Foam leak test method and vacuum box

Abstract

To make it easier for an inspector to check a hole in an inspection body regardless of the size of the diameter.SOLUTION: A foam leakage inspection method according to one aspect includes: applying a foaming liquid to an inspection surface of an inspection object; placing a vacuum box having a transparent window on the inspection surface; forming an inner space with the inspection surface and the vacuum box; observing the foaming liquid on the inspection surface while reducing pressure in the inner space until a differential pressure between the pressure in the inner space and the atmospheric pressure reaches a first pressure; observing the foaming liquid on the inspection surface while maintaining the differential pressure in a state of the first pressure; observing the foaming liquid on the inspection surface while further reducing the pressure in the inner space until the differential pressure reaches a second pressure from the first pressure; and observing the foaming liquid on the inspection surface while maintaining the differential pressure in a state of the second pressure.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a foam leak test method and a vacuum box for use in the foam leak test method. [Background technology]

[0002] A foam leak test method has been known for some time as a method for inspecting the presence or absence of a penetration defect in an object to be inspected (for example, Patent Document 1). There are two types of foam leak test methods: a pressure method and a vacuum method. In the vacuum method of foam leak test, a foam liquid is first applied to the inspection surface of the object to be inspected, and then a vacuum box with a transparent window is placed on the inspection surface of the object to be inspected, and a vacuum is created inside the vacuum box. The inspector detects the presence and location of holes that cause gas leakage by observing the formation of bubbles in the foam liquid applied to the inspection surface through the window of the vacuum box. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-27656 Summary of the Invention [Problem to be solved by the invention]

[0004] In the foam leak test, the ease of observation by the inspector varies depending on the size of the hole. Smaller diameter holes have a smaller flow rate of gas passing through them than larger diameter holes. This means that the amount of foaming is small, making it difficult for the inspector to find the hole. On the other hand, larger diameter holes have a larger flow rate of gas passing through them, so the foaming liquid near the hole is blown away by the gas passing through the hole, making it difficult to detect the hole.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for testing foam leakage and a vacuum box that allow an inspector to easily check holes in an object to be inspected regardless of the size of the hole's diameter. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, one embodiment of the present invention provides a foaming leak testing method that applies a foaming liquid to an inspection surface of an inspection object, places a vacuum box with a transparent window on the inspection surface, and forms an internal space between the inspection surface and the vacuum box. The foaming liquid on the inspection surface is observed while reducing the pressure of the internal space until the differential pressure between the pressure in the internal space and atmospheric pressure reaches a first pressure, and the foaming liquid on the inspection surface is observed while maintaining the differential pressure at the first pressure. The foaming liquid on the inspection surface is observed while further reducing the pressure of the internal space until the differential pressure reaches a second pressure from the first pressure, and the foaming liquid on the inspection surface is observed while maintaining the differential pressure at the second pressure.

[0007] According to the above method, two stages of observation are performed: observing the foaming liquid when the differential pressure between atmospheric pressure and the internal space is at a first pressure, and observing the foaming liquid when the differential pressure is at a second pressure. By setting the first pressure to a relatively low value, when the differential pressure is reduced to the first pressure and maintained at the first pressure, it is possible to prevent the foaming liquid near a relatively large diameter hole from being blown away by the gas flowing into the vacuum box through the hole. This makes it easier for the inspector to detect a relatively large diameter hole when the differential pressure is reduced to the first pressure and maintained at the first pressure. Furthermore, by further reducing the internal space and changing the differential pressure from the first pressure to a second pressure, the total volume of gas passing through the holes and entering the internal space increases compared to when the differential pressure is maintained at the first pressure. This increases the amount of foaming at the holes, making it easier for the inspector to detect a relatively small diameter hole that was difficult to observe when the differential pressure was reduced to the first pressure and maintained at the first pressure. Therefore, according to the above method, the inspector can easily check the hole in the inspection object regardless of the size of the diameter.

[0008] Furthermore, a vacuum box according to one embodiment of the present invention is a vacuum box for foam leak testing that is placed on the inspection surface of an inspection body, and comprises a box body that forms an internal space together with the inspection surface, one or more pipes connected to the box body having a first atmospheric open path, a second atmospheric open path, and a third atmospheric open path for respectively opening the internal spaces to the atmosphere, a first opening / closing valve provided in the first atmospheric open path, a first pressure adjustment valve provided in the second atmospheric open path, a second opening / closing valve provided in the third atmospheric open path, and a second pressure adjustment valve provided between the end of the third atmospheric open path that is open to the atmosphere and the second opening / closing valve.

[0009] According to the above-described vacuum box, the second on-off valve and the second pressure adjustment valve are arranged in series in the flow path for opening the internal space to the atmosphere. When the internal space is evacuated with the first on-off valve closed and the second on-off valve open, the pressure in the internal space can be adjusted to a first pressure adjusted by the first pressure adjustment valve and the second pressure adjustment valve. When the internal space is evacuated with the first on-off valve closed and the second on-off valve closed, the pressure in the internal space can be adjusted to a second pressure adjusted by the first pressure adjustment valve, which is lower than the first pressure. Therefore, when a foaming leak test is performed using the above-described vacuum box, two-stage adjustment of the pressure in the internal space can be easily performed, making it easier for the inspector to identify holes in the test object regardless of their diameter. Furthermore, because the first on-off valve and the first pressure adjustment valve are arranged in parallel, opening the first on-off valve when the internal space is in a vacuum state can quickly raise the pressure in the internal space to atmospheric pressure. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a foaming leak test method and a vacuum box that allow an inspector to easily check holes in an object to be inspected regardless of the size of the hole's diameter. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a foaming leak test device used in a foaming leak test method according to one embodiment of the present invention. FIG. [Figure 2] 1 is a flowchart showing the flow of a foaming leakage test method. [Figure 3] 1 is a graph showing the relationship between the elapsed time in a foaming leakage test method and the differential pressure between atmospheric pressure and the pressure in the space inside the vacuum box. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a foaming leakage test method and a vacuum box according to one embodiment of the present invention will be described with reference to the drawings.

[0013] The foaming leak test method of this embodiment complies with the vacuum method of JIS Z2329. That is, in the foaming leak test method of this embodiment, a foaming liquid is applied to the test surface of the test object, and then a vacuum box with a transparent window is placed on the test surface. Thereafter, the internal space formed by the test surface and the vacuum box is evacuated with a vacuum pump, and the formation of bubbles in the foaming liquid is observed to detect the location of the gas leak.

[0014] FIG. 1 is a schematic diagram of a foaming leak test apparatus 1 used in the foaming leak test method according to this embodiment. The foaming leak test apparatus 1 includes a vacuum box 2, a vacuum pump 3, an exhaust pipe 4 connected to the vacuum pump 3, and a pressure gauge 5. In the following embodiments, the concept of up-down direction corresponds to the concept of up-down direction when the test surface 101 of the test object 100 faces upward as shown in FIG. 1 and the vacuum box 2 is placed on the test surface 101 from above. However, this is used for convenience in explanation and does not limit the orientation of the configuration of the invention to this direction.

[0015] In this embodiment, the test object 100, the presence and location of which is tested by the foaming leak test device 1, is, for example, the bottom of a flat-bottomed, cylindrical, vertical tank. However, the type of test object 100 is not particularly limited. For example, the test object 100 does not have to be the bottom of the tank, but may be the roof or side of the tank. Furthermore, the test object 100 may be a structure other than a tank.

[0016] [Vacuum box configuration] The vacuum box 2 is a vacuum box for a foaming leak test that is placed on the test surface 101 of the test object 100. The vacuum box 2 has a box body 10 and one or more pipes 20 connected to the box body 10.

[0017] The box 10 forms an internal space S together with the inspection surface 101 of the inspection object 100. The box 10 has an upper wall 11 and a peripheral wall 12, and is formed in a substantially rectangular parallelepiped shape with an open bottom. The upper wall 11 is rectangular when viewed from above. The upper wall 11 is transparent. The upper wall 11 is, for example, an acrylic plate. In this embodiment, the entire upper wall 11 is configured as a transparent window that allows the inspector to observe the interior of the internal space S. However, the upper wall 11 may have a portion that configures a transparent window and the remaining portion configured from an opaque material. An inlet / outlet 11a and a through hole 11b are formed in the upper wall 11.

[0018] The peripheral wall 12 is composed of four side walls arranged vertically around the periphery of the upper wall 11. The lower end of the peripheral wall 12 is the opening edge of the vacuum box 2, and is the part that comes into contact with the inspection surface 101 when the inspection object 100 is placed on the inspection surface 101. For this reason, at least the lower end of the peripheral wall 12 is made of a material that can improve the airtightness between the lower end of the peripheral wall 12 and the inspection surface 101 of the inspection object 100. In this embodiment, the entire peripheral wall 12 is made of a sponge-like elastic material.

[0019] The one or more pipes 20 include a first pipe 21 connected to the inlet / outlet 11a of the upper wall 11 and a second pipe 22 connected to the through-hole 11b of the upper wall 11.

[0020] The first pipe 21 allows gas to flow into the internal space S and gas to be discharged from the internal space S. The first pipe 21 is connected to the exhaust pipe 4. That is, one end of the exhaust pipe 4 is connected to the first pipe 21 via a joint 4a, and the other end of the exhaust pipe 4 is connected to the vacuum pump 3. A flow path formed by the first pipe 21 and the exhaust pipe 4 and extending from the inlet / outlet 11a to the vacuum pump 3 is referred to as an exhaust flow path 31. When the vacuum pump 3 is operated, the internal space S is evacuated through the exhaust flow path 31.

[0021] The first pipe 21 also constitutes a first atmosphere open path 41, a second atmosphere open path 42, and a third atmosphere open path 43 for opening the internal space S to the atmosphere, respectively.

[0022] A first on-off valve 51 is provided in the first atmosphere open path 41. A first pressure adjustment valve 61 is provided in the second atmosphere open path 42. A second on-off valve 52 is provided in the third atmosphere open path 43. A second pressure adjustment valve 62 is provided between the second on-off valve 52 and an end 43b of the third atmosphere open path 43 that is open to the atmosphere.

[0023] In this embodiment, the first atmosphere open path 41 branches off from the exhaust flow path 31, the second atmosphere open path 42 branches off from the first atmosphere open path 41, and the third atmosphere open path 43 branches off from the exhaust flow path 31. More specifically, one end 41a of the first atmosphere open path 41 is connected to the exhaust flow path 31, the other end 41b of the first atmosphere open path 41 is open to the atmosphere, one end 42a of the second atmosphere open path 42 is connected to a portion of the first atmosphere open path 41 between the one end 41a and the first on-off valve 51, the other end 42b of the second atmosphere open path 42 is open to the atmosphere, and one end 43a of the third atmosphere open path 43 is connected to the exhaust flow path 31, and the other end 43b of the third atmosphere open path 43 is open to the atmosphere.

[0024] Therefore, in the flow path for opening the internal space S to the atmosphere, the first opening / closing valve 51 and the first pressure regulating valve 61 are arranged in parallel, and the second opening / closing valve 52 and the second pressure regulating valve 62 are arranged in series.

[0025] The first on-off valve 51 and the second on-off valve 52 are each a ball valve. However, the first on-off valve 51 and the second on-off valve 52 do not have to be ball valves and may be other types of on-off valves, such as gate valves or butterfly valves. Furthermore, the first on-off valve 51 and the second on-off valve 52 may be the same type of on-off valve or different types of on-off valves.

[0026] The first pressure regulating valve 61 and the second pressure regulating valve 62 are each a needle valve. However, the first pressure regulating valve 61 and the second pressure regulating valve 62 do not have to be needle valves and may be other types of pressure regulating valves, such as globe valves. Furthermore, the first pressure regulating valve 61 and the second pressure regulating valve 62 may be the same type of pressure regulating valve or different types of pressure regulating valves.

[0027] One end of the second pipe 22 is connected to the through-hole 11b of the upper wall 11, and the other end of the second pipe 22 is connected to the pressure gauge 5. Therefore, the pressure of the internal space S is measured by the pressure gauge 5. The pressure gauge 5 is, for example, a compound gauge that can measure both atmospheric pressure and negative pressure.

[0028] [Flow of foaming leak test] Next, the conditions and flow of the foaming leak test method described in this embodiment will be described with reference to Figures 2 and 3. Figure 2 is a flowchart showing the flow of the foaming leak test method of this embodiment. Figure 3 is a graph showing the relationship between the elapsed time t of the test in the foaming leak test method of this embodiment and the differential pressure P between atmospheric pressure and the pressure in the internal space S. The differential pressure P is a value obtained by subtracting the pressure in the internal space S from the atmospheric pressure.

[0029] (Pressure adjustment work) Prior to the inspection work, the inspector adjusts the aperture of the first pressure regulating valve 61 and the second pressure regulating valve 62 in the following procedure. The first on-off valve 51 is closed, the second on-off valve 52 is closed, and the first pressure regulating valve 61 and the second pressure regulating valve 62 are both fully open, and the vacuum pump 3 is operated. This causes the vacuum pump 3 to reduce the pressure in the internal space S from atmospheric pressure. The inspector then adjusts the aperture of the first pressure regulating valve 61 so that the differential pressure P between the pressure in the internal space S and atmospheric pressure reaches the second pressure P2. Next, the inspector opens the second on-off valve 52 and adjusts the aperture of the second pressure regulating valve 62 so that the differential pressure P between the pressure in the internal space S and atmospheric pressure reaches the first pressure P1. Thereafter, the first on-off valve 51 is opened to return the pressure in the internal space S to atmospheric pressure, and the inspector moves on to the regular inspection work, There is no change in the adjusted opening degrees of the first pressure regulating valve 61 and the second pressure regulating valve 62. This adjustment work is carried out at the start of successive inspection work, and does not need to be carried out for each inspection.

[0030] (Coating process) In the foaming leakage test method, foaming liquid F is first applied to the test surface 101 of the test piece 100 (step S1).

[0031] (Placement process) Next, the vacuum box 2 is placed on the inspection surface 101, and the inspection surface 101 and the vacuum box 2 form an internal space S (step S2).

[0032] (First decompression step) After placing the vacuum box 2 on the inspection surface 101, the foaming liquid F on the inspection surface 101 is observed while reducing the pressure in the internal space S until the differential pressure P between the pressure in the internal space S and atmospheric pressure reaches a first pressure P1 (step S3).

[0033] Specifically, the inspector closes the first on-off valve 51, opens the second on-off valve 52, and operates the vacuum pump 3 while maintaining the adjusted openings of both the first pressure regulating valve 61 and the second pressure regulating valve 62. As a result, the vacuum pump 3 reduces the pressure in the internal space S from atmospheric pressure, and the inspector begins observing the foaming liquid F immediately after the start of depressurization of the internal space S. Meanwhile, the first pressure regulating valve 61 and the second pressure regulating valve 62, whose openings have been adjusted in advance, maintain the differential pressure P between the pressure in the internal space S and atmospheric pressure at a first pressure P1.

[0034] For example, the first pressure P1 is set in the range of 20 kPa or more and less than 60 kPa. In this embodiment, the first pressure P1 is about 55 kPa.

[0035] (1st holding step) After the pressure in the internal space S is reduced to the first pressure P1, the foaming liquid F on the inspection surface 101 is observed while the differential pressure P is maintained at the first pressure P1 (step S4). In this step, the inspector observes the differential pressure P while maintaining the state where the differential pressure P is at the first pressure P1 for a first minimum holding time T1 or more. The first minimum holding time T1 is, for example, 10 seconds.

[0036] (Second decompression step) After the first holding step, the internal space S is further depressurized until the differential pressure P reaches the second pressure P2, while observing the foaming liquid F on the inspection surface 101 (step S5).

[0037] Specifically, after the first holding step, the inspector closes the second on-off valve 52. As a result, the pressure in the internal space S is further reduced by the vacuum pump 3, and the first pressure regulating valve 61, the opening of which has been adjusted in advance, maintains the differential pressure P between the pressure in the internal space S and atmospheric pressure at the second pressure P2.

[0038] For example, the second pressure P2 is set within a range of 30 kPa or more and 80 kPa or less. However, the second pressure P2 is set to a value higher than the first pressure P1. Furthermore, for example, the difference ΔP between the first pressure P1 and the second pressure P2, that is, the value ΔP obtained by subtracting the first pressure P1 from the second pressure P2, is preferably set within a range of 5 kPa or more and 60 kPa or less. In this embodiment, the second pressure P2 is approximately 70 kPa.

[0039] (Second holding process) While maintaining the differential pressure P at the second pressure P2, the foaming liquid F on the inspection surface 101 is observed (step S6). In this step, the inspector observes while maintaining the differential pressure P at the second pressure P2 for a second minimum holding time T2 or more. The second minimum holding time T2 is set longer than the first minimum holding time T1. The second minimum holding time T2 is, for example, 20 seconds.

[0040] (Atmospheric release process) After the second holding step, the internal space S is opened to the atmosphere (step S7). Specifically, the inspector opens the first on-off valve 51. This increases the pressure in the internal space S to atmospheric pressure.

[0041] When a hole h is formed in the inspection object 100, the inspector can observe the foaming of the foaming liquid F around the hole h in at least one of the first depressurization step, the first holding step, the second depressurization step, and the second holding step. After opening the internal space S to the atmosphere, the inspector marks the location on the inspection surface 101 where foaming is confirmed.

[0042] As described above, the foaming leak testing method according to this embodiment performs two observation stages: observing the foaming liquid when the pressure difference P between atmospheric pressure and the internal space S is at a first pressure P1, and observing the foaming liquid when the pressure difference P is at a second pressure P2. By setting the first pressure P1 to a relatively low value, the foaming liquid F near the relatively large-diameter holes h can be prevented from being blown away by the gas flowing into the vacuum box 2 through the holes h during the first depressurization step and the first holding step. Therefore, the inspector can more easily detect the relatively large-diameter holes h during the first depressurization step and the first holding step. Furthermore, by further depressurizing the internal space S to set the pressure difference P to a second pressure P2, the total volume of the gas passing through the holes h increases from the first depressurization step to the second holding step. Therefore, the amount of foaming at the holes h increases, making it easier for the inspector to detect the relatively small-diameter holes h that were difficult to observe during the first depressurization step and the first holding step. Therefore, according to the above method, it becomes easier for the inspector to check the hole h in the inspection object 100 regardless of the size of the diameter.

[0043] It is also possible to open the internal space S to the atmosphere once after the first holding step, mark the locations on the inspection surface 101 where bubbles have been confirmed before completing the first holding step, and then proceed to the second depressurization step. However, if the internal space S is opened to the atmosphere once after the first holding step, the foaming liquid F will enter the holes h of the inspection object 100 due to the gas that has flowed into the internal space S due to the opening to the atmosphere. If the foaming liquid F that has entered the holes h blocks the holes h, it will be difficult to find the holes h in the subsequent second depressurization step and second holding step. In contrast, in this embodiment, the internal space S is further depressurized without being opened to the atmosphere after the first holding step, and therefore it is possible to prevent the holes h from being blocked by the foaming liquid F before the second holding step.

[0044] In the vacuum box 2 of this embodiment, the second on-off valve 52 and the second pressure adjustment valve 62 are arranged in series in a flow path for opening the internal space S to the atmosphere. When the internal space S is evacuated with the first on-off valve 51 closed and the second on-off valve 52 open, the pressure in the internal space S can be adjusted to a first pressure P1 adjusted by the first pressure adjustment valve 61 and the second pressure adjustment valve 62. When the internal space S is evacuated with the first on-off valve 51 closed and the second on-off valve 52 closed, the pressure in the internal space S can be adjusted to a second pressure P2 adjusted by the first pressure adjustment valve 61, which is lower than the first pressure P1. Therefore, when a foaming leak test is performed using the above-described vacuum box 2, two-stage adjustment of the pressure in the internal space S can be easily performed, and as a result, the inspector can easily check the hole h in the test object 100 regardless of its diameter. Furthermore, since the first on-off valve 51 and the first pressure regulating valve 61 are arranged in parallel, when the first on-off valve 51 is opened when the internal space S is in a vacuum state, the internal space S can be quickly pressurized to atmospheric pressure.

[0045] [Other embodiments] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0046] For example, the connection relationship between the exhaust flow path 31, the first atmosphere open path 41, the second atmosphere open path 42, and the third atmosphere open path 43 is not limited to that described in the above embodiment. For example, one end 42a of the second atmosphere open path 42 may be directly connected to the exhaust flow path 31, or the first atmosphere open path 41 and the third atmosphere open path 43 may be indirectly connected to the exhaust flow path 31.

[0047] However, no other flow path is connected between the end 41b of the first atmospheric open path 41 that is open to the atmosphere and the first on-off valve 51, no other flow path is connected between the end 42b of the second atmospheric open path 42 that is open to the atmosphere and the first pressure regulating valve 61, and no other flow path is connected between the end 43b of the third atmospheric open path 43 that is open to the atmosphere and the second on-off valve 52.

[0048] The number of inlet / outlets 11a provided in box 10 does not have to be one, and may be two or more. For example, box 10 may be provided with one or more inlet / outlets 11a other than inlet / outlet 11a connected to vacuum pump 3, and the one or more other inlet / outlets 11a may be connected to first atmosphere open path 41, second atmosphere open path 42, and third atmosphere open path 43. For example, box 10 may be provided with three inlet / outlets 11a to which first atmosphere open path 41, second atmosphere open path 42, and third atmosphere open path 43 are respectively connected.

[0049] The foaming leak test method of the present invention does not necessarily require the use of the vacuum box 2 having the above configuration. For example, the foaming leak test method of the present invention may use a vacuum box that does not include some or all of the third atmosphere release path 43, the second on-off valve 52, and the second pressure adjustment valve 62.

[0050] In the above embodiment, the pressure gauge 5 is provided in the second pipe 22 connected to the through-hole 11b of the upper wall 11, but the pressure gauge may be provided in the first pipe.

[0051] The second minimum holding time T2 may be the same as the first minimum holding time T1, for example, the second minimum holding time T2 may be 10 seconds. [Explanation of symbols]

[0052] 1: Test equipment 2: Vacuum box 3: Vacuum pump 4: Exhaust piping 5: Pressure gauge 10: Box body 11: Upper wall 12: Peripheral wall 20: Piping 31: Exhaust flow path 41: First atmospheric open passage 42: Second atmospheric open passage 43: Third atmospheric open passage 51: First shut-off valve 52: Second shut-off valve 61: First pressure regulating valve 62: Second pressure regulating valve 100: Test piece 101: Inspection surface h: hole F: Foaming liquid S:Internal space

Claims

1. A vacuum box for bubble leak testing placed on the test surface of a test object, a box body that forms an internal space together with the inspection surface; one or more pipes connected to the box body, each pipe having a first atmosphere open path, a second atmosphere open path, and a third atmosphere open path for opening the internal space to the atmosphere, respectively; a first on-off valve provided in the first atmosphere release path; a first pressure regulating valve provided in the second atmosphere open path; a second on-off valve provided in the third atmosphere release path; a second pressure regulating valve provided between the end of the third atmosphere open path that is open to the atmosphere and the second on-off valve.

2. A foaming liquid is applied to the test surface of the test object, a vacuum box having a transparent window and according to claim 1, placed on the inspection surface, the inspection surface and the vacuum box forming an internal space; closing the first on-off valve and opening the second on-off valve, and observing the bubbling liquid on the inspection surface while reducing the pressure in the internal space until a pressure difference between the pressure in the internal space and atmospheric pressure reaches a first pressure; observing the bubbling liquid on the inspection surface while maintaining the differential pressure at the first pressure; the second on-off valve is closed, and the internal space is further decompressed until the pressure difference reaches a second pressure from the first pressure, while observing the bubbling liquid on the inspection surface; A method for testing foaming leaks, comprising: observing the foaming liquid on the test surface while maintaining the differential pressure at the second pressure.

3. maintaining the state in which the differential pressure is at the first pressure for a first minimum retention time or longer; maintaining the state in which the differential pressure is at the second pressure for a second minimum holding time or longer; 3. The method of claim 2, wherein the second minimum holding time is longer than the first minimum holding time.

Images