JPH05172791A - Fatigue crack detection method for corner joint - Google Patents

Abstract

PURPOSE:To prevent occurrence of a significant accident by surely distinguish a root blow hole from a fatigue crack generated later. CONSTITUTION:To a partial weld penetration corner joint where a flange 11 and a web 12 are welded, a vertical probe 16 is provided on the web 12 side putting in between a contact medium 15, and a horizontal wave slanting angle sensors 17, 18 having a refraction angle of 45 degree are also provided, The vertical probe 16 is for measuring the weld penetration depth and the slanting angle sensors 17, 17 are for detecting a round fatigue crack 19 having generated from the root blow hole 14. The weld penetration front position of the joint is detected using the detection signal from the vertical probe 16 and simultaneously, a deeper position than the weld penetration front position is detected using the detection signal from the slanting angle sensors 17, 18. Thus by detecting the string corner reflection wave accompanying the penetration of the fatigue crack, the existence of fatigue crack generation is judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting fatigue cracks in a corner joint for detecting the occurrence of fatigue cracks in a partial penetration corner joint of a bridge.

[0002]

2. Description of the Related Art Conventionally, a partial penetration angle joint in which a flange 1 and a web 2 are welded is often used in a bridge as shown in FIG. It has been pointed out that a circular fatigue crack 5 is generated starting from the root blowhole 4. Therefore, conventionally, the fatigue crack 5 is detected by the ultrasonic flaw detection method shown in FIG. That is, the contact medium 6 is applied to the surface of the web 2 to be flaw-detected, the oblique-angle probe 7 is pressed against the contact medium 6, and the fatigue crack 4 is detected by scanning it in the direction perpendicular to the welding line. There is.

[0003]

However, in the above-described conventional fatigue crack detection method, it is difficult to distinguish the root blowhole 4 and the fatigue crack 5 from the time of manufacture, and only the place where ultrasonic flaw detection is performed at the time of manufacture is manufactured. The occurrence of fatigue cracks could only be recognized from the comparison between the inspection results during maintenance and the inspection results during maintenance. Therefore, there is a demand for a technique capable of surely detecting the fatigue crack 4 by the maintenance inspection.

The present invention has been made in view of the above circumstances, and even if there is no ultrasonic flaw detection data at the time of manufacturing, it is possible to reliably identify a root blow hole from the time of manufacturing and a fatigue crack generated thereafter, and it is important. An object of the present invention is to provide a method for detecting fatigue cracks in a corner joint that can prevent an accident from occurring.

[0005]

A method for detecting fatigue cracks in a corner joint according to the present invention detects ultrasonic waves from a vertical probe vertically from the web surface of the joint to detect reflected waves from the bottom surface of the web. At the same time as detecting the penetration tip position of the joint
Ultrasonic waves from a bevel probe with a refraction angle of approximately 45 ° are made to enter from the web surface of the joint to detect a region deeper than the penetration tip position of the joint, and a reflected wave stronger than a preset reference value is detected. It is characterized in that it is determined that a fatigue crack has occurred at the time of performing.

[0006]

[Operation] When ultrasonic waves are incident from the bevel probe at an angle of 45 ° from the web surface of the joint, if fatigue cracks are generated inside, the ultrasonic waves reflected from the bottom surface of the web will cause fracture surface of the fatigue cracks. It is reflected again and received by the bevel probe. in this case,
100% of incident wave in the range of refraction angle of about 34 ° -56 °
Since it is reflected, it becomes a very strong reflected wave.

When the reflected wave is experimentally examined, it is higher by about 10 to 18 dB than the level of the reflected wave from the artificial defect (lateral hole) provided at the same beam path position. On the other hand, when the level of the reflected wave from the route blowhole was examined, it was 10 to 18d from the level of the reflected wave from the artificial defect (lateral hole).
Many are about B low. Therefore, if a strong level echo is detected in a region deeper than the penetration tip position of the joint, it can be determined that a fatigue crack has occurred.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 1 shows a partial penetration angle joint in which a flange 11 and a web 12 are welded. Reference numeral 13 is a welded portion, and 14 is a root blow hole formed in the welded portion 13.
Then, the contact medium 15 is applied to the web 12 side, a point-focusing vertical probe 16 is provided on the contact medium 15, and a point-focusing (transverse wave) oblique-angle probe with a refraction angle of 45 ° (± 10 °) is provided. Children 17, 18 are provided. The vertical probe 16 is a probe for measuring the penetration depth, and the beveled probes 17, 18 detect circular fatigue cracks 19 originating from the root blow hole 14. It is a probe for, and is arranged at a constant interval.

The detection signal of the vertical probe 16 is sent to a processing circuit (not shown) and known technology (for example, Japanese Patent Application No. 59-37602 filed by the applicant of the present application (Japanese Patent Laid-Open No. Sho 60-60602).
No. 181605, penetration depth measuring method)), the penetration depth of the weld 13 is measured. That is, the probe 1
6, the ultrasonic wave is vertically incident from the surface of the web 12 of the joint to detect the reflected wave from the bottom surface of the web, and the height of the bottom surface echo is 1/2 of the height of the bottom surface echo at the position away from the welded portion 13. In the method of automatically measuring the penetration depth by obtaining the position where ∘, the probe 16 is scanned in the direction perpendicular to the welding line prior to the automatic measurement, and the fluctuation pattern of the bottom echo height at this time Welding by specifying the bottom echo height measurement range during automatic measurement based on the above, and sequentially updating the bottom echo height measurement range at the next scanning line based on the penetration tip position found in the measurement range. Measure the penetration depth of the part.

The present invention detects the penetration tip position of the partial penetration angle joint by using the detection signal from the vertical probe 16 as described above, and at the same time, detects the detection signals of the oblique-angle probes 17 and 18. Using a position deeper than the penetration tip position to detect a strong corner reflected wave accompanying the occurrence of fatigue crack 19,
The presence or absence of fatigue cracks is determined.

Prior to the detection of the fatigue crack 19, however, a partial penetration corner joint test body is manufactured, and test data is collected in advance by a simulated artificial defect to set reference data. This partial penetration angle joint test piece has a plate pressure of 32 mm for the test piece corresponding to the flange 11 and the web 1
The plate pressure of the test piece corresponding to 2 was set to 26 mm, and both test pieces were welded by the submerged arc welding method. As shown in FIG. 2, the web test piece 12a had a diameter of 15 m as an artificial defect.
A horizontal hole (through hole) 20 of m is formed. Web test piece 12
The depth of a is, for example, 50 mm, and the position H where the lateral hole 20 is provided is set to be substantially the same as the thickness of the web 12.

The bevel probe 17 is set to have a small received signal amplification so that it can detect only echoes higher than the level of the reflected wave from the lateral hole 20 by 10 dB or more, and the bevel probe 18 is provided with the lateral probe 20. 20 to 30 depending on the level of the reflected wave from 20
The received signal amplification degree is set to be large so that an echo with a low dB can be detected. The bevel probes 17 and 18 are connected to the signal processing circuit shown in FIG.

In FIG. 3, reference numeral 21 is a transmitter, and the signal output from this transmitter 21 is a channel selector 22.
Is sent as a drive signal to the bevel probes 17 and 18. The signal detected by the bevel probe 17 is supplied to the amplifier 2
It is amplified by 3 and sent to the gate circuit 24. The gate circuit 24 is a circuit for extracting only the ultrasonic waves reflected from a specific position, and the extracted signal is used for the peak detector 2
Output to 5. On the other hand, the signal detected by the bevel probe 18 is amplified by the amplifier 26 and sent to the gate circuit 27. The gate circuit 27 takes out only the ultrasonic wave reflected from the specific position and outputs it to the peak detector 28. The peak detectors 25 and 28 hold the peak voltage of the received signal, convert it into a digital signal by the A / D converter 29, and output it to the CPU (microcomputer) 30. The CPU 30 detects whether or not a fatigue crack has occurred depending on the magnitude of the received voltage. Whether or not this fatigue crack has occurred can be determined as follows.

FIG. 4 schematically shows the intensity distribution of reflected waves when a transverse wave is incident on the fatigue crack 19 generated in the corner joint at an angle of 45 °, and 31 is the fatigue crack 19 and the bottom surface of the web. A region where a strong reflected wave is generated from a corner portion formed by, 32 is a reflected wave generation region from the root blowhole 14, 33,
Reference numeral 34 is a reflected wave generation region from the upper and lower ends of the fatigue crack 19,
Reference numeral 35 is a region where a weak reflected wave from the fracture surface of the fatigue crack 19 is generated.

FIG. 5 shows a state in which the ultrasonic wave reflected on the bottom surface of the web is reflected again on the fracture surface of the fatigue crack 19 and received by the bevel probe 17 in the reflected wave generating region 31 of FIG. There is. In this case, the refraction angle is about 34 as shown in FIG.
In the range of ° to 56 °, the incident wave reflects 100%,
The reflected wave from the reflected wave generation area 31 becomes extremely strong. The strongly reflected wave 31 a from this area 31 is detected by the bevel probe 17.

When the reflected wave is experimentally examined, it is higher by about 10 to 18 dB than the level of the reflected wave from the lateral hole 20 provided at the same beam path position. On the other hand, when examining the level of the reflected wave from the root blowhole 14, the horizontal hole 2
In many cases, the level of the reflected wave from 0 is lower by about 10 to 18 dB. Therefore, when such a strong echo is detected in a region deeper than the penetration tip position as viewed from the surface of the web 12, it can be determined that a fatigue crack has occurred. That is, the vertical probe 16 detects the penetration tip position of the partial penetration angle joint, and at the same time, the transverse wave bevel probe 17 having a refraction angle of 45 ° is used to detect a region deeper than the penetration tip position, In comparison with the reference value obtained experimentally in advance, that is, the reflected wave level from the lateral hole 20, it can be determined that a fatigue crack has occurred when a reflected wave that is 10 dB or more stronger than the reference value is detected.

FIG. 7 shows the states of the reflected waves 33a and 34a from the upper and lower ends of the fatigue crack 19 (regions 33 and 34 in FIG. 4) and the reflected wave 35a from the fracture surface (region 35) of the fatigue crack 19. It is a thing. The level of these echoes is
It is significantly weaker than the reflected wave from the area 31, for example, about 20 to 30 dB lower than the level of the reflected wave of the lateral hole 20, so these reflected waves are detected by the bevel probe 18, and the fatigue crack 19 is detected. Use as data for dimensional judgment. The upper and lower end positions of the region 35 of the fatigue crack 19 in FIG. 4 are determined by detecting the position where the reflected wave 35a from the fracture surface (region 35) disappears.

Next, a case where ultrasonic flaw detection is actually performed using a test body will be described. In this case, the test piece shown in FIG. 2 was used as the test piece, and after the load was repeatedly applied, flaw detection was performed. At the time of this flaw detection, a glycerin-based contact medium 15 is used, a frequency 5 MHz, a point-focusing vertical probe 16 with a transducer diameter of 20 mm, and a frequency 5 MH.
The transverse wave bevel probes 17 and 18 having a z, a vibrator diameter of 20 mm and a refraction angle of 45 ° ± 10 ° were used.

Then, while detecting the penetration tip position by the vertical probe 16 and at the same time the flaw detection is started by the oblique angle probes 17 and 18, the inspection start position is within the penetration depth of 14 to 15 mm. In the region deeper than the tip position, the lateral hole 20 is formed in the bevel probe 17.
Echoes 10 to 14 dB higher than the level of the reflected wave from were detected over a range of 5 mm in the depth direction. Further, an echo lower than the level of the reflected wave from the lateral hole 20 by 23 to 30 dB was detected in the bevel probe 18.

From the above results, when it was judged that the fatigue crack 1 had occurred at the echo detection position and the fracture inspection was conducted, a fatigue crack with a diameter of about 9 mm was found, and the validity of the inspection result was confirmed. Was done.

[0022]

As described in detail above, according to the present invention, while detecting the penetration tip position of the partial penetration angle joint by using the detection signal from the vertical probe, the angle probe of the bevel angle probe is detected at the same time. The detection signal is used to detect a position deeper than the penetration tip position,
Detects strong corner reflection waves associated with the occurrence of fatigue cracks,
Since the presence / absence of fatigue cracks is determined, even if there is no ultrasonic flaw detection data at the time of manufacturing, it is possible to reliably identify the root blowhole that was present during manufacturing and the fatigue cracks that occurred after that, and a serious accident could occur. Can be prevented in advance.

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement state of a probe in a fatigue crack detection method for a corner joint according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a test body.

FIG. 3 is a block diagram showing a processing circuit for a signal detected by a bevel probe.

FIG. 4 is a reflection intensity distribution map in oblique flaw detection.

FIG. 5 is a diagram showing an ultrasonic wave reflection state at a corner portion of a fatigue crack.

FIG. 6 is a diagram showing ultrasonic reflection characteristics of a corner portion of a fatigue crack.

FIG. 7 is a diagram showing the reflection state from the upper and lower ends of the fatigue crack and the fracture surface.

FIG. 8 is a diagram showing a fatigue crack generation state in a partial penetration corner joint of a bridge.

FIG. 9 is a diagram for explaining a conventional fatigue crack detection method for a partial penetration angle joint.

[Explanation of symbols]

11 ... Flange, 12 ... Web, 13 ... Weld, 14 ...
Root blow hole, 15 ... Contact medium, 16 vertical probe, 17, 18 ... Angle probe, 19 ... Fatigue crack, 20 ...
Side hole, 21 ... Transmitter, 22 ... Channel selector, 2
3, 26 ... Amplifier, 24, 27 ... Gate circuit, 25, 2
8 ... Peak detector, 29 ... A / D converter, 30 ... C
PU, 31-35 ... Reflected wave generation area.

Claims (1)

[Claims] 1. An ultrasonic wave from a vertical probe is vertically incident from the web surface of the joint to detect a reflected wave from the bottom surface of the web to detect the penetration tip position of the joint, and the refraction angle is about 45.
Fatigue cracks occur when ultrasonic waves from a beveled probe are injected from the web surface of the joint to detect a region deeper than the penetration tip position of the joint and a reflected wave stronger than a preset reference value is detected. A method for detecting fatigue cracks in a corner joint, which is characterized in that it is determined that a crack has occurred.