A remote-field eddy current probe and method for detecting defects in dissimilar steel welds

Abstract

The present invention discloses a far-field eddy current probe and method for detecting defects in heterogeneous steel welds, including: an excitation unit, a detection unit, a shielding unit, a signal connection joint and a probe housing, wherein the excitation unit is composed of an excitation coil placed inside an excitation magnetic conductive structure, the detection unit is composed of a detection coil tightly circumferentially wound around the outer circumference of the detection magnetic conductive structure, and the shielding unit is composed of a multi-layer composite shielding structure. Aiming at the complex pipeline structure at the heterogeneous steel weld, the present invention has developed a special conformal probe structure, which can complete the detection in a small space and avoid the signal interference caused by the variable diameter section and the thermocouple; it adopts multi-signal channel time-sharing detection, so that the excitation unit and the detection unit between adjacent signal channels are placed in opposite directions, ensuring that both sides of the heterogeneous steel weld can excite and receive eddy current signals; during detection, the probe can rotate around the heterogeneous steel weld for one circle to realize far-field eddy current detection of weld defects, thereby improving detection efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of weld nondestructive testing, and in particular to a far-field eddy current probe and method for detecting defects in welds of dissimilar steels. Background Art

[0002] The connecting pipe at the re-export of the furnace end of the thermal power unit adopts a different-diameter and different-type steel structure, which is welded from pipes of two materials. Affected by the welding process and the service environment, the butt weld at the connection of the different steels is prone to harmful defects, causing pipeline damage and leakage, which in turn affects the service life of the equipment and the safe operation of the thermal power unit. Therefore, it is of great significance to timely detect the health status of the butt weld of the different steels.

[0003] At present, there are several limitations in the detection of the health status of dissimilar steel welds: First, the complex pipeline structure at the dissimilar steel welds causes the problem of narrow detection space. Since the connecting pipe at the furnace end re-export adopts a different diameter structure, there is a variable diameter section on the lower side of the dissimilar steel weld, and in order to monitor the temperature change of the pipeline, a thermocouple is set on the upper side of the dissimilar steel weld. Therefore, due to the influence of the variable diameter section and the thermocouple, some detection parts cannot be reached by using local point detection technologies such as ultrasonic detection. Secondly, there is the problem of defect detection depth. The dissimilar steel welds are welded automatically by argon arc. The appearance and root of the welds are well formed, but due to the influence of welding quality and service environment, cracks mostly originate at the root of the weld on the inner wall of the pipeline and the fusion line. Therefore, it is difficult to detect deep defects in the welds, and surface defect detection methods such as penetration detection and eddy current detection are difficult to achieve. At the same time, there is a problem of insufficient defect detection efficiency. The furnace end pipelines are densely arranged and the space is small. The X-ray detection method requires the placement of a X-ray source and film, and the magnetic particle detection requires the surface to be processed. The time cost of both is high. Therefore, a detection method that can efficiently and reliably detect buried depth defects in dissimilar steel welds needs to be studied urgently. Summary of the invention

[0004] The purpose of the present invention is to provide a far-field eddy current probe and method for dissimilar steel weld defect detection, so as to address the problem of buried depth defect detection of dissimilar steel welds of small-diameter thin-walled reducer pipes at the furnace end re-export of thermal power units.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A remote field eddy current probe for detecting defects in welds of heterogeneous steels, comprising: an excitation unit, a detection unit, a shielding unit, a signal connection joint, a probe housing, a signal excitation module, a signal processing module and a display module;

[0007] The excitation unit is composed of an excitation coil placed inside an excitation magnetic conductive structure, the detection unit is composed of a detection coil tightly wound circumferentially around the outer circumference of the detection magnetic conductive structure, and the shielding unit is composed of a multi-layer composite shielding structure; the probe housing is used to place and fix the excitation unit, the detection unit, the shielding unit and the signal connection connector, and a circular through hole for fixing the signal connection connector is provided at the bottom of the probe housing;

[0008] The remote-field eddy current probe includes two or more signal channels, and the number of signal channels required is increased or decreased according to the specifications and dimensions of the pipeline and the detection space; each signal channel is composed of an excitation unit and a detection unit, and the excitation units and detection units between adjacent signal channels are placed in opposite directions to ensure that the pipelines of two materials on both sides of the weld can be excited and receive eddy current signals; the detection parameters of each signal channel can be changed according to the placement direction of the excitation unit and the detection unit, as well as the defect detection effect and purpose;

[0009] The signal excitation module is used to pass a low-frequency sinusoidal signal to the excitation unit. The excitation coils of the two signal channels are excited by time-sharing to generate alternating excitation fields on the surface and inside of the heterogeneous material pipes on both sides of the weld. The shielding unit is used to block the direct coupling electromagnetic field energy and force the electromagnetic field energy excited by the excitation coil to penetrate into the weld under inspection. The detection unit located in the far field area is used to pick up the changes in the induced voltage signal containing the health status of the weld under inspection, which is amplified and filtered by the signal processing module and then transmitted to the display module, which displays the eddy current impedance plane diagram.

[0010] A further improvement of the present invention is that the exciting coil adopts a cylindrical structure, and the detecting coil has a rectangular structure after being wound and fixed, and both are made of copper enameled wire.

[0011] A further improvement of the present invention is that the longitudinal cross-section of the excitation magnetic conductive structure is in the shape of a "mountain", and the longitudinal cross-section of the detection magnetic conductive structure is in the shape of a "U". The material of the magnetic conductive structure is a high magnetic permeability material such as ferrite or silicon steel, and its specifications and dimensions are selected according to the coil to ensure a close fit between the magnetic conductive structure and the coil.

[0012] A further improvement of the present invention is that the axis of the exciting coil is perpendicular to the axis of the pipeline, and the axis of the detecting coil is parallel to the axis of the pipeline;

[0013] The excitation unit and the detection unit are placed symmetrically across the weld and are both perpendicular to the outer surface of the pipe.

[0014] A further improvement of the present invention is that the shielding unit adopts a multi-layer composite shielding structure, comprising three groups of shielding modules in total;

[0015] The first group of shielding modules consists of an excitation aluminum cover and a detection aluminum cover, which are used to place and fix the excitation unit and the detection unit respectively, and their shapes and sizes are adapted to the excitation unit and the detection unit;

[0016] The second set of shielding modules is composed of a layer of copper and two layers of aluminum, which are used to further attenuate the electromagnetic field energy of the direct coupling channel and avoid signal interference caused by the thermocouple. The copper sheet is placed between the two layers of aluminum, with gaps between adjacent copper and aluminum sheets. The curvature of the copper and aluminum sheets close to the detection surface is selected according to the pipeline specifications.

[0017] The third group of shielding modules is composed of two layers of copper blocks, which are used to attenuate the electromagnetic field energy of the direct coupling channel, as well as fix the excitation unit, the detection unit, the first group of shielding modules and the second group of shielding modules. The curvature of the copper block close to the detection surface is selected according to the pipeline specifications.

[0018] A further improvement of the present invention is that an arc groove is provided at the center of the first layer of copper block to avoid the influence of the weld on the probe scanning, and the size of the arc groove is processed according to the weld width and the excess height.

[0019] A further improvement of the present invention is that a chamfer of a certain angle is set near the pipe diameter change position of the first layer copper block to avoid the problem of being unable to scan due to the probe being too long, and the chamfer angle is selected according to the slope of the pipe diameter change position.

[0020] A further improvement of the present invention is that the first layer of copper blocks is further provided with two circular grooves and three rectangular grooves, the two circular grooves are used to place and fix the excitation unit, the two short rectangular grooves are used to place and fix the detection unit, and the one long rectangular groove is used to place and fix the second group of shielding modules.

[0021] A further improvement of the present invention is that the second layer of copper block is processed with four circular through holes for connecting the coil leads.

[0022] A remote-field eddy current detection method for heterogeneous steel weld defect detection, based on the remote-field eddy current probe for heterogeneous steel weld defect detection, comprises the following steps:

[0023] The far-field eddy current probe is placed on the surface of the inspected pipeline. The arc-shaped groove in the center of the probe matches the pipeline weld, and the chamfer at the end matches the pipe reducer. The probe rotates at a uniform speed along the circumferential weld direction for scanning. The signal excitation module passes a low-frequency sinusoidal signal to the excitation unit. The excitation coils of the two signal channels are excited by time-sharing to generate alternating excitation fields on the surface and inside of the heterogeneous material pipelines on both sides of the weld. The shielding unit blocks the direct coupling electromagnetic field energy, forcing the electromagnetic field energy excited by the excitation coil to penetrate into the inspected weld. The detection unit located in the far-field area picks up the induced voltage signal changes containing the health status of the inspected weld, which are amplified and filtered by the signal processing module and transmitted to the display module. The display module displays the eddy current impedance plane diagram.

[0024] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0025] The present invention provides a far-field eddy current probe and method for detecting defects in heterogeneous steel welds. Aiming at the complex pipeline structure at the heterogeneous steel welds, a far-field eddy current probe with a special conformal structure is developed, which can complete the detection in a small space and avoid the signal interference caused by the variable diameter section and the thermocouple; a multi-signal channel time-sharing detection method is adopted, so that the excitation unit and the detection unit between adjacent signal channels are placed in opposite directions, ensuring that both sides of the heterogeneous steel weld can excite and receive eddy current signals, thereby improving the defect detection probability on both sides of the weld; at the same time, during the detection process, the probe rotates around the heterogeneous steel weld for one round of scanning to realize the far-field eddy current detection of hidden defects in the weld, thereby greatly improving the defect detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the three-dimensional structure of the far-field eddy current probe of the present invention.

[0027] Figure 2 It is a front view of the far-field eddy current probe of the present invention.

[0028] Figure 3 It is a schematic diagram of a far-field eddy current detection method for detecting buried depth defects of dissimilar steel welds in the present invention.

[0029] Figure 4 It is a schematic diagram of the far-field eddy current signal of the buried depth defect of the dissimilar steel weld in the present invention.

[0030] Description of reference numerals:

[0031] 1. Excitation coil, 2. Detection coil, 3. Excitation magnetic conductive structure, 4. Detection magnetic conductive structure, 5. Excitation aluminum cover, 6. Detection aluminum cover, 7. Second set of shielding modules, 8. Third set of shielding modules, 9. Probe housing, 10. Signal connection connector, 11. Signal excitation module, 12. Signal processing module, 13. Display module. DETAILED DESCRIPTION

[0032] In order to make those skilled in the art better understand the technical scheme of the present invention, the present invention is further described in detail below in conjunction with specific embodiments. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0033] like Figure 1 As shown, the present invention provides a far-field eddy current probe for heterogeneous steel weld defect detection, comprising: an excitation unit, a detection unit, a shielding unit, a signal connection connector 10, a probe housing 9, a signal excitation module 11, a signal processing module 12 and a display module 13.

[0034] The excitation unit is composed of an excitation coil 1 placed inside an excitation magnetic conductive structure 3, the detection unit is composed of a detection coil 2 tightly wound circumferentially around the outer circumference of a detection magnetic conductive structure 4, and the shielding unit is composed of a multi-layer composite shielding structure.

[0035] The far-field eddy current probe comprises two or more signal channels, and the number of required signal channels can be increased or decreased according to the specifications and dimensions of the pipeline and the detection space; each signal channel is composed of an excitation unit and a detection unit, and the excitation units and detection units between adjacent signal channels are placed in opposite directions to ensure that pipelines of two materials on both sides of the weld can be excited and receive eddy current signals; the detection parameters of each signal channel can be changed according to the placement direction of the excitation unit and the detection unit as well as the defect detection effect and purpose.

[0036] The excitation coil 1 adopts a cylindrical structure, and the detection coil 2 has a rectangular structure after being wound and fixed, and both are made of copper enameled wire.

[0037] The longitudinal cross-section of the excitation magnetic conductive structure 2 is in the shape of a "mountain", and the longitudinal cross-section of the detection magnetic conductive structure 4 is in the shape of a "U". The material of the magnetic conductive structure is a high magnetic permeability material such as ferrite or silicon steel, and its specifications and dimensions are selected according to the coil, and it is necessary to ensure that the magnetic conductive structure and the coil are closely matched.

[0038] The axis of the excitation coil 1 is perpendicular to the axis of the pipeline, and the axis of the detection coil 2 is parallel to the axis of the pipeline.

[0039] The excitation unit and the detection unit are symmetrically placed across the weld and are both perpendicular to the outer surface of the pipeline.

[0040] The shielding unit adopts a multi-layer composite shielding structure and comprises three groups of shielding modules in total.

[0041] The first group of shielding modules is composed of an excitation aluminum cover 5 and a detection aluminum cover 6, which are used to place and fix the excitation unit and the detection unit respectively, and their shapes and sizes are adapted to the excitation unit and the detection unit.

[0042] The second group of shielding modules 7 is composed of a layer of copper sheet and two layers of aluminum sheets, which are used to further attenuate the electromagnetic field energy of the direct coupling channel and avoid signal interference caused by the thermocouple. The copper sheet is placed between the two layers of aluminum sheets, and a certain gap is left between adjacent copper sheets and aluminum sheets. The curvature of the copper sheet and the aluminum sheet close to the detection surface is selected according to the pipeline specifications.

[0043] The third group of shielding modules 8 is composed of two layers of copper blocks, which are used to attenuate the electromagnetic field energy of the direct coupling channel, as well as fix the excitation unit, the detection unit, the first group of shielding modules and the second group of shielding modules 7. The curvature of the copper block close to the detection surface is selected according to the pipeline specifications.

[0044] An arc groove is arranged at the center of the first layer of copper block to avoid the influence of the weld on the probe scanning. The size of the arc groove is processed according to the weld width and the excess height.

[0045] The first layer of copper blocks is chamfered at a certain angle near the pipe diameter change position to avoid the problem of the probe being too long and unable to scan. The chamfer angle is selected according to the slope of the pipe diameter change position.

[0046] The first layer of copper block is also provided with two circular grooves and three rectangular grooves, the two circular grooves are used to place and fix the excitation unit, the two short rectangular grooves are used to place and fix the detection unit, and the one long rectangular groove is used to place and fix the second group of shielding modules 7.

[0047] The second layer of copper block described herein is processed with four circular through holes for connecting the coil leads.

[0048] The probe housing 9 is used to place and fix the excitation unit, the detection unit, the shielding unit and the signal connection connector 10. A circular through hole for fixing the signal connection connector is provided at the bottom of the probe housing 9. The curvature of the probe housing 9 close to the detection surface is selected according to the pipeline specifications, and its inner cavity size is adapted to the outer shielding module, and is also provided with a central arc groove and end chamfers.

[0049] The present invention provides a remote field eddy current detection method for detecting defects in heterogeneous steel welds, comprising the following steps:

[0050] The far-field eddy current probe is placed on the surface of the inspected pipeline, the arc-shaped groove in the center of the probe matches the pipeline weld, the end chamfer matches the pipeline reducer, and the probe rotates at a uniform speed along the circumferential weld direction for scanning; the signal excitation module 11 passes a low-frequency sinusoidal signal to the excitation unit, and the excitation coils 1 of the two signal channels are excited by time-sharing, respectively generating alternating excitation fields on the surfaces and insides of the heterogeneous material pipelines on both sides of the weld, the shielding unit blocks the direct coupling electromagnetic field energy, and forces the electromagnetic field energy excited by the excitation coil 1 to penetrate into the inspected weld, and the detection unit located in the far-field area picks up the induced voltage signal changes containing the health status of the inspected weld, and transmits them to the display module 13 after amplification and filtering by the signal processing module 12, and the display module 13 displays the eddy current impedance plane diagram.

[0051] Example 1

[0052] A remote-field eddy current probe and method for detecting defects in heterogeneous steel welds according to the present invention is used to detect defects in heterogeneous steel welds of The dissimilar steel welds are tested, where the weld width is 12mm, the upper part is made of T91, the lower part is made of TP347, a thermocouple fixed measuring point is set 30mm above the weld, and there is a thermocouple with a specification of 18mm below the weld. The far-field eddy current probe is placed on the surface of the inspected pipeline. The arc groove in the center of the probe matches the pipeline weld, and the chamfer at the end matches the pipeline reducer. The probe rotates at a uniform speed along the circumferential weld direction to scan. The eddy current impedance plane diagram of the weld buried depth defect is shown in the figure below. Figure 4 shown.

[0053] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A remote field eddy current probe for detecting defects in dissimilar steel welds, characterized in that: include: Excitation unit, detection unit, shielding unit, signal connection connector, probe housing, signal excitation module, signal processing module and display module; The excitation unit is composed of an excitation coil placed inside an excitation magnetic conductive structure, the detection unit is composed of a detection coil tightly wound circumferentially around the outer circumference of the detection magnetic conductive structure, and the shielding unit is composed of a multi-layer composite shielding structure; the probe housing is used to place and fix the excitation unit, the detection unit, the shielding unit and the signal connection connector, and a circular through hole for fixing the signal connection connector is provided at the bottom of the probe housing; The remote-field eddy current probe includes two or more signal channels, and the number of signal channels required is increased or decreased according to the specifications and dimensions of the pipeline and the detection space; each signal channel is composed of an excitation unit and a detection unit, and the excitation units and detection units between adjacent signal channels are placed in opposite directions to ensure that the pipelines of two materials on both sides of the weld can be excited and receive eddy current signals; the detection parameters of each signal channel can be changed according to the placement direction of the excitation unit and the detection unit, as well as the defect detection effect and purpose; The signal excitation module is used to pass a low-frequency sinusoidal signal to the excitation unit. The excitation coils of the two signal channels are excited by time-sharing to generate alternating excitation fields on the surface and inside of the heterogeneous material pipes on both sides of the weld. The shielding unit is used to block the direct coupling electromagnetic field energy and force the electromagnetic field energy excited by the excitation coil to penetrate into the weld under inspection. The detection unit located in the far field area is used to pick up the changes in the induced voltage signal containing the health status of the weld under inspection, which is amplified and filtered by the signal processing module and then transmitted to the display module, which displays the eddy current impedance plane diagram.

2. The remote-field eddy current probe for detecting dissimilar steel weld defects according to claim 1, characterized in that: The excitation coil adopts a cylindrical structure, and the detection coil has a rectangular structure after being wound and fixed. Both are made of copper enameled wire.

3. The remote-field eddy current probe for detecting dissimilar steel weld defects according to claim 1, characterized in that: The longitudinal cross-section of the excitation magnetic structure is in the shape of a "mountain", and the longitudinal cross-section of the detection magnetic structure is in the shape of a "U". The material of the magnetic structure is a high magnetic permeability material such as ferrite or silicon steel. Its specifications and dimensions are selected according to the coil to ensure a close fit between the magnetic structure and the coil.

4. The remote-field eddy current probe for detecting dissimilar steel weld defects according to claim 1, characterized in that: The axis of the exciting coil is perpendicular to the axis of the pipeline, and the axis of the detecting coil is parallel to the axis of the pipeline; The excitation unit and the detection unit are placed symmetrically across the weld and are both perpendicular to the outer surface of the pipe.

5. The remote-field eddy current probe for detecting dissimilar steel weld defects according to claim 1, characterized in that: The shielding unit adopts a multi-layer composite shielding structure, which contains three sets of shielding modules in total; The first group of shielding modules consists of an excitation aluminum cover and a detection aluminum cover, which are used to place and fix the excitation unit and the detection unit respectively, and their shapes and sizes are adapted to the excitation unit and the detection unit; The second set of shielding modules is composed of a layer of copper and two layers of aluminum, which are used to further attenuate the electromagnetic field energy of the direct coupling channel and avoid signal interference caused by the thermocouple. The copper sheet is placed between the two layers of aluminum, with gaps between adjacent copper and aluminum sheets. The curvature of the copper and aluminum sheets close to the detection surface is selected according to the pipeline specifications. The third group of shielding modules is composed of two layers of copper blocks, which are used to attenuate the electromagnetic field energy of the direct coupling channel, as well as fix the excitation unit, the detection unit, the first group of shielding modules and the second group of shielding modules. The curvature of the copper block close to the detection surface is selected according to the pipeline specifications.

6. The remote field eddy current probe for dissimilar steel weld defect detection according to claim 5, characterized in that: An arc groove is arranged at the center of the first layer of copper block to avoid the influence of the weld on the probe scanning. The size of the arc groove is processed according to the weld width and the excess height.

7. The remote-field eddy current probe for detecting dissimilar steel weld defects according to claim 5, characterized in that: The first layer of copper block is chamfered at a certain angle near the pipe diameter change position to avoid the problem of the probe being too long and unable to scan. The chamfer angle is selected according to the slope of the pipe diameter change position.

8. The remote field eddy current probe for dissimilar steel weld defect detection according to claim 5, characterized in that: The first layer of copper block is also provided with two circular grooves and three rectangular grooves, the two circular grooves are used to place and fix the excitation unit, the two short rectangular grooves are used to place and fix the detection unit, and the one long rectangular groove is used to place and fix the second group of shielding modules.

9. The remote field eddy current probe for dissimilar steel weld defect detection according to claim 5, characterized in that: The second layer of copper block is processed with four circular through holes for coil lead connection.

10. A remote field eddy current detection method for heterogeneous steel weld defect detection, characterized in that: The method is based on a remote-field eddy current probe for detecting dissimilar steel weld defects according to any one of claims 1 to 9, and comprises the following steps: The far-field eddy current probe is placed on the surface of the inspected pipeline. The arc-shaped groove in the center of the probe matches the pipeline weld, and the chamfer at the end matches the pipe reducer. The probe rotates at a uniform speed along the circumferential weld direction for scanning. The signal excitation module passes a low-frequency sinusoidal signal to the excitation unit. The excitation coils of the two signal channels are excited by time-sharing to generate alternating excitation fields on the surface and inside of the heterogeneous material pipelines on both sides of the weld. The shielding unit blocks the direct coupling electromagnetic field energy, forcing the electromagnetic field energy excited by the excitation coil to penetrate into the inspected weld. The detection unit located in the far-field area picks up the induced voltage signal changes containing the health status of the inspected weld, which are amplified and filtered by the signal processing module and transmitted to the display module. The display module displays the eddy current impedance plane diagram.

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