JP6808971B2 - How to calibrate ultrasonic flaw detection - Google Patents

Description

The present invention relates to a method for calibrating ultrasonic flaw detection, and more particularly to a calibration method capable of calibrating the size of a defect according to the depth of the defect.

In order for an ultrasonic flaw detector to accurately detect the presence or absence of defects in the flawed material, the level of the defect signal contained in the reflected wave is calibrated in consideration of the attenuation of ultrasonic waves in the flawed material. There is a need. Therefore, for example, Patent Document 1 discloses an ultrasonic flaw detector in which the reception gain for a defect signal is changed according to the depth (reception time) of the defect in the flawed material.

Akira Jinkai 49-148988

By the way, the ultrasonic wave output from the ultrasonic receiver oscillator of the ultrasonic flaw detector is actually a spherical wave having a three-dimensional spread, and it depends on whether it is a convergent wave or a divergent wave in the flawed material. As the ultrasonic intensity at the depth changes, the ultrasonic intensity from each part of the defect with an area spread also changes, so calibrate not only the presence or absence of the defect but also its size (projected area). Otherwise, accurate information about the defect will not be available.

Therefore, in view of such a request, it is an object of the present invention to provide an ultrasonic flaw detection calibration method capable of accurately grasping the presence / absence and size of a defect of a flawed material regardless of the depth of the defect. And.

In order to achieve the above object, in the first invention, a calibrator (1) made of the same material as the material to be detected is provided with circular model defects (11 to 14) having predetermined diameters formed at different depths from the surface. Prepared, ultrasonic waves are oscillated toward the surface of the calibrator (1) in the range in which at least the model defects (11 to 14) are formed by the ultrasonic wave receiving and oscillating means (2), and the reflected waves of the ultrasonic waves are received. A region in which the intensity of the defect signal in the received reflected wave is calibrated (1), the first calibration value for calibrating according to the depth from the surface is obtained, and the calibrated defect signal intensity is equal to or higher than a predetermined value. A second calibration value is obtained to further calibrate the diameter of the calibrator according to the depth from the surface of the calibrator.

According to the first invention, the presence or absence of defects in the flawed material can be reliably known by the first calibration value regardless of the depth thereof, and the size of the defects in the flawed material can be determined by the second calibration value. It can be known accurately regardless of the depth. Moreover, the first calibration value and the second calibration value can be easily obtained.

In the second invention , the first calibration value and the second calibration value are obtained by interpolation curves using polynomials (F (x) and G (x), respectively).

According to the second invention , the first calibration value and the second calibration value can be accurately obtained.

The reference numerals in parentheses indicate the correspondence with the specific means described in the embodiments described later for reference.

As described above, according to the ultrasonic flaw detection calibration method of the present invention, it is possible to accurately grasp the presence / absence and size of defects of the flawed material regardless of the depth of the defects.

It is a top view of the calibrator which shows one Embodiment of this invention. It is a vertical sectional view of a calibrator. It is the figure which showed the intensity of the reflected wave obtained from each model defect by the shading distribution. It is a graph which plotted the intensity at the center of the shading distribution of FIG. 3 according to the depth from the surface of a calibrator. It is a figure which shows the density distribution after calibrating the shading distribution of each model defect in FIG. It is a figure which binarized the concentration distribution of FIG. 6 is a graph in which the diameter of the white region in FIG. 6 is plotted according to the depth from the surface of the calibrator.

It should be noted that the embodiments described below are merely examples, and various design improvements made by those skilled in the art within the scope of the present invention are also included in the scope of the present invention.

Hereinafter, the calibration method of the present invention will be specifically described. FIG. 1 shows a plan view of the calibrator 1 used in the method of the present invention, and FIG. 2 shows a cross-sectional view thereof. The calibrator 1 is a rectangular parallelepiped formed of the same material as the flawed material, and its back surface is scooped out in a plurality of stages. Then, on each step surface, along the center line C of the back surface of the rectangle in a plan view, on the surface at a distance of L1, L2, L3, L4 from the front surface, respectively, a circular flat bottom hole of the same shape is modeled in this embodiment. It is formed as defects 11, 12, 13, and 14. Examples of distances L1, L2, L3, and L4 are 14 mm, 20 mm, 26 mm, and 32.5 mm, respectively, and an example of the diameter of the flat bottom hole is 0.5 mm.

The ultrasonic wave receiving oscillator 2 is positioned above the surface of the calibrator 1, and a convergent ultrasonic wave having a focus on a surface at a distance L2 from the surface is output toward the surface of the calibrator 1. Then, the ultrasonic wave receiving oscillator 2 is reciprocally scanned over the entire surface at an appropriate pitch (for example, 0.1 mm) while maintaining a constant height with respect to the surface of the calibrator 1.

With the above configuration, the received signal obtained from each region of model defects 11 to 14 by receiving the reflected wave while oscillating the ultrasonic wave from the ultrasonic wave receiving oscillator 2 is represented by the distribution of shading according to the intensity of FIG. It becomes as shown in.

In FIG. 4, the horizontal axis is the depth from the surface of the calibrator 1, and the vertical axis is the signal strength at the center of the shading distribution of the reflected waves from each region of the model defects 11 to 14 (this is the signal strength most). It is expensive). From this, the number of samples is n (4 in this embodiment), and the interpolation curve F (x) of the polynomial that connects the central signal intensities of the model defects 11 to 14 with the degree of (n-1) (broken line in FIG. 4). ).

By using the interpolation curve F (x) with the central signal intensity of the reflected wave from the model defect 12 on the surface of the calibrator 1 at a distance of L2, which is the focal point of the ultrasonic wave, as 100%. A calibration value (first calibration value) for converting the central signal strength of the reflected wave from the model defect at an arbitrary depth of the calibrator 1 to 100% can be obtained. By calibrating the intensity of the received signal obtained by the reflected wave from the defect generated in the actual flaw-examined material by such a calibration value, the determination of the presence or absence of the defect is not affected by the depth of the defect. It can be done properly.

Further, in the present embodiment, with respect to the shading distribution (FIG. 5) obtained by calibrating the received signal intensities from each model defect 11 to 14, the intensity is determined to be within, for example, -6 dB with respect to the signal intensity at the center thereof. Regions are extracted by binarization as defect size. The extracted region is shown in white in FIG.

In FIG. 7, the horizontal axis represents the depth from the surface of the calibrator 1, and the vertical axis represents the diameter (binarized diameter) of the white region of each model defect 11-14. Therefore, from this, the number of samples is set to n (4 in this embodiment), and the interpolation curve G (x) of the polynomial in which the diameter values of the model defects 11 to 14 are connected by the degree of (n-1) (broken line in FIG. 7). Ask for.

By using the interpolation curve G (x), a calibration value (0.5 mm in this embodiment) for converting the diameter of the model defect at an arbitrary depth of the calibrator 1 into the actual diameter of the model defect (0.5 mm in the present embodiment). Second calibration value) can be obtained. Then, by using such a calibration value, the size of the defect (projected area) is determined by calibrating the size of the shading distribution of the received signal according to the reflected wave from the defect generated in the actual flaw-detected material. It can be known accurately without being affected by the depth of the defect.

1 ... calibrator, 11, 12, 13, 14 ... model defect, 2 ... ultrasonic receiver oscillator.

Claims (2)

Prepare a calibrator made of the same material as the material to be detected, in which circular model defects of predetermined diameters are formed at different depths from the surface, and on the surface of the calibrator at least in the range where the model defects are formed by ultrasonic receiving and oscillating means. Along with oscillating ultrasonic waves toward the ground, the reflected waves of the ultrasonic waves are received, and a first calibration value for calibrating the intensity of the defect signal in the received reflected waves according to the depth from the surface of the calibrator is obtained. A method for calibrating ultrasonic flaw detection, which comprises obtaining a second calibration value for further calibrating the diameter of a region where the calibrated defect signal strength is equal to or higher than a predetermined value according to the depth from the surface of the calibrator. The method for calibrating ultrasonic flaw detection according to claim 1 , wherein the first calibration value and the second calibration value are obtained by interpolation curves using polynomials, respectively.