RU2285254C1 - Device for demagnetization of main pipelines - Google Patents

Abstract

FIELD: engineering of equipment for non-destructive control of pipes.

SUBSTANCE: permanent magnets are positioned on carrying body, moving along the pipe under effect of gas being transported. Magnets are positioned in rows along perimeter of pipe, directed by poles of the same name towards the surface of pipe. Polarities of magnets in adjacent rows are opposite. Strength of field, created by magnets of first row, provides greatest remaining induction B1 of material of pipe being demagnetized. Strength of field, created by magnets of second row, provides for magnetization of pipe material to remaining induction B2, while B1>B2. Strength of field, created by magnets of third row, demagnetizes material of pipe.

EFFECT: possible reliable demagnetization of high length pipelines, and thus, increased reliability of repeated control of pipes by flaw detecting probes.

4 dwg

Description

The invention relates to a non-destructive magnetic control method for trunk pipelines. When conducting magnetic control of an in-pipe or external inspection, a significant residual magnetization occurs in the pipeline material, which has negative consequences in the further operation of the pipeline.

With subsequent repeated controls by flaw detectors, the residual magnetization reduces the reliability of the results. In addition, when repairing a pipeline by replacing a defective section of a pipe, the residual magnetization field has a negative effect on the electric welding process and does not allow obtaining high-quality welds. Therefore, demagnetization is an integral technological operation of magnetic control of pipelines.

However, at present, there are no devices for the demagnetization of trunk pipelines with a length of about 100 km. Traditional demagnetization devices (solenoids, electromagnets, etc.) can hardly be used due to the difficulty of providing them inside the pipeline with an electric power source of the required power.

One of the promising directions of creating devices for the demagnetization of trunk pipelines is the development of magnetic systems using permanent magnets mounted on a carrier body moving inside the pipeline.

A device is known for the demagnetization of ferromagnetic parts (French Patent No. 2085543). The device is a straight line located permanent magnets connected by magnetic circuits. The magnetic poles facing the demagnetizable part alternate N-S-N-S ... ... When the demagnetizable part moves at an angle to this line, a direction that changes in direction and decreases in it will act. This device has a fundamental drawback, which does not allow it to be used to demagnetize large parts, especially such as a trunk pipeline. The magnetization reversal of a massive part requires a certain time (due to magnetic viscosity, induced currents arising from magnetization reversal). Due to this factor and the fact that the direction of the field changes stepwise during the passage of the magnetic pole, the magnetic state of the demagnetized element of the part will change along the partial asymmetric hysteresis loop, as a result, the part will not be demagnetized.

A device for the demagnetization of small parts using a permanent magnet (ed. Certificate. 1777066). The essence of the device is to create an oscillatory motion of a permanent magnet. During vibrations, the magnet rotates 180 degrees, which changes the direction of the field in the magnetic cores, between which the demagnetized part is placed. Simultaneously with a decrease in the amplitude of the oscillations, the area of magnetic contact with the magnetic cores decreases, which leads to a decrease in the field strength. This device has a drawback. It is complex in design, suitable only for the demagnetization of small parts and cannot be used to demagnetize main pipelines.

Known device "Demagnetizer" by ed. testimonial. No. 654965, in which the permanent magnets of alternating polarity are located in sectors in the form of a ring. The demagnetized part moves in a spiral above this ring, moving away from it. The disadvantage of this device is that it is not suitable for demagnetization of large parts, since it is necessary to move either the demagnetized part or a disk with magnets. In addition, the choice of the field strength of the second sector corresponding to the position of the magnetic state point on the beam of the demagnetizing factor will not ensure demagnetization of even small-sized parts. With this field strength, the point of the magnetic state of the part will remain in the second quadrant and demagnetization will not occur.

A device is proposed that does not have these drawbacks, allowing demagnetization of the main pipeline. The objective of the invention is to provide a device for the demagnetization of the main pipeline with a length of 100 km or more.

The essence of the invention lies in the fact that in the device for the demagnetization of the main pipelines, permanent magnets are located on the carrier body, which can move along and inside the pipe, and are distributed along the perimeter in three circular rows, the planes of which are perpendicular to the longitudinal axis of the pipe and are spaced apart from each other providing after exposure to fields of permanent magnets obtaining the residual magnetization of the pipe sections, and in each row the magnets face the inner surface of the pipe one the polar poles, and the poles of the magnets facing the inner surface of the pipe, in series arranged rows are opposite in sign, while the field strength created by the magnets of the first row provides the greatest residual induction B1 of the material of the demagnetized pipe, the field strength created by the magnets of the second row provides the magnetization reversal of the material pipe to the residual induction B2, while B1> B2, and the field strength created by the magnets of the third row demagnetizes the material of the pipe.

On figa, b shows a diagram of the principle of magnetization-demagnetization of the pipe element, which is the basis of the proposed device. On figa, b is indicated: 1, 2 - magnetic field lines (arrows indicate the direction of magnetization in the material of the pipe element); 3 - pipe element; 4, 5, 6 - consecutive positions of the pole of the permanent magnet when it moves relative to the pipe element; Figa - distribution of magnetic lines during the movement of the pole N in the direction V; figb - distribution of magnetic lines during the movement of the pole S in the direction V. V - the direction of movement of the pole of the magnet. N ', S' - poles of the pipe element.

Figure 2 shows a diagram of the proposed device for the demagnetization of pipelines. 7 - demagnetizable pipe; 8 - the first ring of magnets, 9 - the second ring of magnets; 10 - the third ring of magnets; 11 - carrier body. H1, H2, H3 - field strengths created by rings of magnets; V is the direction of movement of the carrier body.

Figure 3 shows the change in the magnetic state of the pipe material during demagnetization. In Fig. 3 it is indicated: H1 is the field strength created by the magnets of the 1st ring; H2 is the field strength created by the magnets of the second ring; H3 - field strength created by the magnets of the third ring; B1 - residual magnetic induction in the pipe material after exposure and removal of the field H1; Нс - coercive force; B2 - residual induction in the pipe material after exposure and removal of the field H2; K is the beam of the demagnetizing factor. 12, 13, 14 - points of the magnetic state of the pipe material sections in the applied field; 12 ', 13' - points of the magnetic state of the pipe sections on the remanent magnetization. B - magnetic induction (on the ordinate axis); H is the magnetic field strength (on the abscissa axis).

The physical essence of the proposed device.

The magnetization of the pipe elements is carried out by moving the pole of the permanent magnet at the surface of the pipe, the so-called magnetic contact method. The direction of magnetization depends on the direction of movement and the sign of the pole of the magnet. On figa shows a distribution diagram of the magnetic lines of force 1, 2, the poles N ', S' of the pipe element 3 and the successive positions 4, 5, 6 of the pole N when it moves in the direction V. Figure 1b shows the distribution diagram of the magnetic lines of force 1, 2, consecutive positions 4, 5, 6 of the pole S when moving in the V direction and the poles of the pipe element N ', S'. Figures 1 and 2 show that when the polarity of the pole of the magnet moving along the pipe element in the V direction changes, the direction of magnetization in the pipe element changes to the opposite.

Demagnetization is carried out not by exposure to a directionally changing magnetic field (alternating magnetic field), but by a single application of the oncoming field and the subsequent decrease in magnetic induction in the pipe material to residual B1. After reducing the magnetic induction to the residual, a counter field is applied once to the previous one, and the magnetic induction is reduced to the residual - B2. Then again a once-applied magnetic field is applied, and the magnetic induction in the pipe material is reduced to a value taken as zero

The design scheme of the proposed device is shown in figure 2. The device contains permanent magnets distributed around the perimeter inside the demagnetized pipe 7 along three rings 8, 9, 10, which are mounted on a carrier body 11 moving inside the pipe under the influence of gas pressure transported through the pipeline. The planes of the rings are perpendicular to the axis of the pipeline. In each ring, the magnets are directed by the poles of the same name to the surface of the pipe, and in adjacent rings the magnets are directed to the pipe surface by the opposite poles. The distance between the rings is established from the condition under which the impact on any section of the pipeline of the magnetic field of the next ring begins no earlier than the decrease in magnetic induction to the residual from the magnetic field of the previous ring.

Magnetic field strengths should be selected from the following conditions. The magnetization of a pipe after passing through a flaw detector has a wide range of values along the length and perimeter of the pipe. All sections of the pipe must be brought to one magnetic state, to one value of magnetic induction. Therefore, the field strength H1 created by the first ring should be close to the field of technical saturation of the material, taking into account the demagnetizing fields (demagnetizing factor), although its value may be less at small residual fields. The field strength of the second ring should be greater than the coercive force Hc of the material, but such that the residual induction is much less than the residual induction after the action of the field of the first ring, i.e. B2 <B1. The tension of the third ring is established experimentally. After removing this field, the part must be demagnetized to the required level. With a relatively small residual magnetization, the device may contain two rings of magnets, and with a large wall thickness and high residual magnetization of the pipe, it may be necessary to install more than three rings of magnets.

The work of the proposed device is as follows. The device mounted on the carrier body moves in the V direction along the pipe under the action of gas or liquid pressure (in oil pipelines).

The first ring of magnets magnetizes all sections of the pipe around the perimeter by a field of strength H1, leading them to a single magnetic state (point 12) (figure 3). With further movement of the ring 8, the magnetized portion comes into a state of residual magnetic induction (point 12 'lying on the beam K). Then, by the field H2 of ring 9, the magnetic state of this section will be characterized by point 13, and after removal of ring 9, by the point of residual induction 13 '. Under the action of the field H3 of the third ring, the magnetic state will be characterized by point 14. After removal of ring 10, the material of the region under consideration will go into the demagnetized state to the required level. All other sections of the pipe will change their magnetic state in the same way as considered: from the greatest magnetization (point 12) to the demagnetized state of a given level (point 0).

The device can be made to move inside the pipe, as well as to move on the outer surface of the pipe.

Execution example. We have made the proposed device for the demagnetization of pipes with a diameter of 205 mm, a wall thickness of 6 mm, having the following technical data. The type of magnets is neodymium-iron-boron measuring 40 × 20 × 10 mm. The magnets of the first ring on the surface of the pipe create a field of 450 A / cm. In the second ring, the magnets are distributed over a smaller radius and create a field on the pipe surface of 150 A / cm. The magnets of the third ring create a field of 85 A / cm, which is selected experimentally. The distance between the magnet rings is 16.5 cm.

The efficiency of the device was tested on a pipe length of 180 cm. Previously, the pipe was magnetized with strong permanent magnets to obtain the highest residual magnetization field strength, 25-30 A / cm on the side surface of the pipe. The field was measured with an MF-23I magnetometer. After passing through the manufactured device, the remanence was not more than 2 A / cm. The tolerance for demagnetization of new bearing rings is 3.5 A / cm according to current standards, for example, according to the technical requirements of the bearing industry for new bearings, the tolerance for demagnetization corresponds to the specified value.

Thus, the above and justified set of features of the proposed device is necessary and sufficient to obtain a positive effect - demagnetization of long-distance trunk pipelines, about 100 km.

Claims (1)

A device for the demagnetization of pipelines containing permanent magnets, a housing, characterized in that the permanent magnets are located on the carrier body that can move along and inside the pipe, and are distributed along the perimeter in three annular rows whose planes are perpendicular to the longitudinal axis of the pipe and are separated from each other at a distance that ensures, after exposure to the fields of permanent magnets, to obtain the residual magnetization of the pipe sections, with the magnets in each row facing the inner surface pipes with unipolar poles, and the poles of the magnets facing the inner surface of the pipe, in series arranged in rows, are opposite in sign, while the field strength created by the magnets of the first row provides the greatest residual induction B1 of the material of the demagnetized pipe, the field strength created by the magnets of the second row, provides magnetization reversal of the pipe material to the residual induction B2, while B1> B2, and the field strength created by the magnets of the third row demagnetizes the pipe material.

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