hole spanning under short-term hydrostatic pressure tests
TRANSCRIPT
Hole spanning under short-term hydrostatic pressure tests for 3 spray liner products for water service pipes
Introduction The following fact sheet gives the results of 3 short‐term hydrostatic pressure tests for hole spanning on two polyurea spray liner products by 3M‐Skotchkote 269 (S1) and Skotchkote 2400 (S2), and a new polyurethane spray liner product (S3). The S1 and S2 samples tested were both excavated from in service drinking water pipes, while the S3 sample was from a trial installation of the liner product on a new ductile iron pipe section.
The main objective was to evaluate the failure pressures under an introduced defect in the host pipe (circular through‐wall hole) and to observe the failure mechanism in each case.
Methodology
Holes were bored at the center of the pipe to remove the cast iron and the cement mortar liner to expose the spray liner underneath. Figure 1 shows an example of testing for the S3 liner product hole spanning specimen. The pipes were then pressurised (short‐term) to failure (Figure 2). Before pressurising, pipes were held at a constant pressure (<200 kPa), to ensure strain gauges and transducers were recording.
Figure 1: Hole‐spanning test setup for S3 lined pipe
The bored hole sizes were as follows:
S1: 25 mm
S2: 25 mm
S3: 30 mm Average liner thickness at location of failure:
S1: 3.8 mm
S2: did not fail at hole; failed at graphite patch
S3: 2.6 mm
Figure 2: Pressure vs. time chart for the hole spanning tests
Results Failure characteristics
Figure 3 shows failures of each of the pipes tested. The S1 and S3 liner product lined pipes failed at the hole, while the S2 did not. S1 is a ductile liner. Under pressure, the liner failed by a small crack at the center of the hole. S3 failed by blowout in a half moon shape (inner and edge failure). S2 failed in a longitudinal split after the host pipe split. The S2‐lined pipe failed at the opposite side of the hole, at a large corrosion patch covered by a thick graphite layer. In all tests, the spray lined pipes failed well above operational pressure (0.4 – 1 MPa).
The data gathered from these tests will be used for numerical modelling and as a comparison to hole
spanning equations that are being developed at Monash University. For further details on testing, please see the relevant testing reports.
Figure 3: Failure of each specimen