Manufacture of pipes

1. A method of manufacturing a pipe, the method comprising:

pre-heating a mandrel, the mandrel made of a single material having a coefficient of thermal expansion;

cold-gas dynamic spraying of particles of at least one of titanium or titanium alloy directly onto the material of the pre-heated mandrel to produce the pipe; and

allowing the pre-heated mandrel and the pipe to cool prior to removal of the pipe from the mandrel,

wherein the coefficient of thermal expansion of the pre-heated mandrel material is greater than the coefficient of thermal expansion of the pipe, so that separation of the pipe from the pre-heated mandrel takes place by contraction of the pre-heated mandrel away from the pipe when the pre-heated mandrel and the pipe are allowed to cool.

2. The method according to claim 1 , wherein the surface of the pre-heated mandrel is smooth and defect-free.

3. The method according to claim 1 , wherein the composition of the pipe varies along the length and/or across the thickness of the pipe.

4. The method according to claim 3 , wherein the pipe comprises two or more discrete lengths and/or layers of different materials.

5. The method according to claim 3 , wherein the composition of the pipe varies gradually along the length and/or across the thickness of the pipe.

6. The method according to claim 1 , wherein the pipe comprises a material to confer corrosion and/or wear resistance to a surface of the pipe.

7. The method according to claim 1 , wherein the pre-heated mandrel comprises surface features that impart an increased surface area to a corresponding surface of the pipe.

8. The method according to claim 1 , wherein an average size of the particles and the operating parameters of the cold-gas dynamic spraying are selected so the pipe is free of connected micro-voids.

9. The method according to claim 1 , further comprising after removal of the pipe from the mandrel applying a load to an outer surface of the pipe with a roller to at least one of size or finish of the pipe.

10. The method according to claim 1 , further comprising applying a load to an outer surface of the pipe with a roller to at least one of size or finish of the pipe.

11. The method according to claim 1 , wherein the particles have a diameter of 5 to 45 microns.

12. The method according to claim 1 , wherein the mandrel includes a cavity extending through it.

13. The method according to claim 1 , wherein the pipe is adapted to transport fluid either above or below ground or sub-sea, the fluid comprising at least one of acidic or alkaline fluids, water, oil, gas or chemicals.

14. A method of manufacturing a pipe, the method comprising:

pre-heating a mandrel formed entirely of a material having a first coefficient of thermal expansion, the material of the mandrel defining an outer surface of the mandrel;

cold-gas dynamic spraying particles of a second material onto the outer surface of the pre-heated mandrel to produce a pipe such that an inner surface of the pipe forms on the outer surface of the pre-heated mandrel, the second material comprising titanium or a titanium alloy and having a second coefficient of thermal expansion; and

allowing the pre-heated mandrel to contract away from the inner surface of the pipe as the pre-heated mandrel and the pipe cool prior to removal of the pipe from the mandrel such that a difference between the first coefficient of thermal expansion and the second coefficient of thermal expansion separates the mandrel from the pipe.

15. The method according to claim 14 , wherein the outer surface of the pre-heated mandrel is smooth and defect-free.

16. The method according to claim 14 , wherein the composition of the pipe varies along the length and/or across the thickness of the pipe.

17. The method according to claim 16 , wherein the pipe comprises two or more discrete lengths and/or layers of different materials.

18. The method according to claim 14 , wherein an average size of the particles and the operating parameters of the cold-gas dynamic spraying are selected so the pipe is free of connected micro-voids.

19. A method of manufacturing a pipe, the method comprising:

pre-heating a mandrel, the mandrel having an inner surface or core and an outermost surface, the mandrel formed of a material having a first coefficient of thermal expansion at the inner surface or core and the outermost surface thereof;

cold-gas dynamic spraying particles of a second material onto the mandrel to produce a pipe such that an inner surface of the pipe forms on the outermost surface of the mandrel, the second material comprising titanium or a titanium alloy and having a second coefficient of thermal expansion; and

removing the pipe from the mandrel after the pipe and the mandrel have cooled such that a difference between the first coefficient of thermal expansion and the second coefficient of thermal expansion separates the mandrel from the pipe.

20. The method according to claim 19 , wherein cold-gas dynamic spraying particles of the second material onto the mandrel includes the outermost surface of the mandrel having structural features extending therefrom such that an inner surface of the pipe formed on the outermost surface has an increased surface area.