Hydroplus is the pioneer and the sole producer in the world of Fusegates®, a simple and safe system to increase reservoir storage capacity with the help of a non-mechanical structure that sits atop the spillway of a dam. Since inventing the technology in 1989, the company has installed more than 50 Hydroplus Fusegate® Systems around the world.
The 33-year-old Little Para dam, part of the water resource assets of SA Water in Adelaide, Australia, recently presented a new challenge to Hydroplus. The resulting solution represents a unique spillway control system, being the most technically advanced and structurally efficient Fusegates® in the world. The key to the innovation is an all stainless steel structure – the first in the world – and use of Outokumpu’s lean duplex LDX 2101® stainless steel.
The background to the new Fusegate® system was a study that showed the Little Para dam to be deficient in terms of its ability to pass the required maximum floods. The dam failed to comply with modern dam safety standards, and the spillway required upgrading to increase capacity. Consulting engineers of GHD Pty Ltd opted for the construction of a new 52m-long auxiliary spillway controlled by Hydroplus Fusegates®.
The special requirements for the system made the design of the Little Para Fusegates® particularly demanding for Hydroplus: SA Water targeted 100-year design life and virtually no maintenance. In addition, the price of conventional materials including concrete, formwork and reinforcing steel, as well as labor, plant and equipment, had overrun the original budget pricing.
Hydroplus’s engineers completely re-assessed the design approach from previous Fusegate® designs. Besides the customer’s requirements and the financial framework, Hydroplus sought to reduce time on site and deliver a carbon neutral project.
During the "value engineering" stage the idea emerged to utilize a 6m-high composite stainless steel wall section fixed to a 0.5m-thick pre-cast concrete base chamber. This design required approximately 40% less material than a conventional single plate design with stiffeners.
Hydroplus would normally use the 1.4401/1.4404 (316/316L) austenitic grade when stainless steel is used in Fusegates®, but now, with an all-stainless structure, they looked for an alternative. Outokumpu distributor Sandvik Materials Technology recommended the use of Outokumpu’s LDX 2101® duplex stainless steel. Hydroplus was easily convinced, given the yield strength of the duplex grade − close to double compared to austenitic 1.4401/1.4404 − combined with a significant cost advantage.
Bill Hakin, Hydroplus’s Regional Director in Australia, explains that the use of the LDX 2101® duplex stainless steel in a structurally efficient design was a smart solution which reduced risk, time on site and overhead costs compared to the more traditional approach.
According to Hakin, Hydroplus’s experience with duplex LDX 2101® was excellent, with no problems with fabricability, laser cutting or welding. He says, "The quality of the LDX 2101® stainless steel delivered and the accuracy of the cut-to-length and laser cutting contributed significantly to attaining the extremely tight tolerances of the overall fabrication. There were no ‘non-conformance’ reports during the eight-month fabrication period."