DK179251B1

DK179251B1 - Method for making a flexible tubular pipe having a long length

Info

Publication number: DK179251B1
Application number: DKPA201170657A
Authority: DK
Inventors: Alain Droues; Xavier Longaygue
Original assignee: Technip France
Priority date: 2009-05-04
Filing date: 2011-11-29
Publication date: 2018-03-05
Also published as: WO2010128238A1; GB201118078D0; MY154445A; BRPI1014605B1; DK201170657A; GB2481175A; GB2481175B; FR2945099B1; BRPI1014605A2; FR2945099A1

Abstract

The invention relates to a method for making a flexible tubular pipe (22) for conveying hydrocarbons, and to the resulting pipe. The method comprises: providing a sealed pressure sheath (12); providing hammer-hardened metal wires made of austenitic-ferritic stainless steel; winding, with a long pitch, said hammer-hardened metal wires around the pressure sheath (12) in order to form a tensile armor layer (16, 18); and forming an outer sheath (20) around said tensile armor layer. According to the invention, the metal wires made of austenitic-ferritic stainless steel are hammer-hardened by reducing the cross-section thereof by at least 35% in order to obtain hammer-hardened metal wires having a tensile strength higher than 1300 MPa, and then directly winding said hammer-hardened metal wires after the hammer-hardening step, whereby the hammer-hardened metal wires retain the mechanical properties thereof after winding.

Description

<¹θ> DANMARK (10)

<¹²> PATENTSKRIFT

Patent- og

Varemærkestyrelsen (51) Int.CI.: F16 L 11/08 (2006.01) C22 C 38/00 (2006.01) C 22 C 38/08 (2006.01)

C 22 C 38/18 (2006.01) (21) Ansøgningsnummer: PA2011 70657 (22) Indleveringsdato: 2011-11-29 (24) Løbedag: 2010-05-03 (41) Aim. tilgængelig: 2011-11-29 (45) Patentets meddelelse bkg. den: 2018-03-05 (86) International ansøgning nr: PCT/FR2010/050840 (86) International indleveringsdag: 2010-05-03 (85) Videreførelsesdag: 2011-11-29 (30) Prioritet: 2009-05-04 FR 0902149 (73) Patenthaver: Technip France, 6-8 Allée de l'Arche - Faubourg de l'Arche ZAC Danton, F-92400 Courbevoie, Frankrig (72) Opfinder: Alain Droues, 1647 Le Conihout, F-76480 Le Mesnil sous Jumiéges, Frankrig Xavier Longaygue, 1 allée des Bouvreuils, F-78390 Bois d'Arcy, Frankrig (74) Fuldmægtig: Chas. Hude A/S, H.C. Andersens Boulevard 33,1780 København V, Danmark (54) Benævnelse: Method for making a flexible tubular pipe having a long length (56) Fremdragne publikationer:

WO 2006/097112 A2 US 2009/0050228 A1 US 5407744 A US 6282933 B1 (57) Sammendrag:

The invention relates to a method for making a flexible tubular pipe (22) for conveying hydrocarbons, and to the resulting pipe. The method comprises: providing a sealed pressure sheath (12); providing hammerhardened metal wires made of austenitic-ferritic stainless steel; winding, with a long pitch, said hammerhardened metal wires around the pressure sheath (12) in order to form a tensile armor layer (16,18); and forming an outer sheath (20) around said tensile armor layer. According to the invention, the metal wires made of austenitic-ferritic stainless steel are hammer-hardened by reducing the cross-section thereof by at least 35% in order to obtain hammer-hardened metal wires having a tensile strength higher than 1300 MPa, and then directly winding said hammer-hardened metal wires after the hammer-hardening step, whereby the hammerhardened metal wires retain the mechanical properties thereof after winding.

Fortsættes ...

Single figure

Title: Method for making a flexible tubular pipe having a long length

The present invention relates to a process for manufacturing a flexible submarine pipe intended for transporting hydrocarbons and especially for exploiting bearings having a high content of corrosive gases, principally hydrogen sulfide (H2S) and carbon dioxide (CO2). The invention also relates to a pipe obtained by the manufacturing process.

The present invention relates mainly to unbonded flexible pipes as described in the normative documents API 17J Specification for Unbonded Flexible Pipe and API RB 17B Recommended Practice for Flexible Pipe published by the American Petroleum Institute. However, the invention could also apply to bonded pipes and to umbilicals.

Flexible pipes usually comprise, from the inside outward, an internal carcass, an internal sealing sheath, a pressure vault, several tensile armor plies and an external protection sheath.

The internal carcass has the main function of taking up the radial crushing forces, for example those due to the hydrostatic pressure. It is made from a profiled metal strip wound so as to interlock the touching turns of said metal strip. The internal sealing sheath that covers it is more often than not made of plastic and extruded directly onto the carcass. The function of this sheath is to confine the fluid flowing through the pipe. The pressure vault is generally formed from a profiled metal wire wound in a short pitch with touching turns around the internal sealing sheath. The pressure vault thus serves to take up the radial forces due to the pressure of the fluid flowing through the pipe. The function of the tensile armor plies is to take up the tensile forces that are exerted on the pipe. These plies consist of armor wires wound helically with a long pitch around the pressure vault. To balance the structure in torsion, the total number of tensile armor plies is generally even and the plies are crossed one with respect to another. These armor wires are usually of rectangular cross section, but they may also have a cylindrical cross section or a complex geometry of the T, C or Z type. In the present application, the expression winding in a long pitch denotes a helical winding in which the helix angle, expressed in absolute value, is less than 60°, typically between 20° and 55° in the case of the tensile armor plies. The term winding in a short pitch denotes a winding in which the helix angle is close to 90°, in practice between 70° and 85°.

For applications at great depth, it is necessary for the metal reinforcements or tensile armor wires, responsible for taking up the longitudinal forces, to have high mechanical properties, otherwise the structure, burdened by its great length, would prove to be difficult to install and would require a floating production support overly sized in comparison with the conventional supports, thereby entailing very high overcosts.

Now, in general when these reinforcements are made of steel, carbon steel or low-alloy steel, the increase in mechanical properties is to the detriment of the corrosion resistance, thereby making it difficult to develop a flexible pipe intended to operate at very great depth, 2000 m and greater, while being able to withstand highly corrosive hydrocarbons. The intended corrosive hydrocarbons are in particular polyphase hydrocarbons having a high H2S partial pressure, typically 0.5 bar to 5 bar, and/or a high CO2 partial pressure, typically at least 5 bar. Such fluids are generally very acid, their pH typically being less than 4.5. Furthermore, their temperature may exceed 90°C.

Document WO 91/16461 describes a flexible pipe for transporting corrosive hydrocarbons comprising H2S. The pressure vault and the tensile armor wires are made of a carbon steel which is work-hardened and then softened by a restoration heat treatment. However, these steels have insufficient mechanical properties for applications at great depth, since their yield strength R_e and their tensile strength R_m are around 700 and 850 MPa respectively. In the present application, the terms yield strength, elastic limit and Re all denote the stress at the elastic/plastic transition. The terms tensile strength, fracture stress and Rm all denote indifferently the stress at break. The term H2S corrosion denotes any physical degradation in the presence of H2S in aqueous medium, especially generalized corrosion, crevice corrosion, stress cracking and hydrogen embrittlement. A similar solution intended for even more corrosive media than those intended in the aforementioned document is disclosed in document WO 96/28575. The pressure vault and the tensile armor wires are then made of quench and tempered low-alloy carbon steel, giving the pipe better corrosion resistance than carbon steels that are work-hardened and softened. However, as a result their mechanical properties are not any higher, the Re and Rm thereof being around 700 MPa and 850 MPa, respectively, which does not solve the problem of the applications at great depth. Document WO 03/074206 discloses a flexible pipe comprising armor wires made of clad steel. The core of the armor wires is made of a low-alloy or no-alloy carbon steel having high mechanical properties, typically an Rm greater than 1400 MPa, but a low corrosion resistance. The corrosionresistant cladding is made of titanium, titanium alloys, stainless steel, nickel or even nickel alloys. This solution admittedly does solve the problem of applications in a corrosive medium at great depth, but it is essential for the cladding not to have any defect resulting in the local baring of the carbon steel core, thereby imposing very stringent quality requirements. In addition, the process for producing these clad wires is complex and costly.

Documents WO 98/53237, WO 99/49259, WO 00/66927, WO 00/70256, WO 02/095281 and US 2009/0000683 disclose solutions in which the tensile armor wires are made of a composite, especially one based on glass or carbon fiber. These very lightweight composites have both good corrosion resistance and high mechanical properties. However, they are either very expensive or sensitive to chemical ageing, especially hydrolysis in the case of glass fibers.

Document WO 99/42754 discloses a flexible pipe for use in a corrosive medium, comprising, on the one hand, a pressure vault made of steel resistant to H2S corrosion but having moderate mechanical properties and, on the other hand, tensile armor wires that are not very resistant to H2S corrosion but do have high mechanical properties. An impermeable polymeric sheath is inserted between the pressure vault and the armor wires so as to prevent H2S from reaching the tensile armor wires. The object of document WO 2005/028198 is also to improve this idea of a shield. This shield consists of a metal strip wound with overlap and then bonded and sheathed by a polymeric sheath. This shield is more effective in stopping the diffusion of gases than the simple sheath disclosed in document WO 99/42754. In addition, it may be placed directly on the pressure sheath so as to protect both the pressure vault and the tensile armor wires. The object of document EP 0 844 429 is also to improve this idea of a shield. The shield here consists of a polymeric sheath containing a chemically active filler, for example zinc oxide, which can react with the corrosive gases and thus consume them, so as to prevent them from diffusing through the sheath.

These solutions using a shield are not entirely satisfactory, as their reliability relies entirely on the impermeability and effectiveness of the shield. Furthermore, implementing these solutions requires the use of means for draining the internal annular space lying between, on the one hand, the internal sealing sheath and, on the other hand, the shield. Such draining means, which are in particular described in documents WO 2004/085900 and WO 04/040183, are complicated and expensive to implement.

Moreover, it has also been envisaged using duplex stainless steels. In this regard, document WO 2006/097112 describes a flexible pipe that includes a metal layer made of duplex steel having a low nickel content, of less than 3%. This is in particular the case of a duplex steel sold by Outokumpu with the reference LDX 2101. Such a solution does reduce the weight and the cost of the pipe, while still guaranteeing good corrosive resistance. This document also mentions another reference, namely duplex 2205. The metal layer in question is priority-wise the internal carcass, but the document also discloses the application of wires of this material for other reinforcing layers and in particular for the tensile armor wires. However, the above document teaches nothing about the production process and the mechanical properties of the duplex armor wires. Table 2 and the associated comments are limited to showing that, in the case of an internal carcass in which a steel wire is wound in a short pitch, the resistance to collapse or to the crushing strength of the pipe is considerably improved when an LDX

2101 duplex steel is used rather than a simple 316L austenitic stainless steel, going from 165 bar to 210 bar. This increase in the resistance to collapse is in no way surprising, since duplex stainless steels are reputed to have substantially higher mechanical properties than those of austenitic stainless steels. As an indication, the yield strength of a 316 stainless steel strip in the as-cast state, i.e. before profiling, is about 300 MPa, whereas the yield strength of an LDX 2101 steel strip in the as-cast state, before profiling, is about 650 MPa. The profiling operation admittedly increases the mechanical properties, but the tensile strength of profiled duplex steel strip produced according to this prior art remains below 950 MPa.

Document WO 00/00650 discloses a flexible pipe in which the internal carcass is made of stainless steel work-hardened before profiling. The work-hardening operation increases the mechanical properties of the strip, thereby making it possible to lighten the structure and/or increase its resistance to collapse. The intended materials are type 301,304 and 316 austenitic stainless steels. Plowever, this document also mentions duplex steels and gives details about examples using 301 and 316L steel strips work-hardened to C850 and C1000 levels according to the EN 10088-2 standard. In the C1000 state, the tensile strength of these materials, specified in table 17 of this standard, is around 1000 to 1150 MPa. WO 00/00650 also mentions in its table I an example of an internal carcass made from a duplex steel strip work-hardened to the 2B state, having a yield strength of only 720 MPa. The reader may also refer to table 6 of the EN 10088-2 standard, which defines the meaning of the term 2B state. It should be noted that the process for manufacturing such work-hardened strip includes a heat treatment step after the cold-rolling step. WO 00/00650 provides no teaching about the corrosion resistance of the work-hardened stainless steels and in particular about the way in which their corrosion resistance is degraded with work-hardening.

Also, one problem that arises, which the present invention aims to solve, is how to provide a process for manufacturing a flexible pipe in which the stainless steel armor wires not only have a high tensile strength but also a high corrosion resistance.

For the purpose of solving this problem, the present invention relates, according to a first aspect, to a process for manufacturing a flexible tubular pipe for transporting hydrocarbons, of the type in which: an impermeable pressure sheath and wires of austenitic-ferritic stainless steel are provided; said austenitic-ferritic stainless steel wires are work-hardened and said work-hardened wires are wound in a long pitch around said pressure sheath so as to form a tensile armor ply; and an external sheath is then formed around said tensile armor ply; according to the invention, said provided austenitic-ferritic stainless steel wires are workhardened, reducing their cross section by at least 35% so as to obtain work-hardened wires having a tensile strength greater than 1300 MPa, and said work-hardened wires are wound up directly after the work-hardening step, whereby said work-hardened wires retain their mechanical properties after being wound.

Thus, according to one particularly advantageous feature of the invention, the austenitic-ferritic stainless steel wires are greatly work-hardened, reducing their cross section by at least 35% so as to give the technical effect of greatly increase their tensile strength in order for it to reach at least 1300 MPa, but to the detriment of their corrosion resistance. This 35% reduction in cross section corresponds to a degree of work-hardening T (also called the reduction ratio) of the same value, which is measured, as will be explained in greater detail in the rest of the description, by making the difference between the cross sections Sr of the steel wires before reduction and the cross section Sf of the steel wires after reduction and dividing this difference by the cross section of the wires before reduction, i.e. T = (Sr - Sf)/Sf.

Consequently, by virtue of their tensile strength, these wires are able to be used to form tensile armor wires intended for long-length flexible tubular pipes, which can then be suspended above seabeds at great depth. As regards the corrosion resistance, the tensile armor wires are in fact protected inside the annular space of the flexible pipe, between the internal pressure sheath and the external sheath. Specifically, the pressure sheath allows a small portion of the corrosive gases flowing inside to diffuse through its wall, as will be explained below in greater detail. Furthermore, the external sheath preserves the tensile armor wires from the seawater and thus makes it possible to limit the chloride and oxygen contents in the armor wires. Chlorides generally accentuate local pitting corrosion, whereas oxygen promotes overall corrosion of the stainless steel wires.

Advantageously, said armor wires are work-hardened cold and are not subjected to any subsequent softening heat treatment before they are wound cold, so as to produce armor plies. Thus, any relaxation of the crystal lattice of the steel, which would cause its mechanical properties to drop, is avoided.

According to a preferred method of implementing the invention, wires made of an austenitic-ferritic stainless steel containing between 21 and 25% chromium and between 1.5 and 7% nickel are provided so as to be able to obtain, without any risk of degradation, steel wires having a tensile strength greater than 1300 MPa, provided that their degree of work-hardening corresponds to a reduction of at least 35% in their cross section. Moreover, wires made of austenitic-ferritic stainless steel containing between 0.1 and 0.3% nitrogen are preferably provided, thereby making it possible to increase the yield strength and the tensile strength of the steel wires, while maintaining their toughness.

According to one particularly advantageous method of implementation, wires made of austenitic-ferritic stainless steel containing between 21 and 23% chromium, between 4.5 and 6.5% nickel and between 0.1 and 0.2% nitrogen are provided. Thus, the wires may be work-hardened with a reduction ratio of about 36% and may have a tensile strength of 1300 MPa. Advantageously, these wires made of austenitic-ferritic stainless steel have a Rockwell hardness of between 40 and 48 PIRc, for example 40 PIRc. According to one particular embodiment, said austenitic-ferritic stainless steel wires are work-hardened, reducing their cross section by at least 45% so as to obtain work-hardened wires having a tensile strength equal to or greater than 1400 MPa.

Advantageously, said austenitic-ferritic stainless steel wires have a substantially rectangular cross section, with a width of between 5 mm and 25 mm and a thickness of between 2 mm and 7 mm, preferably between 3 mm and 6 mm.

Preferably, at least one carbon steel wire is furthermore wound around said internal pressure sheath in order to form a pressure vault between said internal pressure sheath and said tensile armor ply. Therefore, and as will be explained below, the H2S that diffuses through the wall of the internal pressure sheath is consumed, so as to form especially iron sulfides, and thus does not corrode the stainless steel of the armor plies.

In addition, an intermediate polymeric layer is advantageously formed around said pressure vault before said work-hardened wires are wound in a long pitch, in order to prevent galvanic coupling between said pressure vault and said tensile armor ply. This intermediate layer is produced either by helically winding a strip or by extruding a sheath directly onto the pressure vault.

Furthermore, according to another embodiment of the pressure vault, a duplex stainless steel wire is provided, this being wound around the internal pressure sheath.

According to another aspect, the present invention relates to a flexible tubular pipe for transporting hydrocarbons, obtained by the manufacturing process as described above.

Other features and advantages of the invention will emerge on reading the description given below of particular embodiments of the invention, given by way of indication but implying no limitation, with reference to the single figure in which a flexible tubular pipe structure obtained in accordance with the process of the invention is partially illustrated.

The present invention relates to a process for manufacturing a flexible pipe in which the tensile armor wires are made of highly work-hardened duplex stainless steel. It also relates to a pipe produced according to such a process.

Duplex stainless steels, which are also called austenitic-ferritic stainless steels owe their name to their two-phase structure, comprising substantially equal proportions of austenite and ferrite. This type of stainless steel therefore combines the qualities of the two phases, namely high ductility and resilience of austenite on the one hand, and high toughness and corrosion resistance of the ferrite on the other. Duplex stainless steels therefore basically have good mechanical properties and good corrosion resistance, particularly resistance to localized corrosion and stress corrosion.

They are therefore widely used in the offshore industry, their properties relying on the equilibrium between the austenitic phase and the ferritic phase. During their production and processing, it is necessary to respect the strict rules that guarantee this equilibrium. A duplex steel firstly solidifies in the ferritic domain, and then it is over the course of cooling that a portion of the ferrite is transformed to austenite. The ferrite content in the metal is then directly related to the cooling rate. Too high a cooling rate results in a microstructure with too high a ferrite content. Excessive ferrite lowers the resilience and the ductility. It is recommended to choose a ferrite content between 30 and 60% for duplex steels and between 35 and 65% for superduplex steels.

Conversely, too slow a cooling rate causes grain coarsening, the formation of the σ-phase and the precipitation of nitrides and carbides which, may considerably reduce the mechanical properties and the corrosion resistance.

In practice, a suitable microstructure is obtained by an annealing or annealing/rapid cooling heat treatment, which comprises two successive steps: a step in which the product is heated to a temperature of around 1000°C to 1300°C and a controlled rapid cooling step. This treatment is applied after the hot rolling and/or after the cold working, whether this is by rolling, drawing or swaging.

Table I below gives the chemical composition of the principal duplex steels:

Table I

Category	EN10088 grade	Trade name	%Cr	%Ni	%C	%Mo	%N	PREN
Lean duplex	1.4162	LDX2101® (Outokumpu)	21.5	1.5	0.03	0.3	0.22	25
Lean duplex	1.4362	((Outokumpu) 4362 (Ugitech)	23	4	0.02	0.2	0.1	25-26
Lean duplex		AL2003™ (Allegheny)	21.5	3.7	0.03	1.8	0.17	30
Duplex	1.4462	2205 (Outokumpu) 4462 (Ugitech)	21-23 22	4.5-6.5 5.7	<0.03 0.02	2.5-3.5 3.1	0.1-0.2 0.17	31-38 35
Super-duplex	1.4410	2507 (Outokumpu)	25	7	0.02	4	0.27	42
Hyper-duplex		SAF3207HD (Sandvik)	32	7	<0.03	3.5	0.5	>50

The addition of nitrogen N, which has the property of inducing the γ-phase (austenite), promotes the structural hardening of the steel by a fine interstitial dispersion mechanism, thereby furthermore increasing the yield strength and the tensile strength without degrading the toughness.

The resistance to localized pitting and crevice corrosion, in particular with respect to chlorides, is also improved. It is generally approximated by calculating the PREN, the acronym for Pitting Resistance Equivalence Number, or pitting index, from the following empirical formula: PREN = (Cr%) + 3.3 (Mo%) + 16 (N%). Moreover, the higher the PREN, the better the pitting corrosion resistance. Those duplex steels having a PREN between 40 and 50 are called superduplex steels. Those steels having a PREN greater than 50 are called hyperduplex steels. Duplex steels depleted in molybdenum and/or nickel having a PREN not exceed20 ing 30 are called lean duplex steels. As a general rule, the cost of duplex steels increases with their PREN, the least expensive being lean duplex steels and the most expensive being hyperduplex steels.

Apart from their good localized corrosion resistance, duplex steels are more so 5 reputed for their good stress corrosion resistance in aqueous media comprising high concentrations of H2S and chlorides. Table II below gives the minimum mechanical properties of duplex steels in the annealed state.

Table II

Category	EN 10 088 grade	UNS grade	Trade name	R_e (MPa)	R_m (MPa)	Elongation (%)
Lean duplex	1.4162	S32101	LDX2101® (Outokumpu)	480	700	38
Lean duplex	1.4362	S32304	2304 (Outokumpu) 4362 (Ugitech)	450	670	40
Lean duplex		S32003	AL 2003™ (Allegheny)	520	720	40
Duplex	1.4462	S31803	2205 (Outokumpu) 4462 (Ugitech)	510	750	35
Super-du- plex	1.4410	S32750	2507 (Outokumpu)	560	830	35
Hyper-du- plex		S33207	SAF3207 HD (Sandvik)	700	950	25

As a general rule, superduplex and above all hyperduplex steels are those that have the best mechanical properties and also the highest cost. If the product has been cold-worked, the annealing treatment is usually applied at the end after cold-working, whether this is for flat products of the sheet or strip type, or else for long products such as wires or profiles. Table II above corresponds to this case.

However, the normative documents envisage rarer cases in which such an annealing treatment is not carried out after the cold-working. In such a case, the treatment must obviously be carried out upstream, for example after the hot-rolling. The reader may refer for example to table 6 of the standard EN 10088-2 relating to flat products and where the only case having the abbreviation 2H reDK 179251 B1 lates to a work-hardened cold-rolled sheet for which no heat treatment was applied at the end of transformation. In the case of long products, the reader may refer to table 7 of the standard EN 10088-3 in which materials in the 2H state, corresponding to similar situations for spring steels, are envisaged.

In the context of the present invention, the expression work-hardened duplex denotes a duplex stainless steel product that has undergone, after hot-rolling, cold-working of the rolling and/or drawing and/or swaging type, not having undergone at the end any annealing treatment. This corresponds to the 2H state or cold-worked condition of the aforementioned standard.

In the case of tensile armor wires, two main processes are envisaged. For steel products output by a long-product line, these are the cold-rolling and/or colddrawing of a round wire stock delivered in the annealed state. The wire then undergoes no heat treatment after the rolling and/or drawing. As regards products output by a flat-product line, cold-rolled sheet in the 2H state is provided, the sheet then being slit by a process involving no heating, for example by water-jet cutting, in order to bring it to the desired width. Another possibility is to deliver thick hot-rolled and annealed sheet, which is then split into strips and finally these strips are cold-rolled. In all cases, no heat treatment is carried out after the final cold-rolling or cold-drawing step.

More particularly as regards the work-hardening of austenitic-ferritic stainless steel wire, one important feature of the invention lies in the fact that this is carried out cold after annealing and with a high reduction ratio. This reduction ratio T is measured by the difference in cross sections of the steel wire before Sr and after Sf the final cold-working step divided by the cross section of the wire before working, i.e. T = (Sr-Sf)/S_r, where Sr denotes the cross section of the wire after the annealing treatment and before cold-working, and Sf denotes the cross section of the finished wire after cold-working. The calculation of T therefore takes into account only the work-hardening carried out after annealing.

Table III below presents two examples of work-hardened duplex stainless steel wire:

Table III

Cross section after annealing	Finished cross section after cold-rolling	Reduction ratio T	Duplex grade	HRc hardness of the finished product	Tensile strength (R_m) of the finished product
Round: 8.5 mm diameter	Rectangle: 12 mm x 3 mm	37%	2304	43	1400 MPa
Round: 9.5 mm diameter	Rectangle: 13.3 mm χ 3.4 mm	36%	2205	40	1300 MPa

In the case of 2205 duplex stainless steel in the last row of table III and also in table II, cold-rolling with a reduction ratio T of around 36% enables the tensile strength R_m of the steel wire to be greatly increased, since it goes from 750 MPa after annealing to 1300 MPa after cold-rolling, i.e. an increase of 80%. With regards 2304 duplex steel, the increase exceeds 100% since the tensile strength goes from 670 MPa to 1400 MPa.

The reduction ratios of these two examples of duplex steel wire are equal to or greater than the minimum reduction ratio required for processing a flexible tubular pipe according to the invention, since the tensile strength thereof is 1300 MPa and 1400 MPa respectively.

The work-hardening of stainless steel to increase its tensile strength R_m is a com20 mon practice as indicated in the normative documents EN 10088-2 and EN 100088-3. However, the standard EN 10088-2 relating to plate, sheet and strip mention no highly work-hardened duplex steel, this method of production appearing to be mainly reserved for austenitic stainless steel (see table 18). On the other hand, the standard EN 10088-3 relating to stainless steel wire, and especially to wire used for manufacturing springs, mentions in table B.4 of annex B, for the C1400 state, highly work-hardened 2205 duplex steel wire having a diameter of less than 6 mm and a yield strength of around 1400 MPa.

However, such highly work-hardened wire is intended for the production of springs and has never been intended or even envisaged for producing armor wires for submarine flexible pipes. This is because it is well known that the corrosion resistance of duplex steel is degraded when subjected to substantial cold work-hardening, and this is the reason why these materials are normally used in the annealed state. The invention also lies in the use of such highly work-hardened stainless steel wire, the reduction ratio of greater than 35%, to form tensile armor wires.

Particularly surprisingly, such wire is sufficiently resistant to corrosion so as to be able to be used as tensile armor wires for flexible pipes transporting highly corrosive hydrocarbons.

In addition, the natural solution for increasing the mechanical properties of stainless steel wire without degrading the corrosion resistance is instead to choose steels from the highest range of the duplex steel family, i.e. to choose superduplex or hyperduplex steels.

Finally, the reference standard used by those skilled in the art, namely the NACE MR0175/ISO 15156 standard to which the API RP 17B standard refers to the paragraph Materials - Unbonded Pipe - Pressure and Tensile Armor Layers, recommends, especially in table A.25, not to exceed a hardness of 36 HRc for work-hardened duplex steels that have to be used in a corrosive medium. Now, it turns out that a hardness of 36 HRc corresponds approximately to a tensile strength R_m of 1200 MPa. Consequently, a person skilled in the art would have had to overcome a technical preconception to envisage using work-hardened duplex steels having a tensile strength R_m greater than 1400 MPa and a hardness greater than 43 HRc.

The single figure shows a flexible pipe 22 obtained in accordance with the invention. The structure of the pipe, from the inside outward, will now be described.

Thus, according to a first embodiment of the tubular pipe 22, a carcass 10 consisting of an interlocking metal strip winding is formed that prevents the pipe from collapsing under the effect of the external pressure. Next, an impermeable plastic internal pressure sheath 12 extruded around the carcass 10 is made. This impermeable internal pressure sheath 12 is particularly resistant to the chemical action of the hydrocarbon transported. Next, a profiled metal wire is helically wound in a short pitch around the internal sheath 12 so as to constitute a pressure vault 14 capable of mainly withstanding the pressure of the fluid flowing inside the internal pressure sheath 12.

In addition, a plurality of wires made of austenitic-ferritic stainless steel containing for example between 21 and 23% chromium, between 4.5 and 6.5% nickel and between 0.1 and 0.2% nitrogen is provided. These wires are cold work-hardened with a degree of work-hardening or reduction ratio of greater than 35%. Such a reduction ratio gives them a tensile strength of greater than 1300 MPa.

Said plurality of wires is divided into two approximately equal groups of wires. The wires of the first group are wound in a long pitch, side by side, around said pressure sheath, for example at an angle of between 25° and 35°, to the axis of the pipe in order to form a first armor ply 16, whereas the wires of the second group are also wound in a long pitch, side by side, at substantially the same angle but in the opposite direction in order to form a second tensile armor ply 18 crossed with the first. Finally, an external protective sealing sheath 20 is formed, for example by extruding a polymer, around said second tensile armor ply 18 so as to obtain a flexible tubular pipe 22.

The tensile armor wires are in fact housed in the annular space of the flexible pipe 22, i.e. between the internal pressure sheath 12 and the external sheath 20, and are therefore relatively protected. A first surprising effect is the high level of protection provided by the pressure sheath 12. This is because, even though the internal pressure sheath 12 lets a portion of the corrosive gases diffused therethrough, it turns out that their passage is greatly limited. Thus, for example, when the H2S partial pressure at the center of the pipe is 2 bar, that in the annular space is less than 0.2 bar.

Furthermore, a second unexpected effect is that of the external sheath 20. It turns out in fact that the external sheath 20 has both a favorable effect and an unfavorable effect, but surprisingly the favorable effect predominates. The favorable effect is to limit/prevent contact with seawater and therefore to limit the content of chloride and oxygen in the armor wires. The unfavorable effect is to retard the discharge into the seawater of the corrosive gases that have diffused through the pressure sheath 12, in such a way that a portion of said gases remains trapped in the annular space. If there were to be no external sheath 20 and if the seawater were to be forced between the tensile armor wires, the problem of acid corrosion or embrittlement by H2S would no longer arise, but it would be necessary to use, as is conventional, top-of-the-range duplex steels, namely superduplex or hyperduplex steels, for correctly resisting the pitting corrosion caused particularly by chlorides. However, it turns out that, surprisingly, highly work-hardened duplex steels are more resistant to the acid gases, which have diffused through the pressure sheath 12, than to total immersion in disturbed aerated seawater.

Moreover, a third favorable technical effect appears in the particular case when the flexible tubular pipe 22 includes, as is the case in the aforementioned figure, a pressure vault 14 consisting of wires made of low-alloy or non-alloy carbon steel, which are helically wound in a short pitch between, on the one hand, the internal pressure sheath 12 and, on the other hand, the tensile armor plies 16,18 made of highly work-hardened duplex steel. This surprising effect, which results from the tight confinement in the annular space and from the consumption of a large part of the H2S by reaction with the carbon steel, greatly reduces the hydrogen embrittlement to which the highly work-hardened duplex steel tensile armor wires must be resistant. Many studies were necessary in order to demonstrate this effect. The terms carbon steel and low-alloy steel are defined in particular in the European standard EN 10027. Examples of carbon steel and low-alloy steel that may be suitable for producing the pressure vault 14 are described in documents WO 91/16461 and WO 96/28575. Examples of FM35 non-alloy steel and 32C1 and 30CD4 low-alloy steels may in particular be mentioned, all three being defined according to the French national standardization organization AFNOR.

The annular space is mainly filled with highly confined wires. In the annular space, there is therefore a very high metal surface area relative to the low interstitial volume. In addition, the diffusion of corrosive gases through the pressure sheath 12 is slow, the flow rates involved being low. Consequently, the low flow rate of H2S that has diffused through the pressure vault 14 is in the presence of a very high active surface area of carbon steel, so that a large portion of the H2S is consumed by reacting with this steel to form corrosion products of the iron sulfide type. By virtue of this effect, the flow rate of residual H2S reaching the highly workhardened duplex steel tensile armor wires of the armor plies 16, 18 is extremely low, almost 100 times lower than that corresponding to the case in which the annular space includes no metal layer made of carbon steel. This favorable effect, which prevents excessive acidity, i.e. a low pH, in the annular space, makes it possible in practice to use highly work-hardened bottom-of-the-range or middleof-the-range duplex steels, for example lean duplex steel, as indicated in table II above, or in the severest cases 2205 duplex steel, thereby enabling the production costs of the pipes to be reduced. The galvanic corrosion between, on the one hand, the carbon steel pressure vault 14 and, on the other hand, the duplex steel armor wires, is negligible in most applications. In the severest cases, to avoid this problem, a polymeric intermediate layer of the sheath or wound strip type may be inserted between the pressure vault 14 and the armor plies 16, 18.

According to another embodiment (not shown), the pipe 22 has no pressure vault, and the tensile armor wires are then generally wound at an angle close to 55°, suitably being able to take up the stresses due to the pressure of the transported fluid. In this case, it is preferable to produce the tensile armor wires with a middleof-the-range or top-of-the-range duplex steel, especially type 2205 duplex steel or 2507 type superduplex steel.

Moreover, according to yet another embodiment, it is also envisaged producing the pressure vault 14 with wires made of stainless steel or conventional duplex steel that have undergone little or no work-hardening.

Advantageously, the reduction ratio T of the tensile armor wires is less than 75%, since otherwise, on the one hand, the hydrogen embrittlement resistance becomes too low and, on the other hand, the elongation at break itself becomes insufficient. The elongation at break must remain greater than 5% in order to allow the operation of helically winding the wires to be carried out.

The mode of work-hardening is of great importance. Work-hardening in pure tension parallel to the axis of the wire does not allow the mechanical properties to be increased sufficiently. The best mode of work-hardening is flattening, by rolling between two rolls. For the same reduction ratio, it is the latter mode that seems to provide the best increase in mechanical properties.

The reduction ratio T varies between 35% and 75%, advantageously between 45% and 65%. Tensile strength R_m of the finished wire varies between 1300 MPa and 1600 MPa and more advantageously is 1400 MPa. The hardness of the finished wire varies between 40 HRc and 48 HRc, advantageously 44 HRc.

As regards the choice of steel grade, lean duplex steel, with the reference LDX 2101, as listed in table II, although not very expensive as it contains only a very small amount of nickel, has the drawback of being quite sensitive to crevice corrosion which can be initiated should the annular space be flooded with seawater as a consequence of accidental tear in the external sheath of the flexible pipe. The same applies to lean duplex steel with the reference 2304 and as listed in table II. These materials are therefore reserved for applications in which this risk of tearing can be avoided by other means, especially by reinforcing or protecting the external sheath. However, the steel grade with the reference 2205 in table II is sufficiently resistant to this type of corrosion. 2205 steel becomes sensitive to crevice corrosion only when the temperature exceeds 50°C, this being rare in the annular space of a flexible pipe. Therefore, this steel grade constitutes a good choice for producing work-hardened armor wires according to the invention.

For high-temperature applications, it is advantageous to use work-hardened type

2507 superduplex steels.

The tensile armor wires could also be produced from other steel grades of highly work-hardened stainless steel, especially from austenitic, superaustenitic or nickel-based stainless steels. However, these steels are either of much lower performance or are more expensive than duplex steels. Thus, austenitic stainless steels have markedly lower mechanical properties than duplex steels and must therefore be work-hardened considerably more than duplex steels in order to achieve an R_m of greater than 1300 MPa, which reduces their ductility and their hydrogen embrittlement resistance. Furthermore, superaustenitic stainless steels, especially those containing around 6% molybdenum, and nickel-based stainless steels containing more than 30% nickel have the drawback of being very expensive but mainly because of their high nickel content.

Claims

claims

1.1

Single figure

IMmsH Fäto? Asm TsAßSMASK Öma

SEARCH REPORT - PATENT Application No. PA 2011 70657 1. 1 1 Certain claims were found unsearchable (See Box No. I). 2. 1 1 Unity of invention is lacking prior to search (See Box No. II). A. CLASSIFICATION OF SUBJECT MATTER F16L 11/08; C22C 38/00; C22C 38/08; C22C 38/18 (all version 2006.01) According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Minimum documentation searched (classification system followed by classification symbols) IPC & CPC: C22C; F16L Documentation searched other than minimum documentation to the extent that such documents are searched in the fields DK, NO, SE, FI: IPC classes as above. Electronic database consulted during the search (name of database and, where practicable, search terms used) EPODOC, WPI C. DOCUMENTS CONSIDERED TO BE RELEVANT Category * Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim no. A, D WO 2006/097112 A2 (NKT FLEXIBLES I / S) September 21, 2006 Page 4, paragraph 4; page 8, paragraph 4; page 15, paragraph 1; FIG. 1 - A US 2009/0050228 A1 (COUTAREL, A. et al.) February 26, 2009 Paragraph 0000 A, D US 5407744 A (MALLEN HERRERO, J. et al.) April 18, 1995 - A, D US 6282933 BI (DUP0IR0N, F.) September 4, 2001 - 1 1 Further documents are listed in the continuation of Box C. * Special categories of cited documents: P Document published prior to the filing date but later than the A Document defining the general state of the art which is not priority date claimed. considered to be of particular relevance. T Document not in conflict with the application but cited to D Document cited in the application. An Earlier application or patent but published on or after the filing date. understand the principle or theory underlying the invention. X Document of particular relevance; the claimed invention cannot be considered novel or cannot be considered to involve an inventive step when the document is taken alone. Y Document of particular relevance; the claimed invention cannot be considered to involve an inventive step when the document is combined with one or more other such documents, such L Document which may throw doubt on priority claim (s) or which is cited to establish the publication date of another citation or other special reason (as specified). O Document referring to an oral disclosure, use, exhibition or other betyder. combination being obvious to a person skilled in the art. Document member of the same patent family. Danish Patent and Trademark Office Date of completion of the search report Helgeshøj Allé 81 DK-2630 Taastrun March 8, 2017 Denmark Authorized officer Telephone No. +45 4350 8000 Facsimile No. +45 4350 8001 Peter Eisner Telephone No. +45 4350 8330

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SEARCH REPORT - PATENT Application No. PA 2011 70657 C (Continuation). DOCUMENTS CONSIDERED TO BE RELEVANT Category * Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim no.

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SEARCH REPORT - PATENT Application No. PA 2011 70657 Box No. In Observations where certain claims were found unsearchable

This search report has not been established in respect of certain claims for the following reasons:! □ Claims Nos:

because they relate to subject matter not required to be searched, namely:

A method of producing a flexible tubular tube (22) for the transport of hydrocarbons and of the type in which:

- an impermeable pressure cap (12) is provided,

- threads of austenitic-ferritic stainless steel are provided,

- which austenitic-ferritic stainless steel wires are deformation hardened,

- which deformation-cured wires are wound with a long rise around the pressure sheath (12) so as to form a wood-reinforcing layer (16, 18), and

- an outer sheath (20) is formed around the tensile reinforcement layer, characterized in that the provided austenitic-ferritic stainless steel wires are deformed, thereby reducing their cross-section by at least 35%, so that deformation hardened wires having a tensile strength greater than 1300 MPa are obtained. and that the deformation-hardened wires are wound up directly after the deformation-hardening step, whereby the deformation-hardened wires retain their mechanical properties after being wound.

2. I I Claims Nos:

because they relate to parts of the patent application that do not comply with the prescribed requirements to such an extent that no meaningful search can be performed, specifically:

Method according to claim 1, characterized in that the reinforcing wires are cured by cold deformation.

Process according to claim 1 or 2, characterized in that threads are made of austenitic-ferritic stainless steel containing between 21 and 25% chromium and between 1.5 and 7% nickel.

Process according to any one of claims 1 to 3, characterized in that threads are made of austenitic-ferritic stainless steel and contain between 0.1 and 0.3% nitrogen.

Process according to claims 3 and 4, characterized in that threads are made of austenitic-ferritic stainless steel containing between 21 and 23% chromium, between 4.5 and 6.5% nickel and between 0.1 and 0.2 % nitrogen,

Process according to any one of claims 1 to 5, characterized in that threads are made of austenitic-ferritic stainless steel and having a Rockwell hardness of between 40 and 48 HRC.

Process according to any one of claims 1 to 6, characterized in that the austenitic-ferritic stainless steel wires provided are deformed, thereby reducing their cross-section at least 45%, so that deformation-curing wires having a tensile strength equal to or greater than 1400 are obtained. MPa.

Method according to any one of claims 1 to 7, characterized in that at least one carbon steel wire is wound around the inner pressure sheath (12) in order to form a pressure vault (14) between the inner pressure sheath and the wooden reinforcement layer (16, 18).

Method according to claim 8, characterized in that an intermediate polymeric layer is formed around the pressure vault (14) before the deformation-cured wires are wound with a long rise, to prevent galvanic coupling between the pressure vault (14) and the pressure reinforcing layer (16, 18). ).

Method according to claim 8 or 9, characterized in that a stainless steel wire is provided for forming the pressure vault (14).

Flexible tubular tube for transporting hydrocarbons obtained by the method of any one of claims 1 to 10.

3. I I Claims Nos .: because of other matters.

Box No. II Observations where unity of invention is lacking prior to the search

The Danish Patent and Trademark Office found multiple inventions in this patent application, as follows:

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SEARCH REPORT - PATENT Application No. PA 2011 70657 SUPPLEMENTAL BOX Continuation of Box [.]

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