Be present in the rehabilitation of the underground without disrupting the surface activity.

Close-Fit Slip Lining

A new thermoplastic pipe can be installed in a host pipe with the outside diameter (OD) of the new pipe in a close fit with the inside diameter (ID) of the host pipe. Close-fit  slip lining is an ideal application for the rehabilitation of pressure pipes that are relatively straight or have only modest bends, and that have largely maintained their circular profile.

Close-fit slip-lining is possible because of the memory properties of thermoplastic materials.  Thermoplastic materials will change shape when force is applied to the material either through the application of compression or tension forces. However, they always retrieve their original shape when the external force is removed or internal pressure is applied. This property allows  thermoplastic pipes to be temporarily deformed and pulled into a host pipe. When the new pipe has been pulled to the desired position, tension on the pipe is removed  or internal pressure is applied. This makes the new pipe retrieve its original design shape.   The versatility of thermoplastic pipes has spawned the development of a wide range of innovative close-fit pipe lining systems.  These systems can be classified under one of two generic system types, i.e., concentric reduction/expansion liners and folded liners.

Concentric Reduction / Expansion Liner techniques can be subdivided into two categories: tension deformed liners, (i.e., the roller dies and static die systems) and compression deformed liners.  Tension deformation techniques use either a roller reduction die or static die to reduce the diameter of the thermoplastic pipe. Tension reduction techniques are normally applied to reasonably thick-walled (i.e., structural) thermoplastic pipes owing to the fairly high processing forces they impose on the pipe.

Compression deformed liners are achieved by gripping and pushing the liner through a series of rollers reducing their diameter. The resulting reduction causes an increase in the pipe’s wall thickness, which is substantially retained until the pipe is reverted back to its original form through the application of internal water pressure. The reduced diameter achieved by the compression techniques is relatively stable, i.e., it may take several days or weeks to revert to its natural diameter, unless an internal pressure is applied. The compression techniques, like the tension deformation technique, are normally applied to relatively high and thick-walled thermoplastic pipes.

Folded Liner Insertion Techniques:  Close fit slip-linings can also be achieved via deformation of the thermoplastic pipe to form a C shape.  The liner outside diameter is designed to be slightly less than the minimum internal diameter of the host pipe. This ensures that the liner deploys fully on reversion to avoid the formation of residual longitudinal folds. The folding process may be done either hot during manufacturing or cold during manufacturing or on the job site.

The shape of hot-folded liners is maintained without any additional constraint, while the shape of cold-folded liners has to be restrained using temporary strapping or sheathing. Hot-folded liners are wound onto a reel for transportation to site. Factory-folded liners are typically used for smaller diameter pipes up to 500mm.

The liner is slip-lined into the host pipe and reverted to a round section and close fit within the host pipe using a combination of heat (typically steam at 125°C) and air pressure.  

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