FPSO conversions! Either VLCC to FPSO, FPSO redeployment, or similar engineering works for life extension of naval surface vessels, this bulletin discusses the lessons learned encountered in such "brownfield" projects, with some experience on the issues.

In the early stage of the project, the team should develop a conversion strategy to include the following:

  • Risk analysis
  • Vessel selection and inspections
  • Scope definition and limits
    • Turret integration scope
    • How much of topsides will be done in the shipyard
  • Conversion project execution plan and conversion approach
    • Which scope goes where
    • Base on real evaluation of skills and experience
  • Yard selection
  • Yard team

The FPSO owner company should develop a schema to ensure all pieces of the puzzle fit together at a later stage when FID is approved.

  • Securing the vessel to be converted
  • Long Lead Items
  • Procurement and Engineering Packages
    • Topsides Supplier and Fabricator
    • Turret and Mooring System Supplier/Fabricator
    • Hull Conversion Yard
    • Integration
    • Sail away or Tow Away
  • Installation
  • Commission
  • Operations

During the FPSO selection process, consider the following to size the fit-for-purpose FPSO vessel:

  • Harsh or benign environment
  • Process Flow Diagram
  • Pre-built modules
  • Equipment list
  • Process deck layout
  • Reservoir data & functional requirements
  • Production export route & logistics
  • Storage capacity & buffer storage

The above considerations will provide an initial sizing for your FPSO. Then ask yourself the following questions to ensure the initial sizing meets your project purpose.

  • What is the required design life?
  • Single hull versus double hull: consider coastal state as well as International Maritime Organization regulations, and consider reputational risks.
  • Consider Class requirements in the context of site specific wave conditions: will the structure be adequate?
  • Age and condition: consider degree of hull steel wastage; compare with FPSO required scant-lings.
  • Age and condition: consider trading history and consumption of fatigue life; what modifications will be required to provide the required fatigue life. What fatigue safety factors e.g. Fatigue Methodology Specification (FMS) notation do you require?
  • Overall: pick high quality conversion candidates and be realistic about the repair/replace and refurbishment scope.

Material selection

  • Lower temperature applications e.g. Atlantic Canada, Barents Sea, would require special consideration of steel grades; it may require steel grades that can operate at or below -20 degrees C.
  • Tankers with extensive use of High Tensile Steels (HTS) can be more prone to fatigue cracking; impact of higher stress range may not be reflected in the design of (older) conversion candidates.
  • The use of HTS in certain areas is popular, because of the opportunities for saving weight; however because of the greater stress ranges, this can lead to lighter scant-lings and greater flexing; determination of scant-lings based on Ultimate Limit State (ULS) can lead to Fatigue Limit State (FLS)  problems in certain areas e.g. side shell.
  • “With the increased use of high tensile steel, fatigue issues must receive constant scrutiny and attention. When the stress level is increased through using high tensile steel, attention must be paid to structural detail and stress concentration factors to maintain the same fatigue life. The problem should have been addressed at the design stage. For ships already built and in operation, fatigue life may be calculated retrospectively and an inspection program established, paying attention to detail before the fatigue life expires.”


  • Note: No indication that the higher stress range has any impact on coatings; coating breakdown much more influenced by application/environmental control and formulation.

Vessel Selection

Ensure there is detailed vessel survey and inspection even as the operator on a lease contract

  • Structural survey and thickness measurements
  • Marine systems condition evaluation (pipe-work, valves, equipment)
  • Pick the best hull that your budget will allow
  • Spend enough time and money to establish the condition of the vessel and define upgrade scope
  • Don’t buy on price alone!

Vessel Selection & Success Factors

Reducing uncertainty and unknowns:

  • Good hull, reliable equipment, knowledgeable teams, competent personnel
  • Correct allocation of scope and risks to shipyard
  • Disciplined control of schedule and costs; implement solid project controls (cost and schedule planning - firm change management)

Building relationships:

  • Build strong relationships at all levels – resolves a lot of project issues

Defining common goals:

  • Safety and work targets

Maintaining communications:

  • Clearly defined work scope for each party
  • Identify critical issues together with yard
  • Team building efforts, sharing of lessons learned, regular discussions and reviews

FEED and Scope Definition

Front end and conversion engineering

  • Engineering and procurement responsibility
  • Class approval on key (schedule or integrity critical) items
  • System philosophies for other marine systems
  • Identification of main interface areas/systems
  • Identify compliance requirements (codes and standards)
  • Identify critical path engineering activities

Scope Definition

  • Understand the starting point, and be realistic about condition of existing vessel
  • Be clear on repair/refurbish and replace choices from the start
  • Develop detailed scope, specifications and interface documents
  • Ensure engineering efforts supports scope definition

Scope Definition & Details

Invest significant time & resources on this phase of the project

  • Clearly define work specifications and requirements
  • Responsibility matrix: as detailed as possible
  • Demolition & preservation
  • Company’s and Shipyard’s furnished items with “required-on-site” dates
  • Identify long lead and critical work
  • Work Breakdown Structure by packages
  • Engineering Drawings: “Material Take-Off” of long lead bulk materials
  • Pre-commissioning and commissioning scope
  • Heavy lifts and special resources
  • Dry-docking jobs

Sample bill of quantities for a 2 million barrels storage FPSO

Ballast / slop / COTs blasting and coating Approx 100,000 sq meter
Piping – Deck,Tanks, E/R, P/R, Accommodation Approx 50 km (1,400 tonne)
Electrical Cables Approx 350 km
Steel Work – Renewal Between 800 to 1,200 tonne
New Structures and Modifications – exclude turret Between 1,200 to 1,800 tonne
Moon pool structures (for internal turret) Approx 700 tonne
Turret structural Approx 3,000 tonne
Total weight of modules Approx 6,000 tonne
Man-hours spent About 3.5 million
No of days in dry-dock 45 to 60 days
No of days in Shipyard excluding lead time 11 to 16 months
No of days at anchorage 5 to 10 days