JP2004347478A - Leakage inspection method and leakage inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the burden on an inspection operator in detecting the leakage of a large-scale vessel such as an LNG (liquefied natural gas) storage tank, to save a record of the change in color of a leaking point, or the raw data of the detection result, and to automatically detect the failed part so as to get rid of an oversight of the failed part. <P>SOLUTION: The leakage detection apparatus is composed of a traveling camera part 10, a control part 30, and a note personal computer 40. The traveling camera part 10 includes a truck 11, a camera 12, a filter 13, an upper surface illumination 14, an inclination angle illumination 15, a grip 16, and wheels 17, and transmits image data taken by the camera 12 to the note personal computer 40 via the control part 30. The image data is binarized by the processing of the note personal computer 40. When a black image is included, it is estimated that the change in color of chemicals due to a reactive gas, namely, the gas leakage part, exists, and an alarm is generated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a leak inspection method or a leak inspection device, and is particularly useful when applied to a technology for automatically detecting a defective portion of a weld in a large-scale storage tank such as liquefied natural gas (hereinafter referred to as LNG). is there.
[0002]
[Prior art]
As a leak inspection method of a pressure vessel having a portion where leakage easily occurs, such as a welded portion, an ammonia leak test, a penetrant inspection, and the like are known. These leak inspection methods are nondestructive inspections, and are used as a method that can relatively easily detect leaks with high accuracy. The outline of these inspection methods will be briefly described as follows. First, a chemical that changes its color due to a chemical reaction with a test gas such as ammonia is applied to a welded portion where leakage is likely to occur. Next, a test gas is applied under pressure from the back side of the surface to be inspected on which the agent has been applied. If there is a leak, the test gas passes through the leak and reaches the drug, so that the drug reacts with the test gas to change color at the leak. By detecting this discoloration, it is possible to know the occurrence of the leakage and its location. In the ammonia leak test, the original color of the drug is yellow, and the color of the drug after reacting with ammonia is blue.
[0003]
Patent Literature 1 discloses an invention relating to a storage facility in a bedrock, in which a detection liquid for an ammonia leak test is applied to a hermetically sealed material weld, and ammonia gas is inserted from the inside of the hermetic material to change the detection liquid from yellow to blue. There is disclosed a technique for observing a discolored portion and identifying a leaked portion. Patent Document 2 discloses an invention relating to a tank defect inspection device and an inspection method. The defect inspection apparatus has means for adhering the detection paper reacting with the inspection gas to the surface of the test object and making the surface of the detection paper visible. The inventions described in any of the patent documents use a test gas and observe a color change of a detection liquid or a detection paper which causes a color change due to a chemical reaction with the test gas. These color changes are visually observed. It has become.
[0004]
[Patent Document 1] JP-A-2001-280594
[Patent Document 2] JP-A-11-326109
[0005]
[Problems to be solved by the invention]
With the above-described leak inspection method of detecting a leak by observing a color change due to a reaction with an inspection gas, it is possible to relatively accurately perform a leak inspection of a pressure vessel or the like. However, these leak inspections are to visually confirm the site where the color change has occurred. If the area to be inspected is small, it is sufficient, but in the case of a large container such as an LNG storage tank, the area to be inspected becomes enormous, and the burden on the inspection operator becomes extremely large. In particular, in a 200,000 kiloliter LNG underground storage tank, the total length of the welding line to be inspected reaches as much as 27 kilometers, and the burden on the operator is enormous. Further, since the defective portion is visually detected, it is not possible to leave the detected color change as data except for the case of manual writing in order to leave the detected defective portion in the record. Further, since a defective portion is visually detected, it is impossible to completely eliminate a mistake of the inspection operator, and the defective portion may be overlooked. In particular, when the inspection target area is enormous, it is easy to overlook a defective portion. At present, measures such as performing the same inspection twice are taken to prevent the overlooking of the defective portion.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to reduce the burden on inspection workers in leak inspection of large-scale containers such as LNG storage tanks. It is another object of the present invention to provide a technique capable of keeping a record of a color change at a leak location, which is raw data of an inspection result. It is still another object of the present invention to provide a technique that can automatically detect a defective portion so that the defective portion is not overlooked. It is still another object of the present invention to provide a technique capable of clearly distinguishing a color change of a medicine due to gas leakage from a color change due to dust or the like and appropriately removing noise mixed in an inspection result.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention has the following configuration. That is, in the leak inspection method of the present invention, a step of applying a chemical whose color changes due to a chemical reaction with an inspection gas to a surface to be inspected, and applying the inspection gas from a back surface of the surface to be inspected to which the agent is applied. Exposing or pressurizing, taking an image of the surface to be inspected coated with the medicine by an imaging means and acquiring image data, and determining whether a luminance value of each pixel of the image data is equal to or greater than a threshold value Determining whether or not the image data includes binarized data; and determining whether the binarized data includes a color-changed pixel that reflects a color of the drug that has changed color due to a chemical reaction with the test gas. Determining.
[0008]
That is, in the leakage inspection method of the present application, the discolored portion of the medicine discolored by the inspection gas is photographed by the photographing means, image data is obtained, and this is binarized. If there is a pixel different from the background color in the binarized data, it can be estimated with high probability that the color of the medicine has changed. Therefore, it is possible to detect a pixel different from the background color in the binarized data and detect the presence of a defective portion. In the above invention, it is possible to further include a step of issuing an alarm when it is determined in the determining step that the discolored pixel is included. In this case, the detection of the discolored pixel can be notified to the inspection worker by an alarm. Thus, the inspection operator can easily confirm a defect (leakage point) of a welded portion or the like without relying on visual observation and relying on an alarm. In addition, since the process from image acquisition to alarm issuance can be automatically performed using a computer, it is possible to eliminate oversight of a leak location and reduce inspection errors.
[0009]
Further, in the above-described leakage inspection method, a step of specifying a boundary pixel of a color-changed pixel region that is a group of the color-changed pixels, and a step of scanning a line from the inside to the outside or from the outside to the inside of the color-changed pixel region including the boundary pixel. Determining, and determining the number of gray pixels at which the luminance value of each pixel of the image data in the scanning line changes from a predetermined upper value to a predetermined lower value, wherein the gray pixel number is a predetermined value. In the following cases, the alarm may not be issued.
[0010]
In such a leak inspection method, it is possible to determine the steepness of the color change around the boundary of the discolored area. The photographing means applicable to this leak inspection method is a normal camera such as a CCD, so that a change in the color of the medicine occurring at the leak location can be detected as a difference in contrast in the photographed image. By the way, in the case where dust or the like is mixed in the photographing area, if a contrast is generated in the image due to the dust or the like, there is a possibility that this is erroneously recognized as a leaked portion. However, since the color change caused by the leakage is caused by a chemical reaction, the color change at the boundary becomes continuously blurred. The change slows down at the border. On the other hand, in the case of dust, the change in contrast is not due to a chemical reaction, but reflects the shape of the dust as it is, and the change at the boundary is generally steep. Therefore, in the above-described inspection method, the steepness at the boundary of the discolored pixel region is evaluated as the number of gray pixels based on these findings, and when the number of gray pixels is equal to or less than a predetermined value (that is, the change in the number of predetermined pixels falls within the predetermined number of pixels). It is presumed that this is not caused by a chemical change such as dust, and is excluded from the alarm target. For this reason, this inspection method can effectively remove noise caused by dust and the like, and can improve the detection accuracy of a color change (leakage point) due to a chemical change that is originally desired to be detected.
[0011]
In the inspection method described above, the processing from the step of acquiring the image data to the step of issuing the alarm can be repeatedly performed at predetermined time intervals, or it is detected that the image data has moved by the visual field represented by the image data. The repetition can be performed with a signal from the moving detection unit that performs the operation. Further, the repeatedly acquired image data can be recorded on a large-capacity data recording medium, and can be stored semi-permanently. By storing the data, it is possible to use it as a measure against defects that may occur later or as basic data for long-term reliability data.
[0012]
A leakage inspection apparatus according to another aspect of the present invention applies a chemical whose color changes due to a chemical reaction with an inspection gas to a surface to be inspected, and exposes the inspection gas from a back surface of the surface to be inspected to which the chemical is applied. Or a pressure application, a leak inspection apparatus used for a leak inspection method for detecting the color change of the drug applied to the surface to be inspected generated by the chemical reaction, the inspection surface to which the agent is applied Photographing and image data output means for outputting a photographed image as image data, illuminating means for irradiating the surface to be inspected, controlling the photographing and image data output means, Control means for supplying power to the illuminating means, and data processing means for receiving image data output from the photographing and image data output means and performing data processing on the image data Wherein the data processing means determines whether or not the luminance value of each pixel of the image data is equal to or greater than a threshold value, and generates binary data of the image data. Generating means for determining whether or not the binarized data includes a color-changed pixel reflecting a color of the medicine changed by a chemical reaction with the test gas;
[0013]
Such a leak inspection apparatus can be applied to the above-described leak inspection method. Here, the photographing and image data output means may be one in which a photographing means and an image data output means are integrally configured like a CCD camera, but a photographing means such as a video camera and an image from the photographing means may be used. And image data output means for generating digital image data in response to the signal. In the present application, the image data is digital still image data in mind, but may be moving image data.
[0014]
The illuminating means needs to irradiate the surface to be inspected and irradiate light containing a wavelength component capable of detecting discoloration contained in the captured image. For example, when a color image is handled as image data, it is necessary to include yellow and blue in the reflected light in order to detect that a yellow drug undergoes a chemical reaction and changes its color to blue. Therefore, the light source of the illumination means needs to emit light containing at least a yellow component and a blue component, for example, white light. When the image data is handled as a monochrome image, it may be monochromatic light. In order to detect yellow, which is the primary color of the drug, and blue, which is the reactive color, monochromatic light in the yellow or blue wavelength range may be used as the light source. When a yellow light source is used, the discolored portion (blue) is observed as black, and when a blue light source is used, the discolored portion is observed as white. It is also possible to design the light source to have a light emission wavelength including a blue component and a yellow component (for example, white) and to apply a color filter in front of the photographing means to secure a necessary contrast.
[0015]
The control means controls at least the photographing and image data output means and the lighting means and supplies power thereto, but controls other necessary devices and supplies power. May be. The control means may include a battery which is a power source.
[0016]
As the data processing means, for example, a general computer system can be applied. Considering portability, a notebook personal computer is preferable. A general computer system includes a recording device such as a CPU, a bus, a RAM / ROM, an external recording device such as a hard disk drive, a display device such as a liquid crystal display device or a CRT monitor, an input device such as a keyboard, an interface device, and the like. Hardware resources of various information processing devices. In the present application, software for effectively operating these hardware resources is also included in the components of the data processing means. For example, a program for causing a computer to function, a program component, data necessary for the operation of the program, and the like are components of a data processing unit.
[0017]
The binarized data generation unit and the determination unit can be configured as, for example, computer software. However, for example, these functions may be realized as pure hardware by a dedicated circuit or the like.
[0018]
The leak inspection apparatus further includes an alarm unit that receives an alarm signal and issues an alarm, and the data processing unit generates the alarm signal when the determination unit determines that the color-changed pixel is included. It may further include an alarm signal generating means. Examples of the alarm unit include a unit that notifies the worker by light emission such as a light emitting diode, and a unit that notifies by sound such as a beep sound. In addition, all means for alerting the worker to the five senses are included in the warning means. The alarm signal generation means can be configured, for example, as computer software, like the binarized data generation means or the determination means, but realizes these functions in pure hardware by, for example, a dedicated circuit or the like. There may be.
[0019]
Further, in the leakage inspection device, the data processing unit further includes: a unit that specifies a boundary pixel of a color-changed pixel region that is a group of the color-changed pixels; Means for determining a scanning line from the outside to the inside, and means for determining the number of gray pixels in which the luminance value of each pixel of the image data in the scanning line changes from a predetermined upper value to a predetermined lower value, When the number of gray pixels is equal to or less than a predetermined value, the alarm signal may not be generated. With such a configuration, the above-described inspection method for removing noise due to dust or the like can be realized.
[0020]
Further, the illumination means includes an upper surface illumination unit arranged on a plane perpendicular to a line drawn from the imaging unit of the imaging and image data output unit to the imaging center of the surface to be inspected, and the upper surface illumination unit. And an oblique illumination unit disposed on a plane that is not parallel to the plane that has been set. By incorporating the oblique illumination unit in addition to the top illumination unit, it is possible to prevent unevenness in illuminance on the irradiation surface, and to accurately detect a color change on the inspection surface. In particular, when a light emitting diode is used as a light source, unevenness in illuminance on the irradiation surface is likely to occur. However, by adopting such an oblique illumination unit, occurrence of illuminance unevenness can be effectively suppressed. Also, adopting a light emitting diode as a light source of the lighting means has an effect of reducing power consumption.
[0021]
Further, at least the photographing unit and the lighting means of the photographing and image data output means are installed on a gantry interlocking with a probe contacting the inspection surface, and the gantry is movable on the inspection surface. It can be arranged on the carriage so as to be movable in a direction perpendicular to the surface to be inspected. By adopting such a configuration, the distance between the imaging unit and the surface to be inspected is kept constant, even when the surface to be inspected is not only flat but also partially curved. It is possible to obtain a suitable photographed image.
[0022]
Further, the probe or the wheel of the cart may include a movement detecting unit for detecting a moving distance of the cart. The movement distance detecting means can detect that the carriage has moved by an appropriate distance (for the field of view represented by the image data) and generate a signal that triggers the acquisition of the image data. As the moving distance detecting means, for example, a rotary encoder can be exemplified.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention can be implemented in many different modes and should not be construed as being limited to the description of the embodiments. The same elements are given the same numbers throughout.
[0024]
(Embodiment 1)
FIG. 1 is a diagram showing an example of an LNG tank to which a leakage inspection device or a leakage inspection method according to an embodiment of the present invention is applied. The LNG tank is constructed to be buried underground 1 and has a cold insulator 3 made of, for example, rigid polyurethane foam inside an outer frame 2 made of concrete or the like, and a membrane 4 further inside. A roof 5 is provided at an upper part, and a roof insulation material 6 is provided inside the roof 5. In the drawing, the roof 5 and the roof insulation material 6 are drawn to be raised above, but are actually arranged above the outer skeleton 2 to maintain airtightness.
[0025]
FIG. 2 is an enlarged partial perspective view of the portion A in FIG. Since LNG stored in the LNG tank is stored at a low temperature, the membrane 4 needs to have a structure that can withstand temperature shrinkage. Therefore, as shown in FIG. 2, the membrane 4 adopts a structure having a flat portion 7 and a corrugation portion 8 so that the corrugation portion 8 absorbs expansion and contraction due to a temperature change. Then, the substantial airtightness of the tank is ensured by the membrane 4. Therefore, the membranes 4 are arranged on the inner surface of the tank, and the respective membranes 4 are bonded by welding. Reference numeral 9 shown in FIG. 2 is a welded portion 9 obtained by welding each of the membranes 4. The welded portion 9 is a main inspection target to which the inspection device or the inspection method of the present embodiment is applied. A pipe (not shown) is arranged on the outer frame 2 of the tank, and ammonia as an inspection gas is supplied between the cold insulator 3 and the membrane 4 via the pipe.
[0026]
FIG. 3 is a configuration diagram schematically showing the leakage inspection apparatus according to the present embodiment. The leak inspection apparatus according to the present embodiment includes a mobile camera unit 10, a control unit 30, and a notebook personal computer 40.
[0027]
The mobile camera unit 10 includes a cart 11, a camera 12, a filter 13, a top illumination 14, an oblique illumination 15, a handle 16, and wheels 17. The cart 11 holds each component of the moving camera unit 10 and is movable on the surface to be inspected by wheels 17. The carriage can be moved by the operator pressing the handle 16. The camera 12 is a photographing unit that photographs the surface to be inspected, and may be, for example, a CCD camera. As described later, the camera 12 may include a lens optical system. The filter 13 is provided so that the color change of the surface to be inspected can be photographed with high contrast. For example, a yellow filter can be employed. In this case, it is necessary that the light source of the illumination includes at least light having a wavelength component in the yellow band. Since the color that changes due to leakage is blue, if the light source does not contain a blue component, a yellow filter is unnecessary. However, if the background light contains a blue component, a yellow filter may be used to provide such a background filter. Blue reflected light from the lens does not mix.
[0028]
In the present embodiment, an oblique illumination 15 is provided in addition to the top illumination 14. For example, a light emitting diode can be exemplified as the light source. For example, a ring-shaped illumination having an opening in the center can be exemplified as the top illumination 14, and a rectangular surface illumination can be exemplified as the oblique illumination 15. Although a temporary inspection can be performed only by the top surface illumination 14, when a light emitting diode is used as a light source, irradiation unevenness reflecting the shape of the light source occurs. The provision of the oblique illumination 15 makes it possible to suppress these irradiation irregularities. Further, as shown in FIG. 4, when the membrane 4 is welded by lap welding instead of butt welding, a shadow is easily generated in the welded portion 9. However, the provision of the oblique illumination 15 makes it possible to eliminate the occurrence of shadows.
[0029]
The mobile camera unit 10 is further provided with LEDs 18, 19, 20 and a switch 21. The LEDs 18, 19, and 20 can display an alarm when a defective portion is detected, a shooting state, and a shooting stopped state, respectively. Further, the switch 21 can give an opportunity to start shooting.
[0030]
The control unit 30 includes a camera controller 31, a repeater 32, a signal converter 33, an exposure control circuit 34, a battery 35, a DC / DC converter 36, and a voltage monitor 37. The camera controller 31 obtains image data from the camera 12 and performs control for supplying power to the camera 12 and other camera control. The repeater 32 supplies power to the camera controller 31 and transmits image data obtained from the camera controller 31 to the notebook personal computer 40. The signal converter 33 receives a signal from the notebook personal computer 40, generates a trigger signal to the camera controller 31, and generates light emission signals to the LEDs 18, 19, and 20. Further, the signal converter 33 receives the photographing start signal from the switch 21 and transfers the signal to the notebook personal computer 40. Exposure control circuit 34 receives power supply from battery 35 via DC / DC converter 36 and supplies power suitable for top illumination 14 and oblique illumination 15. The brightness of the top illumination 14 and the oblique illumination 15 can be controlled by the exposure control circuit 34. The battery 35 supplies power to each of the repeater 32, the signal converter 33, and the exposure control circuit 34 via the DC / DC converter 36. The voltage of the battery 35 can be monitored by the voltage monitor 37.
[0031]
The notebook personal computer 40 includes a DIO 41. The DIO 41 is a data input / output port for interfacing data transmission and reception between the notebook personal computer 40 and the signal converter 33. The notebook personal computer 40 can receive image data, and can have, for example, an IEEE 1394 port. Further, the notebook personal computer 40 can include a large-capacity data recording device for recording acquired image data, such as a hard disk drive, a CD-ROM disk drive, and an MO disk drive. It becomes possible to store image data in these large-capacity data recording devices and use them later.
[0032]
FIG. 5 is a diagram showing the mobile camera unit 10 in more detail. The upper diagram is a front view, and the lower diagram is a side view. The top illumination 14 and the oblique illumination 15 are connected to each other by an L-shaped member 101, and the top illumination 14 and the camera 12 are connected by a U-shaped member 102. A filter 13 is connected to a photographing surface side of the camera 12 via a lens optical system 103. A sliding member 105 is connected to the U-shaped member 102 via a crank-shaped member 104, and a fixing member 107 is connected via an L-shaped member 106. The fixing member 107 is fixed to a pole 109 provided with a probe 110 at an end thereof, and the pole 109 is configured to be vertically movable along a sliding member 108 fixed to the carriage 11. The sliding member 105 is configured to be slidable along a pole 111 provided between the carriage 11 and the member 112, and a spring 113 is provided between each of the sliding member 105 and the member 112 and the carriage 11. , 114 are arranged. That is, the camera 12, the filter 13, the top illumination 14, and the oblique illumination 15 provided in the moving camera unit 10 are configured to be vertically movable with respect to the cart 11. FIG. 6 is a side view showing a state in which such vertical movement is performed. Even if the surface to be inspected has the corrugation section 8, the probe 110 detects this and moves the camera and the illumination up and down, so that a good image of the surface to be inspected can be taken without the camera being out of focus. .
[0033]
FIG. 7 is a flowchart illustrating an example of the leakage inspection method according to the present embodiment. First, a chemical for inspection is applied along the welded portion 9 (step 201). Next, ammonia as a test gas is supplied (step 202). The supply of ammonia is made to reach the back surface of the membrane 4 as shown in FIG. It is confirmed whether ammonia has reached the membrane by checking whether ammonia has flown out of the hole of the membrane 4 provided for the monitor in advance (step 203), and the process proceeds to step 204 and subsequent image capturing.
[0034]
The photographing of the image is started by the start of the image scan in step 204. The signal of the switch 21 can be used as a trigger for starting the step 204.
[0035]
In response to the start of image scanning, image data is obtained (step 205). Acquisition of image data can be configured to start sequentially at fixed time intervals, for example, to capture four images per second. Alternatively, a probe 110 provided at the end of the wheel 17 or the pole 109 of the trolley 11 is provided with a rotary encoder, and detects that the camera 12 has traveled, for example, 90% of the field of view (photographing area: 5 cm, for example). Then, the image data may be obtained with this as a trigger.
[0036]
The acquired image data is recorded and stored in a large-capacity recording device such as a hard disk drive (step 206). This allows the raw data of the test to be used later.
[0037]
Next, the obtained image data is binarized. The binarization process is a process of determining whether the luminance value of each pixel of the image data is bright or dark at a predetermined threshold value (for example, 50%) and distributing the pixel value to either a bright or dark value. The threshold can be arbitrarily selected according to the situation of the acquired image. FIG. 8 shows an example of image data before binarization processing and an example of binarized data after binarization processing. FIGS. 8A to 8C show 0.2, 0.45, and 1 mm diameter image data before the binarization processing, respectively, and FIGS. 8D to 8F show the image data of FIGS. ) Is the binarized data after the binarization processing corresponding to each of them. In the case of 0.2 mm image data, it is observed as a black image of one or two pixels. For image data of a larger diameter, black pixel data of a binarized image is obtained according to the size.
[0038]
Next, it is determined whether a black image exists in one screen (within the field of view) of the obtained binary data (step 208). If a black image is present, it can be estimated as a leak location, so a signal for illuminating the LED 18 and the like is generated and an alarm is issued (step 209). When there is no black image (that is, when all the white pixels constitute the binarized data), it is determined that there is no leak location, and the process proceeds to the next image acquisition step (step 205) without issuing an alarm. (Step 208).
[0039]
As described above, it is possible to automatically detect a leak location. Note that image acquisition, image storage, image binarization, or determination of the presence or absence of a black image according to the present embodiment can be realized by software using computer software or components. Existing algorithms can be applied to realize these functions, and those skilled in the art can easily code a program using an existing programming language.
[0040]
(Embodiment 2)
In the first embodiment, an example has been described in which when a black image exists, it is simply estimated to be a leakage location. However, a method of improving the detection accuracy by evaluating the gray pixel distance at the boundary of the black image area can also be used. FIG. 9 is a flowchart showing a modified example of the leakage inspection method according to the present embodiment. The steps from the start (step 301) to the step (step 308) from the start of determining whether there is a black image in the field of view of the binarized image are the same as in the above embodiment. In this modification, when it is determined that a black image exists, the value of the gray pixel distance K is calculated (step 309), and an alarm is issued only when the gray pixel distance K is equal to or more than a predetermined value (number of pixels). (Step 310). FIG. 10 is a flowchart showing an example of calculation of the gray pixel distance K.
[0041]
First, initialization is performed with K = 0 (step 320), and an arbitrary black pixel in the binarized data is extracted and set to the corresponding pixel (step 321). Then, it is determined whether the right neighboring pixel of the corresponding pixel is white (step 322). If it is white, the process proceeds to step 324. If not, the right neighboring pixel of the corresponding pixel is set as the corresponding pixel (step 323). Return to 322. That is, the pixels are scanned rightward up to the boundary pixels that change from black pixels to white pixels.
[0042]
Since the corresponding pixel (black pixel) determined to be white in step 322 is a boundary pixel, the original image (pixel of image data) is extracted (step 324), and whether the luminance value is 0.1 or less is determined. Is determined (step 325). That is, it is determined whether the gray scale of the corresponding pixel is sufficiently black. If it is not less than 0.1, the corresponding pixel is not sufficiently black, so the left adjacent pixel is set as the corresponding pixel (step 326), and the process returns to step 324. In other words, the scanning direction is traced in the opposite direction (left direction) to specify the black pixel at the boundary.
[0043]
If it is determined in step 324 that the luminance value is equal to or less than 0.1, the corresponding pixel is a pixel on the black side of the boundary, so it is determined whether the luminance value of the corresponding pixel is equal to or more than 0.9 (step 324). 327). That is, it is determined whether the luminance value of the pixel is sufficiently white. If the boundary gray area is still gray (the luminance value is between 0.1 and 0.9 is gray here), the determination in step 327 should be NO, so K is increased by 1 and the right neighboring pixel is increased. Is set to the corresponding pixel, that is, one pixel is scanned rightward (step 329), and the process returns to step 324. When this is repeated several times, the corresponding pixel eventually reaches the white side pixel of the boundary area, and the determination in step 327 becomes YES. Then, the process is terminated with the value of K (the number of pixels constituting the gray area) as a return value. Here, the upper value of the brightness value is exemplified as 0.9, and the lower value is set as 0.1 (the highest value is 1). However, 0.9 or 0.1 is merely an example, and other values can be applied. Further, although the scanning direction of the gray area is illustrated as right, the scanning direction is merely an example, and it is needless to say that scanning may be performed in other directions such as left, up, down, and oblique directions.
[0044]
In such an algorithm, as shown in FIG. 11, the boundary of an image in a portion discolored by a chemical reaction is blurred (FIG. 11A), and the boundary of an image generated by dust or the like is sharp (see FIG. 11). 11 (B)). By applying this modified example, it is possible to distinguish between a discolored image of a medicine due to a leak that is originally desired to be detected and an image generated due to dust, and to issue an alarm by eliminating detection of a sharp boundary image due to dust. Become. Therefore, the rate of false alarms included in the alarm can be reduced, and the efficiency of inspection work can be increased.
[0045]
Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the embodiments, and can be modified without departing from the gist thereof.
[0046]
For example, in the above embodiment, the acquired image data may be either a color image or a monochrome image. However, if the image is a monochrome image, it must be a grayscale image. In the above embodiment, the binarization process is performed so that the yellow part is white and the blue part is black. This is because it is assumed that the portion corresponding to the yellow of the image data has high luminance and the portion corresponding to the blue has low luminance.If the correspondence of the image data is reversed, the white or black of the binarized image is obtained. Needless to say, the correspondence is reversed. Further, when the image data is a color image, a luminance value cannot be simply used in the binarization process. In this case, binarization processing can be performed using the color difference. Incidentally, the definition of the color difference is as follows. If the values of the three primary colors are R, G, and B, and the maximum value is normalized by 1, pure red is (R = 1, G = 0, B = 0), and pure green is (R = 0, G = 1, B = 0), and pure blue is (R = 0, G = 0, B = 1). White is (R = 1, G = 1, B = 1) and black is (R = 0, G = 0, B = 0). If this is represented by the color differences C1 and C2 and the luminance Y, for example, C1 = RG, C2 = GB, and Y = (R + G + B) / 3. If the color difference C1 is multiplied by the unit vector X and the color difference C2 is multiplied by the unit vector Y orthogonal to X, the composite vector C1X + C2Y can be thought of as a color vector in a two-dimensional color space. When the image data is a color image, the color of each pixel is evaluated by a distance from a reference point (for example, the origin) in the two-dimensional color space, and a binarization process is performed depending on whether the distance is larger or smaller than a predetermined threshold. It is possible to do.
[0047]
Further, it is also possible to arrange a reflecting mirror instead of or above the top surface illumination 14 of the above-described embodiment, so that the illuminance of the surface to be inspected is made higher or uniform.
[0048]
【The invention's effect】
The effects obtained by typical aspects of the invention disclosed in the present application are as follows. That is, it is possible to reduce the burden on the inspection worker in the leakage inspection of a large-scale container such as an LNG storage tank. Further, a color change at a leaked portion, which is raw data of an inspection result, can be recorded. Further, the defective portion can be automatically detected so that the overlook of the defective portion is eliminated. Furthermore, the color change of the medicine due to gas leakage and the color change due to dust or the like can be distinguished sharply, and the noise mixed in the inspection result can be properly removed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of an LNG tank to which a leakage inspection device or a leakage inspection method according to an embodiment of the present invention is applied.
FIG. 2 is an enlarged partial perspective view of a portion A in FIG. 1;
FIG. 3 is a configuration diagram schematically showing a leakage inspection apparatus according to an embodiment of the present invention.
FIG. 4 is a sectional view showing a part of the membrane 4;
FIG. 5 is a diagram showing the mobile camera unit 10 in more detail, wherein the upper figure is a front view and the lower figure is a side view.
FIG. 6 is a side view showing a state where the camera 12 and the like of the mobile camera unit 10 are moving up and down.
FIG. 7 is a flowchart illustrating an example of a leakage inspection method according to an embodiment of the present invention.
8A and 8B are diagrams illustrating an example of image data before binarization processing and an example of binarized data after binarization processing, wherein FIGS. 2, 0.45, and 1 mm diameter image data, and (D) to (F) are binarized data after binarization processing corresponding to (A) to (C), respectively.
FIG. 9 is a flowchart showing a modified example of the leakage inspection method according to one embodiment of the present invention.
FIG. 10 is a flowchart illustrating an example of calculation of a gray pixel distance K.
11A is a diagram illustrating an example of image data corresponding to a color change generated due to a chemical reaction with a test gas, and FIG. 11B is an example of image data due to dust or the like; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Underground, 2 ... Outer frame, 3 ... Cooling material, 4 ... Membrane, 5 ... Roof, 6 ... Roof cooling material, 7 ... Flat part, 8 ... Corrugation part, 9 ... Welding part, 10 ... Moving camera part, 11 trolley, 12 camera, 13 filter, 14 top illumination, 15 oblique illumination, 16 handle, 17 wheels, 18, 19, 20 LED, 21 switch, 30 control unit, 31 ... camera controller, 32 ... repeater, 33 ... signal converter, 34 ... exposure control circuit, 35 ... battery, 36 ... DC / DC converter, 37 ... voltage monitor, 40 ... notebook personal computer, 101 ... L-shaped member, 102: U-shaped member, 103: lens optical system, 104: crank-shaped member, 105: sliding member, 106: L-shaped member, 107: fixing member, 108: sliding member, 109: pole, 110: search Child, 111 ... Paul, 112 ... member, 113 ... spring, C1, C2 ... color difference, DIO41 ... data input-output ports, K ... gray pixel distance, X, Y ... unit vector.

Claims (13)

Applying a drug whose color changes due to a chemical reaction with the test gas to the surface to be inspected;
Exposure or pressure application of the test gas from the back surface of the surface to be inspected coated with the agent,
Photographing the surface to be inspected to which the medicine has been applied by photographing means, and acquiring image data;
Determining whether the brightness value of each pixel of the image data is equal to or greater than a threshold, and obtaining binarized data of the image data;
Determining whether the binarized data includes a discolored pixel that reflects the color of the drug that has changed color due to a chemical reaction with the test gas;
Leak inspection method including. 2. The leakage inspection method according to claim 1, further comprising: issuing an alarm when it is determined in the determining step that the discolored pixel is included. Identifying boundary pixels of a discolored pixel area that is a collection of the discolored pixels;
Determining a scanning line from the inside to the outside or from the outside to the inside of the discolored pixel region including the boundary pixel,
Determining the number of gray pixels in which the luminance value of each pixel of the image data in the scanning line changes from a predetermined upper value to a predetermined lower value,
Further having
3. The leak inspection method according to claim 1, wherein the warning is not issued when the number of gray pixels is equal to or less than a predetermined value. The leak inspection method according to any one of claims 1 to 3, wherein a process from the step of acquiring the image data to the step of issuing the alarm is repeatedly performed at predetermined time intervals. The process from the step of obtaining the image data to the step of issuing the alarm is repeatedly performed in response to a signal from a movement detection unit that detects that the image data has moved by the visual field represented by the image data. The leak inspection method according to claim 1. The leakage inspection method according to claim 1, wherein the image data is recorded and stored on a large-capacity data recording medium. A chemical whose color changes due to a chemical reaction with a test gas is applied to the surface to be inspected, and the test gas is exposed or pressurized from the back surface of the surface to be inspected coated with the chemical, and is generated by the chemical reaction. A leak inspection apparatus used in a leak inspection method for detecting a color change of a drug applied to the surface to be inspected,
Imaging and image data output means for imaging the surface to be inspected coated with the drug, and outputting the captured image as image data,
Illumination means for irradiating the surface to be inspected,
Control means for controlling the imaging and image data output means and the illumination means to supply power,
A data processing unit that receives image data output from the shooting and image data output unit, and performs data processing of the image data,
The data processing means includes:
Binarized data generation means for determining whether or not the luminance value of each pixel of the image data is equal to or greater than a threshold, and generating binarized data of the image data,
Determining means for determining whether or not the binarized data includes a discolored pixel that reflects the color of the drug that has changed color due to a chemical reaction with the test gas;
Leakage inspection equipment including. The apparatus further includes an alarm unit that receives an alarm signal and issues an alarm, and the data processing unit further includes an alarm signal generation unit that generates the alarm signal when the determination unit determines that the discolored pixel is included. The leakage inspection device according to claim 7. The data processing means further includes:
Means for specifying a boundary pixel of a discolored pixel region that is a collection of the discolored pixels;
Means for determining a scanning line from the inside to the outside or from the outside to the inside of the discolored pixel region including the boundary pixel,
Means for determining the number of gray pixels in which the luminance value of each pixel of the image data in the scanning line changes from a predetermined upper value to a predetermined lower value,
9. The leak inspection apparatus according to claim 7, wherein the warning signal is not generated when the number of gray pixels is equal to or less than a predetermined value. The illuminating unit includes a top illuminating unit arranged on a plane perpendicular to a line drawn from the photographing unit of the photographing and image data output unit to the photographing center of the surface to be inspected, and the top illuminating unit is arranged. The leak inspection apparatus according to any one of claims 7 to 9, further comprising: an oblique illumination unit disposed on a plane that is not parallel to the plane. The leakage inspection device according to claim 10, wherein the light emitting device of the lighting unit is a light emitting diode. At least a photographing unit and the lighting means of the photographing and image data output means are installed on a gantry interlocking with a probe that contacts the surface to be inspected,
The leak inspection apparatus according to any one of claims 7 to 11, wherein the gantry is arranged on a carriage movable on the inspection surface so as to be movable in a direction perpendicular to the inspection surface. 13. The leak inspection apparatus according to claim 12, wherein the probe or the wheel of the cart has a movement detecting unit for detecting a moving distance of the cart.

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