A pipe-in-pipe (PIP) pipeline assembly for the transport of a fluid in a marine environment comprising: (a) a PIP pipeline length comprising at least metal inner and outer pipes and an annular space thereinbetween, the inner metal pipe having an internal diameter ; (b) a PIP bulkhead , having - a first end connected to an end of the PIP pipeline length and comprising at least a metal inner pipe with a first internal diameter , an outer pipe , and an annular space thereinbetween, and - a second end comprising an outer pipe with a second internal diameter , and being able to be joined to a second end of a second PIP bulkhead , wherein the second internal diameter of the second end is greater than the first internal diameter of the first end of the PIP bulkhead; characterised in that the assembly further comprises (c) a sleeve at least partly located within the outer pipe of the second end of the PIP bulkhead, and having a sleeve internal diameter being the same or similar to the internal diameter of the metal inner pipe of the PIP pipeline length, and having two circumferential shoulders and a recess between the shoulders, at least one shoulder being within the second end of the PIP bulkhead, and at least one shoulder being beyond the end of the second end of the PIP bulkhead. (a) a PIP pipeline length comprising at least metal inner and outer pipes and an annular space thereinbetween, the inner metal pipe having an internal diameter ; (b) a PIP bulkhead , having - a first end connected to an end of the PIP pipeline length and comprising at least a metal inner pipe with a first internal diameter , an outer pipe , and an annular space thereinbetween, and - a second end comprising an outer pipe with a second internal diameter , and being able to be joined to a second end of a second PIP bulkhead , wherein the second internal diameter of the second end is greater than the first internal diameter of the first end of the PIP bulkhead; characterised in that the assembly further comprises - a first end connected to an end of the PIP pipeline length and comprising at least a metal inner pipe with a first internal diameter , an outer pipe , and an annular space thereinbetween, and - a second end comprising an outer pipe with a second internal diameter , and being able to be joined to a second end of a second PIP bulkhead , wherein the second internal diameter of the second end is greater than the first internal diameter of the first end of the PIP bulkhead; characterised in that the assembly further comprises wherein the second internal diameter of the second end is greater than the first internal diameter of the first end of the PIP bulkhead; characterised in that the assembly further comprises (c) a sleeve at least partly located within the outer pipe of the second end of the PIP bulkhead, and having a sleeve internal diameter being the same or similar to the internal diameter of the metal inner pipe of the PIP pipeline length, and having two circumferential shoulders and a recess between the shoulders, at least one shoulder being within the second end of the PIP bulkhead, and at least one shoulder being beyond the end of the second end of the PIP bulkhead. <EOS>