An apparatus and method for detecting external cracks in a pipe

Abstract

The application discloses a pipeline outer crack detection device and method, and relates to the field of crack detection. In the device, a current injection electrode and a current feedback electrode are arranged at two ends of a target region on the outer surface of a pipeline. An excitation signal source is connected with the current injection electrode and the current feedback electrode, and provides a high-frequency alternating excitation current for the target region. A measuring electrode pair is arranged in the target region. The measuring electrode pair comprises two electrodes arranged along the propagation direction of the high-frequency alternating excitation current. A processor is connected with the measuring electrode pair, and is used for sampling the potential drop between the measuring electrode pair and temperature normalization. According to the temperature-normalized potential drop signal and a reference signal, whether the target region has a crack is determined. The frequency of the reference signal is the same as that of the high-frequency alternating excitation current, and the voltage amplitude difference between the measuring electrode pair is within a preset range. The application can more simply realize the detection of outer cracks.

Description

Technical Field

[0001] This application relates to the field of crack detection, and in particular to a device and method for detecting external cracks in pipelines. Background Technology

[0002] Currently, the Field Signature Method (FSM) is mainly used for internal corrosion detection in pipelines, but it is ineffective for detecting external cracks. Moreover, during the detection process, a large number of stud electrodes are usually welded onto the steel pipe, and a reference plate is used to partially eliminate the influence of factors such as temperature on the sampling results, which brings certain difficulties to the construction. Summary of the Invention

[0003] The purpose of this application is to provide a device and method for detecting external cracks in pipelines, which can more easily detect external cracks.

[0004] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a pipe external crack detection device comprising: The system includes a processor, an excitation signal source, a current injection electrode, a current feedback electrode, and a measurement electrode pair. The current injection electrode and the current feedback electrode are respectively disposed at both ends of the target area on the outer surface of the pipe. The excitation signal source is connected to the current injection electrode and the current feedback electrode to provide a high-frequency AC excitation current to the target area. The measurement electrode pair is disposed within the target area. The measurement electrode pair includes two electrodes arranged along the propagation direction of the high-frequency AC excitation current.

[0005] The processor is connected to the measuring electrode pair and is used to sample and normalize the potential drop signal between the measuring electrode pair. Based on the temperature-normalized potential drop signal and the reference signal, it determines whether there is a crack in the target area. The frequency of the reference signal is the same as the frequency of the high-frequency AC excitation current, and the voltage amplitude difference between the voltage amplitude and the measuring electrode pair is within a preset range.

[0006] Secondly, this application provides a method for detecting external cracks in pipelines, applied to the aforementioned pipeline external crack detection device. The method specifically includes: The current injection electrode and the current feedback electrode are respectively placed at both ends of the target area on the outer surface of the pipe. The measuring electrode pair is placed in the target area. The excitation signal source is connected to the current injection electrode and the current feedback electrode, and the potential drop signal between the measuring electrode pair is sampled.

[0007] The sampled potential drop signal is normalized by temperature, and the presence of cracks in the target area is determined based on the normalized potential drop signal and the reference signal. The frequency of the reference signal is the same as the frequency of the high-frequency AC excitation current, and the voltage amplitude difference between the voltage amplitude and the voltage amplitude between the measuring electrode pair is within a preset range.

[0008] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides a device and method for detecting external cracks in pipelines. The principle of FSM technology for detecting internal corrosion in steel pipes is as follows: a DC or low-frequency AC current is applied to the pipeline section under test, and the voltage drop between electrode pairs near the internal corrosion defect is "sensed" using the four-point method to determine the presence or absence of internal corrosion. DC and low-frequency AC excitation are effective for detecting internal corrosion, but they are very difficult to detect fine external cracks. This application, based on the skin effect, uses a high-frequency AC excitation signal source to increase the equivalent resistance between the measuring electrode pairs, thereby obtaining a measurement signal with a more obvious amplitude change, which can solve this problem.

[0009] Conventional FSM methods require welding numerous stud electrodes onto steel pipes and using reference plates to partially eliminate the influence of factors such as temperature on the sampling results, which presents certain difficulties in construction. This application utilizes a reference signal with the same frequency as the high-frequency AC excitation current and an amplitude comparable to the voltage amplitude between the measuring electrode pairs to replace the output signal of the reference plate commonly used in FSM. This simplifies system installation and debugging. Furthermore, it performs temperature normalization processing on the potential drop signal between the measuring electrode pairs to eliminate the influence of factors such as temperature on the sampling results. Attached Figure Description

[0010] 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.

[0011] Figure 1 This is a schematic diagram of the structure of a pipe external crack detection device provided in one embodiment of this application.

[0012] Figure 2 The schematic diagram of the external crack detection principle provided in this application.

[0013] Figure 3 This is a schematic diagram illustrating the principle of the four-point method for detecting external cracks.

[0014] Figure 4 Install the top view for the reference board.

[0015] Figure 5Install the side view for the reference board. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] In one exemplary embodiment, such as Figure 1 As shown, a pipe external crack detection device is provided, comprising: a processor, an excitation signal source, a current injection electrode 1, a current feedback electrode 2, and a measuring electrode pair 3; the current injection electrode 1 and the current feedback electrode 2 are respectively disposed at both ends of a target area on the outer surface of the pipe; the excitation signal source is connected to the current injection electrode 1 and the current feedback electrode 2 to provide a high-frequency AC excitation current to the target area; the measuring electrode pair 3 is disposed within the target area; the measuring electrode pair 3 includes two electrodes arranged along the propagation direction of the high-frequency AC excitation current. The frequency of the high-frequency AC excitation current is adjustable in the range of 200Hz-10kHz.

[0019] The processor is connected to the measuring electrode pair 3 to sample and normalize the potential drop between the measuring electrode pair 3. Based on the temperature-normalized potential drop signal and the reference signal, it determines whether there is a crack in the target area. The frequency of the reference signal is the same as the frequency of the high-frequency AC excitation current, and the voltage amplitude difference between the voltage amplitude and the voltage amplitude between the measuring electrode pair 3 is within a preset range. Specifically, the difference can be within 10%.

[0020] In practical applications, the pipe external crack detection device also includes a signal processing circuit, which is connected to the measuring electrode pair 3 and the processor, and is used to amplify and filter the potential drop signal between the measuring electrode pair 3.

[0021] In practical applications, the pipeline is an oil and gas pipeline.

[0022] In practical applications, the two electrodes in the measuring electrode pair 3, the current injection electrode 1, and the current feedback electrode 2 are all spring electrodes. Specifically, these electrodes are directly pressed onto the cleaned pipe surface.

[0023] This application also provides a method for detecting external cracks in a pipe applied to the above-mentioned device. The method includes: setting a current injection electrode 1 and a current feedback electrode 2 at both ends of a target area on the outer surface of the pipe, setting a pair of measuring electrodes 3 in the target area, connecting an excitation signal source to the current injection electrode 1 and the current feedback electrode 2, and sampling the potential drop signal between the pair of measuring electrodes 3.

[0024] The sampled potential drop signal is normalized by temperature, and the presence of cracks in the target area is determined based on the normalized potential drop signal and the reference signal. The frequency of the reference signal is the same as the frequency of the high-frequency AC excitation current, and the voltage amplitude difference between the voltage amplitude of the measuring electrode pair 3 is within a preset range.

[0025] In another exemplary embodiment of this application, the frequency of the excitation signal source is determined using frequency sweeping technology. Given a pipe, the principle for detecting an external crack in a section can be described as follows: Figure 2 As shown: An alternating current is injected into both ends of the pipe through current electrode 4, and a pair of potential drop electrodes 5 are arranged on both sides of the crack on the pipe surface. Due to the presence of the crack, the current between the two potential drop electrodes 5 can only flow around the bottom or periphery of the crack, increasing the equivalent resistance between the two potential drop electrodes 5, thus increasing the potential drop. If DC excitation or low-frequency AC excitation is used, the current is uniformly distributed within the pipe cross-section, and the increase in potential drop caused by the crack is only linearly related to the ratio of the crack area to the area of ​​the entire pipe cross-section. This ratio is usually very small, so the measured potential drop will be very small, and the signal strength and signal-to-noise ratio will be insufficient, making detection difficult. If high-frequency AC current is used for excitation, due to the skin effect, the current will concentrate in a thin layer on the outer surface of the pipe. At this time, its equivalent conductive cross-sectional area will be greatly reduced, and the area ratio of the crack will be correspondingly increased, thus greatly increasing the potential drop at both ends of the crack, making crack detection easier. Theoretically, the higher the frequency of the excitation current, the more obvious the skin effect, and the more obvious the potential drop on both sides of the crack. However, as the frequency increases, the permeability of the pipe material decreases, which reduces the skin effect. Therefore, a balance needs to be found between frequency and permeability to maximize the overall potential drop signal. This is the fundamental reason why this application uses frequency sweeping technology to find the most suitable frequency.

[0026] FSM (Fixed-Screen Detector) uses alternating current to detect external cracks in pipes. The most basic principle is the skin effect of alternating current. This means that when alternating current passes through a conductor, as the frequency increases, the current becomes increasingly concentrated on the surface of the conductor, rather than being uniformly distributed throughout the conductor like direct current or low-frequency current. In simpler terms, it tends to concentrate on the conductor's "skin," hence the name "skin effect." Under the skin effect, the current density is higher closer to the conductor surface and lower further into the conductor. When the amplitude of the alternating current decreases to approximately 36.8% of its initial value from the conductor surface into the conductor, this vertical depth is called the "skin depth."

[0027] The formula for calculating skin depth is: .

[0028] in: δ To reach skin depth, ω ω is the angular frequency, ω = 2π f , f It is the frequency (Hz) of alternating current. μ Let be the magnetic permeability of the conductor. σ Let be the electrical conductivity of the conductor.

[0029] As the formula shows, the skin depth is inversely proportional to the square root of the alternating current frequency. That is, the higher the frequency, the smaller the skin depth. Typically, crack detection using the Alternating Current Potential Drop (ACPD) method, also known as the four-point method, works as follows: Figure 3 As shown, Figure 3In the diagram, the dashed box represents the conductor being monitored, namely the oil and gas pipeline described in this application. The two large solid black circles at the top and bottom are the current injection terminal 6 and the current feedback terminal 7, used to provide AC excitation current to a section of the steel pipe. The two small solid black circles in the middle are electrode pairs used to measure the AC voltage drop. The curve between the electrode pairs represents cracks, and the AC voltage amplitude between them is proportional to the current flowing through them and the resistance between them. Generally, the current injected into the pipeline section is a fixed value, while the equivalent resistance between the electrode pairs is related to the skin depth. The smaller the skin depth, the larger the equivalent resistance, and the larger the AC voltage drop between the electrodes. The surface cracks between the electrode pairs force the AC current to detour, which is equivalent to increasing the equivalent resistance between the electrode pairs, thereby exacerbating the AC voltage drop. In engineering practice, multiple measuring electrode pairs (e.g., 7 pairs) are arranged along the axial direction. Obviously, under normal circumstances, the AC voltage drop between electrode pairs with cracks will be greater than that between electrode pairs without cracks. Obviously, the higher the alternating current frequency, the smaller the skin depth, the deeper the crack, and the more sensitive the crack detection. Therefore, theoretically, increasing the alternating current frequency makes crack detection easier. However, this is not the case in reality. For ferromagnetic materials like oil and gas pipelines, the permeability decreases with increasing frequency, leading to an increase in skin depth. This counteracts the effect of higher frequency, creating a contradiction. Furthermore, the materials of main pipelines and branch pipelines typically differ, resulting in varying permeabilities. This necessitates striking a balance between alternating current frequency and permeability to maximize the crack response; this frequency becomes the "optimal frequency" for measuring pipeline cracks. This optimal frequency can be obtained through complex theoretical calculations for various pipe materials, or it can be determined experimentally. In this application, a "frequency sweeping" technique is used to find this optimal frequency. Various frequency points from 200Hz to 10kHz are set, and by applying multiple frequencies to the steel pipe section, the frequency point that elicits the most severe crack response under comprehensive conditions is found and then fixed as the AC frequency for actual crack detection of the steel pipe in engineering applications. In another exemplary embodiment of this application, the frequency of the excitation signal source is determined using the frequency sweeping technique as follows: Within a preset frequency range, the potential drop between measuring electrode pair 3 on the sample pipeline is measured at various excitation AC frequencies to obtain a potential drop dataset. A crack exists on the sample pipeline; the first electrode of measuring electrode pair 3 is positioned on one side of the crack, and the second electrode on the other side. Based on the potential drop dataset, the excitation AC frequency that elicits the most intense crack response is determined as the optimal excitation AC frequency, which serves as the frequency of the excitation signal source. This addresses the problems of insufficient signal strength and low signal-to-noise ratio during external crack detection, making external crack detection easier. The most intense crack response is manifested by the largest output voltage amplitude between measuring electrode pairs crossing the same crack.

[0030] In another exemplary embodiment of this application, the sampled potential drop signal is temperature normalized. Specifically, based on the sampled potential drop signal, the current temperature of the pipe, and the temperature compensation model, the potential drop between the measuring electrode pair 3 at the target temperature is obtained, resulting in a temperature-normalized potential drop signal. Although this application uses a stable signal source (reference signal) as the initial signal for system acquisition, avoiding the troubles caused by reference board installation and debugging, the influence of temperature cannot be completely eliminated. Previously, with a reference board, the influence of temperature could be reduced to some extent (but not completely eliminated). Now, without a reference board, the influence of temperature is more pronounced. This is reflected in the different resistivity of the steel pipe at different temperatures, and this temperature-dependent resistivity change process is quite significant. This causes the amplitude of the acquired signal to increase with increasing temperature (the higher the temperature of the steel pipe, the greater the resistivity), which in turn makes the data acquired at different temperatures incomparable. To make comparisons, only data with relatively close temperatures can be selected. To ensure the comparability of data collected at all temperatures, the influence of pipe temperature must be completely eliminated. This application, with a sufficiently large amount of collected data, utilizes a linear regression model from machine learning to learn from the temperature and sampling data, deriving a suitable model. This model is then used to fit and normalize all subsequent sampling data, normalizing the data at all temperatures to a specific temperature (e.g., 20°C), thus ensuring comparability and eliminating the influence of temperature on pipe resistivity. Theoretically, as long as the equipment design and manufacturing process remain unchanged (i.e., the equipment batch is consistent), this model can be used for steel pipes of the same material without needing to build a new model for other steel pipes.

[0031] In another exemplary embodiment of this application, the process for determining the temperature compensation model is as follows: At the optimal excitation AC frequency, the potential drop signal between electrode pair 3 is measured at various temperatures in the temperature data set of a healthy pipeline to obtain the sampled data; a healthy pipeline is a pipeline without cracks or with cracks that have not propagated.

[0032] A temperature compensation model is obtained by fitting the temperature data and the sampled data in the temperature dataset.

[0033] In practical applications, the temperature compensation model is: V dec =V_measured-[w×(T-T_mean)+b], where V dec V_measured represents the temperature-normalized potential drop signal, w and b represent the slope coefficient and intercept, respectively, T represents the current temperature of the pipe, and T_mean represents the target temperature.

[0034] In another exemplary embodiment of this application, the preset frequency range is [200Hz, 10KHz].

[0035] In another exemplary embodiment of this application, the target temperature is 20 degrees Celsius.

[0036] In another exemplary embodiment of this application, the presence of a crack in the target region is determined based on the temperature-normalized potential drop signal and a reference signal, specifically by setting δ=V dec / V ref V dec It is the temperature-normalized potential drop signal, V ref It is a reference signal; in the "healthy" area of ​​the pipe without cracks, V... ref Adjust to V dec The condition is such that δ≈1; however, in other areas of the pipe, when δ≥1.1, it is considered that there are cracks between the measuring electrode pairs.

[0037] In this application, a standard signal source (synchronized with the excitation signal) is provided to the system as a reference signal, replacing the reference board commonly used in FSMs. This simplifies system installation and commissioning and eliminates the inherent differences between channels. One purpose of a reference board is to provide the system with a stable reference signal that does not change with the progression of pipe corrosion or cracks. Obviously, the provided standard signal source has the same characteristics and can also eliminate the need to install a reference board, making engineering construction more convenient.

[0038] A typical FSM inspection system includes a reference plate 8 to correct for the effects of factors such as temperature. The top and side views of the reference plate 8 are shown below. Figure 4 and Figure 5 As shown, the system includes a reference plate 8, a reference electrode pair 9, a current injection terminal 6, a current feedback terminal 7, a current bridging terminal 10, a detection electrode pair 11, and thermally conductive adhesive 12. The reference plate 8 is made of the same material as the steel pipe 13 under test, and is bonded to the steel pipe 13 under test through the thermally conductive adhesive 12, so that its temperature is consistent with that of the steel pipe 13 under test. Since the reference plate 8 does not come into contact with corrosive substances such as oil and gas, it is considered to be in a stable state and will not exhibit defects such as corrosion and cracks that are only possible inside pipelines.

[0039] Although the reference plate 8 can partially eliminate numerical variations caused by factors such as temperature and corrosion during the testing process, it brings some trouble to the installation. Especially when the test electrode pair 11 uses patch electrodes, conductive studs must be welded between the reference plate 8 and the steel pipe under test 13 to ensure that the excitation current flows smoothly from the reference plate 8 into the steel pipe under test 13.

[0040] The cross-sectional areas of the reference plate 8 and the steel pipe under test 13 are very different, which leads to a large difference in their current densities. Consequently, the voltage between the reference electrode pair 9 is also very different from the voltage between the detection electrode pair 11 on the steel pipe under the same spacing, which causes some trouble for the signal processing of the subsequent amplification circuit.

[0041] To eliminate this reference board 8, like Figure 3 Similarly, the excitation current flows directly into and out of the steel pipe. This application uses a stable fixed signal source (reference signal) to replace the actual voltage between the reference electrode pair 9 on the reference board 8. This signal source is strictly synchronized with the frequency of the excitation current, and its amplitude is adjusted to be approximately the same as the voltage amplitude between the detection electrode pair 11.

[0042] Using this signal source eliminates the need for the physical reference board 8, saving a hassle in the system installation and debugging process, making the system simpler and more effective (the signal from the stable signal source is much more stable and "cleaner" than the signal from the reference board 8).

[0043] However, changes in pipe temperature affect the resistivity of the pipe material and cause the potential drop to fluctuate with temperature, making it difficult to determine whether the change in potential drop is caused by crack changes or temperature variations. Traditional methods use a reference plate for correction, but this method is relatively crude and ineffective at eliminating the influence of temperature. This application eliminates the reference plate and uses an algorithm to eliminate the influence of temperature by "normalizing" the potential drop changes at all temperatures to a fixed temperature (e.g., 20°C), making the results comparable. This application uses a linear regression model from AI learning to fit the temperature-potential drop curve. By obtaining a sufficient number of potential drop samples (from healthy pipes) at different temperatures, a linear regression model (i.e., a temperature compensation model) is generated for the correction of potential drop samples at all subsequent temperatures.

[0044] This application represents an improvement in installation, commissioning, and data availability, and demonstrates practical engineering feasibility in detecting external cracks in oil and gas pipelines.

[0045] 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.

[0046] 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 device for detecting external cracks in pipelines, characterized in that, The pipeline external crack detection device includes: The system includes a processor, an excitation signal source, a current injection electrode, a current feedback electrode, and a pair of measuring electrodes. The current injection electrode and the current feedback electrode are respectively disposed at both ends of the target area on the outer surface of the pipe. The excitation signal source is connected to the current injection electrode and the current feedback electrode to provide a high-frequency AC excitation current to the target area. The pair of measuring electrodes is disposed within the target area. The pair of measuring electrodes includes two electrodes arranged along the propagation direction of the high-frequency AC excitation current. The processor is connected to the measuring electrode pair and is used to sample and normalize the potential drop signal between the measuring electrode pair. Based on the temperature-normalized potential drop signal and the reference signal, it determines whether there is a crack in the target area. The frequency of the reference signal is the same as the frequency of the high-frequency AC excitation current, and the voltage amplitude difference between the voltage amplitude and the measuring electrode pair is within a preset range.

2. The pipe external crack detection device according to claim 1, characterized in that, The pipeline in question is an oil and gas pipeline.

3. The pipe external crack detection device according to claim 1, characterized in that, The two electrodes inside the measuring electrode pair, the current injection electrode, and the current feedback electrode are all spring electrodes.

4. A method for detecting external cracks in pipelines, characterized in that, The pipe external crack detection device applied to claim 1, the pipe external crack detection method specifically includes: The current injection electrode and the current feedback electrode are respectively set at both ends of the target area on the outer surface of the pipe. The measuring electrode pair is set in the target area. The excitation signal source is connected to the current injection electrode and the current feedback electrode, and the potential drop signal between the measuring electrode pair is sampled. The sampled potential drop signal is normalized by temperature, and the presence of cracks in the target area is determined based on the normalized potential drop signal and the reference signal. The frequency of the reference signal is the same as the frequency of the high-frequency AC excitation current, and the voltage amplitude difference between the voltage amplitude and the voltage amplitude between the measuring electrode pair is within a preset range.

5. The method for detecting external cracks in pipelines according to claim 4, characterized in that, The frequency of the excitation signal source is determined using frequency sweeping technology.

6. The method for detecting external cracks in pipelines according to claim 5, characterized in that, The frequency of the excitation signal source is determined using frequency sweeping technology as follows: Under various excitation AC frequencies within a preset frequency range, the potential drop signal between the measuring electrode pairs on the sample pipeline is measured to obtain a potential drop dataset; a crack exists on the sample pipeline, and the first electrode in the measuring electrode pair is placed on one side of the crack, while the second electrode is placed on the other side of the crack. Based on the potential drop dataset, the excitation AC frequency that elicits the most intense crack response is determined as the optimal excitation AC frequency, which is then used as the frequency of the excitation signal source.

7. The method for detecting external cracks in pipelines according to claim 4, characterized in that, The sampled potential drop signal is normalized to temperature, specifically as follows: Based on the sampled potential drop signal, the current temperature of the pipeline, and the temperature compensation model, the potential drop between the measuring electrode pairs at the target temperature is obtained, resulting in a temperature-normalized potential drop signal.

8. The method for detecting external cracks in pipelines according to claim 7, characterized in that, The process of determining the temperature compensation model is as follows: At the optimal excitation AC frequency, the potential drop signal between the measuring electrode pairs is measured at various temperatures in the temperature data set of a healthy pipeline to obtain the sampled data; a healthy pipeline is a pipeline without cracks or with cracks not propagating. A temperature compensation model is obtained by fitting the temperature data and the sampled data in the temperature dataset.

9. The method for detecting external cracks in pipelines according to claim 6, characterized in that, The preset frequency range is [200Hz, 10KHz].

10. The method for detecting external cracks in pipelines according to claim 4, characterized in that, The target temperature is 20 degrees Celsius.

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