The Stage 5B Expansion Project was commissioned in early April 2010 after an approximate twelve month construction period. Like the two stages prior, works for Stage 5B were predominantly focused on looping. Looping is the process of installing new pipe lengths parallel to the existing asset. There were 11 loops that required 440km of parallel pipe to be installed along the almost 1600km route of the DBNGP.
River Rail and Road Crossings
The Stage 5B Expansion Project required a number of complex river crossings. Loop 0 in WA’s north required three, the Maitland River, the Murray and the Yanyarie River. The project team worked to develop and implement detailed engineering designs and execution methodologies around these crossings and all were delivered successfully and on time.
The crossing of the Fortescue River has been delayed because the bed of the Fortescue has been moving with each cyclone season for the last five years. A detailed river study was required to ensure that the design would be satisfactory for all forecast flood conditions. Construction is now being planned around the next cyclone season.
The project also saw looping cross countless roads and railways and in most cases, the infrastructure had to remain working throughout the construction process.
Construction in a suburb
A major challenge for the project was the fact that Stage 5B required works to occur in the Perth metro area. Ellenbrook is a growing suburb north east of Perth which was developed around the DBNGP Corridor. The corridor is now used as parklands by the community and these parks are highly used pieces of public open space. Homes are also situated very close to the corridor.
Construction in Ellenbrook was significantly modified compared to the normal methods used in open country to reduce the impact on residents. Pipe lengths were reduced from 18 to 12 metres and trenches were open for only up to 300 metres at a time before they were backfilled and the next trench section was dug. This minimised any dust issues and meant there were no open trenches left overnight. Working hours were cut to reduce noise impacts and security patrols and extra fencing ensured the site was secure 24/7.
The pipeline owners were well aware that significant work had to be done with the community well before works began in Ellenbrook. This campaign saw the team become part of the community well in advance and for the duration of this part of the project. This included many community initiatives such as meetings with community leaders, update letters to residents and information stands at shopping centres.
Stage 5B also required construction through working vineyards in the Swan Valley. This raised construction challenges in trying to cause minimum disruption to the vineyards and it also involved significant and ongoing input from the land management team in working with the growers.
As well as the significant looping component of Stage 5B, works were also required on the ten compressor stations along the pipeline route. These stations are the power behind the DBNGP and with all the extra capacity created by the looping, works were required on each station to enable the higher flow rates of gas and ensure a reliable supply.
The compressor stations not only provide the pressure needed to propel the gas down the pipeline, they are also home to the systems that monitor and control the pipeline. The compressor stations are generally a remote form of infrastructure and hence are self sufficient in that they have electricity, water supply and accommodation on site. These sites consist of gas turbine driven compressors, power generators, gas coolers, scrubbers needed to remove solids that may occur inside the pipeline and all control systems to enable remote unmanned operation.
The most complex works were seen at CS1, located in the north of WA near Dampier and CS10 just south of Perth in Kwinana.
CS1 involved replacing a compressor, the unit which creates the gas pressure necessary to push gas through the pipeline. The team used valves and blank flanges to stop the gas entering the old compressor, it was then disconnected from all external connections, removed, replaced with a new larger compressor and reconnected.
The scope of works on CS10 in Kwinana was the most significant. This involved the installation of a new Solar Taurus Gas Turbine Compressor. Before the new compressor unit could be installed it was necessary to relocate the pipeline that feeds gas to the Rockingham and Mandurah areas as it was situated in the location for the new compressor. Once this was done, the civil foundation works were carried out and the equipment installed on the site. Once the new equipment was installed it was connected to the operating system in a second station outage.
Like all construction on the pipeline, the works on the compressor stations require detailed planning because the pipeline needed to remain online during construction. Once construction was completed, the new equipment needed to be connected to the operating pipeline. A compressor station outage of around three days was required to connect the new piping equipment and new electrical systems into the operating facilities. In the case of CS10, the main outages had to be planned around a large gas consumer coming offline, so there was minimal disruption to gas flows.
All compressor station works for Stage 5B were completed successfully with no impact on customer supply.
In all expansions on the DBNGP a highly specialised process known as hot tapping has been carried out to tie the new pipeline into the existing asset.
The gas flow of the DBNGP cannot be interrupted and hot tapping involves welding the new lengths to the DBNGP in a live, high pressure environment.
ZeroHarm comes first
The pipeline owner's ZeroHarm policy was priority at all times during the construction. The safety of the community, those who work on the pipeline, the asset and the environment were the top priority for both DBP and its contractors.
The Stage 5B project was completed in April 2010, adding an extra 110 terajoules per day of firm, full haul capacity. And after three major expansion projects, the pipeline is now almost fully duplicated.
Stage 5 Environmental Reports
The Stage 5 Expansion Project received environmental approval under the State Environmental Protection Act 1986 and the Commonwealth Environmental Protection and Biodiversity Conservation Act 1999. The Environmental approvals for this project are available on the State EPA website and the Commonwealth Department of the Sustainability, Environment, Water, Population and Communities website. Ministerial Statement No. 0735, approving the implementation of this project under the State Act, requires that DBP makes management plans, summary fauna reports and annual environmental compliance reports related to this project publicly available. In line with this requirement, those reports are available via the links opposite. The various management plans are consolidated within the Construction Environmental Management Plan (CEMP).