Session: 02-06-02 Reliability of Mooring and Riser Systems 2

Paper Number: 78408

78408 - The Effect of Pitting Corrosion on Fatigue Performance of Mooring Line Chain Links 

Mooring systems play an important role in the safety of floating production units and must comply with ultimate, accidental, and fatigue limit states criteria defined by design standards and classification societies. However, in the last few decades, many mooring lines failures have been reported in the literature. Most of these were related to fatigue and corrosion degradation in the top chain links, becoming a major concern. Since then, a great effort has been made to improve fatigue assessment methodologies of these elements and to model the effects that are not properly considered in the current design practice, such as the mean tension effect and the chain-link surface roughness due to localized corrosion.

The design practice of mooring lines usually assumes a uniform corrosion model with a constant corrosion rate. That way, corrosion degradation is considered only by reducing the area of the chain link. As a consequence, effects of stress concentration factors due to localized pitting are not directly addressed, and this may lead to an unconservative design.

The present work aims at assessing the stress concentration factor of chain-links with pitting corrosion employing finite element analyses and at comparing the localized pitting against the uniform corrosion stresses conditions in the chain-link hotspots. Results highlight that, even for small pits, fatigue damages are higher than considering a uniform area reduction, showing one feasible way of improving the current fatigue design methodologies.

Presenting Author: Filipe Rezende LACEO/COPPE/UFRJ

Authors:

Filipe Rezende LACEO/COPPE/UFRJ
Marina Simão LACEO/COPPE/UFRJ
Paulo Videiro LACEO/COPPE/UFRJ
Luis Sagrilo LACEO/COPPE/UFRJ