JPH0533721B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a defect measurement method using X-rays, and particularly to a defect measurement method using an X-ray CT device.

(Prior Art) Computer tomography (CT) is a tomography method that uses a computer, and unlike ordinary X-ray photography, it is possible to observe a cross-sectional image of an arbitrary position of the subject. Therefore, it is possible to nondestructively measure defects and structures deep inside the object to be inspected, and it is widely used for medical and industrial purposes.

Currently, the most popular type is X-ray, which draws an image based on the amount of X-ray transmitted through the object
CT devices are the mainstream.

A conventional X-ray CT device consists of an X-ray generator, a slit that narrows down the direction of X-ray irradiation, a turntable on which the object to be inspected is placed and rotated to an arbitrary position, and an X-ray beam transmitted from the object. It consists of an X-ray detector that detects rays, a computer that calculates and synthesizes the intensity of the detected X-rays, and an image display device that displays the calculated and synthesized X-ray intensity.

In addition to the method in which the object to be inspected rotates on a turntable as described above, the X-ray CT system also uses an X-ray generator and detector itself that moves numerically on a trajectory placed around the object A controlled movement method has also been adopted.

In the conventional defect measurement method using the above-mentioned X-ray CT device, the object to be inspected is irradiated with X-rays generated by an integrated radiation source voltage, and many electrical signals of the transmitted X-rays are distributed around the object to be inspected. The X-ray detector provided detects the signals, and a computer processes the individual signals to form a tomographic image, which is then displayed or photographed to serve as information for determining the status of defects and the like.

(Problem to be Solved by the Invention) However, when inspecting objects such as metal parts or steel structures using the conventional defect measurement method using an X-ray CT device, the radiation source of the X-ray CT device used is Since the voltage is generally set to a low voltage of several hundred kilovolts, the intensity of the X-rays is low. Therefore, there is a drawback that it requires a long irradiation time to form one image. In other words, it takes several hours for one measurement, depending on the shape of the object to be inspected, such as the thickness of the plate, which has the disadvantage that the entire measurement process takes an enormous amount of time.

On the other hand, by increasing the source voltage and increasing the X-ray intensity, images can be obtained in a short time, but the contrast of the image decreases, making it difficult to distinguish the shape or internal structure of the defect. The dot was hot.

The present invention was devised to solve the above-mentioned problems, and it shortens the time required for X-ray photography, improves the efficiency of measurement work, and prevents the quality of the captured images from deteriorating. The purpose of the present invention is to provide a defect measurement method that allows easy identification of defects.

[Structure of the invention]

(Means for solving the problems) In order to achieve the above object, the X-ray according to the present invention
The defect measurement method using a CT device uses an X-ray CT device that can adjust the source voltage in multiple stages. First, the object to be inspected is irradiated with high-intensity X-rays generated by the high source voltage. A low-contrast transmission image is created using the X-rays that have passed through the body, and after observing the transmission image and detecting the approximate location of the defect, the source voltage is lowered and the low-intensity X-rays are used to detect the defect. The method is characterized in that a high-contrast transmission image is created by irradiating only the defective part for a predetermined period of time, and the detailed shape of the defective part is measured by observing this transmission image.

(Function) In an X-ray generator whose source voltage can be variably adjusted, the source voltage is first set high to irradiate the entire subject with high-intensity X-rays in a short period of time, and the transmitted X-rays are detected. Create a transparent image. The created transmission image is obtained by irradiating high-intensity X-rays in a short period of time, so the contrast of the image is low and it is unclear. However, the presence or absence of a pseudo defect and its approximate location can be determined.

Next, the source voltage is lowered to generate low-intensity X-rays, and the pseudo-defect portion is irradiated with the X-rays for a predetermined period of time with the irradiation position limited. In this case, the low intensity
Because the line is irradiated for a relatively long time, the resulting image has high contrast and clarity. By observing the image, the detected pseudo-defects can be analyzed in more detail, the authenticity of the defect can be easily determined, and the shape, distribution, and position of the defect can also be accurately measured.

According to the method of the present invention, the source voltage is adjusted according to the purpose of image use, and by first irradiating high-intensity X-rays in a short time, the presence or absence and location of defects can be detected over the entire inspected object. The defect is identified within a short time, and then the suspected defect is locally photographed using low-intensity X-rays, and the resulting high-contrast image allows the state of the defect to be accurately measured. Therefore, the efficiency of measurement work is greatly improved compared to the conventional method, which uniformly irradiates weak X-rays for a long time under low voltage. Furthermore, it is possible to determine the presence or absence of a defect, and to accurately measure the position, distribution, and shape of the defective portion, without degrading the image quality of the photographed image of the defective portion. (Example) Next, an example of the present invention will be described with reference to the accompanying drawings.

Figure 1 shows an X-ray CT for carrying out the method of the present invention.
FIG. 2 is an explanatory diagram showing a configuration example of a device.

In FIG. 1, an X-ray CT apparatus 1 performs X-ray CT by applying a source voltage between a cathode 2 and an anode 3.
An X-ray generator 4 that generates rays, a slit 5 that gives directionality to the generated X-rays, and a turntable 7 on which an object to be inspected 6 is placed and rotated to an arbitrary position.
, an X-ray detector 8 that detects the X-rays transmitted through the object to be inspected 6, a signal table 9 that transmits the detection signal of the detected X-rays, and a computer 10 that computationally synthesizes the detection signals. It includes an image display device 11 that displays X-ray intensity as an image. Note that the line source voltage is configured to be able to be increased or decreased in multiple stages as appropriate in accordance with the shape, thickness, etc. of the object to be inspected.

Next, the principle of detecting and measuring defective parts using the X-ray CT apparatus having the above configuration will be explained with reference to FIG. FIG. 2 is an explanatory diagram illustrating the principle of detecting defects in an object to be inspected using X-rays.

When the object to be inspected 6 having the defective part 12 is irradiated with X-rays having directivity in a thin flux, the object to be inspected 6
The relationship between the X-ray intensities I o _s and I p _s before and after passing through is expressed by equation (1).

I p _s = I o _s e ^- 〓 ^T ...(1) Here, I o _s and I p _s are the X-ray intensity before and after passing through the inspected object 6, e is the base of the natural logarithm, and μ is the absorption coefficient (cm ^-1 ),
T is the thickness (cm) of the object 6 to be inspected.

However, the X-rays actually used are not thin beams with ideal directivity, but have a certain degree of scattering, so considering the influence of the scattered rays,
X-ray intensity I _p before and after passing through the inspected object 6,
The relationship between I _p is expressed by equation (2).

I _p = (1 + n) I _p e ^- 〓 ^T ... (2) where n is the scattering ratio of X-rays.

Next, when there is a hole-like defect 12 in the object to be inspected 6, the intensity of the X-rays passing through this defect 12 I _p ′
is expressed as equation (3). However, it is assumed that there is no X-ray absorption in the holes of the defective part 12 and that the size of the defective part 12 is minute.

I _p ′=(1+n)I _p e ^- 〓 ^T +ΔI ...(3) ΔI=I _p [e ^- 〓 ^(T- 〓 ^T) −e _- 〓 _T ] ...(4) Here, ΔI is the defective part This is the increase in X-ray intensity due to straight-line transmission through 12, and ΔT
is the thickness of the defective portion 12 of the object to be inspected.

The ratio of the difference ΔI in transmitted X-ray intensity between when a defect exists and when there is no defect in the inspected object 6 and the transmitted X-ray intensity I _p when there is no defect, that is, ΔI/I _p , is This is called contrast k, and if the object contrast k is large, a clearer transmitted image can be obtained.

When the subject contrast k is determined from equations (2) and (4), it is expressed by equation (5).

k=ΔI/I _p =I _p [e ^- 〓 ^(T- 〓 ^T) −e ^- 〓 ^T / (1+n)I _p
e- ^- 〓 ^T = 1/1 + n (e〓〓 ^T -1) = μ/1 + n・ΔT ...(5) Therefore, by decreasing the scattering ratio n or setting the absorption coefficient μ large, Transparent images with better image quality can be obtained.

Next, the correlation between the photon energy of the irradiated X-rays, the object contrast, and the imaging time will be numerically examined with reference to graphs.

The relationship between the photon energy of X-rays and the absorption coefficient μ when measuring defects in a steel structure as an object to be inspected is as shown in FIG. That is, when the photon energy is 0.1 MeV and 1 MeV, the absorption coefficient μ is 2 (cm ^-1 ) and 0.5 (cm ^-1 ), respectively.

Further, FIG. 4 shows the relationship between the photon energy of X-rays and the scattering ratio n with respect to the thickness T of the steel. That is, X
The higher the source voltage of the line generator and the higher the photon energy, the smaller the scattering ratio n, and the thinner the thickness T of the steel to be inspected, the smaller the scattering ratio n. By the way, in the case of a steel structure with a thickness T of 5 cm, when the photon energy is 0.4 MeV, the scattering ratio n is approximately 5, which is 1 MeV.
It is about 3 when .

Further, the object contrast k, which determines the quality of the transmitted image that serves as data for analyzing defects, is given by the above equation (5). FIG. 5 shows the relationship between the value of μ/1+n corresponding to the object contrast k and the thickness T of the object to be inspected. In other words, the lower the energy of the X-rays, the higher the object contrast becomes, and a clearer image can be obtained. By the way, in the case of stainless steel (SUS27) with a thickness T of 10 mm, when the X-ray energy is 100 KV, the μ/1 + n value is approximately 0.4 (mm ^-1 ).
In the case of 260KV, it is approximately 0.1 (mm ^-1 ). Therefore, if you want to obtain high contrast,
It is necessary to lower the line source voltage of the line generator.

Further, FIG. 6 shows the relationship between the energy of the irradiated X-rays, the thickness T of the object to be inspected, and the imaging time.
Tube current i flowing through the X-ray generator 4 and imaging time t
The exposure amount e, which is the product of , differs depending on the thickness of the object 6 to be inspected, but if the plate thickness is the same and the tube current is the same, the higher the X-ray energy, the smaller the exposure amount e will be. That is, the higher the energy of the X-ray, the shorter the imaging time. For example, when photographing stainless steel (SUS27) with a thickness T of 5 mm in Fig. 6, if the tube current i of the X-ray generator 4 is 1 mA, and the X-ray energy is 100 KV, the photographing time will be approximately 30 minutes. However, when the X-ray energy is set to 160KV, the imaging time is shortened to about 1 minute. That is,
Imaging time is reduced by a much higher energy ratio than that of X-rays.

Next, the effects of the method of the present invention will be explained based on the above principle.

The method of the present invention is carried out by first adjusting the source voltage of the X-ray generator 4 to generate high-intensity X-rays. Here, the line source voltage varies depending on the shape, material, etc. of the object 6 to be inspected, but is set to about 1 to 2 MeV for general steel structures and metal parts. Next, the generated high-intensity X-rays are irradiated onto the inspected object 6 for a short time, the transmitted X-rays are detected by the X-ray detector 8, and the detection signal is processed by the computer 10 to create a transmitted image 13. The transparent image 13 is displayed on the image display device 11 to determine whether there is a defect.

The transmitted image 13 displayed at this stage has low contrast because it is created by irradiating high-intensity X-rays in a short period of time. Therefore, it is difficult to accurately grasp the detailed shape, distribution, etc. of defects. However, the presence or absence of a defect and its approximate location can be sufficiently determined.

Next, the source voltage is lowered to generate low-intensity X-rays, and the irradiation position is limited to the pseudo-defect portion, and the X-rays are irradiated again for a predetermined period of time. Note that the irradiation position is set numerically by rotating the turntable 7 on which the object to be inspected 6 is placed. The transmission image 13 obtained by this operation has a large absorption coefficient μ, high contrast, and is clear because low-intensity X-rays are irradiated over a relatively long period of time.

Therefore, by observing images with high contrast, the detailed situation of the pseudo defect can be accurately grasped, the authenticity of the defect can be easily determined, and the shape, distribution, and position of the defect can be easily measured. can.

Furthermore, according to the measurement method of the example, the radiation source voltage is adjusted to change the X-ray irradiation intensity, and by first irradiating high-intensity X-rays for a short time, defects can be detected in the entire inspected object. The presence or absence of defects can be roughly ascertained within a short period of time, and then low-intensity X-rays are used to locally photograph the suspected defect, and the resulting high-contrast images can be used to determine the state of the defect in detail. Therefore, the efficiency of measurement work is greatly improved compared to the conventional method in which measurement work was carried out by uniformly irradiating low-intensity X-rays for a long time.

〔Effect of the invention〕

According to the present invention, the source voltage is used differently depending on the purpose of use of the transmitted image and to adjust the imaging time and image contrast. That is, first, the object to be inspected is irradiated with high-intensity X-rays under high voltage to roughly determine the presence or absence of defects over the entire object in a short period of time, and then the defects are detected by the above operation under low voltage. The system is configured to irradiate low-intensity X-rays to the area suspected to be a defect and obtain a clear, high-contrast image, making it possible to accurately measure the shape, location, and distribution of the defect. be.

Furthermore, compared to the conventional method, which uniformly irradiates low-intensity X-rays for a long time, the measurement time is significantly reduced.

[Brief explanation of the drawing]

FIG. 1 shows an X-ray for carrying out the method of the present invention.
An explanatory diagram showing an example of the configuration of a CT device, Fig. 2 is an explanatory diagram showing the principle of detecting defects in an object to be inspected using X-rays, and Fig. 3 shows the relationship between photon energy and absorption coefficient. 4 is a graph showing the relationship between the scattering ratio n and the photon energy and the thickness of the steel. FIG. 5 is a graph showing the relationship between the object contrast and the thickness T of the object to be inspected. FIG. 6 is a graph showing the relationship between the plate thickness T and the exposure amount e. 1...X-ray CT device, 2...cathode, 3...anode,
4...X-ray generator, 5...Slit, 6...Object to be inspected, 7...Turntable, 8...X-ray detector, 9...Signal cable, 10...Computer, 11
...Image display device, 12...Defect part, 13...Image.

Claims (1)

[Claims] 1 Using an X-ray CT device that can adjust the source voltage in multiple stages, the object to be inspected is irradiated with high-intensity X-rays generated by the high source voltage, and the X-rays that have passed through the object are detected. After creating a low-contrast transmission image and detecting the approximate position of the defect by observing the transmission image, the source voltage is lowered and low-intensity X-rays are irradiated only to the defect for a predetermined period of time. A defect measurement method using an X-ray CT device, which is characterized by creating a high-contrast transmission image and measuring the detailed shape of the defect by observing this transmission image.