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

The data in Table 2-1 show clearly that DI and PVC dominate up to 12 inches (300 mm) in diameter.
Over 93% of all PVC is in this range. DI is even more dominant in the 14 to 20 inch (350 to 500 mm)
range, followed by CI, and then asbestos cement. It remains the main material in the 21 to 36 inch (525 to
900 mm) range, but PCCP is the next most used material in this range, followed by reinforced concrete
pipe (RCP), and steel. CI and plastics including polyethylene (PE) and PVC are less widespread in this
size range. PCCP is by far the main material used above 36 inches (900 mm) in diameter, with steel also
representing a significant proportion of pipe.
2.3
Age of System
In contrast to the nation’s water supply and gravity sewer systems, the use of force mains to convey
sewage is relatively recent. As depicted in Figure 2-3, 68% of the force mains in use today have been in
service for 25 years or less. Another 30% have been in service between 25 and 50 years and only 2%
beyond 50 years. Other data sources gave similar results in terms of the age distribution of force mains.
Typically no more than 2% is greater than 50 years old. This contrasts sharply with the water supply
sector in which the average age of water mains in the US is now 45 years with nearly half of pipes aged
more than 50 years old.
2.4
Force Main Location
Figure 2-3. Age of Force Mains (WERF, 2009)
This information might be important in evaluating the accessibility to the external surface of the pipe. As
shown in Figure 2-4, over 91% of the force main pipes are buried, so access to the exterior surface will
require some form of excavation. Less than 1% is installed above ground where access would be easier
and less costly to achieve. A slightly larger percentage, approximately 1.2%, is installed sub-aqueously
where access will be the most difficult.
7