A rupture to a cement-lined mild steel pipe transporting residential waste through Biggera Creek on the Gold Coast required a swift repair solution, and thanks to the innovative system used, the water main was renovated within only two days.
A 50m stretch of the DN600 sewer needed to be renovated and four vertical 12 degree bends were in the pipe’s route. Based on the positive experience from other successful pressure pipe rehabilitation projects, specialist trenchless contractor Interflow proposed to install the Primus Line system.
Not only is Primus Line a flexible relining solution accommodating the operating pressure independently from the host pipe due to a Kevlar reinforcement, it is also able to negotiate bends of up to 45 degrees. In addition, the liner is not glued to the host pipe and hence can also be installed if water is in the host pipe.
The host pipe was cleaned by high pressure cleaning. Having verified the free inside diameter, the Primus Liner DN500 was pulled in and inflated. The contractor installed reducers scaling down DN600 to DN500 before mounting the special termination fittings. The entire renovation works were completed in two days, as work could only be performed during low tide, ensuring minimal impact on the environment.
Design considerations for using Primus Line in sewer rising mains
Primus Line is designed to remain flexible in all operating conditions. Using it in sewer rising mains, like under the Biggera Creek, involves some additional design aspects.
At the beginning and end of the renovated section, Primus Line connectors interlink the Primus Line system and the existing pipe. There is no free inlet and outlet in the connectors’ area, and Primus Line itself is integrated into the network with a spool piece.
In all operating conditions, the liner itself is constantly filled with the transported fluid. Pumping it uphill can be realised with a non-return valve behind the pump and if the pipe runs downhill, technical modifications can provide a constantly filled liner.
Furthermore, along the entire Primus Line section, there will be a steady or constantly increasing/decreasing pressure level. The minimum operating pressure of the system has to be 1.0 bar. The flow velocity in the entire Primus Line section is constant as well. Pipes are usually operated with up to three m/s.
The inside coating of the liner can be made of polyethylene (PE) for residential wastewater applications. If industrial wastewater runs through it, a thermoplastic polyurethane (TPU) coating will be used inside, with a chemical analysis required to determine its suitability. The same is the case for industrial discharge water, but here, the operating temperature also needs to be taken into account. The Primus Line system is designed for an operating temperature of up to 50 degrees Celsius.
If groundwater is seeping into the annulus space between the liner and the host pipe, a discharge pipe can be installed at the lower pit so that groundwater can pour out freely in case of maintenance.
All in all, Primus Line’s singular characteristics and some particularities for its installation in sewer rising mains made it a swift and smart solution for the pipe rehabilitation under the Biggera Creek. It is one of more than 15 successful installations in Australia.