MIL-HDBK-1164
pumping costs. Additionally, linings can correct the structural failures, bridge breaks,
and missing sections in corroded pipe, thus restoring service through a continuous
pipeline. Line water mains in place using one or more of the following general
methods: cement-mortar lining, slip-lining, and in situ formed-tube lining. As a rule,
this work is done on a contract basis by firms specializing in main cleaning and relining.
More information on cleaning and lining may be found in pars. 2.1.4 and 2.2.20.
7.3.2.7
Leak Location and Repair. Leaking pipes reduce the capacity of the
system, waste water, reduce water pressure, and potentially create public safety
hazards. Conduct leak detection surveys at the time of minimum water use. Shut off
all valves, except those that will direct the water flow through the section under study.
Caution: Good practice requires that the fire fighting authorities be
notified before closing any section of the system.
Specific directions for leak detection and repair may be found in the
publications listed in pars. 2.1.4, 2.2.25, and 2.2.41.
7.3.2.8
Thawing Frozen Systems. Pipes may freeze in temperate as well as frigid
zones. In frigid climates, freezing presents a major problem to a water distribution
system, and pipes are normally insulated and heated. In areas where the ground is
permanently frozen, water pipes are placed in heated conduits. In temperate climates,
where freezing is only a seasonal problem, pipes are typically buried below frost
penetration depth. It is also necessary to heat stored water in cold areas. Even with
proper protection against freezing, pipes may freeze. When this happens, operators
should be prepared to thaw the pipes.
a)
Electrical Thawing. Electrical thawing is quick and relatively
inexpensive. The electrical circuit for the thawing operation consists of a source of
current (a DC generator, such as a welding unit, or a transformer connected to an AC
outlet), a length of the frozen pipe, and two insulated wires connecting the current
source and the pipe. As current flows through the pipe, heat is generated and the ice
within the pipe begins to melt. As the water starts to flow, the rest of the ice is
progressively melted by contact with the flowing water. The wires from the current
source may be connected to nearby hydrants, valves, or exposed points at the ends of
the frozen section.
(1)
Current and Voltage. Data concerning the current and
voltage required to thaw various sizes of wrought-iron and cast-iron pipe are given in
Table 24.
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