to avoid reflection from the side surface of the artificial defect formed from the opposite side with a drill.

  FIG. 12 shows a schematic diagram of beam forming according to the prior art. Since it is necessary to arrange vibrators on the entire circumference in the prior art, 632 vibrations (= 360 ° ÷ 0.57 °) are required in the case of an all-around array in order to perform flaw detection with the same beam pitch as in this embodiment. In the staggered arrangement described in Patent Document 1, 960 (= 96 × 10) vibrators are required. As the number of transducers increases, the number of wiring, transmission / reception devices, signal conversion devices (A / D conversion, etc.) for each transducer also increases proportionately, so that the device configuration becomes very complicated and expensive in conventional flaw detection. .

1 ... Array probe 30 ... Subject (round bar steel)
32 ... Water tank 34 ... Subject movement mechanism 36 ... Flaw detection apparatus

Claims (10)

An internal defect inspection method for round steel bars by water immersion ultrasonic inspection,
A plurality of excitation elements are arranged on a substantially circumferential probe surface facing the round bar steel and centered on the central axis of the round bar steel, and the probe surface and the surface of the round bar steel have a predetermined surface. Using an array probe arranged to have a water distance,
Sending and receiving ultrasonic waves from the array probe to the inside of the round bar steel to form a focused ultrasonic beam,
While performing the inspection of internal defects, the relative position of the array bar and the round bar steel in the length direction of the round bar steel is changed, and the results of the flaw detection in the length direction of the round bar steel are stored.
The length direction flaw detection is performed a plurality of times while changing the relative positions of the array probe and the round bar steel in the circumferential direction so that the positions at which the focused ultrasonic beam is formed inside the round bar steel are different from each other. An ultrasonic flaw detection method for round steel bars. The focused ultrasonic beam is formed inside the round bar steel at intervals equal to or less than the beam radius with respect to the circumferential surface centered on the central axis of the round bar steel, and
2. The ultrasonic inspection of a round bar steel according to claim 1, wherein a beam is formed at least once at any point on the circumferential surface as a result of the plurality of lengthwise inspections. Method.   3. The ultrasonic inspection method for round bar steel according to claim 2, wherein the defect distribution for the entire length and the entire circumference of the round bar steel is displayed by synthesizing the plurality of lengthwise flaw detection results.   4. In the synthesis of the flaw detection results, an end portion in the length direction of the round bar steel specimen is detected in each flaw detection result, and the alignment is performed with the position of the end portion aligned as a reference. The ultrasonic flaw detection method of the described round bar steel.   5. The ultrasonic inspection method for round bar steel according to claim 2, wherein a focal depth of the focused ultrasonic beam inside the round bar steel is changed. An internal defect inspection device for round steel bar by water immersion ultrasonic inspection,
A plurality of probe surfaces having a substantially circumferential surface centered on the central axis of the round bar steel and facing the round bar steel for transmitting and receiving ultrasonic waves into the round bar steel to form a focused ultrasonic beam. An array probe in which excitation elements are aligned, and the probe surface and the surface of the round bar steel are arranged to have a predetermined water distance;
While detecting internal defects using the array probe, the relative position of the array probe and the round bar steel in the round bar steel length direction is changed to store the flaw detection results for each round bar steel length direction. Means,
Means for performing the lengthwise flaw detection a plurality of times while changing the relative position in the circumferential direction of the array probe and the round bar steel so that the positions where the focused ultrasonic beam is formed inside the round bar steel are different from each other. When,
A round bar steel ultrasonic flaw detector characterized by comprising: The focused ultrasonic beam is formed inside the round bar steel at intervals equal to or less than the beam radius with respect to the circumferential surface centered on the central axis of the round bar steel, and
The ultrasonic inspection of a round bar steel according to claim 6, wherein a beam is formed at least once at any point on the circumferential surface as a result of the plurality of inspections in the length direction. apparatus.   8. The ultrasonic inspection apparatus for round bar steel according to claim 7, wherein the defect distribution about the entire length and the entire circumference of the round bar steel is displayed by synthesizing the plurality of flaw detection results in the length direction.   9. In the synthesis of the flaw detection results, an end portion in the length direction of the round steel bar specimen is detected in each flaw detection result, and is synthesized by aligning with the position of the end portion as a reference. An ultrasonic flaw detector for the described round bar steel.   The ultrasonic flaw detector for a round bar steel according to any one of claims 7 to 9, further comprising means for changing a focusing depth of the focused ultrasonic beam inside the round bar steel.