In connection with the linking of the district heating network in Stockholm, FORCE Technology has tested and inspected the kilometre-long district heating pipeline – on land and at sea.

Carrying out the demanding task of linking the central and southern district heating network in Stockholm’s inner city has been something of a challenge. Fortum Värme, which supplies district heating to 75% of Stockholm, implemented the project with a view to modernising energy supply and enhancing production and distribution efficiency.

Under Riddarfjärden

This meant laying several kilometres of district heating piping under Riddarfjärden – one of Stockholm’s large fjords. FORCE Technology has been involved in the project from the earliest planning stages right through to inspection of the pipeline 20 metres below the surface of the fjord.

Ultrasound and X-rays

“We carried out constructional control, including calculations, dimensioning and safety inspection. We also carried out a series of ultrasound and X-ray inspections of piping and insulation to check tightness and corrosion protection. A challenging task that had to be implemented on land and at sea”, explains Joakim Lindahl, head of division at FORCE Technology in Stockholm.

The district heating pipeline was delivered in lengths of 16 metres and then welded together to make lengths of 200, 300 and 500 metres. The pipes were then towed into place in stages and welded together before being lowered into the fjord.

On the fjord

“Inspection work on the fjord has been the most challenging of all”, continues Joakim Lindahl. He adds, “We found ourselves with our equipment in dry docks 20 metres under the surface of the fjord. Here we carried out about 150 tests using different inspection methods.”

In autumn 2006, Fortum Värme began the work of linking Stockholm’s inner city district heating network, a task that was completed in the spring of 2008. With the new network, Fortum Värme is better able to exploit the capacity of the district heating stations. For example, some district heating stations can lower production in summer while others increase their output. In addition, in winter, stations can use a variety of different fuels and thus take into account relevant financial and environmental considerations.

Good sparring

Niklas Eriksson from Fortum Värme has this to say about working with Force Technology, “We chose to bring FORCE Technology on board because we have confidence in the company and because we know they have the necessary capacity to work on a project of this magnitude.”

He goes on, “We are extremely satisfied with FORCE Technology’s performance. They have been both flexible, accommodating, open in their communication with us and used their critical professionalism during the whole project. We are extremely satisfied with our collaboration and the technical project result.”