When Sydney Water encountered the failure of one of its high pressure water mains, a range of factors meant that conventional rehabilitation methods were simply not possible. Despite the challenges faced, Primus Line was able to provide an innovative and low-cost solution that has prolonged the life of the water main.
Sydney Water has a long-term contract to supply a large volume of recycled water to the largest steel fabricator in Australia via a mild steel DN500 main. This high pressure main (14 bar) had a catastrophic failure, followed by the undermining of thrust blocks, inclination of thrust blocks and disjoining of sleeve sockets of the pipe, at a major rail crossing in December 2016.
The main was immediately shut down so that the failure could be investigated and the selection of a suitable repair method could be made. Sydney Water kept up supply to the steelworks using potable water.
Sydney Water needed a robust and swift solution. The conventional method of dig and repair was not possible because the failed section was below the railway. Horizontal directional drilling was ruled out because one end of the main was located near a creek, a bridge and many other services.
The option of designing and constructing a pipe bridge was very costly and would have taken too long to execute. Traditional rehabilitation methods, including slip lining, were also ruled out early in the process, as the main has an operating pressure of 14 bar, a number of 45 degree bends and a 90 degree bend.
Solving the problem
Following on from other successful rehabilitation projects with difficult bends and high pressure, Sydney Water decided to repair the main using the Kevlar reinforced Primus Line. On investigation, Primus Line engineers deemed the sweep in the 90 degree bend was too tight and the pressure too high for the medium pressure Primus Line DN500.
In the end, high pressure DN400 Primus Line with an operating pressure of 20 bar and a burst pressure of 100 bar was chosen. The hosting main was carefully inspected and prepared to a standard that did not damage the Primus Line during the installation process and will not harm Primus Line during operation.
A portion of this high pressure main is above ground. As a result of the main failure in 2016, the foundation of a thrust block for the change of direction from the above ground section to the buried railway crossing section had been undermined. External consulting engineers recommended construction of a new thrust block with deep pilings. This was not possible due to its close proximity to the railway track and nearby services.
Sydney Water engineers came up with an innovative solution of continuously extending the Primus Line to where the next existing thrust block was. This measure is expected to allow any thrust at the undermined section to be transferred and restrained by the combination of water filled Primus Line weight and the next thrust block.
This project was installed and self-performed by Sydney Water as in early 2017, Primus Line trainers travelled to Australia to train Sydney Water on how to install Primus Line. One of Primus Line’s true value propositions is that after training there is no investment required to install Primus Line as it is pulled into place via an approved winch and blown into shape via an oil free air compressor.
In this case, Primus Line was the obvious choice as it could navigate the 90 degree bend, maintain the 14 bar operating pressure and offer a fast installation of only 20 minutes with no curing and at a low cost.
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