Page 135 - Trenchless Technology Piping Installation and Inspection

Coatings and Linings for Potable W ater Pipe Distributions 101

3.8 Installation Considerations
Coating and lining thickness must be designed based on the existing
pipe conditions, requirements and future use. Required quality assur-
ance measures may include compliance with design specifications
and expected test results in accordance with applicable contract doc-
uments and manufacturer’s recommendations. The contractor and
installer must be experienced and certified by the manufacturer for
the specific liner application. The thickness of the lining during instal-
lation can be controlled by the flow rate of the lining material and
retrieval speed of the application head. This process is usually auto-
mated and computerized for advanced applications. If desired, the
actual thickness of the liner installation may be determined through
coupon sampling. The contractor may need to submit lined coupons
for owner’s evaluations or for testing.

3.9 Disinfection Methods
Disinfecting of water pipes after renewal has been a common indus-
try practice for many years. The first AWWA standard covering this
practice was approved in September 1947 (as 7D.2-1948). In 1986, the
designation of this standard was changed to AWWA C-651; the latest
revision is ANSI/AWWA C-651-05. There are five main types of dis-
infection methods identified in AWWA standards as summarized
below. It should be noted that according to project location and water
utility regulatory requirements, additional steps (such as several
flushings, requirements for boiling water for a certain period, etc.)
may be required after lining installations.
3.9.1 Tablet Method
AWWA C-651 recommends the use of an average chlorine content of
25 to 150 mg/L for duration of 24 to 72 hours. Preferably, disinfection
should be carried out overnight; however, not on a day before the
weekend or holidays.

3.9.2 Continuous Feed Method
The chlorine may be added in the form of dissolved calcium hypo-
chlorite, sodium hypochlorite, liquid chlorine, or chlorine gas. Among
these, dissolved chlorine gas offers the “best” disinfection; however,
environmental concerns and new regulations have made this option
less desirable. The chlorine concentrations vary from 25 to 60 mg/L
for durations of 24 to 72 hours.

3.9.3 Slug Method
This method is generally used in conjunction with the tablet
method. After the tablet method is completed and flushed, a heavily