After three years of planning, leading pipeline infrastructure company, Interflow, successfully rehabilitated a decommissioned pressure sewer pipeline off Nelson’s bay area.

In 2007, a 1.1km section of DN525 AC sewer in Nelson on New Zealand’s South Island, was deactivated. Passing under the Waimea Inlet, the pipeline was replaced by a new larger pipeline that followed the shoreline.

Fast-forward thirteen years to 2020, the NRSBU determined that there was significant benefit in rehabilitating and recommissioning the pipeline to increase the network’s capacity, provide operational improvements and eliminate capacity-based overflows.

“Our focus was not only how we do the project, but also how we can do it right. We looked at the problem at hand and then went out to find the best available asset solutions that would be suitable and also the most affordable,” stated Nathan Clarke, General Manager of Regional Sewerage and Landfill Services at NRSBU.

The right tools for the job

Options considered included slip lining with polyethylene, open excavation and re-lay, die-reduced close-fit polyethylene, and Primus Line, a flexible Kevlar-reinforced liner.

Primus Line was chosen on the basis of its ability to negotiate bends in the pipeline, long installation lengths, acceptable flow capacity and low environmental impact. Its long predicted service life delivered the required outcomes for this critical NRSBU asset, whilst still being cost-effective and providing rapid installation.

“The Primus Line product allowed us to do our work quickly and effectively,” said Nathan.

“Because of the chosen solution, we didn’t need to access the project’s entire pipeline to complete the job, rather, just the ends. This significantly reduced the impact of the rehabilitation on the inlet and confined works to easily accessible areas that were not ecologically sensitive.”

NRSBU’s decision to utilise Primus Line marked an excellent opportunity for Interflow to perform its first Primus Line job in New Zealand, with its crews prepared to break a new company record with a single pull of 1.1km under the Nelson inlet.

“As the pipeline we rehabilitated ran underwater, our crews operated with specialised equipment and great caution to ensure no discharges into the Waimea Inlet in order to protect Nelson’s sensitive coastline.” stated Interflow’s National Product Manager, Will Zillmann.

“We were able to quickly and effectively rehabilitate the pipe from the ends of a pressured sewer pipeline, therefore providing a cost-effective, sustainable solution for our customer.”