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

0.03% of the overall length. There are a variety of reasons for this lower rate of rehabilitation in sewer
force mains.
The first reason is the lack of consistently reliable and cost-effective sewer force main inspection
methods. Taking a force main out of service for internal inspection is extremely disruptive and costly and
external inspection can cover only a small part of the main. Thus, there is no viable sequence of risk
assessment, inspection, condition assessment, and rehabilitation as there is in gravity sewer networks.
The second reason is that few rehabilitation technologies have been developed specifically for force
mains. The technologies used in gravity sewers are generally not suitable for pressure applications, while
those for water mains are focused more on water quality and corrosion protection than structural
rehabilitation of the pipelines. Structural rehabilitation technologies for pressure pipes are in their
infancy. Some crossover is needed between the sectors to address this issue. The result is that two
management approaches are followed for force main asset management:
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(1) Await failure and replace.
(2) Replace based on age and material rather than on actual condition.
Both strategies have their merits. Many force mains are small in diameter with almost half of force mains
12 inches (300 mm) in diameter or smaller. Inspecting these is difficult and costly and the cost of
obtaining the information may exceed its value. Also, the consequence of failure for many of these mains
may be low. Thus, awaiting failure and replacing with an emergency repair is a cost-effective strategy for
many small diameter, non-critical force mains.
Replacement based on age and material, possibly alongside failure history, is also a viable strategy. With
no direct condition assessment information available, condition cannot be a criterion.
However, neither strategy is adequate for critical force mains, where the consequence of failure is serious.
This is recognized by the utilities and drives their need for inspection technologies and assessment
methodologies that will provide information on likelihood of failure so that critical force mains can be
managed actively and cost-effectively repaired, rehabilitated, or replaced to avoid failure. Future
advances in force main inspection and an improved understanding of the host pipe condition may lead the
way for the increased use of rehabilitation technologies in critical force mains.
Overview of Renewal Technologies
Force mains can operate with a wide range in pressures ranging from just a few feet of head to several
hundred feet of head. Consequently, the list of potentially applicable renewal technologies is quite
lengthy. The designer must consider the operating conditions that the renewal will be subjected to before
selecting suitable candidates.
Some of the technologies presented in this report have not yet been used in a sewer force main to date,
even though they have properties that make them suitable for these applications. System vendors are
constantly making improvements and modifications to their products and services, so they should be
consulted before using any of these listed products in a force main application to ensure compatibility.
A technology-specific datasheet was created for most of the technologies reviewed in this SOT report and
are included in Appendix A. Table 3-1 summarizes the datasheets along with the diameter range and
upper pressure limit for the various renewal methods. Vendor contact information can be found on each
datasheet along with relevant case study information as available.
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