What the end of warranty changes
Under most supply and service agreements the manufacturer warrants the blades against defects in design, materials and workmanship for a defined period after commissioning, commonly two to five years, sometimes longer for blades specifically. During that period a defect found and notified is repaired or replaced at the manufacturer's cost. After it, the owner pays, and a defect that was present all along but not notified in time is treated as if it had never been covered.
The commercial consequence is simple. Every structural defect that the blades left the factory with, every laminate wrinkle, starved bond line, dry-fibre region and delamination, is a warranty matter on the day before expiry and an owner's cost on the day after. The inspection that separates the two is worth more than any other inspection in the blade's life.
Why the manufacturer's inspection is not enough
Most agreements provide for an end-of-warranty inspection by the manufacturer. It is worth having, and it is not sufficient, for reasons that have nothing to do with competence:
- It is carried out by the party whose liability is ending. The inspector's employer pays for whatever is found. That is a structural conflict, not an accusation.
- It is graded on the manufacturer's own scale. Damage categories are not standardised, and the boundary between "monitor" and "repair under warranty" is where the money sits.
- It is usually external. A drone survey sees the surface. The defects that cost most, in the spar cap, the bond lines and the root, are inside.
- It reports condition, not cause. A finding recorded as "trailing edge crack, category 3, monitor" says nothing about whether the bond line was starved at manufacture, which is the question the warranty turns on.
An owner who relies on the manufacturer's report alone has let the counterparty define the claim.
What an independent end-of-warranty inspection must cover
Scope
- Every blade, all four faces, externally, imaged at a resolution that shows whether fibres are exposed, with the rotor positioned so that the leading edge, trailing edge, pressure side and suction side are each seen square on.
- An internal survey of a defined sample, by crawler or technician, covering bond lines, shear webs, the inner skin over the spar caps and the root laminate around the inserts. The sample should be sized by the blade type's known-issue history and increased if the first blades show anything.
- Lightning protection continuity on every blade, and the receptor condition, because a lightning defect notified after expiry is an owner's cost.
- Root bolt tension on a sample, and the root face for moisture.
- Leading edge condition by stage, because erosion that has reached the laminate is a structural finding and may be a coating warranty matter.
Method and records
- A written method statement: positions, camera, resolution, lighting, weather, coverage.
- The commissioning or handover inspection beside it, so that every finding can be classed as new since handover or present at handover. Present at handover is the strongest warranty position there is.
- Every finding tied to a blade serial number, not a turbine position, because blades move between turbines and claims follow serials.
- The repair history for each blade, with method statements, because a repair carried out under warranty is itself a warrantable item.
The known-issue list
Before the inspection, obtain what is known about this blade type and this manufacturing plant: technical bulletins, field notices, retrofit campaigns, and any public failure history. An inspector who knows that a particular blade type has a history of root insert movement or trailing edge disbond at maximum chord looks there first, and looks with the method that can see it. Serial defects are found by people who know what they are looking for.
The claims list
The output is not a report. It is a list of notifiable defects, each with the evidence that it is a defect in design, materials or workmanship rather than wear, damage or misuse, in the form and to the address the agreement requires, submitted before the date the agreement sets. A finding that is not notified correctly is not a claim.
When to start
Later than most owners think is safe. The sequence is: inspect, review, identify claimable items, gather evidence, notify, and then negotiate with a manufacturer who will contest the classification. Agreements often require notification within a defined period of discovery and always before expiry. In our judgement the inspection should be complete at least six months before the warranty ends, which means it is commissioned nine to twelve months before, and for a large fleet earlier. A fleet inspected in the last quarter of its warranty finds the same defects and claims fewer of them.
What to do with contested findings
The manufacturer will classify a proportion of the findings as cosmetic, as operational damage, or as within tolerance. Some of those classifications will be right. The way to tell is not to argue about the category but to establish the cause: a trailing edge crack that started at a void in the adhesive is a workmanship defect whatever category it carries. Where the sum in dispute justifies it, cutting a sample from a repaired or replaced blade and reading the cross-section settles the question in a way no photograph can. That is failure investigation applied before failure, and it is where an independent engineer earns the fee many times over.
After the warranty
The end-of-warranty inspection is also the baseline for the rest of the blade's life. The record it produces, by serial number, with method and categories defined, is what every later inspection report is compared against, what a due diligence at the next transaction reads first, and what an insurer will ask for after a failure. Done properly once, it pays for itself three times.
Frequently asked questions
Is the manufacturer's end-of-warranty inspection enough?
No. It is carried out by the party whose liability is ending, graded on its own scale, usually external only, and it reports condition rather than cause. It should be received, and then checked against an independent inspection.
When should an end-of-warranty blade inspection be done?
Complete at least six months before expiry, commissioned nine to twelve months before. The time is needed for review, evidence, notification and the negotiation that follows. Check the notification requirements in your own agreement.
Does the inspection need to go inside the blades?
Yes, for a sample at least. The defects that cost most, in the spar caps, the bond lines and the root, are not visible from outside, and a claim for them needs evidence that only an internal survey or a cut sample provides.
What if the manufacturer disputes a finding?
Establish the cause rather than argue the category. A cross-section through a contested finding shows whether it originated in manufacture, and that is what the warranty turns on.
How Apex Wind can help
We are an independent blade engineering consultancy in Denmark. We do not carry out inspections and we do not repair blades, so we have no interest in the inspection scope beyond what the owner needs from it. We scope and review end-of-warranty inspections, read the manufacturer's report against the independent one, establish the cause of contested findings and prepare the technical basis for the claims list. That sits within our blade technical due diligence and, where a finding is disputed, our blade failure investigation. If your warranty ends within the next eighteen months, contact us now rather than in the last quarter.