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

2.1
2.0 CHARACTERISTICS OF FORCE MAIN SYSTEMS
It is important to understand the characteristics of force main systems and the typical failure modes and
mechanisms in order to evaluate the most appropriate renewal technologies. The approximate length of
the force main system in the US is 60,000 miles. The Water Environment Research Foundation (WERF)
recently published a report titled Guidelines for the Inspection of Force Mains (WERF, 2009). As part of
this effort, Jason Consultants conducted an electronic survey of all WERF utility subscriber members.
Over 32 utilities responded to the survey with detailed data on their force main systems. The data from
this WERF survey are presented in the next few sections and characterizes the types of pipe materials
used, diameter ranges, ages, location accessibility, and failure modes and mechanisms for force mains
determined from field data.
Material Usage
Figure 2-1 shows the breakdown by pipe material type. DI pipe is the predominant material, representing
47.3% of the total. Ferrous pipe materials (i.e., CI, DI, and steel) represent on average 63.4% of all pipes
used for force mains. Polyvinyl chloride (PVC) pipe at 14.3% is the next largest category of pipe
material. Also, it can be seen that pre-stressed concrete cylinder pipe (PCCP) is used for 11.6% of sewer
force mains, this being predominantly in diameters 24 inches (600 mm) and above.
2.2
Figure 2-1. Pipe Material Usage for Sewer Force Mains (WERF, 2009)
Diameter Distribution
For a breakdown by diameters, as shown in Figure 2-2, approximately 46.6% of all sewer force mains fall
into the diameter range 4 to 12 inches (100 to 300 mm). Another 22.7% is in the diameter range 14 to 20
inches (350 to 500 mm) and 22.2% in the diameter range 21 to 36 inches (525 to 900 mm). Over 91% of
sewer force mains are between 4 and 36 inches (100 to 900 mm) diameter, which are within the non-man
entry size range.
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