Procedure for electroslag coating build-up on internal surface of pipe

FIELD: metallurgy.

SUBSTANCE: strip electrode is fed, it is moved along pipe, and is melted with forming of liquid metal bath. Liquid metal bath is subjected to permanent magnetic field created by two solenoid coil with cores making opposite poles at edges of the strip electrode. Build-up is performed with pipe rotation and with electrode axial movement with core ends location in plane parallel to plane of the strip electrode, at both sides of its side edges. Build-up of the first ring bead is performed at similar supply currents of the solenoid coils. Build-up of the second and next beads is performed at increased by 1.3-3 current of the solenoid coil with core creating "north pole" at edge of the strip electrode at side of the previously build-up metal bead.

EFFECT: invention reduces difference of thicknesses of the build-up coating and its discontinuity as per chemical and phase composition.

3 cl, 2 dwg

 

The invention relates to the field of protective coating on metal surfaces by welding under the flux layer and may find use in the application of protective anticorrosion coatings on inner surface of pipes, equipment for nuclear and chemical industries.

A method of coating electric arc welding under flux on the surface of the pipe, including the use of groups of electrodes that move along the axis of the rotating pipe with a continuous supply of flux, and in the process of welding the pipe from the opposite side is cooled.

(EN 2308364, UK 9/04, UK 31/02, published 20.10.2007)

The disadvantage of this method is the poor quality of the deposited coating, which reduces the operational reliability of the pipe. This is due to the fact that conducting the process in arc welding mode is accompanied by the periodic closure of the arc gap, whereby the deposited layer is obtained heterogeneous.

The closest in technical essence is a method of electric arc welding of metal in the product is submerged, including surfacing with strip electrode and the impact on a bath of molten metal constant magnetic field, formed by two electromagnetic coils with cores, forming opposite poles at the end�in strip electrode, moreover, the ends of the cores are in front of a tape electrode in the direction of the surfacing at the same distance from the axis of the strip electrode and the surface of the product.

(DE 2218078, UK 9/04, UK 35/30 published 25.10.1973)

Specified known method also inherent disadvantages of methods of welding in arc mode. In addition, the known method does not allow to adjust the magnitude of the magnetic field in the coils of the magnetic system, in combination with non-optimal arrangement of the ends of the cores relative to the bath of molten metal does not provide the possibility of obtaining high-quality deposited coating on the inner surface of a pipe having a curvature.

The task and the technical result is to provide a method of surfacing coating on the inner surface of the pipe in electroslag mode, reducing thickness variation of the deposited coatings and the reduction of heterogeneity in chemical composition.

The technical result is achieved in that a method of electroslag surfacing coating on the inner surface of the pipe comprises feeding strip electrode, it moves along the pipe, melting with the formation of the liquid metal bath and the impact of constant magnetic field on a bath of molten metal, which is formed by two electromagnetic coils with cores with �formirovanie opposite poles at the edges of the strip electrode, in the process of welding the pipe and rotate after each full rotation of the pipe by moving belt electrode along the pipe, and the ends of the cores of solenoid coils are placed in a plane parallel to the plane of the strip electrode, both sides from its side edges, facing the first annular bead carried out at the same supply currents to the electromagnetic coils with a core, and the second and subsequent surfacing of rollers is carried out at a magnification of 1.3 to 3 times the current power referred to the spool core in comparison with the supply current when welding the first annular bead and the formation of the "North pole" at the edge of the strip electrode from the previously deposited bead of metal.

The technical result is also achieved by the fact that the ends of the cores are placed at a distance of 5-30 mm from the side edges of the strip electrode, at a height of 5-15 mm from the weld surface of the pipe and at a distance of 0-30 mm from the plane of the strip electrode, but in the process of deposition the outer surface of the pipe over the place surfacing cooled.

The invention can be illustrated by an example using Fig. 1-3, where

1 - trumpet;

2 - surfacing the head with intermediate flux bin;

3 - column for console mounting;

4 - trolley to move NAP�ovocny head along the axis of the pipe,

5 - power source;

6 - basic fluxing bunker;

7 - cassette tape electrode;

8 - stationary remote control;

9 - power source and control panel of the magnetic system;

10 - drive a pair of rollers roller conveyors;

11 - idle pair of rollers roller conveyors;

12 - frame roller conveyors;

13 - heater resistance (for preheating);

14 - cooling system (sprayer and drip tray);

15 - the drip tray.

16 - console;

17 - resistant roller;

18 - the strip;

19 is a liquid metal bath;

20 - slag bath;

21 - a layer of flux;

22 - the bead;

23 - cores;

a, b, C are the coordinates of the placement of the pole tips;

α - the angle of pole tips;

VH- the direction of the surfacing;

N - "North" pole of the magnetic system;

S - "South" pole of the magnetic system.

Electroslag surfacing under flux on the inner surface of the pipe 1 (Fig. 1) nominal diameter DN 850 of steel grade HF were using consumable strip electrode 18 of a width of 60 mm and a thickness of 0.5 mm steel type Cr20Ni10Nb. Filing strip electrode 18 and the flux were using surfacing head 2 (Fig. 1) with intermediate flux hopper placed on the console 16 inside the pipe 1. Console 16,�esenkoy on the column 3 for its fastening, in the area of surfacing was applied flux from the primary flux hopper 6 and the strip 18 from the cassette 7. The axial displacement of the welding head 2 with strip electrode 18 along the pipe 1 was carried out using a truck 4, on which was placed the power source 5, connected to the stationary control unit 8 and the power source control unit of the magnetic system 9. Tube 1 is placed on the rollers of the roller stand is provided with a frame 12, an idle roller 11 and driven by a pair of rollers 10, which was carried out by rotation of the pipe 1. Preheating pipe carried by the heater resistance 13, and the outer surface of the pipe over the place surfacing were cooled with cooling system, including nozzles and drip tray.

Impact on a bath of molten metal 19 constant magnetic field, which was formed by two electromagnetic coils (not shown) with the cores 23, forming opposite poles ("North" and "South") at the edges of the strip electrode 16. The ends of the cores were placed at a distance of 5-30 mm (for example, a=15 mm) from the lateral edges of the strip electrode 18 at a height of 5-15 mm (for example, b=10 mm) from the weld surface of the pipe 1 and at a distance of 0.5-30 mm (for example, C=20 mm) from the plane of the strip electrode 18 (Fig. 2, 3).

This mutual arrangement of the core�at 23 and formed of the molten metal bath 19 to compensate for the forces due to the intrinsic magnetic field of the welding circuit (so-called "magnetic blow"), which lead to the displacement of the molten metal bath and, consequently, to the formation of undercuts in its subsequent crystallization along the line of fusion between the rollers and the base metal. Also you can prevent the formation of slag inclusions in the weld metal.

The ability to change the location coordinates of the ends of the core 23 of the magnetic system relative to the pipe 1 and the strip electrode 18, as well as the ability to control the parameters of the magnetic system (the current in the coils) alter the amount and nature of the impact created by it's magnetic field on formation of weld platens 22, including when using ribbons of different sections.

The welding was performed while rotating the pipe drive rollers 10 (Fig. 1) at a speed of 10 m/h and the axial movement of the surfacing head 2 after the completion of each full revolution of the pipe 1. The first ring roller are deposited at the same currents power solenoid coils supplied from a power source 8 (Fig. 1) coils of the magnetic system, and the second roller and subsequent rollers - when you increase 1.5 times the current of the electromagnetic coil core 23 (Fig. 2, 3) forming the "North pole" at the edge of the strip electrode 18 side earlier napravljen�th roller. This ensured the stability of the process of formation surfaced rollers, their uniform thickness and made it possible to eliminate the offset of the molten metal bath and to correct the defects in the morphogenesis of rollers, such as undercuts, uneven edges, sticky formed between the rollers.

In the process of deposition the outer surface of the pipe is cooled using a sprayer cooling system 14 (Fig. 1). This eliminates the possibility of overheating of the metal filler pipe and caused overheating of the formation of hardening structures in the metal heat affected zone under surfaced rollers. These structural changes may result in the operation of the weld the pipe to the emergence of the so-called "welding" cracks in the metal pipe and the output pipe from service. The use of forced cooling of the pipe using a sprayer greatly reduces the likelihood of "welding" of cracks, i.e. improves the quality surfaced pipe and increase its reliability. The implementation of the method according to the invention has allowed to avoid a short circuit between the pipe and tape electrode, which provided a reduction in the heterogeneity of the deposited coating by chemical composition.

As a result of the implementation of the method of deposition according to the invention on the inner surface of the pipe �ylo obtained homogeneous in chemical composition anti-corrosion protective coating of uniform thickness, without undercutting, zabadani between the rollers, pores, cracks and other defects, which allows to increase the resource of the weld pipes and their reliability as part of the equipment for atomic power stations, installations, petrochemical industry, etc.

1. Method of electroslag surfacing coating on the inner surface of a pipe comprising feeding strip electrode, it moves along the pipe, melting with the formation of the liquid metal bath and the impact of constant magnetic field on a bath of molten metal, which is formed by two electromagnetic coils with cores with the formation of opposite poles at the edges of the strip electrode, characterized in that in the process of welding the pipe and rotate after each full rotation of the pipe by moving belt electrode along the pipe, with the ends of the cores of solenoid coils are placed in a plane parallel to the plane of the strip electrode, both sides from its side edges, with the surfacing of the first ring roller are at the same currents power electromagnetic coil core and the cladding of the second and subsequent rolls is carried out at a magnification of 1.3 to 3 times the current power referred to the spool core in comparison with the supply current when welding the first ring of the roller and forms�ing "North pole" at the edge of the strip electrode from the previously deposited bead of metal.

2. A method according to claim 1, characterized in that the ends of the cores are placed at a distance of 5-30 mm from the side edges of the strip electrode, at a height of 5-15 mm from the weld surface of the pipe and at a distance of 0-30 mm from the plane of the strip electrode.

3. A method according to claim 1, characterized in that in the process of deposition the outer surface of the pipe over the place surfacing cooled.



 

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1 tbl

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1 dwg

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1 ex

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