Page 205 - Trenchless Technology Piping Installation and Inspection

Pipe and Pipe Installation Considerations 169

epoxy, polyester, and vinyl ester. The amount and orientation of the
glass fibers increase the mechanical strength of the pipe. GRP is man-
ufactured using one of the two methods:

1. Centrifugal casting: This is the most widely used method of
manufacture of GRP for municipal applications in North
America. In this process, glass fiber reinforcements, resins
and aggregates are placed in a rotating steel mold. The cen-
trifugal action of the mold removes air from the composite,
resulting in a dense laminate, free of voids. Material proper-
ties can be altered by varying aggregate content, resin type,
and cure and reinforcement type, quantity or orientation. The
pipe is removed from the mold after heat curing.
2. Filament winding: There are two distinct processes for filament
winding––continuous and discontinuous. Filament winding
involves impregnating several glass reinforcing strands with
a matrix resin and then the application of the wetted fibers to
a mandrel under controlled tension in a predetermined pat-
tern. Repeat of this process results in the desired wall thick-
ness. In the continuous process, an advancing mandrel causes
the pipe to form. Fiber rovings, resin, and aggregate are
added to make the pipe. The pipe is then cured and cut into
desired lengths. In the discontinuous process, a standard
length of mandrel is rotated, and resin, glass, and aggregate
are added to produce pipe that is helically reinforced. The
process allows for the formation of a continuous bell-end,
monolithic with the pipe wall.

Applicable Standards
There are currently three widely-used pressure and nonpressure pip-
ing standards, used in trenchless installations. Standard pressure
classes for AWWA C950 include 50, 100, 150, 200, 250, and over 250
psi. From the available pipe diameters, it can clearly be seen that GRP
offers an alternative to other large-diameter traditional piping mate-
rials (Table 4.15).

Pressure Nonpressure Available
Standards Standards Diameters (in.)
— ASTM D3262 8–144
ASTM D3517 — 8–144
AWWA C950 — 1–144
TABLE 4.15 GRP Standards for Trenchless Construction