Cleaning up in the Gulf

December 12, 2011

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It has been nearly two years since the Deepwater Horizon exploded and sank into the Gulf of Mexico. For most of us, the story slipped off our radar a few weeks after the rig exploded (April 20, 2010); the story made headlines again when the well was capped temporarily nearly three months later (July 15, 2010) and again when it was shut down permanently (Sept. 19, 2010).

What has happened since then? The Gulf Coast Ecosystem Restoration Task Force continues to assess and mitigate the effects of oil contamination along the beaches of Louisiana, Mississippi, Alabama, and Florida. The analysis seems well-organized, breaking down the contaminated areas into three zones—subtidal, intertidal, and supratidal—and providing separate reports on the effects on fish, birds, turtles, and other wildlife. So far, so good. But what about the other cleanup?

The other cleanup, you ask? Well, yeah … after burning for two days, the rig sank into the gulf. Although the Bureau of Ocean Energy Management hasn’t made a decision on this particular rig—it weighs more than 30,000 tons and is submerged in more than 5,000 ft. of water—in most cases, rigs must be removed when they are taken out of service. Intact rigs present a challenge: How do you cut apart an oil rig’s structure without compromising its structural integrity? Cutting up a collapsed, sunken oil platform has that problem and others.

Enter Versabar’s VB-10000, a floating crane designed for this task. One of many inventions of Jon Khachaturian, Versabar’s founder, this $100+ million beast consists of two gantries that span two barges. Each gantry has a fixed foot on one of the barges and a pivoting foot on the other barge, which allows it to articulate, absorbing wave motion without stressing the structure.

What is the VB-10000’s truss system made from? Glad you asked. It’s made from the structural material that has the optimum strength-to-weight ratio and loading characteristics: Tube! A lot of tube. Each truss weighs 3,500 tons.

“The largest pipe is 60-inch diameter,” said Tom Cheatum, Versabar’s director of sales and marketing. “The heaviest wall thickness is 1-1/2 in.”

Before it was turned into tube, the raw material was API 2H grade 50 plate. It was rolled and welded using submerged arc welding (SAW); the sections were assembled into trusses using flux-cored arc welding (FCAW). All told, building the project took about nine months start to finish.

How much can it lift? In its current configuration, each of the four winches has been proof-loaded to 1,500 tons, for a lift capacity of 6,000 tons.

“It’s the largest American-flagged lift vessel in the world, and certainly the largest American-made offshore heavy lift system ever built,” Cheatum said.

How big, exactly? It’s 25 stories tall and, well, wider than an oil platform.

“You could fly a 747 through it,” Cheatum said. “The pilot would have 5 feet of clearance on each side.”


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Eric Lundin

Editor
FMA Communications Inc.
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