JP4185841B2 - Method for determining the resolution of a radiographic test image - Google Patents

Description

  The present invention relates to a technique for quantitatively obtaining the resolution of an image in an inspection film obtained by imaging a specimen in a radiation transmission test without using a visual sense, and a technique for obtaining digital image data of the inspection film guaranteed by the quantification. .

  Currently, in a radiation transmission test (hereinafter, also referred to as RT), an inspection film obtained by photographing a test body with a radiation transmission test apparatus is visually inspected by an inspector, and a defect of the test body copied in the inspection film is detected. A method for determining the presence or absence of an image is used. When the specimen is copied onto the inspection film, a radiometer for the transmission test is also copied into the inspection film as a measure of resolution. The standard depends on the inspector's vision.

  Here, the permeability meter for radiation transmission test used to guarantee the resolution of the film to be photographed is a wire-type permeability meter as shown in JIS Z 2306-2000 “Transmission meter for radiation transmission test”. And perforated permeability meter. The wire-type permeability meter is further classified into two types: a general type and a band type. The general wire-type transmissometer has a structure in which seven wires having different diameters are embedded in a plastic or the like with little X-ray absorption. The band-shaped wire permeability meter has a structure in which nine wires of the same diameter are embedded, and is mainly used for photographing a circumferential welded portion of a pipe.

  On the other hand, there are two types of perforated penetrometers: square and circular. The square and circular plates have a thickness equivalent to 2% of the thickness of the discriminating specimen, and It is a shape with a through hole with dimensions related to the plate thickness, such as a circular hole with a diameter equivalent to the thickness, a circular hole with a diameter that is half the plate thickness, or a circular hole with a diameter that is twice the plate thickness. .

  For example, in the case of steel, these transmissometers for radiation transmission tests can be used for film radiography of the radiation transmission test, as shown in JIS Z 3104-1995 “Radiation transmission test method for steel welded joints” It is required for the inspection film that the wire or the hole is imaged in the inspection film and the line or hole can be clearly identified in the inspection film.

  However, whether or not the lines and holes can be clearly identified may depend on the judgment of the individual inspector, and the possibility that the judgment results may differ between the inspectors cannot be denied.

  As one of means for solving this problem, in the conventional RT film digitizing resolving power confirmation method and film digitizing apparatus, when a photographed inspection film is converted into a digital image by the digitizing apparatus, a plurality of line pairs are used. Digital image data by measuring the line width and pitch width of the line pair captured in the film image and comparing the deviation of the line width and pitch width of the resolution confirmation chart with the allowable rate. Has been proposed (for example, see Patent Document 1).

JP 2003-209654 A

  However, in such a conventional RT film digitizing resolving power confirmation method and film digitizing apparatus, since the transmission meter at the time of the radiation transmission test uses a conventional one, the resolution of the inspection film itself after photographing is It is necessary to determine whether or not the image of the circle or the line copied in the film by the perforated permeability meter or the wire-type permeability meter can be visually confirmed. That is, this method provides a method capable of digitizing a film whose resolution has been confirmed while maintaining the resolution when digitalized, and can quantitatively guarantee the resolution of the inspection film itself. It has a problem that it cannot be done.

  Therefore, an object of the present invention is to quantitatively guarantee the resolution of the inspection film itself photographed in the radioactive transmission test.

  Another object of the present invention is to obtain, as digital image data, an image in which the resolution of the inspection film itself taken in the radiographic transmission test is guaranteed without depending on vision.

  The means of the present invention is a method of transferring the radiation transmission test permeability meter into the inspection film at the same time as the test body at the time of filming of the radiation transmission test, and transferring the radiation transmission test transmission meter into the inspection film. The MTF value of the image is determined and the resolution of the image in the inspection film is quantified to ensure the resolution of the radiation transmission test image.

  More specifically, as a transmission meter for a radiation transmission test used at the time of filming of a radiation transmission test, a rectangular slit through hole having a slit width equal to, twice or four times the thickness of the transmittance meter plate, and the slit Using a pair of slits having the same width as the width of the slit, and a radiation transmission test permeability meter having a plurality of pairs, the radiation transmission test permeability meter is placed in the inspection film when filming the radiation transmission test. The MTF according to light and darkness that is imprinted together with a test specimen, and then scanned with a scanner to form digital image data, and is arranged in the slit width direction of an image of a transmissometer for radiation transmission test based on the digital image data A value is obtained to quantify the resolution of the image in the inspection film, and the digital image data relating to the inspection film is To get stored in the storage devices.

  According to the present invention, since the resolution of the inspection film itself photographed in the radiation transmission test can be guaranteed without relying on vision, the reliability of the radiation transmission test is improved.

  The best mode for carrying out the present invention is a radiation transmission test permeability meter used at the time of filming of a radiation transmission test, having a slit width equal to or twice or four times the thickness of the radiation transmission permeability meter. Using a penetrometer with multiple pairs of slits and slit intervals, the radiation tester photographed and photographed the pair of slits and slits along the line pair and the specimen at the same time, and digitized the shot inspection film. Then, the resolution of the inspection film image is quantified and guaranteed by measuring the MTF values related to the light and darkness arranged in the slit width direction of the image of the line pair, and more preferably, the inspection in which the resolution is guaranteed. It is to store and acquire digital image data of film.

  More specifically, as shown in FIG. 1, as a transmission meter for a radiation transmission test used in a radiation transmission test, a transmittance plate is formed on a square plate material 1 having a thickness of 2% of the thickness of the specimen. Transmissometer for radiation transmission test (hereinafter referred to as line pair type transmittance) having a plurality of rectangular slit through-holes 2 having a width equal to or two or four times the thickness and a slit interval 3 having the same width as the slit width. Called the total).

  This is because the current perforated penetrometer has a through hole with a hole diameter equal to the plate thickness, 2 or 4 times the plate thickness of 2% of the test vs. thickness, depending on the radiation transmission test conditions. Considering that the transmission image of the specified through-hole is required to be visible on the film, the dimensional requirement follows this dimensional feature.

  Using the above-mentioned line pair type transmissometer, a bright and dark line pair image formed by the slits and the slit interval is copied into the inspection film of the radiation transmission test, and the entire one inspection film is digitally imaged by a scanner alone. We have established a technology that can guarantee the resolution of the image on the inspection film by measuring the MTF value of the image of the line pair that has been converted and captured.

  As shown in FIG. 1, as a transmission meter for a radiation transmission test used for a radiation transmission test, a rectangular plate material 1 having a plate thickness of 2% of the thickness of a specimen 22 is equal to or twice the plate thickness. Alternatively, a transmission meter for radiation transmission test (hereinafter referred to as a line pair) having three pairs of three rectangular slit through holes 2 having a slit width W of 4 times and a slit interval 3 having the same width S as the slit width W. This is called a shape transmission meter.) The material of the plate member 1 of the line pair type transmissometer is a material that exhibits the same or similar radiation transmission degree as that of the test body 22.

  By making the shape of the rectangular slit through-hole 2 a rectangular slit, a pair of equal-width lines composed of the rectangular slit through-hole 2 and the slit interval 3 can be copied onto the inspection film after the radiation transmission by the radiation transmission test.

Here, the dimension requirements of the line pair type transmissometer are summarized as follows. The relationship between the slit width W of the slit-shaped through-hole 2 (hereinafter referred to as slit 2) and the slit interval S is as follows:
When the slit width W is 1T slit 2 1T = W = S (1) Formula When the slit width W is 2T slit 2 2T = W = S (2) When the slit width W is 4T slit 2 4T = W = S (3) The relationship between the slit width W and the slit length L is as follows:
L> 7 * W (4) Expressions (1), (2), and (3) indicate that the current perforated permeability meter is equivalent to the plate thickness of 2% of the thickness of the test body 22 or Considering that it is required to have a through hole with a double or quadruple hole diameter and that the image of the specified through hole is visible on the inspection film according to the radiation transmission test conditions. This is a dimension requirement that follows the above.

  In this way, by making the slit width of the line pair type transmissometer and the hole diameter of the perforated type permeation meter the same size, the line pair type permeation meter can be used in accordance with the discriminating requirement requirement of the conventional perforated type transmissometer. The image of the meter can be evaluated.

  Further, as shown in the equation (4), by making the slit length L sufficiently large so as to exceed 7 times the slit width W, after the radiation is transmitted, the inspection film 23 has a dark image by the slit 2 and the slit interval 3. A line pair image captured in a bright and dark state with a bright image is easy to see, and a plurality of positions dispersed in the slit length L direction when measuring the brightness of the line pair image in the direction of the slit width W of the line pair image to be described later In addition to being able to measure, it is easy to set the coordinates of the measurement position for the measurement.

  The line pair images of this embodiment are a plurality of pairs of images with a pair of brightness and darkness of the dark portions P1, P2 and P3 and the surrounding bright portions in FIG. In this way, when the brightness of the multiple pairs of images is measured and the multiple pairs of measurement results are averaged, the error is absorbed and the accuracy of the measurement results increases.

  Further, since the slit length L of the slit 2 reaches 7 times the slit width W, the measurement line in the direction of the slit width W indicated by coordinate symbols X11, X12, and X13 for measuring the brightness is in the slit length L direction. In the range surrounded by the coordinate symbols X11 and X13, accurate measurement is possible at any number of locations.

  The flowchart of FIG. 2 shows the test procedure of the radiation transmission test method according to one embodiment of the present invention. The procedure is as follows. First, in step 4, according to the material and thickness of the test body 22 having the welded portion 26 in the center, the material and type of the line pair type permeability meter to be used are determined according to the material of the test body 22. . At this time, since the radiation transmission power differs depending on the material, the material of the line pair type transmissometer is determined to be selected and used as the material of the test body 22.

Next, in step 5, film photographing is performed using the selected line pair type transmissometer. As an example of film photography in a radiation transmission test using a line pair type transmissometer, as shown in FIG. 3, a radiation source 20 is placed at a position where radiation can be applied to the test body 22, and a line pair The permeation meter 21 is placed on the surface of the test body 22 on the radiation source 20 side. Further, the inspection film 23 is disposed on the surface of the test body 22 facing away from the radiation source 20, and the gradation meter 24 is disposed between the inspection film 23 and the test body 22 to perform film photographing. Film photography is performed by irradiating radiation from the radiation source 20 toward the specimen 22 and transmitting the radiation to the specimen 22 including the welded portion 26, the gradation meter 24, and the line pair type transmissometer 21, and inspecting with the transmitted radiation. This is done by exposing the film and copying the transmitted image onto the inspection film 23. On the inspection film 23, the range of L3 in FIG.

At the time of filming, the name 28 of the permeability meter used and the management number 27 of the test are made of heavy metal made of a material that is less likely to transmit radiation than the material of the test specimen 22 and is placed near the line pair type permeability meter 21. Deploy. The line pair type permeation meter 21, the name 28 of the permeation meter, and the test management number 27 may be fixed in advance with a resin or the like. As a result, the name of the line pair type transmissometer 21 and the test management number can be copied with white characters on the inspection film 23 after film shooting, which is useful for subsequent film management.

  On the inspection film 23 photographed in this manner, a bright and dark line pair image by the slit 2 and slit interval 3 portions of the line pair type transmissometer 21 is contained in the inspection film 23 and the radiation of the specimen 22 and its welded portion 26. It is copied with the transmission image.

  In such a radiation transmission test, attribute data such as a management number, a test product name, and a registration date shown in FIG. 4 is obtained in step 6 for each inspection film 23 having a line pair image photographed by the above method. Make a note.

  Here, FIG. 5 shows the tools used from the scanning of the inspection film after photographing to the defect determination and their roles. In step 7, a scanning condition for setting the imaged inspection film 23 to digital image data using the scanner 30 is set.

  Next, in step 8, the inspection films 23 to be converted into digital image data are set one by one in the scanner 30, and scanning processing is performed in step 9. Digital image data obtained by the scanning process is taken into a memory such as a hard disk of the computer 31 in step 10 and an image based on the digital image data is displayed on the display 32. The data structure of the digital image data includes luminance data indicating the degree of light and darkness at each coordinate position in the inspection film 23.

  An outline of an image based on digital image data of the inspection film 23 after photographing shown on the display 32 is shown in FIG. Among the film images 33 on the inspection film 23 after photographing, there are an image 34 of a transmission clock name 28 relating to the line pair type transmissometer 21, an image 35 of the line pair type transmissometer 21, The situation in which the image 36 of the control number 27, the image 37 of the gradation meter 24, and the image 38 of the welded portion 26 are respectively reflected is visible.

  Here, the concept of the MTF value widely used for the purpose of ensuring the resolution of the optical device is applied to the digital image data of the image displayed on the display 32, and in step 11, the resolution of the line pair image is set to MTF. Measure by finding the value. The resolution is measured using the computer 31 according to the procedure of the program flowchart shown in FIG.

  That is, the digital image data of the image of the inspection film 23 after photographing is taken into the computer 31 and set as target data for measuring the MTF value. Next, in step 39, software for measuring the MTF value in the computer 31 is activated. Next, in step 40, the size and contrast of the line pair image are changed by the image adjustment function so that the line pair image can be visually observed. Next, in step 41, the measurement position of the MTF value of the line pair image is the coordinate symbol x11, x12 indicating the position in the slit width direction of the line pair image, that is, in the direction perpendicular to the line pair of the bright and dark lines. , X13 are determined and set, and the measurement lines K1, K2, K3 corresponding to them are determined in the direction of the slit width W of the slit 2. The direction of the slit width W of the slit 2 means the direction of the arrangement of the three dark portions of the line pair image on the screen of FIG. 6 displayed on the inspection film or display.

  As in this embodiment, by making the shape of the slit 2 rectangular, cross sections in a direction perpendicular to the longitudinal direction of the slit 2 are taken at a plurality of positions, for example, measurement lines K1, K2, K3, and the concentration distribution is measured. It becomes possible.

  Next, in step 42, the density distribution in the direction P1 → P2 → P3 along the measurement lines K1, K2, and K3 perpendicular to the slit image is separately measured at the coordinates X11, X12, and X13, that is, the measurement lines K1, K2, and K3. To do.

  In step 42, the density distribution at the coordinates X11, X12, and X13 measured separately for each of the measurement lines K1, K2, and K3 is integrated for each position in the direction P1 → P2 → P3 perpendicular to the slit image in step 43. As shown in FIG. 8, a histogram is created with the vertical axis representing density and the horizontal axis representing the position P1 → P2 → P3 perpendicular to the slit.

  Here, the maximum value (= maximum value) that is the darkest image at the center of each of the dark lines P1, P2, and P3 that are images of the slit 2 in step 44 is obtained and averaged as B, the center of the line pair interval. A, that is, the average value of the two brightest portions between P1 and P2 and between P2 and P3, and the reference value C that is the average value of the portion that becomes the reference brightness, such as both ends of the transmittance meter image The concentration of each is calculated.

  In this way, by integrating or averaging the density obtained in the longitudinal direction of the dark lines P1, P2, and P3 of the line pair image and the direction perpendicular to the longitudinal direction, the influence of noise in the image data is reduced, and more It is possible to calculate an accurate MTF value.

  Using the value obtained by the above method, the MTF value of the line pair image is calculated in step 45 by applying the concept of guaranteeing the resolution of the optical device or the like.

  The MTF (Modulation Transfer Function) value is a value indicating the degree of contrast between light and dark images, and is expressed by the following equation, where I is the intensity level of light and dark.

MTF value = (I (bright) −I (dark)) / (I (bright) + I (dark)) (5) where I (bright) is the highest intensity level value, and I (dark) is the highest. It is a low value. The larger the value, the higher the contrast. Generally, if this value is 0.2 or more, it is considered that identification is possible. Therefore, when the resolution of the line pair image is evaluated, it is 0.2 or more as a threshold value for discrimination.

  Therefore, in the case of this example, the MTF value is calculated by the following equation.

MTF value = {(BC)-(AC)} / {(BC) + (AC)}
= (B−A) / (B + A−2C) (6) Expression If this is 0.2, that is, 20% or more, the digitized film image can be sufficiently identified, and the appropriate resolution as a result of the radiation transmission test. In step 46, it is determined whether or not the MTF value is 0.2 or more. This determination corresponds to the procedure 12 in FIG. Digital image data that has been determined to have an MTF value of 0.2 or higher is stored in the memory of the computer 31 in step 48. This saving corresponds to the procedure 13 in FIG. If it is determined that the MTF value is less than 0.2, in step 46, the digital image data having the line pair image data that has been determined is deleted from the memory of the computer 31 and discarded in step 47.

  In this way, only digital image data whose resolution at the inspection film stage is guaranteed is stored. If it is determined in step 44 that the MTF value is less than 0.2, that is, out of the determination pass range, as in step 12 of FIG. Adjust and execute and repeat the same procedure.

  After that, in step 14 of FIG. 2, the defect determination / sizing software that can determine the presence / absence of a defect from the difference in luminance data at each coordinate position of the inspection film possessed by the digital image data is started, and the MTF is processed by the defect determination / sizing software. Digital image data having a value of 0.2 or more is read from the memory, and further, preparatory work such as saving the digital image data again in a designated memory together with attribute conditions such as test conditions in step 15 is performed. The defect determination / sizing software is a program set in the computer 31, extracts the defect candidate portion by obtaining the luminance of each image and the luminance distribution from the digital image data, and extracts the defect candidate portion thus extracted. Measures the shape, detects only the defect from the shape, and has contents of procedures for displaying information on the defect such as sizing indicating the size and shape of the detected defect and the coordinate position of the defect on the screen of the display 32. is doing.

  The certified examiner looks at the digital image screen of the display 32 on which the image based on the digital image data and the information related to the defect are displayed in the procedure 16, and checks the size and shape of the defect defined in the standards of each industry. The judgment is made by comparing with the permissible value relating to each information. As a result, when it is determined that there is an unacceptable defect, it is determined that repair and remanufacturing is necessary for the product that has become the test body, and therefore the test body is classified as a target for repair and remanufacturing in step 17.

  If no unacceptable defects are found, the radiation transmission test of the specimen is passed in step 18 and an inspection report is created. Here, attribute data such as the above-described digital image data and test conditions are collected and stored in the memory of the computer as information for guaranteeing the quality of the specimen in step 19.

  Since these pieces of information are stored electronically, when data disclosure is required depending on the situation, it is possible to disclose information using WEB or the like. This leads to improved searchability and advanced information management.

  The digital image data relating to the inspection film of the radiation transmission test digitized by the present embodiment quantitatively guarantees the resolution of the film image data by quantitatively evaluating the identification resolution of the line pair image. It is possible to provide a test result that does not vary in resolution determination at an inspection film stage after photographing by an individual.

  At the same time, the inspection film after photographing can be converted into a digital image, simplifying test result management in cooperation with IT technology, rationalizing the test process such as remote radiation test result judgment support, image processing technology It is possible to realize advanced inspection such as defect determination support that makes the best use of.

  The present invention, for example, inspects internal defects in pipes and equipment welds in a non-destructive manner by shooting radiation on pipes and equipment welds in various plants and the surrounding area and shooting the pipes and equipment welds on a film. It can be used for

It is the upper side figure (upper figure) and elevation (lower figure) of the line pair type transmissometer used for the Example of this invention. It is a flowchart which shows the test procedure of the radiation transmission test method by the Example of this invention. The radiation transmission test condition by the Example of this invention is shown, (a) A figure is the elevation view of the condition, (b) A figure is the figure seen from the upper surface of the test body of (a) figure. It is the figure which showed the attribute data registration item of the radiation transmission test by the Example of this invention. It is explanatory drawing which showed the tool used from the scanning of the inspection film by the Example of this invention to defect determination, and its role. It is the figure which showed the display content on the display of the digital image data by the Example of this invention. It is the flowchart which showed the process sequence of the program for measuring the resolution by the Example of this invention. It is a histogram figure of the density | concentration of each position of the line pair image by the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Line pair type transmissometer board material, 2 ... Slit, 3 ... Slit space | interval, 20 ... Radiation source,
21 ... Line pair type transmissometer, 22 ... Specimen, 23 ... Inspection film, 30 ... Scanner,
31 ... Computer, 32 ... Display.

Claims (3)

As a transmission meter for a radiation transmission test, a plate material of a material having a thickness of 2% of the thickness of the test specimen and showing the same or similar radiation transmission degree as that of the test specimen is equal to, twice or 4 times the thickness. Using a rectangular slit through hole with a double slit width and a slit length exceeding 7 times the slit width, and a transmissometer for radiation transmission test with multiple pairs of slit intervals of the same width as the slit width. ,
Radiation was irradiated to the radiographic examination for penetrameter and the specimen, the radiation transmitted through the test penetrameter and the specimen to expose the film in the transmitted radiation, for the radiographic examination was appearing in the film A method for obtaining the resolution of a radiation transmission test image for obtaining an MTF value of an image of a transmission meter.   The digital image data according to claim 1, wherein an image captured on the film is converted into digital image data, the MTF value is obtained based on the digital image data, and the digital image data is obtained when the MTF value is larger than a predetermined value. A method for obtaining a resolution of a radiation transmission test image, characterized by storing. As a transmission meter for a radiation transmission test, a plate material made of the same or similar material as that of the test specimen and having a slit width equal to, twice or four times the plate thickness of the plate material and seven times the slit width is used. Using a rectangular slit through-hole having a slit length exceeding and a slit having the same width as the slit width as a pair, and having a plurality of pairs thereof, the transmittance meter for radiation transmission test The film is exposed to radiation by irradiating the specimen with radiation and the radiation transmitted through the specimen for radiation transmission test and the specimen is scanned with a scanner, and the image reflected on the film is converted into digital image data. MTF values related to brightness and darkness arranged in the slit width direction of the image of the radiation transmission test permeability meter based on the digital image data are obtained, and the MT Value determines whether a predetermined or higher MTF value, the predetermined said digital image data acquisition method radiographic examination image to be saved electronically according to what is determined to MTF value or more.

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