Fabrication of pipe strings using friction stir welding
A method of fabrication by friction stir welding (FSW) at an interface between adjoining components such as pipe lengths of a pipeline has layers of different metals on each side. FSW is performed from one side of the adjoining components by effecting relative movement of a first FSW tool along the interface. FSW is performed from an opposite side of the adjoining components by effecting relative movement of a second FSW tool along the interface. Advantageously, FSW is performed simultaneously from both sides of the adjoining components with the FSW tools applying loads in mutual opposition about the adjoining components.
1. A method of fabricating a pipeline by butt welding at a circumferential interface between components comprising lengths of pipe disposed end-to-end or between a length of pipe and a pipeline accessory, at least one of which components comprises internal and external layers of different metal separated by a boundary comprises:
performing external friction stir welding (FSW) by effecting relative circumferential movement along the interface of an inwardly-facing external FSW tool positioned outside the pipe, which tool spins about a first axis that is substantially radial with respect to a cross-section of the pipe; and
performing internal FSW by effecting relative circumferential movement along the interface of the outwardly-facing internal FSW tool, which tool spins about a second axis that is substantially radial with respect to the cross-section of the pipe;
wherein thermo-mechanically affected zones (TMAZs) produced by the external FSW tool and the internal FSW tool each extend partially through a wall of the pipe; wherein the TMAZ produced by the external FSW tool contacts, intersects or overlaps the TMAZ produced by the internal FSW tool; and
wherein the TMAZs produced by the external FSW tool and the internal FSW tool have depths that extend to or overlap beyond the boundary between the internal and external layers.
2. The method of claim 1 , comprising inserting an internal line up clamp (ILUC) supporting an outwardly-facing internal FSW tool through an interior of the pipeline length until it bridges abutting ends of the pipe lengths, or abutting ends of the pipe length and the pipeline accessory, so as to position the outwardly-facing internal FSW tool inside the pipe in alignment with the circumferential interface, the outwardly-facing internal FSW tool being rotatable with respect to the ILUC.
3. The method of claim 2 , comprising turning the outwardly-facing internal FSW tool around a longitudinal axis of the ILUC to effect relative circumferential movement of the outwardly-facing internal FSW tool along the interface.
4. The method of claim 3 , wherein the ILUC comprises at least two clamping mechanisms and a spine member and wherein the method comprises turning the FSW tool about or with the spine member to effect relative circumferential movement of the outwardly-facing internal FSW tool along the interface.
5. The method of claim 2 , comprising bracing the outwardly-facing internal FSW tool against z-axis forces while performing internal FSW by providing a roller support that extends radially from the outwardly-facing internal FSW towards the opposite internal wall of the pipe.
6. The method of claim 1 , wherein external FSW and internal FSW are performed simultaneously, with the first and second axes substantially in mutual alignment and with the external FSW tool and the internal FSW tool applying loads along those axes in mutual opposition about a wall of the pipe.
7. The method of claim 1 , wherein external FSW and internal FSW are performed simultaneously, with the first and second axes substantially offset so that loads applied by the external FSW tool and the internal FSW tool in mutual opposition about a wall of the pipe balance each other when both of those tools move with respect to the pipe.
8. The method of claim 1 , wherein the external FSW tool and the internal FSW tool are moved in coordination circumferentially relative to the pipe while performing FSW.
9. The method of claim 1 , wherein radial load and spin speed of the external FSW tool and the internal FSW tool are controlled individually while performing FSW.
10. The method of claim 1 , wherein external FSW and internal FSW are performed sequentially in either order.
11. The method of claim 10 , wherein external FSW is performed before internal FSW.
12. The method of claim 10 , further comprising:
applying an internal back-up member to an internal surface of the pipe in alignment with the first axis during external FSW; and
applying an external back-up member to an external surface of the pipe in alignment with the second axis during internal FSW.
13. The method of claim 12 , wherein the internal back-up member is positioned against the internal surface of the pipe by radially-outward movement of the member from an internal line-up clamp that is positioned between the lengths of pipe to bridge the interface.
14. The method of claim 12 , wherein the external back-up member is applied to the external surface of the pipe by the application of radially-inward clamping force to the pipe.
15. The method of claim 12 , wherein the external back-up member is applied to the external surface of the pipe by applying a back-up ring extending around the interface.
16. The method of claim 3 , comprising bracing the outwardly-facing internal FSW tool against z-axis forces while performing internal FSW by providing a roller support that extends radially from the outwardly-facing internal FSW towards the opposite internal wall of the pipe.
17. The method of claim 16 , wherein external FSW and internal FSW are performed simultaneously, with the first and second axes substantially in mutual alignment and with the external FSW tool and the internal FSW tool applying loads along those axes in mutual opposition about a wall of the pipe.
18. The method of claim 17 , wherein external FSW and internal FSW are performed simultaneously, with the first and second axes substantially offset so that loads applied by the external FSW tool and the internal FSW tool in mutual opposition about a wall of the pipe balance each other when both of those tools move with respect to the pipe.
19. The method of claim 18 , wherein the external FSW tool and the internal FSW tool are moved in coordination circumferentially relative to the pipe while performing FSW.
20. The method of claim 19 , wherein radial load and spin speed of the external FSW tool and the internal FSW tool are controlled individually while performing FSW.