An eddy current probe and method for measuring the gap between the outer structures of a double-walled metal tube

Abstract

This invention provides an eddy current probe for measuring the gap between the external structures of a double-layered metal tube. The probe body includes a probe main body with dual excitation coils and an external structure signal receiving coil to form a first set of transceiver eddy current probes for measuring the spacing of the supporting structures outside the double-layered metal tube. A second set of transceiver eddy current probes, consisting of a point excitation coil, a first receiving coil, and a second receiving coil, is located on the probe main body relative to the external structure signal receiving coil to form a second set of transceiver eddy current probes for measuring the gap between the double-layered metal tubes. This invention achieves effective magnetic field penetration through the multi-layered metal tube wall and sensitivity to signals from the external structure by arranging dual excitation coils, an external structure signal receiving coil, a point excitation coil, a first receiving coil, and a second receiving coil on the probe main body. The gap between the external structures is detected by measuring the amplitude response changes of the eddy current signal.

Description

Technical Field

[0001] This invention relates to the field of gap measurement technology for the external structure of double-layer metal tubes, and particularly to an eddy current probe and method for measuring the gap in the external structure of double-layer metal tubes. Background Technology

[0002] The CANDU heavy water reactor body is a horizontally placed cylindrical container (referred to as the pipe container) containing low-temperature, low-pressure heavy water moderator. Numerous horizontally placed fuel channels run through the container. Each fuel channel mainly consists of one pressure pipe, two end components, one pipe, and four retaining clips separating the pipe from the pressure pipe. Due to the long-term operation of the fuel channels in a high-temperature, high-pressure, and high-radiation environment, the dimensions and material properties of the pressure pipe may change. Specifically, the pressure pipe may sag, altering the clearance between it and the external pipe and the injection pipe structure of the liquid injection shutdown system within the pipe container, and potentially leading to contact between various components.

[0003] To ensure the safe and stable operation of nuclear facilities, it is necessary to measure the gap between the drooping fuel channel and the external injection pipe to confirm whether there is sufficient safety margin between the pressure pipe and the injection pipe. Due to limitations in detection conditions, external access is not possible, and detection must be carried out from the inside. This requires the detection tool to be able to sense changes in the position of the external components of the double-layered structure. Further analysis of the gap changes between the external structure and the pressure pipe is then conducted to develop corresponding measures to ensure the safety and reliability of the fuel assemblies during operation.

[0004] Eddy current testing is an important non-destructive testing method for conductive metallic materials, exhibiting high sensitivity in detecting pipe defects and changes in external structure. Based on the structural characteristics of the object under test and the required magnetic field penetration depth, eddy current testing probes with specific functions can be designed and developed to achieve specific testing objectives.

[0005] For the CANDU heavy water reactor pressure tube, its inner diameter is approximately 103 mm and its wall thickness is approximately 4 mm. The external pipes are concentrically arranged with the pressure tube, forming a double-layer pipe structure. The installation distance between the external pipes and the liquid injection pipes perpendicular to the axial direction of the external pipes is approximately 60 mm. Therefore, given the characteristics of the reactor structure and the detection range, the detection tool needs to be able to penetrate the interior of the pressure tube and possess extremely high eddy current magnetic field penetration capability, while also being able to pick up changes in the induced magnetic field caused by changes in the structural spacing. Conventional eddy current detection methods often fail to achieve the required penetration depth (effective magnetic field range) of 60 mm. Therefore, it is necessary to design and develop the probe coil size, number of turns, and signal transmission method between the excitation and receiving coils to meet the requirements of detection range and sensitivity. Increasing the magnetic field strength of the excitation magnetic field can improve the eddy current penetration depth. Due to the extremely high radiation environment inside the pressure tube, conventional methods such as using chip amplification circuits to increase signal excitation and pickup cannot be employed.

[0006] Given that the excitation magnetic field strength needs to be strong enough to penetrate the double-walled structure and achieve long-distance detection of over 60mm, the high penetration depth of low-frequency eddy currents must be utilized, with low frequency as the detection frequency. Simultaneously, the magnetic flux density along the magnetic field transmission path of the excitation coil is analyzed, and a suitable axial position is selected to place the receiving coil, starting from the excitation coil, to achieve the goal of picking up effective eddy current signals. To reduce energy loss during magnetic field transmission, the excitation coil should be as close as possible to the pipe wall surface and adopt an axially wound coil design coaxial with the pressure pipe. The magnetic field strength can be increased by controlling the number of turns of the coil. Considering the complexity of the external structure of the pressure pipe and the circumferential position of the injection pipe relative to the circumferential cross-section of the pressure pipe, a point coil needs to be designed as the receiving coil for the eddy current signal. This point coil is placed at a fixed circumferential position on the detection tool, which can effectively pick up the amplitude change of the eddy current signal of the induced magnetic field at a specific angle (in the direction of the injection pipe). Summary of the Invention

[0007] The purpose of this invention is to provide an eddy current probe and method for measuring the gap between the external structure of a double-layer metal tube. By using a transceiver eddy current line, the invention solves the problem that conventional eddy current probes and far-field eddy current probes cannot detect the distance between the external structure and the tube under test.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] An eddy current probe for measuring the gap between the external structures of a double-layer metal tube includes a probe body. The probe body is provided with dual excitation coils and an external structure signal receiving coil to form a first set of transceiver eddy current probes to measure the spacing of the supporting structures outside the double-layer metal tube. A point excitation coil, a first receiving coil, and a second receiving coil are provided on the probe body at the installation position of the external structure signal receiving coil to form a second set of transceiver eddy current probes to measure the gap between the double-layer metal tubes.

[0010] As one possible implementation, the dual excitation coil is located at the front of the probe body, and the external structure signal receiving coil is located at the rear of the probe body and is attached to the inner surface of the fuel channel pressure tube.

[0011] As one feasible approach, the dual excitation coil is a double ring shape, formed by winding two sets of wires of the same size, and the double excitation coil is coaxial with the probe body.

[0012] As one possible implementation, the external structure signal receiving coil is a cylindrical coil wound with wire, and the central axis of the cylindrical coil is perpendicular to the axis of the probe body.

[0013] As one possible approach, the coil axis of the external structure signal receiving coil is perpendicular to the surface of the fuel channel pressure tube. By adjusting the orientation of the external structure signal receiving coil to accurately locate the external structure and pick up eddy current signals, electromagnetic signal interference in other directions of the outer circumference of the fuel channel pressure tube can be reduced.

[0014] As one possible implementation, the external structure signal receiving coil is pressed against the wall of the fuel passage pressure pipe by a compression spring at the bottom.

[0015] As one feasible approach, the point excitation coil, the first receiving coil, and the second receiving coil are arranged on the same spring block. The spring block uses four compression springs to press the support block containing the coils against the inner wall of the fuel channel pressure pipe. The three coils are located on the same plane of the support block. The point excitation coil, the first receiving coil, and the second receiving coil are arranged sequentially in the axial direction. The point excitation coil generates a magnetic field, and the first receiving coil and the second receiving coil receive eddy current signals generated by the change in the gap between the fuel channel pressure pipe and the external manifold.

[0016] As one possible implementation, the point excitation coil, the first receiving coil, and the second receiving coil are arranged on the same axis.

[0017] As one possible implementation, the probe body has an internal cavity through which the cables of the dual excitation coil, the external structure signal receiving coil, the point excitation coil, the first receiving coil, and the second receiving coil are led out and connected to the instrument used for detection.

[0018] A method for measuring the gap in the external structure of a double-layer metal tube includes the following steps:

[0019] Step 1: Fix the eddy current probe for measuring the gap in the external structure of the double-layer metal tube onto the scanning device, and then connect it to the eddy current meter using an extension cable;

[0020] Step 2: Rotate the eddy current probe for measuring the gap of the external structure of the double-layer metal tube circumferentially using the scanning device, and point the external structure signal receiving coil toward the direction of the external structure.

[0021] Step 3: The eddy current probe for measuring the gap of the external structure of the double-layer metal tube is pushed by the scanning device to perform axial scanning. The eddy current magnetic field is excited by the dual excitation coil, and the eddy current signal data of the external structure is recorded by the external structure signal receiving coil. At the same time, the corresponding position information is obtained by the encoder of the scanning device.

[0022] Step 4: After completing the external structure signal inspection, the eddy current probe for measuring the gap of the external structure of the double-layer metal tube is moved to the axial position of the external structure using the scanning device.

[0023] Step 5: After reaching the designated position, the eddy current probe for measuring the gap of the external structure of the double-layer metal tube is driven by the scanning device to perform a circumferential scan. The eddy current magnetic field is excited by the point excitation coil in the point coil group, and the eddy current signal between the pressure tube and the pipe is recorded by the first receiving coil and the second receiving coil.

[0024] Step 6: Calculate the amplitude and distance of the eddy current signal using measurement software to obtain the external structural distance information.

[0025] Compared with existing technologies, the eddy current probe and method for measuring the gap in the external structure of a double-layer metal tube provided by this invention have the following advantages:

[0026] This invention achieves effective penetration of magnetic field through multi-layer metal pipe walls and sensitivity to external structural signals by setting up dual excitation coils, external structural signal receiving coils, point excitation coils, first receiving coils and second receiving coils on the probe body. The external structural gap is detected by measuring the amplitude response change of the eddy current signal.

[0027] Furthermore, this invention employs a dual-axis winding coil as the winding method for the excitation coil and increases the probe fill factor (coil diameter 95mm, fill factor over 80%), which solves the problem of insufficient magnetic field strength for coil excitation. At the same time, compared with the excitation method of a single coil, the winding method of two coils can greatly reduce the heating of the coil.

[0028] Furthermore, the combination of the large-shaft-wound excitation coil (dual excitation coil) and the point-type receiving coil (external structure signal receiving coil) used in this invention has negligible influence on the multilayer metal tube itself when detecting the external wall structure signal. The amplitude of its eddy current signal is mainly related to the distance from the external structure to the fuel channel pressure tube.

[0029] Furthermore, the point coil combination used in this invention utilizes the indirect coupling effect of the magnetic fields of the excitation coil and the receiving coil to design the distance of the coil in the sensitive area of ​​the gap between the pressure tube and the pipe at a specific distance. This can effectively detect the distance between the fuel channel pressure tube and the external pipe, solving the problem of the influence caused by the change in the gap of the double-layer metal tube itself when measuring the distance of the external structure of the double-layer metal tube.

[0030] For excitation coils of the same size, a dual-axis winding design can increase the magnetic field strength of the excitation coil, while simultaneously increasing the distance between the receiving coil and the large-axis winding excitation coil, thus improving the ability to identify signals from the outer wall structure of the tube. Figure 3 The two curves a and b clearly show that when the distance reaches a certain range, the magnetic flux density of the outer wall structure signal is greater than that of the inner wall, thus effectively identifying the eddy current signal of the outer structure. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the multilayer metal tube external structure gap measuring probe and its external structure provided in an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the multilayer metal tube external structure gap measuring probe provided in an embodiment of the present invention;

[0034] Figure 3 The curves showing the change in magnetic flux density versus distance are provided in the embodiments of the present invention.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1. Probe body; 2. Dual excitation coils; 3. External structure signal receiving coil; 4. Point excitation coil; 5. First receiving coil; 6. Second receiving coil; 7. Fuel channel pressure pipe; 8. External manifold; 9. External liquid injection pipe. Detailed Implementation

[0037] The following detailed description provides further details on specific implementation methods.

[0038] like Figure 1 As shown, the present invention is used for measuring the gap of the outer structure of a multi-layer metal pipe. The object under test consists of a double-layer metal sleeve composed of a fuel channel pressure pipe 7 and an outer pipe 8, and a metal pipe (outer liquid injection pipe 9) arranged perpendicular to its axis outside the double-layer sleeve.

[0039] like Figure 1 and Figure 2 As shown, this invention provides an eddy current probe for measuring the gap in the external structure of a double-layer metal tube, comprising a probe body 1, dual excitation coils 2, an external structure signal receiving coil 3, a point excitation coil 4, a first receiving coil 5, and a second receiving coil 6. The eddy current probe acquires test results by performing axial or rotational scanning inside the object under test.

[0040] The probe body 1 has a cylindrical structure with an internal cavity. The cables of the dual excitation coil 2, the external structural signal receiving coil 3, the point excitation coil 4, the first receiving coil 5, and the second receiving coil 6 are led out through the internal cavity and connected to the instrument used for detection.

[0041] The dual excitation coil 2 is a double ring, made of two sets of wires of the same size. The wound coil is fixed at the front of the probe body 1, and the dual excitation coil 2 is coaxial with the probe body 1.

[0042] The external structure signal receiving coil 3 is a cylindrical coil wound with wire, and its cylindrical central axis is perpendicular to the axis of the probe body 1. The external structure signal receiving coil 3 is arranged at the rear of the probe body 1, and its cylindrical end face is in contact with the inner surface of the fuel channel pressure pipe 7, which reduces the lift-off effect of the coil and thus reduces the measurement error caused by the change of coil position.

[0043] The external structure signal receiving coil 3 adopts a point coil design, with its axis perpendicular to the surface of the fuel channel pressure pipe 7, resulting in a small receiving range. By adjusting the orientation of the external structure signal receiving coil 3, the external structure can be accurately located, and eddy current signals can be picked up without interference from electromagnetic signals in other directions around the outer circumference of the fuel channel pressure pipe. The external structure signal receiving coil 3 is held in place against the pipe wall by a clamping spring at its bottom.

[0044] The point-type excitation coil 4 is a cylindrical coil wound with wire, and its central axis is perpendicular to the axis of the probe body 1. The point-type excitation coil 4 is located symmetrically to the signal receiving coil 3 of the external structure, such as... Figure 2 As shown, the external signal receiving coil 3 is positioned above and attached to the upper surface of the fuel channel pressure tube 7, while the point-type excitation coil 4 is positioned below and attached to the lower surface of the fuel channel pressure tube 7. The cylindrical end face of the point-type excitation coil 4 is attached to the inner surface of the fuel channel pressure tube 7 to reduce the lift-off effect.

[0045] The first receiving coil 5 is also a cylindrical coil wound with wire, and its cylindrical central axis is perpendicular to the probe body axis. The first receiving coil 5 and the point excitation coil 4 are located on the same axis and are used to detect the signal change at the same angular position in the circumferential direction. Its cylindrical end face is in contact with the inner surface of the fuel channel pressure tube 7.

[0046] The second receiving coil 6 is also a cylindrical coil wound with wire, and its cylindrical central axis is perpendicular to the probe body axis. The second receiving coil 6, the point excitation coil 4, and the first receiving coil 5 are all located on the same axis, and its cylindrical end face is in contact with the inner surface of the fuel channel pressure pipe 7.

[0047] The dual excitation coil 2 and the external structure signal receiving coil 3 form a transceiver eddy current probe, which is responsible for measuring the spacing of the support structure outside the double-layer metal tube; the point excitation coil 4, the first receiving coil 5 and the second receiving coil 6 form a transceiver eddy current probe, which is responsible for measuring the gap between the double-layer metal tube.

[0048] The external structure signal receiving coil 3 is used to receive the eddy current signal generated when the magnetic field excited by the dual excitation coil 2 passes through the external structure (external liquid injection pipe 9).

[0049] Point-type excitation coil 4, first receiving coil 5, and second receiving coil 6 are arranged on the same spring block. Four compression springs at the bottom of the spring block hold the support block containing the coils against the inner wall of the fuel channel pressure pipe 7. The three coils are located on the same plane of the support block (in the same circumferential direction, ensuring that the gap at the same position on the outer wall of the pipe is detected), arranged sequentially in the axial direction. The point-type excitation coil 4 generates a magnetic field, and the first receiving coil 5 and the second receiving coil 6 receive the eddy current signals generated by the change in the gap between the fuel channel pressure pipe 7 and the external manifold 8. By acquiring the eddy current signals of the external structure (external liquid injection pipe 9) and the changes in the eddy current signals between the fuel channel pressure pipe 7 and the external manifold 8, the dimensional information of the spacing between the external structures can be obtained. Simultaneously, the axial position information of the external structure can also be obtained through the response of the eddy current signals during axial movement.

[0050] Preferably, in order to ensure that the magnetic field excited by the large shaft winding coil (double excitation coil 2) has sufficient energy and meets the requirements for exciting low-frequency eddy currents, a pair of shaft winding coils are used as excitation coils. While increasing the energy of the excitation magnetic field, the fill factor is designed to be >80%, so that the excitation coil fits the inner wall of the metal tube sufficiently to reduce the energy loss caused by the magnetic field transmission distance.

[0051] For large-shaft wound coils (double excitation coil 2) in low-frequency detection, the main transmission path of their magnetic field is the direct field through the inner wall (such as...). Figure 3 (as shown by curve a) and the indirect field of the outer wall (such as...) Figure 3 As shown in curve b), with the change in position of the external structure signal receiving coil 3 relative to the dual excitation coil 2, its magnetic flux density curve changes significantly at a specific position. The magnetic flux density of the indirect field on the outer wall is greater than that of the direct field on the inner wall, thereby achieving the purpose of responding to and detecting the eddy current signal between the external structure (external liquid injection pipe 9) and the fuel channel pressure pipe 7. Figure 3 As shown in the figure, it can be clearly seen from curves a and b that when the distance reaches a certain range, the magnetic flux density of the outer wall structure signal is greater than that of the inner wall, thus effectively identifying the eddy current signal of the outer structure.

[0052] The fuel channel pressure pipe 7 and the external pipe 8 form a double-layer sleeve structure with a gap of about 7mm between them. By utilizing the response change of magnetic flux density at different positions on the pipe wall, a set of transceiver probes is designed, consisting of a point excitation coil 4, a first receiving coil 5, and a second receiving coil 6. The gap change is identified by the change of eddy current signal detected by the receiving coil.

[0053] The gap between the inner and outer walls of the metal tube is generally small, so the distance between the transceiver coil assembly (point excitation coil 4, first receiving coil 5, second receiving coil 6) is small. They can be fixed on the same support plane and supported by the back spring to keep the entire support plane (coil plane) in contact with the inner wall of the metal tube to reduce the signal lift-off effect caused by probe movement.

[0054] In addition, based on the aforementioned eddy current probe for measuring the gap in the external structure of a double-layer metal tube, this invention provides a method for measuring the gap in the external structure of a double-layer metal tube, comprising the following steps:

[0055] Step 1: Fix the eddy current probe to the scanning device and then connect it to the eddy current meter using an extension cable;

[0056] Step 2: Rotate the eddy current probe circumferentially using the scanning device, and orient the external structure signal receiving coil 3 toward the direction of the external structure.

[0057] Step 3: The scanning device pushes the probe to perform axial scanning, and the large shaft winding coil (double excitation coil 2) excites the eddy current magnetic field. The external structure signal receiving coil 3 records the eddy current signal data of the external structure, and the encoder of the scanning device obtains the corresponding position information at the same time.

[0058] Step 4: After completing the external structure signal inspection, move the eddy current probe to the axial position of the external structure using the scanning device;

[0059] Step 5: After reaching the designated position, the probe is driven by the scanning device to perform a circumferential scan. The eddy current magnetic field is excited by the point excitation coil 4 in the point coil group, and the eddy current signal between the pressure tube and the pipe is recorded by the first receiving coil 5 and the second receiving coil 6.

[0060] Step 6: Calculate the amplitude and distance of the eddy current signal using measurement software to obtain the external structural distance information.

[0061] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An eddy current probe for measuring the gap in the external structure of a double-layer metal tube, comprising a probe body (1), characterized in that, The probe body (1) is provided with a dual excitation coil (2) and an external structure signal receiving coil (3) to form a first set of transceiver eddy current probes to measure the spacing of the support structure outside the double-layer metal tube. The probe body (1) relative to the installation position of the external structure signal receiving coil (3) is provided with a point-type excitation coil (4), a first receiving coil (5), and a second receiving coil (6) to form a second set of transceiver eddy current probes to measure the gap between the double-layer metal tubes. The dual excitation coil (2) is located at the front of the probe body (1), and the external structure signal receiving coil (3) is located at the rear of the probe body (1) and is attached to the inner surface of the fuel channel pressure tube (7). The coil axis of the external structure signal receiving coil (3) is perpendicular to the surface of the fuel channel pressure tube (7). By adjusting the external structure... The orientation of the signal receiving coil (3) is adjusted to accurately locate the external structure and pick up eddy current signals, thereby reducing electromagnetic signal interference from other directions on the outer circumference of the fuel channel pressure pipe. The point excitation coil (4), the first receiving coil (5), and the second receiving coil (6) are arranged on the same spring block. The bottom of the spring block is pressed against the inner wall of the fuel channel pressure pipe (7) by four compression springs. The three coils are located on the same plane of the support block. The point excitation coil (4), the first receiving coil (5), and the second receiving coil (6) are arranged sequentially in the axial direction. The point excitation coil (4) generates a magnetic field. The first receiving coil (5) and the second receiving coil (6) receive eddy current signals generated by the change in the gap between the fuel channel pressure pipe (7) and the external pipe (8).

2. The eddy current probe for measuring the gap in the external structure of a double-layer metal tube according to claim 1, characterized in that, The dual excitation coil (2) is a double ring, made of two sets of wires of the same size, and the double excitation coil (2) is coaxial with the probe body (1).

3. The eddy current probe for measuring the gap in the external structure of a double-layer metal tube according to claim 1, characterized in that, The external structure signal receiving coil (3) is a cylindrical coil made of wire, and the cylindrical central axis of the cylindrical coil is perpendicular to the axis of the probe body (1).

4. The eddy current probe for measuring the gap in the external structure of a double-layer metal tube according to claim 1, characterized in that, The external structure signal receiving coil (3) is attached to the wall of the fuel channel pressure pipe (7) by a compression spring at the bottom.

5. The eddy current probe for measuring the gap in the external structure of a double-layer metal tube according to claim 1, characterized in that, The point excitation coil (4), the first receiving coil (5), and the second receiving coil (6) are arranged on the same axis.

6. The eddy current probe for measuring the gap in the external structure of a double-layer metal tube according to claim 1, characterized in that, The probe body (1) has an internal cavity, and the cables of the dual excitation coil (2), the external structure signal receiving coil (3), the point excitation coil (4), the first receiving coil (5) and the second receiving coil (6) are led out through the internal cavity and connected to the instrument used for detection.

7. A method for measuring the gap in the external structure of a double-layer metal tube, characterized in that, Based on the eddy current probe according to any one of claims 1 to 6, the method includes the following steps: Step 1: Fix the eddy current probe for measuring the gap in the external structure of the double-layer metal tube onto the scanning device, and then connect it to the eddy current meter using an extension cable; Step 2: Rotate the eddy current probe for measuring the gap of the external structure of the double-layer metal tube circumferentially using the scanning device, and point the external structure signal receiving coil toward the direction of the external structure. Step 3: The eddy current probe for measuring the gap of the external structure of the double-layer metal tube is pushed by the scanning device to perform axial scanning. The eddy current magnetic field is excited by the dual excitation coil, and the eddy current signal data of the external structure is recorded by the external structure signal receiving coil. At the same time, the corresponding position information is obtained by the encoder of the scanning device. Step 4: After completing the external structure signal inspection, the eddy current probe for measuring the gap of the external structure of the double-layer metal tube is moved to the axial position of the external structure using the scanning device. Step 5: After reaching the designated position, the eddy current probe for measuring the gap of the external structure of the double-layer metal tube is driven by the scanning device to perform a circumferential scan. The eddy current magnetic field is excited by the point excitation coil in the point coil group, and the eddy current signal between the pressure tube and the pipe is recorded by the first receiving coil and the second receiving coil. Step 6: Calculate the amplitude and distance of the eddy current signal using measurement software to obtain the external structural distance information.

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