Why the inside
Manufacturing defects are laid into the blade when it is made: a wrinkle where the plies did not lie flat, a void where the adhesive did not fill the joint, a dry region where the resin did not reach, a web foot that did not bond over its full length. None of these is visible on the shell. All of them are visible, or leave visible signs, on the inside. An end-of-warranty inspection that only photographs the outside of the blade documents erosion and lightning receptors, which are operating damage, and misses the findings that a claim is built on.
Wind turbine blade defects that start on the inside describes each of these defects. The ones most relevant to a warranty are:
- Laminate wrinkles in the spar cap and root, which are manufacturing by definition.
- Missing adhesive, voids and unbonded lengths in the web-to-shell and trailing-edge joints.
- Dry fibres and resin-starved areas.
- Manufacturing leftovers inside the blade: tools, tape, foam offcuts.
- Repeated findings of the same kind at the same position on several blades, which point to a process fault and a possible serial defect.
What the record has to contain
A finding that cannot be located, dated or reproduced is easy to dispute. A claim rests on a record with five properties:
- Position. Distance from the root and location in the section, so the manufacturer's own inspector can go to the same place and see the same thing.
- Date. Clearly before the warranty end date, with the recording's metadata to prove it.
- Context. Not a close-up alone, but the finding in its surroundings, so its extent and orientation are unambiguous. A 360° recording provides this by default, because the whole sphere around the finding is in the frame.
- Comparability. Where an earlier inspection exists, the same position at the earlier date, so growth or stability can be shown.
- Traceability. Every finding in the report linked to the exact frame it was flagged on, so the report and the evidence cannot drift apart.
A technician's photographs from the root fail on the first point and usually on the third. A distance-tagged recording of the whole blade interior meets all five. Detectra records up to 80 % of the blade length in 8K 360° with the distance from the root on every take, and in Fenestra each finding is flagged on the frame it was seen on, with the report generated from those flags.
Fleet patterns are worth more than single findings
One void in one bond line is a finding. The same void, at the same distance from the root, on twelve blades of the same type, is a manufacturing process fault, and the conversation with the manufacturer is a different one. Finding the pattern requires the whole fleet to be inspected the same way, with findings stored as data with positions rather than as reports. From inspection findings to asset decisions sets out what that takes. For an end-of-warranty campaign, it means inspecting every blade, not a sample, and reviewing them together.
Timing
The inspection needs to be finished, reviewed and reported before the warranty end date, with time for the manufacturer's response and any joint inspection. Working back from the date:
- Review and reporting take time. With a crawler recording, review is about 3 hours per turbine today; for a large fleet that is weeks, not days.
- Capture is fast with a crawler, about 15 minutes per blade and up to 12 blades per day, but it needs stopped turbines and, offshore, weather windows. See Offshore wind blade inspections.
- Planning should start early enough that the campaign is not squeezed into the last quarter of the warranty, when every other owner with the same turbine type is trying to do the same thing.
A fleet that was baselined at commissioning, or at any earlier point, has a comparison ready. One that was not is starting from a single inspection, which still documents manufacturing defects but cannot show growth.
What the inspection does not do
An inspection documents the condition of the blade. Whether a given finding is a warranty matter depends on the contract, the manufacturer's specification and the assessment of an engineer who knows the blade type. The inspection is what puts that engineer in a position to make the case. Without a positioned, dated, frame-traceable record of the inside of every blade, there is no case to make.
Frequently asked questions
When should an end-of-warranty blade inspection be done?
Early enough that the capture, the review, the report and the manufacturer's response all fit before the warranty end date. For a large fleet, planning starts a year ahead; the capture itself is fast with a crawler, but review takes about 3 hours per turbine and the manufacturer needs time to respond.
Why inspect the inside of the blade before the warranty ends?
Because manufacturing defects, wrinkles, adhesive voids, unbonded joints and dry laminate, are inside the blade and leave no mark on the shell while they are small. An external inspection documents operating damage; an internal one documents what the manufacturer built.
What evidence does a blade warranty claim need?
Findings with a position along the blade, a date before the warranty end, the surrounding context in the image, a comparison with any earlier inspection, and a link from every reported finding to the frame it was seen on. Patterns across several blades of the same type strengthen the case considerably.