Wedge (Angle Beam) — Definition & NDT Use

On the job, Wedge sits between the procedure and the indication — its calibration record, serial number, and condition all flow into the inspection report and the audit trail. A piezoelectric element converts the electrical pulse into a mechanical wave at the chosen frequency, transmits it into the part through couplant, and then converts the returning echo back into a voltage that the flaw detector digitises and displays on the screen. The magnetising current creates a field that runs continuous through the part; at a discontinuity the lines of flux squeeze around the gap and break the surface as a leakage field, where dry powder or wet-suspension particles cluster and outline the flaw to the inspector's eye. In a composite, the layered structure means impedance changes at every ply boundary; a true delamination registers as a strong reflector at a depth that the C-scan can map across the part to size the affected area for an engineering disposition. Calibration certificates, condition logs, and traceable serial numbers are what make the difference between an instrument that shows a number and an instrument whose number stands up in court or in front of an auditor.

The instrument's inspection scope is set by its OEM specification, its current calibration certificate, and any customer-specific qualifications that have been logged against it; a Wedge that is in calibration but unqualified for a customer's procedure is still off the job. On aerospace components, NAS 410 personnel qualifications and tighter acceptance criteria mean the same indication may be flagged that would be passed on a structural weld.

A frequent finding in audits is a wedge marked "in-cal" on the spreadsheet but with a current condition (damaged cable, missing cap) that would have invalidated the calibration if checked physically.