JPH0448205A - Corrosion diagnosing method for internal surface of tube - Google Patents

Abstract

PURPOSE:To investigate the corrosion of the tube in a short time without simulation experimentation by stacking a test-piece which have plural standard recesses at the periphery of a part of the tube to be inspected and irradiating it with X rays, forming an X-ray transmission image of the test-piece and the part to be inspected and reading the image by an image sensor. CONSTITUTION:The test-piece 3 having the standard recesses 32 differing in depth is stacked at the periphery of the inspected part 2 of the tub 1 and irradiated with th X rays to form th X-ray transmission image of th test-piece 3 and inspected part 2 on an X-ray film 5, whose X-ray transmission image is read by the image sensor and inputted to an image processing mans. The density of the standard recesses 32 is calculated by subtracting the density of the periphery of the recess positions of th test-piece 3 in the read image from the density of the recesses and a regression expression of the density of th standard recesses 32 and the depth of th standard recesses 32 is calculated. Then the recess depth of the inspected part 2 is calculated from the regression expression of the density and depth of the standard recesses 32 and a calculated recess depth distribution is displayed. Consequently, even a person who is not an expert can obtain the corrosion distribution in a short time without any simulation experimentation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for diagnosing corrosion on the inner surface of a steel pipe during operation using X-ray radiography, and in particular to speeding up the corrosion detection process.

[Conventional technology] Methods for investigating the corrosion status of the inner surface of pipes installed on land or in water while in operation include ultrasonic flaw detection, which uses ultrasonic waves to measure the wall thickness of pipes, and imaging using X-ray transmission. A method of detecting the state of corrosion from X-ray film is used.

According to the ultrasonic flaw detection method, wall thickness can be measured to an accuracy of 0.1 mm. In addition, 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 state of corrosion, and the X-ray transmission method allows the state of corrosion to be easily detected using an X-ray film. The X-ray transmission method is used to investigate the corrosion of pipes not only on land but also in the sea and underwater, as it allows for confirmation and the preservation of the measured data.

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

Conventionally, when investigating the state of corrosion by determining the depth distribution of corrosion from the concentration distribution of this image, a standard depression was made in advance in a pipe with the same diameter and thickness as the pipe to be investigated, and then a standard depression was made in a pipe with the same diameter and thickness as the pipe to be investigated. Conduct a simulation experiment to form an image of a standard concave on an X-ray film for comparison, obtain residual thickness estimation data for the density of this X-ray film, and compare the density of the X-ray film taken of the tube to be investigated with the simulation experiment. The distribution of corrosion and the estimated residual thickness are determined by comparing the density of the X-ray film obtained in 1, and are displayed on a display or printed using an X-Y plotter or the like.

[Problems to be Solved by the Invention] When using the above conventional method to investigate the corrosion distribution of a pipe installed underwater, for example, simulation experiments are always carried out underwater even in the 21st investigation, and the concentration of the X-ray film and It is necessary to determine the characteristics of the remaining thickness estimation data, and each survey requires about 1 to 2 weeks of experimentation. This has the disadvantage that it takes a considerable amount of time and money before conducting an actual investigation.

In addition, in order to obtain the distribution of corrosion,
It is necessary to measure the line film one point at a time with a densitometer.
It takes 2~ to read a sheet of X-ray film (quarter size)
It also had the disadvantage of requiring a long reading time, which required about 3 hours.

Furthermore, in simulation experiments, skill is required to accurately obtain the characteristics and corrosion distribution of the X-ray film concentration and residual thickness estimation data, and this method has the disadvantage that only experts can perform the analysis.

This invention has been made to solve these shortcomings, and provides a method for diagnosing corrosion on the inner surface of a pipe, which can determine the corrosion distribution in a short time without the need for simulation experiments and even for non-experts. The purpose is to

[Means for Solving the Problems] The method for diagnosing corrosion on the inner surface of a tube according to the present invention involves overlapping test pieces having a plurality of standard recesses with different depths in the vicinity of the inspected part of the tube and irradiating X-rays thereon. , form an X-ray transmission image on an X-ray film, read this X-ray transmission image with an image sensor, and calculate the standard dent density by subtracting the density in the vicinity from the density at the dent position of the read image on the test piece, Calculate the regression equation between the standard dent concentration and the standard dent depth, use the regression equation to create the estimated concentration distribution in the base material of the tested area from the concentration distribution at the non-thickness position of the tested part, and calculate the estimated concentration distribution in the base material from the estimated concentration distribution in the base material. Calculate the dent concentration by subtracting the measured concentration of the inspection area, and use the calculated dent concentration to calculate the dent depth of the inspection area from the regression equation of the standard dent concentration and standard dent depth, and calculate the calculated dent depth. It is characterized by displaying the distribution.

In addition, by correcting the depth of the dent in the test area based on the shape of the dent, the dent depth distribution can be determined with higher accuracy.

[Function] In this invention, a test piece having a plurality of standard depressions of different depths is superimposed around the test area of the tube and X-rays are irradiated, and the X-rays of the test piece and the test part are recorded on the X-ray film. Form a transparent image. This X-ray transmission image is read by an image sensor and input to an image processing means.

The image processing means calculates the standard indentation density by subtracting the density in the vicinity from the density at the indentation position of the test piece in the read image, and calculates the error caused by differences in image density and photographic contrast depending on the position of the film surface of the X-ray film. Correct.

Calculate the regression equation between this standard dent density and standard dent depth,
The relationship between image density and recess depth is calculated according to the installation status of the test area.

In addition, the image processing means creates an estimated density distribution of the base material of the inspected area using a regression equation from the density distribution of the unreduced thickness position of the inspected area of the read image, and generates an image that differs depending on the position of the film surface of the X-ray transmission image. Correct density.

Then, the concentration of dents due to corrosion is calculated from the difference between the estimated concentration distribution of the base material and the concentration of each part of the inspected part, and the dent depth of the inspected part is calculated from the regression equation of this dent concentration, the above-mentioned standard dent concentration, and standard dent depth. calculate.

Furthermore, even if the dent depth is the same, the concentration will vary depending on the geometric dimensions of the dent, so by correcting the calculated dent depth of the test area based on the shape of the dent, it is possible to improve the detection accuracy of the dent depth. can.

[Embodiment] Fig. 1 and Fig. 2 show an embodiment of the present invention, Fig. 1 is a layout diagram when performing X-ray photography of a tube to be investigated, and Fig. 2 is a block diagram showing an image processing device. It is.

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

The test piece 3 is made of the same material as the tube 1, and has a plurality of standard depressions 32 with different depths around the test field 31, as shown in FIG. The interior of this standard recess 32 is filled with a substance of the same quality as the contents of tube 1. In addition,
In FIG. 3, the numbers written inside the standard recess 32 each indicate the recess depth. The depth of this standard recess 32 is set so that when an X-ray transmission image is formed on the X-ray film 5, the density and contrast will increase depending on the position of the X-ray film 5. 32 are provided at the center and the periphery, respectively.

An image processing device reads the X-ray transmitted images of the test piece 3 and the subject part 2 and processes them, as shown in FIG. recognition means 6, input means 71 image processing means 81
It has 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 and digitizes the X-ray transmitted image.

The image processing means 8 includes a standard depression density calculation section 11, a feature extraction section 12. Base material concentration calculation unit 13. Dent density calculation unit 14. Concave depth calculation unit 15. It has an image memory 16 and a test piece registration recording section 17.

The standard dent density calculation section 11 inputs the image of the test piece 3 sent from the image recognition means 6 or the image of the test piece 3 stored in the test piece registration recording section 17,
The standard recess density is calculated by subtracting the image density of the standard recess 32 from the image density of the standard recess 32 .

The feature extraction unit 12 calculates a regression equation between the calculated standard dent density and the depth of the standard dent 32 manually entered from the input means 7,
The base material concentration calculation unit 13, which obtains the relationship between the image density and the depth of the recess according to the installation status of the tube 1, extracts the density at the non-thickness position from the image of the test area 2 sent from the image recognition means 6, and calculates the relationship between the image density and the depth of the recess. The estimated concentration distribution of the base material in the inspection part 2 is created using a regression equation.

The dent concentration calculation unit 14 calculates the concentration of dents due to corrosion by determining the difference between the estimated concentration distribution of the base material and the concentration of each part of the test portion 2 .

The dent depth calculation unit 15 calculates the calculated dent density and the feature extraction unit 1.
The dent depth of the test area 2 is calculated from the regression equation of the standard dent density obtained in step 2 and the standard dent depth.

Next, the operation when investigating the corrosion situation of the pipe 1 using this embodiment will be explained.

When investigating the corrosion of the pipe 1, as shown in Fig. 1, the test piece 3 and the X-ray film 5 are placed over the test section 2 of the pipe 1, and the X-ray device 4 irradiates the test piece 3 with X-ray film 5. Then, the X-ray transmission images of the test piece 3 and the subject part 2 are transferred to the X-ray film 5.
to form. The X-ray transmission image of this X-ray film 5 is read by an image sensor such as an image pickup tube of an image recognition means 6 and sent to an image processing means 8 for image processing. In this way, by reading the X-ray transmitted image with an imaging tube or the like, the X-ray transmitted image can be input instantly. Further, with an image pickup tube or the like, an image can be read with a density comparable to that read with a densitometer.

When performing image processing on an X-ray transmission image, as shown in the flowchart of FIG.
Step Sl) When using the registered test piece 3, it is determined whether or not to use the registered test piece 3 stored in the test piece 3. Information on the subject to be examined is read from the image recognition means 6 (step S7).

When the registered test piece 3 is not used, the 32 standard dents of the test piece 3 in 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 52). Then, input the position and outer diameter of each standard depression 32 from the input means 7 to the standard depression density calculation unit 11, and draw the outline of the standard depression 32 on the display means 7 (step S3). The depth of the standard depression 32 is input and stored in the feature extraction unit 12 (step S4).
. Next, the test piece base material concentration measurement position near each standard depression 32 displayed on the display means 7 is inputted to the standard depression concentration calculation unit 11 using the multi-point input means 7 or a mouse (not shown) (step S5). These operations are standard recess 3
2 and register the information (step S6).

Next, information on the standard dent 32 and the test area is read (step S7), and the standard dent concentration calculation unit 11 uses the image signal of the standard dent 32, the position and size of the standard dent 32, and the test piece base material concentration measurement position. The standard concavity density is calculated (step S8). That is, since the density distribution and photographic contrast of the X-ray film 5 are not uniform, in order to reduce the error caused by this, the image density at the test piece base material density measurement position is subtracted from the image density of each standard recess 32, and the image density at the test piece base material density measurement position is calculated. dent 3
Calculate the standard concavity density of 2.

Each of these standard dent densities is sent to the feature extraction unit 12, and a regression equation between the standard dent density and the standard dent depth is calculated from the depth of each standard dent 32 that has been input previously, and the surrounding situation of the pipe l to be investigated is calculated. The correlation between the dent density and the dent depth is determined according to (step S9).

Next, confirm the position of the test portion 2 where a dent has occurred due to corrosion, etc., specify a plurality of positions of the test portion 2 without a dent using the input means 7 or the mouse, and input them to the base material concentration calculation unit 13. (Step 5IO).

The base material concentration calculation unit 13 extracts the density at the specified base material position from the image of the test part 2, creates an estimated base material density distribution of the test part 2 using a regression equation, and calculates the density at the center of the X-ray transmission image. The density difference between the portion and the end portion is corrected (step 5ll).

This base material estimated concentration distribution is sent to the depression concentration calculation section 14,
The dent concentration calculation unit 14 calculates the difference between the estimated concentration distribution of the base material and the concentration of each part of the test part 2, calculates the dent concentration due to corrosion, and sends it to the dent depth calculation unit 15 (step 512). The depth calculation unit 15 uses the sent depression density and the feature extraction unit 12.
The depth of the dent in the test area 2 is calculated using the regression equation between the standard dent density and the standard dent depth obtained in step 513 (step 513). Since the density of the X-ray transmission image may differ, the relationship between the geometric dimensions of the dent and the density is determined through experiments, the dent depth is corrected, and then a dent distribution is created according to the dent depth. Then, it is stored in the image memory 16, and the dent distribution is displayed on the display means 9 as a color dent distribution map and a three-dimensional profile diagram (step S14.515). After performing these processes over the entire test area, it is printed by the printer IO (step 516).

When correcting the dent depth, for example, a shape correction section is provided in the image processing means 8, and while checking the created dent distribution on the screen of the display means 9, the range to be corrected based on the dent shape and the dent diameter are shape corrected. The measured dent depth is multiplied by a coefficient Y calculated using the following formula to correct the dent depth.

Y=f(X)...(1)
Here, X: number where the diameter of the dent is a variable. By correcting the depth of the dent according to the shape of the dent in this way, the depth of the dent and its distribution can be obtained with higher accuracy.

[Effects of the Invention] As explained above, the present invention overlaps a test piece having a plurality of standard indentations with different depths around the test area of a tube, irradiates it with X-rays, and prints the test piece on an X-ray film. Since an X-ray transmitted image of the examined area is formed and this X-ray transmitted image is read by an image sensor and inputted to the image processing means, the X-ray transmitted image can be inputted to the image processing means in a short time. .

In addition, the depth of the dent in the area to be inspected is calculated from the relationship between the standard dent and standard dent density of the test piece in the image input to the image processing means depending on the investigation environment and the dent density due to corrosion, etc., and the dent distribution is displayed. This makes it possible to reliably detect the state of dents due to corrosion, etc., in a live pipe with a fluid such as gas inside.

Furthermore, since the depth of the depression in the test area is calculated by correcting the non-uniform density of the X-ray film, the detection accuracy of the depth of the depression can be improved.

In addition, since the depth of dents can be determined without a simulation experiment, it is possible to investigate corrosion of pipes installed on land or underwater in a short time, and even non-experts can perform pipe investigation 1 diagnosis. be able to.

Further, by correcting the calculated dent depth of the test portion based on the shape of the dent, it is possible to further improve the dent depth detection accuracy.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention, FIG. 1 is a layout diagram when performing X-ray photography of a tube to be investigated, FIG. 2 is a block diagram showing an image processing device, and FIG. 3 is a FIG. 4 is a front view showing the test piece of the above embodiment, and a flow chart showing the operation of the above embodiment. 1...Tube, 2...Test part, 3...Test piece, 31...Test field of view, 32...Standard recess, 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 indentation density calculation unit, 12...
Feature extraction section, 13...Base material concentration calculation section, Step 4...
- Concavity concentration calculation unit, 15... Concavity depth calculation unit, 16
... Image memory, 17... Test piece registration recording section. Figure 1

Claims (1)

[Claims] 1. Test pieces having a plurality of standard depressions of different depths are superimposed near the test part of the tube and irradiated with X-rays to form an X-ray transmission image on an 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 from the density at the dent position of the test piece in the read image, and the regression equation between the standard dent density and the standard dent depth is calculated. , Create the estimated concentration distribution of the base material of the tested part using a regression formula from the concentration distribution of the non-thickness position of the tested part, subtract the measured concentration of the tested part from the estimated base material concentration distribution to calculate the dent concentration, Corrosion on the inner surface of a pipe, characterized in that the calculated dent concentration is used to calculate the dent depth of the test area from a regression equation between the standard dent concentration and the standard dent depth, and the calculated dent depth distribution is displayed. Diagnostic method. 2. The method for diagnosing corrosion on the inner surface of a tube according to claim 1, wherein the depth of the dent in the test portion is corrected by the shape of the dent.