SU1651016A1 - Method of locating pipeline leakage - Google Patents

Abstract

The invention relates to methods for non-destructive testing in pipelines and can be used to detect leaks in pipelines with a unilateral access. The method consists in determining the location of the leak in the pipelines by detecting the excess of acoustic radiation over noise at one point of the pipeline. Initially, the excess of acoustic radiation over noise in the low-frequency range of the operating range is recorded, then acoustic radiation is recorded at higher frequencies and the highest frequency is recorded at which the acoustic radiation of the leak exceeds the noise. The distance to the leak is determined from the graphical dependences of the frequency components of the acoustic radiation to the leak at a corresponding fixed frequency, pre-built for the pipeline. Using the proposed method allows to increase productivity and to ensure the possibility of controlling pipelines with one-way access. 2 Il. s / 1 C

Description

The invention relates to methods for non-destructive testing in pipelines and can be used to detect leaks in pipelines with one-way access.

The aim of the invention is to increase productivity and enhance functionality by locating the leak in one-way access pipelines.

The method consists in determining the location of the leak in the pipelines by detecting the excess of acoustic radiation over noise.

Registration is made at one point in the pipeline. Initially, the excess of acoustic radiation over noise in the frequency range of the operating range is recorded, then acoustic radiation is recorded at higher frequencies and the greatest frequency is recorded at which the acoustic radiation of the leak exceeds the noise, and the distance to the leak is determined by the graphical dependencies previously constructed for the pipeline the frequency components of the acoustic radiation from the distance to the leak at the corresponding fixed frequency.

Fig. 1 shows experimental curves for acoustic emission versus distance for different detection frequencies; in fig. 2 is a block diagram of an acoustic leak detector.

The implementation of the method is possible due to the fact that when a fluid flows from

Oel o

through pipeline defect, broadband acoustic radiation arises with a large amplitude in the frequency range from a few hertz to several hundred kilohertz, varying slightly with changes in the size of the defect. The acoustic radiation signals propagate through the pipe, and as a certain distance goes by, they attenuate, and the high-frequency components travel a smaller distance than the low-frequency ones.

From the graphs shown in FIG. 1, it follows that when detecting acoustic radiation at a point located at a large distance from the leak, low-frequency components predominate. As the leaks approach, high-frequency components of the signal arise, since the attenuation of sound during propagation through the pipe increases with increasing frequency. The dependence of the attenuation coefficient on the frequency of various waves propagating through the pipe is determined by the expression

а К f, where а - attenuation, dB;

K - coefficient taking into account the diameter of the pipe, its material and the nature of the soil from the outside;

f is the frequency of registration of acoustic radiation.

From a pre-determined dependence of the level of acoustic radiation when propagating through a pipe from distance to leakage for different frequencies of recording, it is possible to obtain a quantitative estimate of the distance to a leak.

The device for carrying out the method comprises an electroacoustic converter 1, a preamplifier 2, a step attenuator 3, a low-pass filter 4, a matching stage 5, a mixer 6, a bandpass amplifier 7, a meter 8 of RMS voltage, a recorder 9, a stepwise tunable generator 10.

As an electroacoustic transducer 1, a piezoelectric transducer is used. The preamplifier serves to amplify the signal removed from the piezoelectric transducer in order to improve the ratio of signal characteristics and noise at the input of the attenuator. The step attenuator 3 provides a calibrated damping value of up to 60 dB (in 10 dB steps) in order to provide undistorted gain and measurement in the range of input signals from 0 to 80 dB. A low-pass filter 4 with a cut-off frequency of 200 kHz protects the main band-pass amplifier in the intermediate and mirror reception channels. Matching cascade 5 is designed to match attenuator 3 and mixer 6. Mixer 6 together with a stepped tunable generator 10 carries out the transfer from the frequency range 10 Hz to 200 kHz to the frequency band of the band amplifier 7, equal to (500 ± 1.6) kHz Band amplifier 7 with a constant

A factor of 0 and a constant bandwidth amplify the signal at a frequency of (500 ± 1.6) kHz. The bandwidth is achieved by setting a concentrated

5 selection. The bandwidth of the bandpass amplifier F is chosen from the condition F «Af / n, where D f 0.1–200 kHz is the operating frequency range of the leak detector, and n is the number of frequencies of the stepwise tunable oscillator.

0 The step generator 10 is designed to form the reference sinusoidal frequencies necessary for operation of the mixer 6 and selected in such a way as to record the acoustic radiation at various points in the frequency range 0.1–200 kHz.

The state of the passband, the gain of the amplifier 7 and the gradation in the switching of the generator 10

0 allows measurement and comparison of the spectral power densities of acoustic radiation (AI) at various points in the frequency range. The estimation of the level of AI is carried out according to the recorder 9. The scale of which is calibrated by the rms voltage measured by block 8.

The method is carried out as follows. To access the pipe,

0 hole The receiving transducer 1 is installed on the pipe wall. Initially, the excess acoustic noise over the noise is recorded by a narrow-band measuring device in a low-frequency

5 areas of the working range, making sure that there is a leak. Then go to a higher recording frequency by stepwise switching the frequency of the generator 10. Record the highest frequency when

0 which the acoustic radiation leakage exceeds the noise. The distance to the leak is determined from the graphs of the frequency components of the acoustic radiation from the distance to the leak for the pipeline at the corresponding fixed frequency, pre-built for the pipeline. Graphic dependencies are obtained experimentally using a leak simulator by measuring the level of leakage AI on fixed

frequencies fn in the range of 100 Hz - 200 kHz PG formula

, 4fn-i, where n is the number of fixed frequencies.

The values of the fixed frequencies are chosen from the condition that the frequency range is evenly overlapped, and the initial frequency is chosen based on the noise level of the pipeline. In the given graphs fi 8 kHz,.

For example, the highest frequency is recorded, equal to 84 kHz, at which the acoustic radiation of a leak exceeds the noise. The level of acoustic radiation was 0.1 mV. From the point on the curve (Fig. 1) corresponding to the fixed frequency of the measured level of acoustic radiation, we draw aa a parallel to the ordinate axis. The distance to the leak will be equal to the coordinate of the point of intersection of the straight line drawn parallel to the ordinate axis with the horizontal axis, i.e. 90 m

The use of the proposed method for determining the distance to a leak minimizes leak detection time, shortens pipeline testing time by reducing the bores to 1, thereby increasing productivity and ensuring that unilateral access pipelines can be monitored for which no known leakage can occur.

Claims (1)

5 Formula of Invention A method for determining the location of a leak in pipelines by detecting the excess acoustic radiation above 0 noise, characterized in that, in order to increase productivity and enhance functionality by determining the location of the pipelines with one-sided accessory, registration is carried out at one point of the pipeline, and the acoustic emission is initially recorded above the noise in the low frequency range of the working range, then recorded acoustic radiation at higher frequencies and record the highest frequency at which the acoustic radiation of the leak exceeds the noise, and the distance of up leak was determined by pre-PA5 of the pipeline structure for a graphical dependence of M frequency components of the acoustic radiation from the distance to the leak at a corresponding fixed frequency. 90 t zoo 1 FIG. 2