Page 184 - Trenchless Technology Piping Installation and Inspection

Pipe and Pipe Installation Considerations 149

FIGURE 4.22 Joint cross-section of coupling-joint in AC pipe.

of portland cement and silica. The controlled blending of these basic
raw materials is built up on a rotating steel mandrel and then com-
pacted with steel pressure rollers into a dense homogenous struc-
ture in which a strong bond is affected between the cement and the
asbestos fibers. A smooth interior surface results from this process.
Final curing of the product is done in an autoclave employing high-
pressure steam for dimensional and chemical stability.

Joint Types AC pipes were joined together by means of a gasket-joint
coupling (also referred to as a double-bell coupling joint). The ends of
two pieces of pipe were slipped into the gasketed coupling, effec-
tively creating two water-tight seals. Some manufacturers permitted
angular movements of up to 5° at joints. Figure 4.22 shows a typical
AC pipe joint.

Advantages and Limitations Among its advantages, its long opera-
tional life, immunity to corrosion, light-weight in smaller diameters,
and watertight joints may be mentioned. Known limitations of the
pipe include a low flexural resistance as a whole, easily damaged by
construction equipment because of its brittle nature and a low chem-
ical resistance. Significant research was done to study the effects of
dissolved asbestos fibers in drinking water on human health. AC
pipe manufacturers and the American Water Works Association do
not recommend the use of this piping material where water is highly
aggressive as corrosive water, such as acidic water with a low pH was
more likely to attack piping products.

4.6.2 Vitrified Clay Pipe
The second group of rigid pipes among piping materials is vitrified
clay pipe (VCP). The use of VCP in sanitary sewer systems throughout
the United States is yet to be matched by any other piping material.
For two centuries, VCP was the only commercially available material
capable of withstanding the chemically aggressive environments