JPH04274756A - Ultrasonic flaw detection for pipe - Google Patents

Abstract

PURPOSE:To largely reduce change in ultrasonic wave beam width due to a defect position in a steel pipe, compensate an attenuation amount of ultrasonic waves and make uniform detection sensitivity with respect to various scanning lines. CONSTITUTION:A method for ultrasonic flaw detection of a pipe comprises steps for phase-controlling wave surfaces of ultrasonic beams 4 of a desired number of unit oscillators among a plurality of unit oscillators composing an array-type probe 1 so that the beams are focused to a scanning line 5 which is a center line of the ultrasonic beam 4 to detect flaws and for sequentially varying the desired number of unit oscillators to move a focus position of the ultrasonic beams.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an ultrasonic flaw detection method for pipe bodies (hereinafter collectively referred to as steel pipes) using ultrasonic beams, and particularly relates to an ultrasonic flaw detection method for detecting defects in pipe bodies (hereinafter collectively referred to as steel pipes) using ultrasonic beams. This article relates to an ultrasonic flaw detection method for tubular bodies that performs sensitivity compensation by beam control and ultrasonic attenuation so as to obtain the same detection sensitivity.

0002

[Prior Art] Generally, when evaluating the degree and position of defects in the ultrasonic flaw detection method for pipes, a probe that transmits an ultrasonic beam is scanned in the circumferential direction of the pipe, and the It is very important to find the maximum peak value among the heights of defect echoes reflected from the defect site.

[0003] Conventionally, in order to find the maximum peak value among the defect echoes, an inspector holds a probe and moves the probe position in the circumferential direction to find the maximum peak value of the defect echoes. In addition to the manual flaw detection method, an ultrasonic flaw detection method has been considered in which defects are detected by increasing the size of the probe and using a large diameter ultrasonic beam.

[0004] However, in the former manual flaw detection method, the scanning range of the maximum peak portion of the defect echo is originally very narrow, so the inspector needs to scan the probe with great care. Therefore, there is a problem that the flaw detection work takes a considerable amount of time and only an experienced person can increase the desired flaw detection accuracy.

On the other hand, in the case of the latter ultrasonic flaw detection method, a large-diameter ultrasonic beam is used to detect the defective area, so it is difficult to find the maximum peak value of the defect echo without particularly scanning the probe. is possible. However, since the traveling direction of the ultrasonic beam transmitted from a large probe is parallel at any position on the probe, the ultrasonic beam may be There is a problem in that the beam is dispersed and only a portion of the ultrasonic waves transmitted from the probe contributes to flaw detection.

[0006] Therefore, in order to improve the above-mentioned problems, a system has been developed that uses a large probe and arranges the transducer surface of the probe so that it follows an involute curve. U.S. Pat. No. 4,195,530). When a probe with such a transducer surface is used, the direction of the ultrasonic beam incident on the steel pipe can be kept constant, but as mentioned above, using a large probe can change the diameter of the ultrasonic beam. Since defects are detected by increasing the size of the defect, there is a problem in that the accuracy of determining the defect position is low, and this method has not yet been put into practical use.

Therefore, in recent years, as shown in FIG. 10, an array type probe 1 in which a large number of unit oscillators are arranged linearly, and a desired number i (i=
An electronic scanning type that transmits and receives ultrasonic beams from a group of unit transducers (0 to Ni-1) at once, and selects a group of i units of transducers to perform excitation scanning while sequentially shifting several transducers in a predetermined direction. When testing steel pipes 2, the ultrasonic beam transmitted from the unit transducer group is configured with an ultrasonic flaw detection device, in order to make the incident angle of the ultrasonic beam transmitted from the unit transducer group equal across all scanning lines. A method has been considered in which the phase is controlled so that the direction of the involute curve 3 coincides with the normal direction of the involute curve 3 (Japanese Patent Application Laid-Open No. 59-151057, Japanese Patent Application Laid-Open No. 61-18860). In the figure, C0 is the center of the array type probe 1, C is the center of the unit transducer group for excitation scanning, and d
is the interval of unit oscillators.

The excitation timing of each unit vibrator as described above may be controlled so that the direction of the ultrasonic beam is as shown in the figure, for example, i=0 to N-1 in the figure.
The delay time ti of the timing of exciting the unit oscillator number is expressed by the following equation. ti=i・d・sin(θj)/c

[0009] However, d is the interval between unit oscillators, θj=ta
n-1 (△dj/Yc), c is the sound speed of the propagation medium, △dj
=c−c0, Yc is the distance from the focal point on the X axis to the array type probe.

0010

[Problems to be Solved by the Invention] However, the ultrasonic flaw detection method using the array type probe 1 as described above has not yet reached the level of practical use. The following problems are thought to be the reason for this.

One method is to control the phase of the ultrasonic waves and deflect them in order to make the ultrasonic beams enter the steel pipe 2 at a constant angle of incidence. At this time, the ultrasonic beams are deflected at the center of the array probe. It is strong and attenuates depending on the deflection angle as the distance increases. In other words, since the deflection angles of the ultrasonic waves in each scanning line of the unit transducer group are different, the amount of attenuation of the ultrasonic waves is different for each ultrasonic wave of the unit transducer group.

Another problem is that when actually testing the steel pipe 2 using the array type probe 1, in order to reduce the loss of ultrasonic waves, the ultrasonic wave transmitted from the array type probe 1 is is incident on the steel pipe 2 through a contact medium such as water or resin, but
Since the distance that the ultrasonic beam emitted from each unit transducer group crosses the contact medium is not constant, the amount of attenuation of the ultrasonic wave transmitted from each unit transducer group is different.

Furthermore, as shown in FIG. 11, the wavefront of the ultrasonic wave is approximately parallel to the involute curve 3, and the normal to the wavefront has the same incident angle with respect to the steel pipe 2 at any position. However, since the distance to the steel pipe 2 of each scanning line 5, which is the center line of the ultrasonic beam 4, is different, the ultrasonic wave of each scanning line 5 may vary depending on the position of a defect, such as on the inner surface of the steel pipe. The beam width of the sound wave beam 4 will be different. This means that the detection sensitivity differs depending on the depth position of the defect.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an ultrasonic flaw detection method for a pipe body that minimizes changes in the ultrasonic beam width due to the position of a defect within a steel pipe.

Another object of the present invention is to provide a system for properly compensating the attenuation amount due to the distance difference in the propagation medium of each scanning line and the attenuation amount depending on the deflection angle, and making the detection sensitivity of each scanning line uniform. The purpose is to provide an ultrasonic flaw detection method for the body.

[0016]

[Means for Solving the Problems] First, in order to solve the above problems, the invention corresponding to claims 1 and 2 provides an ultrasonic flaw detection method for pipe bodies, which detects defects in steel pipes using an array type probe. , the ultrasonic beams of a desired number of unit transducers of the plurality of unit transducers constituting the array type probe are phased so as to be focused on a scanning line that is the center line of the ultrasonic beams. This is an ultrasonic flaw detection method for tubular bodies in which flaw detection is controlled and the focal position of the ultrasonic beam is moved while sequentially changing the desired number of unit transducer groups.

The means for focusing the ultrasonic beam on a scanning line determines the number of unit transducers to be used simultaneously so that the defect position in the scanning line is approximately equal to the near field distance, and Each unit oscillator is excited at a predetermined timing so that the ultrasonic beams of a desired number of unit oscillators are focused at a near field distance.

[0018] Next, the invention corresponding to claim 3 provides a method for transmitting data in the propagation medium of each scanning line formed by a desired number of unit oscillators out of the plurality of unit oscillators constituting the array type probe. One or both of the attenuation amount depending on the distance difference and the attenuation amount depending on the deflection angle of the ultrasonic beam of the unit transducer group is determined, and the This is an ultrasonic flaw detection method for tubular bodies that performs sensitivity correction according to the amount of attenuation.

[0019]

[Operation] Therefore, the invention corresponding to claims 1 and 2 takes the above measures, so that even if the distance to the steel pipe differs for each scanning line, the ultrasonic beam at the defect position in the steel pipe is Changes in the width can be suppressed, and therefore, even if the types of defects are different, the difference in detection sensitivity of each scanning line can be reduced.

Furthermore, in the invention corresponding to claims 1 and 2, after determining the attenuation amount depending on the distance difference in the transmission medium and the attenuation amount depending on the deflection angle of the ultrasonic wave, By correcting the sensitivity of the received ultrasonic reception signal based on the amount of attenuation, the detection sensitivity of each scanning line can be made constant.

[0021]

[Examples] Examples of the method of the present invention will be described below. In order to realize the method of the present invention, it is necessary to clarify the width of the ultrasonic beam as well as the amount of attenuation of the ultrasonic wave, which has been a problem with conventional ultrasonic flaw detection methods.

First, let us find the amount of attenuation of ultrasonic waves that depends on the distance difference within the propagation medium. Now, in FIG. 10, the coordinates of the sending point of each scanning line 5, which is the center line of the ultrasonic beam 4 sent from the unit transducer group, that is, the ultrasonic sending center point of each unit transducer group, are (△dj+△ x, Yc), the point of incidence of the scanning line 5 on the steel pipe 2 can be expressed by the coordinate point (x, y) shown in the following equation. x=△dj・y/Yc+△X
...(1)y
={-b+(b2-4・a・c)1/2}/(2・
a) …(2)

However, in the above formula, a=1+(△di/Yc)2, b=2・△X・△di
/Yc, c=△X2 −R2, R=radius of steel pipe 2, j
=0 to Nj-1, Nj = number of scanning lines. Therefore, the distance Wj in the propagation medium of each scanning line 5 can be expressed by the following equation. Wj={(△di+△X-x)2 +(Yc-y)
2 }1/2...(3) Therefore, array type probe 1
Based on the distance W0 of the central scanning line within the propagation medium,
The distance difference △Wj in the propagation medium of each scanning line is △Wj = Wj - W0
…(
4). Therefore, the distance difference △W in the propagation medium of each scanning line
The attenuation amount △G1j that depends on j is △G1j=α・△Wj
...(5)

It can be determined by: α is the attenuation constant of the propagation medium found through experiments. This means that when you select a unit oscillator group in advance, you need to know the center of the unit oscillator group, that is, the distance difference in the propagation medium of the scanning line, and then
If the sensitivity is corrected based on the attenuation amount in equation 5), the influence of the attenuation amount depending on the distance difference within the propagation medium can be removed. next,
Considering that the amount of attenuation that depends on the deflection angle of the ultrasonic wave is the directivity of each unit oscillator, it can be expressed by the following equation. △G (θj) = sin {k・d/2・sin (θj)}/{
k・d/2・sin (θj)}

...(6)
However, in the above equation, k=2πλ, λ=c/f, c: sound speed of the propagation medium, f: ultrasonic frequency, d: width of unit oscillator.

Furthermore, when ultrasonic waves are received by shifting the timing of the unit transducer, that is, so-called phase angle control, the amount of attenuation depending on the phase angle of the ultrasonic waves is expressed by the following equation. △G2j=20LOG{(△G(θj))2 }(
dB) ...(7) Therefore, by performing sensitivity correction on the received signal of each unit transducer based on the attenuation amount in the above equation (7), the influence of the attenuation amount depending on the phase angle of the ultrasound can be removed. . Incidentally, if the timing is not shifted during ultrasonic reception and the reception is performed simultaneously by M unit transducers, the following equation is obtained. △G2j=20LOG{△G(θj)・△G′(θ
j)} …(8)△G′(θj)=sin {k・d
・M/2・sin (θj)}/{k・d・M/2・s
in (θj)} Therefore, the sensitivity correction amount △Gj for each scanning line is △
Gj=△G1j+△G2j (dB)
…(9)

[0026]
It can be expressed as Therefore, if the ultrasonic reception signal received by the unit transducer group is corrected using the sensitivity correction amount ΔGj of equation (9), the sensitivity of each scanning line can be made constant.

Next, a beam control method for minimizing the difference in ultrasonic beam width between each scanning line will be explained. now,
When the half-width of an ultrasonic beam when using the array type probe 1 is investigated, the results shown in FIG. 2 are obtained. In the figure, (a) is the case where the ultrasonic waves are focused closer than the near field distance X0 based on the aperture determined by the unit transducers used simultaneously, and the range in the propagation direction with a constant beam width is Very narrow. Here, X0 = D2 /4λ
It is expressed as D is the aperture width determined by the unit vibrator group. (b) is an example in which the ultrasonic beam is focused near the near field, and the beam width of the ultrasonic beam at that time is, for example,
It remains almost constant up to X2. (c) is an example in which the beam is not focused; in this case, the beam width is constant, but the overall width is wide, so the accuracy of defect position determination is poor. (d) is an example of narrowing the aperture and not focusing. In this case, a narrow beam is obtained, but since the near field distance becomes short, the ultrasonic waves spread quickly, and the beam width at each defect position is It is difficult to make them equal.

Therefore, when considering the above experimental examples comprehensively, it can be seen that it is most effective when the defect position is focused near the near field as in (b) above. Therefore, in order to minimize the difference in the beam width of the ultrasound beam between each scanning line, it is necessary to use unit vibrations that are used simultaneously so that the defect position is approximately equal to the near field distance in the scanning line at the center of the ultrasound beam. All that is required is to determine the number of transducers and the timing to excite each unit transducer so that the ultrasonic waves are focused at a near field distance.

The method for determining the number of unit oscillators and the excitation timing of each unit oscillator will be explained below. In order for the defect position to be located at the near field distance on the scanning line, which is the center line of the ultrasound beam, the number N of unit transducers can be calculated from the aperture width D of the group of unit transducers according to the following formula. can. Now, if near sound field distance D2/4λ=W, then D=N・d

…(10)

Since the following relationship exists, the unit oscillator number N can be determined from this equation. However, W=W
0 +Wf ・Cs /Cw. W0 is the distance in the propagation medium of the scanning line at the center of the ultrasonic beam, Wf is the distance from the point of incidence to the defect, Cs is the ultrasonic sound speed in the steel pipe: 32
30 m/s, Cw is the ultrasonic sound velocity in the coupling medium, λ is the ultrasonic wavelength in the coupling medium, and d is the distance between unit oscillators.

On the other hand, timing control of a group of unit oscillators forming one beam can be determined from the following three delay times. First, in order for the wavefront of one ultrasonic beam to be incident on each surface of the steel pipe at a constant angle of incidence, the following delay time t is required.
1i is required. lm = [{d・(N-1)/2}2 +Yc2
]1/2 li = [d2 ・{(N-1)/2
−i}2 +Yc2 ]1/2 t1i=(li
-lm)/Cw
...(11) However, i = 0 ~ (N-1
). Furthermore, the following delay time t2i is required to focus the ultrasound beam on the defect location. lm = [{d・(N-1)/2}2 +W2
]1/2 li = [d2 ・{(N-1)/2-
i}2 +W2 ]1/2 t2i=(li −l
m)/Cw
...(12) However, i = 0 ~ (N-1)
It is. Furthermore, in order to control the deflection angle so that each scanning line is in the normal direction of the involute curve, the following delay time is required. i・d・sin (θj)/Cw
...(13) Therefore, if the delay time of the unit oscillator group for the j-th scanning line is tij, then tij=t1i+t2i+{i・d・sin (θ
j )/Cw} (14).

Therefore, when transmitting ultrasonic waves, the above (
14) If you excite each unit transducer while shifting it at the timing of the delay time in equation (14), and when receiving ultrasonic waves, you can receive the ultrasonic wave by shifting it at the timing of the delay time in equation (14) above. Changes in beam width can be reduced.

Next, a flaw detection apparatus to which the above-described ultrasonic flaw detection method is applied will be explained with reference to FIG. This device includes a transmission control system 20 that controls the array probe 1 to transmit ultrasound, and a reception control system that controls the reception of the ultrasound by the array probe 1 and compensates for the amount of attenuation. It consists of 30.

This transmission control system 20 is provided with a flaw detection control unit 21 that controls each part based on the arrangement of the steel pipe and the array type probe 1 and other flaw detection conditions. The unit oscillator number determining means 21a determines the number of unit oscillators to be used simultaneously so that the defect position is approximately equal to the near sound field distance in the scanning line of It has an excitation timing creation means 21b that creates delay timings for transmission and reception for several unit oscillators, and sends unit oscillator number data and transmission and reception delay timing signals to the transmission control section 22 and reception control system 30.

In this transmission control section 22, the flaw detection control section 21
In addition to the channel selection means 22a for selecting a transmission channel based on the output of the channel selection means 22a, the multi-channel pulser 23 is provided with a timing control means 22b for controlling the transmission timing of the selected channel. The unit oscillators constituting the element 1 are excited, and an ultrasonic beam is transmitted from a group of unit oscillators corresponding to a selected channel.

On the other hand, in the reception control system 30, a reception control section 31 selects a unit transducer group based on the output of the flaw detection control section 21, and adds the received signals of the selected unit transducer group. A multi-channel attenuator 32 is provided to adjust the strength of the received signals added by the reception controller 31. This multi-channel attenuation unit 32 includes a first attenuation amount calculation means 32a that calculates an attenuation amount that depends on the distance difference in the propagation medium of each scanning line, and a second attenuation amount that calculates an attenuation amount that depends on the phase angle of the ultrasonic wave. It has a sensitivity correction means 32c, etc., which performs sensitivity correction for each scanning line on the received signal obtained from the calculation means 32b and the reception control section 31 based on the two attenuation amounts.

A multi-channel receiving section 33 and a display section 34 are provided on the output side of the multi-channel attenuation section 32. The multi-channel receiving section 33 has a function of amplifying and detecting the output of the multi-channel attenuating section 32, while the display section 34 has a function of displaying flaw detection results based on the amplified and detected output of the multi-channel receiving section 33. .

Therefore, according to the configuration of the flaw detection apparatus as described above, the transmission control section 22 sequentially outputs channel selection and transmission timing signals based on the determination of the number of unit transducers by the flaw detection control section 21 and the transmission delay timing. The multi-channel pulser 23 selects a group of unit transducers based on the output of the transmission control section 22, and transmits ultrasonic waves from each unit transducer while sequentially exciting it at a predetermined timing. As a result, the phase of the ultrasonic waves transmitted from each unit transducer is controlled so that they are focused on the scanning line, so the beam width of the ultrasonic beam at the defect location in the steel pipe changes significantly, as shown in Figure 3. As a result, the difference in defect detection sensitivity between each scanning line can be reduced.

Furthermore, the received signals received by the unit transducer group are added by the reception control section 31, and then added to the multi-channel attenuation section 3.
2, and after calculating the amount of attenuation using the arithmetic expression described above, sensitivity correction is performed on the received signal according to the amount of attenuation, so that the detection sensitivity of each scanning line can be made constant.

Incidentally, FIGS. 4 to 9 are comparison diagrams of defect detection characteristics when using the conventional ultrasonic flaw detection method and when using the ultrasonic flaw detection method according to the present invention. First, FIG. 4 is a defect detection characteristic diagram of each scanning line when no focusing, deflection angle control, or sensitivity correction is performed for a slit defect on the outer surface. In addition, when detecting this defect, the results were obtained by performing mechanical scanning so that the defect echo height was maximized for each scanning line. As is clear from this figure, the defect detection sensitivity difference between each scanning line differs by more than 20 dB due to various factors, and there are many problems with defect detection accuracy.

On the other hand, FIG. 5 shows defect detection characteristics when the phase of the deflection angle of the ultrasonic beam is controlled so that the refraction angle of each scanning line is constant in the conventional method. The sensitivity difference is smaller compared to the flaw detection results, but it is still 1.
A difference of 0 dB or more remains.

On the other hand, FIG. 6 shows the result when the phase angle of the ultrasonic beam is controlled so that the refraction angle of each scanning line is constant, and the sensitivity of the attenuation amount is corrected based on the distance difference in the propagation medium. It is a defect detection characteristic diagram, and a slight difference in detection sensitivity can be seen between each scanning line. Furthermore, FIG. 7 is a defect detection characteristic diagram when the sensitivity of the attenuation amount is corrected based on the distance difference in the propagation medium and the sensitivity correction of the attenuation amount based on the phase angle of the ultrasonic beam. As is clear from FIG. 7, the effect of claim 3 makes it possible to make the detection sensitivity of each scanning line constant for slit-like defects. However, as shown in Figure 8, echo A from the outer surface of the drill hole and echo B from the slit-like defect.
There is a detection sensitivity difference of approximately 5 dB between each scanning line. This means that the detection sensitivity of each scanning line differs depending on the type of defect.

Therefore, as described above, in order to minimize the difference in the ultrasonic beam width of each scanning line, the number of unit transducers used simultaneously during transmission is set to 12, and
When the focal length of the ultrasonic wave was set to 60 mm, which is approximately equal to the near-field distance of 60 mm, the difference in detection sensitivity of the outer surface echo of the drill hole and the echo from the slit-like defect in each scanning line was as shown in Figure 9. , substantially the same detection sensitivity can be obtained between each scanning line regardless of the type of defect. Note that the present invention is not limited to the above embodiments,
Various modifications can be made without departing from the gist of the invention.

[0044]

[Effect of the invention] First, in the invention of claims 1 and 2,
Changes in the ultrasonic beam width of each scanning line can be reduced, and even if the types of defects are different, the difference in detection sensitivity between each scanning line can be reduced.

Next, in claim 3, it is possible to appropriately compensate for the amount of attenuation due to the distance difference in the propagation medium of each scanning line and the amount of attenuation that depends on the deflection angle, and it is possible to equalize the difference in detection sensitivity of each scanning line.

[0046] As a result of the above effects, the same effect as mechanically scanning a single probe in the tube circumferential direction can be obtained electrically, there is no need for manual scanning, and there is no need for manual scanning. It is possible to capture the peak of the defect echo without any problems, and the accuracy and position of the defect can be evaluated with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing an embodiment of a flaw detection apparatus to which the method of the present invention is applied.

FIG. 2 is a diagram showing the half-width of an ultrasound beam formed by an array type probe.

FIG. 3 is a state diagram when flaw detection is performed on a steel pipe by implementing the method of the present invention.

FIG. 4 is a characteristic diagram of defect detection sensitivity when beam control and sensitivity correction are not performed.

FIG. 5 is a characteristic diagram of conventional defect detection sensitivity when the ultrasonic beam is controlled so that the refraction angle of each scanning line is constant.

FIG. 6 is a characteristic diagram of defect detection sensitivity when the ultrasonic beam is controlled so that the refraction angle is constant and attenuation that depends on the distance difference within the newsprint medium is corrected.

[Figure 7] Defect detection when controlling the ultrasonic beam so that the refraction angle is constant and correcting the attenuation that depends on the distance difference within the newsprint medium and the attenuation that depends on the deflection angle of the ultrasonic beam. Characteristic diagram of sensitivity.

FIG. 8: The ultrasonic beam is controlled so that the refraction angle is constant, and the attenuation that depends on the distance difference within the telegraphic medium and the attenuation that depends on the deflection angle of the ultrasonic beam are corrected.
FIG. 3 is a diagram showing the difference in detection sensitivity between two types of defects, ie, a drill hole and a slit-like defect.

[Figure 9] Controlling the ultrasound beam by the method of the present invention,
Further, FIG. 7 is a diagram showing the difference in detection sensitivity between two types of defects, that is, a drill hole and a slit-like defect when sensitivity correction is performed for each scanning line.

FIG. 10 is a diagram showing the direction of an ultrasonic beam when testing a steel pipe using an array type probe.

FIG. 11 is a diagram showing a state in which the width of the ultrasonic beam of each scanning line differs depending on the defect position when scanning is performed using a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1...Array type probe, 2...Steel pipe, 3...Involute curve, 4...Ultrasonic beam, 5...Scanning line, 20...Transmission control system, 21...Flaw detection control section, 22...Transmission control section, 23...Multi-channel Pulsar, 31... Reception control section, 32... Multi-channel attenuation section, 33... Multi-channel receiving section, 34... Display section.

Claims (3)

[Claims] Claim 1: In an ultrasonic flaw detection method for tube bodies in which defects in a tube body are detected using an array type probe, a desired number of unit transducers constituting the array type probe is used. Performing flaw detection by controlling the phase of the wavefront of the ultrasonic beam of the unit transducer group so as to focus it on a scanning line that is the center line of the ultrasonic beam, and sequentially changing the desired number of unit transducer groups. An ultrasonic flaw detection method for tubular bodies that is characterized by moving the focal point of the ultrasonic beam. 2. The means for focusing the ultrasonic beam on a scanning line determines the number of unit transducers to be used simultaneously so that the defect position in the scanning line is approximately equal to the near field distance, and 2. The ultrasonic wave in a tubular body according to claim 1, wherein each unit transducer is excited at a predetermined timing so that the ultrasound beams of the desired number of unit transducers are focused in a near field distance. Flaw detection method. 3. In an ultrasonic flaw detection method for a tube body in which defects in the tube body are inspected using an array type probe, a desired number of unit transducers constituting the array type probe is used. Calculating either or both of the attenuation amount depending on the distance difference in the propagation medium of each scanning line serving as the center line of the unit transducer group and the attenuation amount depending on the deflection angle of the ultrasonic beam in the unit transducer group. . An ultrasonic flaw detection method for pipe materials, characterized in that sensitivity correction is performed on the ultrasonic reception signal received by the unit transducer group according to the attenuation amount.