Page 206 - Trenchless Technology Piping Installation and Inspection

170 Cha pte r F o u r

FIGURE 4.30 GRP fl ush bell-and-spigot joint for trenchless installation.
(Source: Hobas Pipe USA.)

Joints
There are a variety of joints that have been developed over the years
for GRP. The Fiberglass Pipe Handbook (1989) lists the following types:
coupling or bell-and-spigot joints, mechanically coupled joints,
restrained coupling or bell-and-spigot joints, butt and wrap joints,
bell-and-spigot with laminated overlay, bell-and-spigot adhesive
joint, flanged joints, and mechanical joining systems.
HOBAS, the leading manufacturer of municipal GRP, has varia-
tions of the above-described joints. For new trenchless construction,
pipe-jacking in particular, they offer two separate types of joints: flush
bell-spigot joint for gravity flow pipe jacking, and the flush fiber-
wound collar (FWC) coupling for pressure pipe jacking. A third type
of joint exists for use in the renewal of gravity pipe by sliplining.
In the flush bell-and-spigot joint type, as shown in Fig. 4.30, the
sleeve is fitted to the pipe end, which has been machined-down so
that the joint outside the diameter is same as the pipe itself. An elas-
tomeric gasket, contained in a groove on the spigot end of the pipe,
effectively seals the joint. The flush FWC coupling is a modified ver-
sion of the FWC coupling (a filament-wound sleeve with an EPDM
elastomeric membrane, the coupling is bonded to one end of the pipe
during manufacture).
Advantages and Limitations
Table 4.16 outlines some advantages and limitations of GRP. Excellent
internal and external corrosion resistance in natural soils and corro-
sive wastewater and industrial applications has given GRP an advan-
tage over traditional piping materials in large diameters. It also
displays better abrasion resistance than cement-based pipes. It is sig-
nificantly lighter than a concrete pipe of the same diameter. For pres-
sure applications, a variety of available pressure classes makes it
widely desirable to engineers and contractors.
Although GRP is noncorrodible, it is susceptible to strain corro-
sion in the presence of certain chemicals, such as those found in the
sanitary sewers, where pH is less than 4. This can be overcome dur-
ing design, by ensuring that the stresses are kept within a certain
limit. Certain chemical contaminants can permeate the pipe. During
installation, pipe may be damaged by a severe impact force.