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

There is a clear need for assessment methodologies that can work with limited data. These could
potentially be based on Bayesian belief networks. There is also a need for inspection technologies that
can provide data more cost-effectively to support these assessment methodologies. Development of clear
maintenance guidelines, and linking of O&M data, for example cathodic protection system and power
consumption data, to condition assessment is also necessary.
7.2 Capability Gaps
This section will address capability gaps in terms of rehabilitation technologies. The available
rehabilitation technologies generally meet needs well. Despite being developed either for water mains or
gravity sewers, they can readily be adapted for use in force mains. CIPP has a track record in force
mains. The emergence of new CIPP systems based on woven fiberglass and UV-curing, which provides a
much stronger liner with some hoop strength, also has applications in force mains. A gap exists in terms
of a design procedure for CIPP in pressure applications to ensure that long-term performance
requirements can be met.
The combination of tensile strain and potential chemical attack from wastewater can create strain
corrosion problems in polymeric resin-based materials. This was a major problem for the early GRP
pipes, under the name Techite, and there were several failures. The potential for strain corrosion in CIPP
materials in pressure wastewater applications needs to be understood and taken into account in the design
procedures developed.
Sliplining with PVC or HDPE also meets the needs in force mains, as does close-fit lining using either
material. Non-structural methods, such as sprayed liners for internal corrosion protection are also equally
well-adapted to force mains as they are to other pressure pipes provided that the materials used have
adequate chemical resistance to wastewater and mechanical resistance to abrasion, which is more likely in
force mains than in water mains.
The primary capability gaps are access needed to the main and the need to shut down, dewater, and clean
the main for rehabilitation. This is an inevitable feature of any internal rehabilitation technology, as it is
for inspection technologies. This also places a limitation on the use of rehabilitation in force mains. If
the cost and disruption of by-pass pumping to open the main for access approaches that of replacement,
and replacement leads to a longer remaining service life, a Net Present Value calculation may indicate
that replacement is more cost-effective.
There is also a need for emergency repair procedures for lining systems and for utilities to be trained in
their application. Lack of such procedures makes utilities reluctant to rehabilitate force mains, preferring
replacement with materials for which they have emergency repair procedures in place.
7.3 Benefits, Costs, and Challenges in Closing Gaps
Based on the information gathered in this report, Table 7-1 summarizes the technology gaps and the
potential costs and benefits associated with their closure.
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