Performing Remote Visual Inspections of Wind Turbine Blades

Increased investment in wind power generation as a popular source of renewable energy in recent years has led to the rapid growth of the Green Economy, making it a crucial component of our energy mix as the industry evolves.

As many existing wind farms enter their second decade of service, and new sites are popping up everywhere the need for inspections and maintenance is growing quickly. Particularly subject to degradation due to the salt-laden air, higher wind velocities, and prolonged UV exposure, wind farms require regular maintenance, making consistent and frequent inspections vital and necessary to keep them functioning properly and safely. Bird strikes & lightning strikes are the real causes. Imbalances too.

While traditional methods like manned entry of inspection have been dangerous, time-consuming, and costly, new technology is revolutionizing the way we inspect wind turbines. In this article, we will explore how using crawlers for blade interior inspections can improve safety, accuracy, and efficiency.

Erik Wilde from Berkeley, CA, USA, CC BY-SA 2.0 , via Wikimedia Commons

What is a Wind Turbine Inspection?

Wind turbine inspections involve the visual inspection and diagnostic testing of key components, such as:

- Structural components

- Electrical systems

- Mechanical components

During an inspection, technicians look for core defects, delamination, internal damages, corrosion, and other issues that result in decreased energy output. They also inspect the gearbox, generator, and other mechanical and electrical components with specialized equipment to ensure optimal performance.

The data collected during the inspection can be utilized to plan maintenance and repair schedules, which helps ensure that the turbine is operating efficiently and safely, and to maximize its lifespan.

Importance of Wind Turbine Inspections

Turbine blades are typically constructed of fiberglass, balsa wood non-recyclable resins, with an average life expectancy of approximately 25 years, so frequent inspections and preventive maintenance are vital for increasing lifespan and delaying their decommissioning.

Catching defects early on also saves a substantial amount of money on potential repairs or replacements, and can prevent having to shut down energy production in order to wait for replacement parts, which can also be incredibly costly.

Inspections should be conducted 2-3 times per year, or after a significant weather event, such as a hurricane or tornado, to check for damage, ensure the turbine is operating efficiently and safely, and to maximize its lifespan.

Inspections are also conducted when a new or used blade is delivered to the farm to ensure it wasn’t damaged during shipping. Once it’s installed up-tower it’s prudent to conduct another visual assessment to ensure it was not damaged during the crane lift or installation process.

Routine inspections are a legal requirement in many countries, and insurance companies often require them when issuing a policy.

To ensure the safe, reliable, and efficient operation of wind turbines, regular inspections are critical. By identifying and addressing potential issues early on, wind farm operators can prevent failures, minimize downtime, optimize performance, and maximize their investment in renewable energy.

Credit: Lance Cheung | https://www.flickr.com/photos/lancecheungmedia/3718170493

Common Wind Turbine Defects

85% of blade failures are caused by poor maintenance. It’s a straightforward statistic that clearly illustrates the critical importance of regular inspections. These failures can be incredibly costly, with the highest reported failure costing over $6 million USD.

Other common wind turbine defects can include:

- Cracks in the tower, blades, nacelle

- Peeling paint in the tower, blades, nacelle

- Lightning damage to the blades, nacelle

- Corrosion on the tower, nacelle

- Deformation of the blades

- Oil splits in the nacelle

- Skewness or loose connections in the hub that connects to the blades

Critical components, such as the nacelle, which is a chassis at the top of the tower that holds the gearbox and generator, need to be free of cracks or damage, and protected from the elements to ensure optimal performance. Power cables that run from the nacelle to the transformer (typically at the base of the tower) also need to be inspected to protect against power loss and ensure safety. Modern transformers are built to withstand harsh environments, but like all components, also need to be regularly inspected for damage or degradation over time.

Defects can have a significant impact on the safety, reliability, and efficiency of the wind turbines. Regular inspections can assist with the prevention of these structural issues and safety hazards that can lead to equipment failure and further damage that can become quite costly.

Inspections also provide critical data that can be utilized to allow operators to schedule maintenance and repairs based on the actual condition of the turbines, rather than waiting for scheduled inspections. More frequent inspections and predictive maintenance can save considerable time and money, greatly reducing repair costs and improving operational efficiency.

Traditional Methods of Wind Turbine Inspections

Traditional methods of wind turbine inspections require visual inspections by highly trained technicians. This method is notoriously dangerous, time consuming, and costly. Today, three main methods of inspection are used most commonly:

- Manual inspections using humans and ropes

- Ground Inspection by Telescope

- Inspection by Drone

Let’s break down each one in more detail and look at the benefits and drawbacks of these methods.

Manual inspections using humans and ropes

Traditional inspections of wind turbines are typically performed by highly trained rope access technicians that utilize ropes and tethering systems to climb inside and outside wind turbines for visual inspections, maintenance, and repairs.

Flickr: GPA Photo Archive | Credit: Dennis Schroeder / NREL | https://www.flickr.com/photos/iip-photo-archive/23095738005

This method can be incredibly dangerous, since the technicians have to climb great heights to inspect components such as the blades and nacelle. Wind turbines are located in extremely windy areas, so blades often fail due to harsh weather conditions, making regular maintenance and inspections a necessity, exposing technicians to the inherent danger that comes with working at heights or within confined spaces.

Recent data reflects that wind is responsible for 1,000 worker deaths per trillion kWhrs produced, falling just behind coal as the most dangerous methods of energy production. As more turbines are built, more accidents occur. Numbers of recorded accidentsreflect this, with an average of 70 accidents per year from 2002-2006; 138 accidents per year from 2007-2011; 171 accidents per year from 2012-2016, and 222 accidents per year from 2017-2021 inclusive.

The dangers that can occur while working in confined spaces and high altitudes are reflected in the tragic loss of 9 and 21 year old mechanics burnt on top of a wind turbine in Deltawind’s Piet de Wit wind farm in the Netherlands. The two men were atop an 80m wind turbine performing routine maintenance while a circuitry issue sparked an internal fire. The height at which the fire occurred made extinguishing very difficult, and the two men were too far situated inside to escape.

Additionally, the cost and time associated with involving multiple specialized employees in a manual inspection process can quickly add up. An average sized turbine takes roughly 3-6 hours to complete, excluding any preparation and safety procedures. With most organizations recommending two inspections per year, this can quickly add up to weeks or months of expensive and dangerous work depending on the size of the wind farm.

Turbines are also turned off for manual inspections, meaning very costly downtime and loss of revenue and energy from operations being halted. Inspections can take up to a full day to complete, and the blades need to be stopped for an average 4 to 6 days, making this method the most time consuming and expensive. The blades are stopped in the six o'clock position, and the team ascends the tower to look for damage and knock on the blades to determine the condition of the materials.

Ground Inspection by Telescope

Ground inspections of wind turbines are a much safer method of inspection compared to rope access inspections, but this method also comes with its own benefits and drawbacks. Typically, a technician walks around the base of the turbine and visually inspects the tower, foundation, and electrical components, taking pictures, or using a telescope attached to a camera to get a better view of the components located at higher altitudes and detect any cracks or defects.

Credit: image from rawpixel.com

This method can be time-consuming since photographing the blades requires setting up the camera in multiple positions and rotating the blades to capture all sides as thoroughly as possible. It also lacks the precision and visibility of other methods, since the technician is not able to get a close-up view of the blades or components, making it difficult to identify smaller defects or damage.

Ground inspections can also be weather-dependent, as visibility can be limited in fog, rain, or other unfavorable weather conditions. This method is also not effective for offshore wind turbines, further limiting its efficacy. somewhat

The main benefits of ground inspections are safety and cost. Technicians do not need to climb the tower or use specialized equipment to perform the inspection, and because it does not require the use of specialized equipment or highly trained rope access technicians. This method is also effective at identifying issues such as foundation settling or cracks in the tower that may be visible from the ground.

Inspection by Drone

The use of drones for wind turbine inspections has become increasingly popular in recent years. Deploying aerial drones in lieu of workers empowers teams to complete a thorough exterior inspection remotely. This eliminates any concerns of safety, since the pilot can remain on ground level.

Credit: Ana Sibler | https://pixabay.com/photos/wind-farm-drone-wind-turbines-6488218

Additionally, removing any need for prep or safety rope precautions, the inspection can be done by a single operator in less than an hour (about 12% of the time it takes to complete using traditional methods). Beyond improving work efficiencies and employee safety, this also saves the high cost of lost energy production due to downtime per inspection.

Another benefit is the ability to record video and take photos with the drone, allowing for more thorough and precise inspections to notify maintenance crews about damage or operational failure they might have missed from physical inspections with the naked eye.

One downfall of aerial drones for inspection is the lacking performance in confined or inclement conditions. While they are an extremely useful tool for exterior inspections, turbine hubs and blades may prove challenging for navigation and connectivity. Additionally, blades commonly utilize a variety of lubricating fluids, which in an exposed motor system can result in failures. With nothing tethering the vehicle, this can quickly turn into a dangerous retrieval mission.

Using A Crawler For Wind Turbine Inspections

Pipe crawlers are a newer method of wind turbine inspections and may not be as well known to the general public as aerial drones due to their primarily industrial application; however, they are an invaluable tool and growing in popularity for turbine inspections. These vehicles are tethered and land-based, rendering them obsolete for exterior inspections, but they fill the much needed gap of a safe and reliable solution for entering and inspecting the blades, since aerial drones are not effective when it comes to entering the turbine. Traditionally, technicians would be required to crawl these blades during inspections, which can be quite dangerous and result in injury or even death. Turbine blades are generally thin, lubricated confined “tunnels” with no exits, making them a high risk for human workers to enter.

Utilizing a battery powered pipe crawler, workers can either hand-carry or crane/winch hoist the vehicle to the hub. Once atop, a single operator can drive the crawler through the blade, recording footage along the way.

When are Wind Turbine Blades Inspected

Wind turbine inspections are required at various stages of the life cycle to help ensure reliability, safety and performance. This includes on the ground during construction, and in the air on fully constructed turbines.

During construction, wind turbine blades are inspected on the ground before they are installed on the tower. At this stage, technicians look for any manufacturing defects, shipping damage, or other issues that may have occurred during transportation. Once installed, the blades are also inspected for proper installation of the blades and the structural integrity of the turbine.

After the wind turbine construction is completed and it is fully operational, the blades are inspected while the turbine is in operation, or by accessing the blades via specialized platforms or equipment such as cherry pickers or cranes. This is also when drones may be used to inspect wind turbine blades in the air.

How do crawlers work for wind turbine inspections

Robotic crawlers are specialized remotely operated vehicles (ROVs) that can withstand the harsh operating environment and safely access hard-to-reach areas of the turbine to perform close-up inspections that would not be possible or require rope access.

ROV crawlers are typically equipped with bright LED lights and cameras that allow for close-up inspections of the blades and other components, and give operators the ability to navigate inside the blades to get eyes in spaces that are generally not possible to inspect. These cameras can capture high-resolution images and videos, which transmits the data for analysis to a technician remotely operating the vehicle from the ground.

In addition to cameras, crawlers can also be equipped with modular add-ons and sensors, such as sonar, laser scanners, or thermal imaging sensors that can detect defects or damage not visible to the naked eye.

Data captured from inspections can then be reviewed and analyzed, allowing for proactive measures and optimizing of maintenance and repair schedules based on the historical data captured and the ability to analyze the state of structural integrity and wear over time.

Benefits of Using a Crawler

Using ROV crawlers for turbine inspections has many benefits compared to human entry. One key benefit is the limits to which the crawler can survey. Blades will slowly lose diameter as they reach the end, with most being unreachable for the last 30% - they are typically longer than the wingspan of a Boeing 747, to put it into perspective. Using a pipe crawler, workers can get a clear visual of the entire length. A missed defect can be a costly mistake, so the ability to fully inspect the entire blade length is imperative.

Crawlers are also capable of more thorough and precise inspections of assets, giving technicians access to enhanced data accuracy and analysis compared to traditional inspection methods. With the ability to capture high resolution images and video, operators can also analyze data sets to plan and optimize maintenance and repair schedules and ensure structural integrity of assets over time on a more frequent and consistent basis.

This method of inspection is a much safer and reliable solution for inspecting turbine blades, removing the need to send human operators into confined spaces or climb dangerous heights that puts their lives at risk.

Another benefit of using crawlers for turbine inspections is that they are incredibly cost effective, compared to having to hire a team of highly trained rope access specialists and pay per inspection, per turbine. With a crawler, you only have the one time cost of purchase and can use it whenever you need it, with minimal to no repairs needed for potentially years to come.

Using a crawler for turbine inspections is also much less time consuming. Traditional inspections using rope access teams can take approximately 3-6 hours per turbine, whereas using a crawler can take less than an hour to complete a full inspection.

Why Choose Pipe Trekker?

Pipe Trekker manufactures the industry’s first truly portable, battery-operated, submersible crawler systems, leveraging over a decade of design principles and innovations from building underwater robots under the Deep Trekker brand.

Pipe Trekker crawlers are easy to deploy and pilot, requiring no extensive training for first time pilots. Equipped with a lift arm for viewing the tops of pipes, or blades, and high-resolution cameras, operators can live stream inspections in real time and record data for further analysis. With long battery life, Pipe Trekker crawlers are capable of inspecting many turbines in a single day.

Depending on the size of the blade, or pipe width, there are a few models and packages to choose from to best fit your needs. Check out the chart below for a quick comparison of the models and packages available through Pipe Trekker.

We offer a range of proven options to solve many challenges you might face, with accessories like sonar, laser scanners, reporting software integration, and an elevated camera head, to name a few. To learn more about our pipe crawlers, you can also check out our Pipe Crawler Buying Guide.

Whatever your project is, we have a customizable solution for you! Want more information on how Pipe Trekker crawlers can make wind turbine inspections easier, safer, and more affordable for you and your team? Our team of industry experts are available to answer any questions you may have about our pipe crawlers, reach out today!