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