JPH06317567A - Ultrasonic flaw-detection apparatus - Google Patents

Abstract

PURPOSE:To detect the flaw near the surface of a pipe material or a plate material in a wide range and in a state that an S/N ratio is high. CONSTITUTION:A transmitting oscillator 12 and a receiving oscillator 13 are attached to a probe 11 so as to be separated by keeping an interval (b) of one stroke. The oscillators 12, 13 are attached so as to be tilted by the same angle by means of wedges 14, 15. Ultrasonic waves are incident on a material 10 from an incident point 30 at an angle of refraction of theta. The ultrasonic waves advance in the material 10 while they are being reflected at the angle of refraction of theta, and they reach a crack 20. The ultrasonic waves are reflected by the crack 20, they are returned, they reach a radiant point 34, they are passed through the wedge 15, and they reach the receiving oscillator 13. A distance up to the crack 20 is estimated on a display device 21 on the basis of the peak of an output from the receiving oscillator 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detector for detecting defects such as minute cracks near the inner and outer surfaces of pipes, plates and the like.

[0002]

2. Description of the Related Art When a pipe material used in a city gas piping system is cracked or otherwise defective, a gas leak may occur, or the pipe may be damaged and a large amount of gas may be ejected, which is extremely dangerous. is there. Therefore, it is necessary to detect defects such as cracks as early as possible and take measures to prevent danger. An ultrasonic flaw detection method is used as a method for detecting cracks in a pipe material or the like that is actually used for supplying gas or the like. In the ultrasonic flaw detection method, ultrasonic waves are transmitted into a pipe material, ultrasonic waves reflected at a defective portion such as a crack are received, and information such as the size of the crack is obtained from the reflection intensity.

FIG. 8 shows an example of a conventional ultrasonic flaw detection method. A crack 2 exists near the surface of the material 1 such as a gas pipe. When the probe 3 is arranged at a position having a fixed relationship with the crack 2, the crack 2 can be detected. A transducer 4 is attached to the probe 3 by a wedge 5 while being inclined. An ultrasonic wave propagates in the wedge 5 as indicated by the beam center 6 and is refracted so that the ultrasonic wave has a refraction angle θ1 when the ultrasonic wave enters the material 1. The ultrasonic beam refracted so as to have the refraction angle θ1 is totally reflected on the other surface of the material 1 and reaches the crack 2. The ultrasonic wave that has reached the crack 2 is reflected in the opposite direction and returns to the vibrator 4. Therefore, after vibrating the vibrator 4 for a certain period of time, the transmission of ultrasonic waves from the vibrator 4 is stopped, and the vibration of the ultrasonic waves reflected from the crack 2 by the vibrator 4 is received. The vibrator 4 converts electric energy applied from the outside into ultrasonic energy and also converts ultrasonic energy into electric energy by the piezoelectric effect and the magnetostrictive effect. The supply of energy to the vibrator 4 or information received from the vibrator 4 is given to the flaw detection cable 8 via the lead wire 7. Between the case of the probe 3 and the wedge 5,
The sound absorbing material 9 is filled.

FIG. 9 shows changes in the intensity of ultrasonic waves received by the transducer 4 when the crack 3 in the material 1 is detected by the probe 3 shown in FIG. When the ultrasonic wave is transmitted from the oscillator 4, the ultrasonic wave travels through the wedge 5 along the beam center 6, and the wedge 5
The light is refracted at the interface between the material 1 and the material 1 so as to have a refraction angle θ1 and enters the material 1. Although this oscillator 4 is switched to reception immediately after the transmission of ultrasonic waves is completed, it takes time until the mechanical vibration state is attenuated, and a considerably large vibration remains until time t1. Ultrasonic waves in material 1 have a reflection angle θ
At 1, the light propagates while undergoing total reflection and reaches the crack 2. Crack 2
Then, a part of the ultrasonic wave is reflected and travels in the opposite direction at time t.
At, the oscillator 4 is reached.

[0005]

According to the conventional configuration shown in FIG. 8, the output as shown in FIG. 9 is obtained, and the material 1 is obtained.
The distance b1 from the peak position t of the reflected wave from the crack 2 to the crack 2 can be calculated.

That is, since the ultrasonic wave reciprocates from the incident point to the crack 2 by time t, the time required for one way is half of t. If the ultrasonic waves in the material 1 are inclined by the refraction angle θ1 and travel at the sound velocity c1, the following formula 1 is obtained.

[0007]

## EQU00001 ## b1 = 0.5.times.t.times.c1.times.sin .theta.1 In the conventional detection of the crack 2 with the configuration as shown in FIG. 8, the distance b1 to the crack 2 should be calculated by the formula 1 And which surface side it is,
Alternatively, it can be determined whether it is inside the material 1. However, as shown in FIG. 9, the oscillator 4 cannot normally receive the reflected wave from the crack 2 until time t1. That is, it is not possible to detect a short distance defect due to such a dead zone. Also, at time t
The S / N ratio, which is the ratio between the peak time and the surrounding noise level, is a relatively low value of about 2.7 according to the experimental results of the test piece under constant conditions.

For the purpose of actually using the ultrasonic flaw detector, it is important to detect whether or not stress corrosion cracking has occurred in the pipe material or the like. Stress corrosion cracking is promoted by the synergistic effect of the presence of residual stress in the material and the corrosive atmosphere. The residual stress in the material becomes remarkable, for example, in the so-called heat-affected zone in the vicinity of welding. In order to prevent stress corrosion cracking, it is necessary to strictly coat at least the welded portion. For example, even if the material is generally a material having good corrosion resistance, such as SUS304, which is austenitic stainless steel, stress corrosion cracking is likely to occur in a chlorine atmosphere, so that coating is necessary especially near the welded portion. When using an ultrasonic flaw detector, if ultrasonic waves are transmitted and received through the coating film, the S / N ratio will be 60-80%.
Fall to. As shown in FIG. 9, when the S / N ratio is about 2.7, it can be said that the discrimination between the signal and the noise is relatively easy, but when it is about 60%, the discrimination becomes difficult.
Therefore, the conventional structure shown in FIG. 8 cannot sufficiently detect flaws on the material coated with the coating film.

An object of the present invention is to provide an ultrasonic flaw detector capable of detecting a wide range of defects with a good S / N ratio with a simple structure.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a probe main body and a transmitting element which is attached to the probe main body at an angle and transmits ultrasonic waves into a material to be flaw-detected at a predetermined constant refraction angle. And the same distance from the transmitting element on the side opposite to the transmitting direction as far as the transmitting element is separated from the transmitting element by an interval capable of receiving the ultrasonic wave propagating by totally reflecting at the refraction angle between the inner and outer surfaces of the material to be flaw-detected. It is an ultrasonic flaw detector including a receiving element attached at an inclination angle.

[0011]

According to the present invention, the transmitting element is attached to the probe main body in an inclined manner. From the transmitting element, ultrasonic waves are transmitted at a predetermined constant refraction angle into the material to be flaw-detected. The ultrasonic waves that are totally reflected between the inner and outer surfaces of the material at the above-mentioned refraction angle and propagate in the material are reflected by a defective portion such as a crack and return in the traveling direction in the opposite direction. In the propagation direction, that is, on the side opposite to the transmission direction, the receiving element is arranged apart from the transmitting element with the same inclination angle as the transmitting element. The distance is the distance that the reflected wave reaching the transmitting element further propagates by being totally reflected at the refraction angle between the inner and outer surfaces of the material, so that the receiving element receives the ultrasonic wave reflected by a defect such as a crack. To be done. Since the transmitting element and the receiving element are separated from each other, the dead zone hardly occurs in the receiving element. Further, the distance between the transmitting element and the receiving element is the distance that the ultrasonic wave propagates by being totally reflected on the inner and outer surfaces of the material, so that the ultrasonic waves traveling at different angles do not reach the receiving element and the noise is small. Defects can be detected in the state.

[0012]

1 is a block diagram showing the electrical construction of an ultrasonic flaw detector according to an embodiment of the present invention. The probe 11 comes into contact with the surface of the material 10 such as a pipe material or a plate material. The probe 11 includes a transducer 12 for transmission, which is a transmission element.
And the receiving vibrator 13, which is a receiving element, are separately housed. The oscillator 12 for transmission is attached to the wedge 14. The vibrators 12 and 13 are respectively damped by dampers 16 and 17. The sound absorbing material 1 is provided in the space inside the probe 11.
8 is filled. Inside the case, which is the main body of the probe 11,
The acoustic partition plate 19 separates the transmission and reception sections.

The vibrators 12 and 13 have the same shape and have the same resonance frequency, for example, 5 MHz. As the material of the vibrator 4, for example, a porcelain material such as barium titanate is used. The wedges 14 and 15 have the same shape, and acrylic resin or the like is used as the material. Wedge 14,
In the material 10, the ultrasonic wave has a refraction angle θ of, for example, 45.
The vibrators 12 and 13 are held so as to be inclined so as to have an angle of °. The dampers 16 and 17 are made of cloth-containing phenol resin or the like and prevent extra vibrations of the vibrators 12 and 13. The sound absorbing material 18 prevents ultrasonic waves from propagating through the air, and the acoustic partition plate 19 acoustically separates the transmitting unit and the receiving unit. As described above, since the structures related to the vibrators 12 and 13 are almost the same, the manufacture of the probe 11 is easy and the cost can be reduced.

Defects such as cracks 20 present in the material are
It is detected by the display on the display 21. In order to perform this detection, a signal output of 5 MHz is applied from the oscillator 22 to the oscillator 12 for transmission. The display 21 and the oscillator 22 are included in the flaw detector 23. The signal output from the oscillator is given from the oscillator 22 to the vibrator 12 via the connector 24. The signal output from the transducer 13 for reception is given to the display 21 via the connector 25.

The ultrasonic wave transmitted from the transmitting oscillator 12 travels through the wedge 14 and enters the incident point 30 on the surface of the material 10.
Reach In the material 10, the material 10 is refracted to have a refraction angle θ and reaches a reflection point 31 on the surface on the side opposite to the surface on the incident point 30 side. At the reflection point 31, the surface is in contact with air, and the speed of sound in the air is lower than the speed of sound in the wedges 14 and 15. Therefore, the difference from the speed of sound in the material 10 is large, and the ultrasonic wave is totally reflected at the reflection point 31. It is reflected and reaches the reflection point 32 of the crack 20. At the reflection point 32, the traveling direction of ultrasonic waves is reversed,
It returns to the incident point 30 via the reflection point 31. At the incident point 30,
It is further reflected and totally reflected again at the reflection point 33, and the emission point 34
Reach At the emission point 34, part of the ultrasonic waves that have reached the wedge 15 penetrates into the wedge 15 and reaches the transducer 13 for reception.
The distance b between the incident point 30 and the outgoing point 34 is one skip distance that the ultrasonic wave reaches after being totally reflected once at the refraction angle θ.
This distance is twice the plate thickness a when the refraction angle θ is 45 °, for example. Generally, the distance b is selected as expressed by the following equation (2).

[0016]

(2) b = n × 2a × tan θ) where n = 1, 2, 3, ...

The distance to the crack 20 can be determined by the speed of sound in the material 10 and the refraction angle θ. Whether or not the crack 20 has been detected can be determined by whether or not the display on the display 21 changes by, for example, pressing a surface that is separated by that distance.

FIG. 2 is a plan view of the probe 11 shown in FIG. Although it is desirable to select the interval between the transducer 12 for transmission, which is a transmission element, and the transducer 13 for reception, which is a reception element, which is attached to the main body of the probe 11 to be 1 skip as described above, It has been confirmed by experimental results that when the plate thickness a is thin, it may be an integer multiple of 1 skip, for example, about 3 skips.

FIG. 3 shows the state of reflection due to a defect. FIG. 3A shows a state in which the crack 20 exists at a position slightly displaced from the reflection point 32, and the outward path and the return path of ultrasonic waves are slightly deviated. That is, the ultrasonic waves that have reached the reflection point 32 via the outward path 35 are totally reflected and proceed in the direction of 36, are reflected by the cracks 20 and return in the direction of the return path 37. If the stroke indicated by the reference numeral 36 is short, the deviation between the forward path 35 and the return path 37 is small, and the probe 11 shown in FIG. 1 can sufficiently detect the crack 20. Figure 3
In B, the cracks 20 are formed along the grain boundaries 38 of the material 10.
It shows a state that occurs at an angle to the surface. In this state, the deviation between the outward path 35 and the return path 37 is rather small. According to the present embodiment, as described above, it is possible to detect not only when the crack 20 is perpendicular to the surface of the material 10 but also when it is inclined.

FIG. 4 shows the shape of a test piece 40 for confirming the operation of the embodiment shown in FIG. The test piece 40 is preliminarily provided with grooves A, B, C, D, and E which are artificial defects.

FIG. 5 shows the result of ultrasonic flaw detection according to the embodiment shown in FIG. 1 using the same test piece (defect E) as the one shown in FIG. It should be noted that there is no dead zone at time t
The peak of the signal at
That is, the / N ratio is improved to about 5.5.

FIG. 6 shows a state of a test using the test piece 40 shown in FIG. The recorder 41 is supplied with power from the AC power cord 42. A jig 43 is attached to the test piece 40, the angle of the probe 11 is changed, and artificial defects A, B,
The distance from C, D and E can be changed. The results of this detection are shown in Table 1.

[0023]

[Table 1]

In this test, a vertical hole having a diameter of 2.4 mm was bored in each test piece, and the sensitivity was adjusted so that the peak detected by the probe 11 at a position 3.0 skip apart would be 50%. There is. The results in Table 1 show that the S / N ratio before coating is sufficiently high, and the S / N ratio is relatively high even after coating the test piece.

FIG. 7 shows a state in which the welded portion 50 is provided on the material 10 and the coating film 52 is provided in the vicinity of the heat-affected zone 51 around the welded portion 50. City gas uses liquefied natural gas (abbreviated as “LNG”) as one of the raw materials. L
As a pipe material in the NG factory, a pipe material made of a material such as SUS304 of austenitic stainless steel that does not exhibit low temperature brittleness is used. Although such a pipe material is normally at normal temperature, there is a case where LNG flows and it becomes low temperature in an emergency. When such a thermal shock is applied, it is dangerous if cracks or the like occur. Although stainless steel generally has good corrosion resistance, stress corrosion cracking may occur in a chlorine-rich environment near the coast. Therefore, in order to ensure safety, it is necessary to have a complete anticorrosion structure, and painting for shielding from chlorine is necessary. However, this coating is an obstacle to inspecting for stress corrosion cracking. In order to perform ultrasonic flaw detection with the conventional configuration shown in FIG. 8, the coating film 52 must be removed. The removal of the coating film for anticorrosion and the inspection for ensuring reliability may result in an increased risk of corrosion rather than the inspection. Therefore, it is necessary to perform severe coating again after the inspection. According to the results of Table 1, sufficient ultrasonic flaw detection can be performed with the coating applied using the embodiment shown in FIG.

[0026]

As described above, according to the present invention, it is possible to detect defects such as cracks with a high S / N ratio with almost no dead zone. Since the S / N ratio is high, it is possible to detect defects even if a coating film is applied to the surface of the material to be flaw-detected. For pipes that are actually in use,
Although coating is applied to prevent stress corrosion cracking, it is not necessary to remove the coating to detect defects.

Further, since the transmitting element and the receiving element are attached at the same inclination angle, the manufacturing of the ultrasonic probe is simplified and the cost is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an embodiment of the present invention.

FIG. 2 is a plan view of the probe 11 shown in FIG.

FIG. 3 is a diagram showing a path of ultrasonic waves in the vicinity of a crack 20.

FIG. 4 is a view showing a shape of a test piece 40.

5 is a diagram showing the intensity of a received signal in the embodiment shown in FIG.

FIG. 6 is a perspective view showing a configuration for performing an ultrasonic flaw detection test using a test piece 40.

FIG. 7 is a cross-sectional view of welded material 10.

FIG. 8 is a cross-sectional view showing a configuration of a conventional ultrasonic probe.

9 is a diagram showing the signal strength received by the configuration shown in FIG.

[Explanation of symbols]

 10 Material 11 Probe 12, 13 Transducer 14, 15 Wedge 20 Crack 21 Indicator 22 Oscillator 23 Flaw Detector 30 Incident Point 34 Exit Point 40 Specimen 43 Jig 50 Weld Section 51 Heat Affected Zone 52 Painted Film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Futoku Sato, 4-12 1-2 Hirano-cho, Chuo-ku, Osaka-shi, Osaka Gas Co., Ltd. (72) Inventor Tsuyoshi Katayama 2-3-6, Kitakuhoji-cho, Chuo-ku, Osaka No. Non-destructive inspection Co., Ltd. (72) Inventor Katsunori Ohata 2-3-6 Kitakyudera-cho, Chuo-ku, Osaka City Non-destructive inspection Co., Ltd. (72) Inventor Hideaki Sakai 2-3-chome, Kitakyudera-cho, Chuo-ku, Osaka No. 6 Nondestructive inspection Co., Ltd.

Claims (1)

[Claims] 1. A probe main body, a transmitting element that is attached to the probe main body at an angle and transmits ultrasonic waves into a material to be flaw-detected at a predetermined constant refraction angle, and inside and outside of the material to be flaw-detected. A receiving element that is mounted on the probe body at the same inclination angle as the transmitting element, separated from the transmitting element on the side opposite to the transmitting direction by an interval capable of receiving ultrasonic waves that propagate by being totally reflected at the refraction angle between the surfaces. An ultrasonic flaw detector including: