JP3299505B2 - Ultrasonic flaw detection method using magnetostriction effect - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method using a magnetostrictive effect for detecting internal defects and thicknesses of mechanical parts including boiler tubes used in a thermal power plant, other rolled materials, forged products and the like. About.

[0002]

2. Description of the Related Art The inner surface of a boiler tube of a thermal power plant or the like is corroded by steam or the like flowing in the tube, and the wall thickness gradually decreases as the service period becomes longer. When such corrosion progresses, the thinned portion is destroyed by the high-pressure steam, and the operation of the boiler must be stopped. As a precautionary measure, the progress of corrosion is regularly investigated by measuring the thickness of the boiler tube by nondestructive inspection.
Conventionally, for such non-destructive inspection of boiler tubes,
As shown in FIG. 8, measurement is performed by an ultrasonic pulse reflection method using an ultrasonic thickness gauge having a probe 50. In the ultrasonic pulse reflection method, the thickness and the like are measured as follows. First, the surface 5 of the boiler tube 51 to be measured
6 is brought into contact with the probe 50. Next, the vibrator 52 provided in the probe 50 is ultrasonically vibrated with a pulse voltage, and the ultrasonic vibration is transmitted to the boiler tube 51 which is a test object. The position and size of the internal defect 53 of the boiler tube 51 and the surface 56 are measured by measuring the arrival time and the like of the reflected echo of the ultrasonic vibration detected by the probe 50.
It detects the distance (thickness) from to the bottom surface 57.

[0003]

However, the non-destructive inspection of the boiler tube 51 using the above-described probe 50 has the following problems. 1) Usually, a scale 54 having many irregularities made of iron oxide or the like is attached and deposited on the surface 56 of the boiler tube 51. When the probe 50 is brought into direct contact with the bomb, the ultrasonic vibration of the vibrator 52 is applied to the boiler. It cannot be reliably transmitted to the tube 51. For this reason, the scale 54 at the measurement position of the boiler tube 51 is removed in advance using a sanding machine, a sanding blasting machine or the like, and smoothed, and then the adhesion between the two is increased via machine oil, grease, water or the like. It is necessary to make contact.
Therefore, the boiler tube 5 of a thermal power plant with many measurement locations
In the case of 1 and the like, the labor and cost for this pretreatment become large. Further, since the work of removing the scale 54 is performed periodically, the thickness decreases each time the measurement surface is polished, and when the thickness of a specific portion is periodically measured, the correction by the decrease in the thickness is performed. Must be done. 2) The probe 50 needs a damper 55 made of a tungsten-containing epoxy resin or the like in order to suppress the vibration of the vibrator 52 after outputting the ultrasonic pulse as shown in FIG. If the bonded portion between the vibrator 52 and the damper 55 deteriorates due to the vibration of the vibrator 52, the sensitivity of the measured reflected echo fluctuates, and the width of the output pulse becomes wide, so that the measurement accuracy is reduced. There was a problem that it fluctuated easily. 3) The ultrasonic wave applied to the boiler tube 51 by the vibrator (vertical vibrator) 52 made of quartz, barium titanate, or the like is mainly composed of longitudinal waves. Accordingly, the ultrasonic wave generated thereby generally has a longer wavelength than the case where the main component is a transverse wave. For example,
The wavelengths of the longitudinal and transverse waves of the 5 MHz ultrasonic wave in the steel are 1.2 mm and 0.64 mm, respectively. In general, it is more likely that an internal defect having a smaller shape can be detected as the ultrasonic wave having a shorter wavelength is used. In addition, the above-mentioned problem was a problem which occurs commonly also in a rolled material, a forged product, etc. other than a boiler tube. The present invention has been made in view of such circumstances, it is possible to omit the work of removing the scale before measurement, there is no mechanical vibration portion, excellent durability,
Moreover, an object of the present invention is to provide an ultrasonic flaw detection method using a magnetostrictive effect capable of accurately detecting minute internal defects even in a non-contact state.

[0004]

According to the present invention, there is provided a semiconductor device comprising:
The ultrasonic flaw detection method using the described magnetostrictive effect is a boiler tube, a rolled material, or a forged product, on the surface of which a ferromagnetic scale is formed for detecting the thickness or internal defect of the test material having a scale formed thereon. In the ultrasonic flaw detection method, a predetermined changing magnetic field and a constant bias magnetic field that is substantially perpendicular to the surface layer portion are added to the surface layer portion including the scale,
Utilizing the magnetostriction effect, an ultrasonic pulse is generated in the surface layer, and a change in the distortion of the surface layer induced by the internal defect and / or a reflection echo of the ultrasonic wave reflected on the bottom surface is caused by a change in a magnetic field. Detected as

[0005] The magnetostriction effect (magnetostriction) means that when a magnetic substance (magnetic substance component) is magnetized by applying a magnetic field in a specific direction, the magnetic substance expands in the direction of magnetization or contracts in the vertical direction. Is a phenomenon of deformation. Conversely, when the magnetic material is deformed by receiving a stress, the magnetic permeability changes. These magnetostrictive phenomena are remarkably observed in iron, cobalt, nickel and the like. For example, an iron single crystal has a positive magnetostriction (a ratio ΔL / L between the contraction length ΔL and the length L before contraction) in a relatively weak magnetic field, but has a 200
It has magnetic characteristics such that the sign is inverted at a magnetic field of up to 500 Oersted and reaches saturation when the magnetic field is further increased. It is also known that 45 permalloy, nickel and the like are saturated by a very weak magnetic field. The present invention utilizes such a magnetostrictive effect to generate ultrasonic vibration in a surface layer containing a magnetic material, and to detect distortion of the magnetic material in the surface layer caused by this reflection echo as a change in the magnetic field. I have.

Hereinafter, the principle of transmitting and receiving ultrasonic vibrations using the magnetic material in the surface layer will be described in more detail.
For transmission and reception of such ultrasonic waves, 1) the Lorentz effect in which the reception efficiency and the transmission efficiency are proportional to the bias magnetic flux density,
It is considered that three factors of 2) the magnetization effect proportional to the bias magnetization and 3) the magnetostriction effect proportional to the magnetostriction constant are involved. When the coil is brought close to a conductor to which a magnetic field is added by a permanent magnet or an electromagnet, a bias magnetic field generated by the permanent magnet or the electromagnet and a magnetic field fluctuating by the coil act inside the conductor to generate a body force F. The body force F is the resultant force of the respective vectors of the Lorentz force J _L , the magnetizing force J _M , and the magnetostrictive force J _MS (F = J _L + J _M + J _MS ), and the body force F in the ferromagnetic material is the magnetostrictive force J _MS Becomes dominant.
It is known that the Lorentz force J _L , the magnetization force J _M , and the magnetostriction force J _MS follow the following equations (1) to (3), respectively. J _L = J _e × B ₀ (1) J _M = (▽ H) · M ₀ (2) J _MS = （(e · H) (3) Here, J _e is an eddy current vector, and is given by using Maxwell's equation (J _e = rotH) when displacement current is ignored. B ₀ is the magnetic flux density, M ₀ is the magnetization, and H is the magnetic field. e is a magnetostriction constant tensor and represents a magnetostrictive stress generated by a magnetic field. The body force F is calculated by the equation of motion ρ (∂ ² u /
It is converted to an ultrasonic displacement u through ∂t ² ) = ▽ T + F. Here, T is a stress tensor, and ρ is a density. The mathematical symbol (▽) represents a differential operator (Hamilton operator) called Nabla.

A case where an ultrasonic wave enters a region magnetized by a permanent magnet will be described. The magnetic field in the conductor is disturbed by the displacement u due to the ultrasonic wave, and an additional electric field E and a magnetic flux density B as shown in the following formula are excited in the conductor to compensate for the disturbance. E = σ ⁻¹ J + (∂u / ∂t) × B ₀ ··· (4) B = μ ₀ · μ · (H−M ₀ · ▽ u) + e · ε (5) Here, J is the current density, σ is the electric conductivity, μ ₀ is the magnetic permeability in vacuum, μ is the relative magnetic permeability tensor, and ε is the strain caused by ultrasonic waves. The relationship between the electric field E and the magnetic field H is represented by the following Maxwell electromagnetic equation. Where D is the electric flux density,
q is the volume density of the charge. rotE = −∂B / ∂t, ▽ B = 0 (6) rotH = (∂D / ∂t), ▽ D = q (7) and (4) to (4) The magnetic field H and the electric field E in the conductor are obtained by the equation 7). The change in the magnetic field H or the electric field E can be detected using a coil.

[0008] In addition, substances are roughly classified into the following 1) to 4) according to their magnetic behavior. 1) Diamagnetic substance: has a negative magnetic susceptibility and is magnetized in the direction opposite to the applied magnetic field. 2) Paramagnetic substance: has a positive magnetic susceptibility, its magnetization is parallel to the applied magnetic field, and its magnitude is usually proportional to the applied magnetic field. 3) Ferromagnetic substance: A substance in which effective atomic moments are arranged so that effective magnetization exists even in the absence of an applied magnetic field within a certain temperature range. At sufficiently high temperatures, these materials become paramagnetic. 4) Antiferromagnetic substance: A substance in which an effective atomic moment tends to be arranged so that effective magnetization cannot exist in the absence of an applied magnetic field within a certain temperature range. At sufficiently high temperatures it becomes paramagnetic. When such a magnetic substance, especially a ferromagnetic substance, is placed in a magnetic field H, it is magnetized and turns itself into a magnet. The intensity of the induced magnetism is called magnetization M. Magnetic induction B is used to describe the magnetic force everywhere in space, B = H +
Shown at 4πM.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. FIG. 1 is an explanatory view of an electromagnetic ultrasonic flaw detector according to one embodiment of the present invention, FIG.
(B) is an explanatory view showing the operating principle of the probe of the electromagnetic ultrasonic flaw detector at the time of transmission and reception, and FIGS. 3 (a) to 3 (c).
Is a diagram showing a modified example of the probe, FIG.
FIG. 5B is a view showing a modified example of the probe, and FIGS. 5A and 5B.
FIG. 6 is a view showing a modified example of the probe, FIG. 6 is an explanatory view of a use state of the dimension comparison reference piece, and FIGS. 7 (a) and 7 (b) are display portions when measurement is performed in different air gaps. FIG. 4 is an explanatory diagram of a waveform.

An electromagnetic ultrasonic flaw detector 10 according to one embodiment of the present invention will be described. As shown in FIG. 1, the electromagnetic ultrasonic testing apparatus 10 is arranged in a contact or non-contact state on a surface of a boiler tube 11 which is an example of a material to be tested, and is used for detecting a thickness and an internal defect 12 thereof. With the tentacle 13;
A transmitting unit 1 connected to the probe 13 via a high-frequency cable for transmitting a signal for generating a pulse-like magnetic field
4, a reception amplification unit 15 for receiving and amplifying a reflected echo signal output from the probe 13 via a high-frequency cable, a time axis unit 16 for adjusting a detectable distance, and a reception amplification unit 15 A display unit 17 for receiving an amplified signal from the time axis unit 16 and displaying the amplified signal on a CRT screen or the like; and a synchronization control unit for transmitting a synchronization signal of the displayed signal to the transmission unit 14 and the time axis unit 16. 18.

Next, the details of the probe 13 which is a main part of the present invention and its operation state will be described with reference to FIG.
As shown in FIGS. 2A and 2B, the probe 13 has a boiler tube 11 whose thickness or internal defect 12 is to be detected.
Transmission / reception for applying a magnetic field that fluctuates in a predetermined pulse shape to the upper surface portion 20 to generate an ultrasonic pulse, and detecting a change in distortion of the surface portion 20 due to a reflected echo of the ultrasonic wave as a change in the magnetic field. A coil 21 and a permanent magnet 22 for applying an appropriate bias magnetic field in a direction substantially perpendicular to the surface portion 20 are provided. The boiler tube 11 is used for a thermal power plant or the like, and has a surface layer portion 20 made of a scale, which is an example of a magnetic material, formed on the surface thereof. Fe ₂ O formed at a relatively low temperature in this scale
₃ , iron oxide containing Fe ₃ O ₄ etc. (non-stoichiometric compound Fe _x
Since O) is present, the surface portion 20 shows magnetism. In the present embodiment, the probe 13 is arranged on the surface layer portion 20 in a contactless or non-contact state having a predetermined air gap (interval) d without removing the scale portion of the surface layer portion 20. The inspection of the boiler tube 11 can be easily performed. In addition, nickel, permalloy, silicon steel, or ferromagnetic stainless steel can be used as the magnetic component in the surface layer. In this case, even if the inside of the material to be tested is made of the same material as the surface layer, Embodiments can be applied. The ferromagnetic stainless steel refers to austenitic / ferritic, ferritic, martensitic, precipitation hardened stainless steel, or the like. Further, a magnetic film of nickel, cobalt, or the like may be formed on the surface of the material to be tested by thermal spraying or plating, and this embodiment may be applied as a surface layer.

First, as shown in FIG. 2A, a voltage that changes in a pulse form from the transmitting unit 14 is applied to the transmitting / receiving coil 21 so that the voltage is applied to the hatched portion A of the surface layer 20 below the transmitting / receiving coil 21. Generate a fluctuating magnetic field. At this time, since the surface layer portion 20 contains the magnetic substance component magnetized by the permanent magnet 22, the magnetic component changes due to the action of the fluctuating magnetic field (magnetostriction). Ultrasonic waves (ultrasonic vibration) are generated in the surface layer portion 20 due to the fluctuation of the distortion, and the surface layer portion 2
From 0, the light propagates in the thickness direction of the boiler tube 11. Then, the ultrasonic waves are reflected by the inner wall surface 23 of the boiler tube 11 and the internal defect 12 as shown in FIG. The reflected echo of the ultrasonic wave is applied to the surface layer 20.
When the hatched portion B is reached, the variation of the distortion occurs here. Therefore, the magnetic field on the surface layer portion 20 formed by the magnetic material component magnetized by the permanent magnet 22 is disturbed, and fluctuates according to the fluctuation of the distortion. Therefore, an induced current is generated in the transmitting / receiving coil 21 disposed above the surface layer portion 20 due to the fluctuation of the magnetic field. This induced current is amplified by the reception amplifier 15, and a change in the induced current corresponding to the reflected echo on the inner wall surface 23 or the internal defect 12 can be displayed on the screen of the display unit 17 as shown in FIG. .

[0013]

FIG. 3 shows an example of a coil applicable as a transmitting / receiving coil and a probe provided with the coil. FIG. 3A is a view in which FIG.
FIG. 2 is a plan view of a probe 13 having a transmitting / receiving coil 21 of FIG.
Are arranged so as to apply a bias magnetic field in a direction perpendicular to the surface of the probe 13, that is, in a direction perpendicular to the plane of the drawing. FIG. 3B shows a meandering conducting wire 24.
Are arranged parallel to the surface of the probe 25 as transmission / reception coils, and an example of the probe 25 in which a bias magnetic field is applied in a vertical direction by a permanent magnet 26 disposed above the meandering conductor 24 is shown. In this case, since different body forces act on the surface of the material under test immediately below the parallel portion of the meandering meandering wire 24, Rayleigh waves propagating on the surface of the material under test and the surface of the material under test may be affected. A longitudinal wave or the like that propagates inside with an angle can be excited. FIG. 3C shows a probe 30 composed of a spiral coil 27 wound in a track shape and a pair of permanent magnets 28 and 29, which are arranged so that the directions of NS polarities are different from each other. A transverse wave propagating perpendicularly to the surface of the material under test can be transmitted and received under a vertical bias magnetic field applied by the permanent magnets 28 and 29, respectively. When the part to be tested is made of a ferromagnetic material, the characteristic is that the conversion efficiency of the longitudinal wave becomes extremely smaller than that of the shear wave. As described above, ultrasonic flaw detection can be performed appropriately and effectively by selecting the probes to be used in accordance with the shape, distribution state, and the like of the target internal defect.

Next, the arrangement of the coils (one example of the transmitting and receiving coils) 42 and 43 and the permanent magnets 44 and 45 of the probes 40 and 41 of the other modified examples shown in FIGS. 4 and 5 will be described. I do. FIG. 4A shows an example of a probe 40 in which a circular permanent magnet 44 is arranged on a spirally wound coil 42 and further so that the entire coil 42 rides. In this case, a couplant is not required, and a transverse wave of ultrasonic waves vibrating in all radial directions of the coil 42 can be transmitted and received. For the purpose of improving the weldability, increasing the strength, and increasing the toughness, in a rolled steel material to which so-called controlled rolling is applied, the speed of sound varies depending on the propagation direction of the ultrasonic wave due to the rolled texture. It is known to exhibit elastic (acoustic) anisotropy. For example, the main rolling direction (L
The sound speed of the transverse wave oscillating and propagating in the direction (direction) is faster than the sound speed of the transverse wave oscillating and propagating in the direction (direction C) perpendicular to the main rolling direction. Therefore, when such a probe 40 is used, even when the main rolling direction of the material to be tested is unknown, it is possible to measure the ratio of sound speeds (sound speed ratios) that differ depending on the direction. That is, the reflected echo is detected as a waveform having two peaks because the speed of the ultrasonic wave varies depending on the direction of the material (radial direction of the probe) (see FIG. 4B). Based on this, it is possible to calculate the sound speed ratio or to evaluate and determine the acoustic anisotropy of the test material.

FIG. 5 (a) shows a quadrangular probe 41 in which a coil 43 is wound a number of times along the outer periphery thereof, and the whole is formed by four sides. Shows an example in which a permanent magnet 45 is disposed. In this case, it is possible to transmit and receive a transverse wave of ultrasonic waves vibrating in one direction, and when the material to be tested has different acoustic characteristics with respect to the moving direction of the ultrasonic waves, the arrangement of the permanent magnets By changing the position, the time difference until the reflection echo is detected can be detected, and the acoustic characteristics of the material can be accurately evaluated.
For example, when the permanent magnet 45 is arranged at the position indicated by the solid line in FIG. 5A, the reflected echo has a waveform having a peak like the solid line in FIG. When the permanent magnet 45 is arranged, the reflected echo has a waveform as shown by a broken line in FIG. 5B, and a difference occurs in the time when the peak appears. Therefore, by performing such a test, the acoustic characteristics of the material to be tested can be grasped in advance, and highly accurate ultrasonic flaw detection can be performed when, for example, the oblique angle method is applied.

In order to accurately measure the thickness of the boiler tube 11 and the position of the internal defect 12, for example, a predetermined thickness as shown in FIG. 6, for example, 0.005 mm to 0.5 m
m of the nickel plating film 31 (or a nickel sprayed film), and the overall thickness is a specified dimension (for example, 10 mm).
(mm, 25 mm, 50 mm) are prepared in advance. Next, the probe 13 is brought into contact with a portion of a prescribed size,
A high-frequency current flows from the transmitting unit 14 to the transmitting / receiving coil 21 via the high-frequency cable. As a result, an eddy current (J) can be generated in the nickel plating film 31 and the nickel sprayed film serving as the surface layer by the electromagnetic induction. When the bias magnetic field (B) added by the permanent magnet 22 acts on the eddy current (J), the equation J _MS = ▽ (e ·
A magnetostrictive force J _MS shown in H) occurs. This magnetostrictive force J _MS
As a result, the surface layer vibrates, and an ultrasonic pulse is generated. Next, when the reflected echo of the ultrasonic wave reflected by the internal defect 12 reaches the surface layer, the electric charge of the surface layer vibrates to generate a magnetic field, and the fluctuation of the magnetic field generates an induced current in the transmitting / receiving coil 21. I do. This induced current is amplified by the reception amplification unit 15 and, as shown in FIG.
The waveform is displayed on.

Here, a time interval between a waveform T of an ultrasonic wave initially excited on the surface layer, a waveform F corresponding to a reflected echo from the internal defect 12, and a waveform B corresponding to a reflected echo from the bottom, That is, the distances (TF) and (TB) between the respective waveforms on the screen adjusted by the time axis unit 16 correspond to the positions in the test material (boiler tube 11). And
By comparing this distance with waveform data obtained using a dimension comparison reference piece 32 having a predetermined thickness, each position can be detected. Also,
FIG. 7B shows an air gap (interval) d between the probe 13 and the surface layer portion 20 set to 2 mm, that is, a non-contact state.
It is a waveform when the position of the internal defect of the test material whose actual distance from the surface to the internal defect is 4.69 mm is measured,
The distance between (TF) is 4.7 mm, and the measurement sensitivity is 72.0.
dB. On the other hand, the air gap d is 0 mm,
That is, in the data of FIG. 7A measured using the same material under test in the contact state, the distance between (TF) was 4.7 mm, and the measurement sensitivity was 60.0 dB. As described above, in the case of this embodiment, even when the probe 13 is in a non-contact state, the measurement and detection of the internal defect and the thickness can be performed with sufficiently appropriate accuracy. It is not necessary to remove the scale and the like of the section 20, and the inspection of the boiler tube 11 of a thermal power plant or the like in which a large number of measurement points must be periodically measured can be efficiently performed.

The embodiment of the present invention has been described above.
The present invention is not limited to these embodiments, and all changes in conditions without departing from the gist are within the scope of the present invention. For example, in the present embodiment, an example has been described in which a permanent magnet is used as a magnet for generating a bias magnetic field, but this may be replaced with an electromagnet for generating a bias magnetic field of a constant strength. Further, a boiler tube of a thermal power plant or the like was used as the test material, but a rolled material, a forged product, or the like may be used.

[0019]

According to the ultrasonic flaw detection method using the magnetostrictive effect according to the first aspect of the present invention, there is provided a method for testing a test piece comprising a boiler tube, a rolled material, or a forged product having a ferromagnetic scale formed on the surface thereof. An ultrasonic flaw detection method for detecting a thickness or an internal defect, wherein a predetermined fluctuating magnetic field and a constant bias magnetic field substantially perpendicular to the surface layer are added to a surface layer composed of a scale, and a magnetostriction effect is obtained. Ultrasonic pulses are generated in the surface layer by utilizing it, and fluctuations in the distortion of the surface layer induced by internal defects and / or reflected echoes of the ultrasonic waves reflected on the bottom surface are detected as changes in the magnetic field. There is no vibrating part, and it is possible to apply ultrasonic waves to the surface layer and detect reflected echoes returned to the surface layer without depending on the surface unevenness of the surface layer or the adhesion state of scale, etc. previous Internal defects can be accurately detected in a contact state or a non-contact state by omitting the pre-processing operations, such as kale removed. Therefore, the present invention can be applied to a portion where surface pretreatment for measurement is difficult, and ultrasonic inspection can be performed without depending on the surface state.

In particular, since the material to be tested is a boiler tube, a rolled material, a forged product of a thermal power plant or the like, and the surface layer is a scale attached to the surface, the measurement is performed without removing the scale and in a non-contact state. And the measurement becomes efficient.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an electromagnetic ultrasonic flaw detector according to one embodiment of the present invention.

FIGS. 2 (a) and 2 (b) are explanatory diagrams showing the operating principle of the probe of the electromagnetic ultrasonic flaw detector at the time of transmission and reception, respectively.

FIGS. 3A to 3C are diagrams showing modified examples of the probe.

FIGS. 4A and 4B are diagrams showing modified examples of the probe.

FIGS. 5A and 5B are diagrams showing a modified example of the probe.

FIG. 6 is an explanatory diagram of a use state of a reference piece for dimension comparison.

FIGS. 7A and 7B are explanatory diagrams of waveforms of a display unit when measurement is performed in different air gaps.

FIG. 8 is an explanatory diagram of a use state of a probe in a conventional example.

[Explanation of symbols]

10: Electromagnetic ultrasonic flaw detector, 11: Boiler tube (tested material), 12: Internal defect, 13: Probe, 14: Transmitter,
15: Reception amplification section, 16: Time axis section, 17: Display section, 1
8: Synchronous control unit, 20: Surface layer, 21: Transmission / reception coil, 22: Permanent magnet, 23: Tube inner wall surface, 24: Meandering conductor (transmission / reception coil), 25: Probe, 26: Permanent magnet,
27: spiral coil (transmitting / receiving coil), 28: permanent magnet, 29: permanent magnet, 30: probe, 31: nickel plating film, 32: reference piece for size comparison, 40: probe, 4
1: probe, 42: coil (transmitting and receiving coil), 43:
Coil (transmitting / receiving coil), 44: permanent magnet, 45: permanent magnet

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Jouichi Ando 1-9-15-1 Edobori, Nishi-ku, Osaka-shi, Osaka Inside Japan Hocking Co., Ltd. (72) Inventor Mark Burgunder United States Unit 9 and 10 Four, Madison County, Connecticut Topas Road 170 Scientific Technologies Inc. (56) References JP-A-53-99989 (JP, A) JP-A-62-161048 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) G01N 29/00-29/28

Claims (1)

(57) [Claims] An ultrasonic flaw detection method for detecting a thickness or an internal defect of a test material comprising a boiler tube, a rolled material, or a forged product and having a ferromagnetic scale formed on a surface thereof. Applying a predetermined fluctuating magnetic field and a constant bias magnetic field substantially perpendicular to the surface layer portion to the surface layer portion made of the scale, and generating an ultrasonic pulse on the surface layer portion using the magnetostriction effect. An ultrasonic flaw detection method using a magnetostrictive effect, wherein a change in distortion of the surface layer induced by a reflection echo of the ultrasonic wave reflected on the internal defect and / or the bottom surface is detected as a change in a magnetic field.