Method of reeling and unreeling an internally clad metal pipeline

1. A method for winding a pipeline onto a reel, the pipeline having an inner corrosion-resistant metallic liner that is tightly fitted within an outer pipe that is less corrosion-resistant, comprising the operations of:

(a) providing a fluid connection between the pipeline and pumping/pressurizing equipment via a manifold mounted on the pipeline;

(b) pumping, by means of pressurized fluid, a movable plug along a length of pipeline towards a trailing end to fill the length of pipeline with fluid;

(c) locking the plug near the trailing end of the length of pipeline;

(d) pressurizing the fluid in the length of the pipeline to an absolute pressure within a range defined by a lower value of 5 bar;

(e) connecting a leading end of the pipeline to a reel via the manifold;

(f) winding the pipeline onto a reel, while an absolute pressure within the range is maintained within the pipeline;

(g) depressurizing the pipeline;

(h) unlocking the plug; and

(i) joining a further pipeline section to the trailing end followed by repetition of the pumping, locking, pressurizing and winding operations; wherein the absolute pressure in the pipeline is maintained in step (d) by an accumulator connected to the pipeline during the winding operation.

2. The method according to claim 1 , wherein the range is additionally defined by an upper value that is less than 25 bar.

3. The method according to claim 1 , wherein the fluid is pressurized to an absolute pressure of at least 25 bar.

4. The method according to claim 3 , wherein the fluid is pressurized to an absolute pressure of at least 30 bar.

5. The method according to claim 4 , in which steps (b) and (d) are performed by pumping fluid to the leading end of the pipeline.

6. The method according to claim 4 , in which the pressurizing operation is performed by operating a pumping system to fill the length of pipeline with fluid at a first absolute pressure below 25 bar and thereafter to raise the pressure to a second absolute pressure of at least 30 bar.

7. The method according to claim 3 , in which the pressurizing operation is performed by operating a pumping system to fill the length of pipeline with fluid at a first absolute pressure below 25 bar and thereafter to raise the pressure to a second absolute pressure of at least 30 bar.

8. The method according to claim 1 , in which steps (b) and (d) are performed by pumping fluid to the leading end of the pipeline.

9. The method according to claim 1 , in which the absolute pressure in the pipeline is maintained in step (f) by an accumulator connected to the pipeline during the winding operation.

10. The method according to claim 9 in which the accumulator is mounted on the pipe laying reel.

11. The method according to claim 10 in which a further accumulator is provided at the trailing end of the pipeline for maintaining the pipeline pressure during feeding of the leading end of the pipeline onto the pipe laying reel.

12. The method according to claim 11 , wherein the plug is a friction pig which engages frictionally with the wall of the pipeline but whose frictional engagement is overcome, to move the pig along the pipeline, when step (b) is performed, and wherein the pig is locked in position near the trailing end of the length of pipeline in step (c), by abutment against an end cap secured to the trailing end of the pipeline, the end cap being removed from the pipeline prior to step (g).

13. The method according to claim 9 in which a further accumulator is provided at the trailing end of the pipeline for maintaining the pipeline pressure during feeding of the leading end of the pipeline onto the pipe laying reel.

14. The method according to claim 13 , wherein the plug is a friction pig which engages frictionally with the wall of the pipeline but whose frictional engagement is overcome, to move the pig along the pipeline, when step (b) is performed, and wherein the pig is locked in position near the trailing end of the length of pipeline in step (c), by abutment against an end cap secured to the trailing end of the pipeline, the end cap being removed from the pipeline prior to step (g).

15. The method according to claim 1 , wherein the fluid is water.

16. The method according to claim 1 , wherein the plug is a smart pig which is operable to be engaged with the wall of the pipeline, for locking the plug near the trailing end of the length of pipeline.

17. The method according to claim 1 , wherein the plug is a friction pig which engages frictionally with the wall of the pipeline but whose frictional engagement is overcome, to move the pig along the pipeline, when step (b) is performed, and wherein the pig is locked in position near the trailing end of the length of pipeline in step (c), by abutment against an end cap secured to the trailing end of the pipeline, the end cap being removed from the pipeline prior to step (g).

18. A The method according to claim 1 , wherein, after step (i) has been performed for the last pipeline section to be joined to the pipeline, the pipeline is subsequently laid from the reel while the fluid pressure within the entire pipeline is maintained, in a range defined by a lower value of 5 bar absolute, after which the pipeline is depressurized.

19. The method according to claim 1 , wherein the further pipeline section is joined to the trailing end of the length of the pipeline by welding in step (i), the plug being locked at a distance from the trailing end of the length of pipeline in step (c) that avoids damage to the plug during the welding of the further pipeline section.

20. The method according to claim 19 , wherein the distance is about 2 meters.