Damage inspection method

Abstract

Provided is a damage inspection method capable of accurately detecting a damaged part. 【Solution means】A thermal image acquisition step ST1 of acquiring a plurality of thermal images by sequentially imaging an object to be inspected after applying a thermal load at each predetermined time step; for each of the plurality of thermal images, extracting a temperature profile and calculating a temperature difference dT between adjacent evaluation points in a temperature difference calculation step ST2; calculating a change rate dTr of the temperature difference dT for each time step, and calculating an average value dTr ave in a temperature difference change rate calculation step ST3; when the absolute value of the temperature difference dT calculated for the first acquired thermal image exceeds a threshold value R, specifying an evaluation point corresponding to the temperature difference dT as a damage part candidate Pc in a damage part candidate specification step ST4; and among the average values dTr ave corresponding to the damage part candidate Pc, specifying the damage part candidate Pc corresponding to the minimum average value dTr ave as the damage part in a damage part specification step ST5.

Description

Technical Field

[0001] The present invention relates to a damage inspection method capable of accurately detecting damage sites such as cracks existing in an object to be inspected such as a welded joint, while distinguishing them from uneven portions such as welded parts.

Background Art

[0002] Conventionally, for example, as shown in Patent Documents 1 to 3, methods for detecting damage sites such as cracks existing in an object to be inspected using an infrared imaging device have been proposed.

[0003] The method described in Patent Document 1 is a method of obtaining the surface temperature distribution of a defective portion from a thermal image acquired after heating or cooling the object to be inspected, obtaining the spatial differential value of this surface temperature distribution, and detecting the defective portion based on the inflection point thereof. The method described in Patent Document 2 is a method of creating samples (sound and unsound samples) of difference images of thermal distribution images before and after heating of exposed portions of steel materials at sound and unsound steel material joints, and comparing the difference image of the exposed portion of the steel material that is the object to be inspected with the samples to determine whether the object to be inspected is sound or unsound. The method described in Patent Document 3 is a method of determining the presence or absence of a crack based on the intensity change of infrared rays in an infrared image obtained by artificially irradiating an infrared ray to a structure and receiving the reflected infrared ray.

[0004] However, in the methods described in Patent Documents 1 to 3, when the object to be inspected is a welded joint and has uneven portions such as a welded part, there is a risk of erroneously detecting an uneven portion that is originally sound (without damage sites such as cracks) as a damage site.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the problems of the above prior art, and an object thereof is to provide a damage inspection method capable of accurately detecting damage sites such as cracks existing in an object to be inspected such as a welded joint, distinguishing them from uneven portions such as welded portions.

Means for Solving the Problems

[0007] In order to solve the above problems, the present inventors set up a hypothesis and conducted intensive studies. As a prerequisite for the hypothesis, the present inventors considered acquiring a plurality of thermal images showing the temperature distribution of the object to be inspected by imaging the object to be inspected after applying a thermal load at each predetermined time step using an infrared imaging device. Then, for each of the plurality of thermal images, a temperature profile, which is the temperature distribution on a predetermined straight line, was extracted, and based on the temperature profile, the temperature difference dT between adjacent evaluation points located on the straight line was calculated.

[0008] FIG. 1 is a diagram for explaining the hypothesis set up by the present inventors. FIG. 1(a) is a diagram schematically showing the temperature profile obtained immediately after applying a thermal load to the object to be inspected (in the example shown in FIG. 1(a), immediately after the heating is completed). The lower diagram in FIG. 1(a) shows the object to be inspected, and the upper diagram shows the temperature profile at the corresponding position of the object to be inspected shown in the lower diagram. FIG. 1(b) is a diagram schematically showing the temperature profiles obtained immediately after applying a thermal load to the object to be inspected (in the example shown in FIG. 1(b), immediately after the heating is completed) and after a predetermined time has elapsed. The lower diagram in FIG. 1(b) shows the object to be inspected, and the upper diagram shows the temperature profile at the corresponding position of the object to be inspected shown in the lower diagram. The present inventors set up the following hypotheses (1) to (3). (1) As shown in Fig. 1(a), it was considered that at a damaged part such as a crack, due to the heat insulation effect of the voids, the temperature difference dT immediately after applying a heat load would increase. On the other hand, at an uneven part such as a welded part, it was also considered that the temperature difference dT immediately after applying a heat load would increase. (2) As shown in Fig. 1(b), the temperature difference dT caused by an uneven part such as a welded part is temporary (the temperature difference dT is large only immediately after applying a heat load), and the change in the temperature difference dT with the passage of time is large. It was considered that the temperature difference dT would become small after a predetermined time (for example, about 10 seconds). On the other hand, at a damaged part such as a crack, since the heat insulation effect of the voids is the factor causing the temperature difference dT, the change in the temperature difference dT is small over a time period of about 10 seconds. It was considered that the temperature difference dT after the passage of a predetermined time remains large as it was immediately after applying the heat load. (3) Therefore, by evaluating the change rate of the temperature difference dT, it was thought that it would be possible to distinguish between damaged parts such as cracks with a small change rate and uneven parts such as welded parts with a large change rate, and accurately detect the damaged parts without misdetecting the uneven parts.

[0009] Next, the present inventors verified the validity of the above hypothesis by performing a heat transfer analysis. Fig. 2 shows a numerical analysis model (finite element analysis model) of a welded joint that was the subject of performing a heat transfer analysis to verify the validity of the hypothesis. Fig. 2(a) is an overall configuration diagram of the numerical analysis model, and Fig. 2(b) is an enlarged view of the area surrounded by the broken line in Fig. 2(a). As shown in Fig. 2, near the arc welded part of the numerical analysis model, as a damaged part, a crack extending in the plate thickness direction (the vertical direction in Fig. 2) was set with double nodes. The volumetric heat generation rate of 0.023 W / mm 3 was set as a heat load (heating), and the condition was air cooling (natural cooling) for 10 seconds after the heating was completed. As the thermophysical property values (thermal conductivity, density, specific heat) of the welded joint, data collected from a 590 MPa grade steel plate were applied. The air cooling conditions were an ambient temperature of 20°C, an emissivity of the welded joint of 0.8, and the convective heat transfer coefficient of the welded joint assuming natural convection was 11.628 W / (m 2 ·K). Under the conditions described above, heat transfer analysis was performed using the general-purpose non-linear finite element analysis program "Abaqus" manufactured by SIMULIA as software, and the temperature profile, which is the distribution of the temperature T on line A shown by the broken line in Fig. 2(b), was calculated at time steps of 1 second intervals from immediately after the heating ended until 10 seconds had elapsed.

[0010] Fig. 3 is a diagram showing the results obtained by the above heat transfer analysis. The horizontal axis of Fig. 3 indicates the position on line A (the distance from the left end of line A shown in Fig. 2(b)). The vertical axis of Fig. 3 indicates the temperature T and the average value dTr of the change rate dTr described later. ave In Fig. 3, only the temperature profiles immediately after heating, 1 second later, 2 seconds later, 5 seconds later, and 10 seconds later are plotted as the temperature profile, but actually a total of 11 temperature profiles are obtained at time steps of 1 second intervals. The average value dTr of the change rate dTr shown in Fig. 3 ave When calculating, first, for each of the 11 temperature profiles calculated at time steps of 1 second intervals, the temperature difference dT between adjacent evaluation points (adjacent nodes of the numerical analysis model) was calculated. Next, based on the following formula (1), the change rate dTr for each time step of the 11 temperature differences dT was calculated. dTr = |(dT i - dT i-1 ) / dT i | ···(1) In the above formula (1), the subscript i of dT means the time step and is an integer from i = 1 to 10. dT0 means the temperature difference dT immediately after heating ended, dT1 means the temperature difference dT 1 second after heating ended, and dT 10 means the temperature difference dT 10 seconds after heating ended. The same applies to other subscripts. A total of 10 change rates dTr will be calculated.

[0011] And in Fig. 3, the value obtained by averaging the change rate dTr for each time step of this temperature difference dT (the value obtained by dividing the sum of the 10 change rates dTr by 10) is plotted as the average value dTr of the change rate dTr. ave As shown in Fig. 3, in the welded joint, the average value dTr of the change rate dTr ave becomes the minimum value at the position where the crack, which is the damaged part, exists. Compared with this, the average value dTr of the change rate dTr at the position where the arc welding part exists ave is large, so it was found that the hypothesis of the present inventors described above is valid.

[0012] The present invention has been completed based on the findings of the present inventors described above. That is, in order to solve the above problems, the present invention uses an infrared imaging device to sequentially image the inspection target after applying a heat load at each predetermined time step, thereby obtaining a plurality of thermal images showing the temperature distribution of the inspection target. A thermal image acquisition step, for each of the plurality of thermal images, extracting a temperature profile that is the temperature distribution on a predetermined straight line, and based on the temperature profile, calculating a temperature difference dT between adjacent evaluation points located on the straight line. A temperature difference calculation step, calculating a change rate dTr of the temperature difference dT for each time step of the plurality of thermal images, and an average value dTr of the change rate dTr at all the time steps ave A temperature difference change rate calculation step for calculating, and when the absolute value of the temperature difference dT calculated for the first acquired thermal image among the plurality of thermal images exceeds a predetermined threshold value R, identifying the evaluation point corresponding to the temperature difference dT as a damage site candidate Pc. A damage site candidate identification step, and the average value dTr ave Among them, identifying the damage site candidate Pc corresponding to the minimum average value dTr ave as a damage site. The present invention provides a damage inspection method having a damage site identification step.

[0013] In the present invention, the "evaluation point corresponding to the temperature difference dT" means an evaluation point located on either one side determined in advance among the adjacent evaluation points for which the temperature difference dT is calculated. According to the damage inspection method according to the present invention, by the thermal image acquisition step, the temperature difference calculation step, and the temperature difference change rate calculation step, as described above with reference to Figs. 2 and 3, the average value dTr of the change rate dTrave is calculated. And, according to the damage inspection method of the present invention, in the damage site candidate identification step, when the absolute value of the temperature difference dT calculated for the initially acquired thermal image (for example, the thermal image acquired for the inspection target immediately after applying the thermal load) exceeds a predetermined threshold value R, the evaluation point corresponding to the temperature difference dT is identified as a damage site candidate Pc. This damage site candidate Pc may include not only damage sites such as cracks but also uneven portions such as welded joints. However, according to the damage inspection method of the present invention, in the damage site identification step, the average value dTr of the change rate dTr corresponding to the damage site candidate Pc ave among them, the minimum average value dTr ave The damage site candidate Pc corresponding to is identified as the damage site. For this reason, as in the findings of the present inventors described above, damage sites such as cracks with a small change rate dTr (a small average value dTr of the change rate dTr ave with a small average value dTr) and uneven portions such as welded joints with a large change rate dTr (a large average value dTr of the change rate dTr ave with a large average value dTr) can be distinguished, and it can be expected that the damage site can be accurately detected without misdetecting the uneven portion.

[0014] Here, although it is possible to use the damage site identified in the damage site identification step of the damage inspection method according to the present invention as the final inspection result, in order to ensure the certainty of the inspection, it is preferable to further perform a visual inspection on the identified damage site. Also, since only the damage site candidate Pc corresponding to the minimum average value dTr ave is identified as the damage site in the damage site identification step, there is also a possibility of overlooking it if the damage site candidate Pc corresponding to the next smallest average value dTr ave is the damage site.

[0015] In order to avoid the above problems, the damage inspection method according to the present invention includes a visual inspection step of visually inspecting whether there is actually damage at the specified damage site, and in the visual inspection step, if it is not possible to confirm the actual existence of damage, a soundness determination step of determining that the specified damage site is sound, and in the visual inspection step, if it is possible to confirm the actual existence of damage, it is determined that there is damage at the specified damage site, and the average value dTr ave among them, the next smallest average value dTr ave corresponding to the damage site candidate Pc is specified as a new damage site in a second damage site specifying step, and in the visual inspection step, until it is no longer possible to confirm the actual existence of damage, or in the second damage site specifying step, until the next smallest average value dTr ave no longer exists, it is preferable to repeatedly execute the visual inspection step and the second damage site specifying step.

[0016] According to the above preferred method, in the visual inspection step, whether there is actually damage at the specified damage site is visually inspected, so the certainty of the inspection is ensured. And in the first visual inspection step, if it is not possible to confirm the actual existence of damage, in the soundness determination step, it is determined that the specified damage site is sound (that is, it is determined that the damage site specified in the damage site specifying step is a false detection (false detection caused by foreign matter adhesion or a depression that is not a damage), and it is corrected to the correct inspection result). On the other hand, in the first visual inspection step, if it is possible to confirm the actual existence of damage, in the second damage site specifying step, it is determined that there is damage at the specified damage site, and the damage site candidate Pc corresponding to the next smallest average value dTr ave is specified as a new damage site. And in the visual inspection step, until it is no longer possible to confirm the actual existence of damage, or in the second damage site specifying step, until the next smallest average value dTr aveUntil it no longer exists, the visual inspection step and the second damage site identification step are repeatedly executed, so that the risk of overlooking the damage site can be reduced.

Advantages of the Invention

[0017] According to the present invention, damage sites such as cracks existing in an object to be inspected such as a welded joint can be accurately detected by distinguishing them from uneven portions such as welded parts.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0019] Hereinafter, a damage inspection method according to an embodiment of the present invention will be described with appropriate reference to the accompanying drawings. FIG. 4 is a flowchart schematically showing the steps of the damage inspection method according to the present embodiment. As shown in FIG. 4, the damage inspection method according to the present embodiment includes a thermal image acquisition step ST1, a temperature difference calculation step ST2, a temperature difference change rate calculation step ST3, a damage site candidate identification step ST4, and a damage site identification step ST5. Further, as a preferred aspect, the damage inspection method according to the present embodiment includes a visual inspection step ST6, a soundness determination step ST8, and a second damage site identification step ST9 following the thermal image acquisition step ST1 to the damage site identification step ST5. Hereinafter, each step will be described in order.

[0020] <Thermal image acquisition step ST1> In the thermal image acquisition step ST1, by using an infrared imaging device to sequentially image the inspection target after applying a thermal load at each predetermined time step, a plurality of thermal images showing the temperature distribution of the inspection target as shown in, for example, FIG. 6 described later are acquired. The thermal load is not limited to this, but for example, it is applied to the inspection target using a heat gun. The thermal load is not limited to this, but for example, a temperature distribution higher than room temperature is given to a region within the field of view of the infrared imaging device of the inspection target by a heat source of 50°C or more higher than room temperature. The imaging of the inspection target is not limited to this, but for example, it is performed from immediately after applying the thermal load until 10 seconds or more have elapsed. For example, when the imaging of the inspection target is performed at each time step at 1-second intervals from immediately after applying the thermal load until 10 seconds have elapsed, a total of 11 thermal images are acquired.

[0021] <Temperature difference calculation step ST2> In the temperature difference calculation step ST2, for each of a plurality of thermal images, a temperature profile, which is a temperature distribution on a predetermined straight line, is extracted. Based on this temperature profile, as shown in, for example, FIG. 7 described later, the temperature difference dT between adjacent evaluation points located on the straight line is calculated. The evaluation points are, for example, pixels constituting the thermal image, and in this case, the adjacent evaluation points are adjacent pixels. The setting of the predetermined straight line and the extraction of the temperature profile can be executed using predetermined image processing software. The predetermined straight line can be set at an arbitrary position on the thermal image and extend in an arbitrary direction such as the vertical direction or the horizontal direction. However, when a part where damage is likely to exist in the object to be inspected can be predicted in advance, it is preferable to set the straight line so as to pass through this part. Also, the number of predetermined straight lines is not limited to one, and it is also possible to set a plurality of straight lines and repeatedly execute the extraction of the temperature profile and the calculation of the temperature difference dT for each set straight line.

[0022] <Temperature difference change rate calculation step ST3> In the temperature difference change rate calculation step ST3, based on the following formula (1), the change rate dTr of the temperature difference dT calculated for each of a plurality of thermal images at each time step is calculated. dTr = |(dT i - dT i-1 ) / dT i | ···(1) In the above formula (1), the subscript i of dT means the time step. For example, when the imaging of the object to be inspected is performed at each time step at 1-second intervals from immediately after applying the thermal load until 10 seconds have elapsed, and a total of 11 thermal images are acquired, i is an integer from 1 to 10. dT0 means the temperature difference dT immediately after applying the thermal load, dT1 means the temperature difference dT 1 second after applying the thermal load, and dT 10 means the temperature difference dT 10 seconds after applying the thermal load. The same applies to other subscripts. In the above case, a total of 10 change rates dTr are calculated.

[0023] And in the temperature difference change rate calculation step ST3, for example, as shown in FIG. 8 described later, the average value dTr of the change rates dTr at all time stepsave is calculated. In the above case, the value obtained by averaging a total of 10 change rates dTr (the value obtained by dividing the sum of the 10 change rates dTr by 10) is the average value dTr of the change rate dTr ave and is calculated as such.

[0024] <Damage site candidate identification step ST4> In the damage site candidate identification step ST4, among a plurality of thermal images, for the first acquired thermal image (when imaging of the object under inspection is performed at time steps of 1 second intervals from immediately after applying the heat load until 10 seconds have elapsed, and a total of 11 thermal images are acquired, the thermal image acquired immediately after applying the heat load), when the absolute value of the temperature difference dT calculated for the thermal image exceeds a predetermined threshold value R, as shown in FIG. 7 described later, the evaluation point corresponding to the temperature difference dT is specified as the damage site candidate Pc. The predetermined threshold value is determined, for example, by the following formula (2). R [°C] = 2.5 × L [mm] ··· (2) In the above formula (2), L means the distance between adjacent evaluation points for which the temperature difference dT is calculated.

[0025] <Damage site identification step ST5> In the damage site identification step ST5, for example, as shown in FIG. 8 described later, the average value dTr of the change rate dTr corresponding to the damage site candidate Pc ave among them, the damage site candidate Pc corresponding to the minimum average value dTr ave is specified as the damage site.

[0026] By executing the thermal image acquisition step ST1 to the damage site identification step ST5 described above, it is possible to distinguish between damage sites such as cracks with a small change rate dTr (a small average value dTr of the change rate dTr ave with a small average value dTr) and uneven portions such as welded parts with a large change rate dTr (a large average value dTr of the change rate dTr ave with a large average value dTr), and it is expected that the damage site can be accurately detected without misdetecting the uneven portion. Although it is possible to use the damage location identified in the damage location identification step ST5 as the final inspection result, it is preferable to further perform a visual inspection on the identified damage location to ensure the reliability of the inspection. Also, the damage location identified in the damage location identification step ST5 is only the damage location candidate Pc corresponding to the minimum average value dTr ave Therefore, if the damage location candidate Pc corresponding to the next smallest average value dTr ave is the damage location, there is a risk of overlooking it. For this reason, as described above, the damage inspection method according to the present embodiment preferably includes a visual inspection step ST6, a soundness determination step ST8, and a second damage location identification step ST9.

[0027] <Visual Inspection Step ST6 and Soundness Determination Step ST8> In the visual inspection step ST6, a visual inspection is performed to determine whether there is actually damage at the identified damage location. Thus, the reliability of the inspection is ensured. If it is not possible to confirm the actual presence of damage in the visual inspection step ST6 (when "No" in step ST7), in the soundness determination step ST8, it is determined that the identified damage location is sound. That is, it is determined that the identified damage location is a false detection (false detection caused by foreign matter attachment or a depression that is not a damage), and the inspection result is corrected to the correct one. After performing the soundness determination step ST8, the inspection is terminated. In the first visual inspection step ST6, a visual inspection is performed to determine whether there is actually damage at the damage location identified in the damage location identification step ST5. If it is not possible to confirm the actual presence of damage, in the soundness determination step ST8, it is determined that the identified damage location is sound, and thus the part located on the predetermined straight line in the thermal image of the inspection target is sound.

[0028] <Second Damage Location Identification Step ST9> On the other hand, in the visual inspection step ST6, if it is confirmed that there is actually damage (when "Yes" in step ST7), in the second damage site identification step ST9, it is determined that there is damage at the identified damage site, and the average value dTr ave among them, the second smallest average value dTr ave The corresponding damage site candidate Pc is identified as the new damage site.

[0029] Then, in the visual inspection step ST6, until it is no longer possible to confirm the actual existence of damage (that is, until "No" in step ST7 and the inspection is terminated by executing the soundness determination step ST8), or until there is no longer the second smallest average value dTr ave exists (until "No" in step ST10), the visual inspection step ST6 and the second damage site identification step ST9 are repeatedly executed (if "Yes" in step ST10, return to the visual inspection step ST6). In the visual inspection step ST6 after the second time, it will be visually inspected whether there is actually damage at the damage site identified in the second damage site identification step ST9. In this way, by repeatedly executing the visual inspection step ST6 and the second damage site identification step ST9, the possibility of overlooking the damage site can be reduced. Incidentally, the situation where there is no longer the second smallest average value dTr ave exists (when "No" in step ST10) is the case where the visual inspection step ST6 has been executed for all damage site candidates Pc and all damage site candidates Pc have been identified as damage sites in the second damage site identification step ST9.

[0030] Hereinafter, an example in which the thermal image acquisition step ST1 to the damage site identification step ST5 of the damage inspection method according to the present embodiment are executed will be described. FIG. 5 is a perspective view showing a schematic configuration of a welded joint used as an inspection object in this example. The welded joint of this example is a lap joint obtained by arc welding two steel plates with a thickness of 2.6 mm, and there is a crack as a damage site near the arc welding part.

[0031] In this embodiment, in the thermal image acquisition step ST1, a hot air gun is used to blow hot air at about 80°C onto the periphery of the crack for heating. From immediately after the heating ends until 10 seconds have elapsed, an infrared imaging device is used to sequentially image the periphery of the crack of the welded joint every 1 second time step, thereby obtaining a plurality (11 sheets) of thermal images showing the temperature distribution of the periphery of the crack of the welded joint. FIG. 6 shows the thermal image first acquired in the thermal image acquisition step ST1 of this embodiment.

[0032] Next, in the temperature difference calculation step ST2, for each of the plurality of thermal images, a temperature profile, which is the temperature distribution on line B (see FIGS. 5 and 6), is extracted using predetermined image processing software attached to the infrared imaging device. Then, based on this temperature profile, the temperature difference dT of the evaluation points (pixels constituting the thermal image) located on line B is calculated. FIG. 7 shows the temperature profile (distribution of temperature T) extracted from the first acquired thermal image shown in FIG. 6 and the temperature difference dT. The horizontal axis in FIG. 7 indicates the position on line B (distance from the left end of line B shown in FIG. 5). In FIG. 7, the temperature T is plotted with "◆", and the temperature difference dT is plotted with "○" and "●".

[0033] Next, in the temperature difference change rate calculation step ST3, based on the aforementioned formula (1), the change rate dTr of the temperature difference dT calculated for each of the plurality of thermal images every 1 second time step is calculated. In this embodiment, since 11 thermal images were acquired, a total of 10 change rates dTr were calculated. And in the temperature difference change rate calculation step ST3, the average value dTr ave of the change rate dTr at all time steps within 10 seconds is calculated. FIG. 8 shows the temperature profile (distribution of temperature T) extracted from the first acquired thermal image and the average value dTr ave of the change rate dTr calculated using all the thermal images. The horizontal axis in FIG. 8 indicates the position on line B (distance from the left end of line B shown in FIG. 5). In FIG. 8, the temperature T is plotted with "◆", and the average value dTr ave of the change rate dTr is plotted with "□" and "■".

[0034] Next, in the damage site candidate identification step ST4, among a plurality of thermal images, when the absolute value of the temperature difference dT calculated for the first acquired thermal image shown in FIG. 6 exceeds a predetermined threshold value R, as shown in FIG. 7, the evaluation point corresponding to the temperature difference dT was identified as a damage site candidate Pc. In this embodiment, since the distance L between adjacent evaluation points is 0.457 mm, from the above-described formula (2), the threshold value R was set to 1.1425°C. In FIG. 7, the temperature difference dT corresponding to the evaluation point identified as the damage site candidate Pc is plotted with "●", and the other temperature differences dT are plotted with "○". In this embodiment, the number of evaluation points identified as the damage site candidate Pc is five.

[0035] Finally, in the damage site identification step ST5, as shown in FIG. 8, the average value dTr of the change rates dTr corresponding to the five damage site candidates Pc ave (the points plotted with "■" in FIG. 8), among which the minimum average value dTr ave The damage site candidate Pc corresponding to was identified as the damage site. As shown in FIG. 8, the minimum average value dTr ave is the point c, and when the welded joint was visually inspected, it was found that there was a crack in the part corresponding to the point c. Next, the second smallest average value dTr ave is the point d, and when the welded joint was visually inspected, there was no crack in the part corresponding to the point d. From the above-described embodiments, it was found that according to the damage inspection method according to the present embodiment, cracks existing in the welded joint can be accurately detected by distinguishing them from the uneven portions of the arc welding part.

Explanation of Reference Numerals

[0036] ST1... Thermal image acquisition step ST2... Temperature difference calculation step ST3... Temperature difference change rate calculation step ST4... Damage site candidate identification step ST5... Damage site identification step ST6... Visual inspection step ST8... Soundness determination step ST9... Second damage site identification step

Claims

Claim 1 A thermal image acquisition step of acquiring a plurality of thermal images showing the temperature distribution of the object to be inspected by sequentially imaging the object to be inspected after applying a thermal load at each predetermined time step using an infrared imaging device; For each of the plurality of thermal images, a temperature difference calculation step of extracting a temperature profile that is a temperature distribution on a predetermined straight line and calculating a temperature difference dT between adjacent evaluation points located on the straight line based on the temperature profile; Calculate the rate of change dTr of the temperature difference dT for each time step for each of the plurality of thermal images, and calculate the average value dTr of the rate of change dTr at all the time steps ａｖｅ A temperature difference change rate calculation step for calculating the average value dTr of the rate of change dTr at all the time steps A damaged part candidate identification step of identifying, as a damaged part candidate Pc, the evaluation point corresponding to the temperature difference dT when the absolute value of the temperature difference dT calculated for the first acquired thermal image among the plurality of thermal images exceeds a predetermined threshold value R; The average value dTr corresponding to the damage site candidate Pc ａｖｅ Among them, the minimum average value dTr ａｖｅ A damage site specifying step of specifying the damage site candidate Pc corresponding to as the damage site, and having A damage inspection method. Claim 2 A visual inspection step of visually inspecting whether there is actually damage at the identified damaged part; In the visual inspection step, a soundness determination step of determining that the identified damaged part is sound when it cannot be confirmed that there is actually damage; In the visual inspection step, if it is confirmed that there is actually damage, it is determined that there is damage at the identified damage site, and the average value dTr corresponding to the damage site candidate Pc ａｖｅ among them, the second smallest average value dTr ａｖｅ and a second damage site identification step of identifying the damage site candidate Pc corresponding to the new damage site, and having In the visual inspection step, until it becomes impossible to confirm the actual presence of damage, or in the second damage site identification step, until the next smallest average value dTr ａｖｅ ceases to exist, the visual inspection step and the second damage site identification step are repeatedly executed. The damage inspection method according to claim 1.

Images