The inspection process for offshore wind turbines is a crucial step in ensuring the performance and safety of the installations. Each inner and outer blade, which can be up to 75 metres long, undergoes rigorous checks as soon as it leaves the factory. This strict supervision makes it possible to anticipate defects, ensure the traceability of components and limit risks during commissioning at sea.

International challenges and project context

The markets

Initially, France was one of the most dynamic countries in terms of offshore wind farm projects. Recently, this momentum has spread to the rest of Europe. However, Europe is not the only continent involved in the race for wind energy, with Asia and the United States also holding a large share of contracts.

Manufacturing areas

There is no predefined area; this activity is spread across the four corners of the world to match the distribution of markets. However, buyers will favour areas closest to their future fleet in order to reduce their carbon footprint.

Pre-assembly areas

As the name suggests, these areas are used to gather all the components of the wind turbine on land before it is assembled at sea. Here you can find the large blades stored, ready for use as soon as they leave the factory, the tower cabling and even sections of the towers.

The two key stages of inspection during the manufacturing phase

In general, an equipment inspection or QA/QC process consists of two key steps:

• Visual inspections
• The review or documentary analysis.

Blade-specific inspections

During the manufacturing phase, there are numerous inspections and checks. During these inspections, which focus on materials, three areas are carefully observed:

• The leading edge, the first part in contact with the wind
• The trailing edge, the lowest part where the wind will flow over the blade.
• The root, the blade’s entry point.

First, the team of inspectors carries out various inspections of the machine, then our technical expert specialising in offshore blade inspection carries out a more thorough re-inspection. This final inspection adds real value and is based on a document that is adjusted according to the manufacturer’s and/or end customer’s requirements.

On average, our expert spends 1.5 hours analysing a 75-metre blade. This thorough process ensures early detection of anomalies. From February 2024 until the end of July 2025, our expert will be working on a project to inspect 200 wind turbine blades. This represents more than 300 cumulative hours of inspection.

Key monitoring documentation

The manufacturer must provide a tracking document called an Inspection Test Plan (ITP). This document lists all tests and inspections carried out previously, as well as those requested by the customer.

The non-compliance register

Throughout the lifetime of a wind turbine, its identity and integrity will be monitored using the non-compliance register, which contains all critical defects and malfunctions identified during the design phase. The number of defects varies from one wind turbine to another.

Following this thorough analysis, engineers step in to address the defects identified. Each anomaly is dealt with after being noted by our inspector. The duration of the repair varies depending on the severity of the defect: in the most complex cases, it can take up to several months.

The traceability file

The traceability file contains all manufacturing certificates, all test results from the construction phase, and a record of the various stages of the project.

This final documentation is called a BOOK. There are five books in total, each corresponding to a stage in the wind turbine’s life cycle, ensuring complete traceability. It contains the values produced by the wind turbine. These are part of the criteria used by the supplier to decide whether or not the wind turbine is ready to be installed at sea. However, to ensure proper compliance, it is sometimes necessary to call on a third party, often a technical expert, to ensure the neutrality of the energy output scores recorded.

Operation prior to launch

Now that our energy source has been assembled and is ready for delivery to sea, it is time to make one final check to ensure that it is fully capable of performing its mission optimally.

The final inspection of a wind turbine

Our expert carries out a comprehensive inspection of the blade, both inside and outside. He analyses existing defects and any new types of defects that may have occurred during transport by ship or via specific machinery.

This inspection allows us to determine whether the manufacturing process has been followed correctly. For example, it often happens during transport that a defect initially identified as being the size of a thumb triples in size, turning a minor defect into a major one. This can be caused by an accumulation of paint residue or dust.

At this point, it is essential to investigate the origin of the defect, the causes of its appearance, and to update the acceptance criteria.

Namely, small residues inside the wind turbine can clog the drain hole after several years and cause the machine to shut down completely.

The drain hole is a component of the wind turbine that serves two purposes. It allows accumulated water to drain properly and also prevents the turbine from being damaged by lightning.

The purpose of this final check is to ensure compliance at the time of launch, but more broadly over several years.

In certain cases or depending on customer requirements, a final counter-inspection may be carried out to examine: the paintwork, non-compliant repairs or missing fibres.

Post-installation inspection

Once the wind turbine has been installed at sea, the inspection process continues.

Examples of quality control indicators

All wind turbines are equipped with a lightning protection system located on the drain hole, which is connected to the ground after a long route. A significant concentration of water in the blade causes the drain hole to malfunction and can cause the blade to burst. This part is inspected and checked during offshore installation, and a resistance test is planned to check the connections.

Specific tests

The maintenance phases of offshore wind turbines are just as important as the construction inspections of the machine. Beyond installation, maintenance plays a key role in the durability of the equipment. It is important to have offshore wind turbines checked every two years, or even every year. These inspections can be carried out physically or by drones. During these maintenance phases, our technical expert will seek to validate compliance and non-compliance after the assembly stages.

Other resistance tests can be carried out, particularly on the paintwork, paint thickness, blade weight, moment of inertia (rotation) and blade balance, which affects stability.

These various checks, whether carried out upstream or downstream, contribute to the overall reliability of offshore wind farms.

In summary, the inspection of offshore wind turbine blades is a complex process governed by strict quality and safety protocols. This rigour not only guarantees the performance of the installations, but also their reliability, in a rapidly expanding and highly competitive international context.