t was the heaviest-ever offshore lift. Twelve huge propellers linked to satellite positioning and wave-watching systems kept the world’s biggest ship steady within half a metre of its targets – eight lifting points welded to one of Europe’s largest oil and gas platforms.
The Pioneering Spirit’s ability to stay so still at sea is a triumph for all those involved in designing, building and operating the largest vessel in the world.
But guiding the ship’s powerful lifting beams into the receptacles on the underside of the Brent platform demanded yet more ingenuity.
A sophisticated system of sensors and gyroscopes guided huge robotic lifting arms fitted to both bows into the platform’s steel sockets, even as the ship rose and fell a few metres with the waves.
The 382-metre-long vessel then swiftly raised the structure from the three concrete legs that had supported it for four decades.
With Brent Delta held high above the waves by 16 beams each weighing more than 1,600 tonnes, the ship transported it to north-east England.
After arriving near the coastal town of Hartlepool on April 30, Pioneering Spirit transferred Brent Delta onto a 200-metre-long barge for a short final voyage into a specially adapted decommissioning facility run by Able UK.
The landmark operation was the culmination of years of preparation by Able, Shell, the hundreds of engineers involved in constructing and operating the Pioneering Spirit, and a man who has dedicated much of his life to designing and building it.
“This is my life’s dream,” Edward Heerema, founder and President of ship owner Allseas, said. “I’ve been working on this for 30 years.”
Despite being the boss of the company, Heerema remains a hands-on engineer. He oversaw the removal of the topside, his team’s biggest lift so far, from the bridge. And he was on board for the Pioneering Spirit’s maiden heavy lift – a 13,500-tonne platform off the coast of Norway in August 2016.
Before the Brent Delta lift could begin, the ship filled its ballast tanks with water to ensure its two huge bows passed safely beneath the underside of the platform.
Then the captain carefully guided the bows until the platform stood safely in a lifting bay bigger than a football pitch.
Eight giant lifting beams on each bow then extended under the platform, which weighs as much as around 2,000 double-decker buses.
Camera and radar-guidance systems at the end of each beam then helped guide the coupling points onto the underside of Brent Delta, while computers worked to keep everything under tight control, despite the sea swell below.
“The ship’s system looks ahead at the sea motion so it can take into account wave height,” said Allseas site manager Daan Akerboom.
“We also use a military-precision type of GPS receiver. All that data goes into a computer that controls the propellers and makes sure that the ship stays stable within a footprint of half a metre.
“The beams then compensate for that half-a-metre movement. The ship can move up and down but the beams make sure that the centre of those sockets stay where you want them to be. The beams are standing still while the vessel is moving underneath it.”
The lift begins
Once the ship and topside were securely connected, some of the water ballast weighing the ship down was pumped out to transfer around 80% of the topside’s weight onto the vessel.
The Pioneering Spirit then performed another great feat of marine engineering. Using compressed-air pumps on each arm, it raised the 24,200-tonne platform safely away from the legs in 16 seconds.
“It’s always exciting when you do the quick lift,” said Captain Fred Regtop. “To see such a huge weight being lifted so swiftly is really magical.”
The Brent field began production in the 1970s. Delta is one of four large platforms at the field, three of which have ceased production over the last six years.
In total, around 470 oil and gas installations in the UK North Sea will need to be removed over the next few decades.
Heerema hopes the Pioneering Spirit will lift many of those platforms, but he is already dreaming up a vessel capable of taking on the world’s largest offshore installations.
“We have an idea for an even bigger ship for the very biggest platforms,” he says.
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