Apparatus for joining a longitudinal seam in a tube, the apparatus comprising: a spool for progressively unwinding a coiled member into an extended form, wherein the member transitions from a flat form when coiled to a slit tube form when extended having longitudinal edges, in which form the member is resiliently biased, and wherein the member is a bistable reelable composite, being stable in its coiled, flat form and in its extended form and comprising fibre reinforced thermoplastic layers; a drive mechanism for advancing the member from the coil; a joining device positioned downstream of the spool arranged to provide electromagnetic energy to the member in its extended form to cause heating so as to progressively weld together the overlapping longitudinal edges of the slit tube as the member passes the joining device and thereby form a continuous longitudinal seam in the tube, characterised in that: the member comprises a susceptor local to a respective one of the longitudinal edges and the joining device is arranged to provide electromagnetic energy to the susceptor, the member being relatively transparent to electromagnetic energy away from the susceptor so as to provide heating localised to the longitudinal edges of the member, in that the apparatus is movable such that apparatus can move as the joined pipe is progressively formed leaving the joined pipe in situ as new portions are uncoiled and joined, and in that the apparatus comprises a detector downstream of the joining device for testing the join integrity and a control system in communication with the detector, the control system being arranged to receive a signal from the detector indicating an unsound join, and in response to either 1) communicate with the drive mechanism to back up the tube such that the portion of tube with the unsound join is passed again past the joining device and the join reformed or 2) operate a second joining device downstream of the detector to reform the weld. a spool for progressively unwinding a coiled member into an extended form, wherein the member transitions from a flat form when coiled to a slit tube form when extended having longitudinal edges, in which form the member is resiliently biased, and wherein the member is a bistable reelable composite, being stable in its coiled, flat form and in its extended form and comprising fibre reinforced thermoplastic layers; a drive mechanism for advancing the member from the coil; a joining device positioned downstream of the spool arranged to provide electromagnetic energy to the member in its extended form to cause heating so as to progressively weld together the overlapping longitudinal edges of the slit tube as the member passes the joining device and thereby form a continuous longitudinal seam in the tube, characterised in that: the member comprises a susceptor local to a respective one of the longitudinal edges and the joining device is arranged to provide electromagnetic energy to the susceptor, the member being relatively transparent to electromagnetic energy away from the susceptor so as to provide heating localised to the longitudinal edges of the member, in that the apparatus is movable such that apparatus can move as the joined pipe is progressively formed leaving the joined pipe in situ as new portions are uncoiled and joined, and in that the apparatus comprises a detector downstream of the joining device for testing the join integrity and a control system in communication with the detector, the control system being arranged to receive a signal from the detector indicating an unsound join, and in response to either 1) communicate with the drive mechanism to back up the tube such that the portion of tube with the unsound join is passed again past the joining device and the join reformed or 2) operate a second joining device downstream of the detector to reform the weld.