Case Study
The Aasta Hansteen gas field – located approximately 186 miles off the Norwegian coast in the deep waters of the Norwegian Sea – required a floating production platform unlike anything previously built. With water depths exceeding 4,200 feet, a conventional fixed structure was not an option; a Spar platform was the only viable solution at that depth.
The Challenge
The platform’s sheer scale set new benchmarks: a cylindrical hull 50 metres in diameter and 198 metres in total length, tethered to the seabed by mooring lines. The truss section of the Spar – connecting its main legs and brace tubulars – required nodal joints strong enough to withstand immense dynamic stresses throughout the platform’s operational life, in one of the world’s most demanding offshore environments.
The nodes needed to be larger and heavier than any cast steel nodes previously produced. At up to 117 tonnes each – seven tonnes heavier than the previous record – they pushed the boundaries of what the industry had ever attempted.
"With water depths of more than 4,200 feet this is a deep-water application and floating platforms are the only real option at these depths. Sheffield Forgemasters has a unique track record in the supply of this type of component."
Paul Mockford – (Former) Design Director, Sheffield Forgemasters
Our Approach
The team developed a specially formulated grade of steel, engineered to deliver the precise balance of strength, toughness, and weldability required for the application.
Because the strength of the material is developed through heat treatment involving water quenching, these also became the largest castings Sheffield Forgemasters had ever quenched – a further record within a record-breaking contract. Every aspect of the design, metallurgy, and production process was adapted to the extreme scale of the components.
Technip, acknowledged as the global leader in Spar design and construction, and Hyundai, engaged Sheffield Forgemasters – the only company in the world with the combination of foundry capacity, offshore design expertise, and three decades of node supply history needed to deliver at this scale.
The Outcome
The contract marked three simultaneous records: the largest contract ever won by Sheffield Forgemasters, the largest cast steel nodes ever produced, and the largest floating Spar platform ever built. All 12 nodes were designed and supplied for the Aasta Hansteen Spar – the first Spar platform of its type to operate in the Norwegian Sea, and the first built with onboard condensate storage capacity.
The castings form the critical nodal joints in the Spar’s truss section, designed to deliver high strength and fatigue resistance across the platform’s full service life in extreme deep-water conditions. The project further cemented Sheffield Forgemasters’ position as the global benchmark for ultra-large offshore cast nodes, and as the partner of choice for the world’s most technically demanding offshore structures.
