JP2003066016A - Measuring method for depth of defect in structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method capable of accurately measuring the depth of a defect in a structure. SOLUTION: In this measuring method for the depth of the defect in the structure, the defect is delicately advanced by partially applying external force to the defect in the structure, and the depth of the structure is measured by detecting the sound of destruction generated by the defect. Therefore, the depth of the defect such as a stress corrosion crack, a fatigue crack and the like which are easily produced in a welding heat influencing part can be very accurately measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure defect depth measuring method for measuring a defect depth necessary for evaluating a life of a defect existing in a structure.

[0002]

2. Description of the Related Art In non-destructive inspection of structures, the defect detection sensitivity and pass / fail are determined by comparing the detected defect depth with the simulated defect depth allowed in terms of strength. However, if a defect is found in an important structure within the acceptable range, but it cannot be repaired immediately even if it is detected as a defect, the depth of the defect is measured in order to evaluate the life of the structure. There was a need.

The defect depth measuring method includes an eddy current flaw detection method, an electric resistance method, and an end echo method in ultrasonic flaw detection. In the eddy current flaw detection method and the electric resistance method, if there is no defect on the flaw detection surface side, the measurement is performed. It was not possible and the measurement error was large. In addition, although the edge echo method in ultrasonic flaw detection can measure even defects generated from the side opposite to the flaw detection surface, the diffraction wave generated at the edge of the defect is extremely weak, so it can be separated and distinguished from grain boundary noise, etc. Is very difficult, especially in stress corrosion cracking (SCC) that occurs in the weld heat-affected zone of materials such as austenite with large damping, defects may develop finely in a dendritic manner along grain boundaries. It has been difficult to reliably detect the defect depth.

As another method for maintaining a structure, as another method, acoustic sensors are arranged at a plurality of locations on the structure,
By monitoring the minute sound generated in the structure continuously while the structure is in use, the destruction sound generated when a defect occurs or progresses is detected, and each sensor detects the destruction sound. There is an acoustic emission (hereinafter abbreviated as AE) method that identifies the position of the defect by the same triangulation as the epicenter measurement of the earthquake based on the captured time difference. However, with this AE method, the defect can be detected only at the moment when the defect is generated and propagates, and noise from outside always enters during continuous monitoring. Therefore, it is difficult to separate the defect signal and the noise, and it takes a long time. Monitoring was needed.

Further, when a longitudinal ultrasonic wave is incident on the defect tip of a defective structure, a transverse ultrasonic wave whose mode is converted downward by 45 ° with respect to the propagation direction of the defect tip is generated. -1119833), it is difficult to detect the transverse wave generated and the sound propagation route is found in a defect such as SCC in which the direction of the tip of the defect is not clear along the grain boundary. Since it is not clear, the accuracy of the calculated defect tip position was also very poor.

[0006]

As described above, it is difficult to measure the depth of a defect by the conventional method of measuring the depth of a structure defect, and in particular, the effect of welding heat on a material such as an austenitic material having large attenuation is considered. It was almost impossible to distinguish the tip of the defect, which developed in a dendritic manner along the crystal grain boundary of the SCC generated in the part, because it was difficult to distinguish it from the crystal grain boundary.

The present invention has been made in view of the above circumstances, and its problem is that by forcibly advancing a defect finely, the depth of the defect can be accurately measured without continuous monitoring. It is to provide a method for measuring the depth of a structure defect.

[0008]

In order to solve the above-mentioned problems, the invention of a structure defect depth measuring method according to claim 1 is
The depth of the defect is measured by locally applying an external force to the defect of the structure to finely propagate the defect and detecting a breaking sound generated from the defect.

According to a second aspect of the present invention, in the structure defect depth measuring method according to the first aspect, three or more acoustic sensors are arranged in the vicinity of the defect, the time when the external force is generated, and each acoustic sensor. Is characterized in that the position where the destructive sound is generated is specified by calculating from the difference between the time when the destructive sound signal is received and the position of each acoustic sensor.

According to a third aspect of the present invention, in the structure defect depth measuring method according to the first aspect, the external force applied to the defect is
It is characterized in that it is either a mechanical external force due to impact or the like, an external force due to thermal strain due to a temperature difference, or an external force that resonates by adding vibration to the test body.

According to the first to third aspects, it becomes possible to measure the depth of defects such as stress corrosion cracking and fatigue cracking which are likely to occur in the weld heat affected zone with extremely high accuracy.

According to a fourth aspect of the present invention, in the structure defect depth measuring method according to the second aspect, it is an integrated module in which an external force generator and a plurality of acoustic sensors are arranged in advance. According to the fourth aspect, since the external force generator and the plurality of acoustic sensors are integrated into a module, it is not necessary to confirm the position of the acoustic sensors.

According to a fifth aspect of the present invention, longitudinal ultrasonic waves are incident on the defect tip of the structure, and a plurality of transverse waves generated by mode conversion at the defect tip are generated in the vicinity of the defect. The defect tip position is detected by the acoustic sensor placed and is calculated from the difference between the time when the longitudinal ultrasonic wave is generated and the time when each acoustic sensor receives the transverse ultrasonic wave and the position of each acoustic sensor. Is specified. According to the fifth aspect, the position of the defect can be detected by performing mode conversion at the defect tip with a plurality of acoustic sensors, detecting transverse waves propagating in an arbitrary direction.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram for carrying out a structure defect depth measuring method according to a first embodiment (corresponding to claim 1 and claim 2) of the present invention. FIG. Figure (b) is a sectional view thereof.

As shown in the figure, in this embodiment, an external force generator forcibly propagating the defect 3 directly above the defect 3 such as a crack or a crack of the structure 4 detected by a prior nondestructive inspection or the like. 1 is set, and a plurality of acoustic sensors 2 are set so as to surround the external force generator 1.

The present invention utilizes the principle of the AE method described above,
In order to avoid waiting for a long time for the progress of defects, which is a problem of the AE method, the defects are forcibly finely propagated by an external force. Therefore, by applying an external force at any time, it is possible to detect the destructive sound from the defect tip and measure the defect size, especially the defect depth, based on the AE method. The depth measurement can be performed accurately.

Next, various types of external force generators (corresponding to claim 3) used in the present invention will be described with reference to FIGS. 2 to 6. Figure 2 shows a blast type impact type external force generator,
The convex portion 13a is provided in the cylindrical container 10 in which the electrode 11 is arranged on the upper portion.
A piston 13 having a cylinder is provided, and an explosive 12 is packed in a space formed by the cylindrical container 10 and the piston 13.

FIG. 3 shows an air knock type striking type external force generator in which a piston 17 is provided in a cylindrical container 18 and a spring 1 is provided between the piston 17 and the top of the cylindrical container 18.
A shaft 15 to which 4 is attached is provided. When pressurized air is blown from the lower release valve 16 of the spring 14, the piston 17 moves upward.

In the external force generator 1 shown in FIGS. 2 and 3, the piston is abruptly pushed down by the explosive or the spring, and the convex portion attached to the central portion of the piston or the tip of the shaft 15 strikes the defective portion 3 to impact it. At this time, since stress is applied to the tip of the defect 3, the defect 3 progresses finely.

FIG. 4 shows a piezoelectric element type vibration type external force generator, in which a piezoelectric element 21 and a damper 22 are attached to a plate 20. FIG. 5 shows a mechanical vibration type external force generator, in which a motor 23 and an eccentric wheel 24 are attached to a plate 25.

The external force generator shown in FIGS. 4 and 5 causes the piezoelectric effect by the piezoelectric element 21 or mechanical vibration by the eccentric wheel 24 to vibrate the material having the defect 3 at the resonance frequency. As a result, stress is applied to the tip of the defect 3 without exerting a large impact force on the material, and the defect 3 is allowed to progress finely.

FIG. 6 shows a laser type thermal strain external force generator, in which a laser oscillator 31, a lens 32 and a cooling nozzle 33 are attached to a plate 30. This external force generator uses a laser or the like to rapidly heat the surface of the material, and the thermal strain generated at this time similarly causes the defects 3 to finely propagate.

As described above, according to the present invention, the external force generated by the external force generator is applied to the defective portion of the structure, so that the defect 3 progresses minutely, and a sound is generated from the developed portion at the tip of the defect 3 due to the destruction. The destruction sound generated at this time is received by the acoustic sensors 2 arranged around the defect, and the sound generation position is calculated by the same method as obtaining the epicenter location from the reception time difference of each acoustic sensor 2 and the like. That is, the position of the tip of the defect 3 can be detected.

Further, in order to accurately detect the tip position of the defect, it is necessary to accurately grasp the positional relationship between the receiving acoustic sensors 2. Since the acoustic sensor 2 is usually composed of a piezoelectric element, it produces a sound when electrically excited. Therefore, if each sensor 2 is sequentially excited to generate a sound and the other sensor 2 receives this sound and analyzes the sound generation position, it is possible to accurately grasp the mutual positional relationship.

According to this defect detection method, unlike the ultrasonic flaw detection test method in which the reflection of the sound transmitted from the inspection device side is captured, the sound source is only the defect tip portion and the pseudo echo source such as a grain boundary or a shape is generated. Since there is no defect, misidentification of the tip position of the defect is reduced.

FIG. 7 is a perspective view of a second embodiment (corresponding to claim 4) of the present invention. As shown in the figure, in this embodiment, the external force generator 1 and the acoustic sensor 2 are previously arranged on the plate 5 at known positions to form an integrated module. It is not necessary to confirm the position of the sensor 2. Since the defect position identification in the structure is the same as that of the first embodiment of FIG. 1, the description thereof will be omitted.

FIG. 8 is a constitutional view of a third embodiment (corresponding to claim 5) of the present invention, wherein FIG. 8A is a sectional view and FIG.
FIG. 7 is an enlarged view of a portion A of FIG. As shown in the same figure, a longitudinal ultrasonic probe 41 is placed on a structure 40 having a defect 3, and a transverse wave acoustic sensor 42 is arranged so as to surround it. When a longitudinal ultrasonic wave 43 is incident on the defect tip from the longitudinal ultrasonic probe 41, a strong transverse ultrasonic wave 44 which is mode-converted downward by 45 ° with respect to the propagation direction of the defect tip.
Occurs.

However, according to the present embodiment, since the plurality of acoustic sensors 42 are arranged around the defect 3, it is possible to detect the transverse wave 44 propagating in an arbitrary direction by performing mode conversion at the defect tip. Moreover, since the defect position is detected from the difference in the time when the sound is received by each acoustic sensor 42, the accuracy is also improved.

The calculated defect tip position as described above is usually provided as a calculated numerical value. However, especially in the case of SCC etc., the number of defects is not limited to one, and it is difficult to understand the distribution of defects with numerical values alone. Therefore, the defect position detected based on the calculation results is superimposed on the inspection body and three-dimensional. Such a display makes it possible to clearly indicate the status of the defect so that it can be intuitively understood by a third party.

[0030]

As described above, according to the present invention, it is possible to measure the depth of defects such as stress corrosion cracking and fatigue cracking which are likely to occur in the weld heat affected zone with extremely high accuracy. It is possible to evaluate the safety of structures, estimate the remaining life, and detect the repair amount.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention, in which FIG. 1A is a basic layout diagram and FIG. 1B is a cross-sectional view of FIG. 1A.

FIG. 2 is a schematic view of a blast type impact type external force generator used in the present invention.

FIG. 3 is a schematic view of an air knock type impact type external force generator used in the present invention.

FIG. 4 is a schematic view of a piezoelectric element type vibration external force generator used in the present invention.

FIG. 5 is a schematic view of a mechanical vibration type external force generator used in the present invention.

FIG. 6 is a schematic view of a laser type thermal strain type external force generator used in the present invention.

FIG. 7 is a configuration diagram of a second embodiment of the present invention.

8A and 8B are configuration diagrams of a third embodiment of the present invention, in which FIG. 8A is a sectional view and FIG. 8B is an enlarged view of a portion A in FIG. 8A.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... External force generator, 2 ... Acoustic sensor, 3 ... Defect, 4 ... Structure, 5 ... Fixed plate, 10 ... Cylindrical container, 11 ... Electrode,
12 ... Explosive, 13, 17 ... Piston, 14 ... Spring, 15 ... Shaft, 16 ... Release valve, 18 ... Cylindrical container, 20, 25, 30 ... Plate, 21 ... Piezoelectric element, 22 ... Damper, 23 ... Motor, 24 ... Eccentric wheel, 31 ... Laser oscillator, 32 ... Lens, 33 ... Cooling nozzle, 40 ... Structure, 41 ... Longitudinal wave ultrasonic probe, 42 ...
Transverse wave acoustic sensor, 43 ... Longitudinal wave, 44 ... Mode-converted transverse wave.

Claims (5)

[Claims] 1. The depth of the defect is measured by locally applying an external force to the defect of the structure to finely propagate the defect and detecting a breaking sound generated from the defect. Measuring method of structure defect depth. 2. The structure defect depth measuring method according to claim 1, wherein three or more acoustic sensors are arranged in the vicinity of the defect, and a time when external force is generated and each acoustic sensor receives a destructive sound signal. A method for measuring the depth of a defect in a structure, characterized in that the position where the destruction sound is generated is specified by calculating it from the difference between the time and the position of each acoustic sensor. 3. The structure defect depth measuring method according to claim 1, wherein the external force applied to the defect is a mechanical external force due to impact or the like, an external force due to thermal strain due to a temperature difference, or an external force for vibrating and resonating the test body. A method for measuring the depth of a structure defect, which is characterized in that 4. The structure defect depth measuring method according to claim 2, wherein the module is an integrated module in which an external force generator and a plurality of acoustic sensors are arranged in advance. . 5. A longitudinal wave ultrasonic wave is incident on the defect tip of a structure, and a transverse wave generated by mode conversion at the defect tip is detected by a plurality of acoustic sensors arranged near the defect. The defect tip position is specified by calculating from the difference between the time when the longitudinal ultrasonic wave is generated and the time when each acoustic sensor receives the transverse ultrasonic wave and the position of each acoustic sensor. Measuring method of structure defect depth.