Background for revised fatigue analysis methodology of subsea connectors in DNV-RP-C203

This paper presents the proposed changes to the fatigue analysis procedure and design S-N curves for steel forgings in the 2024 edition of the DNV recommended practice DNV-RP-C203. The procedure specifically targets low alloy forgings used in the subsea industry and incorporates important factors such as material strength, surface roughness, mean stress, notch effect, and in-service environment. The availability of additional data from various laboratory test projects since the procedure's initial introduction in 2016 has allowed for a reassessment and improvement of the methodology. Practical experiences gained from several years of use by the industry have also played a crucial role in its development, highlighting the challenge of establishing a consistent methodology that covers different combinations of stress range, mean stress level, and notch radii. The key changes made in the 2024 edition of the recommended practice include improvements in the notch model and revisions to the S-N curves for seawater environment with cathodic protection. These enhancements aim to provide more accurate fatigue analysis results. Additionally, the paper presents practical examples of the fatigue analysis process based on the recommended practice, focusing on simple notched specimens with varying notch radii. Although these specimens may not directly resemble subsea connector systems, their analysis serves to assist users of the recommended practice in calibrating their own fatigue analyses.