JP2000314730A - Vibration fatigue controle method for material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration fatigue control method for a material allowing determination of whether a vibration fatigue in the material is in a progressing state or not by a simple method. SOLUTION: While a normal forced vibration applied to a socket welded part 40 is stopped, an elastic wave is applied by hitting a part of the socket welded part 40 with a hammer to damp the forced vibration, a relative displacement between first and second measuring parts T1, T2 is measured by accelerometers 31, 32. An intensity of an n-th harmonic wave in respect to a base vibration wave at the socket welded part 40 is obtained by analyzing the damping vibration in terms of time-frequency. A displacement width in a transition area where the n-th harmonic wave increases/decreases is obtained as a lower fatigue limit amplitude. Then, while the normal forced vibration is recovered, a management on whether a vibration fatigue is progressing or not is conducted based on whether a relative displacement between the first and the second measuring parts T1, T2 exceeds the lower fatigue limit amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for managing vibration fatigue of a material which may be damaged by vibration fatigue.

[0002]

2. Description of the Related Art For example, in a piping system of a power plant, stress concentration tends to occur at a root portion of a socket weld. In addition, since rotational vibrations of the motor and the turbine are constantly transmitted to the piping system, and the load is repeatedly applied to the root, cracks may occur due to vibration fatigue and leakage may occur.

In order to prevent material destruction due to such vibration fatigue, it is desired to manage whether or not the material is in a state where vibration fatigue is progressing. For example, Japanese Patent Application Laid-Open No. 10-26613 discloses a method. A method as shown was proposed. According to the prior art, the degree of deterioration due to vibration fatigue was monitored based on the reception intensity of the nth harmonic with respect to the fundamental wave having the highest reception intensity by the AE sensor.

However, according to the prior art, in order to reduce the background noise, the phase of the received signal between the two acoustic sensors is adjusted to obtain a difference, or an averaging process is performed. It was complicated.

[0005] The vibration amplitude at which the third harmonic starts to be remarkably generated is the vibration amplitude at which dislocation due to material fatigue starts to multiply,
That is, it was known from an experiment using a standing wave that it almost corresponds to the vibration amplitude at which fatigue starts to progress.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for managing vibration fatigue of a material, which can determine whether or not vibration fatigue of the material is progressing by simple means. I do.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, a method of managing vibration fatigue of a material according to the present invention is characterized in that an elastic wave pulse is applied to a material or temporary forced vibration applied to the material is cut off. This dampens the vibration of this material,
By measuring the displacement of a certain place in the material by the displacement measuring means, time-frequency analysis of the attenuated vibration to determine the intensity of the nth harmonic with respect to the fundamental vibration wave of the material,
The displacement width of the transition region where the nth harmonic increases / decreases is to be determined as the lower limit fatigue amplitude of the material.

When the management method described in the above features is applied to an actual plant or the like, the below-fatigue limit amplitude is obtained in a state in which the normal forced vibration constantly applied to the material is stopped, and the normal forced vibration is calculated. It is preferable to determine whether or not the material is in a vibration fatigue progress state by comparing the displacement width in the given state with the lower fatigue limit amplitude.

In applying the elastic wave pulse, the material may be hit with a hammer or the like, and an accelerometer, a laser displacement meter, or an eddy current displacement meter may be used as the displacement measuring means.

As the material to which the present invention is applied, for example, a socket welded portion having a nozzle and an insertion tube inserted into and welded to the nozzle is suitable. Then, in order to manage this material, the displacement measuring means is attached to the first measuring section in or near the nozzle and the second measuring section of the insertion tube which is separated from the nozzle, and The relative displacement width at which the measuring unit is displaced with respect to the first measuring unit may be the displacement width. As will be described later, the stress is most concentrated on the poor penetration portion at the nozzle, and the crack is likely to be formed. This is because the relative movement of the second measurement unit with respect to the first measurement unit.

[0011]

As described above, according to the feature of the method for managing the vibration fatigue of a material according to the present invention, the displacement width of the transition region where the n-th harmonic increases / decreases by hitting with a hammer or the like is limited to the lower limit of fatigue of the material. By a simple preparatory work of obtaining the amplitude, it has become possible to determine whether or not the material is in a state where vibration fatigue progresses. In addition, since the measurement is a direct measurement in which the amplitude of a certain portion is obtained, it is possible to perform accurate management that is resistant to background noise.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, referring to the attached drawings,
The present invention will be described in more detail. FIG. 1 is a diagram showing an outline of a measuring device 10 for measuring a relationship between an amplitude and an n-th harmonic using a metal piece as a material. This measuring device 10
Is generally a test table 11 holding a metal piece 20 as a material.
An excitation coil 19 for forcibly vibrating the metal piece 20,
A laser displacement meter 14 and the like for measuring the displacement of the measuring section T in the metal piece 20 are provided.

The metal piece 20 is a small piece having a notch 21 made of SUS304.
2 are held near the notch 21. Metal piece 2
The excitation small piece 22 is adhered to the tip of 0, and the metal piece 20 can be vibrated by applying a magnetic force to the excitation small piece 22 by the excitation coil 19 periodically.

The oscillator 17 generates a standing wave, and the amplifier 1
The metal piece 20 is vibrated via the excitation coil 8 and the exciting coil 19. The frequency of the oscillator 17 can be appropriately changed so as to resonate with the metal piece 20, and the frequency of the oscillator 17 is displayed on the counter 17a and is input to the analyzer 15 as a fundamental wave.

The laser displacement meter 14 includes a probe 14a which irradiates and receives a laser beam to a measuring section T which is an appropriate fixed portion of the metal piece 20, and a measuring section which obtains a displacement of the measuring section T based on these laser beams. 14b. The displacement signal of the measuring section T by the laser displacement meter 14 is associated with the fundamental wave of the oscillator 17 by the analyzer 15 as the vibration of the measuring section T, and the personal computer 16 performs the FFT processing.

The amplitude of the measuring section T can be changed by adjusting the output of the oscillator when the amplifier 18 amplifies the resonance wave from the oscillator 17. 6 to 8 show displacement signals of the measuring unit T obtained by adjusting the amplification degree, respectively. FIG. 6 is a graph showing a resonance waveform in a nonlinear region where dislocations of the metal piece 20 multiply, and FIG. 8 is a graph showing a resonance waveform in a transition region where dislocations of the metal piece 20 start to proliferate, and FIG. 8 is a graph showing a resonance waveform in a linear region where dislocations of the metal piece 20 do not multiply.

FIGS. 9 to 11 are graphs showing frequency spectra at resonance of the metal piece 20 at amplitudes corresponding to the amplitudes of FIGS. 6 to 8, respectively. That is, FIG. 9 is a frequency spectrum at the time of resonance in the non-linear region of the metal piece 20, FIG. 10 is a frequency spectrum at the time of resonance in the transition region of the metal piece 20, and FIG.
1 is a graph showing a frequency spectrum of the metal piece 20 at the time of resonance in a linear region.

FIG. 12 is a graph showing a damped oscillation waveform of the metal piece 20 obtained by vibrating the metal piece 20 with a sufficient amplitude and then cutting off the output of the amplifier 18.
FIGS. 13 to 15 are graphs showing frequency spectra obtained from attenuation waveforms at the amplitudes of the measuring unit T which are almost the same as those in FIGS. That is, FIG.
Frequency spectrum in the non-linear region obtained from the damped vibration waveform of 0, FIG. 14 shows the frequency spectrum in the transition region obtained from the damped vibration waveform of the metal piece 20, and FIG. 6 is a graph showing a frequency spectrum at the time.

At the time of resonance shown in FIGS.
It is known that the propagation of dislocations starts from the amplitude at which the second harmonic starts to occur. As shown in FIGS. 13 to 15, it was confirmed that the n-th order harmonic also started to increase from the amplitude at which the propagation of dislocation started similarly even when the attenuation waveform was used.

Among the n-order harmonics, the intensity of the third-order harmonic is most suitable for catching the dislocation multiplication phenomenon. Paying attention to this point, FIG. 16 is a graph showing the relationship between the third harmonic intensity and the amplitude obtained from the damped oscillation waveform of the metal piece 20.
In the graph, white circles are obtained by a test using a resonance waveform, and black circles are obtained by a test using an attenuation waveform. From the same graph, it is possible to perform the same evaluation as the case where the resonance waveform is used even if the attenuation waveform is used, and the displacement width at the measurement unit T in the transition region is about 0.018 mm,
It has been found that the displacement width should be managed as the fatigue limit amplitude of the metal piece 20.

Next, an application example of the present invention to the socket welded portion 40 in an actual piping system will be described.

FIG. 2 shows a measuring device 30 for measuring the relationship between the amplitude and the third harmonic of the n-th harmonic using a pseudo model of the socket welded portion 40 as the material to be tested.
FIG. The socket weld portion 40 fixes the nozzle 43 to a base 42 mounted on a mounting table 41,
The branch pipe 44 is inserted into the insertion recess of the nozzle 43 so that the weld metal 4
5, and a weight 46 serving as a valve or a flange is placed on the branch pipe 44.

FIGS. 3 and 4 show examples of the actual configuration of the pseudo model. A nozzle 43 is welded on a main pipe 47 corresponding to the mounting table 41 and the base 42 via a weld metal 47a. The branch pipe 44 serving as the insertion pipe is inserted into the insertion recess 43 a formed in the nozzle base 43 so that both center axes X coincide with each other, and is welded by the welding metal 45. In the root portion of the weld metal 45, a poor penetration portion 45 a is likely to occur, so that the nozzle 4
Due to the relative displacement of the tip portion of the branch pipe 44 with respect to 3, stress concentration occurs in the poor penetration portion 45 a, and this poor penetration portion 4 a
Cr is easily generated from 5a. In the present embodiment, an object is to prevent the generation of Cr beforehand by managing the dislocation accompanying the vibration fatigue acting on the poor penetration portion 45a by the third harmonic. Taking a thermal power generation facility as an example, the causes of the normal forced vibration include rotational vibration of a turbine or a motor of a water supply pump, surging caused by water flow, and the like.

The measuring device 30 comprises a pair of first and second accelerometers 31 and 32, first and second amplifiers 33 and 34 for amplifying their outputs, and displacements of the first and second accelerometers 31 and 32. And a personal computer 16 for displaying processes and results. The first accelerometer 31 is attached to the first measuring portion T1 which is a fixed location such as the nozzle 43 or the base 42 near the nozzle 43, and the second accelerometer 32 is fixed to the nozzle 43 of the branch pipe 44 at a fixed position. Is mounted on the second measuring unit T2. Then, a temporal graph of the relative displacement of the second measuring unit T2 with respect to the first measuring unit T1 can be obtained from the difference between the accelerations detected by the first and second accelerometers 31 and 32.

FIG. 17 shows a socket weld 40 created by striking a weight 46 sideways with a hammer 35.
4 is a graph showing a damped oscillation waveform at the time of FIG. The vertical axis of this waveform indicates the relative displacement of the second measurement unit T2 with respect to the first measurement unit T1.

FIGS. 18 to 20 show frequency spectra obtained by subjecting the graph of FIG. 17, which is the damped vibration waveform at the socket welded portion 40, to FFT processing by the analyzer 15, respectively. Here, FIG. 18 is a graph showing a frequency spectrum in a nonlinear region, FIG. 19 is a graph showing a frequency spectrum in a transition region, and FIG. 20 is a graph showing a frequency spectrum in a linear region.

On the other hand, FIG. 21 is similar to the damped vibration of FIG. 17, but the third harmonic intensity and amplitude obtained from the damped vibration waveform near the socket weld based on the absolute displacement of the second measuring part T2. 6 is a graph showing the relationship of. In the graph, a black circle indicates measurement using the second accelerometer 32, and a white circle indicates the second measurement unit T.
2 was measured using the above-described laser displacement meter. According to the graph, the lower limit fatigue amplitude of the second measurement unit T2 is 0.073 mm, and considering that the amplitude of the first measurement unit T1 at the time of fatigue limit is about 0.027 mm, the first measurement is performed. Second measuring unit T2 with respect to unit T1
The lower limit amplitude of fatigue at the relative displacement of 0.1 m shown in FIG.
It is appropriate to treat as m.

In practicing the present invention in an actual piping system, first, the power plant and the like are stopped to stop the above-described normal forced vibration. Next, the first and second measuring units T
The first and second accelerometers 31 and 32 are attached to 1, T2, and the like, and a part of the pipe is hit with a hammer 35 or the like to generate damped vibration. At this time, the lower limit fatigue amplitude at the appropriate location is determined by the above-described procedure.

After that, the operation of the power plant or the like is restarted, and the vibration amplitude of the first and second accelerometers T1, T2, etc. is obtained while normally applying forced vibration to the piping system. In this embodiment, when the relative displacement of the second accelerometer T2 with respect to the first accelerometer T1 exceeds the fatigue lower limit amplitude of 0.1 mm, the vibration fatigue of the material in the socket welded portion 40 progresses. It is determined that there is. For this determination, it is desirable to take measures such as mounting a damping device on the piping system so as to reduce the amplitude at the same location. In addition, the same location may be set as a priority monitoring location, and the degree of dislocation multiplication may be estimated by integrating the amplitude and the operation time.

Finally, still another embodiment of the present invention will be described below. In the above embodiment, the material was subjected to temporary forced vibration by a hammer or an electromagnet. However, the means for giving the temporary forced vibration may be a striking device using an urging means, an ultrasonic oscillator using a piezoelectric element, or the like.

In the above embodiment, a socket welded portion for joining a branch pipe to a main pipe has been exemplified as an application object of the present invention. However, as the socket weld 40, for example, FIG.
As shown in (1), an elbow section in which nozzles 43, 43 are attached to both ends of an elbow pipe 51 may be used, and the application of the present invention is not limited to a pipe or a welded section.

In the above embodiment, the amplitude of the displacement in one axial direction is detected. However, vibration fatigue may be managed by detecting the amplitude of displacement in two or more axes.

In the above embodiment, the relative displacement is detected using the accelerometer, but the relative displacement may be detected using a laser displacement meter. Further, as the displacement meter, a non-contact type displacement meter such as an eddy current type displacement meter may be used instead of the accelerometer or the laser displacement meter.

It should be noted that the reference numerals described in the claims are merely for convenience of comparison with the drawings, and the present invention is not limited to the configuration of the attached drawings. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a measuring device for measuring a relationship between an amplitude and an nth harmonic using a metal piece as a material.

FIG. 2 is a diagram showing an outline of a measuring device for measuring a relationship between an amplitude and an nth-order harmonic using a pseudo model of a socket weld portion as a material.

FIG. 3 is a view showing a socket welded portion between a main pipe and a branch pipe to be subjected to the vibration fatigue management method according to the present invention.

FIG. 4 is a sectional view of a main part of FIG. 3;

FIG. 5 is a view showing a socket welded part in an elbow part to be subjected to the vibration fatigue management method according to the present invention.

FIG. 6 is a graph showing a resonance waveform of a metal piece as a material in a nonlinear region.

FIG. 7 is a graph showing a resonance waveform in a transition region of a metal piece.

FIG. 8 is a graph showing a resonance waveform of a metal piece in a linear region.

FIG. 9 is a graph showing a frequency spectrum at the time of resonance in a nonlinear region of a metal piece.

FIG. 10 is a graph showing a frequency spectrum at the time of resonance in a transition region of a metal piece.

FIG. 11 is a graph showing a frequency spectrum at the time of resonance in a linear region of a metal piece.

FIG. 12 is a graph showing a damped vibration waveform of a metal piece.

FIG. 13 is a graph showing a frequency spectrum in a nonlinear region obtained from a damped oscillation waveform of a metal piece.

FIG. 14 is a graph showing a frequency spectrum in a transition region obtained from a damped oscillation waveform of a metal piece.

FIG. 15 is a graph showing a frequency spectrum in a linear region obtained from a damped oscillation waveform of a metal piece.

FIG. 16 is a graph showing the relationship between third harmonic intensity and amplitude obtained from a damped oscillation waveform of a metal piece.

FIG. 17 is a graph showing a damped vibration waveform at a socket weld.

FIG. 18 is a graph showing a frequency spectrum in a nonlinear region obtained from a damped vibration waveform at a socket weld.

FIG. 19 is a graph showing a frequency spectrum in a transition region obtained from a damped vibration waveform at a socket weld.

FIG. 20 is a graph showing a frequency spectrum in a linear region obtained from a damped vibration waveform at a socket weld.

FIG. 21 is a graph showing a relationship between third harmonic intensity and amplitude obtained from a damped vibration waveform near a socket weld.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Measuring device 11 Test stand 12 Clamp 13 Mounting table 14 Laser displacement meter 14a Probe 14b Measuring part 15 Analyzer 16 Personal computer 17 Oscillator 17a Counter 18 Amplifier 19 Exciting coil 20 Metal piece (material) 21 Notch 22 Exciting piece 30 Measuring device 31 1 accelerometer 32 second accelerometer 33 first amplifier 34 second amplifier 35 hammer 40 socket weld (material) 41 mounting table 42 base 43 nozzle 43a insertion recess 44 branch pipe (insert pipe) 45 welded metal 45a Poor penetration part 46 Weight 47 Main pipe 47a Weld metal 51 Elbow pipe T Measurement part T1 First measurement part T2 Second measurement part X Central axis.

Continued on the front page F term (reference) 2G047 AB01 AB07 BA04 BC03 BC04 BC11 CA01 CA03 GA19 GA20 GF06 2G061 AA13 AB04 AB06 BA20 EA02 EA06 EA07 EA09

Claims (5)

[Claims] An elastic wave pulse is applied to the material (20, 40) or the temporary forced vibration applied to the material (20, 40) is interrupted to attenuate the vibration of the material (20, 40). Displacement measuring means (14, 31, 32) means that the material (20, 40) has a predetermined location (T, T1, T1).
The displacement of 2) is measured, and the intensity of the nth harmonic with respect to the fundamental vibration wave of the material (20, 40) is obtained by performing time-frequency analysis of the damping vibration, and a transition region where the nth harmonic increases and decreases. A method for managing vibration fatigue of a material, wherein a displacement width of the material is obtained as a lower limit amplitude under fatigue of the material (20, 40). 2. The fatigue-limited amplitude is obtained in a state in which the normal forced vibration constantly applied to the material (20, 40) is stopped, and the displacement width and the fatigue in the state in which the normal forced vibration is applied are obtained. The vibration fatigue management method for a material according to claim 1, wherein it is determined whether the material (20, 40) is in a state of advancing vibration fatigue by comparing with a limit width. 3. The elastic wave pulse is applied by hitting the material (40) with a hammer (35) or the like, and the displacement measuring means includes an accelerometer (31, 32), a laser displacement meter (14) or a vortex. The method for managing vibration fatigue of a material according to claim 1, wherein a current-type displacement meter is used. 4. A nozzle (43) into which said material (40) is inserted and welded into said nozzle (43).
The method according to any one of claims 1 to 3, wherein the method is (4). 5. The displacement measuring means (31, 32) is separated from the nozzle (43) or a first measuring part (T1) in the vicinity thereof and the insertion tube (44) from the nozzle (43). Attached to the second measuring unit (T2), and the second measuring unit (T2)
The method for managing vibration fatigue of a material according to claim 4, wherein the displacement width relative to the first measuring unit (T1) is defined as the displacement width.