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Challenges for the offshore industry maintenance

21 November 2023
Offshore wind maintenance challenges
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Challenges for the offshore industry maintenance: Cut and hold, or cut and drop?

Credeblug and TECNALIA have settled that question by validating the first grab, cut and hold tool for subsea power cables.

It’s a sunny day of May in Bizkaia. My three-year-old just spotted some luscious red cherries on the village tree, swaying gently in the fresh breeze. Cheerily chirping birds fly around. Sweet sound, but fruit-wise they are unfair competition: not limited by height. Unfazed, I pick-up my son, he hops onto my shoulders and here we go - try to grab the tempting fruits.

But the cherries are just a bit too high. Of course. A series of frustrated attempts and pain sets in my calves and shoulders. The weight of love, I suppose. But finally, this one alluringly red cherry seems within reach of his plump little fingers. Yes son! Grab it, cut it off the branch, and… please don’t drop it on the ground.

Drop it after the cut: a challenge for the offshore industry maintenance

Drop it after the cut. That would be painful for a coveted fruit. But far more so for a power cable in the North Sea, that you’ve been sent to repair in the winter waves. But that’s exactly what you have to do. Because that’s what cable cutting tools do. And that, ever since subsea cable repair operations begun in the late 19th century.

So, you’re dangling your cutter near the seabed, hoisting down 30 meters from the deck of your ship, rolling in the waves. After much groping, your straining eyes finally spot a faint bit of cable on the screen. Your crane operator skilfully weaves the cutter’s jaw onto the cable. Cut. And, immediately, the cable ends fall back to the darkness. Outside your screen. Dropped somewhere on the seafloor.

Now you have to repeat the search in the dark, to grab one of the cut cable’s end, hoist it up on the deck and prepare it for the splicing team. If you pull it off, electricity will come back to the island. Or the offshore wind farm will stop losing nearly a million euros a day. But the waves are growing ever more menacing. And like generations of mariners before, you really wonder - why in the world can’t we just hold onto the stuff we just cut? And that’s a good question. I mean, even a three-year-old can do that.

Improvements in handling tools for subsea cable repairs

Located in the village of Azpeitia in the Basque Country, Credeblug is a family business founded in 1965. Blug is successful in exporting its handling tools across the world and is the winner of many prizes for the quality of its in-house manufactured products, such as the IBJ “Best Grab” award in 2017.

In TECNALIA’s offshore team, we have partnered with them within Wind2Grid, an R&D project supported by a consortium of Basque companies active in the offshore wind sector; and the Basque Government’s Hazitek programme. Blug’s main objective was to explore a new market: handling tools for subsea cable repairs.

Driven by the fast growth in offshore wind, the subsea power cable market is growing some 15% a year and, inevitably, so is the demand for cable repair operations. As far as handling tools for these operations, the most obvious and demanded improvement is the capability to hold on to what you’ve just cut.

  • This would save the repair team much pain, much risk, and much time and money, that corresponding to the additional deployment of another dedicated grab tool, vessel passes and search for each cut end.
  • This may take hours of stressful and uncertain work. And there’s two cuts per repair. By the way, the vessels mobilized for repair operations routinely cost over one hundred thousand euros a day.

Credeblug’s innovative tool combines a cable grab and a cable cutter in one single, hydraulic-powered tool. Compared to existing cable cutters, the grab’s long arms greatly facilitate the localization and picking-up of the cable from the seafloor, because the arms allow for much deeper probing inside the seabed where the cable is typically buried.

It can be used like a grapnel, really. Once the cable is grabbed and secured underwater, the guillotine cutter is activated. Most critically, the grab hangs on tight to the cable after the cut, instead of dropping both cut cable ends to the seafloor. A cut end is then hoisted up securely by the grab, immediately delivered to the deck crew to prepare for the splicing team – no need to deploy another grab tool overboard in the menacing waves…

Successful validation at sea

After extensive testing in Credeblug’s plant in Azpeitia, in March 2023, we conducted its validation at sea. These tests were conducted from the quay of Marbeco, a port services company in the port of Bermeo. Several grab, cut and hold operations were successfully conducted on a real, fully armoured power cable in the water.

As usual, visibility was close to zero near the seabed, which was made of very soft silt where the cable’s own weight was sufficient to sink it and make it invisible to an underwater camera. Even in this controlled environment, the challenge of searching for the power cable and positioning the handling tool were very obvious. This was greatly facilitated, however, by the long arms of the grabbing tool, which allowed for much better groping inside the seabed than would have been possible with existing cable cutters.

The grab worked as designed, grappling the cable from inside the silt and immediately securing it tightly. With the cable grabbed and secured, the guillotine cutter then worked as planned each time. And each time, the grabbing tool held the cut end securely, allowing for immediate hoist up and recovery of the cable end. No cut and drop, no additional deployment of a grabbing tool, and no additional cable-end searching operation. This seems so simple and logical. But it is no exaggeration to say that subsea power cable repair crews worldwide have been waiting for this for tool over a century.

What about the cherry? I’m happy to report success: not dropped. Cut and held. And judging from my boy’s reaction, when picked off the tree with your own grab, cut and hold tool – Mmmh! they just taste much better. So much better that another attempt is immediately in order. Birds beware!

Here we go – cut and hold please!

Joannes Berque

ABOUT THE AUTHOR

Joannes Berque

Joannès Berque is a researcher in renewable energy at TECNALIA. After a PhD in physical oceanography from Scripps in California, he worked with the United Nations for the sustainable use of coastal resources in developing countries. He joined TECNALIA in 2012 and develops new solutions for an affordable, safe and sustainable energy future.
Author:Joannes Berque
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