JPS6044618B2 - Ultrasonic flaw detection method and device for dissimilar metal welds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flaw detection device, and more particularly to an ultrasonic flaw detection method for dissimilar metal welds that can detect defects in dissimilar metal welds, and an apparatus therefor.

One of the extremely difficult problems in ultrasonic testing of metal materials is the inspection of welded parts of dissimilar metals.

Conventional ultrasonic flaw detection methods transmit ultrasonic pulses to the object to be inspected, and estimate the location and size of the discontinuity based on the time and height of the echoes reflected from the acoustic discontinuity in the object. Ta. However, the acoustic discontinuity, that is, the density of the material, includes not only so-called defects but also weld boundaries between dissimilar metals. Therefore, from only the information of the time and height of the reflected echo,
It is almost impossible to distinguish whether a discontinuity is a defect or a weld boundary between dissimilar metals. If the weld boundary is sharp in advance or the defect is located at a considerable distance from the weld boundary, the coordinates of the echo source are calculated from the time of the reflection echo, and the reflected echo due to misalignment is calculated based on pure geometric 13. However, in reality, the solution boundary is unknown and, moreover, the defect is often very close to the weld boundary. As described above, conventional ultrasonic flaw detection methods have the drawback that it is nearly impossible to distinguish between weld boundaries and defects between dissimilar metals. An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an ultrasonic flaw detection method for dissimilar metal welds and an apparatus therefor, which can identify defects in dissimilar metal welds.

A feature of the present invention is that the phase of the ultrasonic reflected echo from the acoustic discontinuity is in phase with the transmitted ultrasonic pulse or reversed depending on the density of the material of the object to be inspected or the magnitude of the acoustic impedance. Focusing on this, ultrasonic pulses are transmitted from positions where the acoustic impedance magnitude relationship of the acoustic discontinuities is opposite, and defects in dissimilar metal welds are detected from the phase relationship of the two reflected echoes from the discontinuities. The reason is that it is designed to detect flaws. The second feature of the present invention is that ultrasonic probes are placed at two positions across a dissimilar metal boundary at the same time or at different times, and the reflected echo when the ultrasonic probe is at each position is The phase and propagation time are memorized, while the position of the ultrasound probe and the refraction angle of the ultrasound pulse are detected respectively, and the coordinates of the reflected echo source are calculated from the propagation time, the position of the probe, and the refraction angle. However, when the respective coordinates match within a predetermined range, the phases of the respective reflected echoes are compared, and when the phases are the same, a signal indicating a defect is sent out. The present invention will be explained in detail below using the embodiments shown in FIGS. 1 to 4, and FIGS. 5 and 6.

1 to 4 are diagrams for explaining the principle of the present invention, and FIG. 1 shows a cross section of an object to be inspected.
1 is an object to be inspected, 2 is an ultrasonic probe, and a portion indicated by a broken line 13 indicates a boundary between the metal 11 and a different metal 12, which is an unknown portion at the beginning of the flaw detection test.

It is now assumed that the acoustic impedance Zll of the metal 11 is smaller than the acoustic impedance Zl2 of the metal 12. Assume that a defect f is located near the boundary 13 of the metal 11. At this time, when the ultrasonic pulse T shown in FIG. 2 is transmitted from the ultrasonic probe 2, a defect 3 which is an acoustic discontinuity is detected.
Alternatively, a reflected echo R1 from the boundary 13 of different metals is received by the probe 2. The propagation time t1 of the reflected echo R1 at this time is determined by the distance relationship with the probe 2. As is clear from the following equation based on the theory of traveling waves, the phase φ1 of the reflected echo R1 is: 3. If the acoustic impedance Z of the material on the incident side is larger (smaller) than the acoustic impedance Zr of the material on the reflective side, the phase φ1 of the transmitted pulse T Opposite (same) as phase
become. In the example of Fig. 2, Z,=Otsu,, Zr=42, indicating that the defect is not from boundary 13, but whether or not it is from the defect f can be determined by the fact that the acoustic impedance of the defect is generally It cannot be confirmed because it is unknown.

Therefore, in the present invention, discrimination between dissimilar metal boundaries and defects, which has been considered difficult in the past, is carried out in accordance with the following order.

When the position of the probe 2 is X1 and the reflected echo R1 is received, (1) the phase φ1 and propagation time t of the reflected echo R1
Remember 1.

(2) From the probe position X1, probe refraction angle θ, and propagation time, calculate the coordinates Xl, Yl of the reflected echo source using (3), (4)
Calculate from the formula.

Here, k1 is a constant determined by the material of the metal 11.

(3) Place the probe 2 at the position X1 of the above coordinates X, Y, as the center? , and at the same time the refraction angle becomes 1θ.

At this time, positions X1 and X2 are located at the dissimilar metal boundary 13 in FIG.
It is a necessary condition that the refraction angle -θ be sandwiched between the surfaces B of 1 and 2, and if this condition is not satisfied, the refraction angle −θ may be set to another refraction angle. In addition, the relationship between Xl, X2, and Xl at this time is
It becomes as follows. (4) What is the position of probe 2? The phase φ and propagation time of the reflected echo R2 received at the time are stored.

(5) Similarly to step (2), the coordinates X2 and Y2 of the reflected echo source are calculated from equations (6) and (7). Here, K2 is a constant determined by the material of the metal 12. (6
) Check that the coordinate relationship satisfies the following equation, that is, that each reflected echo source obtained by moving the probe 2 is the same.

Here, ε is a constant. (7) Compare the phases φ1 and φ2, and if the phases are the same, it is determined that a defect exists at the coordinates Xl and Yl, and if the phases are opposite, it is determined that there is a boundary between different metals.
Next, we will explain the third reason for the determination as shown in (7).
This will be clearly explained using FIG.

Fig. 3 is a cross-sectional view of the object to be inspected showing the positional relationship between the probe positions Xl and X2 and the defect f1 dissimilar metal boundary 13, and Fig. 4 is a waveform diagram of the reflected echo obtained in the case of Fig. 3. . In the case of defect f, the acoustic impedance of the acoustic discontinuity remains unchanged no matter where the probe 2 is located. Therefore, as shown in FIG. 4, no phase change is observed in the reflected echoes R, R2 when the probe 2 is located at Xl and X2. On the other hand, the acoustic impedance of the dissimilar metal boundary 13 is Zl when the probe 2 is at position X1.
l→Zl. , when it is at position X2, it changes as B,→'A1, so the phase of the reflected echo is reversed. Therefore, the phases φ1 and φ2 can be compared, and if they are in the same phase, it can be determined that there is a defect, and ultrasonic flaw detection of dissimilar metal welds becomes possible.
FIG. 5 is a block diagram showing an embodiment of the ultrasonic flaw detection apparatus for dissimilar metal welds according to the present invention. In FIG. It is an ultrasonic probe consisting of a receiving wave receiver, which is excited by a transmission pulse T with a constant period L from an ultrasonic transmitter/receiver 3, and emits ultrasonic waves, and also detects acoustic disturbances inside the subject 1. Continuous part (
It receives a reflected echo R1 from a defect, a boundary between dissimilar metals, etc., converts it into an electrical value, and inputs it to the ultrasonic transceiver 3.

The signal is sent to the next stage waveform memory 4, and the waveform memory 4
stores the phase φ1 and propagation time t1 of the reflected echo R1, and updates the stored contents every cycle L when the transmission pulse T is sent. Reference numeral 5 denotes a position detector for detecting the position of the probe 2, which detects the position X1 and the refraction angle θ, and inputs them to the position converter 6.

Position converter 6 converts input signals X1 and θ into digital quantities. 7 is an input device, and the input device 7 includes data φ1, t1 stored in the waveform memory 4, data Xl, O from the position converter 6, and external input data (constants ε, Kl).
, k2) at a period longer than the period L and sends it to the calculator 8.

Calculator 8 performs calculations according to the flowchart shown in FIG.

Commands for changing the probe position and refraction angle are sent to the calculator 8.
from there to the drive unit 10. The drive unit 10 compares the above command with the current values of X and θ, and positions the probe 2 and sets the refraction angle θ. Incidentally, the flaw detection scanning sequence of the object to be inspected 1 is performed by applying the position setting value 21 from the outside. The final calculation result of the calculator 8, that is, a message such as ``boundary'', ``defect'', or ``unable to determine'' in the final step of the flowchart of FIG. Displayed with Y. The display 9 is of a suitable type, e.g.
Display with C scope etc. According to the embodiment of the present invention described above, since the above-described ultrasonic flaw detection method for dissimilar metal welds is steadily carried out, it is possible to reliably detect defects near dissimilar metal boundaries in dissimilar metal welds. can.

In addition, in the embodiment shown in FIG. 5, one probe 2 is used,
Defects are detected by moving the probes, but from the beginning two probes are used and placed opposite to each other across the boundary between different metals on the surface of the object to be inspected 1. It may be provided, but the effect will not change.

As explained above, according to the present invention, whether the ultrasonic echo is from the dissimilar metal boundary of the dissimilar metal welding part,
Since it is possible to accurately and quickly identify whether the defect is caused by a defect, it has the remarkable effect of being able to reliably detect defects even in the vicinity of the boundary between dissimilar metals in a welded joint of dissimilar metals.

[Brief explanation of the drawing]

Figures 1 to 4 are diagrams for explaining the principle of the present invention, Figure 5 is a block diagram showing an embodiment of the ultrasonic flaw detection device for dissimilar metal welds of the present invention, and Figure 6 is a diagram for explaining the principle of the present invention. 6 is a flowchart of the operation of the calculator of FIG. 5; 11...Object to be inspected, 2...Ultrasonic probe, 3...Ultrasonic transmitter/receiver, 4...Waveform memory, 5... ... Position detector, 7 ... Input device, 8 ... Calculator, 9 ... Display device, 10
・・・・・・Drive unit.

Claims (1)

[Claims] 1. Ultrasonic pulses are transmitted from two positions sandwiching the boundary between dissimilar metals on the surface of the object to be inspected, and if the phases of the respective reflected echoes from the object to be inspected are the same, it is determined that there is a defect. An ultrasonic flaw detection method for dissimilar metal welds, characterized by: 2 Ultrasonic probes placed simultaneously or at different times at two positions sandwiching the boundary between dissimilar metals on the surface of the object to be inspected, and the ultrasonic probe placed at one position and the other of the two positions. a first device for storing the phase and propagation time of each reflected echo from the examined body when a probe is present; and a first device for storing the phase and propagation time of each reflected echo from the examined body; a second device for respectively detecting the refraction angle of the ultrasound pulse; and a second device for detecting the refraction angle of the ultrasonic pulse;
The coordinates of the reflected echo source are calculated from the probe position and refraction angle from the device, and when the respective coordinates match within a predetermined range, the phases of the respective reflected echoes are compared, and the phase is determined. and a third device that determines that there is a defect when they are the same.