Electromagnetic acoustic emission excitation device for pipeline weld crack detection

Abstract

The invention relates to the technical field of nondestructive testing, in particular to an electromagnetic acoustic emission excitation device for pipeline weld crack detection, which comprises a crack-containing pipeline test piece, and an electromagnetic shielding shell, a rectangular permanent magnet and a double D-shaped coil which are arranged above the crack-containing pipeline test piece, when high-frequency alternating current is introduced into the double-D-shaped coil, eddy current is induced under the action of an external magnetic field, the eddy current generates Lorentz force under modulation of the magnetic field, local mass points at the tip of a crack are caused to vibrate, and an acoustic emission signal is excited. The electromagnetic shielding shell can control magnetic field distribution, the magnetic field is focused at the tip of a crack, the placement direction of the double-D-shaped coil is parallel to the crack propagation direction, and the rectangular permanent magnets generate magnetic fields in opposite directions in a straight wire area, so that the stress directions of the two sides of the crack are opposite, and the crack is pulled; the signal-to-noise ratio of generated acoustic emission signals is increased, the detection rate of pipeline weld cracks can be increased, and the method has high application value.

Description

Technical Field

[0001] The invention relates to the technical field of nondestructive testing, and in particular to an electromagnetic acoustic emission excitation device for pipeline weld crack detection. Background Art

[0002] The welding quality of pipelines is the core element to ensure safe and efficient operation of pipelines after they are built. However, various defects will inevitably occur during the welding process. During service, pipelines need to deal with complex and changing environmental conditions and often withstand fatigue loads and impacts, which can easily lead to stress concentration and cracking at pipeline welds, posing a huge safety hazard.

[0003] Electromagnetic acoustic emission technology can couple energy from the excitation coil to the test piece through electromagnetic coupling, thereby stimulating a strong acoustic emission signal at the local defect. This technology has the advantages of non-contact detection, controllable detection process, and sensitivity to tiny defects. Therefore, it has unique advantages in pipeline weld crack detection.

[0004] At present, the conventional electromagnetic acoustic emission excitation device is designed with a spiral coil plus a cylindrical permanent magnet. The displacement generated by the spiral coil spreads outward in a circular shape over time. The sound field directivity is poor and the generated sound field range is large. However, the cracks in the pipeline welds are often relatively small, and the effective utilization area of ​​the spiral coil is low. At the same time, the larger sound field range produces stronger noise, which reduces the signal-to-noise ratio of the acoustic emission signal and is not conducive to the analysis of the acoustic emission signal. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose an electromagnetic acoustic emission excitation device for pipeline weld crack detection, which can improve the signal-to-noise ratio of the acoustic emission signal and enhance the detection rate of pipeline weld cracks and has high application value.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An electromagnetic acoustic emission excitation device for pipeline weld crack detection includes a pipeline test piece containing cracks, an electromagnetic shielding shell arranged above the pipeline test piece containing cracks, a rectangular permanent magnet and a double D-shaped coil;

[0008] The double D-shaped coil is located above the cracked pipe specimen, and the crack is located below the central axis of the double D-shaped coil; the placement direction of the double D-shaped coil is parallel to the crack extension direction;

[0009] The double D-shaped coil includes a straight conductor area and arc-shaped conductor areas located on the left and right sides of the straight conductor area arc, and the projection area of ​​the straight conductor area of ​​the double D-shaped coil on the cracked pipe specimen covers the tip of the crack;

[0010] The rectangular permanent magnet is located above the double D-shaped coil, and the projection area of ​​the rectangular permanent magnet on the cracked pipe specimen is larger than the projection area of ​​the straight wire area of ​​the double D-shaped coil on the cracked pipe specimen;

[0011] The electromagnetic shielding shell is located outside the rectangular permanent magnet, and the rectangular permanent magnet and the straight wire area of ​​the double D-shaped coil are both located inside the electromagnetic shielding shell.

[0012] Preferably, the double D-type coil is composed of two D-type coils, which are arranged opposite to each other on the left and right. The outermost radius, number of coil turns and wire spacing of the two D-type coils are equal, and the two D-type coils are located in the same plane. The two D-type coils are symmetrically distributed along the central axis of the double D-type coil.

[0013] Preferably, there is a gap between the straight wire area and the arc wire area of ​​the double D-type coil so as to reduce the interference of the eddy current in the arc wire area of ​​the double D-type coil on the eddy current in the straight wire area; when high-frequency alternating current is simultaneously passed through the two D-type coils of the double D-type coil, at the same time, the current direction of the straight wire area is the same, and the current direction of the arc wire area is different from the current direction of the straight wire area.

[0014] By adopting the above technical solution: the straight wire area of ​​the double D-type coil here can induce a strong eddy current at the crack tip under the action of the magnetic field, and the eddy current is focused on the crack tip. The direction of the eddy current induced in the arc-shaped wire area of ​​the double D-type coil under the action of the magnetic field is different from the direction of the eddy current in the straight wire area, and the eddy current in the arc-shaped wire area will interfere with the eddy current in the straight wire area.

[0015] Preferably, the length of the bottom surface of the rectangular permanent magnet is greater than the diameter of the double D-shaped coil, and the width of the bottom surface of the rectangular permanent magnet is equal to the width of the straight wire area of ​​the double D-shaped coil.

[0016] By adopting the above technical solution: the size setting of the rectangular permanent magnet here can significantly weaken the magnetic field strength in the arc conductor area of ​​the double D-type coil, thereby weakening the induced eddy current in the arc conductor area of ​​the coil and reducing the interference caused by the eddy current in the straight conductor area of ​​the coil.

[0017] Preferably, the rectangular permanent magnet is composed of two permanent magnets with opposite polarities, the magnetic poles of the two permanent magnets are both located in the vertical direction, one of the permanent magnets has an N pole on the upper side and an S pole on the lower side, and the other permanent magnet has an S pole on the upper side and an N pole on the lower side. The two permanent magnets can generate magnetic fields with opposite directions arranged in parallel in the straight conductor area of ​​the double D-type coil.

[0018] Preferably, the distance between the rectangular permanent magnet and the cracked pipe specimen is ≤3 mm, so as to ensure that the rectangular permanent magnet generates a sufficiently strong magnetic field above the cracked pipe specimen.

[0019] Among them, after the double D-type coil is energized to induce eddy currents, it can generate Lorentz forces with opposite directions on both sides of the crack under the modulation of the magnetic field, which pulls the crack, causes high-frequency vibration of local particles at the crack tip, and stimulates a strong acoustic emission signal.

[0020] Preferably, the electromagnetic shielding shell is a hollow rectangular shell without a bottom surface, the height of the electromagnetic shielding shell is greater than the height of the rectangular permanent magnet, and the projection area of ​​the electromagnetic shielding shell on the cracked pipe specimen is greater than the projection area of ​​the rectangular permanent magnet and the double D-type coil straight wire area on the cracked pipe specimen.

[0021] By adopting the above technical solution: the electromagnetic shielding shell used here can cover the other five surfaces of the rectangular permanent magnet except the bottom surface.

[0022] Preferably, the electromagnetic shielding shell is made of iron-based amorphous nanocrystalline soft magnetic material with high magnetic permeability and high magnetic flux density. According to Ohm's law in the air, the magnetic flux tends to pass through the path with high magnetic permeability and low magnetic resistance. Therefore, the magnetic flux passing through the electromagnetic shielding shell is large, and the magnetic flux passing through the air medium is small, and the magnetic lines of force are guided in the electromagnetic shielding shell.

[0023] By adopting the above technical solution: the other four sides of the electromagnetic shielding shell except the top surface are in the vertical direction, so the direction in which the magnetic lines of force are guided in the electromagnetic shielding shell is also in the vertical direction, and the direction of the magnetic field in the straight conductor area of ​​the double D-type coil is controlled to be in the vertical direction. Among them, the electromagnetic shielding shell can control the magnetic field distribution of the rectangular permanent magnet at the double D-type coil, so that the magnetic field is mainly distributed in the straight conductor area of ​​the double D-type coil, and the direction of the magnetic field is controlled to be mainly in the vertical direction, weakening the magnetic field in the arc conductor area of ​​the double D-type coil, so that the magnetic field is focused on the crack tip.

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

[0025] 1. The present invention uses a double D-type coil, the current direction in the straight conductor area is the same, the induced eddy current direction is also the same, and there is a gap between the straight conductor area and the arc conductor area, so that the eddy current is focused on the crack tip, the sound field has strong directivity, the effective utilization area of ​​the coil is high, and the signal-to-noise ratio of the acoustic emission signal is high.

[0026] 2. The rectangular permanent magnet used in the present invention can generate magnetic fields arranged in parallel and in opposite directions above the straight conductor area of ​​the double D-type coil. After the double D-type coil is energized to induce eddy currents, it can generate Lorentz forces in opposite directions on both sides of the crack under the modulation of the magnetic field, which pulls the crack, causes high-frequency vibration of local particles at the crack tip, and stimulates a stronger acoustic emission signal.

[0027] 3. The electromagnetic shielding shell used in the present invention is made of iron-based amorphous nanocrystalline soft magnetic material, which has high magnetic permeability, high magnetic flux density, etc. It can control the distribution of the magnetic field at the double D-type coil, and control the direction of the magnetic field mainly in the vertical direction, so that the magnetic field is focused on the crack tip, further improving the signal-to-noise ratio of the acoustic emission signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the present invention;

[0029] Figure 2 for Figure 1 A top view of

[0030] Figure 3 The waveform diagram of the high-frequency alternating current passed through the double D-type coil in the present invention;

[0031] Figure 4 is a distribution diagram of eddy current generated at the crack tip after the double D-type coil in the present invention is energized;

[0032] Figure 5 A schematic diagram of the Lorentz force generated at the crack tip at two moments in opposite current directions after the double D-type coil in the present invention is energized;

[0033] Figure 6 It is a schematic diagram of the magnetic flux density at the crack tip when no electromagnetic shielding shell is added in the present invention;

[0034] Figure 7 It is a schematic diagram of the magnetic flux density at the crack tip after the electromagnetic shielding shell is installed in the present invention;

[0035] Figure 8 It is a schematic diagram of the Lorentz force generated at the crack tip after the electromagnetic shielding shell is installed in the present invention. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings, so that those skilled in the art can better understand the advantages and features of the present invention, thereby making a clearer definition of the protection scope of the present invention. The embodiments described in the present invention are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0037] Reference Figure 1-Figure 2 , an electromagnetic acoustic emission excitation device for pipeline weld crack detection, comprising a pipeline test piece 4 containing a crack 5, and an electromagnetic shielding shell 1, a rectangular permanent magnet 2 and a double D-type coil 3 arranged above the pipeline test piece 4 containing the crack 5;

[0038] The double D-shaped coil 3 is located above the pipe specimen 4 containing the crack 5, and the crack 5 is located below the central axis of the double D-shaped coil 3; the placement direction of the double D-shaped coil 3 is parallel to the expansion direction of the crack 5;

[0039] The double D-shaped coil 3 includes a straight conductor area and arc-shaped conductor areas located on the left and right sides of the straight conductor area arc, and the projection area of ​​the straight conductor area of ​​the double D-shaped coil 3 on the pipe specimen 4 containing the crack 5 covers the tip of the crack 5;

[0040] The rectangular permanent magnet 2 is located above the double D-shaped coil 3, and the projection area of ​​the rectangular permanent magnet 3 on the pipe specimen 4 containing the crack 5 is larger than the projection area of ​​the straight wire area of ​​the double D-shaped coil 3 on the pipe specimen 4 containing the crack 5;

[0041] The electromagnetic shielding shell 1 is located outside the rectangular permanent magnet 2 , and the rectangular permanent magnet 2 and the straight conductor area of ​​the double D-shaped coil 3 are both located inside the electromagnetic shielding shell 1 .

[0042] Specifically, the double D-type coil 3 is composed of two D-type coils, which are arranged opposite to each other on the left and right. The outermost radius, number of coil turns and wire spacing of the two D-type coils are equal, and the two D-type coils are located in the same plane. The two D-type coils are symmetrically distributed along the central axis of the double D-type coil 3.

[0043] Figure 3 is a waveform diagram of the high-frequency alternating current passed through the double D-type coil 3. Specifically, there is a gap between the straight wire area and the arc wire area of ​​the double D-type coil 3, such as Figure 3 As shown, when high-frequency alternating current is simultaneously supplied to the two D-type coils of the double D-type coil 3, at the same moment, the current directions in the straight conductor area are the same, and the current directions in the arc conductor area are different from those in the straight conductor area.

[0044] In this embodiment, Figure 4 is the distribution diagram of the eddy current generated at the tip of the crack 5 after the double D-type coil 3 is energized, as shown in Figure 4 As shown, the straight wire area of ​​the double D-type coil 3 can induce a strong eddy current at the tip of the crack 5 under the action of the magnetic field, and the eddy current is focused on the tip of the crack 5. The direction of the eddy current induced in the arc-shaped wire area of ​​the double D-type coil 3 under the action of the magnetic field is different from the direction of the eddy current in the straight wire area, and the eddy current in the arc-shaped wire area will interfere with the eddy current in the straight wire area. Since there is a gap between the straight wire area and the arc-shaped wire area of ​​the double D-type coil 3, the interference of the eddy current in the arc-shaped wire area of ​​the coil on the eddy current in the straight wire area is weakened.

[0045] Specifically, Figure 2 As shown, the length of the bottom surface of the rectangular permanent magnet 2 is greater than the diameter of the double D-shaped coil 3 , and the width of the bottom surface of the rectangular permanent magnet 2 is equal to the width of the straight wire area of ​​the double D-shaped coil 3 .

[0046] In this embodiment, the size setting of the rectangular permanent magnet 2 can significantly weaken the magnetic field strength in the arc conductor area of ​​the double D-type coil 3, thereby weakening the induced eddy current in the arc conductor area of ​​the coil and reducing the interference caused by the eddy current in the straight conductor area of ​​the coil.

[0047] like Figure 1 As shown, specifically, the rectangular permanent magnet 2 is composed of two permanent magnets with opposite polarities, the magnetic poles of the two permanent magnets are both located in the vertical direction, one of the permanent magnets has an N pole on the upper side and an S pole on the lower side, and the other permanent magnet has an S pole on the upper side and an N pole on the lower side. The two permanent magnets can generate magnetic fields with opposite directions arranged in parallel in the straight conductor area of ​​the double D-type coil 3.

[0048] Specifically, the distance between the rectangular permanent magnet 2 and the pipe specimen 4 containing the crack 5 is ≤3 mm, so as to ensure that the rectangular permanent magnet 2 generates a sufficiently strong magnetic field above the pipe specimen 4 containing the crack.

[0049] in, Figure 5 It is a schematic diagram of the Lorentz force generated at the tip of the crack 5 at two moments in opposite directions of the current after the double D-type coil 3 is energized, as shown in Figure 5 As shown, after the double D-type coil 3 is energized to induce eddy current, it can generate Lorentz forces with opposite directions on both sides of the crack 5 under the modulation of the magnetic field, which pulls the crack 5, causes high-frequency vibration of the local particles at the tip of the crack 5, and stimulates a stronger acoustic emission signal.

[0050] It should be noted that the main idea of ​​the traditional optimization of electromagnetic acoustic emission excitation device is to improve the magnet configuration to produce a magnetic field distribution that is more conducive to inducing stronger eddy currents and Lorentz forces. This embodiment controls the size and placement of the rectangular permanent magnet 2 so that the magnetic field is mainly distributed in the straight wire area of ​​the double D-type coil 3. This is the traditional optimization idea, but the Lorentz force generated in the arc wire area of ​​the double D-type coil 3 is different in direction from the Lorentz force generated in the straight wire area, which will still excite interference signals and reduce the signal-to-noise ratio of the generated acoustic emission signal. Therefore, this embodiment proposes an electromagnetic shielding shell 1 that can weaken the Lorentz force generated in the arc wire area of ​​the double D-type coil 3.

[0051] like Figure 1-Figure 2 As shown, specifically, the electromagnetic shielding shell 1 is a hollow rectangular shell without a bottom surface, the height of the electromagnetic shielding shell 1 is greater than the height of the rectangular permanent magnet 2, and the projection area of ​​the electromagnetic shielding shell 1 on the pipeline specimen 4 containing the crack 5 is greater than the projection area of ​​the rectangular permanent magnet 2 and the straight wire area of ​​the double D-type coil 3 on the pipeline specimen 4 containing the crack 5. Among them, the electromagnetic shielding shell 1 covers the remaining 5 surfaces of the rectangular permanent magnet 2 except the bottom surface.

[0052] Specifically, the electromagnetic shielding shell 1 is made of iron-based amorphous nanocrystalline soft magnetic material, and has high magnetic permeability and high magnetic flux density. According to Ohm's law in the air, the magnetic flux tends to pass through the path with high magnetic permeability and low magnetic resistance. Therefore, the magnetic flux passing through the electromagnetic shielding shell 1 is very large, and the magnetic flux passing through the air medium is very small, and the magnetic lines of force are guided in the electromagnetic shielding shell 1.

[0053] In this embodiment, the other four sides of the electromagnetic shielding shell 1 except the top side are in the vertical direction, so the direction in which the magnetic lines of force are guided in the electromagnetic shielding shell 1 is also in the vertical direction, and the magnetic field direction in the straight conductor area of ​​the double D-type coil 3 is controlled to be in the vertical direction.

[0054] in, Figure 6 It is a schematic diagram of the magnetic flux density at the tip of the crack 5 of the electromagnetic acoustic emission excitation device used for pipeline weld crack detection without the electromagnetic shielding shell 1. Figure 7 It is a schematic diagram of the magnetic flux density at the tip of the crack 5 of the electromagnetic acoustic emission excitation device for pipeline weld crack detection after the electromagnetic shielding shell 1 is installed. It can be clearly seen that the electromagnetic shielding shell 1 can control the magnetic field distribution of the rectangular permanent magnet 2 at the double D-type coil 3, the vertical magnetic field is significantly enhanced, and the magnetic field is mainly distributed in the straight conductor area of ​​the double D-type coil 3, and the magnetic field in the arc conductor area of ​​the double D-type coil 3 is weakened, so that the magnetic field distribution is focused on the tip of the crack 5, which meets the design requirements.

[0055] Among them, the eddy current focused in the straight wire area of ​​the double D-type coil 3 combined with the focused magnetic field can generate a focused Lorentz force at the tip of the crack 5, which is Figure 8 and Figure 5 By comparison, it can be seen that Figure 8 The Lorentz force generated in the arc conductor area of ​​the double D-type coil 3 is greatly reduced, while the magnitude and direction of the Lorentz force generated in the straight conductor area of ​​the double D-type coil 3 remain almost unchanged. The Lorentz force is focused on the tip of the crack 5, and the force directions on both sides of the crack 5 are opposite, which has a pulling effect on the crack.

[0056] In summary, the present invention can form focused eddy currents and magnetic fields, thereby generating focused Lorentz forces at the crack tip, and the forces on both sides of the crack are in opposite directions, which pulls the crack and causes high-frequency vibration of local particles at the crack tip, thereby stimulating stronger acoustic emission signals, improving the signal-to-noise ratio of the acoustic emission signals, and enhancing the detection rate of pipeline weld cracks, which has a high application value.

[0057] The description and practice disclosed in the present invention are easy to think and understand for ordinary technicians in the technical field, and several improvements and modifications can be made without departing from the principles of the present invention. Therefore, modifications or improvements made without departing from the spirit of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. An electromagnetic acoustic emission excitation device for pipeline weld crack detection, characterized in that: It comprises a pipeline test piece (4) containing a crack (5), an electromagnetic shielding shell (1) arranged above the pipeline test piece (4) containing the crack (5), a rectangular permanent magnet (2) and a double D-shaped coil (3); The double D-shaped coil (3) is located above the pipe test piece (4) containing the crack (5), and the crack (5) is located below the central axis of the double D-shaped coil (3); the placement direction of the double D-shaped coil (3) is parallel to the expansion direction of the crack (5); The double D-shaped coil (3) comprises a straight conductor area and arc-shaped conductor areas located on the left and right sides of the straight conductor area arc, and the projection area of ​​the straight conductor area of ​​the double D-shaped coil (3) on the pipeline test piece (4) containing the crack (5) covers the tip of the crack (5); The rectangular permanent magnet (2) is located above the double D-shaped coil (3), and the projection area of ​​the rectangular permanent magnet (3) on the pipeline specimen (4) containing the crack (5) is larger than the projection area of ​​the straight wire area of ​​the double D-shaped coil (3) on the pipeline specimen (4) containing the crack (5); The electromagnetic shielding shell (1) is located outside the rectangular permanent magnet (2), and the rectangular permanent magnet (2) and the straight conductor area of ​​the double D-shaped coil (3) are both located inside the electromagnetic shielding shell (1).

2. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 1 is characterized in that: The double D-type coil (3) is composed of two D-type coils, which are arranged opposite to each other on the left and right. The outer radius, number of coil turns and wire spacing of the two D-type coils are equal, and the two D-type coils are located in the same plane. The two D-type coils are symmetrically distributed along the central axis of the double D-type coil (3).

3. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 2 is characterized in that: There is a gap between the straight conductor area and the arc-shaped conductor area of ​​the double D-type coil (3); when high-frequency alternating current is simultaneously supplied to the two D-type coils of the double D-type coil (3), at the same time, the current directions in the straight conductor area are the same, while the current direction in the arc-shaped conductor area is different from the current direction in the straight conductor area.

4. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 1 is characterized in that: The length of the bottom surface of the rectangular permanent magnet (2) is greater than the diameter of the double D-shaped coil (3), and the width of the bottom surface of the rectangular permanent magnet (2) is equal to the width of the straight wire area of ​​the double D-shaped coil (3).

5. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 1, characterized in that: The rectangular permanent magnet (2) is composed of two permanent magnets with opposite polarities. The magnetic poles of the two permanent magnets are both located in the vertical direction. The upper side of one permanent magnet is an N pole and the lower side is an S pole, and the upper side of the other permanent magnet is an S pole and the lower side is an N pole. The two permanent magnets can generate magnetic fields arranged in parallel and in opposite directions in the straight conductor area of ​​the double D-shaped coil (3).

6. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 1, characterized in that: The distance between the rectangular permanent magnet (2) and the pipe test piece (4) containing the crack (5) is ≤3 mm.

7. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 1, characterized in that: The electromagnetic shielding shell (1) is a hollow rectangular shell without a bottom surface. The height of the electromagnetic shielding shell (1) is greater than the height of the rectangular permanent magnet (2). The projection area of ​​the electromagnetic shielding shell (1) on the pipeline test piece (4) containing the crack (5) is greater than the projection area of ​​the rectangular permanent magnet (2) and the straight wire area of ​​the double D-shaped coil (3) on the pipeline test piece (4) containing the crack (5).

8. The electromagnetic acoustic emission excitation device for pipeline weld crack detection according to claim 1, characterized in that: The electromagnetic shielding shell (1) is made of iron-based amorphous nanocrystalline soft magnetic material.

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