JP2010043989A - Defect height estimation method by ultrasonic flaw detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a defect height estimation method by ultrasonic flaw detection capable of precisely estimating a defect height of planar defects present inside a body to be inspected. <P>SOLUTION: In the defect height estimation method by ultrasonic flaw detection, ultrasonic waves are transmitted from an ultrasonic probe arranged on the surface of the body to be inspected to the interior of the body to be detected and defect height of planar defects existing inside the body to be inspected is estimated from the waveform of reflection waves reflected from a reflection source. In the defect height estimation method, a sensitivity calibration level Ac is set in advance by performing ultrasonic flaw detection by a test piece for calibration having a reflection source with a surface in the inside, defect echoes of planar defects are detected by transmitting ultrasonic waves from the ultrasonic probe to the body to be inspected, and defect height of planar defects is estimated from the detected defect echoes by a calculation formula having, as coefficients, the reflection area of the test piece for calibration, a sensitivity calibration level, and the diameter of ultrasonic beams at a detection position of planar defects. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a defect height estimation method by ultrasonic flaw detection that detects a planar defect existing inside an object to be inspected by using an ultrasonic wave, and more particularly, an ultrahigh defect height estimation method that accurately estimates a defect height of a planar defect. The present invention relates to a defect height estimation method by acoustic flaw detection.

  In general, ultrasonic flaw detection is widely used in various industrial fields as one of non-destructive inspection methods for detecting internal defects of an object to be inspected. Defect detection by ultrasonic flaw detection is performed using a phenomenon in which ultrasonic waves are reflected by defects. This is because an ultrasonic probe that transmits and receives ultrasonic waves is placed on the surface of the object to be inspected, ultrasonic pulses are transmitted from the ultrasonic probe, and the reflected echoes are received by the ultrasonic probe. . The received reflected echo is signal-processed, and the presence / absence of a defect inside the object to be inspected is determined based on the presence / absence of the reflected echo having a predetermined height or higher. At this time, as shown in FIG. 15 (a), one probe 1A or 1B that transmits and receives ultrasonic waves is one probe method, and as shown in (b), transmission and reception are separately performed. A method using two probes 1a and 1b is called a two-probe method (tandem method). Such an ultrasonic pulse flaw detection method is often used particularly when detecting a surface defect of a welded portion of a metal material, and this is used for an ultrasonic flaw detection method (JIS Z3060-2002) of a steel welded portion of Japanese Industrial Standard. Are listed. Then, the position of the defect, the defect length, and the defect height are determined based on the position of the reflection source of the reflection echo obtained by ultrasonic flaw detection, the echo height, and the like.

  Regarding the measurement of the defect length, measurement methods such as an L-line detection method and a 6 dB down detection method (JIS Z3060) are standardized. On the other hand, as an evaluation method of the defect height in the plate thickness direction which is effective for life diagnosis, a method using an end echo method, a TOFD method, or the like can be given. In the end echo method, as shown in FIG. 13B, when an ultrasonic wave is incident on the planar defect 7 obliquely from the ultrasonic probe 1, a reflected echo as shown in FIG. Waveform is obtained. The position showing the peak of this reflected echo represents the upper and lower ends of the defect. The height of the defect is determined based on the beam paths from the ultrasonic probe to the upper and lower ends of the defect and the refraction angle of the ultrasonic probe. In the TOFD (Time of Flight Diffraction) method, as shown in FIG. 14, a transmitting probe 1a and a receiving probe 1b are arranged to face each other at a predetermined distance, and the object to be inspected is transmitted from the transmitting probe 1a. When an ultrasonic wave is transmitted, the surface wave that propagates directly on the surface of the object to be inspected by the diffusion of the ultrasonic wave, the diffracted wave or scattered wave that propagates through the tip of the defect, and the reflected wave propagates on the back surface. The incoming bottom surface reflected wave is received by the receiving probe 1b. Among these, a diffracted wave or scattered wave from the tip of the planar defect is detected, and the defect height is measured geometrically based on the propagation time and the distance between the incident points. In the reflection echo method, the sensitivity of the reflection echo is calibrated. Sensitivity calibration is calibration for detecting a reflection echo of a predetermined level from a pseudo defect serving as a reference by performing ultrasonic flaw detection with a test body in which the propagation speed of an ultrasonic pulse and the size of a reflection source are known in advance.

  Here, a specific example of a conventional method for detecting a planar defect by ultrasonic flaw detection is shown in FIG. First, assuming the position of the planar defect of the inspection object and the direction of progress (S51), the flaw detection refraction angle of the probe by the ultrasonic flaw detection method (UT) is selected (S52). Before actually inspecting the object to be inspected, sensitivity calibration is performed using a calibration specimen. The calibration specimen is preliminarily provided with a pseudo defect such as a horizontal hole, and sensitivity calibration is performed based on the reflected echo to set a defect detection level (S54). Then, flaw detection is performed using an ultrasonic probe (S55), and a defect echo is detected based on the obtained reflection echo (S56). The defect length L is obtained from the defect echo by the above-described method, and the maximum echo height A is obtained. As shown in FIG. 16, the defect height H recognizes a reflected echo based on a preset detection level as a defect echo, and determines from the maximum echo height A based on a correlation diagram between the echo height and the defect height. Calculate (S57). As shown in FIG. 11, the correlation diagram between the echo height and the defect height is made up of the correlation between the defect height and the echo height in a predetermined ultrasonic wave, and has a form depending on the plate thickness. FIG. 11A shows a case where 2 MHz ultrasonic waves are used, and FIG. 11B shows a case where 5 MHz ultrasonic waves are used.

As described above, in the edge echo method and the TOFD method, the echo detected for evaluating the defect height of the planar defect is a diffracted wave from the defect edge and is very weak. Therefore, considerable experience and skill are required to accurately obtain a diffracted wave while distinguishing it from other noises. In particular, noise identification with a high noise material such as SUS and echo identification with a minute defect have been difficult.
Therefore, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2007-71755), flaw detection conditions are set based on the material of the welded portion and the groove conditions, and signals are obtained based on waveform data obtained by ultrasonic flaw detection. Perform processing, determine the characteristic value obtained by this signal processing, and compare this signal processing result with the information divided into the defect detection result and material noise signal obtained based on the same signal as this signal processing in advance Thus, a method for discriminating whether a detection signal is a defect detection signal or a material noise signal and evaluating a defect position and a depth based on the identified defect detection signal is disclosed.

JP 2007-71755 A

However, in the conventional ultrasonic flaw detection method represented by Patent Document 1 or the like, if the defect existing inside the inspection object is a planar defect having a certain area, an error is caused in the estimation result of the defect height. There was a problem that was large. This was calculated based on the correlation diagram between the echo height and the defect height when estimating the echo height, but when the echo was originally reflected from a planar defect, the echo height was calculated. Since it depends not on the defect height but on the reflection area of the planar defect, there is a large error in estimating the defect height based only on the echo height, and it is difficult to accurately evaluate the defect height.
Accordingly, the present invention provides a defect height estimation method by ultrasonic flaw detection that makes it possible to accurately estimate the defect height of a planar defect existing inside an object to be inspected in view of the above-described problems of the prior art. For the purpose.

Therefore, in order to solve such a problem, the present invention transmits ultrasonic waves from the ultrasonic probe arranged on the surface of the inspection object to the inside of the inspection object, and based on the reflected wave waveform reflected from the reflection source. In the defect height estimation method by ultrasonic flaws for estimating the defect height of the planar defects present inside the inspection object,
In advance, the sensitivity calibration level is set by performing ultrasonic flaw detection using a calibration specimen in which a reflection source having a surface is provided,
After detecting an echo of a planar defect by transmitting an ultrasonic wave from the ultrasonic probe to the object to be inspected,
Using a calculation formula having coefficients of the reflection area of the calibration specimen, the set sensitivity calibration level, and the ultrasonic beam diameter at the detection position of the planar defect, The defect height is estimated.

According to the present invention, in the estimation of the defect height of the planar defect, in addition to the information of the defect echo height, the reflection area of the calibration specimen, the sensitivity calibration level, and the configuration of the ultrasonic probe (specifications) By using the ultrasonic beam diameter obtained from (2), it becomes possible to estimate the height of the surface defect depending on the reflection area with high accuracy.
Compared with other defect height measurement methods such as the edge echo method and the TOFD method, it is more effective in evaluating the defect height at a microcrack and is not required to detect a weak diffracted wave. This is effective for evaluating the height of defects in noise materials. Therefore, no special inspector skill is required, and the defect height that is important for the life evaluation can be accurately estimated from the echo height information, so that the reliability of the inspection is improved.

In the calculation formula, when the defect length obtained from the defect echo is shorter than the ultrasonic beam diameter, the defect length is used as the ultrasonic beam diameter.
As described above, when the defect length of the planar defect is shorter than the ultrasonic beam diameter, the defect height can be estimated with higher accuracy by using the defect length as the ultrasonic beam diameter. . In addition, when the defect length of the planar defect is equal to or larger than the ultrasonic beam diameter, the ultrasonic beam diameter is used.

Further, the reflection source provided in the calibration specimen is a flat bottom hole or a slit.
In this way, by using a flat bottom hole or slit as a reflection source provided on the calibration specimen, it is possible to easily form a reflection source having a surface at least partially on the calibration specimen. It is.

Furthermore, the ultrasonic beam diameter is determined by detecting the ultrasonic beam directivity angle obtained from the diameter of the ultrasonic probe, the frequency of the ultrasonic wave, and the speed of sound of the inspection object, and the defect echo. It is calculated from the ultrasonic beam path length at the position.
Thereby, an ultrasonic beam diameter can be calculated | required correctly and the estimation precision of defect height can be improved further.

  As described above, according to the present invention, in the estimation of the defect height of the planar defect, in addition to the information of the defect echo height, the reflection area of the calibration specimen, the sensitivity calibration level, and the ultrasonic probe By using the ultrasonic beam diameter obtained from the configuration (specification), it is possible to estimate the defect height of the planar defect depending on the reflection area with high accuracy. In addition, since no special inspector skill is required, the defect height that is important for life evaluation can be accurately estimated from the echo height information, so that the reliability of the inspection is improved.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
The present embodiment shows a method for detecting a planar defect existing inside an inspection object by ultrasonic flaw detection and estimating the defect height. As an object to be inspected, it is widely used in parts, structures, and assemblies that have a possibility of having a planar defect inside, and the position and direction of the planar defect can be assumed to some extent. Examples include a turbine blade implantation portion, a tenon portion, and a welded portion. The ultrasonic flaw detection method used in the present embodiment is an ultrasonic pulse flaw detection method. One probe method, two probe methods (tandem method), and a tandem array method in which a plurality of probes are arranged in an array. Any may be sufficient, and it selects suitably according to a to-be-inspected object. Similarly, any one of the oblique flaw detection and the vertical flaw detection is appropriately selected based on the shape of the object to be inspected, the position of the planar defect, the progress direction, and the like.

With reference to FIG. 1, the processing procedure of the defect height estimation method according to the embodiment of the present invention will be described together with its specific configuration.
First, a planar defect inside the object to be inspected is assumed based on design conditions including the stress of the object to be inspected and past crack occurrence cases (S1). When the object to be inspected is a welded part, it is assumed from the welding conditions. Then, a flaw detection refraction angle of the ultrasonic probe (probe) corresponding to the assumed position and progress direction of the planar defect is selected (S2).

  2 and 3 show an example of the ultrasonic flaw detection method used in this embodiment. FIG. 2 shows a case in which the object to be inspected is a turbine, and FIG. Assuming the position of the crack 7 and the direction of propagation from the shape and stress of the blade implantation groove 511 provided in the disk part 51 of the turbine, ultrasonic waves are incident in a direction substantially perpendicular to the surface of the assumed planar defect 7. Thus, the flaw detection refraction angle of the ultrasonic probe 1 is selected. In this case, oblique flaw detection is used. Since the ultrasonic probe 1 is placed in contact with the surface of the inspection object, a pedestal 3 having a predetermined angle is interposed between the inspection object 51 and the ultrasonic probe 1 as necessary. FIG. 2B shows a case where the crack 7 generated in the tenon portion into which the shrouds 521 and 522 of the blade 52 are fitted is detected. In this case, the ultrasonic probe 1 is installed so that the ultrasonic wave is incident on the assumed crack 7 at a substantially right angle from the tenon portion. Here, vertical flaw detection is used.

  FIG. 3 shows an example of flaw detection of the welded portion. In the welded portion 6 of the inspection object 5, the position and directionality of the planar defect 7 are estimated from the welding conditions, and the flaw detection refraction angle of the ultrasonic probe 1 is determined. Set and bevel inspection. FIG. 3A shows a case where a direct wave that directly applies an ultrasonic wave transmitted from the ultrasonic probe 1 to a defect and a case that uses a reflected wave that applies an ultrasonic wave reflected from the bottom surface of the inspection object 5 to the defect. (B) is a case of using a creeping wave that travels straight along the surface of the inspection object 1 or a creeping wave that is generated when reflecting from the bottom surface of the inspection object 1, and (C) is an ultrasonic wave. This is a case where a mode-converted wave which is reflected and mode-converted is used, and these are appropriately selected depending on the assumed position of the planar defect 7 in the thickness direction.

Next, sensitivity calibration for ultrasonic flaw detection is performed (S3). Sensitivity calibration is performed by detecting the height of the calibration echo by transmitting an ultrasonic wave with an ultrasonic probe to a calibration test body in which a reflection source that becomes a pseudo defect is formed in advance. Set the sensitivity calibration level based on the area.
The pseudo defect is a reflection source having a surface at least partially, and examples thereof include a flat bottom hole and an EDM (electric discharge machining) slit.
FIG. 4A shows a view in which the slit 8 is formed in the blade implantation groove (test body) 51 shown in FIG. 2A, and FIG. 4B shows the same in FIG. 2B. The figure which formed the slit 8 in the tenon part (test body) 52 is shown. At this time, the slit 8 is formed at the same position as the assumed planar defect. FIG. 5 shows a view in which flat bottom holes 9 are formed in the welded portion 6 shown in FIG. This is also formed at the same position as the assumed planar defect.

  When the EDM slit 8 is used as shown in FIG. 6A, the reflection area of the EDM slit 8 is obtained in advance. When the sides of the reflection surface of the EDM slit are a and b, the reflection area (slit dimension) is a × b. When the flat bottom hole 9 is used as shown in FIG. 6B, the reflection area is obtained in advance from the outer diameter φd of the flat bottom hole 9. A sensitivity calibration level Ac is set based on these reflection areas and calibration echoes.

Then, a defect detection level is set in advance (S4), ultrasonic inspection is performed by the inspection object 1 (S5), and an echo representing the defect is detected (S6).
Based on the detected defect echo, the defect length L of the planar defect 7 and the beam path length PL of the defect detection position are obtained.
The defect length L can be determined by a well-known method. For example, the defect length L is determined by an ultrasonic flaw detection method defined in JIS Z3060. In the waveform graph shown in FIG. 7 by ultrasonic flaw detection, the movement distances l ₁ and l ₂ of the ultrasonic probe 1 whose echo height exceeds the L line are defined as the defect length L.

Further, the beam diameter B at the defect detection position is obtained from the beam directing angle φ obtained in advance from the configuration of the ultrasonic probe 1 and the beam path length PL.
The beam directing angle φ is obtained from the probe diameter D, the probe frequency f, the material sound velocity C, and the wavelength λ of the ultrasonic probe 1 by the following equations (1) and (2). Expression (1) is an expression for deriving a zero radiation angle φ ₀ , and expression (2) is an expression for deriving a −6 dB execution directivity angle φ _0.5 .

As shown in FIG. 8, the beam diameter B includes the beam path PL from the ultrasonic probe 1 installed on the surface of the inspection object 5 to the planar defect 7 and the −6 dB execution directivity angle obtained as described above. It can be obtained from the following formula from φ _0.5 .
B = 2 × PL × tan φ _0.5

The defect height H is calculated from the sensitivity calibration level Ac thus obtained, the maximum echo height A, the defect length L, and the beam diameter B (S7).
At this time, the defect length L and the beam diameter B are compared. As shown in FIG. 9, when the defect length L is equal to or larger than the beam diameter B (defect length L ≧ beam diameter B), the following equation (3 ) And (4), the defect height H is calculated. 9A shows the flat bottom hole 9 and the ultrasonic beam region 2 of the calibration specimen, and FIG. 9B shows the planar defect 7 and the ultrasonic beam region 2.

On the other hand, as shown in FIG. 10, when the defect length L is shorter than the beam diameter B (defect length L <beam diameter B), the beam diameter B is set to the defect length L in the above formulas (3) and (4). The defect height H is calculated by the following formulas (5) and (6) replaced with. 10A shows the flat bottom hole 9 and the ultrasonic beam region 2 of the calibration specimen, and FIG. 10B shows the planar defect 7 and the ultrasonic beam region 2.

In these formulas, [pi] d ^2/4 is the reflection area of the flat bottom hole of the calibration specimen, when using the EDM slit becomes a (height) × b (width) (refer to FIG. 6 (a) ).
Thus, as shown in the above-described equations (4) and (6), the defect height H of the planar defect is the reflection area of the calibration specimen, the sensitivity calibration level Ac, and the detection of the planar defect. The defect height of the planar defect can be calculated from the defect echo using a calculation formula having a coefficient of the ultrasonic beam diameter B at the position.

According to this embodiment, in the estimation of the defect height of the planar defect, in addition to the information of the defect echo height, the reflection area of the calibration specimen, the sensitivity calibration level, and the configuration of the ultrasonic probe ( By using the ultrasonic beam diameter obtained from the specification, it is possible to accurately estimate the height of the surface defect that depends on the reflection area.
Compared with other defect height measurement methods such as the edge echo method and the TOFD method, it is more effective in evaluating the defect height at a microcrack and is not required to detect a weak diffracted wave. This is effective for evaluating the height of defects in noise materials. Therefore, no special inspector skill is required, and the defect height that is important for the life evaluation can be accurately estimated from the echo height information, so that the reliability of the inspection is improved.

It is a flowchart which shows the process sequence of the defect height estimation method which concerns on embodiment of this invention. It is a figure explaining the ultrasonic flaw detection method of a turbine blade, (A) is a side view at the time of using oblique flaw detection, (B) is a side view at the time of using a vertical flaw detection. It is a figure explaining the ultrasonic flaw detection method of a welding part, (A) is a case where a direct wave and a 1 time reflected wave are used, (B) is a case where a creeping wave is used, (C) is a case where a mode conversion wave is used. FIG. It is a figure explaining the sensitivity calibration of a turbine blade, (A) is a side view at the time of using oblique flaw detection, (B) is a side view at the time of using vertical flaw detection. It is a figure explaining the sensitivity calibration of a welding part. It is a perspective view which shows the test body for a calibration, (a) is a figure which has a slit as a pseudo defect, (b) is a figure which has a flat bottom hole. It is a figure which shows the waveform graph of a reflective echo. It is a figure explaining the beam diameter of an ultrasonic wave. The figure which compared the ultrasonic beam diameter and defect length shows the case where defect length is longer than a beam diameter. The figure which compared the ultrasonic beam diameter and defect length shows the case where defect length is shorter than a beam diameter. It is a correlation diagram of echo height and defect height, (a) shows the case where the ultrasonic wave is 2 MHz, and (b) shows the case of 5 MHz. It is a flowchart which shows the process sequence of the conventional defect height estimation method. It is a figure explaining an edge part echo method, (a) is a reflected echo waveform figure, (b) is a block diagram. It is a block diagram explaining the TOFD method. It is a block diagram of the general ultrasonic pulse flaw detection method, (a) is a figure which shows the one probe method, (b) is a figure which shows the two probe method. It is a figure explaining the defect detection by a reflective echo.

Explanation of symbols

1 Ultrasonic probe
2 Ultrasonic beam region 3 Base 5 Inspected object 6 Welded part 7 Planar defect 8 Slit 9 Flat bottom hole

Claims (4)

Defects of planar defects existing inside the object to be inspected based on the reflected wave waveform transmitted from the ultrasonic probe arranged on the surface of the object to be inspected to the inside of the object to be inspected and reflected from the reflection source In the defect height estimation method by ultrasonic flaw detection to estimate the height,
In advance, the sensitivity calibration level is set by performing ultrasonic flaw detection using a calibration specimen in which a reflection source having a surface is provided,
After detecting an echo of a planar defect by transmitting an ultrasonic wave from the ultrasonic probe to the object to be inspected,
Using a calculation formula having coefficients of the reflection area of the calibration specimen, the set sensitivity calibration level, and the ultrasonic beam diameter at the detection position of the planar defect, A defect height estimation method by ultrasonic flaw detection, characterized by estimating a defect height.   2. The ultrasonic flaw detection according to claim 1, wherein, in the calculation formula, when the defect length obtained from the defect echo is shorter than the ultrasonic beam diameter, the defect length is used as the ultrasonic beam diameter. Defect height estimation method.   2. The defect height estimation method by ultrasonic flaw detection according to claim 1, wherein the reflection source provided in the calibration specimen is a flat bottom hole or a slit.   The ultrasonic beam diameter is an ultrasonic beam directivity angle obtained from the diameter of the ultrasonic probe, the frequency of the ultrasonic wave, and the speed of sound of the inspection object, and the ultrasonic wave at the defect detection position obtained from the defect echo. The defect height estimation method by ultrasonic flaw detection according to claim 1, wherein the defect height estimation method is calculated from an acoustic beam path.

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