History: Pakenham to Wollert Natural Gas Pipeline

The 93 km pipeline takes gas from the Longford to Dandenong Pipeline to either store it for later use through Dandenong City Gate, or carry it through to the Wollert City Gate to boost pressure in the northern section of the metropolitan ring main.

The pipeline was designed to cater for expected gas demand until after the turn of the century. Following its installation the pipeline well and truly reinforced the existing system, with a design capacity of 21 million cubic metres a day.

The Pakenham to Wollert Pipeline was first considered when the Corporation designed the Albury to Wodonga line in 1974, but detailed work did not get underway until 1977 when Corporation engineers selected the route and contacted property owners and statutory authorities. Part of this preliminary work involved the publication of an environment effects statement, which explained the need for the pipeline, outlined construction methods and emphasised the care that would be taken with the environment.

ln line with its policy of environmental preservation, the Corporation employed conservation consultant Harry Butler for advice on minimising damage to the environment. As a result, route selection avoided national and state parks, and extensive areas of bushland, with the final pipeline traversing only 6.5 km of bushland in total. Efforts were made to preserve clumps of trees in otherwise cleared paddocks, as well as significant trees such as the big red gums near Wollert.

Crossings at roads, railways and streams were undertaken where possible at points where there were few trees. After considering the environmental effects statement and all objections to the Corporation’s proposal, the Ministry of Minerals and Energy granted a permit to own and use a pipeline on 29 March1982, by which time three ministers in the Victorian Liberal Government had overseen the development of the proposal. A few days later the Labor Government came into Power and a new minister, David White, took over the pipeline approvals. He granted the Corporation a licence to construct and operate a pipeline on 8 October 1982, after which work started on the first section of the line between Pakenham and Yellingbo.

The Corporation divided the construction of the line into three stages, both to spread out the total cost over three years and to enable each stage to be completed over the summer. Much of the pipeline corridor is in the mountains east of Melbourne, a high rainfall area, which would have made construction difficult and costly during the winter.

The first section, of the 27 km between Pakenham and Yellingbo, was built over the summer of 1982-83 and was ready for use as a storage reservoir, supplying through Dandenong City Gate by winter 1983.

Early in 1983 there was a re- evaluation of the economics of the original three-year program, and the Corporation decided it would make a considerable saving by completing the project a year ahead of schedule. Stage two, the 38 km between Wollert and Yarra Glen, began in October 1983, and stage three, the 28 km between Yellingbo and Yarra Glen, started a month later.

The Pakenham to Yellingbo section passed through grazing land, then the highly productive country around Gembrook en route to Yellingbo. The terrain proved little trouble to the contractors, Harnett Constructions. Radiography was completed by Engineering Testing and Research Services (ETRS) and pipeline inspection by the Corporation, which had a site office at Gembrook with project engineer Mark Bumpstead and construction supervisor Bob Fraser. Harnett Constructions are also put through the relatively easy middle section between Yellingbo and Yarra Glen along the alluvial flats of the Yarra River. Radiography was completed by Non Destructive Inspection Services (NDIS) and the Corporation, assisted by personnel supplied by BTA Engineering and lnspection, carried out inspection. The site office at Coldstream was manned by Peter Wheelwright, John Lott and Bob Fraser.

Stage two traversed the most difficult terrain. Contractor Spie Capag had to battle the escarpment up from the Yarra River flats, reefs of granite, clay and scoria conglomerate, and basalt plains. The geology of the area forced the contractors to do some lateral thinking and come up with new methods of trench formation, but the experience gave them confidence to tackle any terrain. Radiography for this section was completed by Independent Testing and lnspection Company (INTICO) and inspection was by the Corporation, assisted by personnel supplied by lNTICO. Mark Bumpstead was again project engineer with Brendan Varker as construction supervisor.

The rocky country in stage two, and the Yarra Glen escarpment were the major problems faced during construction. Others were, ironically enough, bushfires and water availability. The Ash Wednesday bushfires swept through the Gembrook area during construction of stage one and two. Upper Pakenham families sheltered in the empty trenches when their homes were threatened. Clearing for the pipeline easement formed an effective firebreak in several of the heavily-timbered areas and some of Harnett Constructions’ equipment was seconded for earthmoving works during and after the fires.

Despite the pipeline crossing several waterways, including the Yarra River three times, water availability in the quantities required for hydrostatic testing had a significant effect in determining the breakdown of the pipeline’s construction stages.

The pipe was laid in a 27 m wide easement, 9 m in from the western or southern boundary. Trenches were 2.1-2.9 m deep, with a minimum cover over the pipe of 1.2 m, or 2 m under watercourses.

The 762 mm pipe predominantly had wall thicknesses of 10.6 mm, with some at 12.7 mm. All pipe was manufactured to API 5L, grade X60. Pipe for the first section was bought from Brazil and the rest from Steel Mains in Western Australia, whose Victorian plant coated all pipes with coal tar enamel and internally lined them with thin-film epoxy. Field welding on all stages was completed by the conventional manual metal arc process.

Field coating of the pipe joints was by the application of shrink sleeves. The line was designed to operate at a maximum pressure of 7,700 kPa. Corrosion protection was supplied by electric current from a pole-mounted transformer-rectifier to a series of earthing beds installed at 10-25 km intervals along the line. Corrosion control test points attached to the pipe were installed every 1.5-2 km. Line valves were installed near roadways at 2-13 km intervals and there are offtake and termination valves at Pakenham and Wollert. Reinstatement works included replacement of topsoil, chipping of cleared shrubs and trees for spreading on backfill clearing of debris, rebuilding of fences, repair of roads and restoration of easements to near as possible original condition.

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