JPH07325070A - Ultrasonic method for measuring depth of defect - Google Patents

Abstract

PURPOSE:To measure the depth of a defect at a high detecting sensitivity without changing the shape of a body to be inspected. CONSTITUTION:Depth of a defect 4 generated in a body 3 to be inspected is measured by the ultrasonic method. A longitudinal wave vertical probe 1 is provided just over the defect 4 generated in the body 3 to be inspected, and a transverse wave angle beam probe 2 is provided opposite to the longitudinal wave vertical probe 1. These probes 1, 2 are used for the double-probe method, and one of them is used for a transmitter, and the other is used for a receiver, and the transmitting time from the transmission of the end echo, of which mode is converted at the tip of the defect 4 for transmission, to the receipt thereof is measured. A result of the measurement is used for an expression obtained on the basis of the transmission route of the ultrasonic beam, which is geometrically obtained, so as to obtain the depth of the defect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention determines the depth (size) of a defect required for evaluating the life of a defect (also called a crack) which is found by nondestructive inspection of a structure. The present invention relates to a method of measuring a defect depth by an ultrasonic method for measuring.

[0002]

2. Description of the Related Art In non-destructive inspection of a structure, the detection sensitivity and pass / fail of a defect are determined in comparison with a simulated defect of a size that is allowable in terms of strength. However, if a defect is found in a critical structure that is within the acceptable range, or if a defect cannot be repaired immediately even if it is detected as a defect, the size of the defect is measured to evaluate the life of the structure. There was a need.

As this defect size measuring method, for example, as disclosed in Japanese Patent Laid-Open No. 54-55493 and Japanese Patent Laid-Open No. 3-146859, the edge portion in eddy current flaw detection, electric resistance method, ultrasonic flaw detection The echo method and the like are known. The eddy current flaw detection method and the electric resistance method have the drawback that measurement cannot be performed unless there is a flaw on the flaw detection surface side, and the measured values vary widely.

Further, in the edge echo method capable of measuring the depth of a defect generated from the side opposite to the flaw detection surface, a transverse wave is mainly applied to the tip of the defect 4 generated in the inspection object 3 as shown in FIG. 4 (a). An edge echo method in which the ultrasonic wave beam, that is, the reflected component 6a of the edge echo obtained by irradiating the transverse wave incident beam 7 is detected by the transverse wave bevel probe 2 based on the end echo method, As shown in FIG. 4B, there is a two-probe end echo method in which the diffraction component 6 of the end echo is detected by the other transverse wave bevel probe 2.

Since these end echoes are extremely weak, the S / N ratio with crystal grain boundary noise, etc. is very poor, and the ultrasonic mode and refraction angle are selected, and ultrasonic waves are applied to the end of the defect 4. Various studies have been made to improve the S / N ratio, such as the use of a focus type flaw detector for focusing.

[0006]

Particularly in a material with large attenuation such as austenitic stainless steel, it is difficult to correctly recognize the signal from the defect edge due to the interference of noise echo, and the edge echo cannot be detected. There were quite a few cases. Therefore, it is impossible to measure the defect profile by measuring the depth in the length direction of the defect at a pitch of several millimeters.

When the inventors of the present invention irradiate the tip of the defect 4 with a longitudinal ultrasonic wave from a direction parallel to the defect plane, the direction of the tip of the defect 4 is about 45 ° below the defect plane. It is confirmed that the reflection component (reference numeral 6a in FIG. 4) or the reflection component (reference numeral 6 in FIG. 4) used in the conventional end echo is 10 times or more stronger than the end component, and the end echo is converted into a transverse wave and emitted. I found it.

This phenomenon occurs in the opposite route, that is, when a transverse ultrasonic beam is applied to the tip of the defect 4 from a direction that makes an angle of about 45 ° with the defect surface, the defect 4 surface starts from the tip of the defect 4. A strong end echo mode-converted into a longitudinal wave is emitted in a direction parallel to and away from the tip of the defect 4.

Heretofore, this mode-converted end echo has not been paid attention because of a difference in sound velocity due to mode conversion, a complicated reflection path, and the like. As described above, according to the conventional end echo method, the measurement is performed even when the S / N ratio is bad, and there is a problem that it is difficult to identify the tip echo of the defect.

The present invention has been made to solve the above-mentioned problems, and enables an extremely strong end echo to be observed without changing the shape of the object to be inspected with respect to a defect generated in the object to be inspected. Excellent measurement of S / N ratio is possible,
An object of the present invention is to provide a defect depth measuring method by an ultrasonic method capable of measuring a defect depth with high measurement accuracy.

[0011]

According to the present invention, in a method for measuring the depth of a defect generated in an object to be inspected by an ultrasonic method, a longitudinal wave vertical probe is located directly above the defect generated in the object to be inspected. And a transverse wave bevel probe facing the longitudinal wave vertical probe, one of these probes for transmitting and the other for receiving, and mode conversion at the tip of the defect. By measuring the propagation time from the transmission to the reception of the end echo that propagates as a result, and applying the calculation result to the calculation formula derived from the propagation route of the ultrasonic beam obtained geometrically, the depth of the defect can be calculated. Characterized by seeking

[0012]

As shown in FIG. 1, the longitudinal wave vertical probe 1 is located directly above the defect 4 on the upper surface of the object 3 to be inspected, and this probe 1
Transverse wave angle probe 2 at a position offset from the angle 3θ
And a longitudinal ultrasonic wave is incident from directly above the defect 4 by the longitudinal wave vertical probe 1 toward the tip of the defect 4. When the incident longitudinal wave ultrasonic beam 5 is applied to the tip of the defect 4, the end echo 6b, which has been converted into a transverse wave mode, is emitted to both sides of the defect 4 at an angle of about 45 °.

The mode-converted end echo 6b is shown in FIG.
Since the echo component is considerably stronger than the reflection component 6a of the end echo and the diffraction component 6 of the end echo described above, it is received by the transverse wave bevel probe 2 as a sufficiently strong echo even if it is reflected once on the bottom surface. The S / N ratio with the grain boundary noise and the like is extremely good.

In FIG. 1, if the plate thickness of the object 3 to be inspected is t, the defect depth is d, and the refraction angle of the transverse wave bevel probe 2 is θ,
The angle at which the transverse wave end echo 6b emitted after mode conversion at the tip of the defect 4 is reflected on the bottom surface of the DUT 3 is also θ. In this case, if the time required for propagation of the longitudinal wave incident beam 5 and the mode-converted transverse wave end echo 6b that is reflected once by the bottom surface is T, then T is expressed by equation (1).

[0015]

[Equation 1] (1) C _L is the acoustic velocity of the longitudinal waves in the object to be inspected in, C _S is the speed of sound of the transverse wave in the formula. From this equation (1), the defect depth d can be obtained as the following equation (2).

[0016]

[Equation 2]

In the above description, the vertical probe was used as the transmitting side and the oblique probe was used as the receiving side in the defect depth measuring method of the present invention, but the oblique probe is used as the transmitting side and the vertical probe is used. The same is true when the tentacle is the receiving side.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a method for measuring the depth of defects by the ultrasonic method according to the present invention will be described with reference to FIG. FIG. 2A shows the size of the object 3 to be inspected. The left side is the side surface in the longitudinal direction and the right side is the side surface in the width direction. The inspected body 3 is a flat plate made of stainless steel (SUS304) having a thickness of 20 mm, a width of 60 mm, and a length of 100 mm, and a fatigue crack is generated as a defect 4 in the central portion.

A longitudinal wave vertical probe 1 is provided directly above a defect 4 generated in an object to be inspected 3, and transverse wave oblique angle probes 2 are provided on both sides of the probe 1 at a predetermined interval. One of these probes 1 and 2 is for transmission and the other is for reception. Which one is selected is determined in advance. The longitudinal sound waves in the inspected body 3 are 5790 m / s and 3100 m / s.

When the vertical probe 1 is arranged above the defect and longitudinal ultrasonic waves are incident toward the tip of the defect, a strong transverse ultrasonic wave is generated in a direction of about 45 ° below the tip of the defect 4.
This transverse wave reflected once by the bottom surface is detected by the transverse wave bevel probe 2.

At this time, the propagation time of the ultrasonic wave transmitted from the vertical probe 1 and received by the transverse wave bevel probe 2 is measured, and the depth of the defect is calculated by the calculation formula (2). You can ask for it.

The measurement results are shown in FIG. 2 (b). Figure 2 (b)
The vertical axis indicates the depth of the defect as the crack height (mm), and the horizontal axis indicates the measurement position (width direction) in (mm). In the figure, the white circles show the measurement results when the bevel probe 2 was placed on the right side, the black circles show the measurement results when placed on the left side, and the solid curve shows the measurement results after the measurement. 3 shows a profile of a crack tip in which the depth of a crack (defect) was actually measured by breaking No. 3.

As is apparent from FIG. 2B, according to this embodiment, the measured values from the left and right are in good agreement with the measured values, and the end echo 6b for detecting the defect depth is detected. It is recognized that the sex is almost 100%.

Next, with reference to FIG. 3, a second embodiment of the method for measuring the defect depth by the ultrasonic method according to the present invention will be described. The second embodiment is an example of measuring the depth of the defect 4 when the defect 4 is formed below the upper surface of the inspection object 3. 3A shows an example in which the depth of the defect 4 is shallow, and FIG. 3B shows an example in which the depth of the defect 4 is deep.

In both FIGS. 3A and 3B, a longitudinal wave vertical probe 1 is provided directly above the defect 4, and a transverse wave oblique angle probe 2 is kept away from the probe 1 in the case of FIG. 3A. In the case of (b), they are provided close to each other.

In the second embodiment, FIGS. 3 (a) and 3 (b) are used.
Since the end echo 6b to be detected together is quite strong, the vertical longitudinal wave component 6b is generated as shown in the figure.
Even if it is reflected by the bottom surface, it can be detected as a sufficiently strong echo, and the depth of the defect 4 can be measured by the same theory as in the first embodiment.

That is, when a longitudinal ultrasonic wave parallel to the defect 4 is incident from the probe 1 through the opening end of the defect 4, a strong transverse ultrasonic wave is generated 45 ° below the tip of the defect 4. The transverse wave ultrasonic wave is detected by the transverse wave oblique angle probe 2.

At this time, the propagation time of the ultrasonic wave from the vertical wave vertical contact 1 to the ultrasonic wave oblique angle probe 2 until it is received and measured by the transverse wave bevel probe 2 is calculated by the above-mentioned calculation formula (2) to detect the defect 4 The depth of can be calculated.

[0029]

According to the present invention, an extremely strong end echo can be observed without changing the shape of the object to be inspected with respect to a defect generated in the object to be inspected, so that the measurement with an excellent S / N ratio can be performed. Possible and expected to improve accuracy. Therefore, by using the present invention, safety evaluation of containers and structures,
The effect is enormous such that the remaining life can be estimated.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view for explaining the action of a method for measuring a defect depth by an ultrasonic method according to the present invention.

FIG. 2A is a side view showing a size of an inspection object according to the first embodiment of the present invention, and FIG. 2B is a curve diagram showing a result of measuring a defect depth of the inspection object.

3A is a schematic sectional view for explaining a second embodiment of the present invention, and FIG. 3B is a schematic sectional view showing another example of FIG. 3A.

4A is a schematic cross-sectional view for explaining a defect depth measuring method by a conventional ultrasonic method, and FIG. 4B is a schematic cross-sectional view showing another example in FIG. 4A.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Longitudinal wave vertical probe, 2 ... Transverse wave oblique angle probe, 3 ... Inspected object, 4 ... Defect, 5 ... Longitudinal wave incident beam, 6 ... End echo,
6a ... Reflection component of edge echo, 6b ... Mode-converted edge echo, 7 ... Transverse wave incident beam.

Front Page Continuation (72) Inventor Shuichi Tateishi 5-10-1 Fuchinobe, Sagamihara City, Kanagawa Nittetsu Technos Co., Ltd.

Claims (3)

[Claims] 1. A method of measuring the depth of a defect generated in an inspection object by an ultrasonic method, wherein a longitudinal wave vertical probe is provided directly above the defect generated in the inspection object, and the longitudinal wave is generated. A transverse wave bevel probe is provided opposite to the vertical probe, one of these probes is used for transmission, and the other is used for reception, and an end echo that propagates after mode conversion at the tip of the defect. It is characterized in that the propagation time from the transmission to the reception of is measured, and the depth of the defect is calculated by applying the measurement result to the calculation formula derived from the propagation route of the ultrasonic beam obtained geometrically. Defect depth measurement method by ultrasonic method. 2. A longitudinal wave ultrasonic wave is incident on the tip of the defect, and a transverse ultrasonic wave generated from the tip is received by a transverse wave bevel probe. Defect depth measurement method by ultrasonic method. 3. The ultrasonic wave of a transverse wave is incident on the tip portion of the defect, and the ultrasonic wave of a longitudinal wave generated from the tip portion is received by a longitudinal wave bevel probe. Method for measuring the depth of defects by ultrasonic method.