JP2019191062A - Ultrasonic flaw detection method and ultrasonic flaw detection device - Google Patents

Abstract

To provide an ultrasonic flaw detection method for an object to be inspected, such as a steel material having a large attenuation due to the propagation of ultrasonic waves, in which the calibration test piece is not required, the reduction of the SN ratio by the DAC correction is suppressed, and the signal-to-noise ratio is improved so as to improve the SN ratio depending on the position of the defect signal.SOLUTION: The ultrasonic flaw detection method includes a first step for receiving an echo of an ultrasonic wave emitted from an ultrasonic probe 2 disposed on the surface of the object to be inspected 1 in the inspection region I of the object 1 to be received by the distance x within the inspection region I of the subject 1; a second step for calculating the attenuation amount of the function f (x) representing the attenuation amount of the noise signal group from the maximum noise signal y in the noise signal group in the test region I in the graph of the signal intensity for the distance x obtained in the first step; and a third step for individually multiplying the noise signal group in the inspection area I by the correction coefficient calculated by the distance x by the function f (x) and increasing the signal intensity of the noise signal group individually.SELECTED DRAWING: Figure 3

Description

  The present invention is, for example, an ultrasonic flaw detection method for an object to be inspected, such as a steel material that is mainly attenuated due to the propagation of ultrasonic waves, for examining the presence or absence of defects that may occur inside the steel material, and to be used in this method. The present invention relates to an ultrasonic flaw detector.

In general, ultrasonic waves are affected by scattering due to crystal grains or the like in the propagation process, and therefore attenuate as the propagation distance increases. Therefore, even if the defect has the same size, the signal strength of the echo decreases as the distance from the flaw detection surface increases.
In order to reduce the influence of the attenuation, a distance amplitude correction (DAC correction) method is used. For example, the A / D converter that converts the echo signal of the ultrasonic wave received by the ultrasonic probe from an analog signal to a digital signal, and the flaw detection surface at the required location of the calibration test piece when the calibration mode is set. Each of the echo signals received by the probe is received through the A / D converter, and the distance amplitude correction value of each echo signal is individually calculated and stored in the DAC table memory. There has been proposed an ultrasonic flaw detector having a microprocessor that receives an echo signal from a specimen through the A / D converter and multiplies the echo signal by a distance amplitude correction value read from the DAC table memory (for example, , See Patent Document 1).

  According to the ultrasonic flaw detector, since the distance amplitude correction is multiplied by the distance amplitude correction value corresponding to the propagation distance, the SN ratio between the defect signal (S) and the noise signal (N) having the same depth is evaluated. In this case, the SN ratio is not affected by the presence or absence of distance amplitude correction (hereinafter referred to as DAC correction). However, in actual flaw detection, in order to evaluate the presence / absence of a defect in a predetermined range of depth (flaw detection region), N (noise signal) when calculating the SN ratio is the highest N in the flaw detection region. Value (noise signal value). That is, since the depth at which the N value is received is often different from the depth at which the S value is received, the presence or absence of the DAC correction affects the calculation of the SN ratio.

For example, the flaw detection shown in FIG. 6 (A) is carried out by ultrasonic flaw detection on a square billet made of a high attenuation material having coarse crystal grains, which is the subject of the present invention. Assume that the waveform is obtained. FIG. 6B shows a flaw detection waveform (pattern) of a general steel material having fine crystal grains, and the signal intensity on the vertical axis is rapidly lowered at a shallow position in the flaw detection depth on the horizontal axis. . At this time, if the flaw detection area is in the range I in FIG. 6C, the noise becomes Na%.
On the other hand, the ultrasonic defect signal is Sa in FIG. 6D when there is a defect at the position of depth a without the DAC correction, and when there is a defect at the position of depth b. 6 (E), and when there is a defect at the position of depth c, Sc in FIG. 6 (F). The SN ratios of the depths a, b, and c are Sa / Na, Sb / Na, and Sc / Na, respectively.

Here, when DAC correction is applied to the waveform, Sa of the defect signal depth a is multiplied by Sa / Sa, Sb of depth b is multiplied by Sa / Sb, and Sc of depth c is Sa / Sc. The doubled waveform is displayed individually. That is, all signal values (s) are Sa.
By the way, when the noise signal N becomes the signals Na, Nb, and Nc for the depths a, b, and c in the healthy part without DAC correction (assuming that Na>Nb> Nc), the noise signal N is as shown in Table 1. here,
(A) When Na ≧ (Sa / Sc) × Nc, N = Na, so Table 1 is obtained.
(B) When Na <(Sa / Sc) × Nc, N = (Sa / Sc) × Nc, so Table 2 is obtained.

That is, depending on the flaw detection conditions (frequency, crystal grain size, defect size, etc.), there is a possibility that the S / N ratio may be lowered by applying the DAC correction. This problem may also occur when the S / N ratio is calculated from the following chart subjected to DAC correction.
The above chart is, for example, when ultrasonic flaw detection is performed along the longitudinal (axis) direction of a long billet having a square cross section, the vertical axis is the highest in the flaw detection area in each cross section for each flaw detection direction. The signal value is plotted, and the distance from the end face of the billet to each cross section in the flaw detection direction is plotted on the horizontal axis.
Moreover, in order to calculate the correction value of the distance amplitude correction, there is a problem that it is necessary to prepare in advance a test specimen for calibration in which artificial defects for different propagation distances are provided.

Japanese Patent Laid-Open No. 1-227056 (pages 1-6, FIGS. 1-6)

  The present invention solves the problems described in the background art, eliminates the need for the calibration test piece, suppresses a decrease in the SN ratio due to distance amplitude correction (DAC correction), and increases the SN ratio depending on the position of the defect signal. An object of the present invention is to provide an ultrasonic flaw detection method for an object to be inspected, such as a steel material that is largely attenuated due to propagation of ultrasonic waves, and an ultrasonic flaw detection apparatus used therefor.

Means for Solving the Problems and Effects of the Invention

In order to solve the above-mentioned problems, the present invention was conceived in that the distance amplitude correction method is performed based on a noise signal group instead of a conventional defect signal standard. It is.
That is, the ultrasonic flaw detection method according to the present invention (Claim 1) is an ultrasonic flaw detection method for detecting the presence or absence of a defect that can be located in the inspection region of the inspection object, and the ultrasonic inspection method disposed on the surface of the inspection object. A first step of receiving ultrasonic echoes transmitted from the acoustic probe into the inspected object for each distance within the inspection region of the inspected object, and a signal intensity obtained in the first step− In the noise signal group in the inspection region that appears in the graph according to distance, a second step of calculating a function representing the attenuation amount of the noise signal group starting from the maximum noise signal, and the noise signal group in the inspection region On the other hand, the method includes a third step of individually increasing the signal strength of the noise signal group by individually multiplying the correction coefficient calculated for each distance by the function.

According to the ultrasonic flaw detection method, the following effects (1) and (2) can be obtained.
(1) In the first step, even if the ultrasonic echo (reflection signal) signal group attenuates exponentially as the distance from the ultrasonic probe side increases in the inspection region, According to the third step of individually multiplying the echo signal group by the correction coefficient calculated for each distance based on the function calculated in the second step, any depth in the flaw detection area can be detected. The DAC correction can be applied without lowering the SN ratio, and the SN ratio can be improved depending on the depth (position) of the defect. Therefore, it is possible to accurately and easily detect the presence or absence of a defect, which will be described later, in the entire inspection area.
(2) Detection can be performed easily and quickly without using the calibration test piece, which has been essential in the conventional distance amplitude correction method.

In addition, as for the said to-be-inspected object, although a cross section is square shape and a long steel material (billet) is illustrated, for example, it is not limited to this.
The distance for each distance is a distance from the surface of the object to be inspected on which the ultrasonic probe is arranged.
Further, the noise signal is an echo signal from a position without the defect.
The function representing the amount of attenuation is displayed as f (x), with the distance x as a variable, decreasing on the curve as the distance x increases.
In addition, when the position (distance) of the maximum noise signal (digital signal) intensity in the inspection area is x1, and an arbitrary position (distance) in the inspection area is x2, the position at the position x2 The correction coefficient H (x2) is displayed as f (x1) / f (x2) (see Formula 1).

(Equation 1)
H (x2) = f (x1) / f (x2)
However, H (x2)> 1

Further, in the present invention, in the first step, a range of 15 to 85% in the ratio of the distance in the subject to be inspected is set as the inspection region, and in the second step, in the ratio of the distance in the subject to be inspected. An ultrasonic flaw detection method (Claim 2) is also provided that detects a maximum noise signal having the highest signal intensity in a region of 15 to 50% and calculates a function representing an attenuation amount of the noise signal group from the maximum noise signal as a starting point. included.
According to this, the first step is performed with the range of 15 to 85% in the ratio of the distance in the inspected body as the inspection area, and in the area of 15 to 50% in the ratio of the distance in the inspected object, A second step of detecting a maximum noise signal having the highest signal strength and calculating a function representing the attenuation amount of the noise signal group from the maximum noise signal as a starting point is performed. Therefore, the effects (1) and (2) can be obtained also by this type of ultrasonic flaw detection method.

Further, according to the present invention, there is a defect in the inspection region of the object to be inspected, and an ultrasonic flaw detection in which an echo signal intensity accompanying the defect is also increased by multiplying the correction coefficient in the third step. A method (claim 3) is also included.
According to this, the said effect (1) can be show | played reliably.

In addition, according to the present invention, the object to be inspected is a long steel material having a square cross section, and ultrasonic waves are transmitted a plurality of times along the longitudinal direction of the steel material, In addition, an ultrasonic flaw detection method (Claim 4) is also included, in which the maximum signal intensity is individually extracted in the inspection region and the presence or absence of a defect is determined based on the value of the signal intensity.
According to this, since the presence or absence of a defect inside the steel material can be detected more accurately, the effect (1) can be obtained more reliably.

  On the other hand, the ultrasonic flaw detector of the present invention (Claim 5) is an ultrasonic flaw detector that detects the presence or absence of a defect that can be located in the inspection region of the inspection object, and is an ultrasonic inspection apparatus disposed on the surface of the inspection object. An A / D converter that converts an echo signal group including an ultrasonic noise signal transmitted from the acoustic probe into the inspected object to a digital signal, and of the inspected object in the digital signal group. A filter that extracts a signal group in a specific frequency band that is included in the inspection region, a gate that extracts the noise signal group in the inspection region by distance, and the maximum noise signal for the noise signal group that is separated by distance And a calculation unit that calculates a function representing the attenuation amount of the noise signal group from the starting point, and a calculation unit that individually multiplies the noise signal group by the correction coefficient calculated for each distance by the function. Special To.

According to the ultrasonic flaw detector, the following effects (3) and (4) can be obtained.
(3) The echo signal group is converted into a digital signal by the A / D converter, and the digital signal group is included in the inspection region and is different from a specific frequency band (for example, a transmitted frequency band). A noise signal group having a frequency is removed by the filter, and a noise signal group having a specific frequency band is extracted for each distance by the gate. Further, for the noise signal group classified according to the distance, the calculation unit calculates a function representing the attenuation amount with the maximum noise signal for each inspection section as a starting point, and calculates the distance according to the distance by the function by the calculation unit. The corrected correction coefficient is individually multiplied to the noise signal group. For this reason, a noise signal having a frequency different from the transmission frequency, for example, electric noise can be used. By filtering the electric noise or the like, the electric noise can be removed and the attenuation function can be accurately obtained. Accordingly, it is possible to provide an ultrasonic flaw detector that can easily and quickly detect the presence or absence of a defect, which will be described later, in the entire inspection region.
(4) The calibration test piece, which has been essential in the conventional distance amplitude correction method, can be omitted, and the flaw detection operation can be simplified.
For the calculation unit, for example, a CPU such as a microprocessor is used.
The transmission frequency (band) is, for example, about 1 to 10 MHz.

According to the present invention, there is also provided an ultrasonic flaw detector in which the echo signal group and the digital signal group in the inspection region include a noise signal and a defect signal due to a defect included in the inspection object ( Claim 6) is also included.
According to this, the echo signal group from the inspection area of the object to be inspected is a noise signal having a signal intensity in which the attenuation amount due to the distance is corrected, and the attenuation amount of the echo signal due to the defect is similarly corrected. Can be enhanced. Therefore, the effects (3) and (4) can be reliably achieved.

Furthermore, in the present invention, the object to be inspected is a long steel material having a square cross section, and ultrasonic waves are transmitted a plurality of times along the longitudinal direction of the steel material, A peak value detector for extracting the maximum digital signal in the inspection region; and plotting means for plotting the digital signal for each of a plurality of cross sections to be inspected along the longitudinal direction of the steel material. An ultrasonic flaw detector (Claim 7) is also included.
According to this, since it becomes possible to accurately detect the presence or absence of the defect in the steel material, the effect (3) can be reliably obtained.

(A), (B) are end views and side views of the object to be inspected, (C), (D) are graphs showing the relationship between the ultrasonic signal intensity and the propagation distance in the object to be inspected, and (E), The chart which shows SN ratio etc. for every flaw detection position along the axial direction of the said to-be-inspected object. The block diagram which shows the outline of the ultrasonic flaw detector of this invention. (A) to (C) are the same graphs showing the second and third steps of the ultrasonic flaw detection method according to one embodiment of the present invention, and (D) and (E) are flaw detection along the axial direction of the inspection object. The side view which shows a position, and the chart which shows SN ratio etc. for every this flaw detection position. (A), (B) is a graph corresponding to FIG. 1 (C), (D) in the ultrasonic flaw detection method of a different form. (A)-(C) are the same graphs as the above which show the 2nd and 3rd step in the ultrasonic flaw detection method of the said different form. (A) is a graph showing a flaw detection waveform pattern of a high attenuation material, (B) is a graph showing a flaw detection waveform pattern of a general steel material, and (C) to (F) are graphs showing a flaw detection waveform pattern for each depth.

Hereinafter, modes for carrying out the present invention will be described.
1A and 1B are an end view and a side view of a steel material (inspected object) 1 having a large attenuation due to propagation of ultrasonic waves.
As shown in the drawing, the steel material 1 has an end face (cross section) that is square (rectangular) and has a long shape. For example, one side is about 50 to 200 mm and the length is several m to several tens m. Dimensions. It is assumed that defects d1 to d3 such as various inclusions and voids are present in the cross section of the steel material 1. For example, as shown in the figure, a virtual inspection region I is set in advance on the center side of the cross section of the steel material 1 and along the longitudinal direction thereof.
As shown in FIGS. 1 (A) and 1 (B), an ultrasonic probe 2 is arranged on the upper surface of the steel material 1 so as to be movable along the longitudinal direction, and a vertical downward arrow in the figure. As shown, ultrasonic waves are transmitted from the ultrasonic probe 2 for each of a plurality of inspection sections at equal intervals.

FIG. 1C is a graph showing the relationship between the ultrasonic propagation distance x and the signal intensity of the ultrasonic echo signal group in the cross section having no defects d1 to d3. The signal intensity indicates a relationship (ratio) when the artificial defect serving as a reference in a test piece serving as an ultrasonic reference is defined as 100%. The inspection region I was 15 to 85% based on the value of ((x / Y) × 100%) when one side of the steel material 1 was Ymm and the propagation distance was xmm.
As shown in FIG. 1C, in the inspection region I except for the vicinity of the upper surface (surface, flaw detection surface) and the vicinity of the lower surface (bottom surface) of the steel material 1, the upper surface on which the ultrasonic probe 2 is disposed. As the distance x from the distance increases, the signal intensity of the ultrasonic echo signal group decreases as a whole (exponentially). Incidentally, the maximum signal strength of the noise signal y in the inspection region I was 21%.

On the other hand, FIG. 1D shows the ultrasonic propagation distance x for each of the three inspection cross sections individually including defects d1 to d3 having the same size, and the signal intensity of the ultrasonic echo signal group for each cross section. It is a graph synthesized into one so as to show the relationship.
As shown in FIG. 1D, in the inspection area sa excluding the vicinity of the upper surface and the lower surface of the steel material 1, as the distance x from the upper surface where the ultrasonic probe 2 is arranged increases, The signal intensity of the ultrasonic echo signal group is attenuated in a curved line, and the signal intensity due to the defects d1 to d3 also decreases sequentially as the distance x increases.
Incidentally, the signal intensity of the defect d1 was 71%, the signal intensity of the defect d2 was 46%, and the signal intensity of the defect d3 was 16%. The signal intensity of the maximum noise signal y in the inspection area sa is 21%, the same as described above.

  And as shown in FIG.1 (E), the chart (list) which plotted the maximum echo signal value for every test | inspection cross section by making the horizontal axis the some test | inspection cross section along the longitudinal direction of the said steel material 1 is shown. Created. As shown in the figure, the maximum noise signal y (signal intensity; 21%) is plotted in each of a plurality of inspection sections without the defects d1 to d3. On the other hand, in the two inspection sections including the defects d1 and d2, the signal intensity (71%, 46%) due to these is larger than the signal intensity of the noise signal y, and thus the signal intensity is plotted.

However, in the inspection section including the defect d3 having the longest distance x, the signal intensity (16%) due to the defect d3 is smaller than the signal intensity of the noise signal y (21%). Is plotted.
Incidentally, the S / N ratio (signal intensity based on the defects d1 to d3 / signal intensity of the noise signal y) for each of the three inspection cross sections including the defects d1 to d3 is as shown in FIG. , (3.4), (2.2), and (0.8). From these results, it is clear that the detection ability decreases as the distance x increases.
In the above example, since the depth at which the noise is detected is different from the depth at which the signal is detected, an improvement (improvement) in the SN ratio by DAC correction can be expected.

FIG. 2 is a block diagram showing the ultrasonic flaw detector 4 of the present invention. In the following, calibration performed on a healthy part having no defect in the steel material 1 will be described.
As shown in FIG. 2, the ultrasonic flaw detector 4 includes a receiver (pulser) 5 connected through a cable 3 extending from the ultrasonic probe 2, and hereinafter, A shown in order by arrows in the figure. / D converter 6, filter 7, gate 8, approximate function calculation unit (calculation unit) 9, DAC correction calculation unit (calculation unit) 10, peak value detection unit 11, and plotting unit 12.
The ultrasonic echo signal group transmitted from the ultrasonic probe 2 via the cable 3 and the receiver 5 is converted into a digital signal by the A / D converter 6, and the transmission frequency ( Noise (for example, electric noise) having a frequency different from that of the band is removed by the filter 7, and a group of noise signals in the inspection region I is extracted by the gate 8 according to the distance x.

Next, for the noise signal group classified by the distance x, the correction unit 9 calculates a function f (x) representing the entire attenuation amount by using the maximum noise signal y for each inspection section as a starting point. The noise signal group is individually multiplied by the correction coefficient H (xn) calculated by the calculation unit 10 for each distance x.
Next, flaw detection is performed on the steel material 1 that is the actual inspection target. At this time, with respect to the noise signal group in the inspection region I and the echo signal due to the defect, the peak value detection unit 11 detects the maximum value (peak value) for each inspection section, and then the plotting unit 12 performs the inspection for each inspection section The maximum value is plotted.
The operation of the ultrasonic flaw detector 4 having the above configuration will be described along an ultrasonic flaw detection method according to an embodiment of the present invention described below.

First, the following calibration is performed using a sound part without defects in the steel material 1.
That is, similarly to the case shown in FIGS. 1A and 1B, the ultrasonic probe 2 is arranged on the upper surface of the steel material 1, and the steel material 1 has an inspection cross section without the defects d1 to d3. On the other hand, ultrasonic waves were transmitted, and echo signal groups due to noise in the inspection area I were received for each distance x as shown in the graph of FIG. 3A (first step).
The echo signal group is transmitted from the ultrasound probe 2 via the cable 3 and the receiver 5 and converted into a digital signal by the A / D converter 6. Of the digital signal group, a frequency different from the transmission frequency. The noise signal group is removed by the filter 7 and the noise signal group in the inspection region sa is extracted by the distance x by the gate 8 as shown in the graph.
Next, with respect to the noise signal groups classified by the distance x, the calculation unit 9 uses the maximum noise signal in the inspection cross section as a starting point, and represents the attenuation amount as shown by a dashed line curve in FIG. A function f (x) is calculated (second step).

Next, the calculation unit 10 individually multiplies the noise signal group by the correction coefficient H (xn) calculated for each distance x by the function f (x) (third step).
For example, when the position (distance) of the maximum noise signal or digital signal intensity in the inspection area I is x1, and an arbitrary position (distance) in the inspection area I is x2 (where x1 <x2) The correction coefficient H (x2) at the position x2 is expressed as f (x1) / f (x2). The correction coefficient H (x2) is always larger than 1. That is, when the position (distance X1) of the maximum noise signal y in the inspection area sa is 35 mm and the position (distance X2) of the defect d2 is 80 mm, the correction coefficient H (x2) at the position x2 is f (35) / f (80).

As a result, the inspection cross section without the defects d1 to d3 in the steel material 1 has the maximum signal intensity of the noise signal group over the entire inspection area sa, as shown in the graph of FIG. Increased below signal y.
The calibration for obtaining the reference waveform is completed by the above steps.

Next, flaw detection is performed on the steel material 1 that is an actual flaw detection target with reference to the reference waveform obtained by the calibration.
First, the peak value detection unit 11 detects the maximum value (peak value) of the noise signal group in the inspection area I and the defects d1 to d3 for each inspection section, and then inspects by the plotting unit 12. The maximum value is plotted for each cross section.
That is, as shown in FIG. 3D, in the longitudinal direction of the steel material 1, the maximum value for each of the plurality of inspection sections from which the ultrasonic waves are transmitted is as shown in the chart of FIG. Either the maximum noise signal y in the inspection region I or the echo signal due to the defects d1 to d3, which are plotted as shown.

Incidentally, the S / N ratio for each of the three inspection sections including the defects d1 to d3 is (4.5), (4.6), (5.8), as described in FIG. Thus, the SN ratio of each defect tends to increase as compared to before the DAC correction.
As described above, according to the ultrasonic flaw detection method of the present invention, the effects (1) and (2) can be obtained, and the ultrasonic flaw detection apparatus 4 exhibits the effects (3) and (4). Can be easily understood.

Next, an ultrasonic flaw detection method having a form different from the above form will be described.
4 (A) and 4 (B) are graphs of FIG. 1 (C) and FIG. 1 (D), and the propagation distance x (mm) from the upper surface of the steel material (inspected object) 1 is expressed as a percentage (ratio:%). It has been replaced with. Further, FIGS. 5A to 5C are obtained by replacing the graphs of FIGS. 3A to 3C in the same manner as described above.
In the ultrasonic flaw detection method of the present embodiment, as shown in FIGS. 4 (A), (B), and FIGS. 5 (A) to (C), the propagation distance from the upper surface in the steel material 1 to the lower surface on the opposite side (x ) In percentage (%), and the flaw detection area (sa) is in the range of 15 to 85%. This range is based on the optimum flaw detection range based on the empirical rules of the inventors. In addition, when the propagation distance x (mm) excluding the inspection region (Sa) is in the range of 0 to 15% and 85 to 100%, it is separately inspected by an eddy current flaw detection method or the like.

Specifically, as a first step, in the upper surface of the steel material 1 (in the propagation distance x (mm) from the flaw detection surface 9), a range of 15 to 85% based on the ratio (%) of the distance x (mm) is set. As an inspection area (I), an ultrasonic echo signal group transmitted from the ultrasonic probe 2 arranged on the upper surface of the steel material 1 to the inspection area (I) of the steel material 1 is shown in FIG. As shown in the graphs of A) and (B), the data is received for each ratio (%) in the inspection area (I).
Next, in the ratio (%) of the propagation distance x (mm) including the inside of the inspection region (sa) shown in the graphs of FIGS. 4A and 4B obtained in the first step, 15 to 50% The maximum noise signal (y) having the highest signal intensity in the region is detected, and the noise signal group in the inspection region (I) is detected from the maximum noise signal (y) as shown in FIG. 5A. A second step of calculating a function f (x) indicating the amount of attenuation is performed.

Further, in many cases, the noise signal when calculating the SN ratio is plotted at a position closest to the flaw detection surface (upper surface side of the steel material 1) in the inspection region (I), and particularly based on the ratio (%). As 15 to 50%.
Furthermore, when the ultrasonic probe 2 is scanned along the upper surface of the steel material 1, the intensity of the noise signal exhibits a waveform that hardly fluctuates, so that the noise signal and the defect signal can be clearly distinguished.

Then, a third step of individually multiplying the noise signal group in the inspection region (I) by the correction coefficient H (xn) calculated for each ratio (%) by the function f (x) is performed.
As a result, the inspection cross section without the defects d1 to d3 in the steel material 1 has a maximum noise intensity over the entire inspection area I as shown in the graph of FIG. Increased below signal y.
On the other hand, in each of the three inspection sections including the defects d1 to d3, as shown in the synthesized graph of FIG. 5C, the signal intensity of the noise signal group is increased over the entire inspection region I, The echo signals resulting from the defects d1 to d3 are also individually increased to a signal intensity that is greater than the maximum noise signal y.
It is clear that the effects (1) and (2) can be obtained by the ultrasonic flaw detection method having the above-described form.

The present invention is not limited to the embodiment described above.
For example, the present invention relates to an ultrasonic flaw detection method using a probe, and can be applied to a phased array flaw detection method using an array probe in addition to a flaw detection method using a probe. .
In addition, the object to be inspected by the ultrasonic flaw detection method is not limited to the steel material 1 as long as it is a solid to which the vertical flaw detection method can be applied, or from various metal or alloy metal members or various materials. It may be a ceramic member or a resin member.
In addition to the upper surface of the steel material 1, the ultrasonic probe 2 is further arranged from one side surface of the same steel material 1 toward the other side surface opposed to the same inspection cross section. The ultrasonic waves may be transmitted twice at different timings.

Further, the ultrasonic flaw detector 4 may be configured to individually calculate the signal strength y of the maximum noise signal in the inspection region I and the SN ratio for each of the defects d1 to d3.
In addition, a display or a printer that displays the chart shown in FIG. 3E may be further connected to the downstream side of the plotting unit 12 of the ultrasonic flaw detector 4.

  According to the present invention, it is possible to accurately distinguish between a noise signal and a defect signal regardless of the propagation distance of the ultrasonic wave propagated to the object to be inspected without using a calibration specimen, and away from the transmission position. An ultrasonic flaw detection method capable of improving the SN ratio at a certain position and an ultrasonic flaw detection apparatus used therefor can be provided.

1 ... Steel (Inspected object)
2 …………… Ultrasonic probe 4 …………… Ultrasonic flaw detector 6 …………… A / D converter 7 …………… Filter 8 …………… Gate 9 ……… ...... Approximate function calculation unit (calculation unit)
10 ………… DAC correction calculation part (calculation part)
11 ………… Peak value detector 12 ………… Plotting means I ……………… Inspection area x ………… Distance d1 to d3… Defect f (x) …… Function

Claims (7)

An ultrasonic flaw detection method for detecting the presence or absence of a defect that can be located in an inspection area of an object to be inspected,
A first step of receiving ultrasonic echoes transmitted from the ultrasonic probe disposed on the surface of the object to be inspected to the inside of the object to be inspected according to the distance in the inspection region of the object to be inspected;
Second step of calculating a function representing the attenuation amount of the noise signal group starting from the maximum noise signal in the noise signal group in the inspection region appearing in the signal intensity-distance graph obtained in the first step. When,
A third step of individually multiplying the noise signal group in the inspection region by the correction coefficient calculated for each distance by the function and individually increasing the signal intensity of the noise signal group,
An ultrasonic flaw detection method characterized by the above. In the first step, a range of 15 to 85% in the ratio of the distance in the inspected body is set as the inspection region,
In the second step, a maximum noise signal having the highest signal strength is detected in an area of 15 to 50% of the distance ratio in the inspected body, and the attenuation amount of the noise signal group is expressed using the maximum noise signal as a starting point. Calculate the function,
The ultrasonic flaw detection method according to claim 1. A defect exists in the inspection area of the inspection object, and the signal strength of the echo accompanying the defect is also increased by multiplying the correction coefficient of the third step.
The ultrasonic flaw detection method according to claim 1 or 2. The object to be inspected is a long steel material having a square cross section, ultrasonic waves are transmitted a plurality of times along the longitudinal direction of the steel material, and the largest in the inspection region for each of the plurality of inspected cross sections. Extract signal strength individually and determine the presence or absence of defects based on the value of the signal strength.
The ultrasonic flaw detection method according to any one of claims 1 to 3. An ultrasonic flaw detector that detects the presence or absence of a defect that may be located within the inspection region of an inspection object,
An A / D converter that converts an echo signal group including an ultrasonic noise signal transmitted from the ultrasonic probe disposed on the surface of the object to be inspected into a digital signal, to a digital signal;
A filter for removing a noise signal group included in the inspection region of the inspected object by removing a noise signal having a frequency different from the transmission frequency included in the inspection region from the digital signal group;
A gate that extracts a group of noise signals in the inspection area according to distance;
For the noise signal group that is classified according to the distance, a calculation unit that calculates a function representing the attenuation amount of the noise signal group starting from the maximum noise signal;
A calculation unit that individually multiplies the noise signal group by a correction coefficient calculated for each distance by the function,
An ultrasonic flaw detector characterized by that. The echo signal group and the digital signal group in the inspection area include a noise signal and a defect signal due to a defect included in the inspection object.
The ultrasonic flaw detector according to claim 5. The object to be inspected is a long steel material having a square cross section, ultrasonic waves are transmitted a plurality of times along the longitudinal direction of the steel material, and the largest in the inspection region for each of the plurality of inspected cross sections. A peak value detector for extracting a digital signal;
Plotting means for plotting the digital signal for each of a plurality of cross sections to be inspected along the longitudinal direction of the steel material;
The ultrasonic flaw detector according to claim 5 or 6.

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