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

(100 mm) taps (SmartBall ® ) in a force main and do not require sophisticated launchers and retrievers.
The minimum pipe diameters for these leak locators are 12 inches (300 mm).
Researchers are also working on perfecting smart pigs that can be used in a live force main. The oil and
gas industry have relied upon intelligent pigs for many years to assess the condition of their transmission
mains. These smart pigs utilize ultrasonic or electromagnetic technology to measure the remaining wall
thickness and find pitting or areas of graphitization in a ferrous pipe. Adaptations for use in a force main
include the use of gas or liquid coupling for ultrasonic transducers. Pigs based on magnetic flux leakage
(MFL) are heavy, but newer pigs based on remote field (See Snake) and eddy current (broadband
electromagnetic [BEM]) technology are finding use in the water and wastewater industry. The See Snake
can be used in a live force main, while the BEM has a limitation on the pressure head.
Acoustic emission monitoring of PCCP to locate active wire breaks is a technology that is now well
employed. Acoustic monitoring does not require launchers or retrievers. Early technology deployed a
string of hydrophones into the flow stream, but that has largely been replaced with the use of externally
mounted accelerometers. The accelerometers are mounted directly on an air release valve or the mortar
coating of the PCCP.
5.2 Renewal Design
The design of a rehabilitation product to renew the life of a distressed sewer force main range from just an
inner corrosion barrier or entail outright structural replacement. Obviously, the factors that will control
the design are the condition of the existing main, including its expected remaining life if further
deterioration is arrested, and the operating conditions under which that main is used. Mains that are
currently operating at full capacity, or are expected to be so in the near term, are not good candidates for
placing a thick liner or sliplining with a smaller diameter pipe, as these will further reduce capacity.
Certainly, some of the newer liners and sliplining pipes have very favorable flow characteristics (i.e., low
friction factors), but that is not always sufficient to make up for the reduced cross-sectional area available
to the flow. If a loss of capacity cannot be tolerated, then the most viable renewal strategy is going to be
replacement.
5.2.1 Degrees of Deterioration. Assuming that some minor loss of flow capacity is acceptable,
then the first thing a designer has to consider is the condition of the force main. The ASTM standards of
practice for reconstruction products have categorized the condition of existing pipes into either partially
deteriorated or fully deteriorated conditions. These conditions are defined as follows (adapted from
ASTM F1216):
• Partially deteriorated – Existing pipe can support the soil and surcharge loads throughout the
design life of the rehabilitated pipe. The pipe may have longitudinal cracks and up to 10%
distortion of the diameter.
• Fully deteriorated – Existing pipe is not structurally sound and cannot support soil and live
loads or is expected to reach this condition over the design life of the rehabilitated pipe. This
condition is evident when sections of the pipe are missing, the pipe has lost its original shape,
or the pipe has corroded.
What is apparent from these definitions is they are more relevant to gravity sewers than to pressurized
mains. There is no consideration given to the existing pipe’s ability to safely carry the internal working
pressure or surge pressure. If a ferrous pipe has lost 40% of its wall thickness and is still handling the
internal working pressure with reasonable factors of safety on hoop tensile stress, is this a partially
deteriorated or fully deteriorated pipe? Or, what about a ferrous pipe that has lost 80% of its wall
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