BLADE INSPECTION & REPAIR KYLE K. WETZEL, PH.D. FIELD INSPECTION OF WIND TURBINE BLADES USING A MICROWAVE INTERFEROMETRIC METHOD

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1 BLADE INSPECTION & REPAIR FIELD INSPECTION OF WIND TURBINE BLADES USING A MICROWAVE INTERFEROMETRIC METHOD CANWEA O&M SUMMIT FEBRUARY 24, 2016 KYLE K. WETZEL, PH.D. KYLE.WETZEL@WETZELENGINEERING.COM WETZEL ENGINEERING, INC GATTIS SCHOOL RD., SUITE 103 ROUND ROCK, TEXAS TEL: (512)

2 Wetzel Engineering Inc Established 2001 New Product Engineering Wind Turbine System Optimization Rotor Blade Aero and Structure Wind Turbine Controls Composites Manufacturing & Repair Blade Forensics Engineering Root Cause Analysis Design Manufacturing Operational Conditions Engineered repair solutions Assessing residual life Copyright 2016 Wetzel Engineering, Inc. All Rights Reserved.

3 Acknowledgements Alex Tran, WEI Engineering Lead for Structural Engineering Responsible for honing the MW technique and shop validation Rob Woodward, Evisive Technologies Sr. Technician on the Project Key Expert on the MW technique Copyright 2016 Wetzel Engineering, Inc. All Rights Reserved.

4 CASE STUDY: BLADE MANUFACTURING DEFECT Situation 6 year old blades failing due to OEM-acknowledged manufacturing defect No other engineering support from the OEM Owner trying to claw back warranty support to the extent of blade replacement Owner needs to understand long-term risk Visual inspections could not fully characterize extent of damage internally and no assessment externally Microwave NDT campaign on a sampling of blades combined with engineering analysis of the impact of the defect on life estimation provided a quantitative assessment of the number of blades at risk for premature failure defined a monitoring protocol

5 BLADE ANATOMY & INSPECTION SCOPE Blade Inspection Area Internal & external blade surfaces Manufacturing defect wrinkles/marcelling of fiberglass layers Impact of marcelling, cracking & disbonding evaluated Correlation of defects/wrinkles in sandwich structure Near root region to area of max chord Blade Sandwich Shell Construction Embedded spar caps & sandwich balsa core material Fiberglass face sheets Standard layout & construction shell panel buckling resistance Thick wall, t wall > ~ up to 30mm or 1.5 in.

6 APPLIED MICROWAVE THEORY Microwave NDT & Setup Near field technique interferometric response Non time-based signal, one-sided technique Sum of transmitted and received signal phase & Receivers B A Object being examined amplitude Transmitter Defect Change in voltage presence of indications 24 GHz probe setup: Penetration depth adequate to penetrate B ¼ λ A fiberglass layers, not completely through Transmitter balsa core Freq. provide sufficient resolution in C-Scan images to distinguish many features to interpret & evaluate

7 LAB INSPECTION VALIDATION Test samples fabricated in-house Validate defects can be identified Establish criteria for distinguishing wrinkles, cracks and disbanding for tracking damage progression Crack Marcelling Scores in Balsa Wood Marcelling Single, large wrinkle Multiple wrinkles in close proximity Crack and surrounding delamination Scores in balsa core identified in scan image Verified depth of penetration through fiberglass achieved Sufficient lab samples for validation Viable solution for identifying volumetric indications on blade in the field

8 FIELD IMPLEMENTATION OF MICROWAVE NDT Challenges in hardware Scan imaging inspection hardware Speed & accuracy Lightweight & robust Adaptable to internal & external blade contours Modular for assembly & disassembly Tight clearance to area of interest Internal blade access External blade platform

9 FINDINGS & EVALUATION OF SCAN RESULTS Evident in images Balsa scores (running horizontal & vertical) Fiberglass fabric overlay Spar cap is also evident External Scan Results Linear indications run axially, appear jagged in shape Indications could not be attributed to any type of embedded geometry Indication of marcelling or cracking Indications/defects in the bonds within fiberglass to spar were easier to interpret Interior Scan Results Surface irregularities were present on interior scanning surface Scan images were similar to the interpretation of radiograph Images circled are result of either cracks or marcelling Combined visual identification of some findings - surface is not painted and natural light shine through to the inside Allows for distinguishing difference between subsurface geometry and flaws

10 CONCLUSIONS First article application for field inspection Microwave NDT technique identified subsurface fiberglass wrinkling & marcelling Scanning/inspection hardware setup: Effective but can be improved Need for a practical setup to maintain probe normality to surface Improvements in setup will aid in improving accuracy of data interpretation and reduced data processing time. Value of one sided technique to provide similar C-scan image results as ultrasonic or radiograph couplant is not required Lab validation & field implementation of technique was proved to be successful and a cost effective solution for blade inspections