RU2020467C1 - Method for detection of through defects in pipelines - Google Patents

Abstract

FIELD: nondestructive testing. SUBSTANCE: method includes excitation in pipeline with diameter D, as SHF wave guide system, of oscillations of the H₁₁ type on working wave length λ_w ≅ 1.71 D and reception of signal radiated by through defect by means of highly sensitive receiver located at distance 1 from pipeline. EFFECT: increased length of continuously controlled length of pipeline. 1 dwg

Description

 The invention relates to the field of non-destructive testing of products and can be used for flaw detection of pipelines filled with gas, oil, oil products under pressure, and more specifically for the detection of through cracks in gas pipelines.

 The most common are through defects having small dimensions, for example 10x0.2 mm, 25x0.2 mm, 12x0.1 mm. However, when a gas pipeline flows through a through defect (crack) at a high speed (up to 700 m / s), an avalanche process of gas pipeline destruction can occur. The length of the defect may increase to hundreds or even thousands of meters. This confirms the urgency of the problem timely and with a high probability of detecting defects in gas pipelines and their elimination at the initial stage of occurrence. It is practically necessary to have continuous monitoring of the condition of pipelines (product pipelines), especially near settlements, railway crossings, industrial and other economic facilities.

 A device for acoustic emission (AE) diagnostics of pipelines [1]. In this device, improving the accuracy of diagnostics of pipelines (gas and oil pipelines) during their testing and operation is achieved by determining the difference in the arrival time of the harmonic components of the AE signal by measuring the signal at two levels of discrimination and measuring the energy parameters of the signal taking into account the attenuation of AE waves in the product material. When the gas flows through the defect, acoustic vibrations (signals) occur. With the help of electro-acoustic transducers installed on the pipe, these signals are received. The time of arrival of various harmonic components of the acoustic signal is noted. Due to the dispersion of sound in the pipeline, the propagation time of various harmonic components of the acoustic signal from the source to the AE receiver is not the same. The difference in the arrival time of these harmonic components is used to judge the distance from the source (defect) to the receiver, thereby determining the location of the defect. The device is complex because of the introduction of additional blocks that determine the attenuation of acoustic waves in the material and increase the accuracy of the spatio-temporal selection of AE signals. Along with the complexity of the processing system, the disadvantages of this device include the low noise immunity of AE receivers in a production environment and the difficulty in determining the location of defects in an extended section of a pipeline. For long sections of pipelines, a large number of ultrasonic transducers would be required. This leads to an additional complication of the system, a decrease in its reliability, and requires a complex and expensive system for collecting, processing, and transmitting information to a control room.

 These disadvantages are partially overcome in the known device for the diagnosis of trunk pipelines [2]. The reliability of the diagnostics carried out using this device is increased due to local loading of the walls of the controlled pipeline with increased pressure of the working medium. The device consists of two units: a power unit and a unit for recording and processing information. The device moves inside the controlled pipeline under the influence of the working environment. The power block creates local increased pressure on the walls of the pipeline. Under the influence of dynamic deformation of the pipeline, electromagnetic radiation occurs, which is perceived by the antenna, also located on the registration and processing unit. By changing the characteristics of this radiation (signal) as a result of the device passing through the pipeline after processing the received information, it is judged that there are defects in the pipeline.

 Despite the fact that this device provides the ability to control extended sections and obtain information about weakened (in terms of mechanical strength) sections of the pipeline, it does not allow you to quickly and reliably provide information about the presence of a defect and its location. Information can only be obtained after retrieving a projectile that has passed the entire controlled section of the pipeline. In fact, with its help, continuous monitoring of the state of the pipeline is impossible, especially necessary in densely populated industrial areas and at intersections with railways and other highways.

 These disadvantages are partially overcome by using the method of recording acoustic emission signals (AE) [3], taken as a prototype. A defect on the surface of a metal product, for example, a pipe located behind a dielectric layer, is detected by the parameters of a microwave wave diffracted on the surface of the product by AE signals that occur when a gas or other product flows under pressure through a through slot. The implementation scheme of this method of detecting AE signals contains a microwave generator and a microwave receiver, a transmitting and receiving antenna, directed to the surface of the controlled product, which is covered with a dielectric layer. The method is implemented as follows. An electromagnetic coherent polarized microwave wave is generated using a generator. By means of a transmitting antenna, they radiate it to the surface of the controlled product, and a diffracted electromagnetic wave is received by a microwave receiver. The electric signal from the output of the microwave receiver is amplified, processed according to the selected parameter and recorded in the signal processing and registration unit. Compare the parameters of microwave radiation obtained earlier when reflected from the surface of the product without defects (and, therefore, without the presence of acoustic emission signals) with the parameters of microwave radiation, changed when acoustic signals appear. By changing the parameters of the recorded microwave field, the presence of AE signals and, therefore, the presence of a defect are noted. This method allows you to remotely record AE signals, and through them the presence of a defect, however, it can only be used to monitor a portion of the controlled product of a limited area, which is most likely to cause defects in it. The sensitivity of the method is rather low, firstly, because of the low intensity of the acoustic emission signal itself, and, secondly, because of the low diffraction efficiency of the incident microwave radiation on AE signals. On the other hand, since the receiver receives, along with the useful signal, intense radiation reflected from a metal surface, such as a pipe, then against the background of this radiation (of the same frequency as the useful signal, but with a different phase), it is difficult to isolate and process the useful signal because of the low signal to noise ratio. The formation of a useful signal is also influenced by interference phenomena arising due to the penetration of an external electromagnetic field into the pipe (diffraction by the slit) and additional reflection from the inner surface of the pipe towards the slit. In this case, the reflection coefficient and phase incursion are complex functions of both the dielectric constant of the pipe coating and the d / λ ratio, where d is the pipe wall thickness, λ is the probe wavelength. Since when a crack is detected by the AE signal, the phase of the diffracted wave is the main informative parameter, and phase sensitive detectors are also sensitive to the signal amplitude, when implementing the method, a large error in detecting the phase shift is caused by the attenuation of the reflected wave in the soil layer, which may be the pipe is closed. Acoustic noise, weather conditions, etc. have a strong influence on the determination of the location of a crack. Both transmitting and receiving channels of the proposed diagnostic system that implements the method are affected. The disadvantages should also include a low degree of isolation of the receiving and transmitting paths. Since in the method and in the device implementing it, the position of the receiver and transmitter is fixed in space, the field of view of the monitored pipe is actually limited by the spot size determined by the radiation pattern of the transmitting antenna. This means that the prototype method does not allow continuous monitoring of the extended pipe section.

 The purpose of the invention is to increase the length of the continuously monitored section of the pipeline.

- l

L ,
(1) где Р_о - мощность электромагнитной волны;
α- коэффициент ослабления электромагнитной волны на щели, в грунте;
G - коэффициент усиления приемника;
Р_аmin - пороговая мощность приемника;
L - длина непрерывно контролируемого участка трубопровода.The goal is achieved in that, as in the prototype, they generate and receive an electromagnetic wave of the microwave range and judging by a change in the parameters of the received microwave signals about the presence of a defect. In contrast to the prototype, a microwave wavelength λ <1.71 D, where D is the diameter of the pipeline, is excited inside the pipeline, which is used as a waveguide for radiated electromagnetic waves. The presence of an end-to-end defect is determined by the microwave signal received by the receiver with a scanning antenna remote from the pipeline by a distance l, determined from the relation:
2

- l

L
(1) where P _o is the power of the electromagnetic wave;
α is the attenuation coefficient of the electromagnetic wave on the gap in the ground;
G is the gain of the receiver;
P _amin is the threshold power of the receiver;
L is the length of the continuously monitored section of the pipeline.

 In practice, the radio wave method is known for detecting objects and determining their position in space by irradiating them with a microwave wave, receiving and processing a reflected signal (active radar), or as a result of the object’s own radiation (passive radar). The proposed method is similar to the active radar method in that part, which also contains the generation of microwave oscillations, the reception and processing of a useful signal. However, it differs from the known method of active radar in that the object (defect) is not irradiated from the outside by a probe pulse and, accordingly, does not reflect part of the microwave energy. Microwave energy in the form of a wave of a given type is supplied and propagated through a waveguide-pipe, and then part of it is radiated through a through defect into free space. This emitted signal is a useful signal that must be registered (detected).

 The main difference between the proposed method for detecting a defect from the known ones is that a signal carrying information about the presence of a defect is actively formed in it, while in methods used, for example, acoustic emission, it is a passive process that is influenced by a large number of factors. When analyzing the patent and scientific and technical literature, the authors did not find information about the use of the radio wave method in the above combination of operations to search for defects in existing pipelines (gas pipelines, oil pipelines). This allows us to consider the method proposed by the authors as having significant differences.

 The drawing shows a structural diagram of a device for implementing the method.

 The device comprises a pipeline 1, a microwave energy input device 2, a transmitter 3, a generator 4, a frequency lock (AFC) 5, a receiving antenna 6, a high-frequency amplifier (UHF) 7, a receiver 8, an indicator 9, an information processing unit (computer) 10 defect 11.

 The principle of operation of a device that implements this method is as follows.

 The pulse of electromagnetic radiation of the microwave range generated by the transmitter 3 by means of the input device 2 excites an electromagnetic wave in the pipeline 1. The type and working wavelength λ is chosen taking into account the attenuation and stability of the field structure (waves) acceptable in practice in a pipeline with a diameter D.

When transmitting electromagnetic energy through waveguides in microwave technology, it is customary to work on the lower type (main) oscillations (Izyumova TI, Sviridov VT, Waveguides, coaxial and strip lines. M .: Energy, 1975). For a circular waveguide, this type is H ₁₁ . Given the diameter of the pipe, the working wavelength is chosen from the ratio:
1.31 D <λ <1.71 D. (2)
If this condition is met, only the main wave H ₁₁ will exist in the waveguide and the transmitted energy will not be redistributed to other types that are less favorable in terms of their propagation in the waveguide. As it propagates through the waveguide pipe, part of the microwave pulse energy is spent on wall losses. When a pulse passes through a section of a waveguide pipeline with a defect, part of the energy is radiated through a gap (defect) 11 into the free space, being an informative signal for detecting and determining the location of a gap defect. This signal is received by the receiving antenna 6, amplified by a broadband high-frequency amplifier (UHF) 7 and fed to the receiver 8, where it is converted to pulses of an intermediate frequency (IF), detected and already fed in the form of a video pulse to the indicator 9 and to the information processing unit 10. On the defect indicator is visually displayed as a brightness mark in a certain azimuthal sector. The processing unit 10 automatically provides information about the detection and location of the defect through the communication channel to the control room. To ensure high sensitivity, the receiver is tuned to the generator frequency. To keep the frequency of the generator 4 in the strip of the receiver 8 in the transmitter 3 provides an AFC. Due to the fact that in the considered scheme, an indicator 9 is used, which is similar to the round-robin indicator (IRF) of a traditional radar, on the screen of which azimuthal and range marks are displayed, the proposed method and device, along with detecting a defect, also allows to determine its coordinates. This is an additional advantage of this method compared to the prototype method.

 Since the position of the gas pipeline is fixed in space, the coordinates of the defect can also be determined topographically, having knowledge of the distance from the antenna (receiver) to the gas pipeline and the defect azimuth read from the indicator screen and transferred to the terrain. Naturally, in this case, the indicator coordinate system is oriented relative to the sides of the horizon. The microwave generator is located directly at the pipeline, and the receiver with the antenna are from the pipeline. To ensure continuous monitoring of a longer section of the pipeline, the receiver with the antenna should be located as far as possible from the pipeline at a given scanning angle of the receiving antenna. The maximum removal will be determined by the power of the generator (transmitter), the sensitivity of the receiver, the characteristics of the antenna, the attenuation parameters of microwave energy in the pipeline waveguide, in the ground, on the defect (gap). The maximum distance of the antenna with the receiver l from the pipeline for a given length L of the monitored section of the pipeline is calculated by the formula (1) obtained using the basic radar equation, which establishes the relationship between the transmitter power and the maximum target detection range, and the solution of the right triangle when the receiver is placed on the normal to pipeline route.

 The minimum removal, in turn, is determined by the minimum required length of the monitored section of the pipeline and the power level that ensures the normal operation of the receiver (preventing failure due to a high signal power level).

 To calculate the maximum distance l of the antenna with the receiver for a given length l of a continuously monitored section of the pipeline (as an example, a gas pipeline), we set the values of the parameters included in relation (1) determined as a result of experimental studies.

Working wavelength λ = 35
The power introduced into the gas pipeline waveguide Р _о = 1˙10 ⁹ W
The threshold power of the antenna (receiver) _Pmin = -130 dB / W
Wave Type H ₁₁
Pipe diameter D = 250 mm
Attenuation in the gas pipeline α _tr = 3.5 dB / km
Attenuation in soil α _gr = 5 dB / m
Defect attenuation α _def = 68 dB
Attenuation due to shielding action of the pipe α _ecr = 9.5 dB
Receive antenna gain G = 550
For the convenience of calculations, we make a number of assumptions that do not affect the accuracy of the calculation.

 Removal of the alleged defect from the microwave energy input point in the gas pipeline is 5 km. The thickness of the soil layer covering the gas pipeline is 1 m.

All components of the attenuation of the power of an electromagnetic wave are combined by a coefficient
α = α + α _{tr c} + α + α _{def scr} ≈100dB
Under these assumptions, the calculation shows that a defect can be detected at a maximum distance from the antenna (receiver) up to a thousand kilometers.

The length of the controlled section of the pipeline is of the same order. These distances are a theoretical estimate obtained for a power level of ≥1 GW and ideal conditions along the propagation path of the signal emitted by the defect. Such power levels are currently achievable only with the help of relativistic microwave electronics (Didenko AN, Yushkov Yu. G. Powerful microwave pulses of nanosecond duration. M: Energoatomizdat, 1984, 112 pp.). When using generators based on a classical magnetron with an output pulse power of, for example, 230 kW, the limiting distance l calculated using formula (1) for a given length L = 5 km of the controlled section and the assumptions made will be ≈10 km. The use of a highly sensitive receiver and antenna with a narrow (≅4 ^о in the horizontal plane) radiation pattern allows, in addition to achieving the main objective of the invention, to increase the accuracy of defect detection.

 Among the existing devices, a domestic mobile gas analysis laboratory is known for searching and detecting through damage to the walls of gas pipelines without opening the soil on the basis of a laser gas analyzer (Technical diagnostic tools: Reference book / V.V. Klyuyev, P.P. Parhomenko, V.E. Abramchuk, etc. / Under the general editorship of V.V. Klyuyev. M.: Mechanical Engineering, 1989. - 672 p.).

 This method, however, is not very suitable for searching for defects, especially in the difficult soil and climatic conditions of Western Siberia, where large deposits of oil and gas have been explored.

 Allowing a fairly accurate analysis of the gas composition (in the absence of extraneous gas outlets), the laboratory is designed mainly for routine inspections of the gas pipeline and is unsuitable for the rapid detection of defects (low, ≈10 km / h speed) on long sections of the gas pipeline, and even more so continuous monitoring in a zone with dense industrial development. In addition, it loses to the device that implements the proposed method in terms of informativeness, expressness and the degree of automation of the collection, processing of information about the defect and the speed of transfer of this data to the district dispatch center. In contrast to the well-known laboratory, the proposed complex can be located near or directly on the route of the radio relay line, providing it with communication channels and telemechanics.

Claims (1)

A METHOD FOR DETECTING THROUGH DEFECTS IN PIPELINES, which consists in emitting and receiving electromagnetic waves of the microwave range and using the parameters of the received microwave waves, characterized in that they use the pipeline as a waveguide for the emitted electromagnetic waves, and the presence of a through defect is determined by microwave the signal received by the receiver, remote from the pipeline at a distance l, determined from the ratio
2

l

L
where λ is the length of the microwave microwave wave, λ <1.71 D, D is the diameter of the pipeline;
P _about - the power of the electromagnetic wave;
α is the attenuation coefficient of the electromagnetic wave in the pipeline, on the gap and in the ground;
G is the gain of the receiver;
P _{a min} is the threshold power of the receiver;
L is the length of the continuously monitored section of the pipeline.

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