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JOINT INDUSTRY PROJECT UPDATE

“A New Approach to Repair of FPSO’s Without Hot Work”

A. T. Echtermeyer, M. J. Larsen & K. P. FischerDNV, Høvik, Norway

presented by

Johan GärdinMobile Offshore Units / FPSO, DNV SEA & ANZ, Singapore

Telephone +65 67791266johan.gardin@dnv.com

www.dnv.com

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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)

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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)

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FPSO In-Service Failures:

INADEQUATE PROTECTION INADEQUATE DESIGN or OVERLOAD

Local or General Corrosion Fracture

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Ideal Repair:ADHESIVE PATCH:

•IN-SITU ON LOCATION

•ONLY REPAIR AREA

•NO CUTTING/WELDING

•MOST GEOMETRIES

•VERY!

•VERY!

•EQUIV. TO WELDING

•20 YEARS EXPERIENCE

NO PRODUCTION STOPNO HOT WORK

NO GOING OFF LOCATION

ADAPTABLE TO ANY CASE

COST EFFECTIVE

QUICK

LOW TECHRELIABLE

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Repair TimescalesExtensive welded repairs

Minor welded repairs

Patch repairs

Shut down production

Wait for weather-window

Wait for weather-window

Production interruptions avoided – only damaged area is shut down

Transit to yard

Shut down production

Clean damaged area

Docking + repair

Repair Repair & cure

Start production

Transit to field & hook up

No interruption in productionMonths Weeks

What Is Adhesive Patch Repair?

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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

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• MATRIX

What Is an Adhesive Patch?

LAMINATE+• REINFORCEMENT

• ADHESIVE

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What Is an Adhesive Patch?

• 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)

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What Is an Adhesive Patch?

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

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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 METHODmust suit material choice and design of patch repair

• Skilled WORKMANSHIP, good PROCEDURESand 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 shipsRepair 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 pipelinesRepair 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 ExperienceThe 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

Loads

Material properties

Structural reliability approach

Qualified repair

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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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Demonstrator Testing

Corroded panel demonstrator Fractured stiffener demonstrator

Detail of notch with strain gauge – ready for 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.

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AcknowledgementDNV 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.

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PHASE 3(?):

MEGA-SCALE TESTING