Fiber optic acoustic pressure sensor and pipeline leakage detection system for pipeline leakage monitoring

Abstract

The present invention discloses an optical fiber acoustic pressure sensor and a pipeline leakage detection system for pipeline leakage monitoring, and relates to the technical field of optical fiber acoustic sensors. In the present invention, the bare fiber of the incident optical fiber has a coated end face with a reflectivity of 8% in the wavelength range of 1520nm to 1580nm; the bare fiber of the reflecting optical fiber has a coated end face with a reflectivity of 90% in the wavelength range of 1520nm to 1580nm; one end of the quartz tubes I and II is flush and connected to the equivalent volume module; a liquid medium is provided in the cavity between the end face of the quartz capillary, the equivalent volume module, the quartz tube III and the film; a hollow limiting plate is fixedly connected to the cavity of the quartz tube III, and the reflecting optical fiber extends out of the quartz capillary and passes through the hollow limiting plate to be rigidly connected to the film. The resonant frequency of the Helmholtz acoustic cavity of the optical fiber acoustic pressure sensor of the present application can reach about 1.15Hz to about 11.5Hz. At 11.5Hz, the sensitivity of the optical fiber acoustic pressure sensor is relatively high.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber acoustic sensors, and specifically designs an optical fiber acoustic pressure sensor for pipeline leakage monitoring and a pipeline leakage detection system. Background Art

[0002] Because the fluids transported in oil and gas pipelines are highly corrosive, toxic, and have a high probability of combustion and explosion, leaks can easily lead to serious consequences. Therefore, oil and gas pipeline leak monitoring has always been a key focus in the petrochemical industry. Currently, oil and gas pipeline leak monitoring primarily includes manual inspections, flow statistics, pressure gradient methods, transient model methods, and acoustic wave detection, among others. Acoustic wave detection is a relatively common monitoring method. In the prior art, acoustic wave detection typically utilizes fiber optic acoustic sensors based on the Fabry-Perot cavity (FP cavity) interferometry principle. However, most existing fiber optic acoustic sensors based on the Fabry-Perot cavity (FP cavity) interferometry principle suffer from low sensitivity. Therefore, this application provides a fiber optic acoustic pressure sensor and pipeline leak detection system for pipeline leak monitoring. Summary of the Invention

[0003] In view of the above-mentioned defects and deficiencies in the prior art, the present application proposes a fiber optic acoustic pressure sensor and a pipeline leakage detection system for pipeline leakage monitoring.

[0004] In order to achieve the above-mentioned object, the present invention adopts the following technical solutions:

[0005] An optical fiber acoustic pressure sensor for pipeline leakage monitoring includes an incident optical fiber with one end located in a quartz capillary tube, and quartz tubes I, II and III are fixedly mounted on the outer side of the quartz capillary tube in sequence;

[0006] The portion of the incident optical fiber located in the cavity of the quartz capillary is a bare fiber. The bare fiber has an incident optical fiber coated end face with a reflectivity of 8% in the wavelength range of 1520nm to 1580nm. The bare fiber portion is fixedly connected to the quartz capillary.

[0007] A reflecting optical fiber is provided in the cavity of the quartz capillary tube. One end of the reflecting optical fiber located in the quartz capillary tube is a bare fiber. The bare fiber has a reflecting optical fiber coated end face with a reflectivity of 90% in the wavelength range of 1520nm to 1580nm. A gap is formed between the coated end face of the incident optical fiber and the coated end face of the reflecting optical fiber.

[0008] One end of the quartz tube and quartz tube II, which are away from the incident optical fiber, are flush and fixedly connected to the equivalent volume module. The corresponding end of the quartz capillary is located outside the cavity of quartz tube I and within the cavity of the equivalent volume module, and the equivalent volume module is located within the cavity of quartz tube III. A liquid medium is provided in the cavity between the end face of the quartz capillary, the equivalent volume module, quartz tube III, and the film.

[0009] A hollow limiting plate is fixedly connected to the cavity of the quartz tube III. The reflecting optical fiber extends out of the quartz capillary and passes through the hollow limiting plate and the rigid connection film.

[0010] Preferably, a protective shell is further included, and the incident optical fiber extends through the cavity of the protective shell into the quartz capillary; one end of the quartz capillary, quartz tube I, quartz tube II, and quartz tube III are all located in the cavity of the protective shell, and the other ends of the quartz capillary, quartz tube I, quartz tube II, and quartz tube III extend out of the cavity of the protective shell; quartz tube III is fixedly connected to the inner wall of the protective shell; one end of quartz tube I and quartz tube II away from the incident optical fiber is the end of quartz tube I and quartz tube II extending out of the cavity of the protective shell, and this end is flush and fixedly connected to the equivalent volume module.

[0011] Preferably, a stainless steel capillary is further included, one end of which extends into the cavity between the end face of the quartz capillary, the equivalent volume module, the quartz tube III and the film, and the other end is located outside the quartz tube III and spirally wound on the outer wall of the quartz tube III.

[0012] Preferably, the quartz tube III is fixedly connected to a mounting platform provided on the inner side wall of the protective shell.

[0013] Preferably, the equivalent volume module is made of a material with deformation and rebound capabilities.

[0014] Preferably, the equivalent volume module is made of rubber or sponge with deformation and rebound capabilities.

[0015] Preferably, the distance between the hollow plate of the hollow limiting plate and the film is 0.27-0.31 mm.

[0016] Preferably, the gap between the incident optical fiber coating end face and the reflective optical fiber coating end face is the cavity length of the FP cavity, and the cavity length is 280 μm-320 μm.

[0017] Preferably, the coated end face of the incident optical fiber is obtained as follows: the bare fiber end face of the incident optical fiber is tilted at an angle of 0°, and a high-reflection film is coated on the bare fiber end face to form the coated end face of the incident optical fiber.

[0018] Preferably, the reflective optical fiber coated end face is obtained by setting the bare fiber end face of the incident optical fiber to an inclination angle of 0° and coating the bare fiber end face with a high reflective film to form the reflective optical fiber coated end face.

[0019] Preferably, the protective shell includes an extension shell and a main shell fixedly connected to the extension shell. The extension shell and the main shell are both cylindrical shell structures with hollow interiors. The hollow part of the extension shell is connected to the hollow part of the main shell. The outer diameter of the extension shell is smaller than the outer diameter of the main shell, and the inner diameter of the extension shell is smaller than the inner diameter of the main shell. The incident optical fiber passes through the hollow part of the extension shell and the hollow part of the main shell in sequence and extends into the quartz capillary.

[0020] Preferably, the bare fiber portion of the incident optical fiber and the quartz capillary are fixedly connected by forming a molten layer through oxyhydrogen flame fusion welding.

[0021] Preferably, the left end of the quartz capillary is located outside the quartz tube I, and the left end of the quartz tube I and the quartz capillary are fixedly connected by a solder layer formed by melting and welding glass solder having a thermal expansion coefficient close to that of quartz.

[0022] Preferably, the left ends of the quartz tube I, the quartz tube II, and the quartz tube III are flush.

[0023] Preferably, the hollow limiting plate includes a cylindrical ring and a hollow plate fixedly connected to the inner side of the cylindrical ring. One end face of the cylindrical ring is flush with the corresponding end face of the hollow plate, and the other end face of the cylindrical ring is 0.27-0.31 mm higher than the other end face of the hollow plate. There is a gap between the hollow plate and the equivalent volume module.

[0024] Preferably, a central hole is provided in the middle of the hollow plate for the reflective optical fiber to pass through; the hollow plate is also provided with at least one pressure balancing hole for balancing the pressure on the left and right sides of the hollow plate; and when the number of pressure balancing holes is greater than or equal to two, the pressure balancing holes are evenly arranged around the central hole.

[0025] Preferably, the outer side surface of the cylindrical ring of the hollow limiting plate is fixedly connected to the fixing platform provided on the inner side surface of the quartz tube III, and the film is fixedly connected to the right end of the quartz tube III.

[0026] Preferably, the thin film is a nickel film.

[0027] Preferably, the Young's modulus of the rubber is 3-15 MPa, the rebound rate is 45%-65%, and the compression deformation is 15%-35%.

[0028] Preferably, the rubber is silicone rubber R401 series rubber produced by Wacker, Germany.

[0029] Preferably, the gap between the mounting hole and the stainless steel capillary tube is filled with sealant to achieve a sealed connection between the mounting hole and the stainless steel capillary tube.

[0030] Preferably, a mounting hole is opened on the tube wall of quartz tube III, one end of the stainless steel capillary extends into the cavity between the end face of the quartz capillary, the equivalent volume module, quartz tube III and the film, and the gap between the mounting hole and the stainless steel capillary is filled with sealant.

[0031] An oil and gas pipeline leak detection system with an acoustic pressure sensor includes a laser. The laser is connected to the first port of a circulator via an optical fiber. The second port of the circulator is connected to the optical fiber acoustic pressure sensor via an optical fiber. The output port of the circulator, i.e., the third port, is connected to a photodetector via an optical fiber. The photodetector is sequentially connected to an acquisition card and a host computer via a signal transmission line.

[0032] A dual-laser oil and gas pipeline leak detection system with an acoustic pressure sensor includes two DFB lasers, two circulators, a wavelength division multiplexer, an optical fiber acoustic pressure sensor, two photodetectors, an acquisition card, and a host computer. The two DFB lasers respectively emit light sources, and the wavelength difference between the two light sources is (2K+1) / 4×FSR, where FSR represents the free spectral range, which refers to the maximum wavelength or frequency interval between two adjacent spectral peaks, and K is an integer. The two DFB lasers are respectively connected to the first ports of the two circulators via optical fibers, the second ports of the two circulators are both connected to the wavelength division multiplexer via optical fibers, and the wavelength division multiplexer is connected to the acoustic pressure sensor via optical fibers. The output ends of the two circulators are respectively connected to the two photodetectors via optical fibers, the two photodetectors are both connected to the acquisition card via signal transmission lines, and the acquisition card is connected to the host computer via signal transmission lines. The output end of the circulator is also the third port of the circulator.

[0033] Compared with the prior art, the beneficial technical effects of the present invention are:

[0034] In the present application, the quartz capillary is made of quartz material, which has a low thermal expansion coefficient and is not significantly affected by temperature. This can effectively reduce the deformation of the quartz capillary in a high-temperature working environment, which may cause the incident optical fiber and the reflection optical fiber to be squeezed, thereby causing lateral misalignment and end face tilt of the incident optical fiber and the reflection optical fiber end faces. In addition, in the present application, the bare fiber portion of the incident optical fiber and the bare fiber portion of the reflection optical fiber are both located in the quartz capillary, and the bare fiber portion of the incident optical fiber and the quartz capillary are fused by hydrogen-oxygen flame, which prevents the bare fiber portion of the incident optical fiber from moving relative to the quartz capillary. In the present application, the reflection optical fiber portion located in the quartz capillary is not fixedly connected to the quartz capillary. Therefore, the reflection optical fiber portion can move along the length direction of the quartz capillary. In addition, the aperture of the quartz capillary is small, and the quartz capillary can also effectively limit the movement of the reflection optical fiber portion along the radial direction of the quartz capillary.

[0035] In the present application, both the end face of the incident optical fiber and the end face of the reflecting optical fiber are coated, and the reflectivity of the coated end face of the incident optical fiber in the wavelength range of 1520nm to 1580nm is 8%, and the reflectivity of the coated end face of the reflecting optical fiber in the wavelength range of 1520nm to 1580nm is 90%. This arrangement increases the contrast of the interference fringes formed by multiple reflections of light in the FP cavity by increasing the reflectivity of the coated end face of the incident optical fiber and the coated end face of the reflecting optical fiber, thereby effectively improving the sensitivity of the optical fiber sound pressure sensor described in the present application.

[0036] In addition, in the present application, the cavity between the quartz capillary end face, the equivalent volume module, the quartz tube III and the film is filled with a liquid medium. The compressibility of the liquid medium is smaller than that of the gas medium. Therefore, when the oil and gas pipeline leaks and generates a strong sound pressure, the fiber optic sound pressure sensor described in the present application can effectively limit the maximum displacement of the film. Since the movement of the film will cause the movement of the reflecting optical fiber, limiting the maximum displacement of the film means limiting the maximum displacement of the reflecting optical fiber, which limits the reflected light. The maximum displacement of the optical fiber means that the problem of damage to the incident optical fiber coating end face and the reflective optical fiber coating end face caused by the collision between the incident optical fiber coating end face and the reflective optical fiber coating end face can be effectively avoided; however, since the filling of the liquid medium will cause the resonance frequency of the Helmholtz acoustic cavity to increase, for this reason, the present application fixes the equivalent volume module on the right end of the quartz tube I and the quartz tube II, and fills the cavity between the quartz capillary end face, the equivalent volume module, the quartz tube III and the film with liquid medium. When the oil and gas pipeline leaks, the leakage point will The infrasonic signal is generated and propagated, and the infrasonic signal generates sound pressure. The sound pressure acts on the thin film of the optical fiber sound pressure sensor. Under the action of the sound pressure, the thin film drives the reflecting optical fiber to move toward the incident optical fiber. The liquid medium compresses the equivalent volume module during the movement, resulting in a smaller volume of the equivalent volume module, which increases the equivalent volume of the Helmholtz acoustic cavity and effectively suppresses the problem of increased resonance frequency of the Helmholtz acoustic cavity. Moreover, it can be seen from the test that the present application effectively reduces the resonance frequency of the Helmholtz acoustic cavity. The resonance frequency of the Helmholtz acoustic cavity The range reaches about 1.15 Hz to about 11.5 Hz. That is, the Helmholtz cavity of the optical fiber sound pressure sensor can resonantly amplify the infrasound signal in the range of about 1.15 Hz to about 11.5 Hz, and the resonant amplification of the infrasound signal can effectively enhance the infrasound signal in the frequency band of about 1.15 Hz to about 11.5 Hz, thereby improving the sensitivity of the optical fiber sound pressure sensor. Moreover, the test results of the optical fiber sound pressure sensor described in Example 1 show that its simulated sensitivity at 11.5 Hz can reach -108 (dB re 1V / μPa). BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1This is a schematic structural diagram of the optical fiber sound pressure sensor according to Example 1 of the present application;

[0038] Figure 2 It is a partial enlarged schematic diagram of the quartz capillary;

[0039] Figure 3 It is a top view of the hollow limiting plate;

[0040] Figure 4 for Figure 3 Cross-sectional view of AA;

[0041] Figure 5 is a schematic diagram of an oil and gas pipeline leak detection system with an acoustic pressure sensor;

[0042] Figure 6 Schematic diagram of a dual-laser oil and gas pipeline leak detection system with an acoustic pressure sensor;

[0043] Figure 7 The test results are obtained by performing a simulated frequency response curve test on the optical fiber sound pressure sensor described in Example 1 within the range of 1 to 500 Hz;

[0044] Figure 8 These are the test results obtained by performing a reflected light intensity simulation test on the optical fiber sound pressure sensor described in Example 1 and the optical fiber sound pressure sensor described in the comparative example.

[0045] In the figure, 1. Incident optical fiber, 2. Reflecting optical fiber, 3. Quartz capillary, 4. Quartz tube I, 5. Quartz tube II, 6. Quartz tube III, 7. Solder layer, 8. Stainless steel capillary, 9. Thin film, 10. Hollow limiting plate, 11. Protective shell, 12. Equivalent volume module, 13. Incident optical fiber coated end face, 14. Reflecting optical fiber coated end face, 15. Melting layer, 16. Pressure balance hole, 17. Central hole, 18. Mounting platform, 19. Cylindrical ring, 20. Hollow plate, 21. Fixing platform. DETAILED DESCRIPTION

[0046] Example 1:

[0047] An optical fiber acoustic pressure sensor for pipeline leakage monitoring, such as Figure 1 As shown, the protective shell 11 includes an extension shell and a main shell fixedly connected to the extension shell. The extension shell and the main shell are both cylindrical shell structures with hollow interiors. The hollow portion of the extension shell is connected to the hollow portion of the main shell. The cavity of the extension shell and the cavity of the main shell together constitute the cavity of the protective shell 11. The outer diameter of the extension shell is smaller than the outer diameter of the main shell, and the inner diameter of the extension shell is smaller than the inner diameter of the main shell. A cylindrical mounting platform 18 is further provided on the inner side wall of the protective shell 11, specifically on the inner side wall of the main shell.

[0048] The incident optical fiber 1 passes through the hollow part of the extension shell and the hollow part of the main shell in sequence and extends into the quartz capillary 3. The portion of the incident optical fiber 1 located in the cavity of the quartz capillary 3 is a bare fiber. The end face of the bare fiber has an inclination angle of 0°, and the end face of the bare fiber is coated with a high-reflection film to form an incident optical fiber coated end face 13. The reflectivity of the incident optical fiber coated end face 13 in the wavelength range of 1520nm to 1580nm is 8%. The bare fiber portion of the incident optical fiber 1 and the quartz capillary 3 are fixed by a molten layer 15 formed by oxyhydrogen flame fusion welding. The bare fiber portion of the incident optical fiber 1 is obtained by removing the polyimide coating of the incident optical fiber 1; specifically, in this embodiment, the incident optical fiber 1 used in this embodiment is a high-temperature resistant single-mode optical fiber with a polyimide coating (purchased from Changfei Optical Fiber and Cable Co., Ltd., the diameter of the high-temperature resistant single-mode optical fiber with a polyimide coating is 155±5μm). The polyimide coating on the incident optical fiber 1 extending into the quartz capillary 3 is removed, so that the portion of the incident optical fiber 1 located in the cavity of the quartz capillary 3 is a bare fiber;

[0049] The left end of the quartz capillary tube 3 is located in the cavity of the main housing, and the right end of the quartz capillary tube 3 extends out of the cavity of the main housing. The quartz capillary tube 3 is provided with a quartz tube I 4, and the left end of the quartz capillary tube 3 is located outside the quartz tube I 4. The left end of the quartz tube I 4 and the quartz capillary tube 3 are fixedly connected by a solder layer 7 formed by melting and welding glass solder having a thermal expansion coefficient close to that of quartz.

[0050] A quartz tube II5 is fixed outside the quartz tube I4, and a quartz tube III6 is fixed outside the quartz tube II5. The left ends of the quartz tubes I4, II5, and III6 are flush, and the quartz tube III6 is fixedly connected to the mounting table 18. The inner diameter of the quartz tube I4 is 1 mm, the inner diameter of the quartz tube II5 is 4 mm, and the inner diameter of the quartz tube III6 is 10 mm.

[0051] The right ends of the quartz tube I4 and the quartz tube II5 are flush, the right end of the quartz tube I4 is located outside the main shell, the right end of the quartz capillary tube 3 is located outside the quartz tube I4, and the right ends of the quartz tube I4 and the quartz tube II5 are fixedly connected to the equivalent volume module 12. The equivalent volume module 12 is cylindrical and annular. The right end of the quartz capillary tube 3 is located in the cavity of the equivalent volume module 12, and the equivalent volume module 12 is located in the cavity of the quartz tube III6.

[0052] A reflective optical fiber 2 is also provided in the cavity of the quartz capillary 3. The end of the reflective optical fiber 2 located in the quartz capillary 3 is a bare fiber, and the bevel angle of the end face of the bare fiber is also 0°. The end face of the bare fiber is coated with a high-reflection film to form a reflective optical fiber coated end face 14. The reflectivity of the reflective optical fiber coated end face 14 in the wavelength range of 1520nm to 1580nm is 90%; in this application, a gap is provided between the incident optical fiber coated end face 13 of the incident optical fiber 1 and the reflective optical fiber coated end face 14 of the reflective optical fiber 2, and the distance d of the gap is the cavity length of the FP cavity; specifically in this embodiment, the cavity length value is 280μm. In this application, a partially enlarged schematic diagram of the quartz capillary is shown as follows: Figure 2 As shown, Figure 2 in L1 represents the length of the incident optical fiber 1 extending into the quartz capillary 3, d represents the cavity length of the FP cavity, L2 represents the length of the reflecting optical fiber 2 extending into the quartz capillary 3, d 、 L1 and L2 The sum is 15mm;

[0053] In this embodiment, the reflective optical fiber 2 also uses a high-temperature resistant single-mode optical fiber with a polyimide coating (purchased from Changfei Optical Fiber and Cable Co., Ltd., the diameter of the high-temperature resistant single-mode optical fiber with a polyimide coating is 155±5μm). The bare fiber portion of the reflective optical fiber 2 is also obtained by removing the polyimide coating at the end of the reflective optical fiber 2 extending into the quartz capillary 3. In this application, only the end of the reflective optical fiber 2 located in the quartz capillary 3 is a bare fiber segment, and the remaining portion of the reflective optical fiber 2 located in the quartz capillary 3 still has a polyimide coating, which is in contact with the inner surface of the quartz capillary 3. In this application, the reflective optical fiber 2 is not fixedly connected to the quartz capillary 3. In this application, the high-reflection coating on the bare fiber end faces of the incident optical fiber 1 and the reflective optical fiber 2 is achieved by Xi'an Femtosecond Fiber Technology Co., Ltd.

[0054] In the present application, the hollow limiting plate 10 includes a cylindrical ring 19 and a hollow plate 20 fixedly connected to the inner side of the cylindrical ring 19. The thickness of the cylindrical ring 19 is 1 mm, the outer diameter is 11 mm, and the inner diameter is 10 mm. The difference between the inner and outer diameters is 0.5 mm. One end face of the cylindrical ring 19 is flush with the corresponding end face of the hollow plate 20, and the other end face of the cylindrical ring 19 is 0.27 mm higher than the other end face of the hollow plate 20. There is a gap between the hollow plate 20 and the equivalent volume module 12. The top view and side view of the hollow limiting plate are as follows: Figure 3 and Figure 4As shown, a central hole 17 is opened in the middle of the hollow plate 20, and the central hole 17 is for the reflection optical fiber 2 to pass through. The hollow plate 20 also has eight pressure balance holes 16. The eight pressure balance holes 16 are evenly arranged around the central hole 17. The pressure balance holes 16 are used to balance the pressure on the left and right sides of the hollow plate 20;

[0055] After the right end of the reflective optical fiber 2 extends out of the quartz capillary 3, it passes through the cavity of the equivalent volume module 12 and the central hole 17 on the hollow plate 20, and is rigidly connected to the film 9. The hollow limit plate 10 is located in the cavity of the quartz tube III 6. The outer surface of the cylindrical ring 19 of the hollow limit plate 10 is fixedly connected to the fixed platform 21 provided on the inner surface of the quartz tube III 6. The film 9 is fixedly connected to the right end of the quartz tube III 6. In this application, the distance between the hollow plate 20 and the film 9 is 0.27mm. The film 9 is a nickel film, which is made of nickel with a Young's modulus of 201GPa, a Poisson's ratio of 0.31, and a density of 8900kg / m³. In this application, the film 9 has an effective radius of 5mm, a thickness of 10μm, and a Young's modulus of 210GPa.

[0056] In the present application, the cavity between the end face of the quartz capillary 3, the equivalent volume module 12, the quartz tube III6 and the film 9 is filled with a liquid medium, which is water; the equivalent volume module 12 is made of rubber or sponge with deformation rebound ability, and the Young's modulus of the rubber is 3-15 MPa, the rebound rate is 45%-65%, and the compression deformation is 15%-35%. The rubber used in the present application can be the silicone rubber R401 series rubber of Wacker, Germany, including R401 / 20 model rubber, R401 / 30 model rubber, R401 / 40 to 70 model rubber, and R401 / 90 model rubber; specifically in this embodiment, the rubber used is R401 / 50 model rubber. In this application, the right end faces of quartz tubes I and II, the inner side of quartz tube III and the cavity surrounded by the film, and the cavity of the stainless steel capillary together constitute the Helmholtz acoustic cavity. That is to say, the part of the quartz capillary beyond the right end face of quartz tube II, the equivalent volume module and the hollow plate are all located in the Helmholtz acoustic cavity. Since the cavity volume of the stainless steel capillary is small, the volume of the part of the quartz capillary located in the Helmholtz cavity accounts for a small proportion of the Helmholtz acoustic cavity, and the volume of the hollow plate in the Helmholtz cavity accounts for a small proportion. Therefore, when calculating the Helmholtz When the volume of the acoustic cavity is V, the cavity volume of the stainless steel capillary, the volume of the quartz capillary in the Helmholtz cavity, and the volume of the hollow plate in the Helmholtz cavity are all negligible. That is to say, the volume of the cavity surrounded by the right end faces of quartz tube I and quartz tube II, the inner side face of quartz tube III, and the film is equal to the volume of the Helmholtz acoustic cavity. In the optical fiber sound pressure sensor described in Example 1, the volume of the cavity surrounded by the right end faces of quartz tube I and quartz tube II, the inner side face of quartz tube III, and the film is equal to the volume of the Helmholtz acoustic cavity. The volume V of the Helmholtz acoustic cavity is approximately 7×10 -7 m 3 , and an equivalent volume module is also provided in the Helmholtz acoustic cavity. The volume of the equivalent volume module (i.e., rubber) in the first embodiment is approximately 4×10 -7 m 3 , the volume of water is about 3×10 -7 m 3 ;

[0057] A mounting hole is also provided on the wall of the quartz tube III6, through which a stainless steel capillary 8 is passed. The inner diameter of the stainless steel capillary 8 is 0.1 mm and the length is 15 cm. The gap between the mounting hole and the stainless steel capillary 8 is filled with sealant. One end of the stainless steel capillary 8 extends into the cavity between the end face of the quartz capillary 3, the equivalent volume module 12, the quartz tube III6 and the film 9, and one end of the stainless steel capillary 8 extending into the above-mentioned cavity is located between the hollow plate 20 and the equivalent volume module 12, and the other end of the stainless steel capillary 8 is located outside the quartz tube III6 and is spirally wound on the outer wall of the quartz tube III6.

[0058] The working principle of this application is:

[0059] When used for leak detection in oil and gas pipelines, the fiber optic acoustic pressure sensor described in this application is installed in the oil and gas pipeline. Under normal conditions, there is static pressure generated by the medium in the oil and gas pipeline. The stainless steel capillary tube 8 provided in the fiber optic acoustic pressure sensor of this application can effectively prevent the thin film of the fiber optic acoustic pressure sensor from being affected by the static pressure in the oil and gas pipeline.

[0060] When an oil or gas pipeline leaks, an infrasonic signal is generated at the leak point and propagates. The infrasonic signal generates sound pressure, which acts on the thin film of the optical fiber sound pressure sensor. Under the action of the sound pressure, the thin film drives the reflecting optical fiber to move toward the incident optical fiber. The movement of the reflecting optical fiber 2 will cause the distance d between the incident optical fiber coating end face 13 of the incident optical fiber 1 and the reflecting optical fiber coating end face 14 of the reflecting optical fiber 2 to become smaller, that is, the cavity length of the FP cavity becomes smaller.

[0061] An oil and gas pipeline leak detection system with an acoustic pressure sensor, such as Figure 5 As shown, it includes a laser, which is connected to the first port of the circulator through an optical fiber, the second port of the circulator is connected to the sound pressure sensor through an optical fiber, the output port of the circulator, that is, the third port, is connected to a photodetector through an optical fiber, and the photodetector is connected to an acquisition card and a host computer in sequence through a signal transmission line; the laser in this embodiment specifically adopts the Koheras BasikE15 narrow linewidth laser of NKT Photonics.

[0062] The working principle of the oil and gas pipeline leak detection system with acoustic pressure sensor is:

[0063] The laser's output light is input into the circulator through its first port. The circulator transmits the light through its second port to the fiber optic sound pressure sensor. After entering the sensor's FP cavity, the light is reflected multiple times by the FP cavity. Some of the light then returns along its original path through the circulator's second port and is then output through the circulator's third port. The optical signal output from the circulator's third port is received by a photodetector, which converts the optical signal into an electrical signal and transmits it to an acquisition card. The acquisition card digitizes the electrical signal and transmits it to the host computer software. The host computer software uses the pre-calibrated relationship between reflected light intensity and cavity length from a standard sensor to demodulate the sound pressure value corresponding to the sound pressure signal generated by an oil or gas pipeline leak. If the sound pressure value exceeds the preset value, a leak is detected in the pipeline.

[0064] Because light entering the FP cavity of the fiber optic sound pressure sensor undergoes multiple reflections within the cavity, the cavity length of the FP cavity affects this reflection process. Therefore, when a pipeline leak occurs, the sound pressure signal generated by the pipeline leak acts on the sensitive diaphragm of the fiber optic FP cavity sound pressure sensor, causing the diaphragm to deform slightly, thereby changing the cavity length of the FP cavity. This change in cavity length causes changes in the multi-beam interference conditions within the cavity, causing the intensity of the light signal reflected from the laser after entering the FP cavity through the circulator to change. This changed light signal is then transmitted through the circulator to the photodetector and converted into an electrical signal. The acquisition card digitizes the electrical signal and transmits it to the host computer software. The host computer software demodulates the sound pressure value corresponding to the sound pressure signal generated by the oil and gas pipeline leak based on the pre-calibrated relationship between the reflected light intensity and the cavity length of the standard sensor. When the sound pressure value exceeds the preset sound pressure value, it indicates that the oil and gas pipeline has leaked, thus realizing the detection of the pipeline leak infrasound signal.

[0065] A dual laser oil and gas pipeline leak detection system with an acoustic pressure sensor, such as Figure 6 As shown, it includes two DFB lasers, two circulators, a wavelength division multiplexer, an optical fiber sound pressure sensor, two photodetectors, an acquisition card, and a host computer. The two DFB lasers respectively emit light sources as detection light signals. The wavelength difference between the two light sources is (2K+1) / 4×FSR, where FSR represents the free spectral range, which refers to the maximum wavelength or frequency interval between two adjacent spectral peaks, and K is an integer. The two DFB lasers are respectively connected to the first ports of the two circulators through optical fibers, and the second ports of the two circulators are both connected to the wavelength division multiplexer through optical fibers. The wavelength division multiplexer is connected to the sound pressure sensor through optical fibers. The output ends of the two circulators are respectively connected to the two photodetectors through optical fibers. The two photodetectors are both connected to the acquisition card through signal transmission lines, and the acquisition card is connected to the host computer through signal transmission lines. The output end of the circulator is also the third port of the circulator.

[0066] The working principle of the dual laser oil and gas pipeline leak detection system with acoustic pressure sensor is:

[0067] Two DFB lasers respectively emit light sources as detection light signals. The wavelength difference between the light sources emitted by the two DFB lasers is (2K+1) / 4×FSR, where FSR represents the free spectral range, which refers to the maximum wavelength or frequency interval between two adjacent spectral peaks. K is an integer. In this embodiment, K is 1, and FSR is 3.225nm. The light output by the two DFB lasers is respectively input into the two circulators through the first ports of the two circulators. The two circulators respectively transmit the light to the wavelength division multiplexer through the second ports of the circulators. The wavelength division multiplexer combines the two light signals and transmits them to the optical fiber sound pressure sensor. After multiple reflections from the P cavity, some of the reflected light returns along its original path and is split into two beams by a wavelength division multiplexer (WDM). The WDM returns the two beams to the two circulators through their second ports, where they are then output through their third ports. The two optical signals output from the third ports of the two circulators are received by two photodetectors, which convert the optical signals into electrical signals and transmit them to an acquisition card. The acquisition card digitizes the electrical signals and transmits them to the host computer software. The host computer software uses the pre-calibrated relationship between the reflected light intensity and the cavity length sound pressure of a standard sensor to demodulate the sound pressure signal corresponding to an oil and gas pipeline leak. If the sound pressure value exceeds the preset value, a leak is detected in the pipeline.

[0068] In the dual-laser oil and gas pipeline leak detection system with an acoustic pressure sensor, two DFB lasers each emit a light source, the wavelength difference between the two light sources being (2K+1) / 4×FSR, where FSR stands for free spectral range, the maximum wavelength or frequency interval between two adjacent spectral peaks, and K is an integer. The two beams of light of different wavelengths are combined using a wavelength division multiplexer and then transmitted to a fiber optic acoustic pressure sensor. The light entering the FP cavity of the fiber optic acoustic pressure sensor is reflected multiple times by the FP cavity, with some of the reflected light returning along the original path and being split into two beams by the wavelength division multiplexer. Two photodetectors respectively convert the two light beams into electrical signals, which are essentially power change signals of the light beams. An acquisition card digitizes the electrical signals and transmits them to the host computer software of the host computer. The host computer software demodulates the sound pressure value corresponding to the sound pressure signal generated when the oil and gas pipeline leaks using the pre-calibrated relationship between the reflected light intensity and the sound pressure of the cavity length using a standard sensor. In the present application, since the two photoelectric detectors can obtain the power change signals of two beams of light with different wavelengths, naturally, after being processed by the acquisition card, the power change signals of the two beams of light with different wavelengths become the power change data of the two beams of light with different wavelengths. When the host computer software of the host computer processes the data, it will be based on the power change data of the two beams of light with different wavelengths, and through the sound pressure relationship between the reflected light intensity and the cavity length pre-calibrated by the standard sensor to demodulate the sound pressure value corresponding to the sound pressure signal generated when the oil and gas pipeline leaks.

[0069] In this application, the wavelength difference between the two DFB lasers is set to ensure that after the wavelength of one DFB laser jumps out of the linear range, the wavelength of the other DFB laser can operate within the linear region. In other words, this application can use the linear relationship between light intensity and cavity length variation in the range of [-λ / 8, +λ / 8] to ensure that the power variation data of at least one beam of light remains within the above-mentioned linear relationship range, achieving the purpose of stabilizing the orthogonal operating point, thereby improving the dynamic range of detection of the optical fiber sound pressure sensor;

[0070] For fiber optic acoustic pressure sensors, improving the stability of the orthogonal operating point can significantly enhance the reliability and sensitivity of pipeline leakage monitoring. The reason is that the stability of the orthogonal operating point directly determines the linear response range of the optical fiber acoustic pressure sensor's output light intensity and sound pressure signal. If the orthogonal operating point drifts, it will cause distortion of the demodulated signal or a decrease in the signal-to-noise ratio. A stable orthogonal operating point can ensure that the cavity length changes caused by the sound pressure are converted into light intensity changes with high precision, thereby accurately capturing the weak acoustic emission signals of pipeline leakage (usually low-frequency, small-amplitude vibrations).

[0071] Example 2:

[0072] The difference between the second embodiment and the first embodiment is that the equivalent volume module used in the second embodiment is made of sponge material.

[0073] Comparative Example:

[0074] In order to verify that, under the condition that the liquid medium of the present application is water, the reflectivity of the incident optical fiber coated end face in the wavelength range of 1520nm to 1580nm is set to 8%, and the reflectivity of the reflective optical fiber coated end face in the wavelength range of 1520nm to 1580nm is set to 90%, compared with the conventional setting of setting the reflectivity of the incident optical fiber coated end face in the wavelength range of 1520nm to 1580nm to 4%, and the reflectivity of the reflective optical fiber coated end face in the wavelength range of 1520nm to 1580nm to 4%, has a significant technical effect; for this purpose, the present application specially sets up a comparative example, the difference between the comparative example and the embodiment 1 of the present application is that, in the comparative example, the reflectivity of the incident optical fiber coated end face in the wavelength range of 1520nm to 1580nm is 4%, and the reflectivity of the reflective optical fiber coated end face in the wavelength range of 1520nm to 1580nm is 4%.

[0075] test:

[0076] (1) In the range of 1~500Hz, the fiber optic sound pressure sensor described in Example 1 is tested for its simulated frequency response curve. The test results are as follows: Figure 7 As shown;

[0077] Depend on Figure 7It can be seen that the frequency response curve shows a clear resonance peak at 11.5 Hz. At this frequency point, the sensitivity of the optical fiber sound pressure sensor described in Example 1 reaches its maximum value of -108 (dB re 1V / μPa). This shows that the optical fiber sound pressure sensor described in Example 1 can effectively detect low-frequency infrasound signals. In other words, the optical fiber sound pressure sensor described in Example 1 has a high perception ability for weak infrasound signals in the low frequency band. Therefore, it is very suitable for scenarios where low-frequency sound waves need to be captured, such as oil and gas pipeline leakage monitoring.

[0078] (2) The optical fiber sound pressure sensor described in Example 1 and the optical fiber sound pressure sensor described in the comparative example were subjected to a reflection light intensity simulation test. The test results are as follows: Figure 8 As shown, Figure 8 In the figure, the blue solid line represents the test results obtained by the simulation test of the reflected light intensity of the optical fiber sound pressure sensor described in Example 1, and the red solid line represents the test results obtained by the simulation test of the reflected light intensity of the optical fiber sound pressure sensor described in the comparative example;

[0079] Depend on Figure 8 It can be seen that the reflected light intensity simulation test results of the optical fiber sound pressure sensor described in Example 1 are stronger than the reflected light intensity simulation test results of the sensor obtained in the comparative example. The higher reflected light intensity means that the optical fiber sound pressure sensor described in Example 1 can capture weaker signal changes. This makes the optical fiber sound pressure sensor described in Example 1 more sensitive to subtle changes in sound pressure caused by pipeline leakage during pipeline leakage monitoring, thereby effectively improving the sensitivity of the optical fiber sound pressure sensor.

[0080] (3) In order to verify that the setting of the liquid medium and the equivalent volume module can effectively reduce the resonant frequency of the Helmholtz acoustic cavity, the present application also specifically calculates the resonant frequency of the Helmholtz acoustic cavity of the optical fiber sound pressure sensor described in Example 1 and the resonant frequency of the Helmholtz acoustic cavity of the optical fiber sound pressure sensor described in Example 2; the specific calculation process is as follows:

[0081] First, the equivalent volume module was removed from the optical fiber sound pressure sensor described in Example 1 to obtain sensor 1. The liquid medium (the liquid medium was water) in sensor 1 was replaced with air to obtain sensor 2. The resonant frequencies of the Helmholtz acoustic cavities of sensor 1 and sensor 2 were calculated respectively. Then, the resonant frequency of the Helmholtz acoustic cavity of the optical fiber sound pressure sensor described in Example 1 was calculated as follows:

[0082] 1) Calculate the resonant frequency of the Helmholtz acoustic cavity of sensor 1 and sensor 2:

[0083] The resonant frequency of the Helmholtz acoustic cavity is calculated as shown in formula (1):

[0084] (1)

[0085] In formula (1), c Indicates the speed of sound in the medium under normal temperature and pressure conditions. In sensor 1, water is the medium, c=1480m / s. In sensor 2, air is the medium, c =343m / s; L represents the length of the stainless steel capillary, L is 15cm; V represents the volume of the Helmholtz acoustic cavity, S represents the cross-sectional area of ​​the stainless steel capillary neck;

[0086] In formula (1), the calculation method of the cross-sectional area S of the stainless steel capillary neck is shown in formula (2):

[0087] S=πr 2 (2)

[0088] In formula (2), r represents the inner diameter of the stainless steel capillary, and r is 0.1 mm in Example 1;

[0089] In formula (1), the volume V of the Helmholtz acoustic cavity is calculated by formula (3):

[0090] V=πR 2 h (3)

[0091] In formula (3), R is the bottom radius of the Helmholtz acoustic cavity, that is, 1 / 2 of the inner diameter of the quartz tube III. R 5mm; h is the height of the Helmholtz acoustic cavity, that is, the distance between the quartz tube I and the film. In Example 1, h is 9 mm. Calculation shows that the volume V of the Helmholtz acoustic cavity in Example 1 is approximately 7×10 -7 m 3 ; Since the cavity volume of the stainless steel capillary is small, the volume of the quartz capillary located in the Helmholtz cavity accounts for a small proportion of the Helmholtz acoustic cavity, and the volume of the hollow plate in the Helmholtz cavity also accounts for a small proportion, therefore, when calculating the volume V of the Helmholtz acoustic cavity, the cavity volume of the stainless steel capillary, the volume of the quartz capillary located in the Helmholtz cavity, and the volume of the hollow plate in the Helmholtz cavity are all negligible. In other words, the volume of the cavity surrounded by the right end faces of quartz tube I and quartz tube II, the inner side surface of quartz tube III and the film is equal to the volume of the Helmholtz acoustic cavity.

[0092] From formulas (1) to (3), it can be seen that the resonant frequency of the Helmholtz acoustic cavity of sensor 1 is f1≈127.8 Hz; the resonant frequency of the Helmholtz acoustic cavity of sensor 2 is f1≈29.62 Hz.

[0093] 2) Calculating the resonant frequency of the Helmholtz acoustic cavity of the optical fiber sound pressure sensor described in Example 1, specifically comprising the following steps:

[0094] First, the equivalent volume V' of the Helmholtz acoustic cavity of the optical fiber sound pressure sensor described in Example 1 is calculated, which specifically includes the following steps:

[0095] In Example 1, the Young's modulus of rubber and water are 10 MPa and 2.19×10 3 MPa, the volume change of rubber and water under the same pressure ∆P is ∆V 材料 , ∆V 材料 The calculation formula is shown in formula (4):

[0096] (4)

[0097] In formula (4), V 材料 Indicates the volume of rubber or water, E 材料 represents the Young's modulus of rubber or water. As can be seen from the foregoing, in the optical fiber sound pressure sensor described in Example 1, the volume of the cavity surrounded by the right end faces of quartz tubes I and II, the inner side of quartz tube III, and the film is equal to the volume of the Helmholtz acoustic cavity. In Example 1, the volume V of the Helmholtz acoustic cavity is approximately 7×10 -7 m 3 , and an equivalent volume module is also provided in the Helmholtz acoustic cavity. The volume of the equivalent volume module (i.e., rubber) in the first embodiment is approximately 4×10 -7 m 3 , the volume of water is about 3×10 -7 m 3 Therefore, when calculating the volume change of rubber under the same pressure ∆P, it is ∆V 材料 When V 材料 Indicates the volume of the rubber, V in Example 1 材料 About 4×10 -7 m 3 When ∆P=1MPa, the volume change of rubber ∆V can be calculated by formula (4). 橡胶 ≈-4×10 -8 m 3 ; When calculating the volume change of water under the same pressure ∆P, it is ∆V 材料 When V 材料 When expressing the volume of water, V in Example 1 材料 About 3×10 -7 m 3 When ∆P=1MPa, the volume change of water ∆V can be calculated by formula (4). 水 ≈-1.36×10 -10 m3 .

[0098] Assuming that the right end faces of quartz tubes I and II, the inner side face of quartz tube III and the film are all filled with water, and no equivalent volume module (i.e., rubber) is set, the volume of water is the volume of the cavity surrounded by the right end faces of quartz tubes I and II, the inner side face of quartz tube III and the film, that is, the volume of the Helmholtz acoustic cavity, that is, V in formula (4) 水 The value is about 7×10 -7 m 3 When ∆P=1MPa, using formula (4), we can know that the volume change of water ∆V 水 ≈-3.196×10 -10 m 3 ;

[0099] When an oil and gas pipeline leak occurs, the pressure generated by the infrasound signal is generally within the pressure range of 0.001~100Pa. Calculation shows that the theoretical maximum sound pressure value of the film deformation in the optical fiber sound pressure sensor described in this application can reach 513.3Pa. Obviously, the theoretical maximum sound pressure value of the film deformation in the optical fiber sound pressure sensor described in this application is greater than 100Pa, which can effectively detect the sound pressure value generated by the infrasound signal. In this pressure range, the volume change of water is negligible. Therefore, this application uses the volume change of water ∆V 水 ≈-3.196×10 -10 m 3 Defined as the volume change of the Helmholtz acoustic cavity The theoretical value of the maximum sound pressure value of the film deformation in the optical fiber sound pressure sensor is calculated as follows:

[0100] First, calculate the pressure sensitivity S of the optical fiber acoustic pressure sensor 压 , the calculation method is shown in formula (5):

[0101] (5)

[0102] In formula (5), R represents the radius of the film, and in this application, R is 5 mm; N represents the thickness, and in this application, N is 10 μm; E represents the Young's modulus, and in this application, E is 210 GPa; Represents Poisson's ratio, in this application is 0.31;

[0103] Then, the maximum deformation of the film 9 is divided by the pressure sensitivity S of the optical fiber sound pressure sensor. 压The maximum sound pressure value that the nickel film can withstand can be obtained. Through calculation, it can be known that in this application, the maximum sound pressure value that the nickel film can withstand is 513.3 Pa; among them, the maximum deformation of the film 9 is 0.27 mm, which is determined by the distance between the hollow plate 20 and the film 9 being 0.27 mm.

[0104] Calculate the equivalent volume change ratio k1 of the Helmholtz cavity when the right end faces of quartz tubes I and II, the inner side of quartz tube III, and the cavity surrounded by the film are all filled with water without setting an elastic module (i.e., rubber). The calculation method of the equivalent volume change ratio k1 of the Helmholtz cavity is shown in formula (6);

[0105] (6)

[0106] In formula (6), ∆V 材料 Indicates the volume change of rubber under pressure ∆P (∆P=1MPa), ∆V 水 It represents the volume change of water under the pressure ∆P (∆P=1MPa), represents the volume change of the Helmholtz acoustic cavity, which is approximately -3.196×10 -10 m 3 ; According to formula (6), the equivalent volume change coefficient of the Helmholtz cavity k1≈125;

[0107] The cavity formed by the right end faces of quartz tubes I and II, the inner side face of quartz tube III and the film is filled with water and fixed with an elastic module (i.e., rubber). Under the conditions of the arrangement of the liquid medium and the equivalent volume module as described in Example 1, the equivalent volume V' of the Helmholtz cavity can be obtained by using the volume V of the Helmholtz acoustic cavity (approximately 7×10 -7 m 3 ) is calculated by multiplying the equivalent volume change proportional coefficient k1; then, the equivalent volume V' of the Helmholtz cavity is substituted into formula (1) to calculate the resonance frequency f2 of the optical fiber sound pressure sensor described in Example 1 after volume equivalent. The calculation results of the resonance frequency f2 are shown in Table 1.

[0108] The resonant frequency f2 of the optical fiber sound pressure sensor prepared in Example 2 after volume equivalent is calculated. The calculation method of the resonant frequency f2 of the optical fiber sound pressure sensor prepared in Example 2 after volume equivalent is different from the calculation method of the resonant frequency f2 of the optical fiber sound pressure sensor prepared in Example 1 after volume equivalent is that the Young's modulus of the sponge is 0.1 MPa, and the volume change ∆V of the rubber under the action of pressure ∆P (∆P=1 MPa) is calculated using formula (4): 海绵 ≈-4×10 -6 m 3 , replace ∆V in formula (6) 橡胶 The value of is replaced by ∆V海绵 The equivalent volume change coefficient of the Helmholtz cavity is calculated by numerical value, and finally the equivalent volume change coefficient of the Helmholtz cavity is compared with the volume V of the Helmholtz acoustic cavity (about 7×10 -7 m 3 ) is multiplied by , and the equivalent volume V' of the Helmholtz cavity is calculated. Then, the equivalent volume V' of the Helmholtz cavity is substituted into formula (1) to calculate the resonance frequency f2 of the fiber optic sound pressure sensor after volume equivalent.

[0109] Table 1 Calculation results of the resonance frequency f2 of the fiber optic sound pressure sensors prepared in Example 1 and Example 2 after volume equivalence

[0110]

[0111] As can be seen from the foregoing, the resonant frequency of the Helmholtz acoustic cavity of sensor one (i.e., the cavity other than the stainless steel capillary cavity of the Helmholtz acoustic cavity is filled only with water) is f1≈127.8 Hz; the resonant frequency of the Helmholtz acoustic cavity of sensor two (i.e., the cavity other than the stainless steel capillary cavity of the Helmholtz acoustic cavity is filled only with air) is f1≈29.62 Hz; and in this application, the cavity surrounded by the right end faces of quartz tubes I and II, the inner side faces of quartz tube III, and the film is filled with water and an equivalent volume module (i.e., rubber) is fixedly provided as described in Example 1, and the liquid medium and the equivalent volume module are arranged (i.e., the arrangement of the liquid medium and the equivalent volume module in the optical fiber sound pressure sensors of Examples 1 and 2 of this application), the obtained resonant frequency f2 of the optical fiber sound pressure sensor after volume equivalent can reach a minimum of about 1.15 Hz and a maximum of about 11.5 Hz. The resonant frequency of the Helmholtz acoustic cavity of the fiber optic sound pressure sensor described in the present application can reach a range of about 1.15 Hz to about 11.5 Hz. That is, the Helmholtz cavity of the fiber optic sound pressure sensor can resonantly amplify the infrasound signal in the range of about 1.15 Hz to about 11.5 Hz, and the resonant amplification of the infrasound signal can effectively enhance the infrasound signal in the frequency range of about 1.15 Hz to about 11.5 Hz, thereby improving the sensitivity of the fiber optic sound pressure sensor. Moreover, by Figure 7 It can be seen that within the range of 1 to 500 Hz, the simulated sensitivity of the optical fiber sound pressure sensor described in Example 1 at 11.5 Hz can reach -108 (dB re 1 V / μPa).

Claims

1. A fiber optic acoustic pressure sensor for pipeline leakage monitoring, characterized by: The invention comprises an incident optical fiber with one end located in a quartz capillary tube, and quartz tubes I, II, and III are fixedly mounted on the outside of the quartz capillary tube in sequence; the portion of the incident optical fiber located in the cavity of the quartz capillary tube is a bare fiber, the bare fiber having an incident optical fiber coated end face with a reflectivity of 8% within the wavelength range of 1520nm to 1580nm, and the bare fiber portion is fixedly connected to the quartz capillary tube; a reflecting optical fiber is provided in the cavity of the quartz capillary tube, one end of the reflecting optical fiber located in the quartz capillary tube is a bare fiber, the bare fiber having a reflecting optical fiber coated end face with a reflectivity of 90% within the wavelength range of 1520nm to 1580nm; and a gap exists between the coated end face of the incident optical fiber and the coated end face of the reflecting optical fiber; One end of quartz tubes I and II away from the incident optical fiber is flush and fixedly connected to the equivalent volume module; the corresponding end of the quartz capillary is located outside the cavity of quartz tube I and within the cavity of the equivalent volume module, and the equivalent volume module is located within the cavity of quartz tube III; a liquid medium is provided in the cavity between the end face of the quartz capillary, the equivalent volume module, the quartz tube III and the film; when a leak occurs in the oil and gas pipeline, an infrasound signal is generated at the leak point and propagates, and the infrasound signal generates sound pressure, which acts on the film of the optical fiber sound pressure sensor. Under the action of the sound pressure, the film drives the reflecting optical fiber to move toward the incident optical fiber, and the liquid medium compresses the equivalent volume module during the movement, causing the volume of the equivalent volume module to decrease, thereby increasing the equivalent volume of the Helmholtz acoustic cavity, and effectively suppressing the problem of increased resonance frequency of the Helmholtz acoustic cavity; A hollow limiting plate is fixedly connected to the cavity of the quartz tube III. The reflecting optical fiber extends out of the quartz capillary and passes through the hollow limiting plate and the rigid connection film. One end of the stainless steel capillary extends into the cavity formed by the end face of the quartz capillary, the equivalent volume module, the quartz tube III and the film, and the other end is located outside the quartz tube III and is spirally wound around the outer wall of the quartz tube III; The equivalent volume module is made of a material with deformation and rebound capabilities; The method for obtaining the coated end face of the incident optical fiber is as follows: the bare fiber end face of the incident optical fiber is tilted at an angle of 0°, and a high-reflection film is coated on the bare fiber end face to form the coated end face of the incident optical fiber; The reflective optical fiber coated end face is obtained as follows: the bare fiber end face of the incident optical fiber is tilted at an angle of 0°, and a high-reflective film is coated on the bare fiber end face to form a reflective optical fiber coated end face.

2. The optical fiber acoustic pressure sensor for pipeline leakage monitoring according to claim 1, characterized in that: The distance between the hollow plate of the hollow limiting plate and the film is 0.27-0.31 mm.

3. The optical fiber acoustic pressure sensor for pipeline leakage monitoring according to claim 1, characterized in that: The gap between the incident optical fiber coating end face and the reflective optical fiber coating end face is the cavity length of the FP cavity, and the cavity length is 280 μm-320 μm.

4. The optical fiber acoustic pressure sensor for pipeline leakage monitoring according to claim 1, characterized in that: The hollow limiting plate includes a cylindrical ring and a hollow plate fixedly connected to the inner side of the cylindrical ring. One end face of the cylindrical ring is flush with the corresponding end face of the hollow plate, and the other end face of the cylindrical ring is 0.27-0.31mm higher than the other end face of the hollow plate. There is a gap between the hollow plate and the equivalent volume module.

5. An oil and gas pipeline leak detection system with an acoustic pressure sensor, characterized by: The optical fiber sound pressure sensor comprises a laser connected to the first port of a circulator, the second port of the circulator is connected to the sound pressure sensor, the output port of the circulator is connected to a photodetector, and the photodetector is connected to an acquisition card and a host computer in sequence; the optical fiber sound pressure sensor is the optical fiber sound pressure sensor according to any one of claims 1 to 4.

6. A dual-laser oil and gas pipeline leak detection system with an acoustic pressure sensor, characterized by: The system comprises two DFB lasers, the two DFB lasers are respectively connected to the first ports of two circulators, the second ports of the two circulators are both connected to a wavelength division multiplexer, the wavelength division multiplexer is connected to a sound pressure sensor, the two DFB lasers respectively emit light sources, and the wavelength difference between the two light sources is (2K+1) / 4×FSR, where FSR represents the free spectral range and K is an integer; the output ends of the two circulators are respectively connected to two photodetectors, the two photodetectors are both connected to an acquisition card, and the acquisition card is connected to a host computer; the optical fiber sound pressure sensor is the optical fiber sound pressure sensor according to any one of claims 1 to 4.

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