The main purpose of insulating pipelines is to prevent heat passage from steam or hot-water pipes to the surrounding air or from the surrounding air to cold-water lines. In some cold regions, insulation also prevents water from freezing in a pipe, especially when the pipe runs outside a building. Thus, hot-water lines are insulated to prevent loss of heat from the hot water, while potable waterlines are insulated to prevent absorption of heat in drinking water. Insulation also subdues noise made by the flow of water inside pipes, such as water closet discharges. Common types of pipe insulating materials are shown in figure 8-12.

The purpose of a drainage system is to carry sewage, rainwater, or other liquid wastes to a point of disposal. Although there are three types of drainage systemsstorm, industrial, and sanitaryonly the latter, which is the most common drainage system installed by the SEABEEs, will be discussed.

The SANITARY DRAINAGE SYSTEM car-ries sanitary and domestic wastes from a source (or collection system) to a sewage treatment plant or facility. Surface waters and groundwaters must be excluded from this system to prevent overload of the sewage treatment facilities.

The types of materials actually used will depend upon whether the installation is underground, outside buildings, underground within buildings, or aboveground within buildings. The availability of certain types of desired piping materials and fittings may also govern the type of pipe actually used.

Figure 8-12.-Types of pipe insulation.

Underground piping outside of buildings may be cast-iron soil pipe, vitrified clay or concrete, or plastic polyvinyl chloride (PVC) pipe, but PVC pipes are the most common. Underground piping within buildings may also be of cast iron, galvanized steel, lead, or PVC; however, cast iron and PVC are the most popular materials used. Aboveground sewage piping within buildings consists of either one or a combination of the following: brass or copper pipe, cast iron or galvanized wrought iron, galvanized steel or lead, and PVC pipe. Again, the reason for the growing popularity of plastic PVC piping is the unique combination of chemical and physical properties it has, ease of installation, and cost effectiveness. Descriptions and characteristics of some of the most common piping materials used in a sanitary drainage system follow.