Session: 02-11-02 Fatigue and Fracture Reliability 2

Paper Number: 104845

104845 - Some Background for the 2023 Revision of the Recommended Practice DNV-RP-C203 Fatigue Design of Offshore Steel Structures 

The recommended practice DNV-RP-C203 Fatigue Design of Offshore Steel Structures has been regularly revised since it was first published in 1998. The reason for these revisions is new data and new learnings from design and in-service experience from installed structures. The standard is also being used for new types of details and structures, and this requires new information to the users of the document. New literature is being published and other standards related to fatigue design is being revised; therefore a regular revision of this document is needed.

The recommended practice DNV-RP-C203 is said to be the most frequently used standard in the world today for design of offshore structures. The standard is being used for fatigue design of different structures such as jackets, risers, pipelines, semisubmersibles, spars, floating production vessels, fixed and floating structures for support of wind turbine structures, different types of connectors, etc. This implies that the content needs to be applicable for many different details where the efficiency and reliability of the methods used are being challenged by the industry. This implies also that significant feedback is made to DNV from different development projects, and it is expected by the industry that new experience and learning is continuously  included in revisions of the standard. Earlier some of the background for the standard has been presented at OMAE conferences in 2005, 2010 and 2016. Some of the content has also been published in a book from 2016. Several improvements of the standard are being included in the 2023 edition and it is appropriate to explain the background for the changes made since 2016 in more detail in a paper. Examples of changes are slopes of the highest S-N curves for welded connections that are improved by grinding, and the transition point between the left and the right part of the S-N curves have been moved to make the design less conservative for these curves. Furthermore, the S-N curves for ground weld toes has been changed. Also, the effect of grit blasting as basis for coating has been made less conservative in terms of calculated fatigue lives. More information on design of single sided tubular joints with potential fatigue crack growth from the weld root has been included. For some joints the effect of tolerances is important, and some more effects of these are included. Furthermore, more refined equations for conical connections frequently used in support structures for wind turbines have been included in the revised standard.

Presenting Author: Arne Fjeldstad DNV

Presenting Author Biography: Arne Fjeldstad is a Principal Engineer working in the Offshore Structures Section in DNV. He has a MSc in mechanical engineering and a PhD in fracture mechanics from the Norwegian University of Technology and Science. He has more than 15 years of experience with strength and fatigue analysis, Risk Based Inspection (RBI), project management, fracture assessment, laboratory testing, verification and technology qualification. His work is currently directed towards fatigue analysis and RBI of offshore structures. He is currently responsible for DNV-RP-C203 and DNV-RP-C210.

Authors:

Inge Lotsberg DNV
Arne Fjeldstad DNV