Riser assembly

1. A riser assembly for transporting production fluids such as oil, gas and/or water from a sub-sea flow line to a floating structure, comprising:

plural segments of flexible pipe each of which is formed as a composite structure of two or more unbonded layers, the layers including an internal sheath for ensuring fluid integrity and a pressure armour layer provided over the internal sheath for resisting internal and external pressure; and

a rigid buoyancy support having at least one buoyancy element at said support, wherein said buoyancy support comprises a rigid pipe member connected at a first and second end thereof in an in-line configuration to an end fitting of two of the plural segments of flexible pipe;

wherein the rigid buoyancy support comprises a plurality of rigid buoyancy supports spaced apart along the length of the riser assembly, each rigid buoyancy support for supporting at least one buoyancy element, and each rigid buoyancy support being connected in an in-line configuration to a respective pair of segments of flexible pipe;

wherein the plural segments of flexible pipe are relatively more flexible than the rigid pipe members of the rigid buoyancy supports;

wherein all of the buoyancy elements of the riser assembly are mounted on rigid pipe members.

2. The riser assembly as claimed in claim 1 wherein each of the plural segments of flexible pipe comprises a portion of flexible pipe body as the respective composite structure.

3. The riser assembly as claimed in claim 2 wherein at least one of the plural segments of flexible pipe further comprises a bend stiffener element secured to a respective end fitting and extending over a zone of the respective flexible pipe body.

4. The riser assembly as claimed in claim 1 wherein:

each buoyancy element is secured to a respective buoyancy support.

5. The riser assembly as claimed in claim 1 wherein:

each buoyancy element is integral with a respective buoyancy support.

6. The riser assembly as claimed in claim 1 wherein said floating structure comprises one of a platform and/or buoy and/or ship.

7. The riser assembly as claimed in claim 1 wherein said sub-sea location comprises a flow line and/or sea-floor installation and/or sub-sea platform.

8. The riser assembly as claimed in claim 1 , wherein the internal sheath comprises a polymer layer and the pressure armour layer comprises a helically wound material.

9. The riser assembly of claim 1 , wherein the layers of the composite structure further include an outer sheath provided over the pressure armour layer.

10. The riser assembly of claim 1 , wherein there are no buoyancy elements mounted on the plural segments of flexible pipe.

11. A riser assembly for transporting production fluids such as oil, gas and/or water from a sub-sea flow line to a floating structure, comprising:

a first segment of flexible pipe;

a further segment of flexible pipe wherein the first and further segments of flexible pipe are formed as a composite structure of two or more unbonded layers, the layers including an internal sheath for ensuring fluid integrity and a pressure armour layer provided over the internal sheath for resisting internal and external pressure; and

a rigid buoyancy support having at least one buoyancy element at said support, wherein

said buoyancy support comprises a rigid sheath member connected to an end fitting of one of said first and further segments of flexible pipe, said sheath member being arranged to extend concentrically over a portion of flexible pipe body of the one of said first and further segments of flexible pipe.

12. The riser assembly as claimed in claim 11 , wherein:

said sheath member has an inner diameter matching a diameter of an outer surface of said portion of flexible pipe body.

13. The riser assembly as claimed in claim 11 , wherein each segment of flexible pipe comprises a portion of flexible pipe body as the respective composite structure.

14. The riser assembly as claimed in claim 13 , wherein a segment of flexible pipe further comprises a bend stiffener element secured to a respective end fitting and extended over a zone of the respective flexible pipe body.

15. The riser assembly as claimed in claim 11 wherein the at least one buoyancy element is secured to the buoyancy support.

16. The riser assembly as claimed in claim 11 wherein the at least one buoyancy element is integral with said support.

17. The riser assembly of claim 11 , wherein the layers of the composite structure further include an outer sheath provided over the pressure armour layer.

18. A method for providing buoyancy at one or more desired locations on a riser assembly for transporting production fluids such as oil, gas and/or water, comprising the steps of:

providing a riser assembly comprising a plurality of segments of flexible pipe wherein each of the segments of flexible pipe are formed as a composite structure of two or more unbonded layers, the layers including an internal sheath for ensuring fluid integrity and a pressure armour layer over the internal sheath for resisting internal and external pressure;

providing a plurality of a rigid pipe members having buoyancy elements mounted thereon, wherein the rigid pipe members are relatively more rigid than the segments of flexible pipe; and

connecting opposing ends of each rigid pipe member to an end fitting of an adjacent flexible pipe segment such that each rigid pipe member is connected to two flexible pipe segments in an in-line configuration;

wherein all of the buoyancy elements of the riser assembly are mounted on rigid pipe members.

19. The method as claimed in claim 18 further comprising the steps of: providing a bend stiffener on each end fitting.

20. The method as claimed in claim 18 further comprising the steps of:

providing a bend stiffener on a remainder end fitting of said respective end fittings.

21. The method as claimed in claim 18 wherein said step of providing providing a plurality of rigid pipe members comprises providing at least one rigid pipe member integral with at least one buoyancy element.

22. The method as claimed in claim 18 wherein said step of providing providing a plurality of rigid pipe members further comprises securing the buoyancy elements to the rigid pipe members.

23. A method for providing buoyancy at one or more desired locations on a riser assembly for transporting production fluids such as oil, gas and/or water, comprising the steps of:

providing a riser assembly comprising a plurality of segments of flexible pipe wherein each of the segments of flexible pipe are formed as a composite structure of two or more unbonded layers, the layers including an internal sheath for ensuring fluid integrity and a pressure armour layer over the internal sheath for resisting internal and external pressure;

proximate to a junction between said segments, providing a rigid buoyancy support; and

providing at least one buoyancy element at said support, wherein

said step of providing a rigid buoyancy support further comprises the steps of:

connecting respective end fittings of adjacent flexible pipe segments together in a back-to-back configuration; and

securing a rigid sheath member to a one of said end fittings, said sheath member extending concentrically over a portion of a flexible pipe body terminated in one end fitting.