RU2029297C1 - Method of magnetic tape-testing of multilayer welded joints - Google Patents

Abstract

FIELD: non-destructive inspection. SUBSTANCE: method involves the steps of: magnetizing a welded joint to be tested together with a magnetic tape applied to it by U-shaped electric magnet and determining quality of welded joint from the results of comparison of obtained magnetogram with a magnetogram obtained in the same way on the check specimen. The method is characterized in that preliminarily of the check specimen and inspected joint zones of maximum probability of the presence of flaws are selected in the transverse direction relative to the joint, comparison is performed in the respective zones and flaw parameters are determined considering that a flaw is the deeper, the closer to the joint symmetry plane it is disposed. EFFECT: enhanced reliability. 2 dwg

Description

 The invention relates to non-destructive testing by a magnetographic method and can be used to control multilayer lap and butt welded joints, mainly one-sided.

 A known method of magnetographic control of products from ferromagnetic materials for the presence of continuity defects, namely, that they carry out the magnetization of the controlled product, transfer the magnetized relief of the surface of the product to a ferromagnetic carrier in contact with the surface of the product, and read information about the magnetic relief from the carrier which judge the presence of defects [1].

 Its disadvantage is the low reliability of control.

 The closest in technical essence and the achieved result to the invention is a method of magnetographic control of multilayer welded joints, which consists in the fact that a magnetic tape is pressed to the surface of the weld, magnetized by a U-shaped electromagnet and the quality of the welded joint is determined by comparing the obtained magnetogram on a ferromagnetic tape with a magnetogram obtained similarly from the surface of a control sample [2].

 Its disadvantage is the low reliability of control of welded joints of multilayer products due to the low accuracy of determining the magnitude of defects.

 The aim of the invention is to increase the reliability of control of welded joints of multilayer products.

 This is achieved by the fact that in the method of magnetographic control of multilayer welded joints, which consists in the fact that the controlled welded joint together with a magnetic tape laid on its surface is magnetized with a U-shaped electromagnet and the quality of the welded joint is determined by comparing the magnetogram with the magnetogram obtained in a similar way on the control sample, according to the invention, previously in the control sample and the controlled connection are allocated zones in the transverse relative but weld location towards the most likely defects magnetogram comparison performed by the corresponding zones, and the defect determining parameters assuming that the defect is located deeper than closer to the plane of symmetry of the product it is.

 In FIG. 1 shows a multilayer butt weld with an indication of the possible places of origin of defects; figure 2 is a functional diagram of one of the devices for implementing the method.

 As the depth of the possible location of the defect 1 increases, it shifts toward the middle of the weld 2. Therefore, the deeper the discontinuity is located, the closer to the middle of the waveform is the impulse caused by the defect. If the signalogram is divided into the areas of the most probable location of the defect for each layer, then when a signal due to the defect appears in such an area, one can judge the depth of the defect, and hence more precisely its size. The above areas can be limited by planes parallel to the plane of symmetry of the seam and located at the same distance from two adjacent defects of the control sample (figure 1). Compare the amplitude of the signal due to the defect in the same areas of the control sample and the controlled product. If the amplitude of the signal from the detected defect exceeds the rejection level, then its value is unacceptable.

 One of the possible devices for implementing the method (Fig. 2) includes a low-pass filter (LPF) for extracting the envelope of the input signal, a level shift circuit (SSA), a comparator, a generator G, a counter of time marks for sweeps, ROM - read-only memory, digital-to-analog converter .

 The device operates as follows.

 The “Start” signal of the angle sensor of the flaw detector reader switches a trigger that allows the generator G to work, which generates time stamps of a given frequency, which are fed to a time counter (Schr), where the frequency of the mark generator is converted to a code proportional to the time elapsed since start signal moment. The time code is the address for the ROM containing pre-set shear levels corresponding to the selected control zones on the control sample and the controlled weld.

 The preparation of the ROM consists in that they measure the control sample and enter the data into the computer. Each time domain of the most probable location of defects has its own value of the shift of the envelope of the phase signal, which is allocated in the low-frequency filters (LPF) and fed to the input of the level shift circuit (CCS). The magnitude of the shift is proportional to the magnitude of the control voltage coming from the output of the digital-to-analog converter (DAC), controlled from the ROM of the shift codes. The introduction of controlled shear and envelope separation schemes can significantly reduce errors caused by the unevenness of the remanent magnetization field and changes in the depth of the defect.

 PRI me R 1. Controlled butt weld 18 mm thick, containing three layers of the same thickness. A wedge-shaped niobium insert 0.5 mm wide was introduced at the depth of the first layer in the weld, which imitated a variable crack. The sample was controlled in the traditional way: the amplitude of the signal caused by a defect in the control object was compared with the amplitude of the signal from the smallest unacceptable defect located in the root of the seam (at the depth of the 3rd layer) of the control sample having the same seam parameters as the controlled sample. When the amplitudes of the signals from defects in the control sample and the controlled object are equal, the defect in the latter turned out to be 2.5 times smaller.

 PRI me R 2. The same sample was controlled by the proposed method. In this case, a control sample was used, which contained a tungsten insert at the depth of each layer, the value of which was equal to the defect of the smallest unacceptable value. Scratches were applied on the seam surface of the control sample parallel to its longitudinal axis, dividing the seam into the areas of the most probable location of defects. The amplitude of the signal from the defect in the controlled object was compared with the amplitude of the signal from the smallest unacceptable defect located in the same area in the weld of the control sample. If the amplitudes of the signals from defects in the control sample and the controlled object are equal, in the latter the defect turned out to be only 15% larger.

 The application of the proposed method will improve the reliability of control of welds of multilayer products.

Claims (1)

 METHOD FOR MAGNETOGRAPHIC CONTROL OF MULTI-LAYERED WELDED COMPOUNDS, which consists in the fact that the controlled welded joint together with the magnetic tape laid on its surface is magnetized with a U-shaped electromagnet and the quality of the welded joint is determined by comparing the magnetogram with the magnetogram obtained in a similar way to the control sample that previously on the control sample and the controlled joint is isolated in the direction transverse to the welded joint uu zone the most likely location of the defects, a comparison is performed magnetogram relevant zones, and defect parameters define, assuming that the defect is located deeper than closer to the plane of symmetry it is a welded joint.

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