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WRc External Hydrostatic
pressure trial of a Konudur 250 OM-PL cured in place repair
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The objective of this test was to investigate
the leak tightness of the Konudur 250 OM-PL local lining system under
external hydrostatic water pressure in accordance with the test specified
in Appendix C of the Specification for Local Sewer Repairs (WRc Ref:
UC 3248/Appendix B).
The cured in place patch repair was
made from three layers of glass fibre fabric which were laid in turn
onto a polyethylene release film and impregnated with a polyurethane
resin. The patch was wrapped around an inflatable packer, inserted
into the clay pipe to be repaired (which had a specified defect) and
compressed against the pipe wall whilst it cured at ambient temperature
for approximately two hours. The performance of the lining was then
tested using the WRc external pressure rig.
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Test Rig Specification
The WRc test rig has been designed and constructed
to allow external water pressure to be applied to a defective clay
pipe which has been repaired using a local lining system.
Photograph 1 shows
the hydrostatic test rig and a schematic of the rig is also shown
in Figure 1. The rig
consists of a 20" steel tube with caps welded to the ends. Two number
DN 350 Viking Johnson Maxidaptors (16 bar pressure rating) are bolted
to these end caps. This is then assembled around the outside of the
clay test pipe and the Maxidaptors tightened to provide a water tight
seal between the rig and the pipe. Inlet and outlet valves enable
water to be pumped into the annulus between the pipe and steel tube.
The pressure in the rig is monitored using a pressure gauge connected
to the outlet valve. |
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Production of Test Piece
A DN 300 clay pipe (OD 380 mm) pipe
approximately 1.5 m long was lined with a 1.2 m long patch repair.
The defect consists of a 100 mm x 100 mm hole in the pipe wall. Lining
took place at the WRc Swindon Offices and was witnessed by a WRc member
of staff.
During the installation of the patch
repair, the defect was placed at the pipe springing to prevent build
up of resin in the hole. The outside of the clay pipe was then coated
with varnish to prevent water permeating through the pipe wall during
the hydrostatic test. |
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Leakage Failure Criteria
The aim of the test was to determine whether the
patch repair system under investigation can prevent infiltration of
ground water through the defective clay pipe. The failure criteria
for leakage is set at 0.5 litres per linear meter per meter of nominal
diameter over a 30 minute period, which is the permissible rate of
infiltration for new sewers, as specified in Sewers for Adoption.
The worst ground water loading conditions to which a sewer will be
exposed will be the maximum depth of the pipe (to invert) in fully
saturated ground. For the purpose of this test, a pressure of 1 bar
(approximately 10 m head) was used, 10 m being the maximum ground
water loading a sewer is likely to experience in the UK. |
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Test procedure
The procedure for testing for leak
tightness is as follows:
1. The test rig was pressured to
10 m head (1 bar) for a period of 2 hours.
2. Any water loss from the rig was
collected and measured over the next 30 minutes.
If the measured flow exceeded 0.5
litres per linear meter per meter of nominal diameter, then the lining
was deemed to have failed. Failure flow rates are given below in table
1.
Table 1. Failure flow rates for leak
tightness in the hydrostatic rig.
| Length of local
lining |
Failure flow
rate |
| 0.5 m |
75 ml |
| 1.0 m |
150 ml |
| 1.2 m (Konudur 250 OM-PL patch) |
180 ml |
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Results
Tested at WRc Swindon on the 12th October
1999.
The test rig was pressurised to 1 bar and the pressure
maintained for 2 hours. The sample wept at the 4 o'clock position
approximately 225 mm from one end of the patch after 15 minutes. The
weeping was initially from a single pin sized defect but at the end
of the 2 hour pre-conditioning period there were a total of five defects
within the general area of the initial weeping.
The 1 bar pressure was then maintained
(by pumping for a further 30 minutes and the flow (loss) of water
from the patch repair was recorded. The loss of water during the 30
minute period was 54 ml which is well within the 180 ml allowance
for a 1.2 m long repair.
The lining therefore passed the
leakage test.
The following table summarises the results of the
hydrostatic test.
Table 2. Summary of Results from Hydrostatic
test
| Lining System |
Recorded Flow |
Leak Test |
| Konudur 250 OM-PL |
58 ml |
Pass |
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Conclusion
The Konudur 250 OM-PL patch repair
system passed the external hydrostatic water pressure (leak tightness)
test carried out in accordance with Appendix C of the specification
for Local Sewer Repair.
This is a one off test and doesn't constitute
a full WRc Approval |
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