JPH0972887A - Flaw detection of pipe by ultrasonic surface acoustic sh wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the flaw on the rear side of a pipe by allowing ultrasonic surface acoustic SH waves to be incident on the pipe being an object to be tested in the peripheral or spiral direction of the pipe and detecting the reflected waves from a flaw such as a crack. SOLUTION: A transmission probe 6 and a receiving probe 7 are arranged in the direction of the pipe axis I of a pipe at an angle θ so that the bottom surfaces of them come into close contact with the surface of a test object 10. Lateral ultrasonic pulses obliquely incident on the pipe axis I from the probe 6 are refracted on the surface of the test object 10 to become surface acoustic SH wave pulses and this pulses sprirally advance along the outer and inner surfaces of the pipe while generates multiple reflection between both surfaces. These pulses are reflected by the crack in the circumferential direction on the rear side of the pipe 8 to advance along the surface opposite to a forward passage of the pipe 8 to be detected by the probe 7. With respect to the crack 4 in the direction of the pipe axis I, the probes 6, 7 are arranged on the plane vertical to the pipe axis I at the same angle α with respect to the pipe axis I in a face symmetric manner so as to be opposed to each other on the same straight line in the direction of the pipe axis I to calculate the position and depth of the crack.

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 for water pipes such as furnace wall pipes of boilers and the like by surface SH waves.

[0002]

2. Description of the Related Art In a furnace wall of a thermal power generation boiler, preheated water pipes are arranged in close contact with each other to prevent heat loss from the furnace wall. Cracks or cracks due to stress corrosion cracking occur. The cracks are regularly inspected at the time of periodic repair of the plant, etc., and if the predetermined safety standard is exceeded, the furnace wall is repaired. Therefore, it is necessary to accurately measure the position and depth of cracks in the water pipe on the furnace wall.

As shown in FIG. 1, a furnace wall tube which is welded to the inside of a furnace wall casing of a boiler of a thermal power plant to form a furnace wall is constructed by welding a furnace wall tube 1 to a metal deposit 2. However, as shown in FIG. 2, cracks 4 often occur inside the portion of the furnace wall tube 1 that contacts the welded portion 3.

On the other hand, the ultrasonic flaw detection method is widely used. For vibrations in which an ultrasonic wave propagates in a solid, longitudinal particles in which particles constituting the solid move in the traveling direction of the ultrasonic wave and a traveling direction of the sound There is a transverse wave that oscillates in the vertical direction, and the transverse wave includes an SV wave that oscillates perpendicularly to the solid surface and an SH wave that oscillates parallel to the solid surface. SH waves traveling along the surface are called surface SH waves. The surface SH wave is a shear wave traveling with a spread of about 15 ° from the flaw detection surface.

Conventionally, as a method of detecting defects such as cracks 4 in the furnace wall tube 1, a flaw detection method using an ultrasonic SV wave has been proposed. As shown in FIG. In case of crack 4 along the circumferential direction of tube 1, furnace wall tube 1
The inside of the furnace wall tube 1 is filled with water 17, the probe 5 is closely attached to the peripheral surface of the furnace wall tube 1 inside the furnace, and ultrasonic waves are emitted through the tube wall of the furnace wall tube 1 and the water 17 in the furnace wall tube 1, An attempt has been made to detect a reflected wave from the crack 4 by the same probe 5.

Further, when the crack 4 along the pipe axis direction is detected by the conventional flaw detection method using the SV wave, as shown in FIG. 3, the SV wave is applied to the surface of the pipe in a plane perpendicular to the pipe axis. An attempt has been made to receive a reflected wave that is obliquely incident, is repeatedly reflected by the outer surface and the inner surface of the tube, reaches the crack 4, and travels backward in the outward path and returns.

On the other hand, it has been proposed to use surface SH waves in order to inspect for the presence or absence of fine cracks during the periodic inspection required for steel materials subject to large loads such as axles for railway vehicles. Yuki Toda et al., "Quantitative Evaluation of Fretting Fatigue Cracks on Railroad Vehicle Axles by Surface SH Waves",
Nondestructive inspection, Volume 40, No. 3, pages 158 to 164 (March 1991, published by the Japan Nondestructive Inspection Association).

Further, a flaw detection method for a fillet weld portion of a steel sheet by a surface SH wave has been proposed (Kenji Yokoyama, "Flaw flaw detection in a fillet weld heel portion by a surface SH wave", ultrasonic TEC.
NO, Volume 6 (1994), February Issue, 15-18
page).

[0009]

The crack 4 along the circumference of the furnace wall tube 1 due to the conventional SV wave of ultrasonic waves shown in FIG.
In the flaw detection method, the ultrasonic waves emitted as shown in FIG. 2 are propagated by alternately moving through mediums having greatly different acoustic impedances such as steel-water-steel-water-steel. It was impossible to clearly detect the target reflected wave from the crack 4 due to reflection at the boundary surface of the medium, attenuation of energy due to mode conversion of ultrasonic longitudinal wave and transverse wave, and generation of noise. .

Further, in the flaw detection method of the crack 4 along the tube axis of the furnace wall tube 1 by the SV wave shown in FIG. 3, the SV wave is repeatedly reflected on the outer surface and the inner surface of the tube, and as a result, the ultrasonic multiple reflection occurs. In this case as well, it was difficult to clearly detect the target reflected wave from the crack 4 due to attenuation of energy due to mode conversion and generation of noise.

Therefore, the present invention provides a flaw detection method capable of nondestructively and accurately detecting a defect of a tube such as a furnace wall tube of a boiler from the surface of the tube opposite to the defect using ultrasonic waves. To aim.

[0012]

In order to achieve the above object,
As a result of intensive studies by the present inventors, a surface SH that propagates a transverse ultrasonic pulse oscillating in a direction parallel to the surface of the test body from the probe along the tube surface at a shallow angle with respect to the tube surface.
When incident as a wave, the surface SH wave is naturally reflected along the curved surface of the tube as a whole while undergoing multiple reflection on both the outer surface and the inner surface of the tube, and is on the back side of the tube as seen from the incident point. Surface SH that reaches and is reflected by cracks
The reflected wave of the wave can be detected by the same probe as that for transmission or the probe for reception and a probe for reception which are separate from each other,
Unlike SV waves, surface SH waves do not undergo mode conversion when reflected on the surface of the tube, so they are not attenuated even with multiple reflections, generate little noise, and can clearly detect defects. The invention was completed.

That is, the present invention provides an ultrasonic flaw detection method for detecting defects such as cracks and holes on the inner and outer surfaces of a test body made of a pipe, wherein an ultrasonic wave composed of transverse waves oscillating parallel to the pipe surface and perpendicular to the traveling direction. A transmitting probe that generates a pulse is brought into close contact with the tube surface, and surface SH waves are emitted from the transmitting probe at a shallow angle to the tube surface in the circumferential direction of the tube or to the tube axis of the tube. On the other hand, the surface SH wave is made incident on the oblique direction and travels along the circumferential direction of the tube or along the spiral direction of the circumferential surface of the tube to reach the defect, and the reflected wave from the defect is transmitted to the transmission probe. A gist is a flaw detection method for a tube by an ultrasonic surface SH wave, which is characterized by detecting a defect by a probe or a separate receiving probe.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the ultrasonic flaw detection method for a solid surface of the present invention will be described in detail with reference to the drawings. FIG. 4 is an explanatory diagram of a method of detecting defects formed by cracks 4 along the circumferential direction of the pipe by the flaw detection method for the pipe using the ultrasonic surface SH wave of the present invention. The test body 10 is formed by welding a plurality of tubes 8 to each other by welding a connecting plate 9 as shown in the sectional view of FIG. 4b.

As the transducers of the transmitting probe 6 and the receiving probe 7 used in the present invention, a transverse wave piezoelectric element in which a crystal is Y-cut, and other piezoelectric elements made of various ceramics are used. The piezoelectric elements 14 of the transmitting probe 6 and the receiving probe 7 are sandwiched between a wedge 15 made of a synthetic resin such as polymethylmethacrylate resin and a backing material 16 made of a synthetic resin as shown in FIG. Wear and configure the probe. The angle with respect to the bottom surface of the piezoelectric element 14, that is, the test body 1
In order to improve transmission and reception efficiency, the incident angle λ of the ultrasonic wave at 0 is set to be substantially equal to the angle called the critical angle at which the refraction angle of the ultrasonic wave incident on the test body 10 such as steel material is just 90 degrees. is necessary.

The transmitting probe 6 and the receiving probe 7 are directed toward the direction along the tube axis I of the tube 8 in an inverted C-shape symmetrically with respect to the tube axis I direction and directed toward the end by an angle θ. Place them side by side. An acoustic binder made of a viscous liquid is thinly applied to the bottom surfaces of the transmission probe 6 and the reception probe 7 to be in close contact with the surface of the test body 10, and ultrasonic waves can be transmitted through the thin layer of the acoustic coupling agent as much as possible. To transmit efficiently. Transverse waves that oscillate parallel to the surface 11 of the tube 8 from the transmission probe 6 are transmitted to the surface 11 at a shallow angle close to the critical angle at which surface SH waves are generated, and the transverse waves obliquely incident on the tube axis I are transmitted. Ultrasonic pulse, test body 1
The light is refracted at the 0 surface and becomes a pulse of the surface SH wave.
As shown in FIG. 5, it propagates in the test body as a transverse wave traveling with a spread of about 15 ° from the surface 11. The surface SH wave traveling along the surface of the tube 8 travels spirally along the surface of the tube 8 while undergoing multiple reflection between the outer surface and the inner surface of the tube 8 like light traveling in an optical fiber. When it reaches the crack 4 in the circumferential direction in the plane perpendicular to the tube axis I on the back side of the tube 8 when viewed from the incident point and is reflected here, the reflected wave is on the opposite side of the tube 8 from the outward path. It advances spirally along the surface, reaches the reception probe 7, and is detected.

The time from pulse emission to echo detection and the echo intensity are displayed on a display device such as an oscilloscope or recorded and read. While emitting ultrasonic pulses from the transmission probe 6 at regular intervals to detect the echo,
While keeping the relative position of the transmitting probe 6 and the receiving probe 7 constant, the scanning is performed along the surface 11 of the test body 10, and from the position and the size of the observed echo, the position and depth of the crack are determined. Ask for

The angle θ of the transmitting probe 6 and the receiving probe 7 with respect to the tube axis direction differs depending on the diameter of the tube 8, and the beam path of ultrasonic waves from the transmitting probe 6 to the crack 4 is 5
It is selected to be 0 to 200 mm, more preferably about 150 to 200 mm. For example, the diameter of the pipe 8 is 20-60 mm
In this case, the angle θ is preferably 15 to 50 °, more preferably 20 to 40 °. If this angle θ is small, the beam path from the probe to the crack 4 becomes too long,
During that time, the surface SH wave is greatly attenuated and the defect detection accuracy is lowered. If the angle θ is too large, noise from the connecting plate 9 becomes large, and it becomes difficult to distinguish the reflected wave from the crack 4.

FIG. 5 shows a crack 4 along the tube axis I direction of the tube 8 by the flaw detection method of the tube by the ultrasonic surface SH wave of the present invention.
It is explanatory drawing of the method of detecting the defect which consists of. Test body 1
The reference numeral 0 indicates that the elongated plate-shaped welding projection pieces 12 are welded symmetrically along the tube axis on both sides of the tube with the center of the tube sandwiched therebetween. The transmitting probe 6 and the receiving probe 7 face each other on the same straight line along the tube axis I direction on the surface of the tube 8 and are inclined at the same angle α with respect to the tube axis I, so that both probes are They are arranged symmetrically with respect to a plane perpendicular to the tube axis I. The angle α is preferably 30 to 60 °. If the angle α is too small, the beam path from the probe to the crack 4 becomes too long, the attenuation of surface SH waves during that time increases, and the defect detection accuracy decreases. Further, if the angle α is too large, noise from the welding protruding piece 12 becomes large, and it becomes difficult to distinguish it from the reflected wave from the crack 4. When the distance d between the transmitting probe 6 and the receiving probe 7 is set to be a distance approximately equal to 2πr / tanα when the outer diameter of the tube 8 is 2r, the distance between the two transducers of the tube 8 is just opposite. A crack 4 is detected.

The transverse ultrasonic pulse emitted from the transmitting probe 6 advances spirally along the surface of the tube 8 as in the case of FIG. 4, and when it reaches the crack 4 in the tube axis I direction, is reflected there. , A spiral that goes in the opposite direction to the forward path, and the receiving probe 7
Is reached and detected.

In the case of the flaw detection method shown in FIGS. 4 and 5, even if there is a welded portion welded to the pipe 8 such as the connecting plate 9 and the welding projection piece 12, there is no problem in flaw detection.

FIG. 6 shows a crack 4 along the direction of the tube axis I of the tube 8 by the flaw detection method of the tube by the ultrasonic surface SH wave of the present invention.
It is explanatory drawing of the other method of detecting. The transmission probe 6 is also used for reception, and a transverse ultrasonic pulse vibrating parallel to the tube surface is incident along the surface 11 of the tube 8 as a surface SH wave in a direction perpendicular to the tube axis I. The incident surface SH wave travels along the circumferential direction of the tube 8 to the back side of the tube 8 and reaches the crack 4. The surface SH wave reflected here returns on the outward path and is detected by the probe 6. It

In actual flaw detection by each of the above-mentioned methods, each probe can be scanned along the tube axis I direction while emitting ultrasonic pulses for flaw detection.

[0024]

【Example】

[Embodiment 1] Three tubes having an outer diameter of 32 mm, a wall thickness of 6.6 mm and a length of 200 mm shown in FIG. 4 are arranged in parallel with a center-to-center spacing of 45 mm, and a connecting plate 9 having a thickness of 7 mm is welded in the space between the tubes. Then, the whole is integrally molded, and at a position 20 mm from the pipe end on one side of the central pipe 8, a depth of 3 mm along the circumference in a plane perpendicular to the pipe axis I.
A test piece 10 was prepared by artificially providing a crack 4 having a cut groove having a length of 20 mm and a width of 0.2 mm. Crack 4 of test piece 10
The transmitting probe 6 and the receiving probe 7 are formed in an inverted C shape on the surface of the tube 8 on the opposite side to the angle θ with respect to the tube axis I direction of 18 °, 27 °, and 45 °. Set the seed angle,
The distance D in the pipe axis I direction from the intersection point O, which is an extension of each center line of the inverted probe C of the transmitting probe 6 and the receiving probe 7, to the crack 4.
Is set so that D = πr / tan θ, where r is the radius of the tube 8. A transverse ultrasonic pulse oscillating parallel to the surface 11 is emitted from the transmitting probe 6 and is incident as a surface SH wave, and the reflected wave detected by the receiving probe 7 is recorded with respect to the time from the pulse emission. , Shown in the flaw detection pattern of FIG.
a shows a result of θ of 18 °, b shows a result of 27 °, and c shows a result of θ of 45 °. In FIG. 7, the reflected wave F is the reflected wave from the crack 4. The peak T is a reflected wave from the tube end, which is a peak of a reflected wave that does not appear in the case of the long actual furnace wall tube 1.

Example 2 A tube having an outer diameter of 32 mm, a wall thickness of 6.6 mm and a length of 200 mm shown in FIG.
The test piece 10 is obtained by welding the welding projection piece 12 of FIG.
Along the tube axis I direction at the center of the tube 8 on one side of the test body 10,
A crack 4 consisting of a cut groove having a length of 30 mm, a depth of 1.5 mm and a width of 0.2 mm is artificially provided. The transmission probe is arranged on a straight line parallel to the pipe axis I on the surface of the pipe 8 on the side opposite to the crack 4 of the test body 10 and at a position symmetrical with respect to a plane perpendicular to the pipe axis I passing through the center of the crack 4. The probe 6 and the reception probe 7 are arranged so as to be diagonally opposed to each other with an angle α = 45 ° with respect to the tube axis I direction. The distance d between the two probes is the radius of the tube 8 r
Then, the distance is approximately equal to 2πr / tanα. A transverse ultrasonic pulse oscillating in parallel with the surface 11 is emitted from the transmitting probe 6 and is incident as a surface SH wave, and the receiving probe 7
The result of recording the reflected wave detected by the method with respect to the time from the pulse emission is shown in the flaw detection figure of FIG. Only the reflected wave peak F from the crack 4 is largely detected.

[Embodiment 3] An outer diameter of 50.8 mm shown in FIG.
The outer surface of the tube 8 having a thickness of 6.5 mm and a length of 455 mm is artificially provided along the tube axis I direction with an outer surface crack 4a consisting of a cut groove having a width of 2 mm and a depth of 3 mm. An inner surface crack 4b formed by a notch having a width of 3 mm and a depth of 3 mm on the inner surface along the direction of the pipe axis I is 120 ° from the outer surface crack 4a.
A test is performed by artificially providing a distant position over the entire length of the pipe, and providing a drill hole 13 having a diameter of 4 mm through the pipe wall at a position 120 ° away from the outer surface crack 4a and the inner surface crack 4b along the circumference of the pipe. Body 10 The transmitting probe 6 is arranged on the surface of the tube 8 just opposite to the inner surface crack 4b in the circumferential direction toward the drill hole 13 in the plane perpendicular to the tube axis I including the drill hole 13. The transmitting probe 6 also serves as the receiving probe. A result of recording a reflected wave detected by the probe 6 with respect to the time from the pulse emission by emitting a transverse ultrasonic wave pulse vibrating in parallel to the surface 11 from the transmission probe 6 and making it incident as a surface SH wave. Is shown in the flaw detection pattern of FIG. The reflection peak F1 from the drill hole 13, the reflection peak F2 from the inner surface crack 4b, and the reflection peak F3 from the outer surface crack 4a are separately detected. According to this flaw detection method, if there are no obstacles in the ultrasonic wave path, all the cracks 4 in the pipe axis I direction on the inner and outer surfaces of the drill hole 13 and the pipe 8 can be detected.

[0027]

According to the method of flaw detection of a tube by the ultrasonic surface SH wave of the present invention, even when the probe cannot be brought close to the defect position like a furnace wall tube, it is circumferentially or spiraled from the opposite side of the tube. By injecting the surface SH wave of the ultrasonic wave in the direction, accurate flaw detection on the back side of the tube becomes possible.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional perspective view of a furnace wall of a boiler for a thermal power plant.

FIG. 2 is an explanatory diagram of a conventional method for detecting cracks in the circumferential direction of a furnace wall tube.

FIG. 3 is an explanatory view of a conventional crack detection method in the axial direction of a furnace wall tube.

FIG. 4 is an explanatory diagram of a method for detecting cracks along the circumferential direction of a pipe by a flaw detection method for a pipe using an ultrasonic surface SH wave of the present invention.

FIG. 5 is an explanatory diagram of a method for detecting cracks along the tube axis direction by a flaw detection method for a tube using an ultrasonic surface SH wave according to the present invention.

FIG. 6 is an explanatory diagram of another method for detecting cracks along the tube axis direction by the flaw detection method for a tube using the ultrasonic surface SH wave of the present invention.

FIG. 7 is an example of a flaw detection figure by a flaw detection method for a tube using the ultrasonic surface SH wave of the present invention shown in FIG.

FIG. 8 is an example of a flaw detection figure by a flaw detection method for a tube using the ultrasonic surface SH wave of the present invention shown in FIG.

9 is an example of a flaw detection figure obtained by the flaw detection method for a tube using the ultrasonic surface SH wave of the present invention shown in FIG.

FIG. 10: Surface SH of ultrasonic waves emitted from the transmission probe
It is a front sectional view showing propagation as a wave.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Furnace wall tube 2 Adhesive metal 3 Welding part 4 Crack 5 Probe 6 Transmitting probe 7 Receiving probe 8 Tube 9 Connecting plate 10 Test body 11 Surface 12 Welding protruding piece 13 Drill hole 14 Piezoelectric element 15 Wedge 16 Rear surface Material 17 water

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Mizumoto 2-10-20 Ebie, Fukushima-ku, Osaka Within Japan Arm Co., Ltd. (72) Inventor, Toshihiko Matsuura 1-3, Dejimanishimachi, Sakai City, Osaka Prefecture Sakai Iron Works Co., Ltd.

Claims (5)

[Claims] 1. In an ultrasonic flaw detection method for detecting defects such as cracks and holes on the inner and outer surfaces of a test body made of a tube, an ultrasonic pulse consisting of a transverse wave oscillating parallel to the surface of the tube and perpendicular to the traveling direction is generated. The transmitting probe is brought into close contact with the tube surface, and surface SH waves are emitted from the transmitting probe at a shallow angle to the tube surface in the circumferential direction of the tube or in an oblique direction with respect to the tube axis of the tube. Incident on the transmitting SH or the surface SH wave to propagate along the circumferential direction of the tube or along the spiral direction of the circumferential surface of the tube to reach the defect, and the reflected wave from the defect is transmitted to the transmitting probe or A method for flaw detection of a pipe by an ultrasonic surface SH wave, which is characterized by detecting by a separate receiving probe and detecting a defect. 2. The defect is a crack extending in the circumferential direction of the pipe, and the transmitting probe and the receiving probe are arranged on the same circumference of the pipe by the same angle θ with respect to the pipe axial direction. The ultrasonic surface SH according to claim 1, wherein the probes are inclined and arranged in an inverted C-shape so as to be directed toward the end and the probes are arranged symmetrically with respect to a plane including the tube axis.
Wave tube flaw detection. 3. The defect is a crack extending in the tube axis direction of the tube, and the transmitting probe and the receiving probe are opposed to each other at a constant distance on the same straight line of the tube surface in the tube axis direction. And both the probes are tilted by the same angle α with respect to the tube axis direction, and the two probes are arranged symmetrically with respect to a plane perpendicular to the tube axis.
A flaw detection method for a tube using the described ultrasonic surface SH wave. 4. The transmission probe is arranged in the circumferential direction of the tube, and the surface SH wave is incident in the circumferential direction of the tube, and the surface SH wave reflected by the defect returns on the outward path. The method for flaw detection of a pipe by an ultrasonic surface SH wave according to claim 1, wherein the detection is performed by a reception probe that also serves as the transmission probe. 5. The method for flaw detection of a tube by ultrasonic surface SH waves according to claim 1, 2, 3 or 4, wherein the test body is a furnace wall tube of a boiler.