A double skinned feed or scavenge pipe assembly comprises; an inner pipe (22) and an outer pipe (23) enclosing the inner pipe and defining an annular space (24) between the inner pipe and the outer pipe and a sleeve (28) configured to slip over the outer pipe (23). Complementary threads (29) are provided on an outer wall of the outer pipe (23) and an inner wall of the sleeve (28). A lock, for example in the form of a locking nut (31) is positioned over the outer pipe (23) when the complementary threads (29) of the outer pipe and sleeve are engaged. The configuration of the assembly is such that, in use, the sleeve (28) is slidable between a first position where the inner pipe (22) is accessible and a second position wherein the inner pipe (22) is completely enclosed.