Material defect detection device and detection method

Abstract

The invention provides a material defect detection device and method, the device comprises a shielding device, a coil probe and a detection device, the coil probe is internally provided with a plane gradient coil, the shielding device is connected with the coil probe, the shielding device is internally provided with a transmission coil, the detection device is arranged in the shielding device, and the transmission coil is connected with the transmission coil. The detection device comprises a coil 3 and a magnetic sensor, the coil 3 is electrically connected with the plane gradient coil, the plane gradient coil is used for skipping over the detection surface of the to-be-detected material, moving and skipping over are carried out, the movement speed of the plane gradient coil is kept consistent, whether the magnetic field of the coil 3 detected by the magnetic sensor is abnormal or not is judged, and if the magnetic field is abnormal, the magnetic sensor is started. The detection surface of the to-be-detected material has defects, so that high-sensitivity detection is realized.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic field measurement and provides a method for detecting material defects. The materials involve various metal or magnetic materials such as oil and gas metal pipelines, rails, engine cylinder liners, boilers, etc. Background Art

[0002] Industrial materials, especially metal materials, are prone to internal defects after long-term use. For example, oil and gas pipelines will inevitably produce various defects during long-term use, such as pipeline rupture, stress deformation, rust, corrosion, etc. In order to avoid pipeline damage during use and cause significant losses, pipelines are usually inspected in the hope of timely repair. Currently, the commonly used methods for measuring material defects include magnetic flux leakage, ultrasonic testing, and x-ray testing. Among them, the sensitivity of the magnetic flux leakage method is not very high, so the defects inside the material cannot be detected in time. Summary of the invention

[0003] In order to overcome the deficiencies in the prior art, the present invention provides a material defect detection method, which realizes high-sensitivity measurement through a detection device. The present application targets the magnetic anomalies caused by defects, and can realize the measurement of internal defects and surface defects in material defects, solving the problem of accurate maintenance and detection of workpieces during use. The applicant made a scratch on the surface of a 10mm steel plate, and then measured it on the other side, measuring a signal with the same characteristics, but the signal was relatively weak. This shows that the measurement depth of the detection device is at least 10mm, and it is fully capable of detecting internal defects in steel.

[0004] To achieve the above-mentioned purpose, the present invention provides a material defect detection device, which includes a shielding device, a coil probe and a measuring device, wherein the shielding device is connected to the coil probe, a transfer coil is provided in the shielding device, a planar gradient coil for detection is provided in the coil probe, the transfer coil is inside the shielding device, the planar gradient coil is outside the shielding device, the planar gradient coil is electrically connected to the transfer coil, the measuring device is arranged in the shielding device, the measuring device includes the transfer coil and a magnetic sensor, and the transfer coil is electrically connected to the planar gradient coil.

[0005] Preferably, at least two of the planar gradient coils constitute one gradient coil group, and the two planar gradient coils are arranged in parallel.

[0006] Preferably, the sensitivity of the magnetic sensor is

[0007] The present invention also provides a detection method for a material defect detection device, which comprises: using the coil probe to sweep over the detection surface or the entirety of the material to be detected, moving and sweeping over and keeping the movement speed of the planar gradient coil consistent,

[0008] Determine whether the magnetic field of the transfer coil detected by the magnetic sensor is an abnormal magnetic field. If it is an abnormal magnetic field, there is a defect on the detection surface of the material to be detected. The magnetic induction intensity and magnetic flux at the defect will change. This is because the defect (such as cracks, holes or internal gaps) will affect the distribution of the magnetic field, resulting in a local abnormal magnetic field in the defect area. According to the electromagnetic induction phenomenon, when the transfer coil passes through the defect, when the magnetic flux changes through the area of ​​the closed coil, an induced electromotive force will be generated in the coil, that is, an induced current will be generated inside the transfer coil, and the weak magnetic field generated by the induced current is the abnormal magnetic field. In practical applications, since the winding directions of coil 1 and coil 2 are opposite, when the two coils pass through the defect respectively, the currents generated therein flow in opposite directions, which are reflected in the magnetic field. The directions of the magnetic fields of the two are opposite, so when passing through the defect, a characteristic peak of positive and negative mutations will be seen in the magnetometer.

[0009] Preferably, the transfer coil and the magnetic sensor are both in a magnetically shielded environment.

[0010] Preferably, the transfer coil is electrically connected to a plurality of planar gradient coils or a plurality of gradient coil assemblies.

[0011] Another object of the present invention is to provide a material defect measurement method, including a pipeline defect measurement method, which specifically comprises the following steps:

[0012] By using the above-mentioned material defect detection device, material defects are measured by measuring the magnetic field generated by the material itself, and magnetic field measurement can be achieved without pre-magnetization. The detection object is a ferromagnetic material and a ferrimagnetic material, such as iron, cobalt, nickel, etc., and a ferrimagnetic material such as ferrite, etc. The device is provided with a shielding device, which is generally a shielding barrel structure made of Permalloy, which can effectively isolate the earth's magnetic field and magnetic noise, and create a near-zero field test environment. The shielding device is provided with a transfer coil and a magnetic sensor (such as a magnetometer), the transfer coil is inside the shielding device, the planar gradient coil is outside the shielding device, the planar gradient coil and the transfer coil are connected to each other by a wire, the coil probe is used to introduce the magnetic field into the shielding barrel, the material to be tested is placed in the shielding device, and through the coil probe, when the planar gradient coil passes over the surface of the material, the magnetic sensor measures the magnetic field generated by the transfer coil, thereby achieving defect measurement. The present invention is a precision measurement, and whether the material to be tested is pre-magnetized does not affect the experimental results.

[0013] The transfer coil is usually a Helmholtz coil or a saddle coil. The magnetic sensor is placed at the geometric center of the transfer coil. The relative position of the magnetic sensor and the coil is fixed, usually directly fixed on the 3D printed structure, and there is no relative movement. The planar gradient coil is a detection device, and its structure is as follows Figure 2As shown. When the gradient coil passes through a defect, the magnetic flux in the gradient coil changes. Defects can cause abnormal distribution of the material's magnetic permeability, disrupting the normal flow of the magnetic field, thereby changing the distribution of the magnetic flux and causing magnetic flux leakage, generating electromotive force and current in the coil. Since the planar gradient coil and the transfer coil are connected to each other with wires, the transfer coil and the gradient coil are in the same loop, generating the same current and thus a magnetic field. The coil probe obtains metal surface information by measuring the magnetic field of the transfer coil.

[0014] The magnetic flux in the coil changes. The faster the magnetic flux changes, the greater the current generated in the coil, and the corresponding magnetic field signal is also greater. However, the faster the better. It is necessary to ensure that the measurement response time is less than the time it takes to pass the defect. Due to the bandwidth limitation of the magnetometer, when the measuring probe passes through a tiny defect, the speed may cause the defect to be missed if the speed is too fast. Assuming that the measurement bandwidth of the magnetometer is 100Hz, its measurement response is 0.01s, and the probe area is 4*4cm. When passing through a defect with a width of 1cm and a depth of 1cm, the probe moves forward at a constant speed. From the time the probe enters the defect to the time it leaves the defect, the total mileage is 9cm, the average speed is 9m / s, and the time it takes to pass through the defect is 0.09s. The measurement response time is much less than the time it takes to pass through the defect, and the magnetic field signal at the defect can be effectively measured at this time. When the speed is too fast, the magnetic field changes faster. When its speed is outside our bandwidth, we will not be able to respond to the magnetic field signal. When the speed is too fast, the magnetic flux in the coil changes faster, the current generated is larger, and the magnetic field generated may exceed the range of the magnetometer.

[0015] Preferably, the sensitivity of the shielding device mainly depends on the setting optimization of the transfer coil and the sensitivity of the magnetometer itself.

[0016] The function of the transmission coil is to introduce the external magnetic field signal into the shielding device. The introduced magnetic field is usually smaller than the actual magnetic field (the induced current generated by the transmission coil will be partially lost after being transmitted through the wire, causing the current received by the magnetometer to be smaller than the actual current). The output signal is weaker, so the sensitivity is higher. Preferably, the transmission coil is optimized, and its sensitivity will change to a certain extent. It is estimated that without optimizing the transmission coil, the sensitivity of the entire device is currently If the transfer coil is optimized, the number of turns, cross-sectional area and material permeability of the coil are increased, and the coil geometry is adjusted, the sensitivity will reach The sensitivity of the magnetometer determines the ultimate sensitivity of our device to a certain extent.

[0017] Preferably, the magnetometer is a SERF atomic magnetometer with a sensitivity of

[0018] Preferably, a planar gradient coil is provided in the coil probe, which can introduce the external magnetic field into a high-sensitivity magnetometer, and the pipeline detection is achieved by measuring the change of the magnetic field through the magnetometer.

[0019] Preferably, the planar gradient coil can eliminate the interference of the earth's magnetic field and other magnetic field noise on the measurement, and when the coil passes over the defect at a certain speed, the magnetic fields sensed by the two coils are different at the same time.

[0020] Preferably, the device can achieve accurate resolution of scratches on the iron plate with width and depth at sub-millimeter level.

[0021] The beneficial effects of the present invention are as follows:

[0022] The magnetic sensor used in this technical method is based on quantum precision measurement technology and is the sensor with the highest detection sensitivity at present. Therefore, during the detection process, it can form a sensitive response to tiny magnetic anomaly models, and can effectively measure internal defects, tiny defects, and even tiny changes in stress of the material, thereby discovering small defects in the material early and avoiding hidden dangers in the safe use of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a system architecture diagram of the detection device of the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the planar gradient coil in the detection device of the present invention;

[0025] Figure 3 This is a diagram showing the arrangement of a gradient coil group for detecting the inner surface of a pipeline by the detection device of the present invention;

[0026] Figure 4 This is a diagram showing the arrangement of a gradient coil group for detecting the outer surface of a pipeline by the detection device of the present invention;

[0027] Figure 5 A system architecture diagram of multiple gradient coil groups of the detection device of the present invention;

[0028] Figure 6 This is a schematic diagram of multiple gradient coil groups of the detection device of the present invention. In actual use, a single planar gradient coil cannot achieve a large-range measurement, so we make multiple coils on a PCB board to achieve a large-range measurement;

[0029] Figure 7 This is a detection diagram of the abnormal magnetic field obtained from the scratch test in Example 1. DETAILED DESCRIPTION

[0030] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present application will be further described below in conjunction with specific embodiments.

[0031] Implementation Case 1

[0032] This embodiment provides a device for material defect detection, which includes a shielding device, a coil probe and a measuring device. The shielding device is connected to the coil probe. The shielding device is provided with a transfer coil. The coil probe is provided with a planar gradient coil for detection. The transfer coil is inside the shielding device, and the planar gradient coil is outside the shielding device. The planar gradient coil is electrically connected to the transfer coil. The measuring device is arranged inside the shielding device. The measuring device includes the transfer coil and a magnetic sensor. The transfer coil is electrically connected to the planar gradient coil. Figure 1 and 2 A set of planar gradient coils usually has two coils. Coils 1 and 2 are two coils in the planar gradient coil. Figure 2 There are two coils with opposite winding directions, namely coil 1 and coil 2, that is, a long wire is first wound clockwise for half, and then turned around and wound counterclockwise for the other half. Each group of coils can realize measurement, and the required number is determined according to the actual situation, because the measurement range of a single coil is limited. The larger the measurement range, the more the number required. In this embodiment, the planar gradient coil is subdivided into two coils, coil 1 and coil 2, and coil 1 and coil 2 together constitute the planar gradient coil. When measuring a defect, the two coils pass over the defect at different times. When coil 1 passes over the defect, the magnetic flux therein changes, thereby generating a magnetic field, and coil 2 has not passed through the defect, so no electromotive force is generated in coil 2. When coil 2 passes over the defect, current is generated, and coil 1 has passed the defect, and no electromotive force is generated. This is the whole process of measurement. Since the winding directions of coil 1 and coil 2 are opposite, when the two coils pass through the defect respectively, the current generated therein flows in opposite directions, which is reflected in the magnetic field. Their magnetic field directions are opposite, so when passing through the defect, a characteristic peak of positive and negative mutation will be seen in the magnetometer.

[0033] Combined with Figure 1 This embodiment provides a pipeline defect measurement method, comprising the following steps:

[0034] Coil 1 and coil 2 form a set of planar gradient coils. When the coils scan and move on the surface of the object to be measured, such as a metal pipe, the magnetic flux received by the coils can be expressed as φ=BS, where B represents the magnetic field strength of the area surrounded by the coils, and S represents the projected area of ​​the coils. As the coils perform scanning motion, the changes in the magnetic field at different positions on the scanning path will form an induced electromotive force, that is, the induced electromotive force in the coils The changing magnetic field consists of two parts, namely the magnetic field change caused by leakage magnetic flux due to material defects, defined as B m , B0 caused by environmental magnetic field noise and inhomogeneity. In this example, a gradient coil group is formed by two coils of the same shape and opposite directions. When the two coils move together, they have the same speed, so the induced electromotive force caused to the environment can cancel each other out, that is, the electromotive force generated by coil 1 is The induced electromotive force generated by coil 2 is

[0035] where dB m1 is the change in magnetic field strength at coil 1 position, dB m2 is the change in magnetic field strength at the position of coil 2. The total induced electromotive force is Assuming there is no material defect at coil 2, dB m2 =0, so

[0036] The gradient coils are connected to another coil 3 (the coil inside the magnetometer, which is a three-axis Helmholtz coil) through cables (wires). The current i of coil 3 is ∝ε, and the magnetic field generated by the weak current is

[0037] Therefore, the magnetic field generated by coil 3 is related to the magnetic field anomaly formed by material defects. However, in some minor defect cases, the magnetic field anomaly formed is very weak, so a high-sensitivity magnetic sensor is used for measurement. In this example, the magnetometer (same as magnetometer) uses a spin exchange relaxation-free (SERF) atomic magnetometer as the magnetic sensor, which needs to work near zero field. Therefore, coil 3 and the SERF atomic magnetometer are placed in a magnetic shielding environment to provide a working environment for the atomic magnetometer and reduce external electromagnetic interference.

[0038] Judgment of magnetic field anomaly, because our planar gradient coil only responds to magnetic field changes within a small range, the magnetic field generated by coil 3 is usually 0. Only when passing through a defect and there is a small range of magnetic anomaly will a magnetic field be generated. The gradient coil is composed of two coils with opposite winding directions. When the two coils pass through the defect position successively, a sudden change magnetic field in the opposite direction will be generated, which is reflected in the magnetometer as a characteristic peak of positive and negative sudden changes.

[0039] In this embodiment, several scratches were made on the iron plate using a metal carving knife for verification, and the width of the scratches was less than 1 mm. Figure 7 .

[0040] Implementation Case 2

[0041] For the defect detection of the inner wall of the pipeline, the planar gradient coil group is arranged as Figure 3Arrange in a ring, set fixedly or placed at a small distance from the material to be tested, and driven to move by the oil and gas pressure in the pipeline and keep sliding close to the pipeline wall. The 8 coils in the planar gradient coil group are on the same plane. If there are defects when passing through one after another, an abnormal magnetic field will occur. The number of planar gradient coil groups can be determined according to the surface density requirements of the measurement.

[0042] Implementation Case 3

[0043] For defect detection on the outer wall of the pipeline, the planar gradient coil group is arranged as follows: Figure 4 Arrange in a ring, set fixedly or placed at a small distance from the material to be tested, and driven to move by the oil and gas pressure in the pipeline and keep sliding close to the pipeline wall. The 8 coils in the planar gradient coil group are on the same plane. If there are defects when passing through one after another, an abnormal magnetic field will occur. The number of planar gradient coil groups can be determined according to the surface density requirements of the measurement. Figure 4 The black square in the middle is the coil layout setting diagram.

[0044] Implementation Case 4

[0045] To save costs, multiple sets of coils can be used for a single sensor, and the information processing method of patrol can be used for measurement. Figure 5 The schematic diagram is as follows. By using the electronically controlled branch opening, the coil 3 is controlled in time to receive the signal of which channel, so as to achieve the measurement of a larger area. The coil can be designed as Figure 6 In this example, a single magnetometer probe is used to correspond to multiple sets of coils. When multiple coils are used at the same time, crosstalk will occur because we cannot determine which coil detected the magnetic anomaly. According to the principle of the magnetometer we use, up to 3 simultaneous detections can be achieved without generating large crosstalk.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A material defect detection device, characterized in that: The invention comprises a shielding device, a coil probe and a measuring device, wherein the shielding device is connected to the coil probe, a transfer coil is arranged in the shielding device, a planar gradient coil for detection is arranged in the coil probe, the transfer coil is arranged inside the shielding device, the planar gradient coil is arranged outside the shielding device, the planar gradient coil is electrically connected to the transfer coil, the measuring device is arranged inside the shielding device, the measuring device comprises the transfer coil and a magnetic sensor, and the transfer coil is electrically connected to the planar gradient coil.

2. The material defect detection device according to claim 1, characterized in that: At least two of the planar gradient coils constitute a gradient coil group, and the two planar gradient coils are arranged in parallel.

3. The material defect detection device according to claim 1, characterized in that: The sensitivity of the magnetic sensor is 4. The detection method of the material defect detection device according to any one of claims 1 to 3, characterized in that: Use the planar gradient coil to sweep across the detection surface of the material to be detected, move and sweep and keep the movement speed of the planar gradient coil consistent, It is determined whether the magnetic field of the transmission coil detected by the magnetic sensor is abnormal. If it is abnormal, there is a defect on the detection surface of the material to be detected.

5. The detection method according to claim 4, characterized in that: The transfer coil and magnetic sensor are both in a magnetically shielded environment.

6. The detection method according to claim 4, characterized in that: The transfer coil is electrically connected to a plurality of planar gradient coils or a plurality of gradient coil assemblies.

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