A single-V butt weld in 1 inch plate has lack of fusion on both fusion faces. Pick the wedge that faces the bevel, find out which leg reaches which face, and see why you scan from both sides of the weld.
Drag the probe along the plate. The probe stays the same; only the wedge changes the angle.
Key points
- Lack of fusion lies along the fusion face, so the beam has to meet the fusion face square-on (at 90°) to get a strong echo.
- Rule of thumb: bevel angle + wedge angle = 90°. A 45° bevel takes a 45° wedge; a 30° bevel takes a 60° wedge.
- Leg 2 (coming back up from the back wall) meets the near-side fusion face square-on.
- With a 30° bevel and a 60° wedge, leg 1 passes through the weld and meets the lower part of the far-side face square-on.
- With a 45° bevel and a 45° wedge, leg 1 runs parallel to the near-side face and never gets into the weld, so you scan from both sides to cover both faces.
- The wrong wedge still hits the flaw, but the sound bounces off to the side: a 45° wedge on a 30° bevel meets the face at 75° and gives only a small echo.