How to conduct integrity checks for FPSO facilities?

At-a-Glance: A robust FPSO integrity check blends risk-based inspection, continuous monitoring, and targeted intrusive surveys across hull, mooring/turret, risers/umbilicals, topsides pressure systems, marine and offloading systems to maximize uptime and safety while minimizing OPEX and emissions.

I. Objective & KPIs

I.1 Objective: Assure mechanical, structural, and safety integrity of the FPSO to sustain safe production at design rates with controlled risk and optimized lifecycle cost.

• I.2 Throughput KPIs: Production uptime = 98.0%; offloading availability = 99.0%.
• I.3 Reliability KPIs: Availability \(A = \dfrac{\text{MTBF}}{\text{MTBF} + \text{MTTR}} \ge 0.98\) for safety-critical elements (SCEs); SIS proof test coverage = 90% within interval.
• I.4 Integrity KPIs: No loss-of-containment (LOC) Tier 1 events; corrosion allowance margin = 2.0 mm; mooring line availability = 99.5%; flexible riser annulus “green” status = 95% of time.
• I.5 OPEX KPIs: Inspection cost = 1.5% of annual OPEX while meeting RBI targets; unplanned maintenance ratio = 20% of total maintenance hours.
• I.6 HSE & Emissions KPIs: TRIR = 0.5; fugitive methane emissions = 0.2% of gas handled; produced-water discharge oil-in-water = 30 mg/L average (estimated).

II. Critical Parameters & Target Ranges

II.A Key Equations

• II.A.1 Corrosion rate: \( \displaystyle CR = \frac{t_0 - t_1}{\Delta t} \quad [\text{mm/y}] \)
• II.A.2 Remaining life: \( \displaystyle RL = \frac{t_1 - t_{\min}}{CR} \quad [\text{years}] \)
• II.A.3 Fatigue cumulative damage (Miner): \( \displaystyle D = \sum_i \frac{n_i}{N_i} \) (acceptable if \(D < 1\))
• II.A.4 Risk metric: \( \displaystyle \text{Risk} = \text{PoF} \times \text{CoF} \)
• II.A.5 Availability: \( \displaystyle A = \frac{\text{MTBF}}{\text{MTBF}+\text{MTTR}} \)

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

III.1 Plan & Scope (Risk-Based)

• 1.1 Build/validate the Asset Register and tag critical Safety-Critical Elements (SCEs): hull/tanks, mooring/turret/swivel, risers/umbilicals, topsides pressure boundaries, ESD/SIS, marine/offloading.
• 1.2 Perform RBI: define Damage Mechanisms (CO2/H2S/erosion/MIC/SCC/fatigue); assign PoF/CoF; set inspection techniques and intervals aligned to RL = 2× interval.
• 1.3 Define SIMOPS and campaign windows: UWILD, rope access, ROV/AUV, class survey windows, production constraints.
• 1.4 Develop Inspection Test Plan (ITP) with acceptance criteria, CML list, hold points, and reporting templates.

III.2 Pre-Mobilization & Readiness

• 2.1 Permits: Confined Space Entry, Work at Height, Hot Work, Over-side work; verify gas testing equipment calibration.
• 2.2 Isolation/LOTO: verify pressure/energy isolation plans for pressurized equipment and electrical systems.
• 2.3 NDT/ROV tooling: UT, PAUT, TOFD, ACFM, MFL, RT (where justified), CP readers, annulus monitors, hydrotest pumps.
• 2.4 Baseline data: last survey thicknesses, CP potentials, mooring tensions, swivel logs, PRV history, SIS proof test records.

III.3 Hull, Structure, and Tanks

• 3.1 External UWILD: ROV general visual inspection (GVI) and close visual inspection (CVI) of shell plating, bilge keels, fairleads, sea chests; measure CP at representative locations; clean and gauge at hot spots.
• 3.2 Internal tanks: gas-free and ventilate; verify safe atmospheres (O2 20–21% v/v; HC = 1% LEL; H2S = 10 ppm); conduct close-up survey, coating assessment (NACE 0–4), UT gaugings on grids; assess pitting depth/area.
• 3.3 Structural hot spots: deck penetrations, turret interface, crane pedestals; PAUT/TOFD of weld toes and suspected cracks; calculate utilization ratios vs. design.
• 3.4 Ballast and bilge systems: function test remote valves; verify segregation; test Hi-Hi level alarms and pumps auto-start.

III.4 Mooring, Turret, Swivel

• 4.1 Mooring lines: verify line tensions vs. metocean; inspect chain links for corrosion/elongation; measure stud loss; ROV CVI on connectors; check fairlead sheaves and brake holding.
• 4.2 Turret bearing: trend temperature/vibration; grease sampling for wear particles; inspect seals; verify lubrication system interlocks.
• 4.3 Fluid/electrical swivel: check leak detection drains; pressure boundary NDE where accessible; torque and tension checks; verify electrical slip ring integrity.
• 4.4 Position keeping: validate GNSS offsets; heading weathervaning friction checks; alarm setpoints and FMEA bypass register clean.

III.5 Risers, Umbilicals, Subsea Interface

• 5.1 Flexible risers: annulus vent monitoring (rate, composition); end-fitting CVI; strakes/buoyancy condition; ACFM on tensile armors where accessible; check bend stiffeners and I-tubes.
• 5.2 Rigid risers/pipelines: ILI or external UT/EMAT; verify CP potentials; review VIV suppression; check supports/clamps and free-spans.
• 5.3 Umbilicals: insulation resistance tests; pressure hold on hydraulic lines; function test safety-critical actuators (SSIV, ESDVs).
• 5.4 Leak detection: deploy acoustic/pressure-balance checks; verify leak detection thresholds and response logic.

III.6 Topside Pressure Systems

• 6.1 Piping/pressure vessels: CML UT; profile RT/PAUT at supports and dead legs; corrosion under insulation (CUI) screening (thermal imaging, lift cladding at suspect zones); verify MAWP vs. operating envelopes.
• 6.2 PRVs/PSVs: remove and bench test by criticality; in-situ lift test where permissible; verify relieving capacity vs. scenarios; tag/traceability check.
• 6.3 Leak testing: nitrogen/helium or soap for low-pressure; hydrotest only where required by code or post-repair; verify reinstatement with calibrated gauges and charts.
• 6.4 Rotating equipment: vibration, thermography, lube oil analysis (particles, TAN/TBN); shaft alignment and coupling integrity.

III.7 E&I, Safety, and Automation

• 7.1 SIS/ESD: execute cause & effect tests; proof test logic solvers; partial/full stroke test of ESD/SDV/HIPPS; verify bypass discipline.
• 7.2 Gas/fire detection: bump test, calibration; verify alarm setpoints (10%/20% LEL) and shutdown voting; firewater pumps auto-start and ring-main pressure tests.
• 7.3 Electrical: IR/PI tests on motors/transformers; thermography of switchboards; earthing/bonding continuity, especially on offloading systems.

III.8 Cargo Handling, Inert Gas, and Offloading

• 8.1 Cargo tanks: IG system performance, O2 < 8% v/v; PV valves test and seat leakage; gauging/overfill alarms functional test.
• 8.2 Offloading hoses/hawser: hydro/vacuum test; electrical continuity; visual inspection for kinks/cover damage; scheduled changeout by condition or time.
• 8.3 Tandem/buoy offloading: ESD interlocks, QCDC function, emergency release testing in safe window; verify communication and DP/heading control logic.

III.9 Documentation & Closeout

• 9.1 Record as-found/as-left data; update digital twin and corrosion circuits; recalculate RL and RBI intervals using equations in II.A.
• 9.2 Raise and risk-rank anomalies (A–D); implement immediate mitigations; plan permanent repairs.
• 9.3 Management of Change (MOC) for any design/operating envelope change; update SCE performance standards.

IV. Risks & Mitigations (HSE, Reliability, Redundancy)

• IV.1 Confined space/tank entry: Gas test continuous; rescue plan; intrinsically safe equipment; cold-work standard—HC = 1% LEL, O2 20–21%.
• IV.2 Over-side/height work: Use certified access systems; weather limits; standby recovery; permit-to-work with SIMOPS review.
• IV.3 Hydrocarbon release: Double isolation and bleed; blind lists; temporary spades tracking; gas testing during reinstatement.
• IV.4 Mooring/turret criticality: Weather window for intrusive work; temporary line load sharing; heading control readiness.
• IV.5 Electrical arc/ignition: Live work minimized; ESD zoning; hot work management; verify bonding/continuity of offloading strings.
• IV.6 Reliability: Spares for SCEs; redundancy in firewater, power, control; maintain bypass logs with time limits and compensatory measures.

V. Optimization Levers (OPEX, Debottlenecking, Data)

• V.1 Condition-based monitoring: Permanent CP, mooring tension, swivel leak and vibration monitoring; flexible riser annulus gas sensors with alarms and trending.
• V.2 Advanced NDT targeting: Data-driven selection of CMLs; phased-array and guided-wave for hidden corrosion; risk hot-spot mapping for supports and dead legs.
• V.3 Digital twin & analytics: Integrate inspection findings, process data, and metocean loads; compute PoF/CoF trajectories; auto-update remaining life and inspection priorities.
• V.4 Coatings/CP strategy: Early spot repairs, anode retrofits via ROV; optimize tank coating specs to extend survey intervals.
• V.5 Campaign bundling: Combine ROV/UWILD, topsides NDT, and hose changeouts to reduce logistics and POB; align with class survey windows.
• V.6 Spare/repair readiness: Hose strings, swivel seals, PRV spares, mooring connectors in stock; framework repair procedures pre-approved.

VI. Verification & Monitoring Plan

VI.A Acceptance & Escalation

• VI.A.1 If \(RL < \) next inspection interval, escalate to mitigation: chemical treatment, clamps, operating envelope reduction, or repair.
• VI.A.2 If mooring tension = 60% MBL persistently, initiate metocean review and operational heading control; at = 80% MBL, execute contingency plan.
• VI.A.3 Any sustained flexible riser annulus pressure: reduce operating pressure, perform gas characterization, plan detailed inspection/repair.
• VI.A.4 Any PSV test out-of-tolerance: replace/retest; review overpressure scenarios.