12 May 2003
Including change 1, 19 January 2007
(6 watts/foot) is the watt density available for a typical electric heat tape. Any watt
density from 4 to 10 watts/foot would be suitable, but insulation thicknesses must be
adjusted to compensate. Insulation thicknesses given in Table C-2 are based upon
polyurethane. Adjust thickness for other insulation materials as based upon their rated
thermal conductivity values. Protect backflow devices, valves, and risers with electric
heat tape and preformed polyurethane insulation kits. Heat tape systems must be
maintainable to be successfully used for the system's expected life span. To improve
maintainability, use multiple sections of heat tape instead of extended single circuits.
The designer may need to consider special heating systems in which heating elements
are placed in channels alongside the pipe. These systems periodically terminate in
accessible junction boxes. Maintenance personnel can then easily replace an
inoperable section. It is also much easier to troubleshoot when the heating system is
divided into reasonable segments with accessible test points.
Sewer and Oily Waste Lines. A combination of electric heat tape and
pipe insulation should be used in accordance with Table C-2 for: (1) exposed gravity
sewer piping which drains fixtures directly; (2) exposed oily waste piping; and (3) for
those portions of exposed pressure lines (sewage and oily waste) which will not
completely drain upon cessation of pumping. Heat tape may not be required (insulation
only) for exposed pressure and gravity sewer and oily waste piping (or portions thereof)
which receive material intermittently and which drain well when pumping stops. Neither
heat tape nor insulation may be required for pipe risers and valves above pier decks
and in drydock galleries.
Protection in Regions III and IV
Fresh Water Lines. For water lines, the preferred method of freeze
protection in these regions is to use a combination of insulation and a flushing of water
through the pipes. Insulation thickness for various pipe sizes, and pipe sizes for which
flushing is necessary, are defined in Appendix C Table C-3. Insulation thicknesses are
such that for expected durations of subfreezing temperatures less than 50 percent of
pipe contents will freeze. Where flushing is indicated, use thermostatically actuated
solenoid valves. Size each valve for a rate at which the entire contents of exposed
piping can bleed in 8 to 12 hours. Thermostats should be in protected locations and
sensors are to be taped to the surface of pipes and under the insulation. Thermostats
should be factory set to open the flushing valves at -1.1 degrees C (30 degrees F) and
to close the valves at approximately 2 degrees C (35 degrees F). Flushing valves
(freeze protection valve) and associated thermostats should be located at each ship's
connection and at any other line extremity to protect the most remote valve component
in the system. Insulation thicknesses given in Table C-3 are based upon polyurethane.
Adjust thickness for other insulation materials as based upon their rated thermal
conductivity values. Insulation must also be applied to backflow devices and valves.
Special care must be taken to prevent the freezing of flushing valves and associated
pipe connections. If water is scarce, or if the winter temperature of buried water mains
is below 7.2 degrees C (45 degrees F), heat tape should be used in lieu of flushing. In
this event, the design should be based upon the data defined in Table C-4.