Unbonded flexible pipe

Abstract

Disclosed is an unbonded flexible pipe for subsea transportation of fluids. The pipe has a length and a centre axis and includes a plurality of layers including at least one polypropylene based layer including a modified polypropylene compound including: at least about 50% by weight of a base polypropylene (base PP) which consists of polypropylene including up to about 10% by weight of one or more co-monomers other than propylene, and at least about 1% by weight of a plastomer including a propylene and at least one co-monomer other than propylene.

Claims

1. An unbonded flexible pipe for subsea transportation of fluids, the pipe has a length and a centre axis and comprises a plurality of layers comprising at least one polypropylene based layer comprising a modified polypropylene compound comprising: at least about 50% by weight of a base homopolymer polypropylene (base PP), and from about 1% to about 15% by weight of a plastomer comprising a copolymer of propylene and at least one co-monomer selected from C4 to C20 alpha olefins wherein the polypropylene based layer is a wound layer having thickness from about 0.1 mm to about 10 mm.

2. The flexible pipe of claim 1, wherein the base PP has a Melt Flow Index (MFI) of from about 0.1 to about 8.0 g/10 min (2.16 kg/10 min at 230 C.).

3. The flexible pipe of claim 1, wherein the base PP has a tensile strength of at least about 12 MPa determined according to ASTM D638.

4. The flexible pipe of claim 1, wherein said modified polypropylene compound comprises at least about 60% by weight of said base PP.

5. The flexible pipe of claim 1, wherein said plastomer is a propylene based plastomer comprising at least 50% by weight of polypropylene.

6. The flexible pipe of claim 1, wherein said plastomer is a propylene based plastomer comprising ethylene comonomer.

7. The flexible pipe of claim 1, wherein said plastomer has a MFI of from about 2.0 to about 15.0 g/10 min (2.16 kg/10 min at 190 C.).

8. The flexible pipe of claim 1, wherein said base PP has a tensile strength at yield which is larger than the tensile strength at yield of the plastomer.

9. The flexible pipe of claim 1, wherein said modified polypropylene compound comprises from about 2% by weight to about 9% by weight of the plastomer.

10. The flexible pipe of claim 1, wherein the pipe comprises at least one metal based armour layer and at least one liquid impervious polymer layer, said metal based armour layer is a carcass and the at least one liquid impervious polymer layer is a pressure sheath, the polypropylene based layer is a wound polypropylene based layer positioned between said carcass and said pressure sheath.

11. An unbonded pipe for subsea transportation of fluids, the pipe has a length and a centre axis and comprises a plurality of layers comprising at least one polypropylene based layer comprising a modified polypropylene compound comprising: at least about 50% by weight of a base homopolymer polypropylene (base PP), and from about 1% to about 15% by weight of a plastomer comprising a copolymer of propylene and at least one co-monomer selected from C4 to C20 alpha olefins, wherein the pipe comprises at least one metal based armour layer and at least one liquid impervious polymer layer and wherein a wound polypropylene based layer is applied between said metal based armour layer of the pipe and said liquid impervious polymer layer.

12. An unbonded flexible pipe for subsea transportation of fluids, the pipe has a length and a centre axis and comprises a plurality of layers comprising at least one polypropylene based layer comprising a modified polypropylene compound consisting of: at least about 50% by weight of a base homopolymer polypropylene (base PP), and from about 1% to about 15% by weight of a copolymer of propylene and at least one monomer selected from C4 to C20 alpha olefins; up to about 10% by weight of other compounded polymer; up to about 25% by weight of reinforcement material and/or filler material and up to about 5% by weight of stabilizer.

13. The flexible pipe of claim 12, wherein the polypropylene based layer is an extruded layer having a thickness of from about 1 mm to about 20 mm.

14. The flexible pipe of claim 12, wherein the polypropylene based layer forms an outermost polymer sheath of said pipe.

15. The flexible pipe of claim 12, wherein polypropylene based layer forms a pressure sheath of said pipe.

16. The flexible pipe of claim 12, wherein the polypropylene based layer forms a thermal insulation layer of said pipe.

Description

EXAMPLES

Example 1

Preparing an Outer Sheath for an Embodiment of an Unbonded Flexible Pipe of the Invention

(1) For the preparation of an outer sheath, the following components are used:

(2) Base polypropylene: A polypropylene having a MFI of 8 g/min (2.16 kg/10 min at 230 C.) and a density of 0.902 g/cm.sup.3, delivered as pellets (ASI Polypropylene 1255-01 Homopolymer from the company A. Schulman Inc.; USA).

(3) Plastomer: An ethylene octene plastomer having a MFI of 10 g/min (2.16 kg/10 min at 230 C.) and a density of 0.882 g/min, delivered as pellets (EXACT 8210 from the company ExxonMobil Chemical; Europe).

(4) Stabilizer 1: A phenolic stabilizer composition SONGNOX 2246, powder composition (based on phenols and obtainable from company SONGNOX; South Korea).

(5) Stabilizer 2: A hindered amine light stabilizer SABO STAB 70, powder composition (obtainable from company SONGNOX; South Korea.

(6) An polypropylene based layer is prepared with the above components in the following amounts.

(7) TABLE-US-00001 Base polypropylene 87% Plastomer 9% Stabilizer 1 3.2% Stabilizer 2 0.8%

(8) An unbonded flexible pipe of 6 inner diameter (15.2 cm) is produced. The unbonded flexible pipe comprises a steel carcass surrounded by an internal pressure sheath of polypropylene surrounded by a pressure armour wound from steel wire. Around the pressure armour are wound two layers of tensile armour made from steel wires. Before applying the outer sheath of modified polypropylene compound the pipe has an outer diameter of approximately 28.4 cm.

(9) The above components are transferred into a pre-mixer in which the blend is mixed and melted (compounded) at a temperature of approximately 220 C., before it is transferred to the extruder.

(10) The extruder is a conventional single screw extruder suitable for polyolefin extrusion with a 120 mm screw diameter and a typical L/D ratio of 30. The temperature setting on the heating zones of the extruder and head ranges from 180 C. to 240 C., and melt temperature is typically 210 C.

(11) The resulting extruded layer (outer sheath) has a thickness of approximately 6 mm.

(12) The outer sheath comprising the polypropylene based layer:

(13) Density: 0.9 g/cm.sup.3

(14) Oxidation induction time: 104 min (OIT according to ASTM D 3895)

(15) Yield Strength: 24.3 MPa

(16) Yield Strain: 12.1%

Example 2

Preparing an Intermediate Sheath for an Embodiment of an Unbonded Flexible Pipe of the Invention

(17) An intermediate sheath is prepared using the following components:

(18) Base polypropylene: A polypropylene having a MFI of 5 g/min (2.16 kg/10 min at 230 C.) and a density of 0.909 g/cm.sup.3, delivered as pellets (ASI Polypropylene 3486-01 Homopolymer from the company A. Schulman Inc. USA).

(19) Plastomer: A polyolefin plastomer having a MFI of 5, delivered as pellets (2.16 kg/10 min at 230 C.) and a density of 0.870 g/cm.sup.3 (AFFINITY EG8200G from the company DOW; USA).

(20) Stabilizer: A phenolic stabilizer composition SONGNOX 2246, powder composition (based on phenols and obtainable from company SONGNOX China).

(21) Filler: Glass fiber (milled glass fibers obtainable from PMI Plastic Materials Inc.; USA).

(22) A polypropylene based layer is prepared with the above components in the following amounts.

(23) TABLE-US-00002 Base polypropylene 55% Plastomer 37% Stabilizer 2.5% Filler 5.5%

(24) An inner part of an unbonded flexible pipe of 6 inner diameter (15.2 cm) is produced. The inner part of the unbonded flexible pipe comprises a steel carcass surrounded by an internal pressure sheath of polypropylene surrounded by a pressure armour wound from steel wire. Around the pressure armour is applied an intermediate sheath intended to serve as an intermediate sheath between the pressure armour and a tensile armour to be applied after the application of the intermediate sheath. Before applying the intermediate sheath of modified polypropylene, the pipe inner part has an outer diameter of approximately 22.4 cm.

(25) The above components are transferred into a pre-mixer in which the blend is mixed and melted at a temperature of approximately 210 C., before it is transferred to the extruder.

(26) The extruder is a conventional polyethylene single screw extruder with a 120 mm screw diameter and an L/D ratio of 30, with a standard screw. The temperature setting on the heating zones of the extruder and head ranges from 180 to 240 C., and melt temperature is typically 210 C.

(27) The resulting extruded layer in the form of the intermediate sheath has a thickness of approximately 5 mm.

(28) The intermediate sheath comprising the polypropylene based layer:

(29) Density: 0.895 g/cm.sup.3

(30) Oxidation induction time: 99 min (OIT according to ASTM D 3895)

(31) Yield Strength: 26.8 MPa

(32) Yield Strain: 9.4%

(33) The intermediate sheath serves to protect the armour layers and have good properties in this respect. Moreover, the intermediate sheath provides thermal insulation.

Example 3

Preparation of a Coating Layer for a Support Tape to be Used for a Layer of an Embodiment of a Pipe of the Invention

(34) For the purpose of preparing a coating layer onto a support tape the following components were provided.

(35) Base polypropylene: A polypropylene random copolymer having a MFI of 0.25 g/min (2.16 kg/10 min at 230 C.) and a density of 0.905 g/cm.sup.3, delivered as pellets (PP RA130E from company Borealis (Borouge Pte LdtBorealis Group); Sweden).

(36) Plastomer: A polyolefin plastomer having a MFI of 5 (2.16 kg/10 min at 230 C.) and a density of 0.870 g/cm.sup.3, delivered as pellets (AFFINITY EG8200G from the company DOW Chemicals; USA).

(37) Stabilizer: A phenolic stabilizer composition SONGNOX 2246, powder composition (based on phenols and obtainable from company SONGNOX China).

(38) Filler: Glass fiber (milled glass fibers obtainable from PMI Plastic Materials Inc.; USA)

(39) TABLE-US-00003 Polypropylene 87.5% Polyolefin co-polymer plastomer 9% Stabilizer 1% Filler 2.5%

(40) The above components are transferred into a pre-mixer in which the blend is mixed and melted at a temperature of approximately 210 C.

(41) A support tape manufactured as disclosed in WO 03/044414 A and having a width of approximately 10 cm and a thickness of approximately 0.5 cm is applied with a coating of the melted mixture. The mixture is applied with a heated nozzle having a temperature of approximately 190 C. After application the coating is allowed to cure at ambient temperature.

(42) The applied coating has a thickness of from approximately 0.5 mm to approximately 1.0 mm and provides wear resistance to the tape.