Chain Out of Plane Bending (OPB) Fatigue Joint Industry Project (JIP) Static Test Program and OPB Interlink Stiffness

Abstract

In 2002, several mooring chains of a deepwater offloading buoy failed prematurely within a very small time frame. These chains were designed according to conventional offshore fatigue assessment using API recommendations. With this first deepwater buoy application, a new mooring chain fatigue mechanism was discovered. High pretension levels combined with significant mooring chain motions caused interlink rotations that generated significant Out of Plane Bending (OPB) fatigue loading. Traditionally, interlink rotations are relatively harmless and generate low bending stresses in the chain links. The intimate mating contact that occurs due to the plastic deformation during the proof loading and the high pretension of the more contemporary mooring designs have been identified as aggravating factors for this phenomenon. A Joint Industry Project (JIP), gathering 26 different companies, was started in 2007 to better understand the Out of Plane Bending (OPB) mooring chain fatigue mechanism and to propose mooring chain fatigue design recommendations. This paper summarizes the quasi static OPB stiffness measurement campaign and the post processing work to derive the OPB interlink stiffness.

Wear Performance of the Mooring Chain Used in Floating Wind Turbines

“…service FPSOs is about 3-6% of MBS [1]. 2) If the tensile load is increased, chain sliding will be restricted, and the chain will be subjected to bending fatigue instead of wear [6]- [8].…”

An Out-of-Plane Bending Fatigue Assessment Approach for Offshore Mooring Chains Considering the Real-Time Updating of Interlink Bending Stiffness

“…A multi-axial criterion is more appropriate than the single-axis-based maximum principal stress criterion for chain fatigue analysis [13]. Furthermore, Rampi et al investigated the interlink stiffness and SCFs of mooring chains subjected to OPB using the FEA approach and proposed multi-axial SCFs based on the Dang Van fatigue criterion [12,14,15].…”

“…The FM method can provide accurate fatigue results and is suitable for accident or local chain fatigue analysis because of its low computational efficiency. Several companies initiated a joint industry project (JIP) to investigate the combined fatigue mechanism and propose recommended practices for mooring chain fatigue design [4,12,14,15,20,21]. A framework for mooring chain combined fatigue analysis based on the SN curve was proposed via numerical and experimental investigations [22].…”