Phased array ultrasonic testing (PAUT) is a powerful tool for girth weld inspection, but calibration is where most errors originate.
A typical PAUT setup for a 20 mm butt weld uses a 5L64-A2 probe with a wedge angle of 36 or 55 degrees, sweeping from 35 to 70 degrees in 1-degree steps. Per ISO 13588, focal laws are set for skip mode at 20-30 mm depth, and sensitivity is calibrated to 80% FSH on a 3 mm side-drilled hole.
Time-corrected gain (TCG) is applied to compensate for attenuation with depth. One common mistake is using an incorrect wedge delay, which shifts the entire beam index and mislocates indications. Another is failing to validate the wedge angle on a calibration block before scanning.
For pipe girth welds, the calibration block must match the pipe geometry and thickness. A curved block with a known reflector at the fusion line ensures accurate sizing. Without proper calibration, even the best focal law will produce unreliable results.
Source: ISO 13588
What steps do you take to verify PAUT calibration before scanning production welds?