JP6643762B2 - Non-contact thickness measurement method for steel structures in liquids - Google Patents

Description

  The present invention relates to a non-contact type thickness measurement method for a submerged steel structure, for example, in which a substance is present on a surface of a submerged steel structure which is an object to be measured installed in a liquid such as the sea. The present invention relates to a non-contact type thickness measurement method of a submerged steel structure capable of appropriately measuring the thickness of the submerged steel structure without removing the attached matter.

  Steel pipe piles and steel sheet piles on piers and quays undergo rust and other factors to reduce wall thickness under severe environmental conditions, and are maintained so that their functions can be exhibited during their useful lives. In order to make such a maintenance plan, the wall thickness of steel pipe piles and steel sheet piles is regularly measured.

  For example, the method of measuring the wall thickness of steel pipe piles and steel sheet piles currently being carried out is as follows. After removing and collecting living organisms manually and polishing the measurement surface of the steel pipe pile using an air sander, use an ultrasonic thickness gauge and attach the ultrasonic thickness gauge probe (transmitter / receiver) to the polished measurement surface Then, an ultrasonic wave is transmitted, the transmission time of the reflected wave from the back surface of the steel plate is measured, and the thickness is calculated.

  However, the above-mentioned conventional thickness measurement method is a manual operation of a diver, and particularly requires a long operation time for removing attached sea creatures, which requires a high operation cost. Further, the attached sea creatures removed from the measurement surface of the steel pipe pile for the thickness measurement must be collected and treated as industrial waste, which requires a cost for waste treatment.

  Furthermore, since the conventional thickness measurement method described above can only measure the thickness of a part of the steel pipe pile due to its method, continuous thickness measurement over the entire length of the steel pipe pile is substantially impossible, and the measured value There was a limit in improving the reliability of

  Therefore, the present inventors have realized a low-cost and highly reliable method capable of realizing a continuous thickness measurement for a submerged steel structure without removing the attached substance attached to the submerged steel structure. A non-contact thickness measurement method for submerged steel structures is proposed.

JP 2008-286610 A

  The non-contact type thickness measurement method of a submerged steel structure described in Patent Literature 1 is an arrangement in which an ultrasonic transducer is spaced apart from a submerged steel structure to be measured in a non-contact state. A step of radiating an ultrasonic wave from the ultrasonic transducer to the submerged steel structure, and receiving a reflected wave reflected from the submerged steel structure by the ultrasonic transducer. The wave receiving step and the reflected wave received in the wave receiving step are correlated to obtain a surface reflected wave from the surface of the submerged steel structure and a back surface reflected wave from the back surface of the submerged steel structure. A correlation processing step of extracting the, and a calculation step of calculating the thickness of the submerged steel structure by calculating a difference in arrival time of the front surface reflected wave and the back surface reflected wave with respect to the ultrasonic transducer. Is performed.

  According to such a non-contact type thickness measurement method for a submerged steel structure, the thickness can be measured without removing the adhered substance attached to the surface of the submerged steel structure. The working time can be reduced, and the working cost can be reduced. Further, according to the present invention, since there is no need to remove the attached matter, no industrial waste is generated, the waste treatment cost can be reduced, and no burden is imposed on the environment.

  In addition to the method described above, in addition to obtaining the difference in arrival time of the front reflected wave and the back reflected wave with respect to the ultrasonic transducer, by measuring the time interval of multiple reflected waves in the submerged steel structure. It is known that the thickness can be calculated.

  However, the conventional non-contact type thickness measurement method of a submerged steel structure, when there is a large amount of deposits, the reflected wave does not immediately attenuate and the reverberation continues for a long time. When it is equal to or larger than the multiple reflection wave, there is a problem that the multiple reflection wave cannot be detected, the thickness cannot be calculated, or the measurement accuracy is significantly reduced.

  In addition, in the conventional method, the measurement distance was set so that the peak value of the sound pressure level of the ultrasonic transducer hits the submerged steel structure in order to obtain a stronger reflected wave, but according to this method, In addition, strong ultrasonic waves will also be applied to the attached matter, and the obtained measurement result will be the sum of reflected waves and multiple reflected waves from both the submerged steel structure and the attached matter, and when analyzing this, There has been a problem that the position of multiple reflection cannot be easily obtained without having specialized knowledge.

  Therefore, the present invention has been made in view of the above-described problems, and even when there are many deposits attached to the submerged steel structure, it is not necessary to have specialized knowledge to perform the submerged steel structure. It is an object of the present invention to provide a non-contact type thickness measurement method of a steel structure in liquid capable of performing thickness measurement.

An arranging step of disposing the ultrasonic transducer in a non-contact state with respect to the submerged steel structure as an object to be measured, and an ultrasonic wave from the ultrasonic transducer to the submerged steel structure. And a receiving step of receiving a reflected wave reflected from the submerged steel structure by the ultrasonic transducer, and performing a correlation process on the reflected wave received in the receiving step. A correlation processing step of extracting a deposit attached to the submerged steel structure and a surface reflected wave and a multiple reflected wave from the surface of the submerged steel structure, and measuring a time interval between the multiple reflected waves. A calculation step of calculating the thickness of the submerged steel structure, and a non-contact type thickness measurement method for performing a process including: The distance from the ultrasonic transducer to the focal length of the ultrasonic transducer Small set, the ultrasonic transducer is a surface in the disc-type formed in a circular arc shape, in the vicinity the center point of the arc ultrasonic waves, wherein Rukoto includes a focus converging type sound source to concentrate.

  Further, in the non-contact type thickness measuring method for a submerged steel structure according to the present invention, the arranging step may be such that a position of a first zero point of a sound pressure distribution on a central axis of the ultrasonic transducer is the above-mentioned. It is preferable to determine the distance between the ultrasonic transducer and the surface of the submerged steel structure so as to be near the surface of the submerged steel structure.

  In the non-contact thickness measuring method for a steel structure in liquid according to the present invention, it is preferable that in the calculating step, a time interval is measured from the positions of the second to fourth multiple reflection pulses.

  The above summary of the present invention does not enumerate all the necessary features of the present invention, and a sub-combination of these features may also be an invention.

  In the non-contact thickness measurement method for a submerged steel structure according to the present invention, weak ultrasonic waves are applied to both the attached matter and the submerged steel structure, but the reflection is repeated between the front surface and the back surface of the submerged steel structure. The reflected wave travels inside the submerged steel structure and is focused inside the submerged steel structure, so that a large reflected wave can be obtained. As a result, the reflected wave from the attached substance is reduced, and the multiple reflection from the submerged steel structure is increased, so that even when the amount of the attached substance is large, the submerged steel structure is not contacted. Can be measured. In addition, since the reflected wave from the attached matter is small and the multiple reflection is large, it is easy to determine the multiple reflection in the measurement result, and even if there is no expert knowledge, the thickness can be easily increased. Can be calculated.

Schematic diagram of reflected wave Analysis waveform of reflected wave Illustration of multiple reflection Diagram showing sound pressure distribution on the horizontal plane of ultrasonic waves transmitted from the transducer Graph showing sound pressure distribution on the central axis of ultrasonic waves transmitted from a transducer Diagram showing sound pressure distribution and measurement position Diagram showing the outline of the experimental equipment Voltage waveform of reflected wave from attached matter A graph showing the distance between the reflected wave from the deposit and the transducer Voltage waveform of reflected wave from steel plate Graph showing the distance between the reflected wave from the steel plate and the transducer Analysis results showing reflected waves from a steel sheet with attached matter Analysis results showing reflected waves from a steel sheet with attached matter Graph showing the relationship between the distance from the transducer to the steel plate and the measured thickness

  Hereinafter, a preferred embodiment for carrying out the present invention will be described with reference to the drawings. It should be noted that the following embodiments do not limit the invention according to each claim, and not all combinations of the features described in the embodiments are necessarily essential for solving the invention. .

[Principle of non-contact thickness measurement]
As shown in FIG. 1, when an ultrasonic wave is propagated through a submerged steel structure such as a steel plate 10 to which an organism such as a shell has adhered as the deposit 40, a reflected wave is reflected from the deposit as shown in FIG. The wave arrives at the receiver in the order of the wave, the reflected wave from the surface of the steel sheet, and the multiple reflected wave. Since the multiple reflected wave is a sound wave that reciprocates in the steel plate, it is continuously measured for a while after the reflected wave from the attached matter and the reflected wave from the steel plate surface disappear. Since the time interval of the multiple reflected waves is the time interval of the ultrasonic waves reciprocating in the steel sheet, the thickness of the steel sheet can be measured by multiplying the obtained sound velocity in the steel sheet and dividing by 2. it can.

  However, multiple reflections from a steel plate placed in water are very weak as compared with surface reflections, and furthermore, when transmitted through an attached matter, ultrasonic waves are attenuated and the energy reaching the steel plate is also attenuated. In the non-contact thickness measuring method for a submerged steel structure according to the present embodiment, the following technical development was performed on the shape of the transducer for detecting such a weak multiple reflected wave, the signal processing to be used, and the like.

[About multiple reflection]
Multiple reflection is caused by the ratio of reflection and transmission of a boundary surface when ultrasonic waves propagate in different media, as in the case where a steel sheet is placed in water and ultrasonic waves are propagated. Here, the acoustic impedance Z1 of seawater is Z1 = 1.48 × 10 ⁶ (Pa · s / m), the acoustic impedance Z2 of the steel plate is Z2 = 46.4 × 10 ⁶ (Pa · s / m), When a steel plate is placed in seawater, the reflectance and the transmittance when the ultrasonic wave propagates from the seawater to the steel plate and when the ultrasonic wave propagates from the steel plate into the seawater are as follows.

  As can be seen from Table 1, the transmittance (TI) of the sound intensity transmitted from the seawater to the steel plate is 0.12, indicating that 12% of the sound energy is transmitted to the steel plate. As shown in FIG. 3, the ultrasonic wave transmitted to the steel plate 10 advances and reaches a boundary surface 11 between the back surface of the steel plate 10 and seawater, where reflection and transmission occur at the boundary surface 11. The reflectivity (RI) of the sound intensity transmitted from the steel plate 10 to the seawater is 0.88, and when ultrasonic waves propagate from the steel plate into the seawater, 88% of the sound energy of the incident wave is reflected into the steel plate 10. Will be returned. Therefore, the ultrasonic waves incident on the steel plate 10 radiate about 12% of the energy into the seawater at both ends of the steel plate 10 and are attenuated while reciprocating within the steel plate 10. As shown in FIG. 3, a phenomenon in which ultrasonic waves repeatedly reflect and reciprocate at both ends of the steel plate 10 is called multiple reflection, and when the incident sound pressure is set to 1, the relationship shown in Table 2 below is obtained. In Table 2, the negative values of the sound pressure of the first and second back reflections indicate that the phases are inverted.

  As is clear from Table 2, the first and second back reflection waves R1 and R2 can be detected with substantially the same sound pressure. Here, since the amount of attenuation such as propagation attenuation is not taken into account, the actually measurable sound pressure is further reduced. However, by measuring the time interval between the first and second back reflected waves R1 and R2, Since the propagation time of the ultrasonic wave reciprocating in the steel plate 10 can be known, the thickness of the steel plate 10 is calculated from the propagation time.

[Design and arrangement of transducers]
In order to measure the thickness of an object in a non-contact manner, it is important to capture weak multiple reflections as described above. Therefore, high-power sound waves are emitted to the object to be measured, and reflected waves are efficiently received. It is preferable to use a large-diameter focal-focusing type transducer capable of performing the above operation.

  The focus-focusing type transducer has a disk-shaped surface and is formed in an arc shape, and includes a focus-focusing type sound source in which ultrasonic waves are concentrated near the center point of the arc. The specifications are a center frequency of 700 kHz, a diameter of 100 mm, Preferably, the radius of curvature is 300 mm. FIG. 4 shows a sound pressure distribution on a horizontal plane including the central axis of the transducer, and FIG. 5 shows a sound pressure distribution on the central axis.

  FIG. 4 is a graph in which the maximum value of the sound pressure distribution is set to 1 and the sound pressure is displayed in five gradations. It can be seen that the ultrasonic waves are strongly distributed cylindrically about 200 to 500 mm from the transducer with the central axis of the transducer being the axis.

  In addition, as shown in FIG. 5, the position of the first zero point of the sound pressure distribution appears at a position of about 200 mm. Conventionally, as shown in FIG. The position of the transducer was set so that the steel plate existed near the focal point of the transducer where the sound pressure distribution had the maximum so that the pressure was applied, but at this position, strong sound pressure was applied to the attached matter As a result, the reverberation of the reflected wave from the deposits overlaps with the multiple reflected waves that reciprocate in the steel sheet, and there is a problem that the multiple reflected waves cannot be detected.

  On the other hand, according to the non-contact thickness measuring method for a submerged steel structure according to the present embodiment, as shown in FIG. 6, the position of the transducer is brought closer to the steel plate, so that the position of the transducer is changed. By setting the focal length smaller than the focal length of the transducer, a strong sound can be applied only to the steel sheet and a weak sound can be applied to the attached matter. As a result, the intensity of the reflected wave from the deposit becomes weaker than the multiple reflected waves that reciprocate propagate in the steel plate, and good measurement is possible.

  The distance between the transducer and the steel plate is preferably set such that the surface of the steel plate comes near the position of the first zero point of the sound pressure distribution on the central axis of the transducer. Further, in order to increase the transmission power in the transmitter / receiver, it is preferable to introduce a pulse compression technique based on a code modulation scheme used for radar and use a Barker code in which the range side lobe is reduced. When transmitting a Barker code from an ultrasonic transmitter / receiver, the Barker code is transmitted to the ultrasonic transmitter / receiver using an ultrasonic signal as a carrier wave and an electric signal modulated according to a change in the Barker code, thereby transmitting the Barker code to the ultrasonic wave. Can be propagated as By using this Barker code, the range side lobe is reduced, and the received signal can be easily identified.

[Measuring method]
The non-contact thickness measurement method for a submerged steel structure according to the present embodiment can be implemented by, for example, an apparatus including a transmitter, a power amplifier, an ultrasonic transducer, an AD converter, and a control analysis computer. Specifically, the ultrasonic transducer is separated from the submerged steel structure such as a steel plate to be measured in a non-contact state with the submerged steel structure (arrangement step). Ultrasonic waves are emitted to the structure (radiation process), the reflected wave reflected from the submerged steel structure is received by the ultrasonic transducer (wave receiving process), and the received reflected wave is correlated. Extracting the deposits adhering to the submerged steel structure and the surface reflected wave and the multiple reflected wave from the surface of the submerged steel structure (correlation processing step), and measuring the time interval between the multiple reflected waves. To calculate the thickness of the submerged steel structure (calculation step). In the disposing step, the distance between the surface of the submerged steel structure and the ultrasonic transducer is set smaller than the focal length of the ultrasonic transducer.

[Measurement result]
Next, a measurement result of a steel plate measurement experiment using the above-described non-contact thickness measurement method for a submerged steel structure will be described.

  As shown in FIG. 7, in this measurement, a steel plate 10 which is an object to be measured, an ultrasonic transducer 20 which radiates an ultrasonic wave to the steel plate 10 to receive a reflected wave or a multiple reflected wave, A linear motion device 30 for varying the distance between the wave device 20 and the steel plate 10 was used.

  First, a mussel shell packed in a bag in place of the steel plate 10 was used as the attached matter 40, and measurement was performed by radiating ultrasonic waves only to the attached matter 40.

  The position of the ultrasonic transducer 20 is moved by using the linear motion device 30, and the distance between the ultrasonic transducer 20 and the attached matter 40 is changed so that the positions of (1) and (2) shown in FIG. The maximum amplitude of the voltage value between them was measured. It should be noted that (1) indicates the time required for the reflected wave from the back surface of the deposit 40 (corresponding to the surface of the steel plate 10) to reach the ultrasonic transducer 20, and (2) assumes that the steel plate 10 is present. Indicates the time at which the tail of the pulse of the fourth multiple reflection wave is measured.

  As shown in FIG. 9, the relationship between the maximum amplitude of the reflected wave voltage from (1) and (2) of the reflected wave voltage from the attached matter 40 and the distance from the transmitter / receiver indicates that the reflected wave from the attached matter 40 decreases as the distance decreases. Can be confirmed to be smaller.

  Next, as shown in FIG. 7, the same measurement as the above-described measurement of the reflected wave from the attached matter was performed using only the steel plate 10 (18.45 mm in thickness).

  FIG. 10 shows a reflection waveform from the steel plate 10 when the distance between the ultrasonic transducer 20 and the steel plate 10 is set to 304 mm. In this reflected waveform, a surface reflected wave exists between (1) and (2), and a second to fourth multiple reflected waves exist between (3) and (4). As shown in FIG. 11, the change in the maximum amplitude voltage of the surface reflected wave and the multiple reflected wave with respect to the distance from the ultrasonic transducer to the steel plate indicates that the surface reflected wave has the same focus as the sound pressure distribution shown in FIG. The amplitude is maximized in the vicinity, and the amplitude of the surface reflected wave decreases as the distance between the ultrasonic transducer and the steel plate decreases, but the amplitude of the multiple reflected wave increases as the distance decreases. The reason for this is that, since the ultrasonic transducer uses a focussed sound source, the ultrasonic waves advance in the steel sheet by repeating multiple reflections, and the multiple reflections increase when the focal length is reached. Conceivable.

  Next, the attached matter 40 in which the shell of mussels was packaged was attached to the steel sheet 10 shown in FIG. 7, and the measurement was performed in a state where the attached matter 40 was attached to the steel sheet 10.

  FIG. 12 is an analysis waveform of a reflected wave when the distance from the ultrasonic transducer to the steel plate is set to 309 mm. This distance of 309 mm indicates that the steel plate exists at a position where the sound pressure level has a peak value at the distance from the center of the ultrasonic transducer shown in FIG. Here, (1) is the position where the surface reflected wave from the steel plate is detected, and between (1) and (2) is the position where the multiple reflected wave is detected, but the surface is affected by the reverberation from the attached matter. Neither reflected waves nor multiple reflected waves can be read from this graph.

  On the other hand, FIG. 13 shows an analysis waveform of a reflected wave when the distance from the ultrasonic transducer to the steel plate is set to 199 mm. This distance of 199 mm indicates that the steel plate exists at a position where the sound pressure level appears as the first zero point at the distance from the center of the ultrasonic transducer shown in FIG. As is clear from FIG. 13, the surface reflected wave can be read at the time of (1) in the analysis waveform, and the multiple reflected wave can be read between (1) and (2). Note that the multiple reflected wave can be confirmed at the pulse position between (1) and (2), but the first multiple reflected wave may overlap with the surface reflected wave, so the second to fourth times It is preferable to calculate the time interval from the pulse position of the multiple reflection.

  FIG. 14 shows a measurement result of a wall thickness measurement value with respect to a distance from the ultrasonic transducer to the steel plate. As is clear from FIG. 14, the thickness measurement results obtained when the steel sheet alone was measured and when there was an attached matter were almost the same when the distance was 219 mm or less. This indicates that the wall thickness measurement can be performed regardless of the presence or absence of.

  As described above, according to the non-contact thickness measurement method for a submerged steel structure according to the present embodiment, the reflected wave from the attached matter is small and the multiple reflection is large, so that the measurement result shows that The discrimination is facilitated, and the thickness can be easily calculated even when there is no special knowledge.

  The non-contact thickness measurement method for a steel structure in liquid described above is based on, for example, creating a program that automatically calculates these time intervals from the positions of multiple reflections to obtain knowledge on the characteristics of ultrasonic waves. It may be configured such that even a measurer who does not have an easy and accurate thickness measurement of a submerged steel structure such as a steel plate. It is apparent from the description of the appended claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  Reference Signs List 10 steel plate, 11 boundary surface, 20 ultrasonic transducer, 30 linear motion device, 40 deposits.

Claims (3)

An arrangement step of disposing the ultrasonic transducer in a non-contact state with respect to a submerged steel structure that is an object to be measured,
A radiation step of radiating ultrasonic waves from the ultrasonic transducer to the submerged steel structure,
A wave receiving step of receiving a reflected wave reflected from the submerged steel structure by the ultrasonic transducer;
Correlation processing is performed on the reflected waves received in the wave receiving step to extract the attachments attached to the submerged steel structure and the surface reflected waves and multiple reflected waves from the surface of the submerged steel structure. A correlation processing step;
By measuring the time interval of the multiple reflected waves, a calculating step of calculating the thickness of the submerged steel structure,
A non-contact thickness measurement method for performing a process including:
The arranging step, the distance between the surface of the submerged steel structure and the ultrasonic transducer is set smaller than the focal length of the ultrasonic transducer ,
The ultrasonic transducer is a surface in the disc-type formed in a circular arc shape, the non-submerged steel structures near the center point of the arc ultrasonic waves, wherein Rukoto includes a focus converging type sound source to be concentrated Contact type thickness measurement method. The non-contact thickness measurement method for a submerged steel structure according to claim 1 ,
The ultrasonic transducer and the ultrasonic transducer so that the first zero point of the sound pressure distribution on the central axis of the ultrasonic transducer is located near the surface of the submerged steel structure. A non-contact type thickness measurement method for a submerged steel structure, comprising determining a distance of a surface of the submerged steel structure. A non-contact thickness measurement method for a submerged steel structure according to claim 1 or 2 ,
The said calculation process measures the time interval from the position of the pulse of the 2nd-4th multiple reflection, The non-contact type thickness measurement method of a submerged steel structure characterized by the above-mentioned.