Second Critical Angle

Second critical angle :-An incident angle that makes the angle of refraction for the shear wave 90 degrees and at this point, all of the wave energy is reflected or refracted into a surface following shear wave.

2nd Critical Angle


Minimum Flaw sizes detectable in Weld Testing :-

Minimum Flaw sizes detectable in Weld Testing :-
Velocity = Frequency x Wavelength(λ)
Wave length (λ) = V / f
Frequency(f) Wave Velocity(V)
Wave length(λ)
in mm
Minimum Flaw size(λ/2)
in mm
0◦ 2 Mhz Longitudinal wave 5.92 x 106 2.96 1.48
70◦ 2 Mhz Shear wave 3.23 x 106 1.615 0.8075
45◦ 2 Mhz Shear wave 3.23 x 106 1.615 0.8075

Question Bank for USFD Training

  1. Normal probe is indicating a crack in Fishplated area connecting bolt hole to head-web junction, the defect is classified as. (a). REM (b) IMR (c) OBS (d) Non-reportable defect.
  2. Piping in Rail Head can be easily detected by (a) 0 degree from top (b) 70 degree from top (c) 0 degree from side (d) 45 degree from side
  3. Poor linearity of horizontal scale of UFD will result in (a) improper location (b) improper size (c) improper orientation (d) no effect on flaw assessment
  4. During side probing by two 45 degree probes to check crack below wheel burn 70% drop of signal height from other end observed, the defect is classified as (a) IMR (b) OBS (c) Non-Reportable defect (d) DFWO
  5. 300 mm range calibration for longitudinal wave is equivalent to (a) 164.83 mm (b) 300 mm shear waves (c) 137.36 mm shear waves (d) 546 mm shear waves
  6. 70 degree central forward probe (during rail testing) is indicating a moving signal of 70% horizontal movement and 50% vertical height on a AT Weld, according to IR specification the defect shall be classified as (a) OBSW (b) Non-reportable defect (c) IMRW (d) IMR
  7. A star crack in bolt hole when tested by 0 degree probe may indicate (a) stationary flaw echo (b) shigting flaw echo with o effect on back echo (c) shifting flaw echo with drop of back echo (d) all these
  8. 70 forward probe (guage face) is indicating moving signal of 40% horizontal scale movement & 60% vertical height on a mid-rail , according to USFD manual, the defect is classified as (a) REM (b) IMR (c) OBS (d) Non-reportable defect
  9. The defect code (numeric) for transverse crack in rail head outside fish-plated area is (a) 112 (b) 212 (c) 111 (d) 211
  10. When sound energy is incident at steel-air interface (a) Most energy is transmitted in air (b) Most energy is reflected back in steel (c) Equal energy is transmitted in air and reflected in steel (d) None of these
  11. While testing for piping by side probing of rail head by normal probe, a flaw echo was observed with multiples the flaw is classified as (a) OBS (b) IMR (c) Non-Reportable defect (d) None of these
  12. In contact ultrasonic testing, defects near the entry surface cannot always be detected because of (a) The far field effect (b) Attenuation (c) The dead zone (d) Refraction.
  13. During testing of single line track, 70 degree central backward probe is indicating a moving signal showing maximum vertical height of 30% and horizontal movement of 60% the defect is classified as (a) REM (b) IMR (c) OBS (d) Non-reportable defect
  14. During Rail testing, 70 guage face probe is indicating a flaw signal of 70% vertical height with 0 to 2 div horizontal movement, the defect is classified as (a) IMR (b) OBS (c) GCC (d) depends upon operator