JPS62261058A - Ultrasonic flaw detector for bolt - Google Patents

Abstract

PURPOSE:To detect a crack with a high reliability and a high accuracy as generated in a clamp bolt of a nuclear pressure cylinder or the like, by inserting a pair of angle beam probes and a vertical probe into an insertion hole for a heating wire of the bolt filled with a coupling liquid. CONSTITUTION:A feed rod 11 which is inserted into an insertion hole 4 for a heating wire for shrinkage fitting of a bolt 2 and supported with a stationary support 12 is rotated and moved up and down with a driver. A ultrasonic probe comprising a vertical probe 50 and pairs of angle beam probes 45, 46, 47 and 48 is provided on the axis of the feed rod 11 to transmit or receive an ultrasonic wave. Ultrasonic waves oscillated by the probes 45-48 and 50 are made incident into the bolt 2 through a coupling liquid circulated into the insertion hole 4. Circumferential thickness of the bolt is measured with the vertical probe 50 while a thread and a crack are detected with the angle beam probes 45-48. The flaw detection data are sent to a signal processor 59 together with detection data from a angle of rotation detector 18 and a feed detector 43 to process and then, displayed on a CRT 71 of an ultrasonic flaw detector 58.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a heating wire for sintering used for tightening a reactor pressure vessel or a steam turbine casing of a nuclear power plant, for example. The present invention relates to an ultrasonic flaw detection device for detecting cracks in a bolt having an insertion hole.

(Prior art) Generally, nuclear reactors, steam turbine casings, etc., which contain high-temperature, high-pressure steam inside, are divided into upper and lower parts on a horizontal plane to facilitate inspection, etc., and flanone are fastened with bolts.

Because tightening this type of bolt requires a very large torque, a hole is drilled along the center axis of the bolt, and a heating wire for tightening is inserted into the hole, causing the bolt to thermally expand. The method used is to apply a strong tensile force to the nut during cooling.

In a steam turbine, the casing is thermally deformed due to thermal expansion and contraction during startup and shutdown (1), so bolts must be tightened (J).
The +j force decreases, and the bolt is repeatedly subjected to thermal fatigue a considerable number of times during use of the steam turbine.As a result, deterioration phenomena occur in the material slope.

Thermal power plants that have been operated as a continuous operation (1), or weekly power plants) have been converted to intermittent operation, with frequent startups and stops in response to fluctuations in demand. There is. The bolts that fasten the steam turbine casings of such thermal power plants are subject to thermal fatigue to an extent that is incomparable to conventional bolts, and there is concern that fatigue cracking may occur.

In a steam turbine, once a bolt cracks or is threaded through, problems such as steam leakage may occur, sometimes leading to the shutdown of the power plant. In order to ensure the stable operation of power generation plants, there is increasing interest in bolt cracking, which can occur over time.

Conventionally, cracks that occur on the end face of such bolts or from the insertion hole of the heating wire for sintering have been detected using ultrasonic waves (for example, FPRI (American Electrode Research Institute), Non
destructive Evalua mouth OnProg
ram: 1984. Nov, (MP-3821
-3R), RP2179-2 (Revo-1-Number 2
179-2)).

This type of ultrasonic flaw detection device is shown in Figs. 14 and 15, in which 7 flanges 1, 1 at the joint of the turbine casing, which is divided into upper and lower parts on the horizontal plane, are fastened with bolts 2 and nuts 3. The bolt 2 is provided with an insertion hole 4 for the heating wire along its central axis. Figure 14 shows bolt 2
The vertical probe r-5 is fixed to the end face of the 15th
The figure shows an angle probe 6 fixed in the insertion hole 4.

(Problems to be Solved by the Invention) By the way, most of the Njl cracks that occur in this type of bolt 2 originate from the bottom of the thread.

To deal with this crack in the bolt 2, as shown in Fig. 14, the method of fixing the vertical probe 5 to the end face of the bolt 2 to detect the crack 2b is to Since the distance becomes long (a good one is about 1 TrL or more), the energy of the ultrasonic wave manually applied to the vertical probe 5 decreases, and the ability to detect cracks decreases.

Also, υ1 is 0 to 20° with respect to the cross section of bolt 2! Most of the cracks progress at an angle θ of σ, and due to the spread of ultrasonic waves in the vertical i+) probe 5, small < The drawback was that it was difficult to detect.

Generally, about 80 cm F)! With 2 bolts of degree length,
The depth dl of the detectable crack 2b is approximately 1 cIRPi! degree.

On the other hand, in the method of detecting cracks 2b by fixing an angle probe 6 to the inner surface of the insertion hole 4 of the heating wire for baking as shown in FIG. 15, ultrasonic waves are emitted from the inner surface of the insertion hole 4. The cross section of the bolt 2 is tilted at an angle α of approximately /15″ to 75° to allow propagation.

The angle probe 6 has better detection accuracy than the vertical probe 5, and the depth d2 of a crack that can be detected in a bolt 2 having a length of about 80 era is about 2.5a++ to 1 cm.

However, flaw detection through the insertion hole 4 of the heating wire for sintering has the disadvantage that it is difficult to bring the bevel probe 6 into complete contact with the inner surface of the hole, and cracks cannot be detected stably.

In addition, Fig. 16 shows a cathode ray tube waveform of an ultrasonic flaw detector, and in the conventional type, when noise n is generated due to the shape of the threaded part of the bolt 2, echoes e from minute cracks are generated.
The disadvantage was that it became impossible to identify the

This drawback was an obstacle to detecting small cracks at the To provide an ultrasonic flaw detection device for bolts that can detect cracks that occur in bolts when tightening valve casings, etc. with high reliability and accuracy, and that can detect insertion holes for heating wires for sintering. be.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the fourth object, the present invention provides a feed rod that is inserted into an insertion hole for a heating wire for sintering of a bolt and supported by a fixed support, and a feed rod that is supported by a fixed support. a drive device for rotating and moving the rod up and down, a rotation angle detector for detecting the amount of rotated angle, a feed amount detector for detecting the L'F movement td, and a drive device for rotating and moving the rod up and down; an ultrasonic probe consisting of a vertical probe J3 and an oblique probe disposed in and transmitting and receiving ultrasonic waves; a coupling liquid supply device for circulating a coupling liquid in the insertion hole; The present invention is characterized by comprising a signal processing device that displays an image of the detection result of the bolt crack position based on the signals from both detectors and the probe r.

(for production) The present invention will be described in detail based on the above configuration.

When the drive device is driven, the feed rod rotates and moves up and down in the bolt insertion hole. During this time, an ultrasonic probe fixed on the shaft of the feed rod receives electrical signals and converts them into mechanical imaging to oscillate ultrasonic waves. The ultrasonic waves propagate through the thick wall of the bolt, are reflected by the bolt's outer periphery, threads, and cracks, and return to the ultrasonic probe, where they are converted into electrical signals. The wall thickness of the bolt in the circumferential direction is measured by the vertical probe f, and threads and cracks are detected by a pair of bevel probes. These data are sent to a signal processing device which is also fed data from the rotation angle and feed ri) detectors. The signal processing device displays the location of the bolt crack on an image based on both data. At this time, a coupling liquid is constantly supplied into the insertion hole, and this coupling liquid ensures stable propagation of the ultrasonic waves.

(Example) The following is an ultrasonic detector for bolts according to the present invention.
Il! An example will be explained with reference to the drawings.

In FIG. 1, reference numeral 1 designates a flange at the joint of a single bottle casing that is divided into upper and lower parts on a horizontal plane, and both flanges 1, 1 are fastened together with bolts 2 and nuts 3. Bolt 2 is a heating wire for hardening (not shown)
It has an insertion hole, and a fixed support 12 is attached to the top.

FIG. 2 is an enlarged view of the mounting portion of the fixed support 12, in which a hollow fixed support 12 G, i, 1: A packing 13 is interposed on the joint surface with the top of the bolt 2, and the hole is inserted into the insertion hole. 4 is screwed into C.

A holder 15 having an n through hole 13 is attached to the same end of the fixed support 12, and a rotating sweater 17 is attached to this holder 15.
and a rotation angle detector 18 are attached. The upper end of the holder 15 includes a thrust bearing 20 and a stop ring 2.
A rotatable rotor 24 is fitted through the rotor 1, and a gear 25 is fixed to the lower end of the rotor 24. This l
! The a-wheel 25 has gears 227 fixed to respective rotation shafts of the rotary motor 17 and the rotation angle detector 18.
are interlocked.

Further, a through hole 29 is bored in the center of the rotating body 24, and several recesses 30 are carved in the hole wall of the n through hole 29 in the axial direction. Several protrusions 32 that engage with the recesses 30 of the through hole 29 are formed along the longitudinal direction on the outer periphery of the feed rod 11 that passes through the rotating body 24, the holder 15, and the fixed support 12, Furthermore, rack-shaped teeth fM35 are carved along the longitudinal direction on a part of the outer periphery. Also, this tooth fl+! A gear 36 meshed with the rotor 35 is fixed to a rotating shaft of a feed motor 38 fixed to the upper end surface of the rotating body 2/I. Note that the reference numeral 43 is a feed through detection fixture fixed to the upper end surface of the holder 15 for detecting the amount of movement of the feed rod 11.

-7j s 40 is a pair fixed to the holder 15.

A movable arm 41 that can be moved upwardly along the guide rod 40.40 is fixed to the end of the feed rod 11.
has been done.

Therefore, when the rotary motor 17 is driven to rotate, the gear 2
The rotary body 24 rotates via 6.25, and accordingly, the feed rod 11 also rotates integrally via the uneven portions 30.32. At this time, the rotation angle detection 318 detects the angle. -h, when the feed motor 38 is driven to rotate, the feed rod 11 moves up and down via the tooth grooves 35 and gears 36. On this occasion,
The amount of movement is detected by the feed amount detector 43.

- An angle probe 45, 46, 47° 48 is arranged at the tip of the horn and feed rod 11, as shown in FIG.
．． These angle probes 45. /16 and /1
7.48 are arranged symmetrically and vertically shifted by 1/2 pitch of the bolt 2, respectively. In addition, the angle probe 4
A contact type vertical probe 50 is arranged between 5.46Jj and 47, 48, and plate bones 51, 51. 51
is attached (Fig. 3(b)). This leaf spring 51
, 51° 51 G, act to bring the vertical probe 50 into close contact with the hole wall surface of the insertion hole 4.

Furthermore, supports 52.52, 52.degree. 52 are attached to the lowermost end of the member on which the angle probes 47.48 are disposed (FIG. 3(b)). This supporter 52, 52.52
．． 52 acts to stabilize the rotation of the feed rod 11 in the insertion hole 4.

Note that the angle probes 47a and 48a are shown in FIGS. 4(a) and 4(b).
As shown in FIG. 3, it may be arranged only on the C side of the vertical probe 50a.

The electrical system is as shown in Figure 1.
control device 55, control device 56, coupling liquid supply 111
Control device 57, ultrasonic flaw detector 58, signal processing device U59,
It is composed of an electrolyte stagnation section 60.

The drive control device 55 is connected to the rotary rotor 17, the rotation angle detector 18, the feed motor 38, and the feed amount detector 43 via a cord 61.

The detection values of the rotation angle detector 18 and the feed rate detector 43 are sent to the control device 56, and the control device 56 sends a signal to drive the rotary motor 17 and the feed rate sensor 338 based on the above-mentioned value. It is sent to the drive control wJ% device 55.

The coupling liquid supply control device 57 is connected to the fixed support 12 and the lower end of the bolt 2 via supply lines 63.1 and outlet lines 64, respectively. The coupling liquid flows into the fixed support 12 through the supply pipe 63, fills the insertion hole 4 of the bolt 2, and returns to the coupling liquid supply a-control device 257 via the discharge pipe 64. circulate within the system. (Thus, the coupling liquid filling the insertion hole 4 acts to stably propagate the ultrasonic waves.

The ultra-high wave flaw detector 58 includes bevel probes 45, 46, . /1.7.48 and the manual probe 50 via: 1-drawer 5, respectively.

Receiving the signal from the ultra-7゛1-wave flaw detector 58, the vertical probe 50 detects the reflected wave from the outer circumferential surface of the bolt 2 via the ultra-8 wave at right angles to the wall. Uke 1] Part 1
The Δni is again sent to the super r'i wave deep wound device 58. This super high quality search 11+! : My 58th A, 'J issue, angle probe 4
5゜46.47.48 propagates ultrasonic waves at an angle of 45' to 75° (refraction angle β) with respect to the cross section of bolt 2, receives reflected waves from threads and cracks, and transmits the signal again. It is sent to the sonic flaw detector 58. The signals from the vertical probe 50 and the oblique probes 4546, 47, and 48 sent to the ultrasonic flaw detector 58 are further sent to the signal processing bag ff159.

Next, the operation of the ultrasonic flaw detection apparatus of the present invention configured as described above will be explained.

The feed rod 11 is rotated or moved up and down in the insertion hole 4 by the rotary motor 17 and the feed motor 38 as described above. A rotation angle detector 18 detects the amount of rotation angle and the amount of vertical movement.
It is detected by the feed amount detector 43, and the rotary motor 17 and the feed L-axis 38 are feedback-controlled based on this detected value.

Each probe 45, 46, 4748a3 at the tip of the feed rod 11
and 50 move through the insertion hole 4 of the heating wire for baking by repeating spiral rotation and vertical movement. During this time, vertical probe 5
0, ultrasonic flaw detector 5 for angle probe 45.447.48
A signal is sent from 8, and each oscillates an ultrasonic wave to the bolt 5. Signals reflected from the outer peripheral surface, threaded portion, and cracks of the bolt 2 are transmitted to each probe 45, 46. /17.48 OJ:bi501
' Received BAM wave flaw detector 58
9. Sent to.

The ultrasonic waves emitted from the center of gravity probe 50 are transmitted to the ultrasonic flaw detector 5
As shown in FIGS. 5(a) and 5(b), the ultra-8 wave reflected by the outer peripheral surface of the bolt 2 is displayed on the cathode ray tube 7o of No. 8 as an oscillation wave s1, and is displayed as waveforms 81 and B2. The distance between each waveform on the cathode ray tube 7o @, 0 is the thickness of the tightening bolt 5.

The ultrasonic wave emitted from the angle probe/17.48 is reflected by the threaded portion 2a and crack 2b of the bolt 2, and is transmitted to the cathode ray tube 71 of the ultrasonic flaw detector 58 as shown in Fig. 6 (aHb).
As shown in , the screw 8 which is 1q with the angle probe 47
11'; 2B signal n1 and angle probe 48
The signal n2 of the threaded portion 2a and the signal n3 of the crack 2b are displayed.

A signal from the vertical probe 50 is sent to a signal processing Jlp device 59 via an ultrasonic flaw detector 58, and the thickness WIJ) of the bolt 2 is calculated here. The rotational angle standard and vertical movement field of the feed rod 11 from the drive control device 55 are also input here, and the predetermined rotational angle ri of the bolt 2 and the wall thickness j at the vertical position are grasped.

On the other hand, a signal from the angle probe/17.48 is further input to the signal processing device 59 via the ultrasonic flaw detector 58. As shown in FIGS. 7(a) and 7(b), since the thickness 1 of the bolt 2 differs depending on the position in the circumferential direction, each bevel probe 47
．． The distance that the ultrasonic waves emitted from 48 travel within the bolt 2 is different.

In this case, the signal processing device? Reference numeral 1259 indicates that the rotational varus position of one bevel probe 47 is used as a reference, and the other bevel probe 4
8, the propagation distance of the ultrasonic signal n5 is determined by the wall thickness difference Δj of the bolt 2.
A correction Δ is applied correspondingly. After equalizing the propagation distances of the ultrasonic signals n and n from the angle probes 47 and 48, the five signal processing devices Signal rl 5 is inverted to form a signal n6, and this signal n6 and the signal n4 from the angle probe 47 are superimposed.

As a result, as shown in FIG. 8(b), the noise generated from the thread shape due to the thread shape is canceled out, and only the signal "17" indicating the presence of even a minute crack can be clearly identified. Ultrasonic signal n7 processed by
The crack position ff1n9 indicated by is shown on the cathode ray tube 1□ control equipment 56 together with the cross section ji]Il of the bolt 2 (FIG. 9).

FIG. 10 shows a block diagram of data processing in the 4ij;-i processing device 59. Each probe 47°4
8. Ultrasonic flaw detection from 50: The signal from the direct probe 50 is sent to 558, and the signal from the direct probe 50 is sent to the signal processor Fi + equipment J 9
is sent to the first beam path δ1 side circuit 78, where:
Pol! The wall thickness 1 of ~2 is measured. The signals from the angle probe 47 and Jζ and /18 are further sent to the arithmetic circuit 79, and here the signal is determined due to the circumferential wall thickness △l of the bolt 2. Be Gl. +in 'p'
2. The results are directly sent to the control circuit 81 via the memory 8o. In this synchronization control circuit 81, the ultrasonic propagation distance of one of the bevel probes 47 is set to the M standard, and the ultrasonic propagation distance of the other bevel probe 48 is corrected to an equal propagation distance ΔL. These two signals are sent to the waveform synthesis circuit 82, where the polarity of one signal is reversed, and then the two signals are combined. The superimposed signals are sent to the gate circuit 84, where the range from which the ultrasonic signal should be extracted is selected and displayed on the display 85. Thereby, the presence or absence of cracks in the bolt 2 can be visually observed as an electric signal waveform. The adjusted signals are further sent to a peak amplitude measurement circuit 86 and a second beam path measurement circuit 87, where the amplitude value and beam path length of the signal waveform within the range selected by the gate circuit 84 are measured four times. This measured value is sent to input data memory 88 and stored. Note that the input data memory 88 contains the angle probe 47°4 from the control device 56.
The position of 8 is also memorized. These amplitude values, beam path lengths, and angle probe position data are stored in the input data menu.
The data is sent from the processor 88 to the arithmetic processing section 89 . In addition, here, the shape of the bolt 2 is obtained from the control 12 II device 56, and the oscillation varus of the ultra-8 waves taken from the angle probes 47 and 48 is shown.
Evening is being sent.

The arithmetic processing unit 89 outputs 91 longitudinal cross-section and transverse positions of the crack in the bolt 2 based on both of the above data, and these are determined by the υ control device? 256 on the display 9o.

All of the above series of signal processing is carried out in accordance with commands from the A-1M microcomputer 91 built into the controller 211 r56.

Furthermore, the signal processing device of this embodiment? ? 59 is super 8 wave detection [:
As shown in FIG. After converting the ultrasonic signal into AC waveforms 100 and 101 and making the beam path lengths equal ((a)' in the same figure), we convert the AC waveform 100 of -force into an AC waveform 102 whose phase is shifted by half a wavelength, and the other AC waveform 102. The AC waveform 101 of FIG.
)).

FIG. 12 shows another embodiment of the bolt ultrasonic flaw detection device according to the present invention. According to this embodiment, the angle probes 110 and 111 fixed to the tip of the feed bar 11 are The bolts 2 are arranged vertically shifted from each other by one bit in the axial direction.

As a result, when the change φ in the circumferential direction of the wall thickness 1 of the bolt 2 is small, the bevel probes 110 and 111 are sent vertically while always sending ultrasonic waves to a fixed position on the screw thread.
The waveform of the ultrasonic signal from the threaded portion 2a displayed on the cathode ray tube 71 of the ultrasonic flaw detector 58 is always constant, and as the angle probe 110° 111 is moved and suspended, the crack 2b that appears temporarily is detected. The signal waveform shown can be easily identified. Furthermore, this signal waveform is processed by a signal processing device 59 to determine the reflection position of the signal waveform, and the reflection position is displayed on the vertical and horizontal cross-section views of the bolt 2 displayed as images on the cathode ray tube of the control device 56. . To this J: So, crack in bolt 2 2b
can be more easily identified.

FIG. 13 shows an embodiment in which the present invention is applied to a bolt hole in a steam turbine casing. According to this example,
At the tip of the feed rod 11, there is a support 115 for holding the tip and an oblique probe 116 directed upward and downward.
, and an oblique probe 117 are fixed to each. An electric signal sent from the ultrasonic flaw detector 58 causes the angle probe 11 to
6. When an ultrasonic wave is emitted from each of the oblique probes 117, the ultrasonic wave is obliquely propagated to the mother vJ 120 via the coupling liquid filled in the bolt hole 118. While the feed rod 11 rotates and is sent toward the person, the ultrasonic waves propagated to the base material 120 are transmitted to the base material 8 around the hole I.
The crack 121 that has occurred at
116, and the electric signal A:; was detected by ultrasonic flaw detector 5.
Sent to 8th. As a result, a signal waveform indicating the presence of the crack 121 is displayed, and it is possible to detect υ1 distortion occurring in the bolt hole with a high positional viscosity.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a pair of bevel probes and a vertical probe arranged vertically are connected to a heating wire insertion hole of a bolt filled with a coupling liquid. While rotating or moving it up and down, the signals detected by both probes are sent to the signal processing nail. Since they are arranged to cancel each other out, only the signals from the cracks are displayed clearly in the image, and even minute cracks can be detected efficiently and with high reliability.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG. 2 is a schematic diagram showing an embodiment of the present invention.
Figure 3 (aHb) and Figure 4 (a) and (b) are schematic diagrams of the ultrasonic probe, Figure 5 (a) and (b) are the bolts. Explanatory diagram of wall thickness measurement, No. 6
Figure (aHb) is an explanatory diagram of the ultrasonic wave signal obtained with the angle probe, Figure 7 (aHb) is an illustration of the beam path correction of the ultrasound signal from the angle probe, Figure 8 ( aHb)1. An explanatory diagram of the small adjustment of the L ultrasonic signal, Fig. 9 is an explanatory diagram of the image display of the crack position d of a bolt, and Fig. 10 is an explanatory diagram of the signal processing yJ! A block diagram of the device, FIGS. 11(a), 11(b), and 11(c) are explanatory diagrams showing other embodiments of the signal processing method, and FIG. 12 is a schematic diagram showing another embodiment of the present invention. Fig. 13 is a schematic diagram showing another embodiment of the present invention, Fig. 14 is a schematic diagram of a conventional flaw detection device, Fig. 15 is a schematic diagram showing a conventional flaw detection device, and Fig. 16 is a schematic diagram of a conventional flaw detection device. FIG. 3 is an explanatory diagram of a super-wave signal r7 generated by the device. 2...Bolt. 4... Insertion hole, 12... Fixed support body, 17... Rotating motor, 18... Rotation angle r detector, 2/1... Rotating body, 38... Feed motor, 43
...Feed amount detection 27, 5 :)・=! j! !
1JIaJI Go) ξ position, 5 6-a, lI II
! location, 57... coupling liquid supply device, 58
...1 piece of ultrasonic wave, 5 pieces...<+:'Fj FP
Neck attachment, 6 devices...denryobu. $ l Fig. $ 2nd Fig. 3 $ 4 Fig. Q Fig. l pu (If bite 6 Fig. (a) (B) E 7 Fig. ta) (1) Drainage 6 Fig. 72L? Fig. 9 Fig. io < C) Figure ff Figure 11 Figure 11 Figure A 14 Figure $15

Claims (1)

[Claims] 1. A feed rod inserted into an insertion hole for a heating wire for sintering a bolt and supported by a fixed support, a drive device for rotating and moving the feed rod up and down, and a rotating a rotation angle detector for detecting the amount of angle moved; a feed amount detector for detecting the amount of vertical movement; a vertical probe disposed on the axis of the feed rod for transmitting and receiving ultrasonic waves; and a pair of oblique probes. An ultrasonic probe consisting of a square probe, a coupling liquid supply device for circulating coupling liquid into the insertion hole, and a bolt detection system based on signals from both detectors and probes. An ultrasonic flaw detection device for bolts, comprising: a signal processing device that displays an image of detection results of crack positions. 2. The drive device includes a rotating body in which the feed rod is relatively movable in the axial direction and is integrally and rotatably fitted together, a rotary motor that rotationally drives the rotating body, and the feed rod. 2. The bolt ultrasonic flaw detection apparatus according to claim 1, further comprising a feed motor for moving the bolt in the axial direction. 3. Connect the coupling liquid supply device to the fixed support and the lower end of the bolt insertion hole through a supply pipe and a discharge pipe, respectively, and supply the coupling liquid to the inside of the supply pipe and the fixed support. Claim 1, characterized in that the coupling liquid is circulated through a series of systems returning to the coupling liquid supply device through the bolt insertion hole and the discharge pipe.
Ultrasonic flaw detection equipment for bolts as described in Section 1. 4. The ultrasonic probe transmits and receives ultrasonic waves in the radial direction of the bolt, and the vertical probe is arranged to be shifted from each other by 1/2 pitch of the bolt in the axial direction, and transmits and receives ultrasonic waves in an oblique direction. 2. The bolt ultrasonic flaw detection device according to claim 1, comprising a pair of bevel probes. 5. The ultrasonic probe includes a vertical probe that transmits and receives ultrasonic waves in the radial direction of the bolt, and a pair of vertical probes that transmit and receive ultrasonic waves in an oblique direction that are arranged one pitch apart from each other in the axial direction of the bolt. 2. The bolt ultrasonic flaw detection device according to claim 1, comprising: an oblique angle probe; 6. The signal processing device corrects the difference in arrival time of the ultrasonic waves transmitted and received by the pair of bevel probes due to a change in the wall thickness of the bolt, and inverts the polarity of one received signal. The bolt ultrasonic flaw detection device according to claim 1, having a function of superimposing one received signal on the other received signal.