JPH06249637A - Method for estimating thickness of thin wall part of pipe - Google Patents

Abstract

PURPOSE:To provide a method by which the thickness of a thin wall part generated at the central part of a pipe between both ends of the pipe can be quantitatively estimated from an exposed film. CONSTITUTION:A radiation generator 20 and film 30 to be exposed to radiation are fitted to the outside of a pipe 10 which becomes an object to be inspected and radiation, such as the gamma-rays, etc., are radiated toward the film 30 from the generator 20 through the pipe 10 and the densities of the sound and thin parts of the pipe 10 are measured from the film 30 after exposure. The thickness of the thin wall part of the pipe 10 is estimated based on the approximate expression of thickness reduction rate empirically obtained in advance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating the depth of wall thinning of a pipe, which can be used for maintenance and inspection of actual pipes in oil plants and the like.

[0002]

BACKGROUND ART Generally, petroleum plants and the like are equipped with piping equipment for transferring various fluids. These pipes are
If it is used for a long time, corrosion or erosion may occur due to the internal fluid flow, or cracks may occur due to pipe vibration, etc. A thinned part occurs. Therefore, in actual piping of these oil plants and the like, maintenance inspection is required in order to find such a thinned portion in terms of its function and safety. Maintenance inspections of such pipes are performed during the operation or regular maintenance of petroleum plants, etc., but in recent years, maintenance inspections have mainly been conducted in a radiation transmission test using gamma rays (iridium 192 radiation source). ing.

FIG. 9 shows an example of a conventional maintenance inspection method for piping by a radiation transmission test. A radiation generator 81 as a radiation source that emits γ rays is attached to the outside of the pipe 80, and a film 82 for radiography is attached to the opposite side of the radiation generator 81 across the pipe 80. There is. The γ rays emitted from the radiation generator 81 are
After passing through 80, the film reaches the film 82, and an imaging mark of the pipe 80 at this time is obtained on the film 82. Then, the thinning depth of the pipe 80 is estimated from the state of the trace of the film 82 photographed in this way. That is, piping
When the thinned portion 85 (two-dot chain line in the figure) is generated at the end portions 83, 84 on both the left and right sides of the figure 80, the thinned portion 85 of the width C in the range B in the figure on the film 82 The light and shade that shows existence appears. Since the shade of the width C appearing on the film 82 is usually a shade that can be visually confirmed, the width C can be measured using a ruler or the like, and the radiation generator 81 can be obtained from the value of the width C. ,
The metal thinning depth of the metal thinned portion 85 can be estimated by calculation in consideration of the arrangement of the pipe 80 and the film 82.

[0004]

However, in such a conventional inspection method, the left and right ends 83, 84 of the pipe 80 are provided.
In the case of the thinned portion 85 existing in (the portion of the film 82 irradiated in the range B in the figure), the thinned depth can be estimated by the method described above, but the central portion of the pipe 80 In the case of a thinned portion 87 (a portion indicated by a two-dot chain line in the figure) existing in 86 (a portion of the film 82 irradiated in the area A in the figure), its existence can be confirmed by the light and shade of the film 82 taken. However, there is a problem that it is difficult to estimate the metal thinning depth.
That is, the depth of the thinned portion 87 in the central portion 86 has been empirically determined from the light and shade appearing on the film 82. Also, the central part of the pipe 80
When it is confirmed that the thinned portion 87 is present in 86, the thinned portion 87
In order to estimate the thickness reduction depth to a certain degree accurately, the attachment positions of the radiation generator 81 and the film 82 are changed to change the shooting direction, and the position of the thickness reduction part 87 is changed to the left and right end portions 83,
There was a problem that it took time and effort to retake the picture again so that it was at the 84th position.

An object of the present invention is to make it possible to quantitatively estimate, from a film after filming, the metal thinning depth of a metal thinning portion generated in a central portion located between both end portions of the pipe. Is to provide an estimation method of.

[0006]

The method of estimating the metal thinning depth of a pipe according to the present invention is intended to achieve the above object by using an approximate expression of the metal thinning rate obtained in advance by an experiment. Specifically, the method for estimating the metal thinning depth of the pipe of the present invention is to attach a radiation generator and a film for radiography to the outside of the pipe to be inspected, and pass the pipe through the radiation generator. Irradiate the film with radiation, measure the film density of the sound part and the thinned part of the pipe from the film after photographing, and approximate the thinning ratio obtained in the experiment in advance using these film concentrations. The thinning depth of the pipe is estimated by an equation. Here, the approximate expression of the thickness reduction rate can be obtained by an experiment or the like using a steel plate test piece.

[0007]

According to the present invention as described above, the radiation is emitted from the radiation generator through the pipe toward the film, and the thinned state inside the pipe is photographed on the film. On the film thus photographed, a portion where the pipe is in a normal state (a sound portion) and a portion where a defect due to the thickness reduction occurs (a thickness reduction portion) appear as a difference in film density. Measure the film density of these healthy parts and thinned parts,
Using these measured values, the thinning depth of the thinning portion formed in the central portion located between the both side ends of the pipe is estimated by an approximate expression of the thinning rate obtained in advance by an experiment. For example, an approximate expression of the metal thinning rate is determined in advance so that the metal thinning rate of the pipe is determined using the value obtained by dividing the difference in the film density between the thin metal portion and the healthy portion by the film density of the healthy portion and the wall thickness of the pipe as a parameter. The thickness reduction rate is calculated by substituting the measured film densities of the healthy portion and the thickness reduction portion and the wall thickness of the pipe into the approximate expression of the thickness reduction rate, and the thickness reduction depth is estimated. Further, the thickness reduction depth of the metal thinning portion generated at both end portions of the pipe can be estimated by the conventional method of FIG. Together with the estimation of the metal thinning depth, it is possible to estimate the metal thinning depth of both side end portions and the central portion of the pipe with one irradiation of radiation, thereby achieving the above object.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 shows the piping 10 in the actual machine to be inspected.
The state of implementation of a radiation transmission test using radiation such as γ-rays for estimating the metal thinning depth is shown. A radiation generator 20 as a radiation source that emits γ rays or the like is attached to the outside of the pipe 10, and a film 30 for radiography is attached to the opposite side of the radiation generator 20 across the pipe 10. ing. The γ-rays or the like emitted from the radiation generator 20 penetrate the pipe 10 and reach the film 30, and an imaging mark of the pipe 10 at this time is obtained on the film 30. Then, as will be described in detail later, by measuring the density of the film 30 photographed in the state of FIG. 1, the thinning depth of the pipe 10 is estimated. Here, as a radiation source of γ rays, etc.,
For example, an Iridium 192 radiation source is used, and
The shooting distance (the distance between the pipe 10 and the radiation generator 20 and the distance between the pipe 10 and the film 30), the shooting time, the radiation source strength, etc., are the pipe diameter of the pipe 10, the surroundings of the pipe 10, etc. It may be appropriately determined according to

In this embodiment, in estimating the metal thinning depth of the central portion 11 of the pipe 10 (the portion of the film 30 irradiated in the range A in the figure), the metal thinning of the pipe 10 is conducted in advance by a separate experiment. Approximate formula (for example, the following formula 6) of the part thinning rate is obtained, the film density of the film 30 photographed in the state of FIG. 1 is measured, and this measured value is approximated by the formula (6). By substituting into, the depth of thinning is estimated. The film density can be measured with a general digital film densitometer or the like. At this time, the approximate expression of the wall thinning rate of the pipe 10 can be obtained, for example, by an experiment as shown in the following five steps (1) to (5). First, piping 10
As shown in FIG. 1, the central portion 11 has a double wall structure including an upper central portion 12 and a lower central portion 13 in the figure,
Gamma rays and the like are transmitted through these double central portions 12 and 13. Therefore, assuming the doubled state of the central portion 11, two upper and lower steel plate test pieces 41, 41 as shown in FIG.
In order to obtain an approximate expression of the metal thinning rate of the pipe 10 by performing an experiment using 42, an approximate expression of the reference metal thinning rate of the steel plate which is the basis is obtained by the three steps (1) to (3) described later. .

In FIG. 2 (A), gamma rays and the like are applied to steel plate test pieces 41,
The shooting arrangement condition for irradiating 42 is shown in FIG. 2 (B).
2C is a plan view of the lower steel plate test piece 42, and FIG. 2C is a cross-sectional view of the steel plate test pieces 41, 42. In FIG. 2A, γ
The radiation generator 20, which is a source of rays such as rays, and the film 30 for radiography are the same as those used in the radiation transmission test for the pipe 10 in the actual machine of FIG. The radiation transmission test for the two steel plate test pieces 41, 42 is performed by transmitting the steel sheet test pieces 41, 42 from the radiation generator 20 in the same manner as the radiation transmission test for the pipe 10 of FIG. 1 described above. Then, shoot the film 30 by irradiating γ rays etc.
After photographing, the film density of the film 30 is measured. Figure 2
In (B) and (C), the steel plate test pieces 41, 42 both have a horizontal length X of 300 mm and a vertical length Y of 90 mm, and have a wall thickness in the range of 1B to 6B as the size of the pipe 10 to be inspected. Assuming that the steel plate thickness T is 3.0 mm, 5.5 mm and 9.2 mm, three kinds of thickness are prepared. Therefore, as the transmission thickness F,
It will be 6.0mm, 11.0mm and 18.4mm.

Further, in each of the lower steel plate test pieces 42, the planned depth is 20%, 40%, 60%, 80 with respect to the steel plate thickness T of the steel plate test piece 42.
%, 100% 5 kinds of artificial thickness reduction parts 43, 44, 45, 46, 47
Is provided. In addition, only the lower steel plate test piece 42 is provided with the artificial thickness reduction parts 43 to 47 is that the lower central part 13
This is because it is assumed that there is a thinned part in the. Generally, in such a radiation transmission test, even if a thinned portion occurs in the central portion 12 on the upper side, the radiation intensity is strong because the distance from the radiation generation device 20 is short, and the radiation in the healthy portion and the thinned portion The transmission amount does not change much. Therefore, the presence of the thinned portion in this portion does not cause inconvenience in the measurement of the lower central portion 13, and occurs in the upper central portion 12 and the lower central portion 13 where the radiation after passing through the internal fluid hits the lower central portion 13. Only the presence of the thinned part can be confirmed. The shooting conditions are the shooting distance (radiation generator 20
The distance H) from the steel plate test piece 41 to the upper surface of the steel plate test piece 41 is constant at 600 mm, and the photographing time is at each transmission thickness F 6.0 mm, 11.0 mm, 18.4 mm.
(For each steel plate thickness T 3.0 mm, 5.5 mm, 9.2 mm)
It is different at 14, 17, and 22 minutes, and the source intensity is constant at 140GBq.

A radiation transmission test was carried out on such two steel plate test pieces 41, 42, and from the results, an approximate expression of the reference thinning rate in the steel plate was obtained by the following three steps (1) to (3). Ask for. In step (1), steel plate test piece
The relationship between the wall-thickness reduction ratio PP of 42 and the concentration difference ΔD / D is obtained as an approximate curve approximate to a quadratic curve for the steel plate test pieces 42 of three thicknesses T. The film density of the artificially thinned portions 43 to 47 appearing in the film 30 photographed in the state of FIG. 2A and the film of the sound portion (base material portion) other than the artificially thinned portions 43 to 47 The value obtained by subtracting the film density (average value) of the sound part from the film density of the artificially thinned parts 43 to 47 by measuring the density
D is obtained, and this density difference ΔD is further divided by the film density (average value) of the sound portion to obtain ΔD / D. In addition, the accurate machining depth of each of the artificial metal thinning portions 43 to 47 is measured, and the machining depth is divided by each steel plate thickness T to calculate the accurate metal thinning rate PP of each part. (See Table 1).

[0013]

[Table 1]

The thinning rate PP of the steel plate test piece 42 thus obtained
The results of graphing the value of and the value of the density difference ΔD / D are shown in FIG. In the figure, the steel plate thickness T is 3.0.
In the case of mm, the thickness reduction ratio PP-concentration difference ΔD / D curve is substantially linear, and when the steel plate thickness T is 5.5 mm and 9.2 mm, it shows a slight curve. The slope becomes steeper as the thickness T increases. These three curves for each steel plate thickness T are approximated by a quadratic curve, and the coefficients B, C
The value of is calculated by the method of least squares. The three curves are defined by the following equation.

## EQU1 ## ΔD / D (PP) = B × PP + C × PP ² Table 2 shows the values of the coefficients B and C of the three curves for each steel plate thickness T obtained by the least squares method.

[0015]

[Table 2]

In step (2), the coefficients B and C of the approximate expression (Equation 1) of the thickness reduction rate PP-concentration difference ΔD / D curve obtained in step (1) are as shown in Table 2 below. The values are different for each thickness T, but these are treated as a function of the steel plate thickness T, and the work of approximating with a quadratic curve is performed. 4 and 5 are graphs of Table 2 in which the horizontal axis represents the steel plate thickness T and the vertical axis represents the coefficients B and C. The curves appearing in FIGS. 4 and 5 are defined by the following equation and approximated by a quadratic curve.

[Equation 2] B (T) = B1 + B2 × T + B3 × T ²

[Equation 3] C (T) = C1 + C2 × T + C3 × T ² Each coefficient B1, B2, B3, of these approximate expressions is calculated by the least squares method.
The results of calculating the values of C1, C2 and C3 are shown in Table 3.

[0017]

[Table 3]

In step (3), an approximate expression (Equation 1) of the metal thinning rate PP-concentration difference ΔD / D curve obtained in step (1)
And the function of the coefficients B and C (Equations 2 and 3) of the approximation expression (Equation 1) obtained in step (2), the approximation expression of the reference thinning rate in the steel plate is obtained. Thinning rate PP-concentration difference ΔD / D Curve approximation formula (Equation 1) is developed for the thinning rate PP, and then the functions (Equations 2 and 3) are substituted into the coefficients B and C to obtain the following equation. An approximate expression of the standard thinning rate for steel sheets can be obtained.

## EQU00004 ## PP (.DELTA.D / D, T) = [-B (T) + {B (T) ² + 4C (T) .DELTA.D / D} ^1/2 ] / 2C (T) The thinning rate PP of is the density difference ΔD / D
And as a function of the steel plate thickness T.

Next, from the approximate expression (Equation 4) of the reference thinning rate in the steel plate obtained by the radiation transmission test for the two steel plate test pieces 41, 42 in steps (1) to (3), In order to derive an approximate expression of the wall thinning rate of the pipe 10, an experiment using a comparative test piece as shown in the following steps (4) to (5) is performed to calibrate between the steel plate and the pipe. Figure 6 shows the outer diameter
A comparative test piece 50 using 60.5 mm and 3.8 mm thick pipe material is shown. The comparison test piece 50 is provided with an artificial metal thinning portion 51, and the metal thinning rate is P1%. This artificial thinning part 51
The thickness reduction rate P1% of Fig. 6 is P1 = 57.9% (2.2 / 3.8 = 0.579) because the working depth is 2.2 mm in Fig. 6, but any value such as 50% is used. Good. The comparative test piece 50 thus provided with the artificial metal-reducing portion 51 is arranged at the position of the pipe 10 shown in FIG. 1 so that the artificial metal-reducing portion 51 becomes the lower central portion 13, and As in the case of the radiation transmission test for the pipe 10 in the actual machine of No. 1, the radiation generator
The film 30 is photographed by irradiating the film 30 with γ-rays or the like through the contrast test piece 50 from 20, and the film density of the film 30 is measured after photographing.

In step (4), the standard thinning rate PP of the steel sheet
Calibration constant K for converting from the pipe to the wall thinning rate P of the pipe 10
Ask for. Artificial wall-thinning part 51 that appeared in the film 30 taken
And the film density of the sound part (base material part) that is a part other than the artificially-thinned part 51 are measured, and the film density of the sound part (average value) is calculated from the film density of the artificially-thinned part 51. The subtracted value ΔD is obtained, and this density difference ΔD is further divided by the film density (average value) of the sound part to obtain ΔD / D. Based on the calculated concentration difference ΔD / D and the wall thickness of the pipe material of 3.8 mm, Δ in the approximate expression (equation 4) of the standard thinning rate in the steel plate described above.
Substitute for D / D and T. If the value obtained by substituting is P2, the metal loss rate that would otherwise be P1% is P2.
Therefore, there is a proportional relationship between the actual metal loss rate P of the pipe 10 and the value PP obtained by calculation using the approximate expression (equation 4) of the standard metal loss rate of the steel plate. Then, the calibration constant K can be determined as a constant value as in the following equation.

[Equation 5] K = P1 / P2 This calibration constant K is a constant value that is unrelated to the wall thickness T of the pipe 10 to be inspected, but when the shooting conditions such as the shooting distance and the radiation source strength are different. Therefore, it is necessary to obtain the calibration constant K for each shooting condition.

In step (5), an approximate expression of the wall thinning rate P of the pipe 10 is obtained using the calibration constant K obtained in step (4). Since it is assumed that there is a proportional relationship between the actual metal thinning rate P of the pipe 10 and the value PP obtained by the calculation using the approximate expression (equation 4) of the standard metal thinning rate of the steel sheet, P1: P2 = Thinning rate P: Standard thinning rate PP is established, and the approximate expression of the thinning rate P of the pipe 10 is calculated by the following equation using this proportional expression and the defining equation of the calibration constant K (Equation 5). Can be asked to.

[Equation 6] P (ΔD / D, T) = PP (ΔD / D, T) × K Therefore, the thinning rate P of the pipe 10 is the difference ΔD in the film density between the thinned portion and the sound portion of the pipe 10. It is obtained as a function of / D and the wall thickness T of the pipe 10. By the above steps (1) to (5), an approximate expression of the metal thinning rate of the pipe 10 used when estimating the metal thinning depth of the pipe 10 in the actual machine can be obtained in advance as preprocessing.

Further, in this embodiment, together with the estimation of the metal thinning depth of the central portion 13 of the pipe 10 by the approximate expression of the metal thinning ratio (Equation 6), the end portions 14 on both sides of the pipe 10 are combined. , 15 (Fig. 1
The estimation of the metal thinning depth of the metal thinning portion occurring at the position (see) is simultaneously performed by the method of the conventional example of FIG. 9 described above. That is, the thickness reduction of both side end portions 14 and 15 and the central portion 13 of the pipe 10 is estimated with one irradiation. Here, when the pipe 10 is arranged horizontally in the longitudinal direction, etc., it is rare that a thinned portion is usually formed in the central portion 12 (see FIG. 1) on the upper side of the pipe 10, When the inspection is necessary (for example, when an abnormality is confirmed from the outside), the mounting positions of the radiation generator 20 and the film 30 are changed, and the radiation is irradiated from another direction again.

According to this embodiment, the following effects are obtained. That is, the approximate expression of the wall thinning rate (Equation 6) is obtained in advance by an experiment, and it is used to calculate the central portion 13 of the pipe 10.
It is possible to estimate the metal thinning depth. Therefore, it is possible to make an accurate estimation as compared with the rough understanding of the metal thinning depth of the central portion 13 based on the conventional experience. Further, in the conventional method, in order to accurately estimate the thickness reduction depth of the central portion 13 of the pipe 10, the mounting positions of the radiation generator 20 and the film 30 are repeatedly changed to change the shooting direction, and a plurality of Although it is necessary to take a number of shots, in the method of this embodiment,
Since it is possible to estimate the metal thinning depths of the both end portions 14 and 15 and the central portion 13 of the pipe 10 with one shot, it is possible to save the labor for the inspection.

Further, an approximate expression of the wall thinning rate of the pipe 10 (Equation 6)
Is the two steel plate test pieces 41, 42 in steps (1) to (3).
It is possible to establish a fairly accurate approximation formula based on the approximation formula (Equation 4) of the standard thinning rate in the steel plate obtained in this experiment by conducting an experiment using. Then, the approximate expression of the standard thinning rate in this steel plate (Equation 4)
Is calibrated by the calibration constant K obtained in the experiment using the comparative test piece 50 in steps (4) to (5) to be an approximate expression (Equation 6) of the wall thinning rate of the pipe 10, and The conversion between the pipe and the pipe is performed accurately, and the reliability of the estimation of the metal thinning depth can be further improved.

Further, the approximation formula (equation 4) of the standard metal thinning rate in the steel sheet is easy to develop because it is approximated by using a relatively simple quadratic curve instead of a complicated high-order curve. Coefficients B and C and coefficients B and C of the approximate expression (Equation 4)
Since existing software etc. can be used for the processing by the least square method when obtaining each coefficient B1 ~ B3, C1 ~ C3 in
The method of the present embodiment can be easily implemented without the need for new equipment or software for calculation. further,
The curves showing the relationship between the plate thickness T of the steel plate shown in FIGS. 4 and 5 and the coefficients B and C in the approximate expression (Equation 4) of the reference thinning rate of the steel plate are approximated by a quadratic curve. However, since it is a curve substantially close to a straight line, it is possible to apply the approximate expression (Equation 4) of the reference wall thinning rate to a range of thicker wall thickness.

In order to confirm the effect of the present invention, the following confirmation experiment was conducted. Nominal diameter 1B, 2B, 4
Three or five types of artificial wall-thinning parts (see Table 4 for processing depth and wall-thinning ratio) are provided in various pipes 10 having B and 6B, and these pipes 10 are shown in FIGS. 7 (A) and (B). A radiation transmission test was conducted under a total of five conditions under the various imaging conditions shown in Table 5 for the two conditions with different arrangements. At the same time, a calibration constant K was also obtained from a test piece having a nominal diameter of 2B. In the arrangement condition of FIG. 7 (A), two conditions with different radiation source strength and shooting distance were obtained, and also in the arrangement condition of FIG. 7 (B), the calibration constant K of a total of three conditions was obtained. . Table 6 shows
The results of this confirmatory experiment are shown. According to this, there is almost no difference between the obtained estimated metal loss rate and the actual metal loss rate (value in parentheses in the table) measured by the dial depth gauge, and the effect of the present invention is remarkable.

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

[Table 6]

A confirmation experiment was also conducted on the thinned portion 60 caused by a natural defect. The film 30 is shown in FIG.
8 shows the state of the thinned portion 60 photographed in FIG.
(B) shows a cross section after the thinned portion 60 has been opened. The imaging conditions are the same as those in the state of FIG. 7A, and the calibration constant K also uses the value in this state. According to the experiment, the film density of the thinned portion 60 is 1.76, and the sound portion around it is healthy.
The film densities of 61 and 62 are 1.54 and 1.55, respectively, and the estimated thinning rate of the thinned portion 60 is 75%.
Table 7 shows the results of this experiment. The area of the opened portion of the thinned portion 60 is very small, and the vicinity of the opened portion (L in FIG. 8B with the opened portion as the center)
The average residual thickness in the range) is for pipe wall thickness 3.9 mm.
The thickness reduction rate of 1.0 mm is 74%, which is 74%. Therefore, the value of 75% of the estimated metal loss rate is in good agreement with the average thickness reduction rate. It is noticeable.

[0031]

[Table 7]

The present invention is not limited to the above-mentioned embodiments, but includes other configurations that can achieve the object of the present invention, and the following modifications and the like are also included in the present invention. That is, in the above-described example, the film density of the artificially-thinned portion 51 appearing in the film 30 that was photographed and the film density of the sound portion (base material portion) other than the artificially-thinned portion 51 were measured. Then, a value ΔD obtained by subtracting the film density (average value) of the sound part from the film density of the artificially thinned part 51 is obtained, and this density difference ΔD is further divided by the film density (average value) of the sound part to obtain ΔD / D. This was calculated, and this ΔD / D was substituted into the approximate expression of the metal thinning rate (Equation 6) to estimate the metal thinning depth of the pipe 10. However, the approximate expression of the metal thinning rate must be a function of ΔD / D. Instead, it is only necessary to use an approximate expression using the film density of the artificially thinned portion 51 and the film density of the sound portion (base material portion). In addition, the approximate expression (Equation 6) of the wall thinning rate of the pipe 10 is
Although it is a function of the wall thickness T of 10, the calibration constant K may be changed for each pipe 10 of each wall thickness T, and the function of only the concentration difference ΔD / D may be used.

Further, the approximate expression (equation 4) of the reference metal thinning rate in the steel plate obtained by the radiation transmission test for the two steel plate test pieces 41, 42 is changed to the approximate expression of the metal thinning rate of the pipe 10 ( Although it is used as the basis of Equation 6), it is not always necessary to obtain an approximate expression of the standard metal thinning rate by a radiation transmission test on such a steel plate. It is also possible to derive an approximate expression for the rate, in which case the value of the calibration constant K can approach 1.0.

Further, in the above-mentioned embodiment, the thinning rate PP-concentration difference ΔD / D curve of the steel sheet and the relationship between the coefficients B and C and the steel sheet thickness T are approximated by a quadratic curve. It may be approximated by another higher-order curve or straight line, and when it is approximated by a higher-order curve, a complicated operation may be performed using a computer or the like so that more accurate estimation can be performed. However, when approximated by a straight line, the accuracy of the estimation is lacking, but there is an advantage that the calculation is easy and it does not take time. Further, in the above embodiment, the least squares method is used as a method for determining the coefficient when these are approximated by a quadratic curve, but other methods including the case of using a higher order curve or a straight line May be used, and for example, approximation may be performed by a line drawn by hand.

Further, when the developing conditions or the developing time of the filmed film 30 are different, it is clear from the result of the investigation that the effect is a difference of about 3% in the thickness reduction rate. The approximate expression (Equation 6) of the wall thinning ratio of 10 may be corrected by this amount, or there is no problem even if this amount is not taken into consideration because it is a difference in the practically allowable range. If the pipe 10 to be inspected has a heat insulating material, the comparison test piece 50 is provided with the heat insulating material of the same material, and the photographing method is the same as the photographing condition of the pipe 10 and the calibration constant K is set. Just ask.

Further, when the metal thinning portion is covered with the oxide scale, the apparent metal thinning depth becomes a value smaller than the true metal thinning depth. Therefore, it is necessary to correct the thickness reduction depth by the thickness of the oxide scale converted to steel. The true thinning depth to be obtained is Y, the apparent thinning depth is Y1, the thickness converted from the oxide scale to steel is Y2, and the specific gravity of the oxide scale is ρ _S
(1700~2100kg / m ^3, on average, 1900kg / m ^3), when the specific gravity of steel and ^{_{ρ Fe (7800kg / m 3)}} , Y1 = Y-Y2 = Y-Y × (ρ S / ρ Fe) = Y × (1-ρ _S / ρ _Fe ) = Y × (1 / 1.32), and the true thickness reduction depth Y is the apparent thickness reduction Y1 of 1.32.
Since the value is obtained by multiplying, the value of the true metal thinning rate when the metal thinning portion is covered with the oxide scale can be obtained by multiplying the apparent metal thinning rate by 1.32. Therefore, in such a case,
It is desirable to perform correction by multiplying the value obtained by the approximate expression of the thickness reduction rate (Equation 6) by 1.32.

[0037]

As described above, according to the present invention, the film densities of the sound portion and the wall-thinning portion of the pipe are measured, and the film-thickness ratio is used to approximate the thinning rate obtained in advance by an experiment. Since the metal thinning depth of the pipe is estimated by the formula, it is possible to quantitatively estimate the metal thinning depth of the metal thinning portion generated in the central portion located between the both side ends of the pipe.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a state of an experiment using the steel plate test piece of the example.

FIG. 3 is a graph showing the relationship between the thickness reduction rate and the film density difference of the steel sheets of the above-mentioned examples.

FIG. 4 is a graph showing the relationship between the coefficient of the approximate expression and the plate thickness of the above embodiment.

FIG. 5 is a graph showing the relationship between the plate thickness and another coefficient of the approximate expression of the above-described embodiment.

FIG. 6 is a cross-sectional view showing a comparative test piece of the example.

FIG. 7 is a configuration diagram showing a state of a confirmation experiment of the present invention.

FIG. 8 is an explanatory view showing a state of piping used in another confirmation experiment of the present invention.

FIG. 9 is a configuration diagram showing a conventional example.

[Explanation of symbols] 10 Piping 11,12,13 Central part 14,15 End part 20 Radiation generator 30 Film 41,42 Steel plate test piece 43 to 47 Artificial wall loss part 50 Contrast test piece 51 Artificial wall loss part 60 Natural defects Thinning part caused by 61,62 Healthy part

Claims (1)

[Claims] 1. A radiation generator and a film for radiation imaging are attached to the outside of a pipe to be inspected, the radiation is irradiated from the radiation generator to the film through the pipe, and the film is photographed. It is possible to measure the film concentration of the sound portion and the thinned portion of the pipe from the film, and to estimate the thinning depth of the pipe by an approximate expression of the thinning ratio obtained in advance by an experiment using these film concentrations. A method for estimating the thinning depth of a characteristic pipe.