Micro-wave guide monitoring method for corrosion under pipeline thermal insulation layer
By deploying microwave antennas on pipelines, applying excitation signals and collecting reflected signals, and calculating the impact response waveform, the problem of the inability to monitor corrosion under the pipeline insulation layer over a large area and efficiently in existing technologies has been solved. This enables early identification of high-risk areas and reduces maintenance workload and costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-19
- Publication Date
- 2026-03-24
Smart Images
Figure CN121721053A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of pipeline corrosion monitoring technology, and in particular to a microwave guided wave monitoring method for corrosion under pipeline insulation layers. Background Technology
[0002] Corrosion under insulation (CUI) is a prevalent and highly hazardous form of corrosion in industrial production environments, primarily occurring on the surfaces of metal pipes, equipment, or storage tanks encased in insulation materials such as rock wool, glass wool, and polyurethane foam. Because CUI is hidden beneath the insulation layer, it is highly concealed and difficult to detect, allowing corrosion to continue developing undetected. This significantly increases the risk of equipment structural failure, sudden leaks, and may even lead to serious accidents such as fires, explosions, poisoning, and environmental damage. Therefore, CUI is widely recognized as one of the most challenging corrosion problems in industrial asset management.
[0003] Currently, there are no mature methods for large-scale CUI or humidity monitoring. Traditional monitoring methods often require removing the insulation layer for testing, which is not only labor-intensive and costly but also disrupts normal production and cannot achieve early, large-scale corrosion risk identification. Therefore, how to achieve large-scale monitoring of corrosion under pipeline insulation layers and identify high-risk corrosion areas at an early stage has become a pressing technical problem to be solved in this field. Summary of the Invention
[0004] The purpose of this application is to provide a microwave guided wave monitoring method for corrosion under pipeline insulation layers, which can realize large-scale monitoring of corrosion under pipeline insulation layers, identify high-risk corrosion areas at an early stage, and improve the efficiency of corrosion monitoring under pipeline insulation layers.
[0005] To achieve the above objectives, this application provides the following solution.
[0006] This application provides a microwave guided wave monitoring method for corrosion under pipe insulation layer, which includes the following steps.
[0007] Obtain basic data of the pipeline to be tested; the basic data includes the pipeline diameter and the insulation layer thickness.
[0008] Based on the basic data of the pipeline under test, a corresponding microwave antenna is deployed in the monitoring area of the pipeline under test.
[0009] An excitation signal is applied to the microwave antenna, and the corresponding reflection signal is collected to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period.
[0010] The impact response waveform is calculated based on the frequency domain data of the excitation waveform and the frequency domain reflection characteristic data.
[0011] Based on the impact response waveform, the corrosion risk of the pipeline under test is assessed, and the corrosion risk assessment result is obtained.
[0012] Optionally, the pipe to be tested includes a metal liner, a non-metallic insulation material, and a metal outer skin. The metal liner is the metal pipe to be monitored. The non-metallic insulation material is wrapped around the outside of the metal liner. The metal outer skin is wrapped around the outside of the non-metallic insulation material, and the metal liner and the metal outer skin form a coaxial waveguide structure.
[0013] After an excitation signal is applied to the microwave antenna, the excitation signal is radiated by the microwave antenna and then propagates in the coaxial waveguide structure in the form of a microwave waveguide.
[0014] Optionally, based on the basic data of the pipeline under test, a corresponding microwave antenna is deployed in the monitoring area of the pipeline under test, specifically including the following steps.
[0015] Based on the basic data of the pipeline under test, determine the number and length of microwave antennas.
[0016] Based on the number and length of the microwave antennas, the microwave antennas are evenly arranged along the circumference of the pipe to be tested, and one end of the microwave antenna is inserted into the insulation material of the inner insulation layer after passing through the outermost metal skin of the pipe to be tested.
[0017] Optionally, the number of microwave antennas is 4 to d / 10, and the length of the microwave antenna is greater than or equal to 1 / 2 of the thickness of the insulation layer, wherein the value of d is equal to the pipe diameter in mm.
[0018] Optionally, an excitation signal is applied to the microwave antenna, and the corresponding reflection signal is collected to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period, specifically including the following steps.
[0019] Excitation sources of different frequencies are injected into the microwave antenna, and a directional coupler is used to transmit the excitation signal generated by the excitation source to the microwave antenna.
[0020] The reflected signal of the reflection channel of the directional coupler is collected, and the S11 signal of the microwave antenna at each frequency is calculated based on the reflected signal.
[0021] Under conditions where there is no water accumulation in the insulation layer, acquire the frequency domain data of the excitation waveform corresponding to the S11 signal.
[0022] According to the preset acquisition cycle, the measurement operations of injecting the excitation source, acquiring the reflected signal, and obtaining the frequency domain data of the excitation waveform are repeated to obtain the frequency domain reflection characteristic data under each acquisition cycle.
[0023] Optionally, the frequency band of the excitation source is 10MHz to 100GHz.
[0024] After applying an excitation signal to the microwave antenna and acquiring the corresponding reflection signal to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period, the microwave guided wave monitoring method for corrosion under the pipeline insulation layer further includes the following steps.
[0025] A network analyzer is used to capture the frequency domain reflection characteristics data of the microwave antenna in a preset frequency band.
[0026] The frequency domain reflection characteristic data is reconstructed into a waveform reflecting the propagation and reflection behavior of electromagnetic waves in the time domain using the IFFT algorithm and window function processing method, which serves as the impact response waveform.
[0027] Optionally, the impact response waveform can be calculated using the following formula.
[0028] h(t) = IFFT(X(ω) / G(ω)).
[0029] Where h(t) represents the impulse response waveform, IFFT(·) is the inverse fast Fourier transform, X(ω) represents the frequency domain reflection characteristic data, and G(ω) represents the frequency domain data of the excitation waveform.
[0030] Optionally, when applying an excitation signal to the microwave antenna, a non-frequency domain scanning method is used to apply a pulse excitation signal to the microwave antenna. The pulse excitation signal is a microwave pulse signal with a frequency of 50MHz to 100GHz and a pulse width of 1ns to 100ns, and the response of the pulse excitation signal is obtained.
[0031] Optionally, the microwave guided wave monitoring method for corrosion under the pipe insulation layer further includes: after obtaining the time domain signal using the receiving circuit, it is subjected to hardware bandpass filtering, and then mixed with the signal of the same transmission frequency using a mixer, and then subjected to low-pass filtering processing using a low-pass filter to obtain the impact response waveform.
[0032] Optionally, the corrosion risk of the pipeline under test is assessed based on the impact response waveform to obtain a corrosion risk assessment result, which specifically includes the following steps.
[0033] Based on the impact response waveform, the changes in the impact response waveform are analyzed to identify impedance anomalies.
[0034] Based on the intensity, location, and duration of the reflected signal at the impedance anomaly point, the corrosion risk under the insulation layer of the pipeline under test is assessed, and the corrosion risk assessment result is obtained.
[0035] According to the specific embodiments provided in this application, this application has the following technical effects.
[0036] This application provides a microwave guided wave monitoring method for corrosion under pipeline insulation. By deploying corresponding microwave antennas in the monitored area of the pipeline under test, and by applying excitation signals and collecting reflected signals, the method determines the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under multiple monitoring periods. This allows for the calculation of the impact response waveform, and based on this waveform, the corrosion risk of the pipeline under test can be quickly and intuitively assessed. This method achieves large-scale and efficient monitoring without removing the insulation layer, enabling early identification of high-risk corrosion areas and improving the efficiency of monitoring corrosion under pipeline insulation. By deploying corresponding microwave antennas according to basic data such as pipeline diameter and insulation layer thickness, the method ensures that the number of microwave antennas matches the circumferential coverage requirements of the pipeline, and that the antenna length is adapted to the signal radiation / reception depth. This avoids insufficient signal coupling or monitoring blind spots caused by improper antenna parameters, laying a hardware foundation for subsequent accurate acquisition of reflected signals and ensuring the effectiveness of the monitoring link. By acquiring the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each cycle, a "benchmark-monitoring" comparison framework is constructed. This framework can amplify the signal differences between no water accumulation (uniform impedance, weak reflection) and with water accumulation (abrupt impedance, strong reflection), avoiding misjudgment based on single monitoring data. This ensures accurate capture of reflection signal changes caused by water accumulation in the insulation layer, providing reliable data support for subsequent identification of corrosion causes. Furthermore, this application calculates the impact response waveform based on both excitation waveform frequency domain data and frequency domain reflection characteristic data. This transforms the abstract frequency domain signal into time domain features including reflection intensity, location, and duration. Reflection intensity corresponds to the severity of water accumulation, reflection location identifies the water accumulation area, and duration reflects the stability of the water accumulation. This quantitative feature avoids subjective judgment errors, shifting corrosion risk assessment from qualitative to quantitative, thereby significantly improving the accuracy of judgment and achieving precise microwave guided wave monitoring of corrosion under the pipeline insulation layer. Attached Figure Description
[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0038] Figure 1This is a schematic flowchart of a microwave guided wave monitoring method for corrosion under pipe insulation layer provided in an embodiment of this application.
[0039] Figure 2 This is a schematic diagram illustrating the principle of a microwave guided wave monitoring method for corrosion under pipe insulation layer, provided in one embodiment of this application.
[0040] Figure 3 This is a schematic diagram of a microwave antenna acquiring signals according to an embodiment of this application. Detailed Implementation
[0041] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0042] The purpose of this application is to provide a microwave guided wave monitoring method for corrosion under pipeline insulation. Based on the coaxial waveguide structure formed by the metal lining and metal skin of the pipeline, the method utilizes the differences in the propagation characteristics of microwaves in media with different dielectric constants to monitor water accumulation and corrosion risk under the pipeline insulation layer. This enables large-scale monitoring of corrosion under the pipeline insulation layer, early identification of high-risk corrosion areas, and improved efficiency of monitoring corrosion under the pipeline insulation layer. It also solves the problem that existing technologies cannot monitor corrosion under the pipeline insulation layer on a large scale, efficiently, and at an early stage.
[0043] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0044] like Figure 1 As shown in the figure, this embodiment proposes a microwave guided wave monitoring method for corrosion under pipe insulation layer, which includes the following steps.
[0045] S1: Obtain basic data of the pipeline to be tested; the basic data includes the pipeline diameter and the insulation layer thickness.
[0046] S2: Based on the basic data of the pipeline under test, deploy corresponding microwave antennas in the monitoring area of the pipeline under test.
[0047] S3: Apply an excitation signal to the microwave antenna and collect the corresponding reflection signal to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period.
[0048] S4: Calculate the impact response waveform based on the frequency domain data of the excitation waveform and the frequency domain reflection characteristic data.
[0049] S5: Based on the impact response waveform, assess the corrosion risk of the pipeline under test and obtain the corrosion risk assessment result.
[0050] As an optional implementation, the pipe to be tested in step S1 includes, from the inside out, a metal liner, a non-metallic insulation material, and a metal outer skin. The metal liner is the metal pipe to be monitored. The non-metallic insulation material is wrapped around the outside of the metal liner. The metal outer skin is wrapped around the outside of the non-metallic insulation material, and the metal liner and the metal outer skin form a coaxial waveguide structure.
[0051] In this embodiment, the coaxial waveguide structure formed by the metal liner and the metal skin is fully utilized. After an excitation signal is applied to the microwave antenna, the excitation signal is radiated by the microwave antenna and then propagates in the coaxial waveguide structure in the form of microwave guided waves.
[0052] As an optional implementation, step S2 involves deploying a corresponding microwave antenna in the monitoring area of the pipe under test based on the basic data of the pipe under test, specifically including the following steps.
[0053] S21: Determine the number and length of microwave antennas based on the basic data of the pipe to be tested.
[0054] S22: Based on the number and length of the microwave antennas, the microwave antennas are evenly arranged along the circumference of the pipe to be tested, and one end of the microwave antenna is inserted into the insulation material of the inner insulation layer after passing through the outermost metal skin of the pipe to be tested.
[0055] As an optional implementation, in step S21, the number of microwave antennas is 4 to d / 10, and the length of the microwave antenna is greater than or equal to 1 / 2 of the thickness of the insulation layer, wherein the value of d is equal to the pipe diameter, and the unit of pipe diameter is mm.
[0056] For example, if the pipe diameter is 250mm, then the number of microwave antennas is 4 to 25.
[0057] As an optional implementation, step S3 applies an excitation signal to the microwave antenna and collects the corresponding reflection signal to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period, specifically including the following steps.
[0058] S31: Inject excitation sources of different frequencies into the microwave antenna, and use a directional coupler to transmit the excitation signal generated by the excitation source to the microwave antenna.
[0059] S32: Collect the reflected signal of the reflection channel of the directional coupler, and calculate the S11 signal of the microwave antenna at each frequency based on the reflected signal.
[0060] The S11 signal, also known as the port 1 reflection coefficient, is a key indicator in the scattering parameters (S-parameters) used to describe the reflection characteristics of single-port or multi-port networks. Its core definition is the ratio of the reflected wave to the incident wave at port 1 when the signal is incident from port 1 and other ports are connected to matched loads. Physically, the S11 signal directly reflects the impedance matching degree. When there is an impedance abrupt change in the monitoring system (such as a microwave antenna or coaxial waveguide structure) (e.g., water accumulation in the insulation layer causing a change in dielectric constant), the incident microwave signal cannot be fully transmitted; some energy is reflected, forming the S11 signal. This signal exists in complex form, containing amplitude and phase information. The amplitude reflects the strength of the reflected energy, and the phase reflects the phase difference between the reflected and incident waves. Both are used together to determine the location and severity of impedance anomalies, which is the source of its core value in corrosion monitoring under pipe insulation layers.
[0061] In this embodiment, when the monitoring system is initially installed and the insulation layer is free of water (in good condition), an excitation source in the 10MHz~100GHz frequency band is injected into the microwave antenna to collect S11 signals at each frequency, forming reference frequency domain data G(ω). At this time, due to the uniform and low dielectric constant of the insulation material, and the consistent impedance of the coaxial waveguide formed by the metal lining and the metal skin, the microwave signal has no obvious reflection, and the amplitude of the S11 signal is extremely small (ideally close to 0, corresponding to a return loss ≤-20dB, i.e., a reflection power ≤1%). This reference data serves as the comparison standard for subsequent judgment of "whether water accumulation exists," directly determining the accuracy of subsequent monitoring. By capturing the microwave reflection characteristics through the S11 signal, non-invasive monitoring is directly achieved, avoiding production interruptions and cost waste caused by removing the insulation layer. When a small amount of water accumulates in the insulation layer (before it causes significant corrosion), the amplitude of the S11 signal has already changed, providing an early warning of CUI risk 1 to 3 months in advance, much earlier than traditional methods (which require corrosion to develop to a certain extent before detection). The impact response waveform derived from the S11 signal can accurately calculate the location of water accumulation (error ≤ 1m), providing a clear target for subsequent maintenance and significantly reducing maintenance workload (traditional methods require section-by-section inspection). Therefore, the S11 signal is the core technology of microwave guided wave monitoring for corrosion under pipeline insulation. Its application throughout the entire process of "benchmark establishment - periodic monitoring - data processing - risk assessment" directly determines the accuracy, efficiency, and engineering value of the monitoring.
[0062] S33: Obtain the frequency domain data of the excitation waveform corresponding to the S11 signal when there is no water accumulation in the insulation layer.
[0063] S34: According to the preset acquisition cycle, repeat the measurement operations of injecting the excitation source, acquiring the reflection signal, and obtaining the frequency domain data of the excitation waveform to obtain the frequency domain reflection characteristic data under each acquisition cycle.
[0064] As an optional implementation, in step S31, the frequency band of the excitation source is 10MHz to 100GHz.
[0065] As an optional implementation, when injecting the excitation source in step S31, the excitation signals of each microwave frequency point are collected sequentially in order from low to high frequency.
[0066] As an optional implementation, after applying an excitation signal to the microwave antenna and acquiring the corresponding reflection signal to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period, the microwave guided wave monitoring method for corrosion under the pipe insulation layer further includes the following steps.
[0067] S35: Use a network analyzer to capture the frequency domain reflection characteristics data of the microwave antenna in the preset frequency band.
[0068] S36: Using the IFFT algorithm and window function processing method, the frequency domain reflection characteristic data is reconstructed into a waveform that reflects the propagation and reflection behavior of electromagnetic waves in the time domain, i.e., the impact response waveform.
[0069] As an optional implementation, in step S4, the impact response waveform is calculated using the following formula.
[0070] h(t) = IFFT(X(ω) / G(ω)).
[0071] Where h(t) represents the impulse response waveform, IFFT(·) is the inverse fast Fourier transform, X(ω) represents the frequency domain reflection characteristic data, and G(ω) represents the frequency domain data of the excitation waveform.
[0072] As an optional implementation, step S5 assesses the corrosion risk of the pipeline under test based on the impact response waveform to obtain the corrosion risk assessment result, specifically including the following steps.
[0073] S51: Based on the impact response waveform, analyze the changes in the impact response waveform and identify impedance anomalies.
[0074] S52: Based on the intensity, location, and duration of the reflected signal at the impedance anomaly point, assess the corrosion risk under the insulation layer of the pipeline under test and obtain the corrosion risk assessment result.
[0075] In this embodiment, the corrosion risk assessment results include low risk, medium risk, and high risk, and the criteria for determining the corrosion risk assessment results are shown in Table 1.
[0076] Table 1. Criteria for Determining Corrosion Risk Assessment Results
[0077] In this embodiment, corresponding maintenance strategies were formulated for areas with different corrosion risk levels, as detailed below.
[0078] (1) Low-risk areas: No maintenance is required, avoiding the cost waste caused by blind disassembly and inspection.
[0079] (2) Medium-risk areas: Only the monitoring cycle needs to be shortened for tracking, and no comprehensive overhaul is required.
[0080] (3) High-risk areas: Clearly define the specific maintenance location (based on the location of reflected signals). Maintenance personnel can accurately remove the insulation layer in this area without having to inspect the entire pipeline insulation layer, which greatly reduces the workload of maintenance and reduces the impact on normal production (such as avoiding the loss of pipeline heat / cold due to large-area disassembly).
[0081] The monitoring principle of the microwave guided wave method for monitoring corrosion under the insulation layer of pipelines in this application is as follows: The pipeline under test includes a metal lining, non-metallic insulation material, and a metal outer skin. The metal lining is the metal pipeline to be monitored, the non-metallic insulation material wraps around the outside of the metal lining, and the metal outer skin wraps around the outside of the non-metallic insulation material, with the metal lining and metal outer skin forming a coaxial waveguide structure. After being radiated by the microwave antenna, the microwave signal propagates in the form of microwave guided waves within the coaxial waveguide structure formed by the metal lining and metal outer skin. When there is no water accumulation in the non-metallic insulation material, the dielectric constant of the non-metallic insulation material is uniform and low, and the microwave signal has no obvious reflection. When there is local water accumulation in the insulation material, since the dielectric constant of water is much greater than that of the insulation material, it will cause a significant change in local impedance within the coaxial waveguide, forming a significant reflecting surface. At this time, an abnormal reflection signal will be generated on the impact response waveform, and the microwave antenna can collect this reflection signal. Based on the intensity (signal amplitude), location (calculated from the signal propagation time of the corresponding pipeline), and duration (the abnormal signal appears in multiple consecutive cycles) of the abnormal reflected signal, the corrosion risk under the pipeline insulation layer can be assessed: when a high-intensity reflected signal exists at the same location for a long time, it indicates that the area has long-term water accumulation and has a high CUI risk, thus enabling microwave guided wave monitoring of corrosion under the pipeline insulation layer.
[0082] like Figure 2 As shown, the metal liner is the metal pipe that needs to be monitored. Figure 2 The orange part in the middle), in order to reduce the loss of heat (or cold) in the pipe, is usually wrapped with non-metallic insulation material, and then covered with a metal outer skin on the outermost side. Figure 2The blue portion (in the image) encases and secures the non-metallic insulation material. In this case, the metal outer skin and metal inner lining will form a coaxial waveguide structure.
[0083] In this embodiment, a microwave antenna is inserted into the metal outer skin and the metal inner lining, and microwaves are radiated ( Figure 2 (As shown in red in the image), the specific implementation method is as follows: Figure 3 As shown, microwaves will propagate as microwave guided waves in the coaxial waveguide structure formed by the metal outer skin and metal lining; due to the low dielectric constant of the insulation material and its relatively uniform distribution within the coaxial waveguide, microwaves will propagate along the coaxial waveguide without significant reflection.
[0084] Localized water accumulation in insulation is a major factor contributing to CUI corrosion. When water accumulates in localized insulation, the local impedance increases significantly due to the high dielectric constant of water, which in turn forms a distinct reflecting surface in the coaxial waveguide, reflecting microwaves.
[0085] microwave signals such as Figure 3 As shown, Figure 3 The horizontal axis represents time, corresponding to the distance the microwave guided wave propagates; the vertical axis represents the microwave signal amplitude. From Figure 3 As can be seen directly, when the insulation layer of the pipe under test contains water, the reflected signal of the microwave guided wave at the water-containing area will fluctuate significantly.
[0086] The frequency domain reflection characteristics data X(ω) of a microwave antenna in a specific frequency band were captured using a network analyzer. Then, IFFT algorithms and window functions were applied to process this data, reconstructing the waveform x(t) reflecting the propagation and reflection behavior of electromagnetic waves in the time domain. Furthermore, since the reflection behavior waveform is the convolution of the impulse response waveform h(t) and the excitation waveform g(t) of the entire waveguide (x(t) = g(t)),... In the frequency domain, h(t) is represented by X(ω) = G(ω) × H(ω)), where G(ω) and H(ω) represent the frequency domain data corresponding to the excitation waveform and the waveguide impulse response waveform, respectively. The excitation waveform is the result of the combined effect of the bandwidth window function and the microwave antenna, acquired by the network analyzer. Before the overall analysis, the frequency domain data G(ω) of the excitation waveform can be obtained through actual measurement; therefore, h(t) = IFFT(X(ω) / G(ω)).
[0087] The impulse response waveform here includes both the pulsed emission signal and the reflected signal. It is important to note that it is best to start sampling from a lower microwave frequency to ensure a longer response time and increase the monitoring distance.
[0088] Step 1: Select the number of microwave antennas to install based on the pipe diameter. When the pipe diameter is d (in mm), use 4 to d / 10 microwave antennas. The antenna length should not be less than half the thickness of the insulation layer. Distribute the antennas evenly along the circumference of the pipe, through the outer skin (i.e., Figure 2 The outermost metal layer is inserted into the insulation material.
[0089] Step 2: By injecting excitation sources of different frequencies into the antenna, the signals are transmitted to the antenna through a directional coupler. The reflected signals are collected in the reflection channel of the directional coupler, and the antenna S11 signal at each frequency is calculated. The frequency domain data of the excitation waveform of the S11 signal obtained when the insulation layer is in good condition and free of water accumulation after the initial installation is completed is G(ω).
[0090] The network analyzer is connected to a directional coupler, which in turn is connected to a microwave antenna. The microwave antenna is inserted into the insulation layer through a hole in the outer metal layer. At the same time, the hole in the outer metal layer is coated with a non-conductive sealing material (such as epoxy resin glue) to prevent water from seeping in through the hole.
[0091] Step 3: Periodically measure the antenna's S11 data using the method in Step 2, and denote the obtained frequency domain reflection characteristic data as X(ω). Further calculate the impulse response waveform h(t) = IFFT(X(ω) / G(ω)). The acquisition period is generally 1 hour to 90 days.
[0092] Step 4: By observing the changes in the impact response waveform h(t), it is possible to analyze whether there are any impedance anomalies. When the moisture content in the insulation material is abnormal, the change in the impact response waveform h(t) is as follows: Figure 3 As shown.
[0093] Step 5: The excitation source frequency described in Step 2 should ideally be selected from a lower microwave frequency (e.g., microwave frequency 100MHz~8GHz) to ensure a longer response time and increase the monitoring distance. The typical frequency band is 10MHz~100GHz.
[0094] Step 6: Assess the corrosion risk based on the changes in the impact response waveform h(t) from Step 4, including the intensity and location of the reflection, and the duration of the continuous reflection signal. If a relatively high intensity reflection persists at the same location for an extended period (e.g., more than 10 days), it indicates a potential long-term risk of water accumulation and corrosion at that location.
[0095] Taking the monitoring scenario of a steam pipeline in a petrochemical enterprise as an example, the microwave guided wave monitoring method for corrosion under the pipeline insulation layer proposed in this application is implemented, including the following steps.
[0096] (1) Pipeline parameters and antenna layout: The diameter of the steam pipeline to be monitored is d=500mm, and the thickness of the insulation layer is 100mm. The number of microwave antennas is calculated according to the formula: 500 / 10=50, 500 / 300≈1.67, and finally 10 microwave antennas are selected. The antenna length is designed to be 60mm (greater than 1 / 2 of the insulation layer thickness, i.e., 50mm). The 10 antennas are evenly distributed along the circumference of the pipeline with equal spacing. They are inserted into the rock wool insulation material through the metal outer skin of the pipeline to ensure that the antennas and the metal inner lining maintain a reasonable distance.
[0097] (2) Reference data acquisition: A network analyzer is used to inject an excitation source in the 10MHz to 50GHz frequency band into the antenna, and the acquisition starts from the low frequency point of 10MHz. The signal is transmitted through a directional coupler, and the S11 signal at each frequency is acquired in the reflection channel. At this time, there is no water accumulation in the pipe insulation layer. The frequency domain data of this state, i.e., the excitation waveform frequency domain data G(ω), is recorded as the reference.
[0098] (3) Periodic monitoring and data processing: The acquisition period is set to 7 days. The above measurement operation is repeated every 7 days to collect the frequency domain reflection characteristic data X(ω) for each period. The frequency domain reflection characteristic data X(ω) and the excitation waveform frequency domain data G(ω) are processed using the IFFT algorithm and Hanning window function to calculate the impact response waveform h(t) for each period.
[0099] Risk assessment results: During monitoring on day 21, a significant reflection signal was observed in the impact response waveform h(t) at a distance of 30m from the antenna deployment point, and the signal strength remained stable for three cycles (21 days). Based on the location and duration of the reflection signal, it was determined that there was long-term water accumulation in the insulation layer at this 30m location, posing a high risk of CUI (Continuous Ingress and Regression). Subsequent maintenance personnel only removed and inspected the insulation layer in this area, confirming the presence of water inside the insulation layer and initial corrosion on the outer wall of the pipe. Anti-corrosion treatment was promptly implemented, preventing further corrosion.
[0100] As an optional implementation method, in addition to the aforementioned frequency sweeping method, a non-frequency domain scanning method is also provided. This non-frequency domain scanning method refers to applying a microwave pulse (with a fixed frequency, which can be 50MHz~100GHz) with a pulse width of 1ns~100ns.
[0101] For pulse-excited signals, analysis method 1 is as follows: First, the time-domain signal H0(t) is obtained and bandpass filtered to extract the amplitude H1(t) of the transmitted pulse frequency component. Then, envelope detection is performed on H1(t) to obtain the impulse response waveform h(t). Finally, the humidity distribution is analyzed based on the impulse response waveform h(t).
[0102] For pulse-excited signals, analysis method 2 is as follows: First, the time-domain signal H0(t) is obtained, and then continuous wavelet transform (CWT) is performed on H0(t). The magnitude value of the scale corresponding to the transmitted pulse frequency is extracted as the envelope to obtain the impact response waveform h(t). Finally, the humidity distribution is analyzed based on the impact response waveform h(t).
[0103] At this time, when applying an excitation signal to the microwave antenna, a non-frequency domain scanning method is used to apply a pulse excitation signal to the microwave antenna. The pulse excitation signal is a microwave pulse signal with a frequency of 50MHz~100GHz and a pulse width of 1ns~100ns, and the response of the pulse excitation signal is acquired. Then, after acquiring the time domain signal using the receiving circuit, it is subjected to hardware bandpass filtering, mixed with a signal of the same transmission frequency using a mixer, and then low-pass filtered to obtain the impulse response waveform h(t). This is another non-frequency domain scanning method for obtaining the impulse response waveform h(t).
[0104] Taking the monitoring scenario of a cold water pipeline in a power company as an example, the microwave guided wave monitoring method for corrosion under the pipeline insulation layer proposed in this application is implemented, including the following steps.
[0105] (1) Pipeline parameters and antenna layout: The diameter of the cold water pipeline is d=300mm and the thickness of the insulation layer is 80mm. Calculate the number of antennas: 300 / 10=30, 300 / 300=1. Select 5 microwave antennas with a length of 50mm (greater than 1 / 2 of the insulation layer thickness, i.e. 40mm). Insert them evenly into the polyurethane insulation material along the circumference of the pipeline.
[0106] (2) Reference data acquisition: Inject an excitation source in the 10MHz to 30GHz frequency band and acquire the frequency domain data G(ω) of the excitation waveform corresponding to the S11 signal when there is no water accumulation in the insulation layer.
[0107] (3) Periodic monitoring and data processing: The acquisition period is set to 15 days. The frequency domain reflection characteristic data X(ω) and the impact response waveform h(t) of each period are collected and processed.
[0108] (4) Risk assessment results: On the 45th day of monitoring, a weak reflection signal appeared in the impact response waveform h(t) at 15m. On the 60th day (the next cycle), the signal intensity increased. It was judged that water accumulation might begin in the area. Personnel were promptly arranged to inspect and found that the seal at the interface of the insulation layer had failed, causing rainwater to seep in. After cleaning up the water and repairing the seal, the reflection signal disappeared in subsequent monitoring, effectively preventing the occurrence of CUI.
[0109] This application fully considers that the main cause of corrosion under the insulation layer is the significantly increased moisture content of the insulation material, leading to corrosion of the outer wall of the metal pipe caused by water. Based on this, this application uses the metal pipe and the outer skin structure of the insulation layer as a coaxial waveguide. After microwaves are introduced, they will propagate along the pipe. When water is present in a localized area of the insulation layer, the impedance within the waveguide changes abruptly, resulting in partial reflection. Measuring the intensity and location of the reflected signal can determine the area where corrosion under the insulation layer may occur. By utilizing the microwave guided wave method for monitoring corrosion under the insulation layer of metal pipes, large-scale monitoring of corrosion under the insulation layer can be achieved. This will help identify specific areas for later inspection and maintenance, facilitating early identification of corrosion-prone areas, significantly reducing maintenance workload, and improving the targeting of inspections.
[0110] The microwave guided wave monitoring method for corrosion under pipeline insulation layer proposed in this application has the following advantages.
[0111] (1) Wide-range monitoring: This application utilizes the characteristic of microwaves propagating along the pipeline in the coaxial waveguide formed by the metal lining and the metal skin, eliminating the need to remove the insulation layer point by point, and enabling wide-range continuous monitoring of long-distance pipelines, thus solving the problem of limited monitoring range of traditional methods. This advantage stems from the technical design of "the metal lining and the metal skin forming a coaxial waveguide structure, with microwaves propagating along the pipeline in the form of guided waves," and the long-distance propagation capability of microwaves ensures the monitoring coverage.
[0112] (2) Early Risk Identification: When a small amount of water accumulates in the insulation layer (the core cause of CUI), the high dielectric constant of water will lead to a significant change in the microwave reflection signal. By analyzing the impact response waveform h(t), the water accumulation area can be identified early, thereby providing an early warning of CUI risk and preventing corrosion from developing into equipment failure. This advantage relies on the technical means of "processing frequency domain data through the IFFT algorithm to obtain the time domain impact response waveform and capture impedance anomalies".
[0113] (3) Reduced maintenance costs: This application can accurately locate areas with CUI risks, providing clear target areas for subsequent inspection and maintenance. It eliminates the need to remove and inspect the insulation layer of the entire pipeline, significantly reducing the workload of maintenance and lowering the manpower and material costs during the maintenance process, while also minimizing the impact on normal production. This advantage is due to the technical design of "determining the risk area based on the location of reflected signals," which enables targeted maintenance.
[0114] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0115] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.
Claims
1. A microwave guided wave monitoring method for corrosion under pipe insulation layer, characterized in that, The microwave guided wave monitoring method for corrosion under the pipeline insulation layer includes: Obtain basic data of the pipeline to be tested; the basic data includes the pipeline diameter and the insulation layer thickness. Based on the basic data of the pipeline under test, a corresponding microwave antenna is deployed in the monitoring area of the pipeline under test; An excitation signal is applied to the microwave antenna, and the corresponding reflection signal is collected to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period. The impact response waveform is calculated based on the frequency domain data of the excitation waveform and the frequency domain reflection characteristic data. Based on the impact response waveform, the corrosion risk of the pipeline under test is assessed, and the corrosion risk assessment result is obtained.
2. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 1, characterized in that, The pipeline under test includes a metal lining, a non-metallic insulation material, and a metal outer skin. The metal lining is the metal pipeline to be monitored. The non-metallic insulation material is wrapped around the outside of the metal lining. The metal outer skin is wrapped around the outside of the non-metallic insulation material, and the metal lining and the metal outer skin form a coaxial waveguide structure. After an excitation signal is applied to the microwave antenna, the excitation signal is radiated by the microwave antenna and then propagates in the coaxial waveguide structure in the form of a microwave waveguide.
3. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 1, characterized in that, Based on the basic data of the pipeline under test, a corresponding microwave antenna is deployed in the monitoring area of the pipeline under test, specifically including: Based on the basic data of the pipeline under test, determine the number and length of microwave antennas; Based on the number and length of the microwave antennas, the microwave antennas are evenly arranged along the circumference of the pipe to be tested, and one end of the microwave antenna is inserted into the insulation material of the inner insulation layer after passing through the outermost metal skin of the pipe to be tested.
4. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 3, characterized in that, The number of microwave antennas is 4 to d / 10, and the length of the microwave antenna is greater than or equal to 1 / 2 of the thickness of the insulation layer, wherein the value of d is equal to the diameter of the pipe, and the unit is mm.
5. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 1, characterized in that, An excitation signal is applied to the microwave antenna, and the corresponding reflected signal is acquired to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period, specifically including: Different frequency excitation sources are injected into the microwave antenna, and a directional coupler is used to transmit the excitation signal generated by the excitation source to the microwave antenna; The reflected signal of the reflection channel of the directional coupler is collected, and the S11 signal of the microwave antenna at each frequency is calculated based on the reflected signal. Under the condition that there is no water accumulation in the insulation layer, the frequency domain data of the excitation waveform corresponding to the S11 signal is obtained; According to the preset acquisition cycle, the measurement operations of injecting the excitation source, acquiring the reflected signal, and obtaining the frequency domain data of the excitation waveform are repeated to obtain the frequency domain reflection characteristic data under each acquisition cycle.
6. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 5, characterized in that, The frequency band of the excitation source is 10MHz to 100GHz; After applying an excitation signal to the microwave antenna and acquiring the corresponding reflected signal to obtain the frequency domain data of the excitation waveform when there is no water accumulation in the insulation layer and the frequency domain reflection characteristic data under each monitoring period, the microwave guided wave monitoring method for corrosion under the pipe insulation layer further includes: A network analyzer is used to capture the frequency domain reflection characteristics data of the microwave antenna in a preset frequency band; The frequency domain reflection characteristic data is reconstructed into a waveform reflecting the propagation and reflection behavior of electromagnetic waves in the time domain using the IFFT algorithm and window function processing method, which serves as the impact response waveform.
7. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 6, characterized in that, The impact response waveform is calculated using the following formula: h(t) = IFFT(X(ω) / G(ω)); Where h(t) represents the impulse response waveform, IFFT(·) is the inverse fast Fourier transform, X(ω) represents the frequency domain reflection characteristic data, and G(ω) represents the frequency domain data of the excitation waveform.
8. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 1, characterized in that, When applying an excitation signal to the microwave antenna, a pulse excitation signal is applied to the microwave antenna using a non-frequency domain scanning method. The pulse excitation signal is a microwave pulse signal with a frequency of 50MHz to 100GHz and a pulse width of 1ns to 100ns, and the response of the pulse excitation signal is obtained.
9. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 8, characterized in that, The microwave guided wave monitoring method for corrosion under the pipe insulation layer further includes: after obtaining the time domain signal using the receiving circuit, it is filtered by hardware bandpass filtering, mixed with the same transmission frequency signal using a mixer, and then low-pass filtered to obtain the impact response waveform.
10. The microwave guided wave monitoring method for corrosion under pipeline insulation layer according to claim 1, characterized in that, Based on the impact response waveform, the corrosion risk of the pipeline under test is assessed to obtain the corrosion risk assessment result, which specifically includes: Based on the impact response waveform, analyze the changes in the impact response waveform to identify impedance anomalies; Based on the intensity, location, and duration of the reflected signal at the impedance anomaly point, the corrosion risk under the insulation layer of the pipeline under test is assessed, and the corrosion risk assessment result is obtained.