- Explaining spar design
- Platform site in deep water
- Strength through heat treatment
A Sheffield Forgemasters’ division has a notable new contract for engineered steel castings. Vulcan SFM will produce cast nodes for the world’s largest floating spar gas production platform.
Vulcan SFM is a specialty design/engineering division supplying the offshore oil-and-gas exploration market. It is an operating unit of Sheffield Forgemasters International Ltd., the British engineering group that has melting and casting operations for steel ingots, foundry and forging capabilities, and large-dimension machining operations. It is expected to complete the material supply by March 2014.
SFIL produces some of the largest custom-engineered castings in the world, some of these weighing up to 350 metric tons. It is the world’s leading supplier of castings to the offshore sector, having designed and manufactured more than 46,000 metric tons of components for such projects.
A spar is a type of floating oil platform used in very deep water, usually as an alternative to conventional platforms. It consists of a large-diameter, single vertical cylinder supporting a deck. The cylinder is weighted at the bottom, and the whole structure is anchored to the seabed.
Statoil ASA will operate the new platform on behalf of itself and two co-investors, OMV and ConocoPhillips. It will be anchored in the Aasta Hansteen deepwater field off Norway.
The spar’s builder is Technip, a specialty contractor of spar platforms. Vulcan SFM will design and supply 12 cast nodes structures, the largest of which weigh 117 metric tons, seven metric tons heavier than the largest nodes ever produced up ‘til now.
“The project to develop the Aasta Hansteen gas field requires the world’s largest spar platform,” according to Paul Mockford, design director at Vulcan SFM. The platform will be located approximately 186 miles off the Norwegian coast, and it will be the first spar platform built with storage capacity. It will be able to store about 25,000 scm of condensate, and export gas via the Polarled pipeline to Norway’s Nyhamna gas plant.
Vulcan SFM will deliver 12 extra-large castings for the structure, which will be operated by Statoil ASA on behalf of its partners OMV, ConocoPhillips and Statoil. These steel castings will form high-strength, fatigue-resistant nodal joints connecting the main leg and tubular braces that form the lower, truss section of the spar platform.
“The Aasta Hansteen Spar is the largest diameter spar which has ever been built, with a diameter of 50 meters and a total hull length of 198 meters, most of which is below the surface of the sea,” Mockford continued. “With water depths of more than 4,200 feet, this is a deepwater application, and floating platforms are the only real option at these depths.”
He noted that the castings would be produced in a specially developed and proven grade of steel offering a balance of strength, toughness, and weldability. “The strength is developed through heat treatment,” he said, “involving water quenching, and these are the biggest castings we have ever quenched.
“Like all the cast nodes we have designed and supplied over the past 30 years, these castings will need to withstand immense stresses when in use,” Mockford emphasized.