STEAM DISTRIBUTION SYSTEMS
Learning Objective: Recognize the purpose, operating principles, and
maintenance procedures of steam distribution systems.
"What good is steam without some means of
transporting it from the steam plant to the user"? In
answer to this question, you will find information in this
chapter about steam distribution systems. A steam
boiler is virtually useless for heating without a good
distribution system for taking the steam to the areas to
be heated. In this chapter, both exterior and interior
steam distribution systems are discussed. Also
discussed in this chapter are maintenance requirements
along with the various components and their purpose in
the distribution system. The term distribution system, as
used in this chapter, refers to the network of piping
required to distribute steam from a boiler room or a
boiler plant through the steam pipes to the equipment
using it. Steam distribution systems are grouped under
two classifications: exterior and interior. The first
discussion pertains to the types of exterior distribution
EXTERIOR STEAM DISTRIBUTION
Learning Objective: Recognize types and
configurations of exterior distribution systems and their
application and maintenance.
The exterior distribution system is further divided
into underground and aboveground systems.
The major underground systems are the conduit and
the utilidor types of systems. These systems are
normally installed only in permanent heating
installations because of their high cost of installation.
In the conduit type of steam distribution system, the
pipe is installed inside a conduit that is usually buried in
the ground below the frost line. The frost line is the
lowest depth that the ground freezes during the coldest
part of the winter. The pipe used for steam is black steel
pipe, which is not as strong as that required for
condensate return lines. The conduit and insulation
serve to protect and insulate the steam pipe. One type of
conduit is shown in figure 3-1. The conduit must be
strong enough to withstand the pressure of the earth and
the usual additional loads imposed upon it.
Several types of materials and various designs are
used in the manufacture of conduit. Common types of
conduit are constructed of masonry cement, galvanized
iron, and steel. The conduit is usually sealed with
asphaltic tar or some other type of sealer to prevent
water from getting into the insulation and deteriorating
it. Insulation may be attached directly to the pipe,
attached to the inner surface of the conduit, or in loose
form and packed between the pipe and the conduit.
The bottom of the trench for the conduit should be
filled with coarse gravel or broken rock to provide
support and adequate water drainage. When water is
allowed to collect, it seeps into the conduit through
porous openings in the sealer. This wets the insulation
and causes it to lose much of its insulating value.
Manholes are required at intervals along the line to
Figure 3-1.One type of steam distribution conduit.