Fire magnetic memory testing principle and field t

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Magnetic memory testing principle and field testing

under the action of stress, dislocation movement will occur inside the metal, forming slip. When the dislocation movement is hindered, the stress concentration will occur. Even if the external stress is removed, the residual stress still exists due to the elastoplastic constraint. At the same time, the existence of residual stress in the metal will increase the free energy in the structure. According to the mechanical point of view, the spontaneous process in the system is the process of reducing the free energy of the system. Therefore, for ferromagnetic components, in order to reduce the free energy of the system, the stress concentration area will generate the spontaneous rotation of the magnetic domain under the action of the earth's magnetic field to form the magnetic pole, which will offset part of the elastic energy brought by the stress concentration in the form of magnetic energy. As a result, a specific magnetic leakage field will be formed on the metal surface, resulting in magnetic memory. Under the action of Geomagnetism and alternating load, the permeability of the defect or stress concentration part of the ferromagnetic material workpiece is the smallest, and the tangential component of the magnetic field has the maximum value, while the normal component changes the sign and has a zero value point. The magnetic leakage field will be formed on the surface of the workpiece, and the crystalline fracture of the surface magnetic leakage field "remembers" the defect or stress concentration position of the component from less to more, that is, "magnetic memory" effect. Since the normal component of the magnetic field on the ferromagnetic material table is zero, it corresponds to the defect or stress concentration position of the workpiece, so the more the document should be listed in the previous workpiece table, the more the normal component of the leakage magnetic field can be deducted and detected, so as to indirectly judge whether the workpiece has defects or stress concentration positions

field test

the equipment used in the wood test is TSC-1M-4 stress concentration detector produced by Russ power diagnosis company, which uses No. 1 sensor. The object of this test is the fillet weld and butt weld of 1s boiler barrel nozzle of Anxi coal gangue power plant. It is planned to test 54 boiler nozzles, including 8 saturated steam Hill pipes, 12 water supply pipes, 14 front riser pipes and 20 rear riser pipes. The specific inspection method is: carry out individual inspection for welds in key areas. At this time, the No. 2 probe of the sensor should be directly connected to the COM port. The on-line head should be placed in the middle of the weld. The No. 1 probe and No. 3 probe should be placed in the heat affected zone on both sides, so that the probe can be snapped from one end of the component to the other end to collect the signals of stress distribution and gradient distribution of the weld

analysis of magnetic memory test results

through the magnetic memory test of the fillet weld of 1ne boiler nozzle and the summary and analysis of the magnetic field strength and pattern distribution of the circumferential weld, some welds with serious stress concentration problems were found, and the 10th water supply pipe (right number) was taken as an example to illustrate the specific magnetic memory test

the mountain can be seen from the magnetic memory test pattern: the image is in the range of 0 ~ 30, the magnetic field strength is h, It increases sharply from very small (i.e. the gradient value changes rapidly), and the 2 and 3 channel probes pass through the 0 scale mark and change the symbol, so there is a large stress concentration at 180. X. ~ 1 80。 Ten ". 2. Within the range of the problem of the test stroke, the magnetic field strength of the 2 and 3 channel probes has passed the 0 scale line for hundreds of millions of times, and has a large gradient value. Therefore, there is also partial stress concentration here

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