WO2020208040A1

WO2020208040A1 - Method for manufacturing an armouring wire of a flexible fluid transport line, and armouring wire and flexible line derived from such a method

Info

Publication number: WO2020208040A1
Application number: PCT/EP2020/059930
Authority: WO
Inventors: Christophe HACQUARD; Alain Droues; Thomas Masse
Original assignee: Technip France
Priority date: 2019-04-08
Filing date: 2020-04-07
Publication date: 2020-10-15
Also published as: FR3094652A1; FR3094652B1

Abstract

The present invention relates to a method for manufacturing an armouring wire for a metallic layer for mechanically reinforcing a flexible fluid transport line intended to be immersed in a body of water. The method comprises the following steps: - providing a metal wire comprising at least a first section (32) and a second section (34), the first section (32) and the second section (34) being joined together at their ends by a weld (40), - thermally annealing the weld (40). The method comprises, before the step of thermal annealing, a step of thermally pre-treating at least a portion of the weld (40), the thermal pre-treatment step being a remelting step or an austenitisation step.

Description

A method of manufacturing an armor wire of a flexible fluid transport line and armor wire and flexible line resulting from such a process

The present invention relates to a method of manufacturing a wire armor of a metallic layer of mechanical reinforcement of a flexible fluid transport line intended to be immersed in a body of water, comprising the following steps:

- supply of a metal wire comprising at least a first section and a second section, the first section and the second section being interconnected at their ends by a weld, and

- thermal annealing of the weld.

The line is including a flexible pipe as described in normative documents published by the American Petroleum Institute (API) API 17J "Specification for Unbonded Flexible Pipe" ^4th Edition May 2014 and API RP 17B "Recommended Practice for Flexible Pipe ^»5th Edition in May 2014. The flexible pipe is preferably unbonded type (" unbonded "in English).

Flexible conduits consist of an assembly of flexible sections or a single flexible section. Flexible pipes generally have a protective outer sheath defining an interior volume and at least one impermeable inner sheath disposed inside the interior volume.

This internal sheath is, for example, a pressure sheath delimiting a passage for the circulation of a fluid. As a variant, the flexible pipe comprises an intermediate sheath disposed between the pressure sheath and the outer sheath.

The fluid circulating in the pipe is, in particular, a hydrocarbon comprising corrosive gases such as carbon dioxide and hydrogen sulfide.

Typically, mechanical reinforcement layers such as armor layers of resistance to radial compressive forces and / or to longitudinal tensile forces formed by layers of generally metallic wires are arranged in the annular space between the internal sheath and the outer sheath, to ensure good mechanical resistance to the flexible line.

In certain cases, the length of the line is very great, in particular in the case of lines adapted for great depths.

Thus, in order to reduce the manufacturing costs of the flexible line, it is known to use armor wires of shorter length and less expensive and to connect them together rather than using a single armor wire more great length and more expensive. This is the case, for example, with metallic armor made from carbon steel or stainless steel armor wires.

The wires of shorter length are joined together by arc welding caused by the passage of electric current between an electrode and the wires, also referred to by its acronym ERW for “Electrical Resistance Welding” or “electric resistance welding” . This welding method involves soldering the ends of metal wires together using a strong electric current, typically with an intensity greater than 5,000 amps, to obtain the armor wire. Primarily during the welding step, the wire ends are held in contact with each other by the application of mechanical pressure.

Generally, the resistance welding technique used is forging welding.

Of course, different resistance welding techniques can be implemented for welding long products such as flexible line metal wires, in particular by applying high pressure to the parts to be welded, such as for example the flash welding, friction welding, diffusion welding or resistance butt welding. These welding techniques are described in standard EN NF ISO 4063 published in February 201 1 by the AFNOR organization.

Armor yarns are often subjected to a corrosive environment, also called “sour environment conditions”, due to the permeation through the sheath of acid gases from the fluids transported, such as for example hydrogen sulfide (FI2S) and carbon dioxide (CO2).

The phenomenon, commonly designated by the English acronym SSC for “Sulfide Stress Craking”, or “corrosion under stress by sulfides” in French, can then lead to the degradation of the mechanical properties of the armor threads by weakening them, in particular at the level welds. For example, cracks and pitting can appear on welds, limiting the use of armor wires in a corrosive environment.

To overcome this problem for steel armor wires, it is known to proceed after the welding step to a tempering heat treatment step, as described in the document "High Strength Metallic Materials for Flexible Pipes: Specifies Environments and Corrosion Behavior »F. Dupoiron & C. Taravel - Condat (2003, January 1). NACE International. The tempering step has the effect of improving the metallurgical quality of the weld and reducing the effect of decarburization. In addition, the tempering heat treatment makes it possible to adjust the hardness as well as the mechanical resistance, such as the elastic limit of the wires, at the level of the weld. Such a method does not always give complete satisfaction depending on the media considered and the welds often exhibit, despite the tempering step, greater fragility to corrosion than the rest of the armor wire.

An object of the invention is to obtain an armor thread having improved resistance to tensile and / or pressure stresses in a corrosive atmosphere compatible with the pressure, temperature and pH conditions present in a flexible transport line. of fluid intended to be immersed in a body of water, the armor wire remaining inexpensive and easy to manufacture.

To this end, the invention relates to a method of the aforementioned type, characterized in that it comprises, before the thermal annealing, a heat pre-treatment step of at least part of the weld, the pre-heat treatment step. heat treatment being a reflow step or an austenitization step.

The process according to the invention may include one or more of the following characteristics, taken alone or in any technically possible combination:

- the heat pre-treatment step is a reflow step during which the solder is melted at least partially;

the solder is melted to an internal thickness greater than or equal to 300 μm;

- the reflow step is carried out over the entire periphery of the solder;

- the reflow step is carried out at a temperature greater than or equal to 1500 ° C;

- the reflow step has a duration of less than or equal to five minutes, and preferably greater than or equal to two minutes;

- the remelting step comprises providing a feed metal;

- The method comprises a preliminary step of welding by forging a first end of the first section with a second end of the second section, the preliminary step comprising the addition of metal between the first end and the second end, the metal being of preferably identical to the metal forming the steel wire;

- the heat pre-treatment step is devoid of the supply of a filler metal;

- the method comprises a preliminary step of welding by forging a first end of the first section with a second end of the second section, the preliminary step advantageously being devoid of any addition of material between the first end and the second end;

the heat pre-treatment step is carried out by electric arc welding, in particular by gas shielded arc welding with a metal electrode, in particular by gas shielded arc welding with a tungsten electrode; - the intensity of the electric arc current is between 30 amps and 60 amps, preferably between 40 amps and 50 amps;

- the annealing step is carried out at a temperature below the temperature of the heat pre-treatment step, preferably the annealing step being carried out at a temperature below 1,100 ° C, preferably between 400 ° C and 900 ° C;

- the annealing step has a duration greater than the duration of the pre-heat treatment step;

- the metal wire is a steel wire, preferably a carbon steel wire.

The invention also relates to an armor thread capable of being obtained by a process as described above.

The invention further relates to a flexible fluid transport line intended to be immersed in a body of water comprising at least one armor wire of the aforementioned type.

The invention will be better understood on reading the description which follows, given solely by way of example, and made with reference to the accompanying drawings, in which:

- Figure 1 is an exploded perspective view of a flexible line according to the invention comprising a plurality of layers of mechanical reinforcement armor yarns;

- Figure 2 is a perspective view of a first section of a first metal wire and a second section of a second metal wire before the forging welding step according to the invention;

- Figure 3 is a perspective view of the resistance welding and forging step of two sections of metal wires according to the invention;

- Figure 4 is a perspective view of a welded armor wire according to the invention;

- Figure 5 is a schematic longitudinal sectional view of a tack wire according to a first embodiment of the invention with exaggerated dimensions at the weld to facilitate understanding;

- Figure 6 is a schematic longitudinal sectional view of a tack wire according to a second embodiment of the invention with exaggerated dimensions at the weld to facilitate understanding;

- Figure 7 is a graphical representation of the thermal cycle applied during the manufacture of the armor wire according to one embodiment of the invention.

A flexible line 10 according to the invention is illustrated in part in Figure 1.

The flexible line 10 is intended to be immersed in a body of water (not shown) and connected at one of its ends to an installation for the exploitation of fluid, in particular of hydrocarbons. The body of water is for example a sea, a lake or an ocean. The depth of the body of water is for example between 50 m and 4000 m.

The fluid operating installation comprises a surface assembly, generally floating, and a bottom assembly which are connected by the flexible line 10.

The flexible line 10 has a central section, illustrated in part in Figure 1, and at each of the axial ends of the central section, an end cap, not shown.

The flexible line 10 extends along an axis A-A ’.

In what follows, the terms "exterior" and "interior" are generally understood to be understood radially with respect to the axis A-A 'of the flexible line 10, the term "exterior" being understood as being relatively more distant. radially to the A-A 'axis and the term "interior" being understood as relatively closer radially closer to the A-A' axis of the flexible line 10.

As illustrated in Figure 1, the flexible line 10 is here a flexible pipe which delimits a plurality of concentric layers around the axis A-A ', which extend continuously along the flexible line 10 to the ends of this one.

In particular, the flexible line 10 comprises a tubular internal sheath 12, a pressure vault 14 and at least one layer of tensile armor 16, 17. Advantageously and depending on the desired use, the line 10 further comprises an internal carcass 20 and an outer sheath 22.

The internal sheath 12 is intended to contain in a sealed manner the fluid transported in the flexible line 10.

The carcass 20, when present, is formed of a profiled metal strip, wound in a spiral. The turns of the strip are advantageously stapled to each other, which takes up the radial crushing forces.

The outer sheath 22 is located outside of the inner sheath 12.

The outer sheath 22 defines an internal volume 23 in which the inner sheath 12 and the mechanical reinforcement layers such as the carcass 20, the pressure vault 14 and at least one tensile armor layer 16, 17 are located.

The outer sheath 22 defines with the inner sheath 12 an annular space 24. The annular space 24 is defined in the interior volume 23.

The outer sheath 22 is waterproof. The outer sheath 22 is configured to prevent the penetration of liquid from the outside of the flexible pipe 10 to the interior volume 23 and to confine the liquid present in the annular space 24.

The pressure vault 14 is located in the annular space 24, outside the internal sheath 12. The pressure vault 14 is configured to take up the forces linked to the pressure prevailing inside the internal sheath 12.

The pressure vault 14 is advantageously formed of a profiled metal wire wound helically around the internal sheath 12.

The winding is short pitch, that is to say that the helix angle formed by the profiled wire with respect to the axis A-A 'of the flexible line 10 is of absolute value close to 90 ° , typically between 75 ° and 90 °.

The profiled wire 25 preferably has a Z-shaped geometry. The Z-shaped geometry makes it possible to improve the general mechanical strength and to reduce the mass of the flexible pipe 10.

Alternatively, the profiled wire 25 has a T, U, K, X or I shaped geometry.

As a variant, the flexible line 10 comprises an additional metallic reinforcing layer or hoop 26 disposed outside the pressure vault 14.

The hoop 26, when present, is formed by a spiral winding of at least one wire, advantageously of rectangular cross section around the pressure vault 14. The winding of the at least one wire is at a short pitch around the hoop. the axis A-A 'of the flexible line 10, that is to say with a helix angle of absolute value close to 90 °, typically between 75 ° and 90 °.

Each tensile armor layer 16, 17 is located in the annular space 24, outside of the pressure vault 14.

In the example shown in Figure 1, the flexible pipe 10 has at least one pair of tensile armor layers 16, 17.

Each pair has a first layer of tensile armor 16 applied to the pressure vault 14, to the hoop 26, to the sheath 12 or to another pair of tensile armor layers 16, 17, and a second layer of tensile armor 17, arranged around the first layer of tensile armor 16.

Each tensile armor layer 16, 17 comprises at least one longitudinal armor element 28 wound with a long pitch around the axis A-A 'of the flexible pipe 10. The helix value is less than 60 °, and is typically between 18 ° and 60 °.

In the example shown in Figure 1, the absolute value of the helix angle of each layer of tensile armor 16, 17 is greater than 45 °, and is in particular between 50 ° and 60 °, and is approximately equal to 55 °.

The armor elements 28 of a first tensile armor layer 16 are wound generally at an opposite angle to the armor elements 28 of a second tensile armor layer 17. Thus, if the angle winding armor elements 28 of the first tensile armor layer 16 is equal to + a, a being between 18 ° and 60 °, the winding angle of the armor elements 28 of the second armor layer tensile strength 17 disposed in contact with the first tensile armor layer 16 is, for example - a, with a between 18 ° and 60 °.

Of course, other polymeric, metallic or composite layers such as a retaining band or an anti-wear band can be arranged within the structure of the flexible line 10, in the interior volume 23.

They are for example arranged between the internal sheath 12 and the pressure vault 14 or between the pressure vault and the tensile armor layers 16,17 or between the first tensile armor layer 16 and the second layer of tensile armor 17 or even between the second layer of tensile armor 17 and the outer sheath 22.

The armor elements 28 are for example formed by at least one armor wire 30.

In addition, the profiled elements 25 forming the pressure vault 14 and / or the wires forming the hoop 26 are for example formed by at least one armor wire 30.

A weave wire 30 according to a first embodiment is shown schematically in Figure 5.

The armor wire 30 comprises at least a first section 32 of a first metal wire and a second section 34 of a second metal wire shown schematically in Figures 2 to 5.

The first section 32 has the shape of a prism extending along a longitudinal axis B-B ’.

In the illustrated embodiment, the first section 32 has the shape of a rectangular parallelepiped extending along the longitudinal axis B-B ’.

More generally, the first section 32 has a cross section S1 perpendicular to the longitudinal axis B-B ’of polygonal shape, in particular square or rectangle.

As a variant, the first section has a cross section S1 defined by a closed curve, for example an elliptical or circular cross section S1.

The cross section S1 has an area of between 10 mm ² and 500 mm ² .

The first section 32 has a length I. The length I of the section 32 is the dimension of said section 32 along the longitudinal axis B-B '.

Advantageously, the length I is between 10 m and 15,000 m.

The first section 32 has a first end 36.

The second section 34 has a shape similar to that of the first section 32, here the shape of a rectangular parallelepiped extending along the longitudinal axis B-B '. The second section 34 has a length G. The length G of the section 34 is the dimension of said section 34 along the longitudinal axis B-B '.

Advantageously, the length G is between 10 m and 15,000 m.

In this example, the length G of the second section 34 is equal to the length I of the first section 32.

The second section 34 has a cross section S2 perpendicular to the longitudinal axis B-B ’.

The cross section S2 of the second section 34 is substantially identical to the cross section S1 of the first section 32.

In the example shown in Figure 2, the first section 32 and the second section 34 are identical.

The second section 34 has a second end 38.

The first section 32 and the second section 34 are interconnected at their ends 36, 38 by a weld 40 obtained after a forging welding operation.

According to a particular embodiment of the invention, during welding, the ends 36, 38 of the first and second sections 32, 34 of the metal wires are melted to form the weld 40.

The weld 40 here consists of a mixture of the materials forming the first section 32 and the second section 34, without the addition of an external material not coming from the first section 32 and from the second section 34.

A more or less extensive area on either side of the weld 40 is also thermally affected during the welding operation. This zone is called the “heat affected zone” (HAZ). This zone is the site of thermal heating by conduction in which there is local modification of the microstructure and of the metallurgical state of the sections 32, 34 of the metal wires.

The heat affected zone has a width L. The width L is the dimension of the HAZ along the B-B ’axis.

The width L is for example between 0.1 mm and 20 mm, preferably between 5 mm and 10 mm.

According to a second embodiment illustrated in FIG. 6, the weld 40 comprises a bead 42 formed by the expulsion of metallic material at the end of the forging welding operation between the two ends 36, 38 of the first and second sections 32 , 34 metal wires.

The bead 42 corresponds to the area where the metallic material of the ends 36, 38 has melted during welding. This area is called the “melted area”. The bead 42, also called burr, has a height h. The height h is the dimension of the bead 42 in a radial direction of the metal wire. In this example, the height h of the bead 42 is between 0.1 mm and 20 mm.

The bead 42 also has a width L2. The width L2 is the dimension of the bead along the B-B ’axis. The width L2 of the bead is strictly less than the width L of the HAZ. In this example, the width L2 of the bead is between 0.1 mm and 5 mm.

According to the particular embodiment, the zone defined by the melted zone and the HAZ has a width L ’. The width L 'is the dimension of the molten zone and the heated HAZ along the B-B axis.

The width L ’is for example between 0.1 mm and 20 mm.

In this example, the armor wire 30 is made of at least one metallic material.

Advantageously, the armor wire 30 is a steel wire. The armor wire 30 is for example a stainless steel wire, commonly referred to as stainless steel, or a carbon steel wire.

By "carbon steel" is understood a steel whose main alloying component is carbon. The carbon content of carbon steel is between 0.12% and 2.0% of the total mass of the alloy.

Preferably, the steel is a low alloy steel, that is to say that the total content of each alloying element, such as for example chromium, manganese, nickel, cobalt, aluminum or molybdenum, is less than 5%.

The armor wire 30 according to the invention exhibits resistance to corrosion and to mechanical forces of pressure and traction which is substantially constant over its entire length. The armor wire 30 does not have a zone of weakness at the weld 40.

The general properties of the weld 40 are improved. A method of manufacturing the armor wire 30 will now be described.

Initially, a first section 32 and a second section 34 of metal wire are manufactured. The manufacture of sections 32, 34 includes a rolling step.

The microstructures of sections 32, 34, in particular the metal grains, are oriented along flow lines parallel to a longitudinal axis B-B '. The sections further include inclusions stretched and / or oriented in the direction B-B ’.

The method of manufacturing the armor wire 30 comprises a preliminary step of welding a first end 36 of the first section 32 of a first metal wire with a second end 38 of the second section 34 of a second metal wire.

During this step, the sections 32, 34 are interconnected by a resistance welding step. In this example, the sections 32, 34 are preferably interconnected by a forging welding step, as illustrated in FIG. 3.

Forging welding is a thermoelectric process for generating heat at the ends of the wire sections to be assembled, associated with a docking force and material expulsion.

During the docking phase, the first end 36 of the first section 32 is brought into contact with the second end 38 of the second section 34, so that the cross section S1 of the first end 36 completely covers the cross section S2 of the second end 38.

In this example, the forging welding step is devoid of any addition of material between the first end 36 and the second end 38.

A strong electric current is applied to the sections 32, 34 and passes through said sections 32, 34 by generating heat at the level of the contact surface between the two ends 36, 38.

In this example, the contact surface is subjected to a temperature between 1000 ° C and 1500 ° C, as illustrated by curve 1 of FIG. 7. For example, the contact surface is subjected to a temperature equal to 1250 ° vs.

Simultaneously with heating at the level of the contact surface between the two ends 36, 38, a mechanical pressure P is exerted along the axis B-B 'on each section 32, 34 so that the first section 32 and the second section 34 exert opposing compressive forces on each other. For example, the pressure P is between 50 MPa and 600 MPa in a direction normal to the cross section S1, S2 of the sections 32, 34 to be welded. A plastic deformation occurs at the level of the contact surface of the ends 36, 38 of the sections 32, 34. The local melting of the metal occurs at the level of said contact surface.

The metal then recrystallizes by creating a weld 40, thus making it possible to metallurgically bond the sections 32, 34 together.

According to the second embodiment, a bead 42 is formed by expelling material towards the periphery of the wire during the welding step, due to the mechanical pressure P exerted while the contact surface of the ends 36, 38 of the sections 32, 34 is melted. Exogenous oxides possibly formed at high temperature during docking are then expelled.

At weld 40, the flux lines are re-oriented parallel to the contact surface and perpendicular to the longitudinal axis B-B '.

The inclusions present in the sections 32, 34 change direction and accumulate at the level of the contact surface. The re-orientation of the flux lines and the accumulation of inclusions at the weld 40 weaken the metal wires when they are in a corrosive environment. This phenomenon is reinforced by a decarburization which occurs to a greater or lesser magnitude at the level of the weld 40. The decarburization at the level of the weld 40 also creates an imbalance between the microstructures of the weld 40 and that of the ZAT. This leads to phenomena of galvanic coupling between the microstructures then reducing the corrosion resistance of the weld 40. Dissolutions around the inclusions which emerge at the surface can also be observed.

Following the welding step, the first section 32 and the second section 34 are integral with one another. A metal wire comprising two sections 32, 34 interconnected at their ends 36, 38 by a weld 40 is thus obtained.

Then, the metal wire is subjected to a heat pre-treatment step of at least part of the weld 40.

According to one embodiment, the heat pre-treatment step is a reflow step.

The purpose of the reflow step is to break the flow lines and redistribute the segregations and inclusions on the surface of the wire. The reflow step is carried out on a welding station different from that used for the step of welding by forging sections 32, 34 together. The sequence of the two steps is quick and easy to implement at the industrial level.

When the reflow step is carried out without the addition of external material, the welding station is for example a heating station equipped with a torch capable of creating an electric arc such as those of the TIG arc welding station type (TIG being l (acronym for "Tungsten Inert Gas"), plasma arc welding, laser arc welding, electron beam arc welding, etc.

Other heating means can be provided such as for example a high frequency induction heating station for heating the surface of the wire, or other techniques for providing high energy over a short period of time, such as a laser.

The reflow step is thus carried out immediately after the soldering step. For example, less than 5 minutes will elapse between the soldering step and the reflow step.

Preferably, the reflow step is performed in position. It is understood by this that the upper face of the wire is heated, then the wire is turned and the side which is above as a result is heated in turn. This technique prevents material from flowing onto the floor. The reflow step is carried out over the entire periphery of the solder 40 using any one of the soldering stations or heat treatment mentioned above.

Preferably, the reflow step is carried out by electric resistance heating.

The presence of the bead 42 facilitates the positioning for the passage of the electric current at the level of the weld 40, by point effect, and thus offers great precision during this step.

According to one embodiment, the reflow step is carried out by gas shielded arc welding with a non-fusible electrode.

The electrode is, for example, a tungsten electrode. Welding is then qualified as Tungsten-Inert Gas welding, identified by number 41 in standard NF EN ISO 4063 and more commonly called TIG welding, TIG being the acronym for "Tungsten Inert Gas".

An electric arc is established between the end of the electrode and the weld 40, under the protection of an inert gas.

The inert gas is, for example, argon, helium or an argon-helium mixture.

The intensity of the electric arc current is typically between 30 amps and 60 amps, preferably between 40 amps and 50 amps.

The remelting step is carried out at a temperature greater than or equal to 1500 ° C, and less than or equal to 3000 ° C, as illustrated by curve 2 in FIG. 7. Preferably, the remelting step is carried out at a temperature. temperature between 1500 ° C and 1700 ° C. For example, the reflow step is carried out at a temperature of 1600 ° C.

The reflow step has a duration of several minutes, preferably greater than or equal to two minutes and less than or equal to five minutes.

As a variant, the reflow step is carried out by means of an energy flash and has a duration of a few seconds, for example a duration of between 10 and 30 seconds.

During the reflow step, solder 40 is at least partially melted.

It is understood by “melted at least partially” that the weld 40 is melted on a remelted zone 44 of a thickness e normal to the longitudinal axis B-B ', the thickness e being less than or equal to the sum of the height h of the bead 42 and of the maximum transverse half-dimension r of the metal wire. Said half-dimension r corresponds to the radius of the wire when the latter has a circular section.

The remelted zone 44 has a thickness e greater than the height h of the bead 42. The thickness e of the remelted zone 44 corresponds to the sum of the height h of the bead 42 and an internal thickness e 'of the remelted zone 44 . Preferably, the internal thickness e ′ is greater than or equal to 300 μm.

The remelted zone 44 has a length L ”greater than L2 and potentially greater than L.

According to a preferred embodiment of the invention, the reflow step is devoid of the provision of a filler metal. When the weld 40 includes a bead 42, said bead 42 provides sufficient material to avoid a reduction in the section of the armor wire 30.

The reflow step changes the microstructure of the wire at solder 40 and HAZ. Following the reflow step, the flux lines at the solder are re-aligned so that there is no more preferential direction of the microstructure.

In addition, the reflow step causes the dispersion of the inclusions present at the solder 40.

Then, the metal wire is subjected to a heat treatment step. Advantageously, the heat treatment step comprises thermal annealing of the weld 40.

The annealing step makes it possible to homogenize the microstructure of the metal wire and thereby adjust the mechanical properties and the hardness of the metal wire.

The annealing step is performed at a temperature lower than the temperature of the remelting step. Preferably, the annealing step is carried out at a temperature below 1,100 ° C, preferably between 400 ° C and 900 ° C, as illustrated by curve 3 in FIG. 7.

The annealing step has a longer duration than the duration of the reflow step.

The annealing step has a duration of between a few seconds and several minutes, preferably between 10 seconds and 5 minutes.

Preferably, the annealing step comprises controlled cooling.

Alternatively, the reflow step is performed by a technique selected from the group consisting of plasma welding, hybrid laser arc welding, electron beam welding and induction heating techniques.

According to another embodiment, the reflow step is carried out with a supply of metal. The filler metal is preferably of composition close to that of the metal of the metal wire, for example the filler metal is identical to the metal of the metal wire. When the reflow step is carried out with the addition of fusible external material, the welding station is for example a welding station of the arc welding type with a coated electrode or of the arc welding type with a fusible wire electrode. The reflow step is carried out for example by arc welding with a coated electrode or by MIG-MAG welding, the acronyms MIG and MAG meaning respectively "Metal inert gas" for metal-inert gas welding and "Metal active gas. »For active metal-gas welding.

As a variant, the armor wire 30 comprises at least three sections connected two by two at their ends by welds 40.

According to this embodiment, the different sections are connected together by welding. Then, the wire thus obtained is then subjected to a remelting step and then to a thermal annealing step.

The wire thus produced is then suitable for being wound around a sheath 12 as described above, or a pressure vault 14, a hoop 26 or even an anti-wear strip (not visible on the Figures), with a long pitch to form an armor wire 30 of at least one armor layer 16, 17.

Advantageously, at least one sheath 22 is formed around the armor layer 16, 17 to finalize the manufacture of the flexible line 10.

According to another embodiment, the heat pre-treatment step is an austenitization step.

Austenitization allows a change in the crystallographic structure of the steel by heating, the iron a being transformed into iron g.

The austenitization step is carried out over the entire periphery of the weld 40 using any of the welding or heat treatment stations mentioned above. The austenitization is carried out over a length greater than L2 and potentially greater than L and over a thickness normal to the longitudinal axis B-B ', the thickness being less than or equal to the sum of the height h of the bead 42 and of the maximum transverse half-dimension r of the wire. Said half-dimension r corresponds to the radius of the wire when the latter has a circular section. Advantageously, the thickness subjected to the austenitization phenomenon is less than or equal to 1 mm. It is said that the austenitization is carried out with the skin of the weld 40.

The austenitization step, which is called deep austenitization, is carried out at a temperature between 1000 ° C and 1400 ° C.

The austenitization step is in this case carried out by a technique making it possible to provide high energy on small thicknesses at the surface over a short time, such as with micro laser or micro plasma welding equipment derived from laser welding. bow.

As a variant, the austenitization step is carried out by high frequency induction welding. In this case, the duration of the treatment is preferably less than 1 minute. The austenitization step modifies the microstructure of the metal wire at the weld 40. Following the austenitization step, new grains are created by nucleation. Said grains having a larger size than the previous grains, the lines of flux at the weld 40 are re-aligned so that there is no longer a preferential direction of the microstructure. Thanks to cooling control, the martensitic microstructure potentially present after the heat pre-treatment step is also removed.

The heat pre-treatment step modifies the microstructure of the metal wire at the weld 40. Following the realignment of the flux lines at the weld, the microstructure no longer has a preferential direction. In addition, in the case where the heat pre-treatment step is a reflow step, the inclusions present at the weld 40 are dispersed.

The armor wire 30 thus obtained exhibits substantially constant corrosion resistance over its entire length. The resistance of the armor wire 30 to corrosion in the presence of combined mechanical forces (SSC) is further improved compared to a welded metal wire which has undergone a simple annealing heat treatment.

As a variant, the method of manufacturing the armor wire 30 further comprises a finishing step. The finishing step is to improve the surface finish of the heat-treated area, by removing any imperfections remaining on the surface of the armor wire 30.

The finishing step is performed between the heat pre-treatment step and the annealing step, or after the annealing step. For example, at the end of the austenitization step, the finishing step removes the bead 42.

The finishing step is carried out manually or by means of a mechanical polishing tool, such as a sander equipped with a flap disc fitted with abrasive paper.

Claims

1. A method of manufacturing an armor wire (30) of a metal layer for mechanical reinforcement of a flexible fluid transport line (10) intended to be immersed in a body of water, comprising the following steps :

- supply of a metal wire comprising at least a first section (32) and a second section (34), the first section (32) and the second section (34) being interconnected at their ends (36) by a weld (40),

- thermal annealing of the weld (40),

characterized in that it comprises, before thermal annealing:

- a heat pre-treatment step of at least part of the weld (40), the heat pre-treatment step being a reflow step or an austenitization step.

2. The manufacturing method according to claim 1, wherein the heat pre-treatment step is a remelting step during which the solder (40) is at least partially melted.

3. The manufacturing method according to claim 2, wherein the solder (40) is melted to an internal thickness (e ’) greater than or equal to 300 μm.

4. The manufacturing method according to any one of claims 2 or 3, wherein the reflow step is performed over the entire periphery of the solder (40).

5. The manufacturing method according to any one of claims 2 to 4, wherein the reflow step is carried out at a temperature greater than or equal to 1500 ° C.

6. The manufacturing method according to any one of claims 2 to 5, wherein the reflow step has a duration of less than or equal to five minutes, and preferably greater than or equal to two minutes.

7. The manufacturing method according to any one of claims 2 to 6, wherein the reflow step comprises providing a filler metal.

8. The manufacturing method according to claim 7, comprising a preliminary step of forging welding of a first end (36) of the first section (32) with a second end (38) of the second section (34), the preliminary step comprising the addition of metal between the first end (32) and the second end (34), the metal preferably being identical to the metal forming the steel wire.

9. The manufacturing method according to any one of claims 1 to 6, wherein the heat pre-treatment step is devoid of the provision of a filler metal.

10. The manufacturing method according to claim 9, comprising a preliminary step of welding by forging a first end (36) of the first section (32) with a second end (38) of the second section (34), the preliminary step being advantageously devoid of addition of material between the first end (32) and the second end (34).

11. The manufacturing method according to any one of the preceding claims, wherein the heat pre-treatment step is carried out by electric arc welding, in particular by gas shielded arc welding with a metal electrode, in particular by gas shielded arc welding with a tungsten electrode.

12. The manufacturing method according to claim 1 1, wherein the intensity of the electric arc current is between 30 amps and 60 amps, preferably between 40 amps and 50 amps.

13. Manufacturing process according to any one of the preceding claims, in which the annealing step is carried out at a temperature below the temperature of the heat pre-treatment step, preferably the annealing step being carried out at a temperature below 1100 ° C, preferably between 400 ° C and 900 ° C.

14. The manufacturing method according to any one of the preceding claims, wherein the annealing step has a duration greater than the duration of the heat pre-treatment step.

15. The manufacturing method according to any one of the preceding claims, wherein the metal wire is a steel wire, preferably a carbon steel wire.

16. Armor wire (30) capable of being manufactured according to any one of the preceding claims.

17. A flexible fluid transport line (10) intended to be immersed in a body of water comprising at least one armor wire (30) according to claim 16.