Wastewater Conveyance - Wastewater Operators - page 199

figure 4.30 Flanged fitting.

4.12.3.1 Screwed Fittings

Screwed fittings are joined to the pipe by means of threads. The
main advantage of using threaded pipe fittings is that they can be easily
replaced. The actual threading of a section of replacement pipe can be
accomplished on the job. The threading process itself, however, which
cuts right into the pipe material, may weaken the pipe in the joint area.
The weakest links in a piping system are the connection points. Because
threaded joints can be potential problem areas, especially where higher
pressures are involved, the threads must be properly cut to ensure that
the weakest link is not further compromised. Typically, the method used
to ensure a good seal in a threaded fitting is to coat the threads with a
paste dope. Another method is to wind the threads with Teflon® ® tape.

4.12.3.2 Flanged Connections

Figure 4.30 shows a flanged fitting. flanged
fittings are forged or cast iron pipe. The lange
is a rim at the end of the fitting that mates with
another section. Pipe sections are also made with
flanged ends. Flanges are joined either by being
bolted or welded together. The flange faces may be ground and lapped
to provide smooth, flat mating surfaces. Obviously, a tight joint must be
provided to prevent leakage of fluid and pressure. Figure 4.31 shows a
typical example of a flanged joint. The mating parts are bolted together
with a gasket inserted between their faces to ensure a tight seal. The pro-
cedure requires proper alignment of clean parts and tightening of bolts.

Key Point: Some flanges have raised
faces and others have plain faces. Like
faces must be matched—a flange with
a raised face should never be joined
to one with a plain face.

4.12.3.3 Welded Connections

Currently, because of improvements in piping technology and weld-
ing techniques and equipment, the practice of using welded joints is
increasing. When properly welded, a piping system forms a continuous
system that combines piping, valves, flanges, and other fittings. Along
with providing a long leakproof and maintenance-free life, the smooth
joints simplify insulation and take up less room.

figure 4.31 Flanged joint.