JP2005083907A - Defect inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect corrosion and marks that may occur at a part, where a visual inspection, or the like is not possible, by allowing a tube to penetrate a pier, abutment, or the like, and to improve the evaluation precision of the depth of corrosion and marks. <P>SOLUTION: Piping 1 erected at the lower portion of a bridge girder of a bridge allows local torsional waves to be propagated from a special SH wave probe 5 for vibrating an entire plate thickness for a measurement part 1a that is hidden by a filler 3 through a bridge abutment 2 and, for example, cannot be viewed. Reflection waves that are reflected from the measurement part 1a that are hidden, for example cannot be viewed, are received by the special SH wave probe 5, and the corrosion, or the like of the measurement part 1a is detected according to a change in the reception signal of the received reflection waves. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, a part of a metal structure made of a metal material on a plate is hidden by another structure, for example, a part of a pipe body constructed on a bridge or the like passes through a bridge pier or an abutment. The present invention relates to a defect inspection method for inspecting corrosion and scratches that may occur at sites where inspection such as visual inspection is difficult, and in particular to improving the evaluation accuracy of the degree of corrosion and the like.

  For example, a pier penetration part of a pipe erected on a bridge tends to collect rainwater, and therefore, corrosion of the outer surface is likely to occur. This pipe pier penetration part is filled with filler etc. between the pipe body and pier, so detect defects such as corrosion and scratches by visual inspection and ultrasonic thickness gauge etc. It is not possible. In addition, even if a general ultrasonic flaw detection method is applied to the measurement site of a tubular body that is provided with a general ultrasonic probe in the exposed portion of the tubular body and penetrates the pier, the necessary supersonic inspection method is applied. The propagation distance of the sound wave becomes long and satisfactory inspection cannot be performed. In addition, when a general ultrasonic flaw detection method is applied, it is necessary to remove the piers and fillers around the pipe body, which requires a lot of time and cost.

  On the other hand, the ultrasonic wave that can propagate the required distance propagates along the surface of the thin structure and uses the guide wave that can be propagated for a long distance, and the corrosion that occurs at the measurement site of the pipe that penetrates the bridge pier. Non-Patent Document 1, Patent Document 1, Patent Document 2, and the like are disclosed as inspection methods.

  In the corrosion inspection method disclosed in Non-Patent Document 1, a flaw detection ring is set on an exposed portion of a pipe body, and a guide wave propagating through a series of displacements from the flaw detection ring is transmitted to a measurement site. The reflected wave reflected from the corroded part is received by the flaw detection ring, and the state of the corroded part is inspected based on the intensity of the received guide wave, so that the corrosion of the pipe is inspected over a long distance. Yes.

  In the corrosion inspection method disclosed in Patent Document 1, an SH wave is propagated from an exposed outer surface of a thin-walled steel pipe to a measurement site where the outer surface of the tubular body is concealed by a SH wave probe, such as a pier penetration part. The reflected wave reflected from the measurement site is received by the SH wave probe, and the corrosion is inspected based on the reflected signal. Since the SH wave used in this corrosion inspection method can propagate as a wave along the outer surface due to its characteristics, the propagation distance becomes longer than that of a normal ultrasonic wave. Further, in this corrosion inspection method, the second SH wave probe is positioned at the opposite side of the first SH wave probe across the concealed measurement site together with the first SH wave probe that transmits and receives SH waves. The reflected signal received by the first SH wave probe is normalized using the signal obtained by arranging the child and receiving the SH wave that has passed through the measurement site by the second SH wave probe. The degree of corrosion is judged.

  In addition, the inspection method disclosed in Patent Document 2 presses the probe at a position separated from the welded portion of the steel structure by a predetermined distance, transmits a surface SH wave toward the welded portion, The reflected wave is received by the probe, and the shape of the weld is determined by comparing the received reflected wave with a typical waveform obtained in advance by experiments.

  Since the guide wave used in the corrosion inspection method shown in Non-Patent Document 1 is a cylindrical wave that propagates with a series of displacements with respect to the entire tube, the reflected wave generated from the corrosion to be detected is a circle. Regarding the circumferential direction, since it is obtained as a single signal, it is generated in accordance with the ratio of the cross-sectional area of corrosion distributed throughout the circumferential direction to the circumferential cross-sectional area of the pipe body. Therefore, even when there are a plurality of corrosions on the same circumference, they cannot be separated and evaluated, and the detection accuracy is reduced for minute corrosion that occurs independently.

Further, since the ultrasonic wave used in the inspection methods of Patent Document 1 and Patent Document 2 is an SH wave that propagates along the outer surface, when the depth of corrosion increases to some extent, the change in the received signal becomes that depth. It becomes difficult to follow. Further, the ultrasonic wave is attenuated under the influence of the coating applied to the outer surface. Therefore, the accuracy may be lowered in the quantitative evaluation of corrosion, particularly in the evaluation of the corrosion depth which is important for the maintenance of the pipe. Furthermore, when the SH wave is propagated, in addition to the wave along the outer surface, a wave having an angle to some extent in the thickness direction often occurs at the same time. As a result, a plurality of wave signals may be included in the reflected signal, and it may be difficult to identify a signal to be used for evaluation of the received signal.
"Inspection Technology" Nippon Kogyo Publishing Co., Ltd. 2003.1 50-53 pages JP 2000-243704 A JP-A-10-221309

  The present invention improves such disadvantages. For example, when a pipe penetrates a pier or an abutment, corrosion and scratches that may occur in parts that cannot be visually inspected are detected with high accuracy. It is another object of the present invention to provide a defect inspection method capable of improving the evaluation accuracy of the depth of corrosion and scratches.

  The defect inspection method of the present invention is a defect inspection method for inspecting corrosion, scratches, etc. occurring in a portion of a metal structure made of a plate-like metal material, a part of which is hidden by another structure. Propagating a local torsional wave from an exposed outer surface portion that is an outer surface of the metal structure, which is close to a portion hidden by another structure, toward a portion hidden by the other structure. A reflected wave reflected from a portion hidden by the body is received, and corrosion or the like of the portion hidden by another structure is detected by a change in the received signal of the received reflected wave.

  The local torsional wave propagating to the metal structure is a single mode in which the phase velocity and group velocity do not change by selecting the frequency according to the plate thickness and natural sound velocity of the plate-like metal material that will be the vibration medium among the multiple modes It is desirable to adopt the vibration form.

  Corrosion etc. is caused by the internal to external surface of the metal structure by vibrating the entire plate thickness by propagating local torsional waves from the exposed outer surface part to the part hidden by the other structure on the outer surface of the metal structure. Any of these can be detected, and the position where corrosion or the like is occurring can be detected with high accuracy.

  In addition, a single mode in which the phase velocity and group velocity do not change by selecting the frequency according to the plate thickness and natural sound velocity of the plate-like metal material that will be the vibration medium from the multiple modes of local torsional waves propagating to the metal structure By virtue of this vibration mode, it is possible to obtain a reflected signal corresponding to the depth of corrosion or the like by vibrating with a uniform displacement distribution over the entire plate thickness, and the degree of corrosion or the like can be detected with high accuracy. Furthermore, since the local torsional wave to be transmitted is a single mode and a plurality of modes are not mixed, a clear flaw detection figure can be displayed, and the position and degree of corrosion or the like can be detected with high accuracy.

  FIG. 1 is a layout view of an inspection apparatus used in the defect inspection method of the present invention. This defect inspection method is a method for inspecting corrosion or the like that occurs in the measurement site 1a that cannot be visually observed because the pipe 1 installed under the bridge girder of the bridge passes through the abutment 2 and is hidden by the filler 3. It has a special SH wave probe 5 mounted on the scanning drive unit 4, an ultrasonic transmission / reception device 6, and a control / diagnosis device 7. The scanning drive unit 4 includes a guide rail 8 fixed to the outer peripheral surface of the pipe 1 close to the abutment 2, and a holding mechanism unit 9 that is movably attached to the guide rail 8. The special SH wave probe 5 transmits a local torsional wave, which is a kind of ultrasonic wave, to the measurement site 1a of the pipe 1 and receives a reflected wave from a defective portion such as corrosion of the measurement site 1a. It is mounted on the holding mechanism unit 9 of the scanning drive unit 4 and is pressed against the exposed tube surface of the pipe 1 with a constant pressure by the holding mechanism unit 9 via a contact medium.

  The local torsion wave transmitted from the special SH wave probe 5 has the same vibration form as the torsion wave (Torsionsl mode) in the cylindrical wave in the guide wave, and the torsion wave vibrates all in the circumferential direction. On the other hand, local torsional waves are those that are generated locally in the circumferential direction. That is, as shown in the schematic diagram of FIG. 2, the local torsional wave is a wave that vibrates locally in the circumferential direction, unlike a cylindrical wave that vibrates the entire circumference. This local torsional wave has a plurality of modes as a vibration form with a phase velocity and a group velocity changing depending on conditions such as a frequency and an incident angle according to a plate thickness of the plate-like metal material, a natural sound velocity, and the like. This vibration form is represented as T (n, m). Here, n and m are mode orders, n represents a change in the circumferential wave displacement distribution, and m represents a thickness displacement wave displacement distribution. In the local torsional wave, since the circumferential direction oscillates locally, the characteristics such as the dispersion curve due to the change in the circumferential direction displacement distribution do not change. As shown in the displacement distribution characteristic diagram of the local torsional wave in the plate thickness direction, the displacement distribution of the local torsional wave is uniform in the plate thickness direction when m = 1, but changes complicatedly when m = 2 and 3.

  The local torsional wave also has velocity dispersion due to the displacement distribution. For example, FIG. 4 shows a phase velocity dispersion curve and a group velocity dispersion curve of a local torsion wave in a tube having a nominal diameter of 400 A and a plate thickness of 7.9 mm. As shown in FIG. 4, in the T (0,1) mode, the phase velocity and the group velocity do not change. If the frequency is 0.2 MHz or less, only the T (0,1) mode can be generated.

  Therefore, the special SH wave probe 5 sets an appropriate incident angle calculated from, for example, the phase velocity obtained from the pipe diameter or plate thickness of the pipe 1 and the transverse wave sound velocity of the wedge used for the special SH wave probe 5. . Also, the frequency is selected according to the pipe diameter and thickness of the pipe so that only the T (0, 1) mode is generated.

  The ultrasonic transmission / reception apparatus 6 generally has a function of sending a high-voltage pulse to the ultrasonic probe, but the special SH wave probe 5 that generates a local torsional wave is used as the ultrasonic probe. When the local torsional wave is used, as shown in FIG. 4, the vibration mode and the speed of sound change depending on the frequency. Therefore, it is necessary to generate high-energy ultrasonic waves in a narrow band. Therefore, in order to generate an appropriate local torsional wave by the special SH wave probe 5, the ultrasonic transmission / reception apparatus 6 transmits, for example, a burst pulse to the special SH wave probe 5. Here, the burst pulse transmitted from the ultrasonic transmission / reception apparatus 6 is a method of using a sine wave having the same frequency as the frequency of the local torsion wave used for measurement as the transmission pulse.

  The control / diagnosis device 7 is composed of, for example, a personal computer, and receives the received signal received by the ultrasonic transmission / reception device 6 by the reflected wave of the local torsion wave received by the special SH wave probe 5 and the special SH sent from the scanning drive unit 4 The circumferential position information of the pipe 1 of the probe 5 is stored, and the stored signal is used as a special SH probe as a flaw detection figure using the group velocity of local torsional waves determined from the pipe diameter, plate thickness, frequency, etc. Displayed for each circumferential position information of the pipe 1 of the child 5.

  A method of detecting defects such as corrosion and scratches generated in the measurement site 1a of the pipe 1 with this inspection apparatus will be described with reference to the flowchart of FIG.

  First, the guide rail 8 is fixed to the outer peripheral surface of the pipe 1 close to the abutment 2, the holding mechanism portion 9 holding the special SH wave probe 5 is attached to the guide rail 8, and the special SH wave probe 5 is attached. Positioning is performed at the initial position in the circumferential direction (step S1). In this state, the ultrasonic transmission / reception device 6 is driven to send a burst pulse to the special SH wave probe 5, and a local torsion wave is transmitted from the special SH wave probe 5 to the measurement site 1a side of the pipe 1 (step S2). ). In this burst pulse, the mode of the local torsion wave transmitted from the special SH wave probe 5 is the T (0, 1) mode alone in which the phase velocity and the group velocity are not accompanied by a change in frequency among the plurality of modes. As described above, the frequency is selected according to the thickness of the metal material of the pipe 1. By selecting the frequency of the burst pulse in this way, a local torsional wave of T (0,1) mode having a uniform displacement distribution in the thickness direction can be transmitted from the special SH wave probe 5.

  The reflected wave from the measurement site 1 a side of the transmitted local torsion wave is received by the special SH wave probe 5, and the signal by the reflected wave is received by the ultrasonic transmission / reception device 6. The local torsional wave of T (0, 1) mode transmitted to the pipe 1 vibrates with a uniform displacement distribution over the entire thickness of the pipe body of the pipe 1, so that it can be detected whether corrosion or the like is present on the inner or outer surface. Can do. Further, the intensity change of the reflected signal easily follows in accordance with the depth of corrosion and the like, and corrosion and the like can be detected with high accuracy.

  When the received signal of the reflected wave is received by the ultrasonic transmission / reception device 6, the control / diagnosis device 7 receives the received signal received by the ultrasonic transmission / reception device 6 and the pipe 1 of the special SH probe 5 sent from the scanning drive unit 4. Circumferential position information is stored (step S4). Thereafter, the position of the special SH wave probe 5 in the circumferential direction is moved by one pitch, and local torsional wave transmission / reception is repeated (steps S5, S6, S7 to S4). When all positions are inspected with respect to the circumferential direction of the pipe 1 (step S5), the inspector operates the control / diagnosis device 7 and uses the group velocity of the local torsional wave from the stored received signal. A flaw detection figure is displayed for each circumferential position information of the pipe 1 (step S7). When displaying this flaw detection figure, the local torsional wave transmitted from the special SH probe 5 is a single T (0,1) mode, and a plurality of modes are not mixed, so that a clear flaw detection figure is displayed. Can do. The inspector evaluates the position where the corrosion or the like is generated from the displayed flaw detection figure and the size thereof (step S8).

  In the above description, the case where one special SH wave probe 5 is moved in the circumferential direction of the pipe 1 and the entire circumferential direction is scanned has been described. However, as shown in FIG. It is also possible to use an array probe 10 in which a plurality of elements 5 are arranged and coupled in the circumferential direction, and to electrically transmit / receive local torsional waves by sequentially switching the individual special SH wave probes 5. By using the array probe 10 having a plurality of special SH wave probes 5 in this way, the measurement time can be shortened. That is, since the contact medium interposed between the special SH wave probe 5 and the pipe 1 has a relatively high viscosity, after the special SH wave probe 5 is pressed against the outer surface of the tube, the signal becomes stable. Although it takes time, the array probe 10 having a plurality of special SH wave probes 5 is used to electrically switch the special SH wave probes 5 one after another, whereby the special SH wave probe 5 is It is possible to shorten the time required for the signal required every time it moves to stabilize. Further, by controlling the timing of exciting the individual special SH probes 5, the sound pressure can be intentionally concentrated and the inspection accuracy can be improved.

  In the above description, the case of inspecting corrosion or the like generated in the measurement site 1a that cannot be visually observed through the abutment 2 of the pipe 1 installed under the bridge girder of the bridge has been explained. Corrosion, breakage, etc. can be detected in the same manner.

It is a layout view of an inspection apparatus used in the defect inspection method of the present invention. It is a schematic diagram which shows the vibration form of a local torsion wave. It is a displacement distribution characteristic view of the thickness direction of a local torsion wave. It is a change characteristic figure of the phase velocity dispersion curve and group velocity dispersion curve of a local torsion wave. It is a flowchart which shows a defect inspection method. It is a layout view of another inspection apparatus used in the defect inspection method of the present invention.

Explanation of symbols

1; piping, 1a; measurement site, 2; abutment, 3; filler, 4; scanning drive unit,
5; Special SH wave probe, 6; Ultrasonic transceiver, 7; Control / diagnostic device,
8; guide rail, 9; holding mechanism, 10; array probe.

Claims (2)

It is a defect inspection method for inspecting corrosion, scratches, etc. occurring in a part of a metal structure made of a plate-shaped metal material, a part of which is hidden by another structure.
Propagating a local torsional wave from an exposed outer surface portion that is an outer surface of the metal structure, which is close to a portion hidden by another structure, toward a portion hidden by the other structure. A defect inspection method characterized by receiving a reflected wave reflected from a part concealed by a body and detecting corrosion of the part concealed by another structure by a change in a received signal of the received reflected wave . The local torsional wave propagating to the metal structure is a single mode in which the phase velocity and group velocity do not change by selecting the frequency according to the plate thickness and natural sound velocity of the plate-like metal material that will be the vibration medium among the multiple modes The defect inspection method according to claim 1, wherein the vibration mode is as follows.

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