Fatigue study of conductor at the conductor guides’ levels on the EKOFISK-K platform

Abstract

This master thesis presents the method & results from a fatigue study of conductor at the conductor guides’ levels & static and dynamic hydrodynamic analysis of a 20’’ conductor installed on the Ekofisk-K platform using the OrcaFlex 9.5 computer program. This study presents only the results from the analyses and does not comment on the program’s efficiency or ability to model the various physical effects. Due to the conductor’s guide situation as well as the gaps between the conductor and it’s guides which was reported by the offshore survey, the fatigue life study of the conductor is highly demanded. The hydrodynamic analysis has been done with a Finite Element Software, the OrcaFlex 9.5, for regular waves for 1, 10 and 100 year return period sea states. Afterward, fatigue calculations have been done according to the output from the hydrodynamic analysis. The main achievements from this study are:  Some factors have been identified as the key factors which have a great influence for the fatigue life analysis of the conductor at the guides’ levels: Bending moment, wall tension of the conductor, both hydrodynamic & structural damping factors are seen to be main sources of uncertainty, the clearances (gaps) between conductor and it’s guides for the different guide decks.  The bending moment could be reduced by reducing the gap for the conductor in the guides.  By choosing the DFF (Dynamic Fatigue Damage) to be 2, the fatigue life of the conductor guides level will not match the requirement for conductor fatigue service life according to this master thesis; it needs inspection and modification. Keywords: Conductor; Bending Moment; Fatigue Analysis; Damping Factors; Hydrodynamic Analysis.