JPH01248052A - Ultrasonic flaw detection method and apparatus therefor - Google Patents

Abstract

PURPOSE:To shorten a flaw detection time, by varying a frequency of an AC current to be supplied to the coil of a probe to change the angle of incidence of an ultrasonic wave generated. CONSTITUTION:An electromagnetic ultrasonic probe comprises a coil 2 and a permanent magnet 1 to be opposed to a material 3 to be inspected. The magnet 1 is made up of rectangular permanent magnet pieces 1a so arranged in parallel and series across the width thereof in two rows that the tops thereof act as S and N poles alternately and a spacer 1b made of a non-magnetic material is inserted between adjacent magnet pieces 1a and 1a. When the coil 2 is fed with an AC current, a metal grid on the surface of the material 3 being inspected vibrates parallel with the surface thereof to generate an ultrasonic wave 4 vertically to the direction of vibration and the ultrasonic wave 4 propagates through the material 3 being inspected at an angle of incidence, which is changed by varying the frequency of a current to be applied to the coil 2. This enables the detection of a flaw across the entire thickness of a butt-weld part simply by performing a scanning along the length of the weld part with a pair of transmitting and receiving probes only once.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic flaw detection method for a thicknesswise portion of a flavoring material to be tested, such as a welded portion of a welded steel pipe.

[Prior Art] Conventionally, when performing ultrasonic flaw detection on a butt weld of a submerged arc welded (SAW) inspected material such as a steel pipe, a weld 20 is provided as shown in Fig. 10. A piezoelectric element is used on the surface of the base material 21, and the incident angle δ3. δ2. Three angle probes a, b, c of δ□
are contacted at different distances from the welding part 20,
Flaw detection is performed by making an ultrasonic beam enter the welded part 20 from each probe and detecting the reflected echo. The reason why a plurality of probes are used in this manner and their positions are different is to perform flaw detection over the entire thickness of the welded portion 20.

[Problem to be solved by the invention]

According to the conventional ultrasonic flaw detection method described above, the main body of the ultrasonic flaw detection apparatus also needs to be equipped with a plurality of signal input channels, which increases the size of the apparatus. On the other hand, when one probe is used, it is necessary to perform scanning to approach and separate from the welded part in order to perform flaw detection of the entire wall thickness, which has the disadvantage that the flaw detection time is long. Such problems are similar in the case of electromagnetic ultrasonic flaw detection.

The present invention has been made in view of the above circumstances, and its purpose is to reduce the amount of ultrasonic waves ( An object of the present invention is to provide an ultrasonic flaw detection method and apparatus that can detect the entire thickness range of a welded part of a material to be inspected with one probe by changing the incident angle of SH waves.

[Means to solve the problem]

The ultrasonic flaw detection method for welded parts according to the present invention uses electromagnetic ultrasound that applies a magnetic field in a direction that intersects the material to be inspected and also passes a current in the direction along the material to be inspected to generate S)l waves in the material to be inspected. The sonic flaw detection method is characterized in that the current is an alternating current and its frequency is changed over time. Further, the ultrasonic flaw detection apparatus of the present invention includes a plurality of magnets arranged in parallel with alternating magnetic poles, a magnetized member arranged to apply a magnetic field in a direction crossing the magnetized member to the inspected material, and a magnetized member and the inspected material. One probe is provided for transmitting and one for receiving, consisting of a coil to be placed between the probe and the material, and the transmitting probe should be made to pass alternating current from a frequency sweep circuit whose output frequency changes continuously. It is characterized by:

[Effect]

The angle of incidence depends on the frequency of the current. Therefore, by changing the frequency, the angle of incidence changes, thereby making it possible to detect flaws in the entire wall thickness.

〔Example〕

Hereinafter, the method of the present invention will be specifically explained based on drawings showing examples thereof. Fig. 1 is a schematic diagram showing the structure and principle of an electromagnetic ultrasonic probe (hereinafter referred to as probe) that transmits and receives SH waves. . The permanent magnet 1 is made by arranging two rows of rectangular parallelepiped permanent magnet pieces 1a arranged side by side in the width direction so that the upper surfaces thereof are alternately SN poles. , Ia, a spacer 1b made of a non-magnetic material and having a width d is inserted to interrupt the magnetic field circuit. The coil 2 is a pancake coil having substantially the same shape and dimensions as the magnet 1 in plan view. Such a probe is used both for transmitting and receiving SH waves. The effect of generating Sll waves using this probe will now be explained. When a current I is passed through the coil 2, an eddy current i in the opposite direction is generated on the surface of the material 3 to be inspected, as shown by the white arrow in the figure. If the magnetic field applied to the material 3 to be inspected by the magnet 1 is B, then a Lorentz force F perpendicular to i and B acts on the surface of the material 3 to be inspected. Here, the direction of magnetic field B is (D+
Since it is reversed at a pitch of d), the direction of action of the Lorentz force F is also reversed at a pitch of (D+d). Also coil 2
When an alternating current is passed through, the direction of action of the Lorentz force F is also reversed every half cycle of the alternating current, and as a result, the metal lattice on the surface of the material to be inspected 3 vibrates parallel to the surface, and perpendicular to the direction of vibration. A SH wave 4 is generated, and the Sll wave 4 propagates within the inspected material 3 at an incident angle θ (FIG. 2). The incident angle θ is changed by changing the frequency of the current applied to the coil 2.

DF (θ) in (1) 2 below represents the directivity characteristic of the Sll wave in the thickness direction of the material to be inspected when the incident angle is θ.

However, M : number of magnet pieces V, : sound speed of S11 wave λ : wavelength of SH wave f : frequency of coil current Also, the relationship between incident angle θ and coil current frequency is as follows (
3) It is expressed by the formula.

Vs = 2 (D+d) ・f-sinθ
-(3) where D and d are probes, ■,
Since is a constant determined depending on the material to be inspected, the incident angle θ can be changed by changing the coil current frequency f.

FIG. 3 is a block diagram showing the configuration of the apparatus of the present invention. The high frequency wave oscillated by the high frequency oscillation circuit 12 is frequency-divided by the frequency divider circuit 13 and input to the frequency sweep circuit 14 . The frequency sweep circuit 14 has upper and lower limit setting switches 15.
The frequency f set by 16.

The input frequency is continuously changed in the range of f2 and outputted, and the output changes in the range of f and -f2 are periodically repeated. A synchronization signal for this repetition is provided to the oscilloscope 17 to synchronize its display. The output of the frequency sweep circuit 14 is amplified by a power amplifier circuit 18 and energized through an impedance matching circuit 19 to the coil 28 of the transmitting probe 5a.

The coil 2 of the reception probe 5b is connected to a signal amplification circuit 21 via an impedance matching circuit 20. The signal detected by the reception probe 5b is amplified and input to the synchronization circuit 22, where it is tuned, and furthermore, the noise is removed by the bandpass filter 23, and the signal is sent to the oscilloscope 1.
7.

FIG. 4 shows a schematic plan view showing the planar layout of the probes 5a, 5b placed on the steel pipe 10 and a corresponding schematic elevation view, showing the extension of the welding part 11 from the SH wave probe 5a. The beam is incident obliquely in plan view with respect to the current direction, and the reflected wave is captured by the probe 5b.

FIG. 5 is a plan view and an elevation view of the probes 5a and 5b, in which the magnet l is fixed to the outer circumference using a frame 24.

In accordance with the long surface curvature of the steel pipe 10, the lower surface is a magnet piece 1a.
, the frame 24 is both concave, and the coil 2 is also curved accordingly.

According to such a device, the incident angle θ shown in FIG. 4 is changed by the action of the frequency sweep circuit 14, so that the entire thickness of the welded portion 11 is detected.

Note that the frequency may not be changed continuously as in the above-mentioned embodiments, but may be changed stepwise, such as by preparing 3.4 types of frequency oscillation circuits and switching between them to energize the coil 2.

When the material to be inspected is steel, three types of frequencies f = 505 (kHz), 583 (kllz) and 1 are applied to the coil 2.
009 (kHz) is applied, and S
Sound speed of H wave ■.

= 3230 (m/sec), width of one permanent magnet piece D = 3
．． 2 (mm) and the width of the nonmagnetic spacer d=o, the incident angle θ is determined as shown in Table 1 for each frequency.

Table 1 Figures 6 to 8 are diagrams showing the Sll-wave directivity characteristics of the probe 5a detected corresponding to each frequency in the cross-sectional direction. It changes simply by changing f.

Figure 9 shows the effective plane dimensions of the permanent magnet WXL = 10 x 32 m
m, frequency r = 505 (kHz), sound speed of Sll wave V
, = 3230 (m/sec) when viewed from above the probe 5a, and the beam width within the surface of the material to be inspected is determined by the size and number of permanent magnet pieces. Therefore, it is only necessary to design a probe having the optimum SH wave beam directivity characteristics by considering the dimensions and shape of the material to be inspected.

〔effect〕

As detailed above, in the method of the present invention, by changing the frequency of the alternating current supplied to the coil of the probe and changing the incident angle of the generated SLL wave, only one pair of transmitting and receiving probes can be used. The entire wall thickness of the butt weld can be detected by scanning once in the longitudinal direction of the weld length. Therefore, the scanning time is short and only one ultrasonic flaw detection device is required.

Further, since there is no need to use a contact medium between the surface of the material to be inspected and the EMAT probe, the present invention has excellent effects such as non-contact and efficient flaw detection.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram explaining the structure and principle of the probe used to carry out the method of the present invention, Fig. 2 is an explanatory diagram showing the direction of action of the Lorentz force generated by the probe and the propagation direction of the Sll wave, and Fig. 3 The figure is a block diagram of the entire device of the present invention, Figure 4 is a schematic diagram showing the implementation state of the method of the present invention, Figure 5 is a plan view and elevation view showing one embodiment of the probe, and Figures 6 to 9. 10 is a diagram showing the beam directivity characteristics of SR waves detected by implementing the method of the present invention, and FIG. 10 is a schematic diagram illustrating the conventional ultrasonic flaw detection method. l...Permanent magnet 2...Coil 5a, 5b...
Probe Holder Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono No. 5 to 5 41 Atsushi 2 (!l 83 Me Atsushi 4I2) Figure 5 Figure 6 Figure 7

Claims (1)

[Scope of Claims] 1. In an electromagnetic ultrasonic flaw detection method in which a magnetic field is applied to a material to be inspected in an intersecting direction and a current is passed in a direction along the material to be inspected to generate SH waves in the material to be inspected, the current An electromagnetic ultrasonic flaw detection method characterized by using alternating current as alternating current and changing its frequency over time. 2. A magnetization member comprising a plurality of magnets arranged in parallel with alternating magnetic poles and arranged to apply a magnetic field in a direction crossing the magnetization member to the material to be inspected, and a magnetization member disposed between the magnetization member and the material to be inspected. Equipped with one probe each for transmitting and receiving, which consists of two coils.
An ultrasonic flaw detection device characterized in that the transmitting probe is configured to allow alternating current to flow through it from a frequency sweep circuit whose output frequency changes continuously.