JPH0695016B2 - Corrosion diagnosis method for inner surface of pipe - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for diagnosing corrosion of an inner surface of a steel pipe during operation by X-ray radiography, and particularly to speeding up a corrosion detection process.

[Prior Art] As a method for investigating the corrosion state of the inner surface of a pipe installed on the ground or in water, an ultrasonic flaw detection method that measures the wall thickness of the pipe using ultrasonic waves or X-ray imaging is used. The method of detecting the state of corrosion from the X-ray film is used.

According to the ultrasonic flaw detection method, the wall thickness can be measured to an accuracy of 0.1 mm. Moreover, although the measurement accuracy of the X-ray transmission method is lower than that of the ultrasonic flaw detection method, it is possible to sufficiently investigate the corrosion condition, and the X-ray transmission method allows the corrosion condition to be easily measured by the X-ray film. Since it can be confirmed and the stored data of the measured data is good, the X-ray transmission method is used not only on the ground but also on the corrosion of pipes in water such as in the sea.

In the imaging method using this X-ray film, only a two-dimensional image perpendicular to the irradiated X-ray can be obtained. Therefore, the density distribution of the image formed on the X-ray film is examined, and the depth of corrosion is determined from the density distribution of this image. A method has been adopted in which the distribution is obtained and displayed to more reliably investigate the corrosion condition.

Conventionally, when investigating the corrosion condition by obtaining the depth distribution of corrosion from the concentration distribution of this image, a standard recess is made in a pipe with the same diameter and thickness as the pipe to be investigated in advance, and it is in the same condition as the site to be investigated. A simulation experiment is conducted to form an image of a standard depression on an X-ray film for comparison, and residual thickness estimation data for the density of this X-ray film is obtained. Then, the concentration of the X-ray film obtained by photographing the tube to be investigated is compared with the concentration of the X-ray film obtained in the simulation experiment to obtain the distribution of corrosion and the estimated residual thickness, and the display is displayed or printed by an XY plotter or the like. is doing.

[Problems to be Solved by the Invention] For example, when investigating the corrosion distribution of a pipe installed in the sea by the above-mentioned conventional method, a simulation experiment is always carried out in water even if it is a single survey, and the concentration of the X-ray film is preliminarily measured. Therefore, it is necessary to obtain the characteristics of the remaining thickness estimation data, and it is necessary to carry out an experiment for 1 to 2 weeks for each survey. Therefore, there is a disadvantage in that it takes a considerable amount of time and money before conducting the actual survey.

Also, in order to obtain the distribution of corrosion, X-Y on the plotter is used.
It is necessary to measure the line film one by one with a densitometer.
2 to read one X-ray film (quarter size)
It takes about 3 hours, and there is also a disadvantage that the reading time is long.

Further, in the simulation experiment, it is necessary to have skill in order to accurately obtain the characteristics of the X-ray film concentration and the residual thickness estimation data and the corrosion distribution, and there is a disadvantage that only a specialist can analyze.

The present invention has been made to solve the above disadvantages, and it is an object of the present invention to provide a corrosion diagnosis method for the inner surface of a pipe, which can obtain a corrosion distribution in a short time without a simulation experiment and even without an expert. It is intended.

[Means for Solving the Problems] A method for diagnosing corrosion of an inner surface of a pipe according to the present invention irradiates an X-ray with a test piece having a plurality of standard recesses having different depths stacked in the vicinity of an inspected portion of the pipe. , An X-ray transmission image is formed on the X-ray film, the X-ray transmission image is read by an image sensor, and the standard dent density is calculated by subtracting the density in the vicinity of the dent position of the test piece of the read image, A regression equation of standard dent concentration and standard dent depth is calculated, and the estimated base metal concentration distribution of the test area is created by the regression equation from the concentration distribution of the non-thickened position of the test area. Subtract the measured density of the test area to calculate the dent density, use the calculated dent density to calculate the dent depth of the test area from the regression equation of the standard dent density and the standard dent depth, and calculate the dent depth. It is characterized by displaying the distribution of height.

Further, by correcting the dent depth of the test portion by the dent shape, the dent depth distribution can be obtained more accurately.

[Operation] In the present invention, a test piece having a plurality of standard recesses having different depths is overlapped around the test portion of the tube and irradiated with X-rays, and the X-ray film is irradiated with X-rays of the test piece and the test portion. Form a transmission image. This X-ray transmission image is read by the image sensor and input to the image processing means.

The image processing means calculates the standard dent density by subtracting the density in the vicinity of the dent position of the test piece of the read image to calculate the standard dent density, and the error caused by the difference in the image density and the photographic contrast depending on the position of the film surface of the X-ray film. To fix.

Calculate the regression equation of this standard dent concentration and standard dent depth,
The relationship between the image density and the depth of the depression is calculated according to the installation status of the part to be inspected.

Further, the image processing means creates an estimated concentration distribution of the base material of the test portion from the density distribution at the non-thickened position of the test portion of the read image by a regression equation, and an image that differs depending on the position of the film surface of the X-ray transmission image. Correct the density.

Then, the dent concentration due to corrosion is calculated from the difference between the base metal estimated concentration distribution and the concentration of each part of the test part, and the dent depth of the test part is calculated from the regression equation of this dent concentration and the standard dent concentration and the standard dent depth. calculate.

Further, even with the same dent depth, since the density varies depending on the geometrical dimension of the dent, it is possible to improve the dent depth detection accuracy by correcting the calculated dent depth of the test portion by the shape of the dent. .

[Embodiment] FIGS. 1 and 2 show an embodiment of the present invention. FIG. 1 is a layout view when an X-ray is taken of a tube to be investigated, and FIG. Is.

As shown in FIG. 1, when investigating the corrosion of the pipe 1, a test piece 3 is placed on the test portion 2 of the pipe 1, and the test portion 2 is irradiated with X-rays from an X-ray device 4. An X-ray transmission image of the test portion 2 and the test piece 3 is formed on the X-ray film 5.

The test piece 3 is formed of the same material as the tube 1, and has a plurality of standard recesses 32 having different depths around the test visual field portion 31, as shown in FIG. The inside of this standard recess 32 is filled with a substance of the same quality as the contents of the tube 1. In FIG. 3, the numbers in the standard recesses 32 indicate the recess depths. The depth of the standard depression 32 is different from that of the standard depression 32 of the same depth when the X-ray transmission image is formed on the X-ray film 5 because the density and the contrast differ depending on the position of the X-ray film 5. Are provided in the central part and the peripheral part, respectively.

The X-ray transmission image of the test piece 3 and the test portion 2 is read into the image processing device and processed. As shown in FIG. 2, the image processing apparatus has an image recognition means 6 for reading an X-ray transmission image photographed on the X-ray film 5, an input means 7, an image processing means 8, a display means 9 and a printer 10.

The image recognition means 6 has an image sensor such as an image pickup tube, and reads an X-ray transmission image and digitizes it.

The image processing means 8 includes a standard depression density calculation unit 11 and a feature extraction unit.
12, a base material density calculation unit 13, a dent density calculation unit 14, a dent depth calculation unit 15, an image memory 16, and a test piece registration recording unit 17.

The standard dent density calculating unit 11 inputs the image of the test piece 3 sent from the image recognizing means 6 or the image of the test piece 3 stored in the test piece registration recording unit 17, and from the image density of the standard dent 32 to the vicinity thereof. The standard image density is calculated by subtracting the image density of.

The feature extraction unit 12 calculates a regression equation between the calculated standard dent concentration and the depth of the standard dent 32 input from the input means 7, and the pipe 1
The base material concentration calculating unit 13 that obtains the relationship between the image density and the dent depth according to the installation status of the base material is extracted from the image of the target portion 2 sent from the image recognition means 6 and the density at the non-thinning position is extracted. The estimated base metal concentration distribution of No. 2 is created by the regression equation.

The dent concentration calculating unit 14 calculates the dent concentration due to corrosion by obtaining the difference between the estimated base metal concentration distribution and the densities of the respective portions of the inspected portion 2.

The dent depth calculation unit 15 calculates the dent depth of the test portion 2 from the regression equation of the calculated dent concentration, the standard dent concentration and the standard dent depth obtained by the feature extraction unit 12.

Next, the operation for investigating the corrosion condition of the pipe 1 according to this embodiment will be described.

When investigating the corrosion of the tube 1, as shown in FIG. 1, the test piece 3 and the X-ray film 5 are placed on the inspected part 2 of the tube 1 so as to overlap with each other, and the X-ray device 4 irradiates the X-ray. Then, the X-ray transmission images of the test piece 3 and the portion to be inspected 2 are transferred to the X-ray film 5
To form. The X-ray transmission image of the X-ray film 5 is read by an image sensor such as an image pickup tube of the image recognition means 6 and sent to the image processing means 8 for image processing. In this way, the X-ray transmission image can be instantaneously input by reading the X-ray transmission image with the image pickup tube or the like. Further, with an image pickup tube or the like, an image can be read at a density similar to that read by a densitometer.

When the X-ray transmission image is image-processed, as shown in the flowchart of FIG. 4, it is first determined whether or not the registered test piece 3 stored in the test piece registration recording unit 17 is used (step S1) When the registered test piece 3 is used, the registered test piece 3 is immediately read from the test piece registration recording section 17 and the information of the test section is read from the image recognition means 6 (step S7).

When the registered test piece 3 is not used, 32 standard dents of the test piece 3 of the X-ray transmission image are read and stored in the standard dent density calculation unit 11 and simultaneously displayed on the display means 9 (step S2). Next, the position and outer diameter of each standard recess 32 are input from the input means 7 to the standard recess density calculating section 11, and the contour of the standard recess 32 is drawn on the display means 7 (step S3). Then, the depth of each standard recess 32 is input from the input means 7 and stored in the feature extraction unit 12 (step S4). Next, the test piece base metal concentration measuring position in the vicinity of each standard recess 32 displayed on the display means 7 is input to the standard recess density calculating section 11 by the plural-point input means 7 or a mouse (not shown). (Step S
Five). These operations are repeated for all the standard depressions 32 to register the information (step S6).

Next, read the information about the standard depression 32 and the test area (step S
7), the standard recess density calculator 11 calculates the standard recess density from the image signal of the standard recess 32, the position and size of the standard recess 32, and the test piece base material density measurement position (step S8). That is, since the density distribution of the X-ray film 5 and the photographic contrast are not uniform, in order to reduce the error due to it, the image density at the test piece base material density measurement position is subtracted from the image density of each standard depression 32 to obtain each standard. The standard recess density of the recess 32 is calculated.

The standard dent concentration is sent to the feature extraction unit 12, and a regression equation of the standard dent concentration and the standard dent depth is calculated from the depth of each standard dent 32 that has been previously input, and the surrounding conditions of the pipe 1 to be investigated. Correlation between the dent density and the dent depth according to is obtained (step S9).

Next, the position of the inspected portion 2 in which the dent is generated due to corrosion or the like is confirmed, and a plurality of positions of the inspected portion 2 in which there is no indentation are designated by the input means 7 or the mouse and input to the base metal concentration calculating section 13. (Step S10). The base metal concentration calculation unit 13 extracts the concentration at the position of the base metal designated from the image of the inspection unit 2 and then the inspection unit 2
The estimated density distribution of the base material is created by the regression equation, and the density difference between the central portion and the end portion of the X-ray transmission image is corrected (step S1
1).

The estimated base metal concentration distribution is sent to the dent concentration calculation unit 14, and the dent concentration calculation unit 14 calculates the difference between the estimated base metal concentration distribution and the densities of the respective parts of the inspected portion 2 to calculate the dent concentration due to corrosion. It is sent to the pit depth calculation unit 15 (step S12). Depth depth calculator 1
Reference numeral 5 calculates the dent depth of the test portion 2 based on the sent dent concentration and the regression equation of the standard dent concentration and the standard dent depth obtained by the feature extraction unit 12 (step S13). Depending on the geometrical dimensions of the depressions, the density of the X-ray transmission image may differ even if the depressions have the same depth. Therefore, the relationship between the geometrical dimensions of the depressions and the density may be found by experiments to determine the depth of the depressions. After correcting the depth, a dent distribution corresponding to the depth of the dent is created and stored in the image memory 16, and the dent distribution is displayed on the display means 9 as a color dent distribution diagram and a three-dimensional profile diagram (step S14). , S15). After performing these processes over the entire test area, printing is performed by the printer 10 (step
S16).

When correcting the dent depth, for example, a shape correction unit is provided in the image processing unit 8, and while confirming the created dent distribution on the screen of the display unit 9, the range for performing the dent shape correction and the dent diameter are shape-corrected. And the coefficient Y calculated by the following equation is multiplied by the dent measurement depth to correct the dent depth.

Y = f (X) (1) Here, X; a number with the diameter of the recess as a variable In this way, by correcting the depth of the recess by the shape of the recess, the depth of the recess and its distribution can be obtained more accurately. be able to.

[Effects of the Invention] As described above, according to the present invention, a test piece having a plurality of standard recesses having different depths is overlapped around a test portion of a tube and irradiated with X-rays, and the X-ray film is used as a test piece. Since the X-ray transmission image of the test portion is formed and this X-ray transmission image is read by the image sensor and input to the image processing means, the X-ray transmission image can be input to the image processing means in a short time. .

In addition, the pit depth of the test area is calculated from the relationship between the standard dent of the test piece and the standard dent density of the image input to the image processing means according to the investigation environment and the dent density due to corrosion etc., and the dent distribution is displayed. By doing so, it is possible to reliably detect the state of the recess due to corrosion or the like in the state of the active tube in which the fluid such as gas is present.

Furthermore, since the unevenness of the density of the X-ray film is corrected to calculate the depth of the recess of the portion to be inspected, the accuracy of detecting the depth of the recess can be improved.

Further, since the depth of the depression can be obtained without a simulation experiment, it is possible to perform a corrosion inspection of a pipe installed on the ground or in water in a short time, and even a non-specialist can perform a pipe inspection and diagnosis. be able to.

Further, by correcting the calculated dent depth of the portion to be inspected by the shape of the dent, the dent depth detection accuracy can be further enhanced.

[Brief description of drawings]

FIGS. 1 and 2 show an embodiment of the present invention, FIG. 1 is a layout diagram when an X-ray is taken of a tube to be investigated, FIG. 2 is a block diagram showing an image processing apparatus, and FIG. FIG. 4 is a front view showing the test piece of the above embodiment, and FIG. 4 is a flow chart showing the operation of the above embodiment. 1 ... Pipe, 2 ... Inspected part, 3 ... Test piece, 31 ...
Test field of view, 32: standard depression, 4: X-ray device, 5:
X-ray film, 6 ... Image recognition means, 7 ... Input means,
8 ... Image processing means, 9 ... Display means, 10 ... Printer, 11 ... Standard pit density calculation section, 12 ... Feature extraction section, 13
…… Base material density calculator, 14 dent density calculator, 15 dent depth calculator, 16 image memory, 17 test piece registration recorder.

Claims (2)

[Claims] 1. A test piece having a plurality of standard depressions having different depths is superposed in the vicinity of a portion to be inspected of a tube and irradiated with X-rays to form an X-ray transmission image on an X-ray film, and X-ray transmission is performed. The image is read by the image sensor, the standard dent density is calculated by subtracting the density in the vicinity of the dent position of the test piece of the read image, and the regression equation of the standard dent density and standard dent depth is calculated. The estimated concentration distribution of the base metal of the test area is created by a regression equation from the concentration distribution at the non-reduced thickness position of the test area, and the measured concentration of the test area is subtracted from the estimated base material concentration distribution of the base material to calculate the dent concentration, and the calculated dent A method for diagnosing corrosion of an inner surface of a pipe, which comprises calculating a dent depth of an inspected portion from a regression equation of the standard dent concentration and the standard dent depth using concentration, and displaying the calculated dent depth distribution. 2. The method for diagnosing corrosion of the inner surface of a pipe according to claim 1, wherein the depth of the recess of the test portion is corrected by the recess shape.