JP2011180102A - Ultrasonic flaw detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To certainly and clearly detect even a fine defect occurring in the inner peripheral surface of a narrow pipe. <P>SOLUTION: Ultrasonic wave UT is output from a focusing type vibrator 31 disposed in an ultrasonic probe 30 toward the inner peripheral surface 1in of the narrow pipe 1. The incidence angle θ of the ultrasonic wave UT to the pipe 1 exceeds 45° and is 55° or smaller or 60° or smaller, and the focusing position F of the ultrasonic wave UT is on the inner peripheral surface side than the half position with respect to the thickness direction of the pipe 1. The ultrasonic wave UT is thus made to enter the pipe 1, so that defective surface echo Ep and defective tip echo Et occur certainly, thereby the defect K can be accurately detected and sized. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic flaw detection method, which is devised so that defects can be detected accurately and reliably when ultrasonic inspection is performed from the inner peripheral side of a tubular body. In particular, the present invention is suitable for inspecting fine defects generated on the inner peripheral surface side of a thin-walled tube (thin tube).

  Many types of pipes are used in various types of plants such as nuclear power plants and steam generation plants. Such pipes are regularly inspected to detect defects and, in some cases, sizing detected defects. (Dimension measurement).

As a technique for detecting and sizing defects from the inner peripheral side of the tubular body, there is a technique using an ultrasonic probe equipped with a focusing type or flat type transducer.
In other words, an ultrasonic probe is placed inside a metal tube, and ultrasonic waves generated from the transducer of the ultrasonic probe are emitted toward the inner peripheral surface of the tube, and then reflected. The ultrasonic wave (reflection echo) is received by the vibrator. From the vibrator, a flaw detection signal corresponding to the received ultrasonic wave (reflection echo) is output, and the flaw detection signal is signal-processed to display an image to detect a defect (see, for example, Patent Document 1). .

  Here, ultrasonic inspection is performed from the inner peripheral side of a thin tube (for example, about 1 mm) and a thin tube (for example, about 1 mm) with a small diameter (for example, about 20 mm in diameter), and stress corrosion cracking (SCC), etc. A conventional method for inspecting defects will be described with reference to FIGS.

8 and 9 show an example in which an ultrasonic probe 10 including a focusing type transducer 11 is arranged inside the thin tube 1. The inside of the thin tube 1 is filled with water, and an ultrasonic wave UT is emitted from the focusing vibrator 11 toward the inner peripheral surface 1 in of the thin tube 1.
FIG. 8 shows a case where a defect K is generated on the outer peripheral surface 1out side of the thin tube 1, and FIG. 9 is a case where a defect K is generated on the inner peripheral surface 1in side of the thin tube 1.

  As shown in FIGS. 8 and 9, a defect tip echo Et is generated from the tip of the defect K (the center side in the thickness direction of the thin tube 1), and a surface shape echo Es is generated from the inner peripheral surface 1in. Among these, the defect tip echo Et is received and detected by the vibrator 11 to detect the height (depth) of the defect K.

Conventionally, as shown in FIGS. 8 and 9, the focused position F of the emitted ultrasonic wave UT is set on the outer peripheral surface 1 out side of the central position in the thickness direction of the thin tube 1, and the ultrasonic wave The incident angle θ at which the UT enters the narrow tube 1 is set to about 45 °.
The incident angle θ is formed by an ultrasonic beam at the center of the ultrasonic wave UT traveling through the narrow tube 1 and a vertical line standing on the inner peripheral surface 1in at the incident position (refractive position) of the ultrasonic beam at the center. It is an angle.

FIG. 10 shows an example in which an ultrasonic probe 20 including a flat vibrator 21 is arranged inside the thin tube 1. The inside of the thin tube 1 is filled with water, and an ultrasonic wave UT is emitted from the flat vibrator 21 toward the inner peripheral surface 1 in of the thin tube 1.
FIG. 10 shows a case where a defect K is generated on the inner peripheral surface 1 in side of the thin tube 1.

  As shown in FIG. 10, the defect tip echo Et is generated from the tip of the defect K (the central side in the thickness direction of the thin tube 1), and the surface shape echo Es and the defect opening echo Eo are generated from the inner peripheral surface 1in. appear. Among these, the defect tip echo Et is received and detected by the vibrator 21 to detect the height (depth) of the defect K.

JP-A-6-148145

  In the example shown in FIG. 8, since the generation positions of the defect tip echo Et and the surface shape echo Es are separated, the defect tip echo Et is received by the vibrator 11, thereby causing the defect K generated on the outer peripheral surface 1out side. Detection and height (depth) sizing are possible.

  However, in the example shown in FIG. 9, since the defect tip echo Et and the surface shape echo Es are close to each other, the surface shape echo Es is superimposed and mixed with the defect tip echo Et. For this reason, even if the defect tip echo Et is received by the vibrator 11, it is difficult to identify the defect tip echo Et, and it is difficult to detect or size the defect K generated on the inner peripheral surface 1in side. Or the discriminability of the defect K was low.

  Further, in the example shown in FIG. 10, since the defect tip echo Et, the surface shape echo Es, and the defect opening echo Eo are close to each other, the surface shape echo Es and the defect opening echo Eo are superimposed on the defect tip echo Et.・ Mixed. For this reason, even if the defect tip echo Et is received by the vibrator 21, it is difficult to identify the defect tip echo Et, and it is difficult to detect or size the defect K generated on the inner peripheral surface 1in side. Or the discriminability of the defect K was low.

Further, in any of the examples in FIGS. 8 to 10, the defect K generated in the thin tube 1 having a thickness of about 1 mm is a fine defect, and the incident angle θ of the ultrasonic UT is as small as about 45 °. In addition, the defect surface echo in which the incident ultrasonic wave is incident on the surface of the defect K and is reflected on the surface is weak.
Since the generation of the defect surface echo is weak as described above, the defect detection using the defect surface echo is not sufficient, and the detection of the defect K and the accuracy of sizing are low. In particular, when the defect K is a fine defect, such a problem becomes remarkable.

  In view of the above prior art, the present invention provides an ultrasonic flaw detection method capable of reliably detecting and sizing defects from the inner peripheral side of the tubular body even if the defects generated on the inner peripheral surface of the tubular body are minute. The purpose is to provide.

The configuration of the present invention for solving the above problems is as follows.
In the method of performing ultrasonic flaw detection by emitting ultrasonic waves from the ultrasonic probe disposed inside the tubular body toward the inner peripheral surface of the tubular body,
Adopting a focusing type transducer as the ultrasonic probe,
The focusing position of the ultrasonic wave emitted from the vibrator is set on the inner peripheral side with respect to the thickness direction of the tubular body from the center position,
Furthermore, the incident angle at which the ultrasonic waves enter the tube body is an angle exceeding 45 °.

The configuration of the present invention is as follows.
When the emitted ultrasonic wave performs axial flaw detection located on the inner surface of the longitudinal section of the tubular body (small diameter (for example, about 20 mm) and thin wall (for example, about 1 mm)), the incident angle is set as follows. , Exceeding 45 ° and within 60 °,
When the emitted ultrasonic wave is subjected to a circumferential flaw detection located on the inner surface of the cross section of the tubular body, the incident angle is more than 45 ° and within 55 °.

The configuration of the present invention is as follows.
The vibrator is characterized in that a focusing range in which ultrasonic waves are focused is long, and the focusing range reaches a position exceeding a half position in the thickness direction of the tubular body.

According to the present invention, since the incident angle of the ultrasonic wave is large, it is possible to reliably generate a defect surface echo even if the tube is thin, and because the ultrasonic focusing position is on the inner peripheral surface side, A defect tip echo can be effectively generated at the tip of the defect.
By receiving such a defect surface echo and a defect tip echo with a vibrator, a defect generated on the inner peripheral surface side of the tubular body can be reliably detected, and the defect profile can be clearly determined. .

The block diagram which shows the ultrasonic flaw detection method which concerns on Example 1 of this invention. The block diagram which shows the ultrasonic flaw detection method which concerns on Example 1 of this invention. FIG. 3 is an image diagram illustrating image processing of a flaw detection signal obtained by the ultrasonic flaw detection method according to the first embodiment of the present invention. Explanatory drawing which shows the display method of each scope. The block diagram which shows the ultrasonic flaw detection method which concerns on Example 2 of this invention. Explanatory drawing which shows the focusing range of an ultrasonic beam. FIG. 6 is an image diagram showing image processing of a flaw detection signal obtained by an ultrasonic flaw detection method according to Embodiment 2 of the present invention. The block diagram which shows the conventional ultrasonic flaw detection method. The block diagram which shows the conventional ultrasonic flaw detection method. The block diagram which shows the conventional ultrasonic flaw detection method.

  Hereinafter, the form for carrying out the present invention is explained in detail based on an example.

FIG. 1 shows an ultrasonic flaw detection method according to Embodiment 1 of the present invention. In the figure, a thin tube 1 is a metal tube having a small diameter (for example, a diameter of about 20 mm) and a thin wall (for example, about 1 mm). The inside of this thin tube 1 is filled with water.
In this embodiment, even a minute defect K such as stress corrosion cracking (SCC) generated on the inner peripheral surface side of the thin tube 1 is detected with high accuracy.

  The ultrasonic probe 30 includes a focusing type transducer 31, and the ultrasonic probe 30 is disposed inside the thin tube 1. Then, the ultrasonic wave UT is emitted from the focusing type vibrator 31 toward the inner peripheral surface 1 in of the thin tube 1.

In this case, the focused position F of the emitted ultrasonic wave UT is set closer to the inner peripheral surface 1 in than the central position in the thickness direction of the thin tube 1, and the incident angle θ at which the ultrasonic wave UT is incident on the thin tube 1 is set. The angle exceeds 45 °.
The incident angle θ is determined by the ultrasonic beam at the center of the ultrasonic wave UT traveling through the narrow tube 1 and the vertical line standing on the inner peripheral surface 1in at the incident position (refractive position) of the ultrasonic beam at the center. The angle formed.
Thus, the setting of the focusing position F and the incident angle θ is a special technical feature in this embodiment.

The incident angle θ will be further described.
In the case of axial flaw detection, that is, as shown in FIG. 1, in the state where the emitted ultrasonic wave UT is emitted obliquely in a state where it is located in the plane of the longitudinal section of the thin tube 1, the incident angle θ is It is over 45 ° and within 60 °.
On the other hand, when circumferential flaw detection is performed, that is, as shown in FIG. 2, in the state where the emitted ultrasonic wave UT is emitted obliquely while being located in the plane of the cross section of the thin tube 1, the incident angle θ Is over 45 ° and within 55 °.
The reason why the upper limit of the incident angle is 60 ° for axial flaw detection and 55 ° for circumferential flaw detection is that when the incident angle is set so as to exceed such an upper limit, the ultrasonic wave UT is narrow tube 1. This is because a component that is reflected without being efficiently incident on the inside is generated.

  In the present embodiment, as shown in FIG. 1, a defect tip echo Et is generated from the tip of the defect K (the center side in the thickness direction of the thin tube 1), and the ultrasonic wave UT is planarized from the defect surface of the defect K. The defect surface echo Ep reflected on the surface is generated, and the surface shape echo Es is generated from the inner peripheral surface 1in.

In this embodiment, since the incident angle θ of the ultrasonic wave UT is a large angle exceeding 45 °, the component that advances in the axial direction of the thin tube 1 out of the ultrasonic wave UT incident on the thin tube 1 becomes large. The reflected ultrasonic wave UT is effectively reflected by the defect surface of the defect K, and the value of the defect surface echo Ep increases.
Further, since the focusing position F of the ultrasonic UT is set on the inner peripheral surface 1in side of the center position with respect to the thickness direction of the thin tube 1, the tip of the defect K generated on the inner peripheral surface 1in side of the thin tube 1 is set. Also, the value of the defect tip echo Et generated by the above increases.
The defect surface echo Ep and the defect tip echo Et having such a large value are received by the vibrator 31, and the flaw detection signals corresponding to the defect face echo Ep and the defect tip echo Et are output from the vibrator 31, respectively. .

On the other hand, as the incident angle θ increases, the traveling direction of the ultrasonic wave UT that travels in water from the transducer 31 toward the inner peripheral surface 1in of the thin tube 1 and the perpendicular line that stands on the inner peripheral surface 1in at the refraction position. The angle δ formed is also increased, and the distance between the position of the defect K and the vibrator 31 is increased in the axial direction.
For this reason, most of the surface shape echoes Es generated from the inner peripheral surface 1 in of the thin tube 1 are not received by the transducer 31.

  While scanning the ultrasonic probe 30 in a state as shown in FIG. 1, an ultrasonic flaw detection inspection is performed at each position of the scanning line, and a flaw detection signal at each position is stored in a processing device and processed.

FIG. 3 is an example in which the flaw detection signal output from the transducer 31 is signal-processed and displayed as an image, which are a C scope, a D scope, a B scope, and an A scope, respectively.
As shown in FIG. 4, the C scope is an image showing the inner peripheral surface 1in in a plane, the D scope is an image showing the thin tube 1 in a cross section, and the B scope is a thin tube. 1 is a vertical cross-sectional image, the A scope is an image in which the horizontal axis represents time and the vertical axis represents the amplitude of the reflected echo, and each scope display is a display mode generally used in ultrasonic flaw detection technology. It is.
In the D and B scopes, Es is an image by surface shape echo, Ep is an image of defect K by defect surface echo, and Et is an image of defect K by defect tip echo.

As can be seen from the scope image of FIG. 3, in this embodiment, the image of the defect K by the defect surface echo Ep and the image of the defect K by the defect tip echo Et can be clearly displayed. It can be clearly separated.
Therefore, the distribution image (profile) of the defect K becomes clear, and oversight of the deepest part of the defect can be reduced.

  As described above, according to this embodiment, the distribution image (profile) of the defect K becomes clear, and even a fine defect can be detected accurately, and the detected defect can be accurately sized. .

  FIG. 5 shows an ultrasonic flaw detection method according to Embodiment 2 of the present invention. In the figure, a thin tube 1 is a metal tube having a small diameter (for example, a diameter of about 20 mm) and a thin wall (for example, about 1 mm). The inside of this thin tube 1 is filled with water.

  The ultrasonic probe 40 includes a focusing type transducer 40, and the ultrasonic probe 40 is disposed inside the thin tube 1. Then, the ultrasonic wave UT is emitted from the focusing type transducer 41 toward the inner peripheral surface 1 in of the thin tube 1.

In this case, the focused position F of the emitted ultrasonic wave UT is set closer to the inner peripheral surface 1 in than the central position in the thickness direction of the thin tube 1, and the incident angle θ at which the ultrasonic wave UT is incident on the thin tube 1 is set. The angle exceeds 45 °.
In the case of axial flaw detection, the incident angle θ is greater than 45 ° and within 60 °. On the other hand, in the case of carrying out circumferential flaw detection, the incident angle θ is greater than 45 ° and within 55 °.

  Further, in this embodiment, the vibrator 41 having a characteristic that the focusing range in which the ultrasonic beam UT is focused and the ultrasonic beam is focused becomes long is employed. Moreover, according to the vibrator 41, the focusing range formed by focusing the ultrasonic wave UT entering the narrow tube 1 exceeds at least a half position in the thickness direction of the thin tube 1, for example, the outer periphery of the thin tube 1 It reaches to the surface 1out.

Here, the length Lz of the focusing range will be described with reference to FIG.
When the diameter of the transducer 41 is D, the distance from the transducer 41 to the focusing position F is Lr, the ultrasonic sound velocity is v, the ultrasonic frequency is f, and the ultrasonic beam diameter at the focusing position is d.
The length Lz of the focusing range is expressed by the following equation.
Lz = 4 ・ v ・ Lr ・ Lr / (f ・ D ・ D)
Further, the diameter d of the focused beam is expressed by the following equation.
d = v · Lr / (f · D)
Using the above relational expression, the diameter of the focused beam does not change so much, and in order to increase the focusing length, the geometrical constraints in the narrow tube are taken into account, and the frequency f, the transducer diameter D, and the focal position are increased. It is necessary to set the distance Lr appropriately.

  Returning to FIG. 5 and continuing the description, in this embodiment, as shown by the dotted line in FIG. 5, when the ultrasonic wave UT is directly incident on the defect, the transducer 41 is the same as in the first embodiment. The defect surface echo Ep and the defect tip echo Et having a large value are received, and flaw detection signals corresponding to the defect surface echo Ep and the defect tip echo Et are output.

When the ultrasonic probe 40 is scanned and reaches the position indicated by the solid line in FIG. 5, the ultrasonic wave incident on the narrow tube 1 from the inner peripheral surface 1in is reflected by the outer peripheral surface 1out in a focused state. To defect K in a focused state. For this reason, the ultrasonic wave UT is effectively reflected by the defect surface of the defect K, and the defect surface echo Ep is generated. At this time, no surface echo is generated.
The generated defect surface echo Ep is focused and travels in the same direction as the incident time in the reverse direction and is received by the vibrator 41. The vibrator 41 outputs a flaw detection signal corresponding to the defect surface echo Ep that has been reflected once on the outer peripheral surface 1out.

  While scanning the ultrasonic probe 40 in the state shown in FIG. 5, an ultrasonic flaw inspection is performed at each position of the scanning line, and a flaw detection signal at each position is stored and processed by the processing device.

FIG. 7 is an example in which a flaw detection signal output from the transducer 41 is signal-processed and displayed as an image, which are a C scope, a D scope, a B scope, and an A scope, respectively.
In the D and B scopes, Es is an image by surface shape echo, Ep is an image of defect K by defect surface echo, and Et is an image of defect K by defect tip echo.

  In the present embodiment, in the D scope, not only the image of the defect K by the defect surface echo Ep by the direct echo, the image of the defect K by the defect tip echo Et, and the image by the surface shape echo Es, but also the defect surface reflected once. An image of the defect K due to the echo Ep is also displayed.

As can be seen from the scope image of FIG. 7, in this embodiment, the image by the defect surface echo Ep and the image by the defect tip echo Et can be clearly displayed and can be clearly separated from the image by the surface shape echo Es. it can.
Further, on the D scope, an image of the defect K by the defect surface echo Ep reflected once is also displayed.
Therefore, the distribution image (profile) of the defect K becomes clearer and the oversight of the deepest part of the defect can be reduced.

  As described above, according to this embodiment, the distribution image (profile) of the defect K becomes clear, and even a fine defect can be detected accurately, and the detected defect can be accurately sized. .

  INDUSTRIAL APPLICABILITY The present invention can be applied to a case where various types of tubes are subjected to an ultrasonic flaw detection inspection in addition to a thin tube such as a heat transfer tube used in a steam generator.

DESCRIPTION OF SYMBOLS 1 Capillary 1in Inner surface 1out Outer surface 10, 20, 30, 40 Ultrasonic probe 11, 21, 31, 41 Oscillator K Defect F Focus position UT Ultrasonic Et Defect tip echo Es Surface shape echo Ep Defect surface echo Eo Defect opening echo

Claims (3)

In the method of performing ultrasonic flaw detection by emitting ultrasonic waves from the ultrasonic probe disposed inside the tubular body toward the inner peripheral surface of the tubular body,
Adopting a focusing type transducer as the ultrasonic probe,
The focusing position of the ultrasonic wave emitted from the vibrator is set on the inner peripheral side with respect to the thickness direction of the tubular body from the center position,
Further, the ultrasonic flaw detection method characterized in that an incident angle at which the ultrasonic wave enters the tube body is an angle exceeding 45 °. In claim 1,
When the emitted ultrasonic waves are flawed in the axial direction located on the inner surface of the longitudinal section of the tubular body, the incident angle is more than 45 ° and within 60 °,
An ultrasonic flaw detection method characterized in that when the emitted ultrasonic wave is subjected to circumferential flaw detection located on the inner surface of a cross section of the tubular body, the incident angle is set to exceed 45 ° and within 55 °. In claim 1 or claim 2,
Ultrasonic flaw detection, wherein the transducer has a long focusing range in which ultrasonic waves are focused, and the focusing range reaches a position exceeding a half position in the thickness direction of the tubular body. Method.

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