2 min

Ultrasonic testing in Nordic region's longest railway tunnel

Kiwa has performed an NDT inspection with ultrasound on the rail joints of the Nordic region's longest railway tunnel. This 22 km long new modern high speed railway line called Follobanen, is located between Norway's capital Oslo and the town of Ski.

Bane NOR, responsible for the maintenance, operation and development of the Norwegian railroad network, has engaged Acciona Ghella Joint Venture (AGJV) to build the main part of the new tunnel. Bengt Åge Fjørtoft, Quality & Systems Manager at AGJV, tells about this extensive project that has been running since 2015, and how Kiwa is involved.

Drilling and welding

“When we drilled the tunnel, we mostly employed around 800 people. Currently, about 380 are working on the plant, including subcontractors”, says Fjørtoft. “The welding of the railway rails is done with flashbutt welding . This welding process provides very high quality compared to aluminum thermal welding, which has been common to use on railways in Norway. “ Fjørtoft continues: “To be able to weld rails with this method directly on the construction site, our subcontractor Vossloh uses a fully automatic mobile welding machine (mobile flashbutt welding machine). It has given very good results.”

Kiwa NDT inspection

When the rails have been welded and sanded, the inspection can be carried out. According to the current standard NS-EN 14587-2, there are requirements for bending test and visual inspection of the rails. In addition, Bane NOR has its own requirement for ultrasonic testing. Ultrasound is a common NDT method which is used to detect any defects and damage in connection with welding in various materials. Kiwa has many years of experience in NDT and is accredited for ultrasound testing according to ISO 17640.

Fjørtoft tells about the inspection: “The requirement is that 15% of the rail joints must be inspected, the tunnel is 20 km long, and the inspector from Kiwa has had to move 8-9 km in each direction from the access to the tunnel runs. He has used an electric bicycle as a means of transport. The entire inspection has taken over a month. So far, only a few minor grinding errors have been revealed.”

Demonstrated high competence

Fjørtoft emphasizes that knowledge of the current regulations was decisive for Kiwa receiving the assignment, he says: “Kiwa could demonstrate good knowledge of requirements and standards.” He adds that AGJV has used several services from Kiwa during the project: “Kiwa has on several occasions taken core samples of concrete for us. Kiwa has also performed adhesion tests to test how well shotcrete sits on surfaces. In addition, Kiwa performed a visual welding inspection of reinforcement at the element factory earlier in the project.“

See how Kiwa inspects the railway tracks in the tunnel on Follobanen using ultrasound in this video:

About the Follo Line project

Follobanen is a new double railway track between Oslo Central Station and Ski Station. The entire Follo Line project includes 64 km of new railway tracks. Follobanen includes the first Norwegian, long railway tunnel with two separate tunnels. Bane NOR plans to start traffic through the new tunnel in December 2022.

Ultrasound testing by Kiwa Norway

Read more about Kiwa Norway’s Ultrasound testing (UT) services.