JP2020118552A - Thickness detection method and piping inspection method - Google Patents

Abstract

To easily and quickly detect the thickness of a detection object from an image which is acquired using a plate that holds a photostimulable phosphor.SOLUTION: The photostimulated luminescence generated by irradiating an IP2 in which a piping image is recorded with a laser beam from a laser beam irradiator 11 is read by a light receiving unit 112 and a photoelectric conversion unit 113, and an image generation unit 114 generates, on the basis of the result of this reading, an X-ray transmission image that indicates the piping. A PC 120 derives the thickness of a thinned portion of the piping on the basis of the X-ray transmission image generated by the image generation unit 114. An equation logY=P*logX+Q is used for the thickness deviation. X represents the thickness of the thinned portion, and Y represents a pixel value that the pixels of the X-ray transmission image have.SELECTED DRAWING: Figure 3

Description

The present invention relates to a thickness detection method and a pipe inspection method to which the thickness detection method is applied.

Conventionally, as in Patent Document 1, an object to be detected such as a pipe is irradiated with an X-ray, and an X-ray film is exposed by an X-ray that has passed through the object to be detected (hereinafter, referred to as a transmitted X-ray), thereby generating an X-ray. There is a technique of measuring the thickness of a detection target object from the density of pixels included in an image formed on a film. On the other hand, as a technique for obtaining an image of an object to be detected by transmission X-rays, there is also a method using a plate (imaging plate) holding a stimulable phosphor as in Patent Document 2. According to Patent Document 2, after irradiating the imaging plate with transmitted X-rays, the imaging plate is irradiated with excitation light to stimulate the stimulable phosphor to emit light, and the emitted light is detected to be recorded on the imaging plate. The image of the object to be detected is read.

JP, 2002-267433, A International Publication No. 2016/136296

When the X-ray film is used, the thickness of the detection target object can be easily determined from the image on the X-ray film by using the known relationship between the thickness of the detection target object and the density of pixels as in Patent Document 1. Attempts have also been made to detect them rapidly. Similarly, there is a demand for a method for easily and quickly detecting the thickness of a detection target object from an image acquired using an imaging plate.

An object of the present invention is to provide a thickness detection method capable of easily and quickly detecting the thickness of a detection target object from an image acquired using a plate holding a stimulable phosphor, and a pipe inspection method applying the same. To do.

The thickness detection method of the present invention comprises an irradiation step of irradiating the stimulable phosphor held on the plate with X-rays that have passed through the object to be detected, and recorded in the stimulable phosphor of the plate in the irradiation step. The image generation step of reading an image of the detection target object and generating an X-ray transmission image showing the detection target object, and the thickness of the detection target object being X, and the X generated in the image generation step. A thickness deriving step of deriving a thickness of the detection target object based on a predetermined relationship that X and Y satisfy when a pixel value of a pixel of the line transmission image is Y. The relation of is expressed by logY=P*logX+Q or a mathematical expression equivalent thereto, where P and Q are known constants.

According to the thickness detection method of the present invention, it is possible to easily and easily determine the thickness of the detection target object from the image acquired by the plate based on a predetermined relationship represented by logY=P*logX+Q or a mathematical expression equivalent to this. It can be detected quickly. The expression "logY=P*logX+Q" is, for example, Y=Q'*(X^P'). Note that "^" indicates exponentiation. In addition, the above mathematical formulas assume that an image is formed such that the pixel value X increases as the thickness Y of the detection target object decreases. However, for example, the present invention may be applied to an image forming method in which the pixel value X′ becomes smaller as the thickness Y becomes smaller. For example, when the present invention is applied to an image forming method having a relationship with X such that X′=A−B*X, log Y=P*log[(A−X ')/B]+Q is used as an equation equivalent to the above equation.

In the thickness detection method of the present invention, in place of the detection target object, with respect to the first to nth reference objects each having a thickness of Y1 to Yn (n: an integer of 2 or more), the irradiation step and the When two steps of the image generation step are executed and Xi (i: an integer of 1 or more and n or less) is set to the pixel value of the i-th reference object, (X, Y)=(Xi, Yi) A reference derivation step of deriving P and Q that satisfy or approximately satisfy the predetermined relationship for i=1, 2,... N; and performing the two steps for the detection target object, It is preferable to include a main detection step of detecting the thickness of the detection target object based on the predetermined relationship using P and Q derived in the derivation step. According to this, P and Q are derived based on the pixel values obtained for the n reference objects. Then, based on the mathematical expression logY=P*logX+Q using the derived P and Q, the thickness of the detection target object can be easily and quickly detected.

The first to n-th reference objects may be objects separated from each other, or at least any two of them may be an integrated object. "P and Q such that (X,Y)=(Xi,Yi) approximately satisfies the above predetermined relationship for i=1, 2,... N" is, for example, for the function logY=P*logX+Q. (X, Y)=(X1, Y1),... (Xn, Yn) curve fitting (fitting).

Further, in the pipe inspection method according to the present invention, the thickness of the pipe may be detected as the detection target object by using the thickness detection method. According to this, the thickness of the pipe can be easily and quickly detected.

Further, in the present invention, a graph output step of outputting to the output means a graph showing a distribution of the pixel value on an imaginary line passing through the thinned portion of the pipe or its vicinity along the X-ray transmission image, and the output. Based on the graph output by the means, a healthy thickness estimation step of deriving an estimated thickness of the thinned portion when it is assumed that no thinning has occurred, and the reduction in the main detection step. It is preferable to evaluate the thickness of the meat portion with respect to the estimated thickness. According to this, it is possible to estimate the thickness of the thinned portion on the assumption that the thinning has not occurred (that is, on the assumption that the sound portion is a healthy portion). Therefore, the thickness of the thinned portion can be appropriately evaluated based on the estimated thickness when there is no thinning.

Further, in the present invention, based on the pixel value and the predetermined relationship with respect to one point on an interpolation curve showing the shape of the graph at the position corresponding to the metal loss portion when it is assumed that the metal loss has not occurred It is preferable to derive the estimated thickness. According to this, the estimated thickness can be appropriately derived based on the interpolation curve when it is assumed that there is no thinning.

Further, in the present invention, in the graph output step, the graph is output to the output means for each of the two virtual lines that are different from each other, and in the sound part estimation step, the two graphs regarding the two virtual lines are output. It is preferable to estimate the thickness of the sound portion based on According to this, since the thickness of the healthy portion is estimated based on the two graphs, the thickness of the healthy portion can be more accurately estimated.

It is a schematic diagram of the process of recording the X-ray transmission image of the pipe and the reference piece on the IP in the pipe inspection method according to the embodiment of the present invention. It is a bottom view (FIG. 2A) and a front view (FIG. 2B) of the reference piece used in the process of FIG. It is a functional block diagram which shows the structure of the image analysis system which analyzes an image based on IP in which the X-ray transmission image was recorded in the process of FIG. It is a flow figure showing a series of flows from recording an X-ray transmission image to deriving a metal thinning rate of piping. It is an example of an X-ray transmission image. 6 is a graph showing a distribution of pixel values on an imaginary line having two points on both ends on the X-ray transmission image of FIG. 5. 6 is a graph showing a distribution of pixel values on an imaginary line having two other ends on the X-ray transmission image of FIG. 5. It is a schematic diagram showing the relation between the X-ray transmission direction and the radial direction of the pipe.

<Embodiment>
A pipe inspection method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 8. The pipe inspection method corresponds to both the thickness detection method and the pipe inspection method of the present invention.

The pipe inspection method according to the present embodiment inspects the corrosion status of each pipe included in the pipe facilities built in office buildings, public facilities such as government buildings, schools, hospitals, hotels, apartments, ordinary houses, pools, etc. On how to do. The pipe to be inspected (hereinafter referred to as the target pipe 3) is installed at various places in the piping equipment. The target pipe 3 is a sanitary pipe (a water supply pipe, a hot water supply pipe, a miscellaneous drainage pipe, a sewage pipe, a rainwater pipe, a fire extinguisher pipe, a sprinkler pipe, etc.) having a cylindrical main body portion, an air conditioning pipe (a cold water pipe, a hot water pipe, a cooling water pipe, Refrigerant pipe, drain pipe, etc.) and water and sewer pipes. The target pipe 3 is made of any one of a steel pipe (carbon steel pipe or the like), a cast iron pipe, a lining steel pipe, a copper pipe, a stainless steel pipe, or the like. The X-ray generator 1, the imaging plate (hereinafter referred to as IP) 2 and the reference piece 4 shown in FIG. 1 are used in the present pipe inspection method. The X-ray generation device 1 is a device that irradiates objects such as the target pipe 3 and the reference piece 4 with X-rays. Corrosion in the target pipe 3 appears as a thinned portion which is a portion where the wall thickness is reduced. Therefore, it is possible to evaluate the degree of corrosion of the target pipe 3 by evaluating how much the thickness is reduced as compared with the sound portion in which no corrosion appears. The reference piece 4 is an object serving as a reference for deriving the thickness of the target pipe 3. As shown in FIG. 2, the reference piece 4 is a metal member including flat plate portions 4A to 4E (first to fifth reference objects in the present invention) having different thicknesses. The reference piece 4 is made of a material corresponding to the material of the target pipe 3. For example, reference pieces 4 made of steel, stainless steel, and copper are used. The thickness of the flat plate portions 4A to 4E has been measured in advance.

The imaging plate 2 has a light-shielding synthetic resin plate and a stimulable phosphor layer formed on the entire surface of the plate. The stimulable phosphor layer is a layer containing a stimulable phosphor. X-rays from the X-ray generator 1 that have passed through the target pipe 3 or the reference piece 4 (hereinafter referred to as transmitted X-rays) and X-rays that have propagated from the X-ray generator 1 without penetrating (hereinafter referred to as The transmitted X-ray) is applied to the surface of the IP2 stimulable phosphor layer side (hereinafter referred to as the irradiation surface). The irradiation time of the X-rays is adjusted so that the dose on the back surface (the surface on the side opposite to the X-ray generation device 1) of the object to be detected becomes a predetermined magnitude (for example, 1000 μSv). The intensity of the transmitted X-rays with which the IP 2 is irradiated decreases as the thickness of the target pipe 3 and the reference piece 4 increases due to absorption and reflection in the target pipe 3 and the reference piece 4. On the other hand, the opaque X-rays are applied to the IP2 without being absorbed by the object. As a result, an image of the target pipe 3 and the reference piece 4 (hereinafter referred to as an X-ray transmission image) is recorded as a latent image on the stimulable phosphor layer of IP2. In the present embodiment, unless otherwise specified, a portion of the target pipe 3 that substantially corresponds to the front surface of the X-ray generator 1, that is, a transmitted X-ray from the X-ray generator 1 is substantially orthogonal to the imaging plate 2. The part that can be considered to be along the direction to be inspected is to be inspected.

The IP2 on which the X-ray transmission image is recorded is analyzed using the image analysis system 100 shown in FIG. The image analysis system 100 includes an IP reading device 110, a computer (hereinafter referred to as PC) 120, a display 131, and an input device 132. The IP reading device 110 includes a laser light irradiator 111, a light receiving unit 112, a photoelectric conversion unit 113, and an image generating unit 114. The laser light irradiator 111 excites the stimulable phosphor in the stimulable phosphor layer by irradiating the irradiation surface of IP2 with laser light, thereby generating stimulated luminescence in the stimulable phosphor layer. Let The light receiving unit 112 has an optical system including a lens and the like that receives stimulated emission. The photoelectric conversion unit 113 photoelectrically converts the stimulated emission received by the light receiving unit 112 into a current according to its intensity. The image generation unit 114 generates image data corresponding to the X-ray transmission image based on the current generated by the photoelectric conversion unit 113. This image data consists of data indicating the pixel value at each pixel forming the X-ray transmission image. Specifically, the image data is composed of data indicating pixel values of pixels arranged in both the vertical direction and the horizontal direction. Each pixel value has a magnitude corresponding to the intensity of stimulated emission generated from the region corresponding to each pixel on the irradiation surface of IP2. In the present embodiment, the larger the pixel value, the greater the intensity of stimulated emission. The intensity of stimulated emission increases as the irradiation amount of transmitted X-rays increases. Therefore, the larger the pixel value, the higher the intensity of the transmitted X-ray, that is, the smaller the thickness of the object.

The PC 120 includes hardware such as a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and hard disk, and software including program data stored in a storage unit such as ROM and RAM. I have it. The functions of the PC 120 described below are realized by the cooperation of these hardware and software. The PC 120 is connected to the display 131. The results of various types of information processing by the PC 120 are displayed on the screen of the display 131. The PC 120 is also connected to an input device 132 such as a keyboard or a pointing device, and accepts user input using these.

Image data representing an X-ray transmission image is transmitted from the IP reading device 110 to the PC 120. An image analysis application and a thickness derivation application are installed in the PC 120. The image analysis application displays various images such as an X-ray transmission image on the display 131 based on the image data, or relates to a specific range in the X-ray transmission image designated based on the user input through the input device 132. The characteristic value is displayed on the display 131. Further, the thickness derivation application functions the PC 120 so as to derive the thickness of the thinned portion of the target pipe 3 and the estimated healthy thickness described later based on the user input of the analysis value acquired as a result of the image analysis. Let

Hereinafter, a series of flows from recording the X-ray transmission image on the IP2 to deriving the metal thinning rate of the target pipe 3 will be described with reference to FIG. First, as shown in FIG. 1, the IP2 is irradiated with X-rays from the X-ray generator 1 while passing through the target pipe 3 and the reference piece 4 (step S1 in FIG. 4; irradiation step in the present invention). Thereby, the X-ray transmission images of the target pipe 3 and the reference piece 4 are recorded in the IP2. Next, the IP reader 110 photoelectrically converts the stimulated emission due to the irradiation of the laser light to read the recorded image of IP2 (step S2). Then, the IP reading device 110 generates image data corresponding to the X-ray transmission image based on the electric current generated by photoelectric conversion and corresponding to the intensity of stimulated emission (step S3). Note that steps S2 and S3 correspond to the image generation process in the present invention.

Next, using the function of the PC 120 by the image analysis application and the thickness derivation application, the image analysis based on the image data generated by the IP reading device 110 and the derivation of the thickness of the thinned portion and the sound portion are performed as follows. It is executed (steps S4 to S12). First, the PC 120 displays an X-ray transmission image on the screen of the display 131 (step S4). The X-ray transmission image of which an example is shown in FIG. 5 includes images of the target pipe 3 and the reference piece 4. The image of the target pipe 3 includes a healthy part that appears relatively white and a plurality of thinned parts 3x that appear black compared to the surroundings. Note that the X-ray transmission image of FIG. 5 is obtained by using the target pipe 3 in which a plurality of round recesses are formed on the pipe wall by metal working as an actual thinned portion due to corrosion, as an example. The same applies to the case of an actual pipe having a thinned portion formed by corrosion.

Next, the PC 120 derives the diameter of the target pipe 3 by deriving the distance between the one end and the other end of the target pipe 3 on the X-ray transmission image (step S5). One end and the other end of the target pipe 3 are designated based on a user input by the input device 132. Crosses P1 and P2 in FIG. 5 are examples of cursor images showing the positions of the one end and the other end thus designated. Next, the representative pixel value for each of the flat plate portions 4A to 4E of the reference piece 4 is derived (step S6). ROI (Region of Interest) analysis performed by the PC 120 is used to derive the representative pixel value. In the ROI analysis, the characteristic value regarding the pixel in the ROI set based on the user input by the input device 132 is derived and displayed on the screen of the display 131. The ROI is preferably set at a position separated from the end of the reference piece 4 as much as possible. This is because at the end of the reference piece 4, the intensity of the transmitted X-ray tends to deviate from the intensity corresponding to the thickness due to the influence of scattered light or the like. In FIG. 5, as an example, characteristic values are displayed for the ROI R1 set in the flat plate portion 4C. In this example, the characteristic value includes the minimum pixel value, maximum pixel value, average pixel value, standard deviation, mode value pixel value, and mode value pixel number in the ROI. Based on this, for example, the average pixel value 2667 is derived as the representative pixel value of the flat plate portion 4C. Other values such as the mode value may be derived as the representative pixel value.

Next, the PC 120 derives the distance from one end of the target pipe 3 on the X-ray transmission image to the thinned portion 3x (step S7). The positions of the one end of the target pipe 3 and the wall-thinning portion 3x are designated based on the user input by the input device 132. Crosses P3 and P4 in FIG. 5 are an example of a cursor image showing the position of the one end and the position of the thinned portion 3x thus designated. Next, the representative pixel value for the thinned portion 3x of the target pipe 3 is derived (step S8). The ROI analysis is used to derive the representative pixel value, as in step S6. The maximum pixel value within the ROI set so as to include the thinned portion 3x is derived as a representative value. In FIG. 5, as an example, characteristic values are displayed for the ROI R2 that is set so as to include only one of the thinned portions 3x. Based on this, the maximum pixel value 2737 is derived as the representative pixel value of the thinned portion 3x.

Next, a pixel value (hereinafter referred to as an estimated sound pixel value) when it is assumed that the metal thinning portion 3x of the target pipe 3 has not been thinned is estimated (step S9). The estimated healthy pixel value is acquired to derive the thickness of the thinned portion 3x when there is no thinning (hereinafter, referred to as the estimated healthy thickness). The estimated healthy pixel value is derived based on the user input made using the input device 132 while referring to the distribution of pixel values on the virtual line passing through the thinned portion 3x. The distribution of pixel values relates to an imaginary line substantially along the length direction of the target pipe 3 and a direction intersecting the length direction of the target pipe 3 (for example, a direction orthogonal to the length direction of the target pipe 3). It is preferred that at least two are used, one associated with a virtual line along the. ROIs R3 and R4 in FIG. 5 are examples of regions corresponding to such virtual lines. The ROI R3 is set in an elongated rectangular shape that passes through the thinned portion 3x along the length direction of the target pipe 3. The ROI R4 is set in an elongated rectangular shape that passes through the thinned portion 3x along the direction orthogonal to the length direction of the target pipe 3. ROIs R3 and R4 are both set based on user input. 6 and 7 correspond to the distribution of pixel values on ROIs R3 and R4. The graph of FIG. 6 shows a distribution of pixel values displayed on the screen of the display 131 by the PC 120 regarding the ROI R3 of FIG. 5 set based on the user input. The range of pixel values in the graph of FIG. 6 is 2121 to 2693. The PC 120 subdivides the ROI R3 into rectangular areas arranged in a row along the length direction of the ROI R3 and having a predetermined size, and calculates the average value of the pixel values in each rectangular area. Then, the PC 120 causes the display 131 to display a graph in which the calculated average value is plotted on the vertical axis and the position of the ROI R3 in the length direction is plotted on the horizontal axis. The graph of FIG. 7 shows the distribution of pixel values displayed on the screen of the display 131 by the PC 120 in the same manner as in FIG. 6 for the ROI R4 of FIG. 5 based on the user input. The range of pixel values in the graph of FIG. 7 is 1321 to 2693, which is wider than that of FIG. The process of displaying the graphs of FIGS. 6 and 7 corresponds to the graph output process of the present invention. The graphs of FIGS. 6 and 7 may be output by an output means other than the display 131. For example, it may be recorded on the recording medium by a printing device connected to the PC 120.

The method of determining the estimated healthy pixel value based on the graphs of FIGS. 6 and 7 is as follows. First, as shown in FIG. 6, an interpolation curve (two-dot chain line) connecting both end points of the peak portions P1 and P2 indicating the pixel value of the thinned portion 3x is virtually set. The interpolation curve is a curve having such a shape that the graph is smoothly continuous between the left side and the right side of the peak portions P1 and P2 when it is assumed that there is no peak portion P1. The interpolation curve is set by drawing a Bezier curve connecting the left end point and the right end point of the peak parts P1 and P2, or by virtually drawing by hand by the user. Next, with respect to the length direction of the ROI, a point on the interpolation curve at the same position as the point having the maximum value in the peak portion P1 (intersection with the alternate long and short dash line) is selected based on the user input by the input device 132. The pixel value of the selected point is provisionally determined as the estimated sound pixel value. Next, regarding the graph of FIG. 7, similarly, one point on the interpolation curve is selected based on the user input by the input device 132. Then, when the user determines that the pixel value of the selected one point is not significantly different from the value tentatively determined based on the graph of FIG. 6, the tentatively determined pixel value is officially the estimated healthy pixel value. Is decided. Note that an average value of the pixel value determined based on the graph of FIG. 6 and the pixel value determined based on the graph of FIG. 7 may be determined as the estimated sound pixel value.

Next, the PC 120 accepts the user input of each representative pixel value of each part of the reference piece 4 and the thickness reduction part 3x derived in steps S6 and S8 and the estimated sound pixel value derived in step S9 (step S10). Then, the PC 120 derives the thickness and the estimated healthy thickness of the thinned portion 3x based on the numerical value input in step S10 (step S11; the thickness deriving step in the present invention). In deriving the thickness of the thinned portion 3x, the following mathematical formula is used.
(Mathematical formula)
logY=P*logX+Q
However, X: thickness of the target object, Y: pixel value at the position where the thickness is desired

First, P and Q are determined based on the pixel value of each part of the reference piece 4. Specifically, the five pixel values of the flat plate portions 4A to 4E acquired in step S6 are X1 to X5, and the thicknesses of the flat plate portions 4A to 4E measured in advance are Y1 to Y5. Then, P and Q are obtained by performing curve fitting (fitting) of (X, Y)=(X1, Y1),... (Xn, Yn) on the function logY=P*logX+Q. For curve fitting, any method such as the least squares method or the maximum likelihood estimation method may be used. Then, the pixel value of the thinned portion 3x input in step S10 is set to Y=Ya, or the estimated sound pixel value is set to Y=Yb, and P and Q acquired as described above and the above mathematical expression are used. As a result, X=Xa corresponding to Ya or X=Xb corresponding to Y=Yb is acquired. Both Xa and Xb thus obtained correspond to the sum of the thicknesses of the wall portions of the target pipe 3x through which the transmitted X-rays are transmitted. The transmitted X-rays are at two places, namely, a wall portion on the front surface side (the side closer to the X-ray generator 1) in the target pipe 3x and a wall portion on the rear surface side (the side farther from the X-ray generator 1) in the target pipe 3x. Pass through the wall. Therefore, both Xa and Xb have a value obtained by adding the thickness of the front wall portion and the thickness of the rear wall portion. Therefore, the PC 120 sets the estimated healthy thickness to half of Xb. In addition, the PC 120 determines the thickness of the thinned portion 3x from Xa based on the premise that the thinned portion of the wall portion of the target pipe 3 has occurred on either the front surface side or the rear surface side. It shall be the value obtained by subtracting the estimated soundness.

Next, the PC 120 calculates the metal thinning rate based on the thickness of the metal thinning portion 3x and the estimated sound thickness acquired in step S11 (step S12). Specifically, the metal thinning rate is acquired as a percentage based on ((Thickness reduction rate)=[(Estimated sound thickness-Thickness of thinned portion 3x)/(Estimated sound thickness)]*100. The thickness and the metal thinning rate of the metal thinning portion 3x acquired in steps S11 and S12 are displayed on the screen of the display 131 (step S13).

The steps S1 to S3 described above and the step of deriving P and Q in step S11 as a whole correspond to the reference deriving step. Further, the above-described steps S1 to S3 and the step of deriving the thickness of the reduced thickness portion 3x in step S11 correspond to the main detection step as a whole.

According to the thickness detection method or the pipe inspection method according to the present embodiment described above, the thickness of the target pipe 3 can be easily and quickly detected based on the above mathematical formula.

Further, according to this embodiment, the image of the reference piece 4 together with the target pipe 3 is recorded in the IP2. Flat plate portions 4A to 4E having different thicknesses are formed on the reference piece 4. Then, P and Q are derived based on the pixel values obtained for these flat plate portions 4A to 4E. Based on the above mathematical formula using P and Q derived in this way, the thickness of the target pipe 3 can be easily and quickly detected.

Further, according to the present embodiment, the estimated healthy pixel value is estimated based on the graphs of FIGS. 6 and 7 on the assumption that the metal thinning portion 3x of the target pipe 3 is not thinned. The thinned portion 3x appears as a local peak portion in the graphs of FIGS. 6 and 7. Therefore, it is easy to estimate the pixel value of the thinned portion 3x when there is no thinning by assuming a graph when there is no peak. Then, based on the estimated sound pixel value, the thickness of the thinned portion 3x when there is no thinning (estimated healthy thickness) is estimated, and based on the estimated healthy thickness and the thickness of the thinned portion 3x. The thinning rate is derived. In this way, the thickness of the thinned portion 3x can be appropriately evaluated based on the estimated thickness when there is no thinning.

Further, in the present embodiment, in deriving the estimated healthy thickness, in the graphs of FIGS. 6 and 7, an interpolation curve showing the shape of the position corresponding to the thinned portion 3x when it is assumed that the thinning has not occurred. To set. Then, the estimated thickness is derived based on the pixel value for one point on the interpolation curve and the above mathematical formula. Therefore, the estimated thickness can be appropriately derived based on the interpolation curve when it is assumed that there is no thinning. Further, in the present embodiment, the estimated healthy thickness is derived based on the two graphs shown in FIGS. 6 and 7. Therefore, the estimated healthy thickness can be accurately derived.

<Example>
Hereinafter, Examples 1 to 4 according to an example of the thickness detecting method and the pipe evaluating method of the present invention will be described.

[Example 1]
In Example 1, the reference pieces a to c having the same structure as the reference piece 4 (flat plate portions 4A to 4E) were set as detection targets. The thickness [mm] and material of the reference pieces a to c are as shown in Table 1 below. Each of the reference pieces has a length of 100 mm in the lengthwise direction and a length of 25 mm in the width direction in a plan view. A to E correspond to the flat plate portions 4A to 4E, respectively.
[Table 1]

RADIOFLEX-200SPS made by Rigaku is used as the X-ray generator 1, UR-1 made by Fuji Film is used as IP2, and Dynamix HR2 made by Fuji Film is used as the IP reader 110, instead of the target pipe 3 and the reference piece 4. The above-mentioned steps S1 to S3 and S6 were executed with the reference pieces a to c as detection targets. The X-ray irradiation conditions were as follows. The tube voltage of the X-ray generator 1 is 200 kV, the distance from the X-ray irradiation window of the X-ray generator 1 to the detection target is 700 mm, and the X-ray irradiation time is 0.3 to 0.4 seconds. The irradiation time was specifically adjusted such that the dose on the back surface of the flat plate portion 4C of each reference piece was 1000 μSv. Next, any four of the flat plate portions 4A to 4E are set as reference portions, and the pixel values of these four reference portions are used to derive and derive P and Q as in step S11 described above. The thickness of the remaining one of the flat plate portions 4A to 4E was calculated using P and Q and the above mathematical formula. Then, the calculated results were compared with the dimensions in Table 1. The results are shown in Tables 2 to 4 below. In the table, “reference part” and “calculation target” indicate the four parts set as the reference part and the remaining one part for which the thickness is calculated. ABCDE corresponds to the flat plate portions 4A, 4B, 4C, 4D, and 4E, respectively. “Thickness” is the result of calculating the thickness of the calculation target. The error indicates the ratio of the difference between the actual thickness and the calculated thickness with respect to the full scale. The full scale is 8 mm for the reference piece a, 6 mm for the reference piece b, and 6 mm for the reference piece c.

[Table 2] (reference piece a)

[Table 3] (reference piece b)

[Table 4] (reference piece c)

[Example 2]
The pipe inspection method according to the above-described embodiment was carried out by using three sample pipes a to c composed of straight pipe (cylindrical) pipes. The same X-ray generator 1, IP2, and IP reader 110 as those used in Example 1 were used, and the X-ray irradiation conditions were the same as those used in Example 1. Each of the sample tubes a to c is composed of two parts obtained by half-dividing one steel tube along the length direction. After forming the first to fifth virtual thinned portions, which are recesses or through-holes that are likened to the thinned portion due to actual corrosion, on the inner surface of each component by metal working, the two components are joined to form the original cylindrical shape. The sample tubes I to C were prepared by returning the sample tubes to the above. From the left, each column of Table 5 shows, from the left, sample tubes a to c, size, parts, thicknesses [mm] of the first to fifth virtual thickness reduction parts, and thickness reduction rates, and measured values [mm] of sound parts. ] Is shown. A and B in the "parts" column indicate one and the other of the half-divided parts. “Penetration” in the “first” column to the “fifth” column indicates a through hole. Numerical values lined up and down in the “first” column to the “fifth” column show the actual measurement value of the thickness on the upper side and the thinning rate with respect to the actual measurement value of the sound portion on the lower side. The measured values are all values measured using a micrometer.
[Table 5]

Regarding the above sample tubes a to c, the results of calculating the thicknesses of the first to fifth virtual thinned portions based on the above embodiment are as shown in Tables 6 to 8 below. The “virtual thinning portion” column indicates which virtual thinning portion. For example, “A-1” indicates the first virtual thinned portion of the component A, and “B-2” indicates the second virtual thinned portion of the component B. The column “Error rate [%]” shows the difference between the calculated value and the measured value.
[Table 6] (Sample tube a)

[Table 7] (Sample tube B)

[Table 8] (Sample tube c)

[Example 3]
RADIOFLEX-200SPS manufactured by Rigaku is used as the X-ray generator 1, BAS-MS 2025 manufactured by Fuji Film is used as the IP2, and R-AXIS-DS3L manufactured by Rigaku is used as the IP reading device 110. Steps S1 to S3 and S6 were performed in the same manner as in Example 1 with the pieces a to c as detection targets. The results are shown in Tables 9 to 11 below. The meanings of the items in Tables 9 to 11 are the same as those in Tables 2 to 4.

[Table 9] (Standard piece a)

[Table 10] (Reference piece b)

[Table 11] (Standard piece c)

[Example 4]
When the piping inspection method was carried out in the same manner as in Example 3 for the sample tubes I to C similar to those in Example 2, the results shown in Tables 12 to 14 below were obtained. The meanings of the items in Tables 12 to 14 are the same as those in Tables 6 to 8.
[Table 12] (Sample tube a)

[Table 13] (Sample tube B)

[Table 14] (Sample tube c)

<Modification>
The above is a description of preferred embodiments of the present invention, but the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope described in the means for solving the problems. It is possible. Hereinafter, modified examples according to the above-described embodiment will be described.

For example, in the above-described embodiment, the target whose thickness is detected is the target pipe 3, but the present embodiment may be applied to an object other than the pipe.

Further, in the above-described embodiment, the target pipe 3 and the reference piece 4 are simultaneously irradiated with X-rays, and these images are recorded in the IP2. However, the images of the target pipe 3 and the reference piece 4 may not be simultaneously recorded in the IP2, but may be recorded at different timings. For example, P and Q may be calculated in advance based on the image of the reference piece 4 before the image of the target pipe 3 is acquired.

Moreover, in the above-described embodiment, the flat plate portions 4A to 4E having different thicknesses are formed on one reference piece 4. However, a plurality of flat plate members having different thicknesses and separated from each other may be used instead of the reference piece 4. Further, although five flat plate portions having different thicknesses are formed on the reference piece 4, 2 to 4 or 6 or more flat plate portions having different thicknesses may be formed.

In addition, in the above-described embodiment, the image analysis application and the thickness derivation application are installed in the PC 120. However, one application having both functions of these two applications may be installed in the PC 120. Alternatively, three or more applications sharing the functions of these two applications may be installed in the PC 120. Note that the thickness derivation application may be in any form as long as it is an application that performs a predetermined calculation based on a numerical value input by the user. For example, spreadsheet software may be used. Further, some functions of the image analysis application and the thickness derivation application may be shared by one or more computers other than the PC 120.

Further, in the above-described embodiment, FIG. 6 or 7 is a graph displayed on the display 131 regarding the ROI R3 or R4 set along the length direction of the target pipe 3. However, instead of the graph of FIG. 6 or FIG. 7, a graph relating to the ROI set to be slightly along the length direction of the target pipe 3 or a direction orthogonal to this may be used. For example, a graph regarding the ROI along the direction in which the angle with the length direction of the target pipe 3 is less than 45° may be used instead of the graph in FIG. 6. Further, a graph regarding the ROI along the direction in which the angle between the length direction of the coping pipe 3 and the direction orthogonal to the direction is less than 45° may be used instead of the graph of FIG. 7.

Further, in the above-described embodiment, the ROIs R3 and R4 are set as regions having a certain width. 6 and 7 are drawn as graphs showing an average value for each rectangular region having a predetermined size arranged in one row along the length direction of each ROI. However, the ROIs R3 and R4 may be set as a region having no width, that is, as a line segment region. In this case, instead of the graphs of FIGS. 6 and 7, a graph showing the pixel value of each pixel applied to the line-shaped ROIs R3 and R4 may be drawn.

Further, in the above-described embodiment, the thickness of the thinned portion 3x is set based on the premise that the thinned wall portion of the target pipe 3 has occurred on either the front surface side or the rear surface side. It is derived. Whether the thinning of the wall portion of the target pipe 3 has occurred on either the front surface side or the back surface side, or both of them, is determined by, for example, X at an angle different from the X-ray transmission image of the above-described embodiment. It is necessary to judge by observing the line transmission image. Thereby, when it is determined that the wall thinning of the target pipe 3 has occurred on both the front side and the back side, the thinning rate of the thinned portion 3x is calculated as follows. It is preferable that the value is evaluated to be a value smaller than the value when it is assumed that the thinning occurs on either the front side or the back side.

Strictly speaking, the thickness of the thinned portion 3x and the like of the target pipe 3 derived by the above-described embodiment is the thickness in the transmission direction of X-rays that pass through the target pipe 3. For example, regarding the portion 3a shown in FIG. 8, the radial direction of the target pipe 3 and the X-ray transmission direction match. Therefore, the thickness of the derived portion 3a is the thickness in the radial direction. However, regarding the portion 3b shown in FIG. 8, the radial direction of the target pipe 3 and the X-ray transmission direction do not match. In this case, the thickness along the X-ray transmission direction different from the radial direction is derived as the thickness of the portion 3a. Therefore, the thickness derived in the above-described embodiment may be corrected to the thickness along the radial direction of the target pipe 3. Specifically, the thickness obtained in the radial direction may be the thickness obtained by multiplying the derived thickness by the cosine at the angle between the radial direction and the X-ray transmission direction. In order to make such a correction, it is necessary to estimate whether the wall of the target pipe 3 is thinned on the front side or the back side. This estimation may be performed, for example, by observing an X-ray transmission image at a different angle from the X-ray transmission image of the above-described embodiment. Further, the direction and distance from the X-ray light source differ depending on the detection position. For example, as shown in FIG. 8, the distance and direction from the X-ray generator 1 in the portion 3a are different from the distance and direction from the X-ray generator 1 in the portion 3b. Therefore, strictly speaking, the dose of X-rays irradiated to the target pipe 3 differs depending on the detection position. In the above-described embodiment, the difference in the irradiation dose due to the difference in the detection position is not considered based on the assumption that the difference in the irradiation dose is not so large. However, P and Q may be calculated or the thickness of the thinned portion 3x may be calculated in consideration of the difference in the X-ray irradiation dose due to the difference in the position on the target pipe 3 or the reference piece 4.

1 X-ray generator 2 IP (imaging plate)
3 Target piping 3x thickness reduction part 4 Reference piece 4A-4E Flat plate part 100 Image analysis system 110 IP reading device 120 PC (computer)

Further, in the present invention, in the graph output step, the graph is output to the output means for each of the two virtual lines different from each other, and in the sound thickness estimation step, two graphs regarding the two virtual lines are output. It is preferable to estimate the thickness of the sound part based on the graph. According to this, since the thickness of the sound part is estimated based on the two graphs, the thickness of the sound part can be more accurately estimated.

Claims (6)

An irradiation step of irradiating the stimulable phosphor held on the plate with X-rays transmitted through the object to be detected,
An image generation step of reading an image of the detection target object recorded in the photostimulable phosphor of the plate in the irradiation step, and generating an X-ray transmission image showing the detection target object,
When the thickness of the detection target object is X and the pixel value of the pixel of the X-ray transmission image generated in the image generation step is Y, the detection is performed based on a predetermined relationship that X and Y satisfy. A thickness deriving step of deriving the thickness of the target object,
When the predetermined relationship is that P and Q are known constants,
logY=P*logX+Q
Alternatively, a thickness detecting method characterized by being expressed by a mathematical expression equivalent to this. Instead of the detection target object, two steps of the irradiation step and the image generation step are executed for the first to nth reference objects each having a thickness of Y1 to Yn (n: an integer of 2 or more). In addition, when Xi (i: an integer of 1 or more and n or less) is the pixel value of the i-th reference object, (X, Y)=(Xi, Yi) is i=1, 2,... A reference derivation step of deriving P and Q that satisfy or approximately satisfy the predetermined relationship,
A main detection step of performing the two steps for the detection target object and detecting the thickness of the detection target object based on the predetermined relationship using P and Q derived in the reference derivation step; The thickness detecting method according to claim 1, further comprising: A pipe inspection method, wherein the thickness detection method according to claim 1 or 2 is used to detect the thickness of a pipe as the detection target object. A graph output step of causing an output means to output a graph showing a distribution of the pixel values on a virtual line passing through the thinned portion of the pipe or the vicinity thereof along the X-ray transmission image,
Based on the graph output by the output means, a healthy thickness estimating step of deriving an estimated thickness of the thinned portion when it is assumed that no thinning has occurred,
The pipe inspection method according to claim 3, wherein the thickness of the thinned portion is evaluated with respect to the estimated thickness in the main detection step. Deriving the estimated thickness based on a pixel value and a predetermined relationship regarding a point on an interpolation curve indicating the shape of the graph at a position corresponding to the thinned portion, assuming that no thinning has occurred. The pipe inspection method according to claim 4. In the graph output step, causing the output means to output the graph for each of the two different virtual lines,
The pipe inspection method according to claim 4 or 5, wherein in the sound part estimation step, the thickness of the sound part is estimated based on the two graphs relating to the two virtual lines.