JPS6327747A - Off-line calibration apparatus for magnetic flaw detector - Google Patents

Abstract

PURPOSE:To calibrate a magnetic flaw detector, by a compact apparatus constituted so that a short steel test piece is employed and can move over a predetermined distance at a required speed from a slow speed to a high a speed through the magnetic flaw detector. CONSTITUTION:A V-grooved roller conveyor apparatus 61 is controlled so that a feed speed is made continuously variable from a slow speed to a high speed and a feed direction is variable in one direction and in the opposite direction. When the former magnetic flaw detector (T-detector)51 is calibrated, the V-groove roller conveyor apparatus 61 feeds a short steel test piece through the detector 51 at a high speed and the calibration of the detector 51 can be performed at this time. When the latter flaw detector (L-detector)52 is calibrated, the V-grooved roller conveyor apparatus 61 feeds the short test piece through the detector 52 at a slow speed and the calibration of the detector 52 can be performed at this time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an apparatus for calibrating a magnetic flaw detector for detecting defects in steel materials that can be magnetized, such as steel pipes and steel bars, prior to use in actual operation. Furthermore, the present invention relates to an off-line calibration device that performs the calibration not on a production line but on a specially provided calibration line.

Steel pipes, steel bars, etc. manufactured by steel manufacturing equipment are inspected for dimensions and defects using one of the inspection equipments. One such inspection device is, for example, an inspection device that applies the principle of magnetic flaw detection, which magnetizes steel material and detects defects such as flaws and holes in the steel material as leakage magnetic flux. .

This inspection device uses leakage magnetic flux to non-destructively inspect steel pipes, steel bars, etc., and can be called a non-destructive inspection device or a magnetic flaw detector.

This magnetic flaw detector is for detecting material flaws or defects located in the circumferential direction and longitudinal direction on the inner and outer surfaces of steel materials, and for detecting flaws in the two directions, Each device is configured to include separate devices. This magnetic flaw detector is commercially available, well known, and already used in industrial production processes, so this
Now, we will only touch on the principles and configuration of this flaw detector itself, and only points related to the present invention.

When using this magnetic flaw detector, it is installed at the appropriate place in the manufacturing process of steel pipes, steel bars, etc., that is, in the production line.
On the other hand, by passing manufactured or processed steel pipes, steel bars, etc., defects existing in the steel materials are inspected.

Steel materials flowing through a production line sometimes have different outer diameter dimensions and other specifications. When steel materials with different characteristics arrive, it is necessary to adjust the height of the flaw detector and the pinch roll each time, and adjust or replace the measuring probe. be. Furthermore, it is necessary to know the sensitivity of the electric signal generated by the flaw detector to a specific flaw on the steel material, which means that the sensitivity of the flaw detector and the measurement standard values such as filter values must be calibrated every time the steel material is different. need to be done.

Conventional technology In order to carry out this type of calibration, a test piece is created by artificially flawing steel pipes, bars, etc. that are actually produced, and the steel material of this test piece is inserted into the production line. The material is passed through a magnetic flaw detector using transport equipment.

By the way, the magnetic flaw detectors targeted in this application include a T-device for detecting defects existing in the circumferential direction of steel materials and an L-device for detecting defects existing in the longitudinal direction of steel materials.
There is a device. Therefore, when calibrating each of the above devices on the production line, in order to calibrate the T-device for circumferential flaws, a test piece of steel with artificial flaws in the circumferential direction is calibrated on the production line. It is necessary to move the steel at the normal conveying speed there, and in order to calibrate the L-device for longitudinal defects, test pieces of steel with artificial longitudinal defects are transferred through the production line. need to be transported.

Regarding the method of using magnetic flaw detectors, it is common to use only the L-device for flaw detection on steel bars. Further, for flaw detection on steel pipes, only the L-device may be used, or the T-device and the L-device may be used together. In such a case where the T-device and the L-device are connected, as mentioned above, the conveyance speed of the steel material of the test piece is different between the two devices, so the T-device and the L-device It was difficult to calibrate both. For this reason, the steel of the test piece is moved twice, and one of the devices is calibrated each time.

Problems to be Solved by the Invention Calibration on a production line, that is, online, requires a long test piece steel material that is the same as the one being produced, and it is difficult to store the test piece. Disadvantages include the need for a large space, interference with peripheral equipment, a large impact on production efficiency, and the difficulty of handling test pieces.

Means for Solving the Problems The present invention is intended to eliminate the above-mentioned inconveniences in calibrating magnetic flaw detectors, and a special calibration device is provided for this purpose.

In the calibration device of the present invention, apart from the production line (online), another off-line calibration line is provided for the purpose of calibration in parallel with this, and a guide is provided extending from the production line to the calibration line, and magnetic flaw detection is performed. The machine is configured to be able to be moved via the guide from the production line to the calibration line or from the calibration line to the production line. Furthermore, a groove-shaped roller conveyor device is provided in connection with the calibration line, and the roller conveyor device partially includes a roller device combined with a pinch roller device. The test piece was a short steel pipe with artificial flaws.
Use steel materials such as steel bars.

Regarding the case where the T-device and the L-device are used together, the above-mentioned V-groove roller conveyor device could not be achieved without using online according to the prior art when the test piece was short. T - The acceleration of the transport speed of the test piece in relation to the equipment, i.e. the test piece is accelerated to a required constant speed before entering the flaw detector, and the test piece is placed at a constant speed as it passes through the flaw detector at that constant speed. The test piece is configured to be able to convey a distance, immediately thereafter stop the test piece, and then shift to fine feed conveyance of the test piece in conjunction with the L-device. In addition, the groove-type roller conveyor device includes an arm for inserting the short test piece, so that when the magnetic flaw detector is placed on the calibration line,
By moving the above-mentioned short test piece steel through the magnetic flaw detector using the above-mentioned channel roller conveyor device, the difficulty of off-line calibration of the magnetic flaw detector can be reduced to T.
This solves the problem for both the -4 and L-devices at once.

As mentioned earlier, the magnetic flaw detector targeted in this application has a T-device for detecting defects existing in the circumferential direction of steel materials and an L-device for detecting defects existing in the longitudinal direction of steel materials.
In this case, for convenience of installation, the above-mentioned groove roller conveyor device of this calibration device is operated by separate drive sources for the former magnetic flaw detection device and the latter magnetic flaw detection device. It is set up like this. However, the individual drive sources are designed to operate in the same manner by a single control device, so even if the channel roller conveyor devices are separate, they operate in exactly the same way. There is. Further, in this groove-shaped roller conveyor device, the speed of conveyance is continuously variable from very low speed to high speed, and the direction of conveyance is variable in one direction or the opposite direction. In the case of the former calibration of a magnetic flaw detection device (T-device), the groove-shaped roller conveyor device is designed to convey a short steel test piece through the device at high speed; This allows for calibration.

In the case of the latter magnetic flaw detection device (L-device), the groove-shaped roller conveyor device conveys a short steel test piece through the device at a very slow speed, and at this time the calibration of the device is carried out. It is now possible to do this.

Embodiment The magnetic flaw detector offline calibration device of the present invention can be used when the flaw detector is T.
- If it is only a device, it can be provided for that device. In addition, if the flaw detector is only an L-device, one check shall be provided for that device.

When a T-device and an L-device are used together as flaw detectors, it can be provided in association with both.

In this section 5, an example in which a T-device and an L-device are used together will be explained as an explanation related to the embodiment of the present invention. In addition, we will select a steel pipe as the type of steel material, make a short test piece using this steel pipe, and describe a calibration device that uses this.

In FIGS. 1 and 2, 50 is an offline calibration device of the present invention. 43 is a production line (online), and 41 is a calibration line (offline). 51 and 52 are magnetic flaw detectors, and 51 is a magnetic flaw detector that detects defects (
52 is a device (hereinafter referred to as T-device) for detecting defects present in the longitudinal direction of the steel pipe (hereinafter referred to as L-device). A groove-shaped roller conveyor device 61 is installed on the calibration line 41 and is constituted by a large number of groove-shaped rollers 1 to 11. The rollers 1 to 5 are driven by a drive unit 12, and the rollers 6 to 10 are driven by a drive unit 13.
driven by. It should be noted, however, that in this case the drive units 12, 13 are only used as two for reasons of construction. Of course, it is also possible to use only one drive unit. This drive unit 12.13
are commonly controlled by a single control device (not shown), so that rollers 1 to 10 are driven in exactly the same way, and the rotation of the rollers is continuously varied from low-speed rotation to high-speed rotation. In addition, the rotation direction of the roller can be freely rotated forward or reverse. Therefore, in the operation of the grooved roller conveyor device, the objects loaded on the rollers can be moved in one direction at very low speed, at any intermediate speed, and at high speed. This can also be done in the direction of the pond. Note that the grooved roller 11 is a free roller.

■For rollers 4.5.6 and 9.10.11, there is a free upper pinch roller - 14, 15, 1 above them.
6 and 17, 18, and 19, respectively. For the upper pinch rollers 14, 15, 16 a pinch roll device 66 is provided, and for the rollers 17, 18, 19 a pinch roll device 67 is provided. In the pinch roll device 66, the lower roller 4 and the upper free roller 14 form one pinch roll pair (Fig. 3).
It is composed of these three pairs.

The unit that is a pair of these pinch rolls guarantees the conveyance speed by automatically moving up and down as the short test piece advances, and also constantly adjusts to accommodate changes in the outer diameter of the short test piece. It is also equipped with an adjustment mechanism to ensure that the bone contact stroke of the pinch roll remains constant.

Next, we will talk about the insertion arm 31 for placing the steel pipe 30 on the groove roller conveyor device.When viewed from the front, this arm has a shallow V-shaped support plate 32 as shown in Figure 4, and is further curved (C). 34, includes a rotation axis 33 of the tune 34.The lower end of the tune 34 is connected to an air cylinder 36 for lifting and lowering the insertion arm via a link rod 35.The support plate 32 of the insertion arm 31 and the tune 34 are 1. 2nd
As is clear from the figure, ■ They are installed in the same line as the groove-shaped roller conveyor device 61, one each between rollers 1 and 2, and between rollers 2 and 3, and are connected by a link rod 35, so that they work together. Operate. That is, in FIG. 1, the V-shaped support plate 32 of the insertion arm stands 1.degree. vertically, and at this time, this V shape is at a higher level than the V-shaped shape of the roller (1), for example.

At this time, the steel pipe 30 is placed on the V-shaped support plate 32 and supported using a crane or the like (not shown) prepared separately. Next, actuate the insertion arm lifting cylinder 36,
Move the lower end of the tune 34 via the link rod 35 (first
In the diagram, push it toward the right). Then, the V-shaped support plate 32 on which the steel pipe 30 is mounted rotates to the left about the rotating shaft 33, and the level of the ■-shaped support plate 320 is lowered. Then, when this level reaches the V-shape of the roller (1), the steel pipe 30 is transferred to the roller. The V-shaped support plate 32 is lowered a little further and is stopped at a position where it has an appropriate clearance from the bottom of the steel pipe.

In this way, the steel pipe is placed on the groove-type roller conveyor device, and this placement can be carried out while the groove-type roller conveyor device is in operation. As a result, the start of transport of a short test piece is performed with almost no run-up, and the stable high-speed transport required by the T-device can be obtained within a limited layout.

Next, referring to the movement of the T-device 51 and L-device 52 of the magnetic flaw detector, 53 and 54 in FIGS. 1 and 2 move the flaw detector from the production line 43 to the calibration line 41 or vice versa. It is a guide means to do so. This guide means is structurally the same for both the guide means 53 and 54, so only the guide means 53 will be explained. 55 carries the T-device 51;
The flaw detection cart itself is movable and rides on a traveling guide rail 56. A traveling rack 57 is provided in the middle of the guide rail, and on the other hand, there is a suitable power source and gear device on the side of the truck 55, one gear of which meshes with the traveling rack as a pinion. ing. As a result, the cart 55 is moved by power on the running rail 56. Also, the trolley 55 has a T
- There is a trolley lifting section 59 on which the device 51 is placed and which itself can be raised and lowered relative to the trolley 55. Regarding the elevating part 59, there is an elevating screw jack 62 on the lower side thereof.
, an elevating guide rail 63 is provided on the side thereof,
Therefore, the T-device 51 can be moved up and down by the operation of the screw jack 62.

The above configuration is the same for the truck 65, and the L-device 5
2 is movable horizontally and linearly on the traveling guide rail, and is vertically movable with respect to the trolley 65.

Further, the present invention is characterized in that a shorter steel pipe test piece is used for calibrating the magnetic flaw detector, unlike that used in actual operation. An example of this test piece is shown in FIG. The length of the test piece pipe 30 is usually about 3 m,
The outer diameter and wall thickness are the same as those that flow through the production line in actual operation. In this case, a flaw is artificially created on the short tube. For example, 71 is a circumferential flaw provided on the inner surface of the steel pipe 30, and 72 is a flaw of the same level made all around the outer surface in the circumferential direction, and is used for calibrating the T-device. Further, 73 is a longitudinal flaw formed on the outer surface of the steel pipe, and 74 is a longitudinal flaw formed on the inner surface of the steel pipe 30, which is used for calibrating the L-device. Short pipe part 8
3 has no artificial flaws. Although this part is not involved in the calibration of the magnetic flaw detector itself, it is added to maintain the stability of the pipe when it is fed into the flaw detector, and 75 is the welded part.

Next, a method of calibrating a magnetic flaw detector using such a calibration device will be explained.

First, a sample of steel pipe with artificial flaws is prepared.

This means that steel pipes with the same outer diameter and other characteristics as the steel pipes in actual operation, which are scheduled to be flown through the production line, are processed into steel pipes with a length of about 3 m that have artificial flaws as described above. This is done by creating a test piece pipe 30.

Next, the flaw detectors 51 and 52 are moved to the recombination line 42, and in this step, the trolley lifting section 59 of the flaw detector is raised and lowered to match the center line of the measuring section of the flaw detector to the steel pipe to be inspected. Adjust so that the center lines of In the case of the present invention, if the level of the flaw detector is set in this way, it can be used for both calibration using test pieces on the calibration line and flaw detection of steel pipes in actual operation on the production line. It is configured as follows.

Next, the flaw detectors 51 and 52 are moved to the calibration line 41. In step 5, the upper roller 1 is
Finely adjust the heights of steps 4 to 19 and the height of the flaw detector to match the dimensions of the test piece pipe.

The test piece 30 is suspended by a crane or the like (not shown) and brought onto the insertion arm 31.

(2) Start the operation of the grooved roller conveyor device 61, and set the conveyor speed to the speed of actual operation in the production line (varies depending on the outer diameter size of the steel pipe). In the case of calibration of the T-device, the speed of the test piece pipe 30 is set to be the same as the conveyance speed during actual operation on the production line. Set appropriately in all ranges of transport speeds.

The insertion arm 31 is lowered by activating the air cylinder 36 for raising and lowering the insertion arm and lowering the ■-shaped plate 32 through the links 35 and 34, and the test piece 30 is rotated at the speed set as described above. ■Place it on the roller. As seen in Figures 1 and 2, the insertion arm 3
1 has two installed in series, which allows the test piece pipe to be placed on the rotating roller so that it does not slip on the roller or cause the pipe to sway. Can be done.

Next, the test piece pipe 30 travels on the roller conveyor at a set speed and enters the T-device 51 which is already positioned in alignment with the calibration line 41 at this point. When the test piece 30 enters the magnetic flaw detector, it may receive a magnetic attraction force from the flaw detector, which may cause the conveyance speed to fluctuate, and the linearity may be impaired while traveling on the roller conveyor 61. . Therefore, in order to keep the test piece 30 stable from these fluctuations,
In relation to the magnetic flaw detector - in the case of 2, the T - device - the rollers 4, 5 and 6 are the pinch rollers 14, 15,
16, as the test piece 30 advances, the test piece is automatically pressed one after another as described above.

Similarly, the pinch rollers 17, 18 and I9 above the VD rollers 9, 10 and 11 press the test piece as it enters. Moreover, when the test piece 30 passes through the pinch roll section, the pinch roller is automatically raised and stopped at a position having a gap of 5 to 10 mm from the top surface of the test piece pipe 30.

When the test piece pipe 30 passes through the T-device at the above-mentioned set speed, the artificially provided circumferential flaw 71.
Calibration is performed by 72. After passing through the T-device, the test piece pipe 30 is temporarily stopped on the roller conveyor using an electric brake. T
- Once the calibration is completed in the device, the groove roller conveyor device advances the test piece pipe 30 into the L-device at medium speed, and the pipe 30 is pressed by the V roller 11 and pinch roller 19. At the same time, the general feeding speed becomes slow feeding, calibration is performed by the longitudinal artificial flaws 73 and 74 provided on the test piece pipe 30, and after passing through the L-device, the channel roller conveyor device stops. . When the calibration is completed, the groove-shaped roller conveyor device is then reversely rotated at a medium speed, and the test piece pipe 30 is moved backwards and returned to the starting position at the left end in FIG. ■Remove from the channel roller conveyor device to complete.

If the calibration result of the T-device or the L-device is bad, the calibration can be repeated independently by selecting either device.

After the magnetic flaw detector has been calibrated in this way, the flaw detector is moved to the production line by the guide means, thereby completing preparations for actual operation.

Although the embodiments in which the present invention is used in combination with the T-device and the L-device have been described above, it is clear from the above that the off-line calibration device of the present invention can be installed by connecting the T-device and the L-device. Calibration device for T-device only, or L
- It will be easily understood that it can be used as a calibration device for the device only, ie as an individual. In this case, it may be necessary to make some structural changes to the position of the insertion arm 31 or the drive of the V-roller conveyor device, but there is no need to make any substantial changes to the main structure of the present invention. There isn't.

Generally, flaws in the longitudinal direction are a problem with steel bars, so in this case flaw detection is performed using only the L-device. Therefore, in this case, a short steel bar test piece having an artificial flaw in the longitudinal direction on its outer surface can be made and used for the off-line calibration device of the L-device. Furthermore, as described above, only the L-device may be used for inspection of steel pipes, and therefore, in this case as well, there may be an off-line calibration device of the present invention for only the L-device. In addition, it is possible to use only the T-device for flaw detection of steel materials, and in this case, the T-
There may be an offline calibration device of the invention for devices only.

Effects of the Invention In the present invention, a short steel test piece is used, and this short test piece is inspected by a magnetic flaw detector.
Since it is possible to move a predetermined distance at any desired speed from very slow to high speed, it has become possible to calibrate a magnetic flaw detector with a compact device. As a result, in the case of the present invention, handling such as production and storage of test pieces is convenient and very easy, and since calibration is performed offline, there is no interference with equipment before and after online operation, and Control complexity is also eliminated. And since we don't use the production line for calibration,
On the production line, for example, when the dimensions of the steel pipes to be flowed change, preparations can be made to accommodate this change, improving production efficiency. In addition, various advantages have arisen, such as increased work safety.

Incidentally, it is naturally possible to incorporate the calibration device of the present invention online without the guide means.

In other words, in this case, the calibration device of these devices is incorporated into the online system that uses only the T-device, only the L-device, or both the T-device and L-3, and the test piece with the required artificial flaw is installed. It is possible to calibrate magnetic flaw detectors online using steel pipes or bars.

[Brief explanation of the drawing]

FIG. 1 is a side elevational view of the offline magnetic flaw detector calibration apparatus of the present invention, with the magnetic flaw detector located on the calibration line. FIG. 2 is a plan view of the off-line calibration device for a magnetic flaw detector according to the present invention, and also shows a production line, a recombination line, and a calibration line, with the magnetic flaw detector located on the production line. FIG. 3 is an elevational view of the pinch roll device taken along arrows ``--'' in FIG. 1. FIG. 4 is an elevational view of the insertion arm taken along the line IV-rV in FIG. FIG. 5 is a side view of the test piece pipe, showing the state of artificial flaws. [Explanation of symbols of main parts] 51...Magnetic flaw detector (T-device) 52...
... Magnetic flaw detector (L-device) 43 ... Production line 41 ... Calibration line 61 ... ■ Channel roller conveyor device 30 ...
... Steel pipe test piece 31 ... Insertion arm 32 ... V-shaped support plate main drawings ... Figure 1';t'3σ

Claims (1)

[Claims] 1. A device for calibrating a magnetic flaw detector for detecting defects in steel materials prior to its use, comprising a calibration line installed parallel to a production line, and a calibration line from the production line. guide means extending into the line and allowing the magnetic flaw detector to be moved from the production line to the calibration line; a V-groove roller conveyor system associated with the calibration line, including a pinch roll system; It consists of a short steel test piece and an arm means for inserting the short test piece into the V-groove roller conveyor device, and the V-groove roller conveyor device connects the magnetic flaw detector to the production line. a magnetic flaw detector, the magnetic flaw detector being configured to be operable to transport the short test piece at a required distance and at a required speed through the magnetic flaw detector for pre-calibration prior to use on the magnetic flaw detector; Flaw detector offline calibration device. 2. The V-groove roller conveyor device required to achieve the purpose of pre-calibration has a conveying speed that is variable from high speed to very low speed, and a conveying direction that is variable in one direction or the opposite direction. An off-line calibration device for a magnetic flaw detector as claimed in claim 1, characterized in that it is configured as follows. 3. said insertion arm means is disposed on said calibration line in line with said V-groove roller conveyor device, said
It has a V-shaped support plate having the same shape in outline as the groove shape of the groove-shaped roller, and the V-shaped support plate supports a short test piece from above to below the level of the V-shaped groove of the V roller. The off-line calibration device for a magnetic flaw detector according to claim 1, characterized in that it is configured to be movable in the opposite direction. 4 A device for calibrating a magnetic flaw detector for detecting defects existing in steel materials prior to its use, comprising a calibration line installed parallel to a production line, and a calibration line extending from the production line to the calibration line for calibrating the magnetic flaw detector. a V-groove roller conveyor device associated with the calibration line and including a pinch roll device; a short steel test piece; arm means for inserting the short test piece into a V-groove roller conveyor device;
Therefore, the V-groove roller conveyor device moves the short test piece over a required distance and at a required speed to calibrate the magnetic flaw detector before using it on the production line. the magnetic flaw detector comprises a T-device for detecting defects present in the circumferential direction of the steel material; The V-groove roller conveyor device is provided in the calibration line in conjunction with the T-device and, during the calibration of the T-device, the V-groove roller conveyor device moves the short test piece through the T-device to a predetermined position. distance,
An off-line calibration device for a magnetic flaw detector, characterized in that it operates to convey the actual steel material at a speed equivalent to the conveyance speed of the actual steel material on a production line, thereby calibrating the T-device. 5. The V-groove roller conveyor device has a conveying speed of
Off-line calibration of a magnetic flaw detector according to claim 4, characterized in that the magnetic flaw detector is configured to be variable from a high speed to a very slow speed, and the direction of conveyance is variable in one direction or the opposite direction. Device. 6. said insertion arm means is disposed on said calibration line in line with said V-groove roller conveyor device and has a V-shaped support plate identical in profile to the groove shape of said V-groove rollers of said conveyor; , and the V-shaped support plate supports a short test piece and is configured to be movable from above to below the V-groove level of the V roller, or vice versa. Section 4 offline calibration device for magnetic flaw detector. 7 A device for calibrating a magnetic flaw detector for detecting defects existing in steel materials prior to its use, comprising a calibration line installed parallel to a production line, and a calibration line extending from the production line to the calibration line for calibrating the magnetic flaw detector. a V-groove roller conveyor device associated with the calibration line and including a pinch roll device; a short steel test piece; arm means for inserting the short test piece into a V-groove roller conveyor device;
Therefore, the V-groove roller conveyor device moves the short test piece over a required distance and at a required speed to calibrate the magnetic flaw detector before using it on the production line. the magnetic flaw detector comprises an L-device for detecting defects present in the longitudinal direction of the steel material, and the V-groove roller conveyor device comprises an L- The V-groove roller conveyor device is associated with the calibration line and, during calibration of the L-device, moves the short test piece a predetermined distance through the L-device onto the production line. 1. An off-line calibration device for a magnetic flaw detector, which operates to stably transport the actual steel material at a very slow speed different from the transport speed of the actual steel material, thereby calibrating the L-device. 8. The V-groove roller conveyor device has a conveying speed of
Off-line calibration of a magnetic flaw detector according to claim 7, characterized in that the magnetic flaw detector is configured to be variable from high speed to very low speed, and the direction of conveyance is variable in one direction or the opposite direction. Device. 9. The insertion arm means is arranged on the calibration line in line with the V-groove roller conveyor device and has a V-shaped support plate that is identical in profile to the groove shape of the V-groove roller of the conveyor. , and the V-shaped support plate is configured to support a short test piece and be movable from above to below the level of the V-shaped groove of the V roller or vice versa. Off-line calibration device for magnetic flaw detector according to Section 7. 10 A device for calibrating a magnetic flaw detector for detecting defects existing in steel materials prior to its use, comprising a calibration line installed parallel to a production line, and a calibration line extending from the production line to the calibration line for calibrating the magnetic flaw detector. a V-groove roller conveyor device associated with the calibration line and including a pinch roll device; a short steel test piece; and an arm means for inserting the short test piece into a V-groove roller conveyor device, and the V-groove roller conveyor device is used to conduct magnetic flaw detection before using the magnetic flaw detector on the production line. , configured to operate to transport the short test piece a pre-calibration distance and at a predetermined speed through the magnetic flaw detector, and the magnetic flaw detector The V-groove roller conveyor device consists of a T-device for detecting defects existing in the steel material and an L-device for detecting defects existing in the longitudinal direction of the steel material. When calibrating the T-device, the V-groove roller conveyor device is provided in the calibration line in association with the T-device and moves the short test piece through the T-device a predetermined distance. In order to convey at a speed equivalent to the conveyance speed of the actual steel material on the production line, and when calibrating the L-device, the V-groove roller conveyor device is
The short test piece is stably conveyed a predetermined distance through the L-device at a very slow speed that is different from the conveyance speed of the actual pipe on the production line, and thereby the T-device and L-device is calibrated. A magnetic flaw detector offline calibration device. 11. The V-groove roller conveyor device is characterized in that the conveyance speed is variable from high speed to very low speed, and the conveyance direction is variable in one direction or the opposite direction. A magnetic flaw detector offline calibration device according to claim 10. 12. said insertion arm means is disposed on said calibration line in line with said V-groove roller conveyor apparatus and has a V-shaped support plate identical in profile to the groove shape of said V-groove rollers of said conveyor; , and the V-shaped support plate is configured to support a short test piece and be movable from above to below the level of the V-groove of the V roller or vice versa. 10. Off-line calibration device for magnetic flaw detector.