The feasibility of standardization of a mono-pile mooring facility for FSRU's

Abstract

As the LNG market continues to grow internationally, Floating Storage and Regasification Units (FSRU’s) have become an increasingly important component as governments and private companies strive for faster, cheaper and more flexible means of re-gasifying. In order to have a FSRU mooring system which is equally fast deliverable, standardization is considered. In this study standardization of the civil structures is investigated for a jetty-type mooring system on exposed locations, more specifically standardization of the breasting dolphins. The considered dolphins consist of a simple steel mono-pile which transfers the mooring loads to the sub-soil and a pile-head which connects the fender to the mono-pile. It was concluded that standardization of the mono-piles is only possible to a certain extent, namely in a conceptual design phase. In this report a standardized work approach is presented regarding the design of the mono-piles. Additionally, multiple pile designs are conceived for varying conditions. In an early design stage, when very little information is available, already some insight can be gained regarding the dimensions and the costs of these piles. In this thesis, also, the pile-head concept is presented which is most suitable for standardization purposes. This is achieved by a Fiber Reinforce Polymers (FRP)-composite, floating structure with a slide-bearing sliding system. The application of composite has some major advantages as it is fatigue resistant, low maintenance, light weighted and corrosion resistant. The form of the pile-head is also optimized for its application so that the fender loads are transferred in the most efficient manner to the mono-pile, while the slide-bearing allows smooth sliding along the pile’s shaft. Next to standardization of the civil structures, the loading conditions are investigated. Since the FSRU is permanently moored at exposed locations, this issue cannot be treated with ‘normal’ mooring of traveling ship, but must be calculated with the aid of numerical software where the relation between the environmental conditions and the load conditions is critical. The application of such software, however, is considered time-consuming for early design stages. An assessment tool is therefore conceived that calculates the design fender loads in a quick and analytical manner. This report shows that this assessment tool can generate rather accurate results, but that its application is limited.