Pipe for control and forced circulation of corrosion-inhibiting fluids in the annulus thereof

Abstract

A pipe is used for control and forced circulation of corrosion-inhibiting fluids in an annulus thereof, the annulus located between an inner pressure barrier and an outer cover of the pipe and containing a number of layers. The pipe includes two layers of tensile armor within the annulus; at least one injection pipe laid helicoidally on the longitudinal extension of the pipe; at least one return pipe laid helicoidally on the longitudinal extension of the pipe; and a ventilation layer within the annulus, the ventilation layer being configured to facilitate the flow of fluids longitudinally through the annulus of the pipe.

Claims

1. A pipe for control and forced circulation of corrosion-inhibiting fluids in an annulus thereof, the annulus being located between an inner pressure barrier and an outer cover of the pipe and containing a number of layers, the pipe comprising: two layers of tensile armor within the annulus; at least one injection pipe laid helicoidally on a longitudinal extension of the pipe; at least one return pipe laid helicoidally on the longitudinal extension of the pipe; and a ventilation layer within the annulus, the ventilation layer comprising ventilation tape providing longitudinal channels relative to a longitudinal axis of the pipe to facilitate a flow of fluids longitudinally through the annulus of the pipe.

2. The pipe according to claim 1, wherein the ventilation tape is laid helicoidally on at least part of the longitudinal extension of the pipe.

3. The pipe according to claim 2, wherein the ventilation tape comprises grooves across a width of the ventilation tape.

4. The pipe according to claim 3, wherein the ventilation tape is laid such that the grooves are aligned, forming the longitudinal channels relative to the longitudinal axis of the pipe.

5. The pipe according to claim 2, wherein the ventilation tape comprises holes through a width of the ventilation tape.

6. The pipe according to claim 5, wherein the ventilation tape is laid such that holes are aligned to form the longitudinal channels relative to the longitudinal axis of the pipe.

7. The pipe according to claim 2, wherein the ventilation tape is made of one of: cloth; metal; polymer; aramid threads; glass filaments; extruded material; and helicoidally braided tapes.

8. The pipe according to claim 1, further comprising a layer of anti-swelling or anti-extrusion tape applied helicoidally on the inner pressure barrier, wherein the tape is applied as successive overlapping loops, and wherein the tape contains holes to allow fluid to pass through.

9. The pipe according to claim 1, wherein the ventilation layer is positioned between two layers of anti-friction tape, the two layers of anti-friction tape being positioned between the two layers of tensile armor.

10. The pipe according to claim 1, wherein at least one injection pipe and at least one collecting pipe are positioned as replacements for wires of the tensile armor.

11. The pipe according to claim 1, wherein at least one injection pipe and at least one collecting pipe are arranged helicoidally within a filling layer, consisting of structural elements that protect the at least one injection pipe and the at least one collecting pipe from radial compression.

12. The pipe according to claim 1, wherein at least one injection pipe and at least one collecting pipe are positioned on the outer cover of the pipe.

13. The pipe according to claim 1, wherein at least one injection pipe and at least one collecting pipe comprise a cross-sectional shape selected from: round; oval; and rectangular.

14. The pipe according to claim 1, wherein at least one injection pipe and at least one collecting pipe comprise metal coated with a polymer layer.

15. The pipe according to claim 1, wherein at least one injection pipe and at least one collecting pipe are of a hose type that is resistant to hydrostatic collapse.

16. The pipe according to claim 1, wherein the ventilation layer is configured to increase an area of voids in a cross-section of the annulus of the pipe.

17. A riser formed by connecting a plurality of pipes according to claim 1.

18. A method of constructing a pipe, the pipe being for control and forced circulation of corrosion-inhibiting fluids in an annulus thereof, the annulus being located between an inner pressure barrier and an outer cover of the pipe and containing a number of layers, the method comprising: providing two layers of tensile armor within the annulus; providing at least one injection pipe laid helicoidally on a longitudinal extension of the pipe; providing at least one return pipe laid helicoidaily on the longitudinal extension of the pipe; and providing a ventilation layer comprising ventilation tape within the annulus to increase an area of voids in a cross-section of the annulus of the pipe, the ventilation layer being configured to provide longitudinal channels relative to a longitudinal axis of the pipe to facilitate a flow of fluids longitudinally through the annulus of the pipe.

19. A method of inhibiting corrosion in a pipe having an annulus, the annulus being located between an inner pressure barrier and an outer cover of the pipe and containing a number of layers, the method comprising: providing corrosion-inhibiting fluid to the pipe annulus via at least one injection pipe laid helicoidaily on a longitudinal extension of the pipe; circulating the corrosion-inhibiting fluid within the annulus of the pipe, including through longitudinal channels relative to a longitudinal axis of the pipe formed in ventilation tape of a ventilation layer provided within the annulus to increase an area of voids in a cross-section of the annulus; and removing corrosion-inhibiting fluid from the pipe annulus via at least one return pipe laid helicoidally on the longitudinal extension of the pipe.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The detailed description presented hereunder refers to the appended figures and their respective reference numbers.

(2) FIG. 1 shows a schematic view of a flexible pipe according to a first optional configuration.

(3) FIG. 1A shows detail 1A from FIG. 1.

(4) FIG. 1B shows a front view of the optional configuration of flexible pipe shown in FIG. 1.

(5) FIG. 2 shows three configurations of cross-section formats adopted for the injecting/collecting pipes.

(6) FIG. 3 shows a schematic view of a flexible pipe according to a second optional configuration.

(7) FIG. 4 shows a schematic view of a flexible pipe according to a third optional configuration.

(8) FIG. 4A shows a view of a ventilation tape laid helicoidally.

(9) FIG. 5 shows detail of a section of ventilation tape, according to an optional configuration.

(10) FIG. 5A shows a closer front view of the section of the configuration of ventilation tape in FIG. 5.

(11) FIG. 6 shows detail D of a section of ventilation tape as shown in FIG. 4, according to an optional configuration.

(12) FIG. 6A shows a closer front view of the section of the configuration of ventilation tape in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

(13) First, it is emphasized that the following description is based on a preferred embodiment. However, as will be obvious to a person skilled in the art, the invention is not limited to this particular embodiment.

(14) The present disclosure relates to a flexible pipe for control and forced circulation of fluids in the annulus thereof. The annulus can comprise a number of layers, including one or more of: at least two layers of tensile armour arranged in at least two directions of braiding; at least one injection pipe laid helicoidally on the entire longitudinal extension of the flexible pipe; at least one return pipe laid helicoidally on the entire longitudinal extension of the flexible pipe. The annulus can comprise a ventilation layer that comprises means for facilitating the flow of fluids. These features will become clearer from the figures and description given hereunder.

(15) FIG. 1 shows a schematic view of a flexible pipe according to a first optional configuration. It can be seen that the flexible pipe comprises an annulus. The annulus comprises a number of layers. Those layers, in the depicted embodiment, include two layers of tensile armour 1 arranged in at least two directions of braiding, a pressure armour 5 and a pressure or fluid barrier 6, besides a carcass 7 (e.g. to help prevent pipe collapse) and an outer sheath 8.

(16) It will be understood that a person skilled in the art of petroleum technology, especially of flexible pipes, will know how to determine the best various elements making up each of these layers.

(17) In addition, the present disclosure envisages employing at least one injection pipe and one return pipe laid helicoidally to replace at least two wires of tensile armour 1. The injection pipe and return pipe can be laid in different directions of braiding.

(18) These injection or return pipes 2 make injection and circulation of fluids possible. The recirculation of fluids can ensure evaporation of the water molecules, including those trapped in the interstices of the tensile armour 1 and of the pressure armour 5 or under the pressure armour 5. Such water molecules may have permeated from the interior of the flexible pipe, and evaporating the water molecules prevents condensation or saturation and the consequent appearance of aqueous phase, which constitutes a necessary condition for the corrosion process. As such, the injection pipes 2 can transport the fluid to the annulus of a pipe segment, from an upstream source (e.g. via an adjacent pipe segment). Conversely, the return pipes 2 can be used to receive fluid from the annulus of a pipe segment and return it to the source (again, e.g. via an adjacent pipe segment). The mechanisms for dispersing and collecting the fluid from the pipe annulus may be provided in connectors at the end of pipe segments, and are not considered in detail in this document.

(19) The fluids that may be employed include: inert gases (such as N.sub.2), non-corrosive gases (such as CH.sub.4), or liquids (such as ethanol and MEG). It is emphasized, however, that a person skilled in the art will be able to determine the best fluids to use, so that this selection does not limit the scope of protection of the present invention.

(20) FIG. 1B shows a front view of the configuration of flexible pipe shown in FIG. 1. It can be seen in this figure that a plurality of wires of the tensile armour 1 has been replaced with injecting/collecting pipes 2, so as to cause intensive recirculation of fluids.

(21) FIG. 1A shows detail 1A from FIG. 1, in which it can be seen that the cross-section format optionally adopted for the injecting/collecting pipes 2 in rectangular in the depicted configuration. This format has the advantage that it is similar to the format of the wires of the tensile armour 1. This can generate less friction between the pipe 2 and the wire of the armour 1.

(22) FIG. 2 shows three possible formats of cross-section format that may be adopted for the injecting/collecting pipes 2. The format options include round 2a and oval 2b formats, besides the rectangular format 2c. It is emphasized, however, that other options may be adopted freely for the convenience of the designer, provided the flow conditions for the particular application are maintained.

(23) Optionally, the injecting/collecting pipes 2 may be metallic. In that case, they may be further coated with a polymer layer to prevent metal-to-metal contact with the tensile armour 1.

(24) FIG. 3 shows a schematic view of a flexible pipe according to a second optional configuration. It can be seen that the flexible pipe comprises an annulus that comprises a number of layers. The layers may include two layers of tensile armour 1 arranged in at least two directions of braiding, a pressure armour 5 and a pressure barrier 6, at least one layer of anti-buckling tapes, at least one layer of anti-wear tapes 4 or anti-buckling tapes, besides the outer sheath and the carcass.

(25) In this optional configuration, the flexible pipe comprises at least one injecting/collecting pipe 2 arranged helicoidally permeated in a filling layer 3, which may be positioned above the layer of anti-wear or anti-buckling tapes 4. As illustrated, a number of injecting/collecting pipes 2 can be arranged helicoidally, throughout the filling layer 3.

(26) When this configuration is adopted, the filling layer 3, as well as the collecting/injecting pipe(s) 2, may be positioned on the outer tensile armour 1, or on the anti-buckling tapes, or on anti-wear tapes 4 (which can be installed on the anti-buckling tapes). This design can be employed with the use of additional anti-buckling tape on the layers of the pipes.

(27) As can be seen, in the optional illustration in FIG. 3, the round format is adopted for the cross-section of the injecting/collecting pipe 2. However, as already stated, any cross-section format may be adopted depending on each application.

(28) When this configuration is adopted, optionally, the injection and return pipes 2 are of the hose type that is resistant to hydrostatic collapse.

(29) In a third optional configuration, the filling layer 3, comprising the injecting/collecting pipe(s) 2 arranged helicoidally, is positioned on an outer cover of each segment. This configuration can provide mechanical protection against damage to the outer cover that may occur during handling and installation of the flexible pipe. This configuration can also use a layer of anti-buckling tape on the layer of injecting/collecting pipes 2.

(30) FIG. 4 shows a schematic view of a flexible pipe according to a third optional configuration. It can be seen that the flexible pipe comprises an annulus that comprises a number of layers. The layers may include tensile armour 1, optionally two or more layers of tensile armour 1 arranged in at least two directions of braiding, a pressure armour 5 and a pressure barrier 6, at least one layer of anti-buckling tapes, and at least one layer of anti-wear tapes 4.

(31) When this configuration is adopted, optionally, the injection and return pipes 2 are of the hose type that is resistant to hydrostatic collapse.

(32) In this figure, it can be seen in particular that the flexible pipe comprises at least one layer of anti-friction tape 9, positioned between the two layers of tensile armour 1 that are arranged in at least two directions of braiding. These tapes are used to minimize friction between the two layers of tensile armour 1. However, the layer of anti-friction tape 9 has the disadvantage that it does not facilitate circulation of fluids through the annulus of the flexible pipe.

(33) For the reason described in the preceding paragraph, it is envisaged that the layers of anti-friction tape 9 should comprise a ventilation layer 10 that comprises means for facilitating the flow of fluids in this region.

(34) Thus, in other words, it is envisaged that the flexible pipe of this configuration should comprise a ventilation layer 10 between two layers of anti-friction tape 9, which in their turn are positioned between two layers of tensile armour 1 arranged radially in at least two directions of braiding.

(35) Optionally, the layers of anti-friction tape 9 comprise an anti-friction tape 9 laid helicoidally on at least part of the longitudinal extension of the flexible pipe.

(36) Similarly, the ventilation layer 10 optionally comprises a ventilation tape 10 laid helicoidally on at least part of the longitudinal extension of the flexible pipe, as illustrated schematically in FIG. 4A.

(37) Optionally, to ensure higher pressure in the injection of fluids, necessary for entrainment of the corrosive fluids, a high-strength tape may be installed on the outer cover of the segment and, if necessary, a protective cover on this tape.

(38) FIG. 5 shows detail of a section of ventilation tape 10, as shown in FIG. 4, according to a first optional configuration of ventilation tape 10. FIG. 5A shows a closer front view (i.e. cross sectionally through the pipe) of the section of the configuration of ventilation tape 10 in FIG. 5.

(39) According to FIGS. 5 and 5A, it can be seen that the ventilation tape 10 comprises grooves 11. The grooves are across the width of the tape 10. As shown, the grooves are arranged in the longitudinal direction of the pipeline, over its entire length. That is, when the ventilation tape 10 is laid helicoidally around the pipe, successive grooves 11 can be aligned, forming channels that facilitate the flow of fluids along the pipe.

(40) FIG. 6 shows detail D of a section of ventilation tape 10, as shown in FIG. 4, according to a second optional configuration of ventilation tape 10. FIG. 6A shows a closer front view of the section of the configuration of ventilation tape 10 in FIG. 6 (i.e. cross sectionally through the pipe).

(41) According to FIGS. 6 and 6A, it can be seen that the ventilation tape 10 comprises holes 12 across the width of the tape 10. It will be understood that this does not necessarily mean the grooves 11 are perpendicular to the sides of the tape 10, but rather that they cross the width of the tape 10 from one side of the tape 10 to the other, and that that crossing may be at an angle. As shown, the holes are arranged in the longitudinal direction of the pipeline, over its entire length. That is, when the ventilation tape 10 is laid helicoidally, successive longitudinal holes 12 can be aligned, forming channels that facilitate the flow of fluids.

(42) Although two different configurations of ventilation tapes 10 have been presented, it is emphasized that a great variety of configurations may be adopted for these tapes, so that the configurations of ventilation tapes 10 are not limited to those presented in FIGS. 5, 5A, 6, and 6A.

(43) Therefore the ventilation layer 10, in any configuration, can provide a larger area of flow in the annulus of each segment of the flexible pipe, increasing the area of voids of the cross-section of the flexible pipe, and consequently making the circulating flow more uniform in the annulus of the structure.

(44) The ventilation layer 10 may be made of any of cloth, metal, polymer, aramid threads, glass filaments, woven material of any type of thread whose configuration is maintained by means of adhesive tape or agglomerating elements, such as polymers or matrices of any material that form a composite component, with the aim of maintaining the geometry of the barrier according to the original configuration of the flexible pipe before the factory hydrostatic test or as closes to this as possible. It may also be extruded, or in the form of tapes laid helicoidally along the segment with grooves 11 as shown in the accompanying figures.

(45) It is emphasized that although the ventilation layer 10 has been positioned, in FIGS. 5 and 6, between two layers of tensile armour 1 arranged in at least two directions of braiding, it may be positioned at different interfaces between layers arranged radially in the annulus. For example, the ventilation layer 10 may be positioned: between the outer armour and the cover or layer superposed on it; and between the barrier, or layer laid on the barrier, and the pressure armour 5.

(46) In addition, in the flexible pipes in which the pressure armour 5 is employed, in order to prevent bubbles or droplets of CO.sub.2 with dissolved water being trapped in positions where they are difficult to remove, or as a result of creep or swelling of the barrier 6, which restricts the circulation of fluids on the inner face of the pressure armour 5, it is possible to employ an anti-swelling or anti-extrusion layer in the form of tape or an extruded layer. This layer can contain holes to avoid formation of a second annulus (i.e. by compartmentalising the main annulus into two concentric annuli), which may cause collapse by rapid depressurization of the flexible pipe. If the tape is laid helicoidally on the barrier 6, with successive helical loops overlapping the previous loop, the tape itself may comprise holes to allow fluid to pass through, for the reasons mentioned above.

(47) The anti-swelling layer can be laid helicoidally during manufacture of the flexible pipeline with the application of sufficient tension for the barrier to be confined. Alternatively, the ventilation layers 10 and the anti-swelling layer may have their functions incorporated in a single layer.

(48) For greater strength, the ventilation layer 10 may comprise a core of material with higher compressive strength, to maintain the geometry of the layers and prevent the development of undesirable failure modes, and may further optionally be covered on the upper and lower faces with a polymer layer that envelops the core.

(49) In addition, the use of anti-wear tapes may make it desirable to: increase the thicknesses that take into account the wear resulting from friction with the metallic layers, due to the cyclic bending loads of the flexible pipe; and/or use composites or metallic materials with the aim of maintaining the configuration of the layers and the radial stiffness of the structure of the flexible pipe. For example, the anti-wear tapes 4 could be coated with polymer material, with the aim of minimizing wear of these tapes or of the armour of the flexible pipe due to the dynamic loading, preventing changes of the configuration of the flexible pipe that cause loosening of its layers.

(50) Optionally, with the aim of obtaining a structure of flexible pipe that is balanced for torsion, when it is subjected to loads such as tension and pressure, the lay angles of the tensile armour 1 may be adjusted with the aim of compensating the torsional imbalance caused by the presence of pipes mounted helicoidally on the body of the flexible pipe.

(51) Thus, the flexible pipe of the present disclosure is capable of allowing flow between any layer of the flexible pipe and of making the conditions of the annulus uniform, reducing the concentration of corrosive gases. These advantages are achieved with the use of individual pipes for communication and control of the annulus of each segment of the flexible pipe. For example, introduction of the ventilation layers 10, described in the preceding paragraphs, facilitate this forced flow.

(52) Optionally, the tensile armouring 1 and/or the pressure armouring, in the structure of the flexible pipe, are coated by anodic metallization for anticorrosive protection additional to the cathodic protection designed for the system of flexible pipes.

(53) Anticorrosive coating, of aluminium and aluminium alloys, applied directly on the surface of steel armour, increases its service life considerably, when in contact with the corrosive medium.

(54) Compressive anticorrosive coating applied directly on the surface of the steel armour is capable of introducing residual compressive stresses in the steel armour, greatly increasing its fatigue life even when subjected to severe plastic deformation.

(55) Therefore the present disclosure provides a flexible pipe capable of allowing displacement of water vapour that has permeated to the annulus, CO.sub.2, H.sub.2S and bubbles or droplets of CO.sub.2 trapped in the metal armouring, in the polymer layers or in the tapes, or at the interfaces and in the interstices of the connector and of the layers or between layers of the annulus of the flexible pipe, and consequently reducing the content of CO.sub.2 or H.sub.2S dissolved in the aqueous phase, through forced circulation of N.sub.2 or of other non-corrosive fluids through said annulus.

(56) The pipe of the present disclosure further allows reduction of the concentration of corrosive gases such as CO.sub.2 and H.sub.2S in the water in the case of flooding of the annulus with water, as well as entraining or breaking the bubbles or droplets of CO.sub.2 with dissolved water, which may be trapped in the metal armouring, in the polymer layers or in the tapes, or at the interfaces and in the interstices of the layers of the pipe in the connector and of the layers or between layers of the annulus of the flexible pipe.

(57) Accordingly, the flexible pipe mitigates the aggressiveness of pitting corrosion, which is one of the factors in the initiation of the process of stress corrosion by CO.sub.2, on maximizing the homogeneity of the corrosive environment of the annulus, besides promoting reduction of the concentration of corrosive gases, as mentioned.

(58) Especially in annular spaces with loss of integrity, the circulation of N.sub.2 or some other fluid at high velocity intensifies the entrainment and expulsion of corrosive fluids out of the annulus via the damaged areas of the outer cover (or holes made after installation of the flexible pipe for directing the flow).

(59) Accordingly, the effects of these corrosive fluids are minimized, extending the possibility of operation until maintenance is effective, if necessary, if the condition of the annulus exceeds the limits of the conditions in which the corrosive fluids initiate the mechanisms of failure mentioned above.

(60) Countless variations falling within the scope of protection of the present application are permitted. This reinforces the fact that the present invention is not limited to the particular configurations/embodiments described above. As such, modifications of the above-described apparatuses and methods, combinations between different variations as practicable, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the spirit and scope of the claims.