JP4784556B2 - Sensitivity correction method for ultrasonic inspection - Google Patents

Description

  The present invention relates to a method of correcting ultrasonic reception sensitivity according to a measurement environment when inspecting a defect of an inspection object using ultrasonic waves.

  Conventionally, regarding the corrosion inspection using ultrasonic waves, “corrosion generated on the outer surface of the thin steel pipe on the rack is well inspected from outside the rack. As a technology for the purpose of this, “SH waves propagated from the exposed outer surface of the thin-walled steel pipe from the SH wave probe 5 to the rack concealed part in the vicinity of the rack 3 and reflected from this part. The waves are received by the SH wave probe 5 and inspected for corrosion based on the reflected signal. Is proposed (Patent Document 1).

  In addition, “As the pipe penetrates the pier or abutment, corrosion and scratches that may occur in parts that cannot be visually inspected are detected with high accuracy, and the depth of corrosion and scratches is evaluated. Improve accuracy. As a technology for the purpose of the above, “a special SH wave probe 5 is used for a measurement site 1 a 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. The local torsional wave is propagated from and the entire plate thickness is vibrated. The reflected wave reflected from the measurement site 1a which is hidden and cannot be visually observed is received by the special SH wave probe 5, and corrosion of the measurement site 1a is detected by a change in the received signal of the received reflected wave. Is proposed (Patent Document 2).

JP 2002-243704 A (summary) Japanese Patent Laying-Open No. 2005-83907 (Abstract)

Generally, in defect inspection using ultrasonic waves, sensitivity calibration and creation of defect evaluation criteria are performed in advance using a test piece made of the same kind of material as the object to be inspected and provided with a reference reflection source.
In this case, when inspecting the defect of the inspection object, the determination of the defect is performed by comparing the measurement result at the time of inspection with the measurement result on the test piece for which the evaluation reference is created.

  Here, the SH (Shear Horizontal) wave used in the techniques described in Patent Document 1 and Patent Document 2 is an ultrasonic wave that oscillates in the horizontal direction with respect to the traveling direction, and is transmitted to the inspection object. The vibration in the shear direction must be transmitted from the contact surface with the object to be inspected. Therefore, the contact medium used for the contact surface between the probe and the object to be inspected needs to use a dedicated medium having a higher viscosity than a general medium. This is common when the SH wave is generated on the test piece and when the SH wave is generated during the inspection.

Due to the characteristics of the generation method of the SH wave as described above, the generated SH wave and its reception sensitivity depend on the measurement environment such as the change in the viscosity of the contact medium, the surface state of the inspection object, the mounting state of the probe, and the like. It can be very different. Moreover, even if it is the same to-be-inspected object, a sensitivity may change when changing a measurement point.
Therefore, since the measurement environment which is a premise differs between the reception sensitivity when the received waveform is measured using the test piece and the reception sensitivity at the time of inspection, calibration processing is necessary.

In this regard, in Patent Document 1, the transmission probe 5a and the reception probe 5b are arranged so as to sandwich the inspection range (FIG. 1), and ultrasonic waves transmitted through the inspection range are received, Used as a calibration signal.
However, this method has a problem from the viewpoint of increasing the size of the inspection equipment, because it is necessary to secure a space for installing the probe on both sides of the inspection range. In addition, in the process of passing through the inspection range, the influence of other elements that change the signal value is introduced, so that it is not necessarily suitable for use as a calibration signal for the measurement environment.

  Regarding the above-mentioned Patent Document 2, there is no particular description regarding sensitivity correction, and there is a problem similar to that of the conventional method.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to correct a difference in reception sensitivity caused by a measurement environment when inspecting a defect of an inspection object using ultrasonic waves. And

  A sensitivity correction method for ultrasonic inspection according to the present invention is a method for correcting reception sensitivity when inspecting a defect of an inspection object using ultrasonic waves, and is used for an evaluation standard for the purpose of defining an evaluation standard. When measuring the test piece, place a calibration probe between the reference reflector and the probe, and measure the received waveform at the calibration probe together with the measurement of the reference reflector. When inspecting a defect of an object, a calibration probe is disposed between the inspection site of the object to be inspected and the probe, and the position of the probe and the calibration probe is determined based on the evaluation criteria. Adjusting the arrangement position so that the position of the probe on the test specimen matches the position of the calibration probe, and attaching the calibration probe in the same mounting state as the mounting state on the evaluation reference test piece, The received waveform of the calibration probe measured using the test specimen for evaluation standard and the defect of the inspection object Comparing the received waveform of the calibration probe measured during the 査, and corrects the reception sensitivity of the probe by the comparison result.

  Also, the sensitivity correction method for ultrasonic inspection according to the present invention is measured when inspecting the peak value of the received waveform of the calibration probe measured using the test piece for evaluation reference and the defect of the inspection object. The reception sensitivity of the probe when inspecting a defect of the inspection object is corrected based on the ratio with the peak value of the reception waveform of the calibration probe.

  In the ultrasonic inspection sensitivity correction method according to the present invention, the ultrasonic wave used by the probe is a transverse wave that vibrates in a horizontal direction with respect to a propagation direction.

  According to the sensitivity correction method for ultrasonic inspection according to the present invention, even if the reception sensitivity varies due to the measurement environment, the reception sensitivity can be corrected based on the reception waveform of the calibration probe. Inspection can be performed with a constant reception sensitivity regardless of the environment.

Embodiment 1 FIG.
FIG. 1 explains how the sensitivity correction method for ultrasonic inspection according to Embodiment 1 of the present invention is implemented. Here, the corrosion inspection will be described as an example.

In FIG. 1A, 10 is a test piece for creating a corrosion evaluation standard, 20a is a measurement probe, 30a is a calibration probe, and 40 is a reflection source for evaluation standard.
The measurement probe 20a can transmit an ultrasonic wave in the direction indicated by the arrow in FIG. 1A, receive the ultrasonic wave reflected by the evaluation reference reflection source 40, and measure the waveform.
The ultrasonic wave transmitted by the measurement probe 20a is also received directly by the calibration probe 30a.

  In FIG. 1B, reference numeral 50 denotes an object to be inspected for corrosion, and reference numeral 60 denotes corrosion existing in the inspection range. The roles of the measurement probe 20b and the calibration probe 30b are the same as those of the measurement probe 20a and the calibration probe 30a in FIG.

  Details of the sensitivity correction procedure using each probe of FIG. 1 will be described later.

FIG. 2 explains the types of transverse waves.
In the inspection using ultrasonic waves, longitudinal waves or transverse waves that do not consider the shape of the propagation medium are generally used. The longitudinal wave has a vibration parallel to the traveling direction of the wave, and the transverse wave has a vibration perpendicular to the traveling direction of the wave.

As shown in FIGS. 2A and 2B, the transverse waves are further classified into two types: (a) SV waves (SV: Shear Vertical) and (b) SH waves (SH: Shear Horizontal).
The SV wave is a wave whose vibration is perpendicular to the wave traveling direction and oscillates in the vertical direction.
The SH wave is a wave whose vibration is perpendicular to the traveling direction of the wave and oscillates in the horizontal direction.

The SV wave is generated by mode conversion of the longitudinal wave. That is, the SH wave is generated by rubbing the propagation medium, whereas the propagation is generated by striking the propagation medium.
That is, when the SH wave is generated, a contact medium (normally gel-like substance is generally used) is applied to a propagation medium (usually the same as the object to be inspected), and the probe is brought into close contact with vibration. The probe is vibrated by the child so that the object to be inspected and the probe are rubbed together.

Due to the generation method of such SH wave, the SH wave and its reception sensitivity can vary greatly depending on the measurement environment such as the change in the viscosity of the contact medium, the surface state of the object to be inspected, the mounting state of the probe, etc. There is sex. Moreover, even if it is the same to-be-inspected object, a sensitivity may change when changing a measurement point.
For example, the viscosity of the contact medium varies with temperature and humidity. Further, the surface state of the inspection object usually varies with each inspection and with the inspection object. Furthermore, the mounting state of the probe is easily changed, for example, by adjusting the force when pressing the probe against the object to be inspected.

  Since the reception sensitivity (the wave height of the reception waveform) is important for determining the size of the defect or the like, the change in the reception sensitivity has a great influence on the defect inspection. Therefore, since the prerequisite environment differs between the reception sensitivity when the received waveform is measured using the test piece 10 and the reception sensitivity at the time of inspection, a calibration process is required.

  Next, the procedure for correcting the reception sensitivity under the configuration described in FIG. 1 will be described step by step.

(1) The test piece 10 for evaluation criteria described in FIG. 1A is prepared, and the measurement probe 20a is arranged. The test piece 10 is provided with an evaluation reference reflection source 40 for simulating the reflection of ultrasonic waves due to defects.

(2) The calibration probe 30a is arranged between the measurement probe 20a and the evaluation reference reflection source 40. The calibration probe 30a is fixed to the test piece 10 by an appropriate fixing method.

(3) The SH wave is transmitted from the measurement probe 20a to the test piece 10, and the ultrasonic wave reflected by the evaluation reference reflection source 40 is received by the measurement probe 20a. At this time, the SH wave transmitted from the measurement probe 20a is also received by the calibration probe 30a.

(4) The peak value of the transmitted wave in the calibration probe 30a is acquired and used as a reference for subsequent actual measurement. Details will be described later.
Here, the transmitted wave is an ultrasonic wave that is directly incident on the calibration probe 30a from the measurement probe 20a. Although the distance that the ultrasonic wave for calibration propagates through the test piece 10 and the inspection object becomes short, it is considered that this is suitable for confirming only the influence of the contact state of the probe. The method is used.

(5) When performing a corrosion inspection (during actual measurement), the distance between the measurement probe 20b and the calibration probe 30b is set to be the same as the measurement on the test piece 10.

(6) The mounting state when the calibration probe 30b is fixed to the object to be inspected is the same as the mounting state of the calibration probe 30a on the test piece 10.

(7) An SH wave is incident from the measurement probe 20b toward the inspection range. The ultrasonic wave reflected by the corrosion 60 is received by the measurement probe 20b. In addition, the SH wave transmitted from the measurement probe 20b is received by the calibration probe 30b.
(8) The reception level of the transmitted wave in the calibration probe 30b is measured, and the peak value is acquired.

(9) The reception peak value in the calibration probe 30a when measured on the test piece 10 is compared with the reception peak value in the calibration probe 30b during actual measurement. Based on the comparison result, the reception level in the measurement probe 20b can be corrected.
As a correction method, for example, a method based on a ratio between a reception peak value on the test piece 10 and a reception peak value at the time of actual measurement, a method based on a difference, and the like can be considered. For example, when correcting based on the ratio, the value of the ratio is multiplied by the reception level in the measurement probe 20b to correct the reception level.

According to the procedure as described in the above (1) to (9), the measurement environment such as the mounting state of the measurement probe 20b is the same as the mounting state of the measurement probe 20a on the test piece 10. Even if it is different from the measurement environment, the reception level of the measurement probe 20b can be corrected by comparing the reception peak value of the calibration probe 30a with the reception peak value of the calibration probe 30b. .
Therefore, since the measurement probe 20b can obtain an accurate reception level regardless of the measurement environment, the state such as the size of the corrosion 60 can be accurately grasped based on the reception level.

  Further, if the measured value of the calibration probe 30a on the test piece 10 is obtained only, the sensitivity correction process can be executed later. Therefore, the test piece 10 is brought to the place where the actual measurement is performed each time. There is no need to go, and it is possible to reduce the weight of the measuring instrument to be carried, which contributes to the convenience of the inspector.

Embodiment 2. FIG.
In the first embodiment, the example in which the inspection is performed using the SH wave has been described.
In the second embodiment of the present invention, an example in which an inspection is performed using a guide wave will be described.
A guide wave is a general term for the types of ultrasonic waves that have characteristics using the influence of the shape of the propagation medium. The guide wave propagates along the waveguide formed by the physical boundary.

FIG. 3 shows the types of ultrasonic waves propagating in the solid.
The classification of the longitudinal wave, the transverse wave, and the transverse wave is as described in the first embodiment.
On the other hand, guide waves have attracted attention in recent years as being used for defect inspection methods for pipes and the like because they dissipate energy and can travel far. Therefore, consider performing defect inspection using SH waves (SH guide waves) propagating along the shape of the propagation medium.

The SH guide wave propagates along the shape of the propagation medium while vibrating in the horizontal direction over the entire plate thickness.
The SH guide wave has a characteristic capable of propagating far. For example, it is possible to inspect a defect by making an SH guide wave incident on an inspection range ahead of about 1 m and receiving the reflected wave.

  When the SH wave is generated, as described in the first embodiment, a change in reception sensitivity due to the measurement environment occurs. Therefore, an accurate defect inspection can be performed by performing a reception sensitivity correction process similar to that of the first embodiment.

For the propagation medium having a cylindrical shape such as a pipe, the portion where the probe is in contact is regarded as a plate locally, and the SH guide is used in the same manner as when the SH guide wave is incident on the plate material. Waves can be propagated.
For example, as in the technique described in Patent Document 2, a frequency that does not generate a mode other than the T (0,1) mode is selected, and the SH0 mode guide wave is propagated to the plate in the same manner as when the SH0 mode guide wave is propagated to the plate. A guide wave is propagated.
Also in this case, when the SH wave is generated, the change in the reception sensitivity due to the measurement environment as described in the first embodiment occurs, so that the accurate defect inspection is performed by performing the reception sensitivity correction process in the same manner. It can be carried out.

  In the above first and second embodiments, the sensitivity correction process when inspecting the corrosion 60 with ultrasonic waves has been described. However, the defect to be inspected is not limited to corrosion, and can be applied to any defect. is there.

  In addition, it has been described that when the SH wave is generated, the probe and the inspection object are rubbed together to cause a change in the reception sensitivity due to the measurement environment. However, the application target of the present invention is limited to the SH wave. However, the present invention can be applied to other measurement forms in which a change in reception sensitivity due to the measurement environment can occur due to the same cause.

The manner in which the sensitivity correction method for ultrasonic inspection according to the first embodiment is performed will be described. This is a description of the types of shear waves. It shows the type of ultrasonic wave propagating in the solid.

Explanation of symbols

  10 Test piece, 20a Measurement probe, 30a Calibration probe, 40 Reflection source for evaluation standard, 20b Measurement probe, 30b Calibration probe, 50 Inspected object, 60 Corrosion.

Claims (3)

A method of correcting reception sensitivity when inspecting a defect of an inspection object using ultrasonic waves,
In the measurement of test specimens for evaluation criteria for the purpose of setting evaluation criteria,
Place a calibration probe between the reference source and the probe,
In addition to measuring the reference reflection source, measure the received waveform with the calibration probe,
When inspecting the inspection object for defects,
Place a calibration probe between the inspection part of the inspection object and the probe,
And,
The position of the probe and the calibration probe
While adjusting the arrangement position so that the position of the probe on the evaluation reference specimen and the position of the calibration probe match,
Attach the calibration probe in the same mounting state as the mounting state on the test piece for evaluation criteria,
The received waveform of the calibration probe measured using the test piece for evaluation criteria,
Compare the received waveform of the calibration probe measured when inspecting the inspection object for defects,
A sensitivity correction method for ultrasonic inspection, wherein the sensitivity of the probe is corrected based on the comparison result. The peak value of the received waveform of the calibration probe measured using the test piece for evaluation criteria,
Based on the ratio to the peak value of the received waveform of the calibration probe measured when inspecting the defect of the inspection object,
The sensitivity correction method for ultrasonic inspection according to claim 1, wherein the reception sensitivity of the probe when inspecting a defect of the inspection object is corrected. The ultrasound used by the probe is
The ultrasonic wave sensitivity correction method according to claim 1, wherein the method is a transverse wave that vibrates in a horizontal direction with respect to a propagation direction.

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