Unbonded flexible pipe

Abstract

An unbonded flexible pipe with a length and bore and an offshore installation are disclosed. The pipe comprises an internal pressure sheath, at least one metallic armouring layer surrounding the internal pressure sheath and at least one additional layer surrounding the metallic armouring layer. The metallic armouring layer comprises helically wound armouring elements which are at least partly covered by a viscous fluid having a kinematic viscosity of at least about 1000 cSt (ASTM D445 or ASTM D2170). The at least one additional layer surrounding the metallic armouring layer provides a gas escape route radially outwards from the metallic armouring layer beyond an outermost layer of the least one additional layer or to a lengthwise gas escape path in or between the at least one additional layer.

Claims

1. An unbonded flexible pipe having a length and bore and comprising an internal pressure sheath, at least one metallic armouring layer surrounding the internal pressure sheath and at least one additional layer surrounding the metallic armouring layer, wherein the metallic armouring layer comprises helically wound armouring elements which are at least partly covered by a viscous fluid having a kinematic viscosity of at least about 1000cSt determined at 100° C., and wherein the at least one additional layer surrounding the metallic armouring layer provides a gas escape route radially outwards from the metallic armouring layer beyond an outermost layer of the least one additional layer or to a lengthwise gas escape path in or between the at least one additional layer.

2. The unbonded flexible pipe of claim 1, wherein the radial gas escape route comprises openings for free gas flow, wherein the escape route comprises openings for free gas flow radially outwards for gas to escape beyond the outermost layer.

3. The unbonded flexible pipe of claim 1, wherein the additional layer(s) comprises a retaining layer of a helically wound tape, said helically wound tape is wound with overlapping edges, said helically wound tape comprises a structure of woven fibres optionally fully or partly embedded in a polymer matrix.

4. The unbonded flexible pipe of claim 3, wherein said retaining layer is wound directly onto the metallic armouring layer with the viscous fluid, said retaining layer is water permeable and comprises a woven structure which is sufficiently tight to retain the viscous fluid with a kinematic viscosity of at least about 1500 cSt.

5. The unbonded flexible pipe of claim 4, wherein said retaining layer is the outermost layer or the flexible pipe comprises one or more water permeable layers outside the retaining layer.

6. The unbonded flexible pipe of claim 1, wherein the additional layer(s) comprises a thermal insulation layer, said thermal insulation layer being helically wound strips of thermal insulation material.

7. The unbonded flexible pipe of claim 6, wherein said thermal insulation layer comprises said gas escape path in the form of one or more channel(s) in the thermal insulation layer, said gas escape path extends to an end of the pipe.

8. The unbonded flexible pipe of claim 6, wherein said thermal insulation layer comprises perforations forming at least a part of said gas escape route.

9. The unbonded flexible pipe of claim 6, wherein said thermal insulation layer has a permeability which is larger than the permeability of the internal pressure sheath with respect to at least one of water, hydrogen sulphide or carbon dioxide.

10. The unbonded flexible pipe of claim 1, wherein said additional layer(s) comprises a protective jacket, said protective jacket is liquid permeable, said protective jacket is perforated and constitutes the outermost layer of the least one additional layer.

11. The unbonded flexible pipe of claim 1 claims, wherein the viscous fluid comprises solid particles having an electrode potential which is lower than the metal of the metallic armouring layer.

12. The unbonded flexible pipe of claim 11, wherein the solid particles comprise components acting as sacrificial anode for the metal of the metallic armouring layer.

13. The unbonded flexible pipe of claim 11, wherein the solid particles comprise chemically active products selected from among metal oxides selected from the group consisting of Fe2O3, PbO, ZnO, NiO, CoO, CdO, CuO, SnO2, MoO3, Fe3O4, Ag2O, CrO2, CrO3, Cr2O3, TiO, TiO2 and Ti2O3, and from among the alkaline and alkaline-earth oxides selected from the group consisting of CaO, Ca(OH)2 and MgO.

14. The unbonded flexible pipe of claim 11, wherein the solid particles comprise chemically active products selected from the group consisting of metal carbonates, metal chlorides, the hydrated forms of metal carbonates and metal chlorides, the hydroxylated forms of metal carbonates and metal chlorides, alkaline carbonates, alkaline-earth carbonates, alkaline chlorides, alkaline-earth chlorides, the hydrated forms of alkaline carbonates, alkaline-earth carbonates, alkaline chlorides, alkaline-earth chlorides and the hydroxylated forms of alkaline carbonates, alkaline-earth carbonates, alkaline chlorides, and alkaline-earth chlorides.

15. The unbonded flexible pipe of claim 1, wherein the viscous fluid is selected from petroleum jelly, grease, vax, bitumen or any combinations thereof.

16. The unbonded flexible pipe of claim 1, wherein the viscous fluid is a cross-linked gel or comprises cross-linked gel particles.

17. The unbonded flexible pipe of claim 1, wherein said metallic armouring layer(s) is encased in an annular encasing space formed by the internal pressure sheath and the at least one additional layer surrounding the metallic armouring layer(s), the amount of viscous fluid in the annular encasing space is sufficient to block for axial gas flow in the annular encasing space in at least a length section of the pipe, said length section has a length of at least about 100 m.

18. The unbonded flexible pipe of claim 1, wherein said metallic armouring layer(s) is encased in an annular encasing space formed by the internal pressure sheath and the at least one additional layer surrounding the metallic armouring layer(s), at least in a length section of the pipe at least about 90% of the encasing space minus space occupied by the metallic armouring layer(s) and optional intermediate anti wear tapes, is occupied by said viscous fluid, said length section has a length of at least about 100 m.

19. An offshore installation comprising an unbonded flexible pipe according to claim 1, wherein at least a length section of the pipe is arranged at deep water with a water depth of at least about 1000 m.

20. The offshore installation of claim 19, wherein the unbonded flexible pipe is arranged for transporting fluid between an upper facility and a subsea facility.

21. The unbonded flexible pipe of claim 1, wherein the radial gas escape route has a minimum permeability radially outwards which is larger than the permeability of the internal pressure sheath with respect to at least one of water, hydrogen sulphide or carbon dioxide.

22. The unbonded flexible pipe of claim 1, wherein the armouring elements are coated with the viscous fluid or are embedded in the viscous fluid.

Description

BRIEF DESCRIPTION OF EMBODIMENTS AND ELEMENTS OF THE INVENTION

(1) The above and/or additional objects, features and advantages of the present invention will be further elucidated by the following illustrative and non-limiting description of embodiments of the present invention, with reference to the appended drawings.

(2) The figures are schematic and are not drawn to scale and may be simplified for clarity. Throughout, the same reference numerals are used for identical or corresponding parts.

(3) FIG. 1 shows a schematic side view of an embodiment of an unbonded flexible pipe of the invention.

(4) FIG. 2 schematically illustrates a cross sectional view of an embodiment of an unbonded flexible pipe of the invention.

(5) FIG. 3 shows a schematic side view of an embodiment of an unbonded flexible pipe of the invention.

(6) FIG. 4 schematically illustrates a cross sectional view of an embodiment of an unbonded flexible pipe of the invention.

(7) FIGS. 5a-5c show sections of three different retaining tapes in a schematic side view of an embodiment of an unbonded flexible pipe of the invention.

(8) FIG. 6 shows a schematic side view of an embodiment of an unbonded flexible pipe of the invention.

(9) FIG. 7 schematically illustrates a cross sectional view of an embodiment of an unbonded flexible pipe of the invention.

(10) FIG. 8 shows a section of a thermally insulating tape.

(11) FIG. 9 illustrates a schematic side view of an embodiment of an offshore installation of the invention.

(12) FIG. 10 illustrates a schematic side view of another embodiment of an offshore installation of the invention.

(13) The unbonded flexible pipe shown in FIG. 1 comprises from inside and out a carcass 1, an internal pressure sheath 2, a metallic pressure armour layer 3, and a pair of cross wound metallic tensile armour layers 4a, 4b and finally an additional layer 5 surrounding the metallic armouring layer, the additional layer is in this embodiment an outer jacket 5. The outer jacket comprises perforations 6 for providing the gas escape route radially outwards from the metallic armouring layer. The metallic armour layers are made from or comprise metallic armouring elements which are helically wound to surround the internal pressure sheath 2. The metallic armouring elements may have any cross-sectional profile e.g. such as it is know from prior art unbonded flexible pipes. The arrow indicates the bore in which a fluid may be transported. The metallic armouring elements are at least partly covered by a viscous fluid which may be as defined above and preferably comprise at least one of grease, vax, bitumen and/or tar.

(14) The outer jacket may advantageously be extruded and perforated. Examples of suitable polymer materials for the outer jacket are high density polyethylene (HDPE), cross linked polyethylene (PEX), polypropylene (PP), polyvinyldifluorid (PVDF) or polyamide (PA).

(15) The unbonded flexible pipe shown in FIG. 2 is a variation of the unbonded flexible pipe of FIG. 1 where the pipe does not have a carcass and where the perforations are smaller.

(16) The metallic armouring layers 3, 4a, 4b are encased in an annular encasing space—referred to as the annulus—formed by the internal pressure sheath 2 and the at least one additional layer 5 surrounding the metallic armouring layers 3, 4a, 4b. The amount of viscous fluid in the annular encasing space is sufficient to block for axial gas flow.

(17) The outer jacket comprises a plurality of perforations 6a for providing the gas escape route radially outwards from the metallic armouring layer. The perforation may advantageous be evenly distributed in the outer jacket along the length of the pipe.

(18) The unbonded flexible pipe shown in FIG. 3 comprises from inside and out a carcass 11, an internal pressure sheath 12, a metallic pressure armour layer 13, and a pair of cross wound metallic tensile armour layers 14a, 14b and finally an additional layer 15 surrounding the metallic armouring layer, the additional layer is in this embodiment a retaining layer 15. The metallic armour layers 13, 14a, 14b are made from or comprise metallic armouring elements which are helically wound to surround the internal pressure sheath 12. The metallic armouring elements are at least partly covered by a viscous fluid which may be as defined above and preferably comprises at least one of grease, vax, bitumen and/or tar.

(19) The retaining layer is advantageously as described above and is wound onto the outermost armour layer 14b, with overlapping edges as illustrated with the lines 15a. In a variation of the embodiment of FIG. 3 the pipe may comprise a jacket outside the retaining layer, wherein the jacket preferably is perforated as discussed above.

(20) FIG. 4 illustrates an unbonded flexible pipe corresponding to the unbonded flexible pipe of FIG. 3. Advantageously, the annulus 17 is substantially filled with the viscous fluid in at least a section of the unbonded flexible pipe.

(21) The retaining layer may simultaneously with acting as a retaining layer for the viscous fluid also act as a holding layer for the tensile armour elements.

(22) FIG. 5a illustrates an example of a tape for the retaining later. The retaining tape is woven very tightly and comprises lengthwise continuous filament yarns A forming warp yarns arranged in the tape length direction and woven with crossing weft yarns B also of filament yarn.

(23) FIG. 5b illustrates another example of a tape for the retaining later. The retaining tape in this example is woven less tightly and it is preferred that a further layer e.g. is applied to cover a retaining layer of the type 5b retaining tape.

(24) FIG. 5c illustrates a further example of a tape for the retaining later. The retaining tape in this example is a very tightly woven aramid tape (Kevlar).

(25) The woven aramid tape is very strong and abrasion resistant and is a preferred choice for the retaining layer.

(26) The unbonded flexible pipe shown in FIG. 6 comprises from inside and out a carcass 21, an internal pressure sheath 22, a metallic pressure armour layer 23, and a pair of cross wound metallic tensile armour layers 24a, 24b and two additional layers 25, 26.

(27) The metallic armour layers 23, 24a, 24b are made from or comprise metallic armouring elements which are helically wound to surround the internal pressure sheath 22. The metallic armouring elements are at least partly covered by a viscous fluid which may be as defined above and preferably comprises at least one of grease, bitumen and/or tar.

(28) The innermost of the additional layers is a thermal insulation layer made from one or more helically wound thermally insulation elements.

(29) The thermal insulation elements may preferably comprise the gas escape path in the form of one or more channel(s) in the thermal insulation layer e.g. as the thermal insulation element illustrated in FIG. 8.

(30) The thermal insulation elements may advantageously be as described in WO 2013/044920 further comprising perforations into the longitudinal holes forming at least a part of the gas escape route.

(31) FIG. 8 shows an example of a thermal insulation element. The thermal insulation element has a length LE which may be from a few meters to several hundreds or even thousand meters. The length of the thermal insulation element may largely depend on it's thickness and thereby how long lengths that may be wound onto a spool in the production.

(32) The thermal insulation element has a number of elongate holes 32 extending in the length LE of the thermal insulation element. The elongate holes 32 may form the lengthwise gas escape paths 32 through which the gas may escape axially along the length of the unbonded flexible pipe.

(33) The thermal insulation element has on the side adapted for facing the annulus a plurality of perforations 31 into the elongate holes 32 to ensure a full gas escape route radially outwards from the metallic armouring layer through the perforations 31 and into the lengthwise gas escape paths 32 from where the gas can be vented e.g. at an end fitting e.g. near or above the water line.

(34) The second of the additional layers is an outer jacket 26. The outer jacket may e.g. be perforated as described above. In an embodiment the outer jacket is liquid impervious and free of perforations.

(35) FIG. 7 illustrates an unbonded flexible pipe corresponding to the unbonded flexible pipe of FIG. 6. Advantageously, the annulus 27 is substantially filled with the viscous fluid in at least a section of the unbonded flexible pipe.

(36) In a variation both the thermal insulation layer 25 and the outer jacket 26 are perforated.

(37) In a variation the thermal insulation element(s) is free of the perforations 31 and instead the material of the thermal insulation element has a permeability which is larger such as at least about 10% larger than the permeability of the internal pressure sheath with respect to at least one of water, hydrogen sulphide or carbon dioxide.

(38) The offshore installation shown in FIG. 9 comprises an unbonded flexible pipe 41 of an embodiment of the invention as disclosed above. The unbonded flexible pipe 41 is a riser arranged for transporting fluid between an upper facility 42 and a not shown subsea facility. The upper facility 42 is a floating unit e.g. a vessel or a platform. Such a floating unit will often be moored using tethering lines or similar. The upper facility 42 is floating at the water line 49.

(39) The riser may reach into very deep water, such as to 1000 m, 2000 or even deeper. The armouring layer(s) in the annulus of the unbonded flexible pipe 41 is substantially embedded in the viscous fluid in at least the lowermost section 43. The lowermost pipe section 43 preferably has a length of at least about 100 m, such as at least about 200 m, such as at least about 500 m.

(40) In a variation thereof the armouring layer(s) in the annulus of the unbonded flexible pipe 41 is substantially embedded in the viscous fluid in substantially the entire length of the pipe e.g. up to 3000 m or even longer.

(41) The offshore installation shown in FIG. 10 comprises an unbonded flexible pipe 51 of an embodiment of the invention as disclosed above. The unbonded flexible pipe 51 is a riser arranged for transporting fluid between an upper facility 52a and a not shown subsea facility 56. The upper facility 52a is arranged below the water line 59 and may for example be a mid-water arch or another submerged facility. A vessel 52b is connected to the upper facility 52a via a jumper 58. The armouring layer(s) in the annulus of the unbonded flexible pipe 51 is substantially embedded in the viscous fluid in at least the lowermost section 53. The lowermost pipe section 53 preferably has a length of at least about 100 m, such as at least about 200 m, such as at least about 500 m.

(42) Further scope of applicability of the present invention will become apparent from the description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.