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In the United States, where it is used in both water and wastewater service, polyvinyl chloride (PVC) is the most commonly used plastic pipe for municipal water distribution systems.

Because of its resistance to corrosion, its light weight and high strength to weight ratio, its ease of installation, and its smoother interior wall surface, PVC has enjoyed rapid acceptance for use in municipal water distribution systems since the 1960s. There are several other types of plastic pipe, but PVC is the most common plastic pipe selected for use in municipal systems and will be the only type of plastic pipe addressed in this section. There are also several different PVC pipe specifications. Only those having AWWA approval will be addressed in this section, since only those should be used for municipal water distribution systems. Highdensity polyethylene pipe (HDPE) is discussed in Sec. 3.4.5.

3.4.2.1 Materials. PVC is a polymer extraded under heat and pressure into a thermoplastic that is nearly inert when exposed to most acids, alkalis, fuels, and corrosives, but it is attacked by ketones (and other solvents) sometimes found in industrial wastewaters. Basic properties of PVC compounds are detailed in ASTM D 1784. ASTM D 3915 covers performance characteristics of concern, or cell classification, for PVC compounds to be used in pressure pipe applications. Generally, PVC should not be exposed to direct sunlight for long periods. The impact strength of PVC will decrease if exposed to sunlight and should not be used in above-ground service.

In North America, PVC pipe is rated for pressure capacity at 23°C (73.4°F). The pressure capacity of PVC pipe is significantly related to its operating temperature. As the temperature falls below 23°C (73.4°F), such as in normal buried service, the pressure capacity of PVC pipe increases to a level higher than its pressure rating or class. In practice, this increase is treated as an unstated addition to the working safety factor but is not otherwise considered in the design process. On the other hand, as the operating temperature

rises above 23°C (73.4°F), the pressure capacity of PVC pipe decreases to a level below its pressure rating or class. Thermal derating factors, or multipliers, are typically used if the PVC pipe will be used for higher temperature services. Recommended thermal derating factors are shown in Table 3.12. The pressure rating or class for PVC pipe at service temperature of 27°C (80°F) would need to multiplied by a thermal derating foctor of 0.88.

The pressure rating or class for PVC pipe at service temperature of 60°C (140°F) would need to multiplied by a thermal derating factor of 0.22.

3.4.2.2 Available sizes and thicknesses. AWWA C900 covers PVC pipe in sizes 100 to 300 mm (4–12 in.). AWWA C905 covers PVC pipe in sizes 350–900 mm (14–36 in). There are important differences in these two specifications that should be understood by the designer.

AWWA C900 PVC pipe is manufactured in three “pressure classes” (100, 150, and 200).

The pressure class selected is typically the highest normal operating system pressure in psi.

AWWA C900 PVC pipe design is based on a safety factor of 2.5 plus an allowance for hydraulic transients (surge). AWWA C905 does not provide for “pressure classes” but refers to PVC pressure pipe in terms of “pressure rating.” As with pressure class, pressure rating also refers to system pressure in psi. While AWWA C905 covers six pressure rating categories (100, 125, 160, 165, 200, and 235), the most commonly available pressure ratings are 165 and 235. The design of AWWA C905 PVC pipe is based on a safety factor of 2.0 and does not include an allowance for surge. In view of this important difference between the two specifications, designers often specify higher pressure ratings of C905 PVC pipe than system pressure would tend to indicate in order to allow for the reduced factor of design safety.

Both C900 and C905 contain required pipe dimension ratios. Dimension ratios define a constant ratio between the outside diameter and the wall thickness. For a given dimension ratio, pressure capacity and pipe stiffness remain constant, independent of pipe size. Table 3.13 presents dimension ratios (DR) with corresponding pressure classes as defined in AWWA C900. Table 3.14 presents dimension ratios with corresponding pressure ratings as defined in AWWA C905.

3.4.2.3 Joints. For PVC pipe, a rubber gasket bell and spigot type joint is the most commonly joint used for typical, municipal buried service, The bell and spigot joint allows

TABLE 3.12 Thermal Derating Factors for PVC Pressure Pipes and Fittings

Source: Handbook of PVC Pipe (1991).

for some pipe deflection (Handbook of PVC Pipe, 1991) without sacrificing water tightness. This joint is not capable of resisting thrast across the joint and requires thrast blocks or some other sort of thrust restraint at bends and other changes in the direction of flow. Mechanical restraining devices are commonly used to provide restraint at PVC pipe joints where necessary.

PVC pipe joints are specified in ASTM D 3139. At connections to fittings and other types of piping, it is also common to detail a plain end (field-cut pipe) PVC pipe. Plain-end pipes are used to connect to mechanical joint ductile iron fittings and to flange adapters.

3.4.2.4 Gaskets. Gaskets for PVC joints are specified in ASTM F 477. As with gaskets for DIP, gaskets for PVC pipe are vulcanized natural rubber or vulcanized synthetic rubber.

Natural rubber is suitable for water pipelines but deteriorates when exposed to raw or recycled wastewater. EPDM is commonly used in water service and nitrile (Buna N), in recycled wastewater.

3.4.2.5 Fittings. AWWA C900 and C905 PVC pipe for municipal use are manufactured in ductile iron pipe OD sizes, so ductile iron fittings, conforming to AWWA C110, are used in all available sizes. See Sec. 3.4.1.5 for a discussion on ductile iron fittings. Although not widely used, PVC fittings, in configurations similar to ductile iron fittings, are also available for smaller line sizes. AWWA C907 covers PVC pressure pipe fittings for pipe sizes 100–200 mm (4–8 in.) in pressure classes 100 and 150.

3.4.2.6 Linings and Coatings. PVC pipe does not require lining or coating.

TABLE 3.13 Pressure Class versus DR-AWWA C900

TABLE 3.14 Pressure Rating versus DR-AWWA C905

*Most commonly used ratings for municipal systems.