A high-temperature expansion joint hoop strain distribution type on-line monitoring method

Abstract

The application discloses a kind of high-temperature expansion joint hoop strain distributed online monitoring method, including acquisition monitoring module, expansion joint sensing module, optical cable connection module, optical path end extinction module;The acquisition monitoring module is constituted by optical frequency domain reflectometer instrument (OFDR) and matched server;Expansion joint sensing module is by temperature sensing optical cable, strain sensing optical cable and is bonded in expansion joint hoop surface by high-temperature resistant glue;Optical cable connection module is constituted by communication optical cable and FC / APC optical fiber joint;Optical path end extinction module is constituted by extinction optical fiber.The beneficial effects of the application are that the optical fiber is protected by the optical fiber metal sleeve, and it is also resistant to high temperature, and it is more suitable for engineering practical application;Each module is connected into an integrated sensing system by optical fiber joint, and temperature strain decoupling is realized by using distributed optical fiber strain demodulation equipment, distributed hoop strain information of expansion joint can be obtained online in real time, and the system has high integration, is convenient to install and reliable.

Description

Technical Field

[0001] This invention relates to the field of high-temperature structural health monitoring technology, specifically to a distributed online monitoring method for the circumferential strain of high-temperature expansion joints. Background Technology

[0002] Expansion joints are critical components in high-temperature piping systems, used to absorb thermal expansion and vibration. Monitoring their circumferential strain is essential for structural health assessment. While traditional resistance strain gauge methods are technically mature, their point-based measurements struggle to capture circumferential strain distribution, they are prone to aging and failure under high-temperature conditions, and their long-term monitoring reliability is low. In practical applications of high-temperature engineering, new requirements are placed on the circumferential strain monitoring system's high-temperature resistance, strain transfer efficiency, temperature-strain decoupling capability, and long-term stability. Fiber optic sensing technology, due to its inherent advantages such as high sensitivity, distributed measurement, and resistance to electromagnetic interference, has become a promising emerging monitoring technology. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a distributed online monitoring method and system for circumferential strain of high-temperature expansion joints, so as to achieve high-precision, distributed, and real-time online monitoring of circumferential strain on the surface of expansion joints under high-temperature conditions.

[0004] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: It relates to a distributed online monitoring method for circumferential strain of high-temperature expansion joints, comprising a data acquisition and monitoring module, an expansion joint sensing module, an optical cable connection module, and an optical path end extinction module; the data acquisition and monitoring module consists of an optical frequency domain reflectometer and a supporting server; the expansion joint sensing module consists of a temperature sensing optical cable and a strain sensing optical cable bonded to the surface of the expansion joint with high-temperature resistant adhesive; the optical cable connection module consists of a communication optical cable and an FC / APC optical fiber connector; and the optical path end extinction module consists of extinction optical fibers.

[0005] According to the above scheme, the acquisition and monitoring module is characterized in that the optical frequency domain reflectometer is used to acquire Rayleigh scattering signals in the optical fiber and transmit the information to the supporting server; the supporting server is equipped with a signal processing module and a temperature strain decoupling module, the signal processing module realizes the conversion from the spectral domain to the distance domain based on the fast Fourier transform, and the temperature strain decoupling module is used to output distributed circumferential strain information.

[0006] According to the above scheme, the principle of the temperature strain decoupling module is as follows:

[0007] In fiber optic sensing, the relative change in optical path length is the core physical quantity. This change is caused by both the change in the fiber's geometric length and the change in the fiber core's refractive index, and can be expressed as:

[0008] (1)

[0009] in, It is the relative change in optical path length. It is the relative change in the geometric length of the optical fiber. It is the relative change in the refractive index of the fiber core.

[0010] According to the above scheme, the relative change in the geometric length of the optical fiber is caused by mechanical strain and thermal expansion. The parameters are respectively expressed as follows:

[0011] (2)

[0012] (3)

[0013] in, It is mechanical strain caused by external force. It's due to the thermal expansion of the optical fiber. This is the thermal expansion coefficient of optical fiber, taken as 0.55e-6. It is the change in external temperature.

[0014] According to the above scheme, the relative change in the refractive index of the fiber core is caused by the elasto-optical effect and the thermo-optical effect. The parameters are respectively expressed as:

[0015] (4)

[0016] (5)

[0017] (6)

[0018] in, Strain changes the amount of refractive index change through the photoelastic effect. It is the change in refractive index directly caused by changes in external temperature. This is the effective optical elasticity coefficient of the optical fiber, taken as -0.22. It is the optical fiber thermo-optic coefficient, taken as 8e-6.

[0019] Substituting equations (2) - (6) into equation (1) yields:

[0020]

[0021]

[0022] (7)

[0023] Dividing both sides of equation (7) by 0.78 yields the total strain of the optical fiber. for:

[0024]

[0025] (8)

[0026] make , Due to temperature strain.

[0027] Therefore, the total strain of an optical fiber can be expressed as the sum of the thermal strain and the mechanical strain. That is:

[0028] (10)

[0029] According to the above scheme, the temperature-sensing optical cable is characterized in that it consists of a metal sheath, a PI single-mode optical fiber, and an FC / APC optical fiber connector. The optical fiber inside the metal sheath is fixed at one end and only responds to changes in external temperature. Temperature strain measured by OFDR It can calculate the change in external temperature. ,Right now:

[0030] (11)

[0031] According to the above scheme, the strain sensing optical cable is characterized in that the optical cable is also composed of a metal sheath, PI single-mode optical fiber, and FC / APC optical fiber connectors. However, the optical fiber inside the metal sheath is fixed at both ends, and changes in external temperature... At the same time, it also responds to the mechanical strain transmitted from the outside world. Total strain measured by OFDR The change in external temperature obtained from equation (11) The temperature-induced strain coefficient K of the optical cable obtained from the experiment can be used to calculate the mechanical strain transmitted from the external environment. Circumferential strain, also known as circumferential strain, is expressed as:

[0032] (11)

[0033] In the above scheme, a section of extinction fiber is also fused to the end of the temperature sensing optical cable to improve the signal-to-noise ratio of the signal collected by the optical frequency domain reflectometer.

[0034] According to the above scheme, the temperature sensing optical cable and strain sensing optical cable are bonded to the surface of the expansion joint to form an expansion joint sensing module. Before bonding, the surface of the expansion joint needs to be roughened by grinding to ensure that the circumferential strain can be effectively transmitted. The adhesive is a high-temperature resistant inorganic adhesive with a long-term operating temperature of not less than 800℃.

[0035] According to the above scheme, the acquisition and monitoring module and the expansion joint sensing module are connected via a communication optical cable and an FC / APC fiber optic connector. The FC / APC fiber optic connector is also used to connect the pigtails of the temperature sensing optical cable and the strain sensing optical cable.

[0036] The beneficial effects of this invention are as follows: It provides a novel distributed online monitoring method for the circumferential strain of high-temperature expansion joints. By physically protecting the optical fiber with a metal sheath, the long-term stability of the fiber under harsh conditions such as high temperature, corrosion, or mechanical friction is significantly improved, making it more suitable for practical engineering applications and effectively extending the service life of the monitoring system. Each functional module is connected in series with FC / APC fiber optic connectors and communication cables to form an integrated continuous sensing system, avoiding the problems of complex wiring and large signal attenuation caused by traditional multi-point wiring. The system has high integration and strong overall reliability. The OFDR, combined with parallel-arranged temperature and strain sensing cables, enables online decoupling of temperature and strain, allowing real-time acquisition of distributed, high-precision, and high spatial resolution strain data throughout the entire circumferential direction of the expansion joint. This solution overcomes the shortcomings of traditional point-based measurements, such as incompleteness and significant temperature interference, providing a data foundation for structural health assessment and early warning of expansion joints. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of a specific embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the principle structure of the expansion joint sensing module in this embodiment.

[0039] Figure 3 This is a schematic diagram of the principle structure of the temperature sensing optical cable and the strain sensing optical cable in this embodiment.

[0040] The components include: 1. Instrument cabinet; 2. Communication optical cable; 3. FC / APC fiber optic connector 1; 4. Expansion joint sensing module 1; 5. Strain sensing optical cable; 6. Expansion joint sensing module 2; 7. FC / APC fiber optic connector 2; 8. Temperature sensing optical cable; 9. Optical path end extinction module; 10. Expansion joint flue gas inlet; 11. FC / APC fiber optic connector; 12. Expansion joint flue gas outlet; 13. Temperature sensing optical cable; 14. Strain sensing optical cable; 15. Expansion joint body; 16. FC / APC fiber optic connector; 17. Fixing adhesive; 18. Metal sleeve; 19. PI single-mode fiber; 20. Extinction fiber. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0042] like Figure 1 The method for distributed online monitoring of circumferential strain in high-temperature expansion joints, as shown, includes an instrument cabinet 1 for storing OFDR testing equipment and supporting servers, expansion joint sensing module 4, expansion joint sensing module 6, and optical path end extinction module 9. Each module is connected via a communication optical cable 2, an FC / APC fiber optic connector 3, and an FC / APC fiber optic connector 7. Taking module 2 as an example, the expansion joint sensing module... Figure 2 As shown, the expansion joint includes a flue gas inlet 10, a flue gas outlet 12, a main body 15, a temperature sensing optical cable 13, and a strain sensing optical cable 14. The temperature sensing optical cable 13 and the strain sensing optical cable 14 are continuously bonded to the surface of the expansion joint circumferentially using high-temperature resistant adhesive and connected via an FC / APC fiber optic connector 11. Figure 3 As shown, the temperature sensing optical cable 13 includes an FC / APC fiber connector 16, a metal sleeve 18, a PI single-mode fiber 19, and an extinction fiber 20. Adhesive 17 is used to fix one end of the PI single-mode fiber 19 inside the metal sleeve 18. The extinction fiber 20 is fused to the end of the PI single-mode fiber 19 to form an optical path end extinction module 9, thereby improving the signal-to-noise ratio of the acquired signal. The strain sensing optical cable 14 has a structure basically the same as the temperature sensing optical cable 13. The difference is that adhesive 17 is used to fix both ends of the PI single-mode fiber 19, and because the strain sensing optical cable 14 has dual FC / APC fiber connectors 16, its end does not require an optical path end extinction module 9.

[0043] The above embodiments are only used to illustrate the design concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes or modifications made based on the principles and design ideas disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A distributed online monitoring method for circumferential strain of high-temperature expansion joints, characterized in that, It includes a data acquisition and monitoring module, an expansion joint sensing module, an optical cable connection module, and an optical path end extinction module; the data acquisition and monitoring module includes an OFDR and a supporting server; the expansion joint sensing module includes a temperature sensing optical cable, a strain sensing optical cable, and high-temperature resistant adhesive; the optical cable connection module includes a communication optical cable and an FC / APC optical fiber connector; and the optical path end extinction module includes an extinction optical fiber.

2. The data acquisition and monitoring module according to claim 1, characterized in that, The OFDR is used to acquire signals and can be directly connected to the supporting server; the supporting server is used for signal processing and temperature-strain decoupling.

3. The expansion joint sensing module according to claim 1, characterized in that, The temperature-sensing optical cable and the strain-sensing optical cable are arranged in parallel and are continuously bonded to the surface of the expansion joint along the circumferential direction using high-temperature resistant adhesive. Before bonding, the surface of the expansion joint is roughened by grinding to ensure that the circumferential strain on the expansion joint surface can be effectively transmitted to the optical fiber. The long-term operating temperature of the high-temperature resistant adhesive is not lower than 800℃.

4. The optical cable connection module according to claim 1, characterized in that, The communication optical cable is used to connect the acquisition and monitoring module to the expansion joint sensing module. The FC / APC fiber optic connector is used to connect the pigtails of the temperature sensing optical cable and the strain sensing optical cable.

5. The optical path end extinction module according to claim 1, characterized in that, The extinction fiber is fused to the end of the temperature sensing optical cable to improve the signal-to-noise ratio of the signal acquired by the optical frequency domain reflectometer.

6. The temperature-sensing optical cable and the strain-sensing optical cable according to claim 3, characterized in that, Both the temperature sensing optical cable and the strain sensing optical cable are made of single-mode optical fiber with a polyimide (PI) coating and are covered with a metal sheath.

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