Techniques for protecting pipe coatings
A method of protecting a layered coating on a length of pipe for subsea use includes applying an edge finisher to the coating to encase an edge of the coating by fusing the edge finisher with the coating or by moulding the edge finisher at an edge of the coating. Where the coating and the edge finisher are of thermoplastics such as PP, fusing can be achieved by injection moulding the edge finisher or by welding a discrete edge finisher component to the edge of the coating. Mirror welding may be employed for this purpose, with a hot plate being interposed between the edge of the coating and the edge finisher.
1. A method of protecting a 5LPP or 7LPP coating comprising alternating layers of solid and foamed polypropylene on a discrete pipe joint for subsea use, the method comprising applying a protective edge finisher of thermoplastics to a cut edge of the coating to encase the cut edge of the coating, heat being applied to melt the thermoplastics of the edge finisher and the polypropylene of the coating at their interface to fuse the edge finisher with the coating, before the discrete pipe joint is transported to a welding location at which fabrication of a pipeline takes place by welding the discrete pipe joint to another discrete pipe joint.
2. The method of claim 1 , wherein the edge finisher is formed by injection moulding at the edge of the coating.
3. The method of claim 2 , wherein the edge of the coating is heated before injection moulding forms the edge finisher.
4. The method of claim 1 , comprising applying a mould tool to the discrete pipe joint while leaving an inner wall of the mould tool spaced from the edge of the coating to define a mould chamber between that wall and the edge of the coating.
5. The method of claim 1 , wherein the edge finisher is a discrete component welded to the edge of the coating.
6. The method of claim 5 , wherein the edge finisher is mirror-welded to the edge of the coating.
7. The method of claim 6 , wherein a hot plate interposed between the edge of the coating and the edge finisher is withdrawn after melting facing surfaces of the edge of the coating and the edge finisher before the edge finisher is pressed against the edge of the coating while those facing surfaces are still molten.
8. The method of claim 7 , wherein the hot plate is withdrawn radially with respect to a central longitudinal axis of the discrete pipe joint to provide clearance for the edge finisher to be pressed against the edge of the coating.
9. The method of claim 1 , followed by affixing an end cap to the discrete pipe joint or to the edge finisher.
10. The method of claim 9 , wherein the end cap is affixed to a portion of the discrete pipe joint outboard of the edge finisher.
11. The method of claim 9 , wherein the end cap is affixed to a protruding part of the edge finisher.
12. The method of claim 1 , followed by machining the edge finisher before welding the discrete pipe joint to a pipe string.
13. The method of claim 1 , followed by field joint coating after welding the discrete pipe joint to a pipe string such that the field joint coating is joined to the edge finisher.