Page 237 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION 5.21

7. Hazardous environment. Where there is a danger that the contents of the pipe or chemi-
cals in the surrounding area could possibly penetrate the jacket and cause a potentially
dangerous situation, cellular glass insulation should be used because it is nonadsor-
bent. A jacket capable of resisting the chemical hazard, usually plastic, must be used
over the glass insulation.
8. Special fire resistance. Again, cellular glass is the best material because it is com-
pletely noncombustible. A jacket of stainless steel provides the best protection.
9. Very hot piping [450°F (230°C) or higher]. Calsil or mineral wool is the material
of choice because of its superior qualities at higher temperatures. A plain jacket or
a breather coating is a good covering. Insulation thickness should be determined to
ensure a low surface temperature, if the piping is accessible to people.
10. Cryogenic piping. Four-in (100-mm)-thick polypropylene should be used.
11. Steam and condensate piping. Calsil or mineral wool should be used.
There are four specific problem areas that have been found to cause the most failures.
First is where workers can walk on insulated pipe after it has been installed, for example, in
boiler rooms and MERs. This will ruin any insulation in short order. Observation of seams
no longer bound together is good evidence that this has occurred. Second is a failure to
properly and completely seal a vapor barrier, particularly around valves and fittings. Water
vapor will enter at these points and saturate the insulation very quickly. On occasion, the
water will run along the pipe and drip far from the actual fault. Third is the failure to prop-
erly support the insulated pipe on a hanger. In order to keep the insulation from becoming
compressed (causing tearing and a loss of insulating value), the weight of the pipe must
be distributed by using a metal shield (if the pipe is small), a length of rigid insulation
between the hanger and the insulated pipe, or, if the pipe and contents are large and heavy,
a block of wood placed on the bare pipe (under the vapor barrier) to support the weight of
the pipe at the hanger. Fourth is the installation of adhesives and self-sticking jacket seals
under extremely dusty conditions, causing dust to be deposited on the adhesive before it is
installed permanently.

FREEZE PROTECTION

FREEZING OF WATER

Much time, effort, and money must be spent to restore service when pipes and mains freeze. In
addition, many times these efforts must be made under very difficult working conditions and
with great urgency. Because of this, it is preferable to design systems that will not freeze.
Studies at the U.S. Army Cold Region Research and Engineering Laboratory (CRREL)
have shown that the dynamics of the freezing process of water in pipes are much more
complicated than originally thought, and that this process is different for static and flowing
water. It was found that when water starts to freeze, flow in a piping system can become
blocked much earlier than previously believed. It was also established that the actual
mechanics of the freezing process are less predictable in terms of both time and heat loss
than was previously believed.
Previously, it was believed that when ice formed inside a pipe or vessel, it started on the
pipe wall and grew uniformly inward until the entire pipe was blocked. It was also thought
that the only apparent difference between the freezing that occurred in static and flowing
water was a difference in the rate due to the heat created by the flowing water.

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