Retrospective Evaluation of Cured-in-Place Pipe - (NEPIS)(EPA ...

The main defects noted during inspections after 1 to 2 years are bulges and deformations caused by
buckling failure of poorly impregnated or cured sections and delamination of coatings.
TW operates a Dynamic Asset Condition Model based on the performance of a group of sewers initially
inspected around 1989 and reinspected periodically. Most sewers in the model focus have been inspected
at least three times since inception. The rate of deterioration is described as not significantly different
from the rate of error in identification in the survey. Over the course of the exercise, terminologies and
classification software have changed. TW used an internal classification scheme SRS2 at the outset and
moved to Examiner software and is currently transitioning towards Infonet. It is hoped that some historic
data can be reclassified using the improved system. Generally, the financing method discourages capital
maintenance, concentrating on investment in new works which enhance profitability, pipe lining is
undertaken on an as-needed basis, particularly where assets are identified as at risk of collapse within five
years.
TW has proposed a type test for CIPP systems that is applied to demonstrate water tightness (see Figure
C-2). CIPP systems satisfying this test may be selected for small diameter sewers, up to 375 mm (14.8
in.) exhibiting serious infiltration. The test (developed by WRc as a collaborative project CP308 -
infiltration reduction properties of CIPP linings) involves setting up an array of five 1 m (3.28 ft) long,
plain ended clay pipes such that the gradient is not more than 50 mm (2 in.) over the length of the test
line. The central pipe is fitted with a lateral connection through which the line may be filled to test
infiltration through the liner wall. The pipes are jointed using mechanical couplings with joint gaps set at
3 and 25 mm (0.12 and 0.98 in.). Each coupling is fitted with top and horizontal ferrule connectors. The
top ferrule connectors are fed from a header tank so as to provide a 5 m (16.4 ft) water head, the test line
is plugged and restrained before pressure testing for leakage under the 5 m head for 15 minutes.
Figure C-2. Setup for CIPP Water Tightness Test Used by TW
The lining is installed under a 3 m (9.84 ft) inversion or inflation head and cured in accordance with
manufacturers recommendations. Mechanical or hydrophilic seals which are deemed part of the system
may be fitted. The lined pipe is subjected to an external head of 5 m (16.4 ft) for 30 minutes using the
horizontal and top ferrule connections as valves in combination to simulate various conditions of
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