Building dams and floodgates to protect communities from the ravages of nature are among the most vital functions of civil engineering. Today, thanks to stainless steel, these structures can be made more resilient than ever.
In the age-old struggle of man versus nature, flood prevention has always been a key battleground, one where proper planning and clever engineering have often been the deciding factor. Dams, floodgates, sea walls and reservoirs, even those built primarily to feed hydroelectric plants or municipal water systems, serve as main lines of defense against flooding.
As such, they're designed to remain intact and functional for long stretches of time despite the most brutal punishment from storms, earthquakes and, in some cases, years of exposure to salt water. What if a simple change in construction materials could make these structures stronger, extend their lifetimes by decades and lower maintenance costs at the same time?
Changing tides
Water control structures are built using a variety of materials though their most critical elements – those consisting of moving parts or subject to high wear and tear – have traditionally been made of wood or painted carbon steel.
Components constructed using these materials, as well as concrete reinforced with carbon steel rebar, are subject to rot and rust, shortening their lifespans and necessitating frequent maintenance. For that reason, engineers in recent years have begun to turn to stronger, corrosion resistant austenitic stainless steel as a replacement material for these components.
Now, however, many are realizing that Forta duplex stainless steel, which has twice the strength as austenitic at the same weight, presents an even better prospect. Using stainless steel instead of carbon steel as reinforcement bar guarantees concrete structures a longer life.
Stronger, lighter, tougher
Flowing through the heart of Tampere, Finland, the Tammerkoski rapids is both an important local resource, supplying four hydroelectric plants, and a valued part of the city’s industrial heritage. When time came in the early 2000s to replace the waterway’s hundred years old wooden floodgate system, Pontek Oy, the company tasked with the structural engineering of the rebuild, at first planned to make the new gates from carbon steel. Hearing about the potential of duplex stainless, however, convinced the company to reconsider.
In the end, Pontek settled on using Outokumpu’s Forta LDX 2101 duplex stainless steel in the main structural parts of the gates, completing the project in 2012. The lighter weight of the gates, a result of the increased strength, is already resulting in substantial cost savings as far less electrical power is required to move them.
The high surface hardness of Forta LDX 2101 also protects the gates against wear caused by ice and floating debris. In terms of longevity, what happens to the material on a micro scale is also significant. Stainless steel, when scratched, naturally develops a protective coating through a process called passivation. The result is that parts made from duplex stainless – if facilities operators so choose – never have to be coated or painted, which has benefits both to lifecycle costs and to the environment.
Lifespans measured in centuries
Finnish engineers aren’t the only ones waking up to the advantages of duplex stainless. The same Outokumpu Forta LDX 2101 was used successfully in the Little Para Dam, a flood spillway attached to the Little Para Reservoir in South Australia. That spillway system was designed to last 100 years.
A similar Outokumpu duplex grade, Forta LDX 2404, went into new waterway sluice gates installed in Gothenburg, Sweden in 2013. Their design life is 120 years, though the gates could theoretically last for centuries if their rubber seals are maintained. Holding back the flood waters is a long-term task, one made all the more urgent by increasing urbanization and the prospects of climate change. In this battle of man versus nature ...and versus time, stainless is our companion.
Are you working on renewing floodgates or dams? – Contact Outokumpu to discuss your project