In this category of close-fit lining, a principally thermal approach to creating the lining is used by what is termed a “Melt-in-Place-Pipe” (MIPP) lining process. This process is applicable for both water mains and sewers. The process involves winching a liner tube, made from an intimately woven fabric of glass fibre and polypropylene filaments, through the pipe to be renewed. A heated pig is then passed through the woven liner to deliver hot air which melts the polypropylene material and encapsulates the glass reinforcement. The molten mixture of glass fibre and polypropylene is then consolidated against the pipe wall using a pressurised silicone rubber inversion tube. Upon contact with the pipe wall the material cools down to form a tightly fitting thin walled, fully structural glass fibre reinforced polypropylene pipe.
The inversion drum is a container that can be pressurised (it is also known as an “elephant”). The inversion tube and its retrieval cable are wound onto the reel of the inversion drum. The free end of the inversion tube is pulled out of the inversion drum nozzle, turned back onto the nozzle and clamped. When the drum is pressurised the inversion tube is forced to invert out of the nozzle and through the guide pipe into the existing pipe where it forces the liner against the existing pipe wall and also pushes the heating pig along the existing pipe.