Renovation of pipe by pressure-tight plastic liner, e.g. polyethylene VPE, PVDF - where folded strip or collapsed tube is inserted in pipe, expanded by heat and pressure and joint welded, e.g. scarfed with embedded heating wire

摘要

Process for renovation of pipes by a pressure-sealed thermoplastic lining in which a plastic strip (4), which may be folded or collapsed to pass into the pipe, is then expanded by heat and pressure to line the pipe and the edge welded to form a sealed lining. A flat strip may be drawn from a drum, heated and folded with edges partially overlapping (e) in Fig.) before introduction into the pipe. The strip may be previously folded as e) or otherwise, before winding on the drum. In either case, the strip, immediately before entry into the pipe, may be heated and drawn over a circular former into a tubular shape with an external diameter less than the internal diameter of the pipe. The edges (3, 5) of the strip may pref. be formed obliquely so that when formed into a tube, they meet in a contact surface which is not radial to the pipe axis, for increased joint strength. The heating, to shape the strip to the pipe wall, may be by hot air, steam or heated pressurised fluid in a (flexible) tube. The pressure to shape the strip to the pipe wall may be carried out by a type of 'salamander' or a thermo-pressure (heated pressurised flexible) tube. The welding of the contact surfaces of the strip edges (3, 5) may be by hot air-, hot wire-, laser- or extrusion-welding. A longitudinal heating wire (24) may be incorporated near the edges (3, 5) of the plastic strip (4) to effect the weld by electrical resistance heating. The plastic strip (4) may consist of PE, crosslinked PE (VPE) or PVDF. The plastic strip (4) may be formed as a composite so that one edge (3) is PE, while the opposite (5") is VPE or PVDF, so that the weld is between dissimilar polymers - said to be advantageous. Alternatively, the lining may be formed of longitudinal strips, at least one of which approximates to a segment of the pipe, and continuously joined initially by thin moulded film regions. Under heat and internal pressure these form a segmental tube with joints between the segments welded as before. USE/ADVANTAGE - Esp for buried pipes, where the prepd plastic strip may be drawn from a drum on the surface into the section of pipe. Compared with EP 0301 697, joining of the strip edges within the pipe permits the lining to accommodate exactly to variations in pipe internal.