Patent Description:
A steel sheet manufactured by a steel manufacturer, etc., may have a flaw on its front or back surface, and such a flaw is detected by an ultrasonic flaw detection device.

When steel is thin, flaw detection using a plate wave or a surface wave is performed by allowing ultrasound to obliquely enter a steel sheet by using a probe. Conventionally, as such an ultrasonic flaw detection device, there is one that detects a surface flaw using a surface wave by allowing ultrasound to obliquely enter a steel sheet from a wheel probe (see, for example, Patent Literature <NUM>).

The article "<NPL>, presents a method with which a Lamb wave of the required mode is generated and detected by electronically adjusting the incident angle using a linear array probe, and its application to flaw detection.

Patent Literature <NUM> discusses an ultrasonic method for testing an inner diameter cladded pipe adjacent to welds comprising use of multiple beams, bands and pulses in addition to pulseshaping and beamforming, spectral and directional averaging, as well as spatial filtering and pattern recognition.

Patent Literature <NUM> discusses a phased array ultrasonic testing apparatus which includes: an array probe for ultrasonic transmission and reception; a transmitter for sequentially exciting transducers of the probe in a predetermined order; a circuit for preparing a composite signal from reception output from the probe; and a circuit for preparing an image signal indicating an internal flaw of a tested body in synchronism with the composite signal in accordance with a transmission beam index point and a steered angle of an ultrasonic main beam.

Patent Literature <NUM> discusses an ultrasonic inspection method for inspecting the surface layer part and deeper parts of a subject by using a double crystal angle probe.

Patent Literature <NUM> discusses an ultrasound testing device for detecting cracks of large area and depth.

Patent Literature <NUM> discusses an ultrasonic test head for testing flaws in a workpiece including two acoustically separate ultrasonic transducers in a common housing.

Meanwhile, there is a case in which an ultrasonic flaw detection device needs to grasp on which one of the front and back sides of a steel sheet a flaw is located. However, the conventional ultrasonic flaw detection device as described, for example, in the above-described Patent Literature <NUM> has difficulty in determining on which one of the front and back a flaw is located.

The invention is made to solve such a problem, and an object of the invention is to provide an ultrasonic flaw detection method capable of determining on which one of the front and back sides of a steel sheet a flaw is located.

According to the invention, the technical problem described above is solved by an ultrasonic flow detection method according to claim <NUM>. An ultrasonic flaw detection method according to the invention includes, in particular: generating ultrasound waves corresponding to transmission signals to be provided to the ultrasonic probe, and sending out the ultrasound waves into a specimen, and receiving echoes of the respective ultrasound waves having propagated through the specimen and outputting the received echoes as reception signals; generating, as the transmission signals, signals that are used by the ultrasonic probe to send out the ultrasound waves to the specimen obliquely at a respective plurality of angles; and determining, from the reception signals, amplitudes of the echoes corresponding to the plurality of angles, and periods of time from when the respective ultrasound waves are sent out until the respective echoes are received, as reception times, and identifying a location of an acoustic discontinuous portion in the specimen from the reception times and a ratio between the amplitudes.

The ultrasonic flaw detection device according to the invention sends out ultrasound waves to a specimen obliquely at a respective plurality of angles, determines amplitudes and reception times of echoes corresponding to the plurality of angles, and identifies a location of an acoustic discontinuous portion in the specimen from the reception times and a ratio between the amplitudes. By this, it can be determined on which one of the front and back sides of the specimen a flaw is located.

To describe the invention in more detail, a mode for carrying out the invention will be described below with reference to the accompanying drawings.

<FIG> is a configuration diagram of an ultrasonic flaw detection device of the present embodiment.

The ultrasonic flaw detection device shown in the drawing includes an ultrasonic probe <NUM> and a transceiver <NUM>. The ultrasonic probe <NUM> is an angle probe, and has a function of transmitting ultrasound waves which are driven by transmission signals to be provided thereto into a steel sheet <NUM> which is a specimen, and receiving echoes of the ultrasound waves having propagated through the steel sheet <NUM> and outputting the echoes as reception signals. The details of the ultrasonic probe <NUM> are shown in <FIG>. As shown in <FIG>, the ultrasonic probe <NUM> includes a wedge 1a and a transducer 1b. The transducer 1b is formed by arraying a plurality of transducer elements.

The transceiver <NUM> has a function of providing transmission signals to the ultrasonic probe <NUM>, and performing signal processing on reception signals which are echoes obtained by the ultrasonic probe <NUM>, and includes a signal processing unit <NUM>, a transmitting unit <NUM>, and a receiving unit <NUM>. The signal processing unit <NUM> includes a transmission signal processing unit 3a and a reception signal processing unit 3b. The transmission signal processing unit 3a has a function of generating, as transmission signals, signals that are used by the ultrasonic probe <NUM> to send out ultrasound waves to the steel sheet <NUM> obliquely at a plurality of angles, and providing the transmission signals to the transmitting unit <NUM>. The reception signal processing unit 3b has a function of receiving, through the receiving unit <NUM>, reception signals obtained by the ultrasonic probe <NUM>, determining, from the reception signals, amplitudes and reception times of ultrasonic echoes corresponding to the plurality of angles, and identifying a location of an acoustic discontinuous portion in the steel sheet <NUM> from the reception times and a ratio between the amplitudes. The transmitting unit <NUM> has a function of generating signals for driving the transducer 1b of the ultrasonic probe <NUM>, on the basis of the transmission signals provided from the transmission signal processing unit 3a. The receiving unit <NUM> has a function of amplifying the reception signals from the ultrasonic probe <NUM>, as necessary, and transmitting the reception signals to the reception signal processing unit 3b in the signal processing unit <NUM>.

<FIG> is a block diagram schematically showing an exemplary hardware configuration of the signal processing unit <NUM>. In an example of <FIG>, the signal processing unit <NUM> includes a processor <NUM> including a CPU, a read only memory (ROM) <NUM>, a random access memory (RAM) <NUM>, a storage <NUM>, a transmission/reception interface circuit <NUM>, a display interface circuit <NUM>, and a display <NUM>. The processor <NUM>, the ROM <NUM>, the RAM <NUM>, the storage <NUM>, the transmission/reception interface circuit <NUM>, the display interface circuit <NUM>, and the display <NUM> are mutually connected through a signal path <NUM> such as a bus circuit.

The processor <NUM> uses the RAM <NUM> as a working memory, and executes an ultrasonic measurement program read from the ROM <NUM> or the storage <NUM>, and thereby implements the functions of the transmission signal processing unit 3a and the reception signal processing unit 3b. The storage <NUM> is a storage unit that is formed using, for example, a volatile memory such as a synchronous DRAM (SDRAM), a hard disk drive (HDD), or a solid-state drive (SSD), and that stores programs corresponding to the functions of the transmission signal processing unit 3a and the reception signal processing unit 3b, and stores processing results. The transmission/reception interface circuit <NUM> is an interface circuit used for signal transmission with the transmitting unit <NUM> and signal transmission with the receiving unit <NUM>. The display interface circuit <NUM> is an interface circuit used for signal transmission with the display <NUM>.

The display <NUM> displays a result of determination of a flaw location. The result may be displayed as characters, or may be displayed using an LED lamp. A display method is not limited thereto.

Next, the operation of the ultrasonic flaw detection device of the present embodiment will be described. First, plate waves that propagate through a steel sheet will be described with reference to <FIG> and <FIG>. <FIG> and <FIG> respectively show the phase velocities and group velocities of plate waves that propagate through a steel sheet with a thickness of <NUM>. As is clear from these drawings, the phase velocity and the group velocity vary depending on the frequency. Note that although many modes propagate in practice, here, three modes, A0, SO, and S <NUM>, are shown. Here, as an example, plate waves that propagate through a steel sheet with a thickness of <NUM> at a frequency of <NUM> will be described.

As shown in <FIG>, when the frequency is <NUM>, the phase velocities of A0 and S0 are both about <NUM>/s, and are almost identical. Therefore, it is conceivable that by setting the angle of incidence of the ultrasonic probe <NUM> in such a manner that a plate wave with a phase velocity of <NUM>/s propagates, a mode having both characteristics of A0 and S0 propagates. In the present embodiment, this mode is called an "A0S0 mode". On the other hand, the phase velocity of S1 is about <NUM>/s. By setting the angle of incidence of the ultrasonic probe <NUM> in such a manner that a plate wave with a phase velocity of <NUM>/s propagates, a plate wave in S1 mode propagates.

A simulation is performed to examine what echoes are to be received when a flaw <NUM> of the steel sheet <NUM> is detected by propagation of plate waves in AOSO mode and S0 mode. <FIG> shows simulation conditions. <FIG> show response characteristics of the ultrasonic probe <NUM> used in the simulation, and <FIG> shows a relationship between time and relative amplitude, and <FIG> shows a relationship between frequency and relative amplitude. In this example, as shown in <FIG>, a narrow band with a center frequency of <NUM> is used. <FIG> are diagrams respectively showing, at a time when the flaw <NUM> is present on the front and back sides of the steel sheet <NUM>, relative positional relationships between the ultrasonic probe <NUM> and the steel sheet <NUM>. As shown in <FIG>, echoes from the flaw <NUM> are obtained with a distance L from the ultrasonic probe <NUM> to the flaw <NUM> changed from <NUM> to <NUM>. <FIG> shows a shape of the flaw. <FIG> shows the flaw <NUM> present on the front side of the steel sheet <NUM>, and when the flaw <NUM> is present on the back side, the flaw shape is vertically reversed.

In the simulation, an angle probe is formed by allowing the transducer 1b to contact with a liquid with a sound velocity of <NUM>/s, and using the liquid as the wedge 1a. In this case, the angle of incidence for generating an AOSO mode with a phase velocity of <NUM>/s is <MAT> by Snell's law. Here, for the convenience of the simulation, the angle of incidence for allowing the AOSO mode to propagate is set to <NUM>°. On the other hand, the angle of incidence for generating an S1 mode with a phase velocity of <NUM>/s is <MAT>.

Here, for the convenience of the simulation, the angle of incidence for allowing the S <NUM> mode to propagate is set to <NUM>°.

<FIG> show echoes obtained when the flaw <NUM> present on the front side of the steel sheet <NUM> is detected by allowing the AOSO mode to propagate at an angle of incidence of <NUM>°. <FIG> show examples of a distance of <NUM> to <NUM>, respectively. As shown in the drawings, the echo height decreases with the distance up to a distance of about <NUM>, but the echo height exhibits an increasing tendency at a distance of <NUM> and more.

<FIG> shows echoes obtained when the flaw present on the front side of the steel sheet <NUM> is detected by allowing the S1 mode to propagate at an angle of incidence of <NUM>°. <FIG> show examples of a distance of <NUM> to <NUM>, respectively. As shown in the drawings, the echo height gradually decreases with the distance.

<FIG> shows changes in echo height relative to the distance at a time when the flaw <NUM> is present on the front side of the steel sheet <NUM>. As shown in the drawing, the echo height of the S1 mode generated at an angle of incidence of <NUM>° gradually decreases with the distance, whereas the echo height of the AOSO mode generated at an angle of incidence of <NUM>° exhibits a complex characteristic in which the echo height decreases and then increases.

<FIG> shows echoes obtained when the flaw <NUM> present on the back side of the steel sheet <NUM> is detected by allowing the AOSO mode to propagate at an angle of incidence of <NUM>°. <FIG> show examples of a distance of <NUM> to <NUM>, respectively. As shown in the drawings, the echo height increases with the distance, but decreases with the distance after the distance exceeds <NUM>. This is a reverse tendency to that at a time when the flaw <NUM> is present on the front side.

<FIG> shows echoes obtained when the flaw <NUM> present on the back side of the steel sheet <NUM> is detected by allowing the S1 mode to propagate at an angle of incidence of <NUM>°. <FIG> show examples of a distance of <NUM> to <NUM>, respectively. As shown in the drawings, the echo height gradually decreases with the distance. This is the same tendency as that at a time when the flaw <NUM> is present on the front side.

<FIG> shows changes in echo height relative to the distance at a time when the flaw <NUM> is present on the back side of the steel sheet <NUM>. As shown in the drawing, the echo height of the S1 mode generated at an angle of incidence of <NUM>° gradually decreases with the distance, whereas the echo height of the AOSO mode generated at an angle of incidence of <NUM>° exhibits a complex characteristic in which the echo height increases and then decreases.

Causes of the occurrence of the characteristics shown in <FIG> and <FIG> will be described with reference to <FIG>. <FIG> shows results of sound field simulation (a distance of <NUM>) obtained when the AOSO mode is propagated at an angle of incidence of <NUM>°. In <FIG>, from <NUM> to <NUM> sound fields near the ultrasonic probe <NUM> are shown, and from <NUM> to <NUM> sound fields near the flaw <NUM> are shown. As shown in the drawing, immediately after incidence on the steel sheet <NUM> from the ultrasonic probe <NUM>, energy of the plate wave is concentrated on the front side of the steel sheet <NUM>. The energy distribution changes little by little with propagation, and when the plate wave reaches the flaw <NUM> present at a location with a distance of <NUM>, the energy of the plate wave is concentrated on the back side of the steel sheet <NUM>.

<FIG> shows a simulated representation of a transition of the energy distribution of the AOSO mode. As shown in the drawing, immediately after incidence on the steel sheet <NUM> from the ultrasonic probe <NUM>, the energy of the plate wave becomes stronger on the front side of the steel sheet <NUM>. After going through a state in which the energy distribution changes with propagation and the front and back sides have a comparable energy distribution, a state in which the energy becomes stronger on the back side is obtained. Thereafter, the plate wave propagates in such a manner that after going through a state in which the front and back sides have a comparable energy distribution again, the energy becomes stronger on the front side. Therefore, changes in echo height relative to the distance are reversed between a case where the flaw <NUM> is present on the front side of the steel sheet <NUM> and a case where the flaw <NUM> is present on the back side of the steel sheet <NUM>. As a result, the AOSO mode has the characteristics shown in <FIG> and <FIG>.

<FIG> shows results of sound field simulation (a distance of <NUM>) obtained when the S1 mode is propagated at an angle of incidence of <NUM>°. In <FIG>, from <NUM> to <NUM> sound fields near the ultrasonic probe <NUM> are shown, and from <NUM> to <NUM> sound fields near the flaw <NUM> are shown. As shown in the drawing, even immediately after incidence on the steel sheet <NUM> from the ultrasonic probe <NUM> and even when the plate wave reaches the flaw <NUM>, a sound field distribution hardly changes, and is substantially uniform in a plate thickness direction.

<FIG> shows a simulated representation of a transition of an energy distribution of the S1 mode. As shown in the drawing, when the plate wave propagates, the energy distribution hardly changes. Since the energy distribution is substantially uniform in the plate thickness direction, changes in echo height relative to the distance are almost the same between in a case where the flaw <NUM> is present on the front side of the steel sheet <NUM> and in a case where the flaw <NUM> is present on the back side of the steel sheet <NUM>. As a result, the S1 mode has the characteristics shown in <FIG> and <FIG>.

As described above, changes in echo height relative to the distance greatly differ between the AOSO mode and the S1 mode. Using these characteristics, it is possible to determine on which one of the front and back sides of the steel sheet <NUM> the flaw <NUM> is present. Specific operation of the ultrasonic flaw detection device of the present embodiment will be described below.

<FIG> is a flowchart showing the operation of the transmission signal processing unit 3a, and <FIG> is a flowchart showing the operation of the reception signal processing unit 3b.

First, the transmission signal processing unit 3a transmits delay signals for the respective arrayed transducer elements of the transducer 1b to the transmitting unit <NUM> so as to obtain the angle of incidence at which the AOSO mode propagates (step ST11). The transmitting unit <NUM> generates excitation signals using the delay signals transmitted from the transmission signal processing unit 3a, to excite the respective arrayed transducer elements of the transducer 1b in the ultrasonic probe <NUM>. An example of <FIG> shows the state of propagation of ultrasound in the wedge 1a in a case in which a delay time assigned to the arrayed leftmost element of the transducer 1b is long and a delay time assigned to the rightmost element is short. Note that the angle of incidence at which the AOSO mode propagates changes depending on the thickness of the steel sheet <NUM>, the sound velocity of the wedge 1a, and the frequency, and thus is not limited to the angle (<NUM>°) shown in the simulation.

Thereafter, plate waves in AOSO mode propagate through the steel sheet <NUM>, and each of the arrayed transducer elements of the transducer 1b in the ultrasonic probe <NUM> receives, as an echo, the corresponding plate wave reflected by the flaw <NUM>, converts the echo into an electrical signal, and transmits the electrical signal to the receiving unit <NUM>. The receiving unit <NUM> amplifies the echo as necessary, and transmits the echo to the signal processing unit <NUM>.

In the signal processing unit <NUM>, the reception signal processing unit 3b assigns a delay time corresponding to each of the arrayed transducer elements of the transducer 1b to the corresponding echo, and combines the echo of each of the transducer elements. The amplitude of the echo is determined as E1 and the reception time of the echo is determined as T1, and the values of the E1 and T1 are stored in the RAM <NUM> or the storage <NUM> that is included in the reception signal processing unit 3b (step ST21). Namely, plate waves in AOSO mode are allowed to propagate through the steel sheet <NUM> by controlling the angle of incidence and the angle at which reception is performed in a phased array system, by which the transmission and reception are performed.

After storing the values of E1 and T1 in the reception signal processing unit 3b, the angle of incidence is changed in the phased array system, to generate plate waves in S1 mode in the steel sheet <NUM>. Namely, the transmission signal processing unit 3a transmits delay signals for the respective arrayed transducer elements of the transducer 1b to the transmitting unit <NUM> so as to obtain the angle of incidence at which the S1 mode propagates (step ST12). Note that the angle of incidence at which the S1 mode propagates changes depending on the thickness of the steel sheet <NUM>, the sound velocity of the wedge 1a, and the frequency, and thus is not limited to the angle (<NUM>°) shown in the simulation.

Thereafter, plate waves in S1 mode propagate through the steel sheet <NUM>, and each of the arrayed transducer elements of the transducer 1b in the ultrasonic probe <NUM> receives, as an echo, the corresponding plate wave reflected by the flaw <NUM>, converts the echo into an electrical signal, and transmits the electrical signal to the receiving unit <NUM>. The receiving unit <NUM> amplifies the echo as necessary, and transmits the echo to the signal processing unit <NUM>.

In the signal processing unit <NUM>, the reception signal processing unit 3b determines the amplitude E2 and reception time T2 of the echo in S <NUM> mode in the phased array system, and stores the amplitude E2 and the reception time T2 in the RAM <NUM> or the storage <NUM> that is included in the reception signal processing unit 3b (step ST22).

As shown in <FIG>, if the frequency is determined, then the group velocity of a plate wave is also determined. Namely, it is possible to estimate, from a reception time of an echo, a distance from the ultrasonic probe <NUM> to the flaw <NUM>. For example, the group velocity of the AOSO mode is substantially <NUM>/s regardless of the frequency, and thus, from T1 × <NUM>/s, a back-and-forth propagation distance of the AOSO mode can be determined. The reception signal processing unit 3b determines a distance from the ultrasonic probe <NUM> to the flaw <NUM>, and sets the distance as L (step ST23).

Changes in echo height relative to the distance as shown in <FIG> and <FIG> are determined in advance by computation or experiment. The reception signal processing unit 3b compares the amplitude E1 of the AOSO mode with the amplitude E2 of the S <NUM> mode, and determines, from characteristics of the echo height relative to the distance, on which one of the front and back sides of the steel sheet <NUM> the flaw <NUM> is present (step ST24). For example, if the characteristics of the echo height relative to the distance are the same as those of <FIG> and <FIG>, then when the value of the distance L is <NUM>, the following relationships are evident:.

The reception signal processing unit 3b displays the determination result on the display <NUM>.

As such, by using the plate waves in the two modes, it is possible to determine on which one of the front and back sides of the steel sheet <NUM> the flaw <NUM> is present.

Note that although the above example describes the configuration and operation for transmitting and receiving the AOSO mode and the S1 mode by the ultrasonic probe <NUM> in the phased array system, the ultrasonic probe <NUM> may send out ultrasound to the steel sheet <NUM> at a plurality of angles by mechanically scanning. For example, a plurality of angles may be obtained by using a type of variable angle probe as the ultrasonic probe <NUM>. In addition, a plurality of angles may be obtained by using a plurality of angle probes having different angles of incidence. In addition, although the above example describes an ultrasonic flaw detection device that uses an angle probe, the angle probe does not need to be used as long as an ultrasonic probe that allows ultrasound to obliquely enter the steel sheet <NUM> is used.

As described above, an ultrasonic flaw detection device of the first embodiment includes: an ultrasonic probe that generates ultrasound waves corresponding to transmission signals to be provided thereto, and sends out the ultrasound waves into a specimen, and receives echoes of the respective ultrasound waves having propagated through the specimen, and outputs the received echoes as reception signals; a transmission signal processing unit that generates, as the transmission signals, signals that are used by the ultrasonic probe to send out the ultrasound waves to the specimen obliquely at a respective plurality of angles; and a reception signal processing unit that determines, from the reception signals, amplitudes of the echoes corresponding to the plurality of angles, and periods of time from when the respective ultrasound waves are sent out until the respective echoes are received, as reception times, and identifies a location of an acoustic discontinuous portion in the specimen from the reception times and a ratio between the amplitudes, and thus, there is an advantageous effect of being able to determine on which one of the front and back sides of the specimen a flaw is located.

In addition, according to the ultrasonic flaw detection device of the first embodiment, a transducer of the ultrasonic probe includes a plurality of arrayed transducer elements, and the transmission signal processing unit generates a set of signals having different delay times corresponding to the respective plurality of transducer elements, as a signal corresponding to each of the plurality of angles, and thus, a configuration for sending out ultrasound waves at the plurality of angles can be easily implemented.

In addition, according to the ultrasonic flaw detection device of the first embodiment, the ultrasonic probe sends out the ultrasound waves to the specimen obliquely at the respective plurality of angles by mechanically scanning, and thus, as the ultrasonic probe, various probes can be selected.

Note that in the invention of the present application, modification to any component of the embodiment or omission of any component of the embodiment is possible within the scope of the invention.

As described above, an ultrasonic flaw detection device according to the invention relates to a configuration in which plate waves in a plurality of different modes are allowed to propagate through a specimen using an ultrasonic probe, and the properties of the specimen are determined from the amplitude ratio and amounts of receive time of a plurality of received echoes, and is suitable for detecting a flaw, including determining on which one of the front and back of a steel sheet the flaw is present.

Claim 1:
An ultrasonic flaw detection method comprising:
generating ultrasound waves corresponding to transmission signals to be provided to an ultrasonic probe (<NUM>) and sending out the ultrasound waves into a specimen (<NUM>), and receiving by the ultrasonic probe (<NUM>) echoes of the respective ultrasound waves having propagated through the specimen (<NUM>) and outputting the received echoes as reception signals;
generating, as the transmission signals, signals that are used by the ultrasonic probe (<NUM>) to send out the ultrasound waves to the specimen (<NUM>) obliquely at a respective plurality of angles; and
determining, from the reception signals, amplitudes (E1, E2) of the echoes corresponding to the plurality of angles, and periods of time from when the respective ultrasound waves are sent out until the respective echoes are received, as reception times (T1, T2), and identifying a location of an acoustic discontinuous portion in the specimen (<NUM>) given by a flaw (<NUM>) by estimating a distance from the probe (<NUM>) to the flaw (<NUM>) from the reception times (T1, T2),
said method characterized by
identifying the location of the flaw (<NUM>) from a ratio between the amplitudes (E1, E2) and the reception times (T1, T2) by determining on which of a front side and a back side of the specimen (<NUM>) the flaw is located using differences between changes in echo height relative to the distance between an AOSO mode and an S1 mode of the ultrasound waves;
configuring the frequency and the angle of incidence of said ultrasound waves to first respective values so that first plate waves of A0 mode and S0 mode propagate through said specimen at the same, first phase velocity; and
configuring the frequency and the angle of incidence of said ultrasound waves to second respective values so that second plate waves of S1 mode propagate through the specimen at a second, different phase velocity,
said AOSO mode being a mode having characteristics of both said A0 mode and said S0 mode.