The material to be used for pipe manufacture must be chosen to suit the operating conditions of the piping system. Guidance of 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, Refiery and Oil Piping, and Refrigeration Piping Systems. The objective being 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 fitings while cast steel is primarily used for special applications. 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 material such as copper and copper alloys are used in power plants in instrumentation and water services wheretemperature is not a prime factor.
 Pipe Schedule
There are two systems used to designate the various wall thicknesses of different sizes of pipe. The older method lists pipe asstandard (S), extra strong (XS) and double extra strong (XXS). The newer method, which is superseding the older method, uses schedule numbers to designate wall thickness. These numbers are 10, 20, 30, 40, 60, 80, 100, 120, 140 and 160. In most sizes of
pipe, schedule 40 corresponds to standard and schedule 80 corresponds to extra strong.

Pipe Fittings
A fiting is used in pipe systems to connect straight pipe sections, adapt to different sizes or shapes and for other purposes, such asregulating (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 fitings, but are usually discussed separately. The purposes of the fitings, 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 direction of a pipe run.
Plugs and Caps for closing off open pipe ends or fitings.
Bushings for connecting pipes of different sizes. The male end fis into a coupling and the smaller pipe is then screwed into thefemale 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 fi. May also be made with oneconnection eccentric for free drainage of water.