SU1748035A1 - Method of magnetographic inspection of welds - Google Patents

Abstract

The invention relates to a magnetographic method of non-destructive testing. The aim of the invention is to increase the sensitivity of the control. the gap of the magnetizing plates and the longitudinal axis of the seam are parallel to each other 2 silt

Description

The invention relates to magnetic flaw detection and can be used to control the quality of butt welded joints made of ferromagnetic materials, mainly ring welded seams of non-rotary small-diameter pipes, as well as small-length welds of products from low carbon and low alloyed steels.

A known method of magnetographic control of welded joints is that a magnetic tape is magnetized onto a weld surface orthogonally to the plane of its symmetry by means of a movable U-shaped electromagnet and rigidly connected with its core and located at an additional + magnetizing distance system in the form of two plates with a bevel of the edge of which the plane of symmetry is parallel to the plane of symmetry of the weld, and the quality of the welded joint is determined t by

magnetic tape recorder

The disadvantage of this method is the low sensitivity of the control, which is caused by the following. The intensity of the field created by the magnetizing system in the form of two plates with bevel edges substantially depends on the distance between the plates. The smaller this distance the higher the field created. The magnetizing plates are parallel The gap between the plates cannot be less than the seam width, since this will cause interference. The gap between the plates with a bevel of the edge will create a non-uniform floor in the seam. field is created unacceptable defects Thus the maximum value of the magnetizing field created by the system will depend on joint width and limited by s

The closest in technical essence to the invention is a method of magnetographic control I conclude

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ate

This means that the magnetic tape is pressed against the controlled area of the product and the product is magnetized together with the tape by a U-shaped electromagnet with a biasing system in the form of two rectangular plates, moving the electromagnet at an angle of about. arctg aa

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to the longitudinal axis of the gap of the magnetizing system, and about the quality of control of su-O t on the magnetic tape obtained on a magnetic tape, where a is the distance between the poles of the device, D is the width of the gap, I is the length of the poles.

The well-known method is characterized by low sensitivity control of butt welded joints. This is explained by the following: Connection magnetization exists by moving the magnetizing device along the seam. To avoid interference from the magnetizing system, the longitudinal axis of the gap between the plates of the magnetizing system and the movement of the magnetizing line along the seam is oriented under the angle of 25 °. 10 ° to the longitudinal axis of the seam The angle is not equal to 0 ° Low sensitivity due to two reasons: First, the magnetizing field is not orthogonal to the plane of defects, which in the 30 welds of low carbon products This and some low-alloy steels are oriented along the seam. Secondly, the recording is read from the tape not along the direction of its magnetization, but across 35 of the tape.

The purpose of the invention is to increase the sensitivity of control of butt welded joints.

The goal is achieved by the fact that according to the method of magnetographic control of welded joints, 40, the magnetic tape is pressed against the seam surface, the weld is magnetized by means of a movable P-45 shaped electromagnet and an additional biasing system rigidly connected to its core rectangular section, before magnetization, the plane of symmetry of the sub-magnetisation system is placed parallel to the plane of symmetry of the seam at a distance of at least 0.5 (L + A) from the plane the bones of symmetry of the seam, and in the process of magnetization the movement of the magnetizing device 55 is carried out across the seam at least b + L where b is the width of the seam; A - width of the gap between the plates of the magnetizing system

Fig. 1 shows the tangential component of the external floor; in fig. 2 is a view of the topography of the resultant field on the surface of a welded joint with a stationary magnetizing device and after magnetizing the welded joint.

With the proposed method of magnetographic control, the same superposition of magnetic fields is recorded on a magnetic tape as in a traditional one. However, the appearance of an external field with a stationary magnetizing device differs significantly. Fig. 1 shows the tangential component of the external field when the magnetizing device is stationary. In this case, a superposition of the fields on the surface of the defect-free seam is observed as a protrusion (Fig. 2).

FIG. 2, a continuous linmei shows the topography of the resultant floor on the surface of the welded joint with a stationary magnetizing device, and the dotted one after moving the magnetizing device,

As the magnetizer moves across the weld along arrow A, the magnetizing field moves, the maximum of which completely crosses the weld. For each point of the weld, the intensity of the magnetizing field increases to a maximum and then decreases. The uneven increase in the floor at the midpoint of the seam and at the edges is due to the fact that the distance from the pseudomagnetisation system to the seam at the edges and midpoint of the seam is different. The qualitative view of the topography of the resulting floor is the same as the traditional one in the absence of defects in the seam. In this case, no interference is observed. However, the intensity of the floor in the neck increases significantly. If the well offset is less than 0.5 (b + a), the submultiplier system creates interference.

For implementing the method, a known device can be used.

Example A sample of steel, St. 3 with dimensions of 250 x 250 x 6 mm was monitored. A weld bead with a width of 12.5 mm and a height of 2.0 mm was made on the sample surface. In the middle of the sample, in the plane of symmetry of the seam, a 1.2 mm wide and 80 mm long groove was made in its root, simulating the depth. The depth of the groove varied smoothly from zero to 2.2 mm. The presence of the defect was monitored by the method of a magnetographic control adopted by the prototype. Magnetic tape type 4701-35 was used. The magnetizing system had the form of plates of rectangular cross section.

4 mm thick. The distance between the plates of the magnetizing system was 5 mm, the angle between the axis of the gap and the longitudinal axis of the seam was about 10 °. The defect began to be detected at a value of 5.2% of the base metal thickness.

PRI me R 2 Described in example 1, the sample was controlled by the proposed method. The same magnetizing device was used as in example 1. In the process of monitoring, the plane of symmetry of the magnetizing system was located at a distance of 20 mm 0.5 (12.5 + 5) mm from the plane of symmetry of the seam, those outside the magnetic tape (width 35 mm tape) The device was moved perpendicular to the axis of the seam for a distance of 40 mm. Reading the record showed that the defect began to be detected when it was 4.5%. Interference from the biasing system was absent.

EXAMPLE 3. The specified sample was magnetized as in Example 2, but the plane of symmetry of the magnetizing system was located 14 mm from the plane of symmetry of the seam. The device was moved perpendicular to the axis of the seam 28 mm. The results of the control were similar to those described in example 2 In this case, two signals followed the signals from the edges of the seam appeared on the signalogram. These signals, located behind the signals from the edges of the seam, did not complicate the interpretation of the signalgram.

EXAMPLE 4 The magnetisation of the same sample containing the defect-free seam was carried out by the proposed method, however, the plane of symmetry of the magnetizing system was located 3 mm from the plane of symmetry of the seam, and the device was moved 6 mm perpendicular to the axis of the seam. the presence of interference from the magnetizing system on the waveform.

The application of the proposed method will increase the sensitivity of the magnetographic control of welded joints

Claims (1)

Claims The method of magnetographic control of welds, which consists in the fact that a magnetic tape is placed on the surface of the weld, is moved relative to the weld by a P-shaped electromagnet with magnetic plates forming a gap between them, and the quality of the weld is determined using a magnetogram. that in order to increase the sensitivity of the control, the magnetization plates are oriented so that the longitudinal axis of the gap was parallel to the longitudinal axis of the seam, and in the process of magnetization during the movement of the magnetizers The device of the projection of the face closest to the weld, in the initial and final positions of the device, was located on the border of the weld. FI.1 Phage. 2