Underground Systems

CHAPTER 3 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 systems. EXTERIOR STEAM DISTRIBUTION SYSTEMS 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. UNDERGROUND 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. Conduit Type 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. 3-1