A stiffener next to this weld means you can only scan from one side. With a 30° bevel and a 60° wedge, legs 1 and 2 can't reach the top of the far-side fusion face from the base metal, but leg 3 can, as long as the A-scan range is long enough to show it. Then compare it with leg 1 from the flush cap.
Drag the probe along the plate. Change the A-scan range with the slider.
Key points
- Sometimes you can only scan from one side of a weld: a stiffener, flange, nozzle or other structure is in the way.
- With a 30° bevel and a 60° wedge, leg 1 meets only the lower part of the far-side fusion face. To reach higher, the probe would have to sit on the weld.
- Leg 3 runs the same way as leg 1 (down at 60°) after leg 2 bounces off the top surface, so it meets the upper far-side face square-on. It bounces off the top surface right where leg 1's probe would sit, so it needs the cap ground flush.
- With the cap ground flush, leg 1 from the cap reaches the same flaw with a much shorter sound path and a stronger echo, if your procedure allows scanning on the weld.
- One skip (leg 1 + leg 2) at 60° in 1 inch plate is 4.000″ of sound path. A leg 3 echo comes after that, so set the range past one skip or the echo is off the screen.
- On leg 3 the sound is heading down from the top again: depth = sound path × cos 60° − 2 × thickness. The instrument's leg and depth readouts do this for you.