JPH01132962A - Electromagnetic ultrasonic wave flaw detecting method - Google Patents

Abstract

PURPOSE:To make it possible to detect initial defects in welding at an early period, by arranging electromagnetic ultrasonic wave probes (EMAT) with a welded part in-between, transmitting a surface wave from one side, receiving the wave on the other side, and measuring the change in sound pressure of the received surface wave from the absence or presence of the defect. CONSTITUTION:A backing material 16 is arranged on one surface of a part between base materials 13. A transmitting EMAT 11 is provided on the surface of the base material 13 on one side of a groove 12. A receiving EMAT 15 is provided on the surface of the base material 13 on the opposite side. At the initial period of welding, an ultrasonic surface wave 6, which is transmitted from the EMAT 11, reaches the EMAT 15 through the base material 13, welded metal 14 and the base material 13. When there is no defect, the sound pressure which is received in the EMAT 15 is high. When a defect is present, the surface wave 6, which is transmitted from the EMAT 11, is instructed with the defect and cannot make progress. Therefore, the surface wave 6 is not received with the EMAT 15. Thus, the sound pressure of the ultrasonic wave is strikingly decreased because of the defect, which has been yielded at the initial period of the welding. The received signal is processed in a processor 20, and the presence or absence of the defect is displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application J] The present invention relates to an electromagnetic ultrasonic flaw detection method that is applied to detecting defects that occur during bath welding of steel structures such as penstocks in hydroelectric power plants.

[Prior Art] When welding steel structures such as penstocks, IW cypress, and bridges, bath welding with a backing material 16 as shown in FIG. 6 is sometimes performed.

When welding the backing material, as shown in Figure 6, the space lO between the tunnel 9 for placing the penstock 7 and the penstock is narrow (recently 60
This is a welding method that is only carried out from the inside 20 of the penstock when it is difficult for workers (such as bath workers and welding area inspectors) to approach the welding area (the distance is increasing from 0 m to about 300 m).

In this case, as shown in FIG.
4, the defect 17 is easily removed. It was desired that the initial welding defects be detected at the same time as # welding, rather than being detected at the completion of full thickness bath welding.

However, with conventional contact-type ultrasonic flaw detection methods that use vibrating elements such as piezoelectric elements, it is difficult to apply them during welding due to problems such as the heat resistance of the probe. It was hoped that a destructive testing method would emerge.

[Problem that the invention seeks to solve]

When using ultrasonic flaw detection as a non-destructive test for initial defects that are likely to occur in the above-mentioned cracked material welding method, the test specimen becomes high temperature, so conventional contact-type methods using vibrators using piezo effect etc. However, it has been difficult to use this method due to problems such as the heat resistance of the ultrasonic probe and the heat-resistant couplant.

[Means for solving problems]

The following method is used to solve the above problems.

In other words, one surface wave is transmitted during non-destructive inspection of @4M4 welds of penstocks, etc.! @Ultrasonic probe (EMAT)
) is placed on one side of the weld, and an electromagnetic ultrasound probe (EMAT) that receives surface waves is placed on the other side of the weld, and changes in the sound pressure of the received surface waves due to the presence or absence of defects are measured. In addition, the initial welding defects were detected.

[Operation] According to the above method, at any time during welding, ultrasonic surface waves are transmitted from one side and received and processed by the other side, and any defects are displayed. This is because the electromagnetic ultrasonic probe can transmit and receive ultrasonic waves without contact even at high temperatures during welding.

In addition, 1) Normal (hereinafter "normal" refers to a contact type using a vibrating element using a piezo effect, etc.) does not require a couplant like in the flaw detection method. There is no need for subsequent treatment of the couplant.

In this way, early defects that are likely to occur can be easily detected.

[Example] A first example in which the electric calm ultrasonic flaw detection method of the present invention is applied to a non-destructive test of a one-sided automatic welding part of a penstock pipe in a hydroelectric power plant is described below.
This will be explained with reference to FIGS.

FIG. 1 is a structural diagram and an explanatory diagram of the flow side, and shows the case where there are no defects. FIG. 2 also shows the case where defects are covered. 3 is an enlarged view of each end of the groove shown in FIG. 1, FIG. 4 is an explanatory view of an electromagnetic ultrasound probe (EMAT), and FIG. 5 is an enlarged view of the coil portion of FIG. 4.

In FIG. 1, an overweight member 16 is disposed on one side between the base materials 13. OEM for sending on the surface of the base material 13 on one side of the groove 12
A reception EMAT 15 is disposed on the surface of the AT 11 and the opposite side facing the EMAT 11. EMAT for reception
The output of 15 is connected to a processing device 20.

In the above configuration, EMAT II for transmitting at the initial stage of welding.
] The transmitted ultrasonic surface waves 6 are transmitted to the base material 13 as shown in FIG. ! Welding area 14゜ Receiving EMAT via base metal 13
Reach 15.

In this case, the surface waves do not propagate through the backing material 16, so there is no risk of attenuation.

If there is no defect as shown in Figure 1, the receiving EMAT15
Although the sound pressure received by the transmitting gMAT 11 is high, if there is a defect as shown in FIG. You will not be able to receive data. Therefore, the ultrasonic sound pressure is significantly lowered due to the defects that occur at the beginning of R contact. This reception signal is processed by the processing device 20, and the presence or absence of a defect is displayed.

Note that since the surface wave 6 travels along the groove 12 surface, the first
The beveled corner portions 18 in the figure impede the propagation of surface waves. Therefore, as shown in FIG. 3, if the processing 19 is performed to give a slightly rounder shape, the propagation will be easier.

An example of the structure and operation of the electromagnetic ultrasonic probe for surface waves (EMAT) will be explained with reference to FIGS. 4 and 5.

The electromagnet 1 is lowered by the excitation coil 2, and a magnetic field is generated in the test specimen 3 in a direction parallel to its surface 4. On the other hand, the coil 5 disposed between the magnetic poles of the electromagnet 1 has a twisted shape as shown in FIG. 5 when viewed from above, and is placed close to the surface of the subject, that is, without contact.

One surface wave 6 can be obtained by setting the pitch P of the coil 5 to % of the wavelength of the island frequency current applied to the coil 5.

In the figure, J indicates the eddy current caused by the coil 5, and F indicates the Lorentz force acting on it.

The reason for applying the surface wave EMATt to this example is as follows.
As shown in the comparison table between the EMAT method and the conventional ultrasonic method in Table 1, the EMAT method generally uses low frequency waves, so it has a greater penetration depth into the specimen than the regular ultrasonic surface wave method. This is because the detectability of initial defects in welding is good.

Table 1 In addition, it goes without saying that the in-situ EMAT has good heat resistance and is easy to apply since it is a non-contact type and does not require a contact medium.

Furthermore, in the normal case of using the contact catalyst IX'c, it is very difficult to hold the probe, but since EMAT is easy, it is also advantageous for automation.

As described above, defects in the initial weld can be easily detected.

[Effects of the Invention] By adopting the method of the present invention, initial defects in welding that are likely to occur in one-sided automatic bath welding can be detected at an early stage, and defects can be detected and repaired at an early stage, reducing costs. ,
Excellent in terms of process and quality.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the gt formation and early welding detection principle of the surface wave 'Kamesho ultrasonic metal exploration method as an embodiment of the present invention (when there are no defects), Fig. 2 is the same as above (when defects exist), FIG. 3 is an enlarged view of each end of the groove in FIG. 1. Fig. 4 shows an example of the configuration of Nimen Kogyo EM A 'l' and a diagram of its generation principle, Fig. 5 shows the coil part of the same as above, and Fig. 6 shows a welded part of a penstock pipe in a conventional or working example of a hydroelectric power plant. The sectional view, FIG. 7, is an enlarged view of the welded portion in FIG. 6. In the figure. 1... TFF1 stone, 2... Excitation coil, 3... Test object, 4... Surface of test object. 5...Coil, 6...Surface wave, F...
・Lorentz force, J... eddy current, P... coil (5
) interval pitch. 7... Penstock, 8... Single side bath connection, 9
...tunnel, 10...space. 11... EMAT (for transmission) 12... Bevel, 13... Base material. 14...Welding metal, 15...EMAT (for reception). 16...1j material, 17...defect. 18... Grooved ends, 19... Rounding. 20... Inside the penstock, 21... Direction of movement of surface waves. Agent Patent Attorney Akatsuki Sakama Figure 5 86 Figure 4 =

Claims (1)

[Claims] In non-destructive testing of welded steel structures such as penstocks, an electromagnetic ultrasonic probe that emits surface waves is placed on one side of the weld, and the other side receives the surface waves. An electromagnetic ultrasonic flaw detection method characterized by detecting initial welding defects by arranging a probe and measuring changes in the sound pressure of received surface waves depending on the presence or absence of defects.