Page 129 - Trenchless Technology Piping Installation and Inspection

Coatings and Linings for Potable W ater Pipe Distributions 95

any renewal method, true project needs should be evaluated and
matched with proven product attributes.
Moisture can weaken a lining’s curing process as well as its ability
to bond to the existing structure. Although moisture is relatively easy
to mitigate in above-surface structures, it cannot be completely avoided
below grade, especially in pipeline structures. Therefore, a lining with
high moisture tolerance offers an adhesion advantage for pipeline
projects. Epoxies and polyureas can generally be formulated to offer
the best moisture tolerance, although some polyurethanes also offer
moderate tolerance or require the use of an epoxy primer. Other attri-
butes to consider include structural enhancement, permeability and
chemical resistance, quick return-to-service, future maintenance and
repair requirements, and ease of tapping and service connections.

3.2 Water Distribution Pipe Applications
Many water utilities are faced with the problem of aging water pipe
networks and the associated increasing costs. It is estimated that most
water utilities have 20 to 30 percent unaccounted water problems due
to aging and leaking water pipeline systems. Major water utilities in
the United States, on average, face 20 to 60 water main breaks per
year causing loss of millions of gallons of treated water and, at the
same time, facing high costs of emergency repairs together with addi-
tional social costs and customer inconvenience. At the same time,
increasingly limited resources require efficient use of available main-
tenance and renewal funds. Leakage, water quality, and structural
failures are few among the various problems faced by water utilities.
Majority of these problems are caused by corrosion, as well as soil
movements, traffic loads, and excessive pressures. Decay of water
pipes and the need for an appropriate corrosion protection lining
material is a great challenge to the water industry. The main objec-
tives of coatings and linings are to provide corrosion protection,
increase hydraulic capacity and water quality, but they can also be
used for structural enhancements. An ideal coating and lining
method, to provide these properties, must not contain any volatile
organic compounds (VOCs), must be environmentally friendly, long-
term durability, resistant to live (hoop, transverse and longitudinal
stresses, vacuum pressure, water hammer) and dead loads (soil
and hydrostatic pressure), chemical attack, and meet all applicable
governmental, regulatory, and industry standards to be safe for pota-
ble water applications (in the United States, all potable water lining
materials need to be certified according to ANSI/NSF 61). Other
desirable properties of the coatings and linings may include rapid
cure, smooth and pinhole-free coating, meeting adhesion require-
ments with the existing pipe, being locally available with certified
and experienced contractors, and being cost-effective.
For structural applications in worker-entry, larger-diameter pipe-
lines, reinforced sprayed cement mortars (shotcrete and gunite) on