JPH0687052B2 - Ultrasonic testing equipment for steel plate - Google Patents

Description

The present invention relates to an ultrasonic flaw detector for steel sheets.

[Conventional technology]

In the conventional automatic ultrasonic flaw detection of steel sheets, a large number of flaw detection heads are arranged in two rows in a staggered pattern at a pitch equal to the effective flaw detection width over the entire area of the central flaw detection area of the steel sheet with the maximum width. A method of performing full-scale flaw detection with one passage regardless of the width of the flaw-detected steel plate (Japanese Patent Publication No. 59-39702), or disposing a large number of flaw detection heads at a pitch twice the effective flaw detection width. ,
A method (Japanese Patent Publication No. 59-39701) in which the entire surface is inspected by passing the plate several times regardless of the width of the steel plate to be inspected is implemented.

[Problems to be Solved by the Invention]

The former is ideal only for flaw detection, but considering the plate width distribution of thick steel plates, the flaw detection head is placed even in the plate width part that is rarely used, so initial investment and running cost (maintenance cost) There is a problem that it becomes a lot.

On the other hand, the latter is a method that emphasizes initial investment and running cost, but has the drawback of lower processing capacity than the former method because it requires several reciprocating passages for flaw detection on a single steel plate. have.

The present invention has a low initial investment and running cost, and
It is an object of the present invention to provide a steel plate ultrasonic flaw detector having sufficient flaw detection processing capability.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a single support [2 ₁ , 2 _{2 which} can move independently at a predetermined position of a steel sheet passing line [L] along its width direction. ]; located behind of the support, over the entire width direction and elongated support which is movable in the width direction [3 _1]; staggered plurality of ultrasonic probes the [S] in the steel plate width direction The flaw detection head [U], which is provided on one of the supports [2 ₂ ] for flaw detection on one side edge in the width direction of the steel plate [Ue ₂ ], and the other of the supports [2 ₂ ] , A flaw detection head [Ue ₂ ] for flaw detection on the other side edge of the steel sheet in the width direction, a flaw detection head [Uft] for flaw detection on the front and rear edges, and on the long support [3 ₁ ] When the area corresponding to the central part inside by a predetermined distance [We] from both side edges in the width direction of the steel sheet to be passed is defined as the central flaw detection area, [3 _1]
Over the entire central flaw detection area (hereinafter referred to as maximum flaw detection area) [Wi] corresponding to the maximum width [W] of the steel sheet to be passed, at a pitch [2P] twice the effective flaw detection width of the flaw detection head. A plurality of arrayed flaw detection heads [Uc] for flaw detection in the widthwise center of the steel plate; ultrasonic waves are transmitted to and received from the ultrasonic probe of each flaw detection head, and the received signal is the internal defect signal of the steel plate. flaw detector for converting into; equipped with its rectangular steel plate plane (1) an apparatus for ultrasonic flaw detection while running through the plate, the long support [3 _1] on, at less than the maximum flaw area [Wi] In the central flaw detection area (hereinafter referred to as the most flaw detection area) corresponding to the maximum width of the steel sheet to be passed, which is in the range of 1/2 or more,
Parallel to the flaw detection head (Uc) for flaw detection in the central portion in the width direction,
And wherein arranged in relation to the staggered arrangement at a pitch (P), flaw detection head [Uo] for flaw detection in the width direction central portion of the steel plate of the largest width; the long support [3 _1] on the The number of flaw detectors (5 _{1 to} 5n, 5o _{1 to} 5on) equal to the number of ultrasonic probes of the flaw detection head [Uc, Uo] included in the most flaw detection area; Depending on the width of the region, the flaw detector (5 _{1 to} 5n, 5o _{1 to} 5on) and the ultrasonic probe (Sc, Uo) of the flaw detection head (Uc, Uo) on the long support (3 ₁ ) The flaw detection control device 4 for selecting [So] is provided.

The symbols shown in brackets [] correspond to the symbols in the drawings described below.

[Action]

The ultrasonic flaw detector of the present invention first performs the steel plate tip edge flaw detection with the front and rear edge edge flaw detection head Uft as shown in FIGS. 1 and 2, and, for example, flaw detection of the central portion of the steel sheet measured at that time. Depending on Wn, the flaw detection heads for both sides of the steel sheet in the width direction are placed on both sides of the steel sheet in the width direction to perform flaw detection. , Wn are (1) Wn ≦ W ₁ , the probe of the flaw detection head for flaw detection in the central portion is arranged in two rows l ₁ and l ₂ in a zigzag pattern at the pitch P in the most flaw detection area W ₁ . Also, of the flaw detectors, the probe (Nn ≧ Wn / P) required for performing the flaw detection on the entire surface of the flaw detection required width Wn of the steel sheet central portion in one pass is selected and selected. Nn
Using Nn flaw detectors, which are connected to each probe in a one-to-one and switchable manner, the whole area of the required flaw width Wn in the central portion of the steel plate is flaw-detected by the first passage.

(2) Wn> In the case of W _1, l ₁ arranged in two rows on the most flaw detection range W ₁
Of the probes Sc of the flaw detection head Uc arranged in the flaw detection area W ₂ on the row and the flaw detector heads and the flaw detectors corresponding to the center flaw detection width Wn of the central portion of the flaw detection steel plate and this The flaw detector for the probe is selected from the flaw detectors 5o _{1 to} 5on for the l ₂ row probe, and 50% of the required flaw width Wn of the central portion is set to 2 by the first passing plate.
When times th strip passing is a long support 3 ₁ equipped with ultrasonic probe by passing plate after shifting stroke P to flaw detection of 50% of the remaining.

As a result, when the maximum flaw detection area W ₁ is 1/2 of the maximum flaw detection area Wi, the number of flaw detectors, which is 2/3 of the total number of the flaw detection probes Sc and So for flaw detection in the central portion of the steel, can be set.

〔Example〕

Examples will be described below with reference to FIGS. 1 to 4.

First, the overall configuration of the ultrasonic flaw detector will be described. This ultrasonic flaw detector comprises a pair of supports 2 ₁ , 2 ₂ and flaw detection heads Ue ₁ , U
e ₂ , Uft, and a four-periphery flaw detection mechanism for flaw detection on the front edge, the rear edge, and both side edges in the width direction of the flaw-detecting steel plate 1 equipped with flaw detectors connected to the probe of each head (not shown) 2, the long support 3 _1, on-board testing head Uc thereto, flaw detection Uo, and probe Sc of each head, So. and flaw detector 5 ₁ through 5n, a steel central portion having a 5o ₁ ～5On Central flaw detection mechanism 3, steel plate passage control, flaw detection start / end control of four circumference flaw detection mechanism and center flaw detection mechanism, flaw detection steel plate of four circumference flaw detection mechanism 2 and center flaw detection mechanism 3 for minimizing flaw detection dead zone Flaw detection control device 4 for performing scanning control to the flaw detection plate and control for selecting the probe and the combination of the probe and the flaw detector used for flaw detection of the central flaw detection mechanism 3 corresponding to the flaw detection steel plate width and the plate passing reference position deviation, The flaw detection signals from the probes of the flaw detection heads of the four-circumferential flaw detection mechanism 2 and the central flaw detection mechanism are sent to the steel plate. The flaw detection device 5 including a plurality of flaw detectors (for the four-circumferential flaw detection mechanism 2 is not shown) for converting into defect information, and the defect information inside the steel plate input from the flaw detection device 5 is organized and aggregated. , A flaw detection data processing device 6, which evaluates and determines the flaw detection result based on the defect assessment judgment criteria of the flaw detection steel plate input from the host computer 7.

Function explanation of each component of the ultrasonic flaw detector The function of each component of the four-circumferential flaw detection mechanism 2, the central flaw detection mechanism 3, the flaw detection device 5, the flaw detection control device 4, and the flaw detection data processing device 6 which constitute the ultrasonic flaw detection device Will be described below.

Four-circumferential flaw detection mechanism 2; flaw detection heads Ue ₁ and U in which a plurality of probes for detecting flaws on the front edge, the rear edge and both side edges in the width direction of the steel plate are staggered
The e ₂ and Uft and these lifting devices have sensors (not shown) for detecting both side edges of the steel sheet in the width direction and both ends of the steel sheet in the longitudinal direction, and the traveling direction (passing line) L of the flaw detection steel sheet 1
And at a right angle to the movable two pair of carriage (support) 2 _1, 2 ₂ mounted on, down left and right of each flaw detection head control signal from the inspection controller 4 for inputting a signal from the sensor .Detecting each edge of the steel sheet by moving it forward and backward to pre-position the probe and attaching it to the front edge or rear edge of the steel sheet with water film on its surface, or both side edges in the width direction. , The front edge or rear edge of the steel plate, and both edges in the width direction are traced to the steel plate so that the dead zone is minimized. Then, the flaw detection is finished, the flaw detection head is raised, the probe is separated from the steel plate, and the flaw detection is finished.

Testing of four circumferential portion of the steel plate 1 is first caused to travel the carriage 2 ₂ in the width direction, the steel plate front end edge portion and the flaw detection by the width Wt with the probe testing head Uft the carriage 2 _2, then the truck 2 ₂ flaw detection head Ue ₁ and bogie 2 ₂ in the width direction both side edges in the probe inspection head Ue ₂ of the bogie 2 ₁ is traveling in the width direction performs flaw detection of width 2 × We, the end of the front edge The inspection head Uft of the truck 2 _{2 on which} the inspection was performed
The probe W is used to detect the width Wt of the rear edge of the steel plate.

Also, as is well known, at the time of flaw detection at the front edge of the steel plate that is first performed, the threading position of the flaw detection steel plate and the steel plate width are detected by the travel distance of the probe of the flaw detection head Uft. Detects the passing position of the steel sheet every moment.

In the above, each flaw detection head is composed of n (usually 4 to 8) probes S as shown by U in FIG. 4, and the flaw detection effective width of each probe S is It is arranged so that the total is the effective flaw detection width P of one flaw detection head U.
However, in many cases, the probes for the four-circumferential flaw detection have different effective flaw detection widths arranged in one flaw detection head.

Central flaw detection mechanism 3; One long carriage capable of moving a plurality of flaw detection heads Uo, Uc for detecting flaws in the central portion excluding both sides We in the width direction of the steel sheet and its lifting device in the width direction of the flaw detection steel sheet 3 ₁ (long support)
It is mounted on the control panel of the flaw detection control device based on the steel plate position information at the time of flaw detection on the four edges described above, and selects only the probe corresponding to the required flaw width Wi at the central portion of the flaw detection steel plate, and near the front edge of the steel plate. The flaw detection head is lowered and the flaw detection is performed on the central portion of the steel sheet while following the flaw detection steel sheet, and the flaw detection head is separated near the rear edge of the steel sheet to complete the flaw detection.

N pieces of inspection head mounted on the long carriage 3 _1, at least in half or more (in this embodiment of the central portion need inspection width of steel strip passing the maximum width W Wi (Wi ≧ W-We ) 1 / 2 and the. the largest flaw area W ₁ of), N1 pieces of inspection heads Uc, each arranged Uo column l _1, l
Every ₂ units are arranged in a zigzag pattern at a pitch twice the effective flaw detection width P of the head, and in the remaining region W ₂ , only N ₂ is arranged in the arrangement line l _1.
The individual flaw detection heads Uc are arranged at a pitch twice the effective flaw detection width P of each flaw detection head.

Each of the flaw detection heads Uc and Uo has n (usually 4) probes (S shown in FIG. 4 and S shown in FIG. 2).
Corresponds to c, So. ), And is arranged such that n times the effective flaw detection width of each probe becomes the effective flaw detection width P of one flaw detection head.

The flaw detection device 5 is composed of a plurality of flaw detectors and detects an internal defect of a flaw detection steel plate.

In principle, each probe of the flaw detection head is connected to the flaw detector in a one-to-one manner, but the N flaw detection heads Uc, U for central portion flaw detection are used.
Of the o, N2 × n probes Sc built in the N2 flaw detection heads Uc arranged only in two rows in the area W ₂ are
Among N1 × n probes Sc, So built in N1 flaw detection heads Uc, Uo arranged in two rows in W ₁ in a staggered manner, probes incorporated in the same number of flaw detection heads Uo not in the same row So is a flaw detector 5o ₁
~5on As can be shared, linked via a changeover switch Rs ₁ ~Rsn coupled controlled by testing the control unit 4.

Inspection control device 4; Mainly based on the plate width measurement value, it is used corresponding to the plate width and the plate passing position of the inspection steel plate among the inspection heads Uc, Uo for central inspection mounted in the central inspection mechanism 3. the selection of the head to be, in addition to performing connection control of the probe and the flaw dexterity changeover switch Rs ₁ ~Rsn used, perform contact and separation plate timing control to testing steel plates of the head. Further, in this embodiment, as is known from the publication of the conventional example, the timing control of the contact / separation plate to the flaw detection steel plates of the flaw detection heads Ue ₁ , Ue ₂ , Uft for four circumference flaw detection mounted on the four circumference flaw detection mechanism 2 and the dead zone are performed. Control of copying of the flaw detection head to the flaw detection steel plate to be minimized, plate width measurement of the flaw detection steel plate, detection of the passage position of the flaw detection steel plate, start and end control of taking in the effective flaw detection signal of the flaw detection device 5, and constant detection steel plate position The conveyance table control is performed to detect and detect the flaw detection steel plate at a predetermined speed (including stop) in the vicinity of each flaw detection mechanism device.

Flaw detection data processing device 6: Inside of the steel plate input from the outside of the high-order computer 7 by processing the internal defect signals of the flaw detection steel plate sent from the flaw detection device 5 as known in the prior art publication Evaluate and judge the calculation result based on the defect evaluation criteria,
Output to the above computer 7, line printer, etc.

1-pass flaw detection and detailed description of pass flaw detection 1) The flaw detection steel plate 1 is conveyed by the conveyance table T and stopped at the front edge detection position of the steel plate.

2) Inspection head Uf with a built-in probe for front and rear edge inspection of steel plate
t is in contact with the flaw detection steel plate, and the flaw detection head Uft itself is moved back and forth until the steel plate edge detection sensor (not shown) attached to the flaw detection head Uft detects one end in the width direction of the front edge of the steel plate. It is moved in the plate width direction by a carriage 2 ₂ which supports the head.

3) when it is detected steel front edges widthwise end, a steel plate front and rear ends flaw detection head Uft by該台vehicles 2 ₂ moves toward the plate width direction end, carrying out the flaw of the steel plate front end edge portion. On this occasion,
Even if the steel sheet is skewed, the flaw detection head Uf can be detected by the flaw detection controller control signal based on the signal from the steel sheet edge detector sensor.
There is no problem because t can be finely adjusted back and forth to imitate the tip of the steel plate.

When the steel sheet edge detection sensor detects the sheet width direction end, the inspection head Uft Complete testing is Hanareban, then move back the carriage 2 ₂ based on the plate width direction end.

Further, at the start of flaw detection and the position and movement distance of the front and rear edge flaw detection head Uft of the steel sheet during flaw detection, the threading position and the steel sheet width of the front edge portion of the steel sheet are calculated.

4) Based on the plate passing position and the steel plate width of the front edge of the steel plate calculated above, the position of the flaw detection heads on both side edges in the width direction of the steel plate and the central region of the steel plate necessary for detecting the central region required width Wn are detected. Select the probe and flaw detector.

However, if the position of the required central flaw detection width Wn of the steel plate is within the region (W ₁ ) in which the flaw detection heads Uc, Uo of the central flaw detection mechanism 3 are arranged in a zigzag pattern, the required central flaw detection width of the steel plate is The probe built in the flaw detection head in the position of Wn and the flaw detector corresponding thereto are selected and the flaw detection operation described in the item 5) or later is performed.

Position of the steel sheet central inspection required width Wn is the case in the region W ₁ and W ₂ when or area W ₂ only astride, a flaw detection head Uc arranged in a row in the region W _2, a region W ₁ From the flaw detection heads Uc on the same row as the flaw detection head Uc in the arranged area W ₂ , select the flaw detection heads within the required flaw detection width Wn of the steel plate in the center, and select the flaw detection heads built into these flaw detection heads. A child and a flaw detector corresponding to the child are selected, and flaw detection operations described in 15) and later described below are performed. At this time, the flaw detectors for the probes Sc arranged in one row in the area W ₂ have the same number of probes So arranged in different rows of the area W _1.
, And the combined flaw detectors 5o _{1 to} 5on are connected by switching the changeover switches Rs _{1 to} Rsn.

5) Two inspection heads Ue ₁ and Ue ₂ for both side edges of the steel sheet in the width direction
To the steel plate for flaw detection, and one end and the other end of the front edge of each steel plate are detected by the steel plate edge detection sensors attached to the flaw detection heads Ue ₁ and Ue _2. The flaw detection heads Ue ₁ and Ue ₂ are moved until the other end is detected.

6) When both ends of the front edge of the steel plate are detected, the transport table T is activated and the flaw detection of the steel sheet width direction both side edges is started while moving the flaw detection steel plate 1.

When the flaw detection steel plate is skewed, the flaw detection head is detected by a scanning signal from the flaw detection control device 4 based on an edge detection signal from a steel sheet edge detection sensor provided in each flaw detection head.
Make Ue ₁ and Ue ₂ follow both side edges of the steel sheet in the width direction.

7) When the front end of the flaw detection steel plate comes under the central flaw detection device mechanism 3, the steel plate is once stopped, and the selected central flaw detection head is connected to the front edge of the steel plate at the inner side in the widthwise central required flaw detection width Wi. Parts to be contacted, and flaw detection of the central part of the steel plate is started.

When the flaw detection steel sheet is skewed, the flaw detection head is moved to one side edge portion of the steel sheet by a trace signal from the flaw detection control device 4 based on the steel sheet skew information at the time of flaw detection on both side edges of the steel sheet width direction. Tell

8) When the trailing edge of the flaw detection steel plate comes directly below the flaw detection heads Ue ₁ and Ue ₂ of the four-circumferential flaw detection mechanism 2, the steel sheet is stopped, flaw detection on both side edges is completed, and the steel sheet side edge flaw detection head Separate Ue ₁ and Ue ₂ .

9) The flaw detection head Uft is brought into contact with the rear edge of the flaw detection steel plate.

10) A steel plate edge detection sensor attached to the flaw detection head Uft,
Move the flaw detection head Uft until one end at the rear edge of the steel plate is detected.

11) If one end of the rear edge of the steel plate is detected, the inspection head Uft
It was moved in the plate width direction by the carriage 2 _2, implementing the flaw of the steel sheet trailing edge. When the steel plate edge detection sensor detects the other end of the steel plate rear edge portion, after the flaw detection is completed and the flaw detection head Uft is released, the conveyance table is activated to start the movement of the flaw detection steel sheet.

When the steel sheet is skewed, the flaw detection head Uft is made to follow the front edge of the steel sheet by a tracing control signal from the flaw detection control device 4 based on the edge detection signal from the steel sheet edge detection sensor of the flaw detection head Uft. It

12) On the other hand, when the rear end of the flaw detection steel plate reaches a predetermined position under the central flaw detection mechanism 3, the steel plate is stopped and the required width for flaw detection in the central portion of the steel plate
After the flaw detection of Wi is completed, the flaw detection head contacted with the material is released.

13) The flaw detection control device 4 controls the above-described operations and the like required for flaw detection of the four-circumferential flaw detection mechanism 2 and the central flaw detection mechanism 3 and controls the transport table T.

14) The defect information inside the flaw detection steel plate during flaw detection is sent from each flaw detector of the flaw detection device 5 to the flaw detection data processing device 6, arranged and edited by the flaw detection data processing device 6. The organized and edited flaw detection results are evaluated and determined based on the evaluation determination criteria from the outside of the host computer 7, and the results are output to the host computer 7 and a line printer (not shown).

With the above, the flaw detection when the flaw detection position inside the steel plate is within the area where the flaw detection heads of the central flaw detector are arranged in a staggered manner is completed.

15) When the position of the required width Wn for flaw detection in the central portion of the steel plate extends to the region W ₂ of the central flaw detection mechanism 3, the first flaw detection in the central portion of the steel plate is performed by the probe So of the flaw detection head Uc in the row l _1. When completed,
After the transport table T is stopped, it is reversed to move the trailing edge portion or the leading edge portion of the steel plate below the central flaw detection mechanism 3 and stop. Furthermore, the long carriage 3 ₁ is moved widthwise only effective width P shift flaw detection head, after Sezzai the flaw steel, flaw detection head used in the steel plate center portion flaw detection of the first time to start the conveying table With the probe described above, the second flaw detection of the central portion of the steel plate is performed while moving the steel plate.

16) For the second flaw detection, after completing the first flaw detection in the same manner as the above 12), perform the above 13) and 14).

When the steel plate is skewed, the long carriage 3 ₁ may be moved along the width direction to trace one side of the steel plate of the flaw detection head using the skew information of the steel sheet at the time of the first flaw detection. If more accurate copying is required, the above item 7) may be carried out after performing the same operations as the items 5) and 6) at the time of the second flaw detection at the time of the second flaw detection. However, in that case, the second flaw detection does not perform flaw detection on both side edges by the flaw detection heads Ue ₁ and Ue ₂ , but detects the position of the steel sheet, that is, detects the threading position and the skew feed amount.

〔The invention's effect〕

As described above, the present invention, the steel plate within the most threaded plate width is detected by one time of the plate running, of the rare plate width of the normal flaw detection frequency that exceeds the most threaded plate width and enters the range of the maximum plate width. Since the test piece is shared with the steel plate within the maximum width of the plate without installing the flaw detector exclusively, it is possible to significantly reduce the initial investment and the maintenance cost.

[Brief description of drawings]

FIG. 1 is a plan view showing the arrangement relationship between the four-circumferential flaw detection mechanism and the central flaw detection mechanism on the threading line. FIG. 2 is a block diagram showing the connection relationship between the probe of the central flaw detection head and the flaw detector. FIG. 3 is a block diagram showing the overall configuration of the ultrasonic flaw detector. FIG. 4 is a plan view showing an arrangement example of the probes of the flaw detection head. 1: Steel plate, 2: Four-sided flaw detection mechanism 2 ₁ , 2 ₂ : Bogie (support) 3: Central flaw detection mechanism 3 ₁ : Long carriage (long support) 4: Flaw detection control device (flaw detection control device) 5 : flaw detector 5 ₁ ~5n, 5o ₁ ~5on: flaw detector (flaw detector) 6: inspection data processing device 7: host computer S, Sc, So: probe (ultrasonic probe) U, Uc, Uo , Uft, Ue ₁ , Ue ₂ : Flaw detection head (flaw detection head) W: Maximum width of plate passing, Wn: Necessary width of central flaw detection Wi: Maximum flaw detection area, l ₁ , l ₂ : Row P: Effective flaw detection width (pitch) T: Transport table, L: Plate passing line Rs _{1 to} Rsn: Changeover switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroki Miyawaki, Inventor 1-11-1 Edamitsu, Hachimanto-ku, Kitakyushu, Kitakyushu, Fukuoka Inside the Engineering Department, Nippon Steel Co., Ltd. (72) Yuro Sugimoto, Kamakura, Kanagawa 325 Machiya Mitsubishi Electric Corporation Kamakura Factory (72) Inventor Yukio Mitani 325 Kamimachiya, Kamakura City, Kanagawa Prefecture Mitsubishi Electric Corporation Kamakura Factory (56) Reference JP-A-59-133457 (JP, A) JP Sho 59-39701 (JP, B2) Japanese Patent Sho 59-39702 (JP, B2)

Claims (1)

[Claims] 1. A pair of supports that are independently movable along a width direction at predetermined positions of a steel sheet passing line; located behind the supports and extending over the entire width direction and in the width direction. A long-distance support that can be moved in a direction; a flaw detection head in which a plurality of ultrasonic probes are arranged in a zigzag manner in the width direction of a steel plate, the flaw detection head being provided on one side of the support for flaw detection on one side edge in the width direction of the steel plate. A flaw detection head, a flaw detection head for flaw detection on the other side edge portion in the width direction of the steel plate, and a flaw detection head for flaw detection on the front and rear edge portions, which are provided on the other side of the support, and on the elongated support, When the central flaw detection area is defined as an area corresponding to the central portion inside by a predetermined distance from both side edges of the steel sheet to be plated, the center corresponding to the maximum width of the steel sheet to be threaded on the long support. Are arranged at a pitch twice the effective flaw detection width of the flaw detection head over the entire flaw detection area. In addition, a plurality of flaw detection heads for flaw detection in the widthwise central portion of the steel plate; flaw detectors that transmit and receive ultrasonic waves to and from the ultrasonic probe of each flaw detection head and convert received signals into internal defect signals of the steel sheet; In a device for ultrasonic flaw detection while running and passing a flat rectangular steel plate, on the long support, 1/2 or more of which is less than the central flaw detection region corresponding to the maximum width of the steel plate to be passed. In the range, in the central flaw detection area corresponding to the maximum width of the steel plate to be passed, parallel to the flaw detection head for flaw detection in the widthwise central portion, and arranged in a staggered arrangement at the pitch, A flaw detection head for flaw detection in the central portion in the width direction of the widest steel plate; an ultrasonic probe of a flaw detection head included in a central flaw detection region corresponding to the widest width of the steel plate to be passed on the long support. The number of flaw detectors equal to the number of An ultrasonic flaw detection device for a steel plate, comprising: the flaw detector and a flaw detection control device that selects an ultrasonic probe of a flaw detection head on the long support body according to a width of a flaw detection region of a portion. .