alternating-current circuit to the pipe being thawed. To
reduce hazards, have a competent Construction
Electrician set and connect transformers, make the
connections, and assist in the thawing process. Where
frequent thawing is necessary at different points,
the transformers may be mounted on a trailer for
Some precautions in electrical thawing are given
Avoid a higher current than listed in table 5-3.
When in doubt, use low current for a longer period.
Select contact points on the pipe as close as
possible to the frozen section.
Assure that contact points are free of rust,
grease, or scale.
Remove meters, electrical ground connections,
and couplings to buildings with plumbing in the
pipeline to be thawed.
If there are gaskets or other insulation at pipe
joints, thaw the pipe in sections between such joints, or
use copper jumpers to close the circuit across insulated
Steam thawing of frozen systems is slower than
electrical thawing and should be used only when
insulating materials in pipes (plastic, transite, and
wood), pipe joints, or couplings make the use of
electricity impractical. In steam thawing, a hose
connected to a boiler is inserted through a
disconnected fitting and gradually advanced as the
steam melts the ice.
Variation of Water Pressure
A change of water pressure can cause much
discomfort to persons using the plumbing system. The
mixture of hot and cold water from a shower can
suddenly vary in temperature or rate of flow when
water is turned on at another outlet. Failure to remedy
this condition could injure somebody, especially if the
temperature is scalding.
When a switch in pressure and water flow occurs
often, look at the water pipes. Check the pipes to see if
they are the proper size in diameter for their length and
height as originally installed. Also look for liming and
corrosion inside the pipes. Enough liming and
corrosion can reduce the diameter of the pipe, causing
low pressure and slow water flow.
Sometimes the trouble occurs after more fixtures
have been installed in the system. When this happens,
the piping is probably overloaded because of the extra
fixtures. Pressure and water flow may also change
when there is too much friction in the pipe, too many
fittings, and the piping changes in direction.
If the pressure at showers changes only when other
outlets are open, you can usually correct the trouble by
installing automatic mixing valves. The only answer to
an increase in the water flow from pipes that are too
small is to replace them with larger pipes.
Q9. What is the most common repair performed on
piping systems due to frozen pipes?
Q10. A 400-foot run of 4-inch cast-iron pipe requires
approximately how many amperes of electricity
for effective thawing if frozen??
LEARNING OBJECTIVE: Recognize types of
pipe and tank leaks and methods for repair.
When a leak develops at a threaded joint of pipe,
one of the most likely suspects is a fractured or
ruptured pipe. Fractures often occur at the end of a
length of pipe because of strain imposed by vibration
of water hammer. It occurs at the end of the pipe
because the wall thickness is decreased and weakened
by threading. The risk of fracture becomes even
greater when the threads are not cut true. In cold
climates, freezing sometimes causes pipes to rupture,
in which case replacement becomes necessary. A loose
or cracked fitting can also cause leakage at the
threaded joint of a pipe. These and other common
failures resulting in pipe leakage make it important for
you to determine the exact location and cause of failure
before commencing any repairs to the piping.
Find and repair leaks in the water piping system as
quickly as possible to prevent serious damage to
footings, walls, floors, plaster, and other parts of the
structure, and to conserve water. Find leaks
systematically by inspecting exposed piping and
valves and by examining walls, floors, and ceilings
around concealed piping. You should also check
gauges, meters, and other water flow recording