This paper presents the method and results from a fatigue study of conductors at the conductor guides’ levels as well as a static and dynamic hydrodynamic analysis of a 20″ conductor installed on a North Sea jacket platform using the OrcaFlex 9.5 computer program. This study presents only the results of the analyses and does not comment on the program’s efficiency or ability to model the various physical effects. Due to the conductor guides’ situation with gaps between the conductor and its guides, which was reported by the offshore survey, there was great demand for a fatigue life study of the conductors. The hydrodynamic analysis was performed with Finite Element Software, the OrcaFlex 9.5, for regular waves for 1-, 10- and 100-year return period sea states. Afterwards, fatigue calculations were carried out according to the output from the hydrodynamic analysis. The main achievements from this study are:

• Some elements have been identified as key factors, which have a great influence on the fatigue life of the conductors at the guides’ levels: bending moment, wall tension of the conductor, hydrodynamic & structural damping factors (which are seen to be main sources of uncertainty) as well as the clearances (gaps) between the conductor and its guides at the different guide decks.

• The bending moment could be reduced by decreasing the gap for the conductor in the guides.

• Selecting a DFF (Dynamic Fatigue Factor) of 2 means that the fatigue life of the conductors at the guide levels will not match the requirement for conductor fatigue service life, according to our analysis; and the conductors need inspection and modification.

This content is only available via PDF.
You do not currently have access to this content.