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North Sea awe

Written by  Elaine Maslin Thursday, 01 June 2017 00:00

The awe inspired during the early days of the North Sea industry was back and in full force for the world’s heaviest offshore lift. Elaine Maslin reports.

Pioneering Spirit, closing in on Brent Delta. Photo from Allseas.

They say good things come to those who wait. On 28 April, a lucky few witnessed a long-awaited, historic lift, 186km northeast of Shetland in the UK North Sea.

After 40 years of production (and more than 900kg annual cheddar cheese consumption), Shell’s 24,300-tonne Brent Delta platform topsides was lifted off its massive concrete legs in one piece by Allseas’ Pioneering Spirit.

Just three days later, the Brent Delta topside had travelled, in one piece, some 380mi to off the coast of Hartlepool, England, where it was transferred to a barge to be skidded on to Quay 6 at Able Seaton Port, for dismantling.

This huge feat of engineering harkens back to the pioneering days of the offshore industry, when the four massive Brent platforms were first installed, three on concrete bases and one on a 31,500-tonne steel jacket. Like then, the scale of the work and the engineering involved made headline news and captured the popular imagination.

The big difference, however, was that Allseas’ Pioneering Spirit was able to lift out the platform – which had been installed in modules – in one piece, a feat that many thought couldn’t happen. The alternative, taking it apart offshore, in a reverse installation, would have been “a nightmare,” according to Alistair Hope, Brent decommissioning project manager, Shell.

Also unlike then, Allseas has access to sophisticated simulators, in Delft, Netherlands, to “trial run” the lift. But, what has driven the ability to perform such a lift (and, in theory, lifts up to 48,000-tonne), using the 382m-long, 124m-wide Pioneering Spirit, is the sheer scale of the hydraulic and compressed air system on board the vessel, combined with dynamic positioning (DP) and powerful controls and computing power to make it all work together – active heave compensation (AHC) on steroids.

A Delta challenge

 

Brent Delta’s topside has three main levels (module support frame, module deck and drilling deck) sitting in 142m water depth, and measuring 74m x 47m, and 44m high to the helideck and 132m-high to the flare tip.

To remove the topsides, the Pioneering Spirit’s eight sets of lifting beams – each with four fast lift cylinders and two hydraulic AHC cylinders, totaling 6000-tonne lifting capacity – worked with the vessel’s DP system and vast 700,000-tonne capacity ballasting system (comprising four pump rooms connected to 87 ballast tanks) to remove the topside from its legs within 12 hours.

After moving the vessel’s bow slot around Brent Delta’s legs (with about 5m tolerance each side), each set of beams was moved into position and connected, via yokes (two weighing 80-tonne and one 135-tonne), with the topside, where it maintains position using the three-way movement AHC system.

A Kongsberg positioning system (driving 12, 4.7m-diameter, 80-tonne-a-piece thrusters) guided by GPS keeps the vessel within about 1.5m of its position. The topsides lifting system, using an optical gyroscope to see where the platform is, compensates for the rest of the motion to within centimeters. All of this is run via remote control, and using huge computational power, to combine all the relevant positioning data – including live and predicted metocean data – and process it live in order to maintain the system’s accuracy.

Once all beams were in place, the vessel started lifting, first through ballasting, to about 80% of topside weight. The final 20% was lifted using compressed air, achieving a “fast lift,” to clear the topside from the concrete legs in 11 seconds, with quick drop ballast tanks being used to follow the motion through in three minutes. The operation is powered by eight, 11.2MW engines across four engine rooms for redundancy.

While it has been a long wait for Allseas, and Shell, to get to the Brent Delta lift, there’s no rest for the Pioneering Spirit. The vessel, which consumes around 200-tonne of fuel a day while steaming and 70-tonne a day while positioning, is contracted to lift the other three Brent topsides, including the 31,000-tonne Brent Charlie platform, as well as installing the huge Johan Sverdrup topsides (weighing 19,000-26,000-tonne) for Statoil, offshore Norway. Immediately following the Brent Delta project, however, the vessel went back to its base in the Maasvlakte, Rotterdam, to mobilize for her next job, laying the TurkStream pipeline in the Black Sea. In 2018-19, Pioneering Spirit will also join Solitaire, laying the twin-pipeline Nord Stream 2 over 1200km through the Baltic Sea.

Lift learnings

And we have lift off. Photo from Allseas.

The first time doing anything offers scope for learning – the Brent Delta lift will help make the future Brent lifts easier. Elaine Maslin reports.

Being overly cautious might be an understatement, but also understandable, when it comes to being the first operator to put the world’s biggest vessel to test, lifting some 24,200-tonne of steel off its legs out in the harsh northern North Sea.

However, lifting the Brent Delta platform has also given Shell and Allseas a chance to see how the next three Brent platforms can be taken out more efficiently, from re-assessing the structural reinforcement required to redesigning lifting points.

“When we started, single lifting was completely new for everyone,” says Allseas’ founder Edward Heerema. “Calculations of reinforcements were initially made with the same great conservatism as for a newbuilt structure that has to withstand the seas for 40 years, which is more than what’s needed for removing a facility. We have learned big lessons. There’s a lot of strength in the topside already. It can be allowed to deform during a lift and during transport, as long as it stays safely together.”

On Brent Delta, eight cruciform lifting points, weighing 120-tonnes in total, were added to the underside of the platform, for the mating with the Pioneering Spirit’s lifting arms. Structural reinforcement was added to the lower decks and three shear restraints, at around 12m-diameter and weighing about 36-tonne each, were installed in each leg, to hold the platform in place after leg cutting.

Bravo on the horizon

Ready for lift off. Photo from Allseas.

By reassessing the engineering codes and allowing a degree of plastic deformation during the lift, the amount of reinforcement work required can be reduced. A lot of this work will be done on Brent Bravo this summer. Spacers will also be fabricated to go on top of the lifting yokes, so that the lifting arms can reach the lifting points on the taller Brent Bravo facility.

“With Delta, we had a very conservative design: eight lifting points, when we would only need six and a lot of steel reinforcement work,” says Alistair Hope, project director of the Brent Decommissioning project, Shell.

Hope says that the learnings from Delta will mean that only about a quarter of the work will be needed for Bravo. “The beauty of this project is that we get to do it four times. Bravo will be considerably more efficient, and so it will be after Bravo,” he adds.

Furthermore, for Bravo, Shell’s engineers came up with an idea to use concrete, for the lifting points, instead of steel. This will be much easier to install, says Duncan Manning, business opportunity manager for Brent, Shell, instead of 15-tonne of steel for each lift point. Welding onto 1970s steel panels isn’t an easy process, he says, having to pre-heat the steel, etc. Instead, creating a box and pouring in the concrete would save time, cost and logistics. “It’s been quite a game changer,” Manning says.

Taking a more realistic approach to what safety margins need to be met will also reduce scope, Heerema says. “You don’t plan for having a storm with 7m wave height on the way to shore, as you know that will not happen,” i.e. if there’s a storm coming, the lift will not take place.

More lessons will be undoubtedly learned on Bravo, and then Alpha, before Charlie – the only Brent facility still in production – is decommissioned.

For Allseas, the learning will continue, as every platform will offer a unique challenge. “Years ago, I thought, once we’ve lifted one it would be easy to adapt to the next one,” Heerema says. “But in fact, every platform is different to the other. Every time there is so much to think about, problem solving, getting the yokes in the right place, fitting them without spending too much money on them. Making use of the intrinsic structure of the topside. The difficulty is that composition of each platform is different. Some are strong, some are flexible and weak.”

Those who dare, win

 

It could be easy to understate the conviction it takes to see through the design and build of a vessel the size of Pioneering Spirit.

Each step of the build, inauguration and then launch of the Pioneering Spirit has felt like this mega-vessel’s major milestone – until the next one.

Having broken the record for the heaviest offshore single lift with the Yme platform (13,400-tonne), offshore Norway, in 2016, and then the Brent Delta topsides in the UK (24,200-tonne), in late April 2017, work will quickly shift to Pioneering Spirit’s next job: its first pipelay project, TurkStream. After that, it will then be the three Johan Sverdrup topsides (19,500-26,000-tonne) installations – the first in 2018 and the second and third in 2019 – which will set yet more milestones for this mega-vessel. The Pioneering Spirit also has work on Nord Stream 2 lined up, and the Brent Bravo lift, setting another record, at 26,000-tonne, which will later be outdone by the Brent Charlie removal, at 31,000-tonne.

Work on the vessel also continues. Next year, an additional 5000-tonne tub-mounted crane will be added to her deck. Fabrication work on its 20,000-tonne capacity jacket lifting system is due to start this year, with installation expected in 2019.

For Allseas’ founder Edward Heerema – who has spent nearly 30 years working on the concept, design and then build of the Pioneering Spirit – the first lift, Yme, could be viewed as the most significant – finally proving the concept. Yet, every project offers new challenges, and the insatiable engineer has even bigger-yet challenges he would like to tackle, such as Amazing Grace, a single lift vessel that would dwarf Pioneering Spirit.

It’s been a long journey since Heerema set up Allseas 32 years ago, with a single pipelay vessel – Lorelay, the first DP pipelay vessel in the world. Allseas has grown and has had no qualms about outstripping its own capacity in the past: Pioneering Spirit doubles the pipelay capacity of Allseas’ Solitaire, which had been the biggest pipelay vessel in the world.

Pioneering Spirit has been in gestation a long time. “We had the idea 30 years ago, when we were a small company. We just had Lorelay and no other money than borrowed money,” Heerema says.

Now, in addition to putting Pioneering Spirit to work, Allseas continues work on Amazing Grace. “We are steadily continuing the design,” Heerema says. “The size of the ship, the dimensions and motion compensation for that ship, is a lot different to Pioneering Spirit, and it takes years to work out a solution you’re happy with.” He says that it’s not just a case of have 50% larger beams, it has to be thought through differently.

There are few companies that could take on such a challenge. “If you have an individual owner, if he decides to take a risk, it’s his risk,” Heerema says. “If you have a big company on the stock market, with analysts only interested in quarterly results, bringing a large and daring concept to life doesn’t fit the mentality and culture of a big corporation. I’m a real engineer, almost only an engineer, so I can go very far in gauging if something can work well or not, and I can combine that with taking the full responsibility on myself. That’s the privilege I have.”

However, he also credits having a creative nucleus – hinting at the group effort behind this vessel, as well as the creativity involved in finding solutions for its multitude of systems.

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