Abstract
Semisubmersible Mobile Offshore Units (MOUs) have been used on the Norwegian Continental Shelf since the mid 1960’s and since the late 1980’s also as production units. During these years a significant amount of experience data has been gathered and systemized.
This paper gives an overview of reported incidents in the period between 2000 and 2020, related to the structure and the maritime systems on semisubmersibles operating on the Norwegian Continental Shelf. Incidents, accidents and damages are reported by operators and rig owners to the PSA. These are summarised in this paper and includes cracks, dents from wave actions, anchor impact on structures, horizontal and vertical wave impacts and ship collisions. In addition, failure of the dynamic position keeping system, mooring system breakage and incidents related to stability and ballasting have been reported.
The paper provides numerical values of the occurrence of many of these incidents, where possible, in addition to an overview of the number of semisubmersibles active on the Norwegian Continental Shelf. In addition, a listing of accidents and incidents are provided and to some extent a summary of the incidents are provided for a possible further evaluation of common causes, importance and the possible consequences of these accidents, incidents and damages.
One fatality due to horizontal wave impact have been experienced in the period evaluated and a continued focus on air gap and wave in deck loading is important. However, these issues have later been better standardized by the class societies and the focus from PSA now is to ensure that the operators and rig owners are operating according to these standards. The main challenge for semisubmersibles continues to be operational issues related to stability and ballasting incidents, both because of the observed frequency and the potential consequence of such incidents.
