FPSO Hull Inspection Singapore — In-Water ROV & Diver Survey of FPSO / FSO Hulls

What Is FPSO Hull Inspection?

An FPSO — a Floating Production, Storage and Offloading unit — is a ship-shaped or purpose-built vessel that receives, processes and stores hydrocarbons at an offshore field, together with its close relatives the FSO (Floating Storage and Offloading unit) and the wider family of floating storage units. Unlike a trading tanker, these vessels are moored on station and stay there for years or decades at a time. FPSO hull inspection is the systematic examination of that vessel's external underwater hull while it remains afloat and in service.

Because the unit cannot be taken out of the water, the inspection is carried out in-water using remotely operated vehicles (ROV) and commercial divers. The scope covers the shell plating and its welded seams, the protective coating system, the sacrificial or impressed-current anodes that make up the cathodic protection system, the marine growth colonising the hull, and the appendages — sea chests and gratings, thrusters or propellers, rudders where fitted, and the boottop and waterline band. In short, it is a full afloat survey of everything below the waterline that a drydock bottom inspection would otherwise cover.

This work sits within the broader family of UWILD (Underwater Inspection In Lieu of Drydocking) and In-Water Survey (IWS) services, applied specifically to the demanding case of a permanently-moored production unit.

Why FPSO Hull Integrity Depends on In-Water Survey

A trading ship returns to drydock every few years, where its bottom is exposed, cleaned and surveyed in the dry. An FPSO does not. It is designed to remain on station and producing for its entire field life, so drydocking is either impractical or economically impossible. That single fact reshapes the whole integrity-management problem: the hull's continued fitness for service has to be demonstrated entirely through in-water survey, accepted by the classification society as substituting for the bottom examination.

Meanwhile the hull is under constant attack. Immersed steel corrodes; the coating system breaks down under years of continuous exposure, wave action and ultraviolet at the waterline; sacrificial anodes deplete and eventually stop protecting the steel; marine growth accumulates and can mask the plating beneath it; and cyclic wave loading drives fatigue at structural details, welds and stress concentrations. None of this stops because the vessel is not moving — if anything, a stationary hull in warm tropical water fouls and corrodes faster than a trading ship.

For that reason classification societies require periodic in-water surveys, with close-up examination of nominated critical areas, so that wastage, coating failure and anode depletion are caught and trended before they threaten hull strength or watertight integrity. The in-water survey is not a formality — for an FPSO it is the primary line of defence for hull integrity.

What an FPSO Hull Inspection Assesses

Each item below is examined, recorded and located to the vessel's shell-expansion and framing references, then compiled for the attending class surveyor.

How the In-Water Survey Is Carried Out

The survey is planned around the class UWILD / IWS requirements and the vessel's own hull-integrity and thickness-measurement programme, so that the surveyor's nominated areas, critical structural details and gauging positions are all covered in a single mobilisation.

An ROV or diver works the hull along a planned grid, capturing high-definition video and still imagery of the plating, welds, coatings and anodes. At each nominated survey position the marine growth is cleaned back so the steel can be examined close-up, ultrasonic thickness readings are taken, and cathodic-protection potentials are logged. A two-way voice and video link lets the attending class surveyor watch the work in real time and direct the ROV or diver to any area of interest, which is what allows the examination to be accepted in place of a dry bottom survey.

The advantages of a well-run in-water survey are clear:

• No production interruption — the unit stays on station and producing while the hull is surveyed around it, avoiding the cost and downtime of demobilising to a yard.
• Class-witnessed, real time — the surveyor directs the ROV or diver live over the video link, so findings are accepted as they are recorded.
• Quantified, traceable data — UT gauging and CP readings turn a visual survey into measured evidence that can be trended survey-on-survey.
• Single mobilisation — hull, anodes, sea chests and appendages are all covered together, and the spread can extend to mooring and risers on the same job.

Every finding is compiled into a report structured to the class requirements, with the imagery, gauging log and CP data packaged so the attending surveyor can endorse the survey and the operator can feed the results into the ongoing hull-integrity programme.

Standards and Class Context

In-water hull inspection of floating units is governed by the rules of the major classification societies — ABS, DNV, Lloyd's Register, Bureau Veritas and ClassNK among them — which set out what an approved in-water survey must cover, how close-up examination and thickness gauging are to be handled, and how the results are recorded. These class rules sit alongside IMO instruments for ship and offshore-unit safety and the diving and ROV practice guidance published by bodies such as IMCA. We work to these frameworks and to the attending surveyor's direction; we do not claim to hold any particular class approval on this page — the class relationship rests with the surveyor and the operator.

Singapore is a natural hub for this work. The region hosts a substantial FPSO and FSO population and a dense concentration of offshore operators, and Singapore's yards, anchorages and support base make it a practical staging point for in-water survey spreads across the wider offshore theatre.

What We Inspect on an FPSO Hull

Why Choose SG Drone Inspections

We are an underwater inspection specialist supporting owners, operators and class attending surveyors with accurate, well-documented in-water survey data for floating units.

Frequently Asked Questions