WTT Blade Inspection & Maintenance 3 — Questions and Answers
Question 1: What is the minimum personal fall arrest system (PFAS) anchor point strength required by OSHA when performing blade maintenance at height?
- 2,500 lbs (11.1 kN)
- 3,600 lbs (16 kN)
- 5,000 lbs (22.2 kN) (Correct answer)
- 7,500 lbs (33.4 kN)
Correct answer: 5,000 lbs (22.2 kN)
OSHA 1926.502 requires fall arrest anchor points to support at least 5,000 lbs (22.2 kN) per attached worker.
Question 2: During a blade inspection, a technician identifies a crack at the trailing edge bond line near mid-span. The FIRST action should be to:
- Apply emergency epoxy filler and return the turbine to service
- Document the damage with photographs and measurements before any repair (Correct answer)
- Immediately cut out the damaged section for replacement
- Notify the turbine OEM and shut down the turbine permanently
Correct answer: Document the damage with photographs and measurements before any repair
Proper damage assessment requires thorough documentation — photos, dimensions, and location data — before any repair action is taken.
Question 3: Which type of blade erosion is caused primarily by repeated impact of airborne particles such as rain, dust, and insects at high tip speeds?
- Galvanic corrosion
- Leading edge erosion (Correct answer)
- Trailing edge fatigue cracking
- Spar cap delamination
Correct answer: Leading edge erosion
Leading edge erosion occurs when high-velocity impacts from rain, sand, and insects progressively erode the blade's leading edge coating and laminate.
Question 4: A 'bond line read-through' on the blade exterior surface most likely indicates:
- Excessive erosion of the gelcoat
- The adhesive joint beneath has caused a surface print-through (Correct answer)
- A manufacturing defect in the core material
- Improper lightning protection bonding
Correct answer: The adhesive joint beneath has caused a surface print-through
Bond line read-through (print-through) is a surface imperfection caused by the structural adhesive bond joint telegraphing through the skin laminate.
Question 5: When grinding a blade surface for a repair patch, what is the minimum feathering ratio (taper ratio) typically required to achieve adequate bond strength?
- 5:1 (5 mm taper per 1 mm depth)
- 12:1 (12 mm taper per 1 mm depth)
- 30:1 (30 mm taper per 1 mm depth) (Correct answer)
- 100:1 (100 mm taper per 1 mm depth)
Correct answer: 30:1 (30 mm taper per 1 mm depth)
A 30:1 taper ratio is the standard minimum for composite blade repairs, ensuring adequate load transfer through the stepped laminate overlap.
Question 6: Infrared thermography is most effective for detecting which type of blade defect?
- Surface erosion depth measurements
- Subsurface moisture ingress and delaminations (Correct answer)
- Lightning strike channel mapping
- Blade natural frequency deviations
Correct answer: Subsurface moisture ingress and delaminations
IRT detects thermal anomalies caused by subsurface defects like moisture-filled voids and delaminations, which have different thermal conductivity than intact laminate.
Question 7: What is the purpose of a peel ply cloth applied during a blade repair lay-up?
- To add additional structural plies to the repair area
- To create a clean, bondable surface texture when removed after cure (Correct answer)
- To prevent exothermic heat buildup during epoxy cure
- To seal the vacuum bag against air infiltration
Correct answer: To create a clean, bondable surface texture when removed after cure
Peel ply creates a textured, contamination-free surface ready for bonding when peeled away after cure, eliminating the need for sanding before subsequent operations.
WTT Blade Inspection & Maintenance 3
What is the minimum personal fall arrest system (PFAS) anchor point strength required by OSHA when performing blade maintenance at height?