JPH07134117A - Foreign matter detecting method by vertical ultrasonic inspection - Google Patents

Abstract

PURPOSE:To easily and surely detect a foreign matter existing in the inside of an examination specimen by ultrasonic inspection. CONSTITUTION:A medium 3 having acoustic impedance Z3 is closely stuck to the bottom face of an examination material 1 wherein the impedance Z3 satisfies the following; Z1<Z3 when Z1>Z2, an Z1>Z3 when Z1<Z2 wherein Z1 and Z2 stand for acaustic impedance of the examination specimen 1 and a foreign matter 2, respectively. The reflected wave from the foreign matter 2 has reverse phase to the reflected wave from the bottom face of the examination material 1. Since the reflected wave from the bottom face is already known, the reflected wave with reverse phase to that of the former wave is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dissimilar material portion existing in a material to be inspected, such as a non-metallic inclusion existing in a steel material,
The present invention relates to a method for detecting a dissimilar material portion which is detected by vertical ultrasonic flaw detection.

[0002]

2. Description of the Related Art A method using vertical ultrasonic flaw detection has been proposed as a method for detecting non-metallic inclusions such as alumina present in steel materials. The principle will be described with reference to FIG.

When an ultrasonic pulse P is vertically incident from the front surface to the back surface of a steel material to be inspected 1, first, a reflected wave S (surface echo) from the front surface is obtained. If there is a non-metallic inclusion that is the dissimilar material portion 2 in the traveling path of the ultrasonic wave, then a reflected wave F (defect echo) from the dissimilar material portion 2 is obtained, and then a reflected wave B from the bottom surface. (Bottom echo) is obtained.

In the actual steel material inspection, it is necessary to extract only the defect echo F from these echoes. The gate is used for this purpose. The gate is set in the range from immediately after receiving the surface echo S to immediately before receiving the bottom echo B, and selectively passes the echo of this period to selectively catch the defective echo F.
The starting point and range of the gate are arbitrarily adjusted with the knob.

[0005]

In the detection of the dissimilar material portion using such ultrasonic flaw detection, when the distance from the surface to the bottom surface of the material to be inspected, that is, the wall thickness changes, the range of the gate is changed accordingly. Need to be adjusted.

For example, with the range of the gate fixed,
When the material to be inspected having a smaller thickness than the target to be set is inspected, as shown in FIG. 1 (B), the bottom surface echo B enters the range of the gate, and the defect echo F and the bottom surface echo B are distinguished from each other. It won't work. On the contrary, when the material to be inspected having a larger thickness than the target to be inspected is inspected, a defect echo F may occur outside the range of the gate as shown in FIG.

There is no problem when the thickness changes depending on the type of the material to be inspected, but when the thickness of the material to be inspected is complicated and the thickness changes within one material, the thickness changes depending on the change. Since it is necessary to adjust the gate range frequently and frequently, it is difficult to apply the method as a practical problem.

An object of the present invention is to provide a method for detecting a different material portion by ultrasonic flaw detection which can easily and surely detect a different material portion existing inside one inspected material even if the thickness of the material changes. To do.

[0009]

SUMMARY OF THE INVENTION A method for detecting a foreign material portion according to the present invention is a vertical superposition method for vertically injecting an ultrasonic wave from the surface of a material to be inspected to the bottom surface thereof and detecting flaws in the material to be inspected based on the reflected wave. A method for detecting a different material portion in an inspected material having an acoustic impedance different from that of the inspected material by acoustic flaw detection, wherein the acoustic impedance of the inspected material is Z ₁ , and the different material portion in the inspected material is Acoustic impedance of Z
When the _2, Z magnitude relationship Z ₁ is for Z ₁
Medium with ₂ magnitude relationship and the acoustic impedance Z ₃ to be reversed, Z ₃ next <Z ₁ when the Z _2> Z ₁ Specifically, the Z ₁ <Z ₃ when the Z _1> Z ₂ Is characterized in that the medium is brought into close contact with the bottom surface of the material to be inspected and a reflected wave whose phase is inverted with respect to the reflected wave from the bottom surface of the material to be inspected is detected.

The medium is brought into close contact with the bottom surface of the material to be inspected,
When ultrasonic waves are vertically incident from the surface to the bottom of the inspected material,
The phase of the reflected wave from the bottom surface is uniquely determined, and
The phase of the reflected wave from the dissimilar material part is opposite to the phase. Therefore, by detecting the reflected wave whose phase is inverted with respect to the reflected wave from the bottom surface of the inspection material, the dissimilar material portion in the inspection material is detected.

[0011]

The principle of detection in the method of the present invention will be described in detail below with reference to FIG.

The inspected material 1 is cast iron (hereinafter Fe), and the foreign material portion 2 in the inspected material 1 is an alumina inclusion (hereinafter Al ₂ O ₃ ).
At this time, consider the case where water is selected as the medium 3 [FIG. 2 (A)].

In general, when the substance B is brought into close contact with the bottom surface of the substance A and an ultrasonic wave is incident from the surface of the substance A to the bottom surface, the sound pressure reflectance r of the ultrasonic wave at the interface between the substance A and the substance B is r.
_AB is represented by _{r AB = (Z B -Z A} ) / (Z A + Z B). Z _A is the acoustic impedance of substance A, Z
_B is the acoustic impedance of substance B. The reflected wave is in phase with the incident wave when r> 0, and r <0.
When, the phase is opposite to that of the incident wave.

Considering the case where the material to be inspected 1 is Fe, the different material portion 2 is Al ₂ O ₃ and the medium 3 is water, with the incident wave as (+) phase, the material 1 to be inspected (Fe) Acoustic impedance Z ₁ = 40 × 10 ⁶
kg / m ² · S Different material part 2 (Al ₂ O ₃ ) acoustic impedance Z ₂ = 43 × 10
⁶ kg / m ² · S Acoustic impedance of medium 3 (water) Z ₃ = 1.48 × 10 ⁶ kg
Since / m ² · S, the sound pressure reflectance r _{1-3 at} the interface between the material 1 to be inspected and the medium 3 is r _1-3 = −0.928 <0. That is, r _1-3 <0 because Z ₁ > Z ₃ . Therefore, the reflected wave from the bottom surface of the material 1 to be inspected is uniquely fixed to the (−) phase in which the phase is inverted with respect to the incident wave.

On the other hand, the sound pressure reflectance r _{1-2 at} the boundary surface between the inspected material 1 and the dissimilar material portion 2 is r _1-2 = 0.036> 0. That is, r _1-2 > 0 because Z ₁ <Z ₂ . Therefore, the reflected wave from the different material portion 2 has the same phase (+) phase as the incident wave, and has the opposite phase to the reflected wave from the bottom surface of the inspected material 1.

Therefore, in this case, if a reflected wave having the same phase as the incident wave is detected, the reflected wave can be basically distinguished from the reflected wave from the bottom surface of the material to be inspected without a gate, and the different material portion 2
Can be detected.

That is, when Z ₁ <Z ₂ , Z ₁ > Z ₃
The different material portion 2 is detected by selecting the medium 3 to be the same and detecting the reflected wave having the same phase as the incident wave.

Next, when the magnitude relation between Z ₁ and Z ₂ is opposite,
That is, consider the case of Z ₁ > Z ₂ . In this case, Z ₁
It is necessary to reverse the magnitude relationship between Z ₁ and Z ₃ so that Z ₁ <Z ₃ . As an example, a case where the material to be inspected 1 is 18-8 stainless steel (hereinafter ST), the dissimilar material portion 2 is Al ₂ O ₃ and gold (hereinafter Au) is selected as the medium 3 is shown [Fig.
(B)].

Acoustic impedance of test material 1 (ST) Z ₁ = 45.7 × 10
⁶ kg / m ² · S Acoustic impedance of different material part 2 (Al ₂ O ₃ ) Z ₂ = 43 × 10
⁶ kg / m ² · S Acoustic impedance of medium 3 (Au) Z ₃ = 62.6 × 10 ⁶ kg
Since / m ² · S, the sound pressure reflectance r _{1-3 at} the boundary surface between the material 1 to be inspected and the medium 3 is r _1-3 = 0.156> 0. Therefore, the reflected wave from the bottom surface of the inspected material 1 is
It is uniquely fixed to the same (+) phase as the incident wave.

On the other hand, the sound pressure reflectance r _{1-2 at} the boundary surface between the material 1 to be inspected and the dissimilar material portion 2 is r _1-2 = -0.030 <0. Therefore, the reflected wave from the dissimilar material portion 2 has a negative (-) phase with respect to the incident wave, and in this case also, the phase is relative to the phase of the reflected wave from the bottom surface of the inspected material 1. It will be inverted.

Therefore, in this case, the different material portion 2 is detected by detecting the reflected wave whose phase is inverted with respect to the incident wave.

[0022] As apparent from the above description, a medium magnitude relationship Z ₁ has a Z ₃ comprising a magnitude relationship opposite Z ₂ with respect to Z ₁ in close contact to the bottom surface of the test material, of the test material The dissimilar material portion of the material to be inspected is detected by detecting the reflected wave whose phase is inverted with respect to the reflected wave from the bottom surface.

Specifically, if the incident wave has a (+) phase, when Z ₁ <Z ₂ , a medium satisfying Z ₁ > Z ₃ is selected, and a reflected wave having the same (+) phase as the incident wave is selected. When Z ₁ > Z ₂ , a medium satisfying Z ₁ <Z ₃ is selected, and a reflected wave having a (−) phase opposite to the incident wave may be detected.

[0024]

EXAMPLES Examples of the present invention will be described below.

FIG. 3 shows the structure of a detector suitable for carrying out the method of the present invention. FIG. 4 shows signal waveforms for explaining the operation.

The detection apparatus is an oscillator 1 that oscillates ultrasonic waves.
Has 0. The ultrasonic waves are emitted from the probe 11 as an AC pulse of one cycle at a right angle to the surface of the inspection object 1.

The material 1 to be inspected is a steel pipe here, and when the material is carbon steel or low alloy steel, the material 1 to be inspected is immersed in water or the like as the medium 3 to inspect the medium. The material 1 is brought into close contact with the bottom surface (inner surface of the tube). In the case of stainless steel, Au, Pt, etc. are used as the bottom surface of the inspection object 1 (inner surface of the pipe).
Need to be closely related to. This closeness is, for example,
This is performed by inserting a thin tubular body of u, Pt, or the like, and cold-expanding this tubular body using an expansion plug to bring it into close contact with the inner surface of the pipe.

Here, the material of the steel pipe as the material to be inspected 1 is carbon steel or low alloy steel, and water is selected as the medium 3. The ultrasonic AC pulse of one cycle transmitted from the probe 11 has a positive signal followed by a negative signal (+) phase. This situation corresponds to the first case of the above-described detection principle, and Z ₁ <Z ₂ and Z ₁ > Z ₃ , so that the reflected wave from the bottom surface of the inspection object 1 has the (−) phase and the inspection object. Material 1
The reflected wave from the dissimilar material portion existing inside the is of (+) phase.

After passing through the medium 3, the ultrasonic waves emitted from the probe 11 are vertically incident from the surface (outer surface of the tube) of the material to be inspected 1 to the bottom surface (inner surface of the tube), and the surface, the dissimilar material portion inside, The light is sequentially reflected on the bottom surface and received by the same probe 11. Each reflected wave received by the probe 11 is converted into an electric signal and enters the gate circuit 12.

In the gate circuit 12, as shown in FIG. 1D, the starting point is set immediately after the reception of the surface echo S, and
The range of the gate is sufficiently extended until the bottom echo B is received, and even if the reception timing of the defect echo F is delayed due to the variation in the thickness of the inspected material 1, the defect echo F passes through the range of the gate. To As a result, the defect echo F, that is, the reflected wave from the different material portion and the bottom surface echo B, that is, the reflected wave from the bottom surface (inner surface of the pipe) of the inspection object 1 normally pass through the gate circuit 12.

The signal passed through the gate circuit 12 is supplied to the amplifier 1
After being amplified by 3, the signal is sent to the detector 14 and the phase measuring device 15 in parallel.

In the phase determiner 15, as shown in FIG. 4 (A), either the positive signal or the negative signal is detected first according to the phase determination levels preset on the (+) side and the (-) side. It is determined whether the reflected wave received from the result is the reflected wave from the bottom surface or the reflected wave from the different material portion.
Here, the reflected wave from the bottom has a (-) phase, so
Since the negative signal and the positive signal are detected in this order, and the reflected wave from the different material portion has the (+) phase, the positive signal and the negative signal are detected in that order, and in the latter case, the defect determination signal is turned ON.

On the other hand, the detector 14 inverts the negative signal into the positive signal in order to determine the magnitude of the signal, and the magnitude determiner 1
Send to 6. As shown in FIG. 4B, the size determiner 16 compares the signal with a preset determination level to determine the size.

Then, in the defect judging device 17 connected to the lower side of the phase judging device 15 and the size judging device 16, the defect judging signal from the phase judging device 15 and the size judging signal from the size judging device 16 are combined. Only when the size determination signal from the size determination unit 16 is ON, the defect determination signal from the phase determination unit 15 is checked whether it is ON or OFF, and the size determination O
It is determined whether the N signal is due to the reflected wave from the bottom surface or the reflected wave from the different material portion. If it is due to the reflected wave from the dissimilar material part, an alarm signal is output, otherwise, no alarm signal is output.

Thus, the dissimilar material portion in the inspected material 1 is detected substantially without depending on the gate.

When the material of the steel pipe to be inspected 1 is stainless steel, Au, Pt or the like is selected as the medium 3. These media 3 are brought into close contact with the inner surface of the tube by the cold drawing or the like described above. This situation corresponds to the second detection principle described above.
Since Z ₁ > Z ₂ and Z ₁ <Z ₃ are satisfied, if one cycle of the ultrasonic AC pulse transmitted from the probe 11 is (+) phase, The reflected wave of () has a (+) phase, and the reflected wave from the different material portion has a (-) phase. Therefore, in this case, the different material portion can be detected by detecting the reflected wave of the (−) phase.

In any case, even if the thickness of one inspected material 1 changes, it is not necessary to change the range of the gate, so that the inspection can be performed very easily with the set conditions fixed.

[0038]

As described above, according to the method of detecting a material portion by ultrasonic flaw detection of the present invention, the medium to be brought into close contact with the bottom surface of the material to be inspected is determined by the magnitude relationship of the acoustic impedances of the material to be inspected and the different material portion. By selecting and making the reflected wave from the dissimilar material part and the reflected wave from the bottom face have mutually opposite phases, two types of reflected waves can be distinguished and the dissimilar material part can be accurately detected without using the gate. . Therefore, even if the thickness of one inspected material changes, it is not necessary to change the setting conditions, and the inspection can be efficiently performed under a single setting condition.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a detection principle and a gate by ultrasonic flaw detection.

FIG. 2 is a schematic diagram for explaining the detection principle in the method of the present invention.

FIG. 3 is a system diagram showing a configuration of a detection device suitable for carrying out the method of the present invention.

FIG. 4 is a waveform diagram for explaining the function of the detection device.

[Explanation of symbols]

 1 Inspected material 2 Dissimilar material part 3 Medium

Claims (1)

[Claims] 1. An acoustic impedance different from the acoustic impedance of a material to be inspected by vertical ultrasonic flaw detection in which an ultrasonic wave is vertically incident from the surface to the bottom of the material to be inspected and the inside of the material is inspected based on the reflected wave. a method of detecting a different material part in the inspection member having, Z ₁ and the acoustic impedance of the test material, when the acoustic impedance of the different material portions in the inspection member and Z _2, large and small with respect to Z ₁ A medium having an acoustic impedance Z ₃ whose relationship is opposite to the magnitude relationship of Z ₂ with respect to Z ₁ is brought into close contact with the bottom surface of the inspected material, and a reflected wave whose phase is inverted with respect to the reflected wave from the bottom surface of the inspected material is generated. A method for detecting a different material portion by vertical ultrasonic flaw detection, which is characterized by detecting.