JPH11281629A - Apparatus and method for ultrasonic flaw detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method, for an ultrasonic flaw detection, in which the influence of a noise is suppressed to a minimum even when a step-shaped array probe in a thin wedge shape is used and in which a defect existing near the surface of an object to be inspected can be detected accurately. SOLUTION: When a step-shaped array probe is used, many noises are contained in a place in which the time elapsed from the radiation of ultrasonic waves is short, and a noise component is reduced gradually as the time elapses. Before an actual flaw detection is performed, a standard test piece whose material is identical to that for an object, to be inspected, being inspected actually and which does not contain any defect at the inside is used. An inspection is performed in the same procedure as an inspection with reference to an ordinary object to be inspected, a signal is acquired, and the signal is used as a reference waveform so as to be stored in a memory 11 for reference waveform. Then, an ultrasonic flaw detection is performed to an actual object to be inspected. A computing operation is performed to find a difference between a signal waveform obtained as its result and a signal regarding the standard test piece which is read out from the memory 11 for reference waveform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic inspection apparatus and an ultrasonic inspection method for non-destructively inspecting defects such as welded portions of steel using ultrasonic waves.

[0002]

2. Description of the Related Art An ultrasonic oblique flaw detection method is known as a method for non-destructively inspecting defects which may occur in a welded portion of a steel material. In this method, a probe is used for making an ultrasonic wave incident on a subject and receiving the ultrasonic wave reflected by the defect. One example of such a probe is disclosed in JP-A-7-22987.
No. 9 is described. The probe described in the publication is an electronic scanning array probe for oblique flaw detection in which a number of ultrasonic transducers are attached to a step-shaped wedge, and these are electronically scanned in a predetermined order and timing. The vertical cross section in the longitudinal direction is as shown in FIG.

[0003] This electronic scanning array probe for oblique flaw detection (hereinafter also referred to as "array probe") has a wedge 50,
It consists of a number of ultrasonic transducers 51 arranged in an array. The dimensions of the wedge 50 are, for example, about 100 mm in length (length in the horizontal direction in FIG. 5), about 10 mm in depth (width in the direction perpendicular to the paper surface in FIG. 5), and thickness (thickness in the vertical direction in FIG. 5). Is about several mm. The bottom surface of the wedge 50 is a flat surface that comes into contact with the surface of the subject. The upper side of the wedge 50 is a step-shaped uneven surface in which peaks and grooves are repeated at a constant pitch, and its vertical vertical section has a sawtooth shape as shown in FIG. The left slope (first slope) of each groove of the uneven surface is parallel to each other, and the right slope (second slope) is also parallel to each other. Ultrasonic vibration 5
Numerals 1 are attached to the first slopes one by one in each groove so that the vibration surface is in contact with the first slope.

The array probe shown in FIG. 5 is arranged close to a welded portion where a steel plate or the like is butt-welded so that its longitudinal direction is perpendicular to the welded portion, and a contact medium (such as glycerin) is interposed therebetween. To bring the bottom surface into contact with the surface of the steel plate. Then, each ultrasonic transducer 51 attached to the wedge 50
Are electronically excited in order from left to right (or right to left), as described below, to generate ultrasonic waves. Further, the ultrasonic wave 51 also detects a reflected wave which is returned by the ultrasonic wave being reflected in the steel material. From the characteristics of the detected reflected wave, the presence or absence of a defect at the welding location and the position of the defect are examined. By sequentially exciting and measuring each ultrasonic transducer 51 attached in the longitudinal direction in this way, it is possible to scan in the thickness direction of the welding location,
In addition, by performing such an operation every time a predetermined distance is moved while moving along the welding location, the entire welding location can be scanned.

[0005] The attenuation of an ultrasonic wave propagating in a medium increases as the propagation distance increases. For this reason, if the propagation distance of the ultrasonic wave in the wedge differs depending on the ultrasonic transducer from which the ultrasonic wave is emitted, the amplitude of the ultrasonic wave incident on the subject also becomes
It depends on the ultrasonic transducer. For this reason, the probe before the array probe using the thin wedge as a whole as shown in FIG. 5 was proposed, that is, the distance from the ultrasonic transducer to the boundary surface between the subject and the ultrasonic transducer was changed In the case of transducers that differ depending on the transducer, it was necessary to change the oscillation intensity of the ultrasonic transducer according to the propagation distance in the wedge, or to make some corrections to the measurement value based on the received reflected wave .

[0006] On the other hand, in the electronic scanning array probe for oblique flaw detection described in the above-mentioned publication, the center normal of the first slope on which the ultrasonic vibrator 51 is arranged is aligned with the bottom surface of the wedge 50. Since the lengths until they intersect are all equal, the propagation distance in the wedge is equal for each ultrasonic transducer. For this reason, FIG.
In the case of the array probe shown in (1), there is an advantage that the above-described correction is not required.

In the array probe shown in FIG. 5, the ultrasonic transducer 51 is attached to a slope (first slope) that is inclined from the surface of the subject for the following reasons. Generally, a transverse wave having a refraction angle of 45 ° to 70 ° is used for flaw detection of a welding point. The sound speed of longitudinal ultrasonic waves inside the acrylic resin generally used as the material of the wedge is 273.
0 m / sec, the speed of sound of the shear wave ultrasonic wave in a standard steel material is 3230 m / sec. The angle of incidence of longitudinal ultrasonic waves at the interface with the steel material must be in the range of 37 ° to 53 °.

However, the width of one ultrasonic transducer is 1 mm.
If the flaw detection frequency is calculated as 5 MHz, the directivity angle of this ultrasonic transducer is about 31 °, and if the ultrasonic transducer is arranged on a plane parallel to the subject, the incident angle is set to the above angle range. It is not possible. For this reason, in order to set the incident angle within the above-mentioned angle range, it is necessary to tilt the ultrasonic transducer with respect to the subject. For this purpose, in the array probe of FIG. 5, the ultrasonic transducer 51 is attached to every other slope of the step-shaped uneven surface of the wedge 50.

Next, a method of electronically scanning the ultrasonic transducer 51 will be described with reference to FIG. 6 which shows a block diagram of a conventional ultrasonic flaw detector. The operation of each unit shown in FIG. 6 is controlled by a control unit such as a microprocessor (not shown). As shown in FIG. 6, the ultrasonic flaw detector includes an ultrasonic generator 1 and an ultrasonic receiver 20.
It is roughly divided into 0.

Referring to FIG. 6, a pulse generator 60 generates a pulse signal to be supplied to an ultrasonic vibrator provided on the wedge 50. For example, when the number n of the ultrasonic transducers 51 is 128
In the case where ultrasonic waves are generated as a set of 16 continuous ultrasonic transducers, pulse signals for 16 channels are generated. This pulse signal is supplied to a phase delay pulse generator 61, where a predetermined phase delay process is performed on each pulse. According to the aspect of the phase delay, the traveling direction of the ultrasonic wave in the subject can be controlled. The multiplexer 62 determines which of the 128 ultrasonic transducers is to be supplied with a pulse. The pulser 63 performs an operation of converting the internal pulse into a high-voltage pulse and supplying the high-voltage pulse to the ultrasonic transducer.
The pulse signal output from the pulser 63 is supplied to the corresponding ultrasonic transducer 51 at a timing determined by the above-described phase delay pulse generator.

Which ultrasonic transducer 51 is used for detecting the ultrasonic wave reflected inside the subject can be freely selected depending on the inspection mode. n preamplifiers 6
4, the operation of selecting a set of preamplifiers corresponding to a set of ultrasonic transducers 51 whose ultrasonic waves are to be detected includes:
This is performed by the multiplexer 65. The signal from the selected preamplifier is supplied to the phase delay circuit 66, where the signal from each ultrasonic transducer 51 is delayed by a predetermined timing and returned to the same phase. The signals are added to each other by an adder 67. As a result of such addition processing, a signal waveform as shown in FIG. 7 is obtained.

FIG. 7 shows time on the horizontal axis and signal strength on the vertical axis. The time on the horizontal axis is the time measured starting from the point at which the ultrasonic wave was emitted toward the object, and if the defect existing in the object is near the surface of the object, the ultrasonic wave returning from it The time until the echo is detected is short,
If the defect is deep in the subject, it takes a long time until the ultrasonic echo returning from the defect is detected.

This signal is converted into a digital signal by an A / D converter 68, stored in a waveform memory 69, and subjected to various data processing as required. Also,
The signal added by the adder 67 is converted into an analog signal C
It can also be displayed on a display 70 such as an RT.

[0014]

By the way, as shown in FIG. 7, a signal contains many noise components at a short time after the ultrasonic wave is emitted toward the subject. The main reason is that the shape of the wedge 50 is stepwise as shown in FIG.

The entire ultrasonic wave emitted from the ultrasonic transducer 51 cannot be made incident on the subject, and a part of the ultrasonic wave is reflected on the boundary surface between the wedge 50 and the subject and remains in the wedge. Such ultrasonic waves gradually attenuate while propagating in the wedge, but if the shape of the wedge 50 is made thinner as a whole as shown in FIG. The light is reflected by the surface and returns to the original ultrasonic transducer. Such an ultrasonic wave is detected as noise at a place where the time since the emission of the ultrasonic wave is relatively short, and the noise gradually decreases as time passes.

Therefore, a signal based on a defect existing in a relatively shallow part of the subject where the ultrasonic echo returns in a short time overlaps with a place having a lot of noise components as shown in FIG. In such a case, the smaller the defect is,
Ultrasonic echoes therefrom are also small, and therefore the signal may be buried in noise and not properly detected. The present invention has been made based on the above circumstances, and minimizes the effects of noise even when a stair-like array probe having a thin wedge is used, and detects defects near the surface of the subject. It is an object of the present invention to provide an ultrasonic flaw detection apparatus and an ultrasonic flaw detection method capable of accurately detecting a defect.

[0017]

According to the first aspect of the present invention, there is provided an ultrasonic flaw detector which transmits an ultrasonic wave into a subject by using a stepped array probe. In the ultrasonic flaw detector which receives the ultrasonic waves returning from the subject using the step-shaped array probe and inspects the defects in the subject, the step-shaped array probe has no defect inside. Reference waveform storage means for storing, as a reference waveform, the signal waveform of the ultrasonic wave transmitted into the subject and received by the staircase array probe, and a test object to be examined by the staircase array probe. And a calculating means for calculating a difference between the signal waveform of the ultrasonic wave transmitted to the staircase array probe and received by the reference waveform storing means and the reference waveform stored in the reference waveform storing means. Ultrasonic flaw detector.

According to a second aspect of the present invention, there is provided the ultrasonic flaw detector according to the first aspect, further comprising display means for displaying a waveform obtained by a calculation result of the calculation means. According to a third aspect of the present invention, in the ultrasonic flaw detector according to the first or second aspect, it is further possible to automatically determine whether there is a defect in the subject based on a calculation result obtained by a calculation result of the calculation means. It is characterized by having a judging means for judging the situation.

According to a fourth aspect of the present invention, there is provided an ultrasonic flaw detection method, wherein an ultrasonic wave is transmitted into a subject using a stepped array probe, and the ultrasonic wave is transmitted from the subject using the stepped array probe. In the ultrasonic flaw detection method for receiving a returning ultrasonic wave and inspecting a defect in the object, an ultrasonic wave is transmitted into the object having no defect therein by the step-shaped array probe, and the ultrasonic wave is transmitted. Receiving the signal waveform by the step-shaped array probe and storing the signal waveform in a storage means as a reference waveform; and transmitting ultrasonic waves into the subject to be inspected by the step-shaped array probe, A step of receiving a sound wave by the staircase array probe and performing a difference operation between the signal waveform and the reference waveform stored in the storage unit, and a signal waveform obtained as a result of the difference operation, There is a defect in the test object And determining step how or, characterized in that it comprises a.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of an ultrasonic flaw detector according to the present invention. However,
As the probe, the same stair-shaped electronic scanning array probe for oblique flaw detection as that shown in FIG. 5 is used, and therefore, the illustration and description of that portion are omitted here. Also, in FIG. 1, the same portions as those in FIG. 6 are denoted by the same reference numerals or corresponding reference numerals, and description thereof will be omitted.

In FIG. 1, after the adder 67 of the ultrasonic receiving unit 2, the A / D converter 10, the reference waveform memory 11,
6 in that a difference circuit 12 and a waveform memory 13 are provided. When performing actual flaw detection with the ultrasonic flaw detector shown in FIG. 1, first, a standard test piece made of the same material as the test object to be actually tested and having no defect therein is used. Inspection is performed in the same procedure as the inspection for, and a signal waveform is obtained. FIG. 2 shows an example of a schematic waveform of a signal obtained based on the standard test piece. 2, like FIG. 7, the horizontal axis represents time, and the vertical axis represents signal strength.

In the present embodiment, the electronic scanning array probe for oblique flaw detection shown in FIG. 5 is used. Contains a lot of noise, and the noise component gradually decreases over time. However, in the case of FIG. 2, since there is no defect inside the standard test piece, a signal due to the defect is not included.

When a signal waveform as shown in FIG. 2 is obtained by the adder 67, the A / D converter 10 converts this analog signal into a digital signal and stores it as a reference waveform in the reference waveform memory 11. I do. Next, ultrasonic flaw detection is performed on the actual subject. Here, it is assumed that flaw detection has been performed on a subject having a defect near the surface. FIG. 3 shows the signal waveform obtained at this time. When FIG. 3 is compared with FIG. 2, a waveform which seems to be a signal from a defect can be seen in a portion with much noise, but it is not clear from the waveform alone whether or not the signal is from a defect.

The signal waveform shown in FIG.
After being converted into a digital signal by the differential circuit 1
2, where a calculation is performed to obtain a difference between the reference signal and the signal of the standard test piece read from the reference waveform memory 11. FIG. 4 shows the waveform of the signal obtained as a result of this calculation. As described above, the main cause of the noise that frequently occurs in a place where the time since the emission of the ultrasonic wave is short is the ultrasonic wave remaining inside the wedge. For this reason, the waveform of the noise in this portion is almost constant depending on the electronic scanning array probe for oblique flaw detection used. From this, when the difference between the signal waveform shown in FIG. 3 and the signal waveform shown in FIG. 2 is obtained, noise caused by the ultrasonic wave remaining in the wedge is canceled out, and as shown in FIG. Only the signal waveform from the defect included in the obtained waveform can be extracted. As a result, the signal after performing such processing has an improved SN ratio, and it is possible to accurately perform inspection of a defect existing inside the subject, particularly at a portion relatively shallow from the surface of the subject.

Although the difference circuit 12 only performs the difference calculation between the two waveforms, an appropriate display (not shown) such as a CRT display is provided, and the calculation result of FIG. When displayed, it becomes possible for the person in charge to visually determine immediately whether there is a defect. Also, for example, based on the operation result of the difference circuit 12, an algorithm is provided for determining that there is a defect in the subject when a value exceeding a certain threshold is obtained, and the presence or absence of the defect is automatically determined. It can be made to make a judgment.

The present invention is not limited to the above embodiment, and various changes can be made within the scope of the invention.
For example, in the above embodiment, the reference waveform was obtained using the standard test piece, but instead of using such a standard test piece,
Perform preliminary tests on some of the actual subjects,
It is also possible to take a difference between the obtained signal waveforms and select a set of those in which noise is canceled out, and use the waveform of one of the signals as a reference waveform. According to this method, there is an advantage that labor for preparing a standard test piece can be omitted.

[0027]

As described above, according to the present invention,
The S / N ratio can be improved in a relatively short period of time after generating ultrasonic waves, which has been a problem when using a thin step-like array probe as a whole. It is possible to provide an ultrasonic flaw detection apparatus and an ultrasonic flaw detection method capable of accurately detecting a defect present in a relatively shallow portion from the surface of a subject, which has been difficult.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of an ultrasonic flaw detector according to the present invention.

FIG. 2 is a diagram illustrating an example of a schematic waveform of a signal obtained based on a standard test piece.

FIG. 3 is a diagram showing an example of a signal waveform obtained when flaw detection is performed on a subject having a defect near the surface.

FIG. 4 shows a result obtained by calculating a difference between a signal obtained when a flaw detection is performed on an object having a defect near the surface and a signal of a standard test piece read from a reference waveform memory. It is a figure showing a signal waveform.

FIG. 5 is a vertical cross-sectional view in the longitudinal direction of the electronic scanning array probe for oblique flaw detection.

FIG. 6 is a block diagram of a conventional ultrasonic flaw detector.

FIG. 7 is a diagram showing a signal waveform obtained by performing a process of returning signals from the respective ultrasonic transducers to the same phase and then adding these signals to each other.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ultrasonic generator 2 ultrasonic receiver 10 A / D converter 11 reference waveform memory 12 difference circuit 13 waveform memory 50 wedge 51 ultrasonic transducer 60 pulse generator 61 phase delay pulse generator 62 multiplexer 63 pulser 64 preamplifier 65 Multiplexer 66 Phase delay circuit 67 Adder 68 A / D converter 69 Waveform memory 70 Display 200 Ultrasonic receiver

Claims (4)

[Claims] An ultrasonic wave is transmitted into a subject using a stepped array probe, and an ultrasonic wave returned from the subject is received using the stepped array probe. In the ultrasonic flaw detector for inspecting a defect, a signal waveform of an ultrasonic wave transmitted into a subject having no defect inside by the stepped array probe and received by the stepped array probe is referred to as a reference waveform. A reference waveform storage unit that stores the signal waveform of an ultrasonic wave transmitted into a subject to be inspected by the stepped array probe and received by the stepped array probe, and the reference waveform storage Calculating means for calculating a difference from the reference waveform stored in the means. 2. The ultrasonic flaw detector according to claim 1, further comprising display means for displaying a waveform obtained by a calculation result of said calculation means. 3. The ultrasonic flaw detector according to claim 1, further comprising: automatically judging whether there is a defect in the subject based on a calculation result obtained by a calculation result of the calculation means. An ultrasonic flaw detector comprising a determination means for determining whether or not the ultrasonic inspection is performed. 4. A stepped array probe is used to transmit ultrasonic waves into a subject, receive ultrasonic waves returned from the subject using the stepped array probe, and receive ultrasonic waves from the subject. In the ultrasonic flaw detection method for inspecting a defect, an ultrasonic wave is transmitted into a subject having no defect inside by the stepped array probe, and the ultrasonic wave is received by the stepped array probe. A step of storing the signal waveform in the storage means as a reference waveform, transmitting an ultrasonic wave into the subject to be inspected by the stepped array probe, and receiving the ultrasonic wave by the stepped array probe. Performing a difference calculation between the signal waveform and the reference waveform stored in the storage unit; and determining whether there is a defect in the subject to be inspected from the signal waveform obtained as a result of the difference calculation. Determining whether or not Ultrasonic flaw detection method comprising and.