Material Challenges For Arctic Offshore Applications, a Reliability Study of Fracture of a Welded Steel Plate Based On Material Toughness Data At -60°C

Horn, Agnes Marie (Det Norske Veritas) | Hauge, Mons (Statoil)

OnePetro 

ABSTRACT:

A five year Arctic material research project supported by The Research Council of Norway, oil companies, offshore suppliers and contractors is run by Sintef. The main goal of the project is to establish criteria and solutions for safe and cost-effective application of materials for hydrocarbon exploration and production in Arctic regions. One main task for the project is to carry out material and toughness testing of carbon steel at -60°C in order to qualify steel for low temperature applications. The obtained toughness results so far shows large scatter and with some results below code requirements set by e.g. ISO 19902 for fixed steel offshore structures and DNV-OSF-101 for seam welds for offshore pipelines and risers It must be mentioned that the test program is comprehensive and not required by any of the recognised international codes discussed in this paper. This paper will address the qualification of materials and welding procedures in recognised offshore codes today, their limitations and challenges they can cause when applied at very low design temperatures. In addition, a case study where the annual probability of failure for a welded steel plate has been evaluated based on the achieved material test data at -60°C from the Arctic Material R&D Project.



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. Some actions have been taken to develop new standards e.g. within ISO19906, 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 temperatures. The case study has evaluated data for a 420 MPa welded steel plate, where different hypothetical surface flaws have been analysed.