A pipe end double magnetic head longitudinal non-contact alternating current magnetization flaw detection system

Abstract

This invention discloses a pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system, belonging to the field of magnetic particle flaw detection technology. The system includes: a distal magnetization branch and a proximal magnetization branch forming a longitudinal magnetic circuit passing through the same detection zone with a second magnetic head; adjusting the current based on an intelligent magnetic flux sensor to ensure that the magnetic flux amplitude of the two branches is the same when individually magnetized; rotating the pipe and continuously spraying magnetic suspension, with the two branches alternately magnetized at equal numbers of complete AC cycles, switching only when the current crosses zero, and imaging to determine the suspected display location; after cleaning, individually connecting the two branches and spraying equal amounts of liquid twice to determine the early-display branch and the late-display branch, magnetizing in segments according to late-display, early-display, and late-display stages, and re-inspecting in reverse order after cleaning; the two branches are magnetized together in the same direction, with the total magnetic flux amplitude equal to the magnetization amplitude of a single branch; reversing the pipe, judging and demagnetizing according to the change in display with the re-inspection order, magnetization branch, or liquid flow direction. This invention can reduce false magnetic indications and distinguish between defects and false indications.

Description

Technical Field

[0001] This invention relates to the field of magnetic particle inspection technology, and in particular to a pipe-end dual-magnetic-head longitudinal non-contact AC magnetization inspection system. Background Technology

[0002] Magnetic particle testing is suitable for detecting surface and near-surface defects in ferromagnetic pipe fittings. For pipe end testing, an AC magnetic yoke or electromagnetic coil is typically positioned on both sides of the pipe end to apply a longitudinal alternating magnetic field to the testing area. Simultaneously, the pipe fitting is rotated, and fluorescent magnetic suspension is sprayed onto both the inner and outer surfaces. The leakage magnetic field generated at material discontinuities attracts magnetic particles, which fluoresce under ultraviolet illumination. The results are then assessed by a camera or inspectors based on the display's position, orientation, and shape. After testing, the pipe end is demagnetized.

[0003] Conventional magnetic particle testing of pipe ends has two shortcomings: First, when a single magnetic entry point is continuously applied or the magnetic entry point is changed, the magnetic powder accumulation caused by local magnetic reluctance changes may be retained simultaneously with the defect display, and the powder accumulation related to the magnetic entry point is not easily weakened; Second, the re-examination of suspected defects often involves repeating the same magnetization and spraying process along the original rotation direction, lacking cross-verification of changes in the magnetic entry sequence and changes in the liquid flow direction, making it difficult to accurately distinguish between defect displays and false displays of powder accumulation in the liquid flow. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a tube-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system to solve the problems of the existing technology, such as the difficulty in weakening the powder accumulation related to the magnetization position and the interference of liquid flow powder accumulation in the display and judgment of defects.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system, comprising: forming longitudinal magnetic circuits through the same detection zone with the second magnetic head by the distal and proximal magnetic input branches of the first magnetic head; adjusting the branch current according to the output of the intelligent magnetic flux sensor of the second magnetic head to make the magnetic flux amplitude of the two branches individually magnetized the same; rotating the pipe and continuously spraying magnetic suspension liquid to make the two branches alternately magnetized with an equal number of complete AC cycles, switching only when the excitation current crosses zero, acquiring images and obtaining suspected display positions; cleaning the suspected display positions, sequentially connecting the two branches individually and spraying liquid in two equal amounts, determining the early display branch and the late display branch according to the display sequence, magnetizing in three segments: late display branch, early display branch, and late display branch, and re-inspecting in reverse order after cleaning; making the two branches magnetized together in the same phase and direction with the total magnetic flux amplitude equal to the magnetization amplitude of a single branch, reversing the pipe, determining the result and demagnetizing according to whether the display changes with the re-inspection sequence, the magnetic input branch, or the direction of liquid flow.

[0007] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the longitudinal magnetic circuit passing through the same detection zone includes: a distal magnetic input branch and a proximal magnetic input branch are spaced apart along the pipe axial direction and each is equipped with an independent magnetic core, and a non-magnetic partition is provided between the two independent magnetic cores; the second magnetic head is located on the pipe end bevel side and is equipped with an intelligent magnetic flux sensor; when the two magnetic input branches are respectively connected, the magnetic flux passes through the same detection zone along the pipe axial direction and enters the second magnetic head.

[0008] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the adjustment of the branch current includes: the intelligent magnetic flux sensor accumulating the absolute value of the induced voltage between adjacent voltage zero-crossing points, dividing the accumulated value by twice the number of turns of the induction winding to form the magnetic flux amplitude; determining the magnetic flux amplitude of the far-end magnetic input branch as the target magnetic flux amplitude, adjusting the current of the near-end magnetic input branch until the absolute value of the difference between the two magnetic flux amplitudes is not greater than the magnetic flux resolution of the intelligent magnetic flux sensor, forming equal magnetic flux magnetization control data; when the allowable current boundary is reached but the tuning is not completed, the non-contact air gap is adjusted and readjusted.

[0009] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the alternating magnetization includes: the far-end magnetization branch and the near-end magnetization branch respectively operate continuously for three complete AC cycles, and are switched only when the excitation current crosses zero in the positive direction; the unconducted magnetization branch remains disconnected, and the magnetic flux amplitude of the currently connected branch is maintained at the target magnetic flux amplitude; continuous spraying is maintained during the branch switching period, and the magnetization of the two magnetization branches is completed before the pipe rotation speed meets the requirement of leaving the spraying area at the same position.

[0010] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the step of obtaining the suspected display position includes: a rotary encoder triggering the inner surface linear array light-collecting camera and the outer surface linear array light-collecting camera to acquire image rows and form a strip image; using maximum inter-class variance to determine the image segmentation grayscale, and recording the continuous bright areas that reach the number of consecutive scan rows as suspected display areas; determining the axial position and circumferential position according to the image column position and the rotary encoder trigger pulse to form a suspected display record.

[0011] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the two equal-volume liquid spraying includes: performing alternating amplitude reduction demagnetization and cleaning the suspected display position; during the separate magnetization of the far-end magnetic input branch, two equal volumes of magnetic suspension liquid are applied sequentially and two liquid spraying images are acquired; after demagnetization and cleaning again, the near-end magnetic input branch completes the same operation with the same magnetic flux amplitude, liquid spraying volume, rotation direction and scanning speed.

[0012] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the determination of early-displaying branches and late-displaying branches includes: the magnetic input branch that forms a display after the first application of magnetic suspension is recorded as the earlier-displaying magnetic input branch, and the magnetic input branch that forms a display only after the second application of magnetic suspension or does not form a display is recorded as the later-displaying magnetic input branch; when the two magnetic input branches at the same position have different display formation times, the early-displaying branch and the late-displaying branch are determined; when the display formation times are the same or the display positions are different, the early-displaying branch and the late-displaying branch are not established.

[0013] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the magnetization is divided into three segments: late-display branch, early-display branch, and late-display branch. After cleaning, the segments are re-inspected in reverse order. The specific steps are as follows: when the early-display branch and the late-display branch are established, two re-inspections are completed in sequence according to the late-display branch, early-display branch, late-display branch, and early-display branch; when the early-display branch and the late-display branch are not established, two re-inspections are completed in sequence according to the far-end magnetization branch, near-end magnetization branch, far-end magnetization branch, and near-end magnetization branch; the single-branch magnetic flux amplitude, spraying conditions, and imaging conditions are the same in the two re-inspections.

[0014] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the common magnetization includes: two magnetization branches connected to a dual-channel AC power supply sharing a zero-crossing trigger signal with the same winding polarity, and the branch current of the two magnetization branches being magnetized individually being scaled synchronously with a common magnetization scaling factor; the common magnetization scaling factor is gradually increased from zero until the absolute value of the difference between the total magnetic flux amplitude of common magnetization obtained by the intelligent magnetic flux sensor and the magnetic flux amplitude of single-branch magnetization is not greater than the magnetic flux resolution of the intelligent magnetic flux sensor.

[0015] As a preferred embodiment of the pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system of the present invention, the determination of results and demagnetization includes: acquiring forward rotation common magnetization images and reverse rotation common magnetization images respectively under the same magnetization conditions, spraying conditions and imaging conditions; recording the display as a defect when it maintains the same material coordinates and does not change with the direction of the magnetization branch and the liquid flow; recording the display as a false display related to the magnetization branch when it changes with the direction of the magnetization branch; recording the display as a false display of liquid flow powder accumulation when it reverses with the direction of the liquid flow; recording the display as a switching anomaly when it only appears after the branch is switched and cannot be reproduced by single branch magnetization and common magnetization; when a fixed display and an extension portion that changes with the liquid flow coexist, only the fixed display is included in the defect display; after the detection conclusion is formed, the current of the two magnetization branches is gradually reduced to zero and the residual magnetic field is checked.

[0016] The beneficial effects of this invention are as follows: by adjusting the magnetic flux through dual-branch equal-flux tuning, the difference in magnetic flux amplitude caused by the different magnetic circuit impedances of the two longitudinal magnetic circuits is reduced; by alternating magnetization and continuous spraying throughout the complete cycle, the pseudo-indications related to the magnetization position are weakened; and by spraying liquid of equal volume, reversing verification and rotating in the opposite direction, the defect indications and different pseudo-indications are accurately distinguished. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a tube-end dual-head longitudinal non-contact AC magnetization flaw detection system.

[0019] Figure 2 This is a schematic diagram of alternating magnetization and continuous spraying for a complete alternating cycle.

[0020] Figure 3 This is a schematic diagram of two equal-volume spraying tests conducted in reverse order.

[0021] Figure 4 This is a schematic diagram for the joint determination of common magnetization and display changes. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0025] Reference Figures 1-4 As one embodiment of the present invention, this embodiment provides a pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system, comprising the following steps: The magnetic flux calibration module enables the far-end and near-end magnetic input branches of the first magnetic head to form longitudinal magnetic circuits passing through the same detection zone with the second magnetic head. Based on the output of the intelligent magnetic flux sensor of the second magnetic head, the branch current is adjusted so that the magnetic flux amplitude of the two branches magnetized individually is the same.

[0026] Specifically, the pipe fitting to be inspected is placed horizontally on a rotating roller, with the end face of the pipe as the axial zero point. A detection zone of 250mm to 300mm is formed by measuring from the end face of the pipe to the pipe body. The first magnetic head is installed on the outside of the pipe fitting. The first magnetic head includes a distal magnetic inlet branch and a proximal magnetic inlet branch. The proximal magnetic inlet branch is located between the distal magnetic inlet branch and the detection zone. The magnetic pole working surfaces of the proximal magnetic inlet branch and the distal magnetic inlet branch are arranged at intervals along the axial direction of the pipe fitting. The axial projections of the two magnetic pole working surfaces do not overlap. Both magnetic pole working surfaces are located on the side of the detection zone away from the pipe end. The second magnetic head is installed on the bevel side of the pipe end. The magnetic pole working surface of the second magnetic head faces the bevel and end face of the pipe end.

[0027] The far-end magnetization branch and the near-end magnetization branch each use independent high-permeability pure iron magnetic cores. A non-magnetic partition is set between the two high-permeability pure iron magnetic cores. The two high-permeability pure iron magnetic cores are respectively wound with branch excitation windings. The far-end magnetization branch and the near-end magnetization branch are installed on the same servo bracket and keep the magnetic circuit isolated. A non-contact air gap of 5mm to 15mm is maintained between the working surface of the magnetic pole of the far-end magnetization branch and the working surface of the magnetic pole of the near-end magnetization branch and the outer wall of the pipe fitting, respectively. A non-contact air gap of 5mm to 20mm is maintained between the working surface of the magnetic pole of the second magnetic head and the bevel of the pipe end.

[0028] Preferably, the far-end magnetization branch and the near-end magnetization branch use the same magnetic pole working surface size, and the two non-contact air gaps are adjusted to the same value by the servo bracket.

[0029] The common excitation winding of the second magnetic head includes a first common winding segment and a second common winding segment with the same number of turns, the same winding direction, and mutual insulation. The induction winding is insulated from both common winding segments. The first power output channel, the branch switching unit of the far-end magnetization branch, the branch excitation winding of the far-end magnetization branch, and the first common winding segment are connected in series to form a far-end excitation circuit. The second power output channel, the branch switching unit of the near-end magnetization branch, the branch excitation winding of the near-end magnetization branch, and the second common winding segment are connected in series to form a near-end excitation circuit. The two power output channels are electrically isolated from each other and only share an electrically isolated zero-crossing trigger signal.

[0030] When a single branch is magnetized, only the corresponding excitation circuit is connected; when both branches are magnetized, the two excitation circuits are connected in the same phase and direction, and the currents of the two branches return to their respective power output channels and do not converge on the conductors. The magnetomotive forces generated by the two common winding segments are added in the second magnetic head, and the induction winding obtains the composite magnetic flux.

[0031] After the far-end magnetic inlet branch is connected, the magnetic flux enters the outer wall of the pipe fitting through the working surface of the magnetic pole and the non-contact air gap of the far-end magnetic inlet branch, passes through the detection zone along the axial direction of the pipe fitting, and then enters the second magnetic head through the pipe end bevel and the non-contact air gap of the second magnetic head; after the near-end magnetic inlet branch is connected, the magnetic flux enters the outer wall of the pipe fitting through the working surface of the magnetic pole and the non-contact air gap of the near-end magnetic inlet branch, passes through the same detection zone along the axial direction of the pipe fitting, and then enters the second magnetic head through the pipe end bevel and the non-contact air gap of the second magnetic head.

[0032] Among them, the two longitudinal magnetic circuits only change the magnetization position on the outer wall of the pipe, without changing the position of the detection zone and the second magnetic head.

[0033] Furthermore, the intelligent flux sensor includes an induction winding, an induction voltage acquisition circuit, a voltage zero-crossing recognition circuit, a time integration circuit, and a digital output interface.

[0034] The induction winding adopts a high input impedance acquisition method, and the induction winding does not form a conductive connection with the common excitation winding.

[0035] After the branch excitation current enters a stable alternating state, the voltage zero-crossing identification circuit determines the adjacent voltage zero-crossing points at both ends of a half-wave of the same polarity of the induced voltage. The time integration circuit accumulates the product of the absolute value of the induced voltage and the sampling interval between two adjacent voltage zero-crossing points. The accumulated value is divided by twice the number of turns of the induction winding to form the magnetic flux amplitude at the second magnetic head.

[0036] It should be noted that the unit of the accumulated value is volt-second, which has the same dimensions as the Weber, while the unit of magnetic flux amplitude is Weber.

[0037] Preferably, after each single magnetization branch is connected, three complete AC cycles are continuously supplied. The first two complete AC cycles establish stable alternating magnetization, and the third complete AC cycle completes the magnetic flux amplitude measurement. A complete AC cycle starts from the first positive zero crossing of the excitation current and ends at the next positive zero crossing of the excitation current.

[0038] Using three complete AC cycles can avoid the transient voltage when the branch is first connected, and at the same time avoid the detection cycle being affected by excessively long setting time.

[0039] The remote magnetization branch is connected first, while the near-end magnetization branch remains disconnected at both ends. The controller searches the excitation process table according to the pipe material, outer diameter, and wall thickness, selects the initial current of the remote magnetization branch, and outputs the initial current of the remote magnetization branch within the range of AC magnetization power supply not exceeding 100 amperes and total ampere-turns of excitation winding not exceeding 18,000 ampere-turns. After the remote magnetization branch completes three complete AC cycles, the intelligent flux sensor forms the flux amplitude of the remote magnetization branch. The controller determines the flux amplitude of the remote magnetization branch as the target flux amplitude and records the initial current of the remote magnetization branch as the operating current of the remote magnetization branch.

[0040] It should be noted that the excitation process table is established on process evaluation pipe fittings of the same material, outer diameter, and wall thickness. During process evaluation, the A1 15 / 50 test piece is fixed to the test strip, and the branch current is gradually increased starting from the minimum adjustable current of the AC magnetization power supply. After each increase, three complete AC cycles, magnetic suspension spraying, and ultraviolet imaging are completed. The image processor uses maximum inter-class variance segmentation of the test piece image. When each line segment of the specified graphic on the test piece forms a continuous bright area that reaches the number of consecutive scan lines, and when two adjacent images under the same branch current meet the conditions, the branch current, target magnetic flux amplitude, and excitation process table version number are written into the excitation process table. When two adjacent images are inconsistent, the test piece is cleaned and demagnetized, and then re-imaged under the same branch current. Two adjacent images are used to eliminate single spraying fluctuations. The same operation is repeated for thick-walled pipe fittings using CX230-430 test pieces.

[0041] The magnetic flux amplitude generated at the second magnetic head by the far-end magnetization branch, the magnetic flux amplitude generated at the second magnetic head by the near-end magnetization branch, and the target magnetic flux amplitude satisfy the following expression: ; in, This represents the flux amplitude when the distal input branch is magnetized independently. This represents the flux amplitude when the near-end input branch is magnetized alone, and the target flux amplitude is taken as... This indicates the flux resolution of the intelligent flux sensor.

[0042] It should be noted that, , and All units are Weber.

[0043] After the magnetic flux amplitude of the far-end magnetization branch is determined, the controller disconnects the far-end magnetization branch when the excitation current crosses zero in the positive direction, and then connects the near-end magnetization branch, using the operating current of the far-end magnetization branch as the initial excitation current of the near-end magnetization branch.

[0044] When the magnetic flux amplitude of the near-end magnetization branch is lower than the target magnetic flux amplitude, the controller increases the near-end magnetization branch current by adjusting the step size according to the minimum current of the AC magnetization power supply; when the magnetic flux amplitude of the near-end magnetization branch is higher than the target magnetic flux amplitude, the controller decreases the near-end magnetization branch current by adjusting the step size according to the minimum current.

[0045] After each adjustment, three complete AC cycles are reintroduced and the flux amplitude of the near-end magnetization branch is measured until the absolute value of the difference between the flux amplitude of the near-end magnetization branch and the target flux amplitude is not greater than the flux resolution of the intelligent flux sensor. The operating current of the near-end magnetization branch is recorded. When the current of the near-end magnetization branch reaches the allowable current boundary but still cannot complete the equal flux tuning, the controller stops excitation, and the servo bracket synchronously adjusts the non-contact air gap of the two magnetization branches within the allowable air gap range. Then, the flux amplitude tuning of the far-end magnetization branch and the near-end magnetization branch is completed again.

[0046] It should be noted that the flux resolution of the intelligent flux sensor is the difference between the flux amplitudes recorded in two adjacent valid digital output codes in the digital output code-flux amplitude calibration table, with the unit being Weber; when the target flux amplitude is the same as a certain item in the table, the larger value among the differences between the preceding and following flux amplitudes is taken; the digital output code-flux amplitude calibration table is generated by factory metrology calibration.

[0047] It should be noted that the allowable current boundary is the minimum value among the rated output current of the AC magnetizing power supply, the rated allowable current of the branch excitation winding, and the overcurrent protection setting current of the equipment. The value range is greater than 0 amperes and not greater than 100 amperes, while also satisfying that the total ampere-turns of the excitation winding is not greater than 18,000 ampere-turns. Exceeding the allowable current boundary can easily cause overload of the AC magnetizing power supply or excessive temperature rise of the excitation winding. If the allowable current boundary is set too small, it is easy to trigger the non-contact air gap adjustment prematurely when the magnetic circuit is normal.

[0048] In one possible implementation, the branch switching unit uses two sets of anti-parallel thyristors and an RC snubber network. The excitation current zero-crossing detection circuit collects the actual output current of the AC magnetizing power supply. The controller only turns off the currently conducting magnetizing branch when the excitation current crosses zero in the positive direction after the end of a complete AC cycle. After the currently conducting magnetizing branch is turned off, the magnetizing branch to be connected is turned on. The two sets of anti-parallel thyristors are electrically interlocked to prevent the two single branches from conducting simultaneously during the setting process.

[0049] After recording the operating current of the near-end magnetization branch, the controller sequentially connects the far-end magnetization branch and the near-end magnetization branch, with each magnetization branch operating for three complete AC cycles.

[0050] When the absolute value of the difference between the magnetic flux amplitude of the far-end magnetic input branch and the magnetic flux amplitude of the near-end magnetic input branch is not greater than the magnetic flux resolution of the intelligent magnetic flux sensor, the operating current of the far-end magnetic input branch, the operating current of the near-end magnetic input branch, and the target magnetic flux amplitude are locked to form equal magnetic flux magnetization control data.

[0051] It should be noted that the sampled value of the induced voltage, the half-wave integral value, and the zero-crossing pulse of the excitation current are not stored after the current control is completed; the equal flux setting limits the change between the two single-branch magnetizations to the change of the magnetization position, so as to avoid the same current forming different magnetization degrees under different magnetic circuit impedances.

[0052] The alternating magnetization module rotates the pipe and continuously sprays magnetic suspension, so that the two branches are alternately magnetized in equal numbers of complete AC cycles, switching only when the excitation current crosses zero, acquiring images and obtaining the suspected display position.

[0053] Specifically, the controller retrieves the flux equalization magnetization control data, which records the target flux amplitude, the operating current of the far-end magnetization branch, and the operating current of the near-end magnetization branch. The controller sets the far-end magnetization branch as the first conducting magnetization branch, keeps the near-end magnetization branch disconnected at both ends, and applies AC excitation current to the far-end magnetization branch according to the operating current of the far-end magnetization branch. After the far-end magnetization branch completes a fixed number of complete AC cycles, the controller turns off the far-end magnetization branch when the excitation current crosses zero in the positive direction. After the far-end magnetization branch is turned off, the controller turns on the near-end magnetization branch and applies AC excitation current to the near-end magnetization branch according to the operating current of the near-end magnetization branch. After the near-end magnetization branch completes the same number of complete AC cycles, the controller turns off the near-end magnetization branch when the excitation current crosses zero in the positive direction, and then turns on the far-end magnetization branch again, cyclically switching between the far-end and near-end magnetization branches for a complete AC cycle.

[0054] Preferably, the far-end magnetization branch and the near-end magnetization branch each operate continuously for three complete AC cycles. During the operation of each magnetization branch, the intelligent flux sensor performs a half-wave integral of the induced voltage with the same polarity to form the flux amplitude of the current complete AC cycle. The controller compares the flux amplitude of the current complete AC cycle with the target flux amplitude, generates an adjustment command to increase or decrease the current by a minimum adjustment step, and updates the branch current at the positive zero-crossing position of the excitation current at the beginning of the next complete AC cycle. The updated branch current remains unchanged in the next complete AC cycle.

[0055] The current regulation only applies to the currently conducting magnetization branch, while the operating current of the non-conducting branches in the far-end and near-end magnetization branches remains locked.

[0056] It should be noted that each magnetization branch operates continuously for three complete AC cycles. The first complete AC cycle establishes the longitudinal magnetic field after branch switching, the second complete AC cycle maintains magnetic powder adsorption, and the third complete AC cycle completes magnetic flux amplitude verification. When each magnetization branch operates for only one complete AC cycle, the transient process after branch switching tends to occupy the main magnetization time. When each magnetization branch operates continuously for two complete AC cycles, the duration of stable magnetization is relatively short. When each magnetization branch operates continuously for more than three complete AC cycles, the continuous adsorption time of loose magnetic powder at a single magnetization position increases, and the weakening effect of continuous spraying on path-related aggregation decreases. Three complete AC cycles take into account the stability of the alternating magnetic field, magnetic powder adsorption, and timely switching of the magnetization position.

[0057] When the first complete AC cycle begins at the far-end magnetic inlet branch, the magnetic suspension delivery pump starts simultaneously. The outer surface spray head continuously sprays the magnetic suspension onto the outer surface of the pipe end, and the inner surface spray head continuously sprays the magnetic suspension onto the inner surface of the pipe end. Both spray heads remain open during the switching between the far-end and near-end magnetic inlet branches, and the magnetic suspension delivery pump maintains the same liquid supply status, without stopping due to the closing or opening of the magnetic inlet branch or the excitation current crossing zero. The magnetic suspension forms a continuous liquid film on the outer and inner surfaces of the pipe end, respectively, and leaves the spraying area along the rotation direction of the pipe fitting.

[0058] Furthermore, before the rotating mechanism is started, the controller registers the current angle of the rotary encoder as the circumferential zero position mark.

[0059] The rotating mechanism drives the pipe to rotate at a constant speed around the pipe axis after continuous spraying begins.

[0060] The controller calculates the linear velocity of the detection belt surface based on the outer diameter of the pipe and the rotation speed set by the rotating mechanism. Then, it divides the arc length covered by the spray area along the circumference by the linear velocity to determine the dwell time of a single position on the pipe surface as it passes through the spray area.

[0061] The controller adjusts the rotation speed of the rotating mechanism to ensure that the residence time of a single position on the pipe surface through the spray area is not less than the sum of the longest duration of a magnetization segment and the duration of the next two complete magnetization segments; only complete AC cycles in which both the start and end points are within the residence time are counted in the number of magnetizations, ensuring that both magnetization branches complete a complete magnetization segment for the same position.

[0062] As an example, when each magnetization segment of the distal magnetization branch and the proximal magnetization branch includes three complete AC cycles, the dwell time is no less than nine complete AC cycles.

[0063] It should be noted that the first three complete AC cycles are used to cover the worst-case scenario where the inspected position enters the spray area midway through the magnetization section, and the subsequent six complete AC cycles are used to ensure that each of the two magnetization branches completes a complete magnetization section.

[0064] Before any inspected location on the pipe fitting surface leaves the spray area, both the far-end and near-end magnetic inlet branches complete single-branch magnetization of the same inspected location.

[0065] In one aspect, the actual defect is located within the detection zone traversed by both longitudinal magnetic paths; when the distal magnetic input branch is working, a leakage magnetic field is generated near the actual defect; when the proximal magnetic input branch is working, a leakage magnetic field is still generated near the actual defect, and the actual defect location continuously receives magnetic powder replenishment during continuous spraying; the local magnetic reluctance concentration caused by the longitudinal magnetic path formed by the distal magnetic input branch within the detection zone loses the continuous adsorption provided by the distal magnetic input branch during the operation of the proximal magnetic input branch; the local magnetic reluctance concentration caused by the longitudinal magnetic path formed by the proximal magnetic input branch within the detection zone loses the continuous adsorption provided by the proximal magnetic input branch during the operation of the distal magnetic input branch; the continuously flowing magnetic suspension carries the unstable adsorbed magnetic powder away from its original aggregation position; the equal magnetic flux magnetization control data ensures that the magnetic flux amplitude of the two longitudinal magnetic paths passing through the second magnetic head is the same, and the switching of the magnetic input branch only changes the magnetic input position, without increasing the total magnetic flux amplitude to strengthen any local aggregation.

[0066] As a preferred method, the outer surface linear array camera and the inner surface linear array camera face the outer and inner surfaces of the tube end, respectively. The ultraviolet excitation sources on both surfaces remain on during camera acquisition. For each equiangular trigger pulse generated by the rotary encoder, the outer and inner surface linear array cameras acquire one line of grayscale image. The image processor arranges the grayscale image lines according to the order of the rotary encoder trigger pulses, forming a strip image of the outer and inner surfaces of the tube end. When the rotary encoder reaches the circumferential zero mark again, the image processor confirms that a complete circumference acquisition has been completed.

[0067] The image processor performs dark field correction and brightness uniformization on the strip images of the outer and inner surfaces of the tube end.

[0068] Dark field correction uses camera dark field images acquired when the ultraviolet excitation source is off and the magnetic suspension spraying stops, while brightness uniformity uses illumination images acquired when the ultraviolet excitation source is on for a verified defect-free pipe section.

[0069] The image processor creates a grayscale histogram for the corrected grayscale image, and sequentially uses each grayscale level as a candidate segmentation grayscale. The image pixels are divided into a low grayscale group and a high grayscale group according to the candidate segmentation grayscale. The pixel count ratio and average grayscale of the two groups are calculated respectively. The product of the pixel count ratio of the two groups and the square of the average grayscale difference are calculated. The candidate segmentation grayscale with the largest product is selected as the image segmentation grayscale.

[0070] The image processor groups spatially adjacent pixels with a gray level not lower than the image segmentation gray level into a continuous highlight region.

[0071] The image processor checks whether a continuous bright area spans the number of consecutive scan lines determined by the camera's spatial resolution and the minimum detectable defect width. Continuous bright areas that reach the number of consecutive scan lines are recorded as suspected display areas, while isolated bright spots that do not reach the number of consecutive scan lines are treated as magnetic powder flicker or camera noise and are not recorded as suspected display areas.

[0072] It should be noted that the number of continuous scan lines is first calculated by dividing the minimum detectable defect width by the single-line coverage width of the camera in the circumferential direction of the pipe fitting, and then rounded up. The number of continuous scan lines is determined by the camera's spatial resolution and the minimum detectable defect width, and a fixed value that is detached from the camera's performance and inspection requirements is not used. When the number of continuous scan lines is too small, isolated fluorescent magnetic particles are likely to form false indications. When the number of continuous scan lines is too large, the indications of real defects with small widths are likely to be excluded.

[0073] The image processor determines the axial position of the suspected display based on the column position of the suspected display area in the strip image and the camera axial calibration relationship. It determines the circumferential position of the suspected display based on the rotary encoder trigger pulse of the scan line where the suspected display area is located. It also distinguishes between suspected displays on the outer surface of the tube end and suspected displays on the inner surface of the tube end according to the image source. The image processor retains the axial position, circumferential position, surface category, and local image for each suspected display, forming a suspected display record.

[0074] After the pipe completes a full circumference rotation, the controller stops the AC excitation current and the magnetic suspension spray, and checks whether the rotary encoder trigger pulse covers the full circumference, whether the two magnetic input branches complete continuous alternation, and whether the inner and outer surface images cover the entire detection zone; when all three checks are completed, a valid full circumference detection record is formed; if any check is not completed, the controller does not form a valid full circumference detection record and re-acquires the missing area.

[0075] Among them, the induced voltage sampling value, half-wave flux amplitude, excitation current zero-crossing pulse, and local images that do not form suspected displays are not stored after the current control or image screening is completed.

[0076] The sequence retest module cleans the suspected display position, connects two branches separately in sequence and sprays liquid in two equal amounts, determines the early display branch and the late display branch according to the display order, magnetizes the late display branch, early display branch and late display branch in three segments, and retests in the reverse order after cleaning.

[0077] Specifically, the controller retrieves suspected display records and equal flux magnetization control data.

[0078] Among them, the suspected display record records the axial position, circumferential position, surface type and local image of the suspected display; the magnetic flux magnetization control data records the target magnetic flux amplitude, the working current of the far-end magnetization branch and the working current of the near-end magnetization branch.

[0079] The controller drives the rotating mechanism to rotate the tube according to the suspected circumferential position, and stops the rotating mechanism when the suspected circumferential position enters the local imaging area.

[0080] The controller adjusts the axial acquisition range of the linear array light-collecting camera according to the suspected axial position, and enables the outer surface spray head and the outer surface linear array light-collecting camera according to the surface type, or enables the inner surface spray head and the inner surface linear array light-collecting camera.

[0081] Before the local retest begins, the controller shuts off the two magnetization branches and selects the higher value from the working current of the far magnetization branch and the working current of the near magnetization branch to determine the initial local demagnetization current.

[0082] The far-end magnetization branch completes the positive half-cycle magnetization and negative half-cycle magnetization sequentially under the initial local demagnetization current. When the excitation current crosses zero, the controller switches to the near-end magnetization branch, and the near-end magnetization branch completes the positive half-cycle magnetization and negative half-cycle magnetization sequentially.

[0083] After the two magnetization branches complete the positive and negative half-cycle magnetization, the controller adjusts the step size according to the minimum current of the AC magnetization power supply to reduce the local demagnetizing current, and repeats the positive and negative half-cycle magnetization of the two magnetization branches until the local demagnetizing current is reduced to zero, forming alternating amplitude reduction demagnetization.

[0084] After alternating amplitude reduction and demagnetization is completed, the cleaning nozzle sprays a carrier liquid without magnetic powder onto the suspected display location. The rotating mechanism drives the tube to rotate back and forth in the local imaging area, and the cleaning nozzle washes away the residual magnetic powder.

[0085] The image processor performs dark field correction, brightness uniformization, and maximum inter-class variance segmentation on the cleaned local image.

[0086] When the local image no longer forms a continuous bright area occupying the original suspected axial and circumferential display positions, the controller stops cleaning; when the local image still forms a continuous bright area, the controller continues to spray a carrier liquid without magnetic powder and repeats local imaging.

[0087] Furthermore, before inspecting pipe fittings of the same specification, the metering pump, under a fixed outlet pressure and a fixed pumping frequency, gradually increases the number of pumping strokes according to the minimum stroke increment, and the linear array focusing camera collects images before and after liquid spraying.

[0088] The image processor calculates the grayscale difference between the image before and after spraying, and uses the maximum inter-class variance to determine the segmentation grayscale to form a wetted region. When the wetted region covers each axial pixel column of the local imaging area, the wetted regions in adjacent scan rows are connected, and no liquid-carrying area connected to the surface wetted region is formed outside the lower edge contour of the pipe, the current pumping stroke number is recorded. The pumping stroke number that first meets the above conditions is determined as the single spraying stroke number.

[0089] The first and second portions of magnetic suspension use the same number of single-spray strokes, outlet pressure, and pumping frequency to ensure that the two portions of magnetic suspension are of equal volume.

[0090] When the remote magnetization branch is retested separately, the near magnetization branch is kept disconnected at both ends. The remote magnetization branch completes three full AC cycles according to the operating current of the remote magnetization branch. The intelligent magnetic flux sensor keeps the magnetic flux amplitude of the remote magnetization branch at the target magnetic flux amplitude.

[0091] During the continuous magnetization of the distal magnetic input branch, the metering pump applies the first portion of magnetic suspension fluid, the rotating mechanism drives the suspected display position through the local imaging area, and the linear array light-collecting camera acquires the first distal spray image.

[0092] The controller keeps the remote magnetic input branch magnetized separately, without cleaning the suspected display position. The metering pump continues to apply the second portion of magnetic suspension. The rotating mechanism drives the suspected display position through the local imaging area again in the same direction and at the same local scanning speed. The linear array light-collecting camera obtains the second remote spray image.

[0093] After the second remote spray image is acquired, the controller performs alternating amplitude reduction demagnetization to clean the suspected display location again.

[0094] When the near-end magnetization branch is tested separately, the far-end magnetization branch is kept disconnected at both ends. The near-end magnetization branch completes three full AC cycles according to the working current of the near-end magnetization branch. The intelligent magnetic flux sensor keeps the magnetic flux amplitude of the near-end magnetization branch at the target magnetic flux amplitude.

[0095] The metering pump sequentially applies the first and second portions of magnetic suspension in the same liquid supply method. The rotating mechanism drives the suspected display position through the local imaging area in the same direction and at the same local scanning speed. The linear array light-collecting camera sequentially acquires the first and second proximal spray images.

[0096] It should be noted that by using two equal-volume sprays, the first magnetic suspension testes whether the suspected defect location can form stable adsorption when less magnetic powder enters the detection area, and the second magnetic suspension testes whether the newly added magnetic powder only accumulates delayedly along the liquid flow direction. When only one magnetic suspension is applied, it is impossible to distinguish between the later-formed true defect display and the defect that has not yet been fully supplied with powder. When more than three magnetic suspensions are applied continuously, the loose magnetic powder in the detection area increases, and the flow and aggregation can easily cover the differences caused by changes in the magnetic path. The two equal-volume sprays retain the information on the order of defect formation while controlling the total powder supply.

[0097] The image processor examines the first distal spray image, the second distal spray image, the first proximal spray image, and the second proximal spray image, respectively.

[0098] If a single magnetic input branch forms a continuous bright area at the original suspected axial and circumferential positions after the first application of the magnetic suspension, the single magnetic input branch is recorded as the magnetic input branch that formed the display earlier. If a single magnetic input branch does not form a continuous bright area after the first application of the magnetic suspension, but forms a continuous bright area after the second application of the magnetic suspension, the single magnetic input branch is recorded as the magnetic input branch that formed the display later. If a single magnetic input branch does not form a continuous bright area after both applications of the magnetic suspension, the single magnetic input branch is merged into the magnetic input branch that formed the display later.

[0099] When the far-end magnetization branch and the near-end magnetization branch have different display formation sequences, the magnetization branch that forms a display earlier is determined to be the early display branch, and the magnetization branch that forms a display later or does not form a display is determined to be the late display branch.

[0100] The controller first performs alternating demagnetization with decreasing amplitude, then cleans the suspected display position, and after cleaning, it performs three magnetization stages consecutively.

[0101] The first magnetization section connects to the late-display branch, the second magnetization section connects to the early-display branch, and the third magnetization section connects to the late-display branch again.

[0102] Each magnetization section operates continuously for three complete AC cycles, and adjacent magnetization sections are switched only when the excitation current crosses zero in the positive direction; the metering pump maintains continuous spraying during the three magnetization sections, and the intelligent magnetic flux sensor maintains the magnetic flux amplitude of each magnetization section at the target magnetic flux amplitude.

[0103] Before the first magnetization stage begins, the rotating mechanism moves the suspected display position to the starting side of the local imaging area; during the execution of the three magnetization stages, the rotating mechanism drives the suspected display position through the local imaging area in the same direction at a fixed local scanning speed, and the linear array light-gathering camera continuously acquires local image rows; after the three magnetization stages are completed, the image processor arranges the local image rows into a late-display branch priority verification image.

[0104] The controller performs alternating demagnetization with reduced amplitude again, then cleans the suspected display location. After cleaning, the branch order of the three magnetization segments is reversed.

[0105] The first magnetization section connects to the early-display branch, the second magnetization section connects to the late-display branch, and the third magnetization section connects to the early-display branch again.

[0106] Each magnetization section continues to operate for three complete AC cycles, and adjacent magnetization sections switch when the excitation current crosses zero in the positive direction. The metering pump maintains continuous spraying with the same flow rate and the same spraying time, and the intelligent magnetic flux sensor maintains the same target magnetic flux amplitude.

[0107] The rotating mechanism moves the suspected display position back to the starting side of the local imaging area, and then drives the suspected display position through the local imaging area in the same direction and at the same local scanning speed.

[0108] After the three magnetization segments are completed, the image processor generates the early-display branch priority verification image.

[0109] It should be noted that three magnetization segments can form a branch sequence in a single local retest where the same magnetization branch is located in the first and last segments, and different magnetization branches are connected in the middle magnetization segment. When only two magnetization segments are used, it is impossible to verify whether the suspected pattern can continue to form in the original position when the first magnetization branch is reconnected after the middle circuit switching. When more than four magnetization segments are used, the number of branch switching and magnetic powder supply time increase, and the accumulation of loose magnetic powder can easily weaken the difference between two opposite branch sequences. Each magnetization segment can work continuously for three complete AC cycles, which can avoid the transient process at the beginning of the branch switching and retain the timely switching effect. When there are fewer than three complete AC cycles, the duration of stable magnetization is insufficient, and when there are more than three complete AC cycles, the continuous adsorption time of a single magnetization path increases.

[0110] The priority retest of late-display branches does not strengthen the magnetic input branches that have already formed a clear display, but rather increases the effect of weaker magnetic input paths on suspected display locations.

[0111] The actual defect is located within the detection zone shared by the distal and proximal longitudinal magnetic circuits. During the priority retest of the late-display branch, leakage magnetic adsorption can still be formed at the original axial and circumferential positions.

[0112] The local magnetic reluctance concentration caused by the longitudinal magnetic circuit formed by the early-manifesting branch within the detection zone makes it difficult to maintain continuous adsorption when the late-manifesting branch occupies the first and third magnetization sections.

[0113] Continuous spraying in the middle switching and both sides of the magnetization section continuously drives the loose magnetic powder to move.

[0114] The early-display branch is prioritized for retesting the magnetization section occupied by the two input branches. Only the order of the input branches is changed, without changing the total number of complete AC cycles, the target magnetic flux amplitude, the spray flow rate, the spray time, or the local imaging conditions.

[0115] If the display is formed after the first magnetic suspension is applied in both the far-end magnetic input branch and the near-end magnetic input branch, or only after the second magnetic suspension is applied in both branches, or if no display is formed in either branch, or if the display positions are different, then the early display branch and the late display branch are not established.

[0116] The controller first sequentially completes three magnetization stages using the far-end magnetization branch, the near-end magnetization branch, and the far-end magnetization branch again. After completing the three magnetization stages, it performs alternating amplitude reduction demagnetization and cleans the suspected display location. After cleaning, it then sequentially completes the three magnetization stages again using the near-end magnetization branch, the far-end magnetization branch, and the near-end magnetization branch again. The two retests maintain the same total number of complete AC cycles, target magnetic flux amplitude, spray flow rate, spray time, and local imaging conditions.

[0117] The image processor performs positional registration between the late-display branch priority verification image, the early-display branch priority verification image, or the two fixed branch order verification images and the local image in the suspected display record.

[0118] In this process, axial position registration uses the same axial pixel column, while circumferential position registration uses the circumferential zero mark and the total number of pulses per revolution of the rotary encoder. After the rotation direction changes, before the liquid spraying and imaging begin, the rotating mechanism crosses the circumferential zero mark once along the changed direction, and resets the rotary encoder count to zero when it reaches the circumferential zero mark again. The image processor reverses the scan lines of the reverse rotating image and subtracts the reverse cumulative pulse number from the total number of pulses per revolution of the rotary encoder to form the forward circumferential pulse sequence number. The forward rotating image and the reverse rotating image are registered using the same axial pixel column and the same forward circumferential pulse sequence number, without generating additional continuous coordinate data.

[0119] The image processor records whether the suspected display remains in the original axial and circumferential positions, whether it changes with the magnetic input branch occupying the first and third magnetization sections, and whether it only spreads along the liquid flow direction after the second magnetic suspension is applied, thus forming a local re-examination record.

[0120] The local re-inspection record saves four single-branch spray images, two three-magnetization-section re-inspection images, showing the order of formation, changes in display position, the development of liquid flow direction, and a re-inspection completion mark; the induced voltage sampling value, half-wave flux amplitude, excitation current zero-crossing pulse, and temporary images that have not entered the local re-inspection record are not stored after the current control or image screening is completed.

[0121] The joint judgment module magnetizes the two branches in the same phase and direction, and the total magnetic flux amplitude is equal to the magnetization amplitude of a single branch. The pipe fitting is reversed, and the result is determined and demagnetized according to whether the display changes with the retest sequence, the magnetic branch or the direction of fluid flow.

[0122] Specifically, the continuity of encoder pulses is used to verify whether the circumferential range of the detection band has completed a full circumference acquisition. Based on the axial position, circumferential position, and surface type in the suspected display records, the re-inspection completion mark in the local re-inspection records is searched item by item.

[0123] When the coverage information in the valid records of the whole cycle detection indicates the existence of an uncovered area, the controller rotates the pipe to the first encoder pulse position of the uncovered area, maintains continuous spraying of magnetic suspension, and alternates magnetization of the far-end magnetization branch and the near-end magnetization branch with an equal number of complete AC cycles, switching only when the excitation current crosses zero, until the inner surface linear array light-collecting camera and the outer surface linear array light-collecting camera complete the acquisition of the uncovered area; when the local re-inspection record does not contain the re-inspection completion mark of a certain suspected display position, the pipe is repositioned according to the axial position, circumferential position and surface type in the suspected display record, and the cleaning, single branch equal amount of spraying and segmented magnetization in reverse order are completed to generate a local re-inspection record before entering common magnetization; when the suspected display record is empty, the local re-inspection completion mark is not used as an entry condition.

[0124] In one aspect, the excitation winding of the far-end magnetization branch and the excitation winding of the near-end magnetization branch are connected to a dual-channel AC power supply according to the polarity of the installation end, and the dual-channel AC power supply shares the zero-crossing trigger signal.

[0125] During the positive half-cycle, the magnetic flux generated by both branches enters the tube wall from the first magnetic head and converges towards the second magnetic head; during the negative half-cycle, the magnetic flux generated by both branches reverses simultaneously.

[0126] The dual-channel AC power supply uses a common magnetization proportional coefficient to synchronously scale the currents of the two branches. The current relationship during the common magnetization increment adjustment period is expressed as follows:

[0127]

[0128]

[0129] in, This indicates the current amplitude in the distal magnetized branch during common magnetization. This represents the current amplitude in the near-end magnetization branch during common magnetization. This represents the current common magnetization ratio. This indicates the amplitude of the operating current for individual magnetization of the remote magnetization branch. This indicates the amplitude of the operating current for individual magnetization of the near-end magnetization branch. This represents the total common magnetization flux amplitude obtained by the intelligent flux sensor of the second magnetic head. This represents the target flux amplitude of a single branch within the equal flux magnetization control data. This represents the fixed common magnetization ratio coefficient.

[0130] Specifically, the common magnetization ratio coefficient ranges from 0 to 1. The controller divides the minimum current adjustment step of the dual-channel AC power supply by the working current amplitude of the separately magnetized far-end magnetized branch and the working current amplitude of the separately magnetized near-end magnetized branch, and selects the larger of the two ratios as the initial ratio increment. When the common magnetization ratio coefficient is 0, the current of both magnetized branches is 0, and the intelligent flux sensor records the zero-input flux reading. The controller increases the common magnetization ratio coefficient step by step from 0 according to the initial ratio increment, and takes 1 when the value after the increase exceeds 1. The current of the two magnetized branches changes synchronously only at the zero-crossing position of the same excitation current. After each change of the common magnetization ratio coefficient, the intelligent flux sensor integrates the subsequent complete half-wave of the same polarity induced voltage, divides the absolute value of the integral by twice the number of turns of the induction coil, and then subtracts the zero-input flux reading to obtain the measured total flux amplitude.

[0131] It should be noted that dividing the absolute value of the integral by twice the number of turns of the induction coil is because the change in magnetic flux covered by the half-wave of the same polarity induced voltage is equal to twice the magnetic flux amplitude; dividing only by the number of turns of the induction coil will make the calculated value of the magnetic flux amplitude twice the actual value, and using a larger divisor will underestimate the magnetic flux amplitude; starting the common magnetization proportional coefficient from zero can prevent abrupt magnetic flux changes at the moment the two branches are connected; using a non-zero proportional coefficient for direct connection can easily form instantaneous powder agglomeration unrelated to material discontinuities.

[0132] When the target magnetic flux amplitude of a single branch is located between two adjacent measured total magnetic flux amplitudes, a new common magnetization ratio coefficient is calculated according to the proportional position of the target magnetic flux amplitude of the single branch between two adjacent measured total magnetic flux amplitudes, and a complete AC cycle is reapplied and the measurement is repeated.

[0133] When the difference between the measured total magnetic flux amplitude and the target magnetic flux amplitude of a single branch is not greater than the magnetic flux resolution of the intelligent magnetic flux sensor, the common magnetization ratio coefficient is fixed.

[0134] If the current in any branch increases to the individual magnetization operating current but still fails to achieve the target magnetic flux amplitude for that branch, the controller stops excitation and prompts the user to check the head gap, winding polarity, and branch wiring.

[0135] It should be noted that the flux resolution of the intelligent flux sensor is used as the minimum difference for common magnetization adjustment because smaller differences cannot be reliably distinguished by the intelligent flux sensor, and relaxing the difference will cause the common magnetization image to be affected by changes in flux strength. The common magnetization scaling factor simultaneously scales the individual magnetization current of the two branches to maintain a predetermined ratio between the current amplitudes of the two magnetized branches. The total common magnetization flux amplitude is kept at the target flux amplitude of a single branch, which can prevent uncontrolled enhancement of magnetic powder adsorption capacity caused by the simultaneous connection of the two branches. The common magnetization image is used to reflect the change in magnetic field distribution when the two magnetized positions act simultaneously, and by limiting the total common magnetization flux amplitude, the brightness enhancement caused by the increase in total flux is avoided from being mistaken for defect enhancement.

[0136] As a preferred method, after fixing the common magnetization ratio coefficient, the suspected display position is brought into the camera's field of view according to the material coordinates in the suspected display record; first, alternating amplitude reduction demagnetization is used to eliminate residual magnetization, and then non-magnetic carrier liquid is used to clean the suspected display position until no continuous bright area is retained under ultraviolet illumination; alternating amplitude reduction demagnetization applies a complete AC cycle to the far-end magnetization branch and the near-end magnetization branch in sequence, and after the two branches complete the same level of current magnetization, the current is reduced together until the current is zero; switching and amplitude reduction are both performed when the current crosses zero; the pipe is kept in the rotation direction used for full-circle detection, the metering pump is kept in the single spray volume, outlet pressure and spray duration used for local re-inspection, the dual-channel AC power supply applies AC current in the same phase and direction according to the fixed common magnetization ratio coefficient, and the inner surface linear array focusing camera or the outer surface linear array focusing camera acquires common magnetization images according to the surface category in the suspected display record.

[0137] After the common magnetization image acquisition is completed, the alternating amplitude reduction demagnetization and cleaning of suspected display positions are performed again. The rotary motor keeps the absolute value of the rotation speed constant and changes the rotation direction. The nozzle position, liquid volume, outlet pressure, ultraviolet illumination intensity, camera exposure time and common magnetization ratio coefficient remain unchanged, and the common magnetization image is acquired again.

[0138] Preferably, the nozzle sprays liquid radially towards the upper part of the detection zone along the pipe fitting. Before acquiring the common magnetization image, the controller shuts off the two magnetization branches. Under the condition that the liquid volume, outlet pressure, and absolute value of rotation speed remain unchanged, the pipe fitting is driven to rotate in the forward and reverse directions, respectively. After each restart of spraying, the linear array focusing camera continuously acquires two liquid film images. The image processor determines the circumferential movement direction of the liquid flow based on the circumferential position change of the liquid film front in the two liquid film images. When the circumferential movement direction of the liquid flow is opposite during forward and reverse rotation, the current absolute value of rotation speed is fixed and two common magnetization images are acquired. When the circumferential movement direction of the liquid flow does not reverse, the rotation speed is adjusted step by step within the allowable rotation speed range of the rotating mechanism and repeatedly confirmed. When the allowable rotation speed boundary is reached and the re-verification still does not reverse, the common magnetization re-verification is stopped and the liquid spraying conditions are prompted to be adjusted. The two common magnetization images use the same absolute value of rotation speed, magnetization conditions, spraying conditions, and imaging conditions, so that the circumferential extension change can be attributed to the change in liquid flow direction.

[0139] Furthermore, the same material coordinates are represented by the same axial pixel column and the positive circumferential pulse sequence number, and the suspected display images, single-branch segmented spray images, mutually reversed sequence segmented magnetization images, common magnetization images, and reverse rotation common magnetization images are jointly analyzed.

[0140] In one aspect, the main body of the bright area maintains the same material coordinates in the suspected display image, the single-branch multi-spray image, the reversible sequence segmented magnetization image, and the common magnetization image. The main body of the bright area does not change with the first magnetic input branch connected, nor does it change with the circumferential movement direction of the thin-layer liquid flow. When the bright area extends along the circumferential or oblique direction and has a transverse component with the longitudinal magnetic flux, the main body of the bright area is recorded as a defect display.

[0141] Furthermore, when the main body of the bright area maintains the same material coordinates while the edge of the bright area extends in the opposite direction to the thin liquid flow, the controller records the fixed bright area as a defect and excludes the extension portion that extends in the opposite direction to the liquid flow from the defect length.

[0142] Among them, the partial re-inspection record shows that the bright area appears, disappears, or moves with the change of the segmented magnetization sequence. When no bright area fixed to the raw material coordinate is formed in the common magnetization image, and the reverse rotation does not reverse the direction of change of the bright area, the bright area is recorded as a pseudo-display related to the magnetization branch. When the bright area expands along the direction of the thin liquid flow, and the direction of expansion of the bright area is reversed after the reverse rotation, and there is no main body of the bright area fixed to the same material coordinate in each image, the bright area is recorded as a pseudo-display of liquid flow powder accumulation. When the bright area only appears after the two branches are switched, and the bright area no longer appears in the single branch magnetization image and the common magnetization image, and the segmented magnetization image with the reverse sequence shows that the bright area changes with the first connected magnetization branch, the valid record of the whole cycle detection is marked as invalid and written into the reason for the switching abnormality, and no workpiece defect conclusion is directly formed. After the operator checks the zero-crossing trigger and branch interlock, eliminates the switching abnormality, and then completes the whole cycle alternating magnetization, continuous spraying and image acquisition of the detection belt again.

[0143] In one possible implementation, when the same suspected display simultaneously has a fixed bright area as the main body, a side bright area that changes with the magnetic branch, and an extended bright area that extends in the opposite direction of the liquid flow, the display range is separated according to the stability of the material coordinates, the relationship of the change of the magnetic branch, and the relationship of the change of the liquid flow direction. Only the fixed bright area is included in the defect display. When the common magnetization image does not form a fixed bright area, but the single branch multi-spray image and the mutually reverse sequence segmented magnetization image both maintain a fixed bright area as the main body on the same material coordinate, or when multiple changes cannot form a unique explanation, the suspected display is recorded as a manual review item and the representative image used for judgment is retained. The failure of the common magnetization image to form a fixed bright area is not used as the sole basis for excluding defect displays, recording it as a false display, or forming a conclusion that no defect was found.

[0144] When the suspected display record is empty, the pipe is made to pass through the working area of ​​the two magnetic heads in the rotation direction and the reverse rotation direction used for full circumference detection. After the intelligent magnetic flux sensor of the second magnetic head obtains the target magnetic flux amplitude of a single branch during the passage of the pipe, a detection conclusion of no suspected display is found is formed, and the local re-inspection image is not saved.

[0145] After the test results are formed, stop spraying and keep the pipe rotating. The dual-channel AC power supply maintains the two branches in the same phase and direction, and keeps the ratio between the current amplitude of the far-end magnetized branch and the current amplitude of the near-end magnetized branch unchanged. After each complete AC cycle, reduce the common magnetization ratio coefficient according to the minimum stable adjustment of the dual-channel AC power supply.

[0146] The detection zone continuously passes through the area of ​​action of the two magnetic heads in the circumferential direction, and the common magnetization ratio coefficient gradually decreases to zero. The dual-channel AC power supply is disconnected when the excitation current crosses zero. The operator uses a residual magnetic field detector to check along the circumferential direction of the detection zone. If the residual magnetic field does not meet the applicable acceptance specifications, the demagnetization is repeated in stages until the residual magnetic field meets the applicable acceptance specifications.

[0147] As an example, the residual magnetic field detector uses a calibrated Hall effect magnetic field strength meter with a measurement range of not less than ±2mT and a resolution of not more than 0.01mT. The operator selects eight measuring points at equal intervals along the circumference on the outer surface of the detection strip, places the sensitive direction of the detection probe along the axial and circumferential directions of the pipe fitting, and reads the absolute values ​​of the residual magnetic field in both directions at each measuring point. When all readings are not greater than 0.3mT, a demagnetization qualification mark is formed. If any reading is greater than 0.3mT, the demagnetization is repeated step by step with decreasing amplitude and the test is repeated.

[0148] The final inspection record retains the fitting number, valid inspection records for the entire week, common magnetization ratio coefficient, coordinates of suspected display materials, inspection conclusion, representative images used for judgment, and demagnetization qualification mark.

[0149] In summary, this invention reduces the difference in magnetic flux amplitude caused by the different magnetic circuit impedances of the two longitudinal magnetic circuits by adjusting the dual-branch equal magnetic flux; it weakens the pseudo-indications related to the magnetic entry position by alternating magnetization and continuous spraying throughout the complete cycle; and it achieves accurate differentiation between defect indications and different pseudo-indications by equal amount of liquid spraying, reversible verification, and reverse rotation.

[0150] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system, characterized in that, include: The magnetic flux calibration module enables the far-end magnetization branch and the near-end magnetization branch of the first magnetic head to form longitudinal magnetic circuits passing through the same detection zone with the second magnetic head. The module adjusts the branch current according to the output of the intelligent magnetic flux sensor of the second magnetic head so that the magnetic flux amplitude of the two branches magnetized individually is the same. The alternating magnetization module rotates the pipe and continuously sprays magnetic suspension liquid, so that the two branches are alternately magnetized with an equal number of complete AC cycles. The connection is only switched when the excitation current crosses zero, and the image is acquired to obtain the suspected display position. The sequence retest module cleans the suspected display position, connects two branches separately in sequence and sprays liquid in two equal amounts, determines the early display branch and the late display branch according to the display order, magnetizes the late display branch, early display branch and late display branch in three segments, and retests in the reverse order after cleaning. The joint judgment module magnetizes the two branches in the same phase and direction, and the total magnetic flux amplitude is equal to the magnetization amplitude of a single branch. The pipe fitting is reversed, and the result is determined and demagnetized according to whether the display changes with the retest sequence, the magnetic branch or the direction of fluid flow.

2. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 1, characterized in that, The longitudinal magnetic circuit passing through the same detection zone includes: The far-end magnetization branch and the near-end magnetization branch are spaced apart along the axial direction of the pipe and are each equipped with an independent magnetic core. A non-magnetic partition is set between the two independent magnetic cores. The second magnetic head is located on the bevel side of the tube end and is equipped with an intelligent magnetic flux sensor; When the two magnetic input branches are connected, the magnetic flux passes through the same detection zone along the axial direction of the pipe and enters the second magnetic head.

3. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 2, characterized in that, The regulating branch current includes: The intelligent magnetic flux sensor accumulates the absolute value of the induced voltage between adjacent voltage zero-crossing points, and divides the accumulated value by twice the number of turns of the induction winding to form the magnetic flux amplitude. The magnetic flux amplitude of the far-end magnetic input branch is determined as the target magnetic flux amplitude. The current of the near-end magnetic input branch is adjusted until the absolute value of the difference between the two magnetic flux amplitudes is not greater than the magnetic flux resolution of the intelligent magnetic flux sensor, thus forming equal magnetic flux magnetization control data. If the setting is not completed even after reaching the allowable current boundary, adjust the non-contact air gap and readjust.

4. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 3, characterized in that, The alternating magnetization includes: The far-end magnetization branch and the near-end magnetization branch operate continuously for three complete AC cycles, and are switched only when the excitation current crosses zero in the positive direction. The non-conductive input branch remains open, and the magnetic flux amplitude of the currently conductive branch remains at the target magnetic flux amplitude; During branch switching, continuous spraying is maintained, and the pipe rotation speed is sufficient to complete the magnetization of the two magnetized branches before leaving the spraying area at the same position.

5. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 4, characterized in that, The process of obtaining the suspected display location includes: The rotary encoder triggers the inner surface linear array light-collecting camera and the outer surface linear array light-collecting camera to acquire image rows and form a strip image; The image segmentation gray level is determined by the maximum inter-class variance, and the continuous bright areas that reach the number of consecutive scan lines are recorded as suspected display areas; The axial and circumferential positions are determined based on the image column position and the rotary encoder trigger pulse, forming a suspected display record.

6. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 5, characterized in that, The two equal-volume sprayings include: The alternating amplitude reduction demagnetization was performed and the suspected display position was cleaned. During the separate magnetization of the remote magnetic input branch, two equal amounts of magnetic suspension were applied in sequence and two spray images were acquired. After demagnetization and cleaning, the near-end magnetization branch performs the same operation with the same magnetic flux amplitude, liquid volume, rotation direction and scanning speed.

7. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 6, characterized in that, The determination of early-emerging branches and late-emerging branches includes: The magnetic input branch that forms and appears after the first application of the magnetic suspension is recorded as the earlier magnetic input branch that forms and appears. The magnetic input branch that forms and appears only after the second application of the magnetic suspension or does not form and appears is recorded as the later magnetic input branch that forms and appears. When the two magnetization branches at the same position form the display at different times, the early display branch and the late display branch are determined. When the display formation is the same or the display positions are different, the early display branch and the late display branch are not established.

8. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 1 or 7, characterized in that, The process involves magnetizing the branch in three segments—the late-emerging branch, the early-emerging branch, and the late-emerging branch again—and then re-examining it in reverse order after cleaning. The specific steps are as follows: When establishing early-displaying and late-displaying branch roads, two re-inspections are carried out in sequence as late-displaying branch road, early-displaying branch road, late-displaying branch road, and early-displaying branch road, late-displaying branch road, early-displaying branch road; If early-discovery branches and late-discovery branches are not established, two re-inspections are carried out in sequence according to the far-end magnetic entry branch, the near-end magnetic entry branch, the far-end magnetic entry branch, and the near-end magnetic entry branch, the far-end magnetic entry branch, and the near-end magnetic entry branch. The single-branch magnetic flux amplitude, spraying conditions, and imaging conditions were the same in both re-tests.

9. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 1, characterized in that, The common magnetization includes: The two magnetization branches are connected to a dual-channel AC power supply with the same winding polarity and a shared zero-crossing trigger signal, so that the branch current when the two magnetization branches are individually magnetized is synchronously scaled by a common magnetization ratio coefficient. The common magnetization ratio coefficient increases gradually from zero until the absolute value of the difference between the total common magnetization flux amplitude obtained by the intelligent flux sensor and the flux amplitude of a single branch magnetization is no greater than the flux resolution of the intelligent flux sensor.

10. The pipe-end dual-magnetic-head longitudinal non-contact AC magnetization flaw detection system as described in claim 5 or 9, characterized in that, The determination of the result and demagnetization include: Under the same magnetization, spraying, and imaging conditions, forward rotation co-magnetization images and reverse rotation co-magnetization images were acquired respectively. A defect is indicated when the material coordinates remain the same and do not change with the direction of the magnetic inlet branch and the fluid flow. When the display changes with the magnetization branch, it is recorded as a pseudo-display related to the magnetization branch; When the display shows a reversal of the liquid flow direction, it is recorded as a false display of liquid flow agglomeration. A switching anomaly is only recorded when it occurs after a branch switching and cannot be reproduced by single-branch magnetization and common magnetization. When both a fixed indicator and an extended portion that changes with the fluid flow exist simultaneously, only the fixed indicator is included in the defect indicator; After the test results are formed, the current in the two magnetic input branches is gradually reduced to zero and the residual magnetic field is checked.

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