GB2535944A

GB2535944A - Highly resistant flexible tubular conduit and production method

Info

Publication number: GB2535944A
Application number: GB1610694.0A
Authority: GB
Inventors: Demanze Frédéric
Original assignee: Technip France SAS
Current assignee: Technip Energies France SAS
Priority date: 2013-12-27
Filing date: 2014-12-26
Publication date: 2016-08-31
Anticipated expiration: 2034-12-26
Also published as: BR112016014988B1; WO2015097422A1; CN106030178B; CN106030178A; FR3016019A1; DK201670453A1; GB201610694D0; GB2535944B; FR3016019B1

Abstract

The invention relates to a method for producing a flexible tubular conduit (10) for transporting hydrocarbons, and to a flexible tubular conduit produced thereby. Said method is of the type comprising the following steps: a) a thermoplastic fluoropolymer that can be shaped in the melted state is supplied; b) said fluoropolymer is shaped in the melted state in order to produce a sealed tubular sheath (12) having an inner wall (21); and, c) armouring wires are spiralled around said sealed tubular sheath (12) in order to form an assembly of layers of armouring wires (14, 16, 18); while the inner wall (21) is left free.

Description

Highly resistant flexible tubular pipe and production method The present invention relates to a method for manufacturing a flexible tubular pipe and to a flexible tubular pipe obtained using said method.

s One envisaged field of application is that of the flexible tubular pipes used in the field of the transportation of hydrocarbons and described in the normative documents API 17J, "Specification for Unbonded Flexible Pipe', API 16C, "Choke and Kill Systems", and API 7K, "Rotary Drilling Hose" published by the American Petroleum Institute.

The flexible tubular pipes intended for the transportation of hydrocarbons usually comprise an internal sealing sheath made from a polymer material defining a flow path, inside which the hydrocarbon or sludge is able to flow. Furthermore, the internal sealing sheath is covered, on the one hand, by a pressure vault made of shaped wires wound with a short pitch so as to be able to withstand the radial stress caused by the circulation of the fluid inside the internal sealing sheath and by the hydrostatic pressure and, on the other hand, with a layer of tensile armor made from metal wires wound with a long pitch and intended partially or completely to absorb the tensile loadings and the radial internal loadings applied to the tubular pipe. In addition, the tensile-armor layer is generally covered by an external sealing sheath intended to prevent the ingress of water through the layers of armor and of the pressure vault. The region situated between the internal sealing sheath and the external sealing sheath, which includes the pressure vault and the at least one tensile-armor layer, defines the annular space of the pipe. In spite of these precautions the external sealing sheath may, during use of the flexible tubular pipe on the seabed, happen to become holed and pressurized water may enter the thickness of the pipe and apply radial load to the internal sealing sheath. When that happens, and when the pressure of the hydrocarbon inside the internal sealing sheath drops, this sheath has a tendency to collapse on itself and become damaged.

Hence, in order to overcome this, the flexible tubular pipes are equipped, inside the internal pressure sheath, with a metal carcass made of an interlocked metal tape wound in a short-pitch helix at an angle of close to 90° with respect to the longitudinal axis of the flexible tubular pipe. Such a flexible tubular pipe is known by its English name of "rough-bore".

On top of that, the service conditions of flexible tubular pipes are becoming increasingly harsh because the production of hydrocarbons is being performed in increasingly deep offshore waters. As a result, the hydrocarbon is generally hotter and, obviously, the hydrostatic pressure is greater. Hence, notably in order to withstand the high temperatures and the chemical nature of these hydrocarbons, use is made of sealing sheaths made from materials with to superior properties and, in particular, of thermoplastic fluoropolymers. Reference may be made to document W096/30687, which describes a flexible tubular pipe equipped with an internal metal carcass covered with a thermoplastic fluoropolymer sealing sheath.

Thus, in a first step in the manufacture of the flexible tubular pipe, a fluoropolymer sheath is extruded coaxially onto a metal carcass. This sheath therefore, as soon as it has been extruded, finds itself resting against the metal carcass. Its internal wall thus follows the roughnesses of the metal carcass because the polymer is still in the viscous state before it is completely cooled. Thereafter, the sealing sheath thus supported by the metal carcass is successively covered with layers of helically-wound armor wires.

However, incipient cracks are found in the internal wall of the sealing sheath, at the discontinuities in the metal carcass. On top of that, the residual stresses that arise at these discontinuities may lead to a decohesion of the sealing sheath if the pipe is suddenly depressurized. Also, local deplastification of the sealing sheath is observed and this impairs the mechanical performance thereof.

So, one problem that arises and that the present invention seeks to resolve is that of being able to preserve the sealed tubular sheath throughout the service life of the pipe in a harsh marine environment.

To this end, the present invention, according to a first subject matter, proposes a method for manufacturing a flexible tubular pipe intended for the transportion of hydrocarbons, said method being of the type comprising the following steps: a) providing a thermoplastic fluoropolymer able to be shaped in the molten state; b) shaping said fluoropolymer in the molten state in order to obtain a sealed tubular sheath having an internal wall; and c) helically winding armor wires around said sealed tubular sheath to form a set of layers of armor wires; and, in step b), said internal wall is freed.

Thus, one feature of the invention lies in the shaping of the fluoropolymer in the molten state in order to create the sealed tubular sheath. Specifically, as soon as it has been formed, while the polymer is still in the rubbery state, the internal wall of the tubular sheath is freed and as a result evolves toward the to solid state in the free air. Also, the internal wall of the tubular sheath may be freed during an optional heat treatment step performed after the step of shaping it 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 a controlled cooling. Thus, in comparison with the methods according to the prior art, in which the internal wall of the tubular sheath is pressed directly against a metal carcass that has roughnesses and gaps, according to the present invention, the cooling of the internal wall and its transition toward the solid state take place uniformly and evenly over the entire cylindrical surface of the internal wall. As a result, no incipient cracks or residual stress appears in the internal wall of the tubular sheath. As a result, the service life of the tubular sheath inside the pipe is increased. Furthermore, and surprisingly, the absence of a metal carcass is not at all detrimental to the internal tubular sheath even when the flexible tubular pipe is installed at great depth and is carrying hot hydrocarbons. Flexible tubular pipes without a metal carcass are well known and are known by their English term "smooth-bore" pipes. However, these are used in specific conditions in which the hydrostatic pressure is low, namely close to the surface of the marine environment in an offshore situation and/or to carry fluids in an on-shore environment, the fluids or hydrocarbons being relatively sour and laden with gas.

So, it would appear that the disadvantages of a flexible tubular pipe without an internal metal carcass and used under harsh temperature and pressure conditions are largely compensated for by the qualities of the internal tubular sheath obtained at the time of manufacture. These technical qualities appear to be associated with a dissipation of the mechanical stresses through the thickness of the sheath and also with the absence of incipient cracks. Specifically, the fact that the internal tubular sheath is not extruded onto a metal carcass allows the polymer material to contract thermally thereby reducing residual stresses.

It is possible to imagine producing flexible tubular pipes without an internal metal carcass from materials that creep less such as PEEK, which stands for polyetheretherketone. However, these materials have two major disadvantages.

First of all, they have excessive stiffness which means that they need to have very large bend radii. And as a result, at manufacturing level, that requires very large spools and, in use, means it is not possible to have configurations compatible with the space available on drilling platforms for example. The second aspect is that during high-temperature aging above the Tg which for is PEEK is around 145°C, the matrix becomes more rigid with a sharp drop in elongation properties. Substantially 20% to 5% is lost, which is somewhat incompatible with highly dynamic stress loadings.

According to one particularly advantageous embodiment of the invention, a thermoplastic fluoropolymer that has a melting point higher than 300°C or even higher than 310°C is provided. As a result, its ability to withstand the transportation of hot hydrocarbons will be correspondingly improved. For preference, perfluoroalkoxy is supplied from which to create the sealed tubular sheath.

Unlike polytetrafluoroethylene, perfluoroalkoxy is easily worked in a molten state, and has the same mechanical strength and chemical resistance properties thereas. By contrast, perfluoroalkoxy is less sensitive to creep than is polytetrafluoroethylene.

Furthermore, during the processing in the molten state, said internal wall of the tubular sheath is formed in such a way as to obtain a smooth internal surface. As a result, in the absence of surface unevennesses, the internal wall evolves even more, from a rubbery state toward a solid state in a completely uniform manner.

For preference, a pressure-armor wire is wound in a short-pitch helix around said sealed tubular sheath to form a pressure-armor layer capable of withstanding pressure. This pressure-armor layer, against the internal wall of which the external wall of the sealed tubular sheath will press, notably makes it possible to absorb the internal and external radial stresses caused by the pressure of the hydrocarbon inside the sealed tubular sheath and the hydrostatic pressure applied by the external environment. Advantageously, an anti-creep layer is applied between the internal sealing sheath 12 and the pressure-armor layer 14 in order to limit the creep of the fluoropolymer into the io discontinuities formed by the contiguous turns of the pressure vault. In addition, a plurality of tensile-armor wires are wound in a long-pitch helix around said pressure-armor layer to form at least one tensile-armor layer capable of withstanding tension. The tensile-armor wires are intended to absorb the tensile forces applied to the flexible tubular pipe and, partially or completely, the internal pressure applied by the hydrocarbon flowing along inside the sealed tubular sheath. These tensile forces are naturally applied when the flexible tubular pipe is suspended from the surface of the marine environment and extends down to the seabed immediately below. Further, the greater the depth of water, the higher these forces are.

In addition, and according to another step, an external sealing sheath made of a polymer material is advantageously formed around said set of layers of armor wires, so as to prevent the annular space of the flexible tubular pipe which comprises the set of layers of armor wires from becoming flooded, because since these wires are made of steel, they corrode more rapidly if they come into contact with the water.

For preference, the method also further comprises another step whereby a metal layer is formed around said one external sealing sheath, for example a metal carcass, a pressure vault, or even tensile-armor.

According to a second aspect, the present invention relates to a flexible tubular pipe intended for the transportation of hydrocarbons, said flexible tubular pipe comprising, on the one hand, a sealed tubular sheath formed of a thermoplastic fluoropolymer and having an internal wall, and, on the other hand, a set of layers of armor wires helically wound around said sealed tubular sheath. Said internal wall of said sealed tubular sheath is advantageously free. The advantages of such a pipe stem essentially from the way mentioned hereinabove in which it is manufactured. So, said thermoplastic fluoropolymer employed preferably has a melting point higher than 300°C, or even higher than 310°C. According to one particularly advantageous feature of the invention, said thermoplastic fluoropolymer is perfluoroalkoxy. In addition, said internal wall has a smooth internal surface. It therefore has no roughnesses or incipient cracks.

For preference, said set of layers of armor wires comprises a pressure- armor wire wound in a short-pitch helix around said sealed tubular sheath to form a pressure-armor layer capable of withstanding pressure. Also, said set of layers of armor wires comprises a plurality of tensile-armor wires wound in a long-pitch helix around said pressure-armor layer to form at least one tensile-ts armor layer capable of withstanding tension. In addition, the flexible tubular pipe further comprises an external sealing sheath made of polymer material situated around said set of layers of armor wires.

Further specifics and advantages of the invention will become apparent from reading the description given hereinafter of one particular embodiment of the invention which is given by way of nonlimiting indication with reference to the attached drawings in which: - figure 1 is a schematic perspective cut away view of a flexible tubular pipe obtained according to the method according to the invention; and - figure 2 is a flow diagram of the various steps of the method according to the invention.

Reference will be made first of all to figure 1 in order to describe the various elements of a flexible tubular pipe 10 obtained according to the method according to the invention.

Thus, the flexible tubular pipe 10 comprises, from the inside toward the outside, an internal sealing sheath 12, a pressure vault or pressure-armor layer 14, two tensile-armor layers 16, 18 and an external sealing sheath 20.

The internal sealing sheath 12 is an extruded fluoropolymer sheath the purpose of which is to confine the hydrocarbon flowing along inside the pipe 10 against the internal wall 21 thereof. The method for manufacturing the fluoropolymer sheath 12 will be described in greater detail later on in the s description. For preference, use is made of perfluoroalkoxy by way of polymer material from which to form the sealing sheath 12. This material, aside from having good performance in terms of mechanical properties and ability to resist chemical agents, has the advantage that it can be extruded easily through the extruders commonly used to form the sealing sheaths. Such is not, for 10 example, the case with PTFE, which stands for polytetrafluoroethylene, which can be converted only through a method involving the compression molding of PTFE powder, the component obtained thereby then being sintered at a high temperature to cause the particles of powder to coalesce; or alternatively, through a highly specialized granular extrusion process referred to as "RAM extrusion" in which a piston fan extruder is fed with a pre-sintered powder which is then compressed strongly within a die situated inside a heating jacket so as to fuse the grains of powder together.

In the case of the pressure vault 14, also referred to here as a pressure-armor layer, this is formed of a shaped metal wire wound at a short pitch with contiguous turns at an angle close to 90° with respect to the longitudinal axis of the flexible tubular pipe around the internal sealing sheath 12. It is thus able to absorb the radial forces associated with the pressure of the fluid flowing along inside the pipe 10 and those associated with the hydrostatic pressure exerted by the surrounding environment.

As for the tensile-armor layers or plies 16, 18, these have the role of absorbing the tensile forces applied longitudinally to the flexible tubular pipe 10, notably when the latter is suspended between the seabed and the surface of the offshore environment, and the internal pressure of the hydrocarbon flowing along inside the internal sealing sheath 12. These armor plies 16, 18 are respectively made up of two pluralities of metal armor wires wound in a long-pitch helix in opposite directions and at an angle of between 20° and 55° with respect to the longitudinal axis of the flexible tubular pipe, around the pressure vault 14. In figure 1, they crisscross so as to balance the reaction of torsion loadings. Thus, the pressure-armor layer 14 and the tensile-armor layers 16, 18 constitute a set of layers of armor wires forming reinforcing layers.

The protective external sealing sheath 20 made of a polymer material is extruded around the armor plies 16, 18. The invention could also apply to pipes having no external sealing sheath. Moreover, other layers such as a retaining layer or an anti-wear layer, which have not been depicted because they are optional, may cover the tensile-armor plies 16, 18 or be interposed therebetween. The retaining layer comprises at least one tape wound in a to short-pitch helix around the tensile-armor plies 16, 18. It provides containment for these tensile-armor plies 16, 18, preventing them from swelling. The antiwear layer comprises at least one tape wound in a short-pitch helix around the tensile-armor ply 16 so as to prevent a phenomenon whereby the tensile-armor plies 16, 18 wear by rubbing together.

Optionally, an external metal reinforcing layer such as a metal carcass, a pressure vault or a tensile-armor layer is optionally wound around the protective external sealing sheath 20 in order to protect it effectively against any external damage.

Reference is now made to figure 2 to describe the various steps in the method for manufacturing a flexible tubular pipe according to the invention.

According to a first step a), a thermoplastic fluoropolymer, for example perfluoroalkoxy, is supplied in the form of granules or in powder form. This polymer has all the advantages of polytetrafluoroethylene in terms of melting point because it is close to 327°C, the melting point of perfluoroalkoxy being around 307°C, and also in mechanical terms because its elastic modulus is close to 600 MPa. Moreover, it also has excellent chemical inertia. By contrast, it can easily be extruded, unlike polytetrafluoroethylene. Its fluidity index, characterized by its MFR, which stands for melt flow rate, measured under an applied load of 5 kg and for a temperature of 372°C, is, for example, comprised between 0.5 and 15 g/10 min, preferably between 1.5 and 3 g/10 min. This fluoropolymer is supplied in the form of granules or in powder form and is loaded into an extruder so as to be shaped in a step b). The extruder comprises, upstream, a fluoropolymer storage hopper and, downstream, a head for extruding a tubular sheath. The storage hopper and the extrusion head are connected to one another by means of an endless screw equipped with heating means so as, on the one hand, to bring the fluoropolymer from a solid state to a molten state and, on the other hand, drive it through the extrusion head in the molten state. The extrusion head has an annular chamber through which the fluoropolymer in the molten state flows axially so as to form a cylindrical layer with a thickness comprised between 0.5 and 2 cm for example, on leaving the lips of the extruder and with a diameter comprised between io 5.08 cm (2") and 50.8 cm (20"), preferably between 7.62 cm (3") and 15.24 cm (6").

Advantageously, the extrusion head is equipped with sonotrodes so that high-powered sound or ultrasound waves can be generated in such a way as to cause certain parts in direct contact with the molten polymer, notably those is situated close to the outlet of the extrusion head at the point where the molten polymer is at its most viscous to vibrate. These vibrations, with an amplitude of the order of 1 micrometer to 0.01 millimeter, and at a frequency comprised between 5 kilohertz and 200 kilohertz, have the effect of making it easier for the polymer to flow by reducing the coefficient of friction at the metal-polymer interface.

Also, the cylindrical layer is extruded at a low rate because the fluoropolymer in the molten state is sensitive to the phenomenon of the shearing of the material 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 toward a cooling system such as a sizer, preferably a vacuum sizer so as, on the one hand, to fix the outside diameter of the tube at the desired dimensions and, on the other hand, to cool the layer in a controlled fashion. The sizer consists of a set of tooling items machined to the shape of the profile of the axisymmetric cylindrical layer and temperature regulated. For example, the sizer is of the bushing type, the type of rings or collars, or alternatively the dry bushing type. Channels are machined in the thickness of the wall of the sizer and allow for the circulation of a coolant, for example water. As a result, they cool the cylindrical layer that is axisymmetric or exhibits circular symmetry. Also, the internal surface of the sizer over which surface the external surface of the cylindrical layer slides has a number of pierced orifices. These are connected, via ducts, to a vacuum pump. Thus, the hot walls of the cylindrical layer are held firmly against the internal surface of the sizer by suction, thus keeping the cylindrical layer in the desired shape as it solidifies. The positive pressure differential created between the outside of the layer under suction and the inside thereof which is at atmospheric pressure makes it possible to ensure that the internal wall 21 of the layer does not fold in to on itself and that it thus forms, as the fluoropolymer in the molten state flows, an axisymmetric tubular sheath.

Having passed through the sizer, the tubular sheath is driven axially in translation even though it is only partially cooled. In order to complete its solidification and allow it to be wound onto a storage reel later, the tubular sheath is led toward a cooling tank. Cooling takes place by immersion, preferably by spraying. This then yields a sealed tubular sheath the surface of the internal wall 21 of which is free of roughnesses and is smooth. This is because the internal wall 21 being free during the cooling phase means that residual surface stresses are reabsorbed during this phase leading to an even surface. The advantage with this material is that, in the molten state, it is perfectly translucent, making it possible visually to detect the presence of any bubble or contamination. This is of the greatest possible importance given the very high pressure and temperature levels to which the finished structure will be subjected.

Next, in a third step c), the set of layers of armor wires as before mentioned will be helically wound around this rigid sealed tubular sheath, using a wire spiraling machine and an armor-laying machine in succession.

The sealed tubular sheath is then covered with the set of layers of armor wires, is driven once again through an extruder, in a fourth step d), so that a sealed protective sheath made from a polymer material which is not necessarily a fluoropolymer, is applied.

The flexible tubular pipe obtained according to the method described hereinabove is also a subject of the invention.

As a result, since the tubular pipe has no carcass, the internal sealing sheath 12, because of the subsequent method of manufacture, experiences no interaction with the metal carcass during the process whereby it cools and becomes rigid. As a result, no phenomenon of the plastic collapsing into the discontinuities of the carcass with the potential of causing decohesion of the material and the appearance of cracks occurs. Further, no phenomenon of residual stresses that could lead to blistering and/or also to decohesion of the sealing sheath during sudden depressurization of the pipe occurs.

Claims

CLAIMS1. A method for manufacturing a flexible tubular pipe (10) intended for the transportion of hydrocarbons, said method being of the type comprising the following steps: a) providing a thermoplastic fluoropolymer able to be shaped in the molten state; b) shaping said fluoropolymer in the molten state in order to obtain a sealed tubular sheath (12) having an internal wall (21); c) helically winding armor wires around said sealed tubular sheath (12) to form a set of layers of armor wires (14, 16, 18); characterized in that, in step b), said internal wall (21) is freed.
2. The method of manufacture as claimed in claim 1, characterized in that, in step a) a thermoplastic fluoropolymer that has a melting point higher than 300°C is provided.
3. The method of manufacture as claimed in claim 1 or 2, characterized in that, in step a) perfluoroalkoxy is supplied.
4. The method of manufacture as claimed in any one of claims 1 to 3, characterized in that, in step b) said internal wall (21) is formed in such a way as to obtain a smooth internal surface.
5. The method of manufacture as claimed in any one of claims 1 to 4, characterized in that, in step c), a pressure-armor wire is wound in a short-pitch helix around said sealed tubular sheath (12) to form a pressure-armor layer (14) capable of withstanding pressure.
6. The method of manufacture as claimed in claim 5, characterized in that, in step c), a plurality of tensile-armor wires are wound in a long-pitch helix around said pressure-armor layer (14) to form at least one tensile-armor layer (16, 18) capable of withstanding tension.
7. The method of manufacture as claimed in any one of claims 1 to 6, characterized in that it further comprises a step d), whereby an external sealing sheath (20) made of a polymer material is formed around said set of layers of armor wires (14, 16, 18).
8. The method of manufacture as claimed in claim 7, characterized in that it further comprises a step e), whereby a metal layer is formed around said one external sealing sheath (20).
9. A flexible tubular pipe (10) intended for the transportation of hydrocarbons, said flexible tubular pipe comprising, on the one hand, a sealed tubular sheath (12) formed of a thermoplastic fluoropolymer and having an internal wall (21), and, on the other hand, a set of layers of armor wires (14, 16, 18) helically wound around said sealed tubular sheath (12); characterized in that said internal wall (21) of said sealed tubular sheath to (12) is free.
10. The flexible tubular pipe as claimed in claim 9, characterized in that said thermoplastic fluoropolymer has a melting point higher than 300°C.
11. The flexible tubular pipe as claimed in claim 9 or 10, characterized in that said thermoplastic fluoropolymer is perfluoroalkoxy.
12. The flexible tubular pipe as claimed in any one of claims 8 to 10, characterized in that said internal wall (21) has a smooth internal surface.
13. The flexible tubular pipe as claimed in any one of claims 9 to 12, characterized in that said set of layers of armor wires (14, 16, 18) comprises a pressure-armor wire wound in a short-pitch helix around said sealed tubular zo sheath to form a pressure-armor layer (14) capable of withstanding pressure.
14. The flexible tubular pipe as claimed in claim 13, characterized in that said set of layers of armor wires (14, 16, 18) comprises a plurality of tensile-armor wires wound in a long-pitch helix around said pressure-armor layer (14) to form at least one tensile-armor layer (16, 18) capable of withstanding tension.
15. The flexible tubular pipe as claimed in any one of claims 9 to 14, characterized in that it further comprises an external sealing sheath (20) made of polymer material situated around said set of layers of armor wires (14, 16, 18).