Flooded Member Detector

What Is a Flooded Member Detector?

Flooded Member Detection (FMD) also called Flooded Member Inspection (FMI) is a non-destructive test that determines whether seawater has entered a normally air-filled tubular member. Because most platform members are designed to remain dry and buoyant, the presence of water is a reliable indicator of a through-wall defect, such as a crack or weld failure. These breaches often occur after extreme weather events or impact, and without inspection the ingress of water, or “flood,” typically goes completely undetected.

Detecting a flooded member early is a core part of any structural integrity and asset-integrity programme. You can read a fuller technical explanation on our dedicated flooded member detection application page.

How Ultrasonic Flooded Member Detection Works

A Cygnus ultrasonic flooded member detector uses a single-element, high-power piezo composite probe operating at 0.5 MHz. The probe is placed against the member by a diver or ROV, and a built-in contact sensor confirms correct alignment before any reading is taken. Ultrasound is then transmitted into the member: the way the signal behaves reveals whether the internal cavity is air-filled (dry) or water-filled (flooded).

The result is processed by purpose-designed software at the surface and shown as a simple DRY (green) or FLOODED (red) indication, supported by A-scans for verification. Every reading is logged and can be exported to PDF and Excel for reporting. Unlike gamma radiography, this ultrasonic testing (UT) method uses no radioactive isotopes, which removes the licensing, exclusion-zone and health-and-safety burden associated with radiation-based subsea inspection equipment.

Cygnus Ultrasonic FMD Systems

The Cygnus flooded member detection system is built around one clever idea: a single core instrument that can be deployed by either a diver or an ROV. The system comprises the probe and self-aligning probe handler, the subsea electronics unit and the surface reporting software. Because the same unit is shared between divers and ROV pilots, you avoid buying two separate tools a design innovation that delivers real savings.

Cygnus FMD System for Diver

Purpose-built for underwater flooded member inspection, the Cygnus FMD System for Diver gives diving teams an easy, reliable way to test tubular members by hand. The self-aligning probe handler ensures correct contact with the member regardless of the angle or direction of approach, and its compact design reaches hard-to-access geometry such as K-nodes where other flooded member inspection equipment cannot. A simple DRY/FLOODED result is displayed and logged at the surface.

Cygnus FMD System for ROV

The Cygnus FMD System for ROV brings the same intelligent electronics and fail-safe software to ROV flooded member detection. Designed by our ultrasonic specialists with years of subsea experience, it is operable by ROV pilots of varying experience and uses an RS232 full-duplex data link suitable for fibre multiplexers. Built in high-grade acetal for the harshest environments, it pairs naturally with our wider range of ROV-mountable subsea inspection equipment.

FMD Accessories & Consumables

A range of FMD accessories completes and maintains your system:

• FMD Umbilical Cable a 120 m OEM-matched tether that preserves power and signal integrity to full depth.
• System Test Piece used to run a full system test before deployment, giving you a documented, defensible verification of the equipment.
• Probe Holder Handles Stainless Steel D-Handle, T-Bar and Fishtail options to suit diver handling or ROV manipulators.

You can also browse all spares and accessories for the wider Cygnus range.

Ultrasonic vs Gamma vs Acoustic FMD: Which Method?

There are three established technologies for flooded member inspection, and the right choice depends on your scope, structure and environment.

Gamma radiography is often deployed when an entire subsea platform requires inspection. But for interim or one-off inspections, an ultrasonic offshore flooded member detector is an excellent, far more economical alternative it is safe, requires little specialist expertise and can be deployed quickly by an on-platform dive team or ROV pilot without outsourcing to a radiation contractor.

Key Benefits

Safe. No gamma rays and no radioactive sources, eliminating radiation paperwork, exclusion zones and the associated health-and-safety logistics.

Cost-effective. The system is owner-operated and extremely easy to learn, so inspections can be carried out by your own team across a range of experience levels without the cost of external contractors.

Reliable. A purpose-designed algorithm combines advanced signal processing, advanced peak detection and low-distortion, low-noise data acquisition to deliver the highest possible Probability of Detection (PoD) and eliminate false readings. A measurement is only ever taken once the contact sensor confirms correct probe contact and alignment, and any loss of contact is flagged at the surface.

Rugged. Built to the highest standards in high-grade acetal for the harshest subsea environments, and backed by a three-year warranty.

Versatile. The compact probe reaches difficult geometry such as K-nodes, works to a depth of 300 msw, and the same unit deploys by both diver and ROV. A built-in System Test Function lets you verify the equipment before every dive.

Applications & Industries

Flooded member detection is essential wherever normally dry tubular members must be confirmed sound:

• Offshore oil & gas routine and post-storm inspection of jacket legs, braces, risers and caissons as part of offshore inspection and IRM programmes.
• Offshore wind & renewables foundations and transition pieces exposed to fatigue and impact.
• Subsea pipelines and connectors confirming integrity in dynamic subsea
• Naval, defence and marine infrastructure mooring systems, piers and submerged structures.

FMD complements wider corrosion-monitoring and wall-loss programmes. Many operators pair an FMD system with underwater ultrasonic thickness gauges to build a complete picture of subsea asset integrity, and with oil and gas pipeline inspection tools topside.

Technical Specifications

Why Choose Cygnus

Cygnus was founded in 1983 and has spent four decades building robust, simple-to-use ultrasonic testing equipment for corrosion inspection and subsea IRM. Our flooded member detectors are designed and manufactured in the UK, supported by ISO 9001-certified quality systems, a three-year warranty and worldwide service. Learn more about why customers choose Cygnus, explore Cygnus’ role in NDT, or read our customer reviews.

Every system is backed by responsive technical support and a global network of calibration and repair centres.