What are the procedures for FPSO maintenance inspections?

At-a-Glance: FPSO maintenance inspections are planned, RBI-driven campaigns aligned with class and statutory surveys, focusing on Safety-Critical Elements (SCEs) to maximize uptime and minimize simultaneous operations risk. Execution blends onstream condition monitoring, periodic NDT, and confined-space/ROV/drones to reduce outages and assure integrity.

I. Objective Definition and Key KPIs

• 1.1 Objective: Assure hydrocarbon containment, structural/marine integrity, and functional availability of SCEs on an FPSO through risk-based, class-compliant inspections with minimal production impact.
• 1.2 Scope (estimated): Hull and tanks, turret/swivel, mooring and risers, topsides process/utility systems, rotating equipment, electrical/instrumentation/SIS, marine/offloading systems, safety and lifesaving equipment.
• 1.3 Primary KPIs:
  • Production uptime = 98.0%
  • SCE functional availability = 99.5%
  • Inspection compliance = 98.0% (on-time WOs); backlog age = 30 days
  • Leak frequency = 0.5 per 100,000 equipment-hours; Loss of Containment (LOC) = 0 Major
  • Corrosion rate = 0.3 mm/yr (coated tanks/piping, estimated); Remaining Life = 5 years (key circuits)
  • PSV test compliance 100%; SIS proof test coverage = 95%
  • Mooring line tension excursions > Alarm = 1 per month; turret bearing vibration within limits 100%
  • OPEX for inspection = target budget; CO2e intensity trending down

II. Critical Parameters and Target Ranges

II.A Key Formulas Used

• 2.1 Corrosion rate (from UT): \( \mathrm{CR} = \dfrac{t_1 - t_2}{\Delta t} \) [mm/yr]
• 2.2 Remaining life: \( \mathrm{RL} = \dfrac{t_{\mathrm{meas}} - t_{\min}}{\mathrm{CR}} \) [years]
• 2.3 Availability: \( A = \dfrac{\mathrm{MTBF}}{\mathrm{MTBF} + \mathrm{MTTR}} \)
• 2.4 Risk (qualitative RBI): \( \mathrm{Risk} = \mathrm{PoF} \times \mathrm{CoF} \)
• 2.5 Inspection interval (simplified): \( \mathrm{TI} = \dfrac{\mathrm{RL}}{\mathrm{SF}} \) with safety factor \( \mathrm{SF} \) typically 2–4 for SCEs

III. Step-by-Step Procedure / Workflow / Checklist

III.A Planning and Preparation

• 3.1 Define basis (RBI and compliance):
  • 3.1.1 Develop/refresh RBI for hull, tanks, piping circuits, pressure systems, mooring, risers, turret/swivel, cranes, hoses.
  • 3.1.2 Map to class/flag/authority survey requirements (Annual, Intermediate 2.5-year, Special 5-year, dry dock/afloat where applicable).
  • 3.1.3 Identify SCEs and impairment windows; include performance standards and acceptance criteria.
• 3.2 Campaign scheduling:
  • 3.2.1 Align inspection campaigns with cargo tank availability, offloading schedule, weather windows, and turndown periods.
  • 3.2.2 Reserve logistics: ROV support vessel, rope access, drones, NDT techs, confined space rescue, test benches for PSVs.
  • 3.2.3 Freeze SIMOPS matrix; define which SCEs can be bypassed and under what safeguards.
• 3.3 Work packs and permits:
  • 3.3.1 Issue CMMS work orders with job steps, drawings, P&IDs, isometrics, prior findings, NDT techniques, acceptance criteria.
  • 3.3.2 Prepare isolation plans and LOTO; instrument inhibits with authorization; MOC for any temporary defeat/bypass.
  • 3.3.3 Pre-job HAZID/JSA; toolbox talks; emergency and rescue plan (confined space, working at height).

III.B Execution by System

• 3.4 Hull and Tanks (internal/external):
  • 3.4.1 Gas-free: drain, water-wash, purge/inert then ventilate to safe entry conditions; continuous gas monitoring.
  • 3.4.2 Entry controls: permit, attendant, rescue kit, calibrated meters; staging or rope access inside tanks.
  • 3.4.3 Inspection: coating survey, UT grids, MFL on deck plates, close-up of longitudinals/frames, pitting mapping, scallop/strake checks.
  • 3.4.4 External: ROV hull survey, CP potential logging, sea chest/gratings, overboard spool thickness, shell penetrations.
  • 3.4.5 Repair: coating touch-up, hot/cold work per permit, structural repairs as per class-approved procedures.
• 3.5 Mooring System and Subsea:
  • 3.5.1 Real-time tension review; download trends for fatigue assessment; alarm setpoint verification.
  • 3.5.2 ROV inspection: chain/wire/rope, connectors, fairleads, clump weights, seabed touchdown; measure wear/corrosion; NDT on critical links.
  • 3.5.3 Integrity actions: replace worn inserts, renew anodes, grout repairs as needed; update fatigue life model.
• 3.6 Turret, Swivel, and Bearings:
  • 3.6.1 Vibration, temperature, lubrication sampling; borescope of bearings/gears where access allows.
  • 3.6.2 Swivel leak checks, seal condition, pressure/vent routing; function test rotation and locking systems.
  • 3.6.3 Structural checks: spider deck, chain tables, padeyes; NDT of welds in high-stress zones.
• 3.7 Risers, Umbilicals, and Flowlines:
  • 3.7.1 Annulus vent gas and pressure trending; sample for hydrocarbons; compare against baseline.
  • 3.7.2 ROV visuals: bend stiffeners, collars, buoyancy, VIV suppression; touch point wear checks.
  • 3.7.3 Pigging readiness checks on production/injection lines; verify integrity of pig traps, closures, and reliefs.
• 3.8 Topsides Pressure Systems:
  • 3.8.1 External inspection: corrosion under insulation (CUI) screening via thermography/PEC; supports, clamps, deadlegs; leak survey.
  • 3.8.2 Internal inspection (as scheduled): vessels, columns, separators; tray/packing condition; nozzle erosion; UT/MPI/DPI/ACFM as applicable.
  • 3.8.3 PSV management: remove/bench test/calibrate or inline test; verify tag mapping to protected volumes; reinstall with certs.
  • 3.8.4 Heat exchangers: bundle pulls, eddy current/tube UT, cleaning, differential pressure baselining.
• 3.9 Rotating Equipment:
  • 3.9.1 Online condition monitoring: vibration (overall and spectra), process/thermals, performance curves; lube oil analysis.
  • 3.9.2 Borescopes on turbines/compressors; alignment checks; coupling inspection; valve actuator stroke tests.
  • 3.9.3 Function tests under degraded modes (one-train operations) with risk controls in place.
• 3.10 Electrical/Instrumentation/SIS/F&G:
  • 3.10.1 Ex inspections (EEHA): sample strategy for equipment categories; rectify defects by priority.
  • 3.10.2 Loop checks and proof testing of ESD, HIPPS, blowdown, firewater auto-start; verify cause & effect logic.
  • 3.10.3 F&G detectors calibration; hot and cold smoke tests; gas mapping verification if changed layouts.
  • 3.10.4 UPS/battery tests; earthing/ bonding continuity; IR thermography on switchgear/MCCs.
• 3.11 Marine/Offloading Systems:
  • 3.11.1 Cargo handling: gauging equipment, inert gas system, P/V valves, vent masts; cargo pumps VIB/DP.
  • 3.11.2 Hoses/reels: visual/internal exam, pressure test, electrical continuity; emergency release coupling test.
  • 3.11.3 Ballast/bilge: pump performance, valve function, overboard line condition, OWS compliance.
• 3.12 Safety and Lifting Equipment:
  • 3.12.1 Firefighting: deluge nozzles flow test, hydrant pressure, foam systems proportioning; thermal imaging for coverage.
  • 3.12.2 Lifesaving: lifeboats, davits, immersion suits; weekly visual, annual load tests per code.
  • 3.12.3 Cranes: structural NDT, wire rope sheaves, SWL load test, AOPS/MOPS testing.
• 3.13 Documentation and Close-out:
  • 3.13.1 Record findings with geo-tags/photos, UT grids, reports; update RBI, drawings, baseline data.
  • 3.13.2 Raise punch list and corrective WOs with criticality ranking; verify retest of repaired items.
  • 3.13.3 Update class/flag survey status, SCE impairment logs, and as-built dossiers.

IV. Risk & Mitigation (HSE, Reliability, Redundancy)

• 4.1 HSE Hazards:
  • 4.1.1 Confined spaces, toxic/flammable atmospheres (H2S, VOCs); inert gas risks.
  • 4.1.2 Working at height, over side, and dropped objects during rope access and crane ops.
  • 4.1.3 Hot work and ignition sources; electrical arc flash; pressure/energy releases.
  • 4.1.4 SIMOPS with production, offloading, and marine operations; weather/heave.
• 4.2 Mitigations:
  • 4.2.1 Permit-to-Work, LOTO, gas testing, continuous monitoring, rescue plans, trained standby.
  • 4.2.2 Engineered controls: barriers, nets, tool lanyards, secondary retention; scaffolding inspections.
  • 4.2.3 Temporary system impairments managed with MOC, isolation plans, additional firewatch, and compensating safeguards.
  • 4.2.4 Weather windows, heave limits for ROV and hose tests; stop-work authority enforced.
• 4.3 Reliability/Continuity:
  • 4.3.1 Maintain redundancy on utilities (power, air, firewater); plan single-point-of-failure work during turndown.
  • 4.3.2 Critical spares staged; vendor standby; contingency vessel for subsea scope.
  • 4.3.3 Pre/post-functional tests to confirm restoration; rollback plan for aborted interventions.

V. Optimization Levers (Data, Maintenance Strategy, Debottlenecking)

• 5.1 RBI maturity: Quantify PoF/CoF with updated corrosion models, fatigue usage, and consequence mapping to reduce low-value inspections and extend intervals where RL supports.
• 5.2 Digitized condition monitoring: Online vibration/AE sensors on turret bearings, motor currents, thermography, corrosion probes; automated exception alerts.
• 5.3 Robotics and remote methods: Drones for flare/stack and topside structure; magnetic crawlers inside tanks; ROVs for hull/mooring to defer entries and reduce risk.
• 5.4 Campaigning and SIMOPS optimization: Batch UT/MFL by area; align PSV pulls with vessel entries; combine hose/crane tests with offloading downtime.
• 5.5 Repair strategies: Composite wraps for local pipe defects; onstream leak sealing; weld overlays and cladding for chronic erosion points.
• 5.6 Chemistry and flow assurance: Targeted inhibitor injection, corrosion coupon/ER probe feedback loops; proactive pigging schedules to control under-deposit corrosion.
• 5.7 Spares and turnaround readiness: Kitting of NDT/repair consumables; critical path planning with float; cold-eyes review to shave hours off impairments.
• 5.8 Performance analytics: KPI dashboards for backlog, SCE availability, inspection hit rate, repeat defects; drive RCFA and bad-actor elimination.

VI. Verification & Monitoring Plan (What to Measure, How Often)

VI.A Acceptance and Escalation

• 6.1 Thresholds: Any SCE failing acceptance criteria triggers immediate risk assessment, temporary safeguarding, and repair plan.
• 6.2 Trend triggers: If \( \mathrm{CR} \) increases by = 0.1 mm/yr or \( A \) drops below target, re-run RBI and adjust intervals \( \left( \mathrm{TI} = \dfrac{\mathrm{RL}}{\mathrm{SF}} \right) \).
• 6.3 Verification: Independent QA of NDT data, 10% re-measure on UT grids; third-party witness for statutory tests.