A pipe can be defined as a tube made of metal, plastic, wood, concrete, or fiberglass. Pipes are used to carrying liquids, gases, slurries, or fine particles. A piping system is generally considered to include the complete interconnection of pipes, including in-line components such as pipe fittings and flanges. Pumps, heat exchanges, valves, and tanks are also considered part of the piping system. Piping systems are the arteries of our industrial processes and the contribution of piping systems is essential in an industrialized society.
Piping Material
The material to be used for pipe manufacture must be chosen to suit the operating conditions of the piping system. Guidance in selecting the correct material can be obtained from standard piping codes. As an example, the ASME Code for Pressure Piping contains sections on Power Piping, Industrial Gas and Air Piping, Refinery, and Oil Piping, and Refrigeration
Piping Systems. The objective is to ensure that the material used is entirely safe under the operating conditions of pressure, temperature, corrosion, and erosion expected. Some of the materials most commonly used for power plant piping are discussed in the following sections.
- Steel – Steel is the most frequently used material for piping. Forged steel is extensively used for fittings while cast steel is primarily used for special applications. The pipe is manufactured in two main categories – seamless and welded.
- Cast Iron – Cast iron has a high resistance to corrosion and to abrasion and is used for ash handling systems, sewage lines, and underground water lines. It is, however, very brittle and is not suitable for most power plant services. It is made in different grades such as gray cast iron, malleable cast iron, and ductile cast iron.
- Brass and Copper – Non-ferrous materials such as copper and copper alloys are used in power plants in instrumentation and water services where the temperature is not a prime factor.
Pipe Fittings
A fitting is used in pipe systems to connect straight pipe sections, adapt to different sizes or shapes, and for other purposes, such as regulating (or measuring) fluid flow. Pipe Fittings (especially uncommon types) require money, time, materials, and tools to install, and are an important part of piping and plumbing systems. Valves are technically fittings but are usually discussed separately. The purposes of the fittings, shown in Fig. 3 may be generally stated as follows:
- Elbows – for making angle turns in piping.
- Nipples – for making close connections. They are threaded on both ends with the close nipple threaded for its entire length.
- Couplings – for connecting two pieces of pipe of the same size in a straight line.
- Unions – for providing an easy method for dismantling piping.
- Tees and Crosses – for making branch line connections at 90º.
- Y-bends – for making branch line connections at 45º.
- Return Bends – for reversing the direction of a pipe run.
- Plugs and Caps – for closing off open pipe ends or fittings.
- Bushings – for connecting pipes of different sizes. The male end fits into a coupling and the smaller pipe is then screwed into the female end. The smaller connection may be tapped eccentrically to permit free drainage of water.
- Reducers – for reducing pipe size. Has two female connections into which the different-sized pipes fit. May also be made with one connection eccentric for free drainage of water.
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