Evaluation of Premature Failure of Links in the Docking System of a FPSO

Abstract

Oil production in offshore areas has increased in recent years, especially with deeper water creating new challenges to be overcome. In this scenario, the mooring systems of floating units need to withstand higher operating loads. The mooring system is designed to keep the FPSO (Floating Production Storage and Offloading) properly positioned. Being fundamental to the integrity of risers and the platform itself, the failure can cause the overloading of other lines and generate the collapse of the whole mooring system in an extreme environmental situation, so the design and material selection are essential to the success of the venture. This work presents the investigation of the premature failure in some lines of the mooring system for an FPSO, in this case links in class R3. There were flaws in the weld between the link and the stud, with the subsequent complete failure of link. Some analyses were performed to understand the problem, including chemical composition, microstructural evaluation, hardness, corrosion potential, numerical analysis and fatigue tests. Finally, we concluded that the use of materials from different links to the stud generated a localized corrosion leading to increased local tensions and the failure by fatigue.