Offshore Dry-Docking of FPSOs: A Response to Industry Needs
Authors: Hellinga Arthur , Terpstra Taco 
Published: June 2014

The bonanza of floating production, storage and offloading units (FPSOs) that were commissioned over a decade ago have come to an age whereby offshore asset integrity management and maintenance require continued focus of the operators and regulators. FPSOs have originally been designed for continuous service for periods up to 25 years. However, reality has shown that although designed to strict criteria, structural and hull maintenance shortcomings have become apparent after prolonged periods, subsequently prompting remedial actions or extensive offshore maintenance campaigns.

Dockwise has recognized the industry's need and has swiftly responded to it by developing a concept that provides unique and practical offshore dry-docking solutions based on its versatile heavy lift vessel " Dockwise Vanguard", which has been in operation since January 2013.

The offshore dry-docking concept is based on lifting the FPSO out of the water by submerging the " Dockwise Vanguard" underneath the FPSO offshore without disconnecting it from its mooring system and leaving the flow lines connected. Subsequently, by raising the vessel, and thus lifting the FPSO out of the water, a stable working platform is created for performing the necessary scope of work to the FPSO hull, appendages and mooring system.

Dockwise has developed this concept in-house by merging their extensive experience in heavy marine transport and offshore installation, further enhanced with the in-house knowledge of hydrodynamic behavior and analysis of interacting floating bodies. Not only the offshore loading operation and analyses have been refined by Dockwise but also the operational and practical aspects of conducting offshore hull repair and survey activities have been developed. Local legislative aspects, project logistics, safety studies, hazardous area classification, and utilities and services supply to a partially live and manned FPSO are all part of this in-house study.

This paper presents the outcome of a development program Dockwise has initiated in order to respond to an emerging need within the industry. A detailed insight into both the theoretical and practical aspects of this novel concept, as well as the decisions and considerations made by the Dockwise Engineers, Operational staff and the feedback from the industry are presented.

INTRODUCTION

The inception and introduction of the " Dockwise Vanguard" with its bow-less concept and unprecedented load carrying capacity opened the market for not only dry-transportation of the more traditional semi-submersibles and other floating production units, such as the " Jack St. Malo" semi in 2013, but also that of FPSOs. This is demonstrated by the contracts for ENI's Goliat FPSO and Moho North FPU that will be dry-transported from South Korea to Norway in 2014 and West Africa in 2016 respectively. Parallel to the introduction of the " Dockwise Vanguard??, Dockwise has also been in close contact with owners and operators of floating production facilities about offshore discharge of these units into the field rather than discharging at a sheltered location.

Introducing the " Dockwise Vanguard", with the offshore discharge studies on-going and the first feedback from the industry regarding dry-transportation led to discussions with FPSO owners and operators to go a step further and investigate the opportunity of using the same marine asset for offshore dry-docking complete floating production units. Subsequently, Dockwise has responded to this request from the industry by entering into in-house studies and investigation of this concept.

In this paper the market opportunities for dry-docking complete FPSOs offshore, or near shore, as well as operational aspects are discussed. Furthermore, a framework for an internal development program is presented and subsequent studies to the hydrodynamic and structural aspects are followed by a safety and HAZID assessment. All this led to an Approval In Principle (AIP) from ABS in 2012.