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

Location
Table 4-5. Denver 8-in. Liner Annular Gap Measurements
North End of
Specimens
(mm)
South End of
Specimens
(mm)
29
North End of
Remaining Pipe
(mm)
South End of
Remaining Pipe
(mm)
Crown 3.31 0.66 1.04 0.13
45° crown – Right SL 0.10 0.44 0.64 0.20
Right spring line 2.55 0.43 0.46 0.58
Right haunch 0.58 0.43 0.64 0.58
Invert 1.76 0.59 0.71 1.24
Left haunch 0.68 0.43 0.20 0.20
Left spring line 0.89 0.59 0.20 0.20
45° crown – Left SL 0.10 0.57 0.64 0.20
4.2.8 Liner Thickness. A total of 72 readings were taken to measure the thickness at different
locations around the pipe circumference. These readings were taken using a caliper with a resolution of
+0.0001 in. The average thickness of the liner is shown in Figure 4-6. The thickness of the liner was
found to vary slightly around the circumference of the liner with the maximum thickness at the crown
(5.98 mm ± 0.07 mm) and slightly lower values at the spring line (5.93 mm ± 0.11 mm) and the invert
(5.91 mm ± 0.09 mm). This was attributed mostly to the erosion of the polyurethane coating layer
(approximately 0.38 mm thick), originally placed on the internal surface of the liner, at the invert zone.
The average measured thicknesses after 25 years in service were all slightly lower than the designed
thickness of the liner (6 mm) although some individual readings were higher. No ultrasonic field
measurements of liner thickness were possible in the field and when attempted in the laboratory the
measurements were not successful. A discussion of this issue is provided in Section 6.
Figure 4-6. Average Thickness at Different Locations on the Liner