State of Technology Report for Force Main Rehabilitation, Final ...

Rolldown
Rolldown was developed in the late 1980s by Subterra (a division of Daniels Contractors Ltd., UK) as a
complement to Swagelining and was used in the British Gas renovation program. Rolldown uses
standard grade PE (PE3408) and is available in diameters from 4 to 20 inches (100 to 500 mm).
Depending on diameter and starting DR of the stock liner, pressure ratings up to 232 psi (16 bar) are
achievable. Rolldown has been installed up to 5,000 feet (1,524 meters) in one insertion. The PE pipe
holds its reduced diameter indefinitely prior to reversion, which allows for interruptions during the
insertion process which is not possible with a tension-based system. The string of PE pipes can be pulled
through a bend of up to 11.25 degrees. After insertion, the line is reverted to its original diameter by
water pressure. Standard couplings are attached to the ends of the PE pipe and used to reconnect to
fittings or the existing main.
3.4.3.2 Fold-and-Form Close-Fit Lining – PE. Another method of achieving a close-fit PE liner is
to fold the PE pipe into a “C” or heart shape to facilitate insertion of the liner into the host pipe, and then
to revert the liner back to its original round shape by the use of heat and/or pressure to form a close-fit.
The folding process can be carried out in the factory or on site, depending on the diameter of the PE liner.
A further distinction can be made, as illustrated in Figure 3-13, for factory-folded liners, as to whether the
reversion uses heat to help re-round the PE pipe. Both factory-folded and on-site folded technologies, as
shown in Figure 3-13, are discussed below.
Figure 3-13. Summary of Fold-and-Form Close-Fit Lining Technologies
Factory-Folded PE Close-Fit Lining
Uliner and Sureliner (shown in Figure 3-13) are no longer commercially available.
Subcoil
Subcoil is another close-fit PE liner jointly developed by Subterra and United Utilities. Subcoil is a
close-fit PE pipe that is factory folded and held in a “C” shape. The pipe is shipped to the jobsite on large
spools. After insertion, the liner is pressurized with water at ambient temperature breaking the temporary
bands holding the pipe in a “C” shape and reverting the pipe back to its original dimensions. Proprietary
couplings are then attached to the end of the exposed pipe sections and make-up pieces inserted to
reconnect to the existing main. Insertions of up to 3,500 feet (1,067 meters) have been achieved. Subcoil
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