What is different offshore
Access is the cost. Onshore, a technician drives to the turbine. Offshore, the transfer is a vessel day, a walk-to-work gangway or a boat landing, and a limited number of people on the turbine at a time. Whatever the inspection method, it is paid for in vessel time and crew time before any inspection happens.
Weather sets the schedule. Transfers and work at height depend on wave height and wind speed. Inspection windows are short, and a method that needs a full shift inside a blade may not get one. A method that needs a short stop per blade fits into the windows that exist.
Downtime is expensive. Offshore turbines are large, and an offshore hour of lost production is worth more than an onshore one. Any method that keeps the rotor stopped for hours per turbine is competing with production.
Blades are larger. Offshore blades are longer, with longer bond lines, thicker root laminates and a greater distance between the root and the part of the blade that matters most. The gap between what a technician can reach from the root and what is actually there is wider than onshore. See What an internal blade inspection covers.
Lightning is more frequent. Offshore turbines are tall, exposed and often the highest structures for kilometres. Strike rates are higher, and the internal lightning conductor is inspected less often because getting inside is hard. Lightning damage inside a wind turbine blade covers what to look for.
Salt and moisture. Water ingress and corrosion at receptor connections and conductor joints are more common at sea. Standing water in the tip is a mass and an ice risk in northern waters.
What an offshore internal inspection has looked like
A confined-space entry from the root: two technicians at least, a rescue plan, breathing air monitoring, the turbine locked for the duration, and coverage that ends a short way past the root. The report is a set of photographs without a position reference. Because the cost is high and the coverage small, most offshore fleets have had internal inspections only when something forced them: a failure elsewhere in the fleet, a serial defect notice from the manufacturer, or an insurer's requirement.
What changes with a crawler
Detectra was built with offshore access in mind, and LUKAN has inspected blades offshore in Germany with it. The relevant numbers:
- 3.7 kg, two transport cases. The whole kit, crawler, tablet, cable, batteries and chargers, travels as hand-carried luggage on a vessel and up a turbine.
- About 15 minutes of capture per blade. The rotor is stopped, the blade locked, the crawler placed in the root and driven up to 80 % of the blade length and back. Three blades fit inside a single weather window with time to spare.
- Up to 12 blade inspections per day on one set of batteries, which in offshore terms means several turbines from one transfer.
- No one in the blade. The operator stays at the root with the tablet. The confined-space rescue plan for the blade interior is not needed for the inspection itself.
- Offline by design. The tablet joins the crawler's own wireless link and the recordings are stored on board. No connection to shore is needed during the inspection.
- Review onshore. The recordings are uploaded to Fenestra when the crew is back, and the review, about 3 hours per turbine today, is done at a desk by whoever knows the blade type best, not by whoever was on the boat.
The result is that an internal inspection stops being an exceptional campaign and becomes something that can be added to a routine maintenance visit: the same vessel, the same crew, an hour more per turbine.
Planning an offshore internal campaign
A few things that help:
- Pick the turbines by risk, not by convenience. Turbines with recorded lightning strikes, external trailing-edge findings or a blade type with a known serial defect go first.
- Pair it with work already scheduled. The transfer is the cost. An internal capture on a turbine already stopped for other maintenance costs only the capture time.
- Baseline the fleet before the warranty ends. Offshore blade warranties end on a date, and the evidence has to exist before it. End-of-warranty blade inspections explains what the record needs to contain.
- Keep the review off the vessel. Nobody reviews footage well on a moving ship at the end of a shift. Capture at sea, review onshore, and compare against the previous recording of the same blade.
- Keep the data in your own systems. Fenestra stores the recordings and findings in the customer's own SharePoint, hosted in the EU, so the record belongs to the owner and outlives any single contractor relationship.
Frequently asked questions
Why is offshore blade inspection more expensive than onshore?
Because access is paid for in vessel time, crew time and weather windows before any inspection begins, and because a stopped offshore turbine loses more production per hour. The inspection method has to fit inside those constraints.
How long does an internal blade inspection take offshore?
With Detectra, about 15 minutes of capture per blade with the rotor stopped and the blade locked. Up to 12 blades can be captured in a day on one set of batteries. The review is done onshore afterwards, about 3 hours per turbine today.
Does an internal crawler need a connection to shore?
No. The tablet connects to the crawler's own wireless link, and the recordings are stored on board the crawler until they are uploaded to the cloud portal after the visit.