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

Overall, the liners appear to be holding up well despite the shortfall in thickness over the design
thickness. The flexural modulus value for the 36-in. liner after 21 years of service was below the ASTM
F1216 requirement for the original installation, but no visible signs of liner distress were observed.
6.4 Summary of Data and Observations for All Sites
6.4.1 Visual Observations. The observed visual condition of all of the liners retrieved was
excellent. In the older liners, the older type of polyurethane coating (sealing layer) for the felt was eroded
or missing in those areas regularly exposed to sewage flow. For the newer liner with a PE layer, this
coating layer was still intact. The older form of coating was considered a sacrificial layer, but it has now
been replaced by the major felt manufacturers with either a PE layer or a more durable form of
polyurethane layer.
6.4.2 Annular Gap. Annular gap measurements were made with a feeler gauge for the Denver 8in.
liner, the Columbus 8-in. liner, and the Columbus 36-in. liner. Across all the sites, the annular gaps
measured ranged between less than 0.13 mm and a maximum of 3.31 mm. For the Denver 8-in. liner, the
average gap measurement was 0.9 mm. For the Columbus 8-in. liner, the gap measurements were well
distributed in value and varied from 0.10 mm to 3.31 mm with an average value of 0.35 mm. For the
Columbus 36-in. liner, the readings were mostly less than 0.127 mm, but with a maximum value of 1.64
mm. Sounding of the crown of the liner in situ in the Columbus 36-in. liner indicated that an annular gap
did exist in this liner from around the 11 o’clock position to the 1 o’clock position. In general, the liners
were still effectively tight against the host pipe. There was evidence of good mechanical interlock in the
large diameter liners installed in the brick sewers, but there was no evidence of significant adhesion of the
liner to the host pipe.
6.4.3 Liner Thickness. The liner thickness was measured at a large number of locations for all of
the liners sampled. Measurements were carried out using a caliper, micrometer, and an ultrasonic
thickness tester. The caliper and micrometer measurements are the main measurements discussed in this
section and are provided in Table 6-1. The ultrasonic testing equipment did not work well on the liner
field samples and testing into the cause of this issue is discussed in Appendix B.
Table 6-1. Summary of Thickness Measurements for All Samples
Caliper/ Values Design
Micrometer Measured Thickness
Measurement Set Location Values (mm) by Others (mm)
Crown 5.98±0.07 -
Denver 8-in.
Spring line 5.93±0.11 -
6
Invert 5.91±0.09 -
Denver 48-in. downstream Crown 13.9±0.3 - 13.5
Denver 48-in. upstream Crown 14.2±0.2 18 18
Crown 5.72±0.12
Columbus 8-in.
Spring line 5.73±0.09 7.5 6
Invert 5.70±0.10
Columbus 36-in.
(field measurement) Upper
haunch
14.2±1.5 -
15 *
Columbus 36-in.
(laboratory measurement)
11.9±0.3 -
*
Original design thickness not known; assumed to be the same as the liner used for the adjacent line.
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