1. 19-1 NDE Lessons Learned NDE is a part of design process Don’t assume that QA-NDE will address all needs (capabilities are often overestimated) Don’t assume that applicable, reliable NDE procedure is available—There are no Easter baskets Don’t assume that NDE technician can provide NDE engineering capabilities Demand calibration, written procedures & detection capability demonstration (POD)

2. 19-2 Summary Damage tolerance/durability was revolution Revolution in NDE was necessary to meet (DT/D) requirements Quantification of NDE (QNDE) debunked many beliefs in QA-NDE capabilities Probability of detection (POD) became standard metric for NDE capabilities QNDE is quantified measure of DT/D QNDE applications support efficient engineering structures & service life extension

3. 19-3 The future is in your hands!

4. 19-4 Supplemental Slides

5. 19-5 Integrated Systems Engineering Is Required NDE in: Design Production Maintenance Life extension Reduce risk!!

6. 19-6 Focus on Metals Damage tolerance—damage modes –Cracks –Stress –Environment Crack size—critical characteristic NDE—shift from detection to reliable detection of cracks at a quantified size (detection capability)

7. 19-7 Static Case—Original Production Static case –Stress concentration –Cracks are stress risers –Specimen will fail at crack site

8. 19-8 Retirement for Cause “Engineering structures are now retired safely from service because of observed damage & not because they have simply been in service for a 1-design lifetime” —Stephen Hopkins on ASTM standardization

9. 19-9 Quantitative NDE Required for RFC Management Reliable NDE detection of: –Cracks in manufacturing that could grow to critical size during service of component OR –Cracks in manufacturing or service that could grow to critical size before next inspection cycle Lessons Learned/Application – System management by damage tolerance/durability

10. 19-10 Panel Production Shear (both grain orientations) Identify Starter notches by electro-discharge machining Crack initiation & growth in bending fatigue Crack size distribution from 0.003″–0.500 ″ long Machine off starter notches Submit to inspection

11. 19-11 Panel Production (cont.) Crack initiation Crack growth Remove crack initiator (both sides of panel) Varying crack sizes Multiple specimens with cracks of with cracks of varying sizes

12. 19-12 Panel Configurations PM 19-12

13. 19-13 Varying Crack Configurations PM 19-13

14. 19-14 NDE Detection Variance Flaws of same size do not produce same signal level NDE output is not same over wide range of flaw sizes Human operators do not work at same level NDE procedures vary Detection is probabilistic

15. 19-15 NDE Application Variables Ultrasonic inspection of a billet using focused transducers Eddy current inspection of surface cracks PM 19-7

16. 19-16 NASA POD Length Depth Signal level vs. crack size PM 19-17

17. 19-17 Variables POD Is Dependent On Flaw (artifact) Test object NDE: –Method –Materials –Equipment –Procedures –Process Calibration Acceptance criteria/decision variables Human factors

18. 19-18 Quote on Models George E.P. Box Department of Industrial Engineering University of Wisconsin-Madison “All models are wrong, but some are still useful.”

19. 19-19 NDE Application Variables Multiple cracks at critical locations

20. 19-20 Challenges Representative cracks at inspection target size Crack shape (assumed depth ½ of length) Calibration—master gauging PM 19-24, 25

21. 19-21 QNDE Applications Integral to NASA programs Integral to Air Force programs Extended to other industries Has been integral in life extensions of critical structures >50% of required FAA directives for aircraft (flight safety) Integral to most failure analyses involving structures

22. 19-22 Design/NDE Revolutions Damage tolerance/durability (DT/D) in design was revolution in structural integrity DT/D was also revolution in NDE USAF approach –Assumed reliability detected crack size Assumptions were incorrect NASA approach –Assess capabilities of common NDE methods that might be applied

23. 19-23 NDE Lessons Learned DT/D was also revolution in NDE –Required performance-based assessment –Long-held beliefs & assumptions were challenged, many discarded –Traditional QA procedures were/are found inadequate for many applications Reliable NDE had been assumed & must now be demonstrated (QNDE)

24. 19-24 Aloha Airlines/NDE Flight 243, Boeing 737-200: April 28, 1988, Honolulu, HI NDE –NDE/inspection advisory had been issued, but had not been addressed at Aloha –NDE “return to flight” solution was mandated for similar aging aircraft –Aloha aircraft use accumulated fatigue damage at an accelerated rate (greater need for QNDE)

25. 19-25 Aloha Airlines (cont.) NDE challenge

26. 19-26 NDE Lessons Learned—Aloha Validate design & safety assumptions Routine maintenance/safety assumptions based on ability of inspections to detect damage may be wrong Lifecycle management may require repair &/or replacement of critical elements Multisite damage may be a special challenge to NDE

27. 19-27 Sioux City IA, DC-10 Catastrophic uncontained fan disk burst –At time of failure, engine had 41,009 hrs & 15,503 cycles Disk burst caused by fatigue crack initiated from metallurgical defect on surface of fan bore Defect formed during manufacture of disk & was not detected during inspections Debris from fan failure destroyed hydraulic lines in tail & loss of aircraft control Aircraft was destroyed by impact & fire –285 passengers & 11 crewmembers –111 fatalities, 47 serious injuries & 125 minor injuries

28. 19-28 Sioux City IA, DC-10 (cont.)

29. 19-29 NDE Lessons Learned QA-NDE may be inadequate Material damage analysis may show QA-NDE to be inadequate Change in NDE method (eddy current) was necessary to meet quantified requirements Development & demonstration of new NDE methods may be required Engineering structures are now retired safely from service because of observed damage

30. 19-30 Gemini Event—cracking in 2nd-stage tanks To skirt To barrel TO DOME Weld Crack Scan direction Ultrasonic transducer

31. 19-31 Gemini (cont.) Event –Cracking in 2 nd -stage tanks –Cracks could compromise forward dome Root cause –Y-chord heat treat process control error –Welded into 40 Gemini & Titan II tanks Interim action –Ultrasonically inspect to select largest cracks –Function proof load to demonstrate tolerance Corrective action –Correct heat treat process –Receiving inspection of all chords

32. 19-32 Engineering Lessons Learned— Gemini Critical processes require rigorous process monitor & control Critical processes performed by vendors require special attention & receiving inspection verification Nondestructive evaluation/testing often used for interim assessments & corrective action Nondestructive evaluation often essential in design, testing & validation

33. 19-33 Aloha Airlines Event –In-flight fuselage rupture Root cause –Management/maintenance –Widespread fatigue damage Interim action –Focused inspections –Failure analysis Corrective action –Focused inspections/repair –Changes in process & analysis methods

34. 19-34 Engineering Lessons Learned— Sioux City Aircraft critical systems isolation must be provided Combined effort precluding rotor failures & mitigating effects in event of failure High-energy uncontained engine failures can have catastrophic results Very small metallurgical defects in critical rotating parts can have catastrophic effects Reliable inspection processes must be qualified & rigorously applied Management of maintenance & inspection are required