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

3.4 Rehabilitation
In this report, rehabilitation will focus on the renewal aspects of sewer force mains where the existing
pipe becomes part of the renewal work. If the rehabilitation is to provide only corrosion protection, or the
existing pipe is only partially deteriorated, then the remaining structural strength of the existing pipe is
incorporated into the fabric of the completed system. For fully deteriorated situations, the existing pipe
acts merely as a right-of-way for the installation of the structural liner.
As shown in Figure 3-6, rehabilitation methods will include the use of spray-on linings, close-fit linings,
CIPP, and woven hose lining systems. Technologies for each of these rehabilitation categories are
discussed in this report in addition to cleaning requirements prior to rehabilitation. Because only limited
rehabilitation work has been undertaken to date on sewer force mains, many of the systems available were
originally developed for water main rehabilitation, but can be adapted to sewer force mains. Sewer force
mains have some characteristics in common with water mains. Both tend to be relatively shallow buried
and both operate under internal pressure. However, they also have some significant differences. An NSF
61 certification is not required for a force main as it does not carry potable water for human consumption.
Force mains also do not have service connections, which must be reinstated to restore service to
stakeholders. Force mains transport raw sewage, which can release hydrogen sulfide (H2S) gas at high
points or near discharges, leading to microbiological corrosion of the pipe material. Also, it is usually
very difficult to take a force main out of service for an extended period of time (unless redundancy
exists), which will necessitate by-pass pumping during any cleaning or rehabilitation effort.
Figure 3-6. Rehabilitation Approaches for Force Mains
3.4.1 Cleaning Requirements. All of the rehabilitation methods require some cleaning of the
interior surface of the original pipe. The extent of cleaning will depend on the chosen method of renewal.
Spray-on linings will require the most extensive cleaning as the lining material must adhere to the surface,
followed by close-fit and CIPP liner products. Sliplining is considered a replacement method, but it
requires the least intensive cleaning as contact with the host pipe is not achieved.
Cleaning methods for force mains would include power boring, which is recommended for spray-on
polymer liners, foam pigs, mechanical scrapers, and water jet cleaning. Chemical cleaning with
hydrochloric (HCl) acid is intended mainly for the removal of tuberculation (ferric oxide) and is therefore
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