Steel pipe end magnetic flux leakage flaw detector

Abstract

The invention relates to the technical field of steel pipe nondestructive testing, in particular to a steel pipe end magnetic flux leakage flaw detector. The steel pipe end magnetic flux leakage flaw detector comprises a rack, a magnetizing coil and a probe system are installed on the rack in a sliding mode, a translation driving mechanism is arranged on the rack, the probe system comprises a probe, a probe lifting driving mechanism and a probe rotating driving mechanism, and a magnetic conductive pipe system is further arranged on the rack. The magnetic conductive pipe system comprises a magnetic conductive pipe, a magnetic conductive pipe lifting driving mechanism and a magnetic conductive pipe translation driving mechanism, the magnetic conductive pipe is located in front of the magnetizing coil and located on the same straight line with the center of the magnetizing coil and the center of the probe, and the magnetic conductive pipe is equal to the detected steel pipe in diameter so as to be in butt joint with the end of the detected steel pipe. When the coil reaches the end part of the detected steel pipe, the end part of the detected steel pipe is saturated and magnetized, so that the detection blind area of the end part of the steel pipe is eliminated, the interference of the magnetic pole effect of the end part of the steel pipe on a detection signal is eliminated, and the defect detection of the end part of the steel pipe is realized.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology for steel pipes, and in particular to a magnetic flux leakage flaw detector for the ends of steel pipes. Background Technology

[0002] After steel pipes are manufactured, they need to be inspected to determine if there are any defects. Magnetic flux leakage (MFL) testing technology is widely used in the non-destructive testing of steel pipes due to its advantages such as fast detection speed, high accuracy, and ease of automation. Currently, a commonly used MFL testing device is a dual-coil magnetizer, which has two magnetizing coils with a probe array between them. Each probe contains a magnetic sensor. The steel pipe is driven at high speed through the dual-coil magnetizer, where the magnetizing coils magnetize the pipe, creating a saturated magnetic field. This allows the probe to contact the outer surface of the pipe for detection. In defect-free areas, the magnetic lines of force converge and do not refract into the external space. However, in defective areas, the magnetic resistance is higher, causing the magnetic lines of force to refract from the defect interface into the external space, forming a leakage magnetic field. The presence of defects is detected by picking up this leakage magnetic field.

[0003] The existing double-coil magnetizer has a blind zone for steel pipe end detection when applied. The specific reasons are as follows: (1) An end effect will occur at the end of the steel pipe. When the end of the steel pipe just enters the magnetization coil, the magnetization coil is made up of steel pipe as iron core. The coil is gradually changed from a energized hollow coil to an iron core coil, which leads to an increase in its impedance. At this time, the magnetization circuit current under the action of the regulated DC power supply becomes smaller, the magnetic field of the magnetization coil weakens, and the magnetic lines of force cannot be effectively concentrated at the end of the steel pipe to form a saturated magnetic field. The magnetization at the end of the steel pipe is insufficient, and the leakage magnetic field generated at the defect location is very small, which cannot reach the magnetization intensity required for detection, thus creating a blind zone for detection; (2) The end of the steel pipe After passing through the magnetization coil, a magnetic pole effect is formed at the end of the steel pipe, generating a strong magnetic field, which greatly interferes with the probe that detects at the end of the steel pipe. The detection signal baseline will deviate positively, resulting in the failure to pick up the leakage magnetic field generated by the defect, thus causing missed detection; (3) The end of the steel pipe is mostly the main stress-bearing part. For steel pipes used in certain special scenarios, such as oil pipes and casings used in oil fields, in order to improve the end strength, the end of the steel pipe is usually set as a thickened end and has a tapered threaded structure. Since the shape of the thickened end and the tapered threaded section is irregular, the detection probe cannot adapt to the surface curvature of these areas, resulting in missed detection.

[0004] Currently, solutions to the blind zone caused by magnetic flux leakage testing (MFLT) at the ends of steel pipes can be broadly categorized into two types: one is to increase the magnetization intensity at the ends of the steel pipes, attempting to generate a saturated magnetic field at the initial stage of magnetization, thereby meeting the conditions for detecting end defects. However, due to the large order-of-magnetic permeability difference between air and ferromagnetic materials, even a significant increase in magnetization intensity yields minimal results and substantially increases equipment size and manufacturing and operating costs. The other is to employ various filtering methods to balance or eliminate signal interference from end detection, but these methods cannot eliminate the impact of reduced end defect signals caused by insufficient magnetization. Therefore, the existence of blind zones in end detection during MFLT testing of steel pipes remains a challenge in the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a magnetic flux leakage flaw detector for steel pipe ends, so as to solve the problem that existing magnetic flux leakage flaw detectors for steel pipe ends have blind spots and cannot detect defects at the ends of steel pipes.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A magnetic flux leakage flaw detector for steel pipe ends includes a frame. A magnetizing coil and a probe system are slidably mounted on the frame in a front-to-back direction. The frame is equipped with a translation drive mechanism for driving the magnetizing coil and probe system to move back and forth. The probe system includes a probe, a probe lifting drive mechanism for driving the probe to rise and fall, and a probe rotation drive mechanism for driving the probe to rotate. The probe is used to extend into the interior of the steel pipe and fit against the inner wall surface of the steel pipe to detect defect locations. The frame is also equipped with a magnetic tube system, which includes a magnetic tube, a magnetic tube lifting drive mechanism for driving the magnetic tube to rise and fall, and a magnetic tube translation drive mechanism for driving the magnetic tube to move back and forth. The magnetic tube is located in front of the magnetizing coil and is on the same straight line as the center of the magnetizing coil and the probe. The magnetic tube has the same diameter as the steel pipe being tested and is connected to the end of the steel pipe being tested.

[0007] Furthermore, the lifting action component of the magnetic tube lifting drive mechanism is connected to a support rod extending forward and backward, and the support rod is provided with a clamping structure, in which the magnetic tube is clamped and fixed.

[0008] Furthermore, the clamping structure is a clamp, and the support rod is connected to the edge of the clamp and is located radially outside the magnetic tube.

[0009] Furthermore, the clamping structure is detachably connected to the support rod.

[0010] Furthermore, the magnetic tube system also includes a fixed base, which is fixedly installed on the frame. The magnetic tube translation drive mechanism includes a magnetic tube drive motor and a sliding block that is connected to the magnetic tube drive motor. The fixed base is provided with a sliding groove that extends forward and backward. The sliding block is slidably installed in the sliding groove. The magnetic tube lifting drive mechanism is set on the sliding block.

[0011] Furthermore, the magnetic tube lifting drive mechanism includes a lead screw and nut mechanism connected to the sliding block. The moving nut of the lead screw and nut mechanism is connected to the support rod. One of the support rod and the sliding block is fixedly connected to a guide sleeve extending vertically, and the other is fixedly connected to a guide rod. The guide rod is slidably installed in the guide sleeve.

[0012] Furthermore, a set screw is provided between the rotating lead screw and the moving nut of the lead screw and nut mechanism.

[0013] Furthermore, the probe includes a cylindrical shell, with a guide head at the front end of the cylindrical shell for guiding the probe into the steel pipe, and a strip magnetic probe unit is radially and elastically floating on the outer circumferential surface of the cylindrical shell, the strip magnetic probe unit being used to fit against the inner wall of the steel pipe being tested.

[0014] Furthermore, on the outer circumferential surface of the cylindrical shell, rollers are arranged in a row along the axial direction of the cylindrical shell between two adjacent strip magnetic probe units. The rows of rollers and the strip magnetic probe units are arranged alternately and at equal intervals in the circumferential direction of the cylindrical shell.

[0015] Furthermore, the frame is equipped with front and rear extending slides, in which sliders are slidably installed, and the magnetizing coil and probe system are fixedly installed on the sliders.

[0016] Beneficial Effects: This invention is a pioneering creation. The frame is equipped with a magnetic tube system. Before testing, the magnetic tube is aligned with the end of the steel pipe to be tested. The height and forward / backward movement of the magnetic tube can be adjusted via a magnetic tube lifting and translational drive mechanism to ensure alignment. The probe height is adjusted via a probe lifting drive mechanism to ensure the center of the steel pipe, magnetic tube, magnetizing coil, and probe are aligned. Then, the translational drive mechanism moves the magnetizing coil and probe system forward. The magnetizing coil is energized first to excite the magnetic tube, and then to the steel pipe to be tested. When it reaches the end of the steel pipe, the end is saturated with magnetization. The probe enters the steel pipe, and the probe rotation drive mechanism drives the probe to rotate inside the steel pipe for testing. By adding a magnetic tube to the end of the steel pipe being tested, it is equivalent to replacing the end of the steel pipe with the magnetic tube. During the movement of the magnetizing coil, the magnetic tube is first energized, and then the steel pipe being tested is energized. When it reaches the end of the steel pipe being tested, the end of the steel pipe being tested has already been saturated with magnetization. This can eliminate the detection blind zone caused by insufficient magnetization when the end of the steel pipe first enters the magnetizing coil, and can also eliminate the interference of the magnetic pole effect of the end of the steel pipe on the detection signal, thereby realizing the detection of defects at the end of the steel pipe. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the magnetic flux leakage flaw detector for steel pipe ends according to the present invention; Figure 2This is a schematic diagram of the magnetic tube system. Figure 3 for Figure 2 Schematic diagram of the clamping structure; Figure 4 for Figure 2 Enlarged view of point A in the middle; Figure 5 for Figure 2 Enlarged view of point B in the middle; Figure 6 This is a schematic diagram of the transmission connection between the probe system and the translation drive mechanism; Figure 7 This is a schematic diagram showing the connection between the bottom of the probe bracket and the translation drive mechanism; Figure 8 This is a schematic diagram of the magnetization coil. Figure 9 for Figure 1 Schematic diagram of the middle slide; Figure 10 This is a schematic diagram of the probe extending into the steel pipe being tested. In the diagram: 1. Steel pipe under test; 2. Transmission wheel; 3. Photoelectric switch; 4. Magnetic tube system; 401. Magnetic tube; 402. Clamping structure; 403. Bolt; 405. Support rod slot; 406. Support rod; 407. Sliding block; 408. Guide sleeve; 409. Guide rod; 410. Height adjustment sleeve; 411. Handwheel; 412. Set screw; 413. Slide groove; 414. Magnetic tube drive motor; 415. Height adjustment screw; 416. Fixing sleeve; 417. Anti-disengagement ring; 418. Fixing base; 5. Magnetizing coil; 501. Through hole; 502. Heat dissipation hole; 503. Coil frame; 504. Coil; 505. Base; 6. Slider; 7. Probe system; 701. Probe bracket; 702. Probe lifting motor; 703. Reducer; 704. Worm gear mechanism; 705. Probe lifting screw; 706. Probe rotary motor; 707. Probe lifting plate; 708. Probe translation motor; 709. Probe translation lead screw; 710. Probe; 711. Probe lifting plate slide groove; 712. Connecting plate; 713. Columnar housing; 714. Spring; 715. Roller; 716. Guide head; 717. Strip magnetic probe unit; 8. Slide rail; 801. Slide rail groove; 9. Frame. Detailed Implementation

[0018] This invention provides a magnetic flux leakage (MFL) flaw detector for steel pipe ends, primarily addressing the problem of blind spots in existing MFL detectors that fail to detect defects at the pipe ends. The basic concept of this invention is as follows: before testing, a magnetic tube is connected to the end of the steel pipe to be tested, effectively replacing the pipe end position. A magnetizing coil is energized first to excite the magnetic tube, and then to excite the steel pipe under test. By the time the coil reaches the end of the steel pipe, it has already achieved saturation magnetization. This eliminates the blind spot caused by insufficient magnetization when the pipe end initially enters the magnetizing coil, and also eliminates interference from the magnetic pole effect at the pipe end on the detection signal, thus enabling the detection of defects at the pipe end.

[0019] Based on the above inventive concept, the embodiments of the present invention will be described in detail below.

[0020] like Figure 1 As shown, the magnetic flux leakage flaw detector for steel pipe ends includes a frame 9. The frame 9 is equipped with a magnetizing coil 5, a probe system 7, and a magnetic tube system 4. The frame 9 has a sliding track 8 extending forward and backward, within which two sliders 6 are slidably installed, arranged opposite each other. The magnetizing coil 5 and the probe system 7 are both fixedly mounted on the two sliders 6 with screws. The frame 9 is equipped with a translation drive mechanism to drive the magnetizing coil 5 and the probe system 7 to move back and forth on the sliding track 8. The magnetic tube system 4 is fixedly installed on the sliding track 8. The magnetic tube system 4 includes a magnetic tube 401, which is located in front of the magnetizing coil 5 and aligned with the center of the magnetizing coil 5 and the probe 710. The magnetic tube 401 has the same diameter as the steel pipe 1 being tested and is connected to the end of the steel pipe 1 being tested.

[0021] like Figure 2 As shown, the magnetic tube system 4 includes a fixed base 418, which is fixedly mounted on a slide rail 8 on the top of the frame 9. The fixed base 418 is equipped with a magnetic tube lifting drive mechanism for driving the magnetic tube 401 to rise and fall, and a magnetic tube translation drive mechanism for driving the magnetic tube 401 to move back and forth. The magnetic tube translation drive mechanism includes a magnetic tube drive motor 414 mounted on the fixed base 418 and a sliding block 407 slidably connected to the magnetic tube drive motor 414. The magnetic tube drive motor 414 is a stepper motor. The fixed base 418 is provided with a sliding groove 413 extending back and forth, and the sliding block 407 is slidably mounted in the sliding groove 413. The magnetic tube lifting drive mechanism is mounted on the sliding block 407. The magnetic tube lifting drive mechanism is slidably connected to the magnetic tube 401. The magnetic tube drive motor 414 drives the sliding block 407 to slide back and forth, thereby driving the magnetic tube lifting drive mechanism and the magnetic tube 401 to move back and forth.

[0022] The magnetic tube lifting drive mechanism includes a height adjusting sleeve 410 and a height adjusting screw 415 threadedly installed within the height adjusting sleeve 410. The height adjusting screw 415 and the height adjusting sleeve 410 constitute a screw-nut mechanism. The height adjusting screw 415 is the rotating screw of the screw-nut mechanism, and the height adjusting sleeve 410 is the moving nut of the screw-nut mechanism, which is also the lifting action component of the magnetic tube lifting drive mechanism. Figure 5 As shown, the sliding block 407 is provided with a fixed sleeve 416. The lower end of the height adjusting screw 415 is anti-detached and fitted into the fixed sleeve 416 through an anti-detachment ring 417, and is rotatably connected to the fixed sleeve 416, allowing it to rotate freely within the fixed sleeve 416. Figure 2 As shown, a support rod 406 extending forward and backward is fixedly connected to the height adjusting sleeve 410. A guide rod 409 extending vertically is fixedly connected to the support rod 406. A guide sleeve 408 extending vertically is fixedly connected to the sliding block 407. The guide rod 409 is slidably installed in the guide sleeve 408, preventing the support rod 406 and the height adjusting sleeve 410 from rotating circumferentially. When the height adjusting screw 415 is rotated, the height adjusting sleeve 410 moves up and down, thereby driving the support rod 406 and the magnetic tube 401 fixed on the support rod 406 to rise and fall.

[0023] To prevent the center height of the magnetic tube 401 from shifting due to vibration, such as Figure 4 As shown, a set screw 412 is disposed between the height adjusting sleeve 410 and the height adjusting screw 415. After the center height of the magnetic tube 401 is adjusted, the set screw 412 presses against the height adjusting screw 415 to ensure that the center height of the magnetic tube 401 remains unchanged during the testing process. For ease of operation, a handwheel 411 is fixedly connected to the upper end of the height adjusting screw 415, and the height adjusting screw 415 can be rotated by the handwheel 411.

[0024] like Figure 2 As shown, a clamping structure 402 is provided on the support rod 406, and the magnetic tube 401 is clamped and fixed within the clamping structure 402. Using this clamping method to fix the magnetic tube 401 prevents vibration of the magnetic tube 401 on the support rod 406 from causing connection failure between the magnetic tube 401 and the steel pipe 1 under test, ensuring that the center height of the magnetic tube 401 remains constant during the testing process, and that the center of the magnetic tube 401 and the center of the steel pipe 1 under test are always aligned. (See also...) Figure 3The clamping structure 402 is a clamp, which includes two semi-circular clamp bodies. Each semi-circular clamp body has connecting ears at both ends. One connecting ear has a support rod slot 405 for clamping onto the outer surface of the support rod 406. The openings at both ends of the clamp are locked together with bolts 403. The support rod slot 405 is located at the edge of the clamp, and the support rod 406 is radially outside the magnetic tube 401. This arrangement allows the central channel of the magnetic tube 401 to be open, ensuring that the probe 710 can pass smoothly through the magnetic tube 401. The clamp is fixed to the support rod 406 with bolts 403. Loosening the bolts 403 allows the clamp to be removed. A suitable clamp can be selected based on the diameter of the magnetic tube 401 to be clamped.

[0025] like Figure 6 As shown, the probe system 7 includes a probe bracket 701, a probe 710, and a probe lifting drive mechanism and a probe rotation drive mechanism mounted on the probe bracket 701. The probe bracket 701 has a connecting seat at its bottom, which is fixedly connected to the slider 6 at the top of the frame 9 by screws. The probe lifting drive mechanism includes a probe lifting motor 702, which is connected to a worm gear mechanism 704 via a reducer 703. The worm gear of the worm gear mechanism 704 is connected to a vertically extending probe lifting screw 705. A probe lifting plate 707 is threaded onto the probe lifting screw 705. The rotation of the probe lifting screw 705 drives the probe lifting plate 707 to move up and down. The probe bracket 701 has a probe lifting plate groove 711. The sliders on both sides of the probe lifting plate 707 slide and engage within the probe lifting plate groove 711, restricting the probe lifting plate 707 to slide only vertically on the probe bracket 701 and ensuring smooth lifting and lowering of the probe lifting plate 707. The probe rotation drive mechanism is mounted on the probe lifting plate 707 and is connected to the probe 710. The lifting of the probe lifting plate 707 drives the probe 710 to rise and fall, adjusting the center height of the probe 710. The probe rotation drive mechanism is a probe rotation motor 706, which is connected to the probe 710 to rotate it. It is understood that the probe lifting drive mechanism can also be other structures. For example, it could be a linear motor, fixed to the top plate of the probe bracket 701, with its output shaft extending downwards and fixedly connected to the probe lifting plate 707 to drive the probe lifting plate 707 to rise and fall.

[0026] like Figure 7As shown, the probe bracket 701 has a connecting plate 712 at its bottom. A probe translation screw 709 extending forward and backward is threaded onto the connecting plate 712. The probe translation screw 709 is connected to a probe translation motor 708. The probe translation motor 708 drives the probe translation screw 709 to rotate, thereby moving the probe bracket 701 forward and backward. The probe 710 is mounted on the probe bracket 701, and the probe bracket 701 moves the probe 710 forward and backward. Since both the probe system 7 and the magnetizing coil 5 are fixedly mounted on the slider 6 with screws, see [reference needed]. Figure 1 Therefore, the probe system 7 will move back and forth together with the slider 6 and the magnetizing coil 5. The connecting plate 712 and the probe translation screw 709 form a screw-nut mechanism. The connecting plate 712, the probe translation screw 709, and the probe translation motor 708 together constitute a translation drive mechanism for driving the magnetizing coil 5 and the probe system 7 to move back and forth. Of course, in other embodiments, the translation drive mechanism can also be a linear motor. The output shaft of the linear motor is fixedly connected to the slider 6, the probe bracket 701, or the magnetizing coil 5, thereby driving the magnetizing coil 5, the slider 6, and the probe system 7 to translate back and forth together. The translation drive mechanism can also be a telescopic cylinder or other transmission mechanism capable of outputting linear motion, which will not be listed here.

[0027] The structure of the magnetizing coil is as follows Figure 8 As shown, the device includes a coil holder 503, which is a hollow cubic structure. The bottom of the coil holder 503 has a base 505 with screw mounting holes. Two screws are used to fix the magnetizing coil 5 to the slider 6. A coil 504 is installed inside the coil holder 503. The coil 504 has a through hole 501 in its center. Heat dissipation holes 502 are also provided on the coil holder 503 around the coil 504 to accelerate heat dissipation from the coil 504.

[0028] The structure of the slide rail 8 on the frame 9 is as follows Figure 9 As shown, the slide 8 has two slide grooves 801 on both sides, and a slider 6 is slidably installed in the two slide grooves 801. The top of the slider 6 has a stepped structure that is lower at the front and higher at the back. The higher stepped surface of the rear section of the slider 6 is used to install the probe system 7, and the lower stepped surface of the front section of the slider 6 is used to install the magnetizing coil 5. Both the probe system 7 and the magnetizing coil 5 are fixed on the slider 6. The forward and backward movement of the probe system 7 drives the slider 6 and the magnetizing coil 5 to move synchronously. The magnetizing coil 5 does not require a separate drive mechanism to drive its forward and backward movement, thus simplifying the device structure.

[0029] like Figure 10As shown, the probe includes a cylindrical outer shell 713 extending forward and backward. A guide head 716 is provided at the front end of the cylindrical outer shell 713 to guide the probe 710 into the steel pipe. A strip magnetic probe unit 717 is radially and elastically floating on the outer circumferential surface of the cylindrical outer shell 713. Multiple springs 714 are axially spaced between the strip magnetic probe unit 717 and the outer circumferential surface of the cylindrical outer shell 713. After the probe 710 enters the steel pipe 1 being tested, the strip magnetic probe unit 717 is subjected to the squeezing force of the inner wall of the steel pipe. Under the action of the springs 714, the strip magnetic probe unit 717 is pressed tightly against the inner wall of the steel pipe 1 being tested. Two strip magnetic probe units 717 are provided and are evenly distributed circumferentially. Two rows of rollers 715 are provided on the outer circumferential surface of the cylindrical housing 713 along the axial direction of the cylindrical housing 713 to support the probe 710 as a whole on the inner wall of the steel pipe. The two rows of rollers 715 are evenly distributed in the circumferential direction. One row of rollers is located in the gap on one side of the two strip magnetic probe units 717, and the other row of rollers is located in the gap on the other side of the two strip magnetic probe units 717. The two strip magnetic probe units 717 and the two rows of rollers 715 are arranged alternately and at equal intervals in the circumferential direction of the cylindrical housing 713. Of course, there is no limitation on the number of strip magnetic probe units 717 and the number of rows of rollers 715. When there are more than three strip magnetic probe units 717, rollers 715 are arranged in rows along the axial direction of the cylindrical housing 713 between every two adjacent strip magnetic probe units 717. The strip magnetic probe units 717 and the rows of rollers 715 are arranged alternately and at equal intervals in the circumferential direction of the cylindrical housing 713. The advantage of this arrangement is that it ensures uniform force on the probe in all circumferential parts, allows the probe to rotate more smoothly inside the steel pipe being tested, and the two or more strip magnetic probe units are evenly distributed in the circumferential direction, which fully guarantees the detection range and improves the detection accuracy.

[0030] like Figure 1 As shown, the magnetic flux leakage flaw detector for steel pipe ends can be equipped with a steel pipe conveying mechanism. The conveying wheel 2 of the steel pipe conveying mechanism is a V-shaped wheel. The steel pipe 1 to be tested is placed on the V-shaped wheel and conveyed to the inspection station. A set of opposing photoelectric switches 3 is fixed on the slide rail 8 at the top of the frame 9 of the magnetic flux leakage flaw detector for steel pipe ends. One photoelectric switch 3 is a transmitting switch, and the other is a receiving switch. When the steel pipe 1 to be tested has not reached the inspection station, the receiving switch can receive the light normally. When the steel pipe 1 to be tested is conveyed to the inspection station, the emitted light is blocked by the steel pipe 1 to be tested, and the receiving switch cannot receive the light, which indicates that the steel pipe has been conveyed to the correct position, and the conveying stops.

[0031] Before starting the test, select a magnetic tube 401 with a suitable size according to the specifications of the steel pipe 1 to be tested, adjust the center height of the magnetic tube 401 to be consistent with the center height of the steel pipe 1 to be tested, and adjust the height of the probe 710 so that the center of the steel pipe 1 to be tested, the magnetic tube 401, the magnetizing coil 5 and the probe 710 are on the same straight line, and align the magnetic tube 401 with the end of the steel pipe 1 to be tested; then, drive the magnetizing coil 5 and the probe system 7 forward through the translation drive mechanism. The magnetizing coil 5 is energized to first excite the magnetic tube 401, and then to excite the steel pipe 1 to be tested. When it reaches the end of the steel pipe 1 to be tested, the end of the steel pipe 1 to be tested has been saturated with magnetization. The probe 710 enters the steel pipe 1 to be tested and is in close contact with the inner wall of the steel pipe 1. The two rows of rollers 715 support the probe 710 as a whole on the inner wall of the steel pipe, so that the probe 710 can rotate under the drive of the probe rotation motor 706 to perform the test. When the set detection length is reached, the probe rotation motor 706 stops rotating, the probe translation motor 708 stops and reverses, driving the magnetizing coil 5 and the probe 710 to exit the steel pipe 1 under test. At the same time, the system provides a reverse current to the magnetizing coil 5, generating a reverse magnetic field to demagnetize the magnetized steel pipe 1 under test and the magnetic tube 401. The detection signal is transmitted to the flaw detection system for digital processing and the detection result is output.

[0032] This invention adds a magnetic tube 401 to the end of the steel pipe 1 being tested, which is equivalent to replacing the end of the steel pipe. When the magnetizing coil 5 is energized, the magnetic tube 401 is first energized, and then the steel pipe 1 being tested is energized. When the magnetizing coil 5 reaches the end of the steel pipe 1 being tested, the end of the steel pipe 1 being tested has been saturated with magnetization. This can eliminate the detection blind zone caused by insufficient magnetization when the end of the steel pipe first enters the magnetizing coil 5, and can also eliminate the interference of the magnetic pole effect of the end of the steel pipe on the detection signal, thereby realizing the detection of defects at the end of the steel pipe.

[0033] Furthermore, this invention employs internal steel pipe wall inspection, eliminating the influence of irregular outer pipe shapes on the inspection process and enabling blind-spot-free inspection of various steel pipe ends. This invention utilizes an automated control and stepper drive system, achieving fully automated and precise control throughout the inspection process. This invention uses a single coil for both excitation and demagnetization, employing DC excitation and reverse DC demagnetization to achieve precise demagnetization and minimize residual magnetism after inspection.

[0034] Of course, the present invention is not limited to the embodiments described above.

[0035] For example, in another embodiment, the magnetic tube is no longer clamped and fixed. Instead, a support base is provided on the support rod, and the support base has an upward-facing groove. The magnetic tube is placed in the groove of the support base, and a flexible band is used to tighten the magnetic tube onto the support base.

[0036] For example, in another embodiment, the clamp and the support rod are fixed in a non-removable manner and can be welded together.

[0037] For example, in another embodiment, the magnetic tube translation drive mechanism adopts a lead screw and nut mechanism. The rotating lead screw of the lead screw and nut mechanism extends back and forth, and the translation nut of the lead screw and nut mechanism is guided and slidably mounted on the fixed seat in the back and forth direction. The magnetic tube lifting drive mechanism is set on the translation nut.

[0038] For example, in another embodiment, the magnetic tube lifting drive mechanism uses a magnetic tube lifting motor. The magnetic tube lifting motor is fixedly mounted on a sliding block on a fixed base. The output shaft of the magnetic tube lifting motor is upward, and a support rod extending forward and backward is fixedly connected to the output shaft. The support rod is equipped with a clamping structure, and the magnetic tube is clamped and fixed within the clamping structure. Besides a magnetic tube lifting motor, a telescopic cylinder can also be used to drive the support rod, thereby driving the magnetic tube to lift and lower. Of course, other drive mechanisms can also be used; there are many drive mechanisms that can achieve linear output motion, which will not be listed here.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A magnetic flux leakage flaw detector for steel pipe ends, characterized in that: The system includes a frame on which a magnetizing coil and a probe system are slidably mounted along the front-to-back direction. The frame is equipped with a translation drive mechanism for driving the magnetizing coil and probe system to move back and forth. The probe system includes a probe, a probe lifting drive mechanism for driving the probe to rise and fall, and a probe rotation drive mechanism for driving the probe to rotate. The probe is used to extend into the interior of a steel pipe and fit against the inner wall of the steel pipe to detect defects. The frame is also equipped with a magnetic tube system, which includes a magnetic tube, a magnetic tube lifting drive mechanism for driving the magnetic tube to rise and fall, and a magnetic tube translation drive mechanism for driving the magnetic tube to move back and forth. The magnetic tube is located in front of the magnetizing coil and is on the same straight line as the center of the magnetizing coil and the probe. The magnetic tube has the same diameter as the steel pipe being tested and is connected to the end of the steel pipe being tested.

2. The magnetic flux leakage flaw detector for steel pipe ends according to claim 1, characterized in that: The lifting mechanism of the magnetic tube has a supporting rod that extends forward and backward connected to its lifting action component. The supporting rod is equipped with a clamping structure, and the magnetic tube is clamped and fixed in the clamping structure.

3. The magnetic flux leakage flaw detector for steel pipe ends according to claim 2, characterized in that: The clamping structure is a clamp, and the support rod is connected to the edge of the clamp and is located on the radial outside of the magnetic tube.

4. The magnetic flux leakage flaw detector for steel pipe ends according to claim 2, characterized in that: The clamping structure is detachably connected to the support rod.

5. The magnetic flux leakage flaw detector for steel pipe ends according to claim 2, characterized in that: The magnetic tube system also includes a fixed base, which is fixedly installed on the frame. The magnetic tube translation drive mechanism includes a magnetic tube drive motor and a sliding block that is connected to the magnetic tube drive motor. The fixed base is provided with a sliding groove that extends forward and backward. The sliding block is slidably installed in the sliding groove. The magnetic tube lifting drive mechanism is set on the sliding block.

6. The magnetic flux leakage flaw detector for steel pipe ends according to claim 5, characterized in that: The magnetic tube lifting drive mechanism includes a lead screw and nut mechanism connected to the sliding block. The moving nut of the lead screw and nut mechanism is connected to the support rod. One of the support rod and the sliding block is fixedly connected to a guide sleeve extending vertically, and the other is fixedly connected to a guide rod. The guide rod is slidably installed in the guide sleeve.

7. The magnetic flux leakage flaw detector for steel pipe ends according to claim 6, characterized in that: A set screw is provided between the rotating lead screw and the moving nut of the lead screw and nut mechanism.

8. The magnetic flux leakage flaw detector for steel pipe ends according to any one of claims 1-7, characterized in that: The probe includes a cylindrical shell with a guide head at the front end for guiding the probe into the steel pipe. A strip magnetic probe unit is radially and elastically floating on the outer circumference of the cylindrical shell, and the strip magnetic probe unit is used to fit against the inner wall of the steel pipe being tested.

9. The magnetic flux leakage flaw detector for steel pipe ends according to claim 8, characterized in that: On the outer circumference of the cylindrical shell, rollers are arranged in a row along the axial direction of the cylindrical shell between two adjacent strip magnetic probe units. The rollers and the strip magnetic probe units are arranged alternately and at equal intervals in the circumferential direction of the cylindrical shell.

10. The magnetic flux leakage flaw detector for steel pipe ends according to any one of claims 1-7, characterized in that: The frame is equipped with front and rear extending slides, and a slider is slidably installed in the slides. The magnetizing coil and probe system are fixedly installed on the slider.

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