Robust Material Qualification For Arctic Applications

Horn, Agnes Marie (Det Norske Veritas, and SINTEF, and Statoil) | Østby, Erling (Det Norske Veritas, and SINTEF, and Statoil) | Hauge, Mons (Det Norske Veritas, and SINTEF, and Statoil) | Aubert, Jean-Michel (Det Norske Veritas, and SINTEF, and Statoil)

OnePetro 

ABSTRACT

Oil and gas exploration and production is moving into arctic areas. The reduction in ice-covered areas has rendered northern routes more advantages and in addition it is anticipated that as much as 25% of the undiscovered oil and gas resources can be found in the Arctic. There is a lack of rules and standards that provide guidelines for material selection and qualification of materials for offshore and onshore structures in Arctic areas. Some actions have been taken to develop new standards e.g. ISO19906 Arctic Structure, however the guideline does not specify material requirements except for the statement that material shall have adequate toughness in order to behave ductile at low temperature. Material related standards like EN10225, API 2W and Norsok are not developed for low temperature applications and are generally applied for service temperatures down to -10°C (Norsok covers down to -14°C). For lower temperature, it is up to the designer to show fit for purpose of the selected material. Hence, one major challenge for designers is to specify adequate toughness requirements at an early stage of the design process for low temperature applications. This paper will discuss factors that influence the required CTOD toughness value at an early stage of a design process by discussing the following topics: required qualification and testing, utilization/robustness of a structure, weld defect size, residual stress, constraint effect and tensile properties.



INTRODUCTION

There is a lack of rules and standards that provide guidelines for material selection and qualification of materials for offshore and onshore structures in Arctic areas. Most of the offshore construction steels are purchased according to EN 10225 "Weldable structural steels for fixed offshore structures technical delivery conditions" which only provide requirements for Charpy values. No guidelines on CTOD toughness values are provided. For designers it can be challenging to decide the adequate CTOD requirements at an early stage when material is ordered, since limited design analyses have been carried out.