Pressure Vessel Wall Corrosion Depth Monitoring System and Method Based on Optical Sensor Array

Abstract

The application discloses a kind of pressure vessel wall corrosion depth monitoring system and method based on optical sensor array.The system includes: a group of optical sensor array, each sensing unit is integrated with fiber bragg grating (FBG) and dispersion confocal sensor (CCM) in the same place, wherein FBG is used for temperature measurement and spatial positioning, and CCM is used for non-contact measurement to the distance of pressure vessel inner wall;A time-domain control tunable swept laser;Signal processing unit is used to receive and demodulate the reflected signal from FBG and the reflected spectrum of CCM;Central processing unit is used to control the time-domain control tunable swept laser, and receive the demodulation data of the signal processing unit, and execute corrosion depth calculation.The application effectively solves the corrosion depth monitoring problem of online, high-precision, multi-point, temperature self-compensation that traditional monitoring method is difficult to realize by the high integration of sensor and the multiplexing of function, significantly improves the reliability and safety of monitoring.

Description

Technical Field

[0001] This invention belongs to the field of pressure vessel and pressure-bearing equipment safety monitoring, non-destructive testing (NDT / NDE) and structural health monitoring (SHM), specifically involving a pressure vessel wall corrosion depth monitoring system and method based on an optical sensor array. Background Technology

[0002] Pressure vessels are critical equipment in industries such as petrochemicals, energy, and chemicals, operating for extended periods in high-temperature, high-pressure, and corrosive environments. The bottom of these vessels is particularly susceptible to accelerated localized corrosion due to media deposition, water accumulation, and crevice corrosion. Corrosion leads to thinning of the vessel walls, reducing their pressure-bearing capacity and significantly increasing the risk of leaks or even explosions.

[0003] Currently, the main methods for detecting corrosion in pressure vessels include ultrasonic thickness measurement, radiographic testing, and eddy current testing. These traditional methods have the following drawbacks:

[0004] (1) Offline operation: Most tests need to be carried out after the equipment is stopped, emptied and cleaned, which makes it impossible to monitor the real-time status of the equipment in operation. The monitoring cycle is long and rapid corrosion cannot be detected in time.

[0005] (2) Point measurement: such as handheld ultrasonic thickness gauges, which are inefficient and require ultrasonic coupling agent, making it difficult to achieve large-area coverage and easily missing local severe corrosion points.

[0006] (3) Environmental constraints: X-ray inspection poses radiation hazards; ultrasonic inspection usually requires a coupling agent and is sensitive to surface roughness.

[0007] (4) Temperature effect: During operation, temperature fluctuations on the container wall will cause thermal expansion and contraction of the material, which will significantly affect the measurement accuracy. Traditional methods often ignore or cannot effectively compensate for this error.

[0008] Therefore, for pressure vessel corrosion depth monitoring, there is an urgent need for a new technology that can achieve high precision, multi-point array, real-time online operation, adaptability to the pressure vessel environment, and temperature compensation. Optical sensing technology is generally better suited to meet these requirements. For distance measurement, laser interferometry and laser triangulation are commonly used, but these two methods require a quiet environment, have poor noise immunity, and are quite difficult to assemble and adjust, making them unsuitable for distributed monitoring of production pressure vessels.

[0009] Fiber Bragg grating (FBG) technology offers advantages such as intrinsic safety (no electrical sparks), immunity to electromagnetic interference, corrosion resistance, small size, light weight, and ease of distributed measurement. Currently, FBG-based sensor networks are used for temperature and strain monitoring; however, a single FBG suffers from difficulties in decoupling temperature and pressure sensing, leading to inaccurate single-parameter measurements or complex dual-parameter decoupling, and it cannot be directly used for distance measurement. Furthermore, while Fabry-Perot (FP) sensors in fiber optic sensing exhibit extremely high sensitivity to pressure, they are also affected by temperature and cannot achieve non-contact distance measurement.

[0010] Therefore, how to design a non-contact distributed monitoring system that can achieve large-scale, high-precision, distributed monitoring on medium and large pressure vessels, and effectively decouple the two key parameters of temperature and distance, while simplifying the system structure and reducing costs, is a problem that urgently needs to be solved in the current technical field. Summary of the Invention

[0011] To address the problems existing in the prior art, this invention aims to provide a pressure vessel wall corrosion depth monitoring system and method based on an optical sensor array. This method enables high-precision, real-time, online monitoring of multi-point corrosion at the bottom of the pressure vessel, and combines a time-domain tunable laser with FBG wavelength addressing to achieve precise positioning and in-situ temperature compensation, significantly improving the reliability and accuracy of monitoring.

[0012] This invention achieves high-precision, real-time, distributed corrosion monitoring of pressure vessels through innovative sensor integration, light source multiplexing, signal processing, and algorithm design, and also possesses temperature self-compensation capabilities. The technical solution for achieving the objectives of this invention is as follows:

[0013] An online monitoring system for corrosion depth of the bottom wall of a pressure vessel based on an optical sensor array includes:

[0014] An array of optical sensors is arranged above the bottom wall of a pressure vessel; the optical sensor array includes several sensing units, each sensing unit co-located and integrates a fiber Bragg grating (FBG) and a dispersive confocal sensor (CCM), wherein the FBG is used for temperature measurement and spatial positioning, and the CCM is used for non-contact measurement of the distance to the inner wall of the pressure vessel;

[0015] A time-domain controlled tunable sweep laser is connected to the sensor array via an optical fiber circulator and a beam splitter;

[0016] The signal processing unit is used to receive and demodulate the reflection signal from the FBG and the reflection spectrum from the CCM;

[0017] The central processing unit is used to control the time-domain controlled tunable sweep laser, receive demodulated data from the signal processing unit, and perform corrosion depth calculation.

[0018] The signal processing unit includes an FBG demodulator and a spectral demodulator; the FBG demodulator is used to demodulate the Bragg wavelength reflected by the FBG in conjunction with the time-domain scanning signal to identify the probe position and temperature, and the spectral demodulator is used to analyze the spectral signal reflected by the CCM to determine the peak wavelength.

[0019] The signal processing unit is configured to:

[0020] a) By combining the time-domain scanning signal with the unique Bragg wavelength reflected by each FBG unit demodulated by the FBG demodulator, the position of each CCM probe in the sensor array can be identified;

[0021] b) Calculate the real-time temperature at the corresponding location based on the Bragg wavelength offset reflected back by each FBG;

[0022] c) Receive and perform preliminary demodulation analysis on the spectrum returned by the CCM to determine the peak wavelength, and calculate the original distance value from the sensor probe to the inner wall of the pressure vessel based on this.

[0023] The central processing unit is used to send time-domain control signals and trigger signals to the time-domain controlled tunable sweep laser, and to receive demodulated data from the signal processing unit; the central processing unit performs thermal error compensation on the original distance value based on the temperature data, and calculates the corrosion depth and real-time wall thickness.

[0024] The central processing unit is equipped with a thermal expansion compensation algorithm module. This module calculates the distance measurement error caused by temperature based on the temperature change measured by FBG, the thermal expansion coefficient of the pressure vessel wall material, and the thermal expansion coefficient of the sensor unit mounting structure, and compensates for the original CCM distance value.

[0025] The central processing unit is also equipped with a corrosion depth calculation module, which calculates the corrosion depth and remaining wall thickness of each monitoring point in real time based on the compensated distance value, the initial installation distance and the original wall thickness data.

[0026] The central processing unit is configured as follows:

[0027] a) By combining real-time temperature data, thermal scaling error compensation is performed on the original distance value to obtain... t Precise distance at all times;

[0028] b) Based on the known probe installation height and initial container wall thickness, calculate... t The wall thickness is determined at any given time, thus allowing the corrosion depth to be calculated.

[0029] c) Combining the positioning achieved by the reflected wavelengths of each FBG sensing unit with the corresponding temperature and corrosion depth at that location, to achieve... t A two-dimensional distribution map of temperature and corrosion depth of the entire bottom wall of the pressure vessel is visualized at all times.

[0030] The FBG and CCM in each sensing unit are physically co-located and integrated within a pressure-bearing plate above the bottom wall of the pressure vessel, and the FBG has a unique initial Bragg wavelength as the address code for probe spatial positioning; the central processing unit identifies the spatial address encoding of each sensing unit by recognizing the matching relationship between the reflected wavelength and a preset wavelength set.

[0031] The time-domain controlled tunable sweep laser operates in a wavelength range of 1300nm to 1650nm, with a sweep resolution better than 0.5pm, and its output spectral width meets the measurement range requirements of the dispersive confocal sensor.

[0032] A method for online monitoring of corrosion depth of the bottom wall of a pressure vessel based on the system, comprising:

[0033] Multiple co-located integrated FBG and CCM sensing units are installed above the bottom wall of the pressure vessel, and the initial wall thickness and initial distance measurement value at each point are recorded.

[0034] Start the time-domain controlled tunable sweep laser to emit a scanning light signal to the sensor array;

[0035] The position of each sensing unit is identified by the wavelength characteristics of the reflected light signal, and the temperature response of the FBG and the distance response of the CCM are acquired simultaneously.

[0036] Real-time temperature is calculated based on the change in FBG reflection wavelength, and the CCM measurement distance is compensated by combining the thermal expansion coefficient model.

[0037] Based on the compensated distance and initial installation parameters, the corrosion depth at each point is calculated, and a two-dimensional distribution map is generated.

[0038] A safety warning is triggered when the corrosion depth at any monitoring point exceeds a preset threshold.

[0039] The method includes the following steps:

[0040] 1) Installation and initialization: The sensor array, including the fiber Bragg grating (FBG) and the dispersive confocal sensor (CCM), is encapsulated within the pressure plate above the bottom wall of the pressure vessel. After encapsulation, the original wall thickness W at each probe location is measured and recorded. 0m and the initial distance D between the probe and the bottom wall of the pressure vessel 0m , where m is the probe address number (m=1, 2, 3...);

[0041] 2) Signal transmission and positioning: The central processing unit controls the start of the time-domain controlled tunable sweep laser to emit scanning laser. The optical signal is transmitted to the sensor array through optical fiber, beam splitter, and circulator. The signal processing unit combines the time-domain scanning signal and the peak reflected wavelength response from the FBG received at time t to achieve precise positioning of the sensing unit at position m.

[0042] 3) Signal acquisition and preliminary processing; combined with time-domain pulse signals, the signals of each integrated sensing unit at position m at time t are acquired synchronously. Among them, the FBG demodulator analyzes the reflected Bragg wavelength from the FBG sensing unit; the spectral demodulator analyzes the signal peak wavelength in the spectrum reflected back from the bottom wall of the pressure vessel via the CCM.

[0043] 4) Temperature and initial distance calculation; the signal processing unit sends the demodulated FBG signal to the central processing unit to calculate the real-time temperature at position m at time t. T m Meanwhile, the demodulated CCM reflectance spectrum signal is sent to the central processing unit to calculate the initial measurement distance from position m at time t to the bottom wall of the container. After one scan cycle, the real-time temperature and initial measurement distance at all positions can be calculated.

[0044] 5) Temperature compensation and corrosion depth calculation; using the obtained real-time temperature... T m Thermal error compensation is performed on the original measurement distance to obtain the corrosion depth at each point, and then the current wall thickness is calculated by combining it with the original wall thickness. d m ;

[0045] 6) Data analysis and early warning; real-time display of two-dimensional distribution maps of temperature, corrosion depth and wall thickness at each monitoring point; when the corrosion depth and wall thickness at any monitoring point exceed the preset threshold, an alarm is triggered and the location is provided.

[0046] The beneficial effects of this invention are:

[0047] It can be installed on pressure vessels long-term, providing 24 / 7 uninterrupted monitoring during normal equipment operation. By deploying a sensor array, it can simultaneously monitor multiple key locations on the bottom of the pressure vessel, forming a two-dimensional and locally three-dimensional temperature and corrosion depth distribution map. This "area" monitoring is far superior to traditional "point" measurement, effectively avoiding the omission of severely corroded local areas. This completely changes the traditional offline detection mode, enabling real-time capture of corrosion dynamics and effective early warning of rapidly developing localized corrosion and the dynamic response of the pressure vessel. It avoids safety hazards caused by excessively long detection cycles, greatly improving the safety of equipment operation. This invention uses co-located integrated FBG and CCM sensing units to acquire the temperature of the monitoring points in real time, and uses this as a basis to execute a precise temperature compensation algorithm to obtain accurate corrosion depth. This effectively solves the serious interference caused by temperature fluctuations in industrial settings on measurement accuracy, ensuring the accuracy and reliability of wall thickness measurement results over a wide temperature range.

[0048] The pressure vessel corrosion monitoring solution provided by this invention integrates the advantages of online, real-time, distributed, high precision, temperature self-compensation, and intrinsic safety, effectively overcoming many bottlenecks of existing technologies, and has extremely high engineering application value and broad market promotion prospects.

[0049] Of course, not all of the above-mentioned beneficial effects can be achieved by any of the technical solutions of the present invention. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of a pressure vessel wall corrosion depth monitoring system based on an optical sensor array according to the present invention.

[0051] Among them, the central processing unit 1, FPGA 2, signal processing unit 3, time-domain controlled tunable sweep laser 4, CCM (dispersion confocal sensor) 5, fiber optic beam splitter 6, FBG (fiber Bragg grating) 7, communication fiber optic cable 8, FBG demodulator 9, spectral demodulator 10, and fiber optic circulator 11.

[0052] Figure 2 for Figure 1 A detailed view of a part of the scene.

[0053] Multiple small or micro CCMs are encapsulated in a pressure plate above the bottom wall of a pressure vessel. One end receives incident light through an optical collimator. The focal spectrum reflected back from the bottom wall of the pressure vessel is reflected by a beam splitter to a confocal aperture and enters the optical fiber network. The entire array communication is achieved by optical fibers and multiple circulators. Detailed Implementation

[0054] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0055] Reference Figure 1The present invention relates to an online monitoring system for corrosion depth of the bottom wall of a pressure vessel based on an optical sensor array, comprising a set of optical sensor arrays arranged in the pressure plate above the bottom wall of the pressure vessel; the optical sensor array includes several sensing units, each sensing unit co-located and integrated with FBG 7 and CCM 5.

[0056] FBG has two functions:

[0057] a) Temperature sensing: The Bragg wavelength of the FBG has a highly sensitive linear response to temperature, which can be used to measure the local temperature at the probe location in situ with precision.

[0058] b) Spatial positioning: Each FBG in the array is assigned a unique, pre-set initial Bragg wavelength (λ). B0(m) This wavelength acts like an "address code" for each probe, and is identified and determined through time-domain scanning characteristics.

[0059] The function of CCM is to achieve high-precision distance measurement: CCM uses a dispersive lens to disperse broadband light into a continuous focal spectrum in the axial direction. When the focal point of a certain wavelength of light falls exactly on the inner wall surface of the pressure vessel, the light of that wavelength will be effectively reflected back to the probe. By identifying this peak reflection wavelength through spectral analysis, the distance from the probe end face to the inner wall of the container can be determined with micron or submicron precision according to the pre-calibrated "wavelength-distance" relationship curve.

[0060] Both sensors are precisely encapsulated within the same mechanical housing, embedded in the pressure plate above the bottom wall of the pressure vessel, forming a physically co-located integrated sensing unit. This co-location design ensures data synchronization and coupling at the monitoring location. The FBG can achieve physical address positioning based on time-domain wavelength scanning, while its measured temperature serves as the real-time ambient temperature, providing a delay-free and spatially bias-free temperature compensation data source for subsequent precise CCM distance measurements. The two sensors are highly decoupled, capable of independent measurement as well as high-precision temperature compensation measurement through signal and data fusion. Multiple such integrated sensing units are installed in a predetermined layout (such as a grid) within the encapsulated pressure plate, which is then fixed to the bottom of the pressure vessel. All probes are connected in series or parallel via optical fibers to form a distributed sensing network capable of covering a large area.

[0061] A time-domain controlled tunable swept-frequency laser 4 is connected to the sensor array via an fiber optic circulator 11 and a fiber optic beam splitter 6. To simplify the system structure, reduce cost, and improve reliability, this invention combines wavelength division multiplexing (WDM) technology, incorporating multiple beam splitters and circulators, and employs a single broadband time-domain controlled tunable swept-frequency laser to drive the entire optical sensing network. This light source meets the following two key characteristics:

[0062] Wide tuning range: Its scanning wavelength range is 1310~1650nm, with a resolution of 0.1pm, which can completely cover the initial Bragg wavelength of all FBGs in the array, as well as the maximum drift range of these wavelengths that may be caused by changes in operating temperature.

[0063] Wide-spectrum output characteristics: The wide-spectrum characteristics and time-domain sweep resolution of this laser during scanning or its own inherent characteristics can provide a sufficiently wide spectral range for CCM as its measurement light source, satisfying the dispersion and ranging range of CCM throughout the entire measurement range, and also satisfying the distance measurement resolution of the dispersive confocal sensor CCM.

[0064] This design achieves a high degree of light source reuse. The same time-domain controlled sweep beam, with its narrow linewidth at a specific moment, is used for wavelength demodulation of the FBG, while the broad spectrum formed throughout the entire scan cycle is used for distance demodulation of the CCM. This avoids the need for two separate light sources (one for FBG interrogation and one for CCM illumination), significantly simplifying the optical path design and reducing system complexity and potential points of failure.

[0065] Signal processing unit 3 receives and demodulates the reflected signal from FBG7 and the reflected spectrum from CCM5. The optical signal returned by the sensor array is a complex signal that mixes all FBG reflected signals and all CCM reflected spectra. The task of the signal processing unit is to accurately separate and demodulate it: a fiber optic circulator is used to extract the returned signal from the main optical path, and then a broadband fiber optic beam splitter combined with WDM technology is used to split the mixed signal into two paths according to a certain ratio. One signal is sent to a high-speed FBG demodulator. High-speed FBG demodulators are usually based on scanning lasers, matched gratings, or tunable Fabry-Perot (FFP) filter technology. This scheme can work in conjunction with the frequency-scanning light source at its front end, using the wavelength scanning of the light source itself as a demodulation method (i.e., frequency-scanning demodulation). By synchronously recording the reflected light power and the instantaneous wavelength of the frequency-scanning laser, the reflected spectrum can be constructed, thereby finding the peak wavelength. This demodulator, combined with time-domain controlled wavelength control and wavelength division multiplexing technology, can track and resolve the characteristic center wavelength λ reflected from each FBG in real time. B (m,t) is then transmitted to the central processing unit. Another signal is fed into a high-resolution spectrometer (spectral demodulator). This instrument analyzes the received broadband signal and, using a peak addressing algorithm, precisely identifies the wavelength λ of the strongest energy in the spectrum returned by each CCM probe. d (m,t) is sent to the central processing unit.

[0066] The central processing unit 1 controls the time-domain controlled tunable sweep laser 4, receives demodulated data from the signal processing unit 3, and performs corrosion depth calculations. The central processing unit 1 sends scan control signals to the time-domain controlled tunable sweep laser 4 via the FPGA 2 and sends synchronization trigger commands to the signal processing unit 3. As the core of control and data processing, the central processing unit has two main functions:

[0067] (a) Send a time-domain control signal to the time-domain controlled tunable sweep laser and simultaneously send a synchronization trigger signal to the two demodulators to ensure that the temperature data and distance data collected at the same time are strictly corresponding, laying the foundation for subsequent data fusion processing.

[0068] (b) Execute the core algorithm; for the Bragg wavelength signal at time t sent back by the FBG demodulator, combine it with the initial wavelength λ B0(m) The position and temperature information of probe m can be obtained simultaneously with the time-domain pulse signal. T (m,t).

[0069] The sensor array unit consists of multiple sensor probes co-located and integrated with FBG7 and CCM5. These probes are encapsulated in a pressure plate and connected to subsequent units via communication optical fiber 8.

[0070] The output light of the time-domain controlled tunable sweep laser 4 enters the main optical path through the fiber optic circulator 11. The mixed signal light returning from the sensor array passes through the fiber optic circulator 11 again and is split by the fiber optic beam splitter 6.

[0071] The signal processing unit includes an FBG demodulator 9 and a spectral demodulator 10. The FBG demodulator 9 is responsible for demodulating temperature and location information, while the spectral demodulator 10 is responsible for demodulating distance information.

[0072] The central processing unit 1 is usually a PC industrial control computer. Its main function is to send time-domain control of the tunable sweep laser 4 through FPGA2, and at the same time send synchronous trigger signal commands to the two demodulators in the signal processing unit—FBG demodulator 9 and spectral demodulator 10—to receive demodulated signals from FBG7 and CCM5.

[0073] An FBG7 and a CCM5 are co-located within the pressure plate above the bottom wall of the pressure vessel. The FBG7 is connected in series with the input optical fiber. The CCM5 contains a special miniaturized dispersive lens, referenced... Figure 2 .

[0074] When the system is working, the optical signal emitted by the time-domain controlled tunable sweep laser 4 enters the probe. When the scanning wavelength of the time-domain controlled tunable sweep laser 4 matches the Bragg wavelength of the FBG7, the FBG7 will strongly reflect the light of that wavelength, forming a reflected signal that returns along the original path.

[0075] Simultaneously, the broadband component (time-domain accumulation) of the time-domain controlled tunable swept laser 4 enters CCM5 and is dispersed axially by the dispersive lens, forming a sequence of colored light spots distributed along the optical axis. Only light of a specific wavelength λ... D It can precisely focus on the inner wall of a pressure vessel. Light of this wavelength is reflected by the inner wall, and most of the energy can be collected by the lens and returned along the original path, forming a dispersive confocal reflection signal.

[0076] Reference Figure 1 , 2 The monitoring method of the present invention is as follows:

[0077] Step S1: Initialization and Calibration. Before commissioning or during maintenance of the pressure vessel, encapsulate the sensor array within a pressure-bearing plate above its bottom wall. Accurately measure and record the original wall thickness W at each probe location. 0m and the initial distance D between the probe and the bottom wall of the pressure vessel 0m Where m is the probe address number (m=1, 2, 3...). Meanwhile, at the reference temperature (T... ref Record the initial Bragg wavelength λ for each FBG. B0(m) For each CCM, calibration is performed to establish a correspondence function between "peak reflection wavelength and measurement distance". d m = f m (λ d This function is stored in the central processing unit.

[0078] Step S2: Signal Transmission and Positioning. After system startup, the central processing unit, through the FPGA and signal processing unit, controls the time-domain controlled tunable sweep laser to periodically perform frequency sweeping, transmitting interrogation and measurement light signals. The sweeping range is 1310~1650nm, with a resolution of 0.1pm. Combined with the time-domain pulse signal, the peak wavelength response of the FBG reflected back at time t is captured, achieving precise positioning of the sensing unit at location m.

[0079] Step S3: Signal Acquisition and Preliminary Processing. The optical signal, which combines all the returned signals from the sensors, is sent in real time to the FBG demodulator and the spectrometer demodulator through an optical fiber circulator and an optical fiber beam splitter. Combining the time-domain pulse signal and the position, the FBG demodulator analyzes the reflected Bragg wavelength λ of the FBG sensing unit at position m at time t. B (m,t). The spectral demodulator then analyzes the peak wavelength λ of the signal returned by the CCM at position m at time t. d (m,t).

[0080] Step S4: Temperature and Initial Distance Calculation. The central processing unit calculates the real-time temperature based on the wavelength drift of the FBG. The wavelength change of the FBG is mainly affected by temperature and strain, and their relationship is as follows:

[0081] Δλ B = λ B (m,t) - λ B0(m) = S T · Δ T + S ε · ε

[0082] Since the sensor probe is encapsulated in a stress-relieving structure, the effect of strain ε is negligible. Therefore, the temperature change ΔT(m,t) can be simplified as follows:

[0083] Δ T (m,t) = T (m,t) - T ref = [λ B (m,t) - λ B0(m) ] / K T

[0084] in, K T It is the temperature sensitivity coefficient of FBG (pre-calibrated).

[0085] Simultaneously, based on the working principle and calibration relationship of the CCM, the initial distance between the CCM and the bottom wall at time t is calculated:

[0086] d o (m,t) = f (λ o(m,t) )

[0087] Step S5: Temperature Compensation. Temperature changes cause thermal expansion and contraction of the container wall and probe mounting structure, affecting the accuracy of distance measurement. The simplified compensation formula is as follows:

[0088] d (m,t) = d o (m,t) - Δ d (m,t)

[0089] Among them, thermal error Δ d (m,t) = [α v * W (m,t) + α m * H m ] * Δ T (m,t). αv and α m These are the coefficients of thermal expansion of the container material and the probe mounting base, respectively. H m This refers to the mounting bracket height. Current wall thickness. W When (m,t) is unknown, this equation needs to be solved iteratively or approximated by the initial wall thickness when the temperature change is small.

[0090] Step S6: Calculation of corrosion depth and wall thickness. Combine this with the original recorded distance D between the CCM and the bottom wall during initial installation and calibration. 0m The temperature-compensated distance measured by CCM at time t d (m,t) can be used to calculate the corrosion depth at location m. C (m,t) is:

[0091] C (m,t)= d (m,t)- D 0m

[0092] By combining the initial wall thickness during installation and calibration with the calculated corrosion depth, the wall thickness at position m at time t can be accurately calculated as follows:

[0093] W (m,t) = W 0m - C (m,t)

[0094] Step S7: Distribution Map Visualization and Early Warning. The central processing unit (CPU) calculates the corrosion depth of all monitoring points m. C (m,t) and wall thickness W (m,t) data are integrated and displayed in real time as a two-dimensional distributed monitoring map on a human-computer interaction interface in the form of cloud maps, curves, or lists. The corrosion depth at any point is then considered. C (m,t) and wall thickness W When (m,t) exceeds the preset safety threshold, the system will automatically issue an audible and visual alarm.

[0095] In summary, this invention cleverly combines the positioning and temperature measurement functions of an FBG (Fast-Fast Packing Gear) with the high-precision ranging function of a dispersive confocal sensor within a single probe, and utilizes a single tunable light source for driving, thus constructing a complete online monitoring solution. It not only solves the real-time and accuracy problems of corrosion monitoring, but also overcomes the interference of complex temperature environments in industrial settings on measurement results through a built-in temperature compensation mechanism, demonstrating extremely high engineering application value and promising prospects for widespread adoption.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the framework and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An on-line monitoring system for the corrosion depth of the bottom wall of a pressure vessel based on an array of optical sensors, characterized in that, The system comprises: a set of optical sensor arrays arranged above the bottom wall of the pressure vessel; the optical sensor array comprises a plurality of sensing units, each of which is co-located with a fiber Bragg grating (FBG) and a chromatic confocal sensor (CCM), wherein the FBG is used for temperature measurement and spatial positioning, and the CCM is used for non-contact measurement of the distance to the inner wall of the pressure vessel; a time-domain controlled tunable swept laser connected to the sensor array through a fiber circulator and a beam splitter; a signal processing unit for receiving and demodulating the reflected signals from the FBG and the reflected spectrum of the CCM; a central processor for controlling the time-domain controlled tunable swept laser and receiving the demodulation data from the signal processing unit to perform corrosion depth calculation; the signal processing unit is configured to: a) identify the position of each CCM probe in the sensor array by combining the time-domain scanning signal with the FBG demodulator to demodulate the unique Bragg wavelength reflected by each FBG unit; b) calculate the real-time temperature at the corresponding position according to the Bragg wavelength offset reflected by each FBG; c) receive and preliminarily demodulate the spectrum returned by the CCM to determine the peak wavelength and calculate the original distance value from the sensor probe to the inner wall of the pressure vessel based on the peak wavelength; the central processor is configured with a thermal expansion compensation algorithm module that calculates the distance measurement error caused by temperature based on the temperature change measured by the FBG, the thermal expansion coefficient of the pressure vessel wall material, and the thermal expansion coefficient of the installation structure of the sensing unit, and compensates the original distance value of the CCM; the central processor is also configured with a corrosion depth calculation module that calculates the corrosion depth and remaining wall thickness of each monitoring point in real time based on the compensated distance value, the initial installation distance, and the original wall thickness data.

2. The system of claim 1, wherein: the signal processing unit comprises an FBG demodulator and a spectrum demodulator; the FBG demodulator is used to demodulate the Bragg wavelength reflected by the FBG in combination with the time-domain scanning signal to identify the probe position and temperature, and the spectrum demodulator is used to analyze the spectrum signal reflected by the CCM to determine the peak wavelength.

3. The system of claim 1, wherein: the central processor is used to send time-domain control signals and trigger signals to the time-domain controlled tunable swept laser and receive demodulation data from the signal processing unit.

4. The system of claim 1, wherein: the central processor is configured to: a) applying a thermal expansion error compensation to the raw distance values based on real-time temperature data, resulting in t accurate distances; b) calculating the corrosion depth from the known probe mounting height and the initial container wall thickness t the wall thickness at the moment in time, and thus the corrosion depth; c) combining the localization achieved by the reflected wavelengths of each FBG sensing unit with the temperature, corrosion depth of the corresponding location, achieving t the visualization of the two-dimensional distribution of the temperature, corrosion depth of the entire bottom wall of the pressure vessel at any moment.

5. The system of claim 1, wherein: the FBG and CCM in each sensing unit are physically co-located and packaged in a pressure-bearing plate above the bottom wall of the pressure vessel, and the FBG has a unique initial Bragg wavelength as an address code for spatial positioning of the probe; the central processor identifies the spatial address code of each sensing unit by identifying the matching relationship between the reflected wavelength and the preset wavelength set.

6. The system of claim 1, wherein, The wavelength range of the time-domain controlled tunable swept laser covers 1300nm to 1650nm, the swept resolution is better than 0.5pm, and the output spectrum width meets the measurement range requirement of the dispersion confocal sensor.

7. A method for on-line monitoring of the corrosion depth of the bottom wall of a pressure vessel based on the system of claim 1, characterized by, The method comprises the following steps: Install the plurality of co-located integrated FBG and CCM sensing units above the bottom wall of the pressure vessel, and record the initial wall thickness and initial distance measurement value of each point; Start the time-domain controlled tunable swept laser, and emit a scanning light signal to the sensing array; Identify the position of each sensing unit through the wavelength characteristics of the reflected light signal, and synchronously acquire the temperature response of the FBG and the distance response of the CCM; Calculate the real-time temperature according to the change of the reflected wavelength of the FBG, and compensate the measured distance of the CCM in combination with the thermal expansion coefficient model; Calculate the corrosion depth of each point according to the compensated distance and the initial installation parameters, and generate a two-dimensional distribution map; When the corrosion depth of any monitoring point exceeds the preset threshold, trigger a safety warning.

8. The method of claim 7, wherein, The method comprises the following steps: 1) Installation and initialization; encapsulate the sensor array containing fiber Bragg grating FBG and dispersion confocal sensor CCM in the pressure plate above the bottom wall of the pressure vessel, and measure and record the corresponding original wall thickness W at each probe position after encapsulation 0m And the original distance D between the probe and the bottom wall of the pressure vessel 0m Where m is the address number of the probe, m = 1, 2, 3... 2) Signal emission and positioning; the time-domain controlled tunable swept laser is started by the central processing unit to emit a scanning laser, and the light signal is transmitted to the sensor array through the optical fiber and the optical splitter and circulator; the signal processing unit combines the time-domain scanning signal and the peak reflected wavelength response from the FBG received at time t to realize accurate positioning of the sensing unit at position m; 3) Signal acquisition and preliminary processing; In combination with the time-domain pulse signal, the signals of each integrated sensing unit at position m at time t are synchronously acquired, wherein the FBG demodulator analyzes the reflected Bragg wavelength from the FBG sensing unit, and the spectrum demodulator analyzes the signal peak wavelength in the spectrum reflected back from the bottom wall of the pressure vessel by the CCM; 4) Temperature and initial distance calculation; the signal processing unit delivers the demodulated FBG signal to the central processor to calculate the real-time temperature at position m at time t T m At the same time, the demodulated CCM reflection spectrum signal is delivered to the central processor to calculate the initial measured distance from the container bottom wall at position m at time t. After a scanning period, the real-time temperature and the initial measured distance at all positions can be calculated. 5) Temperature compensation and corrosion depth calculation; using the real-time temperature obtained T m Thermal error compensation is performed on the original measured distance to obtain the corrosion depth of each point, and the current wall thickness is calculated by combining the original wall thickness d m ; 6) Data analysis and warning; a two-dimensional distribution map of the temperature, corrosion depth and wall thickness of each monitoring point is displayed in real time, and when the corrosion depth and wall thickness of any monitoring point exceed the preset threshold, an alarm is triggered and the location is given.

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