Page 197 - Trenchless Technology Piping Installation and Inspection

Pipe and Pipe Installation Considerations 161

coated using an electrocoating process that achieves a uni-
form thickness and provides superior corrosion resistance.
When the pipe arrives at a jobsite, the bell already contains
the casing with the grip ring inserted in it, and no additional
hardware is needed to provide a restrained joint. Internally
restrained PVC pipe is suitable for HDD or for direct-bury
applications that require a restrained joint. The brand names
for the product are Bulldog , Diamond Lok 21 , Eagle Loc
TM
TM
TM
TM
900 , and Royal Bulldog .
Advantages and Limitations
The greatest contributor to the rapid adoption of PVC pipe in water
and sewer systems is its inherent ability to withstand both internal
and external corrosion. Vast amounts of corrodible piping materials
are being replaced each year by PVC. Pipes with proprietary joints for
trenchless installation have high tensile strengths, allowing for long
lengths to be pulled in at a time. Abrasion resistance has been an
advantage over alternative cementitious piping materials. Low inter-
nal friction enables the use of smaller-diameter pipe in both pressure
and gravity applications.
The sensitivity to temperatures on a long-term basis requires
thermoplastics such as PVC to be derated in pressure applications.
Pipe that is not formulated with a higher amount of ultraviolet inhib-
itor results in lowered impact strength after 2 years of continuous
exposure to sunlight. PVC cannot be deflected longitudinally as much
as alternative thermoplastics. The minimum bending radius for fus-
ible PVC pipe is about 250 times the pipe diameter. Poor bedding can
cause excessive deflection and failure in thinner wall pipe. PVC pipe
is more susceptible than alternate thermoplastics to rapid crack prop-
agation. Rapid crack propagation could result in long running cracks
(hundreds of feet) in the event pressurized pipe is impacted or
improperly tapped. Table 4.11 presents a summary of the advantages
and limitations of PVC pipe.

4.7.3 Polyethylene Pipe
Polyethylene (PE) belongs to a group of thermoplastics known as
polyolefins, materials made by polymerization of olefin gases includ-
ing ethylene, propylene, and butylene.
Polyethylene (PE) was first discovered by a German scientist, Hans
von Pechman in 1898, but the discovery was never commercialized. PE
was rediscovered in the United Kingdom in 1933 by the Imperial
Chemical Company and later commercialized in 1939 to manufac-
ture insulation for telephone and coaxial cables. The development
of low-pressure reactors in the late 1950s greatly improved the
commercial manufacture of PE resins, and led to the commercial