A system (2) for relining an undersea pipeline (5), said pipeline (5) having and inlet (13) and outlet (11) beneath sea level (8), comprising a coiling drum (3) positioned above sea level and having a length of liner (1) reeled thereon; said coiling drum (3) arranged to deliver said liner (1) to the inlet (13); an actuator engaged with a leading end of said liner and arranged to apply a tensile force (6) to said liner (1) so as to draw said liner through the pipeline; wherein the liner is of a composite construction having a fiber core.