stainless integral to design
A dam upgrade project in South Australia has achieved a world-first zero carbon footprint for water infrastructure and has used stainless steel as part of the unique design. The Little Para Dam upgrade incorporates a Hydroplus Fusegate System, with stainless steel fabrication carried out by ASSDA Accredited Fabricator LWA Engineering.
The Fusegates are similar to those built at Jindabyne for the Snowy Hydro in 2007, featuring a cast in-situ concrete design with stainless steel inlet wells and seal fixings in order to provide a 100 year design life and virtually no maintenance. However, for the Little Para dam upgrade, SA Water accepted the lean duplex stainless steel (LDX 2101) proposed by CivilTEC for the superstructure of the units for the following reasons:
- it would provide similar corrosion resistance to 316 grade stainless steel, but with a higher tensile strength (450N/mm²) and at a much lower price;
- an off-site fabrication system would reduce the amount of time required on site at Little Para from eight months to just six weeks, thereby reducing site administration overheads and running costs for all parties involved; and
- the extremely efficient design (by WSP Group) used far less construction materials than would normally be required for a project of this nature and LDX 2101 is manufactured using approximately 65 per cent recycled material.
LWA Engineering Managing Director Larry Watson said LWA Engineering had been working with ASSDA Major Sponsor Sandvik on the stainless steel components of the project.
“With a Carbon Pollution Reduction Scheme on the agenda, a zero carbon footprint has never been more important,” Mr Watson said.
“One of the main reasons SA Water wanted to use this design with this material came down to the reduction in carbon footprint which minimised the offset required to achieve zero emissions. This is the first zero carbon infrastructure project in the country.”
The walls of the Fusegate bucket are formed from a composite steel shell comprising two 4mm thick stainless steel ‘skin’ plates spaced 150mm apart. A lattice work of ribbing is then welded onto the plates.
Around 70 tonnes of LDX 2101 were supplied by Sandvik for the walls and internal ribbing of the five Fusegates. The material was imported in 4mm thick coil form, which was then cut to length at Sandvik’s Sydney premises, with ribs being cut in Melbourne (RCR Laser) and Adelaide. The wall panels were cut on Sandvik’s 2m-4m laser bed to within ±0.2mm of accuracy.
LWA Engineering marked out the 2m high inner and outer ‘skins’ to form the composite wall panels and spot welded the vertical and horizontal 40mm-4mm thick LDX ribs in position before pre-setting and stitch welding. When the two ‘skins’ were brought together they were fixed in position using a 12mm diameter stainless steel rod which is pushed through 13mm holes in the overlapping lugs and welded at the top and bottom rib location.
Each Fusegate wall was fixed to a pre-cast concrete base chamber using a continuously welded stainless steel base plate cast into the concrete during pre-casting. Prefabricated inlet wells comprising 8mm thick LDX plate continuously welded along splice points were bolted into place on site.
The composite wall design saved about 40 per cent of the stainless steel required when compared with a traditional single-plate design.
The Little Para Dam spillway upgrade will be completed in early 2010.