JP2015051450A - Radiation flaw detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect shallow corner cracks with high sensitivity, regardless of the thickness of steel strips.SOLUTION: A radiation source 2 irradiates obliquely radiation to casting surfaces of the corner part A of a rectangular steel strip S which is casted through continuous casting, a detector 3 detects the radiation which is irradiated by the radiation source 2 to transmit through the steel strip S, a control unit evaluates the cracks of the corner part A using the radiation detected by the detector 3. A wedge material T is preferable to be provided on a path of radiation from the radiation source 2 to the detector 3 such that the attenuation of the radiation transmitted through the steel strip S without cracks is constant without respect to the path. A cooling mechanism are preferable to be provided for cooling the radiation source 2 and the detector 3. In addition, the radiation source 2 and the detector 3 are preferable to be housed in a case with a window portion 41 formed in the opaque window material for infrared ray to irradiate or detect radiation through the window portion 41.

Description

  The present invention relates to a radiation flaw detector that detects cracks in a corner portion of a steel piece.

  Conventionally, a steel piece, which is a semi-finished product cast by continuous casting, may have cracks (hereinafter referred to as corner cracks) at the corners. If this corner crack can be detected at the stage of a steel slab, it can be suppressed from becoming a defective product after rolling by a treatment such as care. Thus, for example, Patent Document 1 discloses a technique for detecting a corner crack by taking a thermal image of a steel piece. Further, as described in Non-Patent Document 1, a radiation transmission flaw detection method for inspecting the inside of an object by irradiating the object with radiation (X-rays) and detecting the transmitted radiation is an industrial-use method. Widely used for non-destructive testing and medical diagnosis. Patent Document 2 discloses a technique for measuring the thickness of a steel plate by detecting the transmitted radiation by irradiating the steel plate with radiation.

JP 2012-73055 A JP 2012-93314 A

Japan Nondestructive Inspection Association, “Radiation Transmission Test I”, 2006 edition, p3-7

  However, in the technique described in Patent Document 1, since only the surface of the steel slab can be observed by the thermal image, the unevenness in the vicinity of the surface and the corner crack where the crack (crack) reaches the inside of the steel slab are distinguished. It was difficult to detect separately. Even when a scale or the like has covered the surface of a steel piece, it was difficult to detect a corner crack.

  On the other hand, if the method of detecting the transmitted radiation by irradiating the object with radiation is used, the corner cracking reduces the absorption of the radiation by the depth of the crack and increases the transmitted radiation. By evaluating strength, corner cracks can be measured. In this way, according to the radiation transmission flaw detection method that evaluates the inside of the steel slab from the difference in attenuation (change rate of attenuation) due to the path of the radiation that passes through the inside of the steel slab, is the crack reaching the inside? It is possible to detect corner cracks even when determining whether or not the scale has covered the surface of the steel piece.

  However, in general, in the radiation transmission flaw detection method, the change rate of the detectable attenuation amount in the radiation transmission path is about 1% to 10%. The change in attenuation in the radiation transmission flaw detection method for the steel slab is caused by the change in the thickness of the steel slab on the path. Here, many steel pieces cast by continuous casting have a plate thickness of 200 mm or more. In order to detect a change rate of 5% attenuation with respect to a steel piece having a thickness of 200 mm, the crack cannot be detected unless the crack depth is 10 mm or more. Therefore, it is difficult for the radiation transmission flaw detection methods described in Non-Patent Document 1 and Patent Document 2 to accurately detect corner cracks in a steel piece having a large plate thickness.

  This invention is made | formed in view of the above, Comprising: It aims at providing the radiation flaw detector which can detect a shallow corner crack with high sensitivity irrespective of the plate | board thickness of a steel piece.

  In order to solve the above-described problems and achieve the object, a radiation flaw detector according to the present invention is a radiation flaw detector that evaluates cracks in a corner portion of a rectangular steel piece cast by continuous casting using radiation. An irradiation means for irradiating the cast surface of the corner portion of the steel slab obliquely, a detection means for detecting the radiation irradiated by the irradiation means and transmitted through the steel slab, and detected by the detection means Evaluation means for evaluating cracks in the corner portion by using the emitted radiation.

  Further, in the above-described invention, the radiation flaw detector according to the present invention is installed on the path of the radiation from the irradiation means to the detection means, and the attenuation amount of the radiation that passes through the steel slab without cracks is the path. It is characterized by comprising a wedge material configured so as to be constant regardless.

  The radiation flaw detection apparatus according to the present invention is characterized in that, in the above invention, a cooling mechanism for cooling the irradiation means and the detection means is provided.

  In the radiation flaw detector according to the present invention, in the above invention, the irradiation means and the detection means are accommodated in a case including a window portion formed of a window material opaque to infrared rays, and the window portion is interposed therebetween. The radiation is irradiated or detected.

  According to the present invention, shallow corner cracks can be detected with high sensitivity regardless of the thickness of the steel slab.

FIG. 1 is a schematic diagram showing a configuration of a radiation flaw detector according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing a steel piece to be flawed by the radiation flaw detector according to the present embodiment. FIG. 3 is a schematic view showing one cross section of a corner of a steel piece to be flawed by the radiation flaw detector according to the present embodiment. FIG. 4 is a schematic diagram showing one cross section of a corner of a steel piece to be flawed by the radiation flaw detector according to the present embodiment. FIG. 5 is a view showing a steel piece to be flawed by the radiation flaw detector of the present embodiment. FIG. 6 is a diagram for explaining the rate of change of the path length in the steel slab between the healthy part and the cracked part of the steel slab. FIG. 7 is a diagram for explaining the rate of change of the path length in the steel slab between the healthy part and the cracked part of the steel slab considering the amount of radiation attenuation at the window. FIG. 8 is a diagram for explaining the rate of change of the path length in the steel slab between the healthy part and the cracked part of the steel slab in consideration of the arrangement of the wedge material and the amount of radiation attenuation at the window part. FIG. 9 is a diagram showing the relationship between the incident point and the rate of change of the path length in the steel slab in the case of FIGS. FIG. 10 is a diagram showing the relationship between the incident point by the conventional radiation flaw detection method and the rate of change of the path length in the steel slab.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. Moreover, in description of drawing, the same code | symbol is attached | subjected and shown to the same part.

  First, the configuration of the radiation flaw detector according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the radiation flaw detector 1 of the present embodiment includes a radiation source 2 that irradiates radiation, a detector 3 that detects radiation that has passed through a flaw detection object, and the radiation received by the detector 3. A control unit (not shown) that reads the intensity and evaluates the flaw detection object.

  The radiation source 2 is accommodated in the case 4 and emits radiation through the window 41 of the case 4. The detector 3 is realized by, for example, a digital X-ray line sensor or the like and receives radiation through the window 41 of the case 4.

  The control unit is realized by a general-purpose computer such as a workstation or a personal computer, and controls each component of the radiation flaw detector 1 using a memory that stores a processing program and a CPU that executes the processing program. The control unit controls irradiation of radiation from the radiation source 2 and reception of radiation by the detector 3, and reads the intensity of the radiation received by the detector 3 to evaluate the flaw detection object.

  FIG. 2 is a perspective view of a steel piece S that is a target for flaw detection in the radiation flaw detector 1 according to the present embodiment. As shown in FIGS. 1 and 2, the radiation source 2 irradiates the casting surface of the corner portion A surrounded by the broken line of the steel piece S obliquely. The radiation source 2 of the present embodiment irradiates radiation at an incident angle of 30 ° to 60 ° with respect to the cast surface of the steel slab S. The detector 3 is installed so as to face the radiation source 2 through the corner portion A of the steel piece, and receives the radiation irradiated from the radiation source 2. The radiation flaw detector 1 moves the source 2 and the detector 3 relative to each other in the casting direction B of the steel slab indicated by an arrow in FIG. Detect flaws and detect corner crack C.

  FIG. 3 is a schematic diagram showing one cross-section of the corner portion A of the steel piece S that is the object of flaw detection by the radiation flaw detector 1 of the present embodiment. As shown in FIG. 3, the radiation source 2 transmits radiation to a certain region of the corner portion of the steel piece and is detected by the detector 3. At that time, the radiation source 2 irradiates the radiation so that the maximum value D of the thickness of the steel piece S on the radiation path is about 20 mm.

  It is desirable that the radiation source 2 and the detector 3 include a cooling mechanism (not shown). The cooling mechanism is realized by, for example, a cooling device that cools the inside of the case 4. Thereby, when the steel piece S is high temperature, damage to the radiation source 2 and the detector 3 by the radiant heat can be prevented.

  The window part 41 of the case 4 of the radiation source 2 and the detector 3 is preferably made of a window material that is opaque to infrared rays. For example, a thin metal plate such as an aluminum plate, a steel plate, or a copper plate may be used as the window material. Thereby, since the radiant heat is interrupted when the steel piece S is at a high temperature, damage to the radiation source 2 and the detector 3 can be prevented. Moreover, according to such a window part 41, when the above-mentioned cooling mechanism is provided because of the high thermal conductivity, the window part 41 is quickly cooled by this cooling mechanism. Damage to the vessel 3 can be effectively prevented.

  It is desirable that the amount of radiation attenuation when passing through the window 41 is small. In the present embodiment, the radiation attenuation amount at the window portion 41 is adjusted to 2 mm or less in terms of the thickness of the steel piece.

  FIG. 4 is a schematic diagram showing one cross-section of the corner portion A of the steel piece S that is the object of flaw detection by the radiation flaw detector 1 of the present embodiment. As shown in FIG. 4, it is desirable to arrange the wedge material T on the path of the radiation irradiated from the radiation source 2. The wedge material T is arranged such that the plate thickness d2 of the wedge material T on this path increases as the plate thickness d1 of the steel piece S on the path of radiation decreases. In this way, the wedge material T is arranged so that the attenuation amount of the radiation transmitted through the healthy part where the steel piece S is not cracked is constant regardless of the path. Thereby, the sensitivity of corner crack detection is improved, and the intensity of the radiation received by the detector 3 can be prevented from being locally increased and damaged.

  As described above, according to the radiation flaw detector 1 of the present embodiment, the radiation source 2 irradiates the corner portion A of the steel slab S with radiation, thereby shortening the radiation path. Shallow corner cracks can be detected with high sensitivity regardless of the plate thickness. Further, by arranging the wedge material T, it is possible to make the attenuation amount of the radiation transmitted through the healthy part where the steel piece S is not cracked constant regardless of the route. Thereby, the sensitivity of corner crack detection can be improved, and the intensity of the radiation received by the detector 3 can be prevented from being locally increased and damaged. By providing the radiation source 2 and the detector 3 with the cooling mechanism, damage to the radiation source 2 and the detector 3 due to the radiant heat can be prevented when the steel piece S is at a high temperature. Further, by using a window material that is opaque to infrared rays for the window portion 41, the radiation heat of the steel piece S to be flawed is cut off, so that the radiation source 2 and the detector 3 can be prevented from being damaged. Further, since the window material of the window portion 41 has high thermal conductivity, the window portion 41 is quickly cooled by the cooling mechanism, so that the radiation source 2 and the detector 3 can be effectively prevented from being damaged.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

(Example)
Hereinafter, the radiation attenuation rate will be described with reference to an example in which a steel piece S provided with a cavity simulating a corner crack is targeted for flaw detection. FIG. 5 is a view showing a cross section of one corner portion A of the steel piece S of the present embodiment. As shown in FIG. 5, a cavity simulating a corner crack is arranged in a corner portion A in the steel piece S to be flaw detected in the present embodiment. The cavity is disposed on each of the two casting surfaces in contact with the corner portion A at a depth of 1 mm in a range of 0 to 10 mm from the intersecting line a of the two casting surfaces. In this embodiment, the radiation source 2 irradiates the steel piece S with radiation having an incident angle of 45 ° shown by a broken line in FIG. 5 while moving the incident point, and the intensity of the radiation detected by the detector 3 is detected. From the change, the controller detected a change in the amount of radiation attenuation and detected a corner crack. Here, the incident point is specified by the distance x from the intersection line a of the corner portion A.

  In the conventional radiation flaw detection method (conventional example), cracks are detected by radiation with an incident angle of 90 ° indicated by a dotted line in FIG. Therefore, as described above, the detection of cracks having a depth of about 1 to 10% with respect to the thickness of the steel slab S was the limit. For example, if the thickness of the steel slab S is 200 mm and the detection limit is 5%, detection of a crack with a depth of 10 mm is the limit.

FIG. 6 shows the difference (rate of change) in the path length (path length in the slab) of the radiation passing through the slab S between the healthy part without the scratch (crack) of the slab S and the cracked part where the corner crack is generated It is a figure for demonstrating. Here, since radiation attenuates by passing through the steel slab S, the rate of change of the path length in the steel slab corresponds to the radiation attenuation rate. As shown in FIG. 6, the path length L in the billet of radiation at the healthy part is expressed by the following equation (1).

On the other hand, the path length L ′ in the slab of radiation at the cracked part is expressed by the following equation (2).

Therefore, when ΔL = L−L ′, the rate of change in the path length in the steel slab (ΔL / L) is expressed by the following equation (3).

FIG. 7 is a view for explaining the rate of change of the path length in the steel slab between the healthy part and the cracked part of the steel slab S in consideration of the amount of radiation attenuation at the window part 41. Here, the window part 41 was adjusted to be 0.5 mm in terms of the thickness of the steel slab S. As shown in FIG. 7, the path length L in the billet of radiation at the healthy part is expressed by the following equation (4).

On the other hand, the path length L ′ in the steel slab of radiation at the crack is expressed by the following formula (5).

Therefore, the rate of change (ΔL / L) of the path length in the billet is expressed by the following equation (6).

FIG. 8 shows the change rate of the path length in the slab between the healthy part and the cracked part of the steel slab S in consideration of the radiation attenuation in the window 41 when the wedge material T is arranged on the radiation path. It is a figure for demonstrating. Here, the wedge material T is such that the path length through the steel slab S and the wedge material T is equal to the path length of the reference path in any path, with the path in the steel slab at the incident point x = 10 mm as the reference path. Arranged. In FIG. 8, it is shown adjacent to the steel piece S for simplification. Further, the window 41 is adjusted to 0.5 mm in terms of the thickness of the steel slab. As shown in FIG. 8, the path length L in the billet of radiation at the healthy part is represented by the following formula (7).

On the other hand, the path length L ′ in the steel slab of radiation at the crack is expressed by the following formula (8).

Therefore, the rate of change (ΔL / L) of the path length in the billet is expressed by the following equation (9).

  FIG. 9 is a diagram showing the relationship between the incident point and the rate of change of the path length in the steel slab based on the above formulas (3), (6), and (9). Moreover, FIG. 10 is a figure which shows the relationship between the incident point by a prior art example, and the rate of change of the path length in a steel slab. As shown in FIG. 10, according to the conventional example, the change in the detected radiation attenuation is a change in the radiation attenuation due to the crack of the steel piece S with respect to the plate thickness of 200 mm. Is not greater than the detection limit of 5%.

  On the other hand, according to the present embodiment, as shown in FIG. 9, when neither the attenuation amount in the window portion 41 nor the wedge material T is taken into consideration (corresponding to the above equation (3)), the window portion 41 is used. In the case of considering the amount of attenuation at the window 41 and the wedge material T (corresponding to the above equation (6)), the case of considering the amount of attenuation at the window 41 and the wedge material T (corresponding to the above equation (9)), It was confirmed that the rate of change in the amount of attenuation of radiation due to a crack having a depth of 1 mm was larger than the detection limit of 5%, and the crack could be detected. Thereby, according to the present Example, it was confirmed that a corner crack can be detected with high accuracy regardless of the thickness of the steel piece S.

DESCRIPTION OF SYMBOLS 1 Radiation flaw detector 2 Radiation source 3 Detector 4 Case 41 Window part S Steel piece T Wedge material

Claims (4)

A radiation flaw detector for evaluating, using radiation, cracks in a corner portion of a rectangular steel piece cast by continuous casting,
Irradiating means for irradiating radiation to the casting surface of the corner portion of the steel piece obliquely;
Detection means for detecting the radiation irradiated by the irradiation means and transmitted through the steel piece;
Evaluation means for evaluating cracks in the corner portion using the radiation detected by the detection means;
A radiation flaw detector characterized by comprising:   A wedge material is provided on the radiation path from the irradiation means to the detection means, and is configured such that the attenuation of the radiation passing through the steel piece without cracks is constant regardless of the path. The radiation flaw detector according to claim 1.   The radiation flaw detector according to claim 1, further comprising a cooling mechanism that cools the irradiation unit and the detection unit.   The irradiation unit and the detection unit are housed in a case having a window portion formed of a window material opaque to infrared rays, and irradiate or detect the radiation through the window portion. The radiation flaw detector according to any one of 1 to 3.

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