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

utilities or foundations. For partially deteriorated mains, close-fit liners can be extremely cost-effective
for rehabilitating a main especially in congested, built up areas. The City of New York had a
deteriorating 150 year old 48 inch (1,200 mm) CI water main running down Madison Avenue. Insituform
Blue was able to install 10,000 feet (3,049 meters) of its new interactive HDPE liner (PolyFlex DR 50) in
several stages with minimal disruption to traffic and business.
Some pipelines even get “misplaced” and end up with structures built directly over them. Jason
Consultants recently had a project where a 48 inch (1,200 mm) PCCP water main was found to be in
significant distress. Eight manufactured homes were located directly on top of this main. In this case,
rehabilitation was the only viable cost-effective solution. The pipeline was sliplined with steel pipe of a
smaller diameter and the annular space was grouted.
4.4 Maintenance
One of the issues continually raised by O&M personnel is the question of repairing a break in a sewer
force main that has been rehabilitated or sliplined. Utilities usually keep on-hand repair clamps,
replacement pipe sections and special adapter fittings so an emergency repair can be made on a main that
bursts at an inconvenient time. Crews are trained to work with those pipe materials that are
predominantly used by the utility and are knowledgeable about how to repair a burst or leaking joint in
such materials. The methodology for repairing a break in a ferrous main that has been lined with a closefit
PE liner or a CIPP liner is not generally known. As such, O&M personnel are reluctant to accept
rehabilitation options over offline replacement with known materials. The industry has to do a better job
of developing training tools and repair kits to alleviate this concern. Otherwise, cost-effective
rehabilitation schemes are being overlooked in favor of replacement.
4.5 Condition Assessment and Asset Criticality
Condition assessment plays a major role in asset management decisions and provides indirect and direct
data on the host pipe condition to assist in decision-making between repair, rehabilitation, and
replacement technologies. Improvements in condition assessment practices may lead to a better
understanding of the host pipe condition and therefore increased confidence in the use of semi- or fullystructural
rehabilitation technologies.
Due to the difficulties associated with inspecting force mains, especially those that cannot easily be taken
out of service for more than a few minutes, little if any inspection is carried out by most utilities. WERF,
in recognizing this growing need for condition assessment, funded a research project to develop
guidelines for inspecting sewer force mains. Originally, the target of the research was on ferrous mains,
which represents over 58% of the force main population, but later it was expanded to cover all possible
force main materials. The recently published report is titled Guidelines for the Inspection of Force Mains
(WERF, 2009) and can be reviewed for detailed information on the SOT for force main inspection and
condition assessment.
Risk-based investigation (RBI) involves consideration of both the likelihood of failure and the
consequence of a failure for a given pipe system. Criticality is often expressed as the product of these two
factors. Assets with a high consequence of failure may warrant further investigation by gathering both
indirect and direct data on the host pipe condition. Indirect data can include factors such as the age of a
pipeline, whether the pipeline has any external corrosion protection or is installed in an environment
considered corrosive, history of previous failures in the main, presence of inoperative air release valves,
operating conditions (pressure, surge, burial depth) versus the pipe’s original design rating, and more.
External or internal inspection can also yield direct data on the pipe condition. Inspections might include
either small portions or the entire pipeline being surveyed for signs of deterioration. In the case of a
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