| Refurbishment & modernisation
Stainless steel secures sustainability
Daniel Svedberg, Outokumpu Business Development Manager, explains how a switch to duplex stainless steel has played a crucial role for the Lossen hydropower plant in Sweden. As well as saving weight on the emergency flood gates so they could be operated by the hydraulic system, the material has also eliminated the need for an expensive protective coating on the side exposed to water
HYDROPOWER IS CURRENTLY SWEDEN’S largest source of renewable energy while also providing around 45% of the country’s electricity generation. That means ensuring the safety and reliability of the dams that serve the generating turbines is crucial. One of the most important plants is the 156MW Långå hydroelectric station served by the Loosen dam, situated in Härjedalen in the middle-west of Sweden along the tributaries of the river Ljusnan. The Lossen dam was built in 1959-1962 and is 1600m long with a maximum reservoir capacity of 500 million m3
Is a coating operation more expensive . A breach of this dam would have major
consequences for the downstream area, since it would cause secondary dam failures on all dams down to the Baltic Sea. To avoid potential loss of life and the impact on the Swedish economy, the Lossen dam was the subject of a major upgrading and improvement program in the previous decade. This included two hydraulically- operated emergency flood gates, installed upstream in 2016, which is where Outokumpu’s duplex stainless steel has played an important role.
Weight saving gives a lift
One of the major challenges facing the designers of the emergency flood gates was to reduce their weight down so that they could be operated by the hydraulic system. This is why duplex stainless steel was selected, as it has a higher strength than conventional constructional steel and no corrosion allowance is needed. The advantage of duplex stainless steel is that it combines the best properties of both main types of stainless steel – ferritic and austenitic. The result is a range of alloys that provide corrosion resistance, cost competitiveness and high strength. A lean duplex stainless steel features lower amounts
of expensive alloying elements, such as nickel and molybdenum, providing an especially cost-effective solution. So, by specifying Outokumpu’s Forta LDX 2101, it was possible to reduce the wall thickness of the flood gates by over 30%, with a corresponding and very significant saving in weight.
Double-sided approach Forta LDX 2101 was used to manufacture the
water-facing side of the flood gates. Since corrosion resistance is not so important for the dry side, this was constructed from painted carbon steel. A special dissimilar welding process was used to attach the stainless plate to the carbon steel structure.
than stainless steel? Another important reason for selecting stainless steel was that the gates are very bulky. That meant they had to be transported from the fabricator to the dam with the water side facing the trailer floor. This would have caused significant damage to any coating, requiring a further coating to be applied on site. The fabricator estimated the cost for on-site coating to be far more expensive than selecting stainless steel, in a range of €200-300k. The advantage of stainless steel surface is that if the surface is scratched it benefits from the self-healing properties of the microscopically thin chromium oxide that forms immediately. This ensures continuous protection against corrosion, so there was no issue in handling the transportation of the gates.
Still in brand new condition The latest inspection of the Lossen dam gates was
carried out in August 2024. After over eight years in service the stainless steel was found to still be in brand new condition.
Think again about stainless steel In most cases, stainless steel is overlooked for this
type of application, since the corrosion issues may not be considered as severe. However, when a designer looks further to consider the whole lifetime of the dam equipment, including all aspects of operations and future maintenance costs, then stainless steel quickly becomes a competitive option. The key benefits are: No future inspection and maintenance that would be required for coated steel. Eliminating the potential for costly downtime. No extra coating step to be carried out in a dedicated facility optimised for painting operations No need to design and fabricate a coating-friendly structure (i.e. drainage, rounded corners) A more sustainable approach in terms of recyclability and no micro plastic waste.
Top: The upstream side of the Lossen dam’s emergency flood gates are protected with duplex stainless steel plates
Middle: The installation of the flood gates in 2016 Bottom: Craning a flood gate into position
www.waterpowermagazine.com | June 2025 | 35
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