FR2941160A1 - Torch for arc welding of a first edge of a metal piece with a second edge of the metal piece, comprises a body with an elongated tungsten electrode having a free end, a device for supply of fused welding wire, and guiding devices - Google Patents

Abstract

The arc welding torch comprises a body (1) with an elongated tungsten electrode (5) having a free end projecting out of the torch body, a device (7) for supply of fused welding wire (6) at the free end of the electrode, and guiding devices (4) connected to the torch body and laterally positioned on the electrodes. The axis of the electrode and the central plane of the wire supply device are present in a common plane. The guiding devices are arranged laterally relative to the common plane. The electrode and the wire supply device are arranged one over the other. The arc welding torch comprises a body (1) with an elongated tungsten electrode (5) having a free end projecting out of the torch body, a device (7) for supply of fused welding wire (6) at the free end of the electrode, and guiding devices (4) connected to the torch body and laterally positioned on the electrodes. The axis of the electrode and the central plane of the wire supply device are present in a common plane. The guiding devices are arranged laterally relative to the common plane. The electrode and the wire supply device are arranged one over the other so that the fuse wire is brought at the free end of the electrode. The angle formed between the axis of the electrode and the axis of the fuse wire is 10-30[deg] . Each guide device includes a sliding block, and a contact surface facing outward and contacting with the welding joint when the electrode and the guiding device are inserted between the welding joint to form a seal. A first and a second unit are arranged for receiving guide wire symmetrically arranged about the axis of the electrode and to alternately receive a portion of the inlet device of the fuse wire. The first and second units comprise passages supplied in the torch body. An independent claim is included for a process for arc welding of a first edge of a metal piece with a second edge of the metal piece.

Description

The invention relates to an arc welding torch and the use of this torch for arc welding of so-called narrow joint preparations. In the field of energy, experience feedback from orbital welding of large diameter tubes, that is to say typically tubes of more than 150 mm in diameter, intended to transport in particular oil and gas , tends to show that in terms of fatigue and corrosion behavior, the realization of the welded joints according to the so-called narrow joints or narrow gap, as illustrated in Figure 1, does not meet the current operating conditions. More specifically, Figure 1 shows a typical configuration of narrow joint between two tubes 11, 12 of ferritic steel plated, to be welded together. The spacing E between the two walls of the circular edges at the ends of the tubes 11, 12 to be welded is generally greater than 10 mm. The walls are not strictly parallel to each other but slightly inclined at an angle of a few degrees, typically 1 to 2 °, relative to the vertical.

The preparation of the mechanical machining veneer shall allow the right of the joint axis to ensure a constant EP plating thickness of 2.5 mm regardless of the thickness delivered with a constant 1.5 mm heel T and without spacing. Indeed, as shown in Figure 2a, there is generally a critical zone 40 in root pass 41 at the level of the cord foot which becomes all the more critical as we are currently moving towards the implementation of tubes ferritic stainless steel or nickel base, for which the realization and quality of the root passes will be more difficult to master by welding techniques currently implemented. FIG. 2a illustrates problems currently encountered in the welded tubes, namely, on the internal side of the tube, excess thicknesses 43 of excessive cords, typically of more than 3 mm, and connection angles AR of the cord / base metal thickness of 110 mm. ° to 120 °, thus too closed, which thus generate geometric effects of notches favorable to the concentrations of stresses and to a rupture by premature fatigue, and constitute traps with retention of products, being able to cause preferential corrosions according to the products conveyed by the tube considered.

Currently, the orbital TIG welding process, which is an adaptation of the conventional TIG welding process, is mainly used for welding tubes of small thicknesses, typically from 0.8 to about 4 mm, for which the quality criterion is predominant. Reliability of the process has also made it possible to develop narrow-seam welding applications of greater thicknesses whose performance in terms of productivity, that is to say of high cost, have restricted the field of application essentially to the nuclear field. Moreover, the MIG welding process using a solid wire or a flux-cored wire to realize, in semi-automatic welding, the root passes, and then in automated welding, the filling passes is commonly applied for the pipes of diameter up to about 15 cm to 60 cm (6 to 24 inches approximately). However, if the compromise between quality and productivity, in the different versions of the MIG process, is more attractive at the time of its realization, the practical implementation of this method shows that a significant improvement must be made both in terms of reliability and reliability. productivity, given the higher cost of material retained and their implementation. In addition, the method of STT (Surface Tension Transfer) is more commonly used for the realization of root passes, the main advantage of which lies in the reduction of the projection rate with respect to a conventional MIG process. This method is, on the one hand, limited in yarn speed, therefore in performance (welding speed) and, on the other hand, its cold welding regime leads to unfavorable cord shapes, such as those shown diagrammatically in FIG. . Finally, the so-called CMT welding process (for Cold Meta / Transfer or cold metal transfer) could advantageously replace the STT process in some applications since the CMT process can be likened to a mechanical short arc process obtained through a movement. back and forth of the wire in the melt. However, this CMT process is a low energy process which can therefore give rise to fears of medium or high thickness, ie greater than 2 mm, in the orbital welding of problems of lack of fusion or bonding. It should be noted that these considerations also apply to the welding of pressure-sensitive devices of greater thickness, that is to say greater than 2 mm, mainly alloyed and high-alloy CrMo steels, containing at least 5% by weight alloying elements. Indeed, these materials require special metallurgical precautions and welding procedures, including preheating and temperature between passes, controlled welding energy, shape of cords in multi-pass welding, total hydrogen content in the lowest possible cords. As a whole, these precautions are just as restrictive as those for tube welding.

The problem to be solved is therefore to propose an arc welding torch making it possible to efficiently weld narrow-gap configurations, in particular of the bottom pass or passes, which can be used in particular. orbital welding of tubes, for example by splicing tubes or pipelines or the like, and a welding method using such a torch. The solution of the invention is an arc welding torch comprising a torch body provided with an elongate tungsten electrode having a free end projecting out of the torch body; and a wire feeding device designed for and adapted to bring a welding fuse wire at the free end of the electrode, characterized in that it further comprises at least one guide device, integral said torch body, arranged to be positioned out of the torch body and laterally to the electrode. Depending on the case, the torch of the invention may comprise one or more of the following features: it comprises two guiding devices arranged laterally and on either side of the electrode. the axis of the electrode and the median plane of the wire feeding device are included in a common plane, and the one or more guiding devices are arranged laterally with respect to said common plane. the electrode and the wire feeding device are arranged relative to each other so that the fuse wire is brought to the free end of the electrode and that the angle formed between the axis of the electrode and the axis of the fuse wire is between 10 and 30 °. - The guide device or devices comprise at least one guide pad, preferably each guide device comprises a guide pad. at least one guiding device comprises an outwardly directed contact surface intended to come into contact with at least one of the edges to be welded when the electrode and said at least one guiding device are inserted between said edges to be welded forming between them a weld joint. - The torch body comprises first and second wire guide receiving means arranged symmetrically with respect to the axis of the electrode and for receiving alternately at least a portion of the fuse wire feeding device. the first and second wire guide receiving means comprise passages arranged in the torch body. The invention also relates to a method of arc welding a first edge of a metal part with a second edge of a metal part, said first and second edges being arranged opposite the one of the other being spaced apart from each other by a non-zero distance E, in which a) a torch as described above is implemented, b) positioning the free end of the electrode, the end of the fuse wire feed device 30 and said at least one torch guide device in the space E between said edges to be welded, at least one guide device 4 resting on the surface of one of said edges, c) welding of the two edges with each other by relative displacement of the torch between said edges to be welded with simultaneous progressive melting of the fusible wire 35 by means of an electric arc. forming at the free end of the electrode and deposition of molten metal from the melting of the wire fuse between said edges so as to form a weld joint between said edges, after solidification of the metal, and d) the torch is guided during step c) between said edges to be welded by means of said at least one guiding device which bears on the surface of at least one of said edges during the period of movement of the torch between said edges. Depending on the case, the method of the invention may include one or more of the following features: - the two edges form with each other a narrow joint type configuration and are spaced apart from each other a distance E at the bottom of the chamfer less than 10 mm, preferably between 8 and 9 mm. - The two edges are located at the end of two tubular structures to be welded to each other, for example tubes to be roped, or pipelines, ducts, ferrules ... The method of the invention makes it possible to retain, by the use of the device of the invention, the quality and compactness of the cord obtained with a TIG process and in particular the quality of the (or) root pass performed. Indeed, it has been demonstrated that, when the method of the invention is used to weld orbital tubes, the torch of the invention makes it possible to improve the internal profile of the root pass, such as illustrated in Figure 2b, by removing the geometric connection faults. More specifically, the welding torch of the invention makes it possible to obtain, on the inner side of the tubes 11, 12, an AR connection angle greater than approximately 140 to 150 °, and an internal cord allowance S less than 2 mm. approximately, typically 1 to 1.5 mm, which leads to a better compactness (radiographic) cords. It should also be noted that there are no adherent deposits on the inner side or between-pass filling, such as silicate deposits, which can adversely affect the cleansing operations of the lines before they are put into service, or their resistance to corrosion.

As shown diagrammatically in FIGS. 3 and 4b, a wire feed device 7, also called wire guide assembly 7, is integrated in the nozzle 8 of the torch so as to control the arrival of the fuse wire 6 at a precise angle so that to brush the pointed end of the electrode 5, which accelerates the fusion of the wire 6 in the hottest region of the arc and significantly improves the deposition rate with respect to the deposition rate of a TIG process in configuration classic called orbital TIG. This increase in the deposition rate can thus make it possible to use this method for the complementary filling phases and therefore to implement only one method for the entire welding operation of the seal. The feeding of the wire feeder 7 in welding wire is done in a conventional manner by means of a wire reel.

In fact, the torch shown in section view from the side in FIG. 3 comprises: in the upper part, a metal torch body 1, for example made of a CuZnPb-type alloy, comprising all the arrivals for the current, the high frequency used during priming, cooling water and shielding gas. an insulating intermediate portion 2 made of heat-stable thermoplastic, for example polyether-ether-ketone or PEEK (PolyEtherEtherKetone) or the like. - An active part 3 can be adjusted in height, depending on the application envisaged, particularly directly depending on the thickness of the material to be welded and / or efficiency of the cooling circuit. As detailed in FIGS. 4a and 4b (which is a bottom view of FIG. 3), according to one embodiment of the invention, the active part 3 comprises the electrode 5, the wire guide assembly 7 and, on its lateral external walls, two lateral guide pads 4 which provide electrical and thermal insulation functions and allow to obtain operating conditions of good slip and correct centering of the torch relative to the edges of the chamfer carried by the assembly to realize. These guide pads 4 are preferably interchangeable and quick assembly / disassembly to ensure a minimum time of immobilization of the torch, if they must be replaced, especially in case of excessive wear thereof.

The lateral guide pads 4 are introduced into the joint to be welded between the two walls forming the end edges of the parts to be welded together, which edges are generally machined and positioned facing each other, as illustrated on FIG. 4a which is a front view of the torch of FIG. 3, part of the active end 3, in particular the pointed free end of the tungsten electrode 5 and the arrival of the wire 6, is introduced between the two walls to be welded in a narrow gap configuration. During welding, when moving the torch in the narrow joint, that is to say the chamfer area between the two tubes 11, 12 to be spliced and welded together, as shown in Figure 10, the skids 4 of flat rectangular shape or consisting of small spherical balls crimped on a thin metal wall, are rubbed on said end edges of the tubes 11, 12 to maintain the electrode 5 always at the same distance from said two edges and thus ensure a regular welding and effective from one or both of the baseline passes and subsequent passes. In other words, these guide shoes 4, preferably made of ceramic or a metallic material coated with ceramic and mechanically fixed to the metal body of the active part, make it possible mainly to ensure lateral sliding of the torch, as well as good centering. the torch relative to the narrow joint plane, and incidentally an electrical and thermal insulation thereof relative to the edges of the parts to be welded together. Their rapid assembly and disassembly allows a minimum time of immobilization of the torch during this operation. Furthermore, the body 1 of the torch preferably comprises first 8 and second 9 wire guide receiving means arranged symmetrically with respect to the axis of the electrode 5 and for receiving alternately at least a portion of the device. fed 7 fuse wire 6 so as to distribute it before or after the electrode 5, when considering the welding direction, depending on the welding position considered. In other words, the reciprocating wire guide receiving means 8, 9 make it possible to have a double and symmetrical position of arrival of the wire 6 at the pointed end of the electrode 5 and this, according to a angle of the order of 20 ° relative to the axis of the electrode, as shown schematically in Figures 5a and 5b. This makes it possible to adapt the distribution position of the wire 6 to the selected welding position: upward or downward vertical positions. The first 8 and second 9 wire guide receiving means may be passages, such as holes, formed in the torch body 1, which advantageously comprise a machined portion, for example threaded, to allow attachment in this portion of the guide -fil 7, that is to say the wire feeding device 7, a portion of which may comprise a reciprocal fixing means, for example threaded, and / or able to cooperate with that of the machined portion, thereby permitting a joining of the wire guide 7 to one or the other of the first 8 and second 9 torch body receiving means 1. The preset wire guide assembly 7 is advantageously positioned from the upper part of the torch of to facilitate its change, if necessary, without the need to disassemble the torch or out of a joint in progress. From there, depending on the configuration of the joint to be made, the space and the available travel ..., it is possible to make the wire 6 arrive indifferently by one or other of the wire arrival positions 6 provided in the torch. To do this, it will suffice to arrange all or part of the wire guide or wire feeding device 7 in the first 8 or, as the case may be, in the second receiving means 9 of wire guide 7 and of then introduce the wire 6 to be delivered in the immediate vicinity of the electrode 5, that is to say so as to brush the end of said electrode 5 while remaining away from it by a distance of less than 2 mm, typically between 0.5 and 1.5 mm approximately.

It should be noted that, if necessary and according to the intended application, the angle of arrival of the wire 6 with respect to the axis of the tungsten electrode 5 may be greater than or less than 20 °, typically angle is between 10 and 40 °, typically between 20 and 30 °. Preferably, this angle remains constant and conditions the corresponding transfer regimes. However, one could imagine providing a suitable adjustment mechanism to adjust the desired arrival angle via the wire guide assembly 7. Preferably, the set guide wire 7 preset is positioned by the upper part of the torch being fixed in one or the other of the first 8 and second 9 wire guide receiving means, so as to facilitate its change if necessary without the need to completely disassemble the torch or out of a joint in progress.

The other incoming wire, when not used as a wire guide 7, that is to say the wire guide receiving means 8 or 9 not occupied by it, can serve either to supplying the torch with a complementary gas flow capable of modifying the arc regime, or the introduction of an optical fiber monitoring the fusion of the wire and the welding bath.

The internal profile the active part of the torch, which is illustrated in FIG. 6, is defined so as to keep at the outlet of the torch a uniform laminar gas flow forward and on the melt. To do this, a diffuser of sintered material or metal fabric 10 is integrated with the body 1 of the torch on the upstream path of the protective gas used.

The gas flow must also effectively protect the exit portion of the electrode 5 and mainly the terminal hot part subjected to significant oxidation that can cause barbs of tungsten oxide WxO2y, both in stationary regime and during the time of relative displacement torch-parts to be welded which is called in practice welding speed.

Moreover, servocontrols are integrated in the torch to ensure its proper operation, namely: an arc voltage regulating device 21 to maintain a constant electrode / room distance, in particular to guarantee constant penetration during the execution of the root and remelting passes if necessary; - a device for controlling several modes of transfer of metal from the wire, for example a drop transfer and a liquid bridge transfer, resulting from a wire pulse combined with a pulsation of direct current of the generator (see Figure 7), resulting in alternating hot regime / cold regime (ie base current and low wire speed) in the melt thus ensuring better flexibility for all-position welding.

Figure 7 illustrates different combinations of wire (VO) pulsation and current pulsation (I) used to melt the wire during the welding time (time t in abscissa) for which, around a mean wire speed (Vfm), the wire will be pulsed at a higher speed or peak wire velocity (Vfc) and at a lower velocity or base wire velocity (Vfb) .An average intensity (Im) will be applied simultaneously on said wire which will evolve between a higher intensity (Icrest). ) and a lower intensity (I base) Moreover, F represents the pulse frequency and T the pulse period These combinations as defined allow a timing of the two drop transfer modes for low wire speeds, for example 0.5 to 3 m / min for an ER308LSi stainless steel wire with a diameter of 1.2mm, and liquid bridge transfer for higher wire speeds, for example for this same wire at 6 to 8 m / min, resulting from a pulsation of wire combined with a pulsation of direct current resulting in the melt alternating hot regime / cold regime. The hot regime corresponding to the base speed (Vfb) liquid bridge speed range of 6 to 8 m / min and the cold drop speed at a peak wire speed (Vfc) of 6 to 8 m / min.

These pulsations in phase (Fig. 7, left part) or in counter-phase (Fig. 7, right part) thus provide the process with better flexibility for welding in all positions depending on whether we prefer, for example, filling by the wire to the detriment of vertical penetration rising and flat, or so the penetration of welding at the expense of filling in position welding to the ceiling.

The torch of the invention can operate with a specific power source and reel but also, with some routine adaptations. As an illustrative and non-limiting example of an embodiment of the invention, a welding torch according to the invention has been connected to commercially available equipment, namely a TIG welding power source. Plasma N450 from Air Liquide Welding and a wire feeder DIXWDE 312 from Dinse in order to obtain welding current pulsations of amplitude between 10 and 450 A, with a frequency of about 200 Hz, a wire speed from 2 to 10 m / min, a pulse frequency of 10 to 50 Hz, preferably less than 20 Hz. For this tube welding application, the integrated torch with two degrees of freedom in its linear displacements as illustrated in FIG. 8, namely: along the Z axis: vertical displacement controlled by a voltage self-regulation system; arc relative to the bottom of the chamfer, and - along the X axis: horizontal displacement both by self-centering in the plane of joint by the sliding pads according to 20 of solidarity with 22, which a mechanical assembly of motorization of welding equipment. It is easily understood that the actual centering of the torch is in fact made by sliding the pads on the vertical edges of the chamfer formed by the end walls of the two parts 11, 12 to be welded together. As fuse wire 6, solid wires or cored wires of the metal core type (Meta / Corecl) can be used. For solid wires, the transfer of metal from the molten end of the wire 6 to the seal may be of droplet type or by liquid metal bridge. The first favors the compactness of cords and the refinement of microstructure of the molten metal, as well as the flexibility of the process in the case of degraded preparations. On the other hand, the second favors the welding speed and / or the deposition rate. For cored wires, the fusion is very different from that of the solid wires. For example, as shown in FIG. 9, which is a photograph taken by means of a high-speed camera, typically 2000 to 10,000 images / sec, it is possible to distinguish during the fusion of this flux-cored wire 30, the external transfer of the metal strip 33 melted to the liquid bath 32 30 via a liquid bridge type transfer mode in fine drops, and the internal fusion of the filler 34 formed of metal filling elements in globular assimilated regime strongly oriented toward the electrode In the case of solid wires, the gases used to effect gaseous protection of the weld joint in the course of production are chosen from argon, helium, nitrogen and mixtures of argon and hydrogen. . In particular, Ar / H2 gas mixtures are preferably used for welding austenitic stainless steels and solid or plated nickel bases, but Ar / He / H2 gas mixtures for welding these same materials in a narrow gap configuration.

In addition, for the Meta / Cored cored wires, the shielding gases will be chosen from argon, helium and their mixtures. The torch of the invention is also modular thanks to its active part which is adaptable according to the intended application, for example the thickness to be welded and the specific operating conditions (materials, preheating, temperature between passes). Thus, it is possible to adapt the distance wire / electrode according to the shade and the diameter of the wire used. The torch of the invention may advantageously be used for welding metal tubes or metal structures of circular or tubular shape and with a thickness of between 12 and 150 mm, and with a diameter of at least 15 cm. Thus, there may be mentioned the welding of tubes, pipelines or the like in rotary narrow gap configuration, for example in the context of a prefabrication, or in narrow-gap orbital configuration during a final assembly on site. In both cases, this essentially concerns homogeneous assemblies, that is to say that the assembled materials are the same and in the same configuration on both sides of the joint axis, for example ferritic / ferritic. , austenitic stainless steel / austenitic stainless steel, nickel base / nickel base, stainless steel ferritic steel or nickel base / stainless steel ferritic steel or nickel base ... We can also mention the welding of pressure devices of high thickness, in which it is It is possible to meet the two types of assemblies which are not only homogeneous but also heterogeneous (tubings), that is to say which differ in the material grades, or even their configuration.

Claims (11)

Revendications1. An arc welding torch comprising: - a torch body (1) provided with an elongate tungsten electrode (5) having a free end projecting from the torch body (1) and - a feed device wire (7) designed and capable of bringing a welding fuse wire (6) at the free end of the electrode (5), characterized in that it further comprises at least one guiding device (4), integral with said torch body (1), arranged to be positioned outside the torch body (1) and laterally to the electrode (5). 2. Torch according to claim 1, characterized in that it comprises two guide devices (4) arranged laterally and on either side of the electrode (5). 3. Torch according to one of claims 1 or 2, characterized in that the axis of the electrode (5) and the median plane of the wire feeding device (7) are included in a common plane, and the or the guiding devices (4) are arranged laterally with respect to said common plane. 4. Torch according to one of claims 1 to 3, characterized in that the electrode (5) and the wire feed device (7) are arranged relative to one another so that the fuse wire (6) is brought to the free end of the electrode (5) and the angle formed between the axis of the electrode (5) and the axis of the wire (6) fuse is between 10 and 30 °. 5. Torch according to one of claims 1 to 4, characterized in that the or the guide devices (4) comprise at least one guide pad, preferably each guide device (4) comprises a guide pad. 6. Torch according to one of claims 1 to 5, characterized in that at least one guiding device (4) comprises an outwardly facing contact surface intended to come into contact with at least one of the edges to soldering when the electrode (5) and said at least one guiding device (4) are inserted between said solder edges forming between them a weld joint. 7. Torch according to one of claims 1 to 6, characterized in that the body (1) torch comprises first (8) and second (9) means for receiving wire guide arranged symmetrically with respect to the axis of the electrode (5) and for alternately receiving at least a part of the feeder (7) of the fuse wire (6) 8. Torch according to one of claims 1 to 7, characterized in that the first (8) and second (9) wire guide receiving means (7) comprise passages arranged in the body (1) torch. A method of arc welding a first edge of a metal piece with a second edge of a metal piece, said first and second edges being arranged opposite one another being spaced from each other by a non-zero distance E, in which a) a torch according to one of the preceding claims is implemented, b) positioning the free end of the electrode (5) the end of the feeder (7) of fuse wire (6) and said at least one guide device (4) of the torch in the space (E) between said edges to be welded, at least one guiding (4) coming to bear on the surface of one of said edges, c) welding of the two edges with each other by relative displacement of the torch between said edges to be welded with simultaneous progressive fusion of the wire fuse (6) by means of an electric arc forming at the free end of the electrode (5) and deposition of molten metal from the fusio n of the fuse wire between said edges so as to form a solder joint between said edges, after solidification of the metal, and d) the torch is guided during step c) between said edges to be welded by means of said at least one guiding device (4) which bears on the surface of at least one of said edges during the period of movement of the torch between said edges. Method according to claim 9, characterized in that the two edges form with each other a narrow joint-like configuration and are spaced from each other by a distance (E) at the bottom of the chamfer less than 10 mm, preferably between 8 and 9 mm. 11. Method according to one of claims 9 or 10, characterized in that the two edges are located at the end of two tubular structures to be welded to one another.