CN106030178B - High resistance flexible tubular pipe and method of manufacture - Google Patents

Abstract

The present invention relates to a method for manufacturing a flexible tubular conduit (10) for transporting hydrocarbons, and to a flexible tubular conduit manufactured thereby. The method comprises the following steps: a) providing a thermoplastic fluoropolymer which is formable in a molten state; b) shaping said thermoplastic fluoropolymer in the molten state so as to produce a sealed tubular sheath (12) having an inner wall (21); and c) helically winding armor wires around the sealed tubular jacket (12) to form an assembly of armor wire layers (14, 16, 18); while the inner wall (21) is free.

Description

High resistance flexible tubular pipe and method of manufacture

Technical Field

The present invention relates to a method for manufacturing a flexible tubular conduit and to a flexible tubular conduit obtained with said method.

Background

One conceivable field of application is that of Flexible tubular pipes used in the field of hydrocarbon transportation, which is described in the american petroleum institute published standard documents API 17J, "Specification for underbonded Flexible Pipe", API 16C, "hook and Kill Systems" and API 7K, "road Drilling Hose".

Flexible tubular conduits intended to transport hydrocarbons typically comprise an inner sealing sheath made of a polymeric material and defining a flow path within which the hydrocarbon or mud can flow. Furthermore, the inner sealing sheath is covered, on the one hand, by pressure struts (vaults) made of shaped wires (shaped wires) wound at short pitches so as to be able to resist the radial stresses induced by the fluid circulating inside the inner sealing sheath and by the hydrostatic pressure, and, on the other hand, by a tensile armour layer made of metal wires wound at long pitches, intended to absorb partially or totally the tensile and radially internal loads applied to the tubular duct. In addition, the tensile armour layers are typically covered by an outer sealing sheath intended to prevent water ingress through the armour layers and pressure struts. The region between the inner and outer sealing sheaths, including the pressure struts and the at least one tensile armour layer, defines an annular space of the pipe. Regardless of these precautions, the outer sealing sheath may be perforated just during use of the flexible tubular pipe on the seabed, and water under pressure may enter the thickness of the pipe and apply a radial load to the inner sealing sheath. When this occurs, and when the pressure of the hydrocarbon within the inner sealing sheath drops, the sheath has a tendency to collapse on itself and be damaged.

To overcome this, therefore, flexible tubular conduits are equipped with a metallic carcass inside an internal pressure sheath, made of interlocked metallic strips wound at an angle close to 90 ° with respect to the longitudinal axis of the flexible tubular conduit, spiralled with a short pitch. Such flexible tubular conduits are known by their english name "rough-bore".

On top of this, the service conditions of flexible tubular pipelines have become more severe, as the production of hydrocarbons is carried out in deeper and deeper offshore waters. Thus, the hydrocarbons are generally hotter and, obviously, the hydrostatic pressure is greater. Thus, in particular in order to withstand the high temperatures and chemical nature of these hydrocarbons, use is made of a sealing sheath made of a material having excellent properties, and in particular a thermoplastic fluoropolymer. Reference may be made to WO96/30687 which describes a flexible tubular duct equipped with an inner metal shell covered with a thermoplastic fluoropolymer sealing sheath.

Thus, in a first step in the manufacture of the flexible tubular conduit, the fluoropolymer sheath is coaxially extruded onto the metal casing. Once the sheath has been extruded, the sheath thus rests against the metal casing. The inner wall thereof thus follows the roughness of the metal casing, since the polymer is still in a viscous state before it has completely cooled down. After this, the sealing sheaths, thus supported by the metal casing, are successively covered with a layer of helically wound armor wires.

However, incipient cracks are found in the inner wall of the sealing boot at discontinuities in the metal shell. Above that, if the pipe is suddenly depressurized, the residual stress created at these discontinuities can lead to a decondensation force (decohesion) of the tight-sealing jacket. Also, local de-molding (deplastic) of the sealing boot is observed and this impairs its mechanical properties.

Disclosure of Invention

One problem that arises and which the present invention seeks to solve is therefore the ability to retain the sealed tubular sheath during the service life of the pipeline in a harsh marine environment.

To this end, according to a first subject, the invention proposes a method for manufacturing a flexible tubular pipe intended for the transport of hydrocarbons, comprising the following steps: a) providing a thermoplastic fluoropolymer which is formable in a molten state; b) shaping said thermoplastic fluoropolymer in the molten state so as to obtain a sealed tubular sheath having an inner wall; and c) helically winding armor wires around the sealed tubular jacket to form a set of armor wire layers; and in step b), the inner wall is released.

It is thus a feature of the present invention that the fluoropolymer is formed in the molten state to produce a sealed tubular sheath. In particular, once it has been formed, the inner wall of the tubular sheath is released while the polymer is still in the rubbery state and therefore evolves towards the solid state in free air. Also, the inner wall of the tubular sheath may be released during an optional heat treatment step, which is performed after the step of shaping in the molten state, during which step it is kept at a temperature below its melting point for a determined length of time, followed by controlled cooling. Thus, in contrast to the method according to the prior art, in which the inner wall of the tubular jacket is pressed directly against the metal casing with roughness and gaps, the cooling of the inner wall and its transition to the solid state according to the invention occurs uniformly and homogeneously over the entire cylindrical surface of the inner wall. Therefore, no initial cracks or residual stresses occur in the inner wall of the tubular sheath. Thus, the service life of the tubular jacket within the pipe is increased. Furthermore and surprisingly, the absence of a metallic casing is not fatal to the inner tubular sheath even when the flexible tubular conduit is installed at extreme depths and is transporting hot hydrocarbons. Flexible tubular pipes without a metal carcass are known and are known by their english term "smooth-bore" pipes. However, they are used under conditions where the hydrostatic pressure is low, i.e. close to the surface of the marine environment in an offshore situation, and/or where fluids, fluids or hydrocarbons are relatively acidic and have gases, are transported in an onshore environment.

It can therefore be seen that the drawbacks of flexible tubular conduits without an internal metal casing and used under severe temperature and pressure conditions are significantly compensated by the mass of the internal tubular sheath obtained at the time of manufacture. These technical qualities are associated with the dissipation of mechanical stresses through the thickness of the sheath and with the absence of incipient cracks. In particular, the fact that the inner tubular sheath is not extruded to the metal shell allows the polymeric material to thermally shrink, which thereby reduces residual stresses.

It is conceivable to make the flexible tubular conduit without the inner metal sheath from a less creeping material, such as PEEK, which stands for polyetheretherketone (polyetheretherketone). However, these materials have two major disadvantages. First, they have excessive stiffness, which means that they require very large bending radii. And therefore, at the manufacturing level, it requires very large spools and in use means that it cannot have a configuration compatible with the available space on, for example, a drilling platform. The second aspect is that during high temperature curing above Tg (Tg of about 145 ℃ for PEEK), the matrix becomes harder and the elongation properties are significantly reduced. Essentially 20% to 5% loss, which is somewhat incompatible with high dynamic stress loads.

According to a particularly advantageous embodiment of the present invention, a thermoplastic fluoropolymer is provided, having a melting point higher than 300 ℃, or even higher than 310 ℃. Thus, its ability to resist the transport of hot hydrocarbons will be correspondingly improved. Preferably, a perfluoroalkoxy compound is provided that produces a sealed tubular sheath.

Unlike polytetrafluoroethylene, perfluoroalkoxy compounds work readily in the molten state and have the same mechanical strength and chemical resistance elasticity. In contrast, perfluoroalkoxy compounds are less susceptible to creep than polytetrafluoroethylene.

Furthermore, during the treatment in the molten state, said inner wall of the tubular sheath is formed so as to obtain a smooth inner surface. Thus, in the absence of surface unevennesses, the inner wall evolves from the rubbery state toward the solid state even in a completely uniform manner.

Preferably, pressure armour wires are helically wound around the sealed tubular sheath at a short pitch to form a pressure armour layer capable of withstanding pressure. This pressure armour layer, the outer wall of which will press against the inner wall of the pressure armour layer, in particular makes it possible to absorb internal and external radial stresses caused by the pressure of the hydrocarbons inside the sealed tubular sheath and by the hydrostatic pressure exerted by the external environment. Advantageously, a creep resistant layer is applied between the inner sealing sheath 12 and the pressure armor 14 to limit the fluoropolymer creep to discontinuities formed by abutting loops of the pressure struts. Additionally, a plurality of tensile armour wires are helically wound around the pressure armour layer at a long pitch to form at least one tensile armour layer capable of resisting tension. The tensile armor wires are intended to absorb tensile forces applied to the flexible tubular conduit and partially or completely absorb internal pressure applied by hydrocarbons flowing therealong within the sealed tubular sheath. These tensile forces are naturally applied when the flexible tubular conduit is suspended from the surface of the marine environment and extends below the seabed. In addition, the greater the water depth, the higher these forces.

In addition, according to a further step, an outer sealing sheath made of polymeric material is advantageously formed around the set of layers of armor wires, in order to prevent the annular space of the flexible tubular duct comprising the set of layers of armor wires from overflowing, since the wires are made of steel and will corrode more rapidly if they come into contact with water.

Preferably, the method further comprises a further step wherein a metal layer is formed around the one outer sealing sheath, such as a metal casing, pressure struts or even tensile armour.

According to a second aspect, the invention relates to a flexible tubular pipe intended for the transport of hydrocarbons, comprising, on the one hand, a sealed tubular sheath formed of a thermoplastic fluoropolymer and having an inner wall, and, on the other hand, a set of layers of armor wires helically wound around said sealed tubular sheath. The inner wall of the sealed tubular sheath is advantageously released. The advantages of such a pipe mainly derive from the above-described method of manufacturing it. Therefore, the thermoplastic fluoropolymer used preferably has a melting point higher than 300 ℃ or even higher than 310 ℃. According to a particularly advantageous feature of the invention, the thermoplastic fluoropolymer is a perfluoroalkoxy compound. In addition, the inner wall has a smooth inner surface. It therefore has no roughness or incipient cracking.

Preferably, the set of armor wire layers comprises pressure armor wires helically wound around the sealed tubular jacket at a short pitch to form a pressure armor layer capable of withstanding pressure. And the set of armor wire layers comprises a plurality of tensile armor wires helically wound around the pressure armor layer at a long pitch to form at least one tensile armor layer capable of resisting tension. In addition, the flexible tubular conduit further comprises an outer sealing jacket made of a polymeric material and positioned around the set of armor wire layers.

Drawings

Other characteristics and advantages of the invention will become clearer upon reading the following description of a particular embodiment of the invention, given as a non-limiting example and with reference to the accompanying drawings, in which:

figure 1 is a schematic perspective cut-away view of a flexible tubular conduit obtained according to the method according to the invention; and

fig. 2 is a flow chart of the steps of the method according to the invention.

Detailed Description

Reference is first made to figure 1 in order to describe the various elements of a flexible tubular duct 10 obtained according to the method according to the invention.

The flexible tubular duct 10 thus comprises, from the inside outwards: an inner sealing sheath 12, a pressure strut or pressure armor 14, two tensile armor layers 16, 18, and an outer sealing sheath 20.

The inner containment sheath 12 is an extruded fluoropolymer sheath whose purpose is to confine the hydrocarbon flowing along it within the pipe 10 against its inner wall 21. The method for making the fluoropolymer jacket 12 will be described in more detail in the specification below. Preferably, a perfluoroalkoxy (perfluoroalkoxy) polymer material is utilized from which the sealing boot 12 is formed. This material, in addition to having excellent properties in terms of mechanical properties and resistance to chemical agents, has the advantage that it can be easily extruded through the extruders normally used to form sealing sheaths. This is not the case, for example, with PTFE (standing for polytetrafluoroethylene), which can be converted only by processes involving compression molding of PTFE powder, the parts thus obtained then being sintered at high temperatures, resulting in agglomeration of the powder particles; or alternatively, by a highly specialized grain extrusion process (known as "RAM extrusion") in which a piston machine extruder (piston fan extruder) is fed with pre-sintered powder, which is then forced to press in a die located within a heated enclosure to fuse the particles of the powder together.

In the case of the pressure struts 14 (which are also referred to herein as pressure armour layers), this is formed by a shaped wire wound around the inner sealing sheath 12 at a short pitch adjacent winding at an angle of close to 90 ° to the longitudinal axis of the flexible tubular pipe. Thereby being able to absorb radial forces associated with the pressure of the fluid flowing along it inside the pipe 10 and radial forces associated with the hydrostatic pressure exerted by the surrounding environment.

As for the tensile armour layers or plies 16, 18, they have the effect of absorbing tensile forces applied longitudinally to the flexible tubular conduit 10, particularly when the flexible tubular conduit 10 is suspended between the seabed and the surface of the offshore environment, and the internal pressure along which the hydrocarbons flow within the inner sealed sheath 12. These armor plies 16, 18 are each made up of two sets of multiple metal armor wires wound around the pressure struts 14 in opposite directions and at an angle of 20 ° to 55 ° relative to the longitudinal axis of the flexible tubular pipe, in a long pitch helix. In fig. 1, they cross in order to balance the reaction of the torsional load. Thus, the pressure armor 14 and tensile armor 16, 18 comprise a set of armor wire layers that form a reinforcing layer.

A protective outer sealing jacket 20 made of a polymeric material is extruded around the armor plies 16, 18. The invention is also applicable to pipes that do not have an outer sealing jacket. In addition, other layers (not shown as they are optional) such as a retention layer or an abrasion resistant layer may cover or be interposed between the tensile armor plies 16, 18. The retention layer comprises at least one tape helically wound around the tensile armour layers 16, 18 at a short pitch. It provides a hold back for the tensile armor plies 16, 18 to prevent them from swelling. The wear resistant layer comprises at least one tape helically wound around the tensile armour layer 16 at a short pitch in order to prevent wear phenomena caused by the tensile armour layers 16, 18 rubbing together.

Optionally, an outer metallic reinforcement layer, such as a metallic casing, pressure struts or tensile armour layer, is optionally wrapped around the protective outer sealing jacket 20 to effectively protect it from any external damage.

Reference is now made to fig. 2 for describing the various steps in the method for manufacturing a flexible tubular conduit according to the present invention.

According to a first step a), the thermoplastic fluoropolymer (for example perfluoroalkoxy) is supplied in the form of granules or in the form of a powder. This polymer has all the advantages of polytetrafluoroethylene in terms of melting point (since the melting point is close to 327 ℃ C., the melting point of perfluoroalkoxy is approximately 307 ℃ C.) and in terms of mechanical properties (since its elastic modulus is close to 600 MPa). In addition, it is also excellent in chemical inertness. By contrast, it can be easily extruded, unlike polytetrafluoroethylene. The fluidity index (which is characterized by its MFR, which represents the melt flow rate, measured at an applied load of 5kg and a temperature of 372 ℃) is, for example, comprised between 0.5 and 15g/10min, preferably between 1.5 and 3g/10 min.

The fluoropolymer is supplied in the form of granules or in the form of a powder and loaded into an extruder for shaping in step b). The extruder comprises a fluoropolymer storage hopper upstream and a head for extruding the tubular sheath downstream. The storage hopper and the extrusion head are connected to each other by a worm equipped with heating means in order to bring the fluoropolymer from the solid state to the molten state on the one hand and to drive it through the extrusion head in the molten state on the other hand. The extrusion head has an annular chamber through which the fluoropolymer in the molten state flows axially to form, upon exiting the lip of the extruder, a cylindrical layer having a thickness of, for example, 0.5 to 2cm and a diameter of 5.08cm (2 ") to 50.8cm (20"), preferably 7.62cm (3 ") to 15.24cm (6").

Advantageously, the extrusion head is equipped with a sonotrode (sonotrode), so that high-power acoustic or ultrasonic waves can be generated to cause vibrations in the parts in direct contact with the molten polymer, in particular those parts located close to the outlet of the extrusion head where the molten polymer is at its maximum viscosity. These vibrations, having amplitudes on the order of 1 micron to 0.01 millimeter and frequencies of 5 kilohertz to 200 kilohertz, have the effect of making the polymer more flowable by reducing the coefficient of friction at the metal-polymer interface.

Also, the cylindrical layer is extruded at a low speed, because the fluoropolymer in the molten state is sensitive to material shearing phenomena as it leaves the extrusion head. The addition of additives such as boron nitride allows this undesirable effect to be eliminated.

The cylindrical layer is driven towards a cooling system, such as a sizing mill, preferably a vacuum sizing mill, in order to fix the outer diameter of the pipe at a desired dimension on the one hand and to cool the layer in a controlled manner on the other hand. The sizing mill includes a set of tooling pieces that are machined to the shape and adjusted temperature of the profile of the axisymmetric cylindrical layer. For example, the sizing mill is of the bushing type, ring type or collar type, or alternatively of the dry bushing type. The channels are machined in the thickness of the wall of the sizing mill and allow the circulation of a coolant, such as water. Thus, they cool cylindrical layers that are axisymmetric or exhibit circular symmetry. Also, the inner surface of the sizing mill, on which the outer surface of the cylindrical layer slides, has a plurality of perforations. These perforations are connected to a vacuum pump via pipes. Thereby, the hot wall of the cylindrical layer is held firmly against the inner surface of the sizing mill by suction, thereby keeping the cylindrical layer in the desired shape as it solidifies. The positive pressure difference established between the outside of the layer under suction and its inside under ambient pressure makes it possible to ensure that the inner wall 21 of the layer does not bend itself and that it thus forms an axisymmetric tubular sheath as the fluoropolymer flows in the molten state.

After having passed the sizing mill, the tubular sheath is driven in axial translation, even if it is only locally cooled. To complete its solidification and allow it to be subsequently wound onto a storage reel, the tubular sheath is guided towards the cooling tank. The cooling takes place by immersion, preferably by spraying. This then results in a sealed tubular sheath, the surface of the inner wall 21 of which is free from roughness and smooth. This is because the inner wall 21 is free during the cooling phase, which means that residual surface stresses are reabsorbed during this phase leading to a flat surface. The advantage in the case of this material is that in the molten state it is perfectly transparent, so that the presence of any bubbles or contaminants can be visually detected. This is particularly important in view of the very high pressure and temperature levels that the finished structure will experience.

Next, in a third step c), using a wire coiling machine and an armor laying machine in succession, the previously mentioned set of armor wire layers will be helically wound around the rigid sealed tubular sheath.

In a fourth step d), the sealed tubular sheath is then covered with the set of layers of armor wires, driven again through the extruder, so as to apply a sealed protective sheath made of a polymeric material, which is not necessarily a fluoropolymer.

The flexible tubular conduit obtained according to the above-described method is also the subject of the present invention.

Thus, because the tubular conduit does not have a shell, the inner sealing sheath 12, due to the subsequent manufacturing method, does not undergo interaction with the metal shell during the cooling and hardening process. Thus, no phenomena of plastic collapse into the discontinuities of the shell occur, which potentially leads to the occurrence of deconcentration forces and cracks of the material. Furthermore, no phenomena of residual stress occur during the sudden decompression of the pipe, which phenomena can lead to blistering and/or to a force of attenuation of the sealing sheath.

Claims (16)

1. A method for manufacturing a flexible tubular pipe (10) intended for the transport of hydrocarbons for use in harsh marine environments, comprising the steps of:

a) providing a thermoplastic fluoropolymer which is formable in a molten state;

b) shaping said thermoplastic fluoropolymer in the molten state so as to obtain a sealed tubular sheath (12) having an inner wall (21);

c) helically winding armor wires around the sealed tubular jacket (12) to form a set of armor wire layers (14, 16, 18);

characterized in that, in step b), a cylindrical layer is extruded and a sizing mill is provided to fix the outer diameter of the pipe at the desired dimensions and to cool it in a controlled manner, and said inner wall (21) is released, and wherein the inner wall of the tubular sheath is released during a heat treatment step, which is performed after the step of shaping in the molten state, during which step it is kept at a temperature below its melting point for a determined length of time, followed by controlled cooling, said inner wall (21) being free during the cooling phase, so that residual surface stresses are reabsorbed during this phase leading to a flat surface;

wherein no incipient cracks or residual stresses occur in the inner wall of the tubular sheath;

and wherein an ultrasonic generator is provided in the extrusion head in which the cylindrical layer is extruded, the ultrasonic generator being used to generate sound waves or ultrasonic waves to vibrate portions in direct contact with the molten polymer;

and wherein the sizing mill includes a set of tooling pieces that are machined to the shape of the profile of the axisymmetric cylindrical layer and to a temperature that is regulated, and the inner surface of the sizing mill has a plurality of perforations over which the outer surface of the cylindrical layer slides, the perforations being connected via tubing to a vacuum pump, the hot wall of the cylindrical layer being held firmly against the inner surface of the sizing mill by suction to hold the cylindrical layer in the desired shape as it solidifies, and wherein the positive pressure differential established between the outside of the cylindrical layer under suction and its inside at ambient pressure is such that the inner wall of the cylindrical layer is not itself kinked and it forms an axisymmetric tubular sheath as the fluoropolymer flows in the molten state.

2. The method of claim 1, wherein the sizing mill is a vacuum sizing mill.

3. The method according to claim 1 or 2, wherein in step a) a thermoplastic fluoropolymer having a melting point higher than 300 ℃ is provided.

4. The method according to claim 1 or 2, wherein in step a) a perfluoroalkoxy compound is supplied.

5. Method according to claim 1 or 2, characterized in that in step b) the inner wall (21) is formed to obtain a smooth inner surface.

6. A method as claimed in claim 1 or 2, wherein in step c) pressure armour wires are helically wound around the sealed tubular sheath (12) at a short pitch to form a layer (14) of pressure armour wires capable of withstanding pressure.

7. A method according to claim 6, wherein in step c) a plurality of tensile armour wires are wound helically around the layer of pressure armour wires (14) at a long pitch to form at least one layer of tensile armour wires (16, 18) capable of resisting tension.

8. A method according to claim 1 or 2, further comprising a step d) in which an outer sealing sheath (20) of polymeric material is formed around the set of layers of armour wires (14, 16, 18).

9. The method of claim 8, further comprising step e), wherein a metal layer is formed around one of said outer sealing sheaths (20).

10. A flexible tubular pipe (10) intended for the transport of hydrocarbons, obtained according to the method of any one of claims 1 to 9, comprising on the one hand a sealed tubular sheath (12) formed of thermoplastic fluoropolymer and having an inner wall (21), and on the other hand a set of layers of armor wires (14, 16, 18) helically wound around the sealed tubular sheath (12);

characterized in that said inner wall (21) of said sealed tubular sheath (12) is released during the molten state forming phase and cooling phase of the manufacturing process of said flexible tubular duct.

11. Flexible tubular conduit according to claim 10, wherein said thermoplastic fluoropolymer has a melting point higher than 300 ℃.

12. Flexible tubular conduit according to claim 10 or 11, characterized in that said thermoplastic fluoropolymer is a perfluoroalkoxy compound.

13. Flexible tubular conduit according to claim 10 or 11, characterized in that the inner wall (21) has a smooth inner surface.

14. Flexible tubular duct according to claim 10 or 11, characterized in that said set of layers of armor wires (14, 16, 18) comprises pressure armor wires which are helically wound around the sealed tubular sheath at a short pitch to form a layer of pressure armor wires (14) which is able to resist pressure.

15. A flexible tubular duct according to claim 14, characterized in that said set of layers of armor wires (14, 16, 18) comprises a plurality of tensile armor wires wound helically around the layer of pressure armor wires (14) at a long pitch to form at least one layer of tensile armor wires (16, 18) capable of resisting tension.

16. Flexible tubular duct according to claim 10 or 11, characterized in that it further comprises an outer sealing sheath (20), said outer sealing sheath (20) being made of a polymeric material and being positioned around said set of layers of armor wires (14, 16, 18).

Images