Lesson 11: Time of Flight Diffraction Flashcards
When performing weld inspections with time of flight diffraction (TOFD):
a. a single scan can be performed that will detect all discontinuities from shallow surface discontinuities to lack of fusion or porosity.
b. the appropriate angle must be selected to be perpendicular to the weld preparation angle.
c. mid-wall discontinuities can be detected and sized even if they are not oriented perpendicular to the sound beam.
d. the reference level must be set accurately since indication evaluation is based primarily from signal amplitude.
c. mid-wall discontinuities can be detected and sized even if they are not oriented perpendicular to the sound beam.
When performing weld inspections with TOFD:
a. the A-scan display is normally set as an RF display so differences in phase can be seen.
b. the A-scan display is normally set as a positive half-wave display so discontinuities that have a positive phase shift can be seen.
c. the A-scan display is not used except for calibration before the inspection.
d. only the shear waves are used.
a. the A-scan display is normally set as an RF display so differences in phase can be seen.
Which of the following probe combinations must be used for carrying out TOFD?
a. Highly damped, large diameter, high frequency.
b. Low damping, small diameter, high frequency.
c. Highly damped, small diameter, high frequency.
d. Highly damped, small diameter, low frequency.
c. Highly damped, small diameter, high frequency.
A longitudinal UT scan with incident beam perpendicular to the entry surface will ____________ show diffracted wave signals?
a. always
b. not
c. sometimes
d. intermittently
b. not
For performing TOFD testing, what is the minimum number of probes are required?
2
In what area are the results of TOFD uncertain due to the dead zone?
a. In the wall center.
b. Top surface.
c. Bottom surface.
d. Top and bottom surface.
d. Top and bottom surface.
TOFD testing is best used on heavy thickness weld testing at 0.5 in. (12 mm) on account of:
a. good resolution at higher depths.
b. dead zones.
c. high probability of discontinuity detection at more depth.
d. side lobes.
b. dead zones.
Ideally, when using TOFD on a discontinuity-free test object, the total number of signals of interest will be:
3
An encoder is used to find the:
length or location of the discontinuity
The length of the total area tested by TOFD is 19.7 in. (500 mm), but the data collected only covers 19.3 in. (490 mm). The most likely reason for this discrepancy is:
improper synchronization of the encoder.
Encoding of TOFD data is generally done along how many axes?
a. single axis.
b. dual axis.
c. triple axis.
1
The typical wedge angle in TOFD inspection is:
a. greater than the first critical angle.
b. greater than the second critical angle.
c. perpendicular to the entry surface.
d. smaller than the first critical angle.
d. smaller than the first critical angle.
The wave traveling between the probes at the test surface is called the:
a. lateral wave.
b. backwall signal.
c. tip diffraction signal.
d. discontinuity signal.
a. lateral wave
Which type of display is most commonly used to set and calibrate TOFD inspections?
a. A-scan.
b. RF stacked A-scans.
c. C-Scan.
d. D-Scan.
b. RF stacked A-scans.
TOFD probes are used in a variation of which of the following ultrasonic techniques?
a. Pitch-catch.
b. Pulse-echo.
c. Through-transmission.
d. Dual beam.
a. Pitch-catch
