The Gold Coast City Council in Queensland operates a DN 600 sewer rising main crossing under the Biggera Creek. The cement-lined mild steel pipe transporting residential waste water through the creek was ruptured. Therefore, a swift repair solution was required.
A stretch of 50 metres needed to be renovated. Four vertical bends with 12 degrees each were in the pipe’s route. Based on the positive experience from other successful pressure pipe rehabilitation projects, specialist trenchless contractor Interflow Pty Ltd. 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. Moreover, 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. After having verified the free inside diameter, the Primus Liner DN 500 was pulled in and inflated. The contractor installed reducers scaling down DN 600 to DN 500 before mounting the special termination fittings. The entire renovation works were completed in two days as work could only be performed during low tide, thus causing only minimal impact on the environment.
Design considerations for using Primus Line® in sewer rising mains
An outstanding feature of Primus Line® is that it remains flexible in all operating conditions. Using it in sewer rising mains like under the Biggera Creek involves nevertheless some additional design aspects:
At the beginning and end of the section to be renovated, Primus Line connectors interlink the Primus Line® system and the existing pipe. There is no free inlet and outlet in the connectors’ area. Primus Line® itself will be 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. 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 3 m/s.
The inside coating of the liner can be made of PE for residential waste water applications. If industrial waste water runs through it, a TPU inside coating will be used. A chemical analysis will be required to determine its suitability. The same is the case for industrial discharge water. Here, the operating temperature needs additionally to be taken into account. The Primus Line® system is designed for an operating temperature of up to 50 degrees Celsius.
If ground water is seeping into the annulus space between the liner and the host pipe, a discharge pipe shall be installed at the lower pit so that ground water 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. One of more than 15 successful installations in Australia.
