Flexible armoured pipe with a retaining layer of metal elongate strip

Abstract

The present invention relates to a flexible armoured pipe having a centre axis and including an internal pressure sheath and an outer sheath, where the radial distance between the internal pressure sheath and the outer sheath defines an annulus. The annulus includes at least one tensile armour layer surrounded by at least one retaining layer constituted by an elongate metallic strip wound around the at least one tensile armour with a winding angle of at least 65° in respect of the centre axis.

Claims

1. A flexible armoured pipe having a centre axis and comprising an internal pressure sheath and an outer sheath, the radial distance between said internal pressure sheath and said outer sheath defining an annulus, said annulus comprising at least one tensile armour layer surrounded by at least one retaining layer constituted by an elongate metallic strip wound around the at least one tensile armour layer with winding angle of at least 65° in respect of the centre axis, wherein the elongate metallic strip is non-interlocked and has a bending stiffness lower than 1/10 of a bending stiffness of a wire forming the at least one tensile armour layer.

2. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has a width/thickness ratio in the range of 2 to 300.

3. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has a width in the range of 20 to 150 mm.

4. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has a thickness in range of 0.5 to 10 mm.

5. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has a thickness which is up to ½ of the thickness of the wire forming the at least one tensile armour layer.

6. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip is wound with a winding angle in respect of the centre axis in the range of 70° to 85°.

7. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip is wound with a gap between adjacent windings, said gap being in the range of 1 mm to 350 mm.

8. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip is wound with an overlap zone between adjacent windings, said overlap zone having a zone width in the range of 1 mm to 100 mm.

9. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip is provided with a surface which is rougher in the overlap zone than in the remaining surface.

10. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has a tensile strength of 250 MPa or more when measured according to ASTM E8/E8M-13 (2013).

11. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has rounded edges.

12. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has a substantially rectangular cross section.

13. A flexible armoured pipe according to claim 1, wherein the elongate metallic strip has an undulated cross section.

14. A flexible armoured pipe according to claim 1, wherein the at least one tensile armour is wound from an elongate member with a winding angle in respect of the centre axis in the range of 10° to 50°.

15. A flexible armoured pipe according to claim 1, wherein the annulus comprises a pressure armour and wherein the elongate metallic strip has a bending stiffness lower than 1/10 of a bending stiffness of a wire forming the pressure armour.

16. A flexible armoured pipe according to claim 1, wherein the annulus comprises a pressure armour, which is wound from an elongate member with a winding angle in respect of the centre axis in the range of 75° to 90°.

17. A flexible armoured pipe having a centre axis and comprising an internal pressure sheath and an outer sheath, the radial distance between said internal pressure sheath and said outer sheath defining an annulus, said annulus comprising at least one tensile armour layer surrounded by at least one retaining layer, wherein the at least one retaining layer comprises two or more elongate metallic strips, said two or more elongate metallic strips being wound around the at least one tensile armour layer with a winding angle of at least 65° in respect of the centre axis and in a parallel track with the same winding directions in respect of the centre axis, and wherein the two or more elongate metallic strips each have a bending stiffness lower than 1/10 of a bending stiffness of a wire forming the at least one tensile armour layer.

18. A flexible armoured pipe having a centre axis and comprising an internal pressure sheath and an outer sheath, the radial distance between said internal pressure sheath and said outer sheath defining an annulus, said annulus comprising at least one tensile armour layer surrounded by at least two retaining layers constituted by elongate metallic strips, said elongate metallic strips of the at least two retaining layers being wound with different winding angles in respect of the centre axis, wherein the elongate metallic strips each have a bending stiffness lower than 1/10 of a bending stiffness of a wire forming the at least one tensile armour layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention will now be described in further details with reference to embodiments shown in the drawing in which:

(2) FIG. 1 shows an unbonded flexible pipe;

(3) FIG. 2 shows a flexible pipe according to the invention;

(4) FIG. 3 shows a section of a flexible pipe according to the invention;

(5) FIG. 4 shows an embodiment of a retaining layer according to the invention;

(6) FIG. 5 shows an embodiment of a retaining layer according to the invention;

(7) FIG. 6 shows an embodiment of a retaining layer according to the invention;

(8) FIG. 7 shows a retaining layer comprising holes;

(9) FIG. 8 shows a retaining layer comprising perforations;

(10) FIG. 9 shows a retaining layer;

(11) FIG. 10 shows a cross section of an elongate strip for a retaining layer;

(12) FIG. 11 shows a cross section of an elongate strip for a retaining layer;

(13) FIG. 12 shows a cross section of an elongate strip for a retaining layer.

(14) The figures are not accurate in every detail but only sketches intended to the show the principles of the invention. Details which are not a part of the invention may have been omitted. In the figures the same reference numbers are used for the same parts.

(15) FIG. 1 shows an unbonded flexible pipe 1. The pipe 1 comprises from the inside and outwards a carcass 2 to support the internal pressure sheath 3. The internal pressure sheath 3 is surrounded by a pressure armour 4 and a first tensile armour 5 and a second tensile armour 6. The outermost part of the pipe 1 is the outer sheath 7. Between the internal pressure sheath 3 and the outer sheath 7 is formed an annulus in which the armour layers are located.

(16) FIG. 2 shows an unbonded flexible pipe 10 according to the invention. As the unbonded flexible pipe shown in FIG. 1 the pipe 10 comprises a carcass 2, internal pressure sheath 3, a pressure armour 4, a first tensile armour 5 and a second tensile armour 6 and an outer sheath 7. However, the pipe 10 further comprises a retaining layer 11 surrounding the second tensile armour 6 which is the outermost armour layer. The retaining layer 11 is surrounded by the outer sheath 7 which form a barrier for ingress of fluid such as sea water to the armour layers.

(17) The carcass 2 is made from elongate strips of duplex steel with an “S-shaped” cross-section which allow adjacent windings to interlock. The strips are wound with a winding angle of 87° in respect of the axis of the pipe. The carcass 2 is placed in the bore 8 of the pipe and serves to protect the internal pressure sheath 3 against damage, e.g. in case of certain pressure drop.

(18) The internal pressure sheath 3 is made from polyvinylidene fluoride which is extruded onto the outer surface of the carcass 2. The internal pressure sheath 3 forms the bore 8 in the pipe and provides a substantially fluid tight barrier between the bore and the armour layers on the outer side of the internal pressure sheath 3.

(19) The pressure armour 4 placed on the outer surface of the internal pressure sheath 3 is wound from profiled strips of carbon steel. The winding angle is approximately 85° in respect of the axis. The pressure armour serves to protect the internal pressure sheath if the pressure suddenly increases.

(20) The first and the second tensile armour 5, 6 protect the pipe toward axial stress. The tensile armour layers are made from elongate strips of carbon steel. The elongate strips are wound with a winding angle of approximately 55° in respect of the axis. In the particular embodiment the two layers are wound in opposite directions in respect of the axis.

(21) The pipe 10 shown in FIG. 2 comprises a retaining layer 11 according to the invention. The retaining layer 11 is made from an elongate strip of carbon steel. The strip is wound around the outer tensile layer 6 with a winding angle of approximately 82° in respect of the axis. The retaining layer 11 serves to reduce radial displacement of the tensile armour layers 5, 6.

(22) The outermost layer of the pipe 10 is the outer sheath 7 which is made from polyethylene and extruded onto the retaining layer 11. The outer sheath 7 provides a substantially fluid tight barrier between the environment and the metallic layers in the pipe.

(23) FIG. 3 shows a section of the pipe 10 according to the invention and depicted in FIG. 2. The pipe 10 comprises from the inside and out a carcass 2, made from duplex steel and having an “S-shaped” cross section which makes it possible for adjacent windings to interlock.

(24) Outside and surrounding the carcass 2 is the internal pressure sheath 3, which forms the bore 8. The internal pressure sheath is made from polymer material and extruded onto the carcass 2.

(25) Around the outer surface of the internal pressure sheath 3, the elongate profiled metal strip forming the pressure armour 4 is wound. The tensile armour layers 5 and 6 are wound around the pressure armour 3 and the outer tensile armour layer 6 is surrounded by the retaining layer 11 formed by an elongate metal strip.

(26) Finally the pipe 10 comprises the outer sheath 7 of polymer material.

(27) In FIG. 3 the centre axis of the pipe 10 is indicated by a dotted line 9.

(28) FIG. 4 shows an embodiment of a retaining layer 11 according to the invention. In this particular embodiment the retaining layer 11 are wound around the tensile armour layer 6 with tight adjacent windings without gaps.

(29) FIG. 5 shows an embodiment in which the retaining layer 11 is wound around the tensile armour 6 with gaps 12 between adjacent windings.

(30) FIG. 6 shows an embodiment in which the windings of the retaining layer 11 have overlap zones 13.

(31) FIG. 7 shows a part of an elongate metallic strip 14, which metallic strip 14 may be wound up to form the retaining layer. The elongate metallic strip 14 comprises holes 15 which are spaced apart from each other with the same mutual distance along the length of the elongate metal strip 14. The holes may e.g. serve to reduce the risk of formation of gas pockets in the flexible pipe.

(32) FIG. 8 also shows a part of an elongate metallic strip 16, which may be wound up to form the retaining layer. This elongate metallic strip 16 comprises perforations 17 which are distributed in discrete areas 18 along the length of the elongate metallic strip 16. The perforations 17 may also serve to reduce the risk of formation of gas pockets in the flexible pipe.

(33) FIG. 9 shows an embodiment in which a first retaining layer 11a constituted by an elongate metallic strip is wound around the tensile armour layer 6 and a second retaining layer 11b constituted by a metal strip 19b is wound around the first retaining layer 11a.

(34) FIG. 10 shows a cross section of an elongate metallic strip 20 for a retaining layer. In this embodiment the metallic strip has rounded edges 21 which reduces the risk of damage on the outer sheath.

(35) FIG. 11 shows a cross section of an elongate metallic strip 30 for a retaining layer, which has an oval cross section. Such a cross section may also reduce the risk of damage to the outer sheath and also make it easier to wind the elongate metallic strip 30 with windings with overlap to form the retaining layer.

(36) FIG. 12 shows a cross section of an elongate metallic strip 20 for a retaining layer having an undulated cross section. The undulations may reduce optional axial displacement between the retaining layer and the outer sheath.