JPH07198362A - Method and apparatus for measurement of decrease in wall thickness of pipe - Google Patents

Abstract

PURPOSE:To measure a decrease in wall thickness on the basis of an ultrasonic porpagation speed inside a pipe material by a method wherein ultrasonic pulses are made to impinge and a vibration cycle which appears in a self-correlation function is found on the basis of its reflected-pulse envelope signal. CONSTITUTION:A pulse signal, from a transmission part 2, which is output by the measurement execution instruction of a control part 1 is changed into ultrasonic pulses by an ultrasonic probe 3, and the pulses are made to impinge vertically to the outer wall surface 4a of a pipe 4. After the pulses have been made to impinge, they are reflected partly by its inside wall rear 4d, and they are transmitted partly through its outer wall rear 4c and its surface 4a. The transmitted and reflected ultrasonic pulses are detected 3, and they are output as received waves by a reception part 5. From the envelope signal, of the received waves, which has been generated by a detection circuit 6, a signal processing part 7 extracts waveform data after the elapse of a definite time td after transmission waves have been transmitted, and its self-correlation function phi (tau) is computed. Then, a vibration cycle which appears in the function phi (tau) is found, it is regarded as the time required when ultrasonic waves go back and forth inside the pipe between an inner wall and an outer wall, a pipe wall thickness d=vT/2 is obtained on the basis of an ultrasonic propagation speed inside a pipe material, and the thickness is displayed 8 as a decrease in wall thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nondestructive inspection method and apparatus for measuring the amount of thinning of pipes used in nuclear power plants, thermal power plants, chemical plants, etc. from outside the pipes by using ultrasonic waves. .

[0002]

[Industrial application] In nuclear power plants, thermal power plants, etc., for example, in a bent portion of a pipe through which high-temperature / AC-speed steam flows, there is a case where thinning due to erosion / corrosion such as impact corrosion occurs. It is known to cause problems in equipment maintenance.

For this reason, a plurality of reflected pulses are generated by receiving a reflected wave from the back surface of the inner wall of the pipe when an ultrasonic pulse is incident from the outside of the pipe and repeating reflection between the inner and outer walls of the pipe contained in the received wave. A non-destructive inspection method has been developed in which the wall thickness is measured from the time difference between them.

According to the conventional method, the influence of the transmitted wave or the dead time of the receiving section on the output of the detection circuit, which is the received wave as illustrated in FIG. 3 or the envelope waveform of the received wave as illustrated in FIG. Of the reflected ultrasonic pulse appearing after that, waiting for a time td during which the influence of P appears, the peaks P ₁ , P ₂ ,. ．
Is detected directly, and the peak appearance time t ₁ ,
t ₂ ,. ． The time difference T = t ₂ −t ₁ was calculated from this, and this was used as the time required for the ultrasonic waves to reciprocate in the pipe material between the inner and outer walls.

[0005]

As described above, in the method of reading the peak of the direct reflection pulse from the received waveform, as shown in FIG.
When the amount of thinning is small as shown in (a) or FIG. 4 (a), the reflected ultrasonic pulse can be identified relatively easily.

However, when the wall thickness is reduced, the inner wall surface is not flat so that the reflected wave is scattered and the wave height is attenuated as shown in FIG. 3 (b) or 4 (b). However, there is a problem that it is difficult to identify the reflected ultrasonic pulse.

Therefore, an object of the present invention is to solve the above problems of the prior art and to accurately measure the time difference between reflected pulses even when the height of the received ultrasonic wave is attenuated due to the progress of thinning of the pipe. It is an object of the present invention to provide a method and an apparatus for measuring pipe wall thinning, which can measure the current wall thickness, and thus the amount of wall thinning, by using a known ultrasonic wave propagation velocity in the pipe material.

[0008]

In order to achieve the above object, the pipe thinning measuring method according to the present invention receives a reflection pulse after a certain time has elapsed after an ultrasonic pulse is incident from the outside of the pipe, and the reflection pulse is received. Autocorrelation function φ of the envelope signal of
The vibration period T appearing in (τ) is obtained, and the pipe wall thickness d is calculated as d = vT / 2 using the ultrasonic wave propagation velocity v in the pipe material.

Further, the pipe thinning measuring device according to the present invention is
After receiving the ultrasonic pulse from the outside of the pipe and receiving the reflected pulse after a certain period of time, obtain the cepstrum of the envelope signal of this reflected pulse, and within the range of the keflencity expected from the wall thickness in the normal state, the cepstrum is the maximum. Is calculated as T, and the pipe wall thickness d is calculated as d = vT / 2 using the ultrasonic wave propagation velocity v in the pipe material.

Further, the pipe thinning measuring device according to the present invention is
An ultrasonic probe that is attached to the outside of the pipe and that emits and detects ultrasonic waves, a transmitter that sends an ultrasonic pulse signal to the ultrasonic probe, and a pipe from the pipe detected by the ultrasonic probe. A receiving unit that receives a reflected pulse as a received wave, a detection circuit that generates an envelope signal of the received wave, and an autocorrelation function φ (τ of the envelope signal after a certain time has elapsed from the emission of the ultrasonic pulse signal. ) Is calculated, the vibration period T appearing in φ (τ) is calculated, and the ultrasonic wave propagation velocity v in the pipe material is calculated.
Is used to calculate the pipe wall thickness d as d = vT / 2.

Further, the pipe thinning measuring device according to the present invention is
An ultrasonic probe that is attached to the outside of the pipe and that emits and detects ultrasonic waves, a transmitter that sends an ultrasonic pulse signal to the ultrasonic probe, and a pipe from the pipe detected by the ultrasonic probe. A receiving unit that receives a reflected pulse as a received wave, a detection circuit that generates an envelope signal of the received wave, a cepstrum of the envelope signal after a certain time has elapsed from the emission of the ultrasonic pulse signal, and a normal operation is calculated. The autocorrelation function φ (τ) is calculated, where T is the kefstrity that maximizes the cepstrum within the range of the expected kefrenity from the wall thickness of the state, and the vibration period T appearing in φ (τ) is calculated to determine the ultrasonic wave in the pipe material. The pipe wall thickness d is d = vT / 2 using the propagation velocity v.
And a signal processing unit for calculating

[0012]

According to the pipe thinning measurement method and device of the present invention as defined in claim 1 or 3, waveform data is extracted from the envelope signal of the received ultrasonic wave after a certain time td has elapsed after transmitting the transmitting wave. , Its autocorrelation function φ (τ) is calculated, and φ
The vibration period T appearing in (τ) is calculated, and the ultrasonic wave
As the time required to reciprocate in the pipe material between the outer walls, the pipe wall thickness d = vT / 2 is obtained from the ultrasonic wave propagation velocity v in the pipe material.

In the pipe thinning measurement method and apparatus according to the present invention, the cepstrum obtained by inverse Fourier transform of logarithmic power spectrum density is analyzed instead of the autocorrelation function. Then, the wall thickness of the pipe is obtained with T as the kefrensi that maximizes the cepstrum within the range of the round-trip propagation time between the inner and outer walls expected from the wall thickness in the normal state.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of a pipe thickness reduction measuring device showing an embodiment of the present invention. The pipe thickness reduction measuring apparatus of the present embodiment is equipped with an ultrasonic probe 3 which is attached to the outside of the pipe 4 to emit and detect ultrasonic waves, and a transmission unit which sends ultrasonic pulse signals to the ultrasonic probe 3. 2, a receiving unit 5 that receives a reflected pulse from the pipe 4 detected by the ultrasonic probe 3 as a received wave, a detection circuit 6 that generates an envelope signal of the received wave, and an ultrasonic pulse signal The autocorrelation function φ (τ) of the envelope signal after a lapse of a certain time from the emission is calculated, the vibration period T appearing in φ (τ) is calculated, and the ultrasonic wave propagation velocity v in the material of the pipe 4 is used to make the pipe 4 The wall thickness d of d = v
A signal processing unit 7 that calculates T / 2, a display unit 8 that outputs and displays the wall thickness and / or the amount of wall thinning of the pipe 4, and a control unit 1 that controls the execution of the above processes.

The pulse signal output from the transmission unit 2 in response to the measurement execution command issued from the control unit 1 is converted into an ultrasonic pulse by the ultrasonic probe 3 placed in the vicinity of the outer wall surface 4a of the pipe 4 as the pipe 4 Is perpendicularly incident on the outer wall surface 4a. The incident ultrasonic pulse propagates inside the tube wall, part of which passes through the inner wall surface 4b, and part of which is reflected by the inner wall back surface 4d. The reflected ultrasonic pulse reaches the outer wall rear surface 4c, a part thereof is transmitted, a part of it is reflected again, and while repeating this, the wall surface has a curvature and is attenuated by scattering or the like.

The reflected ultrasonic pulse transmitted through the outer wall surface 4a is detected by the ultrasonic probe 3 and output from the receiver 5 as a received wave.

The signal processing unit 7 receives the envelope signal of the received wave generated by the detection circuit 6 as an input and calculates the pipe wall thickness, and the display unit 8 directly or directly displays the wall thickness in the normal state. The output is displayed as the difference in the amount of metal loss.

FIG. 2 shows the internal structure of the signal processing unit 7 according to the present invention. The time window processing unit 10 outputs a measurement execution command from the control unit 1 and then outputs a predetermined fixed time t.
The received wave envelope signal from the time point after the elapse of d is extracted.

The autocorrelation function analysis unit 11 calculates the autocorrelation function φ (τ) of the signal. FIGS. 5A and 5B show autocorrelation functions obtained from the t> t _d portion of the detection circuit output examples shown in FIGS. 4A and 4B, respectively.

The peak detection processing section 12 uses the autocorrelation function φ.
Two adjacent maximum values φ (τ ₁ ) and φ (τ ₂ ) of (τ) are selected, and delay times τ ₁ and τ ₂ that give the maximum value are output. At this time, a method of selecting two or more continuous maximum values can be adopted.

The cycle determining unit 13 calculates T = τ ₂ −τ ₁ from the selected delay time value. However, τ ₂ > τ ₁ . When two or more delay times are selected, the average value of the delay times between the adjacent maximum values is calculated as T.

The wall thickness calculating unit 14 indicates that the ultrasonic wave is
As the time required to reciprocate between the outer walls, the pipe wall thickness d = vT using the known velocity v of the ultrasonic wave propagating in the pipe material.
Calculate / 2.

As is apparent from the comparison between FIG. 4 (b) and FIG. 5 (b), even when the thinning progresses and it is difficult to identify the reflected ultrasonic pulse even if the received wave envelope signal is directly observed, In the autocorrelation function, the influence of irregular signal components is reduced and periodic vibration appears, and the position of the maximum value can be easily identified.

According to the configuration of this embodiment, waveform data after a lapse of a fixed time td after transmitting a transmission wave is extracted, its autocorrelation function φ (τ) is calculated, and the vibration period T appearing in φ (τ) is calculated. The ultrasonic wave velocity v in the pipe material is calculated as the time required for the ultrasonic wave to reciprocate in the pipe material between the inner and outer walls.
Since the pipe wall thickness d = vT / 2 is obtained more, even when the pipe wall thickness is reduced and the wave height of the received ultrasonic wave is attenuated,
The time difference between the reflected pulses can be measured accurately and from this the current wall thickness, and thus the amount of wall thinning, can be measured using known ultrasonic wave propagation velocities in the piping material.

Next, another embodiment of the present invention will be described. The present embodiment is different from the case where the signal processing unit of FIG. 1 is shown in FIG. 2 and is configured as shown in FIG.

That is, for the received wave envelope signal extracted by the same time window processing unit 10 as in FIG. 2, the cepstrum (Cepstrum: Cepstrum: e.g., "Pattern Information Processing" by Shin Nagao, Electronic Information Processing, Electronic Page 17 of The Institute of Communications Engineers, University Series I-4, Corona Publishing (1983)
). Cepstrum is a quantity obtained by inverse Fourier transform of logarithmic power spectral density (logarithmic APSD), and its variable has a dimension of time and is called quefrency.

The reason why the cepstrum is effective is as follows.
Now, the envelope signal of the reflected ultrasonic pulse from the back surface of the inner wall of the pipe that is received first is y (t), and thereafter the envelope signal of the reflected ultrasonic pulse that is received with a delay of time T while gradually decreasing in amplitude. Letting z (t) be the signal obtained as a composite wave in which the signals overlap, this composite wave is expressed as z (t) = y (t) + Σα · y (t−T) (1).

This Fourier transform is Z (jω) = {1 + Σα · exp (-jωT)} · Y (jω) (2) Here, α represents the attenuation factor of the wave height while the ultrasonic wave reciprocates between the inner and outer walls of the pipe by reflection. From this formula, the APSD of the composite wave is as follows.

Φz (ω) = Φy (ω)  [C ₁ + C ₂ cos (ωT)] (3) C ₁ and C ₂ are constants that depend on α, and this expression shows that the APSD of the composite wave is APS of single reflection pulse envelope signal
It means that ripple-like vibration is shown with a cycle of 1 / T along D and Φy (ω). Therefore, this vibration period can be obtained by the cepstrum analysis.

FIG. 7 shows the APSD output from the time window processing unit 10.
In the example shown in FIG. 1, vibration with a cycle of 1 / T appears.

FIG. 8 shows the cepstrum obtained as the output from the cepstrum analysis section. Figure 8
As shown in Fig. 6, there may be a plurality of peaks in the cepstrum other than the peak at the required kefrency q = T. However, in the peak detection processing unit 12 of FIG. Using T = q _H predicted for thickness and T = q _L predicted for wall thickness slightly smaller than the allowable limit of wall thickness reduction, q _L <T <q _The kefrensi with the maximum cepstrum within the range _H is determined as T. Thickness calculator 14
Calculates the pipe wall thickness based on T.

According to the configuration of this embodiment, the cepstrum obtained by the inverse Fourier transform of the logarithmic power spectrum density is analyzed, and the cepstrum is within the range of the round-trip propagation time between the inner and outer walls expected from the wall thickness in the normal state. Since the kefleency that maximizes the value of T is used to obtain the pipe wall thickness, even if the wave height of the received ultrasonic wave is attenuated due to the progress of the pipe wall thickness reduction, the time difference between the reflected pulses can be accurately measured. It is possible to measure the current wall thickness and thus the amount of wall thinning using known ultrasonic wave propagation speeds in the material.

[0033]

As described above, according to the configuration of the present invention, the time difference between the reflected pulses can be accurately measured even if the wave height of the received ultrasonic wave is attenuated due to the progress of the thinning of the pipe. It is possible to measure the current wall thickness and thus the amount of wall thinning using known ultrasonic wave propagation velocities in the piping material. As a result, the wall thickness measurement accuracy of the pipe with the reduced wall thickness is improved, which makes it possible to find the pipe that has more problems in maintenance, prevent accidents and failures, shorten the repair period, and reduce the work involved. Reduction of radiation exposure is expected. Further, this is effective in improving the reliability and operating rate of the plant.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a pipe thickness reduction measuring device according to the present invention.

FIG. 2 is a block diagram showing a detailed configuration example of a signal processing unit in FIG.

FIG. 3 is a diagram showing an example of a waveform of a received wave of a reflected pulse of ultrasonic waves, in which (a) shows a case where a thinning amount is small,
(B) shows the case where the amount of thinning is small.

4 is a diagram showing an example of an output waveform of the detection circuit shown in FIG.
(A) shows the case where the amount of thinning is small, and (b) shows the case where the amount of thinning is small.

FIG. 5: Autocorrelation function φ of envelope signal of reflected pulse
An example of (τ) is a figure, (a) shows a case where the amount of thinning is small, and (b) shows a case where the amount of thinning is small.

6 is a block diagram showing another detailed configuration example of the signal processing unit in FIG. 1. FIG.

FIG. 7 is a diagram showing an example of the power spectrum density of the envelope signal of the reflected pulse.

FIG. 8 is a diagram showing an example of a cepstrum of an envelope signal of a reflected pulse.

FIG. 9 is a block diagram showing a configuration example of a signal processing unit of a conventional pipe thickness reduction measuring device.

[Explanation of symbols] 1 control unit 2 transmission unit 3 ultrasonic probe 4 piping 4a piping outer wall surface 4b piping inner wall surface 4c piping outer wall back surface 4d piping inner wall back surface 5 reception unit 6 detection circuit 7 signal processing unit 8 display unit 10 time window processing unit 11 autocorrelation function analysis unit 12 peak detection processing unit 13 period determination unit 14 wall thickness calculation unit 15 cepstrum analysis unit

Claims (4)

[Claims] 1. A vibration period T which appears in an autocorrelation function φ (τ) of an envelope signal of the reflected pulse after a reflected pulse has been received after a certain time has passed after an ultrasonic pulse is incident from the outside of the pipe.
Is calculated, and the pipe wall thickness d is calculated as d = vT / 2 by using the ultrasonic wave propagation velocity v in the pipe material. 2. A reflected pulse is received after a certain time has elapsed after an ultrasonic pulse has been incident from the outside of the pipe, the cepstrum of the envelope signal of this reflected pulse is determined, and it is within the range of the keflencity expected from the wall thickness in a normal state. The pipe thickness reduction measuring method is characterized in that the keflencity that maximizes the cepstrum is calculated as T, and the pipe wall thickness d is calculated as d = vT / 2 using the ultrasonic wave propagation velocity v in the pipe material. 3. An ultrasonic probe mounted outside the pipe for emitting and detecting ultrasonic waves, a transmitter for sending ultrasonic pulse signals to the ultrasonic probe, and detection by the ultrasonic probe. A receiving unit that receives a reflected pulse from a pipe as a received wave, a detection circuit that generates an envelope signal of the received wave, and a self of the envelope signal after a certain time has elapsed from the emission of the ultrasonic pulse signal. A signal processing unit that calculates the correlation function φ (τ), obtains the vibration period T appearing in φ (τ), and calculates the pipe wall thickness d as d = vT / 2 using the ultrasonic propagation velocity v in the pipe material. A pipe thinning measuring device characterized by comprising: 4. An ultrasonic probe attached to the outside of a pipe for emitting and detecting ultrasonic waves, a transmitter for sending ultrasonic pulse signals to the ultrasonic probe, and detection by the ultrasonic probe. A receiver for receiving a reflected pulse from the pipe as a received wave, a detection circuit for generating an envelope signal of the received wave, and a cepstrum of the envelope signal after a certain time has elapsed from the emission of the ultrasonic pulse signal. Is calculated, and the autocorrelation function φ (τ) is calculated with T being the kefstrity that maximizes the cepstrum within the range of the keflencity expected from the wall thickness in the normal state, and the vibration cycle T appearing in φ (τ) is calculated. A pipe thinning measuring device, comprising: a signal processing unit that calculates a pipe thickness d as d = vT / 2 by using an ultrasonic wave propagation velocity v in a material.