EP0813613B1 - Method for making steel wires and shaped wires, and use thereof in flexible ducts - Google Patents

Abstract

PCT No. PCT/FR96/00363 Sec. 371 Date Nov. 4, 1997 Sec. 102(e) Date Nov. 4, 1997 PCT Filed Mar. 8, 1996 PCT Pub. No. WO96/28575 PCT Pub. Date Sep. 19, 1996A method for making steel wires, wherein an elongate shaped wire is produced by rolling or drawing steel consisting of 0.05-0.5% C, 0.4-1.5% Mn, 0-2.5% Cr, 0.1-0.6% Si, 0-1% Mo, no more than 0.25% Ni, and no more than 0.02% S and P, and a first heat treatment is performed on the shaped wire, including at least one step of quenching under predetermined conditions to achieve an HRC hardness of at least 32, a predominately martensitic and bainitic steel structure and a small amount of ferrite. A shaped wire and a flexible tube for conveying an H2S-containing effluent are disclosed.

Description

The present invention relates to elongated elements of great length, such as steel wires to reinforce flexible pipes intended for the transport of effluent under pressure. The invention relates to a method of manufacturing these reinforcing threads, the wires obtained by the process and the flexible pipes which include such wires reinforcement in their structure.

We know applications in which we use for the transport of fluids, in particular hydrocarbons, flexible pipes reinforced by sheets of armor made up of steel wires. In some cases, these lines are placed in conditions in which they are subjected to an atmosphere corrosive, for example in the presence of acidic fluids containing sulfurized products. In addition, in the case where such flexible pipes are arranged in large water depths, they must, more and more, present performances very high mechanical strength in terms of resistance to internal pressure, to load axial, to the external pressure following the great depth of immersion water.

In flexible pipes, sealing is provided by one or more polymer sheaths, mechanical resistance to internal and external pressure and to external mechanical stress, is produced by one or more layers of armor constituted by steel wires or profiles having a specific profile.

Generally, the flexible tube comprises at least one of the following armor plies: a carcass of resistance to external pressure in wires or profiles placed at an angle close to 90 ° relative to the axis. a sheet of resistance to internal pressure (called vault) laid at an angle greater than 55 °, the elongated elements of the carcass and the vault preferably being staplable wires, and at least one layer of armor of tensile strength installed at an angle of less than 55 °. According to another mode, the vault and the tensile armor are replaced by two layers of symmetrical armor reinforced at an angle of about 55 °, or by two pairs of layers reinforced at 55 °, or by a set of at least at least two plies, the winding angle of at least one ply being less than 55 ° and the winding angle of at least one other ply being greater than 55 °. The steel of the wires making up the armor must be chosen in such a way that these wires, given their cross-section, provide the mechanical resistance necessary in service, at the same time as they resist corrosion, in particular in certain cases in the presence of H ₂ S.

These steel wires, generally shaped by hot rolling or drawing or cold, can have profiles, that is to say straight sections, various: substantially flat or flat, U-shaped, T-shaped, Z-shaped, with or without hooking means on a neighboring, or circular, wire.

• des soufflures sous la surface de l'acier ("Hydrogen Blistering", on parle alors de "Blister"), ou des fissurations internes (dites en gradin), pouvant apparaítre en l'absence de contraintes et pouvant être aggravées en présence de contraintes résiduelles,
• une fragilisation résultant en ruptures différées dans le cas où l'acier est mis sous contraintes (corrosion sous contraintes par l'hydrogène).

In the case of use in the presence of acid gas, essentially H ₂ S and CO ₂ , in addition to generalized corrosion, there may be problems associated with the penetration of hydrogen into the steel. Indeed, H ₂ S or rather the ion HS ^- ) is an inhibitor of recombination of the hydrogen atoms produced by reduction of the protons on the surface of the steel. These hydrogen atoms are introduced inside the metal and recombine there, thus being at the origin of two types of deterioration:

• blowing under the surface of the steel ("Hydrogen Blistering", we then speak of "Blister"), or internal cracks (so-called tiered), which can appear in the absence of stresses and can be aggravated in the presence of stresses residual,
• embrittlement resulting in deferred fractures in the event that the steel is placed under stress (corrosion under stress by hydrogen).

NACE standards have been provided to assess the suitability of a steel structural element to be used in the presence of H ₂ S. The steels must undergo a test on a representative sample, under stress in H ₂ S medium with a pH 2.8 to 3.4 (NACE Test Method TM 0177 relating to stress cracking effects, commonly known as "Sulfide Stress Corrosion Cracking" or SSCC), to be considered as usable in the manufacture of metallic structures which must resist the effects of corrosion under stress in the presence of H ₂ S.

Another NACE standard (TM 0284) relates to hydrogen-induced cracking effects, commonly known as "Hydrogen Induced Cracking" or HIC. The test procedure recommended by the above standard consists in exposing samples, without voltage, in a seawater solution saturated with H ₂ S, at ambient temperature and pressure, at a pH between 4, 8 and 5.4. The procedure plans to then carry out metallographic examinations to quantify the cracking of the samples, or to note the absence of cracking. An additional criterion for evaluating the damage to the samples may be the determination of the mechanical characteristics after the HIC test. This criterion does not appear in the NACE TM 0284 standard. Applicants were thus led to define an additional evaluation method consisting in carrying out tensile tests on the samples to determine the mechanical characteristics after HIC and to compare these results with the mechanical characteristics. before HIC. This method has proved to be particularly advantageous in the case of the armouring threads targeted by the present invention, these threads being subjected to a regime of longitudinal uniaxial stresses. by comparison with the wall of steel tubes. tubes which constitute the main application of NACE standards. Another complementary method is to compare the loss of Z neck loss (%) before and after the HIC test. the difference should be relatively small and preferably less than 30%.

The conditions of exploitation of underwater deposits having become more and more severe, it appeared recently that the qualification of the materials for their use in the presence of H ₂ S must aim at the case of more acid medium, the pH being able to fall up to about 3. We were thus led to specify that. in some cases. the tests according to standard NACE TM 0284 must be carried out in a saturated solution of H ₂ S having a pH, for example of 3 or 2.8, similar to the solution defined by standard NACE TM 0177, and no longer with a pH at least 4.8.

According to currently known techniques. the armouring wires of the hoses, in particular for the transport of fluids comprising H ₂ S, are produced with mild or semi-hard carbon-manganese steels (0.15 to 0.50% carbon) having a ferrite-perlite structure, to which, after cold forming of the wire rod, an appropriate annealing heat treatment is applied to bring the hardness to the accepted value, if necessary.

The NACE 0175 standard defines that such carbon-manganese steels are compatible with an H ₂ S medium if they have a hardness less than or equal to 22 HRC. It has thus been verified that armor wires as described above, made of carbon-manganese steel and having a ferrite-pearlite structure, can be produced by cold forming followed by annealing so as to satisfy the traditional NACE criteria. We know a process described in document FR-A-2661194 for obtaining a steel of hardness greater than 22 HRC compatible with H ₂ S according to NACE TM 0177 and TM 0284 standards, the solution used for tests according to TM 0284 having a pH between 4.8 and 5.4.

However, it has been found that carbon steels with a ferrite-perlite structure are unable to withstand the HIC tests satisfactorily according to the procedure of standard TM 0284 when these tests are carried out in a more acid medium. for example with a pH of around 3 corresponding to the conditions now encountered in certain cases of exploitation of petroleum deposits. These results unacceptable have been obtained even in the event that the final heat treatment is more pushed so as to obtain an HRC hardness of less than 22 HRC.

There is therefore a need for the production of armouring wires for hoses, a steel which, on the one hand, is compatible with H ₂ S under the new conditions described above and which, on the other hand, or of a composition and a relatively conventional and unsophisticated production procedure with the aim of keeping manufacturing costs sufficiently low.

Furthermore, the steels and the production methods used to make the armouring wires for the hoses must be such that the forming wire can be produced in very large continuous lengths, of the order of several hundred meters or several kilometers. The wire thus manufactured is wound on spools for its subsequent use to produce the armor plies of the hoses. In addition, and despite the very large unit length of the wires thus produced, it is important that they can be connected by welding during the winding operation during the manufacture of the hose. In order to reconstitute in the weld zone, the specified properties of the steel, in particular the resistance to H ₂ S, a heat treatment is to be provided after welding. But it is important, in order not to excessively overload the manufacturing costs, that this heat treatment after welding makes it possible to achieve the goal set in a sufficiently short time, a few minutes if possible. preferably less than 30 minutes.

In the case where compatibility with H ₂ S is not required (production of "sweet crude"), carbon steels in the raw cold-forming state are also commonly used, also having a ferrite-perlite structure, but having significantly higher values of mechanical strength and hardness. However, it has been observed that the increase in mechanical strength beyond certain limits, leads for such steels to have insufficient ductility taking into account the preformation and reinforcement operations which must be carried out with the armor wire. .

The object of the present invention is to describe a process for obtaining an elongated element of great length intended for the manufacture of flexible tube, the elongated element having optimized mechanical characteristics as well as, in an application according to the invention , good resistance to H ₂ S.

• on fabrique un fil de forme de grande longueur par laminage ou tréfilage à partir d'un acier comportant les éléments suivants :
  • de 0,05% à 0,8% de C,
  • de 0,4% à 1,5% de Mn, de préférence moins de 1% de Mn,
  • de 0 à 2,5% de Cr, entre 0,25 et 1,3%,
  • de 0,1% à 0,6% de Si,
  • de 0 à 1% de Mo,
  • au plus 0,50% de Ni,
  • au plus 0.02% de S et de P, et de préférence S inférieur ou égal à 0,005%,
  • avec éventuellement, en complément de l'action du Si, un calmage avec de l'aluminium ou du silico-calcium,
• on effectue un traitement thermique comprenant au moins une opération de trempe du fil de forme dans des conditions déterminées pour obtenir une dureté HRC supérieure ou égale à 32 et de préférence supérieure ou égale à 35, et pouvant avantageusement atteindre ou dépasser 50,
• la structure de l'acier du fil de forme ainsi obtenu étant à prédominance martensitique-bainitique.

The present invention relates to a method for manufacturing a steel form wire, this wire being very long and capable of being used as the armor wire of a hose. The method is defined in claim 1 and comprises the following steps:

• a long form wire is manufactured by rolling or drawing from a steel comprising the following elements:
  • from 0.05% to 0.8% of C,
  • from 0.4% to 1.5% of Mn, preferably less than 1% of Mn,
  • from 0 to 2.5% of Cr, between 0.25 and 1.3%,
  • from 0.1% to 0.6% of Si,
  • from 0 to 1% of Mo,
  • at most 0.50% of Ni,
  • at most 0.02% of S and P, and preferably S less than or equal to 0.005%,
  • with possibly, in addition to the action of Si, a calming with aluminum or silico-calcium,
• a heat treatment is carried out comprising at least one operation of quenching the shaped wire under determined conditions to obtain an HRC hardness greater than or equal to 32 and preferably greater than or equal to 35, and which can advantageously reach or exceed 50,
• the steel structure of the shaped wire thus obtained being predominantly martensitic-bainitic.

The amount of ferrite will preferably be low, in particular less or equal to 10%, and advantageously less than or equal to 1%.

According to a variant of the present invention, the carbon content C can be greater than or equal to 0.08%, preferably greater than or equal to 0.12% and the steel may have at most 0.4 Si.

The forming wire can be produced by cold forming, in particular by rolling or drawing from a wire rod. The wire rod could be hot rolled with controlled cooling, for example of the STELMOR type, so as to drive at values of Rm lower than 850 MPa. In the case of wire rods having a Rm value greater than 850 MPa, it may be advantageous to subject them to a annealed to soften the shade at Rm <850 MPa.

The shaped wire can also be obtained directly by hot rolling. In in this case, the tensile strength Rm of the wire will preferably also be less than 850 MPa, either after rolling or after a softening annealing in order to facilitate the operations of handling the elongated element, before or during the operations of quenching.

The process thus normally includes a preliminary forming step to hot, either from a wire rod subsequently transformed into a form wire by forming cold, either directly from the form wire. In both cases, the wire thus formed hot has a predominantly ferritic-pearlitic structure, but may include hard areas, such as martensite. Preferably. before any operation subsequent cold forming and / or quenching, the steel must have a limit of rupture Rm less than 850 MPa, this property being obtainable. is directly after hot forming, either through an annealing-softening treatment.

Preferably, the quenching operation can be carried out continuously in the process.

The process may include, in addition to said quenching, a treatment thermal expansion. In this case, the HRC hardness limitation must be higher or equal to 32, and preferably greater than or equal to 35, must be respected after the relaxation treatment.

The relaxation treatment can be carried out in a bundle in an oven.

The quenching and the said stress relief treatment can be carried out on parade, preferably online, which allows the production of very long wires necessary for the production of flexible armor plies.

• entre 0,1% et 2,5% de Cr, de préférence entre 0,25 et 1,3%,
• entre 0,1% et 1% de Mo,

l'acier étant ainsi du type faiblement allié et pouvant correspondre à des nuances courantes dans l'industrie et de coût relativement limité.According to a first variant of the present invention, the carbon content C can be less than or equal to 0.45%, preferably less than or equal to 35%, and the steel comprises at least one of the following two alloying elements. , in small quantities:

• between 0.1% and 2.5% of Cr, preferably between 0.25 and 1.3%,
• between 0.1% and 1% of Mo,

steel is thus of the low-alloy type and can correspond to nuances common in the industry and of relatively limited cost.

Such a steel, containing a limited content of Cr and / or Mo can possibly not contain any other alloying element or dispersoid. However, it will not depart from the scope of the present invention if the steel contains a little dispersoid, such as vanadium, titanium or niobium, in particular for low carbon steels, the carbon content being equal to or greater than 0.05%. In this case, the vanadium content can be limited to a low value so as to avoid too long annealing time after welding, preferably the vanadium content will be less than or equal to 0.10%.

According to another variant of the invention. the carbon content of the steel can be greater than or equal to 0.4%, while remaining less than 0.8%, and correspond to a standard hard or semi-hard carbon-manganese steel, classic in wire drawing or cables. without the addition of an alloying element such as Cr or Mo. The steel may possibly contain a small amount of dispersoid, such as can be found commonly found in commercial steels. Such steels can be included in the range of steel FM40 to FM80. according to AFNOR standard.

The quenching heat treatment may include passage through an oven austenitization at a temperature above the AC3 point of the steel grade of the wire. then in a zone of quenching in a fluid of drasticity adapted at the same time to the shade steel and the size of the wires, the temperature and the residence time being adapted according to the grade to obtain a grain size between the indices 5 and 12, and advantageously between indices 8 and 11, according to standard NF 04102. The structure obtained after quenching, can be predominantly martensitic with a percentage between 0 and 50% lower bainite or predominantly lower bainite with a percentage between 0 and 50% martensite. Preferably, the bainite is in the lower bainite state and not higher bainite. Preferably, the structure can contain only a small amount of ferrite.

The production process can end with the quenching operation. of preference followed by a relaxation treatment.

• au défilé entre 300 et 550°C, la vitesse étant adaptée à la section du fil de façon à obtenir la dureté selon la présente invention, supérieure ou égale à 32 HRC,
• en botte dans un four entre 150 et 300°C.

The temperatures of the stress relief treatment can be:

• in the process between 300 and 550 ° C., the speed being adapted to the section of the wire so as to obtain the hardness according to the present invention, greater than or equal to 32 HRC,
• in a bale in an oven between 150 and 300 ° C.

The wire thus obtained may not be able to withstand H ₂ S under certain operating conditions, but it can be very advantageously used as armouring wire for flexible conduits thanks to its excellent optimized mechanical properties, in particular by the combination of a high mechanical strength and a ductility higher than that which can be obtained with known methods. The rupture limit Rm can reach 1000 to 1600 MPa, equal to or greater than that of the most resistant armor wires currently known, and the elongation at break can be greater than 5%, possibly greater than 10% and possibly exceeding 15% in some cases. Whereas for known steel wires having a level of resistance comparable to the work hardened state, these have an elongation at break not exceeding 5%.

According to a particular embodiment of the invention in order to obtain optimized shaped wires resistant to H ₂ S, the method may include, after the quenching heat treatment, optionally supplemented by an expansion treatment, a final heat treatment of tempering under determined conditions to obtain a hardness greater than or equal to 20 HRC and less than or equal to 35 HRC.

The conditions of the final tempering treatment can be adapted so as to obtain a hardness less than or equal to 28 HRC, compatible with operating conditions which can provide an environment with a pH close to 3.

In all cases, after quenching and final tempering, as defined, including at pH close to 3, a steel according to the present invention does not exhibit blistering or crack in HIC tests, and furthermore does not show cracking when subjected to tests according to standard NACE 0177 (SSCC) with a tensile stress at less than 60% of the elastic limit and up to approximately 90% of this last.

The final income can be made at the parade, online or separate.

The final income can be made in a bundle in an oven.

The tempering temperature can be at most equal to a lower temperature from about 10 ° C to 30 ° C relative to the AC temperature at the start of austenitization of steel, in order to avoid excessive coalescence of carbide which could lead to a decrease in characteristics.

At the end of production, the wire is wound on a spool so that it can be subsequently mounted on a spiral or armeuse for the manufacture of armor of the flexible driving.

• Formage du fil par transformation à froid:

Generally speaking. in particular in order to obtain the best possible mechanical strength characteristics, the steel grade can be optimized according to the process for forming the form wire from the wire rod:

• Wire forming by cold transformation:

It has been found that this method of implementing the invention allows to obtain interesting results by choosing a weak steel alloy, or carbon steel type.

The content of alloying elements, while being low, must be sufficient to obtain after quenching a predominantly martensitic or bainitic structure with little ferrite (we can thus, in the most favorable cases, obtain a structure containing nearly 100% martensite and commonly, at least 90% martensite and bainite).

a) risque de formation d'une quantité de martensite excessive dans la structure du fil machine, par le simple effet du refroidissement suivant le formage à chaud du fil machine.

b) dureté du fil machine trop élevée pour pouvoir effectuer correctement le laminage à froid de transformation du fil machine en fil de forme selon les dimensions spécifiées.

Furthermore, the content of alloying elements must be limited to relatively low values. Indeed, if this content exceeds certain limits (which can be determined by a person skilled in the art by carrying out several successive tests), this results in consequences making the wire unfit for cold processing operations:

a) risk of formation of an excessive amount of martensite in the structure of the wire rod, by the simple effect of cooling following the hot forming of the wire rod.

b) hardness of the wire rod too high to be able to correctly carry out the cold rolling transforming the wire rod into shaped wire according to the specified dimensions.

• Formage du fil par laminage à chaud:

It has thus been found that it is possible, between too weakly alloyed steels and excessively alloyed steels, to find steels having an optimized content of alloying elements so as to produce by cold rolling of shaped wires of characteristics particularly interesting after quenching and tempering.

• Wire forming by hot rolling:

This process reduces manufacturing costs. It also allows to obtain wires with the shape of larger sections than cold rolling.

The invention thus makes it possible to produce a shaped wire having after quenching a relatively homogeneous martensitic or bainitic structure throughout the thickness of the wire, despite the increase in the thickness of the wire. We can thus obtain, in the most favorable cases, up to approximately 100% martensite. content total in martensite and bainite being commonly, at least equal to 90%.

Such a result is obtained by using a more alloyed steel grade than the steels recommended for forming by cold rolling. Such steels more strongly allies would have been difficult to use or even unsuitable for rolling to cold.

According to the invention, it is possible, in particular, to produce shaped wires having both high mechanical strength and excellent resistance in the presence of H2S by cold transformation, even if the wrought induces global deformations or strong local. This is achieved although a high level of cold deformation risk, depending on the deformation rate and the shade, of causing excessive strength increases and a reduction in ductility that can lead to faults during subsequent forming operations. According to a mode particular implementation, cold forming comprising at least two stages successive cold processing, an intermediate processing operation thermal is carried out between the first and the last cold transformation step. For example, the intermediate heat treatment operation can be carried out between a preliminary drawing operation and the beginning of rolling. or between two passes successive lamination.

Such an intermediate intermediate heat treatment can be carried out various ways known in metallurgy, so as to lower the mechanical strength, preferably below 850 MPa, and to recover the ductility allowing the cold processing.

The invention also relates to a wire of constant cross-section shape and very long, suitable for use as the armor wire of a flexible pipe according to two variants defined in claims 20 and 21.

Tempered bainitic martensitic type steel, the tempering may be more or less pronounced, especially such as a trigger income, so that the thread obtained has the ductility necessary for its subsequent use as a wire armor, or as a quality income making the wire suitable for use in the presence of H2S.

Preferably, the bainitic martensitic structure is predominantly martensitic with a percentage between 0 and 50% of bainite inferior or predominantly lower bainite with a percentage between 0 and 50% of martensite. Preferably, the structure may contain only a small amount of ferrite. The wire can have a hardness greater than 20 HRC. Preferably, the size of the austenitic grain lies between indices 5 and 12, and advantageously between indices 8 and 11. according to standard NF 04102.

The form wire can have a section having at least one of the forms following general: U, T, Z, rectangular or round.

The section of the form wire can have a width L and a thickness e. and to have the following proportions: L / e greater than 1 and less than 7. The thickness may vary between 1 mm and 20 mm, up to 30 mm.

The profile of the form wire may include means for hooking with a wire adjacent.

• entre 0,1% et 2,5% de Cr, de préférence entre 0,25 et 1,3%.
• entre 0,1% et 1% de Mo.

In a first variant of the shaped wire according to the present invention, the carbon content C can be less than or equal to 0.45%, and the steel comprises at least one of the following two alloying elements, in small quantity :

• between 0.1% and 2.5% of Cr, preferably between 0.25 and 1.3%.
• between 0.1% and 1% of Mo.

In this variant, the carbon content C can be greater than or equal to 0.08%, preferably greater than or equal to 0.12% and the steel may contain at most 0.4% of Si. The steel may for example contain from 0.12% to 0.35% of C.

In another variant of the shaped wire according to the invention, the carbon content steel may be greater than or equal to 0.4%, while remaining less than 0.8%, and correspond to a standard carbon-manganese hard or semi-hard steel, classic in wire or cable drawing, without adding any alloying element such as Cr or Mo, with possibly a small amount of dispersoid. Such steels can be understood in the FM40 to FM80 steel range, according to the AFNOR standard.

According to a first embodiment, the shaped wire according to the invention can have an HRC hardness greater than or equal to 32, preferably greater than or equal to 35. The wire thus obtained may not be able to resist H ₂ S under certain operating conditions, but it can be used very advantageously as armouring wire for flexible pipes thanks to its excellent optimized mechanical properties, in particular by the combination of high mechanical strength and ductility greater than that which can be obtained with known methods. The breaking limit Rm can reach 1000 to 1600 MPa., Preferably greater than or equal to 1200 MPa. Such a wire can advantageously be used to make the armor of hoses intended for the transport of weakly corrosive crude oil ("sweet crude"), degassed oil ("dead oil") or water. The process for producing such a wire can end in a quenching operation, preferably followed by an expansion treatment.

According to another embodiment, the shaped wire according to the invention can have an HRC hardness greater than or equal to 20, preferably less than or equal to 35. The wire thus obtained can have properties of resistance to H ₂ S under the operating conditions described above, in particular following HIC tests in very acidic medium (pH close to 2.8 or 3). The mechanical resistance Rm can be of the order of 700 to 900 MPa under a pH close to 3 and can reach at least 1100 MPa with a higher pH. The stress applied in the SSCC tests according to NACE, with a pH close to 2.8, can be at least 400 MPa and can reach 600 MPa.

If the SSCC tests are carried out with a pH greater than 3, the allowable stresses may be higher, up to approximately 90% of the Elastic limit.

With a view to their use as armouring wire for flexible pipes intended the transport of crude oil comprising acid gas, in particular H2S and CO2, the method according to the invention makes it possible to form steel wires of the type tempered martensite-bainite whose structure has carbide nodules extremely fine in a state of very great dispersion in a ferrite matrix issue by income from a martensite-bainite structure. It is interesting to compare this steel to other steels already offered or used to make armouring wires intended for the same use, such as steels obtained by spheroidization treatment from of a hardened ferrite-perlite structure, these steels also comprising elements of carbide in a ferritic matrix. The spheroidized carbide elements of these steels are considerably less fine and less dispersed than in the case of steel according to invention, which clearly identifies the difference between the two types of material. In addition, it appears that the superior properties of form wire according to the invention, in terms of mechanical resistance and compatibility with H2S, by comparison with the wires of the prior art, in particular in spheroidized steel, can have a relationship to having a much finer nodular structure and scattered.

It should be noted that the invention has the particular advantage that from the same batches of wire rod and by carrying out the same quenching operations. optionally expansion, one can produce, depending on the needs, either steel wires which are very mechanically resistant but do not sometimes have the required properties of resistance to H ₂ S, or wires which are resistant to H ₂ S even in the most severe conditions. In the first case, the production range ends with the quenching operation. preferably followed by relaxation. In the other case, the manufacturing range is continued by an additional final income stage.

The invention can be applied to a flexible tube for transporting an effluent comprising H ₂ S, the tube possibly comprising at least one layer of reinforcements of reinforcement under pressure and / or under tension comprising wires form according to the invention.

The present invention will be better understood and its advantages will appear more clearly on reading the following examples, in no way limiting.

Example 1:

15 mm diameter circular section wires were produced from a chromium-molybdenum type steel conforming to grade 30CD4 of the AFNOR standard (equivalent to the ASTM 4130 standard in correspondence with the number UNS G41300). The steel used has the following composition:
C: 0.30% Mn: 0.46% Cr: 0.90% If: 0.32% Mo: 0.18% Ni: 0.12% S = 0.003% P = 0.009%

The quenching operation was carried out at the parade at the speed of 1.8 m / minute with high frequency induction heating to 980 ° C-1000 ° C, then oil quenching. The expansion treatment was carried out in the oven for hours at 180 ° C.

After these thermal quenching and relaxation treatments. the hardness of the wire is of 40 HRC (Rm = 1200 MPa) and its structure is predominantly martensitic. The grain size corresponds to an index 8 of standard NF 04.102.

Heat treatments in the oven for 2 hours lead to the following mechanical characteristics: Temp. (° C) 600 620 645 655 675 HRC hardness 30 28 26 24 22

Threads thus heat treated having a hardness between 22 and 26 HRC satisfy the SSC NACE TM 0177 tests for 30 days under the following uni-axial tension constraints (T): Tension stress Characteristics of steel (depending on income) T (MPa) HRC Re (MPa) Rm (MPa) 500 22 650-680 760-800 550 24 680-700 800-830 450 26 700-750 830-860

After these NACE tests, tensile tests on the test pieces show that the mechanical characteristics and in particular the elongation at break are not affected, remaining very close to the values obtained before the NACE test.

HIC tests carried out according to the NACE TM 0284 procedure, but in a solution called "NACE TM 0177" type (pH = 2.8) instead of synthetic seawater (pH approximately 5) reveal a non-sensitivity to cracking. step for these three hardness levels (22, 24 and 26 HRC): CLR = 0% CTR = 0% CSR = 0%

In addition, welds made by induction or resistance heating, with axial compression, supplemented by income treatments of less than 5 minutes, pass the SSC NACE TM 0177 test at 400 MPa uniaxial tension. Of preferably post-weld tempering temperatures should be higher than that of metal tempering and below the start temperature austenitization AC1, preferably 20 to 30 ° C lower than AC1.

In the industrial manufacture of hoses, such welding operations are essential for connecting the unitary sections of wires. It should be noted that it is particularly interesting to obtain good results in the NACE tests on the sons and also the possibility of quickly carrying out the income operation after welding. It has been found, for example, that the time required for such treatment of income exceeds 30 minutes if the steel contains more than 0.10% of vanadium and that, consequently, the use of this steel is not recommended for the applications targeted by the present invention, whereas a priori. he would seem obvious to resort to the addition of vanadium for a use of this kind.

From a slightly different steel, also of type 30CD4, and having the following composition:
C = 0.31%, Mn = 0.66%, Si = 0.23%, Cr = 1.02%, Mo = 0.22%, Ni = 0.24%, S = 0.010%, P = 0.009 %,

a wire was made having a T section (height 14 mm, width 25 mm). After a process of quenching in the procession and a treatment of relaxation, the wire has a hardness 40 HRC.

After having returned to the oven for approximately 3 hours at a temperature in the region of 650 ° C., the following mechanical characteristics are obtained according to the hardnesses between 23 and 25 HRC: HRC Re (MPa) Rm (MPa) 23 675 790 24 715 815 25 740 854

The HIC tests carried out as for the 15 mm round wire, show the same results of absence of cracking.

SSCC tests give at least a uniaxial tension value of 400 MPa for each hardness.

Example 2:

Shaped wires have been produced from a chromium-molybdenum type steel conforming to grade 12CD4 defined by the AFNOR standard comprising:
C: 0.14% Mn: 0.74% Cr: 1.095% Si: 0.203%
Mo: 0.246% Ni: 0.24% S = 0.006% P = 0.008%

From a round wire rod 8 mm in diameter (having a stress on the breaking of approximately 750 MPa), a flat wire 9 mm wide and thick was obtained 3 mm (9x3) by wire drawing and cold rolling.

• Traitement de revenu au four :

The quenching was carried out with oil in the process followed by a relaxation income in the process in a lead bath in a temperature in the vicinity of 500 ° C. We obtain a hardness of 40 HRC and a breaking stress of 1240 MPa. The grain size corresponds to an index 8 of standard NF 04.102.

• Income treatment in the oven:

The table below makes it possible to compare the mechanical characteristics of the wires before and after the HIC test carried out according to the NACE TM 0284 procedure but in a solution called "NACE TM 0177" (pH = 2.8) instead of sea water. synthetic (pH about 5): HRC Re Rm AT (%) Z (%) After relaxation, before final income: 40 Before HIC 1140 1230 18 81 After HIC 1100 1177 18.4 77 After final income: 570 ° C 28 Before HIC 790 850 24 85 After HIC 800 861 22 67 600 ° C 26 Before HIC 740 830 26 66 After HIC 750 792 23 72 630 ° C 24 Before HIC 720 796 28 64 After HIC 670 746 24 70 640 ° C 22 Before HIC 700 781 30 82 After HIC 640 731 24 76

• Traitement de revenu au défilé :

The wires, after tempering treatment adjusted so as to obtain 24 HRC, passed the tests according to the NACE TM 0177 procedure (Method A) under 500 MPa of stress.

• Income processing at the parade:

The tempering was carried out at a speed of 15 m / minute by medium frequency induction heating at different powers leading to the following mechanical characteristics as a function of the temperature measured at the output of the heating coil: T self output (° C) 680 700 710 HRC hardness 29 28 26

In the two cases of tempering treatment (tempering in the oven or in the parade), HIC tests are carried out for each hardness level, according to the NACE TM 0284 procedure, but in a solution called "NACE TM 0177" type (pH = 2 , 8) instead of synthetic sea water (pH around 5). The tests reveal a non-sensitivity to step cracking for the different hardness levels (from 22 to 28 HRC for the treatment in the oven and from 26 to 29 for the treatment in the parade): CLR = 0% CTR = 0% CSR = 0%

Example 3:

Carbon-manganese steels with addition of chromium between 0.1 and 1%, suitable quenching and tempering, in accordance with the range 20C4 to 40C1 according to the AFNOR standard.

1) - In grade 35C1 (0.35 of C), rectangular wires (9x3) are made with a steel having the following composition:
C = 0.35%, Mn = 0.75%, Si = 0.26%, Cr = 0.35%
S = 0.02%, P = 0.02%, without addition of molybdenum or nickel.

• Traitement de revenu au four :

After oil quenching and expansion treatment, 40 HRC hardness wires and Rm = 1310 MPa are obtained. The grain size corresponds to an index 8 of standard NF 04.102.

• Income treatment in the oven:

During a treatment of approximately one hour at the following temperatures, the hardnesses are obtained: Temp. income 450 ° C 500 ° C 550 ° C 600 ° C HRC 27.3 27.2 26.1 22

• Traitement de revenu au défilé :

After HIC tests according to the NACE TM 0284 procedure but in a so-called "NACE TM 0177" solution (pH = 2.8) instead of synthetic sea water (pH approximately 5), the following mechanical characteristics are obtained compared to those measured before HIC: HRC Re Rm AT (%) 27 Before HIC 730 890 16 After HIC 730 890 14.5 22 Before HIC 705 780 18 After HIC 710 780 20

• Income processing at the parade:

For a temperature of 700 ° C, the wire obtained has a hardness of 27.5 HRC, Re = 710 MPa, Rm = 940 MPa and A = 14.6%

In both cases of income treatment, the HIC tests carried out according to the NACE TM 0284 procedure. but in a so-called "NACE TM 0177" solution (pH = 2.8) instead of synthetic seawater (pH around 5) reveals non-sensitivity to step cracking for hardness levels between 22 and 27 HRC.

In the case of parade income treatment (HRC = 27.5) the SSC tests NACE TM 0177 (Method A) are satisfied under an axial tension of 400 MPa.

2) -We carry out tests on a 9x3 rectangular wire manufactured at from a steel conforming to grades 18C4 or 20C4 according to AFNOR standards. The composition includes: C: 0.18% - Mn: 0.85% - Si: 0.11% - Cr: 0.91 -Ni: 0.174% - Mo: 0.039% - S and P = 0.015%.

Oil quenching is carried out, followed by an expansion treatment, to obtain a hardness of 39 HRC and Rm = 1180 MPa. The grain size corresponds to an index 8 of standard NF 04.102.

Tempering in the oven for about 4 hours was carried out at temperatures 510 ° C, 525 ° C and 540 ° C to obtain the hardnesses of 26, 24 and 22 HRC.

HIC tests. made in a solution called "NACE TM 0177" (pH = 2.8) instead of synthetic sea water (pH about 5), give the same results satisfactory than before.

The SSCC test is satisfied according to the hardness (22 to 26 HRC) under a constraint between 400 and 450 MPa.

For a round wire with a diameter of 13 mm, in the same steel and following equivalent treatments, the mechanical characteristics can be given depending on the hardness: HRC Re (MPa) Rm (MPa) 23 700 790 24 720 805 25 740 825

3) -Using a variant of the shade with 0.35% C described above. wires with a thickness of between 2 and 7.5 mm and a width between 5 and 15 mm are produced, with a steel having the following composition:
C = 0.33%, Mn = 0.73%, Si = 0.21%, Cr = 0.34%
S = 0.015%, P = 0.007%,

After water quenching and stress relief treatment, wires of hardness 380 are obtained Vickers (40 HRC) and Rm = 1400 MPa. The grain size corresponds to an index 11 of standard NF 04.102.

After tempering treatment in an oven at 615 ° C for 15 minutes (equivalent result which can be obtained by treatment at 680 ° C for approximately 1 minute), a final wire is obtained having an HRC hardness of 24, with a breaking limit Rm = 828 MPa and an elastic limit Rp _0.2 = 724 MPa. HIC type tests have shown that this wire does not exhibit any sensitivity to cracking in the presence of H2S, the tests being carried out according to NACE TM 0284 standard, but in a solution according to NACE TM 0177 with pH = 2.7.

SSCC type stress corrosion tests according to the standard NACE TM 0177 could reach a duration of 720 hours without the appearance of a break nor crack. In one case, the stress reached 90% of the elastic limit, i.e. 652 MPa, the pH being 3.5. In another case, the pH was very low 2.7, the applied stress being 600 MPa, or 83% of the elastic limit.

Claims (28)

1. A method of manufacturing a steel wire suitable for use as a reinforcing wire for a flexible pipe comprising the following steps:

   a formed wire of a long length is manufactured by rolling or wire drawing to the final dimensions using a steel essentially comprising the following elements:

   from 0.05% to 0.8% of C

   from 0.4% to 1.5% of Mn,

   from 0 to 2.5% of Cr,

   from 0.1% to 0.6% of Si,

   from 0 to 1% of Mo,

   at most 0.50% of Ni,

      at most 0.02% of S and P,

   heat treatments are conducted, said wire having a breaking limit Rm which does not exceed 1600 MPa after the heat treatments, characterised in that

   a first heat treatment is applied comprising at least one quenching operation of the formed wire, optionally followed by an expansion heat treatment, under specified conditions to obtain a hardness HRC higher than or equal to 32 and a steel structure of said wire that is predominantly martensitic-bainitic,

   optionally, after the first heat treatment, a final heat tempering treatment is applied.
2. A method as claimed in claim 1, such that the hardness after the first heat treatment is greater than or equal to 35 HRC.
3. A method as claimed in one of the preceding claims, such that the formed wire is transformed into a machine wire by cold-processing and such that said machine wire is manufactured and/or thermally treated so as to obtain a Rm value less than approximately 850 MPa.
4. A method as claimed in one of claims 1 and 2, such that the formed wire is obtained directly by hot-rolling, optionally followed by an annealing operation for softening purposes in order to obtain a Rm value of the formed wire of less than approximately 850 MPa.
5. A method as claimed in one of the preceding claims, such that the quenching operation is performed continuously on the fly.
6. A method as claimed in one of the preceding claims, such that the first heat treatment incorporates an expansion treatment as a complement to said quenching.
7. A method as claimed in one of the preceding claims, such that said expansion treatment is conducted in bundles in a furnace.
8. A method as claimed in one of claims 1 to 6, such that said quenching and said expansion treatment are conducted on the fly.
9. A method as claimed in one of the preceding claims, such that the steel contains:

   at most 0.45% of C and at least one of the following two elements:

   between 0.1% and 2.5% of Cr,

   between 0.1% and 1% of Mo.
10. A method as claimed in one of claims 1 to 8, such that the steel contains:

    between 0.40% and 0.8% of C,

    no meaningful quantity of Cr and Mo,

    optionally, a low quantity of dispersoids.
11. A method as claimed in one of the preceding claims, such that said quenching includes passage through an austenitizing furnace at a temperature higher than the AC3 point of the steel, then in a quenching zone with a fluid having a quenching rate adapted to the grade of steel and the size of the wires.
12. A method as claimed in one of claims 6 to 11, such that the temperatures of said expansion treatment are:

    between 300 and 550° C if treated on the fly,

    between 150 and 300°C if treated in bundles in the furnace.
13. A method as claimed in one of the preceding claims, such that it includes, after the first heat treatment, a final tempering heat treatment under specified conditions to obtain a hardness higher than or equal to 20 HRC and less than or equal to 35 HRC.
14. A method as claimed in claim 13, such that the hardness is less than or equal to 28 HRC.
15. A method as claimed in one of claims 13 or 14, such that the final tempering is conducted on the fly.
16. A method as claimed in one of claims 13 to 14, such that the final tempering is conducted in bundles in a furnace.
17. A method as claimed in one of claims 13 to 16, such that the temperature of the final tempering is at most equal to a temperature of approximately 10°C to 30°C below the AC1 temperature at which austenite starts to form in the steel.
18. A method as claimed in one of claims 1 to 17, such that said acid contains between 0.08% and 0.8% of C and Si lower than or equal to 0.4.
19. A method as claimed in claim 18, such that said steel contains from 0.12% to 0.8% of C.
20. A formed wire of a long length and constant section designed for use as a reinforcing wire for a flexible pipe, having a breaking limit Rm which is not more than 1600 MPa and made from a steel essentially comprising the following elements:

    at most 0.45% of C,

    from 0.4% to 1.5% of Mn,

    from 0.1% to 0.6% of Si,

    at most 0.50% of Ni,

    at most 0.02% of S and P,

    Cr and/or Mo,

    characterised in that the steel contains at least one of the following elements:

    between 0.1% and 2.5% of Cr,

    between 0.1% and 1% of Mo,

    in that it has a structure that is predominantly martensitic-bainitic and in that it is obtained using the method as claimed in any one of claims 1 to 9 and 11 to 18.
21. A formed wire of a long length and constant section designed for use as a reinforcing wire for a flexible pipe, having a breaking limit Rm which is not more than 1600 MPa and made from a steel essentially comprising the following elements:

    from 0.40% to 0.8% of C,

    from 0.4% to 1.5% of Mn,

    from 0.1% to 0.6% of Si,

    at most 0.50% of Ni,

    at most 0.02% of S and P,

    no meaningful quantity of Cr and/or Mo,

    optionally a small quantity of dispersoids, said section of the wire being of a width L and a thickness e being of the following proportions: L/e is greater than 1 and lower than 7, where e is less than or equal to 30 mm, characterised in that it has a predominantly martensitic-bainitic structure.
22. A formed wire as claimed in one of claims 20 or 21, such that it has a hardness HRC higher than or equal to 20.
23. A formed wire as claimed in one of claims 20 to 22, such that it has a hardness greater than or equal to 32 HRC, a value Rm greater than 1000 MPa and a stretch at breaking point greater than or equal to 5%.
24. A formed wire as claimed in one of claims 20 to 22, such that it has a hardness greater than or equal to 20 HRC and less than or equal to 35 HRC and a Rm greater than 700 MPa.
25. A formed wire as claimed in one of claims 20 to 24, such that the profile of the section incorporates means for hooking onto an adjacent wire.
26. A formed wire as claimed in claim 20, such that said steel contains from 0.08% to 0.4% of C and Si less than or equal to 0.4
27. A formed wire as claimed in claim 26, such that said steel contains from 0.12% to 0.35% of C.
28. A flexible pipe for transporting an effluent containing H₂S, characterised in that it has at least one layer of armouring reinforced to withstand pressure and/or traction containing formed wires as claimed in one of claims 20 to 27.