CN113962046A

CN113962046A - Gas pipe network anomaly detection system and method

Info

Publication number: CN113962046A
Application number: CN202011548658.8A
Authority: CN
Inventors: 艾刚; 刘应华
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-12-24
Filing date: 2020-12-24
Publication date: 2022-01-21

Abstract

The invention discloses a gas pipe network abnormity detection system, which comprises: the optical fiber, the laser source, the optical decoupling system and the signal processing unit; the optical fiber is tightly attached to the lower part of the peripheral wall of the pipeline for conveying the gas; the laser source is connected with the optical decoupling system, the optical decoupling system is connected with the optical fiber, and the signal processing unit is connected with the optical decoupling system; the laser source sends forward light pulses to the optical fiber through the optical decoupling system; the optical coupling system is used for receiving the returned reverse optical pulse of the Brillouin scattering when encountering an abnormality, separating the reverse optical pulse from the forward optical pulse, and sending the separated reverse optical pulse to the signal processing unit; the signal processing unit is used for analyzing the reverse light pulse to determine the specific position of the abnormal occurrence. The system adopts an optical fiber sensing method, can realize abnormal detection of the gas pipe network by utilizing the Brillouin scattering phenomenon, and particularly has good detection effect on abnormal conditions of fluid (such as water) flowing in the low-pressure gas pipe network due to leakage.

Description

Gas pipe network anomaly detection system and method

Technical Field

The invention relates to the field of gas pipeline detection, in particular to a system and a method for detecting abnormity of a gas pipe network.

Background

The safety of gas pipeline networks is important for the safe and reliable delivery of gas, and although all safety requirements are fulfilled during the installation of the gas network, the integrity of the gas network sometimes cannot be guaranteed due to intentional or unintentional third party damage (e.g., land movement, earthquakes, tree roots, corrosion or excavation work, etc.). Therefore, it is very important to be able to detect the abnormal condition (such as leakage) in the gas pipe network accurately and in time. The currently adopted methods mainly comprise the following steps:

1) the method comprises the steps of calculating a pipeline monitoring method, wherein a monitoring system and equipment consisting of a plurality of pressure sensors, flow sensors and temperature sensors are used for analyzing the probability of abnormity of a gas pipeline;

2) in the high-pressure pipeline, analyzing the vibration wave generated by the rarefied gas in the leakage by adopting an acoustic pressure wave method;

3) in a steady state, a balance method is adopted, a flowmeter is used for replacing different measuring points, and the flow of the gas is monitored by adopting differential analysis;

4) detecting leaks using analysis of pressure/flow data using statistical methods;

5) establishing a real-time transient model, and processing the flow in the pipeline by using a mathematical algorithm on the basis of classical mechanics;

6) infrared thermographic pipeline analysis, detecting the location of the leak using the difference in thermal conduction between the transport fluid and the dry soil;

7) arranging an acoustic emission detector in the high-pressure pipeline to detect the leakage position through a low-frequency acoustic signal;

8) a steam sensing pipe leakage detection method of installing a pipe along an entire pipe and detecting a change in a state of a fluid inside the pipe;

9) distributed optical fiber sensors based on Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS). As shown in fig. 1, the DTS system measures temperature changes caused by leakage using a fiber channel installed in the axial direction of a pipe. In a DTS system, sensors with high sensitivity and resolution are used to capture the small temperature changes at the leak. Sensors with high resolution are very expensive, making these technologies economically inefficient, greatly limiting their practical application in industry.

In addition, the above 9 methods are mostly suitable for detecting leakage of a high-pressure gas pipeline, and are difficult to apply to a low-pressure gas pipeline, especially to a low-pressure gas pipeline for handling the problem of water inflow caused by leakage, because in the low-pressure gas pipeline for conveying gas, although the flow rate of the gas is very high, the gas pressure is very low, which may be as low as 2kPa, and thus when a micro leakage occurs, the physical signal of the leakage position is too weak to be detected, so that it is very urgent to design a detection system which is low in cost, can accurately detect the abnormality in the gas pipeline network, and is especially suitable for the low-pressure gas pipeline.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art. To this end, it is an object of the present invention to provide a gas network anomaly detection system and method.

The technical scheme of the invention is as follows: an anomaly detection system for a gas pipeline network, comprising: the optical fiber, the laser source, the optical decoupling system and the signal processing unit; the optical fiber is tightly attached to the lower part of the peripheral wall of the pipeline for conveying gas; the laser source is connected with the optical decoupling system, the optical decoupling system is connected with the optical fiber, and the signal processing unit is connected with the optical decoupling system; the laser source sends out forward light pulses to the optical fiber through the optical decoupling system; the optical coupling system is used for receiving a backward optical pulse of Brillouin scattering returned when encountering an abnormality, separating the backward optical pulse from the forward optical pulse, and sending the separated backward optical pulse to the signal processing unit; the signal processing unit is used for analyzing the reverse light pulse to determine the specific position of the abnormal occurrence.

Further, the pipeline is a plastic pipeline.

Further, the pipe is a polyethylene pipe.

Further, the optical decoupling system is composed of two optical circulators.

A gas pipe network anomaly detection method applies the detection system, and comprises the following steps: s1, the laser source sends forward light pulses to the optical fiber through the optical decoupling system, and the forward light pulses generate reverse light pulses of Brillouin scattering when encountering abnormity; s2, the optical decoupling system receives the returned reverse light pulse of the Brillouin scattering, decouples and separates the reverse light pulse and the forward light pulse, and sends the separated reverse light pulse to the signal processing unit; s3, the signal processing unit analyzes the reverse light pulse and determines the specific location where the abnormality occurs.

Compared with the prior art, the invention has the following beneficial effects:

the system adopts an optical fiber sensing method, can realize the abnormal detection of the gas pipe network by utilizing the Brillouin scattering phenomenon, particularly has good detection effect on the abnormal condition of the inflow fluid (such as water) caused by leakage in the low-pressure gas pipe network, and the optical fiber used by the system can be buried with the monitored pipeline, has compact structure, has immunity to electromagnetic interference, can realize real-time monitoring and quick response, has low cost and is convenient to popularize and use.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts:

FIG. 1 is a diagram of the position of an optical fiber of a prior art DTS system;

FIG. 2 is a schematic representation of Rayleigh, Raman, and Brillouin scattering;

FIG. 3 is a system schematic of the present invention;

FIG. 4 is a position diagram of an optical fiber of the present invention;

FIG. 5 is an interface diagram of a pipe with 1/3 height of deposited water in a finite element simulation;

FIG. 6 is a grid-divided view of a pipe with 1/3 high level of deposited water inside;

FIG. 7 is a strain profile of a steel pipe with 1/3 high level of deposited water;

FIG. 8 is a strain profile of a steel pipe with 1/2 high level of deposited water;

FIG. 9 is a strain distribution of a steel pipe with 2/3 high level of deposited water inside;

FIG. 10 is a strain profile of a polyethylene pipe with 1/3 high level of deposited water inside;

FIG. 11 is a strain profile of a polyethylene pipe with 1/2 high level of deposited water inside;

fig. 12 is a strain profile of a polyethylene pipe with 2/3 high level of deposited water inside.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. In the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "vertical", "circumferential", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.

In the present invention, unless otherwise specifically stated or limited, the terms "mounted," "connected," "fixed," and the like are to be construed broadly and may, for example, be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the description of the present invention, "the first feature" and "the second feature" may include one or more of the features. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In addition, the above 9 methods are mostly suitable for detecting leakage of high-pressure gas pipelines, and are difficult to apply to low-pressure gas pipelines, especially difficult to apply to the problem of water inflow of low-pressure gas pipelines (such as gas distribution pipelines) due to leakage, so that in these low-pressure pipelines for conveying gas, although the flow rate of gas is high, the gas pressure is low, which may be as low as 2kPa, and when a tiny leakage occurs, the physical signal of the leakage position is too weak to be detected.

In view of the above, the inventor creatively designs a gas pipe network anomaly detection system, which is a distributed optical fiber sensing system based on brillouin scattering, and can detect and locate the position of fluid (such as water) flowing in due to leakage in a low-pressure gas pipe network.

For the convenience of describing the working principle of the present system, the scattering phenomenon generated by the light propagating in the optical fiber will be briefly described below with reference to fig. 2 and 3.

The light wave propagating in the fiber is mostly forward propagating, but a small portion of the light is scattered due to the non-uniform structure of the amorphous material of the fiber in the micro-space. There are three main types of scattering processes in optical fibers: rayleigh scattering, raman scattering and brillouin scattering, which differ in their scattering mechanisms.

This scattering effect can be detected by analyzing the spectral structure of the medium by spectroscopic methods, as shown in fig. 2. According to the characteristics of the optical medium for transmitting the light waves, Rayleigh, Brillouin and Raman scattering can respectively generate respective working wavelengths. The operating wavelength of Rayleigh scattering is taken as a reference wavelength, and two spectral components of Brillouin scattering and Raman scattering are symmetrically distributed at two sides of the reference wavelength in the spectral structure. The spectral components to the right of the reference wavelength are referred to as stokes components and the spectral components to the left of the reference wavelength are referred to as anti-stokes components. The stokes/anti-stokes spectral components associated with brillouin scattering are red-shifted and blue-shifted due to temperature changes. Raman scattering is different and its anti-stokes component is only sensitive to temperature variations. The amplitude of the light backscattered by the raman anti-stokes component is affected by the intensity change of the light when there is a temperature change. If the intensity of the incident light is low, a spontaneous scattering phenomenon occurs when the high intensity of the incident light generates a stimulated scattering effect.

Among the different scattering mechanisms, the present invention contemplates the use of the brillouin effect, which is sensitive to strain (epsilon) and temperature (T). Through spectroscopic analysis, the maximum amplitude of scattering of the brillouin backscattered light waves is at a uniform wavelength because of constructive interference. This operating wavelength may be defined as the resonance wavelength and it depends on the characteristics of the optical medium in which the brillouin effect occurs. If a change in strain or temperature occurs, the resonant wavelength may be red-shifted or blue-shifted depending on the stokes component of interest, thereby facilitating detection.

A gas network anomaly detection system according to an embodiment of the present invention is described below with reference to fig. 3 and 4 of the accompanying drawings, the system including: the optical fiber, the laser source, the optical decoupling system and the signal processing unit. The optical decoupling system here consists of two optical circulators.

The optical fiber is tightly attached to the lower part of the peripheral wall of the pipeline for conveying the gas; the laser source is connected with the optical decoupling system, the optical decoupling system is connected with the optical fiber, and the signal processing unit is connected with the optical decoupling system; the laser source sends forward light pulses to the optical fiber through the optical decoupling system; the optical coupling system is used for receiving the returned reverse optical pulse of the Brillouin scattering when encountering an abnormality, separating the reverse optical pulse from the forward optical pulse, and sending the separated reverse optical pulse to the signal processing unit; the signal processing unit is used for analyzing the reverse light pulse to determine the specific position of the abnormal occurrence.

The detection method of the system comprises the following steps:

s1, the laser source sends forward light pulses to the optical fiber through the optical decoupling system, and the forward light pulses generate reverse light pulses of Brillouin scattering when encountering abnormity;

s2, the optical decoupling system receives the returned reverse light pulse of the Brillouin scattering, decouples and separates the reverse light pulse and the forward light pulse, and sends the separated reverse light pulse to the signal processing unit;

s3, the signal processing unit analyzes the reverse light pulse and determines the specific location where the abnormality occurs.

Specifically, the pipe may be, for example, a low-pressure gas pipe, and the abnormality may be, for example, that water enters the low-pressure gas pipe due to leakage, and because the pressure in the low-pressure gas pipe is very low, when the pipe leaks, a large amount of water enters the pipe through the leakage and is deposited at the bottom of the pipe, and the pipe is strained by applying gravity of the large amount of deposited water to the pipe, and because the optical fiber is tightly attached to the lower side of the outer peripheral wall of the pipe, the strain of the pipe transfers the optical fiber, so that the optical fiber also generates a corresponding strain, and at this time, the forward light pulse generates brillouin scattering at a position and generates a backward light pulse, and the optical decoupling system and the signal processing unit may analyze the backward light pulse, and finally determine a specific position where the abnormality occurs.

When determining a specific position, the following method can be adopted for calculation: due to variations in the properties of the optical material, the optical waveguide that is scattered along the fiber path is subject to modulation of the optical amplitude, phase and wavelength. To detect this modulation of light (i.e., strain and temperature changes), time and frequency domain methods may be employed. If the input light wave exciting the fiber is an advancing optical pulse and the duration of the pulse (i.e., the pulse width) is t, then the position of the modulated source (i.e., temperature and strain) can be measured by analyzing the time delay between the advancing input pulse and the returning scattered pulse. The spatial resolution R (i.e., the accuracy of the positioning) of the system, which is limited by the pulse duration, is

Here, c is the speed at which light propagates in vacuum, and n is the group refractive index of the optical fiber.

To verify the effect of the strain produced by the deposition of water, the inventors performed the following using finite element softwareAnd (4) simulating the surface. The gas pipeline can be roughly divided into a metal pipeline and a plastic pipeline, so that two materials commonly used by an urban gas pipe network are adopted in a simulation mode: steel and polyethylene. The water deposition depths are 1/3, 1/2, and 2/3, respectively, of the internal height (inner diameter) of the tube. And (3) simulating the change of the strain of the pipeline wall by adopting a structural mechanics module of finite element software. The outer diameter of the pipe is 315mm and the thickness is 15 mm. The density of water is 995.6kg/m³So that the gravitational bulk load of water is 9756.88N/m³. The boundary conditions of the periphery of the pipe are fixed, and the other boundary conditions are free.

1. The material of the pipeline is steel

In finite element software, an inventor selects steel AISI 340, and the attribute parameters are as follows: young's modulus of 2.05X 10¹¹Pa, Poisson's ratio of 0.28, density of 7850kg/m³。

1.1 Water is deposited in the pipe to a depth of 1/3 mm of the inner diameter of the Steel pipe

The interface diagram of the pipe with 1/3 height of deposited water inside is shown in fig. 5. Geometry CO1 represents the pipe wall and CO2 represents the sediment water.

Fig. 6 shows the meshing of the pipes with 1/3 high level of deposited water inside. The number of mesh points was 7300, the number of finite elements was 13888, and the area ratio of the finite elements was 0.429.

FIG. 7 shows a strain profile for a steel pipe with 1/3 high level of deposited water. The maximum strain at the bottom of the tube can be derived from the figure to be-0.23 mu epsilon.

1.2 Water is deposited in the pipe to a depth of 1/2 of the inner diameter of the pipe

FIG. 8 shows a strain profile for a steel pipe with 1/2 high level of deposited water. The maximum strain at the bottom of the tube can be derived from the figure to be-0.35 mu epsilon.

1.3 Water is deposited in the pipe to a depth of 2/3 of the inner diameter of the pipe

FIG. 9 shows a strain profile for a steel pipe with 2/3 high level of deposited water. The maximum strain at the bottom of the tube can be derived from the figure to be-0.46 mu epsilon.

2. The material of the pipeline is polyethylene

In finite element softwareThe material selected by the inventor is polyethylene, and the property parameters are as follows: young's modulus of 1X 10⁹Pa, Poisson's ratio of 0.28, density of 930kg/m³。

2.1 Water was deposited in the pipe to a depth of 1/3 inches of the inner diameter of the polyethylene pipe

Figure 10 shows the strain profile of a polyethylene pipe with 1/3 high deposition water inside. The maximum strain at the bottom of the tube can be derived from the figure as-36 mu epsilon.

2.2 Water is deposited in the pipe to a depth of 1/2 of the internal diameter of the polyethylene pipe

Figure 11 shows the strain profile of a polyethylene pipe with 1/2 high deposition water inside. The maximum strain at the bottom of the tube can be derived from the figure as-54 mu epsilon.

2.3 Water is deposited in the pipe to a depth of 2/3 of the inner diameter of the polyethylene pipe

Figure 12 shows the strain profile of a polyethylene pipe with 2/3 high deposition water inside. The maximum strain at the bottom of the tube can be derived from the figure as-68 mu epsilon.

3. Summary of the above simulation results

The above simulation results can be summarized as follows using the following table 1:

TABLE 1 summary of simulation results

Under the current technical conditions, the resolution of the system is about +/-10 mu epsilon to +/-30 mu epsilon, namely, the strain signal of the steel pipeline generated by water deposition cannot be detected by the system. However, considering that in a gas transmission and distribution pipe network, polyethylene pipes will be more and have a trend of replacing steel pipes in the future, therefore, the system has a wide prospect in the aspect of monitoring low-pressure pipes in the future, and is expected to become one of the most promising effective technical means for solving the abnormal problem of the underground pipe network.

While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An anomaly detection system for a gas pipe network, comprising: the optical fiber, the laser source, the optical decoupling system and the signal processing unit;

the optical fiber is tightly attached to the lower part of the peripheral wall of the pipeline for conveying gas;

the laser source is connected with the optical decoupling system, the optical decoupling system is connected with the optical fiber, and the signal processing unit is connected with the optical decoupling system;

the laser source sends out forward light pulses to the optical fiber through the optical decoupling system;

the optical coupling system is used for receiving a backward optical pulse of Brillouin scattering returned when encountering an abnormality, separating the backward optical pulse from the forward optical pulse, and sending the separated backward optical pulse to the signal processing unit;

the signal processing unit is used for analyzing the reverse light pulse to determine the specific position of the abnormal occurrence.

2. The system of claim 1, wherein the pipe is a plastic pipe.

3. The system of claim 2, wherein the pipes are polyethylene pipes.

4. The system of claim 1, wherein the optical decoupling system comprises two optical circulators.

5. A method for detecting the abnormity of a gas pipe network, which is characterized in that the detection system according to any one of claims 1-4 is applied, and the detection method comprises the following steps: