How Early Constructability Thinking Reduced Shutdown Risk on a Live FPSO Electrical Upgrade

The Challenge

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Following an Operations Readiness Review on a client's FPSO, the topside Earth Fault Monitoring (EFM) system associated with the vessel’s LV IT electrical distribution network was identified as non-functional. The installed legacy Bender system had multiple standing alarms, no reliable fault localisation capability and limited visibility of insulation faults across critical topside electrical systems.

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The FPSO's electrical distribution philosophy relies upon a fully functional IT earthing arrangement to maintain continuity of supply following a first earth fault. Operation without a functioning EFM system reduced fault visibility and increased operational and maintenance risk across both production and emergency electrical systems.

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Further engagement with the OEM confirmed that key installed components were obsolete and unsupported. The challenge was therefore not simply equipment replacement, but the development of a safe, buildable execution strategy capable of reinstating full EFM functionality within live offshore switchboards approaching 25 years in service.

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A major constraint identified early in the project was the existing installation of the EFM current transformers (CTs) on confined switchboard busbar droppers. Full replacement of these CTs would require intrusive busbar dismantling and extended shutdown durations across both the main Process & Utilities Switchboard and the Emergency Switchboard.

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Katoni Engineering’s Role

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Katoni Engineering were engaged to support the full project lifecycle from DEFINE phase assessment through offshore survey, Basis of Design development and detailed engineering execution support.

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Working alongside the client and two supporting companies, Katoni:

• Assessed the condition and operational status of the existing EFM installation
• Defined replacement philosophies for both the Process & Utilities Switchboard and the Emergency Switchboard
• Developed offshore survey scopes targeting constructability and isolation strategy development
• Carried out intrusive offshore switchboard surveys alongside vendor specialists
• Identified operational constraints associated with temporary generation and emergency power arrangements
• Defined pre-TAR and shutdown execution methodologies
• Developed a pragmatic fallback strategy balancing operational risk against intrusive construction scope

What We Did Differently

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Focused on Execution Practicality Early.

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Rather than treating the project as a straightforward equipment replacement, the study focused heavily on how the works could realistically be executed offshore within shutdown constraints.

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The offshore survey confirmed that the existing CT locations represented the only technically viable positions for full circuit earth fault monitoring. However, replacement of these CTs required dismantling confined busbar sections within live switchboards, significantly increasing construction duration and outage requirements.

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Katoni therefore developed a staged execution philosophy:

• Existing CTs would initially be retained where possible
• New Bender equipment would be installed and commissioned against the existing CT infrastructure
• Existing CTs would then be functionally verified using system diagnostics and commissioning testing
• Only CTs identified as defective would be replaced during follow-on managed shutdown activities

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This approach reduced unnecessary intrusive busbar works while maintaining a compliant fallback strategy where required.

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Reduced Shutdown Scope Through Pre-TAR Works

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A phased construction strategy was developed to maximiseworks completed ahead of the shutdown period.

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Pre-TAR activities included:

• Installation of a new remote EFM panel for the Emergency Switchboard
• Installation of containment and new communications cabling
• Preparation of temporary power arrangements
• Installation of non-intrusive EFM hardware
• Verification and identification of existing wiring infrastructure

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This significantly reduced the volume of work requiredduring switchboard outages.

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Developed a Buildable Emergency Switchboard Solution

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The existing Emergency Switchboard EFM installation did not comply with modern switchboard segregation expectations, with components installed across instrumentation and ACB compartments.

Katoni developed a revised arrangement relocating all new EFM equipment into a dedicated remote-mounted panel within the emergency switchroom. This improved maintainability, reduced operational risk and avoided further intrusive modifications within the emergency switchboard itself.

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Outcome

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Katoni Engineering delivered a complete engineering package supporting progression from DEFINE phase through detailed engineering execution.

The project established:

• A practical and phased offshore execution strategy
• A reduced-risk approach to CT replacement
• A compliant and maintainable EFM architecture for both switchboards
• A temporary generation philosophy supporting staged outages
• A pre-TAR installation strategy reducing shutdown critical path duration
• A detailed Basis of Design aligned with offshore operational constraints
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The resulting strategy provided the client with flexibility to balance outage duration, construction risk and operational impact while maintaining a clear fallback path should CT replacement ultimately be required.

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Value Delivered by the Study

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The project moved beyond a conventional equipment replacement exercise and focused on delivering a realistic offshore execution strategy for ageing live electrical infrastructure.

By challenging the assumption that all CTs required immediate replacement, Katoni reduced the extent of intrusive switchboard intervention while retaining a compliant fallback strategy where defects were identified.

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Early focus on constructability, temporary generation arrangements and phased execution allowed critical shutdown activities to be reduced and de-risked before progressing into execution.

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The project demonstrated Katoni Engineering’s ability to combine electrical system expertise, offshore operational understanding and pragmatic delivery planning to support complex brownfield electrical modifications on ageing offshore assets.

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