What is different offshore

Access and cost

Onshore, a failed blade is reached by road and a crane within days. Offshore, every step needs a vessel: crew transfer for inspection, a jack-up or heavy lift vessel for a blade exchange, and a weather window for each. The direct cost of an intervention is an order of magnitude higher, and the elapsed time is set by the sea state, not by the engineering. The consequence for the investigation is that there is usually one visit to do the forensic work properly, and it has to be planned as such.

Blade size and loads

Offshore blades are now well over 100 metres. The scaling problems of very large blades, which we set out in technology qualification for blades over 100 m, are all present: thicker laminates that are harder to infuse and inspect, longer bond lines, greater sensitivity to wrinkles in thick spar caps, and root joints carrying bending moments that no previous blade generation has carried. The margin for a manufacturing deviation is smaller, and its consequence larger.

Evidence recovery

Onshore, the debris field is walked and photographed. Offshore, part of the blade may be on the seabed or drifting, and what is recovered has been in salt water. The fracture surfaces that carry most of the evidence about the initiating cause are the first thing damaged by handling and immersion. Securing the blade remains, photographing them before recovery, and keeping fracture surfaces dry and unhandled after recovery matters more offshore than anywhere else, and it is rarely done well without someone on the vessel whose job it is.

Fleet exposure

Very large blades are made in few plants with recent processes. When a failure is traced to a manufacturing deviation, the population that shares the process is the whole supply from that plant, and the cost of inspecting or replacing it offshore is what makes the serial defect question the decisive one. The two most public offshore blade failures of 2024 illustrate both outcomes: one was attributed by the turbine manufacturer to an installation error at sea, an isolated event (offshoreWIND.biz, 25 July 2024); the other to a manufacturing deviation, followed by the reinspection of about 150 blades from the same factory (Vineyard Gazette, 24 July 2024). Which of the two a failure is decides whether the insurer is looking at one claim or a fleet.

Third parties and the public record

Offshore debris is a hazard to shipping and fishing, and an offshore failure is a public event in a way an onshore one usually is not (Fishing News, 5 September 2024). Regulators, the marine authority and the press will all want a statement of cause before the investigation has produced one. An independent expert's early view of what the evidence supports, suggests and cannot yet determine is often the only defensible thing to say.

What an independent offshore investigation covers

The core is the same as onshore: establish the initiating cause, the sequence of events, when the cause entered the blade and whether it is isolated or serial. Offshore adds specific items to the scope.

  • Planning the single visit. What will be photographed, sampled and measured on the turbine and on the recovered remains, in what order, before the weather closes the window.
  • Installation records. Offshore blades are lifted at sea, often in marginal conditions, and installation damage is a live candidate. Lifting logs, sea state at installation, any recorded contact, and the pre-installation inspection are evidence.
  • Marine and environmental data. Wind and wave conditions at the time of failure, against the design basis and the site conditions the type certificate assumed.
  • SCADA and control state. As onshore, but with attention to any curtailment, control strategy or extreme event mode active at the time.
  • Recovered remains. Custody, handling and preservation of the fracture surfaces from the moment of recovery, because the laboratory analysis depends on them.
  • The laboratory analysis. Attendance at the manufacturer's laboratory as observing expert, because the mechanism is fixed there and offshore blades rarely offer a second chance to sample.
  • The population. Which blades share the plant, mould and production period, what inspection method can see the suspected defect, and which turbines can operate in the meantime.

The insurer's, owner's and lender's questions

The parties want the same technical answer for different decisions, and offshore the sums make each decision larger. The insurer needs to know whether the policy responds and whether there is a recovery against the manufacturer or the installer, which is set out in blade failure insurance claims. The owner needs to know which turbines can run and what the warranty position is. The lender needs an independent technical position before restart or the release of funds. A report that separates what the evidence supports from what it suggests, with the confidence in each conclusion stated, is what lets all three act.

Monitoring and inspection offshore

Because access is expensive, the value of early warning is higher offshore than anywhere else, and it is where blade condition monitoring systems most often justify their cost. It is also where the inspection interval is most often stretched for budget reasons, and where a serial defect therefore has longest to develop unseen. In our judgement an offshore fleet with a blade type of recent design and a single supplying plant should have its inspection regime set by that risk, not by the standard interval.

Frequently asked questions

Why are offshore blade failures more expensive than onshore?

Every intervention needs a vessel and a weather window, the blades are larger, and the fleet exposure from a serial defect is larger because very large blades come from few plants. The engineering is the same; the logistics and the sums are not.

Can the cause of an offshore blade failure be established if part of the blade is lost at sea?

Often, yes. The initiating cause is usually near the root, the spar cap or a bond line, and the remains on the turbine carry the fracture surfaces that matter. The recovered pieces add to it. What is lost is usually consequential damage, not the origin.

Should an independent expert be on the vessel?

For the forensic visit, yes. There is usually one chance to photograph, sample and preserve the evidence properly, and it should not be left to the party whose product failed or to a crew whose priority is the exchange.

How does an offshore investigation deal with the manufacturer's root cause analysis?

The same way as onshore: by being present at the laboratory analysis, reviewing the reasoning, and stating independently what the evidence supports. Offshore, the difficulty of taking further samples makes presence at the first analysis more important, not less.

How Apex Wind can help

We are an independent blade engineering consultancy in Denmark, working for insurers, owners, lenders and their lawyers on onshore and offshore blade failures. We are independent of every turbine and blade manufacturer, sell no repairs or hardware and take no referral fees. Our blade failure investigation and root cause analysis covers the forensic visit, the recovered remains, attendance at the manufacturer's laboratory and the serial defect assessment across the fleet. Where the failure becomes a claim or a dispute, we provide expert witness and dispute support. If a blade has failed offshore, contact us before the first vessel sails.