WTT Blade Inspection & Maintenance 2 — Questions and Answers
Question 1: Which NDT method uses high-frequency sound waves to detect internal delaminations in wind turbine blades?
- Infrared thermography
- Ultrasonic testing (Correct answer)
- Magnetic particle inspection
- Dye penetrant testing
Correct answer: Ultrasonic testing
Ultrasonic testing transmits high-frequency sound waves into the blade material and analyzes reflections to locate internal delaminations and voids.
Question 2: What is the primary purpose of the gelcoat layer on a wind turbine blade?
- To add structural rigidity to the blade
- To protect the underlying laminate from UV radiation and moisture (Correct answer)
- To reduce blade weight for improved aerodynamics
- To increase electrical conductivity for lightning protection
Correct answer: To protect the underlying laminate from UV radiation and moisture
The gelcoat is a surface coating that protects the structural laminate beneath from UV degradation, moisture ingress, and erosion.
Question 3: When inspecting a blade's leading edge, a technician finds a section where the paint has bubbled but the laminate beneath appears intact. This is best described as:
- Interlaminar shear failure
- Coating delamination (Correct answer)
- Core shear fracture
- Gel coat crazing
Correct answer: Coating delamination
Coating delamination refers to the separation of the protective paint or gelcoat layer from the underlying laminate without structural damage to the composite.
Question 4: A technician notices a faint 'click' sound when tapping along a blade surface with a coin or small hammer. This tap-test result indicates:
- The blade has adequate resin saturation
- A void or delamination beneath the surface (Correct answer)
- Normal cured composite resonance
- Blade over-tension due to wind loading
Correct answer: A void or delamination beneath the surface
A hollow or clicking sound during a tap test indicates a subsurface void or delamination where the laminate has separated from adjacent layers or core material.
Question 5: Which adhesive system is most commonly used for bonding wind turbine blade shear webs and skins during repair?
- Cyanoacrylate (super glue)
- Polyester resin
- Two-part epoxy structural adhesive (Correct answer)
- Polyurethane sealant
Correct answer: Two-part epoxy structural adhesive
Two-part epoxy structural adhesives provide the high bond strength, fatigue resistance, and environmental durability required for blade structural repairs.
Question 6: What does a 'spanwise' crack orientation mean in terms of blade inspection?
- The crack runs parallel to the blade chord from leading to trailing edge
- The crack runs along the length of the blade from root to tip (Correct answer)
- The crack is located within the internal spar cap
- The crack propagates in a circular pattern around the blade root
Correct answer: The crack runs along the length of the blade from root to tip
Spanwise cracks run along the long axis of the blade from root toward tip, following the blade's span direction.
Question 7: Before entering a wind turbine blade for an internal inspection, which hazard must be assessed due to the blade's enclosed composite structure?
- Electrostatic discharge from blade rotation
- Oxygen-deficient atmosphere from resin off-gassing (Correct answer)
- Radio frequency interference from nearby turbines
- Thermal runaway from embedded heating elements
Correct answer: Oxygen-deficient atmosphere from resin off-gassing
Enclosed blade interiors can accumulate toxic fumes or become oxygen-deficient from curing resin off-gassing, requiring atmospheric testing before entry.
WTT Blade Inspection & Maintenance 2
Which NDT method uses high-frequency sound waves to detect internal delaminations in wind turbine blades?