JPH0244027B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a means for measuring the depth position and dimensions of planar defects such as cracks with high accuracy by ultrasonic flaw detection, and in particular, uses ultrasonic echoes from the edge of the defect. This invention relates to a method for measuring the location and size of defects.

Conventionally, as a means of measuring the depth position and dimensions of a defect using ultrasonic echoes from the defect edge, the one-probe method is used to capture the echo from the defect edge and calculate its position geometrically. The edge peak echo method was adopted. As shown in FIG. 1, this method measures the beam path to the upper end echo 8 and lower end echo 8' of the planar defect 4 with one probe,
This was a method of geometrically measuring the positions of both ends of the planar defect and the size of the planar defect from the beam path length W and the refraction angle .theta. of the probe. Note that a and b in Figure 1
are schematic diagrams of waveforms observed on a cathode ray tube, c, d
is an explanatory diagram of the measurement procedure corresponding to a and b.

It is known that this method generally provides a fairly good measurement accuracy for machined slit-like defects, but it is known that the measurement accuracy for natural defects is considerably poor. This is because the edge echo itself is extremely weak, and the crack edge and crack surface have quite complex shapes, so echoes other than the edge echoes occur near the edge, and these echoes Since it is extremely difficult to distinguish between the edge echo and the edge echo, echoes other than the edge echo may be mistaken for the edge echo.Since the beam has a bulge, echoes from areas other than the center beam also exist, and the fracture surface Also, depending on the situation at the tip, an echo contributed by parts other than the center beam may be generated, which may be larger than when the center beam hits, and may be mistaken for an echo from the tip.

On the other hand, another method that uses ultrasonic echoes from the edge of a planar defect is the diffraction echo method, which captures the echo from the edge of the defect using a two-probe method and calculates its position geometrically. has been proposed by Silk et al. This method is a two-probe method in which two transmitting and receiving bevel probes 1 and 1' are placed facing each other on the same surface of the test piece with a planar defect 4 in between, as shown in Figure 2. Therefore, there is an advantage that the number of extra echoes received is small, and that the defect position can be accurately estimated even if the received echo is an echo contributed by a portion deviating from the center beam. Note that a and b in Figure 2 are the first images observed on a cathode ray tube.
Waveform diagrams similar to figures a and b, and figures c and d explanatory diagrams of measurement procedures corresponding to figures a and b. However, in this case as well, the echo from the edge is extremely weak, and depending on the direction of incidence in natural defects, the edge echo may not be recognized, or an echo from a different route due to mode conversion etc. may be mistaken as an edge echo. Therefore, it has been difficult to accurately determine edge echoes in the case of natural defects.

In other words, when an ultrasonic beam is incident within a range of refraction angles at the edges of a planar defect that are perpendicular or nearly perpendicular to the surface of the test piece, edge echoes are emitted on both sides using the edges as a power source. is a wave generated as a result of the wave diffraction phenomenon at the edge of a planar defect,
As mentioned above, this echo is extremely weak, so the end echo and the echo from a nearby part may overlap, making it difficult to distinguish between the end echoes.
Due to the influence of the inclination of the defect edge, strong edge echoes may not be recognized from only one direction.

Therefore, the present inventors developed a method for accurately detecting weak edge echoes by receiving the edge echoes on both sides of the defect, which was received only on one side of the defect in the conventional method, and using both sides to comprehensively detect the weak edge echoes. It has been found that the detection accuracy of edge echoes can be significantly improved by making a determination based on the following. This is achieved by placing two bevel probes facing each other with the defect in between, on the same surface of the specimen, and transmitting and receiving signals simultaneously. By aligning the end echoes received by both probes in time, the distances from both probes to the defective end become equal, so the incident points of the two probes and the defective end The line segment connecting the three points forms an isosceles triangle, and the depth from the test material surface to the defect edge is 2 times the isosceles triangle.
We have obtained the knowledge that the length of the perpendicular line that divides into equal parts can be easily and extremely accurately determined.

The present invention was made based on this knowledge, and its gist is that two bevel probe test pieces for the same frequency are placed on the same surface, facing each other with a planar defect in between. At the same time, a transmission pulse is sent, and the echo from the top or bottom of the planar defect is received by each probe, and the reflected component of the edge echo and the diffraction component of the edge echo by the opposite probe are detected. Adjust the beam path of both probes to be the same using the interference wave with This is an ultrasonic flaw detection method that is characterized by the ability to measure depth with high precision.

The contents of the present invention will be explained in detail below using the drawings. FIG. 3 schematically shows the generation of echoes from the defect edge, where a is for the upper edge of the defect and b is for the lower edge of the defect. When the ultrasonic pulse 2 is aimed at the edge of the defect 4 from the angle probe 1, edge echoes 3 are generated on both sides of the defect with the tip of the defect as the sound source.
occurs.

FIG. 4 is a diagram for explaining the relationship between the arrangement of the bevel probe and the end echo with respect to the defect in the case of the present invention. Although the figure shows the case of the defective upper end, the same applies to the lower end. Two probes 1 and 1' placed opposite each other on the same surface of the test piece with a defect 4 between them.
Ultrasonic pulses are transmitted more simultaneously. At this time, the ultrasonic wave from one of the probes 1 generates an echo at the end of the defect 4, but since this end echo is emitted in all directions, a part of it is sent to the probe 1 as a "reflection component". The other part returns as echo 3, and the other part enters the other probe 1' as a diffracted component echo 3'.Similarly, the ultrasonic echo from the other probe 1' also returns as echo 3'' and 3'. It enters each probe as an echo.

Here, since the frequencies of the ultrasonic waves generated by both probes are the same, the reflected component echoes 3, 3'' and the diffracted component echoes 3, 3' entering each probe interfere with each other. When the beam path lengths of both probes are equal, interference increases and the peak value increases.This improves the signal-to-noise ratio, making it possible to reliably capture edge echoes that are weak and difficult to detect in the past.

FIG. 5 is a diagram illustrating the arrangement of an oblique probe for a defect and how to determine the defect position according to the present invention, in which a is a schematic plan view and b is a side (cross-sectional) view. First, a flaw is detected using the probe 1 from a line perpendicular to the defect, and an end echo is drawn on the cathode ray tube. If the end echo cannot be determined on the cathode ray tube, an echo that is thought to be the end peak is drawn. Next, probe 1
The probes 1' are placed at opposing positions on the center line with the defect in between, and the echoes in this case are also drawn on the cathode ray tube. In this state, the probe 1' is moved back and forth so that both end echoes are aligned at the same position on the cathode ray tube time axis. If it is not possible to match the echoes from both probes by simply sending the probe 1' back and forth, the probe 1 is also finely adjusted back and forth to search for a matching point. By performing such an operation, even if the end echo is not clear from only one side, the end echo becomes clear due to the combined effect of overlapping and adding the end echo from the opposite side. When the echoes from both probes are matched on the time axis, the line connecting the incident points A and B of the two probes and the tip C of the defect is a line whose angle is (90−θ)°. Form an equilateral triangle. Here, if the distance between the two probes is y, and the beam path from one probe to the defect edge is W, then the depth d to the defect edge is It can be found as Further, the defect exists at a position y/2 in front of the two probes. The above is for the case where the upper end is targeted, but it goes without saying that the determination can be made in exactly the same way for the defective lower end.

In this way, by using the method of the present invention, it is possible to magnify and find edge echoes from the group of echoes that appear on the cathode ray tube. Through this operation, the line segment connecting the two probes and the defect edge forms an isosceles triangle exactly, and the depth position of the defect is accurately determined as the length of the perpendicular line that bisects the isosceles triangle. And it's easy to find.

Next, an embodiment of an apparatus for implementing the ultrasonic flaw detection method according to the present invention will be described. FIG. 6 is an explanatory diagram showing an example of one embodiment of the device of the present invention. Synchronization part 6
A transmitter/receiver unit 5 with timing control of
The ultrasonic pulses simultaneously transmitted from 5' are defect 4.
It is reflected at the end of the signal, converted into an electric signal by the probes 1, 1', amplified and detected by the transmitter/receiver sections 5, 5', and sent to the two-phenomenon cathode ray tube 7 via the time axis sections 9, 9'. In FIG. 6, a lateral waveform is shown, and the waveform of the output B on the probe 1' side is shown reversed with respect to the output A on the probe 1 side. Finely adjust the positions of the probes 1 and 1', and continue making fine adjustments until the end echo waveforms 8'' and 8 match on the time axis.At this time, the beam path length W and the two probes 1, Distance y between points of incidence of 1″
is read, and the depth d to the defect edge is measured using equation (1). In the device of the present invention, the synchronizing section 6, the transmitting/receiving sections 5, 5', the angle probes 1, 1', and the time axis sections 9, 9' are of the general type used in ordinary ultrasonic flaw detectors. It is convenient for the two-phenomenon cathode ray tube 4 to have a scale on the horizontal axis so that the beam path can be read.

Next, the effects of the present invention will be explained in more detail using Examples. Figure 7 shows the depth from the surface to both ends of an internal crack that occurred near the perpendicular groove surface of a K-groove weld in a direction substantially perpendicular to the surface using the method according to the present invention and the end peak. It is a comparative explanatory diagram measured by an echo method. All probes have a frequency of 5M
Hz and a refraction angle of 45° were used. The test piece was a steel material (SM50B) with a base material thickness of 38 mm, and 100% glycerin was used as the couplant. In FIG. 7, the solid line shows the value actually measured by cutting the defective part, the dotted line shows the estimated value using the method according to the present invention, and the dashed line shows the estimated value using the edge peak echo method. According to the edge peak echo method, the estimation error was ±5 mm, whereas
By using the present invention, the estimation error can be reduced to ±0.5mm.
can be improved.

In this way, when estimating the position and size of a planar defect in ultrasonic flaw detection, by applying the present invention, the estimation accuracy can be significantly improved compared to conventional methods.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the edge peak echo method, Figure 2 is a diagram for explaining the diffraction echo method, Figure 3 is a schematic diagram showing the generation of edge echoes, and Figure 4 is a diagram for explaining the edge echo method. A diagram for explaining the relationship between the arrangement of the probe and the end echo for the defect according to the present invention,
FIG. 5 is a diagram illustrating the arrangement of a probe for a defect and how to determine the defect position according to the present invention, FIG. 6 is an explanatory diagram showing an example of an embodiment of the apparatus according to the present invention, and FIG. This is a chart showing a comparison with a conventional method (edge peak echo method). 1, 1': Angle probe, 2: Transmission pulse, 3,
3', 3'', 3: Edge echo, 4: Planar defect,
5, 5': Transmission/reception section, 6: Synchronization section, 7: 2 phenomenon cathode ray tube, 8, 8', 8'', 8: End echo waveform, 9, 9': Time axis section, W: Beam path, θ:
Refraction angle, y: Distance between the incident points of two probes, d:
Depth to defect edge.

Claims (1)

[Claims] 1. Place two bevel probes for the same frequency on the same surface of the test piece, facing each other with a planar defect in between, and send transmit pulses at the same time to probe from the top or bottom of the planar defect. The beam path of both probes is made the same by using the interference wave between the reflected component of the end echo and the same refraction component of the end echo from the opposite probe. This ultrasonic flaw detection method is characterized by adjusting the beam path value and measuring the depth from the surface of the specimen to the tip of the planar defect with high precision based on the value of the beam path and the distance between the incident points of the two probes. .