Upgrading bridge construction


The 60-year-old heavily trafficked Söderström Bridge needed a heavy-duty overhaul to improve its safety and carry heavier traffic flows.


The old beams under the rails will be switched to high-strength Forta stainless steel girders, a cost-efficient, futureproof solution that minimizes maintenance and reduces carbon footprint.


Steel grade: 600 tonnes of high strength Outokumpu Forta LDX 2404 duplex stainless steel

An old suburban railway bridge between Stockholm’s Old Town and the trendy district of Södermalm is being repaired by using stainless steel structures. The 174-meters-long Söderströmsbron consists of four railway bridges and is one of the busiest bridges in town. It is a vital part of the city’s subway and suburban railway infrastructure, with some 330,000 passengers daily.

The five-track carbon steel bridge, built in 1957, will be repaired for safer travel and higher traffic volumes in the future. Old bridge beams underneath the rails will be changed to that of a stainless steel structure within a timeframe of two years, 2017–2018.


Ready-made delivery

“It’s a one-meter-tall pre-fabricated beam structure consisting of two beams for each track, connected by a truss structure. We deliver altogether 600 tonness of high strength Forta duplex stainless steel to the project, explains Mladen Perkovic, Head of Outokumpu Plate Service Center Nordic in Degerfors, Sweden.

Outokumpu delivers ready-made beam trusses to the renovation project. The heavy plates to be welded to finished beams come from Outokumpu’s rolling mill in Degerfors. Outokumpu’s partner Stål & Rörmontage AB fabricates the final bridge components, which are then lifted to their places by a crane on a pontoon.


Easy maintenance

The new girders in high strength duplex stainless steel Forta LDX 2404 minimize the need for maintenance. “Stainless steel beams will pay off within 30 years when anticipating the repainting of the carbon steel beams. All maintenance can be done on the spot so no road closures or traffic diversions are needed. This is very positive from the environmental perspective and a clear added value to the customer,” Perkovic points out.

Using stainless means that corrosion problems, typical to heavily used bridges such as this one on Lake Mälaren, are avoided altogether. “The life cycle of a stainless steel bridge is considerably longer than that of a traditional carbon steel construction. Stainless means a low carbon footprint and cost-effectiveness, and it looks good, too. I believe we’ll see a lot of stainless steel bridges in the future. This is just the beginning,” foresees Perkovic.

Recommended products and insights

Degerfors PSC, Sweden

Expertise built over more than a century sets Outokumpu’s Degerfors Plate Service Center apart from its competitors. Deep expertise and advanced innovation make Degerfors PSC the premier solution for complex projects.

Degerfors Quarto Plate, Sweden

Outokumpu’s largest plate mill, Degerfors would be noteworthy for its output alone. But Degerfors is also famed as a leading global manufacturer of tailor-made stainless steel quarto plates.

How to build a bridge that saves a fortune

Our expert Andy Backhouse explains how the right grade of stainless steel can create a structure that resists corrosion and minimizes maintenance needs over a typical bridge lifetime.

Stainless steel for bridges

Bridge projects are in a class of their own – just like Outokumpu stainless steel. Marked by harsh environments, heavy lifetime usage and high aesthetic expectations, bridges demand special considerations upfront if they’re to go the distance.


The Forta range contains duplex and other high strength stainless steels that enable thinner structures and weight reduction (measured in Rp0.2 > 400 MPa. PRE 16 to 43).

Specialized components

Specialized components for specialized needs. Beams, hollow section tubes and bent profiles for structural design

Recommended reading

Global megatrends article

Taking the sustainable path towards building bridges that endure and inspire


Materials in bridges: a designer’s perspective


Design standards and sustainability in structural engineering


Welding of stainless steel bridges


New opportunities with modular bridges


Sustainability is driving the adoption of duplex steel

Case Sodertalje bridge

Bridging the way to a more sustainable and economical future


The future belongs to sustainable bridges


Economic drivers for selecting stainless steel