Could the Nord Stream Pipelines be Repaired?

[By Christina Benjaminsen]

"Most things can be fixed on the seabed, but how deep the damage lies is a significant factor. For depths of up to 180 metres, a diver-assisted system can be used. Operations in deeper waters, on the other hand, must be controlled 100 percent remotely,"

That's what Ragnhild Aune, international welding engineer (IWE), researcher and senior advisor at SINTEF says. Now the expertise of her and her colleagues is particularly relevant after what appears to be sabotage of the gas pipelines Nord Stream 1 and 2. 

Controlling an operation 100 percent remotely is a far more demanding exercise than repairing with the help of divers. But the solutions for this are also in place. 

Aune and her work colleagues have more experience than most with such technology. They have contributed to the development of qualification and welding procedures for both Nord Stream 1 and 2, and with lifetime analysis and assessment of possible fracture damage for Nord Stream 1.

Always ready

The SINTEF researcher believes that Norwegian actors are well prepared for what could happen in the event of an accident. "It is not impossible to repair major pipe damage," says Aune.

Damage is rare, but it has happened. Causes include material fatigue, impact, unwanted chemical processes, twisting and other unexpected physical events.

Fortunately, the Nord Stream pipelines lie in "shallow waters" - in this case, the damage sites are at a depth of around 100 meters.

This makes it possible to carry out the repairs with a diver-assisted system where emergency procedures for hyperbaric welding - i.e. welding underwater and at great depths - are already in place.

But how is it actually possible to weld underwater? The technology was developed at SINTEF and NTH in Trondheim in the seventies and eighties, says Aune.

Welding under pressure, so-called hyperbaric welding, is a time-consuming operation - it requires in practice to build an "artificial atmosphere" around the welding site itself.

This is done by lowering a chamber over the pipe damage and emptying it of water. This happens by pressurizing the air in the chamber to keep the water out.

Divers can then enter the chamber and set up welding equipment around the pipeline, not unlike what actually happens in space when astronauts go in and out of a space station. The welding itself is controlled remotely by welding operators who are on a special boat that lies above the pipe damage. Exactly how this must happen is fine-tuned according to the depth of the damage.

"The pressure at the different sea depths causes the welding arc to behave differently so that welding parameters have to be changed. So there is no 'straight ahead' exercise," says the SINTEF researcher.

Part of the "repair squad"

Aune says that SINTEF is an operational partner in PRSI, which stands for "Pipe Repair and Subsea Intervention". This is a contingency pool operated by Equinor, and consists of several oil and gas companies. The pool has access to specialists in hyperbaric welding and the necessary equipment, such as diving boats, pressure chambers and ROVs - which makes it possible to weld together pipes, among other tasks.

"We are now awaiting word from Equinor, which manages PRSI, and are prepared to contribute with our part of the work. If the damage is extensive, parts of the pipeline must be cut out and replaced with new pipe parts that are welded together with the existing pipeline," says Aune. The only thing that limits what is possible is the financial framework.

This article appears courtesy of Gemini News and may be found in its original form (in Norwegian) here.