Pulse Eddy Current Device and Detection Method for Distinguishing Corrosion Defects on Inner and Outer Surfaces of Metals

Abstract

The present invention discloses a pulsed eddy current device and a detection method for distinguishing internal and external surface corrosion defects of metals. The method includes placing an excitation coil above a non-damaged metal specimen to be measured, recording the detection signals of TMR sensors in each channel as reference signals; placing the excitation coil above the metal specimen to be measured, recording the detection signals of TMR sensors in each channel as detection signals; taking the ratio of the detection signal of each channel to the corresponding reference signal respectively to generate a ratio curve for each channel; placing all the ratio curves in the same coordinate system to form a full-channel ratio change curve graph, and judging whether there are internal defects or external defects in the metal specimen to be measured according to the change trend of the curves in the full-channel ratio change curve graph. This application can accurately judge the position of corrosion defects, especially can effectively identify internal and external surface corrosion defects, and significantly improve the accuracy and reliability of detection.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline defect detection, and particularly to a pulsed eddy current device and a detection method for distinguishing corrosion defects on the inner and outer surfaces of metals. Background Art

[0002] Pressure-bearing equipment such as pipelines, storage tanks, and gas cylinders are prone to corrosion defects on their inner and outer surfaces due to long-term exposure to corrosive environments. This not only leads to a decline in equipment performance but also triggers major safety accidents such as leakage and explosion. Therefore, timely detection and accurate assessment of the corrosion condition are crucial for the safe operation and life management of the equipment.

[0003] Pulsed eddy current testing (PECT) is an efficient non-destructive testing technology with the ability of non-contact detection and penetration of the coating layer, and can effectively detect defects such as metal corrosion. It is suitable for high-temperature and high-pressure environments and can be used to detect workpieces with complex shapes. It mainly extracts characteristic quantities through the time-domain response signal, such as signal analysis methods like peak time, zero-crossing point, slope, etc., to achieve the detection and quantification of defects in the case of a coating layer. At present, the characterization of defects by this technology is mainly achieved through the remaining wall thickness of the workpiece, and mainly focuses on the detection and quantification of internal corrosion defects. However, in the actual working condition environment, there may be both internal and external corrosion defects on the surface of the workpiece, making the existing signal analysis methods have limitations and affecting the detection results. For pulsed eddy current testing technology, there is currently no suitable method to distinguish internal and external surface defects of metals at the same time. How to accurately distinguish internal and external corrosion defects without removing the coating layer is still a major difficulty in the existing technology.

[0004] Currently, the retrieved pulsed eddy current method for distinguishing internal and external surface corrosion defects is "A Ferromagnetic Pipeline Flaw Detection Device and Internal and External Detection Method Based on Pulsed Eddy Current (Authorized Announcement Number CN 114965680 B, November 15, 2024)". By inputting reverse pulse signals into two excitation coils to form a uniform tangential magnetic field, first, a set of reference signals is obtained by adjusting the height of the TMR sensor on a defect-free specimen; and detection signals are obtained on specimens with surface defects and internal defects respectively. The defect information is judged by whether there are intersections between the detection signals and the set of reference signals in the same coordinate system and the time period of the intersections. This method can distinguish the internal and external defect positions of the specimen. However, there are still some deficiencies. This method requires multiple adjustments of the position of the TMR sensor to collect the initial reference signal set at the same lift-off height, which takes a lot of time and is complex to operate. If the number of reference signals is too small, there will be misjudgment and omission of defect information, etc.

[0005] Therefore, the pulsed eddy current device and method for distinguishing corrosion defects on the inner and outer surfaces of metals provided by this application solve the current situation of complex operation and misjudgment or omission of defect information due to too few reference signals in existing tests. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a pulsed eddy current device and method for distinguishing corrosion defects on the inner and outer surfaces of metals, which can distinguish corrosion defects on the inner and outer surfaces of metals in the case of a coating layer and can achieve simultaneous detection of corrosion defects on the inner and outer surfaces of metals.

[0007] In order to achieve the above object, a pulsed eddy current detection method for distinguishing corrosion defects on the inner and outer surfaces of metals provided by the present invention includes the following steps:

[0008] S1. Place the excitation coil above the non-damaged metal test piece to be measured, and record the detection signals of each channel of the TMR sensor as the reference signal.

[0009] S2. Place the excitation coil above the metal test piece to be measured, and record the detection signals of each channel of the TMR sensor as the detection signal.

[0010] S3. Divide the detection signal of each channel by the corresponding reference signal respectively to generate a ratio curve for each channel.

[0011] S4. Place all the ratio curves in the same coordinate system to form a full-channel ratio change curve graph, and judge whether there are internal defects or external defects in the metal test piece to be measured according to the change trend of the curves in the full-channel ratio change curve graph.

[0012] Further preferably, in S4, when judging whether there are internal defects or external defects in the metal test piece to be measured according to the change trend of the curves in the full-channel ratio change curve graph, it includes:

[0013] S401. Divide all the ratio curves in the full-channel ratio change curve graph into three stages according to time periods, where the time period of the first stage is 0 - 0.005 s, the time period of the second stage is 0.005 s - 0.02 s; the time period of the third stage is after 0.02 s.

[0014] S402. Analyze the change trend of all the ratio curves in the second stage. When there is no intersection among the ratio curves of different channels in the second stage, it is judged as an external surface corrosion defect; when there is an intersection among the ratio curves of different channels in the second stage and the magnitudes of the curves are reversed, it is judged as an internal surface corrosion defect.

[0015] The present invention also provides a pulsed eddy current device for distinguishing corrosion defects on the inner and outer surfaces of a metal, which is used to implement the steps of the above-mentioned pulsed eddy current method for distinguishing corrosion defects on the inner and outer surfaces of a metal. It includes a detection module and an analysis module. The detection module includes a housing and an excitation coil and a multi-channel TMR sensor arranged inside the housing;

[0016] The excitation coil is parallel to the test piece and sends a pulsed excitation to the test piece;

[0017] The multi-channel TMR sensor is used to receive the magnetic field detection signal fed back by the test piece in the direction parallel to the axis of the excitation coil;

[0018] The analysis module is used to receive the detection signals of the multi-channel TMR sensor.

[0019] According to the detection signals of each received channel, respectively, make a ratio with the corresponding reference signal to generate a ratio curve for each channel; place all the ratio curves in the same coordinate system to form a full-channel ratio change curve graph, and judge whether there are internal defects or external defects in the metal test piece to be measured according to the change trend of the curves in the full-channel ratio change curve graph.

[0020] Further preferably, the multi-channel TMR sensor is formed by arranging a plurality of identical TMR sensors in a linear array, and with the line perpendicular to the diameter of the TMR sensor arrangement as the dividing line, the structures on both sides are symmetrical to ensure that the detection data obtained by the TMR sensors on both sides are the same.

[0021] Further preferably, in the multi-channel TMR sensor, a TMR sensor is arranged at the center position between two coils, and the other TMR sensors are evenly spaced along the diameter direction of the excitation coil, and the outermost TMR sensor is located at the outer edge of the excitation coil.

[0022] Further preferably, the uniform spacing is calculated according to the following formula:

[0023] The center spacing ΔS of the TMR sensors is:

[0024] ΔS = D / (N - 1);

[0025] Wherein, D is the diameter of the excitation coil, N is the number of TMR sensor excitations, and N is not less than 5.

[0026] Further preferably, when obtaining the reference signal or the detection signal,

[0027] A low-frequency square-wave current of 2 Hz is passed through the excitation coil, the signals received by each channel of the TMR sensor are recorded and converted into voltage signals, and the voltage signals are recorded as the reference signal U0 or the detection signal.

[0028] A pulsed eddy current device and detection method for distinguishing corrosion defects on the inner and outer surfaces of metals disclosed in the present application do not require multiple adjustments of the position of the TMR sensor, can accurately determine the position of corrosion defects, especially can effectively identify corrosion defects on the inner and outer surfaces, and significantly improve the accuracy and reliability of detection. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of a pulsed eddy current device for distinguishing corrosion defects on the inner and outer surfaces of metals provided in an embodiment of the present invention.

[0030] Figure 2 It is a flow chart of a pulsed eddy current detection method for corrosion defects on the inner and outer surfaces of a pulsed eddy current metal provided in an embodiment of the present invention.

[0031] Figure 3 It is a diagram showing the positional relationship between a pulsed eddy current device and a metal specimen to be tested under the condition of a coating layer provided in an embodiment of the present invention.

[0032] Figure 4 It is a curve graph of the overall detection data of outer surface corrosion provided in an embodiment of the invention.

[0033] Figure 5 It is an enlarged view of the curve graph of the detection data of the second stage of outer surface corrosion provided in an embodiment of the invention.

[0034] Figure 6 It is a curve graph of the overall detection data of inner surface corrosion provided in an embodiment of the invention.

[0035] Figure 7 It is an enlarged view of the curve graph of the detection data of the second stage of inner surface corrosion provided in an embodiment of the invention.

[0036] In the figure: 1. Excitation coil; 2. TMR sensor; 3. Shell; 4. Metal specimen; 5. Coating layer; 6. Outer surface corrosion defect; 7. Inner surface corrosion defect; 2-1. First TMR sensor; 2-2. Second TMR sensor; 2-3. Third TMR sensor. Detailed Embodiments

[0037] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0038] Embodiment 1

[0039] As Figure 1 shown, a pulsed eddy current device for distinguishing corrosion defects on the inner and outer surfaces of metals provided in an embodiment of one aspect of the present invention includes a detection module and an analysis module. The detection module includes a shell 3 and an excitation coil and a multi-channel TMR sensor arranged inside the shell;

[0040] It includes a detection module and an analysis module. The detection module includes a housing and an excitation coil 1 and a multi-channel TMR sensor 2 arranged inside the housing.

[0041] The excitation coil 1 is parallel to the test piece and sends a pulsed excitation to the test piece. The excitation coil 1 is set to one and is arranged in the center. In this embodiment, as Figure 1 shown, the rectangles on both sides of the dashed line respectively represent the cross-sectional views of the left and right sides when the excitation coil is cut along the middle horizontal axis. The excitation coil 1 is formed by winding enameled wire into a circular coil and is loaded with a periodic pulsed square wave signal. This excitation signal is transmitted to the excitation coil 1 through a power amplifier to generate a primary magnetic field.

[0042] The multi-channel TMR sensor is used to receive the magnetic field detection signal fed back by the test piece in the direction parallel to the axis of the excitation coil. Further preferably, the multi-channel TMR sensor is composed of a plurality of identical TMR sensors arranged in a linear array, and with the line perpendicular to the diameter of the TMR sensor arrangement as the dividing line, the structures on both sides are symmetric to ensure that the detection data obtained by the TMR sensors on both sides are the same.

[0043] In the multi-channel TMR sensor, a TMR sensor is arranged at the center position between the two coils, and the other TMR sensors are evenly spaced along the diameter direction of the excitation coil. The outermost TMR sensor is located at the outer edge of the excitation coil.

[0044] Further preferably, the even spacing is calculated according to the following formula:

[0045] The center spacing ΔS of the TMR sensors is:

[0046] ΔS = D / (N - 1);

[0047] where D is the diameter of the excitation coil, N is the number of TMR sensor excitations, and N is not less than 5. Through this arrangement method, it can be ensured that the sensors are evenly distributed on the excitation coil, thereby improving the balance of signal acquisition and the accuracy of the detection result.

[0048] The excitation coil 1 and the TMR sensor 2 are encapsulated in the device housing 3, and the device housing 3 is mainly made of engineering plastic material.

[0049] The analysis module is used to receive the detection signals of the multi-channel TMR sensor. According to the detection signals of each received channel, the ratio is taken with the corresponding reference signal respectively to generate a ratio curve for each channel; all the ratio curves are placed in the same coordinate system to form a full-channel ratio change curve graph, and according to the change trend of the curves in the full-channel ratio change curve graph, it is judged whether the metal test piece 4 to be tested has internal defects or external defects.

[0050] Specifically, the pulse eddy current detection method provided in Embodiment 2 below is used to determine whether internal defects or external defects occur in the metal specimen to be tested.

[0051] Embodiment 2

[0052] As Figure 2 shown, a pulse eddy current detection method for distinguishing corrosion defects on the inner and outer surfaces of a metal includes the following steps:

[0053] S1. Place the excitation coil above the non-damaged metal specimen to be tested, and record the detection signals of each channel of the TMR sensor as the reference signal. Specifically, pass a low-frequency square wave current of 2 Hz into the excitation coil 1. At this time, record the signals received by each channel of the TMR sensor and convert them into voltage signals. This signal is used as the reference signal U 0；

[0054] S2. Place the excitation coil above the metal specimen to be tested, and record the detection signals of each channel of the TMR sensor as the detection signal; place the pulse eddy current device on the surface of the metal specimen to be tested, as Figure 3 shown. The object to be inspected includes a metal specimen 4 and a coating layer 5. The thickness of the specimen is 10 mm, and the thickness of the coating layer is 20 mm. Among them, an external surface corrosion defect 6 and an internal surface corrosion defect 7 are provided on the metal specimen 4.

[0055] Place the pulse eddy current device above the area of the specimen with an external surface corrosion defect, and pass a low-frequency square wave current of 2 Hz into the excitation coil 1. Record the signals received by each channel of the TMR sensor and convert them into voltage signals as the detection signal U x

[0056] S3. Calculate the ratio of the detection signal of each channel to the corresponding reference signal respectively to generate the ratio curve of each channel;

[0057] The formula is:

[0058]

[0059] Among them:

[0060] is the ratio calculated for the i-th TMR channel;

[0061] is the detection signal received by the i-th TMR channel above the area of the specimen with an external corrosion defect;

[0062] is the reference signal received by the i-th TMR channel above the intact area of the specimen.

[0063] Since the excitation coil 1 is circular and the TMR sensors 2 are linearly arranged, and the two sides are symmetric with the line perpendicular to the diameter of the arrangement of the TMR sensors 2 as the dividing line, the detection data obtained by the TMR sensors on both sides are the same. Therefore, only the detection data on one side need to be analyzed. The selected TMR sensor numbers are 2-1, 2-2, and 2-3.

[0064] S4. Place all the ratio curves in the same coordinate system to form a full-channel ratio change curve graph, as Figure 4 shown. According to the change trend of the curves in the full-channel ratio change curve graph, determine whether there are internal defects or external defects in the metal specimen to be tested.

[0065] In S4, when determining whether there are internal defects or external defects in the metal specimen to be tested according to the change trend of the curves in the full-channel ratio change curve graph, it includes:

[0066] S401. Divide all the ratio curves in the full-channel ratio change curve graph into three stages according to time periods. The time period of the first stage is 0 - 0.005 s, the time period of the second stage is 0.005 s - 0.02 s; the time period of the third stage is after 0.02 s;

[0067] S402. Analyze the change trend of all the ratio curves in the second stage. When the ratio curves of different channels have no intersection in the second stage, it is judged as an external surface corrosion defect; when the ratio curves of different channels intersect in the second stage and the curve amplitudes show a magnitude reversal, it is judged as an internal surface corrosion defect.

[0068] The first stage (signal rapid decay stage): The signal shows rapid rise and decay, and the time period is 0 - 0.005 s; the second stage (eddy current expansion transition stage): The signal gradually spreads and tends to be stable, and the time period is 0.005 s - 0.02 s; the third stage (steady-state expansion stage): As the eddy current spreads in the material to reach a stable state, the time period is after 0.02 s, as Figure 4 shown.

[0069] Take Figure 4 the curves in the second stage for analysis, and the partial enlarged view is as Figure 5 shown. It can be seen that the ratio curves of each channel in this stage have no intersection with each other, and this feature is used as the basis for judging the external surface corrosion defect.

[0070] Embodiment 3. Different from the above embodiments, this embodiment detects a metal specimen with internal defects.

[0071] Place the pulsed eddy current device above the area of the specimen with internal surface corrosion defects, and apply a 2 Hz low-frequency square-wave current to the excitation coil 1. Record the signals received by the TMR sensors in each channel and convert them into voltage signals as the detection signal U y 。

[0072] Calculate the ratio of the detection signal of each channel to the corresponding reference signal respectively. The formula is:

[0073]

[0074] Where:

[0075] is the ratio calculated for the i-th TMR channel;

[0076] is the detection signal received by the i-th TMR channel above the area with corrosion defects in the specimen;

[0077] is the reference signal received by the i-th TMR channel above the intact area of the specimen.

[0078] Since the excitation coil 1 is circular and the TMR sensors 2 are linearly arranged, and taking the line perpendicular to the diameter of the arrangement of the TMR sensors 2 as the dividing line, the structures on both sides are symmetric, so the detection data obtained by the TMR sensors on both sides are the same. Therefore, only the detection data on one side needs to be analyzed. The selected TMR sensors are the first TMR sensor 2-1, the second TMR sensor 2-2, and the third TMR sensor 2-3.

[0079] Furthermore, divide the obtained ratio curve into time periods. The first stage (signal rapid decay stage): The signal shows rapid rise and decay, and the time period is 0 - 0.005 s; The second stage (eddy current expansion transition stage): The signal gradually spreads and tends to be stable, and the time period is 0.005 s - 0.02 s; The third stage (steady-state expansion stage): As the eddy current diffuses in the material to reach a stable state, the time period is after 0.02 s, such as Figure 6 shown.

[0080] Take Figure 6 the curve of the second stage in it for analysis. The partial enlarged view is as shown in Figure 7 shown. It can be seen that the ratio curves of each channel intersect in this stage, and the curve amplitudes reverse. Take this feature as the basis for judging the internal surface corrosion defects.

[0081] In the actual detection process of metal equipment corrosion defects, analyze the second-stage curve of the ratio curve calculated according to the steps of the present invention. When there is no intersection between the ratio curves of each channel, it can be judged as an external surface corrosion defect; when the ratio curves of each channel intersect and the curve amplitude reverses, it can be judged as an internal surface corrosion defect.

[0082] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A pulsed eddy current detection method for distinguishing corrosion defects on the inner and outer surfaces of metals, characterized in that: It includes the following steps: S1. Place the excitation coil above the non-damaged metal specimen to be measured, and record the detection signals of the TMR sensors in each channel as the reference signals; S2. Place the excitation coil above the metal specimen to be measured, and record the detection signals of the TMR sensors in each channel as the detection signals; S3. Divide the detection signal of each channel by the corresponding reference signal respectively to generate the ratio curves of each channel; S4. Place all the ratio curves in the same coordinate system to form a full-channel ratio change curve graph, and judge whether there are internal defects or external defects in the metal specimen to be measured according to the change trend of the curves in the full-channel ratio change curve graph.

2. The pulsed eddy current testing method for distinguishing internal and external surface corrosion defects of metals according to claim 1, wherein , In S4, when judging whether there are internal defects or external defects in the metal specimen to be measured according to the change trend of the curves in the full-channel ratio change curve graph, it includes: S401. Divide all the ratio curves in the full-channel ratio change curve graph into three stages according to time periods, where the time period of the first stage is 0 - 0.005 s, the time period of the second stage is 0.005 s - 0.02 s; the time period of the third stage is after 0.02 s; S402. Analyze the change trend of all the ratio curves in the second stage. When there is no intersection of the ratio curves of different channels in the second stage, it is judged as an external surface corrosion defect; when the ratio curves of different channels intersect in the second stage and the curve amplitudes reverse in size, it is judged as an internal surface corrosion defect.

3. A pulsed eddy current device for distinguishing corrosion defects on the inner and outer surfaces of a metal, characterized in that, The steps for implementing the pulsed eddy current detection method for distinguishing internal and external surface corrosion defects of metals described in any one of the above claims 1 - 2 include a detection module and an analysis module. The detection module includes a housing and an excitation coil and a multi-channel TMR sensor arranged inside the housing; The excitation coil is parallel to the specimen to be tested and sends a pulsed excitation to the specimen to be tested; The multi-channel TMR sensor is used to receive the magnetic field detection signal returned by the specimen to be tested and parallel to the axis direction of the excitation coil; The analysis module is used to receive the detection signals of the multi-channel TMR sensor, divide the detection signal of each received channel by the corresponding reference signal respectively to generate the ratio curves of each channel; place all the ratio curves in the same coordinate system to form a full-channel ratio change curve graph, and judge whether there are internal defects or external defects in the metal specimen to be measured according to the change trend of the curves in the full-channel ratio change curve graph.

4. The pulsed eddy current device for distinguishing corrosion defects on the inner and outer surfaces of a metal according to claim 3, characterized in that, The multi-channel TMR sensor is formed by arranging a plurality of identical TMR sensors in a linear array, and taking the line perpendicular to the diameter of the TMR sensor arrangement as the dividing line, the structures on both sides are symmetrical to ensure that the detection data obtained by the TMR sensors on both sides are the same.

5. The pulsed eddy current device for distinguishing internal and external surface corrosion defects of metals according to claim 4, characterized in that, In the multi-channel TMR sensor, a TMR sensor is arranged at the center position between the two coils, and the other TMR sensors are arranged at equal intervals along the diameter direction of the excitation coil, and the outermost TMR sensor is located at the outer edge of the excitation coil.

6. The pulsed eddy current device for distinguishing internal and external surface corrosion defects of metals according to claim 5, wherein The equal interval is calculated according to the following formula: The center spacing ΔS of the TMR sensor is: ΔS = D / (N - 1); Among them, D is the diameter of the excitation coil, N is the number of TMR sensor excitations, and N is not less than 5.

7. The pulsed eddy current device for distinguishing internal and external surface corrosion defects of metals according to claim 3, characterized in that, When obtaining the reference signal or the detection signal, a low-frequency square-wave current of 2 Hz is passed through the excitation coil, the signals received by each channel of the TMR sensor are recorded, and they are converted into voltage signals, which are denoted as the reference signal U0 or the detection signal.

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