Steel Pipes from the North Sea Used in New School

For over 20 years, AF Offshore Decom has received steel from installations in the North Sea, sorted the material, and sent it for recycling. Most of it becomes reinforcement bars in new buildings or bolts for tunnels.

Now, AF Offshore Decom and AF Bygg Oslo have found a specific use for steel pipes from platforms, without the steel being recycled through remelting. The pipes are so-called bracings or struts from the platform's substructure, also known as the jacket.

A total of 28 steel pipes, each three to four metres long, was delivered to the construction site in Bjørvika in March.

"We have several interesting initiatives and projects on how we can find more ways to reuse what we receive at Vats. For example, we have delivered steel to a multi-purpose hall, marine growth is used as an additive to topsoil, and fire extinguishers are delivered for reuse," says John Roger Midtun, site manager at AF Environmental Base Vats.

The biggest challenge is that the platforms from the North Sea vary in size and weight. "Steel plates from the platforms are often easier to reuse directly. The challenge with the steel pipes in the jacket is that the dimensions vary. At the same time, they require minimal processing if used for purposes where they are not part of a load-bearing structure," says project engineer Jonas Guriby Dahl and portfolio manager Håkon Jenserud at AF Environmental Base Vats.

Through the research project "Oppsirk," AF Offshore Decom leads a consortium looking at the possibility of upcycling maritime steel. Upcycling involves reusing materials for a different purpose so that the quality or value of the material increases. This project was the inspiration when Jonas and others at AF Offshore Decom began exploring the possibilities for more reuse of the steel delivered to AF Environmental Base Vats. As a building engineer with experience from AF Byggfornyelse, he could more easily see what could be relevant for direct reuse in a construction project.

After an internal announcement, he got a response from Mohsen Shafighi at AF Bygg Oslo. Shafighi works as a design and environmental manager on the new  School in Bjørvika, responsible for foundation work and cast-in-place concrete. Oslobygg (Oslo Municipality) is the client.

Oslobygg requires reuse in its projects. At the new School in Bjørvika, at least two reused materials must be incorporated into the project.

The jacket often arrives standing at the AF Environamental Base. Marine growth is removed before they are toppled, i.e., laid down in a controlled manner.

"Since this is a pilot, we removed the pipes closest to the ground before toppling was carried out. This allowed us to map the dimensions and look more closely at the possibilities," he says. Going forward, this mapping can take place earlier, before arrival at Vats.

Often, the dimensions are already described in the design phase based on what is standard. "When working with materials from the North Sea, you have to use the steel and dimensions available. Going forward, the ambition is to get involved earlier in a construction or infrastructure project. In this case, we were dependent on Mohsen at AF Bygg Oslo being engaged and pushing to make this happen," says Jonas.

The new school is being founded with steel core piles. In this process, the bracings from the platforms are placed in the ground first, then steel casing pipes are placed inside the bracings down to the bedrock. Finally, massive steel piles are installed in the casing pipes.

"When the pipes are placed, they are filled with concrete and function as corrosion protection. This is an important function in an area where the ground mainly consists of marine sediments," says Mohsen, emphasising that this project is not only an important contribution to increased reuse. It is also a good example of how we can collaborate internally to find good solutions across units.

AF Offshore Decom has sorted over 400,000 tonnes of steel for recycling. Most of the steel is sent to a recycler that emits 85% less CO2 compared to traditional iron ore-based production. The steel is turned into reinforcement bars for new buildings and bolts for tunnels. This process results in a reduction of 1.9 kg of CO2 emissions for every kilogram of steel recycled. Direct reuse would further enhance environmental savings.

Jonas wishes he could supply twice as many steel pipes. A pilot project like this might make more designers aware of the possibilities of reusing steel. The opportunity to reduce climate emissions by 70 to 80% is significant. Our ambition is to find profitable and climate-friendly solutions where a higher proportion of the steel we receive can be reused directly for new purposes without remelting.