A METHOD FOR PRODUCING A FLEXIBLE PIPE AND A FLEXIBLE PIPE

Abstract

A method for producing a flexible pipe for offshore transport of fluids such as oil and gas, the method includes: extruding the internal pressure sheath of polymer material; winding one or more armor layers around the extruded internal pressure sheath; extruding the outer sheath of polymer material; at least one of the extruded sheaths of polymer material is extruded continuously along the length of the pipe wherein at least one zone A and at least one zone B are extruded along the length of the pipe and zone A is extruded from a polymer including polypropylene, and the extruded sheath in zone A has an Youngs-modulus E.sub.A zone B is extruded from a thermoplastic vulcanizate polymer, and the extruded sheath in zone B has an Youngs-modulus E.sub.B, where E.sub.B<0.9×E.sub.A and the polymers forming zone A and B are switched during extrusion to provide a continuous sheath.

Claims

1-20. (canceled)

21. A method for producing a flexible pipe for offshore transport of fluids, wherein said pipe having a length L.sub.p and a bore with a diameter D.sub.Bore and comprises at least one continuous extruded sheath of polymer material, wherein the method comprises extruding said at least one continuous extruded sheath of polymer material is extruded continuously along the length of the pipe, wherein at least one zone A and at least one zone B are extruded along the length of the pipe and wherein: zone A is extruded from a polymer comprising polypropylene (PP), and where the extruded sheath in zone A has a Youngs modulus E.sub.A; zone B is extruded from a thermoplastic vulcanizate polymer (TPV), and the extruded sheath in zone B has a Youngs modulus E.sub.B, where E.sub.B<0.9×E.sub.A; and wherein the polymers forming zone A and B are switched during extrusion.

22. The method according to claim 21, wherein the flexible pipe comprises from the inside and out an internal pressure sheath of polymer material, one or more armor layers and an outer sheath of polymer material, said method comprises: extruding the internal pressure sheath of polymer material; winding one or more armor layers around the extruded internal pressure sheath; extruding the outer sheath of polymer material; and extruding one or more intermediate sheaths of polymer between the internal pressure sheath and the outer sheath of polymer material; wherein the extrusion of at least one of the extruded sheaths of polymer material is provided by the extrusion of said least one continuous extruded sheath of polymer material.

23. The method according to claim 21, wherein the extruded sheath in zone A has a Youngs modulus in the range 700 to 1200 MPa.

24. The method according to claim 21, wherein the length of the zone A is in the range 100 to 3000 m.

25. The method according to claim 21, wherein the length of the zone B is in the range 5 to 500 m.

26. The method according to claim 21, wherein the extruder temperature when extruding zone A is T.sub.A and the extruder temperature when extruding zone B is T.sub.B and wherein the difference between T.sub.A and T.sub.B is less than 25° C.

27. The method according to claim 21, wherein the extruder temperature is in the range 160-260° C.

28. The method according to claim 21, wherein the diameter D.sub.Bore of the bore is at least 5 cm (2 inches).

29. The method according to claim 22, comprising the further step of providing a carcass and wherein said internal pressure sheath being extruded onto the carcass.

30. The method according to claim 21, wherein said at least one continuous extruded sheath of polymer material extruded with at least one zone A and at least one zone B along the length of the pipe is selected from an internal pressure sheath, an outer sheath or an intermediate sheath.

31. The method according to claim 22, wherein one or more armor layers comprises a pressure armor.

32. The method according to claim 22, wherein said one or more armor layers comprises a tensile armor.

33. A flexible pipe for offshore transport of fluids, said pipe having a length L.sub.P and a bore with a diameter D.sub.B, wherein said flexible pipe comprises at least one continuous extruded sheath of polymer material, said at least one continuous extruded sheath of polymer material comprising at least one zone A and at least one zone B along the length of the pipe, said sheath in zone A comprises polypropylene (PP) and having a Youngs modulus E.sub.A, said sheath in zone B comprises a thermoplastic vulcanizate polymer (TPV) and having a Youngs modulus E.sub.B, wherein E.sub.B<0.9×E.sub.A, and wherein said sheath comprising zone A and zone B is continuous along the length of the pipe.

34. The flexible pipe of claim 33, wherein said pipe comprises from the inside and out at least an internal pressure sheath of polymer material, one or more armor layers, an outer sheath of polymer material, and one or more intermediate sheaths of polymer material, wherein at least one of the sheaths of polymer material is provided by said at least one continuous extruded sheath of polymer material.

35. The flexible pipe according to claim 33, wherein zone A has a Youngs modulus in the range 700 to 1200 MPa.

36. The flexible pipe according to claim 33, wherein the pipe comprises a carcass.

37. The flexible pipe according to claim 34, wherein one or more armor layers comprises a pressure armor.

38. The flexible pipe according to claim 34, wherein one or more armor layers comprises a tensile armor.

39. The flexible pipe according to claim 33, wherein the flexible pipe comprises one or more intermediate layers selected from insulating layers, anti-creep layers and anti-skid layers.

40. The flexible pipe according to claim 34, wherein the pipe has a minimum bending radius (MBR) of 5 m.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0080] The invention will now be described in further details with reference to embodiments shown in the drawing in which:

[0081] FIG. 1 shows an unbonded flexible pipe;

[0082] FIG. 2 shows unbonded flexible pipe with intermediate layer;

[0083] FIG. 3 shows a production line for extruding a polymer sheath;

[0084] FIG. 4 shows an extruder which can be fed with two different polymers;

[0085] FIG. 5 shows a section of a flexible pipe according to the invention; and

[0086] FIG. 6 shows a flexible pipe according to the invention installed between a floating facility and the seabed.

[0087] The figures are not accurate in every detail but only sketches intended to 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.

[0088] 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 an extruded layer of a polymer, which is extruded onto the carcass 2.

[0089] The internal pressure sheath 3 is surrounded by a pressure armor 4 and a first tensile armor 5 and a second tensile armor 6. The outermost part of the pipe 1 is the outer sheath 7, which is also an extruded layer. Both the internal pressure sheath 3 and the outer sheath 7 are substantially fluid tight.

[0090] Between the internal pressure sheath 3 and the outer sheath 7 is formed an annulus in which the armor layers 4, 5 and 6 are located. The armor layers are made from metallic materials and, therefore, susceptible to corrosion. The armor layers are protected in the annulus between the internal pressure sheath 3 and the outer sheath 7. As the sheaths 3 and 7 forming the annulus are substantially fluid tight the sheaths are able to significantly reduce the risk that harmful and corrosive substances enter the annulus. One harmful substance is seawater which may be present on the outer side of the outer sheath 7. Other harmful substances may be corrosive gases, such as CO.sub.2 and H.sub.2S, which may be present in the fluid transported in the bore 8 of the pipe 1. The internal pressure sheath 6 and/or the outer sheath 7 can be provided according to the invention.

[0091] FIG. 2 shows another embodiment of an unbonded flexible pipe 1. In this embodiment the pipe 1 comprises from the inside and outwards an internal pressure sheath 3. The internal pressure sheath 3 is an extruded layer of a polymer, which has been extruded as a free standing structure as the pipe 1 does not comprise a carcass.

[0092] The internal pressure sheath 3 is surrounded by a pressure armor 4. Outside the pressure armor 4 two counter wound helical layers of tensile armor 5, 6 are applied. Between the first tensile armor 5 and the pressure armor 4 an intermediate sheath 9 is interposed. As the case of the pipe shown in FIG. 1 the outermost part of the pipe 1 is the outer sheath 7. Both the internal pressure sheath 3, the intermediate sheath 9 and the outer sheath 7 are extruded layers of polymer material and one or more of the layers can be extruded according to the invention.

[0093] The flexible pipe according to the invention can in principle be produced in well-known production facilities for producing flexible pipes. FIG. 3 shows a production line 10 for extruding a polymer sheath.

[0094] The production line 10 comprises a pay-off device or drum 11 on which a carcass 2 has been reeled up. The carcass is delivered to the extruder 13 by a caterpillar device which pulls the carcass 2 from the drum 11 and feeds it into the extruder 13.

[0095] In the extruder 13 a polymer sheath is extruded onto the carcass 2 and the carcass with the extruded sheath enters a first cooling zone 14 allowing the extruded sheath to cool. In the embodiment shown in FIG. 3 the extruded sheath is further cooled in cooling zones 15 and 16.

[0096] After the cooling the carcass with the extruded sheath passes a caterpillar device 17 before it is reeled up on a drum 18.

[0097] In this production line the carcass with the extruded sheath is reeled up on the drum 18. However, in other production lines the carcass with the extruded sheath can be conveyed directly to zones in which armor layers and additional polymer sheaths are applied.

[0098] The cooling zones 15 and 16 are in some production lines omitted and the cooling takes place in the zone 14 only.

[0099] Additional polymer sheaths may be extruded onto the flexible pipe in a similar manner.

[0100] FIG. 4 shows an extruder device 13 in which the extruded types of polymer can be shifted along the length of the pipe.

[0101] The extruder device 13 comprises a hopper 20 to which polymer material can be fed. The extruder device also comprises an extruder part 21 comprising a screw and heating devices. In this embodiment a carcass 2 is fed to the extruder part 21 at one end and leaves the extruder part 21 at the opposite end with a polymer sheath 3 extruded onto the carcass.

[0102] The extruder device also comprises two feeding devices 22 and 24 which can deliver polymer material to the hopper 20 of the extruder. The delivering of polymer material from the feeding devices 22 and 24 to the hopper 20 is controlled by metering devices 23 and 25. The metering devices 23 and 25 can be operated manually or by an automated process.

[0103] The feeding device 22 may comprise TPV material and the feeding device 24 may comprise PP. Thus, it is possible to make an easy shift between TPV and PP in the extruder 13 when extruding the sheath 3. The shift can be performed instantly or gradually. However, in the extruder the two polymers will mix up and form a zone in the extruded sheath were the polymers are intermixed.

[0104] FIG. 5 shows a section 30 of a flexible pipe according to the invention. The pipe section comprises an armor layer 31 onto which a polymer sheath 32 is extruded to cover the armor layer.

[0105] The polymer sheath 32 comprises a zone A comprising polypropylene and a zone B comprising TPV. Between the zones A and B the extruded sheath 32 comprises a zone 33 with no sharp borderlines in which the polymers are intermixed.

[0106] FIG. 6 shows a flexible pipe 1 according to the invention installed between a seabed 41 and a sea surface 42. At the sea surface 42 the flexible pipe is installed to a platform 44 on a floating facility 43.

[0107] The flexible pipe extends from the platform 44 to a subsea well 45 located at the seabed 41.

[0108] The flexible pipe 1 comprises two zones B at each end and one zone A between the two zones B. The outer sheath of the flexible pipe 1 is manufactured according to the invention and in zone A the outer sheath is made from extruded polypropylene and in the zones B the outer sheath is made from extruded thermoplastic vulcanizate polymer. Thus, the outer sheath in the end zones B provides more flexibility to the pipe than the longer mid zone A.

Example

[0109] A flexible pipe is extruded according to the invention. The extruded pipe has a length of approx. 100 m and the outer sheath is extruded according to the invention.

[0110] Flexible pipe comprises a carcass on which an internal pressure sheath of polyethylene with thickness of approx. 8 mm is extruded.

[0111] On the outer side of the internal pressure sheath a first metal strip is wound with an angle of approx. 87° to form a pressure armor. Two layers of a second metal strip are cross-wound around the pressure armor with an angle of approx. 45° to form tensile armors.

[0112] The flexible pipe is now ready for the extrusion of the outer sheath onto the tensile armor.

[0113] The TPV is Santoprene 203-50 from Exxon Mobile.

[0114] The PP is ASI Polypropylene 3486-01 Homopolymer from A. Schulman Inc.

[0115] The two polymer grades are delivered as pellets and the TPV grade is dried 2 hours at approx. 80° C. before the extrusion.

[0116] The extrusion of the outer sheath with thickness approx. 8 mm is performed on a conventional single screw extruder with a 120 mm screw diameter and an L/D ratio of 25-30.

[0117] The temperature setting on the heating zone of the extruder ranges from about 160 to about 185° C. and with a head temperature of approx. 185° C. the typical melt temperature outside of the extruder will be approx. 190° C.

[0118] After extrusion of a first zone based on TPV and with a length of approx. 20 m the polymer in the hopper is shifted to PP, which is transported into the extruder and extrusion continued to extrude a second zone having a length of approx. 80 m without or with only very small adjustments of the parameters.

[0119] After extrusion through the head the outer sheath is cooled in air and subsequently in a cooling bath with temperature gradient to secure efficient slow cooling to avoid phase changes and tension the polymer structure.

[0120] After the cooling outer sheath extruded by TPV (first zone) has a Youngs modulus of approx. 500 MPa and the outer sheath extruded by PP has a Youngs modulus of approx. 1000 MPa.