FPSO Side Shell Impact Proctection
Authors: Bond James , Ferro Angelo , Kennedy Stephen J. 
Published: May 2011

Traditionally the impact requirements set out by MARPOL for FPSO's and FSO's have been addressed by creating internal cofferdams or external sponsons. Intelligent Engineering has demonstrated that its Sandwich Plate System (SPS), a unique steel-polymer-steel composite materials technology, in the form of a compact double hull (CDH) can offer equivalent protection to either an internal cofferdam or external sponson.

The paper describes the structural engineering study conducted to confirm the impact resistance of the SPS Overlay 20-30-Existing CDH for the prescribed impact between an offshore supply vessel and the FPSO in way of the boat landing area.

Based on the results from the structural dynamic analysis using LS-DYNA, to simulate bow and stern collisions for various collision angle and locations, the following conclusions were made;The SPS 20-30-Existing CDH provides an impact resistant hull structure that is able to withstand the minimum accepted industry standard specified design condition 5000 tonne displacement OSV colliding with the specified FPSO at 2m/s without rupture of the crude oil tanks. As an integral part of the FPSO structure, it not only meets but exceeds the requirements of MEPC/Circ 406 " Guidelines for Application of MARPOL Annex I Requirements to FPSOs and FSUs??, providing 97,000 kJ of energy absorption capacitySPS CDH provides a package of risk reduction benefits over that of cofferdams and external sponsons that include; a significant increase in local impact resistance, a strengthened side shell that reduces critical fatigue stresses, schedule reduction for fabrication and installation, reduced risks during fabrication, less maintenance and eliminates the risks and costs for through life void space inspections.

Further, case studies describe the conversion cost, schedule benefits and operational benefits of the SPS CDH as installed on projects completed to date including the FPSOs P57, P58, MV22 and Aseng. Project approvals have been granted by Det Norske Veritas and the American Bureau of Shipping.

Introduction

Intelligent Engineering Limited (IE) has developed and patented the Sandwich Plate System (SPS), which integrates a steel-elastomer-steel composite structural laminate in place of conventional stiffened steel plates. The resulting structure has greatly enhanced impact absorption capability compared to conventional steel structures.

A study was commissioned by Single Buoy Moorings (SBM) to confirm the feasibility of installing an SPS-based fendering system to protect the side shell structure on an FPSO in way of the boat landing areas. The objective was to design a SPS Overlay solution to meet the relevant requirements of IMO MARPOL Annex I and eliminate the need to install cofferdams in these areas, thus maximising the deadweight capacity of the FPSO, minimizing conversion and life cycle costs of the asset, reducing inspection and maintenance requirements and creating an inherently safer design both in terms of construction and operation.

This paper describes objectives of the study, requirements for the confirmatory analysis, the design conditions, analysis methodology and gives a summary of results that confirm the improved impact resistance of two SPS Overlay solutions, with either a 20 mm or a 30 mm steel overlay faceplate and a 30 mm polyurethane elastomer core, fendering systems to impact between an offshore support vessel and a typical FPSO.