Method for Evaluating Defects in Refractory Materials

Abstract

To provide a refractory body defect evaluation method capable of easily obtaining relative position relation and its change of defects existing inside a refractory body.SOLUTION: A refractory body defect evaluation method evaluates defects existing inside a refractory body. The refractory body defect evaluation method includes: a transmission image data acquisition process for acquiring transmission image data of a refractory body; and an analysis process for performing topological analysis with respect to the transmission image data acquired in the transmission image data acquisition process.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a method for evaluating defects in refractories, and more particularly to a method capable of easily grasping the relative positional relationship of defects existing inside the refractories and changes thereof.

Background Art

[0002] Refractories such as refractory bricks are widely used as materials that can withstand high temperatures in iron-making facilities and other facilities that require high-temperature processes. For example, in a steelworks, refractories are used as the lining of blast furnaces and converters.

[0003] However, refractories used in such high-temperature environments have a problem of being damaged by the impact received during operation. A typical damage form of refractories is thermal spalling. That is, cracks are generated and propagated by repeatedly receiving stress caused by temperature changes, and as a result, peeling and destruction occur in the refractories.

[0004] Such damage to refractories does not occur instantaneously but occurs after a certain period of time. Therefore, in order to suppress the damage caused by the spalling phenomenon that occurs over this long period and improve the furnace life of refractory equipment, it is necessary to understand the behavior of cracks generated and propagated inside the refractories. And for that purpose, it is required to measure and evaluate information on cracks existing in the refractories and voids (pores) that can be the starting points thereof. In the following description, cracks and voids (pores) are collectively referred to as defects.

[0005] Conventional methods for evaluating defects existing inside refractories and the like include, for example, the following.

[0006] In Non-Patent Document 1, a method for evaluating the apparent porosity of refractories using the dry weight, underwater weight, and saturated water weight is defined.

[0007] In Non-Patent Document 2, a method for evaluating the pore size distribution of fine ceramics by the mercury intrusion method is defined.

[0008] In Non-Patent Document 3, a method for evaluating defects inside a refractory using an X-ray CT scanner has been proposed.

[0009] In Patent Document 1, a technique for detecting defects in a ceramic substrate has been proposed by irradiating the ceramic substrate with linearly polarized light and observing the light reflected or transmitted through the ceramic substrate via a polarizer.

[0010] Also, in Patent Document 2, a technique for measuring the thickness of the gap between bricks in a lining for a heat-resistant container composed of a plurality of refractory bricks using ultrasonic waves has been proposed.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0012]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0013] According to these prior arts, although defects existing inside refractories and the like can be evaluated, there are the following problems.

[0014] For example, although the apparent porosity and pore size distribution can be evaluated by the methods of Non-Patent Documents 1 and 2, since variously shaped defects are complexly distributed inside actual refractories, it is impossible to accurately evaluate the properties of refractories only from the simple apparent porosity and pore size distribution. In order to evaluate the properties of refractories, particularly how cracks occur and propagate when a load is applied to the refractories, more detailed information about the positions of individual defects and the relative positional relationships of a plurality of defects is required. In addition, since it is necessary to fill water or mercury inside the pores during measurement by the above method, pores communicating with the surface of the refractory (open pores) can be measured, but pores not communicating with the surface (closed pores) cannot be measured.

[0015] On the other hand, in the case of methods using polarized light or ultrasonic waves as in Patent Documents 1 and 2, it is considered that information about closed pores can also be obtained. However, even with these methods, it has been difficult to accurately evaluate the detailed distribution of individual defects and the relative positional relationships of a plurality of defects.

[0016] Also, if X-ray CT scanning is used as proposed in Non-Patent Document 3, detailed position information of internal defects can be obtained. However, the transmission image data obtained by X-ray CT scanning is extremely complex and its analysis is difficult. In particular, in order to understand the behavior of cracks generated and propagated inside the refractory, it is necessary to grasp the generation and growth behavior of defects when a load is applied to the refractory. And for that purpose, it is necessary to perform an analysis including the relative positional relationships of a plurality of adjacent defects. However, the actual situation is that such advanced analysis methods have not been established from the transmission image data obtained by methods such as X-ray CT scanning.

[0017] The present invention has been made in view of the above actual situation, and an object thereof is to provide a method for evaluating defects in a refractory that can easily grasp the relative positional relationship of defects existing inside the refractory and changes thereof.

Means for Solving the Problems

[0018] The present invention has been made based on the above findings, and the gist thereof is as follows.

[0019] 1. A method for evaluating defects in a refractory for evaluating defects existing inside the refractory, comprising: a transmission image data acquisition step of acquiring transmission image data of the refractory; an analysis step of performing topological geometric analysis on the transmission image data acquired in the transmission image data acquisition step; A method for evaluating defects in a refractory, characterized by including the above.

[0020] 2. The method for evaluating defects in a refractory according to 1 above, wherein the topological geometric analysis in the analysis step is performed using persistent homology.

[0021] 3. The method for evaluating defects in a refractory according to 1 or 2 above, wherein the acquisition of the transmission image data in the transmission image data acquisition step is performed using an X-ray CT scanner.

Effects of the Invention

[0022] According to the method of the present invention, defects existing three-dimensionally inside the refractory can be evaluated nondestructively. In the method of the present invention, by using topological geometric analysis, information on the size and distribution of defects can be quantified and easily grasped from the transmission image data obtained by a method such as X-ray CT scanning. Thereby, defects that cause breakage can be specified, and the stability (safety) of the refractory can be accurately evaluated.

Brief Description of the Drawings

[0023]

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Mode for Carrying Out the Invention

[0024] Hereinafter, the present invention will be described in detail. Note that the present invention is not limited to this embodiment.

[0025] The method for evaluating defects in refractories according to an embodiment of the present invention is a method for evaluating defects existing inside the refractory, and includes a transmission image data acquisition step of acquiring a transmission image of the refractory, and an analysis step of performing topological analysis on the transmission image data acquired in the transmission image data acquisition step.

[0026] [Refractory] As the refractory, any refractory can be targeted without particular limitation. The refractory may be either a shaped refractory or an unshaped refractory. Examples of the refractory include, but are not limited to, MgO-C bricks, Al2O3-SiC-C bricks, high-alumina bricks, chamotte bricks, magnesite bricks, silica bricks, castable refractories, plastic refractories, mortars, and insulating refractories. Note that a castable refractory is a refractory that can be cast (castable) during construction. Also, a plastic refractory is literally a refractory with plasticity (plastic).

[0027] [Defect] The method of the present invention targets defects existing inside the refractory. Here, "defect" refers to a structural defect (also referred to as a structural flaw) existing inside the refractory and includes cracks and voids (open pores and closed pores).

[0028] [Transmission Image Data Acquisition Step] In the method of the present invention, first, transmission image data of the refractory is acquired (transmission image data acquisition step). The method for acquiring the transmission image data is not particularly limited, and any method can be used as long as it can acquire transmission image data including information on defects inside the refractory. From the perspective of versatility, it is preferable to acquire the transmission image data in the transmission image data acquisition step using an X-ray CT scanner. It is also possible to acquire the transmission image data using synchrotron radiation X-rays, which are superior in luminance and directivity compared to an X-ray tube, which is a general X-ray source.

[0029] [Analysis Step] Next, perform topological geometric analysis on the transmission image data obtained in the transmission image data acquisition step (analysis step). As described above, there are a large number of fine defects inside the actual refractory, and their sizes and positions are not uniform, but are three-dimensionally and complexly distributed. Therefore, the transmission image data obtained by a method such as X-ray CT scan is very complex, and it is not easy to understand the distribution of defects and their influence on material properties as it is. Therefore, by extracting relatively easy-to-understand parameters from the vast amount of defect information contained in the transmission image data through topological geometric analysis, it becomes possible to easily grasp the relative positional relationship of the defects existing inside the refractory and its changes.

[0030] Hereinafter, the case of using persistent homology as the topological geometric analysis will be described, but the topological geometric analysis in the present invention is not limited to this, and any method can be used.

[0031] Persistent homology is an analysis method as described in Non-Patent Document 4. Hereinafter, its outline will be described.

[0032] As an example, the case of analyzing the point group arrangement on a two-dimensional plane as shown in FIG. 1 by persistent homology will be described. Here, each point represents the position of the object to be analyzed (defects in the case of the present invention). Then, circles centered on each of the points are virtually set, and the radius of the circles is increased.

[0033] When focusing on the four points 1, 2, 3, and 4 surrounded by the broken line among the points shown in FIG. 1, the circles centered on each point exhibit the behavior shown in FIG. 2 as the radius is increased to r1, r2, r3, r4, r5. In persistent homology, when the radius of the circle is increased in this way, attention is paid to the generation and disappearance of holes formed between adjacent circles.

[0034] That is, at the time when the radius is r1, the circles do not touch each other (Fig. 2(a)). However, when the radius is increased to r2, four circles touch each other, and a hole is formed between the circles on the point arrangement 1-2-3-4 1-2-3-4 (Fig. (2b)). Then, when the radius is further increased to r3, as a result of the circumferences of the upper and lower circles touching each other, the hole 1-2-3-4 disappears, and it is divided into two holes 1-2-4 and hole 2-3-4 (Fig. (2c)). The correspondence relationship between the generation and disappearance of this hole 1-2-3-4 is called the birth-death-pear of the virtual circle radius pair (r2, r3) when the hole 1-2-3-4 is generated and disappears, which represents the point arrangement 1-2-3-4. Among the elements that make up the birth-death-pear, the one corresponding to the generation of the hole is called the birth value, and the one corresponding to the disappearance of the hole is called the death value.

[0035] Furthermore, when the radius of the virtual circle is increased and it becomes r4, one of the two holes, hole 2-3-4 disappears (Fig. (2d)). When the radius further becomes r5, the remaining hole 1-2-4 also disappears (Fig. (2e)). (r3, r4) and (r3, r5) corresponding to the point arrangements 2-3-4 and 1-2-4 respectively are obtained as the birth-death-pears representing each point group arrangement.

[0036] Note that the birth value means half of the maximum adjacent distance of the point group surrounding the hole, and the death value means the radius of the circle inscribed in at least two points of that point group. From this, it can be seen that the birth value and the death value are numerically represented by the proximity distance between the point groups surrounding the hole and the size of the hole surrounded by the point group respectively. Also, the larger the difference between the birth value and the death value, the more distinguishable it becomes as an element showing a characteristic point group arrangement that spreads over a wider space.

[0037] In the birth-death-pear obtained in this way, the structural information of the original point cloud data is aggregated. The diagram obtained by plotting the obtained birth-death-pear with the birth value on the horizontal axis and the death value on the vertical axis is called a persistent diagram (PD). By using the persistent diagram, the structural information of multiple point cloud arrangements can be visually represented and quantitatively analyzed. Note that there are degrees in the persistent diagram. The 0th-order persistent diagram represents the connected components of the point cloud, the 1st-order persistent diagram represents the formation of 2D holes by the point cloud, and the 2nd-order persistent diagram has information on the point cloud arrangement related to the formation of 3D cavities, respectively.

[0038] When applying persistent homology to the actual analysis of refractory defects, the 1st-order persistent diagram considering the volume of the defects is used. First, for each defect existing in the transmission image data obtained in the transmission image data acquisition step, a sphere (defect volume equivalent sphere) having the same volume as each defect volume is arranged so that the center of the defect volume equivalent sphere coincides with the centroid of each defect (Fig. 3(a)). Then, as shown in Figs. 3(b) to (d), the radius of each defect volume equivalent sphere is increased. The sphere with the increased radius of the defect volume equivalent sphere is hereinafter referred to as a virtual sphere.

[0039] When the radius is gradually increased, at a certain point, a 2D hole surrounded by virtual spheres centered on points 1, 2, and 3 as shown in Fig. 3(c) is generated. Therefore, consider the plane containing triangle 1-2-3 at this time. On the plane, draw a tangent from the contact point or intersection point of the virtual sphere cross-section to the cross-section circle of the defect volume equivalent sphere, and take the length of the tangent as the birth value. 1-2-3 When the radius is further increased, at a certain point, the hole as shown in Fig. 3(d) disappears. Therefore, at this time, take the length of the tangent drawn from the intersection point of the virtual sphere cross-section to the cross-section circle of the defect volume equivalent sphere as the death value.

[0040] When the radius is further increased, at a certain point, the hole as shown in Fig. 3(d) disappears. Therefore, at this time, take the length of the tangent drawn from the intersection point of the virtual sphere cross-section to the cross-section circle of the defect volume equivalent sphere as the death value. 1-2-3 When the radius is further increased, at a certain point, the hole as shown in Fig. 3(d) disappears. Therefore, at this time, take the length of the tangent drawn from the intersection point of the virtual sphere cross-section to the cross-section circle of the defect volume equivalent sphere as the death value.

[0041] Figures 4 and 5 are diagrams showing the results when the refractory defect evaluation method of the present invention is actually applied to alumina refractories. Specifically, first, a sample with a diameter of φ10 mm and a height of 10 mm was cut out from an alumina refractory with an apparent porosity of 14.8%. Next, the internal structure of the sample was measured using an X-ray CT scanner to obtain three-dimensional transmission image data (Figure 4). Next, the transmission image data was subjected to topological geometric analysis using the persistent homology described above to analyze the void distribution. Figure 5 is an example of a persistent diagram obtained by the above analysis.

[0042] Thus, even in complex porous materials such as refractories, analysis using persistent homology is possible.

[0043] Also, even if the sampling position of the refractory changes, the identity of the material can be evaluated by performing topological geometric analysis such as persistent homology.

[0044] Furthermore, by analyzing the change in the persistent diagram when conditions change, such as applying mechanical loads (bending load, compressive load, etc.) to the refractory material, the changes occurring in the material can be tracked.

[0045] For example, when a bending load or a compressive load is applied and cracks occur inside the refractory, a new combination of birth value and death value occurs in a certain region on the persistent diagram. Furthermore, when these cracks grow and adjacent cracks merge, the combination of birth value and death value in a certain region on the persistent diagram decreases. In this way, the changes in the refractory material can be understood from the changes in the persistent diagram.

[0046] Furthermore, by performing inverse analysis and correlation analysis from the persistent diagram, it is also possible to identify initial cracks and voids that are prone to crack generation or sensitive to fracture.

[0047] Thus, according to the method for evaluating defects in refractories of the present invention, it is possible to non-destructively and visually evaluate how cracks occur as a mechanical load is applied to the refractory.

Example

[0048] Hereinafter, the actions and effects of the present invention will be described using examples. Note that the present invention is not limited to the following examples.

[0049] Using the method for evaluating defects in refractories of the present invention, it was evaluated how voids (cracks) occur inside the refractory when a mechanical load is applied to the refractory sample. As the refractory sample, an alumina refractory with an apparent porosity of 14%, a diameter of 10 mm, and a height of 10 mm was used.

[0050] A compressive load was applied to the refractory sample in the following pattern. (1) No load (initial state) (2) Apply a load of 4.3 kN (corresponding to 70% of the compressive strength) (3) Unload (4) Apply a load of 5.0 kN (corresponding to 80% of the compressive strength) (5) Unload

[0051] The load-crosshead displacement curve when the compressive load was applied in the above pattern is shown in FIG. 6.

[0052] Then, at each of the above (1) to (5) time points, the void distribution of the refractory sample was photographed using an X-ray CT scanner to obtain transmission image data, and the void and crack distribution in the obtained transmission image data was analyzed using two-dimensional persistent homology.

[0053] The two-dimensional persistence diagrams at each of the above (1) to (5) time points are shown in Fig. 7. The above (1) corresponds to Fig. 7(a), the above (2) corresponds to Fig. 7(b), the above (3) corresponds to Fig. 7(c), the above (4) corresponds to Fig. 7(d), and the above (5) corresponds to Fig. 7(e). In Figs. 7(b) and 7(c), compared with Fig. 7(a), the number of points increases in the range of death values from 400 to 600 (the area indicated by the broken line in the figure). From this, it can be seen that cracks in the range of 400 μm to 600 μm newly occurred due to applying a load equivalent to 70% of the compressive strength, and the cracks remained even after unloading.

[0054] However, looking at Figs. 7(d) and 7(e), by applying a load equivalent to 80% of the compressive strength and then unloading, the number of points in the range of death values from 400 to 600 decreases. From this, it can be seen that some of the newly generated cracks in the range of 400 μm to 600 μm merged due to applying a load equivalent to 80% of the compressive strength.

[0055] Thus, according to the method for evaluating defects of the refractory of the present invention, when a load is applied to the refractory, it is possible to easily grasp how defects occur and merge.

Claims

1. A method for evaluating defects in a refractory, which evaluates defects existing inside the refractory, comprising: wherein the refractory is a shaped refractory or an unshaped refractory, a transmission image data acquisition step of acquiring transmission image data of the refractory in each of a state where a mechanical load is applied to the refractory and a state where no mechanical load is applied; an analysis step of performing a phase geometric analysis on the transmission image data acquired in the transmission image data acquisition step; and wherein the mechanical load is a bending load or a compressive load, characterized in that it is a method for evaluating defects in a refractory.

2. The method for evaluating defects in a refractory according to claim 1, wherein the phase geometric analysis in the analysis step is performed using persistent homology.

3. The method for evaluating defects in a refractory according to claim 1 or 2, wherein the acquisition of the transmission image data in the transmission image data acquisition step is performed using an X-ray CT scanner.

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