JPH04291149A - Ultrasonic flaw detection method for steel pipe and device - Google Patents

Abstract

PURPOSE:To enable S/N and flaw-detection performance to be improved by moving relative positions of a steel pipe and a probe so that a focus of the ultrasonic probe on an outer periphery face of the steel pipe moves along a spiral-shaped channel groove of an inner periphery face. CONSTITUTION:A plurality of spiral-shaped channels 3 exist on an inner periphery face of a steel pipe 1 and ultrasonic probes 15b and 15a are placed at positions of an outer periphery face 4 opposing each top portion 3a and a bottom portion 3b. The ultrasonic output from the probes 15a and 15b is focused near the bottom portion 3b and the top portion 3a of the inner periphery face. Its reflection wave enters the probes 15a and 15b again and is input to a flaw detector 20 separately. A positional relationship between the steel pipe 1 and the probes 15 is relatively changed by a movement control mechanism so that the focus of the probes 15 moves along the top portion 3a or the bottom portion 3b. Thus the ultrasonic focus can be continuously detected without deviating from a portion of the channel 3 which is set once. The flaw detector 20 receives the reflection wave due to a defect from each probe 15 by a plurality of reception circuits and then displays it.

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 and apparatus for detecting defects in a steel pipe having a plurality of parallel spiral grooves formed on its inner peripheral surface using an ultrasonic probe.

0002

[Prior Art] For example, some steel pipes used for boiler equipment piping are designed to improve heat transfer efficiency or reduce turbulent flow when fluids such as steam, water, or pressurized water flow through the steel pipes. Some products have a plurality of spiral grooves formed on their inner circumferential surface for the purpose of preventing this. Note that a steel pipe having a spiral groove formed on its inner circumferential surface in this manner is sometimes called a rifle tube.

FIG. 9(a) is an external view showing the structure of such a steel pipe, and FIG. 9(b) is an axial cross-sectional view showing the steel pipe 1 of FIG. 9(a) cut in the axial direction. , FIG. 9(c) is a radial cross-sectional view showing the steel pipe 1 of FIG. 9(a) cut in the diametrical direction. As shown in the figure, a plurality of spiral grooves 3 are formed in the inner circumferential surface 2 of the steel pipe 1 in parallel with each other. The spiral groove 3 has a trapezoidal cross-sectional shape. and,
The spiral grooves 3 adjacent to each other form a peak 3a projecting in the axial direction and a trough 3b facing the outer circumferential surface 4. Therefore, the thickness t of the steel pipe 1 is thicker at the peaks 3a (t=tT) and thinner at the valleys 3b (t=tB).

In the ultrasonic flaw detection method that uses ultrasonic waves to detect defects existing on the surface and inside of the steel pipe 1, as shown in FIG. An ultrasonic probe 5 made of, for example, an oblique probe or a vertical probe is disposed at one location. Then, a pulse signal is applied from a flaw detector (not shown) to the vibrator 5a in the ultrasonic probe 5 via a signal line, and the ultrasonic wave is transmitted from the vibrator 5a to the steel pipe 1. The ultrasonic waves output from the vibrator 5a enter the steel pipe 1 from the outer peripheral surface 4, propagate within the steel pipe 1, and are largely reflected at the inner peripheral surface 2. Therefore, the vibrator 5a receives the surface reflected wave reflected by the outer circumferential surface 4 and the bottom reflected wave reflected by the inner circumferential surface.

[0005] Furthermore, if a defect exists inside the steel pipe 1 and on each surface 4, 2, a defect reflected wave reflected by the defect is received by the vibrator 5b. Therefore, when the received ultrasonic signal received by the vibrator 5a is displayed on, for example, a CRT display device, a defect reflected wave caused by the defect appears, so that the location of the defect and the approximate size of the defect can be grasped.

Furthermore, since defects in the steel pipe 1 in which the spiral groove 3 as described above is formed occur frequently in the axial direction on the inner circumferential surface 2 and the outer circumferential surface 4, flaw detection is generally carried out targeting axial flaws on the inner and outer surfaces. conduct. That is, the receiving sensitivity of the ultrasonic waves received by the ultrasonic probe 5 is adjusted so that defects near the inner peripheral surface 2 and defects near the outer peripheral surface can be detected with a high S/N.

[0007] Before carrying out ultrasonic flaw detection on the actual steel pipe 1, as shown in FIG. Adjust the sensitivity of detected defect reflected waves. In addition,
Artificial defects A, B, C, and D are formed on the outer circumferential surface 4 and inner circumferential surface 2 of the peak portion 3a of the spiral groove 3, and on the outer circumferential surface 4 and inner circumferential surface 2 of the valley portion 3b, respectively. 5%t=depth 0.
2mm) is an artificial defect. Then, each of the artificial defects A to D of this comparison test piece 6 is adjusted to an optimal refraction angle using means such as eccentricity so that the best S/N can be obtained in a stationary state. Moreover, the steel pipe 1 used for this comparison test piece 6 is 50.8 mm.
It has an outer diameter of 5.6 mm and a thickness of 5.6 mm.

[0008]

[Problems to be Solved by the Invention] However, since the spiral groove 3 is formed on the inner circumferential surface 2 and the thickness t of the steel pipe 1 differs greatly between the peaks 3a and the valleys 3b, The path in which the generated ultrasonic waves are reflected on the inner surface of the peak portion 3a and returns to the transducer 5a is significantly different from the path in which the ultrasonic wave is reflected on the inner surface of the valley portion 3b and returns to the transducer 5a. There is also a path where the light is reflected by the wall at the boundary between the mountain portion 3a and the valley portion 3b and returns. Therefore, the path that is output from the ultrasonic probe 5 and returns to the ultrasonic probe 5 is greatly influenced by the spiral groove 3 formed on the inner circumferential surface 2 and cannot be uniquely determined. As a result, the S/N ratio, which is the ratio between the defective reflected waves and the noise caused by various other scattered reflected waves, is significantly reduced.

[0009] Therefore, the height of the reflected wave (echo) displayed on the CRT display device may not be constant, or it may disappear.
Also, the position in which it appears changes constantly. Therefore, C.R.
Determining which position of the defect the reflected wave displayed on the T display device is caused by, and further determining whether the reflected wave is caused by the defect or the reflected wave from the inner circumferential surface 2. Problems arise, such as difficulty in

Furthermore, since the ultrasonic probe used is the normal vertical probe shown in FIG. 10 or the normal oblique probe, the ultrasonic waves output from the transducer 5a spread widely, There is also the problem that the light hits the peaks 3a and valleys 3b and is scattered, further reducing the S/N.

In order to eliminate this inconvenience, ultrasonic flaw detection is performed with high detection sensitivity on the steel pipe itself before the spiral groove 3 is formed on the inner circumferential surface 2 of the steel pipe 1, and then A two-step flaw detection method is considered in which the completed steel pipe after the spiral groove 3 has been formed is flaw-detected by lowering the detection sensitivity.

[0012] A one-step flaw detection method is also conceivable, in which ultrasonic flaw detection is performed at a detection sensitivity corresponding to the peak portion 3a having a thick thickness t (t=tT) in the final state in which the helical groove 3 is formed. In this case, the detection sensitivity for defects in the valley portion 3b becomes lower than the optimum detection sensitivity.

Furthermore, in the final state in which the spiral groove 3 is formed, the outer circumferential surface and the inner circumferential surface of the peak portion 3a are inspected using dedicated ultrasonic probes, and the outer circumferential surface and the inner circumferential surface of the trough portion 3b are inspected. A method of detecting flaws on the inner circumferential surface using dedicated ultrasonic probes may also be considered. In this case, the detection sensitivity of each ultrasonic probe that detects flaws on the outer circumferential surface and inner circumferential surface of the peak portion 3a is set to a detection sensitivity corresponding to the thickness tT of the peak portion 3a, and The detection sensitivity of each ultrasonic probe for detecting flaws on the surface is set lower than the detection sensitivity corresponding to the thickness tB of the valley portion 3b, that is, the detection sensitivity of the peak portion 3a.

However, each of the flaw detection methods described above still has the following problems. That is, in the two-step flaw detection method, there is a concern that defects (scratches) may occur at positions corresponding to the peaks 3a during the process of forming the spiral groove 3. Furthermore, since the two-step flaw detection increases the number of steps, equipment and flaw detection work efficiency are reduced.

In each of the above-mentioned flaw detection methods, the detection sensitivity of each ultrasonic probe is determined at each thickness tT when the steel pipe 1 is in a static state.
, tB. but,
In reality, flaw detection work is performed while moving the relative positions of the steel pipe 1 and each ultrasonic probe. Therefore, the trajectory of the ultrasonic probe 5 seen from the inner circumferential surface 2 of the steel pipe 1 is as shown in FIG.
As shown by the arrows, the peaks 3a and troughs 3b of the spiral groove 3
cross the Therefore, each ultrasonic probe will detect flaws in the steel pipe 1 whose thickness t varies greatly, so the above-mentioned problem will not be solved in any way.

The present invention has been made in view of the above circumstances, and is designed to move the focal point of an ultrasonic probe disposed on the outer circumferential surface of a steel pipe along a spiral groove on the inner circumferential surface. By moving the relative position between the steel pipe and the ultrasonic probe,
The peaks and valleys of spiral grooves can always be detected with the best detection sensitivity, and noise components caused by thickness changes are reduced as much as possible.
It is an object of the present invention to provide an ultrasonic flaw detection method for steel pipes and an apparatus therefor, which can improve S/N and significantly improve flaw detection performance.

[0017]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an ultrasonic probe that faces the outer peripheral surface of a steel pipe in which a plurality of mutually parallel spiral grooves are formed on the inner peripheral surface. ,
In an ultrasonic flaw detection method for steel pipes that detects defects on the surface and inside of steel pipes by transmitting and receiving ultrasonic waves from this ultrasonic probe to and from the steel pipes,

0018
]The ultrasonic probe is created by relatively changing the positional relationship between the ultrasonic probe and the steel pipe so that the focus of the ultrasonic probe moves along the peaks or valleys of the spiral groove. Defect detection is performed continuously with the child.

[0019] In addition to the above-mentioned means, according to the ultrasonic flaw detection method for steel pipes according to another invention, the outer circumference of the steel pipe is At least twice as many ultrasonic probes as the number of spiral grooves are arranged along the direction.

Furthermore, an ultrasonic flaw detection device for steel pipes according to another invention includes an ultrasonic probe having at least twice the number of helical grooves disposed along the outer circumferential direction of the outer circumferential surface of the steel pipe; An ultrasonic probe support mechanism that supports each ultrasonic probe so that the focal point of each ultrasonic probe is located at the peaks and valleys of the spiral groove, and this ultrasonic probe support mechanism. Movement control that relatively changes the positional relationship between the ultrasonic probe and the steel pipe so that the focal point of each supported ultrasonic probe moves along the peaks or valleys of each spiral groove. The device includes a mechanism and a signal processing unit that detects the location and size of a defect from the received ultrasonic signals output from each ultrasonic probe.

In still another invention, the movement control mechanism is configured such that the focal point of each ultrasonic probe supported by the ultrasonic probe support mechanism moves along the peak or trough of each spiral groove. The steel pipe movement control device rotates the steel pipe around its axis and moves it in the axial direction.

[0022]

[Operation] According to the method and device for ultrasonic flaw detection of steel pipes configured as described above, the ultrasonic probe disposed on the outer peripheral surface of the steel pipe is formed of an ultrasonic probe having a focal point. There is. The ultrasonic waves output from each ultrasonic probe are focused near the peaks or valleys of the spiral groove formed on the inner circumferential surface of the steel pipe. That is, in a stationary state, the detection sensitivity is adjusted so that defects existing in peaks or valleys are detected in the best condition.

Then, the relative positional relationship between the steel pipe and the ultrasonic probe changes so that the focal point of the ultrasonic probe moves along the peaks or valleys of the spiral groove. For example, a steel pipe is moved in the axial direction while being rotated around the axis. Therefore, even if the steel pipe is moved, the focus of the ultrasonic wave will not deviate from the peaks or valleys of the spiral groove once set. Therefore, moving the steel pipe does not change the path of the ultrasonic waves output from the ultrasonic probe and received by the ultrasonic probe again. As a result, the S/N of the defect reflected wave due to the defect does not decrease.

Further, in another invention, the number of ultrasonic probes is twice or more the number of spiral grooves formed along the outer circumferential direction of the steel pipe, and the number of ultrasonic probes is twice or more the number of spiral grooves formed along the outer circumferential direction of the steel pipe. It is arranged. Therefore, the focus is set evenly over the peaks and valleys of each spiral groove. Therefore, for example, when the steel pipe is moved while being rotated, the peaks and valleys of all the spiral grooves are simultaneously detected. Therefore, the flaw detection work efficiency is greatly improved. Further, the signal processing section detects the location and size of the defect from the received ultrasonic signals output from each ultrasonic probe.

Further, in the ultrasonic flaw detection apparatus for steel pipes of another invention, each ultrasonic probe is disposed in the circumferential direction of the outer peripheral surface of the steel pipe by the ultrasonic probe support mechanism, and This allows the steel pipe to rotate around its axis while moving it in the axial direction.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a system configuration diagram showing an entire ultrasonic flaw detection apparatus to which an ultrasonic flaw detection method for steel pipes according to an embodiment is applied.

The movement of a test carrier 11 carrying a steel pipe 1 as a test object is controlled along the inspection line 10. The steel pipe 1 is rotated around its axis at a constant speed by a plurality of rotating rollers 12 arranged on both sides. Further, a position sensor 13 is provided on the inspection line 10 to detect the moving position of the test carrier 11. Further, above the inspection line 10, an ultrasonic probe support mechanism 14 is movably provided, for example, on a support movement mechanism fixed to the ceiling of the building. A large number of ultrasonic probes 15a and 15b are attached to the lower surface of this ultrasonic probe support mechanism 14 so as to face the outer peripheral surface 4 of the steel pipe 1.

Note that the ultrasonic probes 15a, 1 of channel A and channel B at the leading position on the position sensor 13 side
5b is a sensor for controlling the moving speed and rotational speed of the steel pipe 1.

A calibration line 16 is arranged parallel to the inspection line 10, and on this calibration line 16, a calibration carrier 18 is loaded with a calibration steel pipe 17 in which an artificial defect is formed.
movement is controlled. The ultrasonic probe support mechanism 14 is moved to the inspection line 10 by the aforementioned support movement mechanism.
It can be moved arbitrarily above and on the calibration line 16 as shown by arrows in the figure.

A monitoring control device 19 is provided near the calibration line 16 to control the operation of the entire ultrasonic flaw detection device. This monitoring and control device 19 includes an ultrasonic probe 15.
a, 15b, a flaw detector 20 as a signal processing unit that detects defects and thickness, a display 21 that displays the flaw detection results, a steel pipe movement control device 22 that controls the movement of the steel pipes 1 and 17, and a printer 23 that prints out the flaw detection results. , a storage section 24 for storing flaw detection results, a computer 25 for controlling the operation of each section, and the like are housed.

FIG. 2 is a front view of the ultrasonic probe support mechanism 14. As shown in the figure, when the steel pipe 1 moves to the lower position of the ultrasonic probe support mechanism 14, each ultrasonic wave probe 15
a and 15b are controlled in position by the operation of their respective manipulators 26 so that they come into contact with the outer circumferential surface 4 of the steel pipe 1 via water. As shown in FIG. part ultrasonic probe array and the valley part 3 of the spiral groove 3
The ultrasonic probes are divided into rows of peak ultrasonic probes in channel B facing channel B.

Next, the operation of the steel pipe movement control device 22 is shown in FIG.
~Explained using FIG. 6. As mentioned above, the ultrasonic probe 15b of channel B at the leading position
b, so as shown in Fig. 5(a), the flaw detector 2
Each echo T on the surface and the bottom of the valley 3b obtained at 0
, B1 corresponds to the thickness at the valley portion 3b. In addition, the ultrasonic probe 15a of channel A
is opposed to the peak 3a of the inner circumferential surface 2, so as shown in FIG. Yamabe 3
It corresponds to the thickness at part a.

However, as shown in FIG.
When the ultrasonic probe 15a is located between the peak 3a and the valley 3b, as shown in FIG. 5(b), in addition to the echo B2 of the peak 3a, there is an echo B1 corresponding to the valley 3b. appear.

At this time, the waveform shown in FIG. 5(a) corresponding to the wall thickness measurement is obtained on the probe 15b. In addition, the probe 15
In a, the echo height B1 from the valley 3b (gate 1)
The waveform shown in FIG. 5B is obtained in which the echo height B2 (gate 2) from the peak portion 3a is detected. In this state, the echo heights B1 and B2 appearing on the probe 15b are compared, and when the difference of B1 > B2 is 1/2 or more, the rotation speed is increased, while the difference of B1 < B2 is increased. is 1/
What is necessary is to control the moving speed of the test carrier 11 carrying the steel pipe 1 and the rotation speed of the rotary roller 12 that rotates the steel pipe 1 so as to reduce the rotation speed when the steel pipe 1 is opened twice or more. FIG. 6 shows the ultrasonic probes 15a of each channel A and B,
15b is a control block diagram for measuring the thickness t of the steel pipe 1 and controlling the rotational speed and moving speed of the steel pipe 1. FIG.

Under the control of the steel pipe moving speed control device 22 configured as described above, each ultrasonic probe 15a, 15b of each channel A, B is moved to a specified peak 3a or valley on the outer circumferential surface 4 of the steel pipe 1. Faithfully follow the opposing surface of section 3b.

For example, eight mutually parallel spiral grooves 3 are formed on the inner circumferential surface 2 of the steel pipe 1. The thickness tT of the peak portions 3a of the spiral grooves 3 adjacent to each other is greater than the thickness tB of the valley portions 3b. As shown in FIG. 3, ultrasonic probes 15a and 1 are placed at positions facing each peak 3a and each trough 3b of the eight spiral grooves 3 on the outer peripheral surface 4.
5b is disposed in a position facing this outer circumferential surface 4. Each of the ultrasonic probes 15a and 15b is connected to a flaw detector 20 in the monitoring and control device 19 via a dedicated signal line.

Each of the ultrasonic probes 15a and 15b is composed of, for example, a focusing type probe, which has the highest sensitivity near its focal point, can narrow down the ultrasonic beam, and has small beam dispersion. Therefore, defects can be detected with high S/N. Further, the focal position can be easily changed by adjusting the curvature of the acoustic lens of each incorporated vibrator. The focus of each ultrasonic probe 15a corresponding to each peak 3a is adjusted to be located near the inner surface of the peak 3a, and the focus of each ultrasonic probe 15b corresponding to each valley 3b is adjusted to be located near the inner surface of the peak 3a. The focal point is adjusted to be located near the inner surface of the valley portion 3b.

[0038] Also, the ultrasonic probe 15 having this focal point
In a and 15b, the range of ultrasonic waves that are sensitively received by the vibrator is relatively narrow, so ultrasonic flaw detection can be performed in a relatively narrow range. That is, the incidence of scattered ultrasound caused by ultrasound output from other adjacent ultrasound probes is suppressed.

Each of these 16 ultrasonic probes 15a, 1
5b is independently supported by each manipulator 26 of the ultrasound probe support mechanism 14, as described above. In addition, each of the ultrasonic probes 15a, 15b does not directly contact the outer surface 4 of the steel pipe 1, but water is supplied between the ultrasonic probes 15a, 15b and the outer surface 4 by a water supply facility (not shown). Supplied. That is, since each of the ultrasonic probes 15a and 15b is disposed on the outer circumferential surface 4 through water, ultrasonic waves are smoothly input and output into the steel pipe. This measurement method is generally called the water invasion method.

[0040] The flaw detector 20 includes a transmitting circuit that sends out pulse signals at regular intervals to each of the ultrasonic probes 15a and 15b, and a receiving circuit for receiving ultrasonic waves output from each of the ultrasonic probes 15a and 15b. A plurality of receiving circuits that receive signals and a CRT display device that displays reflected waves received by each of the receiving circuits are incorporated. This flaw detector 20 also incorporates a data recording device that records reflected waves caused by defects received by each receiving circuit. Note that each ultrasonic probe 15a,
The detection sensitivity of 15b is determined by adjusting the amplification degree of each receiving circuit. Specifically, as shown in FIG. 1, a calibration steel pipe 17 having an artificial defect is used.

Next, the relationship between the detection sensitivity and noise level of the ultrasonic flaw detection system for steel pipes constructed as described above is shown in FIG. The calibration steel pipe 17 has a flaw depth (defect size) of 0.1 mm, which is smaller than the standard, and 0.3 mm, which is larger than the standard.
The measurement was performed using a total of five types of calibration steel pipes 17: mm, 0.4 mm, and 0.5 mm. In addition, the ultrasonic probes 15a and 15b used for the measurement have an oscillation frequency of 5 MHz,
The vibrator has a diameter of 8 mm and a focal length of 30 mm.

The measurement results are shown in FIGS. 8(a) and 8(b). As is clear from this measurement result, for the reference defect of 0.2 mm, the noise level when detecting flaws A and C existing on the outer circumferential surface 4 as shown in Fig. 8(a) is 46 dB. As shown in 8(b), scratches B exist on the inner circumferential surface 2,
The noise level when detecting D is 43 dB. Then, S is expressed as the ratio between the obtained detection sensitivity and the noise level.
/N can secure approximately 20 dB against external scratches A and C,
In addition, about 19 dB could be secured against internal scratches B and D. It goes without saying that as the defect size (flaw depth) increases, the defect detection sensitivity increases and the S/N also improves.

[0043] In order to confirm the above-mentioned effect, the inventor
Using the same five calibration steel tubes 17, measurements were performed using a conventional method in which the calibration steel tubes 17 were not rotated. The measurement results are shown in FIGS. 8(c) and 8(d). The ultrasonic probe used for this measurement was an angle probe with an oscillation frequency of 5 MHz, a transducer having a rectangular shape of 6 x 12, and a refraction angle set at 40 degrees. was used. Therefore, naturally, this ultrasonic probe does not have a focal point. Then, an acrylic resin was interposed between the vibrator and the outer circumferential surface 4 of the steel pipe 1, and measurement was performed by a direct contact method.

As shown in FIG. 8(c), the noise level when detecting scratches A and C existing on the outer peripheral surface 4 is 47 dB, and as shown in FIG. 8(d), the noise level when detecting scratches A and C existing on the inner peripheral surface 2 is wound B
, D is detected at a noise level of 47 dB. However, since a plurality of types of ultrasonic waves reflected at the peaks 3a, troughs 3b, and the interface between the peaks 3a and troughs 3b are incident on the vibrator, the defect detection sensitivity is significantly reduced. As a result, S is expressed as the ratio between the obtained detection sensitivity and the noise level.
/N is approximately 8 dB for external scratches A and C, and approximately 1.5 dB for internal scratches B and D. By the way, the lowest S/N limit that can be detected is said to be approximately 3 (=10 dB), and external flaws can be barely detected, but internal flaws cannot be detected at all. Therefore, it became clearer that the S/N of the example device shown in FIGS. 8(a) and 8(b) was significantly improved compared to the conventional method.

In this way, each ultrasonic probe 15a, 15
Since the S/N of the reflected wave caused by the defect obtained from b is greatly improved, even minute defects present in the peaks 3a or troughs 3b of the spiral groove 3 can be detected with high accuracy.

Further, along the outer circumferential direction of the outer circumferential surface 4 of the steel pipe 1, a focal point is set along each peak 3a and each valley 3b of the spiral groove 3, respectively. Since the dedicated moving ultrasonic probes 15a and 15b are provided, the ultrasonic waves output from each probe will not cross the adjacent peaks 3a or troughs 3b. Therefore, since the path length of the ultrasonic waves being detected does not change, the reflected waves do not move on the display screen of the CRT display device in the flaw detector 20 and are displayed as if they were stationary. . Therefore, the screen becomes very easy to monitor for the observer, and the mental burden on the observer can be reduced.

[0047] Further, as each of the ultrasonic probes 15a and 15b, a focusing type probe capable of obtaining a narrow band-shaped sound field is adopted,
Further, dedicated probes 15a and 15b are assigned to the peaks 3a and troughs 3b, respectively, and each location on the inner circumferential surface 2 is detected with a focused focus. Therefore, scattering of ultrasonic waves hitting the peaks 3a and troughs 3b can be prevented, and the S/N of reflected waves caused by defects can be further improved.

Furthermore, since the peaks 3a and the valleys 3b are measured using dedicated ultrasonic probes 15a and 15b,
It is possible to easily identify whether the defect reflected wave (echo) displayed on the CRT display device is the outer surface or the inner surface of the peak portion 3a, or the outer surface or the inner surface of the valley portion 3b.

It should be noted that the present invention is not limited to the embodiments described above. In the embodiment, each ultrasonic probe was arranged one-to-one with each peak 3a and each valley 3b, but if the width of the peak 3a and valley 3b is wide, one peak 3
Two or more ultrasonic probes 15a, 1 in a or valley 3b
5b may be provided.

[0050]

As explained above, according to the method and apparatus for ultrasonic flaw detection of steel pipes of the present invention, the ultrasonic probe disposed on the outer peripheral surface of a steel pipe having a spiral groove on the inner peripheral surface can be The relative positional relationship between the ultrasonic probe and the steel pipe is changed so that the focal point moves along the spiral groove. Therefore, the peaks and valleys of the spiral groove are detected using dedicated ultrasonic probes, and always with the best detection sensitivity. the result,
It is possible to reduce noise components caused by thickness changes as much as possible, improve S/N, and significantly improve flaw detection performance.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an entire ultrasonic flaw detection device for steel pipes according to an embodiment of the present invention;

[Fig. 2] A side view showing the ultrasonic probe support mechanism of the same embodiment device;

[Fig. 3] A schematic cross-sectional view showing the main parts of the device according to the embodiment,

[Fig. 4] A diagram showing the mounting position of each ultrasonic probe in the same embodiment device,

[Figure 5] Echo waveform diagram obtained with each ultrasound probe in the same example device,

[Fig. 6] A block diagram showing the steel pipe movement control device of the same embodiment device,

[Figure 7] Cross-sectional view of the calibration steel pipe used in the same example device,

[Fig. 8] A diagram showing the detection sensitivity characteristics of the same embodiment device and the detection sensitivity characteristics of the conventional method,

[Figure 9] Diagram showing the configuration of a steel pipe with a spiral groove,

[
Figure 10: Diagram showing the conventional ultrasonic flaw detection method,

[Figure 11
] A diagram showing a comparative test piece used in the conventional method,

[Figure 12
] A diagram showing the moving direction of an ultrasound probe in a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Steel pipe, 2... Inner peripheral surface, 3... Spiral groove, 3a... Mountain part, 3
b...Trough, 4...Outer peripheral surface, 10...Inspection line, 11...Test carrier, 12...Rotating roller, 14...Ultrasonic probe support mechanism, 15a, 15b...Ultrasonic probe, 19...Monitoring Control device, 20...flaw detector, 25...computer.

Claims (4)

[Claims] 1. An ultrasonic probe is placed opposite the outer circumferential surface of a steel pipe in which a plurality of parallel spiral grooves are formed on the inner circumferential surface, and an ultrasonic wave is applied to the steel pipe from the ultrasonic probe. In the ultrasonic flaw detection method for steel pipes, which detects defects existing on the surface and inside of the steel pipe by transmitting and receiving the The ultrasonic probe is characterized in that defects are continuously detected using the ultrasonic probe by relatively changing the positional relationship between the ultrasonic probe and the steel pipe so as to move in a spiral manner. Ultrasonic flaw detection method for steel pipes. 2. At least twice as many ultrasonic probes as the number of spiral grooves are provided along the outer circumferential direction of the steel pipe so that the focal point moves along the peaks and valleys of all the spiral grooves. 2. The method of ultrasonic flaw detection for steel pipes according to claim 1. 3. Defects existing on the surface and inside of the steel pipe are eliminated by transmitting and receiving ultrasonic waves to and from the outer peripheral surface of the steel pipe, in which a plurality of parallel spiral grooves are formed on the inner peripheral surface of the steel pipe. An ultrasonic flaw detection device for a steel pipe that detects ultrasonic flaw detection, comprising: an ultrasonic probe having at least twice the number of spiral grooves disposed along the outer circumferential direction of the outer circumferential surface of the steel pipe, and each of the ultrasonic probes. an ultrasonic probe support mechanism that supports each of the ultrasonic probes so that the focal point of each ultrasonic probe is located at the peaks and troughs of the spiral groove; A movement control mechanism that relatively changes the positional relationship between the ultrasonic probe and the steel pipe so that the focus of each ultrasonic probe moves along the peaks or valleys of each of the spiral grooves. and a signal processing unit that detects the location and scale of the defect from the received ultrasonic signals output from each of the ultrasonic probes. 4. The movement control mechanism moves the focal point of each ultrasonic probe supported by the ultrasonic probe support mechanism along the peak or valley of each spiral groove. 4. The ultrasonic flaw detection apparatus for steel pipes according to claim 3, wherein the apparatus is a steel pipe movement control device that moves the steel pipe in the axial direction while rotating the steel pipe around its axis.