Method and devices for improving the productivity of welding two concentric metal pipes

Abstract

A method for welding the end (23) of an outer metallic tube (2) to a concentric inner metallic tube (1), the tube (2) comprising an inner face (21), an outer face (22) and at least one lateral face (24), the tube (1) comprising an inner face (12) and an outer face (12) and having a diameter smaller than the diameter of the outer tube (2), which comprises the following steps: machining (101) of the end (23) of the tube (2) so as to create on the lateral face (24) of the tube (2) a lip (25) extending from the inner face (21) of the tube (2) and having a thickness (e) smaller than the thickness (E) of the tube (2), deformation (103) of the tube (2) so as to reduce the distance between the lip (25) and the outer face (11) of the tube (1), and welding (104) of the end (23) of the tube (2) to the outer face (11) of the tube (1). Figure 6

Description

Title of the invention: Method and devices for improving the productivity of welding two concentric metal pipes FIELD OF THE INVENTION

[0001] The technical field of the present invention relates to a method of welding two tubes arranged concentrically and more particularly the end of an external tube to an internal tube. STATE OF THE ART

[0002] In the oil sector, insulated double-jacketed pipes have been used for several decades to minimize their heat exchange with the environment. They are formed by successively assembling by welding sections of double-jacketed pipes of lengths between 6 meters and 50 meters. The aim is to reduce the heat transfer between a hot or cold fluid circulating in said pipe and the external environment.

[0003] The applications are often petroleum, but can also concern other fields such as for example the transport of very hot air in the field of concentrated solar energy, vegetable oils or cryogenic fluids such as liquefied ammonia, Liquefied Natural Gas (LNG) or liquefied hydrogen.

[0004] The pipes are in the form of double-walled pipes comprising an outer tube welded at its ends to an inner tube. This configuration defines a sealed annular space in which it is possible to reduce the pressure in order to optimize the thermal performance of the insulation and to mechanically protect the thermal insulation system from the external environment (humidity, pressure, mechanical aggression). Such a “Pipe-in-Pipe” configuration according to the established Anglo-Saxon terminology is also found in triple-walled pipes, consisting of three tubes arranged one inside the other, or in parts intended to ensure the thermal insulation or sealing of the pipes.

[0005] The closing of this annular space is sometimes achieved by folding the outer tube onto the inner tube by plastic deformation while respecting geometric constraints such as the welding clearance and then welding the two tubes.

[0006] Depending on the thickness of the external tube, generally from 4 mm to 30 mm, the number of welding passes is between 3 and 20. This number also depends on the welding process, the inclination of the part to be welded, whether or not the part is rotated during welding and the size of the weld throat.

[0007] The industrial solution represented by said welding process must jointly meet technical and economic criteria and constraints.

[0008] The production of a structurally sound weld between the two tubes and which minimizes the risks of fatigue failure requires in particular that the first pass melts the lower corner, or root, of the external tube.

[0009] If the root is not melted, this results in a geometric shape which causes a local increase in the stress level during mechanical stresses and therefore a reduction in the number of stress cycles to failure. When the alloy lends itself to it, this type of defect is generally detected by ultrasonic inspection methods which detect an abnormal echo coming from the root leading to the rejection of the weld.

[0010] The implementation must also be economically satisfactory, this implies in particular a limited welding time (by depositing a high quantity of solder) while minimizing the risk of defects leading to repair of the welds.

[0011] In the case of the welding of annular spaces in “Pipe-in-pipe” systems, the molten metal is deposited on a convex surface (the inner tube), often in rotation: it is therefore understood that the inconsiderate increase in the deposition rate (and therefore in the welding power) leads to the extension of the weld pool to the point where it could flow, in particular around the periphery of the tube before solidifying. This leads to defects, a loss of raw material and reduced efficiency of the weld.

[0012] Furthermore, each completed welding pass leads to an increase in the temperature of the part to be welded, making it necessary to stop the welding to allow cooling and thus avoid making the bath uncontrollable due to this excessive increase in its temperature. The specifications of the welding processes also generally include a limitation of the maximum interpass temperature which must be respected.

[0013] These stopping phases are detrimental to the general productivity of the assembly process, and contribute, due to the multiplication of stopping and restarting of the welding, to the multiplication of the risk of defects.

[0014] Achieving this type of welding reliably and repeatably in a manual process requires skilled and highly qualified welders. In a mechanized or automatic process, this requires advanced mastery of multiple variables and parameters, such as, for example, the positioning of the welding torch, the rotation speed of the tube, the feed speed of the filler wire, the electrical voltage, the current, etc.

[0015] Even without taking into account the dexterity of the welders, certain welding conditions remain difficult to control and are sources of the appearance of defects, for example: • a lack of penetration or collapse of the weld pool towards the inside of the annular space between the inner and outer pipes,

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[0021] due to a non-constant weld gap (too large or too small), • variable axial penetration of the weld depending on the weld gap leading to the appearance of false positives during ultrasonic inspection, and • the entrapment of oxides under a weld pass moving in an uncontrolled manner, • variable thermal conditions acting on the weld pool; in fact, depending on the variable spacing of the weld gap and the position of the welding torch relative to the root, the thermal propagation in the external tube varies and leads to variable and uncontrollable solidification conditions. These parameters are all the more difficult to control as the tube is small and therefore convex, consequently conducive to the flow of a spread weld pool which is also obtained elsewhere when seeking to increase productivity. This variability of conditions plays a negative role in the search for a set of parameters allowing acceptable welds to be produced. The objective of the present invention is to provide a method for welding two tubes arranged concentrically within each other, making it possible to overcome the aforementioned drawbacks. Statement of the invention The invention therefore relates, in its first subject, to a method of welding the end of a metal outer tube to a metal inner tube, the outer tube and the inner tube being arranged concentrically within each other, the outer tube comprising an inner face, an outer face and at least one lateral face, the inner tube comprising an inner face and an outer face and having a diameter smaller than the diameter of the outer tube, characterized in that said method comprises: • a step of machining the end of the outer tube so as to create on the lateral face of the outer tube a lip extending the inner face of the outer tube and having a thickness smaller than the thickness of the outer tube, • a step of deforming the outer tube so as to reduce the distance between the lip and the outer face of the inner tube, and • a step of welding the end of the outer tube to the outer face of the inner tube. According to one embodiment of the method of the invention, after the step of machining the end of the outer tube and before the step of deforming the outer tube, machining and / or brushing of the inner face of the lip is carried out. According to another embodiment of the method of the invention, the lip has a thickness of between 1 mm and 8 mm.

[0022] According to yet another embodiment of the method of the invention, the lip has a length of between 1 mm and 8 mm.

[0023] According to yet another embodiment of the method of the invention, the lip has a radius of curvature of between 1 mm and 4 mm.

[0024] According to yet another embodiment of the method of the invention, at the end of the machining step, the lip forms with the lateral face of the external tube an angle of between 90° and 120°.

[0025] According to yet another embodiment of the method of the invention, at the end of the step of deforming the outer tube, the distance between the lip and the outer face of the inner tube is between 0 mm and 2 mm. According to a particular embodiment, the preferred target distance between the lip and the outer face of the inner tube is 1 mm, a variation less than or equal to plus or minus 0.9 mm, plus or minus 0.7 mm, plus or minus 0.5 mm, or even plus or minus 0.3 mm, may be permitted.

[0026] According to yet another embodiment of the method of the invention, the welding step is carried out by melting the lip so that the molten bath resulting from the melting of the lip wets the outer tube and the inner tube.

[0027] According to one embodiment of the method of the invention, the welding step comprises the concomitant cooling of the weld. According to a particular embodiment of the method of the invention, the weld is cooled by evaporation or conducto-convection of a cooling liquid, preferably water, in contact with the reverse face of the weld, i.e. on the internal face of the internal tube at the weld zone.

[0028] A very first advantage of the method according to the invention is that it makes it possible to make the weld between the external tube and the internal tube more reliable.

[0029] Another advantage of the method according to the invention is that it makes it possible to reduce the risks of lack of fusion of the internal corner of the external tube since the latter is replaced by the lip, and since the lip is metallurgically bonded to the external tube. This connection was in the art until now ensured by the first welding pass which presented a risk of poor execution. This configuration therefore makes it possible to gain both in reliability of the welding process and in productivity.

[0030] Yet another advantage of the method according to the invention is that it makes it possible to control the welding clearance between the lip and the inner tube since the lip can conform to the irregularities in shape of the inner tube.

[0031] Yet another advantage of the method according to the invention is that it makes it possible to control the quantity of energy supplied to the external tube for welding, which contributes to controlling the risk of extension of the weld pool.

[0032] This control is particularly improved by cooling the internal tube by its internal face concomitantly with the welding.

[0033] Furthermore, cooling concomitant with the weld makes it possible to reduce the risks of trapping oxides under the first weld pass, and thus to eliminate reasons for rejecting the weld.

[0034] Yet another advantage of the method according to the invention is that the weld pool is in a more stable thermal environment, the spacing of the weld clearance and the position of the welding torch relative to the root being less subject to variability.

[0035] Yet another advantage of the method according to the invention is that it allows better control of the penetration of the weld during solidification.

[0036] A particular advantage of the cooling optionally carried out in the third step of the method of the invention is that it makes it possible to reduce the interpass temperature and therefore to accumulate more passes without needing to interrupt the welding due to the rise in temperature of the tube.

[0037] Another particular advantage of the method incorporating the cooling carried out in the third step of the method of the invention is that it makes it possible to weld with more power (and therefore to obtain a higher molten metal deposition rate, i.e. a faster weld) since energy can be efficiently removed by cooling. This method therefore makes it possible to weld with very energetic techniques (sub-flux welding) also on tubes of small diameter, in particular with a diameter of less than 350 mm, preferably less than 300 mm, or even less than 250 mm.

[0038] Yet another advantage of the method according to the invention is that it makes it possible to increase the amplitude of the possible interval of acceptable welding intensities, which translates into a more robust method, i.e. more tolerant of control deviations, allowing controlled quality of the weld.

[0039] Another advantage of the method according to the invention is that it makes it possible to reduce the thermal intensity to which the operator is exposed, which makes the work of the operator carrying out the welding easier.

[0040] In its second subject, the invention also relates to a metal outer tube intended for a double-walled pipe, said outer tube comprising an internal face, an external face and at least one lateral face located at the end of said outer tube, the end being capable of being welded to the metal inner tube so as to form said double-walled pipe, said inner tube comprising an internal face and an external face and having a diameter smaller than the diameter of the outer tube, characterized in that the outer tube comprises a lip located on the lateral face, extending the internal face of the outer tube and having a thickness less than the thickness of the outer tube.

[0041] Advantageously, the lip has a thickness of between 1 mm and 8 mm, a length between 1 mm and 8 mm, a radius of curvature between 1 mm and 4 mm and forms an angle between 90° and 120° with the lateral face of the external tube.

[0042] A third subject of the invention relates to a device for cooling the welding zone when welding the end of a metal outer tube to a metal inner tube, said device comprising cooling means capable of cooling the welding zone by bringing a cooling liquid, preferably water, into contact with the internal face of the internal tube. In one embodiment, these cooling means allow cooling by evaporation or conducto-convection of the cooling liquid. As explained previously, the method of welding the end of a metal outer tube to a metal inner tube, when it comprises cooling by the internal face of the internal tube of the welding zone, significantly increases productivity gains, and makes it possible to obtain welds that are more resistant to crack propagation, particularly at low temperatures.

[0043] In a particular embodiment, the cooling device is a conducto-convection cooling device which comprises: • a plug intended to be inserted into the internal tube, said plug comprising: - two cheeks adapted to close the internal tube, said cheeks, when said device is inserted into the inner tube, thus defining with the wall of the inner tube a compartment into which the coolant is introduced, - at least one axis on which the cheeks are fixed, • a system for circulating the coolant in the compartment.

[0044] In another particular embodiment, the device is an evaporative cooling device which comprises:

[0045] • a plug intended to be inserted into the inner tube, the plug comprising:

[0046] - two cheeks adapted to close the internal tube, said cheeks, when said device is inserted into the inner tube, thus defining, with the wall of the inner tube, a compartment into which the coolant is introduced,

[0047] - at least one axis on which the cheeks are fixed,

[0048] - at least one means for spraying a cooling liquid on the reverse side of the weld, that is to say on the internal face of the internal tube at the level of the weld, inside the compartment formed by the plug,

[0049] - at least one extraction means, outside the compartment formed by the plug, steam formed by the cooling liquid in contact with the reverse side of the weld, when it is being welded,

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[0063] • a system fluidly connected to the steam extraction means which allows the suction of steam outside the compartment formed by the plug. In another embodiment, the cooling device is an evaporative cooling device that comprises: - A plug intended to be inserted into the inner tube, the plug comprising: a cheek adapted to close the inner tube 1, said cheek when said device is inserted into the inner tube, thus defining, with the wall of the inner tube, a section of the inner tube into which the coolant is introduced, - at least one means for spraying a cooling liquid on the reverse side of the weld, i.e. on the internal side of the internal tube at the weld, inside the section of the internal tube defined by the cheek. A fourth object of the invention is also the caps of the aforementioned cooling devices adapted to implement the cooling of the internal tube by evaporation or by conducto-convection. Brief description of the drawings Other characteristics, advantages and details of the invention will be better understood on reading the additional description which follows in relation to the drawings in which: [Fig.l] represents an example of a profile section of the inner tube and the outer tube at the end of the outer tube machining step of the process, [Fig.2] represents examples of different machining of the end of the external tube, [Fig.3] represents an embodiment of the lip, [Fig.4] represents a schematic example of a profile section of the inner tube and the outer tube at the end of the deformation step of the process, [Fig.5] represents a schematic example of a profile section of the inner tube and the outer tube at the end of the welding step of the method according to the invention, [Fig.6] is a diagram representing a method according to the invention, [Fig.7] shows the performance of welds obtained according to a method of the invention. A, Charpy test; B, Vickers hardness measurement, [Fig.8] shows an embodiment of a conducto-convection cooling device for the inner face of the inner tube in operation at the weld of the end of an outer tube to the outer wall of an inner tube, [Fig.9] shows an embodiment of an evaporative cooling device for the inner face of the inner tube in operation at the weld of the end of an outer tube to the outer wall of an inner tube. [Fig. 10] shows a photograph of a polished profile section of the junction between the outer tube and the inner tube before welding as it can be obtained at the end of the deformation step of the method according to the invention.

[0064] DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0065] It is specified that when intervals of measurements of physical quantities are specified in this document, they are understood to include limits, unless otherwise specified. Welding process

[0066] As described above, an object of the invention relates to a method 100 as illustrated in [Fig.6] for welding a metal outer tube 2 to a metal inner tube 1 arranged concentrically one inside the other. The method 100 according to the invention makes it possible, for example, to weld the end 23 of an outer tube 2 to an inner tube 1 so as to form a double-walled fluid transport pipe. The pipe formed then has a sealed annular space 3 between the outer tube 2 and the inner tube 1. Obviously, the welding method 100 according to the invention can be applied to any element having a metal outer tube 2 to a metal inner tube 1 arranged concentrically one inside the other, whatever the use of this structure. In other words, this welding method 100 is not restricted in its application in which the inner tube 1 is intended to convey a fluid.

[0067] Prior to welding, the outer tube 2 is positioned around the inner tube 1 so that the two tubes are concentric. Concentric, within the meaning of the invention, when referring to the inner tube 1 and the outer tube 2, means tubes that share the same center. In the technical field of the invention, the shape of the tubes may vary, in other words the tubes 1 and / or 2 may not be perfectly circular. Thus, the diameters and thicknesses of the tubes may vary over their length by a few millimeters due to the production method. Thus, with regard to industry standards, tubes are considered acceptable if diametrical variations of the order of 1%, preferably less than or equal to 1% and thickness variations of less than or equal to 10%, preferably less than or equal to 5% are observed.The person skilled in the art will know that the concept of concentricity allows a deviation from the geometric concentricity of up to several mm. The inner tube 1 therefore has a diameter smaller than the diameter of the outer tube 2. It will be understood that this method 100 can be applied to any pipe comprising a tube arranged in another tube. More particularly, this pipe may be a so-called double-walled pipe (called Pipe-in-Pipe in English terminology) as previously described, but also a triple-walled pipe (Pipe-in-Pipe-in-Pipe, in English terminology), which by definition comprises a . so-called double-walled pipe surrounded by a tube.

[0068] The outer tube 2 comprises an inner face 21 opposite the inner tube 1, an outer face 22 opposite the inner face 21 and at least one lateral face 24. The lateral face 24 corresponds to the end 23 of the outer tube 2 intended to be welded to the inner tube 1.

[0069] The internal tube 1 comprises an external face 11 located opposite the external tube 2 and an internal face 12 opposite the external face 11. The internal face 12 of the internal tube 1 thus delimits the conduit in which a fluid can be transported, but not necessarily.

[0070] [Fig.l] represents a profile section of the inner tube 1 and the outer tube 2 arranged concentrically within each other. They delimit between them the annular space 3.

[0071] The inner tube 1 comprises an inner face 12 and an outer face 11.

[0072] The external tube 2 is shown here machined at the end of the machining step 101 of the end 23 of the outer tube 2 of the method 100. It comprises an inner face 21, an outer face 22 and an end 23.

[0073] In one embodiment, the machining of the end 23 of the external tube 2 intended to be welded to the external face 11 of the internal tube 1 takes place on the site of installation of the pipe, by means, for example, of an orbital machining machine (in English terminology “Pipe Facing Machine”, PFM)

[0074] The end 23 of the outer tube 2 is represented by a lateral face 24 and a lip 25. It is intended to be welded to the outer face 11 of the inner tube 1 so as to seal the annular space 3.

[0075] The lip 25 is located on the lateral face 24. It extends the internal face 21 of the external tube 2. As will be mentioned later, the lip 25 is intended to be melted at the welding step 104 of the method 100 to allow the welding of the end 23 of the external tube 2 onto the internal tube 1.

[0076] The lip 25 has a structure making it possible to make the welding step more reliable. Its fusion by a manual welding process or by an automated mechanized welding process also makes it possible to generate a sufficient molten bath 26 to allow the simultaneous wetting of the end 23 of the outer tube 2 and the outer face 11 of the inner tube 1. It also has a sufficient volume of material so that the first welding pass of the end 23 ensures the metallurgical contact of the outer tube 2 on the outer face 11 of the inner tube 1.

[0077] To do this, the lip 25 has a thickness e less than the thickness E of the external tube 2. The thickness e of the lip 25 may in particular be a function of the thickness E of the external tube 2. Thus, the thickness e of the lip 25 may be between 5% and 50% of the thickness E of the external tube 2.

[0078] [Fig.2] shows different machining operations of the end 23 of the outer tube 2 resulting in different embodiments of the lip 25.

[0079] The lip 25 has, for example, a thickness e of between 1 mm and 8 mm. Preferably, the thickness e is between 2 mm and 4 mm.

[0080] The lip 25 is also machined so as to have a length L corresponding to the distance between the lateral face 24 and the free end of the lip 25. The length L is for example between 1 mm and 8 mm. Preferably, the length L is between 2 mm and 4 mm. The lip 25, by virtue of its length L, is thus made more accessible for melting, which reduces the risks of lack of melting at the inner corner which would appear in its absence on the lateral face 24.

[0081] The lip 25 is also machined so as to have a radius of curvature R with the lateral face 24. The radius of curvature R is for example between 1 mm and 4 mm. Preferably, the radius of curvature R is between 2 mm and 3 mm. The radius of curvature R ensures a transition between the lateral face 24 and the lip 25 which does not promote the enclosing of oxides in the molten pool 26.

[0082] The lip 25 is also machined so as to form an angle α with the lateral face 24. The angle α is for example between 90° and 120°. Preferably the angle α is between 90° and 105°.

[0083] Thus, the lip 25 can adopt a so-called J-shaped configuration in which the angle α is equal to 90°.

[0084] The lip 25 can also adopt a so-called half-V configuration in which the angle α is between 91° and 135°.

[0085] The lip 25 can also adopt a so-called triangular or trapezoidal configuration; in this embodiment, the lip 25 does not extend the internal face 21 of the external tube 2 but constitutes a triangular or trapezoidal protuberance at the end 23 of the external tube 2.

[0086] Other similar chamfer geometries (side face 24) making it possible to eliminate the recessed inner corner of the outer tube 2 will be recognized by those skilled in the art.

[0087] These different machining configurations of the end 23 of the external tube 2 make it possible in particular to optimize the subsequent welding as a function of parameters such as the thickness E of the external tube 2, the thickness of the internal tube 1, the material constituting the external tube 2 and the internal tube 1, the welding clearance, the welding technique or even the means used for the fusion of the lip 25.

[0088] [Fig. 3] represents an embodiment of the lip 25 after a possible step comprising machining and / or brushing 102 of the internal face of the lip 25 before a deformation step 103. This possible step makes it possible to machine and / or brush the internal face of the lip 25 so as to improve its wetting properties with respect to the molten bath 26.

[0089] [Fig.4] represents the inner tube 1 and the outer tube 2 machined at the end of the deformation step 103. This step consists in particular of deforming the outer tube 2 so as to reduce the distance between the lip 25 and the outer face 11 of the inner tube 1. This step 103 is commonly called the “crushing” step because the inner tube 1 is crushed onto the outer tube 2.

[0090] The distance resulting from this step corresponds to the welding clearance. It corresponds to the distance that the first welding pass must fill.

[0091] Thanks to the particular configuration of the lip 25, the bending takes place beyond the contact with the internal tube 1 and leads to the deformation of the lip 25. After the bending, the elastic rebound of the external tube 2 leads to a weld clearance of less than approximately 1 mm.

[0092] It is also possible to achieve a weld clearance equal to 0 mm by performing a sufficiently powerful crunch to deform the inner tube 1 to its elastic limit. The elastic rebound of the inner tube 1 then accompanies that of the outer tube 2 and the lip 25 remains in contact with the inner tube 1. This is illustrated by the photograph shown in [Fig. 10].

[0093] Thus, at the end of step 103, the distance between the lip 25 and the external face 11 of the internal tube 1 is between 0 mm and 2 mm or even between 0 mm and 1 mm.

[0094] The particular configuration of the end 23 of the external tube 2, due to its machining and the production of the lip 25, therefore makes it possible to better control the distance between the lip 25 and the internal tube 1 resulting from the second step 103. Greater control of this distance over the entire circumference of the internal tube 1 makes it possible to improve the reliability of the subsequent welding.

[0095] [Fig.5] represents the weld between the end 23 of the outer tube 2 and the inner tube 1 carried out during the welding step 104 of the method 100 according to the invention.

[0096] In this particular configuration of the end 23 of the outer tube 2, the objective is to melt the lip 25 so that the molten bath 26 resulting from the melting of the lip 25 wets the inner tube 1 and the outer tube 2. Since the melting of the lip 25 is not subject to variable positioning of the inner tube 1 and the outer tube 2, the quantity of energy supplied to the outer tube 2 is better controlled, which ensures a more stable thermal environment for the molten bath 26.

[0097] The risk of lack of fusion of the lower corner of the outer pipe 2 is greatly reduced because the lower corner is eliminated by construction and replaced by the end of the lip 25 which is more accessible.

[0098] The penetration of the weld after solidification is also less variable since it only depends on the viscosity properties of the liquid metal and its interaction with the inner tube 1 and the outer tube 2 by wetting.

[0099] Achieving a healthy weld thus requires less dexterity on the part of the welder and can be performed over a wider range of welding parameters, which makes welding more reliable with the method 100 according to the invention.

[0100] This remains true for automatic welding processes. The inventors have found that the adjustment range of the intensity and voltage parameters allowing a defect-free weld to be produced is greater in the case of welds with a lip 25 machined according to the method 100 according to the invention.

[0101] By way of example, on tubes of identical diameter and thickness, and with welding parameters identical at all points except for the lip-shaped machining 25 of the end 23 of the external tube 2, the welding intensity range allowing a weld deemed acceptable to be obtained has been multiplied by more than 4, going from a range of 450 ±30 A to 450 ±140 A. Thus, by using the welding method 100 according to the invention, the weld can be carried out at an intensity of between 310 A and 590 A, depending on the constraints inherent, for example, to the materials and / or to the desired speed of the assembly.

[0102] The welding step 104 may comprise the cooling concomitant with the welding of the internal face 12 of the internal tube 1. This allows a gain in productivity of the process 100 due to the control of the temperature of the welding zone which contributes to an increase in the speed of the welding and the quality thereof for the aforementioned reasons. The cooling is carried out by evaporation or conducto-convection of a cooling liquid. The cooling liquid may be selected from: water, a water + glycol mixture, a water + alcohol mixture. The person skilled in the art will be able to determine which is the most suitable liquid, and in the case of a cooling liquid consisting of a water + glycol or water + alcohol mixture, the proportions of glycol or alcohol to be considered. Water is a particularly preferred cooling liquid.Evaporation consists of the projection (or vaporization) of droplets of the coolant liquid onto the inner face 12 of the inner tube 1 which evaporate upon contact with it, the exchange of calories results in a drop in temperature of the inner tube 1, particularly in the welding zone. During cooling by conducto-convection, the heat transfer occurs by direct contact between the inner face 12 of the inner tube 1 and the coolant (conduction). The heat is then transferred by movement of the molecules during a local change in the temperature of the coolant (convection).

[0103] This cooling takes place during the greater part of the welding step 104. It can take place over the entire duration of the welding step 104. It can take place over the entire duration of the method 100 according to the invention. The duration or the initiation and / or the stopping of the cooling can vary according to the cooling mode chosen such as evaporation or conducto-convection. In the particular mode of cooling by evaporation, for example, it is understood that the spraying is only carried out from the moment when the temperature of the welding zone is sufficient to allow the evaporation of the coolant projected in the form of droplets in contact with the welding zone.

[0104] In a preferred embodiment, the cooling of the weld is carried out by spraying a mist of water droplets on the internal face 12 of the internal tube 1 promoting evaporation. Cooling by evaporation is particularly effective and rapid. Outer tube 2 comprising a lip 25

[0105] A second object of the invention relates to an external tube 2 of a pipe comprising a tube arranged in another tube comprising a lip 25 located on its lateral face 24, said lip 25 extending its internal face 21 and having a thickness e less than the thickness E of said external tube 2.

[0106] Advantageously, the lip 25 has a thickness e of between 1 mm and 8 mm, a length L of between 1 mm and 8 mm, a radius of curvature R of between 1 mm and 4 mm and forms an angle a of between 90° and 120° with the lateral face 24 of the external tube 2.

[0107] The lip 25 is in particular machined according to the different possibilities set out above and illustrated for example in [Fig.2] or in [Fig.3], in particular by varying independently any one of the dimensions e, a, L or R.

[0108] Cooling devices for the welding zone and plugs intended to close the internal tube L

[0109] The applicant has developed devices 200 specially adapted to the cooling step concomitant and optional with the welding step 104 of the end 23 of the external tube 2 on the external face 11 of the internal tube 1.

[0110] This cooling step via the internal face 12 of the internal tube 1 contributes positively to the productivity gains of the process 100. On the one hand, the cooling thus carried out on the internal face of the weld makes it possible to avoid pauses aimed at cooling the tube and controlling the temperature of the weld pool 26 to avoid the extension of the weld pool 26 and drips always associated with defects leading to rejection of the weld). In addition, controlling the temperature and keeping it below 350°C, as is made possible in particular by the cooling devices 200, according to the invention makes it possible to envisage using higher welding powers allowing an even greater saving of time with equal or even higher weld quality. On the other hand, and surprisingly, the defect rate of the welds is particularly reduced, which leads to a particularly reduced rejection or rework rate.Furthermore, the cooling of the welding zone and therefore of the tubes, in addition to the advantages in terms of productivity, allows a substantial reduction in the intensity of thermal radiation. to which the operator is exposed, which constitutes an appreciable gain for ergonomics and work.

[0111] Finally, in a completely advantageous manner, the implementation of the method 100 of the invention comprising the cooling of the weld by the internal face 12 of the internal tube 1, allows the control of the hardness and resistance properties of the welds (as illustrated by [Fig.7]). It is thus possible to determine conditions for generating optimal welds, with balanced hardness and resilience (resistance) properties.

[0112] In a particular embodiment, the cooling device 200 is a conducto-convection cooling device which comprises: • A plug 201 intended to be inserted into the internal tube 1, the plug 201 comprising: - two cheeks 202,203 adapted to close the internal tube 1, said cheeks 202,203, when said device 200 is inserted into the internal tube 1, thus defining with the wall of the internal tube 1 a compartment 204 into which the cooling liquid is introduced, - at least one axis 205 on which the cheeks 202, 203 are fixed, • a system 207 for circulating the coolant in the compartment 204.

[0113] In this device 200, one of the cheeks 202, 203 is pierced with orifices allowing circulation in the system 207 for circulating the coolant through the compartment 204 by means of a piping circuit. This circulation makes it possible to evacuate the coolant heated in the compartment 204 under the effect of the welding in operation, and to continuously supply the compartment 204 with a coolant of suitable temperature. In a particular embodiment, this piping circuit can be connected to a reservoir 206 intended to receive the coolant, as shown in [Fig. 8], the system 207 for circulating the coolant and the reservoir 206 then constituting a closed circuit.In another particular embodiment, the device 200 may comprise a source of coolant connected as an input (such as a connection to a water network) to the compartment 204 via a pipe 208, and a discharge pipe 211 for extracting the heated coolant from the compartment 204 (for example connected to a wastewater network).

[0114] Thus, the piping circuit of the circulation system 207 may comprise a pipe 208 configured to bring the cold coolant at the inlet to the compartment 204. The pipe 208 may comprise at least one valve 209 which makes it possible to control the communication between the compartment 204 and the source of the coolant (for example the reservoir 206). The pipe 208 may also comprise at least one pump 210 which makes it possible to generate the incoming flow of coolant into the compartment 204.

[0115] The piping circuit may comprise a pipe 211 configured to extract the heated coolant from the compartment 204, for example to the tank 206 or a wastewater network as mentioned previously. The pipe 211 may also comprise at least one valve and / or at least one pump to contribute to the circulation and control of the flow of coolant.

[0116] The reservoir 206 and / or the piping system 207 may also comprise cooling means configured to accelerate the drop in temperature of the coolant, for example circulating in the pipe 211 or present in the coolant reservoir 206.

[0117] In one embodiment, the cap 201 may comprise several axes 205, a central axis 205 allows the fixing of the two cheeks 202, 203, and 3 additional axes 205, 2 of which are made up of pipes pierced with holes allowing the entry of cooling liquid into the compartment 204, and another axis 205 also pierced with holes which allows the exit of the cooling liquid.

[0118] In another particular embodiment, the cooling device 200 is an evaporative cooling device which comprises: • A plug 201 intended to be inserted into the internal tube 1, the plug 201 comprising: - two cheeks 202,203 adapted to close the internal tube 1, said cheeks 202,203, when said device 200 is inserted into the internal tube 1, thus defining, with the wall of the internal tube 1, a compartment 204 into which the cooling liquid is introduced, - at least one axis 205 on which the cheeks 202, 203 are fixed, - at least one means 212 for spraying a coolant onto the reverse side of the weld, that is to say on the internal face 12 of the internal tube 1 at the level of the weld, inside the compartment 204, - at least one means 213 for extracting, outside the compartment 204, the steam formed by the cooling liquid in contact with the reverse side of the weld, during the weld, and allowing the maintenance of a pressure in the compartment 204 lower than the ambient pressure, • a system 218 fluidly connected to the steam extraction means 213 which allows the steam to be sucked out of the compartment 204 formed by the plug 201.

[0119] An embodiment of this device 200 installed in the internal tube 1 is presented [Fig.9].

[0120] Advantageously, the at least one spraying means 212 is adapted to create and project onto the internal face 12 of the internal tube 1 a cloud of droplets. Indeed, the spraying (or misting) of the coolant in the form of a cloud of droplets, by multiplying the contact surface between the coolant and said internal face 12, allows faster and more efficient cooling due to greater evaporation efficiency.

[0121] In a particular embodiment of this evaporative cooling device 200, the at least one spraying means 212 consists of at least one nozzle 217 placed at the end of a pipe 214 in which the cooling liquid circulates and which allows the dispersion and / or spraying of the cooling liquid on the internal face 12 of the internal tube 1 in contact with the reverse face of the weld. The pipe 214 is fluidically connected to a pipe 215 itself fluidically connected to a supply of cooling liquid, for example to a reservoir 206 containing the cooling liquid, as illustrated in [Fig.9]. Obviously any other supply of cooling liquid can be used, for example, in the case of using water as cooling liquid, a connection to a water network.The fluid connection between the coolant supply and the pipe 215 may comprise a pump 219 for propelling the coolant into the compartment 204 through the at least one nozzle 217. In a particular embodiment, the evaporative cooling device 200 comprises means for adding a flow of compressed air, or any other auxiliary vaporization fluid, to the incoming flow of coolant (for example in the tube 215); in fact, the addition of an auxiliary vaporization fluid can effectively contribute to the formation of the cloud or mist of coolant droplets having finer droplets and therefore ensure more efficient and faster cooling. Any neutral gas, such as nitrogen, can also constitute a suitable vaporization fluid.The professional will know how to choose an auxiliary vaporization fluid suitable for welding activities.

[0122] In a particular embodiment of the spraying means 212, illustrated in [Fig.9], several pipes 214 are fluidly connected to the pipe 215: allowing the spraying of the inner tube 1 in several places and thus even more efficient cooling of the inner tube 1. The pipes 214 can be located at several different places along the pipe 215, and / or distributed around the circumference of the pipe 215. For example, two pipes 214 can be fluidly connected to the pipe 215 at the circumference of the pipe 215, facing each other, i.e. at 180° from each other at the circumference of the pipe 215. This configuration allows the spraying of the inner wall 12 of the inner tube 1 in two places spaced 180° apart and therefore ensures a homogeneous distribution of the coolant; in an even more particular embodiment each of the two pipes 214 comprises a nozzle 217 at its end adapted to generate the cloud (or mist) of droplets near the internal face 12 of the internal tube 1.

[0123] In a particular embodiment, the at least one extraction means 213 outside the compartment 204, of the steam formed by the cooling liquid in contact with the reverse side of the weld, consists of a pipe 216 pierced with a plurality of holes 220 arranged on the pipe 216. In a particular embodiment at least a portion of the plurality of holes 220 is located at right angles to the spraying zone, through which the steam is sucked. In one embodiment the holes 220 of the plurality of holes 220 extend all along the pipe 216.In an even more particular embodiment, in the extraction means 213, the pipe 216 is fluidically connected to a system 218 which makes it possible to create a vacuum and, thus, allows the suction through the plurality of holes 220 of the cooling liquid vapor formed by the evaporation of the latter in contact with the internal face 12 of the internal tube 1 in the welding zone and, possibly, of the auxiliary vaporization fluid. In one embodiment, the system 218 making it possible to create a vacuum and allowing the suction of the vapor is such as a vacuum pump, for example located outside the device 200.

[0124] In a particular embodiment, as shown in [Fig.9], the axis 205 comprises the pipe 216 and the pipe 215, the cheeks 202, 203 being able to be fixed on the pipe 216.

[0125] The evaporation cooling device 200 may include means for measuring the pressure in the compartment 204. Controlling the pressure in the compartment 204 allows adjusting the evaporation temperature of the water and thus more finely controlling the temperature of the soldering part. Optionally, these means may control the vacuum pump 218 and / or the pump 219 to regulate the internal pressure of the compartment 204 according to a setpoint. The evaporation cooling device 200 may include means for measuring the temperature inside the compartment 204. Optionally, these means may control the vacuum pump (system 218) and / or the pump 219 to regulate the internal temperature of the compartment 204 according to a setpoint. Indeed, the temperature can also be controlled by modifying the spraying flow rate.

[0126] An additional fluid evacuation and suction system may be associated with this device 200 in order to prevent recondensation of gases and vapors generated by cooling on the sensitive elements of the welding equipment and welding materials (such as the filler metal or the welding flux).

[0127] In a preferred embodiment, as shown in [Fig.9], the axis 205 on to which the cheeks 202, 203 are fixed comprises the pipe 215 and the pipe 216 which are integral, and the cheeks 202, 203 are fixed on the pipe 216. As illustrated in [Fig. 9], in a particular embodiment, the pipe 215, which is fluidically connected to the at least one pipe 214 bringing the liquid to the at least one nozzle 217, is inserted into the pipe 216 of the extraction means 213. In an even more particular embodiment, the at least one pipe 214 passes through the pipe 216 through a hole 220 of the plurality of holes 220, preferably without closing it.

[0128] In one embodiment, the cheeks 202, 203 are fixed to the axis 205 by means of a plate 221 (not shown in [Fig.9]) comprising an articulation means such as a ball bearing, which allows the cheeks 202, 203 (which in operation of the plug 201 are integral with the internal tube 1) to rotate around the axis 205, while the nozzle 217 remains fixed in space. This advantageously allows the spraying zone to be moved to the reverse side of the weld despite the rotation of the Pipe in Pipe conduit. In one embodiment, the spraying takes place on the internal face 12 of the internal tube 1 at 90° relative to the welding location on the external face 11. In another embodiment, the spraying takes place on the internal face 12 of the internal tube 1 at right angles to the welding location on the external face 11.

[0129] Advantageously, a weight can ballast the axis 205 to help prevent it from rotating when the Pipe in Pipe conduit rotates around it. The rotation speed applied to the axis 205 is advantageously adjusted so as to allow optimal cooling of the welding zone. In one embodiment, the rotation speed applied to the axis 205 causes the at least one nozzle 217 to move in the opposite direction at the same movement speed as the welding.

[0130] The plug 201 intended to be inserted into the inner tube 1 of the pipe makes it possible to create a compartment 204 suitable for implementing the cooling step concomitant with the welding step 104 of the end 23 of the outer tube 2 on the outer face 11 of the inner tube 1. The two cheeks 202, 203 are preferably surrounded by seals which ensure a seal at the injunction of said cheeks 202, 203 with the inner face 12 of the inner tube 1. These seals are, for example, made of silicone suitable for high temperature use (such as, for example, from 100 to 200°C) and having the robustness properties suitable for the operations of the plug 201 and for industrial mass production, for example of several thousand pieces.

[0131] It is understood that the sealing of the compartment 204 formed by the plug 201 does not have to be absolute, in particular due to the native surface condition of the tubes used (for example in raw steel) which may be irregular. The compartment 204 formed by the plug 201 must be sufficiently sealed to allow the proper implementation of the cooling of the welding zone, in particular by evaporation or conducto-convection as described previously. Thus, it can be accepted that the cooling liquid cooling can bead through the plug 201, provided that this leak always allows, for example, filling of the compartment 204 with the coolant suitable for cooling by conducto-convection, or for creating and maintaining the vacuum necessary for evacuating the coolant vapors by the system 218 allowing the suction of the vapor outside the compartment 204 formed by the plug 201. A plug 201 having two cheeks 202, 203 and forming a compartment 204 when arranged in the internal tube 1 makes it possible to avoid exposing the operator to the vapor formed, possibly to the auxiliary vaporization fluid and to reduce exposure to the noise thereof. The implementation of such a plug 201 for the cooling step is therefore particularly advantageous for the operator in terms of work ergonomics.

[0132] In a less preferred embodiment, the evaporative cooling device 200 comprises: - A plug 201 intended to be inserted into the inner tube 1, the plug 201 comprising: a cheek adapted to close the inner tube 1, said cheek when said device 200 is inserted into the inner tube 1, thus defining, with the wall of the inner tube 1, a section of the inner tube 1 into which the coolant is introduced, - at least one means 212 for spraying a cooling liquid onto the reverse face of the weld, i.e. onto the internal face 12 of the internal tube 1 at the weld, inside the section of the internal tube 1 defined by the cheek.

[0133] Also, this device 200 can comprise at least one means for adding a flow of compressed air, or any other auxiliary vaporization fluid, into the flow of cooling liquid, which contributes, as mentioned above, to the formation of the cloud or mist of droplets of cooling liquid, and in particular makes it possible to optimize the cooling speed and its amplitude.

[0134] This device 200 may also comprise at least one means for extracting the steam formed by the cooling liquid in contact with the reverse side of the weld, such as a suction hood, an extractor, a fan, an extraction arm, etc.

[0135] As mentioned, cooling via the internal face 12 of the internal tube 1 allows a gain in productivity by making it possible to accelerate the welding, by avoiding pauses (or by reducing their number) and / or by allowing the use of higher welding powers associated with higher quantities of filler metal in each pass, and by reducing the number of rejects due to the greater quantity of metal deposited per unit of time). Surprisingly, the applicant has also observed that the method 100 can allow the control of the properties physical characteristics of hardness and resilience of the weld and thus to aim for balance within the weld, between these two characteristics, rather than being subject to them. Experimental tests

[0136] Temperature test

[0137] Temperature measurements were taken at the weld at each pass.

[0138] It was determined, regardless of the welding method tested, that without cooling of the internal wall of the inner tube, the temperatures in the weld could reach 400°C and vary over a large amplitude due to the application of pauses in the weld, whereas the temperature observed with a device for cooling the internal wall of the inner tube is stable throughout the welding process and on average between 150 and 200°C, once the first temperature increase passes have been carried out.

[0139] Charpy test

[0140] The Charpy test is a resilience test which consists of an impact bending test, carried out on a pendulum hammer. This test provides information on the fracture behavior of the material tested, and in particular on the energy required to propagate an initiated crack. Welding codes impose a minimum value for this test in order to be able to consider a welding procedure qualified, for example 45 J / cm2 in the case of the DNV-ST-F101 standard.

[0141] The measurements were carried out for samples for which cooling at different temperatures of the internal face of the inner tube was applied to the weld zone, and samples for which the usual pause technique was applied.

[0142] The obtained results presented [Fig.7] A show a significant increase in the weld resilience, and that the fracture remains sufficiently ductile even at -70°C, in the samples treated by cooling the inner wall of the inner tube. The average absorbed energy is well above the limit set by the DNV-ST-F101 standard. Satisfactory results according to this standard are only obtained for samples without cooling from -20°C.

[0143] Vickers hardness measurement

[0144] This measurement consists of deforming the part to be evaluated using a square-based pyramid-shaped indenter with an apex angle of 136°. The diagonal of the permanent impression after removal of the indenter is then measured and compared to a hardness scale.

[0145] The test load applied here is 9.8 daN for 10 to 15 s.

[0146] As shown in [Fig.7] B, in almost the entire weld there is an increase Vickers hardness modification in the sample for which cooling of the internal wall was carried out concomitantly with welding, in comparison with a sample for which the usual technique of pausing between passes was applied. The invention can allow the cooling parameters to be controlled to obtain an improvement in resilience and an improvement in productivity, while maintaining an acceptable increase in hardness.

Claims

Claims

1. Method (100) for welding the end (23) of a metal outer tube (2) to a metal inner tube (1), the outer tube (2) and the inner tube (1) being arranged concentrically within each other, the outer tube (2) comprising an inner face (21), an outer face (22) and at least one lateral face (24), the inner tube (1) comprising an inner face (12) and an outer face (11) and having a diameter smaller than the diameter of the outer tube (2), characterized in that said method (100) comprises: • a step of machining (101) the end (23) of the outer tube (2) so as to create on the lateral face (24) of the outer tube (2) a lip (25) extending the inner face (21) of the outer tube (2) and having a thickness (e) smaller than the thickness (E) of the outer tube (2), • a step of deformation (103) of the outer tube (2) so as to reduce the distance between the lip (25) and the outer face (11) of the inner tube (1),and • a step of welding (104) the end (23) of the outer tube (2) to the outer face (11) of the inner tube (1).,

2. Method (100) according to claim 1, characterized in that there is carried out, after the machining step (101) and before the deformation step (103), a step comprising machining and / or brushing (102) of the internal face (21) of the lip (25).

3. Method (100) according to claim 1 or 2, characterized in that the welding step (104) comprises the concomitant cooling of the weld by evaporation or conducto-convection of a cooling liquid, preferably water, brought into contact with the reverse face of the weld, that is to say with the internal face (12) of the internal tube (1) at the weld.

4. Method (100) according to any one of the preceding claims, characterized in that the lip (25) has a thickness (e) of between 1 mm and 8 mm.

5. Method (100) according to any one of the preceding claims, characterized in that the lip (25) has a length (L) of between 1 mm and 8 mm.

6. Method (100) according to any one of the preceding claims, characterized in that the lip (25) has a radius of curvature (R) of between 1 mm and 4 mm.

7. Method (100) according to any one of the preceding claims, characterized in that at the end of the machining step (101), the lip (25) forms with the lateral face (24) of the external tube (2) an angle (a) of between 90° and 120°.

8. Method (100) according to any one of the preceding claims, characterized in that at the end of the deformation step (103), the distance between the lip (25) and the external face (11) of the internal tube (1) is between 0 mm and 2 mm.

9. Method (100) according to any one of the preceding claims, characterized in that the welding step (104) is carried out by melting the lip (25) so that the molten bath (26) resulting from the melting of the lip (25) wets the outer tube (2) and the inner tube (1).

10. Metal outer tube (2) of a double-walled pipe, said outer tube (2) comprising an inner face (21), an outer face (22) and at least one lateral face (24) located at the end (23) of said outer tube (2), the end (23) being capable of being welded to a metal inner tube (1) so as to form said double-walled pipe, said inner tube (1) comprising an inner face (12) and an outer face (11) and having a diameter smaller than the diameter of the outer tube (2), characterized in that said outer tube (2) comprises a lip (25) located on its lateral face (24), extending its inner face (21) and having a thickness (e) less than the thickness (E) of the outer tube (2).

11. Outer tube (2) according to claim 10, characterized in that the lip (25) has a thickness (e) of between 1 mm and 8 mm, a length (L) of between 1 mm and 8 mm, a radius of curvature (R) of between 1 mm and 4 mm and forms an angle (a) of between 90° and 120° with the lateral face (24) of the outer tube (2).