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Converted tankers into FPSO:Life extension’s structural challenges

Damien THIERYOffshore Project Engineer

Bureau Veritas HO [email protected]

2MCE Deepwater Development 2014 - Madrid

Introduction: converted tankers into FPSO

► In 2014: Conversions represent approximately 70% of the F(P)SO units

► Forecast of F(P)SO orders over the next period (2014-2018):

• Conversion 55%

• New built 25%

• Redeployment 20 %

► 2 phases should be taken into account:

► Life extension: when the asset exceeds its design life

Tanker Service

FP(S)O Service


Contents

►1. Hull structure challenges

►2. Structural analysis

• Strength assessment

• Fatigue assessment

►3. Integrity management System

►4. Conclusion


Hull structural challenges

► Previous history: as trading services and during the transit

RAO Roll RAO Pitch

RAO Roll

RAO Pitch


Hull structural challenges: Tanker service

► What are the main hull degradation processes of a tanker ?

• Corrosion

• Fatigue cracks / fatigue accumulated damage

► What is the current hull condition ?

• Is the operating history (log book) fully known ?

• Are previous inspection / repair reports available ?

• Which is the outcome from the condition assessment survey (corrosion) ?

• How site environmental conditions compare with tanker class notation ?


Hull structural challenges: FPSO Service

► How to ensure the hull is eligible to be converted ?

• Which are the results of feasibility study and in terms of strength and fatigue ?

• Design conversion verification by structural assessment: forecast future

condition and expected end of life.

• What are the necessary repairs to face the FPSO service life ?

• IMR strategy to be defined in order to ensure the operational continuity

• Is there an Asset Integrity Management System planed ?


Structural Analysis


Structural Analysis

► Input for the structural analyses :

� Key structure drawings

� Capacity plan

� Trim & stability booklet

� Weight distribution

� Tanker speed and trading routes history

� Towing/transit speed and route

� Repair history, detected failures, damages, particular findings:

cracks, indents, impacts, pitting, …

� Corrosion “as is” condition or reassessed scantlings

� FPSO operational Loading conditions, Loading/Unloading

sequence

� Site metocean conditions

� Hydrodynamics & heading analysis results

� Mooring analysis results (mooring loads at hull interface)


Structural Analysis: Strength analysis

FINDINGS

►Strength analysis

Design waves applied on the model to maximize load

parameters.

• Yielding verification

• Buckling verification


Structural Analysis: Fatigue analysis

► Fatigue analysis

• Operational loading condition + transit condition

• Assessment of typical locations (determined by experience & fatigue scan)

• Analysis of previously detected cracks on board

• Assessment of repair solutions


Structural Analysis: Particular areas

Turret-Hull Interface

Crane Pedestals

Topsides stoolsHopper knuckle


Structural Analysis

►Outputs of structural analysis

• Remaining life assessment

• Inspection plan definition based on “hot spot maps”

• Determination of repair/modification solution

• To avoid further cracking

• To insure sufficient corrosion margin

• To avoid integrity issues resulting in production down time

• To avoid hot work or dry dock

Area 1

Area 3Area 2

Area 4


Integrity management System

Operator & Partners

ensuring that FPSO inspection plan is carried out and updated with documents

(modifications, inspection findings, corrective actions …)

Marine operation

department

Project Team Inspection Plan

Production

department

Contractor

Site inspectors

Safety

department

Maintenance

department

Classification Society


Conclusion

► Corrosion and structural integrity are the main challenges

► Finite Elements Analyses and Asset Integrity System

provide answers regarding :

• The status of the hull structure = condition assessment

• If the unit is suitable for intended = life extension

• How to anticipate / minimize / avoid offshore structural work before

going offshore

• Follow-up in service (Class surveys, operator inspections)

►Tanker service

• Trading routes

• Damages and repairs

• Surveys

• Structural analysis

►FPSO service

• Sites conditions

• Expected service life

• Structural analysis

• Inspection & Maintenance

CONVERSION

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