JP2000266732A - Ultrasonic flaw detection method and flaw detection device for steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an ultrasonic flaw detection for a steel pipe having acoustic anisotropy, in the same way as for a steel pipe not having acoustic anisotropy. SOLUTION: An acoustic velocity distribution function inputting means 10 inputs a data indicating a relationship between a refraction angle and an acoustic velocity of an object to be inspected. By using a flaw detection refraction angle and beam width inputted by a flaw detection conditions inputting means 11 and the data indicating a relationship between the refraction angle and the acoustic velocity, an incidence angle/beam width calculating part 12 calculates an incidence angle and a beam width inside a linear array type probe 1 necessary for achieving these flaw detection refraction angle and beam width. A delay time calculating part 13 calculates a delay time of each transducer of the linear array type probe 1 necessary for achieving the incidence angle determined by the incidence angle/beam width calculating part 12 and provides it to an array flaw detector 15. An operating transducer number calculating part 14 calculates a number of transducers necessary for achieving the ultrasonic beam width inside the linear array type probe 1 determined by the incidence angle/ beam width calculating part 12 and provides it to the array flaw detector 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for oblique flaw detection of defects generated in a welded steel pipe using ultrasonic waves, and more particularly, to acoustic anisotropy of a steel sheet used for a welded steel pipe. The present invention relates to an oblique flaw detection method and apparatus that can accurately detect flaws with the same probe even when the flaws are different.

[0002]

[Prior Art] JIS G 0584 is used as a flaw detection method for steel pipe welds.
A method described in "Ultrasonic inspection method for arc welded steel pipe" is known. Although not directly indicated in the scope of this standard, the base material of the object to be inspected in these standards is usually a rolled steel plate. Since these steel sheets have been rolled at 900 ° C. or higher, they are elastically and acoustically isotropic. Therefore, if flaw detection is performed with a probe having a predetermined nominal refraction angle, flaw detection with a refraction angle close to the nominal value can be actually performed. However, in recent years, in order to meet the needs of steel pipes with excellent weldability and low-temperature toughness, T
Control rolled steel sheets, such as MCP steel, have been used.

[0003] Since these steel sheets are subjected to controlled rolling, a rolling texture is partially developed, and the resulting steel sheet has acoustic anisotropy exceeding a certain limit. Therefore, in performing the oblique flaw detection, the refraction angle greatly differs from the nominal value, and as a result, the beam width in the body to be inspected differs from the design value, and the sensitivity may be significantly reduced in a specific direction.

The following is a specific example. Feel
The direction of energy propagation due to the attenuation of ultrasonic waves in the child wedge
Acrylic was used for the wedge material, ignoring the correction of the drift.
Incident angle θ of probe with refraction angle of 70 °_iIs given by Snell's law
And given by the following equation (1). θ_i= Sin^-1(v_i・ Sinθ_r/ v_r) = Sin^-1(2730 ・ Sin70 ゜ / 3230)… (1) That is, θ_i = 52.58 °. Where θ_rIs the refraction angle, v_i
Is the speed of sound in acrylic, V _rIs the speed of sound in steel.

[0005]

However, when a steel pipe having acoustic anisotropy is inspected using these probes, the refraction angle changes, and the ultrasonic beam does not pass through the target inspection position. There is a problem.

If the probe having the incident angle θ _i is applied to a test object having a sound speed of 3000 m / s, the refraction angle θ _r ′ is given by the following equation (2), and θ _r ′ = Sin ⁻¹ ( v _r · Sin θ _i / v _i ) = Sin ⁻¹ (3000 · Sin 52.58 ゜ / 2730) (2) θ _r ′ = 60.78 °. Conversely, the probe at the incident angle θ _i
By applying the test subject of 0 m / s, the refraction angle theta _r "is given by _{(3), θ i" =} Sin -1 (v r · Sinθ i / v i) = Sin -1 ( 3400 · Sin52.58 ゜ / 2730) (3) θ _r ″ = 81.53 °.

As described above, when the sound speed is a value apart from 3230 m / s (including the case where there is acoustic anisotropy), the nominal refraction angle and the flaw detection refraction angle are greatly different. Obviously, this fact makes it difficult to transmit an ultrasonic beam to a desired position, but also causes the following problem. That is, if the refraction angle deviates from the nominal value, the beam divergence also changes. The spread of the beam is determined by the wavelength of the ultrasonic wave and the size of the transducer. In the case of oblique flaw detection, the size of the transducer is represented by "apparent transducer width D '". . Using the “apparent oscillator width D ′”, the zero radiation angle of the directivity angle φ _-6 when the echo height becomes -6 dB is expressed by the following equation (4). φ _-6 = Sin ⁻¹ (0.5144 · λ / D ′) (4) where l is the wavelength of the ultrasonic wave.

Further, the actual vibrator width D of the width D and the apparent transducer 'relationship, since the refraction angle theta _r and the incident angle theta _i expressed by the following equation (5), D' = Cosθ r D / Cos θ _i (5) After all, the directivity angle φ _-6 is the incident angle θ _i , the refraction angle θ _r , the wavelength λ,
The following formula (6) is used using the transducer width D. φ _-6 = Sin ^-1 (0.5144 · λ · Cosθ _i / (D · Cosθ _r ))… (6)

Now, the wavelength of the flaw detection ultrasonic wave is set to 0.8075 mm (4 MHz).
z), assuming that the transducer width is 9 mm, if the refraction angle is 70 ° in a probe with a nominal refraction angle of 70 °, φ _-6 = Sin ^-1 (0.5144 ・ 0.8075 ・ Cos52.58 ° / (9 ・Cos70 °)), φ _-6 = 4.7 °. However, when the refraction angle of this probe with a nominal refraction angle of 70 ° becomes 60.8 ° (that is, the sound speed of the steel plate is about 3000 m / s), φ _-6 = Sin ^-1 (0.5144 ・ 0.75 ・ Cos52.58 ° / (9 · Cos 60.8 °)), f ₋₆ = 3.1 °, and the probe with the nominal refraction angle of 70 ° has a refraction angle of 81.5 ° (that is, the sound velocity of the steel sheet is about 34
00m / s), φ _-6 = Sin ^-1 (0.5144 · 0.85 · Cos 52.58 ° / (9 · Cos 81.5 °)), so that φ- ₆ = 11.5 °.

As described above, since the refraction angle deviates from the nominal value due to the change in the speed of sound, and the beam spread changes accordingly, it can be seen that the sensitivity significantly changes.

In addition, the conventional method has the following difficulties in addition to the above problems. In other words, the amount of steel pipe to be produced is in line with demand.
Often the outer diameter changes. Each time, the flaw detection conditions such as the refraction angle change, so that a probe replacement operation occurs, and the ultrasonic flaw detection line may become a neck process in consideration of the entire process.

The present invention has been made in view of the above circumstances, and a method of performing ultrasonic flaw detection on a steel pipe having acoustic anisotropy in the same manner as on a steel pipe having no acoustic anisotropy. It is an object to provide a device. More specifically, since the test object has acoustic anisotropy, the speed of sound changes depending on the propagation direction, and even when the flaw detection refraction angle is significantly different from the nominal refraction angle, flaw detection can be performed at a predetermined refraction angle. It is an object of the present invention to provide an ultrasonic flaw detection method and apparatus capable of performing flaw detection with the same sensitivity without a difference in the spread of ultrasonic waves even in a relationship between a refraction angle and an incident angle different from the case of a normal rolled material.

Another object of the present invention is to provide a flaw detection method and apparatus capable of performing flaw detection without changing a probe even if the thickness or outer diameter of a test object flowing through an ultrasonic flaw detection line of a steel pipe changes. I do.

[0014]

A first means for solving the above-mentioned problem is an ultrasonic flaw detection method for detecting a defect generated in a welded steel pipe having acoustic anisotropy, wherein the steel sheet constituting the steel pipe is provided. The relationship between the incident angle and the refraction angle is determined from the sound velocity distribution function of, and ultrasonic waves are transmitted at a predetermined incident angle and beam width using a linear array type probe so as to follow the relationship, and the specified refraction angle and An ultrasonic flaw detection method for steel pipes, wherein flaw detection is performed with a beam width.

A linear array type ultrasonic probe oscillates transducers of a transducer group installed therein sequentially from one side with a delay time, so that various types of transducers different from the surface on which the transducers are installed are provided. An ultrasonic wave having a wavefront in a direction can be generated. Therefore, even if the sound speed of the test object is different from the standard one due to acoustic anisotropy or the like, the incident angle can be changed, and the refraction angle can be set to a desired angle. Furthermore, the width of the ultrasonic beam can be changed by changing the number of transducers that oscillate the ultrasonic wave, and the resulting spread of the ultrasonic beam can be set to a desired angle. That is, in this method, flaw detection with the same refraction angle and beam spread is always possible even if the sound speed of the test object changes.

At the same time, flaws of various refraction angles can be detected with one probe, so that a single probe can be used for any object having any outer diameter and thickness. In the ultrasonic inspection line, the time for exchanging the probe can be saved.

A second means for solving the above-mentioned problems is as follows:
An ultrasonic flaw detector for detecting defects generated in a welded steel pipe having acoustic anisotropy. The ultrasonic flaw detector is capable of changing an effective oscillator width and an incident angle by changing a delay time between an operating oscillator and each oscillator. A linear array type probe that can be used, a sound velocity distribution setting means for giving a sound velocity distribution function of a steel sheet constituting a steel pipe with respect to a refraction angle, and a flaw detecting device for detecting a flaw at a prescribed refraction angle and beam width based on the sound velocity distribution function. A first computing unit for calculating an incident angle and a beam width of a linear array type probe, and a delay time of each transducer for oscillating ultrasonic waves in an incident angle direction by the linear array type probe. Second to calculate
And a third calculator for calculating the number of operating transducers for providing a predetermined beam width and beam spread of ultrasonic waves used for flaw detection
An ultrasonic flaw detector for steel pipes (claim 2), comprising:

In the present means, the sound velocity distribution setting means inputs a sound velocity distribution function of the steel sheet with respect to the refraction angle. Then, the first computing unit calculates the sound velocity distribution function of the steel sheet from
Calculate the incident angle and beam width of the linear array probe.
The second computing unit calculates the delay time of each transducer in the linear array so that the linear array probe can obtain an ultrasonic wave at the obtained incident angle. The third computing unit is used to obtain the obtained beam width and beam spread.
Determine the number of operating transducers in the linear array probe.
Then, the determined number of transducers are excited based on the determined delay time of each transducer in the linear array. Thereby, oblique flaw detection can be performed at a predetermined refraction angle and beam width.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiment, a case will be described as an example in which a welded portion of a welded steel pipe of a longitudinal joint having acoustic anisotropy is detected by a linear array type ultrasonic probe. First, for comparison, FIG. 8 shows an example of flaw detection using a conventional angle beam probe.

In this example, the steel pipe 31 to be inspected is
Thickness and outer diameter are 30.2mm and 457.2mm, respectively. In addition, when this steel pipe is subjected to flaw detection at a position where the refraction angle is 70 ° and the distance (PWD) between the probe 32 and the welded part 34 is 80 mm, as shown in FIG. Since the ultrasonic beam 33 is vertically incident on the portion, a defect echo can be detected with a high detection rate.

In this embodiment, a linear array type probe as shown in FIG. 1 is used instead of the oblique probe in FIG. In FIG. 1, 1 is a linear array probe, 2 is a transducer, 3 is an ultrasonic beam, and 4 is a sound absorbing material. The linear array type probe is well known, but FIG.
It is assumed that the linear array type probe 1 shown in Fig. 1 has an acrylic wedge and the vibrator 2 has an inclination of 37.42 degrees with respect to the flaw detection surface. Also, the vibrator row is composed of about 20 vibrators 2, and the distance between the vibrators 2 is 1 mm.

By exciting each of the transducers 1 with a time difference, the angle of the wavefront of the ultrasonic beam 3 can be changed, and therefore, the incident angle of the ultrasonic wave incident on the object to be measured is changed. be able to. Note that a sound absorbing material 4 is provided in the wedge of the linear array type probe 1 so as to absorb sound waves reflected on the end faces of the wedges so that the sound waves irregularly reflected do not become noise sources. The speed of sound in the wedge is 2730
m / s.

FIG. 2 is a diagram showing a state in which an object to be inspected having no acoustic anisotropy is detected by this linear array type probe. In the following drawings, the same reference numerals are given to the same components as the components shown in the figure numbers smaller than that figure, and the description is omitted. In FIG. 2, 5 is a delay circuit, 6 is a wedge, 7 is an ultrasonic wave front in the wedge, 8 is a test object,
Reference numeral 9 denotes an ultrasonic beam inside the object.

In FIG. 2, (a) shows the dependence of the speed of sound on the angle of refraction. Since there is no acoustic anisotropy, the speed of sound is constant regardless of the angle of refraction. When detecting such a material, as shown in (b), the delay circuit oscillates the respective vibrators 2 at the same time without adding a delay time so that the incident angle of the ultrasonic wave is 52.58 °. Can be
According to Snell's law, ultrasound can be transmitted and received at a refraction angle of 70 °. At this time, if the number of transducers 2 is selected so that the ultrasonic beam width in the wedge becomes 9 mm,
As can be calculated from (Equation 6), the -6 dB directivity angle φ _{- 6 of the} ultrasonic wave in the body to be inspected is-= 4.7 °, which is 1/4 to 3/4 in the thickness direction.
Flaw depth can be detected.

Next, FIG. 3 shows an example of a state in which an object to be inspected having acoustic anisotropy is detected using this linear array type probe. In this case, due to acoustic anisotropy,
It is assumed that the relationship between the speed of sound and the angle of refraction is as shown in FIG. At this time, the sound speed in the direction of the refraction angle of 70 ° is 34
Since it is 00 m / s, the delay time given to each transducer 2 by the delay circuit 5 is changed so that the incident angle of the ultrasonic wave becomes 48.98 ° as shown in FIG. Thereby, according to Snell's law, ultrasonic waves can be transmitted and received at a refraction angle of 70 °. The actual delay time Dt between adjacent transducers can be calculated by the following equation. Δt = d · Cos (δθ) / V _wedge (7) where V _wedge is the speed of sound in the _wedge , d is the interval between the transducers, and Δθ
Is the difference between the angle between the normal to the transducer surface and the propagation direction of the ultrasonic wave.

[0026] Therefore, this case is Dt = 3.66 × 10 ^-7 sec delay time, Dt = 3.66 × 10 ^over closer to the object to be inspected in order is the earliest excitation vibrators farther from the object to be inspected ⁷ sec
Excited with a delay. Further, if the width of the transmitted ultrasonic beam is set to 10 mm, the beam spread in the body to be inspected becomes Φ _{- 6} = 4.6 °, and the same portion as when there is no anisotropy can be detected.

Next, FIG. 4 shows an example of a state in which a test object having another acoustic anisotropy is detected by using this linear array type probe. In this case, it is assumed that the relationship between the speed of sound and the angle of refraction is as shown in FIG. At this time, since the sound velocity in the direction of the refraction angle of 70 ° is 3000 m / s as shown in the figure, the delay time given to each transducer 2 by the delay circuit 5 is changed as shown in FIG. °. Thereby,
According to Snell's law, ultrasonic waves can be transmitted and received at a refraction angle of 70 °.

The actual delay time Dt between adjacent transducers is
It can be calculated by equation (7). In this case, Dt = 3.64 × 10 ^-7 sec
Dt = 3.64 × 10 ^-7 se in the order that the transducer closer to the test object is excited first
Excited with a delay of c. Further, if the width of the transmitted ultrasonic beam is set to 8 mm, the beam spread in the body to be inspected is Φ _-6 = 4.5 °, and the same portion as when there is no anisotropy can be detected.

FIG. 5 is a block diagram showing a device configuration as an example of an embodiment of the present invention for realizing such a flaw detection method. 5, reference numeral 10 denotes sound velocity distribution function input means, 11 denotes flaw detection condition input means, 12 denotes an incident angle / beam width calculator, 13 denotes a delay time calculator, 14 denotes a working oscillator number calculator, and 15 denotes an array flaw detector. It is.

The sound velocity distribution function input means 10 has a function of inputting data indicating the relationship between the refraction angle of the test object and the sound velocity. Actually, numerical data may be input manually or data may be transferred from a host computer. The flaw detection condition input means 12 sets flaw detection conditions (the outer diameter and thickness of the inspection object, the flaw detection site, the flaw detection angle, the number of flaw detection skips, the beam width, and the like).

The incident angle / beam width calculation unit 12 receives the flaw detection refraction angle, the beam width (inside the non-inspection body) input by the flaw detection condition input unit 11, and the data indicating the relationship between the refraction angle and the sound speed. Is used to calculate the incident angle and the beam width in the linear array type probe 1 to obtain these flaw detection refraction angles and beam widths. These calculations include Snell's law,
The relational expression as shown in Expression (6) is used.

For example, given data indicating the relationship between the refraction angle and the speed of sound as shown in FIG.
The beam width calculator 12 calculates the correspondence between the incident angle and the refraction angle as shown in FIG. 6B according to the sound speed in the wedge of the probe used. For this, Snell's law is used. Then, when the flaw detection refraction angle is given from the flaw detection condition input means 11, the corresponding incident angle is obtained. of course,
The incident angle may be obtained from the given refraction angle and the condition of the probe by using the relationship of (a) and Snell's law, without previously obtaining the correspondence as in (b).

The delay time calculator 13 calculates the delay time of each transducer of the linear array type probe necessary to obtain the incident angle obtained by the incident angle / beam width calculator 12, and calculates the delay time of the array flaw detector. Give to 15. For example, equation (7) is used to calculate the delay time.

The number-of-operating-vibrators calculating section 14 calculates the number of vibrators necessary for obtaining the ultrasonic beam width in the linear array type probe 1 obtained by the incident angle / beam width calculating section 12. To the array flaw detector 15. Array flaw detector 15
Using these values, the angle of incidence and the beam width of the linear array probe 1 are controlled to perform flaw detection.

FIG. 7 shows an example of the detailed structure of the array flaw detector. In FIG. 7, 16 is a trigger signal (transmission signal) generator, 17 is a transmission electronic switch group, 17 'is a reception electronic switch group, 18 is a transmission delay circuit group, 18' is a reception delay circuit group, 19 Is a pulser group, 20 is a preamplifier group, 21 is an adder, 22 is a variable amplifier, 23 is a gate,
24 is an echo height calculator, and 25 is a judgment means.

The trigger signal generator 16 generates a signal at the transmission timing of the ultrasonic wave. The signal is sent to the transmission electronic switch group 17. At this time, the transmission electronic switch 19 is turned on only for the number of vibrators calculated by the working vibrator number calculation unit 14, and is off for the rest. When the transmission electronic switch group 17 is turned on, the transmission signal is sent to the transmission delay circuit 18 where the transmission signal is delayed by the delay time of the excitation timing of each transducer. The delay time of the transmission signal is determined by the value calculated by the delay time calculator 13.

The transmission signal delayed by a predetermined time is sent to the transmitter group 19. The transmitter group 19 transmits a high-voltage pulse to each vibrator 2 at the timing when the transmission signal is transmitted. The high voltage pulse is converted into an ultrasonic wave by each transducer 2, and the ultrasonic wave is transmitted from the linear array probe 1 in a direction according to the Huygens principle. The transmitted ultrasonic wave 9 propagates through the test object 8 and, if there is a reflector, returns to the linear array probe 1 and is converted into an electric signal by the transducer 2.

Each of the received electric signals is amplified by a preamplifier group 20, passed through a receiving electronic switch group 17 ', guided to a receiving delay circuit group 18', and added by an adder 21 to the respective signals. You. At this time, in the reception electronic switch group 17 ', the one corresponding to the transmission electronic switch group 17 which is on is on, and the others are off. Also, the receiving delay circuit group 18 '
Is applied so that the ultrasonic wave returned to the linear array probe 1 is received at the same angle as the incident angle,
This is the same as the delay time given to the transmission delay circuit 18.

Therefore, the output of the adder 21 is an ultrasonic signal which is incident on the linear array probe from the test object 8 at the same angle as the incident angle. The signal leaving the adder 21 is
As with a normal ultrasonic flaw detector, a signal from only the flaw detection site is extracted by a gate 23 via a variable amplifier 22. And
The echo height calculating means 24 detects the value of the maximum reflected echo, and the judging means 25 judges the presence or absence of a defect.

[0040]

As described above, according to the present invention,
Even if the test object has acoustic anisotropy and there is a sound velocity distribution depending on the propagation direction, it is necessary to calculate the relationship between the incident angle and the refraction angle specific to the test object using the sound velocity distribution function. It is possible to calculate the incident angle for flaw detection at a large flaw detection refraction angle.
In addition, since a flaw is detected using a linear array type probe that can generate ultrasonic waves in various directions by giving an appropriate delay time to generate ultrasonic waves at the incident angle, acoustic anisotropy is reduced. Even if different, a single probe can perform flaw detection similar to a normal steel plate.

Furthermore, by making the number of transducers used to oscillate ultrasonic waves variable, the apparent transducer width can always be equalized even if the refraction angle changes. Therefore, flaw detection can always be performed with a constant spread of ultrasonic waves, so that there is an effect that defects are not overestimated or underestimated.

Further, when the present invention is applied to automatic flaw detection of a joint weld or the like in a steel pipe manufacturing process, even if the shape (for example, wall thickness / outer diameter ratio) of a product flowing in a line changes, the probe can be used. Since no replacement is required, inspection efficiency is also improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a linear array probe.

FIG. 2 is a diagram illustrating a state in which a test object having no acoustic anisotropy is detected using a linear array probe.

FIG. 3 is a diagram showing an example of a state when a test object having acoustic anisotropy is detected using a linear array probe.

FIG. 4 is a diagram showing an example of a state when a test object having another acoustic anisotropy is detected using a linear array probe.

FIG. 5 is a block diagram showing a device configuration as an example of an embodiment of the present invention.

FIG. 6 is a diagram showing data indicating a relationship between a refraction angle and a sound speed, and a corresponding relationship between a refraction angle and an incident angle.

FIG. 7 is a diagram showing an example of a detailed structure of the array flaw detector.

FIG. 8 is a diagram showing an example of flaw detection using a conventional oblique probe.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Linear array type probe, 2 ... Transducer, 3 ... Ultrasonic beam, 4 ... Sound absorbing material, 5 ... Delay circuit, 6 ... Wedge, 7 ... Ultrasonic wave front in a wedge, 8 ... Test object, 9: Ultrasonic beam inside the object to be inspected, 10: Sound velocity distribution function input means, 11: Flaw detection condition input means, 12: Incident angle / beam width calculation unit, 13 ...
Delay time calculation unit, 14: number of operating oscillators calculation unit, 15: array flaw detector, 16: trigger signal (transmission signal) generator,
17: transmission electronic switch group, 17 ': reception electronic switch group, 18: transmission delay circuit group, 18': reception delay circuit group, 19: pulser group, 20: preamplifier group, 21
... Adder, 22 ... Variable amplifier, 23 ... Gate, 24 ... Echo height calculator, 25 ... Determining means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Matsufuji 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Takeo Shimizu 1-2-1, Marunouchi, Chiyoda-ku, Tokyo F-term (reference) in Nippon Kokan Co., Ltd. 2G047 AA07 AB01 AB07 BB02 BC07 EA10 GB02 GF17 GF22

Claims (2)

[Claims] An ultrasonic flaw detection method for detecting a defect occurring in a welded steel pipe having acoustic anisotropy, wherein a relation between an incident angle and a refraction angle is obtained from a sound velocity distribution function of a steel plate constituting the steel pipe, and the relation is obtained. Ultrasonic flaw detection method for a steel pipe, wherein ultrasonic waves are transmitted at a predetermined angle of incidence and beam width using a linear array type probe and flaw detection is performed at a prescribed angle of refraction and beam width. . 2. An ultrasonic flaw detector for detecting a defect generated in a welded steel pipe having acoustic anisotropy, wherein an effective vibrator width and incidence are changed by changing a delay time between an operating vibrator and each vibrator. A linear array type probe whose angle can be changed, a sound velocity distribution setting means for giving a sound velocity distribution function of a steel plate constituting a steel pipe with respect to a refraction angle, and a prescribed refraction angle / beam width based on the sound velocity distribution function. The first calculator for calculating the incident angle and beam width of the linear array type probe for detecting flaws, and the respective vibrations for oscillating ultrasonic waves in the direction of the incident angle with the linear array type probe A second calculator for calculating the delay time of the transducer, and a third calculator for calculating the number of operating transducers for providing a predetermined beam width and beam spread of ultrasonic waves used for flaw detection. Inspection equipment for steel pipe .