The probe cannot rest on top of the bead, and a vertical beam would in any case miss cracks lying edge-on. The solution is to enter from the side, with an angled beam.
- ✓ Angled wedge generating shear waves in the material
- ✓ Access to the bead from the adjacent area, without resting on it
- ✓ Typical angles of 45°, 60° and 70° depending on thickness and geometry
- ✓ Flaw orientation decisive for detectability
Inspecting a weld bead presents two obstacles. The first is geometric: the surface of the bead is irregular and the probe does not rest on it reliably. The second is physical: cracks and lack of fusion develop mainly along the sidewalls of the joint, hence almost parallel to the direction of a vertical beam, which would graze them without producing a useful reflection.
The angle beam probe solves both. The transducer is mounted on an angled wedge that rests on the base metal, beside the bead; the pulse enters the material at an angle and, through refraction at the interface, propagates as a transverse wave, or shear wave, in an oblique direction.
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The beam thus generated reaches the bead from inside the material and meets the sidewall flaws at an angle favourable to reflection. Moving the probe forward and back explores different depths, also exploiting the path that reflects off the opposite surface before reaching the joint.
How the angle is chosen
| Factor | How it affects the choice |
|---|---|
| Joint thickness | Determines which angle covers the entire section of the bead |
| Joint geometry | Butt, corner or T joints require different access |
| Expected flaw orientation | The beam must meet them so as to generate a reflection |
| Space available beside the bead | Limits how far the probe can move back |
| Applicable code | May prescribe angles and scanning techniques |
Probe, wedge and calibration
The refraction angle depends not only on the wedge but also on the material the wave enters: the same wedge produces different angles in different materials. This is why the actual angle and the beam exit point must be checked on a reference block before starting the inspection.
The evaluation curves are then built on the same calibration: changing the wedge means redoing the curve. This is why wedges and reference blocks travel together with the instrument.
Instruments and accessories
| Element | Use |
|---|---|
| Dakota FX70-DL | Field weld inspection with angle beam probes |
| Dakota FX81-DL | Benchtop version for laboratory and workshop |
| Probes and accessories | Transducers, wedges, cables and couplants |
| Calibration blocks | Checking the actual angle and the beam exit point |
Frequently asked questions
For two reasons: the surface of the bead is irregular and does not guarantee reliable coupling, and a vertical beam would meet the sidewall flaws almost parallel, without producing a useful reflection.
No. The actual angle in the material depends on refraction at the interface and therefore also on the material itself: it must be checked on a reference block before the inspection.
It depends on thickness and geometry. The choice of angle, and the possible use of different angles, follow the applicable code and the configuration of the joint to be inspected.
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Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
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