Why the inside, and why now
Manufacturing defects live inside the blade: adhesive that did not fill the joint, plies that did not lie flat, a web foot that bonded over part of its length, resin that did not reach the fibres, and the objects a factory leaves behind. None of them shows on the shell. An external commissioning inspection documents the paint, the leading edge and the receptors, which are the parts least likely to have a manufacturing problem, and leaves the parts most likely to have one unrecorded.
Timing matters for two reasons. The first is contractual: most supply agreements give the owner a window after handover to report defects, and after that the burden of proof shifts. The second is comparison: a finding at year four can only be called growth if there is a record from year zero showing what was there. Without a baseline, every later finding is "existing condition, cause unknown", which is the manufacturer's favourite phrase. End-of-warranty blade inspections sets out what that comparison has to look like.
What a new blade interior should look like
Inspectors who have only ever seen blades in service are sometimes unsure what "good" looks like. A new blade, seen from the inside, should show:
- Continuous adhesive fillets along the web feet and the trailing edge, with squeeze-out on both sides. Squeeze-out is a good sign: it means the joint was filled. Gaps in the fillet are the finding, not the excess.
- A flat, even laminate surface on the spar caps and shells, with no ridges, waves or pale patches.
- A dry interior. No pooled water, no moisture staining, no condensation marks running from the tip.
- A fixed lightning conductor, attached at every fixing point along its route, with tight, clean connections at the receptor blocks and at the root.
- Clear drainage holes at the tip, and a sealed balancing chamber where the design has one.
- Nothing loose. No tools, tape, cups, foam offcuts, cable ties or grinding dust.
Wind turbine blade defects that start on the inside describes the defects in detail; the list above is what their absence looks like.
What commonly turns up in new blades
Across new blades of every make, the same handful of findings come back:
- Voids and gaps in the adhesive, most often in the web-to-shell bond where the shells were closed. Short gaps are common; long unbonded runs are a defect.
- Manufacturing leftovers: masking tape, foam blocks, plastic sheeting, occasionally a tool. Anything loose will migrate toward the tip and abrade the laminate as the blade turns.
- Wrinkles in the spar cap or the root build-up, visible as a ridge or a change in reflection. These matter because they grow into delamination under fatigue, and they are unambiguously manufacturing.
- Resin drips and dry patches: cosmetic on their own, but a dry patch next to a bond line is a moisture path.
- Conductor not fixed along part of its length, or a receptor connection that was left finger-tight.
- Water from transport or storage, especially in blades that stood tip-down at a port for a season.
Each of these is easy to document now and hard to argue about later.
How to run it
The inspection is the same procedure as any internal inspection, with the turbine stopped and the blade locked. With Detectra the crawler enters through the root hatch and records up to 80 % of the blade length in 8K 360° video, about 15 minutes of capture per blade, so three blades fit inside a short stop and up to 12 blades fit in a day. Two details matter more at commissioning than at any other time:
- Record the whole blade, not just what looks wrong. The value of a baseline is that it shows the sound areas too. A later finding at 30 metres is only "new" if the baseline shows 30 metres was clean.
- Keep the position on every recording. Detectra tags every take with the distance from the root, so a void at 23 metres on blade B of turbine 7 is a place, not a description, and the year-four inspection can go straight back to it.
The recordings are reviewed at a desk, about 3 hours per turbine today, and the findings live in Fenestra as the fleet's baseline: one record per finding with its position, its severity, its frame and its date, in the customer's own SharePoint.
What to do with the findings
Three groups, three actions:
- Report to the manufacturer inside the contractual window: unbonded lengths, wrinkles, dry laminate, loose conductor, leftovers. Attach the frame, the position and the recording metadata. Ask for a joint inspection where the finding is material.
- Agree monitoring for findings that are within tolerance but worth watching: small voids, minor resin defects. Their position is in the baseline; the next inspection checks them.
- Fix immediately anything loose inside the blade and any blocked drainage, whichever party does it. These are cheap now and expensive after a year of rotation.
The same pattern across several blades is a separate conversation. Six blades of one batch with the same gap at the same distance is a process fault, not six coincidences, and Serial defects are found by inspecting every blade the same way and reviewing them together.
The baseline pays off at the end of the warranty
The end-of-warranty inspection is the commissioning inspection run again, on the same blades, at the same positions, with the two recordings side by side. A void that has not changed in five years is closed out. A void that has become a crack is a claim with a date on both ends. Owners who have both recordings negotiate from evidence; owners who have neither negotiate from photographs taken at the root.
Frequently asked questions
Should a commissioning inspection include the inside of the blade?
Yes. Manufacturing defects are inside: adhesive voids, wrinkles, dry laminate, unfixed conductors and leftovers. An external inspection documents the shell, which is the part least likely to have a manufacturing problem, and leaves the load-carrying structure unrecorded.
What does a good new blade look like from the inside?
Continuous adhesive fillets with squeeze-out on both sides, flat and even laminate, a dry interior, a lightning conductor fixed at every point along its route, clear drainage holes, and nothing loose.
How long does a commissioning inspection with a crawler take?
About 15 minutes of capture per blade with Detectra, with the turbine stopped and the blade locked; up to 12 blades in a day. Review takes about 3 hours per turbine, and the findings become the baseline in Fenestra.