Offshore Blade Inspection: Salt Fog, Wind and Transfer Cost

What this stage covers

The scope is a blade on a marine site, inspected with the fewest personnel and the widest usable window. A crawler sealed to IP67 and NEMA 4X runs in salt fog, a 100 m fibre link or a 4G and 5G radio link keeps the technician on the nacelle or deck, and a single technician runs the scan while the analysis team works ashore.

What the inspection includes

• A crawler sealed to IP67 and NEMA 4X with operation rated to minus 20 °C for continuous salt-fog exposure
• A 100 m fibre-optic tether or a 4G and 5G radio link for single-technician remote operation
• A 6 h hot-swappable battery for a full shift without a return to the vessel
• Real-time data push to an onshore dashboard so the analysis team never leaves the office

Where the value sits

The driver is the transfer cost and the window. A technician transfer by crew transfer vessel runs EUR 800-1,500 a day, and a window that closes after a few hours leaves a blade uninspected until the next one. A crawler rated to 15 m/s against the 10 m/s rope limit adds roughly 40 % to the operable window in the North Sea, and keeping one technician on the nacelle while the scan runs from the deck removes the rope team from the transfer count. The lead-edge threshold an offshore programme works to also tightens to 3 mm under DNV-ST-0126, so the scan has to resolve a smaller defect on the same blade.

How to plan this stage

Run these checks in order. By Step 5 the scan, the threshold and the record are aligned to the stage.

1. Fix the acceptance threshold. Start from the threshold the zone carries, not from the method you happen to own. IEC 61400-5 Section 11 asks for volumetric detection of indications 6 mm and larger in the laminate plane, and DNV-ST-0126 tightens the leading edge to 3 mm, so the threshold is set before the probe is chosen.
2. Read the geometry off the drawing. Measure the thickness and the curvature the probe has to travel. A spar cap up to 80 mm of unidirectional laminate and a root transition of changing radius are two different scan problems, and the radius decides how the array is coupled.
3. Choose the modality pair. Pick modules by defect geometry, not by habit. PAUT images planar separations that lie parallel to the plies, TOFD catches volumetric clusters whatever their orientation, and running both on a 256-channel system puts the two mechanisms in one pass.
4. Automate the scan path. Put the probe on an encoder-driven carriage and let the path, not the technician, set coverage. A 600 mm spar cap falls to one longitudinal pass at 500 mm/s on a linear array, where a single-element probe needs 20 parallel passes and runs about five times longer.
5. Lock the evidence chain. Write the coverage map, the daily calibration and the indication log to the blade serial while the scan is running. It is the difference between a 3-day type-certification audit and a 3-hour document review, and it is what ISO 9712 qualification is there to sign.

Every figure on this page traces to our own product and field documentation, so a claim here can be checked against the datasheet it came from.