FPSO (Floating Production, Storage and Offloading)
An FPSO is a ship-shaped floating offshore facility that receives produced hydrocarbons from subsea wells, separates and treats them, stores the oil in its hull, and offloads to shuttle tankers — inspected to a combination of marine-class (DNV, ABS), API, and operator-specific NDT scopes.
Definition
FPSO NDT scope includes hull inspection (class-society driven), topsides process equipment (pressure vessels, piping, heat exchangers per API 510/570), risers and turret, and mooring chains. Confined-space entry, marine coatings, and salt-air corrosion drive specific NDT challenges.
What it is
A floating production, storage and offloading vessel — a ship-shaped or converted hull carrying process facilities, with crude stored in the hull and periodically offloaded to a tanker.
Damage mechanisms in service
Inspection combines marine classification requirements with process plant integrity: hull structure and ballast tanks under class survey, topsides process equipment under pressure equipment regimes, and the turret and mooring under their own. Fatigue is a dominant hull mechanism because the structure is permanently on station in a seaway.
Governing codes
Classification society rules govern hull and marine systems; API and ASME codes govern topsides; API 579 supports fitness-for-service where damage is found.
The common oversight
Treating hull and topsides as separate integrity worlds. Hull deflection affects topsides supports and piping stress, and the interfaces are where problems concentrate.
Where FPSO fits in an inspection programme
A term is only useful when it connects to a decision. FPSO appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
Riser — A riser is the pipe segment that conveys produced hydrocarbons from the seabed to a surface facility (platform or FPSO), subject to dynamic loading, corrosion, and fatigue, inspected by ROV-deployed UT, ACFM, and visual methods.
Jacket — A jacket is the steel tubular space-frame substructure of a fixed offshore platform, founded on piles and supporting the topsides above the waterline, inspected for fatigue cracking at nodes, marine growth, and CP performance.
Topsides — Topsides are the surface modules of an offshore facility (platform or FPSO) above the splash zone — including process equipment, utilities, accommodation, and helideck — inspected per API 510/570/653 with the additional challenges of offshore logistics and mar
Wellhead — A wellhead is the pressure-containing surface assembly at the top of an oil or gas well that provides the structural and pressure interface to the casing strings and supports the Christmas tree and other surface equipment.
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
An FPSO is a floating production, storage and offloading unit — a ship-shaped vessel moored on station that receives well fluids, separates and treats them, stores the crude in its hull tanks and offloads to a shuttle tanker. For inspection purposes it is two assets in one hull: a marine structure and a process plant.
That split governs everything about how it is inspected. The hull is classed marine structure, surveyed under a classification society regime with annual, intermediate and special periodical surveys on a five-year cycle, and its damage mechanisms are the ones that afflict ships — fatigue cracking at side shell longitudinal connections, coating breakdown and corrosion in ballast and cargo tanks, and wastage around the turret and mooring interface. The topsides are process equipment and are inspected on the API regime that any plant would use, against corrosion under insulation, erosion in sand-bearing production streams and the rest. The complication that has no shore analogue is that an FPSO does not drydock. It stays on station for years or decades, so the hull inspection that a trading tanker gets in dock has to be delivered in place — internal tank surveys during planned entries, and underwater inspection in lieu of drydocking for the external hull, using divers or remotely operated vehicles.
Source: Classification society rules for floating production installations from DNV, ABS and Lloyd's Register; IACS Unified Requirements and the survey regime for hull structure; API RP 2FPS for planning, designing and constructing floating production systems; API RP 571 for topsides damage mechanisms; API 510 and API 570 for topsides pressure equipment and piping.
The two inspection regimes running simultaneously on one FPSO
Hull and marine systems
Process topsides
Governing regime
Classification society rules, flag and coastal state
API inspection codes, operator's own programme
Survey cycle
Annual, intermediate, special periodical on a five-year cycle
Interval by measured corrosion rate and consequence
Dominant mechanisms
Fatigue at structural connections, ballast and cargo tank corrosion, mooring and turret wastage
Corrosion under insulation, erosion-corrosion, sour service cracking
Access constraint
No drydock; close-up survey needs staging or rope access, external needs UWILD
Live plant; shutdown windows govern internal access
Primary methods
Ultrasonic thickness gauging campaigns, magnetic particle and ACFM on welds, visual close-up
Ultrasonic thickness and corrosion mapping, radiography, penetrant and magnetic particle
Consequence of deferral
Class condition or suspension
Loss of production integrity basis
One asset, two audiences. Class surveyors and the operator's API inspectors are asking different questions about the same steel.
Why the turret concentrates so much inspection attention
The turret is where the moorings and the risers meet the hull, and on a weathervaning FPSO it is also where the vessel rotates around a fixed point. It therefore carries the highest structural loads on the unit, sees relative motion, and sits in a splash and immersion environment that accelerates corrosion — a combination not found anywhere else on the vessel.
It is also the least accessible major structure. Inspection frequently needs confined space entry, rope access or subsea intervention, and each of those constrains which NDT methods are practical. Alternating current field measurement is often preferred over magnetic particle at the turret because it tolerates coatings and surface condition that would otherwise require blasting in an awkward location.
Because access is expensive, turret inspection rewards planning that other areas do not need. A campaign that reaches the structure without a clear list of what is being examined and to what acceptance criteria has spent the access budget without buying a defensible result.
What underwater inspection in lieu of drydocking actually substitutes for
A trading tanker enters dry dock periodically so the external hull can be examined, coatings renewed and appendages checked. An FPSO on a long field life cannot do that without shutting in production, so class accepts underwater inspection in lieu of drydocking, delivered by divers or by remotely operated vehicles.
It substitutes for the survey, not for the maintenance. Coating condition, weld examination on external structure, thickness measurement at selected locations and inspection of appendages are all achievable in water; the renewal work that a dock permits is not, which is why hull coating and anode design on an FPSO carry design margins that a trading vessel would not need.
The quality bar is set by what the surveyor can actually see and verify. That makes video and positional record-keeping part of the deliverable rather than a nicety, because the survey has to be reviewable after the fact by someone who was not in the water.
Where the two regimes have to talk to each other
The most common failure on FPSO inspection programmes is not a missed flaw. It is a boundary — a component that the class regime treats as topsides and the operator's API programme treats as marine, inspected by neither because each assumed the other held it.
Deck penetrations, structural supports carrying process equipment, and the pipework crossing between topsides and hull are the usual candidates. Fixing it is administrative rather than technical: an asset register that assigns every item to one regime explicitly, reviewed when the topsides are modified.
Atlantis works the procedure and personnel layer that both regimes rely on — written practice, NDT procedure development and Level III approval, and independent review of survey and inspection data before it supports a fitness-for-service or class decision. Request a consultation to scope a review.
What does FPSO stand for?
Floating production, storage and offloading. It is a ship-shaped vessel moored on station that receives fluids from subsea wells, separates and treats them on its topsides, stores the resulting crude in hull tanks and periodically offloads to a shuttle tanker rather than exporting through a pipeline.
Why are FPSOs not drydocked?
Because they remain on station for the field life, and taking one to dock means shutting in production and disconnecting moorings and risers. Classification societies therefore accept underwater inspection in lieu of drydocking, performed by divers or remotely operated vehicles, to satisfy the external hull survey requirement in place.
What damage mechanisms affect an FPSO hull?
The ones that afflict ship structures: fatigue cracking at side shell longitudinal end connections and other structural discontinuities, coating breakdown and consequent corrosion in ballast and cargo tanks, and wastage around the turret and mooring interface where loads, motion and immersion combine.
Which NDT methods are used on FPSO hull structure?
Ultrasonic thickness gauging campaigns for wastage, close-up visual examination for coating and structural condition, and magnetic particle or alternating current field measurement on welds for fatigue cracking. ACFM is often preferred at difficult locations because it tolerates coatings and surface condition that magnetic particle would not.
How are FPSO topsides inspected differently from the hull?
Topsides are process equipment and follow the API inspection regime — API 510 for pressure vessels, API 570 for piping, with damage mechanisms from API RP 571 such as corrosion under insulation and erosion-corrosion in sand-bearing streams. The hull follows classification society survey cycles instead.
What is the most common gap in an FPSO inspection programme?
Boundary items. Deck penetrations, structural supports carrying process equipment and pipework crossing between topsides and hull can fall between the class regime and the operator's API programme, each assuming the other covers them. An asset register assigning every item to one regime explicitly is the fix.
Frequently asked
Does an FPSO hold a class certificate like a trading ship?
Yes, issued by a classification society under rules for floating production installations, and maintained through annual, intermediate and special periodical surveys. Findings can result in conditions of class that must be cleared within a stated period.
How is a converted tanker different from a purpose-built FPSO for inspection?
A conversion carries the fatigue history of its trading life, so the baseline for remaining fatigue life is not zero. Structural inspection planning on a conversion should be informed by that prior service rather than treating the hull as new at the point of conversion.