SNL Researchers Assess Wind Turbine Blade Inspection and Repair Methods

May 18, 2015

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A picture of several wind turbine blade panels set out on a table and held in place with metal clamps.

Flaws in wind turbine blades emanating from the manufacturing process are an important factor in blade reliability. Blade failures can cause extensive down time and lead to expensive repairs, which increase both cost and cost-uncertainty for manufacturers and wind farm operators. Augmenting this risk, over the past decade, blades have become larger and relatively lighter with the use of carbon fiber. Because of the opacity of carbon fiber, it is not possible to visually inspect the blades, placing increased requirements on inspection technology to ensure their quality and reliability. To reduce uncertainty in the blade manufacturing process and improve their design and performance, the U.S. Department of Energy’s Sandia National Laboratories (SNL) is working with industry to evaluate nondestructive inspection (NDI) technologies. There are many different types of NDI technologies including, but not limited to, ultrasonic, microwave, shearography, and thermography. As the name implies, NDI techniques are used as a means to evaluate the integrity of the blade while avoiding a destructive test such as cutting the blade cross section.

NDI requirements, methods, and practices currently vary widely within the wind industry. Different blade manufacturers and blade service companies use different NDI methods on blades in the factory and in the field, leading to uncertainty in the actual condition of the blades. A rigorous, statistical evaluation of NDI capabilities is a key step in SNL’s efforts to improve blade reliability.

In 2010, SNL formed the Blade Reliability Collaborative (BRC) to bring together industry, labs, and academia to address current and emerging issues regarding wind turbine blade failures. Through the knowledge gained from the BRC, SNL scientists have now created the world’s first set of wind turbine blade inspection panels and begun an experiment to quantify the performance of conventional and advanced inspection systems.

Based on extensive input from industry reviewers, the researchers designed the panels to replicate critical wind turbine blade structures, but with carefully designed flaws embedded in them. The first test campaign, Wind Inspection NDI Experiment (WINDIE), used a set of panels that contained flaw types, sizes, and locations that were known by the inspection technicians. This allowed manufacturers to screen and improve existing NDI technologies. WINDIE was completed in 2014. A follow-on probability of detection test campaign is ongoing and uses a set of panels that contain flaws of which the inspection technicians are not aware. This allows researchers to quantify the NDI technologies’ flaw detection abilities. By studying NDI technologies’ effectiveness and improving them, the results of these experiments will reduce uncertainty in the blade manufacturing process, improving the design and manufacturing of wind turbine blades. The results will also inform how blade inspections are conducted at manufacturing facilities and wind farms, thereby improving maintenance and repair procedures for wind turbine blades.

SNL is actively seeking participants for the probability of detection experiment from NDI technology vendors, blade service companies, and blade manufacturers in this study.