FPSO Bilge-Keel Crack Analysis | Subsea Photogrammetry

BILGE KEEL HERO IMAGE

ROV-deployed photogrammetry confirmed and measured a hairline crack on an FPSO bilge-keel in three planes — and identified unrectified weld deviations from the fabrication drawing.

During a routine UWILD hull inspection, a Norwegian operator identified a potential crack on the bilge-keel of a 25-year-old FPSO. With the structural implications of a confirmed defect requiring precise measurement across all three planes (and the asset still in service) the operator needed dimensional data they could take directly to engineering and class.

Two immediate problems presented themselves:

  • Getting the camera close enough to a hairline crack-like indication while maintaining correct ROV position.
  • Reliably working the ROV at the awkward hull angle where the bilge-keel sits.

Viewport3 were engaged on the back of an existing relationship, having previously delivered actionable 3D data for the client’s subsea assets in the Norwegian sector.

FPSO Bilge Keel crack location confirmation - Photogrammetry - Subsea
FPSO Bilge Keel crack tracing - 3D Photogrammetry - Subsea
FPSO Bilge Keel crack tracing - 3D Photogrammetry - Subsea
FPSO Bilge Keel deviation analysis - 3D photogrammetry
FPSO Bilge Keel deviation analysis - 3D Photogrammetry - Subsea
FPSO Bilge Keel 3D Scanning - Awkward capture angle
Comparison to CAD - missing stiffener weld - FPSO Bilge Keel - Subsea 3D photogrammetry
Raw image - FPSO Bilge Keel Crack - Subsea 3D photogrammetry
Raw image - FPSO Bilge Keel Crack - Subsea 3D photogrammetry

Following discussions with the marine contractor’s ROV team, a work method was agreed, with equipment and personnel being mobilised to Bergen to join the vessel soon after.

Given the challenge of capturing a hairline crack, this wasn’t a job suited to remote support. The team comprised a day-shift supervisor and a night-shift capture technician, with a digital stills, synchronised strobe system and sufficient processing power to reconstruct the 3D data as it was collected.

High-resolution still imagery was used throughout, ensuring dimensional assurance of +/- 0.1mm. In-scene scale references were embedded in the dataset — meaning accuracy is verifiable in the data itself, not just assumed at capture time.

The image dataset was processed into a high-fidelity 3D model and analysed using modern reverse-engineering techniques.

The crack was confirmed. With its presence established, the client instructed Viewport3 to extend the capture area — giving onshore engineering teams the flexibility to assess options for a diver-stage installation and potential removal of the entire bilge-keel.

The dimensionally assured outputs issued to the client covered:

  • Crack measured across all three planes it presented on
  • Several welds identified as non-compliant against the fabrication drawing, on both bilge-keel structures — flagged from the same dataset during our 3.4u inspection
  • Marginal warping of the hull behind both bilge-keels
  • Slight warping of bilge-keels 1 and 2
  • No evidence of cracking on bilge-keel 1

The client received everything the onshore engineering team needed to make a fully informed decision — with no further offshore measurement required.

Start a conversation about your project

Get in touch arrow_outward
Edited-Jamie-Cameron-JO232-Viewport3-Clamp-render-B