DEVICE AND METHOD FOR LEAK DETECTION OF A MAGNETIC FLOW AND ASSOCIATED METHOD

Description

[0001] The present invention relates to a method of magnetic flux leakage control for the non-destructive testing of an object comprising at least one ferromagnetic part.

[0002] Such control makes it possible in particular to check the condition of an object in the context of maintenance operations, for example, of parts of a nuclear reactor.

[0003] US 4 602 212 B describes a device for the non-destructive testing of an object. To achieve this, the device uses a combination of eddy current generation and magnetic flux leakage detection.

[0004] However, fault detection by such a device is complex because it requires the analysis of several data provided by sensors.

[0005] US 2014 / 191751 A1 relates to a magnetic testing method and apparatus that allow for the accurate detection of a defect by magnetizing a test object to such a degree that the object becomes magnetically saturated.

[0006] DE 11 2015 006279 T5 describes an inspection apparatus for diagnosing damage to cables, comprising a stirrup that applies a magnetic field to place a cable in a state of magnetic saturation, an alternating magnetic field application device that provides an alternating magnetic field to the cable by supplying a constant current to an axial coil in the axial direction thereof to cause the generation of an eddy current and an eddy magnetic field inside the cable.

[0007] US 4 303 883 A describes an apparatus that first magnetizes a base metal with an alternating flux to pass through the weld bead of the base metal and the resulting leakage flux from the weld bead is detected by at least one flux-seeking element to generate an alternating signal.

[0008] US 5,331,278 A describes an object control device comprising a DC magnet for enabling the measurement of a magnetic hysteresis loop of said object, an AC magnet for applying a weak AC magnetic field to said object for enabling the measurement of a minor magnetic hysteresis loop of said object, and a magnetic sensor for measuring said magnetic hysteresis loop and said minor magnetic hysteresis loop of said object.

[0009] One of the aims of the invention is to propose a non-destructive testing method allowing for simple detection of defects.

[0010] For this purpose, the invention relates to a control method according to claim 1.

[0011] This method allows for the detection of magnetic flux leakage by measuring the magnetic field along the normal axis. When correlated with the generated magnetic field, this measurement then allows for the detection of a defect causing the magnetic flux leakage.

[0012] Measuring the magnetic field along the normal direction also increases the measured signal and reduces measurement noise. This makes detection easier and faster.

[0013] The process control device may also have one or more of the following characteristics, considered individually or in all technically possible combinations: The magnetic field measurement unit comprises at least one magnetic field sensor, preferably at least one giant magnetoresistive magnetometer; the alternating supply current has an intensity between 1 A and 15 A; the electromagnet has a U-shape comprising at least one north arm and at least one south arm, the at least north arm and the at least south arm being adapted to be placed against the surface of the object to be controlled; the magnetic field measurement unit is located between the north arm and the south arm; the device is configured so that the measurement unit is spaced from the surface of the object to be controlled by a distance of less than 2 cm, preferably less than 1 mm.

[0014] The control method may also have one or more of the features of claims 2 and / or 3, considered individually or according to all technically possible combinations.

[0015] Other features and advantages of the invention will become apparent from the detailed description given below, by way of example and not limitation, with reference to the attached figures, including: [ Fig 1 ] there figure 1 is a schematic view of a control device for a control method according to an embodiment of the invention in operation with an object to be controlled that does not have a defect, [ Fig 2 ] there figure 2 is a schematic view of the control device of the figure 1 with an object to be inspected that has a defect, [ Fig 3 ] there figure 3 is an example of measuring the normal and tangential components of the magnetic field using the measuring unit of the control device. figure 1 to the right of a defect, and [ Fig 4 ] there figure 4 is an example of the normal component of the figure 3 after applying a filter.

[0016] A control device 10 for a control method according to an embodiment of the invention is shown in the figures 1 And 2 .

[0017] The inspection device 10 is designed for non-destructive testing by magnetic flux leakage of an object comprising at least one ferromagnetic part. More specifically, the part of the object to be inspected is ferromagnetic.

[0018] The object has an external surface.

[0019] The control device 10 is configured to be placed against the external surface of the object, so as to control the object. More specifically, the control device 10 is capable of controlling the object up to two centimeters (2 cm) deep from the external surface.

[0020] By checking, we mean detecting a defect, such as a crack, in the object.

[0021] The control device 10 includes a power supply unit 12, a magnetizing unit 14, a measuring unit 16 and a calculating unit 18.

[0022] The power supply unit 12 is capable of generating an alternating current supply. The power supply unit 12 includes, for example, an electric current generator.

[0023] The power supply unit 12 has, for example, an activated state in which it generates an alternating supply current and a deactivated state, in which it does not generate a supply current.

[0024] The power supply unit 12 has two connection terminals between which the supply current is generated.

[0025] The alternating power supply has a frequency between 0.1 Hz and 100 Hz.

[0026] Such a frequency makes it possible in particular to limit any eddy currents generated in the object, which could disrupt the control.

[0027] More specifically, the frequency of the AC power supply is adjustable at least within a given range between 0.1 Hz and 100 Hz.

[0028] The ability to adjust the frequency allows the magnetic field lines to penetrate the inspected material to varying depths. This, in particular, provides a better characterization of the detected defect at depth.

[0029] The alternating supply current has an intensity between 1 A (amperes) and 15 A, more particularly between 2 and 10 A, and even more particularly between 4.5 A and 5.5 A.

[0030] More specifically, the intensity of the alternating supply current is adjustable at least within a given range between 1 A and 15 A, more specifically between 2 and 10 A, and even more specifically between 4.5 A and 5.5 A.

[0031] Such a frequency and intensity allows, in particular, working in a magnetically unsaturated zone, that is to say, the magnetic excitation does not tend towards a plateau as a function of the induction.

[0032] The magnetizing unit 14 includes an electromagnet 20 adapted to generate a magnetic field parallel to a surface of the object to be controlled in the presence of an alternating supply current.

[0033] In the example shown, the device comprises, for example, a single magnetizing unit 14 including a single electromagnet 20, more particularly a single magnet formed by an electromagnet. The single electromagnet includes, for example, two or four poles or possibly more.

[0034] The electromagnet 20 here has two poles, more specifically a so-called north pole 22 and a so-called south pole 24.

[0035] In the example shown, the electromagnet 20 has a U shape comprising a north arm 26 and a south arm 28, the north arm and the south arm being adapted to be placed against the surface of the object to be controlled.

[0036] More specifically, the north branch 26 and the south branch 28 each include a contact surface 27, 29 intended to be placed against the surface of the object to be controlled.

[0037] The contact surface 27, 29 is complementary to the surface of the object to be controlled. In the example shown, each contact surface 27, 29 is flat.

[0038] The electromagnet includes a north coil 30 wound around the north branch 26, forming the north pole 22, and a south coil 32 wound around the south branch 28, forming the south pole 24.

[0039] The electromagnet 20 is made of a material with high relative magnetic permeability, designed to reduce eddy currents. The electromagnet comprises, for example, a stack of plates, for example of iron and silicon or iron and nickel or other amorphous materials.

[0040] Each coil is made from a material with high electrical conductivity, for example copper.

[0041] The north coil 30 and the south coil 32 are identical.

[0042] The coils each have 20 turns, in a wire with a cross-section of 0.8 mm².

[0043] Each coil 30, 32 is wound around a respective main axis DS, DN. The main axes extend parallel to each other.

[0044] The main axes DS, DN are here perpendicular to the contact surfaces 27, 29.

[0045] The electromagnet 20 is designed so that the main axes DS, DN of the coils 30, 32 extend perpendicularly to the surface of the object being controlled.

[0046] The winding of each coil 30, 32 extends between a distal end and a proximal end.

[0047] The distal end is designed to be closer to the surface of the object being controlled than the proximal end.

[0048] The proximal ends of the coils are connected together.

[0049] The distal end of the north coil 30 is connected to one of the connection terminals of the power supply unit 12, the distal end of the south coil 32 being connected to the other of the connection terminals of the power supply unit 12.

[0050] The power supply unit 12 is configured to supply the electromagnet 20 with the alternating supply current generated by the power supply unit 12.

[0051] The unit of measurement 16 of the magnetic field is suitable for measuring the magnetic field at least along a normal axis DM.

[0052] The normal axis DM is intended to be perpendicular to the surface of the object to be controlled.

[0053] The normal axis DM is parallel to the main axes DS, DN of the coils 30, 32.

[0054] Measurement along the normal axis DM increases the measured signal and reduces measurement noise, compared to measurement along the direction tangential to the magnetic field lines.

[0055] There figure 3 presents the measurement by the sensor f N along the normal direction and the measurement by the sensor f T along the direction tangential to the field lines of the magnetic field.

[0056] More specifically, on the figure 3 represented are the said oscillating measures, as well as the envelope of said measures.

[0057] The unit of measurement of the magnetic field includes at least one sensor 34, here a single sensor 34.

[0058] The sensor is, for example, capable of measuring the magnetic field along three axes, one of which is the normal axis.

[0059] The sensor is, for example, a giant magnetoresistance (in English " Giant Magnetoresistance » or GMR).

[0060] Alternatively, the sensor is a Hall effect sensor or a tunnel magnetoresistance (TMR), or any other magnetic field sensor.

[0061] Alternatively, the unit of measurement comprises a plurality of sensors, for example, a multi-element array. Each element of the array is, for example, a giant magnetoresistive sensor. This makes it possible, in particular, to scan a larger area in a given time.

[0062] The magnetic field measurement unit 16, more specifically the sensor 34, is located between the north branch 26 and the south branch 28, more specifically equidistant.

[0063] The normal axis DM is, for example, located in the same plane as the main axes DS, DN of the coils 30, 32.

[0064] The device is configured such that the measuring unit 16, more particularly the sensor 34, is spaced from the surface of the object to be controlled by a distance of less than 2 cm, preferably less than 1 mm, during control, more particularly that a periphery of the sensor is stuck against the surface of the object.

[0065] The computing unit 18 is capable of detecting a defect in the object to be inspected from the magnetic field measured along the normal axis DM and the magnetic field generated by the electromagnet 20. More particularly, the defect has an extension in a direction substantially perpendicular to the direction of the magnetic field lines, more particularly a dimension in said direction greater than or equal to three centimeters.

[0066] The calculation unit 18 is linked to the measurement unit 16, so that the data measured by the measurement unit 16 is communicated to the calculation unit 18.

[0067] More specifically, the calculation unit 18 includes a calculator 36, the calculator 36 being connected to the measuring unit 36, more specifically to the sensor 34.

[0068] The computing unit 18 is also capable of controlling the activation of the power supply unit and / or the frequency of the generated power supply current and / or the intensity of the generated power supply current.

[0069] The computing unit 18 is then connected to the power supply unit 12, more specifically to the generator.

[0070] An example of a control method according to the invention will now be described.

[0071] The control process is, for example, carried out at a temperature between 15 and 40°C.

[0072] Alternatively, the control process takes place at a temperature between -50°C and 500°C, more specifically between -50°C and 250°C.

[0073] The control process includes the following steps: placement of a control device 10 as described above against a surface of the object to be controlled, supplying the electromagnet 20 by the power supply unit 12 with an alternating supply current having a frequency between 0.1 Hz and 100 Hz, measurement of the magnetic field along the normal axis DM by the measuring unit 16, and detection of the possible presence of a defect in the object to be controlled by analysis of the magnetic field measured along the normal axis DM and the magnetic field generated by the electromagnet 20.

[0074] More specifically, during the detection of the possible presence of a defect, the product of the magnetic field measured along the normal axis DM and the magnetic field generated by the electromagnet is calculated.

[0075] The component of the magnetic field along the normal axis DM is more easily observable than the component along a direction perpendicular to the normal axis DM, called tangential to the surface.

[0076] The magnetic field generated by the electromagnet 20 is, for example, calculated from the intensity and frequency of the supply current, as well as parameters of the electromagnet 20, such as parameters of the coils 30, 32.

[0077] In a particular embodiment, a low-pass filter is applied to said product or previously to the measurement performed by the measuring unit 16, an example of a filtered measurement f F being shown on the figure 4 .

[0078] This makes it possible in particular to reduce background noise from the electronics which may interfere with the signal, and / or to eliminate the "frequency" component observed on the unfiltered signal.

[0079] A sudden change in the raw signal, the product, or the product on which the low-pass filter has been applied, if applicable, is then detected.

[0080] When the sensor passes over a fault, the signal varies by a factor of at least two, more particularly if the signal is multiplied by two.

[0081] Observing a sudden change in the signal indicates the presence of a fault.

[0082] The noise level remains at its nominal value. The noise is likely to be due to the acquisition electronics used, the excitation magnetic field, the magnetic history of the material such as the presence of a remanent magnetic field for example, the external magnetic field including in particular the Earth's magnetic field and / or other parameters.

[0083] The control device also includes a signal display, which shows the signal variation on the screen. A visual inspection allows for the detection of a signal increase indicative of a fault.

[0084] In a particular embodiment, the computing unit 18 is also capable of calculating a map of the object on which the various detected defects are represented. The display device is then advantageously designed to display this map of the object.

[0085] The control device also includes an alarm system, for example audible and / or visual.

[0086] Such a control device makes it possible to detect defects forming an angle between 45° and 90° with the magnetic field lines generated by the electromagnet in the object to be controlled up to a depth from the surface equal to 2 cm.

[0087] The control device is designed to be moved on the external surface of the object so as to control the entire object to be controlled up to two centimeters deep from the surface.

[0088] Calculation unit 18 is also capable of performing la Mapping of the object takes into account the movements of the control device. Alternatively, the electromagnet 20 is such that the magnetizing unit is capable of generating a magnetic field of greater or lesser intensity. The electromagnet is, for example, made of a different material such as a stack of iron / nickel plates, or an amorphous material, and / or with more or fewer windings on the poles.

[0089] Alternatively, the electromagnet 20 has a different shape than the U shape in order to optimize the propagation of field lines through the object to be inspected.

[0090] Alternatively, the electromagnet 20 comprises four or more poles so as to detect faults in different orientations in a single pass.

[0091] Alternatively, this device can measure magnetic fields other than normal fields at the surface of the part.

[0092] Such a device allows the recording of control signals on which the presence of a fault is visible. Computer processing of the signal makes the information more readable, for example by increasing the signal-to-noise ratio.

[0093] Such a control device is simple in design and also allows a defect to be detected in an object using a simple process without altering the object.

[0094] Such a device makes it possible to automate the control of the object, for example by integrating the control device into a robot, a table extending tangentially to the external surface or any other suitable system.

[0095] Such a device also makes it possible to detect a defect with a lower intensity magnetic field and without using polluting effluent compared to so-called "classical" magnetic particle testing.

Claims

1. A method of testing an object containing at least one ferromagnetic material by magnetic flux leakage, the method comprising the following steps: - placement of a magnetic flux leakage testing device (10) for non-destructive testing of an object comprising at least one ferromagnetic part against a surface of the object to be tested, the testing device (10) comprising: - a power supply unit (12) capable of generating an alternating supply current, - a magnetisation unit (14) comprising an electromagnet (20) adapted to generate a magnetic field parallel to a surface of the object to be tested in the presence of an alternating supply current, the power supply unit (12) being configured to supply the electromagnet (20) with that current, - a magnetic-field measuring unit (16) capable of measuring along a normal axis (DM), said normal axis (DM) being designed to be perpendicular to the surface of the object to be tested, and - a calculation unit (18), - supplying of the electromagnet (20) with an alternating current having a frequency between 0.1 Hz and 100 Hz, and - measurement of the magnetic field along the normal axis (DM) by the measuring unit (16), characterised in that the calculation unit is capable of detecting a defect in the object to be inspected based on the magnetic field measured along the normal axis (DM) and the magnetic field generated by the electromagnet (20), and in that the testing method comprises a step of detecting the possible presence of a defect in the object to be inspected by analysing the magnetic field measured along the normal axis (DM) and the magnetic field generated by the electromagnet (20), the step of detecting the possible presence of a defect comprising a step of calculating the product of the magnetic field measured along the normal axis (DM) and the magnetic field generated by the electromagnet (20).

2. A method of monitoring as claimed in claim 1, comprising a step of applying a low-pass filter to the product prior to the step of detecting an increase in the product, the method comprising a step of detecting an increase in the product after application of the low-pass filter.

3. Control method according to claim 1 or 2, in which a defect is detected when the product is multiplied by a factor of two or more.