Zinfra deliver for ActewAGL in Hume, ACT

Zinfra undertakes case boring as part of the Hume Mains Extension project.

Zinfra undertakes case boring as part of the Hume Mains Extension project.

Needing to deliver approximately 30,000 scm/h into the gas distribution networks in the projected growth areas in the Australian Capital Territory and in Queanbeyan over the next 20 years, ActewAGL contracted Zinfra to construct a new 5 km primary main and a new primary regulating station (PRS) at Hume.

These new facilities will ultimately supply natural gas to approximately 25,000 customers, as well as providing long-term capacity for prospective large consumers, and long-term supply into the Hume-Tuggeranong Interconnection supplying the southern ACT.

The Hume Primary Main Extension (PME) Project involved the design, construction and commissioning of 5 km of DN250 steel high-pressure primary gas pipeline, operating to 6.895 MPa, and built and constructed to AS2885.

This new pipeline connects the existing primary network to the new Hume PRS, a separate project delivered by Zinfra and completed in February 2015, and was tied-in to the existing network in three places.

The Hume PME Project also required installation of 0.2 km of DN250 steel high-pressure secondary gas pipeline to connect the Hume PRS to the existing secondary network and associated infrastructure supplying the district of Jerrabomberra.

Construction of the pipeline included:

  • Open cut construction;
  • In-service welding to live gas main;
  • A hot-tap;
  • Two major water crossings; and,
  • Four cased bores.

A hot-tap was required to connect the pipeline to the existing primary main at Jerrabomberra package off-take station (POTS). To maintain the ability to pig the existing primary main, a hot-tap fitting was specially designed with a spherical tee and guide bars.

Pigging pipework was also constructed at either end of the pipeline to allow pig launching facilities to be connected to inspect the integrity of the pipeline.

There were numerous challenges and complexities to the project:

  • Development Application (DA) approval – original design included the removal of many trees that was not approved during the DA process. The solution, achieved through rigorous negotiations with ACT government agencies, was to relocate the final 2 km within private land.
    • Existing services – multiple existing services, including those for a nearby correctional facility, were at risk when trenching. Extensive investigation and stakeholder management, including AC mitigation, surveys, collection of Dial Before You Dig and private land owner information, and non-destructive pot-holing, meant there were no service strikes throughout the project.
  • Proximity to the Monaro Highway – traffic control, including some lane closure at stipulated times, was required throughout the project. Zinfra had to carefully manage time and resourcing to ensure the project remained on schedule.
  • Subterranean rock – completing the Monaro Highway crossing was complex, with rock slowing drilling to as little as 6 m a day.

The project was completed on time and under budget. Excellent site safety supervision, and a strong culture of safety within Zinfra, meant the project was completed with no lost-time injuries or medical treatment injuries.

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