JPH08110327A - Ultrasonic flaw detecting method for heterogeneous material - Google Patents

Abstract

PURPOSE: To provide a method for flaw detecting in which a clear echo can be observed from a defect with high resolution by using an array type probe even in the case of a test piece of a heterogeneous material like a material having high damping capacity or a centrifugal casting tube. CONSTITUTION: The frequency of a radiating ultrasonic wave is n. A delay time in which a phase correction delay time within ±1/(2n)sec or less different at each transceiver 1 and each radiation is added to the delay time of each transceiver 1 is applied, an ultrasonic wave is radiated from each transceiver into a heterogeneous test piece 6, its reflected wave is received by each transceiver 1, and the receives waves of the respective transceivers are added. The echo signal obtained by the addition is stored for the radiations of the ultrasonic waves many times, the combination of the phase correction delay time in which its echo signal becomes maximum is selected, a flaw is detected from the echo obtained by the combination of the delay times, thereby improving the flaw detecting performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flaw detection method suitable for flaw detection such as stress corrosion cracking of a welded portion of a centrifugal casting pipe used as a primary cooling pipe of a pressurized water reactor, and a flaw detection inside a heterogeneous test body. The present invention relates to an ultrasonic flaw detection method capable of accurately performing.

[0002]

2. Description of the Related Art A conventional ultrasonic probe for ultrasonic flaw detection is a method of emitting a directional ultrasonic beam into a test body from a single transmitter / receiver which usually has a constant area and receiving the reflected wave. Is done by.

On the other hand, as a probe mainly used in the ultrasonic echo diagnostic method of the human body, an array in which a large number of transmission / reception elements composed of elongated rectangular transducers as shown in FIG. A shape probe is used.
An electronic switch is connected in series to each of the transmitting and receiving elements so that each oscillator can be turned on and off independently.
If different delay times are sequentially applied to the adjacent transducers and the ultrasonic waves are emitted by linear scanning while shifting the phase little by little from each transmitting / receiving element, the delay time can be selected to move in any given direction as shown in FIG. Ultrasonic waves can be incident.
Further, each transmitting / receiving element is scanned a number of times to emit an ultrasonic wave, and the difference in delay time τ given to the adjacent transmitting / receiving element is changed little by little for each scanning. Can be scanned to change to. Further, as shown in FIG. 3, by giving a delay time to each transmission / reception element and making the ultrasonic wave enter the test body, the ultrasonic wave can be made to be focused on one point in the test body.

Further, an array type probe in which transmitting / receiving elements are arranged in a grid or concentric circles on a plane is also known.
By adjusting the delay time given to each transmitting / receiving element of the three-dimensional array type probe, the ultrasonic waves can be incident on the test body so as to be focused on one point in the test body.

"Non-destructive inspection," Vol. 36, No. 10, No. 7.
On page 63, the method of injecting parallel ultrasonic beams into the test body by an array type probe in which transmitting and receiving elements are linearly arranged by the electronic scanning ultrasonic flaw detection method and focusing on one point in the test body are described. A method for detecting flaws is disclosed by the method of incident light on.

[0006]

SUMMARY OF THE INVENTION The conventional single transmitter / receiver emits a directional ultrasonic beam into a test body and detects a reflected wave thereof, for example, primary cooling of a pressurized water reactor. When a flaw such as stress corrosion cracking of a welded portion of a centrifugally cast pipe used as a pipe is tested, the centrifugally cast pipe grows into a columnar crystal from its surface toward the inside during casting, and a columnar crystal with different properties. Are arranged in parallel and become an extremely inhomogeneous material, and since the propagation speed of ultrasonic waves greatly differs depending on each part of the crystal structure, when an ultrasonic beam is obliquely incident from the surface adjacent to the welded part of the test body, In addition to the reflected waves from the defective part, extremely complicated forest-like reflected waves are observed and it is impossible to perform flaw detection. Even when the ultrasonic beam is obliquely incident, the echo from the direction perpendicular to the surface is larger than the target echo from the defect in the oblique direction from the incident point, and the target echo cannot be observed.

Further, even if a parallel ultrasonic beam or an ultrasonic beam focused on one point is incident on the test body using the above-mentioned array type probe, it is extremely inhomogeneous like a high attenuation material or a centrifugal casting pipe. In the case of a test piece made of a material, even if an echo reflected from a defect is received by each transmitting / receiving element and received by each transmitting / receiving element, ultrasonic waves are generated due to the non-uniformity of the material of the ultrasonic wave reciprocating path from each transmitting / receiving element to the defect. Have different propagation speeds, and there is a difference in the time it takes for echoes that are incident from each transmitting / receiving element and reflected from the same defect to return to each transmitting / receiving element, and there is a phase difference in the ultrasonic waves. Even if the waves are superposed, a clear echo cannot be observed.

Therefore, according to the present invention, even for a test body made of a material having a high damping capacity or an extremely non-uniform material such as a centrifugally cast tube, a clear echo from a defective portion can be obtained with high resolution by using an array type probe. It is an object to provide a flaw detection method that can be observed.

[0009]

In order to achieve the above object,
As a result of intensive studies by the present inventors, the array type probe in which the transmitting and receiving elements are arranged one-dimensionally or two-dimensionally An ultrasonic wave from each transmitting / receiving element is provided so as to emit an ultrasonic wave from each transmitting / receiving element with an appropriate delay time and to further provide a phase difference within ± 2/1 of the wavelength to correct the phase shift. The delay time of emission is further added with the phase correction delay time which is different for each transmitting and receiving element,
Select a combination of phase correction delay times that drive each transmitter / receiver, scan multiple times, emit ultrasonic waves from the transmitter / receiver, and add echoes received by each transmitter / receiver to obtain the echo with maximum intensity. However, the added echo at that time is recorded as an echo at the test position, and the presence of a defect in the test body and its position can be detected by gradually moving the test position and sweeping the surface of the test body. It was found that even a test body made of an inhomogeneous material in which reflection noise strongly appears due to non-uniformity inside the test body can perform accurate flaw detection, and has completed the present invention.

That is, according to the present invention, an ultrasonic beam emitted from each transmitting / receiving element of an array type probe in which a large number of ultrasonic transmitting / receiving elements are arranged linearly or in a plane is focused on one point in a homogeneous medium. By giving different delay times to each transmitting and receiving element, sequentially emitting ultrasonic waves whose phases are slightly shifted from each transmitting and receiving element into the test body, and repeating the reception of the reflected wave many times in the ultrasonic flaw detection method. , Where n is the frequency of ultrasonic waves to be emitted, the delay time of each transmission / reception element is further different for each transmission / reception element and for each emission ± 1 / (2
n) A delay time obtained by adding the phase correction delay time within seconds is applied to each transmitting / receiving element to emit an ultrasonic wave into the inhomogeneous test body, the reflected wave is received by each transmitting / receiving element, and the received wave of each transmitting / receiving element is received. Add, and store the echo signal obtained by adding for multiple ultrasonic emission, select the combination of phase correction delay time that maximizes the echo signal, from the echo obtained by the combination of the delay time The gist is the ultrasonic flaw detection method for heterogeneous materials, which is characterized by finding defects and improving flaw detection performance.

Next, an example of the ultrasonic flaw detection method for a solid surface according to the present invention will be specifically described with reference to the drawings. FIG. 4 is an explanatory view of the ultrasonic flaw detection method for a heterogeneous material of the present invention.
Independent pulse generators 2 are connected to transmitting / receiving elements 1 arranged one-dimensionally as shown in FIG. 1 or two-dimensionally as shown in FIG. 5, and the same trigger signal generator 3 is connected to a digital variable delay circuit 4 and A trigger pulse is input to the pulse generator 2 via the phase correction delay circuit 5. The trigger signal generator 3 repeatedly emits a trigger pulse at a constant cycle. The variable delay circuit 4 delays the ultrasonic wave emitted from each transmitting / receiving element 1 so that the ultrasonic wave incident on the test body 6 is focused at a predetermined depth if the test body 6 is homogeneous. A trigger pulse is applied to each transmitting / receiving element 1. The delay amount of each variable delay circuit 4 is controlled by a digital amount calculated by a computer so that the focusing condition is satisfied.

The phase correction delay circuit 5 changes the frequency of ultrasonic waves to n.
Then, a delay amount of ± 1 / (2n) seconds or less is randomly generated, and the random delay time is further given to the trigger pulse output from the variable delay circuit 4 and input to the phase correction delay circuit 5. , Which is applied to the pulse generator 2. The pulse generator 2 receives the trigger pulse and applies, for example, a high frequency pulse for ultrasonic wave generation of 1 to 10 MHz to the transmitting / receiving element 1.

As the two-dimensional array type probe, the one in which the transmitting / receiving elements 1 are arranged in a lattice, the one in which they are concentrically arranged, or the like is used. In either case, the delay time of the variable delay circuit 4 is controlled according to the distance from the center of the probe 7,
Is a homogeneous test body whose ultrasonic wave propagation velocity is approximately equal to the average value of the entire test body 6 as a whole, the envelope surface of the tip of the wave of the ultrasonic waves emitted from a large number of transmission / reception elements 1 Travels spherically, and the delay time is controlled so that the ultrasonic waves are focused on one point of a predetermined depth in the test body 6. For example, assuming that the depth from the surface of the test body 6 to the focal point of the ultrasonic beam is H, the horizontal distance from the focal point to each transmitting / receiving element 1 is D, and the average ultrasonic wave propagation velocity in the test body is V, each transmitting / receiving element 1 delay time T of the variable delay circuit 4, T = T ₀ - controlled to be ^{((H 2 + D 2)} 1/2 -H) / V. However, T ₀ is a constant corresponding to the maximum delay time of the delay times of the variable delay circuits 4.

In each of the above embodiments, the variable delay circuit 4 and the phase correction delay circuit 5 are independently provided and both delay circuits are arranged in series for the sake of easy understanding, but in reality, the variable delay circuit is shown. 4 is provided, and as a digital signal for controlling the variable delay time, in the case of a homogeneous material, a digital amount corresponding to the delay time focused on one point is further added to a digital amount corresponding to the random phase correction delay time. It is desirable to control the delay time of the variable delay circuit 4 by using a digital amount and inputting this as a control signal to the variable delay circuit 4. Then, the variable delay circuit 4 alone can control the same delay time as described above.

With a single trigger pulse generated from the trigger signal generator 3, ultrasonic waves are sequentially transmitted from each transmitting / receiving element 1 at a delay time calculated by adding a random phase correction delay time to the delay time calculated so as to focus on one point. Fire. The reflected wave from the inside of the test body 6 is received and detected by the transmission / reception element 1. The trigger signal generator 3 generates a trigger pulse a very large number of times at a constant cycle, and a delay time calculated for each transmission / reception element 1 so that each trigger pulse is focused to one point and a random number different for each transmission / reception element 1 Gives a delay time equal to the sum of all delay times. The signals detected by the transmission / reception elements 1 are stored, given a random number of times of random phase correction that are different a certain number of times (for example, several hundred times), and each transmission / reception element 1 emits an ultrasonic wave. The reflected waves are received, the received waves are superimposed and added, and the echo is observed. The detected echo is stored in memory, and for the largest echo among the echoes detected in many tests, the time from the trigger pulse emission to the detection of that echo,
By recording the intensity of the echo, displaying it on a display device such as an oscilloscope, and reading it, the distance (depth) from the test point to the defect and the degree of the defect can be known.
By moving the test position little by little and scanning the surface of the test body, it is possible to detect the presence and position of a defect in the test body.

In the above description, it is completely unknown in advance what kind of combination of the phase correction delay times is given to each transmitting / receiving element 1, so that the combination of the phase correction delay times is selected at random. Although the method of finding the optimum combination of phase correction delay times by repeating the transmission and reception of ultrasonic waves a very large number of times has been described, in reality, the optimum combination is found by the transmitting and receiving elements of the array type probe. Even if the number of 1 is about 10 to 20, it is necessary to try the astronomical number of times and the efficiency is not good.

Therefore, as a method for finding the optimum combination, any known experimental design method for efficiently obtaining this kind of optimum combination can be applied. For example, a plurality of transmitting / receiving elements of the array type probe are divided into several groups, and only for the transmitting / receiving elements 1 belonging to one group of the groups, the phase correction delay time is within a range of ± 1 / (2n) seconds. , The phase correction delay time of the transmission / reception elements 1 of the other groups is fixed and the test is performed. Only for the randomly set groups, the optimum phase correction delay time combination is obtained, and this operation is sequentially performed. It is possible to finally obtain the most optimal combination as a whole by performing each group, obtaining a temporary optimal combination as a whole, and repeating this many times.

The random phase correction delay time is not set completely at random, but a plurality of levels are set at equal intervals within a range of ± 1 / (2n) seconds, and one of the levels is set. It is desirable to use a random selection method. For example, when m is a natural number, the number of levels is 2m + 1
In case of, + m / (2mn), + (m-1) / (2
mn), + (m-2) / (2mn), ..., +1
/ (2mn), 0, -1 / (2mn), -2 / (2m
n), ..., 2m + 1 levels of phase correction delay time are set at equal intervals such as −m / (2mn) seconds. If the phase correction delay time is randomly selected and set from the levels thus set, it is possible to reduce the number of repeated tests for finding the optimum value combination.

As another example of the method of finding the optimum combination, the following method can be used. First, a plurality of transmission / reception elements of the array type probe are divided into two groups, and the phase correction delay time of all the transmission / reception elements of one group is fixed to the same value, while all the transmission / reception elements of the other group are fixed. While maintaining the same phase correction delay time, the total delay time is changed all at once at a fixed interval within a range of ± 1 / (2n) seconds to set the delay time at which the received echo becomes the largest. locate. Next, the delay time of the group that has just found the optimum delay time remains fixed at that optimum value, and the same delay time is maintained for all the transmission / reception elements of the other group in the same manner within ± 1. By gradually changing at regular intervals during / (2n) seconds, the delay time at which the received echo becomes maximum is found. This completes the first stage. Next, each group of the transmission / reception elements is further divided into two groups, into a total of four groups, and the three groups are fixed to the optimum delay time found earlier, and the remaining one group is Similarly, for all the transmission / reception elements of the group, the echoes received by changing all the transmission / reception elements of the group at the same time gradually at a constant interval within ± 1 / (2n) seconds while keeping the same delay time. Find the largest delay time and fix it. Now one of the other three groups
In the same way, the delay time is changed little by little in the same way, and the optimum value is found and fixed to that value. Then, the delay time is gradually changed all at once for one of the remaining two groups, and the optimum value is found and fixed to that value. Finally, for the remaining one group, the delay time is similarly changed little by little and fixed to the optimum value. This completes the second stage. Next, each of the above four groups is further divided into two groups for a total of 8
Divided into 1 group, the delay time of 7 groups remains fixed,
For one group, the delay time is gradually changed all at once and fixed to the optimum value as in the above. .... Continue this kind of operation. Each group is divided into halves one after another, the number of groups is increased to 2, 4, 8, 16 and the same operation is repeated. Finally, each group has one transmission / reception. Repeat until configured with elements. By scanning the delay time of each group once at each stage by the above method, when the delay time of other groups is changed, the optimum delay time of the fixed group is already searched for by finding the optimum delay time due to its influence. Since the value may have changed, delay time is set to 1 for each group at each stage.
Instead of scanning only once, it is also possible to repeat the scanning of the delay time for each group a plurality of times so that each group is sequentially rotated a plurality of times.

The ultrasonic probe 7 is mechanically sequentially moved and scanned along the surface of the test body 6 to detect flaws. When flaw detection is performed on an annular welded portion of a pipe, an annular guide can be provided along the welded portion, and the probe 7 can be automatically moved on the guide.

[0021]

According to the ultrasonic flaw detection method for a heterogeneous material of the present invention, the material of the propagation path through which the ultrasonic waves reciprocate from the transmitting / receiving element 1 of the array type probe to the defect is not uniform due to the heterogeneity of the test piece. Since they are uniform, the propagation speed of ultrasonic waves is different, and if they are made of a uniform material, ultrasonic waves are emitted under the condition that the reflected waves having a focused phase on the defective portion and returning to each transmitting / receiving element 1 are returned. However, the phase of the reflected wave returning to each transmission / reception element 1 is shifted due to the inhomogeneity of the ultrasonic wave propagation medium in the middle. By giving various phase correction delay times and attempting to input the ultrasonic waves from each transmitting / receiving element 1, it is possible to select the optimum combination of the phase correction delay times such that the phases of the received ultrasonic waves are aligned. As a result, even if there is unevenness in the material of the test body, it is possible to make a correction so that the phases of the reflected waves due to the unevenness are made uniform, and to clearly observe the echo from the defect.

[0022]

EFFECTS OF THE INVENTION According to the ultrasonic flaw detection method for inhomogeneous materials by ultrasonic waves of the present invention, precise flaw detection can be performed even on a test piece made of an inhomogeneous material such as a high attenuation material or a centrifugal casting pipe. be able to.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of a one-dimensional array type probe.

FIG. 2 is a diagram illustrating an electronic scanning principle of a one-dimensional array type probe.

FIG. 3 is a principle diagram of a method of focusing an ultrasonic beam from a one-dimensional array type probe.

FIG. 4 is an explanatory diagram of an ultrasonic flaw detection method for a heterogeneous material of the present invention.

FIG. 5 is a perspective view of an example of a two-dimensional array type probe.

[Explanation of symbols]

 1 Transmitting / receiving element 2 Pulse generator 3 Trigger signal generator 4 Variable delay circuit 5 Phase correction delay circuit 6 Specimen 7 Probe

Claims (3)

[Claims] 1. An ultrasonic beam emitted from each transmitting / receiving element of an array type probe in which a large number of ultrasonic transmitting / receiving elements are arranged linearly or in a plane form so as to converge at one point in a homogeneous medium. By giving different delay times to each transmitting and receiving element, sequentially emitting ultrasonic waves whose phases are slightly shifted from each transmitting and receiving element into the test body, and emitting in the ultrasonic flaw detection method in which the reflected wave is repeated many times When the frequency of ultrasonic waves is n, a delay time is added to the delay time of each transmission / reception element and a phase correction delay time within ± 1 / (2n) seconds, which is different for each transmission / reception element and for each emission. Then, ultrasonic waves are emitted from each transmitting / receiving element into the inhomogeneous test body, reflected waves are received by each transmitting / receiving element, the received waves of each transmitting / receiving element are added, and the echo signal obtained by adding is echoed over multiple times. Memorize about sound wave emission, its eco Signal selects the combination of the maximum phase correction delay time, finding the defect from the obtained echo combination of the delay time, ultrasonic flaw detection method of heterogeneous material, characterized in that to improve the flaw detection performance. 2. The probe is moved along the surface of the test body,
The ultrasonic flaw detection method for a heterogeneous material according to claim 1, wherein scanning is performed. 3. The ultrasonic flaw detection method for a heterogeneous material according to claim 1, wherein the heterogeneous specimen is a high damping material or a centrifugal casting tube.