Optical fiber infrasound sensor for high pressure fluid pipelines and detection method, system thereof

Abstract

The present disclosure belongs to the technical field of safe operation and maintenance of paint pipelines, and particularly relates to a fiber-optic infrasound sensor for a high-pressure fluid pipeline and a detection method and system thereof, which comprises a base in a cylindrical structure, a bellows fixedly connected to one side of the base in an axial direction and coaxially arranged with the base, a fiber-optic ferrule in a cylindrical structure with an axial center through hole arranged on the axis of the base and the bellows, a sensing fiber-optic cable penetrating through the axial center through hole, an optical beam interference cavity arranged between the end surface of the sensing fiber-optic cable and the inner reflective surface of the bellows, and a fiber-optic wavelength demodulator arranged on the side of the base away from the bellows and electrically connected with the sensing fiber-optic cable.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of safe operation and maintenance of paint pipelines, and particularly relates to an optical fiber infrasound sensor for a high-pressure fluid pipeline and a detection method and system thereof. BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] Oil and gas pipeline leakage monitoring mainly includes manual inspection, flow statistics method, pressure gradient method, acoustic detection method, etc. When oil and gas pipeline, especially gas pipeline, leaks, high-pressure gas is released at high speed, which forms vibration at the leakage site and propagates in the form of sound waves to both ends. The sound wave carries rich information about pipeline leakage, including infrasound, ultrasonic wave, negative pressure wave, etc., among which the low-frequency part of the sound wave component is strong, has the propagation characteristics of long wavelength and slow energy attenuation, and has a long propagation distance. By installing an infrasound sensor for detecting infrasound signals in the pipeline range, real-time monitoring of pipeline leakage signals can be achieved at a long distance.

[0004] Infrasound detection in a pressure pipeline requires the sensor to detect the dynamic pressure signal of weak infrasound at a high static pressure background. Conventional piezoelectric sensors have a limited dynamic range under the action of high static pressure in the pipeline, which in turn reduces the pressure resolution and the response sensitivity to the alternating pressure generated by the infrasound. Some people have proposed an infrasound sensor suitable for high-pressure gas pipelines, which can receive a sound pressure of 0.05 Pa; some related research reports an infrasound sensor for gas pipeline leakage detection, which can convert the pulse charge according to the pipe diameter and pressure of the gas pipeline to obtain the final detection result. The Rosemount 3051CD sensor has a pressure resolution of 0.025 Pa. There is still a need for a sensor with higher pressure resolution, and it is difficult for electronic sensors to detect weak pressure fluctuations under a high-pressure background. For example, to detect a pressure fluctuation of 1 mPa under a pressure of 10 MP, the dynamic range reaches 10 10 , which exceeds the dynamic range of a 24-bit high-precision acquisition card, and the cost of a high-bit acquisition card and a digital conversion transmission system is extremely high, which is difficult to realize. In addition, there are still bottlenecks in the safety of signal transmission of electronic sensors, detection in flammable and explosive gas environments, and miniaturization.

[0005] Optical fiber sensor has high sensitivity, intrinsic passive, detection of intrinsic safety in flammable and explosive environment, long distance transmission, easy miniaturization and other advantages. Someone has studied a kind of MEMS optical fiber acoustic sensor based on ultra-small GRIN lens and performance test method, the acoustic pressure sensitivity is 21.63 nm / Pa, but the process is complex, and the measurement range is small;Someone proposes a kind of high sensitivity infrasound sensor, which uses optical fiber to measure diaphragm vibration, but only applies to low pressure environment;Someone proposes a kind of optical fiber EFPI infrasound wave sensor and infrasound signal detection system, which uses polymer film, and the measurement range is small, which is not suitable for pressure detection of high pressure pipeline. SUMMARY

[0006] In order to solve the above problems, the present disclosure provides an optical fiber infrasound sensor for high pressure fluid pipeline and its detection method and system, which designs an optical fiber infrasound sensor suitable for high pressure working environment in oil and gas pipeline, overcomes the defects of existing conventional electronic sensor in high pressure oil and gas pipeline detection, long distance signal transmission, safety, miniaturization and measurement dynamic range, and the adaptability of conventional optical fiber infrasound sensor in high background pressure and pipeline fluid medium, realizes the low cost, simple structure and easy manufacturing of infrasound sensor.

[0007] According to some embodiments, the first aspect of the present disclosure provides an optical fiber infrasound sensor for high pressure fluid pipeline, which adopts the following technical scheme:

[0008] An optical fiber infrasound sensor for high pressure fluid pipeline, comprising:

[0009] A base in cylindrical structure;

[0010] A corrugated pipe fixedly connected to one side of the base in axial direction and coaxially arranged with the base;

[0011] An optical fiber ferrule in cylindrical structure with axial center through hole arranged on the axis of the base and the corrugated pipe;

[0012] A sensing optical fiber penetrating through the axial center through hole, and an optical beam interference cavity is arranged between the end face of the sensing optical fiber and the inner reflection face of the corrugated pipe, and the inner reflection face is the inner bottom face of the corrugated pipe away from the base;

[0013] An optical fiber wavelength demodulator arranged on the side of the base away from the corrugated pipe and electrically connected with the sensing optical fiber.

[0014] As a further technical limitation, the outer diameter of the corrugated pipe is consistent with the diameter of the base.

[0015] As a further technical limitation, the end of the sensing fiber disposed inside the bellows adopts a polished sensing fiber end face, which is expanded by heat expansion to expand the fiber core of the sensing fiber.

[0016] As a further technical limitation, the inner surface of the inner reflection surface is coated with a reflection enhancement film.

[0017] As a further technical limitation, the fiber acoustic sensor for high-pressure fluid pipelines further comprises a balance spring disposed inside the base and the bellows, one end of the balance spring is disposed on the side of the inner reflection surface of the bellows, and the other end extends out of the bellows, and the length of the balance spring after complete compression is greater than the length of the bellows in the axial direction.

[0018] Further, the outer diameter of the balance spring is greater than the inner diameter of the bellows to ensure the supporting effect of the balance spring on the bellows.

[0019] According to some embodiments, the second aspect of the present disclosure provides a detection method for a fiber acoustic sensor for high-pressure fluid pipelines, which adopts the following technical solution:

[0020] A detection method for a fiber acoustic sensor for high-pressure fluid pipelines, comprising:

[0021] Obtaining the reflection spectrum information of the interference light;

[0022] Extracting the peak or valley wavelength position in the obtained reflection spectrum information, and calculating the interference order of the interference light peak or valley;

[0023] According to the obtained interference order of the interference light peak or valley, the interference cavity length of the interference light peak or valley is calculated, and the cavity length detection of the fiber acoustic sensor in the high-pressure fluid pipeline is completed.

[0024] As a further technical limitation, the interference order k of the interference light peak or valley is wherein m represents the serial number of the last interference light peak or valley, λ1 is the wavelength of the first interference light peak or valley, λ m v is the wavelength of the mth interference light peak or valley.

[0025] As a further technical limitation, the interference cavity length d ave of the interference light peak or valley is i v wherein λ1 is the wavelength of the first interference light peak or valley, λ i v is the wavelength of the i th interference light peak or valley, the serial number of the last interference light peak or valley is m, and Interger is the integer part.

[0026] According to some embodiments, the third aspect of the present disclosure provides a detection system of a fiber-optic infrasound sensor for a high-pressure fluid pipeline, which adopts the following technical solutions:

[0027] A detection system of a fiber-optic infrasound sensor for a high-pressure fluid pipeline, comprising:

[0028] An acquisition module configured to acquire reflection spectrum information of the interference light;

[0029] A calculation module configured to extract a peak or trough wavelength position in the acquired reflection spectrum information, and calculate an interference order of the peak or trough of the interference light;

[0030] A detection module configured to calculate an interference cavity length of the peak or trough of the interference light according to the obtained interference order of the peak or trough of the interference light, and complete cavity length detection of the fiber-optic infrasound sensor in the high-pressure fluid pipeline.

[0031] Compared with the prior art, the present disclosure has the following beneficial effects:

[0032] The present disclosure adopts a fiber-optic structure to detect infrasound waves, which can realize long-distance analog transmission of signals, and the sensor is intrinsically passive, and is intrinsically safe in a flammable and explosive environment; the present disclosure proposes a long-interference cavity length fiber-optic interference structure and a dynamic interference order tracking algorithm, which breaks through the limitation of the deformation range of a conventional sensor sensitive element and the number of electrical acquisition bits, and realizes more than 10 10 dynamic range, and realizes weak infrasound signal detection in a high-pressure pipeline; the fiber-optic infrasound sensor adopted has no special optical components, and has low cost, simple structure and easy manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0033] The drawings accompanying the specification of the present disclosure serve to provide a further understanding of the present disclosure, and the illustrative embodiments of the present disclosure and their descriptions serve to explain the present disclosure, and do not constitute an improper limitation on the present disclosure.

[0034] Figure 1 is a structural schematic diagram of a fiber-optic infrasound sensor for a high-pressure fluid pipeline in the first embodiment of the present disclosure;

[0035] Figure 2 is a structural schematic diagram of a base in the first embodiment of the present disclosure;

[0036] Figure 3 is a structural schematic diagram of a fiber-optic ferrule in the first embodiment of the present disclosure;

[0037] Figure 4 is a structural schematic diagram of a sensing fiber in the first embodiment of the present disclosure;

[0038] Figure 5 is a structural schematic diagram of a bellows in the first embodiment of the present disclosure;

[0039] Figure 6 This is a flowchart of the detection method of the fiber optic infrasound sensor for high-pressure fluid pipeline in Embodiment 2 of this disclosure;

[0040] Figure 7 This is a structural block diagram of the detection system for a fiber optic infrasound sensor used in a high-pressure fluid pipeline according to Embodiment 3 of this disclosure;

[0041] Among them, 010 is the base; 011 is the external mounting thread; 012 is the internal mounting thread; 020 is the fiber optic ferrule; 021 is the variable diameter hole; 030 is the sensing fiber; 031 is the end face; 032 is the expanded fiber core; 040 is the bellows; 041 is the internal reflecting surface; 042 is the mounting base; 050 is the balance spring; 010 is the fiber wavelength demodulator; 102 is the signal processing unit; and 103 is the cavity length detection unit. Detailed Implementation

[0042] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0043] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0044] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] In this disclosure, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements in this disclosure, and do not specifically refer to any component or element in this disclosure, nor should they be construed as limiting this disclosure.

[0046] In this disclosure, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this disclosure based on the specific circumstances, and they should not be construed as limitations on this disclosure.

[0047] Where there is no conflict, the embodiments and features described herein can be combined with each other.

[0048] Example 1

[0049] Embodiment 1 of this disclosure introduces an optical fiber infrasound sensor for high-pressure fluid pipelines.

[0050] Electronic sensors face challenges in long-distance signal transmission, safety during detection in flammable and explosive gas environments, and miniaturization. High background pressure results in weak detection signals, necessitating a large dynamic range for the sensors. For example, detecting a 1 MPa pressure fluctuation at 10 MPa requires a dynamic range of 10... 10 This exceeds the dynamic range of high-precision acquisition cards, and high-bit acquisition cards and digital conversion and transmission systems are extremely expensive and difficult to implement.

[0051] Conventional fiber optic infrasound sensors do not have the dynamic range required for detecting weak infrasound signals in high-pressure pipelines, their material structure is not suitable for pipeline fluid media under high background pressure, and their structure and manufacturing process are relatively complex.

[0052] This embodiment proposes an optical fiber infrasound sensor suitable for high-pressure fluid pipelines, overcoming the problems of existing conventional electronic sensors in long-distance signal transmission, safety, miniaturization, and dynamic range of measurement in high-pressure oil and gas pipelines. It also overcomes the problems of dynamic range of measurement and adaptability of conventional optical fiber infrasound sensors to pipeline fluid media under high background pressure, realizing a low-cost, simple, and easy-to-manufacture infrasound sensor.

[0053] like Figure 1 The fiber optic infrasound sensor shown is for use in high-pressure fluid pipelines and includes:

[0054] Base 010 is used to mount the fiber optic infrasound sensor;

[0055] The fiber optic ferrule 020 is a cylindrical structure with a central through hole, which is installed inside the base 010 and sealed well with it;

[0056] The sensing fiber 030 passes through the central through hole of the fiber ferrule 020 and is well sealed to it. Its end face 031 is a polished flat surface, and the fiber core is expanded by thermal expansion.

[0057] The bellows 040 is connected to the base 010 and is well sealed. Its inner reflective surface 041 is a smooth plane, thus forming a multi-beam interference cavity with the end face 031 of the sensing fiber 030.

[0058] A balance spring 050 is disposed inside the base 010 and the bellows 040. One end of the spring is disposed on the inner reflective surface 041 side of the bellows 040, and the other end extends out of the bellows 404 into the base 010.

[0059] Supporting between the corrugated pipe 040 and the inner reflecting surface 041 to adjust the sensitivity;

[0060] The fiber wavelength demodulator 101 is used to detect the reflection spectrum of the optical beam interference cavity formed by the inner reflecting surface 041 and the end face 031;

[0061] The signal processing unit 102 is used to detect the peak or valley wavelength position in the reflection spectrum detected by the fiber wavelength demodulator 101 in real time;

[0062] The cavity length detection unit 103 is used to calculate the peak and valley orders and the cavity length of the optical beam interference cavity formed by the inner reflecting surface 041 and the end face 031 through the peak or valley position detected by the signal processing unit 102, and to obtain the corresponding relationship between the cavity length and the pressure through pressure calibration.

[0063] As shown in Figure 1 and Figure 2 The base 010 is a cylindrical structure made of stainless steel material, and a through hole is opened in the central axis. An outer mounting thread 011 and an inner mounting thread 012 are provided on the side with the mounting hole. Through the outer mounting thread 011, the sensor can be mounted on the threaded hole of the monitored pipeline, and sealed by a sealant.

[0064] As one or more embodiments, the base 010 is a cylindrical structure made of stainless steel material, and a through hole is opened in the central axis. The through hole has a thread inside. An outer mounting thread 011 and an inner mounting thread 012 are provided on the side with the mounting hole. Through the outer mounting thread 011, the sensor can be mounted on the threaded hole of the monitored pipeline, and sealed by a sealant.

[0065] As shown in Figure 1 and Figure 3 The fiber ferrule 020 is a stainless steel cylindrical structure, with a central through hole and a variable diameter hole 020. The fiber ferrule 020 passes through the through hole of the base 010, the outer diameter of which matches the through hole of the base 010, and is connected and sealed to the base 010 by welding.

[0066] As one or more embodiments, the fiber ferrule 020 is a stainless steel cylindrical structure, with an outer mounting thread, a central through hole, and a variable diameter hole 020. The fiber ferrule 020 passes through the through hole of the base 010, and the outer side is linked to the through hole of the base 010 by a thread.

[0067] As one or more embodiments, the fiber ferrule 020 is a cylindrical structure with a central hole, which is mounted in the base 010 and connected with it by screwing. The bellows 040 is connected with the base 010 and well sealed, and its inner reflecting surface 041 is a smooth plane, thus forming a multi-beam interference cavity with the end surface 031 of the sensing fiber 030. By adjusting the screwing between the fiber ferrule 020 and the base 010, the cavity length of the multi-beam interference cavity can be adjusted.

[0068] As shown in Figure 1 , Figure 5 and , the bellows 040 is a stainless steel seamless welded bellows, and the mounting base 042 is welded on it. The bellows 040 is connected with the base 010 by screwing of the mounting base and well sealed by welding or sealant. There are at least two ways to make the inner reflecting surface 041 of the bellows 040 a reflecting surface. The inner reflecting surface 041 is made a smooth plane by polishing treatment; the inner reflecting surface 041 is made a reflecting surface by electroplating treatment to enhance the reflectivity of the inner reflecting surface 041. The balance spring 050 is supported between the base 010 and the inner reflecting surface 041 to adjust the sensitivity. Preferably, the diameter of the bellows 040 is 10 mm, the elastic coefficient of the balance spring 050 is 7.9×10 4 N / m~7.9×10 5 N / m, and the length of the balance spring 050 after complete compression is greater than the length of the sensing fiber 030 and the fiber ferrule 020 exposed from the base 010. Ignoring the elastic coefficient of the bellows 040, the deformation of the bellows 040 under pressure is about 1 mm / MPa~0.1 mm / MPa.

[0069] It should be noted that the length of the balance spring 050 after complete compression is greater than the length of the bellows 040 in the axial direction; the outer diameter of the balance spring 050 is greater than the inner diameter of the bellows 040 to ensure the supporting effect of the balance spring 050 on the bellows 040.

[0070] As shown in Figure 1 , Figure 3 and Figure 4As shown, the sensing fiber 030 is a single-mode fiber. Its end face 031 is obtained by flat cutting with a fiber optic cleaver and then polished to form a reflective plane. A thermal expansion process is used to expand the fiber core near the end face 031, thereby focusing the light beam in the fiber. The sensing fiber 030 passes through the central through-hole of the fiber optic ferrule 020. The position of the sensing fiber 030 is adjusted so that the distance between the end face 031 and the inner reflective surface 041 of the corrugated tube 040 reaches a preset distance (generally set to 0.5cm to 1cm), and is well sealed with epoxy resin or low-melting-point glass flux filled in the central through-hole of the fiber optic ferrule 020. The light beam in the sensing fiber 030 passes through the thermal expansion core area near the end face 031, forming a focused beam, and forms a first reflection at the end face 031. The focused transmitted beam can form a second reflection through the inner reflection surface 041, which is far away from the end face 031 (generally set to 0.5cm to 1cm), and interferes with the first reflected beam formed at the end face 031. The beam then reflects and interferes back and forth, forming multi-beam interference.

[0071] The pigtail of the sensing fiber optic cable 030 connects to the fiber optic wavelength demodulator 101. Light emitted from the fiber optic wavelength demodulator 101 is transmitted through the sensing fiber optic cable 030 to the interference cavity formed by the end face 031 and the inner reflecting surface 041. The reflection spectrum information of the interference light is then transmitted back to the fiber optic wavelength demodulator 101 through the sensing fiber optic cable 030. The fiber optic wavelength demodulator 101 then converts the collected reflection spectrum information of the interference light into a digital signal and sends it to the signal processing unit 102. The signal processing unit is typically a computer processor or a microcontroller, which uses the digital signal to detect the peak or trough wavelength positions in the reflection spectrum detected by the fiber optic wavelength demodulator 101 in real time.

[0072] Example 2

[0073] Embodiment 2 of this disclosure introduces a detection method for an optical fiber infrasound sensor used in high-pressure fluid pipelines, which employs the optical fiber infrasound sensor for high-pressure fluid pipelines described in Embodiment 1.

[0074] like Figure 6 The method for detecting fiber optic infrasound sensors used in high-pressure fluid pipelines, as shown, includes:

[0075] Obtain the reflection spectrum information of the interference light;

[0076] Extract the peak or trough wavelength positions from the acquired reflection spectrum information, and calculate the interference order of the peak or trough of the interferometric light;

[0077] The interference cavity length of the interference light peak or trough is calculated based on the interference order of the obtained interference light peak or trough, and the cavity length detection of the fiber optic infrasound sensor in the high-pressure fluid pipeline is completed.

[0078] As one or more implementations, the interference order k of the interference light peak or valley is wherein m represents the serial number of the last interference light peak or valley, λ1 is the wavelength of the first interference light peak or valley, and λm is the wavelength of the mth interference light peak or valley. m v is the wavelength of the mth interference light peak or valley.

[0079] As one or more implementations, the interference cavity length d of the interference light peak or valley is ave wherein λ1 is the wavelength of the first interference light peak or valley, and λm is the wavelength of the mth interference light peak or valley. i v is the wavelength of the mth interference light peak or valley, and m is the serial number of the last interference light peak or valley. Integer is the down-rounding number.

[0080] In combination with the cavity length detection unit 103 in Embodiment One, the corresponding relationship between the cavity length of the fiber-acoustic sensor and the pressure is obtained through pressure calibration.

[0081] Through the external mounting thread 011, the sensor can be mounted on the threaded hole of the monitored pipeline and sealed by a sealant.

[0082] Under the high-pressure background pressure of the monitored pipeline, the bellows 040 deforms. If the deformation of the bellows 040 under pressure is 1 mm / MPa, and the distance between the end face 031 and the inner reflection surface 041 of the bellows 040 is 10 mm, then the maximum pressure resistance of the sensor is 10 MPa. The high-pressure background pressure in the pipeline causes the bellows 040 to deform under the background pressure, and the cavity length of the interference cavity formed by the end face 031 and the inner reflection surface of the bellows 040 is less than 10 mm. The threads between the fiber ferrule 020 and the base 010 are adjusted, and the detection algorithm provided in this embodiment is used for detection, so that the cavity length of the interference cavity is 1 mm to 2 mm. At this time, when the weak acoustic wave signal acts on the bellows 040 of the sensor, the slight pressure change causes the bellows 040 to produce slight deformation, causing the cavity length of the interference cavity formed by the end face 031 and the inner reflection surface of the bellows 040 to change slightly. By using the cavity length detection algorithm 103 provided in this embodiment to detect the cavity length in real time, a cavity length change resolution of about 0.001 nm can be obtained. According to the deformation of the bellows 040 under pressure, which is 1 mm / MPa, the corresponding pressure change resolution is about 0.001 Pa, that is, the measurement of the weak acoustic signal under high pressure background can be realized.

[0083] ​This embodiment employs an optical fiber structure for infrasound sensing, enabling long-distance analog signal transmission. The sensor is inherently passive, making it inherently safe for use in flammable and explosive environments. A long-cavity optical fiber interference structure and a dynamic interference order tracking algorithm are proposed, overcoming the limitations of conventional sensors' sensitive element deformation range and electrical acquisition bit depth, achieving over 10... 10 The dynamic range enables the detection of weak infrasound signals inside high-pressure pipelines; the fiber infrasound sensor used has no special optical components, is low in cost, simple in structure, and easy to manufacture.

[0084] Example 3

[0085] Embodiment 3 of this disclosure describes a detection system for an optical fiber infrasound sensor used in high-pressure fluid pipelines.

[0086] like Figure 7 The detection system shown is a fiber optic infrasound sensor for high-pressure fluid pipelines, comprising:

[0087] The acquisition module is configured to acquire the reflection spectrum information of the interference light;

[0088] The calculation module is configured to extract the peak or trough wavelength positions in the acquired reflection spectrum information and calculate the interference order of the interference light peak or trough.

[0089] The detection module is configured to calculate the interference cavity length of the interference light peak or trough based on the interference order of the obtained interference light peak or trough, and complete the cavity length detection of the fiber optic infrasound sensor in the high-pressure fluid pipeline.

[0090] The detailed steps are the same as the detection method of the fiber optic infrasound sensor for high-pressure fluid pipelines provided in Example 2, and will not be repeated here.

[0091] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0092] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A fiber optic infrasound sensor for high-pressure fluid pipelines, characterized in that, include: The base is cylindrical in structure. A bellows is fixedly connected to one side of the base along its axial direction and is coaxially arranged with the base. The fiber optic ferrule has a cylindrical structure with a central through hole on the axis and is disposed on the axis of the base and the corrugated tube. A sensing optical fiber passes through the central through-hole of the axis, and a beam interference cavity is provided between the end face of the sensing optical fiber and the inner reflecting surface of the corrugated tube. The fiber optic wavelength demodulator is located on the side of the base away from the corrugated tube and is electrically connected to the sensing fiber optic cable. A balance spring is disposed inside the base and the bellows, with one end disposed on the inner reflective surface side of the bellows and the other end extending out of the bellows. The length of the balance spring after full compression is greater than the axial length of the bellows.

2. The fiber optic infrasound sensor for high-pressure fluid pipelines as described in claim 1, characterized in that, The outer diameter of the bellows is consistent with the diameter of the base.

3. The fiber optic infrasound sensor for high-pressure fluid pipelines as described in claim 1, characterized in that, The end of the sensing fiber located inside the corrugated tube is a polished sensing fiber end face, and the core of the sensing fiber is expanded by thermal expansion.

4. The fiber optic infrasound sensor for high-pressure fluid pipelines as described in claim 1, characterized in that, The inner surface of the inner reflective surface is coated with an anti-reflective film.

5. The fiber optic infrasound sensor for high-pressure fluid pipelines as described in claim 1, characterized in that, The outer diameter of the balance spring is larger than the inner diameter of the bellows.

6. A detection method for an optical fiber infrasound sensor used in a high-pressure fluid pipeline according to any one of claims 1-5, characterized in that, include: Obtain the reflection spectrum information of the interference light; Extract the peak or trough wavelength positions from the acquired reflection spectrum information, and calculate the interference order of the peak or trough of the interferometric light; The interference cavity length of the interference light peak or trough is calculated based on the interference order of the obtained interference light peak or trough, and the cavity length detection of the fiber optic infrasound sensor in the high-pressure fluid pipeline is completed.

7. The detection method of an optical fiber infrasound sensor for a high-pressure fluid pipeline as described in claim 6, characterized in that, The interference order of the peaks or troughs of the interference light for ;in, m Indicates the sequence number of the last interference light peak or trough. λ 1 is the wavelength of the first interference light peak or trough. λ m v It is the first m The wavelength of an interference light peak or trough.

8. The detection method of an optical fiber infrasound sensor for a high-pressure fluid pipeline as described in claim 6, characterized in that, The interference cavity length of the interference light peak or trough for ;in, λ 1 is the wavelength of the first interference light peak or trough. λ i v It is the first i The wavelengths of the interference light peaks or troughs, and the sequence number of the last interference light peak or trough is... m Integer is used to round down to the nearest integer.

9. The detection system for an optical fiber infrasound sensor in a high-pressure fluid pipeline according to claim 1, characterized in that, include: The acquisition module is configured to acquire the reflection spectrum information of the interference light; The calculation module is configured to extract the peak or trough wavelength positions in the acquired reflection spectrum information and calculate the interference order of the interference light peak or trough. The detection module is configured to calculate the interference cavity length of the interference light peak or trough based on the interference order of the obtained interference light peak or trough, and complete the cavity length detection of the fiber optic infrasound sensor in the high-pressure fluid pipeline.

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