Penetrant flaw detection method and penetrant flaw detector

Abstract

To provide a penetrant flaw detection method and a penetrant flaw detector with a reduced penetration time of a penetrant.SOLUTION: A penetrant flaw detection method sequentially includes a heating step 40, a penetration step 31, a cooling step 41, a cleaning step 32, a developing step 33, and an observation step 34. A penetrant flaw detector 1 capable of executing the penetrant flaw detection method comprises a coil 51 capable of high-frequency induction heating or one or more steam injection units as heating means for the heating step 40. The heating step 40 includes heating a surface of an object to be inspected by 20 degrees or more in terms of absolute temperature within 10 seconds.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a penetrant inspection method and device, and more particularly to a method and device for penetrating a penetrant into the surface of an object to be inspected without adhering thereto. [Background technology]

[0002] Penetrant testing has long been known as a non-destructive testing method for detecting minute opening defects on the surfaces of products made of non-magnetic materials such as aluminum, titanium, austenitic stainless steel, and ceramics, which are manufactured as industrial materials.

[0003] Conventionally known penetrant inspection methods include a penetrant process in which a penetrant is applied to the surface of the test object to allow the penetrant to penetrate into the open defects present on the surface of the test object, a cleaning process in which excess penetrant that has not penetrated into the defects and remains on the surface of the test object is removed by a cleaning liquid so that the penetrant remains only in the defects, a development process in which a uniform thin layer of developer is formed on the surface of the test object after the cleaning liquid has dried, and the penetrant that has penetrated into the defects is sucked out to reveal a defect indication pattern on the layer surface, and an observation process in which the defect indication pattern is confirmed under irradiation with visible light or ultraviolet light. If the surface of the test object has oil stains or the like before the penetrant process, a pre-cleaning process is performed to clean the surface using an organic solvent or the like. The penetrant is usually a non-volatile, highly penetrating liquid obtained by dissolving a red dye or a fluorescent dye in a petroleum-based mixed solvent, an aromatic solvent, or the like, and adding a plasticizer, a surfactant, or the like. A method is also known in which an organic solvent that dissolves the penetrant or water is used as a cleaning liquid for cleaning the excess penetrant.

[0004] Patent Document 1 discloses a penetrant testing method in which the heating of the surface of a test specimen in the drying process that follows a cleaning process in which excess penetrant is washed away with water is carried out by induction heating, which causes self-heating through resistance loss of eddy currents induced near the surface of the test specimen. Although this is an excellent drying process, there are still problems with shortening the time required for the process of penetrating the penetrant.

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-167462 Summary of the Invention [Problem to be solved by the invention]

[0006] Thus, in the conventionally known penetrant inspection method, in the penetration step of penetrant penetrating into the open defect part present on the surface of the object to be inspected, a long penetration time was required to allow the penetrant to fully penetrate into the open defect part. The long penetration time in the penetration step causes the penetration step to become a bottleneck, reducing the work efficiency of the line, and a large space is required for the penetration step, which has been a problem. When the object to be inspected is a relatively large billet, etc., a space is required to store multiple billets for the penetration step, so in factories with a large production volume, it is necessary to secure a large space to store a large number of large billets, which has also been a problem. Therefore, the conventional penetrant inspection method has been practically unable to target parts with a large production volume or parts that must be inspected in real time. The present invention provides a penetrant inspection method and a penetrant inspection device used therefor to solve these problems. [Means for solving the problem]

[0007] Therefore, the penetrant inspection method of the present invention is a penetrant inspection method which sequentially comprises a penetrant step of applying a penetrant liquid to the object to be inspected, a cleaning step of removing the penetrant liquid from the surface of the object to be inspected, and an observation step of observing an indication pattern, and is characterized in that the penetrant inspection method further comprises a heating step prior to the penetrant step, and the heating step is a step of heating the surface of the object to be inspected by 20 degrees or more in absolute temperature.

[0008] In addition, the penetrant flaw detection method of the present invention is characterized in that the penetrant flaw detection method further includes a cooling step after the penetrating step is completed and before the cleaning step is started.

[0009] Furthermore, in the penetrant inspection method of the present invention, the heating means in the heating step is a means using high-frequency induction heating or steam heating, and the heating time by the heating means in the heating step is 10 seconds or less.

[0010] In addition, in the present invention, the penetrant flaw detection device is equipped with a heating means, a penetrating means, a cleaning means, and an observation means, and the heating means is characterized in that a coil is arranged around the object to be inspected and is configured to be able to heat the surface of the object to be inspected by high-frequency induction heating.

[0011] In addition, in the present invention, the penetrant flaw detection device is equipped with a heating means, a penetrating means, a cleaning means, and an observation means, and the heating means is characterized in that one or more steam injection parts are means for injecting steam near the surface of the object to be inspected. Effect of the Invention

[0012] The penetrant inspection method of the present invention is a penetrant inspection method which sequentially comprises a penetrant step of applying a penetrant liquid to the object to be inspected, a cleaning step of removing the penetrant liquid from the surface of the object to be inspected, and an observation step of observing the indication pattern, and is characterized in that the penetrant inspection method further comprises a heating step before the penetrant step, and the heating step is a step of heating the surface of the object to be inspected by 20 degrees or more in absolute temperature, so that a penetrant inspection method which can penetrate the penetrant liquid into an open defect in a short period of time can be provided.

[0013] Furthermore, in the penetrant inspection method of the present invention, the penetrant inspection method is characterized in that after the penetrant process is completed, a cooling process is further included before the cleaning process is started, so that a penetrant inspection method can be provided that can penetrate the penetrant into the open defect in a short period of time.

[0014] In addition, the penetrant inspection method of the present invention is characterized in that the heating means in the heating step uses high-frequency induction heating or steam heating, and the heating step is characterized in that the heating time by the heating means is 10 seconds or less, thereby providing a penetrant inspection method that can penetrate the penetrant into the open defect in a short period of time.

[0015] Furthermore, in the present invention, the penetrant flaw detection apparatus is equipped with a heating means, a penetrating means, a cleaning means, and an observation means, and the heating means is characterized in that a coil is arranged around the object to be inspected and is configured so that the surface of the object to be inspected can be heated by high-frequency induction heating, thereby making it possible to provide a penetrant flaw detection apparatus that can penetrate a penetrating liquid into an open defect in a short period of time.

[0016] Furthermore, in the present invention, the penetrant flaw detection apparatus is equipped with a heating means, a penetrating means, a cleaning means, and an observation means, and the heating means is characterized in that one or more steam injection sections are means for injecting steam near the surface of the object to be inspected, so that a penetrant flaw detection apparatus can be provided that can penetrate a penetrating liquid into an open defect in a short period of time. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a flowchart of a conventional penetrant inspection method. [Diagram 2] 1A and 1B are schematic cross-sectional views showing the transition of the state around the flaw 12 in a conventional penetrant inspection method, in which (W) is the state before the penetrating process 31 is performed, (X) is the state immediately after the penetrating liquid 21 is applied to the flaw 12 during the penetrating process 31, (Y) is the state around the flaw 12 when the penetrating time has elapsed from the state (X) during the penetrating process 31, and (Z) is the state around the flaw 12 after the cleaning process 32. [Diagram 3] FIG. 2 is a flowchart of a penetrant inspection method according to the present embodiment. [Figure 4] 13 is a schematic cross-sectional view showing the transition of the state around the flaw 12 in the penetrant inspection method of this embodiment, in which (W) is the state before the penetrant process 31 is performed, (X) is the state immediately after the penetrant liquid is applied to the flaw 12 during the penetrant process 31, (Y) is the state around the flaw 12 when the penetrant time has elapsed from the state (X) during the penetrant process 31, and (Z) is the state around the flaw 12 after the cleaning process 32. [Diagram 5] FIG. 2 is a perspective view of a portion of the penetrant flaw detection device according to the present embodiment. [Figure 6] 6A to 6C are diagrams showing a part of the penetrant flaw detection device according to the present embodiment of FIG. 5, in which (X) is a side view thereof, (Y) is a top view thereof, and (Z) is a front view thereof. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the details of the embodiment of the present invention will be described with reference to the drawings. First, the penetrant inspection method according to the present embodiment will be described. FIG. 1 is a flow chart of a conventional penetrant inspection method. FIG. 2 is a schematic cross-sectional view showing the transition of the state around the flaw 12 in the conventional penetrant inspection method, and the state transitions in the order of (W), (X), (Y), and (Z). Of these, (W) represents the initial state before the penetrant step 31 is performed. (X) represents the state immediately after the penetrant is applied to the flaw 12 in the penetrant step 31, (Y) represents the state around the flaw 12 when the penetrant time has elapsed from the state of (X) in the penetrant step 31, and (Z) represents the state around the flaw 12 after the cleaning step 32. FIG. 3 is a flow chart of a penetrant inspection method as an example of an embodiment according to the present invention. FIG. 4 is a schematic cross-sectional view showing the transition of the state around the flaw 12 in the penetrant inspection method according to the present embodiment, and the state transitions in the order of (W), (X), (Y), and (Z). Among them, (W) represents the initial state before the penetration step 31 is performed. (X) represents the state immediately after the application of the penetrant to the flaw 12 during the penetration step 31, (Y) represents the state around the flaw 12 when a penetration time shorter than the conventional time has elapsed from the state of (X) during the penetration step 31, and (Z) represents the state around the flaw 12 after the cleaning step 32. FIG. 5 is a perspective view of a part of the penetrant flaw detection device according to this embodiment, and is a perspective view showing the state in which the test object 10 passes between the coils 51 as it flows through the line. The coils 51 and rollers 61 for the heating step 40 are illustrated, but other devices such as the penetration means for performing the penetration step 31, the cleaning means in the cleaning step 32, and the observation means in the observation step 34 are omitted from the illustration. FIG. 6 is a side view of a part of the penetrant flaw detection device according to this embodiment of FIG. 5. As in FIG. 5, FIG. 6 also illustrates the coils 51 and rollers 61 for the heating step 40, but other devices such as the cleaning means in the cleaning step 32 and the observation means in the observation step 34 are omitted from the illustration. FIG. 6(X) is a side view of these, (Y) is a top view of these, and (Z) is a front view of these from the front, which is the left direction in FIG. 6(X). In this disclosure, for ease of explanation, when simply referring to the upper side, it refers to the upper side in Figures 6(X) and (Z), and when simply referring to the lower side, it refers to the lower side in Figures 6(X) and (Z).

[0019] The steps shown in FIG. 1 are a flow chart showing the steps of a conventional penetrant inspection method. In the conventional penetrant inspection method, a penetrant step 31, a cleaning step 32, a developing step 33, and an observation step 34 are sequentially performed. This will be described in detail with reference to the state around the flaw 12 shown in FIG. 2. Each of (W) to (Z) in FIG. 2 is a cross-sectional view showing an enlarged view of the flaw 12, which is a target for detection in the penetrant inspection method, on the inspection object 10. First, FIG. 2(W) shows the state before the penetrant step 31 shown in FIG. 1. In the state shown in FIG. 2(W), the flaw 12 has a defect opening 13 and a defect interior 14. The flaw 12 is formed in a shape having the defect opening 13 on the surface 11, which is the surface of the inspection object 10.

[0020] Next, the penetrating step 31 shown in Fig. 1 will be described in detail. The penetrating step 31 is performed by applying the penetrating liquid 21 to the surface 11 of the object to be inspected 10. Methods of application include coating, immersion in the penetrating liquid, etc. The penetrating liquid 21 may be a liquid having a composition in which a fluorescent dye or a red visible dye is dissolved in an oily solvent and a surfactant is further added to the liquid to make it removable by washing with water, or a liquid in which a fluorescent dye or a red visible dye is dissolved in an oily solvent.

[0021] FIG. 2(X) shows the state immediately after the penetrant 21 is applied to the surface 11 in the penetrant step 31. Since the penetrant 21 is applied to the surface 11 immediately, the penetrant 21 has not yet penetrated into the defect interior 14, which is the inside of the flaw 12. In the conventional penetrant flaw detection method, the penetrant 21 does not penetrate sufficiently into the defect interior 14 from the defect opening 13 unless a certain long penetration time is passed after the penetrant step 31. FIG. 2(Y) shows the state after the long penetration time has passed. In FIG. 2(Y), the penetrant 21 has sufficiently penetrated and penetrated into the defect interior 14. However, since the penetrant 21 covers the surface 11, it is necessary to remove the penetrant 21 from the surface 11 by the cleaning step 32 shown in FIG. 1. Therefore, in the cleaning step 32, the cleaning liquid is applied to the surface 11 from, for example, the direction of the arrow in FIG. 2(Y) so as to wash away the penetrant 21. This causes a transition from the state of FIG. 2(Y) to the state of FIG. 2(Z).

[0022] Next, the state of Fig. 2(Z) will be described in detail. The state of Fig. 2(Z) is a state in which the penetrant liquid 21 that filled the surface 11 of the inspection object 10 has been washed away with a cleaning liquid in the cleaning step 32, and the penetrant liquid 21 has been removed. Although the penetrant liquid 21 has been removed from the surface 11, the penetrant liquid 21 remains inside the defect 14 as it has penetrated therein.

[0023] Next, the developing step 33 will be described. First, in the state shown in FIG. 2(Z), the penetrant 21 remains only inside the defect 14. In this state, the flaw 12 is so fine that the presence of the penetrant 21 is difficult to detect with the naked eye. Therefore, a white inorganic fine powder or a dispersion of the white inorganic fine powder in water or a solvent is applied to the surface 11 as a developer so as to form a uniform thin layer on the test object. Examples of the white inorganic fine powder include magnesium carbonate powder and calcium carbonate powder. Then, the uniform thin layer of the white inorganic fine powder formed on the surface 11 causes a capillary phenomenon, sucking out the penetrant 21 inside the defect 14, thereby forming a rainbow pattern (defect indication pattern). This defect indication pattern shows the defect opening 13 in an enlarged manner, making it easy to detect with the naked eye.

[0024] As for the observation step 34, in addition to visual observation, the indication pattern can be observed using a method in which a fluorescent penetrant is used and then a black light is used in a dark room, or an image is generated using an imaging device or the like and then inspected.

[0025] Next, the penetrant inspection method according to the present invention and the penetrant inspection device 1 using this method will be described in detail with reference to Figs. 3 and 4. The steps shown in Fig. 3 are a flow chart showing steps of the penetrant inspection method as an example of an embodiment according to the present invention. Fig. 4 is a cross-sectional view showing an enlarged view of the periphery of a flaw 12, which is a detection target in the penetrant inspection method, on an object 10 in each of Figs. (W) to (Z). Unlike the conventional method, the penetrant inspection method according to the present embodiment includes a heating step 40 shown in Fig. 3. In the heating step 40, heating is performed toward the surface 11 shown in Fig. 4(X) by a heating means. The heating means may be a method using high-frequency induction heating, a method using steam or dry steam, a method using hot air, or a method using infrared heating, or other known means may be used. By heating the surface 11 and the surface vicinity 16 by the heating means, the air inside the defect 14 expands, making it easier to draw in the penetrant liquid 21. In addition, in this disclosure, steam refers to steam with a steam temperature of 70 degrees or more, and dry steam refers to steam with a steam temperature of 100 degrees or more. Furthermore, when simply referring to steam, dry steam is included.

[0026] The penetrant inspection method according to an embodiment of the present invention will be described in more detail with reference to Figs. 3 and 4. The penetrant inspection method according to an embodiment of the present invention shown in Fig. 3 is a method in which a heating step 40, a penetrant step 31, a cooling step 41, a cleaning step 32, a developing step 33, and an observation step 34 are sequentially performed. In this manner, the penetrant inspection method according to this embodiment first performs the heating step 40. In the heating step 40, the surface 11 is heated by a heating means in the initial state shown in Fig. 4(W), and then the penetrant step 31 is performed. In the heating step, it is preferable to heat the surface 11 to 20 degrees Celsius or more in absolute temperature. This means that the penetrant inspection is usually performed at room temperature, and therefore the surface 11 is heated to 20 degrees Celsius or more from room temperature. By heating in this manner, the penetration time is significantly reduced.

[0027] In this disclosure, the penetration time refers to the time required from the end of the process of applying the penetrant liquid 21 to the surface 11 of the object to be inspected 10 in the penetration process 31 until the penetrant liquid 21 has sufficiently penetrated into the interior 14 of the defect for penetrant testing and the defect is ready to proceed to the next cleaning process 32.

[0028] In the heating step 40, it is preferable to raise the absolute temperature of the surface 11 by 20 degrees Celsius or more, and it is even more preferable to raise the absolute temperature of the surface 11 by 50 degrees Celsius or more by the heating means. When the absolute temperature of the surface 11 is raised by the heating means by 50 degrees Celsius or more in this manner, it is preferable that the penetrant liquid 21 can penetrate into the defect interior 14 to such an extent that a relatively large flaw of about 10 to 50 microns in size can be detected in a penetration time of about 5 to 10 seconds in a penetrant inspection of a billet or the like.

[0029] Next, in the heating step 40, it is preferable from the viewpoint of thermal diffusion that the heating time required to raise the temperature of the surface 11 by 20 degrees Celsius or 50 degrees Celsius or more in absolute temperature is 10 seconds or less. In general, a heating time of 1 to 3 seconds is more preferable because it can more effectively suppress thermal diffusion and can heat only the surface vicinity 16. In the penetrant inspection method disclosed herein, the surface vicinity 16 is heated as a target. As a result, the inner part of the test object 10 is cooled down from the surface vicinity 16 and is at room temperature even after the heating step 40, and the inner part of the test object 10 generates a cooling effect on the surface vicinity 16, so it is preferable to set the heating time to 1 to 3 seconds or less. In particular, when the heating means is high-frequency induction heating, only the surface vicinity 16 is heated, so that the cooling effect can be generated more effectively by setting the heating time to a short time. A heating time of 1 to 3 seconds is preferable because only the surface vicinity 16 has heat, and the heat capacity that needs to be cooled is reduced. When the heating means is high-frequency induction heating or steam, if the heating time is long, such as 10 seconds or more, the inner part of the test object 10, which is located inside the surface vicinity 16, will be heated due to thermal diffusion. Therefore, it will take a long time to cool down, and the penetration time will also be extended.

[0030] The penetrant step 31 in the penetrant inspection method according to this embodiment shown in Fig. 3 is performed by applying the penetrant liquid 21 to the surface 11 of the object 10 to be inspected. This results in a transition to the state shown in Fig. 4(X). The penetrant liquid 21 may be applied by a known method such as application by spraying or immersion in a penetrant liquid tank. Examples of the penetrant liquid 21 include a liquid having a composition in which a fluorescent dye or a red visible dye is dissolved in an oily solvent and a surfactant is further added to the liquid to make it removable by washing with water, or a liquid in which a fluorescent dye or a red visible dye is dissolved in an oily solvent, but other known liquids may also be used.

[0031] In the penetration step 31, after the penetrant liquid 21 is applied, the penetrant liquid 21 is left attached to the surface 11 and the cleaning step 32 is not started until the penetration time has elapsed. This allows the penetrant liquid 21 to penetrate into the defect interior 14. By going through the heating step 40 of the penetrant flaw detection method according to the present embodiment, this penetration time can be made shorter than usual. Specifically, what previously required 5 to 10 minutes or more is reduced to about 5 to 15 seconds. The use of a heating means is preferable because it allows the penetrant liquid 21 to sufficiently penetrate into the defect interior 14 even if the penetration time is shortened.

[0032] Next, the cooling step 41 shown in FIG. 3 will be described in detail. The cooling step 41 is preferably performed during the permeation time after the application of the permeation liquid 21 in the permeation step 31. However, the cooling step 41 may not be provided. In that case, as another example of this embodiment, a permeation time may be provided between the permeation step 31 and the cleaning step 32 in which the cooling step 41 is not performed. The specific content of the cooling step 41 is to blow cold air or pour room temperature water or cold water toward the vicinity of the surface 11 to which the permeation liquid 21 is attached in the state of (X) in FIG. 4 after the permeation step 31. This generates a cooling effect that cools the surface 11 and the surface vicinity 16. The cooling effect also cools the air inside the defect 14 and causes it to contract. This draws the permeation liquid 21 into the defect 14. By performing the cooling step 41, such a cooling effect is generated, so that the permeation time from the cooling step 41 to the cleaning step 32 can be shortened. As causes of the cooling effect in the vicinity of the surface 11 and the surface vicinity portion 16, cooling from the inside portion of the test object 10 and cooling by the penetrant 21 are also important.

[0033] Next, the cleaning step 32 shown in FIG. 3 will be described. In the cleaning step 32, as shown in FIG. 4(Y), the penetrant liquid 21 has sufficiently penetrated into the defect interior 14 from the defect opening 13. In other words, the penetrant liquid 21 has sufficiently penetrated into the defect interior 14. However, the penetrant liquid 21 covers the surface 11, and therefore needs to be removed. For this reason, the penetrant liquid 21 is removed from the surface 11 by the cleaning step 32 shown in FIG. 3. For this reason, in the cleaning step 32, the cleaning liquid is applied to the surface 11 from, for example, the direction of the arrow in FIG. 4(Y) so as to wash away the penetrant liquid 21. This causes a transition from the state of FIG. 4(Y) to the state of FIG. 4(Z).

[0034] Next, the developing step 33 will be described. First, in the state shown in FIG. 4(Z), the penetrant 21 remains only inside the defect 14. In this state, it is difficult to detect the presence of the penetrant 21 with the naked eye. Therefore, as a developer, a white inorganic fine powder or a powder obtained by dispersing the white inorganic fine powder in water or a solvent is applied to the surface 11 so as to form a uniform thin layer on the test object. As the white inorganic fine powder, a powder such as magnesium carbonate powder or calcium carbonate powder that is known to be used as a developer may be used. Then, the uniform thin layer of the white inorganic fine powder formed on the surface 11 causes a capillary phenomenon, sucking out the penetrant 21 inside the defect 14, thereby forming a rainbow pattern (defect indication pattern). This defect indication pattern shows the defect opening 13 in an enlarged manner, making it easier to detect with the naked eye and improving the detection accuracy.

[0035] However, the penetrant inspection method of the present invention may be performed by a known method such as a non-developing method without the development step 33. In the case of the non-developing method, the development step 33 is not performed to apply a developer, and the indication pattern of the penetrant is observed as is. For this reason, it is preferable to use a fluorescent penetrant from the viewpoint of convenience of observation in the observation step 34, but the present invention is not limited to this.

[0036] As for the observation step 34 shown in FIG. 3, the indication pattern can be observed by visual inspection or by using known means such as a method of using a fluorescent penetrant and then a black light in a dark room, or a method of generating an image using an imaging device and inspecting it.

[0037] Next, referring to Figs. 5 and 6, a method using high-frequency induction heating, which is one of the heating means in the penetrant inspection method according to the present embodiment, and a penetrant inspection device 1 capable of carrying out this method will be described in detail. Fig. 5 is a diagram showing a coil 51 arranged to surround the periphery of the object 10 to be inspected, which is a configuration suitable for an assembly line inspection process, and Figs. 6(X), (Y), and (Z) are side, top, and front views thereof. In the penetrant inspection device 1 of the present invention, the object 10 to be inspected is placed on a plurality of rollers 61 and can be moved by the rollers 61. The coil 51 is provided between the plurality of rollers 61. The coil 51 is used for high-frequency induction heating, which is the heating means of the penetrant inspection device of the present invention. The coil 51 shown in Figs. 5 and 6 is a through coil for performing high-frequency induction heating by the through coil method. The coil 51 shown in Figs. 5 and 6 is stored in a case, and the through coil is stored inside the case, centered around a large central hole provided in the coil 51. In this embodiment, high-frequency induction heating is performed by passing an alternating current through the coil 51, but other known means may be used, such as a pancake coil method in which a pancake coil is used instead of the through coil.

[0038] The penetrant inspection device 1 of the present invention may be provided with a cleaning means and an observation means in addition to the heating means. In the penetrant inspection device 1 shown in Figs. 5 and 6, after high-frequency induction heating by the coil 51, a cleaning means may be provided for performing a cleaning step 32 for removing the penetrant liquid 21 from the test object 10 sent by the roller 61, and further, as a subsequent step, a developing means for performing a developing step 33 and an observation means for performing an observation step 34 may be provided. However, since there is a non-developing method, the developing means may not be provided. As the cleaning means, a mechanism for applying a cleaning liquid to the test object 10 by means of spraying or coating is preferable, and as the developing means, a spraying or coating device for applying a developer or developing solution to the surface 11 of the test object 10 is preferable, and as the observation means, it is preferable that the observation means is composed of an imaging means for capturing still or moving images, a recording medium, a display medium, etc., but for each of them, a known one may be used as appropriate.

[0039] Next, the heating means in the penetrant inspection method and penetrant inspection device 1 of this embodiment will be described in more detail. As the heating means, a high-frequency induction heating method, a steam or dry steam method, a hot air method, and an infrared heating method can be used. When using hot air, it is preferable to use dry air, and known means can be used as devices for implementing these heating means. Moreover, the heating means is configured to be able to implement the heating step 40.

[0040] Next, the operation of the high-frequency induction heating method, which is the heating means in the penetrant inspection method and penetrant inspection device of this embodiment, will be described in detail. In the high-frequency induction heating, the test object 10 is heated using the coil 51. In Figs. 5 and 6, the through coil method is used, in which the test object passes through the annular coil 51 to detect flaws, but the high-frequency induction heating may be performed using the pancake coil method, in which the coil is formed in a flat and spiral shape. In the high-frequency induction heating method, an alternating current, which is a current whose magnitude and direction change periodically with time, is passed through the coil. Then, in the magnetic field that changes due to the alternating current, an eddy current is generated by electromagnetic induction. This eddy current generates Joule heat, and eddy current loss, which is heat loss of electromagnetic energy, occurs. The test object 10 is heated by this eddy current loss, etc. The current passed through the coil 51 is high-frequency, and specifically, it is preferable to use one having a frequency of 20 kHz to 450 kHz. High-frequency induction heating has the characteristic that the surface vicinity 16, which is in the vicinity of the surface 11 of the object to be inspected 10 shown in FIG. 4(W), is heated intensively, while the area inside the surface vicinity 16 is not heated very much.

[0041] It is known that the heating of the surface vicinity 16 by this high frequency induction heating is performed up to a depth of a penetration depth δ from the surface 11 of the object 10 to be inspected. In this embodiment, the penetration depth δ shown in FIG. 4(W) is preferably set to 0.2 mm to 1 mm, and more preferably set within a range of 0.2 mm to 0.3 mm. The dimensions of the object 10 to be inspected are about 10 to 50 meters in length and 50 mm to 500 mm in diameter. The calculation formula for the penetration depth δ is shown in Equation 1, where p is the resistivity (uΩ·cm) of the metal, u is the relative permeability, and f is the frequency (Hz).

[0042]

number

[0043] If the penetration depth δ is within a range of 0.2 mm to 0.3 mm, the surface vicinity 16 shown in Fig. 4(W) is heated, and the inner part of the test object 10 therebetween is in an unheated state close to room temperature. It is preferable that the heating means be high-frequency induction heating, since after the heating step 40, heat from the surface vicinity 16 is released to the inner part of the test object 10, producing a cooling effect.

[0044] As an example of an embodiment of the penetrant inspection device and penetrant inspection method of the present invention, the operation when high-frequency induction heating is used as the heating means will be described in detail below. In the heating step 40 performed in the state of FIG. 4(W), the range from the surface 11 to the penetration depth δ shown in the figure is the surface vicinity 16. The penetration depth δ in this case is an arbitrary value when an arbitrary penetration depth δ is set in advance in the design of the heating step 40. When high-frequency induction heating is performed as the heating means in the heating step 40, the surface vicinity 16 is heated first. Next, the air on the surface 11 adjacent to the surface vicinity 16 and the air inside the defect 14 are heated. By heating the air, the air remaining inside the defect 14 is heated when the state of FIG. 4(X) is reached in the penetrant step 31 shown in FIG. 3. During the penetration time, the heated air is cooled and contracted by the cooling effect of the cooling from the part inside the surface vicinity 16 of the test object 10, the cooling by the penetrant 21, and the cooling by the cooling step 41. As the air inside the defect 14 contracts, a force acts to draw the penetrant liquid 21 into the defect 14, and the time it takes for the penetrant liquid 21 to permeate into the defect 14 is shortened.

[0045] Next, the penetrant inspection method and penetrant inspection device of the present invention are applicable to materials in which eddy currents do not easily flow, and the case where the heating means is steam or, among steam, dry steam will be described in detail. In the case of dry steam, although not shown, as an example of this embodiment, the penetrant inspection device 1 is provided with one or more steam injection units. The steam injection unit is composed of an injection nozzle, a hose, a steam supply source, etc., but as long as it can inject steam onto the surface 11, it may be by any suitable known means. The steam injection unit injects dry steam or steam toward the surface 11. At this time, the steam or dry steam preferably has a steam pressure of 0.03 megapascals or more. As a result, the air on the surface 11 becomes heated steam. Then, the steam penetrates into the inside 14 of the defect and fills the inside 14 of the defect. In addition, by heating not only the surface 11 but also the surface vicinity 16 as a target, the air inside the defect 14 is prevented from cooling immediately. By heating in this manner, the air remaining inside the defect 14 is heated when the state of Fig. 4(X) is reached in the permeation step 31 shown in Fig. 3. After the permeation step 31, this heated air is cooled during the permeation time by the cooling effects of the cooling from the portion inside the surface vicinity portion 16 of the object 10, the cooling by the permeation liquid 21, and the cooling step 41, and the steam is condensed. As the steam inside the defect 14 condenses, a pressure difference occurs between the air inside the defect 14 and the atmospheric pressure, and the permeation liquid 21 is drawn into the defect 14. In this way, the permeation time required for the permeation of the permeation liquid 21 into the defect 14 is shortened.

[0046] In the case of an embodiment in which steam is used as the heating means of the penetrant inspection device and penetrant inspection method of the present invention, for example, at a gauge pressure of 0 MPa, the specific volume of saturated water at a saturation temperature of 100 degrees Celsius is 0.00104 m^3 / kg, while saturated steam has a volume of 1.673 m^3 / kg, which is approximately 1700 times larger. This results in a large change in volume, and the generation of a large pressure difference, making it possible to significantly shorten the penetration time.

[0047] As an example of an embodiment of the penetrant inspection device and penetrant inspection method according to the present invention, when the heating means is hot air, the heating action and the fact that the surface vicinity portion 16 is heated are the same as in the case of steam or dry steam. In addition, the heating means may be a combination of high-frequency induction heating and hot air, steam, or dry steam, or a combination of high-frequency current heating and hot air, steam, or dry steam. In addition, high-frequency induction heating, steam, or hot air may be combined with infrared heating. Such a combination is preferable because it further reduces the heating time.

[0048] Next, the relationship between performing the heating step 40 and the faster penetration time will be described. When the surface 11 is heated to 50 degrees Celsius in absolute temperature by the heating means in the heating step 40, theoretically, when air at 25 degrees is raised by 50 degrees in the heating step 40, for example, the volume expands and increases by 17 percent. In this state, the penetration step 31 is performed and the penetrating liquid 21 is applied to the surface 11. Then, in addition to the force of the penetrating liquid 21 itself trying to enter the inside 14 of the defect, the volume of the air inside the defect 14, which expanded by 17 percent, returns to its original state as the temperature approaches normal temperature, and the volume decreases by about 17 percent. This makes it possible to instantly draw a large amount of the penetrating liquid 21 into the inside 14 of the defect.

[0049] As an example of an embodiment of the penetrant inspection device and penetrant inspection method according to the present invention, the case where the heating means is only hot air or only infrared heating will be described. When only these means are used, the heating time, which is the time required to heat the surface 11 to 20 degrees Celsius or more in absolute temperature, may take about one minute or more. Therefore, even if the surface vicinity 16 is heated, thermal diffusion occurs, and the inner part of the object 10, which is closer to the surface vicinity 16, also becomes hot. In this case, the cooling effect on the surface vicinity 16 due to the inner part of the object 10 being at room temperature is weakened. Therefore, it is particularly preferable to provide a cooling process 41.

[0050] Next, as an example of an embodiment of the penetrant inspection device and penetrant inspection method according to the present invention, the case where the heating means is only steam or only high-frequency induction heating will be described. When the heating means is only hot air or only infrared heating, it is difficult to heat the surface 11 to 20 degrees Celsius or more in absolute temperature within 10 seconds, whereas when the heating means is only steam or only high-frequency induction heating, it is fully possible to heat the surface 11 to 20 degrees Celsius or more in absolute temperature even if the heating time is within 10 seconds. Therefore, when the heating means is only steam or only high-frequency induction heating, the heating time can be kept within 10 seconds, and as a result, thermal diffusion is sufficiently suppressed. Therefore, when the heating means is only steam or only high-frequency induction heating, it is preferable to provide the cooling process 41, but the cooling process 41 may not be provided.

[0051] Furthermore, as another example of an embodiment of the penetrant inspection method according to the present invention, the penetrant step 31 may be started in the middle of the heating step 40. For example, if the heating step 40 is performed for 10 seconds, the penetrant step 31 may be started after 5 seconds have elapsed, and application of the penetrant liquid 21 to the surface 11 may begin. In this case, the timing for starting the penetrant step 31 is preferably 3 seconds or more after the heating step 40 has been started. Since the application of the penetrant step takes several to 15 seconds, starting the penetrant step 31 in the middle of the heating step 40 is preferable because it is possible to shorten the time required for the entire penetrant inspection method by several to 10 seconds.

[0052] Next, the penetrant inspection device 1 of the present invention will be further described. The penetrant inspection device 1 of the present invention may include a heating means for performing the heating step 40, a penetrating means for performing the penetrating step 31, a cooling means for performing the cooling step 41, a cleaning means for performing the cleaning step 32, a developing means for performing the developing step 33, and an observation means for performing the observation step 34. As the penetrant inspection device, a known means such as a means for applying the penetrant liquid 21 to the object 10 by a spraying device may be used, as the cooling means, a known device for blowing cold air, as the cleaning means, a coating device for applying the cleaning liquid to the object 10, as the developing means, a device for applying the developing liquid to the object 10, as the observation means, as well as visual observation, a video or still image capturing device, etc., may be used for each of the known means. In addition, the penetrant inspection device 1 of the present invention may be appropriately designed so that the penetrant inspection method of the present invention can be implemented.

[0053] The present disclosure can be suitably used for the purpose of inspecting defects in billets and the like made of non-magnetic materials as the inspection subject 10. However, the present disclosure is not limited to this, and can be widely used in the inspection of products that require flaw detection. [Explanation of symbols]

[0054] 1, Penetrant testing equipment 10. Test object 11, surface 12. Damage 13. Defective opening 14. Defect inside 16. Near surface 21, Penetration liquid 31, Penetration process 32. Cleaning process 33, Development process 34. Observation process 40,Heating process 41, Cooling process 51. Coil 61, Roller δ Penetration depth

Claims

1. A penetrant inspection method including a penetrant step of applying a penetrant to an object to be inspected, a cleaning step of removing the penetrant from the surface of the object to be inspected, and an observation step of observing an indication pattern, The penetrant inspection method further includes a heating step prior to the penetrating step, The penetrant inspection method, wherein the heating step is a step of heating the surface of the test object by 20 degrees or more in absolute temperature.

2. The penetrant inspection method according to claim 1 , further comprising a cooling step after the penetrating step is completed and before the cleaning step is started.

3. 3. The penetrant inspection method according to claim 1, wherein the heating step is performed using a heating means that employs high-frequency induction heating or steam heating, and the heating step is performed for a heating time of 10 seconds or less using the heating means.

4. A penetrant inspection device for carrying out the penetrant inspection method according to claim 1, The penetrant flaw detector includes a heating means, a penetrant means, a cleaning means, and an observation means, The penetrant flaw detection device is characterized in that the heating means is configured such that a coil is disposed around the object to be inspected and that the surface of the object to be inspected can be heated by high-frequency induction heating.

5. A penetrant inspection device for carrying out the penetrant inspection method according to claim 1, The penetrant flaw detector includes a heating means, a penetrant means, a cleaning means, and an observation means, The penetrant inspection device is characterized in that the heating means is a means for injecting steam near the surface of the object to be inspected using one or more steam injection units.

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