JP2001235450A - Crack detection method of thin piping welding part and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently detect the presence of the inferiority of a welding part in thin piping such as instrument piping with high reliability. SOLUTION: An ultrasonic wave transmitted from an ultrasonic probe 11 is reflected by using a triangular mirror 14 to be incident on the welding part 3 of the thin piping 2a, the reflected wave is detected by the ultrasonic probe 11, and the transmission wave is detected by an ultrasonic probe 12 arranged on the contrary side to judge the presence of the inferiority of welding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flaw detection method and a flaw detection apparatus for inspecting a welded portion of a thin pipe such as an instrumentation pipe by using an ultrasonic wave.

[0002]

2. Description of the Related Art Instrumentation pipes such as hydraulic pipes and pneumatic pipes are made of stainless steel, steel or copper, and are connected by joints or welding. However, important things such as instrumentation piping in nuclear power plants are generally SUS
It is connected by welding using stainless steel piping such as -304. Such an instrumentation pipe is a small-diameter thin-walled pipe having a diameter of about 10 mm to 20 mm and a thickness of 1.5 m.
m to about 3 mm. Generally, connection of pipes by welding is performed by abutting the ends of the pipes. If the pipe ends are not welded in a completely melted state, the strength is reduced or leakage occurs. Further, when this welded portion was confirmed by a radiation transmission test, it was found that even if there was a poor penetration that adhered to the joint, it could not be confirmed on the inspection film, and no other suitable inspection method was found.

FIG. 6A illustrates the principle of inspection of a welded portion using ultrasonic waves. Ultrasonic waves a transmitted at an angle α from an ultrasonic probe 1 are incident on the pipe wall of a pipe 2. At this time, it is refracted by the angle β and irradiates the weld 3. In a state where the welded portion 3 is completely melted and formed, that is, a state where the welding is normally performed, the ultrasonic waves a are scattered and attenuated by the welded portion 3, and the reflected wave does not substantially exist. However, as shown in FIG. 6 (b), in the state where there is a poor penetration part in the welded part 3, the reflected wave b
Is generated, the defective welding can be detected by detecting the reflected wave b with the ultrasonic probe 1.

[0004]

In thin-walled pipes such as instrumentation pipes, the pipe ends generally tend to adhere to each other.
The small gap 5 is not generated in the portion where the penetration is poor as described above, and the adhesion portion 6 is rarely formed in the portion where the penetration is poor in the welded portion 3 of the thin pipe 2a, for example, as shown in FIG. Absent. In addition, the reason why a small gap is formed in the poorly penetrated portion is based on the case where the pipes are not in a good butted state and some inappropriate welding conditions. Since such a contact portion 6 does not reflect the ultrasonic waves a, it is difficult to detect a welding defect only by detecting a reflected wave. Therefore, an object of the present invention is to solve such a problem, and an object of the present invention is to provide a new flaw detection method and a flaw detection apparatus for that purpose.

[0005]

As a result of various studies on the relationship between the contact portion 6 and the ultrasonic wave as described above, the incident ultrasonic wave is not reflected, but the transmitted wave to the opposite side as shown in FIG. c was found to be detectable. When the gap 5 exists as shown in FIG. 6B, the reflected wave b is detected as described above, but the transmitted wave c to the opposite side is not detected. The present invention has been made based on such findings. That is, the flaw detection method for a welded portion in a thin-walled pipe according to the present invention is characterized in that the quality of the welded portion is determined by detecting both a reflected wave and a transmitted wave of an ultrasonic wave applied to the welded portion. (Claim 1).

In the above method, in the case of normal welding in which the penetration of the weld is sufficient, the reflected and transmitted ultrasonic waves are not substantially detected (because the ultrasonic waves are greatly attenuated at the weld), and the welding is not performed. When the penetration of the part is insufficient and there is a gap in the part, the reflected wave is detected but the transmitted wave is not detected, and when the penetration of the welded part is insufficient and the contact part exists in the part, , The reflected wave is not detected, but the transmitted wave is detected. Therefore, it is possible to determine the state of the welded portion accurately and with high reliability from these pieces of information.
In the flaw detection method, the incident angle (α) of the ultrasonic wave to the thin-walled pipe can be in a range of 24 ° to 26 ° (Claim 2). In this range, the reflected and transmitted waves can be detected with a high S / N ratio by focusing and inspecting the ultrasonic beam at the welded portion of the thin pipe. Further, in the flaw detection method, it is possible to switch and irradiate ultrasonic waves from both sides of the welded portion 3 (claim 3). By switching the irradiation of the ultrasonic waves in this way, the quality of the welded portion can be more accurately inspected.

Next, a flaw detector of the present invention is a device for flaw-detecting a welded portion of a thin-walled pipe by using an ultrasonic wave, and comprises a support and a pair of ultrasonic detectors supported by the support with the transmitting and receiving surfaces facing each other. A probe, supported by the support, and reflects ultrasonic waves from one ultrasonic probe to be incident on a welded portion of a thin-walled pipe, and transmits a transmitted wave from the welded portion to the other ultrasonic wave. And a triangular mirror for reflecting light to a probe. By using the above device, the flaw detection method of the present invention can be efficiently performed. Furthermore, thin-walled piping 2a
In this apparatus, the ultrasonic probes 11 and 12 are used as focusing probes, and the triangular mirror 14 is used.
The ultrasonic beam that is reflected by the laser beam and incident on the welded portion 3 of the thin pipe 2a is focused by the welded portion 3 so that the reflected wave and the transmitted wave are increased in S / S
It can be characterized in that detection is performed using the N ratio. (Claim 5) Further, in the flaw detection apparatus, it is possible to further comprise a mounting body for mounting the support to the thin-walled pipe (Claim 6). By using such a mounting body, the flaw detector can be stably mounted on the thin-walled pipe.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial sectional view showing an example of the flaw detector according to the present invention, and FIG. 2 is a right side view thereof. In these figures, a flaw detector 10 includes a pair of ultrasonic probes 1 supported on a support 13 with transmission / reception surfaces 11a and 12a facing each other.
The ultrasonic probe includes a triangular mirror 14 and an acoustic medium (water) 22 supported by a support 13 and arranged between the ultrasonic probes 11 and 12. Support 1
3 is detachably mounted on the thin-walled pipe 2a by the mounting body 15. The ultrasonic probe 11 and the ultrasonic probe 12 having the same structure are focusing probes, in which a vibrator is accommodated in a cylindrical casing, and the transmitting and receiving surfaces 11a and 12a are coaxial. As described above.

The support 13 is formed in a gate shape, and the ultrasonic probes 11 and 12 are detachably mounted in mounting holes penetrating both legs. For example, the attachment holes are screw holes, thread portions are formed on the outer peripheral surfaces of the casings of the ultrasonic probes 11 and 12, and the ultrasonic probes 11 and 12 are provided in the screw holes of the attachment holes.
The ultrasonic probe 1 is screwed and attached.
The relative positional relationship between 1 and 12 can be adjusted accurately and easily. A prism type triangular mirror 14 is attached to an intermediate portion inside the support 13 formed in a gate shape by bonding or the like. The triangular mirror 14 is made of, for example, an isosceles triangular stainless steel block, and one of the two mirror-polished reflecting surfaces irradiates the ultrasonic wave transmitted from the ultrasonic probe 11 to the welding portion 3 at a predetermined angle, The ultrasonic wave reflected by the welding portion 3 is received by the ultrasonic probe 11. The other of the reflection surfaces transmits ultrasonic waves (transmitted waves) transmitted through the welded portion 3 to the ultrasonic probe 1.
2 to receive.

FIGS. 3A and 3B show the relationship of reflection of ultrasonic waves by the triangular mirror 14, which is transmitted from the ultrasonic probe 11 (not shown) located on the right side. The ultrasonic wave a is reflected by the triangular mirror 14 and the thin pipe 2 is formed at an angle α.
a, and is refracted at an angle β to irradiate the weld 3. As shown in FIG. 3A, when a minute gap 5 exists due to poor penetration of the welded portion 3, the reflected wave b
4 and is received by the ultrasonic probe 11. FIG. 3 (b)
When the contact portion 6 exists due to poor penetration of the welded portion 3 as shown in FIG. 3, the transmitted wave c is incident on the triangular mirror 14 from the opposite side as shown in the figure, and the ultrasonic probe (shown in FIG. Zu) to receive. Although the flaw detection method of the present invention is suitably applied to the thin-walled pipe 2a as described above, according to experiments, it is preferable that the incident angle (α) of the ultrasonic wave to the thin-walled pipe 2a be in the range of 24 ° to 26 °. was gotten. Incident angle (α) is 24
If it is smaller than °, the S / N ratio tends to be small and the detection accuracy tends to be reduced. Conversely, if the incident angle (α) is larger than 26 °, the transmitted wave c will be small and it will be difficult to detect. For example, when the incident angle (α) is set to 25.6 °, the corner angle of the triangular mirror 14 is calculated to be 32.2 °, and the angle β of the ultrasonic wave after refraction becomes 65 °.

In FIGS. 1 and 2, a mounting body 15 used to mount the support 13 on the thin pipe 2a is
The whole is horseshoe-shaped, and its middle part is opened in the vertical direction to form a flat frame. Then, the middle part and the lower part of the support 13 are fitted to the upper part. Both sides on the lower surface side of the mounting body 15 have a mounting portion 17 formed in an inverted V shape,
The support 13 is stably mounted on the thin-walled pipe 2a by straddling the mounting portion 17 over the thin-walled pipe 2a. In the state where the support body 13 is supported by the mounting body 15 in this manner, a space surrounded by the thin-walled pipe 2a, the transmitting and receiving surfaces 11a and 12a of the ultrasonic probes 11 and 12, the triangular mirror 14, etc. Is filled with water for the purpose of transmitting ultrasonic waves and focusing the ultrasonic beams at the welded portions. Therefore, a sealing material such as a rubber packing is attached along a gap between each device in contact with the space and a gap between each device and the thin pipe 2a. In addition, on both sides of the mounting body 15 or on both sides of the support body 13, a pouring and discharging port (not shown) for pouring and discharging water into the space is provided.

FIG. 4 is a front view of the flaw detector 10 of FIG. 1 and a driving device 18 for holding the flaw detector. The driving device 18 rotates the flaw detector 10 by 360 ° along the outer circumference of the thin-walled pipe 2a, and further slides in the axial direction of the thin-walled pipe 2a. The driving device 18 includes a gripper 19 that grips the flaw detector 10 together with the mounting body 15, a reciprocating drive unit 20 that reciprocates the gripper 19 in the axial direction of the thin pipe 2a,
The reciprocating drive unit 20 is moved 360 ° along the outer circumference of the thin pipe 2a.
A rotation drive unit 21 for reversible rotation is provided. Gripper 1
9 can use, for example, an electromagnetic chuck, and the reciprocating drive section 20 can use a servomotor or the like. The rotary drive unit 21 to which the reciprocating drive unit 20 is attached has, for example, a main body and a tubular body connected to the main body, and drives a plurality of drive rollers provided on the inner peripheral portion of the tubular body by a drive device such as a servomotor. By doing so, the main body can be configured to be reversibly rotated along the outer periphery of the thin-walled pipe 2a. The tubular body may be a hinge type, and the lower part may be opened and closed so that it can be attached to and detached from the thin-walled pipe 2a.

Next, a method for inspecting a welded portion of a thin pipe using the above-described flaw detector will be described. First, as shown in FIG. 4, the driving device 18 is mounted on a portion of the thin pipe 2a close to the welded portion 3. Next, after the flaw detection device 10 supported by the mounting body 15 is gripped by the grip portion 19, the reciprocating drive unit 20 is driven by an operation signal from, for example, a separately provided control unit (not shown), and Is aligned with the weld 3 as shown in FIG. For this alignment, for example, a reference line may be provided on the support 13 or the mounting body 15, and the welded portion 3 may be made to coincide with the reference line.

Next, water is injected into the space through which the ultrasonic wave passes in the support 13 and the ultrasonic drive 11 transmits the ultrasonic wave according to a control signal from the control unit according to the start command, and the rotation drive unit 21 transmits the ultrasonic wave. To rotate the flaw detector 10 around the thin-walled pipe 2a at a constant speed of 360 °, and welding from reflected waves or transmitted waves along the entire circumference of the welded portion 3 received by the ultrasonic probes 11 and 12. Check the quality of the part. For completeness, it is preferable to switch the transmission of the ultrasonic wave to the ultrasonic probe 12 and reversely rotate it by 360 ° to perform the same inspection. In that case, the ultrasonic probe 12 detects a reflected wave, and the ultrasonic probe 11 detects a transmitted wave. By doing so, it becomes possible to detect when the axes of the two thin-walled pipes do not coincide with each other at the welded portion and a step occurs there. That is, reflection from either side occurs at the step, and the presence of the step is detected.

Next, FIG. 5 shows an example of inspection of the above-mentioned various welds 3. In each drawing of FIG. 5, the vertical axis represents the intensity (%) of the reflected wave, and the horizontal axis represents the rotation angle (0 ° to 360 °). In the figures, (a), (c) and (e) show reflected waves obtained by detecting the ultrasonic wave transmitted from the ultrasonic probe 11 with the same ultrasonic probe 11, (b), (d) and (f). ) Is a transmitted wave detected by the ultrasonic probe 12 of the ultrasonic wave transmitted from the ultrasonic probe 11. (A) and (b) show the case of normal welding where the penetration of the welded portion 3 is sufficient, and neither the reflected wave nor the transmitted wave is detected. (C) and (d) show the case where the penetration of the welded portion 3 is insufficient, where the gap 5 (see FIG. 6 (b)) exists in the welded portion 3 and the reflected wave from that portion is detected. No transmitted wave is detected. (E) and (f) show the case where the penetration of the welded portion 3 is insufficient, and the contact portion 6 (see FIG. 6 (c)) exists in the welded portion 3, and the reflected wave from that portion is not detected. However, a transmitted wave is detected.

When judging the quality of the welded portion 3 by the flaw detector 10, it is not practically inconvenient to inspect only the central portion of the welded portion 3, but it is not practically inconvenient. A similar inspection can be performed for the center of the part 3 and two points every 0.2 mm before and after the part 3 (a total of five places). In that case, the reciprocating drive unit 20 of the drive device 18
Is driven each time to adjust the alignment. As described above, by inspecting a plurality of portions along the axial direction of the thin-walled pipe 2a at 360 °, there is an advantage that the three-dimensional state of the welded portion 3 can be determined.

[0017]

As described above, according to the flaw detection method for a thin-walled pipe weld of the present invention, the presence or absence of a welding defect in a thin-walled pipe weld can be determined accurately and with high reliability. Further, in the flaw detection method for a welded portion of a thin-walled pipe according to the present invention, the incident angle (α) of the ultrasonic wave to the thin-walled pipe is set to 24 ° to 26 °.
The reflected wave and the transmitted wave can be detected at a high S / N ratio by focusing and inspecting the ultrasonic beam at the welding portion of the thin-walled pipe in such an incident angle (α) range. can do. Further, in the flaw detection method for a thin-walled pipe welded portion of the present invention, ultrasonic waves can be switched and irradiated from both sides sandwiching the welded portion 3 and thereby the welded portion can be inspected from both sides. It can be done more accurately.

Next, the flaw detection method described above can be carried out efficiently by using the flaw detection apparatus for a welded portion of a thin pipe according to the present invention. In the flaw detector for a welded portion of a thin-walled pipe according to the present invention, a mounting body for mounting a support to the thin-walled pipe can be further provided. By using such a mounted body, the flaw detector can be stably mounted on the thin-walled pipe. can do.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of a flaw detector according to the present invention.

FIG. 2 is a right side view of FIG.

FIG. 3 is a diagram showing a reflection relationship of an ultrasonic wave by a triangular mirror 14;

FIG. 4 is a front view of the flaw detector 10 and a driving device 18 that grips the flaw detector.

FIG. 5 is a diagram showing an example in which a weld 3 is inspected by the flaw detection method of the present invention.

FIG. 6 is a view for explaining the principle of inspection of a weld using ultrasonic waves.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic probe 2 Pipe 2a Thin-walled pipe 3 Welded part 5 Gap 6 Adhesive part 10 Flaw detector 11 Ultrasonic probe 11a Transmitting and receiving surface 12 Ultrasonic probe 12a Transmitting and receiving surface 13 Support body 14 Triangular mirror 15 Mounting body 16 Support unit 17 Mounting unit 18 Drive unit 19 Holding unit 20 Reciprocating drive unit 21 Rotation drive unit 22 Water a Ultrasonic wave b Reflected wave c Transmitted wave

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motonori Yasunaga 4-10-13 Ibori, Kokurakita-ku, Kitakyushu-shi, Fukuoka F-term (reference) 2N047 AB01 AB07 BA01 BA03 BB02 BC07 EA04 EA09 GA06 GB26

Claims (6)

[Claims] 1. A method for ultrasonically flaw detecting a welded portion 3 of a thin pipe 2a by detecting both a reflected wave and a transmitted wave of an ultrasonic wave applied to the welded portion 3 to judge the quality of the welded portion 3. A method for detecting flaws in a thin-walled pipe weld. 2. An incident angle (α) of an ultrasonic wave to the thin pipe 2a.
The method for detecting flaws in a thin-walled pipe weld according to claim 1, wherein the angle is in the range of 24 to 26 degrees. 3. The method of detecting flaws in a thin-walled pipe weld according to claim 1, wherein the ultrasonic waves are switched and irradiated from both sides of the welded part. 4. An apparatus for ultrasonically flaw-detecting a welded portion 3 of a thin pipe 2a, comprising: a support 13;
a and 12a are opposed to each other and a pair of ultrasonic probes 11 and 12 supported by the support 13 and an ultrasonic wave supported by the support 13 and transmitted from one ultrasonic probe 11 And a triangular mirror (14) for reflecting the incident light into the welded portion (3) of the thin pipe (2a) and reflecting the transmitted wave from the welded portion (3) to the other ultrasonic probe (12). Flaw detector for pipe welds. 5. An apparatus for detecting flaws in a welded portion 3 of a thin-walled pipe 2a by ultrasonic waves, wherein the ultrasonic probes 11 and 12 are used as focusing probes and reflected by a triangular mirror 14 to reflect the welded portion 3 of the thin-walled pipe 2a. The flaw detector for a thin-walled pipe welded part according to claim 4, wherein the ultrasonic beam incident on the thin-walled pipe is focused at the welded part 3 to detect a reflected wave or a transmitted wave at a high S / N ratio. 6. The flaw detector for a thin-walled pipe weld according to claim 4, further comprising a mounting body 15 for mounting the support 13 to the thin-walled pipe 2a.