RU2335819C2 - Method of demagnetisation of large-size soft-magnetic products and device to this effect - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: in compliance with the invention the product is subjected to the magnetic field effect from inside the large-side product by moving the magnetising belt made up of, at least, two wedge-like permanent magnet unlike poles. The aforesaid poles magnetise the product to ensure an opposed magnetisation which allows the subsequent self-demagnetisation due to a high demagnetisation factor of the magnetised band and low coercive force of the soft-magnetic material. The soft-magnetic pipeline demagnetisation incorporates a soft-magnetic casing with its surface accommodating, at least, one magnetisation belt made up of regularly arranged wedge-like permanent-magnet poles facing the pipeline inner surface. The brushes made from the soft-magnetic reinforced cables are attached to the poles outer surface.

EFFECT: shorter demagnetisation without affecting welding quality at hard-to-reach points.

14 cl, 7 dwg

Description

Application area.

The invention relates to the demagnetization of long ferromagnetic products, such as pipelines, laid in inaccessible areas or under water, which are magnetized during operation or after magnetic and electro-acoustic control.

State of the art

When welding pipelines with direct current in installation, field and repair conditions, a magnetic blast effect arises that impedes the normal welding process (arc burning becomes unstable, molten metal splashes, etc.), which leads to various defects in welds (lack of penetration, slag inclusions, etc. .). This is due to the impact on the welding arc of magnetic fields. Particularly negatively on the stability of combustion of the welding arc is affected by longitudinal magnetization.

The process of magnetic preparation of the pipe is an integral part of the welding process and significantly affects the speed of welding. Particular care should be taken to prepare and perform welding during the repair of underwater pipelines, since under these conditions it is practically impossible to carry out demagnetization technological operations by known methods.

Known methods for the demagnetization of long products, in particular pipes, in which the product is exposed to a magnetic field from a certain maximum value to zero created by the coil, and the product is moved inside the magnetizing coil. The magnetic effect can be pulsed (Japanese patent JP 62254409, op. November 6, 1987), or sinusoidal (Japanese patent JP 2003264107, publ. September 19, 2003).

The disadvantage of these methods is that they cannot be applied in operating conditions of long products, in particular a pipeline, which has many points of support.

A known method of demagnetization of long products, in which the product is exposed to a magnetic field with an amplitude decreasing from a certain maximum value to zero (Japanese patent JP 7110271, publ. April 25, 1995). The magnetic field is created due to the circular motion of the electromagnet mounted on the trolley. The change in the intensity of the magnetic field is achieved due to the movement of the cart and the change in current in the coil of the electromagnet.

The disadvantage of these methods is that they cannot be applied in operating conditions of long products, in particular a pipeline, which has many points of support.

Known methods of demagnetizing long products, in particular pipes, in which the product is exposed to a magnetic field from a certain maximum value to zero created by a coil, which is manually wound on a pipe at the joints prepared for welding. (Stefansky V.A., Shangin A.M. Methods of demagnetization of pipelines and experience of their application in the gas industry // Welding production. 2004. No. 10. - S.35-41). This method can be used in operating conditions of the pipeline.

The disadvantage of this method is its complexity and high material costs. To demagnetize by this method, it is necessary to have a powerful power supply with current regulation in a wide range, as well as a long winding copper cable. So, for example, when winding on a pipe with a diameter of 1440 mm ten turns of cable (KOG with a cross section of 50 mm ² ), its total length is 50 m and its weight is about 35 kg. At least three to four people must be involved in cable winding. The demagnetization process takes a large amount of time and extends the work of welding one pipe joint by 1 hour.

Closest to the claimed method (prototype) is a method of demagnetization of long products, in which the product is exposed to an alternating magnetic field with an amplitude decreasing from a certain maximum value to zero (RF patent 2258272, publ. February 20, 2005)

The demagnetization of the product is carried out by an excited coil of the coil through a ferromagnetic core. The coil is moved along the surface of the product, while the demagnetization is carried out in stages and locally. The demagnetizable product is divided into sections inversely proportional to the thickness of the product or the wall thickness of the product and the residual induction of the magnetic field of the product material, and the coil is oriented so that the vector of the first demagnetizing magnetic field momentum is perpendicular to the vector of the product’s own field intensity and oppositely directed tension vector in another section. After exposure to all local areas, the residual magnetization is removed by additional exposure to the last area by reducing the magnitude of the magnetic flux excited in antiphase relative to the effect on the remaining areas.

The disadvantage of this method is its complexity and high material costs. For demagnetization by this method, it is necessary to have a powerful current source with adjustable current in a wide range.

The demagnetization process takes a large amount of time and extends the work of welding one pipe joint by 1 hour.

Known magnetic cleaning in-tube pistons, similar in design to the claimed device and performing a magnetic effect on the walls of the pipeline. The magnetic effect on the walls of the pipeline is due to the movement of the piston, when approaching a certain area, the field increases, and when removed, decreases. Their design is based on a cylindrical body on which magnet belts are fixed. On the end faces of the body are mounted supporting-motor elements made of wear-resistant polyurethane of high strength, which provide centering of the piston in the pipeline, bear the weight of the piston and ensure its movement.

So, a device for cleaning the internal cavity of the pipeline [AS RF 1417943, publ. August 23, 1988] has three magnet belts mounted on the surface of the casing, and the device for cleaning the internal cavity of the pipeline (AC RF 1340836, publ. September 30, 1987) is equipped with two magnet belts. Belts in these devices are made with radially spaced poles of magnets. Also known magnetic cleaning device (US patent 5461746, publ. October 31, 1995), containing two belts with longitudinally spaced poles of magnets. Magnetic belts can also be placed in flanges that are mounted on the end faces of the cylindrical body (US patent 3673629, publ. July 4, 1972), or they can be made in one segment (US patent 5699577, publ. December 23, 1997 )

The main function of these devices is the removal of ferromagnetic debris (residues of welding electrodes, scale, etc.). For these purposes, the magnetic field should be maximum inside the pipeline and have an open (open) pole. Additionally, magnets allow you to determine the location of the magnetic piston in the pipeline. To this end, some magnets under the influence of gas pressure make oscillatory motions (AS RF No. 1340836) or rotational motions (US patent 3673629).

When these devices pass inside the pipeline, they have a minimal demagnetizing effect on the walls of the pipeline and cannot be used for demagnetization.

Closest to the claimed device (prototype) in terms of design and the nature of the magnetic effect on the walls of the pipeline is an in-line flaw detector with transverse magnetization (RF patent 2144182, publ. January 10, 2000)

A flaw detector for in-pipe inspection of pipelines is intended for movement in the examined pipeline by the flow of the product transported through it. It contains a cylindrical base with musculoskeletal elements. Musculoskeletal elements provide centering of the device in the pipeline and bear the weight of the device. The pressure difference created by the snug fit of the musculoskeletal elements to the walls of the pipeline ensures the movement of the device in the examined pipeline by the flow of the product transported through it. Musculoskeletal elements are made in the form of cuffs. On the base are fixed belts of magnets (electromagnets) with poles facing the inner surface of the pipeline. To minimize magnetic resistance, brushes are installed on the surface of the magnets made of a material with a low coefficient of abrasion and rods of soft magnetic material. Between the poles of the magnets are multi-link magnetically sensitive converters. The magnets in the second belt are mounted with an offset relative to the first belt by πd / 2n, where n is the number of pole pairs. Inside the base there is a device for controlling the speed of the flaw detector, in the form of a bypass pipe for bypassing the product transported through the pipeline.

The magnetizing belts magnetize the walls of the pipeline in strips with pairwise opposite directions of the magnetic field in each section, and the magnetization of the strips is carried out to the saturation level, which is necessary for the qualitative measurement of defects. However, it can be considered that the flaw detector partially demagnetizes the walls of the pipeline, since they decrease the longitudinal magnetization, which especially affects the quality of welding work. But demagnetization occurs only in the areas between the brushes, and thus less than half the pipe is demagnetized.

The disadvantage of this device is that the poles in this flaw detector are made rectangular and wide. In this case, after the passage of the flaw detector there remains a sufficiently wide loop with a longitudinal direction of magnetization at the passage of each magnetic pole (Fig. 7). This does not allow to reduce the residual magnetization of the pipe (demagnetize) to a level that does not affect the quality of welding work.

Under the influence of the second magnetic belt with an offset relative to the first, the general picture of magnetization will not practically change, only a general shift (rotation) of the sections with pairwise counter magnetization will occur.

Disclosure of the invention.

The objective of the invention is to reduce the time of demagnetization of long products, providing a level of demagnetization that does not affect the quality of welding, as well as the possibility of demagnetization in hard-to-reach places, in particular under water.

In the method, the problem is solved in that in order to demagnetize long products from soft magnetic materials, the product is subjected to a magnetic field with an amplitude decreasing from a certain maximum value to zero, the magnetic effect is carried out by at least one magnetizing pole in a local area in the form of a belt, and changing the magnetic of the field is achieved by changing the magnetic force of the pole and moving it along the product, and magnetization is carried out from the inside of the product by at least two different poles in a belt which the product is magnetized strips with counter-parallel magnetization, allowing subsequent samorazmagnichivanie products due to the large demagnetizing factor magnetized strip and a small coercive force magnetic material.

The width of the magnetized strips is selected depending on the thickness of the pipeline, the previous value of the residual magnetization and the minimum residual magnetization, to which it is necessary to demagnetize the product.

The number of magnetizing belts is selected depending on the thickness of the pipeline, the previous value of the residual magnetization and the minimum residual magnetization, to which it is necessary to demagnetize the product.

The width of the magnetization strips and the level of their magnetization of each subsequent belt is less than the previous one.

The speed of movement is selected depending on the thickness of the product. The speed of movement is from 0.1 to 10 m / s.

For the device, the problem is solved by the fact that in the device for demagnetizing pipelines made of soft magnetic materials, including a cylindrical body made of soft magnetic material with supporting-motor elements, at least one magnetizing belt is placed on the surface of the cylindrical body, consisting of evenly spaced poles formed of permanent magnets with reversed magnets to the inner surface of the pipeline with poles, on the outer surface of which brushes are made of reinforced cables made of magnet soft material, wherein the poles are made wedge-shaped.

The magnetizing belt acts on each pipe section first with the bases — end (widest) ends of the wedge-shaped poles, magnetizing the pipe segments in opposite directions and until saturated. Then, each element of the pipe is affected by subsequent elements of poles of smaller sizes and with less magnetizing force. Thus, after the impact of the projectile on the walls of the pipeline, there remain segments magnetized counter-parallel, with a minimum level of magnetization, as well as a narrow magnetic loop, in the region of the passage of the central zone of the poles, with longitudinal magnetization and a minimum level of magnetization.

For a lower level of demagnetization of the walls of the pipeline, a projectile with two magnetizing belts is used, the second belt having a larger number of poles. In this case, when passing the second magnetizing belt, a larger number of poles acts on the walls, but with less magnetizing force. Thus, after the impact of a projectile with two magnetizing belts, narrower bands remain on the pipeline walls, magnetized counter-parallel with a lower level of magnetization, as well as a narrower magnetic loop, in the region of the passage of the central zone of the poles, with longitudinal magnetization and with an even lower level magnetization.

Additionally, after the passage of the device, the pipe walls are demagnetized due to the large demagnetizing factor of the individual pipe segments.

A brief description of the drawings, revealing the design of the device.

Figure 1 shows a General view of the device;

figure 2 presents a side view of the device with an 8-pole magnetizing belt;

figure 3 presents a side view of the device with an 8-pole magnetizing belt and a 12-pole magnetizing belt;

figure 4 is given a radial section of the device:

figure 5 shows a diagram of the magnetization of the walls of the pipeline, after exposure to the device;

figure 6 shows the possible forms of wedge-shaped poles;

Fig.7 shows the nature of the magnetization of the pipeline after exposure to a flaw detector with a transverse magnetizable (prototype).

The implementation of the invention.

A device for demagnetization of pipelines contains a cylindrical body 1 made of soft magnetic material (Fig.1-3). On the end faces of the body are installed flanges 2 on which the supporting-motor elements 3 are fixed. The supporting-motor elements 3 provide centering of the device in the pipeline and bear the weight of the device. The pressure difference created by the tight fit of the musculoskeletal elements 3 to the walls of the pipeline ensures the movement of the device in the examined pipeline by the flow of the product transported through it. Musculoskeletal elements 3 can be made in the form of cuffs made of wear-resistant polyurethane of high strength, or in the form of discs also made of polyurethane. At the ends of the supporting-motor elements 3, rollers 4 and plates 5 of wear-resistant ceramic materials can be installed. Inside the housing 1 there are means for controlling the speed of the device (not shown in the drawings), in the form of an adjustable bypass pipe for bypassing the product transported through the pipeline. In the bow of the device, a bracket 6 and a cowl are attached 7. The bracket 6 is used for transport and loading operations, for installing the demagnetizer in the pipeline, as well as for its coupling with an additional device for demagnetization, when creating a multi-section demagnetizer.

On the surface of the housing 1 is attached one magnetizing belt 8 (figure 2) or two magnetizing belts 8 and 9 (figure 3). Each of the belts 8 and 9 consists of poles 10 evenly spaced around the circumference (Fig. 4), formed of permanent magnets 11, on the outer surface of which are attached brushes 12 of cables 13, fixed to the base 14, made of soft magnetic material. A distinctive feature of the claimed device is that the poles 10 are made wedge-shaped. The wedge-shaped poles 10 are created by reducing the number or size of permanent magnets 11 and, accordingly, reducing the size of the brushes 12 (the number of cables 13). The shape of the poles 10 and their number can be different, depending on the thickness of the walls and material of the pipeline, as well as the velocity of the projectile. Fig. 6 shows the most used versions of the poles 10. Fig. 6 (a) shows a wedge-shaped pole with an elongated base, (c) with flat faces, (c) with stepped faces, (d) with convex faces, ( f) and (f) - with asymmetric (beveled) faces.

The magnetizing belt 8 contains an even number of poles 10, with alternating N and S poles of permanent magnets 11, which causes the magnetization of the pipe 15 to be segmental around the circumference (figure 4). The direction of magnetization in adjacent pipe segments 16 is counter-parallel and along the circumference of the pipe. The magnetizing belt 8 may contain four, six, eight or more magnetic poles 10. Moreover, several magnetizing belts 8 can be installed in one device, or two devices with a different number of magnetic poles 10 can be combined into a coupler. The sizes and number of magnetic poles 10 in each magnetizing belt 8 are calculated based on the dimensions of the pipeline (diameter, wall thickness), the magnitude of the previous magnetization of the pipeline, and the level of residual magnetization to which the pipeline must be demagnetized. Figure 3 shows a device with two magnetizing belts 8 and 9. Belt 8 contains eight poles 10, and belt 9 contains twelve poles 10.

Permanent magnets 11 can be made on the basis of Al-Ni-Co-Fe alloy (ALNIKO), on the basis of SmCo alloy (SAMARIUM-COBALT), which has a unique combination of strong magnetic properties, corrosion resistance and stability at high temperatures, as well as on the basis of NdFeB alloy (NEODIME-IRON-BOR).

The device is stored in a pipeline, where it begins to move under gas pressure. Previously, using a speed control system, the speed is set in the range from 0.1 to 10 m / s. The higher the speed of movement of the device, the larger the size of the magnetic poles should be 10. During movement, the device magnetizes segmental and counter-parallel to the circumference in each section of the pipe, magnetizes the pipe wall 15 in the form of strips with a transverse direction of magnetization.

In front of the projectile, the magnetization is directed along the pipe. On each section of the pipe 15, the magnetizing belt 8 is first affected by the bases (the widest) of the ends of the wedge-shaped poles 10, magnetizing the segments 16 of the pipe 15 in the opposite direction and until saturated. Then, each element of the pipe 15 is affected by the subsequent elements of the poles 10, of smaller sizes and with less magnetizing force. Thus, after the device is exposed to the pipeline walls, there remain strips magnetized counter-parallel with the minimum level of magnetization, as well as a narrow magnetic loop, in the region of the passage of the central zone of poles 10, with longitudinal magnetization and a minimum level of magnetization.

For a higher level of demagnetization of the walls of the pipeline, a projectile with two magnetizing belts 8 and 9 is used, with the second magnetizing belt 9 having a larger number of poles 10. In this case, when passing the second magnetizing belt 9, a larger number of poles acts on the walls, but with less magnetizing force. To eliminate the mutual influence of the magnetizing belts 8 and 9, they are performed with some bias. Thus, after exposure to a device with two magnetizing belts 8 and 9, narrower bands remain on the pipeline walls, magnetized counter-parallel with a lower level of magnetization, as well as a narrower magnetic loop, in the region of the passage of the central zone of poles 10, with longitudinal magnetization and with an even lower level of magnetization. Figure 5 shows the magnetization levels over the cross section of the pipe after passing through the 8-pole, 8- and 16-pole, as well as 8- and 24-pole devices.

Additionally, after the passage of the device, the pipe walls, magnetized transversely, are demagnetized due to the large demagnetizing factor of the individual pipe segments.

Quality control of the device was carried out at the stand. A piece of pipe with a diameter of 1440 mm and a length of about 30 meters was used as the object of demagnetization. The levels of residual magnetic field induction were measured in a gap of 5 mm wide. The device - the projectile-demagnetizer PMR-800 had eight poles, the length of the body 1449 mm. A demagnetizer shell was passed, both after a flaw detector with a longitudinal magnetization of DMT-800, and after a flaw detector with transverse magnetization of DMTP-800.

It is known that the level of induction in the cutting should be no more than 8-10 mT. The welder does not notice the presence of a magnetic field with an induction level of up to 8 mT; in the induction range of 8–10 mT, the welder observes an increase in the excitement of the metal in the weld pool, with induction above 10 mT, metal spraying from the weld zone begins, and with induction above 30 mT, welding is practically impossible (S.A. Volokhov. Experience of demagnetizing pipes on trunk pipelines using the latest technology // Welding production. 1999).

Tests have shown that a projectile with a longitudinal magnetization system DMT-800 magnetizes the metal of the pipe to a very large value of residual induction, about 0.7-1 T. This corresponds to the field in the pipe groove with a gap of 5 mm of the order of 200 mT. Welding of such pipes without preliminary demagnetization is impossible. In this case, the demagnetizing factor N practically does not play a role, since the length of the pipe is equal to infinity. A projectile with a transverse magnetization system DMTP-800 magnetizes metal to a value of the order of 0.5-0.6 T.

The field in the pipe cut with a gap of 5 mm after passing the demagnetizer PMR-800 (an 8-pole projectile with one magnetizing belt) in the first case, the field decreased by 20-30 times and amounted to about 10 mT, in the second case 7 mT.

After skipping the device in both cases, a sufficiently low level of residual magnetization was ensured, which ensured a high quality of welding work.

Calculations show that if you take a device with two magnetizing belts 8 and 9, this will lead to a decrease in the residual field by another 20-30 times.

Claims (14)

1. The method of demagnetization of long products from soft magnetic materials, mainly pipelines, in which the long product is exposed to a magnetic field, which is carried out by at least one magnetizing belt with magnetizing poles, and a change in the magnetic field is achieved by moving the magnetizing belt along the long product, characterized in that the magnetization is from the inside of a long product magnetizing belt containing at least two opposite poles, made by wedge-shaped and formed by permanent magnets. 2. The method according to claim 1, characterized in that the width of the magnetized strips is selected depending on the thickness of the product, the value of the previous remanent magnetization and the level of minimum remanent magnetization to which it is necessary to demagnetize the product. 3. The method according to claim 1, characterized in that the number of belts is selected depending on the thickness of the pipeline, the magnitude of the previous remanent magnetization and the level of minimum remanent magnetization to which the product must be demagnetized. 4. The method according to claim 1, characterized in that the distance between the magnetizing belts is selected depending on the thickness of the pipeline and the magnitude of the previous remanent magnetization. 5. The method according to claim 1, characterized in that the width of the magnetization bands and the level of magnetization for each subsequent magnetizing belt is less than the previous one. 6. The method according to claim 1, characterized in that the speed of movement of the magnetizing poles is selected depending on the lengthy thickness of the product. 7. The method according to claim 4, characterized in that the speed of movement of the magnetizing poles is from 0.1 to 10 m / s. 8. Device for demagnetizing long products from soft magnetic materials, mainly pipelines, including a cylindrical body made of soft magnetic material with supporting-motor elements, at least one magnetizing belt is placed on the surface of the cylindrical body, consisting of magnetizing poles uniformly spaced around the circumference formed by permanent magnets with the poles facing the inner surface of the long product, on the outer surface of which brushes of three owls made of magnetic material, characterized in that the magnetizing poles formed by the permanent magnets are made oppositely wedge. 9. The device according to claim 8, characterized in that the sizes of the magnetizing poles formed by permanent magnets and their number are selected depending on the thickness of the lengthy product, the previous value of the residual magnetization and the minimum residual magnetization to which it must be demagnetized. 10. The device according to claim 8, characterized in that the number of magnetizing belts is selected depending on the thickness of the lengthy product, the previous value of its residual magnetization and the minimum residual magnetization to which it needs to be demagnetized. 11. The device according to claim 8, characterized in that each subsequent magnetizing belt has a larger number of magnetizing poles. 12. The device according to claim 8, characterized in that the magnetizing wedge-shaped poles are made with an elongated base. 13. The device according to claim 8, characterized in that the magnetizing wedge-shaped poles are made with stepped faces. 14. The device according to claim 8, characterized in that the magnetizing wedge-shaped poles are made with beveled faces.

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