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Module 1: Plastic Pipes and Fittings

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Introduction to Plastic Pipes and Fittings

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Plastic has revolutionized plumbing, a trade that for hundreds of years was based on metal pipe and fittings. Plumbers use plastic today in a wide variety of ways: drain, waste, and vent (DWV) piping; water distribution; chemical waste system; and fuel gas piping.

There are both advantages and disadvantages to using plastic pipes. Plastic piping also has different properties that a plumber should be aware of before starting a task.

Advantages to Using Plastic Pipe and Fittings
• Most plastic pipes and fittings are chemically inert, meaning they do not react with other substances or materials. So, they can withstand most chemicals that are used in the home, office, or factory.

• Strong and durable, plastic pipes and fittings also require little maintenance because they are generally resistant to corrosion and do not pit or scale.

• The use of plastic pipe helps to eliminate fire. During the installation process, no welding or soldering is involved. Therefore, it is less likely that fires will occur.

Disadvantages to Using Plastic Pipes and Fittings
• Temperature changes causes plastic to expand and contract more than metal.

• Plastic pipes can also be flammable, and give off fumes when they burn. In addition, fumes from solvent chemicals used to join plastic pipes are harmful.

• Plastic piping needs to be stored under cover during a construction project to protect it from the sun.

Properties of Plastic Pipe
Plastic contains polymers, a long chain of molecules that manufacturers can mold, cast or force through a die into desired shapes.

There are two general categories of plastic: thermoplastic and thermosetting. Click on each category to know more:

Thermoplastic
Thermoplastic pipes can be repeatedly softened by heating and hardened by cooling. When softened, thermoplastic can be molded into desired shapes.

Thermosetting
Thermosetting pipes change chemically when heated. Once hardened by heat or chemicals, it is hardened permanently.

Properties of Plastic Pipe
In addition, plastic pipes can be either rigid or flexible.

Rigid pipes are straight and maintain their shape. Flexible pipes bend, and require more support.

A flexible pipe is often referred to as tubing. Manufactures sell flexible pipe in coil.

The construction of plastic piping can vary as well. Pipes can be solid wall or cellular core wall construction. Solid wall does not contain trapped air.

Plastic Pipes and Fittings
Plastic pipes are manufactured with various wall thicknesses, commonly called schedule or size dimension ratios (SDRs).

SDR relates wall thickness to diameters of the pipe, using a set ratio of wall thickness to diameter. As the pipe diameter gets bigger, the wall gets thicker.

Note:
Plumbers must use plastic pipe and fittings that are labeled and approved for use in plumbing systems.