[0029] The principle diagram of the detection method of the present invention is as follows figure 1 As shown, the measured component 1 is covered with a coating layer 2 with a thickness of H, and the coating layer 2 is wrapped with a magnetically conductive protective layer 3 with a thickness of h. The upper end of the permanent magnet 4 is adsorbed on the left and right ends of the yoke 7, and the polarities of the magnets at both ends are perpendicular to the measured component 1 and opposite. The lower end of the permanent magnet 4 is adsorbed (or lifted a certain distance) on the magnetic protective layer 3. The permanent magnet 4 , The yoke 7 and the magnetic protective layer 3 form a closed magnetic path, magnetize the magnetic protective layer 3 to deep saturation or deep saturation, reduce the permeability of the magnetic protective layer material, and increase the penetration depth of the eddy current. The attenuation of the eddy current on the magnetic conductive protective layer 3 is reduced, so that more eddy current energy acts on the measured component 1. A square wave excitation is applied to the sensor excitation coil 6 to induce eddy currents in the measured component 1. The thickness of the measured component 1 is measured by observing the attenuation curve of the induced voltage in the sensor detection coil 5, so as to realize the conductivity of the measured component 1. Corrosion detection of ferromagnetic components in protective layers of magnetic materials. When the magnetic protective layer is not magnetized, the magnetic field distribution in the measured component is as follows figure 2 As shown, the magnetic field distribution in the measured component is as follows when the magnetic protective layer is magnetized to deep saturation image 3 As shown, the comparison shows that magnetizing the magnetically conductive protective layer 3 to deep saturation significantly increases the intensity of the magnetic field generated by the excitation coil 6 in the measured component 1, that is, reduces the attenuation of the eddy current on the magnetically conductive protective layer 3.
[0030] Such as Figure 4 As shown, the detection device of the present invention includes a pulse eddy current sensor 8, a signal excitation circuit 9, a signal processing circuit 10, an A/D conversion circuit 11 and a portable computer 12 connected in sequence. The signal excitation circuit 9 provides square wave excitation to the pulsed eddy current sensor 8. The pulse eddy current sensor 8 is used to excite and induce an eddy current in the measured component 1 and receive the secondary magnetic field signal generated by the eddy current, convert it into a voltage signal, and transmit it to the signal processing circuit 10. The signal processing circuit 10 amplifies and filters the obtained signal, and transmits it to the A/D conversion circuit 11. The A/D conversion circuit 11 converts the received analog signal into a digital signal and sends it to the portable computer 12 for processing. The portable computer 12 realizes the functions of signal acquisition and control, signal display and data storage, processes the received data, discriminates signal characteristics, and obtains corrosion information of the tested component 1.
[0031] Figure 5 It is a cross-sectional view of a pulse eddy current sensor 8 which includes an aviation socket 13, a handle 14, an end cover 15, a stainless steel sheet 16, a housing 17, a disc 18, an excitation coil 6, a detection coil 5, a permanent magnet 4 and a yoke 7. The permanent magnet 4 and the yoke 7 constitute a magnetization unit. The handle 14 and the end cover 15 are connected by hexagon socket countersunk head screws, and the end cover 15 and the housing 17 are connected by cross recessed pan head screws. The excitation coil 6 and the detection coil 5 are fixed at the bottom center of the inner cavity of the housing 17, and the upper end is pressed down by the disc 18. The disc 18 and the housing 17 are connected by stainless steel slotted countersunk screws; the upper end of the permanent magnet 4 is attracted to the magnetic The left and right ends of the yoke 7 have magnet polarities along the axial direction of the sensor and are opposite; the stainless steel sheet 16 is connected with the yoke 7 and the housing 17 by stainless steel slotted cylinder head screws to fix the permanent magnet 4 and the yoke 7; excitation coil The lead wires of 6 and the detection coil 5 are connected to the aviation socket 13.
[0032] Figure 6 Shown is the structure diagram of another pulse eddy current sensor realized by the inventive method. The sensor 8 includes an aviation socket 13, a handle 14, an end cover 15, a housing 17, an excitation coil 6, a detection coil 5, a disc 18, and a DC magnetization. The coil 19 and the coil bobbin 20. The DC magnetizing coil 19 is the magnetizing unit. The handle 14 and the end cover 15 are connected by hexagon socket countersunk head screws, and the end cover 15 and the housing 17 are connected by cross recessed pan head screws. The excitation coil 6 and the detection coil 5 are fixed at the bottom center of the inner cavity of the housing 17, the upper end is pressed down by the disc 18, and the disc 18 and the housing 17 are connected by stainless steel slotted countersunk screws; the DC magnetizing coil 19 is wound around the coil On the frame 20, the coil frame 20 and the shell 17 are connected by slotted countersunk screws; the leads of the excitation coil 6 and the detection coil 5 are connected to the aviation socket 13.
[0033] The realization of the magnetization unit in the pulse eddy current sensor is not limited to the above two, it can also be combined with a magnet and a coil, or change the position of the magnetization unit, as long as a closed magnetic path can be formed between the magnetization unit and the measured component.
[0034] Figure 7 In order to use the device of the present invention to test the sample diagram, the sample is a stepped Q235 steel plate with a length of 1000 mm and a width of 500 mm. The thickness of the area ① is 20 mm, and the thickness of the area ② is 18 mm.
[0035] Figure 8 It is the signal waveform diagram of the sample area ① and area ② of the rock wool coating layer (rock wool thickness H=120mm) with the pulse eddy current test without magnetization. The vertical axis represents the induced voltage (V), and the horizontal axis represents the time (ms ). The initial parts of the two curves are straight lines and almost overlap each other, and then respectively transition to curve segments with different curvatures. The curve of area ② is located below the curve of area ①, that is, the thinner the measured area, the faster the induced voltage decays. The steeper.
[0036] Picture 9 It is the signal waveform diagram of the sample area ① and area ② with the white iron cover (thickness h=0.5mm) and the rock wool coating (the rock wool thickness H=120mm) with the pulse eddy current test when magnetization is not applied. The axis represents induced voltage (V), and the horizontal axis represents time (ms). Due to the influence of the tinplate on the eddy current signal, the shape of the two curves is lost Figure 8 The characteristics of the middle curve, and the signal-to-noise ratio becomes worse.
[0037] Picture 10 In order to use the present invention to detect the signal waveforms of the sample area ① and area ② with the tinplate protective layer (the tinplate thickness h=0.5mm) and the rock wool coating layer (the rock wool thickness H=120mm), the vertical axis represents the induced voltage (V), the horizontal axis represents time (ms). Picture 10 The shape, signal-to-noise ratio and Figure 8 Basically consistent, it can be seen that the present invention can effectively eliminate the influence of the magnetically conductive protective layer on the signal.
[0038] In actual testing, the method of the present invention can be used to perform omni-directional testing of ferromagnetic components with magnetically conductive protective layers, including the following steps:
[0039] (a) Magnetize the magnetically permeable protective layer to saturation or deep saturation;
[0040] (b) Select a group of areas on the tested component;
[0041] (c) Set the pulsed eddy current sensor on the protective layer of one of the areas, then apply a square wave excitation in the sensor excitation coil, and measure the attenuation of the induced voltage in the sensor detection coil after the square wave drops to a low level curve;
[0042] (d) Obtain the induced voltage attenuation curve of each area in this group of areas according to step (c);
[0043] (e) Compare the attenuation curves of the induced voltages and select the gentlest induced voltage curve as the reference curve;
[0044] (f) Using the reference curve as a benchmark, infer the relative thickness of the area corresponding to other induced voltage curves, and judge the corrosion of each area of the component under test.
