Method for detecting welding edge of thick-wall workpiece welding seam under high-temperature environment based on low-frequency far-field eddy current

Abstract

The invention relates to a low-frequency far-field eddy current-based method for detecting a welding edge of a thick-wall workpiece welding seam in a high-temperature environment, and belongs to the field of thick-wall workpiece welding seam detection. A far-field eddy current probe of the far-field eddy current flaw detection system is placed on the surface of a weld joint of a workpiece to be detected, the probe is started to move along the weld joint, signals transmitted from a receiving coil are monitored in real time, and the received signals are processed and analyzed to identify defects in the weld joint. The device has the advantages that the adopted far-field eddy current probe comprises the exciting coil and the receiving coil, signals collected by the probe are processed and analyzed in real time, the accuracy and reliability of a detection result are ensured, the detection efficiency of the welding seam of the thick-wall workpiece is improved, the risk of missing detection is reduced, and a powerful guarantee is provided for industrial safety production; the detection sensitivity and depth can be improved, online detection can be achieved, namely, defect detection is conducted synchronously in the welding process, and the production efficiency and safety are greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of thick-wall workpiece weld detection, and in particular relates to a method for detecting thick-wall workpiece welds while welding in a high-temperature environment based on low-frequency far-field eddy currents. Background Art

[0002] The welding of thick workpieces is widely used in important equipment in aerospace, electric power, chemical industry and marine engineering. The welding quality is directly related to the safety and reliability of the final product, and the non-destructive testing of welded structures is particularly important. The welding of thick wall workpieces generally adopts automated welding, which has a large heat input. The welding process includes multi-layer and multi-pass welding, and non-destructive testing needs to be carried out after each layer or each pass of welding is completed. For interlayer welds of thick-walled workpieces, in traditional nondestructive testing technology, X-rays or DR can be used for testing when the welding thickness is small. When the welding reaches a certain thickness, the difficulty of X-ray penetration increases; ultrasonic testing needs to be cooled to room temperature after welding before it can be carried out, and the weld surface needs to be polished. Thick-walled workpieces often have double V or double U-shaped grooves, which restricts the placement of the probe and makes it difficult to achieve effective testing; penetrant testing can only detect surface opening defects, but not internal defects of the weld. At the same time, the applicable temperature range of penetrant testing is 5~50℃, and testing cannot be carried out immediately after welding; the temperature range of magnetic particle testing is also at room temperature. Similar to penetrant testing, it is necessary to deal with surface welding slag splashing, etc. In addition, the form and size of the groove restrict the placement of the magnetic yoke, which affects the detection effect and efficiency. Comprehensive analysis of existing common methods shows that there is no effective method for rapid defect detection in high temperature environment during the welding of thick-walled workpieces.

[0003] Remote field eddy current testing is a non-destructive testing technology based on the principle of electromagnetic induction, which uses the eddy current effect: when the excitation coil generates an alternating magnetic field through alternating current, eddy currents are generated inside the conductive material. When these eddy currents flow in the conductor, they are affected by the internal defects, geometry and material properties of the material, thus achieving non-contact detection. In a remote field eddy current testing system, the probe usually consists of an excitation coil and one or more secondary coils. The excitation coil is responsible for generating the alternating magnetic field, while the secondary coil is located in the far field area of ​​the excitation coil to detect the changes in the magnetic field caused by the changes in the eddy current. The distance between the secondary coil and the excitation coil is usually more than 20 times the diameter of the probe, which enables the secondary coil to detect deeper defect signals. When there are defects inside the conductive material (such as cracks, corrosion, holes, etc.), the defects will change the distribution and intensity of the eddy current, thereby affecting the magnetic field signal detected by the secondary coil. By analyzing the changes in these signals, the location, size and nature of the defects can be inferred. Modern remote field eddy current testing systems are usually equipped with advanced signal processing technologies, such as Fourier transform, filtering, etc., to improve the accuracy and reliability of detection. Remote field eddy current testing is a non-contact testing method that can leave the surface untreated or simply treated and is not affected by temperature.

[0004] The skin effect is an important factor that restricts the depth of eddy current detection defects. It refers to the phenomenon that when electromagnetic waves propagate inside a conductor, the electromagnetic field intensity decays exponentially with increasing depth. In eddy current testing, skin depth (δ) is an important parameter to measure the detection depth. Its calculation formula is:

[0005] Where f is the frequency of the excitation signal, μ is the magnetic permeability of the conductor being measured, and σ is the electrical conductivity of the conductor being measured. Due to the high magnetic permeability of ferromagnetic materials, their skin depth is much smaller than the skin depth in non-ferrous magnetic conductor materials of the same conductivity, which limits the detection depth of traditional eddy current testing technology.

[0006] In engineering, workpieces with a wall thickness of more than 40 mm are generally called thick-walled workpieces. Due to the large wall thickness, complex welding process, and high welding thermal cycle and welding stress during welding, defects such as cracks, pores, lack of fusion and lack of penetration are easily generated. For example, in the field of nuclear power, the thickness of the welds of large pressure vessels can reach 40-200 mm, or even thicker. The manufacturing quality and operation quality inspection of these welds are crucial to prevent nuclear leakage. However, due to the large thickness of the welds, the traditional method is to perform penetration testing after each layer or each welding is completed, which not only affects production efficiency, but also cannot effectively detect internal defects. Summary of the invention

[0007] The present invention provides a method for detecting thick-walled workpiece welds while welding in a high-temperature environment based on low-frequency far-field eddy currents, so as to solve the problem that due to the large thickness of the weld, the traditional method is to perform penetration testing after each layer or each welding pass is completed, which not only affects the production efficiency but also cannot effectively detect internal defects.

[0008] The technical solution adopted by the present invention comprises the following steps: (1) Place the far-field eddy current probe of the far-field eddy current flaw detection system on the weld surface of the workpiece to be tested; (2) Start the probe and move it along the weld; (3) Real-time monitoring of the signal transmitted from the receiving coil; (4) Process and analyze the received signals to identify defects in the weld.

[0009] In step (1) of the present invention, the far-field eddy current flaw detection system comprises a far-field eddy current probe, a phase amplitude detector, a data acquisition card, a power amplifier, an oscillator and a microcomputer, wherein the far-field eddy current probe comprises an excitation coil and a receiving coil, wherein the oscillator is electrically connected to the excitation coil via the power amplifier, the receiving coil is electrically connected to the phase amplitude detector, the phase amplitude detector is electrically connected to the data acquisition card and the oscillator respectively, and the data acquisition card is electrically connected to the microcomputer.

[0010] The distance between the exciting coil and the receiving coil of the present invention is 50 mm.

[0011] The wall thickness of the workpiece to be inspected in step (1) of the present invention is 15.5 mm to 200 mm.

[0012] In step (2) of the present invention, after the probe is started, the excitation signal frequency generated by the excitation coil is 100 Hz.

[0013] In step (2) of the present invention, after starting the probe, the excitation signal amplitude generated by the excitation coil is 3A.

[0014] In step (2) of the present invention, the probe moves at a constant speed of 0.1 m / s to scan the weld area.

[0015] In step (4) of the present invention, the signal transmitted from the receiving coil of the probe is amplified and filtered.

[0016] In step (4) of the present invention, abnormal peaks in the signal can be accurately detected by analyzing the signal, and these peaks directly correspond to defects in the weld.

[0017] The defect of the weld in step (4) of the present invention is a defect 3-5 mm deep from the weld surface.

[0018] The advantage of the present invention is that the far-field eddy current probe used includes an excitation coil and a receiving coil, and its design enables effective detection of defects 3-5mm deep from the weld surface under low-frequency 100Hz excitation. Experimental results show that transverse through-hole defects with a diameter of 2mm can be detected. The signals collected by the probe are processed and analyzed in real time to ensure the accuracy and reliability of the detection results, which not only improves the detection efficiency of thick-walled workpiece welds, but also reduces the risk of missed detection, providing a strong guarantee for industrial safety production; it solves the limitation problem of the prior art in the detection of defects in thick-walled workpieces, is not limited by the skin depth, and is particularly suitable for the detection of thick-walled workpiece welds, ensuring the quality and safety of the welded structure, and can not only improve the sensitivity and depth of detection, but also realize online detection, that is, defect detection is performed simultaneously during the welding process, which greatly improves production efficiency and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of a simulation model for remote-field eddy current detection of defects in thick-walled workpiece welds; Figure 2 This is the mesh division diagram of thick wall far-field eddy current detection; Figure 3 This is the magnetic field line distribution diagram of thick wall far-field eddy current detection; Figure 4 This is the thick wall far-field eddy current defect setting diagram; Figure 5 It is the circuit principle block diagram of the remote field eddy current flaw detection system; Figure 6 This is a physical picture of the remote field eddy current testing instrument; Figure 7 It is a schematic diagram of the structure of a remote field eddy current probe; Figure 8 This is a physical picture of the far-field eddy current probe; Fig. 9 It is the waveform diagram of the defect location. DETAILED DESCRIPTION

[0020] The following steps are involved: (1) Place the far-field eddy current probe of the far-field eddy current flaw detection system on the weld surface of the workpiece to be tested; (2) Start the probe and move it along the weld; (3) Real-time monitoring of the signal transmitted from the receiving coil; (4) Process and analyze the received signals to identify defects in the weld.

[0021] In step (1) of the present invention, the far-field eddy current flaw detection system comprises a far-field eddy current probe, a phase amplitude detector, a data acquisition card, a power amplifier, an oscillator and a microcomputer, wherein the far-field eddy current probe comprises an excitation coil and a receiving coil, wherein the oscillator is electrically connected to the excitation coil via the power amplifier, the receiving coil is electrically connected to the phase amplitude detector, the phase amplitude detector is electrically connected to the data acquisition card and the oscillator respectively, and the data acquisition card is electrically connected to the microcomputer.

[0022] The distance between the exciting coil and the receiving coil of the present invention is 50 mm.

[0023] The wall thickness of the workpiece to be inspected in step (1) of the present invention is 15.5 mm to 200 mm.

[0024] In step (2) of the present invention, after the probe is started, the excitation signal frequency generated by the excitation coil is 100 Hz.

[0025] In step (2) of the present invention, after starting the probe, the excitation signal amplitude generated by the excitation coil is 3A.

[0026] In step (2) of the present invention, the probe moves at a constant speed of 0.1 m / s to scan the weld area.

[0027] In step (4) of the present invention, the signal transmitted from the receiving coil of the probe is amplified and filtered.

[0028] In step (4) of the present invention, abnormal peaks in the signal can be accurately detected by analyzing the signal, and these peaks directly correspond to defects in the weld.

[0029] The defect of the weld in step (4) of the present invention is a defect 3-5 mm deep from the weld surface.

[0030] The present invention is further described below through experimental examples.

[0031] (1) In the process of designing the remote field eddy current probe, a three-dimensional model is first established using simulation software. The model accurately simulates the geometric structure of the probe, including the excitation coil, the receiving coil, and their relative positions to the steel plate to be tested. Figure 1 As shown in the figure, the excitation coil and the receiving coil are designed to be placed concentrically to ensure that the magnetic field can effectively penetrate the steel plate and return to the receiving coil. Then, detailed meshing is performed to ensure the accuracy of the simulation, especially near the interface between the coil and the steel plate, where the mesh is denser to capture the subtle changes in the electromagnetic field. Figure 2 As shown in the figure, it clearly shows the high-density grids in key areas such as around the coil and near the surface of the steel plate, as well as the gradually sparse grid layout towards the inside. Through these simulation steps, it is possible to perform high-sensitivity detection of 3mm deep defects in 15.5mm thick steel plates at an operating frequency of 100Hz, and at the same time determine the 3A AC current passed through the excitation coil, which is the optimal value determined based on simulation and experiments to maximize the detection depth and signal strength.

[0032] (2) In the simulation verification phase, the distribution of magnetic lines of force was analyzed, such as Figure 3 As shown in the figure, the distribution of magnetic field lines in thick wall remote field eddy current testing is demonstrated, which helps to understand how the magnetic field penetrates the steel plate and affects the signal of the receiving coil. Figure 4 A detailed view of the defect setup is provided, which provides the basis for accurately emulating real-world inspection scenarios in simulation.

[0033] (3) In terms of hardware design, Figure 5 The circuit diagram of the remote field eddy current flaw detection system is described, the connection mode and working principle of each component of the system are shown, and the actual remote field eddy current detection instrument is also manufactured, such as Figure 6 As shown, and specially designed remote field eddy current probes, such as Figure 7 and Figure 8As shown in the figure, the schematic diagram and the actual picture of the probe are shown respectively.

[0034] (4) In terms of detection parameter setting, the control unit sets the amplitude of the excitation signal to 3A based on the simulation results. This is the optimal magnetizing current determined experimentally to ensure that the maximum eddy current signal response can be obtained at a detection frequency of 1kHz. This parameter is adjusted through the digital interface of the control unit to adapt to different detection environments and workpiece material characteristics.

[0035] (5) During the actual inspection process, the probe scans the weld area at a constant speed, with the speed controlled at 0.1m / s to ensure full coverage and inspection of every part of the weld. The movement of the probe is controlled by a precision servo motor to ensure uniformity and repeatability of the scan. The signal processing unit receives the signal from the probe in real time, and performs amplification and filtering to extract useful inspection information.

[0036] (6) In the data processing and analysis stage, the signal after pre-amplification, bandpass filtering and digital filtering is subjected to spectrum analysis to accurately identify and quantify the signal changes caused by defects and detect abnormal peaks in the signal. These peaks directly correspond to the defects in the weld. The waveform when there is a defect is as follows: Fig. 9 As shown in the figure, the waveform trough values ​​obtained will be different for different defect depths. By extracting the trough values ​​of different defect signals, key data is provided for identifying the defect size, and the calculation formula for the defect size is derived using the linear fitting method. Then, the specific location and size of the defect can be accurately calculated through the optimized calculation formula. The software interface provides real-time data visualization functions, including detailed signal waveform diagrams, spectrum analysis diagrams, and defect location diagrams, to ensure that users can intuitively verify and analyze the accuracy of the test results. In addition, it can automatically record and deeply analyze historical signal data to help users understand and identify the signal characteristics of different types of defects and further improve the detection accuracy. Through these detailed data processing and analysis steps, defects in welds can be accurately identified, and real-time data visualization and analysis results can be provided, thereby ensuring that non-destructive testing of thick workpiece welds achieves high accuracy and high efficiency.

[0037] (7) Before actually manufacturing the probe, the probe design is verified by simulation software to ensure that the probe can achieve the best detection effect at the expected operating frequency and current. The simulation results are used to guide the experimental settings, including the position of the probe, the movement speed, and the parameters of the excitation signal. The experiment verifies the accuracy of the simulation results and is used to further calibrate the simulation model.

[0038] (8) Considering the high temperature environment that may be encountered in actual applications, the system was tested under simulated conditions of 350°C. The test results show that high temperature has no significant effect on the detection capability of the system, and the detection sensitivity and accuracy of the system remain stable at high temperatures.

[0039] The system is applied in actual industrial environment to perform online inspection of thick workpiece welds in service. The position and movement speed of the probe, as well as the parameter settings of the signal processing unit, are adjusted according to the on-site conditions to adapt to different inspection environments and requirements. The system shows good stability and reliability in actual application, providing an effective solution for non-destructive inspection of thick workpiece welds.

[0040] Through the above specific experiments, this system not only verifies its detection capability in the experiment, but also optimizes the probe design and detection parameters through simulation, thus improving the accuracy and efficiency of detection. The consistency between simulation and experimental results further proves the reliability and effectiveness of this system.

Claims

1. A method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current, characterized in that: The following steps are involved: (1) Place the far-field eddy current probe of the far-field eddy current flaw detection system on the surface of the weld to be tested; (2) Start the probe and move it along the weld; (3) Real-time monitoring of the signal transmitted from the receiving coil; (4) Process and analyze the received signals to identify defects in the weld.

2. According to claim 1, a method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current, characterized in that: In the step (1), the far-field eddy current flaw detection system comprises a far-field eddy current probe, a phase amplitude detector, a data acquisition card, a power amplifier, an oscillator and a microcomputer, wherein the far-field eddy current probe comprises an excitation coil and a receiving coil, wherein the oscillator is electrically connected to the excitation coil via the power amplifier, the receiving coil is electrically connected to the phase amplitude detector, the phase amplitude detector is electrically connected to the data acquisition card and the oscillator respectively, and the data acquisition card is electrically connected to the microcomputer.

3. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 2, characterized in that: The distance between the exciting coil and the receiving coil is 50 mm.

4. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 1, characterized in that: The thickness of the weld to be tested in step (1) is 15.5 mm to 200 mm.

5. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 1, characterized in that: After the probe is started in step (2), the excitation signal frequency generated by the excitation coil is 100 Hz.

6. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 1, characterized in that: After the probe is started in step (2), the excitation signal amplitude generated by the excitation coil is 3A.

7. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 1, characterized in that: In step (2), the probe moves at a constant speed of 0.1 m / s to scan the weld area.

8. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 1, characterized in that: In the step (4), the signal transmitted from the receiving coil of the probe is amplified and filtered.

9. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 1, characterized in that: In step (4), abnormal peaks in the signal can be accurately detected by analyzing the signal, and these peaks directly correspond to defects in the weld.

10. The method for detecting thick-walled workpiece welds under high temperature environment while welding based on low-frequency far-field eddy current according to claim 9, characterized in that: The defect of the weld in step (4) is a defect 3-5 mm deep from the weld surface.

Images