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“A New Approach to Repair of FPSO’s Without Hot Work”
A. T. Echtermeyer, M. J. Larsen & K. P. Fischer DNV, Høvik, Norway
presented by
Johan GärdinMobile Offshore Units / FPSO, DNV SEA & ANZ, Singapore
Telephone +65 [email protected]
www.dnv.com
JOINT INDUSTRY PROJECT UPDATE
Slide 3
Typical FPSO In-Service experience:
Structural and materials protection issues:
• Integrity of Hull (3 of 4 suffer cracking in tank boundaries)
• Integrity of Ballast and cargo piping (construction standards for cargo and ballast piping appear inadequate. Weld failures, corrosion & subsequent leaks)
• General corrosion and coating issues (need for good inspection programme)
(Source OLF, Norway: data for 4 FPSO)
Slide 4
FPSO In-Service Inspection:
Ballast tank surface area 100,000 – 200,000 m2
The inspectability of most FPSO’s and tankers is a nightmare. Design for inspectability rarely enters the design engineer’s mind
until he has to participate in the inspection himself. ” (R. G. Bea)
Slide 5 Local or General Corrosion Fracture
FPSO In-Service Failures:
INADEQUATE PROTECTION INADEQUATE DESIGN or OVERLOAD
Slide 6
Ideal Repair:
NO PRODUCTION STOP
NO HOT WORK
NO GOING OFF LOCATION
ADAPTABLE TO ANY CASE
COST EFFECTIVE
QUICK
LOW TECH
RELIABLE
ADHESIVE PATCH:
•IN-SITU ON LOCATION
•ONLY REPAIR AREA
•NO CUTTING/WELDING
•MOST GEOMETRIES
•VERY!
•VERY!
•EQUIV. TO WELDING
•20 YEARS EXPERIENCE
Slide 7
Repair Timescales
Shut down production
Transit to yard
Docking + repair
Transit to field & hook up Months
Wait for weather-window
Shut down production
Repair
Start production
Weeks
Wait for weather-window
Clean damaged area
Repair & cure
No interruption in production
Extensive welded repairs
Minor welded repairs
Patch repairs
Production interruptions avoided – only damaged area is shut down
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Principle:
• A damage (e.g. hole, crack, corrosion) is discovered and needs repair
• A patch is fabricated from a structural laminate
• The patch is adhesively bonded to the substrate to repair the damage
What Is Adhesive Patch Repair?
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• MATRIX
What Is an Adhesive Patch?
LAMINATE+
• ADHESIVE
• REINFORCEMENT
Slide 10
• ALTERNATIVE PRODUCTION METHODS:
• WET LAY-UP (Dry Reinforcement and Resin applied directly to substrate by roller and cured in situ)
• PRE-PREG (Impregnated patch and adhesive applied to substrate and cured together under heating)
• INFUSION (Dry Reinforcement and low viscosity Resin applied directly to substrate and cured in situ under vacuum bag)
What Is an Adhesive Patch?
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Typical patch materials depend on application:
• MATRIX POLYMERS:• Epoxy, Polyester, Vinylester, Urethane...• REINFORCEMENT:• Glass fibre, Carbon fibre, other high performance fibre
types.• Multi orientation (csm), Woven roving (0°/90°), Uni-
directional, or Combination mats• ADHESIVES:• Structural adhesive: May be identical to the matrix or a
dedicated structural adhesive
What Is an Adhesive Patch?
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Design, Production, Installation
• Optimum PATCH DESIGN depends on damage type, location, strength requirements, working conditions during application, available time for repair...
• Choice of production and installation METHOD must suit material choice and design of patch repair
• Skilled WORKMANSHIP, good PROCEDURES and QUALITY ASSURANCE during design and production / installation is paramount!
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Limitations to Patch Repair
• Some polymers may be SHE HAZARDS• Substrate CLEANLINESS is critical• STIFFNESS may be difficult to achieve• SHEAR AREA between patch and
substrate must be adequate• PEELING STRESS must be avoided
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Opportunities with Patch Repair
• ‘Smart materials’ for performance monitoring
• Tailor-made directional properties• Lightweight – easy handling
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Current Applications of Patch RepairsCurrently used for rehabilitation within:• Infrastructure / civil engineering• Navy vessels• Process plant piping • Offshore piping and non-structural applications
Extension to FPSOs could be:• Structural applications, such as:
– Reinforcing corroded panels (compensating for loss of thickness)
– Bridging of cracks in stiffeners or brackets (relieving hot spot stress)
– Strengthening of decks, frames bulkheads etc. to carry additional equipment
• Non-structural applications, such as: – Bridging of cracks or holes in platforms etc
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Application Examples, DML
Deck repairs on naval ships
Repair carried out during scheduled maintenance docking:
Avoids time-consuming removal / protection of mechanical / electrical outfitting prior to welding
All photos courtesy of DML Composites
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Application Examples, DML
Rehabilitation of pipelines
Repair can be permanent or temporary
Repair can often be carried out without shutdown of production:
Avoids expensive down-time
All photos courtesy of DML Composites
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Application Examples, DML
Repair of flare tower:
Repair carried out offshore
Repair completed without hot work, avoiding fire hazard
All photos courtesy of DML Composites
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Qualification of Patch Repairs for FPSO
DNV is currently developing a qualification guideline for adhesive patch repairs of FPSO
Key objectives include:• Provide a LINK between existing DNV documents for
design of offshore ships and design of composite components
• Provide SPECIFIC GUIDANCE on design and qualification requirements for patch repairs on FPSO
• Develop and test demonstration examples to establish QUALIFICATION TEST requirements
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Use of DNV’s Reliability Experience
The basic functional requirements for a patch are simple:• The required strength and stiffness must be restored
• The repair must resist the local environment
• The growth of the damage must be stopped
• Additional strengthening may be required if the damage is due to a design flaw
Acceptance criteria for patch repairs are developed based on:
• DNV experience with FPSO and ships in general
• Recently developed acceptance criteria for composite materials
Safety factors calibrated to
ensure consistent safety level
Qualified repair
Loads
Material properties
Structural reliability approach
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Use of existing DNV documents
DNV-OS-C101 Design of offshore steel structures, general
DNV-OS-C102 Structural design of offshore ships
DNV-RP-C203 Fatigue strength of offshore steel structures
DNV Rules for ships provide background
Qualification procedure for
adhesive patch repairs
DNV-OS-C501 Composite ComponentsDNV-RP-A203
Qualification procedures for new technology
Specific information and technical background for patch repair design and qualification
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Demonstration Examples
Key objectives:• Demonstrate principles in patch design and
in qualification process • Provide information on failure modes and
general performance of generic patch repair designs
• Establish base cases to be used as reference when designing full scale patch repairs
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Demonstration Examples
Two demonstrators are chosen:“The corroded panel” – simulating corrosion damage and
leakage in tank or shell plating
“The fractured stiffener” simulating a fatigue crack in a beam (local or global stiffening member)
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Corroded Panel Demonstrator
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Panel Repair: Production Sequence
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Fractured Stiffener Demonstrator
Artificial crack
Composite repair by ”pre-preg” or prefab plates
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Corroded panel demonstrator Fractured stiffener demonstrator
Detail of notch with strain gauge – ready for testing
Demonstrator Testing
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Continued Work in a Phase 2
2004-2006:• Extension of test programme
(small scale testing – bond zone properties)• Updating the document with more test
results• Establishing more repair base cases• Performing a full scale field repair on an
FPSO in operation
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Conclusions
• Fire Adhesive patch repairs enable field repairs of FPSOs and other offshore structures without hot work.
• Hazards and shut-down requirements are minimised.
• A framework for quality assurance and procedures for qualification of patch repairs will help avoid basic design and production errors, which could potentially lead to repair failures.
• This JIP will result in an official DNV document providing such a framework.
• Successful full scale field demonstrations will pave the way for patch repairs as an accepted technology in the future.
Slide 30
Acknowledgement
DNV would like to thank the following companies in Phase 1 of the JIP “Qualification of Adhesive Bonding in Structural Repairs of FPSO’s” for the permission to present this paper:
• ConocoPhillips• Norsk Hydro• Petrobras (CENPES)• Petronas (PRSS)• Shell-Enterprise Oil• Statoil
DNV would also like to thank Devonport Royal Dockyard Ltd (DML) for their cooperation in the JIP and also for their contribution to this paper.
Slide 31
PHASE 3(?):
MEGA-SCALE TESTING
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