NDT.net - September 1999, Vol. 4 No. 9
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Questions & Answers
- Time of Flight Diffraction Technique (TOFD)
by Rolf Diederichs *

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1TOFD is suitable for: - 1
a) Flaw Sizing and Flaw Detection
b) For Flaw Detection
c) Not for Flaw Detection
d) Partially for Flaw Detection
2TOFD is an economical technique. - 2
a) Yes
b) No
3TOFD was invented approximately in Year - 2
a) 1975
b) 1980
c) 1985
d) 1990
4TOFD has shown a higher Probability of Detection (POD) than other NDT Methods? - 2
a) Yes
b) No
5The TOFD principle is based on evaluation of theEditor -
a) Diffraction Signals at Crack Edges
b) Amplitude of the echo hight
c) Sound attanuation
d) Frequency
6How many Probes TOFD uses?Editor -
a) 4
b) 3
c) 2
d) 1
7In what direction to the weld the scan is performed for initial flaw detection?Editor -
a) transverse and longitudinal
b) transverse
c) longitudinal
8Probes used for TOFD must deliver the performance:Editor -
a) High Bandwidth
b) Narrow Bandwidth
c) Low Frequency
d) High Frequency
9Diffracted Signals vs. Pulse Echo Signals are - 3
a) higher
b) weaker
c) the same
10In what area TOFD is uncertain?Editor -
a) In the wall center
b) Near surface
c) Far surface
d) Near and Far surface
11The interpretation of TOFD images is Editor -
a) easy
b) very difficult
c) needs experience
12TOFD shall be combined with - 4
a) Radiography
b) Pulse Echo
13TOFD can be applied for the same scope of materials as Pulse Echo TechniqueEditor -
a) Yes
b) No
14Can it happen that mode conversion causes virtually defects where there are none? - 4
a) Yes
b) No
15Shall TOFD technique be used for Flaw Detection without combination with other Methods? - 4
a) Yes
b) No
16A true crack size of 35 mm was measured by TOFD as - 5
a) 10 mm
b) 30 mm
c) 5 mm
d) 40 mm
17What is the ideal number of signals used to size a flaw using TOFD? - 6
a) 2
b) 3
c) 4
d) 5
18The TOFD image is similar to a - 6
a) A-scan
b) B-scan
c) C-scan
d) P-scan
19What kind of probes are usually applied with TOFD? - 6
a) longitudinal
b) transversal
20Is there a Standard or Guideline for TOFD available? - 7
a) No
b) Yes
c) only a Draft
21Is it necessary to define a gain or an amplitude level when using TOFD? - 8
a) Yes
b) No
22What probes are suitable for a working range 10 mm to < 30 mm? - 9
a) 2 to 5 MHz
b) 5 to 10 MHz
c) 10 to 15 MHz
23Is one probe setup (2 probes at a fix distance) suitable? - 1
a) Yes
b) No
24What is the shortest near surface dead zone (in mm)? - 10
a) 1
b) 2
c) 3
d) 6
25What method can perform more exact sizing? - 3
a) TOFD
b) Reflection method
26Is it true that an ASME Code has accepted TOFD in lieu of radiography examination for thicknesses over 4 inch ? - 11
a) Yes
b) No
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References

1. The TOFD Method - Between Radiography and Ultrasonic in Weld Testing, Erhard, U. Ewert
2. Celebrating TOFD's 25th anniversary, Inspection Solutions No. 65, March 1999
3. Time of flight diffraction technique TOFD - an alternative to radiography?, Review of a regional DGZfP working group meeting, Rolf Diederichs
4. Review of some Lectures and the Panel Discussion of the DGZfP 98, Rolf Diederichs
5. Critical Argument regarding the European TOFD Draft standard (TOFD), Review of a DGZFP Ultrasonic Workshop, by Rolf Diederichs
6. The Time-of-Flight-Diffraction-Technique (TOFD)Principles, Ultrasonic Testing Encyclopedia (NDTnet)
7. The British TOFD standard BS 7706 - Guide to Calibration and setting-up of the Ultrasonic Time of Flight diffraction (TOFD) technique for defect detection, location and sizing of flaws, Summarize by Rolf Diederichs
8. Time of Flight Diffraction Technique (TOFD) - An Ultrasonic Testing Method for all Applications?, A. Hecht
9. ENV 583-6 Non-destructive testing - Ultrasonic examination part 6: Time of Flight diffraction technique as a method for defect detection and sizing, Summarize by Rolf Diederichs
10. The Time-of-Flight-Diffraction-Technique, N. Trimborn
11. TOFD - the emerging ultrasonic computerized technique, for heavy wall Pressure Vessel welds examination, G.Nardoni et al

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