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Time of Flight Diffraction (ToFD)

Time of Flight Diffraction (ToFD). Topics. What is ToFD History How does it work Applications Advantages Challenges Performance & Cost Conclusion. What is ToFD ?. T o FD = T ime o f F light D iffraction

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Time of Flight Diffraction (ToFD)

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  1. Time of Flight Diffraction(ToFD)

  2. Topics • What is ToFD • History • How does it work • Applications • Advantages • Challenges • Performance & Cost • Conclusion

  3. What is ToFD ? • ToFD = Time of Flight Diffraction • ToFD = Highly accurate Ultrasonic inspection technology, principally intended for weld inspection • Technology Design has also developed a rastered ToFD application for effective area scanning

  4. History • ToFD discovered in the 1950’s by Maurice Silk & others of AEA (UK) • Developed in the early 1970’s by AEA (UK). • Gained wider acceptance in the 1980/90’s by the efforts of Sonomatic & others • Equipment more portable and efficient in the 90’s – Technology Design leads the way • Development of QC codes in late 90’s/2K’s

  5. How does ToFD work?

  6. How it works Reflection BRICK PLANK Back

  7. How it works cont’d Diffraction BRICK PLANK

  8. How it works cont’d Diffraction Rx Tx DEFECT

  9. Rx Tx How it works cont’d Practically

  10. Rx Tx Lateral Wave + Pos Amplitude dB Time mseconds - Neg How it works cont’d

  11. Rx Tx Diffracted Signals + Pos Amplitude dB Time mseconds - Neg How it works cont’d

  12. Rx Tx Backwall Reflection + Pos Amplitude dB Time mseconds - Neg How it works cont’d

  13. 6 5 4 3 2 1 Tx Rx How it works cont’d Data Collection

  14. + Pos Amplitude dB - Neg How it works cont’d Phase Reversal Time = µ seconds or Millimetres

  15. How it works (cont’d) Greyscale Image Presentation Surface Depth Top of defect Backwall Bottom of defect Length

  16. ToFD Scan Length mm Depth/Time µ Seconds or mm

  17. APPLICATIONS • Critical plant items in construction and in-service • Pressure Systems – Vessels, pipelines, pipe-work • Storage facilities – Tanks, spheres • Tubed Vessels - Boilers, Heat Exchangers, Condensers • Service induced defects & structural damage • Stress/chemically assisted micro-cracking - SCC, LTHA, HHA, SOHIC • Corrosion/erosion profiling - especially weld root erosion • Thick wall components > 300mm • Clad/lining interface bond/cracking • Fabrication QC - includes ‘in-situ’ construction

  18. Advantages of ToFD • Highly Accurate and Sensitive • Increased Evidence • Fast • Comprehensive Coverage • Meaningful Presentation • Fast Reporting / Decision Making • Permanent Record ofAll Parameters • Offline Interpretationand Measurement • Objective Assessment. • ExcellentRepeatability.

  19. Challenges • Reduced near surface resolution (approx. 3– 5mm) • Additional B-scans necessary for transverse positioning • Sees everything (down to grain structure) so interpretation can be complicated if material/weld quality is poor • Should not be used with conventional ultrasonic acceptance criteria

  20. Performance & Cost • Most validated of all NDT techniques - DDT trials in UK, PISC (International), NIL (Netherlands), EPRI (US) • TOFD outperformed other methods in trials • Faster, safer and more cost effective • Increased defect detection ability (POD) = safer, added value to plant • Reduced ‘false calls’(FCR) = less repairs and production downtime

  21. In Conclusion • ToFD as an Inspection Tool Is: • Fast • Proven • Cost Effective • ToFD PROVIDES: • High POD and Low FCR • Accuracy • Real-time Sentencing • Transparent Recording of Results • Permanent Record • Repeatability

  22. Thank you for your attention

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