Weldability of High Toughness X100 Seamless Pipes With a New Low Carbon Alloying Concept for Arctic Offshore Structural Applications
- Stephan Scherf (Vallourec Deutschland GmbH) | Silke Harksen (Vallourec Deutschland GmbH) | Ralf Hojda (Vallourec Deutschland GmbH) | Daniel Strötgen (Vallourec Deutschland GmbH)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- high toughness, weldability, Arctic steel grade, X100, seamless pipe, CTOD, low carbon steels, strength level 690 MPa
- 0 in the last 30 days
- 10 since 2007
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Today's offshore projects access very complex fields under extreme conditions, so that structural applications must be qualified for such harsh environments. Among them are very low design temperatures down to – 60 °C and below, at which high strength levels combined with high toughness of the material must be guaranteed fully in compliance to the world's leading offshore classification companies (e.g. DNV GL and ABS).
Vallourec met this market need by development of a new steel grade for seamless quenched and tempered hollow sections with a strength level of X100 / S690 up to wall thickness of 40 mm. This presented steel grade is already qualified according to DNV GL for toughness class F (- 60 °C), grade VL FO690QT.
The new steel grade is based on a micro-alloyed low carbon concept, comprising a maximum carbon content of 0.08 wt.-% and a maximum CEIIW of 0.57 wt.-% (Pcm of 0.27 wt.-%). Both values are by far below offshore requirements and are highly beneficial for excellent weldability of this steel class. with increasing strength levels and wall thicknesses, not only the base material has to be excellent in its behavior, but also the weld seam and all its critical zones must show outstanding mechanical properties for safe operation of the offshore units. Hence, more attention has to be paid to welding procedures and consumables, so that required mechanical properties and high toughness at low temperatures (- 60 °C) can be guaranteed. The results of the presented alloy development are fully in compliance with DNV GL and ABS Offshore and Ship Rules and even exceed the requirements. This innovative concept provides for customers and designers a weldable high strength pipe with excellent toughness producible with wall thicknesses up to 40 mm for various applications in severe cold climate conditions.
Latest developments in the market for offshore applications are in need of increased cost efficiency and high reliability of pipe products which are excellent in their mechanical properties. Especially seamless hot formed hollow sections are of major importance for this industry. Accessibility of new reservoirs are challenging: offshore projects have to move from the North Sea to colder climate regions e.g. to the Norwegian and Barents Sea. In these extreme areas a high total resource of oil and gas is hidden, yet unexplored due to harsh environmental conditions like ice, icebergs, swells, storm loads and sometimes extremely low service temperatures down to – 60 °C and lower.
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