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

As summarized in Table 4-10, the initial thermal program (steps 1-4) was performed to remove any
previous thermal history. The final heat scan step (step 5) of the temperature program was used for
quantification as this scan contains a known thermal history. The calculated Tg values are summarized in
Table 4-12.
Table 4-12. Sample Tg Determination (Denver 8-in. Liner)
Sample Run Tg (°C)
Invert 1 122.65
Invert 2 117.52
Crown 1 122.31
Crown 2 119.11
Spring line 1 134.63
Spring line 2 129.76
Virgin Resin 1 123.57
Virgin Resin 2 124.59
The average Tg for the control samples was 124.08°C (+/- 0.72°C) and the average Tg for the field
samples was 124.33°C (+/- 6.57°C) as measured by ASTM Method E1356-08 with DSC. In general, an
increase in the Tg is a function of curing and represents the increase in the molecular weight of the resin
system (Perkins-Elmer, 2000). The Tg results suggest a similar level of curing between the virgin resin
(control sample) and the aged material samples, with the field samples exhibiting slightly higher
variability in Tg values from the spring line to invert.
4.2.17 CCTV Inspection of Area Sewers for Denver 8-in. Site. The City of Denver ordered
CCTV scans of the lines in the area from which the sample was retrieved. Also, historical maintenance
reports of these lines were requested. A total of nearly 5,800 ft of sewer line was imaged in the period
September 24-28, 2009. A preliminary review of the CCTV reports suggested that the liner is in good
condition overall. Several tap break-in defects were noted as well as lining failure at undercut
connections, which could allow for root intrusion between the lateral outer wall and the liner covering the
interior of the main pipe. This could be attributed to the robotic cutters used by the industry 25 years ago,
which were far less sophisticated and accurate than the units used today. Some of the images reveal root
intrusion via tap connections, resulting in a partial blockage of the sewer line, but the liner itself appears
to be intact in these images. On the line stretch in the alley between Garfield Street and Jackson Street
(between 3 rd and 4 th Avenues), at chainage 212.6 ft, there is what appears to be a liner failure in the
vicinity of a tap break in. Another liner failure was found at the alley between Jackson Street and
Garfield Street, from the first manhole north to the first manhole south to 1 st Avenue. At chainage 20.8 ft,
a bulge was found at the invert of the liner that prevented further advancement of the CCTV equipment.
A third liner failure location was identified in the line running in the alley between Jackson and Harrison
Streets, as it crosses 3 rd Avenue, at chainage 239.8 ft. This liner failure appears to be attributed to
improper restoration of a nearby lateral connection. A significant portion of the polyurethane coating was
hydrolyzed along this line. A lining failure attributed to a connection cut shift was noted at 2 nd Avenue
and Jackson Street. Similar occurrences of a liner connection cut shift were noted on a couple of other
lines. A location where the liner appears to be detached from the host pipe was located at chainage 39 ft,
in the alley between 3 rd Avenue and Garfield Street.
46