The L6 Boremain is believed to have been installed in the early 1930s and it is thought that the pipe was shipped to Australia from the UK. Considering its age, the 460 mm diameter cast iron cement lined pipe has provided excellent service to the Water Corporation but a number of recent failures have signalled the end of its life. Sections of pipe removed prior to lining showed signs of cracking and there was no cement lining remaining.
The pipe runs under the Water Corporation’s head office in Leederville with a number of critical assets sitting both above and adjacent to the pipe. The client considered a number of renewal options including laying a new pipeline next to the existing, boring a new pipeline via an alternative route, and structural rehabilitation in-situ.
The latter option was by far the most cost effective solution and the client accepted a proposal from Insituform Pacific to install a structural close fit high density polyethylene (HDPE) liner within the existing main, using its proprietary PolyFold system.
While an 8 Bar liner was sufficient to cope with the maximum operating pressure of 7 Bar, the client decided on a 10 Bar liner as they could afford the additional diameter loss due to the close fit nature of the liner.Article continues below…
The PolyFold system takes a locally manufactured HDPE welded pipe and mechanically folds it on site, thereby reducing its size by up to 40 per cent of the original diameter. This makes it very easy to push the liner pipe through the deteriorated pipe. The folded shape of the pipe is maintained during insertion by the use of sacrificial bands that are placed as the folded pipe exits the machine. Following insertion, the pipe is reverted back to its original shape by the use of water pressure, which breaks the sacrificial bands and pushes the liner against the host pipe.
The 110 metre section of pipe was rehabilitated in a single installation with the liner insertion taking just one day after initial cleaning and CCTV. The process was actually slowed down by limited available space to string out the HDPE liner. Therefore, short lengths were inserted with additional lengths welded on as required. The installation of end fittings, reversion, and pressure testing were completed within two days and the pipeline was ready for reinstatement. This was accomplished with only two small access pits at either end of the works.
While this was the first PolyFold project completed by Insituform in Australia, the system has been widely used and tested for a number of years in Europe, North America and Asia. The system was recently tested in accordance with EN 14409-3 Plastics piping systems for renovation of underground water supply networks- Part 3: Lining with close fit pipes to ensure that the pipe is not affected by the folding process.
Another key benefit of the PolyFold system is that the liner pipe is ‘pushed’ through the folding rollers as opposed to being ‘pulled’ through the machine. Pulling increases the risk of over-stressing the liner during installation, as well as stretching the liner to the point that excessive ‘recoil’ is experienced during reversion. The pushing mechanism also reduces the site safety risk of high winch loads.
This was another successful example of the excellent results that can be achieved when an innovative contractor and client work in partnership to think outside the box.